WO2019132039A1 - Clad steel plate - Google Patents

Abstract

The present invention provides a clad steel plate having a plurality of regions in layered form, the plurality of regions having differing compositions in the plate thickness direction, and the clad steel plate also having excellent yield and high corrosion resistance and machining properties. This clad steel plate is layered in either a surface layer region/transition region/inner layer region or a surface layer region/transition region/inner layer region/transition region/surface layer region configuration in the plate thickness direction. The surface layer region extends in the plate thickness direction from the surface to a position where the Cr concentration is 95% of the Cr concentration at the surface. The transition region extends in the plate thickness direction from a position adjacent to the surface layer region to a position where the Cr concentration is 13.0% by mass or higher. The inner layer region is adjacent to the transition region. The width of the transition region is at least 5 μm on average. The average thickness of the surface layer region is at least 5% of the total thickness of the steel plate but less than the thickness of the inner layer region. The degree of integration of the αFe phase of the inner layer region in the (222) plane is 60-100% (inclusive).

Description

Clad steel plate

The present invention relates to a clad steel sheet containing Cr, which has high production stability (yield), is excellent in processability and corrosion resistance such as deep drawing and press forming, and is also excellent in ridging resistance and toughness.

Conventionally, ferritic stainless steel contains 10.5% or more of Cr in a steel plate in order to impart corrosion resistance. In order to further improve the corrosion resistance, it is necessary to increase the Cr content.
However, as the Cr content increases, there is a problem that the accumulation of crystal grains in the {111} orientation of the αFe layer, which is necessary for securing the formability of the steel sheet, is reduced to deteriorate formability. In addition, with the rise in prices of rare metals, the problem of rising alloy costs has also arisen.

As a technique for securing corrosion resistance while suppressing alloy cost, a technique for increasing the Cr concentration of only the surface layer portion of the steel sheet by diffusion of Cr is known from Patent Documents 1 and 2, and the like.
With these techniques, the corrosion resistance of the steel plate can be secured to a certain extent with a small amount of Cr, but if the Cr content of the steel material in the central layer is reduced to increase the accumulation of {111} oriented grains, the corrosion resistance of the steel plate as a whole decreases. I will. In addition, nothing is disclosed about the improvement of the processability in the case of using a ferritic stainless steel or the like having poor processability as a base material.

With respect to such problems, there are the techniques of Patent Documents 3 and 4 as techniques for enhancing workability by providing a steel plate with a specific crystal orientation while forming an alloying region such as Cr in the steel plate.
In Patent Document 3, a metal such as Al or Cr is adhered to the surface of a steel plate having an Al concentration of less than 6.5% by mass as a second layer by means such as plating or rolling cladding, and then the base steel plate is cold-rolled And then heat-treating and recrystallizing the steel sheet, which discloses a steel sheet having a high {222} plane density.

Further, in Patent Document 4, a depth of 0.1 to 50 μm from the surface of a steel sheet is obtained by subjecting a steel sheet having a composition of an α-γ transformation component system containing 3% by mass to less than 13% by mass of Cr to a specific heat treatment. Cr concentration part of 10.5 mass% or more is formed over the range of 1%, and Cr of which {222} plane accumulation of α-Fe phase is 60% or more and 99% or less over almost the entire thickness Disclosed is an additive high corrosion resistant steel sheet.

The present inventors have previously formed {100} oriented grains in the surface layer by strong processing such as blasting as control of the texture in Si-containing steel in Patent Document 7, while maintaining the projected grain size on the surface In order to grow in a columnar shape at the center of the steel sheet, clusters (colonies) of {100} crystal orientation are made to be continuously present in the rolling direction with a relatively large particle size, thereby enhancing the {200} plane accumulation of the entire steel sheet. Although the technology has been disclosed, Patent Document 4 utilizes this technology.

Furthermore, while it is set as the lamination steel plate which used the steel which contains Cr for one side of a steel plate, and giving crystal orientation to a steel plate, there exists a technique of patent document 5 and 6 as a technique which improved workability.
Patent Document 5 shows a laminated steel plate in which a plurality of steel plates made of one or both of carbon steel and alloy steel are laminated and integrated, and an α-Fe phase or a γ-Fe phase in both the steel plate surface and the thickness center of the laminated steel plate Of {222} plane accumulation with respect to the steel plate surface of one or both of 60% or more and 99% or less and {222} plane accumulation degree of 0.01% or more and 15% or less; A technology that can achieve a combination of high strength, improved surface roughening resistance, and improved corrosion resistance by significantly increasing the surface integration degree and improving the machinability of laminated steel plates and selecting the type of each layer of laminated steel plates. Is disclosed.

In Patent Document 6, a master piece steel plate of an α single phase system and a material steel plate of an α-γ transformation system are laminated, and both steel plates are integrated by bonding by means of rolling or the like, and then integrated into a steel plate. Heat treatment to heat after being heated to a temperature of more than A3 transformation point and less than 1300 ° C and cooling to grow seed of crystal orientation of masterpiece steel plate over the entire steel plate, thereby producing a steel plate having a high {222} plane integration degree It discloses technology.

Patent Documents 8 and 9 disclose a technique for forming an alloying region such as Cr in a steel plate as well as Patent Documents 3 and 4 while at the same time giving a specific crystal orientation to the steel plate to enhance workability. There is.
In Patent Document 8, the surface layer portion of a steel plate having a Cr concentration of less than 3 to 13% is subjected to hot-dip plating or the like to concentrate Cr, ensure corrosion resistance, perform predetermined cold rolling, and then heat and cool and recrystallize. Disclosed is a steel sheet excellent in toughness, having a high {222} plane concentration and a fine equiaxed crystal.
In Patent Document 9, the surface layer portion of a steel plate having a Cr concentration of 3 to less than 13% is subjected to hot-dip plating or the like to concentrate Cr to ensure corrosion resistance, perform predetermined cold rolling, and then heat and cool and recrystallize. In the surface layer, grains of {222} plane density are not grown, and the central layer has a structure including large crystal grains grown from the {111} -oriented grains in the surface layer toward the inside of the steel plate. The technology of the steel plate which can make grain size differ is disclosed.

Japanese Examined Patent Publication No. 6-27318 Japanese Patent Application Laid-Open No. 5-70926 International Publication No. 2008/62901 JP, 2014-088611, A JP, 2009-256734, A JP, 2012-197485, A International Publication No. 2011/52654 JP 2017-214623 A JP, 2017-214624, A

In Patent Documents 3 and 4, it has become possible to achieve both corrosion resistance and processability, but Cr is diffused from the Cr film on the surface to the inside, and it is difficult to thicken the Cr film itself. The thickness of the Cr-concentrated layer in the surface layer of the steel plate formed by the diffusion of Cr is not sufficient, and there is a problem in the thickness of the region with high Cr concentration in the surface layer of the steel plate and the productivity of the steel plate Forming a region having a high Cr concentration with a certain width or more to further enhance the corrosion resistance, and obtaining a high average r value so as to obtain a steel plate having further enhanced workability by a more productive method Is desired. Furthermore, there is a problem that it is difficult to apply a very thin steel plate such as a foil because of the formation of a film.
Further, in Patent Documents 5 and 6, although steel plates processed to a predetermined thickness are laminated, and steel plates are bonded by cold or warm rolling, the steel plates are bonded in cold or warm In rolling, there is a problem in integration of steel plates, and it is difficult to adhere to a bonding interface of steel plates having a large area so that no foreign matter or space intervenes, and there is also a problem in productivity.
Furthermore, in Patent Document 6, a long time is required for the heat treatment, the Cr concentration in the surface layer is apt to decrease, and there is also a further problem regarding productivity. More specifically, Patent Document 6 can obtain the excellent characteristics described in the examples, but from the viewpoint of stable production, the variation in the degree of integration of the αFe {222} plane is large, and the production stability (yield) Is not high.

Furthermore, although ferritic stainless steels have the problem of securing ridging resistance and the problem of inferior toughness compared to austenitic stainless steels, Patent Documents 3 to 6 show no solution for the problems. It has not been.
In Patent Document 8, it has become possible to achieve corrosion resistance, processability and toughness. Moreover, in patent document 9, it became possible to achieve corrosion resistance, workability, and ridging resistance. However, in Patent Documents 8 and 9, as in the problems of Patent Documents 3 and 4, Cr is diffused from the Cr film on the surface to the inside, and it is difficult to thicken the Cr film itself. The thickness of the Cr-concentrated layer in the surface layer of the steel sheet formed by the diffusion of Cr is not sufficient, and there are problems in the thickness of the region with high Cr concentration in the surface part of the steel sheet and the productivity of the steel sheet.

Therefore, in the present invention, in a clad steel plate including a form such as a clad steel pipe containing Cr and a clad steel foil, both the workability and the corrosion resistance are both enhanced at a high level, and further the occurrence of ridging is suppressed and the toughness is enhanced. An object of the present invention is to provide such a steel plate with high productivity by suppressing the variation of the αFe {222} plane integration degree.

The inventors of the present invention previously suppressed Cr content by concentrating Cr in a surface layer portion of a steel plate having a relatively low Cr content of less than 13% as disclosed in Patent Document 4. In order to ensure the corrosion resistance and to improve the formability of {111} crystal orientation while improving the formability, consider (a) optimizing the rolling ratio of cold rolling in the manufacturing process of steel sheet. {222} texture can be formed in the surface layer, (b) a Cr film is formed on the surface of the steel sheet, and Cr is diffused in the heating process in the process of increasing the Cr concentration in the surface layer of the steel sheet by heat treatment The {222} texture of the region is preserved by making the α single phase texture, and then the texture can be grown over the entire steel plate by heating and cooling to a temperature exceeding the A3 transformation point, and the formability is excellent Good steel plate structure It was found to be.

In the present invention, a clad steel plate obtained by cold rolling a clad material in which regions having different Cr concentrations are formed by a hot-rolled clad method instead of using a steel plate having a Cr film formed on the surface as (c) a steel plate before heat treatment. By using the same, a {222} texture can be formed by the same heat treatment as in Patent Document 3, and a layer with a high Cr concentration and a uniform concentration can be left in the surface layer with a certain thickness or more. It has been found that a clad steel sheet having further enhanced corrosion resistance and formability can be obtained with good productivity.
Furthermore, in Patent Document 6, from the viewpoint of stable manufacturing, there is a problem that the dispersion of the αFe {222} plane integration degree is large, and the manufacturing stability (yield) is not high. It is found that the crystal grains of the outer material are used as the seeds of the γ⇒α transformation of. This is because the γ⇒α transformation in the cooling process proceeds at once when passing through the A3 point temperature, so that the adhesion between the outer material (with Cr) and the base material is insufficient when the interface is insufficient. It is considered that the yield is not high because it becomes difficult to pass the crystal orientation to the base material by using the crystal grains of the material as seeds. That is, in the clad in the warm state described in Patent Document 6, it is presumed that the adhesion between the outer material (with Cr) and the base material (without Cr) is insufficient. Adhesion is enhanced when hot rolling is used, but it is difficult to avoid a decrease in yield when using crystal grains of the outer material as a seed. Therefore, the present inventor diffuses Cr of the outer material (alloy material A) to the base material (steel material B) in a high temperature state, and uses the outer material as the original seed on the base material side of the interface between the outer material and the base material. If a new α-Fe phase stabilization region of a predetermined thickness is formed and this newly formed α-Fe phase stabilization region is used as a new seed, γγα transformation of the base material upon cooling is generated. It has been found that the crystal orientation according to the new species is stabilized and a high yield can be obtained.
Furthermore, with regard to ridging, focusing on the point of suppressing ridging by the anisotropy of the crystal grains in the surface layer of the steel sheet, (d) {111} orientation including {100} orientation grains in the {222} texture of the surface layer If grains other than grains are formed, the orientation group other than {222} in the surface layer does not grow significantly even by the heat treatment, while the steel sheet central layer proceeds from the {111} -oriented grains in the surface layer toward the inside of the steel sheet. It turned out that it becomes a structure | tissue containing the large crystal grain which grew, the magnitude | size of the crystal grain of a steel plate surface layer and a steel plate center layer can be varied, and the subject of a ridging resistance can be solved.
Further, with regard to toughness, paying attention to the point that the crystal grains of the steel plate are refined by recrystallization, (e) the {222} texture is once formed by the above heat treatment, and then this steel plate is cold-rolled When recrystallized by heat treatment at the second α phase temperature, the {222} texture is not largely lost in the recrystallization, and the steel plate is fine equiaxed with the {222} plane integration maintained high It turned out that it became grain, and the problem of toughness could be solved.
The summary of the present invention made as a result of such study is as follows.

(1)
In a clad steel plate having a plurality of layers having different compositions in the thickness direction,
It is a laminated structure of surface layer region-transition region-internal layer region or surface layer region-transition region-internal layer region-transition region-surface region in the thickness direction,
The surface layer region is a region from the surface to a position where the Cr concentration is 95% of the Cr concentration of the surface in the plate thickness direction,
The transition region is a region from a position adjacent to the surface layer region in the thickness direction to a position where the Cr concentration is 13.0 mass% or more,
The inner layer region is a region adjacent to the transition region,
The width of the transition region is at least 5 μm on average,
The average thickness of the surface layer region is 5% or more of the total thickness of the steel plate and less than the thickness of the inner layer region,
The {222} plane accumulation degree of the αFe phase in the inner layer region is 60% or more and 100% or less,
The average composition of the surface region is mass%,
Cr ≧ 13.8%, C ≦ 0.1500%, P ≦ 0.040%, S ≦ 0.0300%, N ≦ 0.2000%, Si ≦ 2.500%, Mn ≦ 1.20% Furthermore, selectively, Al ≦ 8.000%, Mo ≦ 2.500%, Ga ≦ 3.50%, Nb ≦ 1.000%, Sn ≦ 1.800%, Ti ≦ 2.000% V ≦ 2.00%, W ≦ 6.00%, Zn ≦ 4.00%, Ni ≦ 0.6%, Cu ≦ 0.80%, Co ≦ 0.01%, B ≦ 0.01%, At least one element selected from the group consisting of Ca ≦ 0.01%, Ta ≦ 0.01%, Mg ≦ 0.01%, the balance being Fe and impurities,
The average composition of the inner layer region is mass%,
0% <Cr <13.0%, C ≦ 0.0800%, P ≦ 0.040%, S ≦ 0.0300%, N ≦ 0.2000%, and optionally 0.1 % ≦ Ni <1.0%, 0.10% ≦ Mn <1.00%, Cu ≦ 0.01%, Co ≦ 0.01%, B ≦ 0.01%, Ca ≦ 0.01%, Ta A clad steel sheet comprising at least one or more elements selected from the group consisting of ≦ 0.01% and Mg ≦ 0.01%, with the balance being Fe and impurities.

(2)
The steel sheet according to item (1), wherein the {222} plane integration degree of the αFe phase in the surface layer region is 60% or more.

(3)
The steel plate according to item (1) or (2), wherein a ratio Br / Ar of the average crystal grain diameter Br of the inner layer region and the average crystal grain diameter Ar of the surface layer region is 1.5 or more.

(4)
The random intensity ratio of {222} <112> of the αFe phase in the half thickness of the inner layer region is 16 or more, as described in any one of the items (1) to (3). steel sheet.

(5)
The steel plate according to any one of the items (4), wherein the random strength ratio of {222} <112> of the αFe phase in the half thickness of the surface layer area is 16 or more.

(6)
The steel plate according to any one of items (1) to (5), which has a texture in which grains having an average particle diameter of 50 μm or less exist in the thickness direction in the inner layer region.

(7)
Further, an X layer is provided outside the surface area,
The composition of the X layer is 16.0% ≦ Cr ≦ 26.0%, 6.0% ≦ Ni ≦ 22.0%, C ≦ 0.1500%, P ≦ 0.045%, S ≦ 10% by mass. Characterized by 0.0300%, N ≦ 0.4000%, Si ≦ 5.000%, Mn ≦ 10.00%, Mo ≦ 4.000%, Cu ≦ 2.50%, balance: Fe and impurities The steel plate according to any one of the items (1) to (6).

(8)
The steel plate according to any one of the items (1) to (7), which has a form of a thin steel plate or a foil having a thickness of 0.004 mm or more and 3 mm or less.

(9)
A steel pipe manufactured from the steel plate according to any one of items (1) to (7), having a thickness of 0.004 mm or more and 3 mm or less.

(10)
A steel container manufactured from the steel plate according to any one of items (1) to (7), having a thickness of 0.004 mm or more and 3 mm or less.

Here, the {222} plane accumulation degree is 11 planes {110}, {200}, {211}, {310}, {222}, {321} for the plane orientation of the αFe layer parallel to the steel plate surface. The integrated intensities of {411}, {420}, {332}, {521}, {442} are measured, and each of the measured values is divided by the theoretical integrated intensity of the randomly oriented sample and then divided. The ratio of the {222} intensity to the total of 11 planes is determined as a percentage.

In the present invention, a layer having a relatively high Cr concentration as the surface layer and a low layer as the inner layer is configured to have different Cr concentrations in the thickness direction of the steel plate, and {111} oriented grains having excellent workability in the steel plate inner layer Can be formed into a steel plate with excellent workability and corrosion resistance.
Furthermore, by making the grain size of the surface layer of the steel sheet finer than the grain size of the inner layer of the steel sheet, it is possible to provide a steel sheet excellent in workability, corrosion resistance and ridging resistance at low cost.

It is a schematic diagram of the boundary vicinity of the alloy material A and the steel materials B for demonstrating the process for obtaining the clad steel plate excellent in manufacture stability, workability, and corrosion resistance. It is a figure for demonstrating the distribution condition of Cr in a clad steel plate or its precursor for every manufacturing process. It is a schematic diagram of the boundary vicinity of the alloy material A and the steel materials B for demonstrating the process for obtaining the clad steel plate excellent in manufacture stability, workability, corrosion resistance, and toughness.

In the following description,% of element content shall mean mass%. In addition, the crystal orientation in the steel sheet and the measured degree of surface integration are described by crystal plane orientation parallel to the surface of the steel sheet. In addition, with regard to the degree of surface integration, the annihilation rule in the X-ray measurement of the crystal plane is applied, which is caused by the crystal structure of the body-centered cubic that is the α phase of Fe. That is, for example, with regard to crystal orientation, {100} and {111} are used, and with respect to the texture and the degree of surface integration determined by measurement, {200} and {222} are used. It represents information on crystal grains.

The present invention, in a clad steel plate having a plurality of regions in different layers in the layer thickness direction, has a high Cr concentration in the surface layer and a Cr concentration lower than the surface layer in the layer following the surface layer, with a high {222} plane density By forming a layer having a uniform Cr concentration in the surface layer, it is possible to obtain a clad steel sheet having a form such as a steel pipe or steel foil excellent in corrosion resistance and workability.
It should be noted that the Cr concentration, the surface integration degree and the grain size may be changed independently in the thickness direction. That is, the change behavior of the above-mentioned characteristic value in the thickness direction does not necessarily coincide, and the surface region, the transition region and the inner layer region are distinguished by the Cr concentration as described later, but {222} at this boundary There is no need for the surface concentration to change from less than 60% to 60% or more, or to have a clear change in particle size. Thus, in the present invention, changes in concentration, changes in texture, and changes in crystal grain size do not occur rapidly at the same boundary.
Of course, depending on the boundaries clearly distinguished in the thickness direction, the Cr concentration, the area density, and the grain size change greatly at the same time, and even in the region between the boundaries, these characteristics change with similar behavior. The effect is not lost.

Below, the reason for limitation of each condition and preferable conditions are demonstrated about the structure of the clad steel plate of this invention, and the manufacturing method of the steel materials.

Composition of clad steel plate [Basic aspect of clad steel plate]
The clad steel plate of the present invention is a clad steel plate having a plurality of layers in which the compositions are different in the thickness direction in layers, and the surface layer region-transition region-inner layer region or surface region-transition region-inner layer region- It has a laminated structure of transition region-surface region. This clad steel plate is an α-Fe single-phase component system, an alloy material A having a relatively high Cr concentration containing Cr, and an α-γ transformation component system which is an α-Fe phase at normal temperature, and the average Cr concentration is higher than that of the alloy material A It can be obtained by cladding a low steel material B. Due to the cladding, in the Cr concentration distribution in the thickness direction, Cr diffuses from the alloy material A having a relatively high Cr concentration to the steel material B having a relatively low Cr concentration. Therefore, the surface layer region and the inner layer region exist in the thickness direction, and a transition region in which the Cr concentration transitively changes exists between them. Here, the surface layer region is defined as a region from the surface to a position where the Cr concentration is 95% of the Cr concentration on the surface in the thickness direction. The transition region is defined as a region from the position adjacent to the surface layer region in the thickness direction to the position where the Cr concentration is 13.0 mass% or more. The inner layer region is defined as the region adjacent to the transition region. Furthermore, the width of the transition region is 5 μm or more on average. Further, the average thickness of the surface layer region is 5% or more of the total thickness of the clad steel plate and less than the thickness of the inner layer region, and the {222} plane integration degree of the αFe phase in the inner layer region is 60% or more and 100% or less.
The average composition of the surface area is mass%,
Cr ≧ 13.8%, C ≦ 0.1500%, P ≦ 0.040%, S ≦ 0.0300%, N ≦ 0.2000%, Si ≦ 2.500%, Mn ≦ 1.20% Furthermore, selectively, Al ≦ 8.000%, Mo ≦ 2.500%, Ga ≦ 3.50%, Nb ≦ 1.000%, Sn ≦ 1.800%, Ti ≦ 2.000% V ≦ 2.00%, W ≦ 6.00%, Zn ≦ 4.00%, Ni ≦ 0.6%, Cu ≦ 0.80%, Co ≦ 0.01%, B ≦ 0.01%, It contains at least one or more elements selected from the group consisting of Ca ≦ 0.01%, Ta ≦ 0.01%, and Mg ≦ 0.01%, with the balance being Fe and impurities.
The average composition of the inner layer area is mass%,
0% <Cr <13.0%, C ≦ 0.0800%, P ≦ 0.040%, S ≦ 0.0300%, N ≦ 0.2000%, and optionally 0.1 % ≦ Ni <1.0%, 0.10% ≦ Mn <1.00%, Cu ≦ 0.01%, Co ≦ 0.01%, B ≦ 0.01%, Ca ≦ 0.01%, Ta It contains at least one or more elements selected from the group consisting of ≦ 0.01% and Mg ≦ 0.01%, with the balance being Fe and impurities.
In addition, although the clad steel plate of this invention can be arbitrary plate thickness from plate to foil in plate thickness, although the shape also includes a state of a plate and a press-formed state, hereinafter, the steel plate will be described. However, the same applies to other forms.

(Layer structure)
First, the definition of the surface layer region, the transition region, and the inner layer region will be described.
The surface layer region defined by the present invention is a region in the thickness direction from the surface to a position where the Cr concentration is 95% of the Cr concentration on the surface. Because Cr diffuses from the alloy material A having a relatively high Cr concentration to the steel material B having a relatively low Cr concentration by cladding, generally in the surface region, the Cr concentration is from the surface region to the inner layer region Decrease towards In order to clarify the boundary with the transition region, a region from the surface to a position where the Cr concentration is 95% of the Cr concentration of the surface is defined as a surface region.
The transition region is a region from the position adjacent to the surface layer region in the thickness direction to the position where the Cr concentration is 13.0 mass% or more. The transition region overlaps the region in which Cr diffuses from the alloy material A having a relatively high Cr concentration to the steel material B having a relatively low Cr concentration in the thickness direction, and one of the boundaries is adjacent to the surface region In the position, the other boundary is in the position where the Cr concentration is 13.0 mass% or more. In the transition region, the α-Fe phase is stabilized because the Cr concentration is 13.0 mass% or more. In addition, the width of the transition region in which Cr is 13.0% by mass or more is 5 μm or more on average.
The inner layer region is the layer adjacent to the transition region. The inner layer region has a Cr concentration of less than 13.0% by mass. When the Cr concentration is 13.0% by mass or more, since it is an α single phase component, formation of a texture due to transformation progress does not occur in heat treatment, and it becomes difficult to secure a high {222} surface integration degree. This inner layer region can be obtained by using, as a base material, a steel material B which is an α-γ transformation component system which is an α-Fe phase at normal temperature and whose average Cr concentration is lower than that of the alloy material A.
The steel sheet of the present invention is a steel sheet in which the surface layer region, the transition region and the inner layer region are formed in layers, or a laminated structure of surface layer region-transition region-inner layer region-transition region-surface layer region.
The Cr concentration distribution and the steel plate average of the Cr concentration can be determined by performing line analysis on the cross section in the thickness direction of the steel plate using EPMA. Thereby, the thicknesses of the surface layer region, the transition region and the inner layer region can be measured in the following manner. The cross section of the steel plate is measured by EPMA analysis to measure the Cr concentration profile in the thickness direction, and the width of the region from the surface of the steel plate to a position where the Cr concentration is 95% of the Cr concentration on the surface is taken as the width of the surface region. The width of the region having a Cr concentration of 13.0 mass% or more from the position adjacent to the surface region is taken as the width of the transition region. The width of the region where Cr is more than 0% by mass and less than 13.0% by mass from the position adjacent to the transition region is the width of the inner layer region. Moreover, the Cr concentration profile in the depth direction can be measured by GDS analysis, and the widths of the surface layer region, the transition region, and the inner layer region can be similarly measured.
In addition, the mass percentage of the average composition of the surface layer area measures the Cr concentration profile in the plate thickness direction by EPMA analysis of the cross section of the steel plate, and from the surface of the steel plate to a position where the Cr concentration is 95% of the Cr concentration of the surface The width of the region of (1) was taken as the surface region, and the width was determined by the analysis value of the surface region.
In addition, the mass% of the average composition in the inner region was determined by an analysis value within a range in which the change in Cr concentration is constant.
In addition, although a layer to which Cr diffused is present from the alloy material A to the steel material B having a relatively low Cr concentration due to cladding, in the clad steel plate, the position of the interface between the alloy material A and the steel material B is confirmed be able to. Specifically, after mirror-polishing a cross section of the clad steel plate of the present invention, the position of the interface between the alloy material A and the steel material B is confirmed from the difference in contrast by etching with a known etchant such as aqua regia. be able to. In addition, thin oxide layers and the like exist partially on the surfaces of the alloy material A and the steel material B, which are the materials of clad steel sheets, and these oxide layers and the like are both hot-rolled and cold-rolled for cladding. Since it partially exists at the interface, the position of the oxide layer or the like can be confirmed by a known analysis method such as an electron microscope, and the position of the interface between the alloy material A and the steel material B can be confirmed based on this.
The transition region includes an α-Fe phase stabilization region in which Cr newly formed on steel material B is 13.0 mass% or more, and steel material B (corresponding to the inner layer region) which is an α-γ transformation component system It acts as a new species that causes γ⇒α transformation when heating and cooling to A3 point or more. Since the new species is formed on the side of the steel material B (base material), the crystal lattice is easily aligned when the steel material B (base material) or the inner layer region is transformed from γ to α, and the crystal orientation is stabilized. .
The transition region is formed to have an average width of 5 μm or more in the thickness direction, whereby the transition region includes new species with a sufficient width. The crystal orientation of the steel material B or the inner layer region is stabilized following the new species. If the transition region has a width of 10 μm or more on average, the crystal orientation is more stabilized. If the transition region has a width of 15 μm or more on average, the crystal orientation is further stabilized.

Next, the lamination structure of the steel plate will be described.
In the steel plate of the present invention, from the surface side of the steel plate, it has a lamination structure of surface layer region-transition region-inner layer region in the plate thickness direction, or a surface layer region-transition region-inner layer region-transition region-surface layer region. The most typical lamination configuration is a lamination configuration of surface layer region-transition region-inner layer region-transition region-surface region region, in which both sides of the inner layer region are sandwiched by transition regions and further sandwiched by surface regions. Alternatively, the surface layer region-transition region-inner layer region may be stacked, in which the surface region and the transition region are formed only on one side of the inner layer region. With such a configuration, it is possible to achieve both workability and corrosion resistance.
In the following, the conditions to be satisfied by the present invention will be described for the surface layer region, the transition region and the inner layer region, but if there are a plurality of surface region, transition region and inner layer region in the steel sheet, all the layers There is a need to satisfy each condition.

(Composition of surface area)
The surface layer region is a region in which the concentration of the ferrite forming element is relatively high in the steel sheet either alone or together with Cr. The ferrite forming element is at least one or more elements of Al, Ga, Mo, Nb, Si, Sn, Ti, V, W and Zn.

In the present invention, the Cr concentration in the surface layer region is defined by the average concentration in the surface layer region. The reason for this is that in the present invention, the variation of the Cr concentration in the surface layer region is allowed. In the present invention, this concentration is 95% by mass or more of the Cr concentration of the surface. Needless to say, the Cr concentration at any position in the thickness direction in the surface layer region is higher than the average Cr concentration in the entire steel plate, and Cr at any position in the thickness direction of the transition region and the inner layer region Higher than concentration. Therefore, the average Cr concentration of the surface layer region defined here is higher than the average Cr concentration of the entire steel plate and higher than the average concentration of the transition region and the inner layer region. The average Cr concentration in the surface layer region is 13.8% or more. This is because the Cr concentration is reduced by diffusion from the surface of the surface layer region toward the transition region. That is, if the average Cr concentration in the surface region is 13.8% or more, the Cr concentration at the boundary between the transition region and the surface region is 95% or more of the surface of the surface region, and the Cr concentration in the transition region is 13 It is realized that .0% or more. In order to obtain higher corrosion resistance, the average Cr concentration in the surface layer region is preferably 18.0% or more, more preferably 20.0% by mass or more.

In the present invention, the region Ae of uniform Cr concentration may further be present in the thickness direction within the fluctuation of ± 3% by mass on the surface of the surface region.
In this method, the surface layer material having a high Cr concentration and the center layer material having a relatively low Cr concentration are laminated, clad hot rolling, cold rolling, a clad steel plate is manufactured, and the surface layer portion is heat treated. Can be formed by the remaining area of the original surface layer material.

By arranging the region Ae having such a uniform Cr concentration with a width of 1 μm or more in the thickness direction of the surface of the surface region, it is possible to prevent the occurrence of pitting on the surface due to the formation of pinholes due to distortion during molding. It is effective in preventing material deterioration due to corrosion due to fatigue and environmental conditions that cause cracking. That is, the corrosion resistance can be more effectively enhanced by increasing the Cr concentration in the surface layer region and expanding the Cr uniform region in the thickness direction of the surface layer region.
Such an effect can not be obtained unless the width in the thickness direction of the region Ae is 1 μm or more.

In the present invention, the concentration distribution of the contained elements in the steel plate thickness direction is not particularly limited. However, as described later, Cr diffusion toward the inside of the steel plate from the uniform region of the Cr concentration on the surface side In the manufacturing method that utilizes Fe diffusion from the surface to the surface of the steel sheet, the center of the steel sheet is low, and the Cr concentration is higher toward the surface of the steel sheet. With regard to the corrosion resistance, the effect of the Cr concentration on the surface of the steel sheet is particularly large, so 13.0 mass% or more, further 18.0 mass% or more, even in the region Ae of uniform Cr concentration on the surface, not the entire Cr concentration part. It is an effective means to control so that it becomes more than 20.0 mass% from the viewpoint of coexistence of alloy cost and corrosion resistance, and such means is by making a clad steel plate using materials having different Cr concentration. It can be realized more easily.

The surface layer area is mainly composed of Cr-containing alloy material A of α single phase component system, and the average composition is mass%, CrCr13.8%, C ≦ 0.1500%, P ≦ 0.040%, S It contains ≦ 0.0300%, N ≦ 0.2000%, Si ≦ 2.500%, and Mn ≦ 1.20%. The processability is improved by lowering the carbon content and reducing the nitrogen content within the above range. Moreover, it is preferable that P and S be small from the viewpoint of corrosion resistance, and it is preferable to be in the above-mentioned range from the balance of the refining cost and the like. Increasing Cr and adding Mn are effective in improving the corrosion resistance and are preferable.
Furthermore, when adding Cr and the above-mentioned ferrite forming element to the surface layer region, the content of the ferrite forming element is preferably in the following range.
Average composition is mass%, Al ≦ 8.000%, Mo ≦ 2.500%, Ga ≦ 3.50%, Nb ≦ 1.000%, Sn ≦ 1.800%, Ti ≦ 2.000%, V ≦ 2.00%, W ≦ 6.00%, Zn ≦ 4.00%.
In addition, for the purpose of improving the characteristics of the surface layer region, etc. within the range that does not lose the effects of the present invention, the average composition of the surface layer region is Ni ≦ 0.6%, Cu ≦ 0.80% by mass%. At least one of ≦ 0.01%, B ≦ 0.01%, Ca ≦ 0.01%, Ta ≦ 0.01%, and Mg ≦ 0.01% may be selectively included. The lower limit value of these selectively contained elements may be 0 mass%. The balance is Fe and impurities.
The surface region needs to maintain the αFe single phase composition. In the Fe-Cr system, if Cr is 13.0 mass% or more, it is an α-Fe single phase. Ni can be added to enhance corrosion resistance, but Ni is a γ-Fe phase forming element. Even in such a case, the average composition is, by mass%, Al ≦ 8.000%, Mo ≦ 2.500%, Ga ≦ 3.50%, Nb ≦ 1.000%, Sn ≦ 1.800%, Ti ≦ Stabilizing as an α-Fe single phase by adding at least one or more ferrite forming elements of 2.000%, V ≦ 2.00%, W ≦ 6.00%, Zn ≦ 4.00% It becomes possible. If the content of each ferrite forming element is larger than the upper limit value, the workability is unfavorably deteriorated. The specific addition amount can be defined as a range for maintaining the α single phase system by phase diagram calculation using the CALPHAD method. Thus, as long as the surface layer region maintains the αFe single phase, it is possible to add the γFe phase forming element and the αFe phase forming element corresponding thereto. Among the ferrite forming elements, Al and Mo have the effect of improving the high temperature oxidation resistance, and Mo, Nb, Ti, V and W have the effect of stabilizing the passivation film and improving the corrosion resistance. Nb and Ti have the effect of reducing the C and N which are solid-solved in combination with C and N to improve the workability. Cu, which is a γ-Fe phase forming element, has an effect of improving strength by precipitation hardening, and can be added at 3.00 mass% or less. Although Zr has a small amount of solid solution in the α-Fe phase and the γ-Fe phase, addition of 1% by mass or less has an effect of reducing C and N which are solid-bonded with C and N to improve workability.
In addition, the above-mentioned elements such as Al are optional additional elements and do not need to be contained, and the addition amount can be appropriately adjusted in accordance with the effects expected from the respective elements. As a lower limit of the addition amount of each element, the following may be used in mass%. Al: 0.600%, Mo: 0.500%, Ga: 0.90%, Nb: 0.400%, Si: 0.900%, Sn: 0. 100%, Ti: 0.700%, V : 0.60%, W: 1.20%, Zn: 0.80%.

(Composition of transition region)
The average Cr concentration in the transition region is 13.0% by mass or more in the context of a method of controlling the texture by transformation described later. As a result, finally, the degree of {222} plane integration of the inner layer region is increased, and good processability can be easily obtained. The transition region is a region in which the base material of the surface layer region and the base material of the inner layer region are clad and formed between the surface layer region and the inner layer region, and the Cr concentration transitively changes. The composition of the transition region is defined to have a Cr concentration of 13.0 mass% or more, but is not particularly defined for elements other than Cr, and may be defined according to the composition of the surface layer region and the inner layer region .

(Composition of inner layer area)
In the present invention, the Cr concentration of the inner layer region is defined by the average concentration of the inner layer region. This is done because in the present invention, the Cr concentration fluctuation in the inner layer region is allowed. In the present invention, this concentration is less than 13.0% by mass. Since the inner layer region is a region where the Cr concentration is lower than the average value, it necessarily contains Cr, but in the present invention, the necessary corrosion resistance is ensured in the surface layer region, so the lower limit of the Cr concentration in the inner layer region is Not provided
Needless to say, the Cr concentration at any position in the thickness direction in the inner layer region is lower than the average Cr concentration in the entire steel sheet, and at any position in the thickness direction in the surface region or transition region. Lower than Cr concentration. Therefore, the average Cr concentration of the inner layer region defined here is lower than the average Cr concentration of the entire steel plate and lower than the average concentration of the surface region or the transition region.

In relation to the manufacturing method of controlling the texture by the transformation described later, the inner layer region is based on the steel material B of the α-γ transformation component composition, which is the α phase at normal temperature, and the average composition is mass%, 0% <Cr <13.0%, C ≦ 0.0800%, P ≦ 0.040%, S ≦ 0.030%, N ≦ 0.2000% may be contained. Alternatively, it is preferable to further contain one or both of Ni and Mn in the range of 0.1% ≦ Ni <1.0%, 0.10% ≦ Mn <1.00%. Furthermore, the average composition of the inner layer region is selectively in mass%, Cu ≦ 0.01%, Co ≦ 0.01%, B ≦ 0.01%, Ca ≦ 0.01%, Ta ≦ 0. It may contain at least one or more elements selected from the group consisting of 01% and Mg ≦ 0.01%. The balance is Fe and impurities.

When Cr is 13.0% by mass or more, since it is an α single phase component, formation of a texture due to transformation progress does not occur in heat treatment, and it becomes difficult to secure a high {222} plane integration degree. The processability is improved by lowering the carbon content and reducing the nitrogen content within the above range. Moreover, it is preferable that P and S be small from the viewpoint of corrosion resistance, and it is preferable to be in the above-mentioned range from the balance of the refining cost and the like.
Ni and Mn are preferable elements for making the effect of the present invention remarkable particularly in terms of selectivity of crystal orientation and grain growth behavior in the manufacturing method of controlling the texture by the transformation described later. When Cr is contained in a range of less than 13.0 mass% and Ni and Mn are further contained as the composition of the inner layer region, Ni: 0.1 mass% or more, Mn: 0.10 mass% or more The workability and corrosion resistance are both significantly improved. If the content of Ni and Mn is 1.0% by mass or more, the processability is deteriorated, so less than 1.0% by mass is preferable. Although the lower limit concentration of Cr in the inner layer region is more than 0% by mass, even when a material having a Cr concentration of 0% by mass is used as the steel material B, an alloy material used as a base material of the surface layer region In the inner layer region including Cr diffusion from A, the average Cr concentration is more than 0 mass%. For the purpose of improving the characteristics of the inner layer region, etc. within the range not to lose the effects of the present invention, the average composition of the inner layer region is selectively Cu by 0.01%, Co ≦% by mass. Even containing at least one element selected from the group consisting of 0.01%, B ≦ 0.01%, Ca ≦ 0.01%, Ta ≦ 0.01%, Mg ≦ 0.01% Good.

With regard to the composition of the surface layer region, the transition region, and the inner layer region, as long as the content of the essential element Cr is in the above range, the impurities or impurity elements inevitably mixed in from the raw materials etc. or in the refining process The composition of a known Cr steel or stainless steel containing various elements other than Cr can be applied to obtain predetermined characteristics. In other words, the impurities may be components that do not affect the effects of the present invention. Therefore, as described above, the inclusion of γ-forming elements such as Ni and Cu is permitted as long as the surface layer region maintains the α single phase system. Specifically, the combination of the elements and the allowable content can be defined as a range in which the α single phase system is maintained by phase diagram calculation using the CALPHAD method. On the other hand, also in the inner layer region, the inclusion of α-forming elements such as Al, Mo, Ga, Nb, Sn, Ti, V, W, Zn, etc. is acceptable as long as the α-γ transformation system is maintained. Specifically, the combination of the elements and the allowable content can be similarly defined as a range for maintaining the α-γ transformation system by phase diagram calculation using the CALPHAD method. Remaining unavoidable impurities are acceptable as long as they do not inhibit the effects of the present invention. The transition region is a region formed by cladding the base material of the surface layer region and the base material of the inner layer region and forming a layer between the surface layer region and the inner layer region and reducing the Cr concentration from the surface layer region to the inner region . The composition of the transition region is defined to have a Cr concentration of 13.0% by mass or more, and maintains an α single phase system. The transition region is not particularly defined for elements other than Cr, and may be defined according to the composition of the surface layer region and the inner layer region.

(Thickness of surface area)
The average thickness of the surface layer region is 5% or more of the total thickness of the steel and less than the thickness of the inner layer region. When the surface layer area exists on both sides of the clad steel plate, the thickness is on one side. If the thickness is less than 5%, it is sufficient to start with the {111} -oriented grains of the surface layer as shown in FIG. 1 (d) in relation to the manufacturing method of controlling the texture by transformation described later. It is difficult to make the {222} plane accumulation degree inside the steel plate 60% or more. Moreover, 5% or more is also required from the point of securing corrosion resistance.
When the average thickness of the surface layer region is equal to or greater than the thickness of the inner layer region, the Cr content of the entire steel sheet increases and the alloy cost increases, but the effect on the improvement of corrosion resistance and workability (texture controllability) Saturate.
The specific thickness is selected from the range of 0.05 μm to 1000 μm according to the thickness of the steel material.

(Thickness of transition region)
The thickness of the transition region is formed to have an average width of 5 μm or more in the thickness direction. If the thickness is less than 5 μm, in relation to the manufacturing method of controlling the texture by the transformation described later, starting from the {111} -oriented grains of the surface layer, the grains are internalized as shown in FIG. 1 (d) It is difficult to make the {222} plane accumulation degree inside the steel sheet 60% or more. If the transition region has a width of 10 μm or more on average, the crystal orientation is more stabilized. If the transition region has a width of 15 μm or more on average, the crystal orientation is further stabilized. The upper limit of the thickness of the transition region is not particularly limited. However, since the transition region is a region formed between the surface layer region and the inner layer region, it may be defined according to the thickness of the surface layer region and the inner layer region.

(Thickness of inner layer area)
The thickness of the inner layer region is preferably 4 μm or more and 3 mm or less. If the thickness is less than 4 μm, it will be very difficult to preferentially grow surface layer {111} -oriented grains inside the steel sheet in connection with the manufacturing method of controlling the texture by transformation described later. Further, if the thickness is more than 3 mm, {111} oriented grains can not be sufficiently grown to the inside of the steel plate, and it becomes difficult to obtain a steel plate with good workability.

(Group organization)
In the basic aspect, for the inner layer region, the {222} plane accumulation degree of the αFe phase to the plate surface is defined. The {222} plane accumulation degree is at an arbitrary position in the thickness direction of the steel plate, and the α crystal 11 plane of {110}, {200}, {211}, {310}, {alpha} parallel to the steel plate surface. Integral intensities of 222}, {321}, {411}, {420}, {332}, {521}, {442} were measured, and each of the measured values was divided by the theoretical integral strength of the randomly oriented sample. After that, it is determined as a percentage of {222} intensity to the sum of 11 planes of divided values. The integral intensity of the sample having a random orientation uses the theoretical integral intensity.

That is, the {222} plane density is expressed by the following equation (1).
{222} surface integration degree = [{i (222) / I (222)} / Σ {i (hkl) / I (hkl)}] × 100 (1)
However, the symbols are as follows.
i (hkl): Measured integrated strength of {hkl} plane in the measured sample I (hkl): Theoretical integrated strength of {hkl} plane in the sample having random orientation :: Sum of 11 planes of α-Fe crystal where: The integral strength of each crystal plane at any position in the thickness direction is obtained by applying a general EBSD method to a plate surface where the thickness section has been polished. The surface integration degree of the crystal orientation of the surface layer region and the inner layer region was calculated at the center of each layer, that is, at the half thickness position of each layer.

In the present invention, as to the texture, according to the characteristics of the steel plate, the aspect is divided as follows.
(I) Steel sheet having a {222} plane accumulation degree of αFe phase in the inner layer region of 60% or more and 100% or less (basic aspect)
(Ii) A steel plate having a structure in which grains having an average particle diameter of 50 μm or less exist in the thickness direction in the inner layer region in the steel plate of (i) above

Here, as a common basic aspect, a steel plate excellent in corrosion resistance and workability having a {222} plane integration degree of the αFe phase in the inner layer region of (i) of 60% or more and 100% or less will be described. The steel plate of (ii) will be described later.
<Area concentration of surface area>
The surface integration degree of the surface layer region is not particularly defined in the basic form from the viewpoint of workability. Since machinability is basically ensured by increasing the {222} plane integration degree of the inner layer area layer, the {222} plane integration degree of the surface layer area is a value measured at the central position in the thickness direction of the surface area. If it is 30% or more, the whole processability can be secured. This value is obtained in the production of a general clad steel plate.
In particular, in order to obtain excellent bending workability, it is preferable to set the {222} plane integration degree to 60% or more.

<Area integration degree of inner layer area>
The inner layer region has a {222} plane integration degree of 60% or more and 100% or less. The surface integration degree is measured at the central position in the thickness direction of the inner layer region, as in the above-described surface region.
When the {222} plane integration degree is less than 60%, the workability of the clad steel plate is not sufficient, and for example, as shown in the examples described later, the ear height after deep drawing of a cylinder with a drawing ratio of 2 It is impossible to obtain a formability of 1.5 mm or less.
Also, the degree of integration may be 99% or less. If it exceeds 99%, the production may be difficult, or the processability may be nearly saturated.

<Ratio of particle size of surface area and inner layer area>
In this steel plate, the ratio Br / Ar of the average crystal grain size Br in the inner layer area to the average crystal grain size Ar in the surface layer area may be 1.5 or more. If this particle size ratio is less than 1.5, the ridging resistance can not be improved. Since the ridging resistance can be improved if the lower limit value of the particle size ratio is determined, the upper limit value is not defined. It is preferable to increase the lower limit value of the particle size ratio to 3.0 because the ridging resistance can be further improved. The upper limit of the particle size ratio is preferably 5.0 or less from the viewpoint of further improving the ridging resistance.
The average crystal grain size of each layer is determined by performing the structure observation in the same cross section for each of the surface layer region and the inner layer region determined by line analysis of EPMA in the cross section in the plate thickness direction of the steel sheet. The average grain size is measured by first polishing the surface to be observed to a mirror surface level and then contrasting grain boundaries with a known etching solution (eg, aqua regia or Nytar) according to the steel sheet composition. To make it possible to distinguish individual crystal grains. Thereafter, the number N of crystal grains present in a predetermined length L is counted, and a method called a line segment method in which L / N is an average crystal grain diameter is used.

[Other Aspects of Clad Steel Plate]
The clad steel plate having the texture different from that of the basic form (ii), the clad steel plate having the surface layer region and the inner layer region and the D layer as the intermediate layer and / or the X layer as the outermost layer will be described. The description of the parts common to the basic aspect is omitted.

(Steel plate of (ii) above)
This steel plate has a structure in which grains having an average particle diameter of 50 μm or less exist in the thickness direction in the inner layer region in the steel plate of (i), thereby achieving corrosion resistance and workability (and further, ridging resistance). In addition, it is a steel plate excellent in toughness.
In the method of controlling the texture by phase transformation described later, the {111} -oriented grains in the surface region grow toward the inner layer region. For this reason, in a thin steel plate having a thin plate thickness or a steel plate having only one surface region, there may be a case where one crystal grain is formed in the thickness direction of the plate. In this aspect, after the steel sheet of the form (i) is once formed, cold rolling and recrystallization are further used to form a plurality of fine crystal grains in the thickness direction of the sheet.
<Area concentration of surface area, inner layer area>
In this steel sheet, the {222} plane integration degree of the surface layer region and the inner layer region is 50% or more in the surface layer region and 60% or more in the inner layer region in order to improve workability. The upper limit is 100% or less.
When the {222} plane density in each layer is less than the lower limit, the processability is not sufficient. For example, as shown in the examples described later, the ear height is 1 after cylindrical deep drawing with a drawing ratio of 2 A formability of not more than .5 mm can not be obtained. Also, the degree of integration may be 99% or less. If it exceeds 99%, the production may be difficult, or the processability may be nearly saturated.

<Grain composition of steel plate>
In this steel plate, the average grain size of the entire inner layer region is made of crystal grains of 50 μm or less.
This rule is high, as will be described later, by placing relatively coarse crystal grains with a {222} plane density of 60% or more up to the inside of the steel sheet and then introducing strain by cold rolling to recrystallize { This is because the inventors have found that it is possible to form fine crystal grains over the entire steel sheet while maintaining the degree of surface integration.
When the grain size exceeds 50 μm, sufficient improvement in toughness can not be obtained.
The recrystallized structure and the grain size can be determined by a known method for the steel sheet after heat treatment. For example, a layer corresponding to the surface layer region and the inner layer region is cut out as a steel plate by polishing or the like, a cross section of the steel plate is polished and etched, and a metal structure is observed with an optical microscope to specify a recrystallized structure and The diameter when the cross-sectional shape of the circle is a circle may be determined as the crystal grain size.

[Clad steel plate having D layer]
In the present invention, in addition to the steel plate in which the surface layer region, the transition region and the inner layer region are laminated, the steel composition of the region Ae having an average composition of Cr: less than 3.0% by mass as the inner layer region There may be a steel plate having a D layer having a high concentration of the ferrite forming element on the inner side.

In the layer D, as described later, Al ≦ 12.000%, Mo ≦ 6.500%, Ga ≦ 4. In mass% between the alloy material A for the cladding surface layer and the steel material B for the cladding central layer. 0%, Nb ≦ 4.00%, Si ≦ 5.000%, Sn ≦ 3.000%, Ti ≦ 3.000%, V ≦ 3.00%, W ≦ 6.00%, Zn ≦ 4.00 % Of Fe-based alloy containing at least one ferrite-forming element, and the ferrite-forming element is removed from film D during the process of hot rolling of clad steel plate production and heat treatment described later. By diffusion to both sides, after the heat treatment, it is formed to overlap with the transition region inside the region Ae.

The D layer is composed of a region in which the concentration of the ferrite forming element is higher than the average concentration in the surface layer region, and the thickness thereof is 0.05 μm or more.
By having such a D layer inside the steel, the {222} plane integration degree of the inner layer region can be further highly integrated, thereby further improving the workability and increasing the average r value of the steel Can.

Note that setting the average composition of the inner layer region to less than 3.0% by mass of Cr reduces the amount of Cr to further improve the processability and shortens the rolling process step in production, for example, once This is to increase the rolling reduction and reduce the number of passes.

[Clad steel plate having X layer]
In the present invention, in addition to the steel plate in which the surface layer region and the inner layer region are laminated, the outermost layer further includes an X layer on one side or both sides of the clad steel plate. The outermost layer may be also referred to as the outermost layer or the outermost layer. In the clad steel plate including the outermost layer, the outermost layer is the layer positioned outermost on the basis of the inside of the steel plate. In the clad steel plate which does not contain the outermost layer, the surface region is located at the outermost side, unless otherwise specified. The composition of the X layer is, in mass%, 16.0% ≦ Cr ≦ 26.0%, 6.0% ≦ Ni ≦ 22.0%, C ≦ 0.1500%, P ≦ 0.045%, S ≦ 0.0300%, N ≦ 0.4000%, Si ≦ 5.000%, Mn ≦ 10.00%, Mo ≦ 4.000%, Cu ≦ 2.50%, balance: Fe and impurities. By providing the X layer on the outermost layer, the corrosion resistance and the like are improved. The thickness of the X layer can be appropriately adjusted according to the required corrosion resistance and the like, and the material cost can be reduced by thinning the thickness of the outermost layer containing expensive Ni. The addition of Mo is effective in improving the corrosion resistance. Addition of Cu is effective to improve the sulfuric acid resistance. When the content of Cr is 24.0% by mass or more and the content of Ni is 6.0% by mass or more, a two-phase mixed structure of a ferrite phase and an austenite phase is formed, and stress corrosion cracking resistance and pitting resistance are improved. In addition, strength and toughness are improved by forming a two-phase mixed structure.

[Other characteristics etc.]
(Random intensity ratio)
The {222} <112> orientation is an orientation that increases the average r value of the steel plate, and the random strength ratio of {222} <112> of the αFe phase at 1⁄2 thickness of the inner layer region is 16 or more desirable. Furthermore, it is more desirable that the random intensity ratio of {222} <112> of the αFe phase in the half thickness of the surface layer region be 16 or more simultaneously. When the random strength ratio is 16 or more, a clad steel plate having an average r value of 2.6 or more can be obtained. The upper limit value of the random intensity ratio is 50 in order to increase the average r value.
The random intensity ratio is a relative intensity based on the X-ray intensity of the random sample. The sample for X-ray diffraction may be adjusted by polishing the steel plate so that the half thickness portion of the surface layer region or the inner layer region is the measurement surface.

(Average r value)
The average r value of the clad steel sheet obtained by the present invention is desirably 2.0 or more, and more desirably 2.6 or more.
The average r value is measured using a tensile test using JIS 13 B or JIS 5 B test pieces, and from the change in the distance between marked points after 10% or 15% tension and the change in sheet width, the average r value It may be calculated according to the definition. If the uniform elongation is less than 10%, it may be evaluated by giving a tensile deformation of 3% or more and the uniform elongation or less. Assuming that the measured value r0 in the 0 ° direction, the measured value r45 in the 45 ° direction, and the measured value r90 in the 90 ° direction with respect to the rolling direction, the average r value is given by (r0 + r90 + 2 × r45) / 4.

(Others)
As a form of a clad steel plate, it has a form of a board, a thin plate, and foil which hot-rolled and cold-rolled a clad material and then heat-treated and manufactured it. In addition, it includes tubes, cylinders, containers and the like which are produced by bending, deep drawing, ironing and the like using them as materials.
In addition, the surface of the clad steel plate may be subjected to surface treatment such as known plating for a known purpose, if necessary. The effect of the present invention is not lost by this.

Method of Producing Clad Steel Plate Subsequently, the method of production of the present invention will be described with reference to the drawings.
The clad steel sheet of the present invention can be any thickness from sheet to foil in sheet thickness, and it includes those in the form of sheet and in the state of press-formed. However, the other forms are also the same. In addition, although the clad steel plate in which the surface layer region and the transition region are disposed on both sides of the inner layer region is described as an example for each form of the above-described texture, the cladding in which the surface region, the transition region and the inner layer region are disposed The same applies to steel plates.
The control of the Cr concentration distribution and the crystal orientation described below utilizes basically the same phenomenon as the techniques disclosed by the present inventors in Patent Documents 4 and 6. That is, the crystal growth along the direction of the element concentration is used as a basic principle by utilizing diffusion and transformation in heat treatment.

However, in the steel plate of Patent Document 4, a Cr-enriched portion is formed in the surface layer, but since it is difficult to thicken the Cr film itself, the thickness of the Cr-enriched layer of the steel plate surface layer formed by diffusion of Cr from the Cr film. Even not enough. Therefore, there is a problem that it is likely that the case where sufficient corrosion resistance can not be obtained in the case where a scratch or the like occurs.
Further, in the steel plate of Patent Document 6, the base material is transformed according to the crystal orientation of the outer material, using the outer material thicker than that of Patent Document 4 as a seed, but the adhesion between the outer material and the base material is insufficient And the problem is that the yield of the desired product is not high.

The inventors have found that high yield can be obtained. That is, Cr of the outer material (alloy material A) is diffused into the base material (steel material B) in a high temperature state to form a precursor region in which new α-Fe is generated. The precursor region is a region which is formed in the base material B and in which the Cr concentration is higher than the Cr concentration of the original base material. It is possible that the crystal orientation according to the new species is stabilized and a high yield is obtained if the γγα transformation of the base material is generated when cooling with the new α-Fe generated in the precursor region as a new seed. I found it.

In order to efficiently form the precursor region on the base material (steel material B), the clad material in which the alloy material A and the steel material B are laminated is hot-rolled into a hot-rolled clad steel plate. The inventors have found that it is sufficient to form a region having a predetermined Cr concentration range from the interface of the steel material B to the steel material B side with a predetermined width in the thickness direction.

The method for forming a new species in the base material, that is, the method for forming the precursor region has been newly found by the present inventor. Here, the clad steel plate of the present invention is obtained by laminating clad materials, hot rolling, heat treating, cold rolling and further heat treating, and depending on each process, the clad steel plate or its precursor The distribution of Cr changes. Then, the method for forming a new seed in a base material is demonstrated below, referring the condition in each process of FIG.

The new type precursor region is a region which is formed in the base material B and in which the Cr concentration is higher than that of the original base material. More specifically, in the precursor region, from the interface between the alloy material A and the steel material B of the hot rolled clad steel plate on the side of the steel material B, a region of 13.0 mass% or more of Cr averages from the interface in the plate thickness direction Present in a width of 30 μm or less, more preferably in a width of 20 μm or less, more preferably in a width of 10 μm or less, and in the region of the steel material B adjacent thereto, Cr is 10.0% by mass or more and 13.0 It is a region in which less than% by mass is present at an average width of 5 μm or more, more preferably an average width of 10 μm or more, still more preferably an average width of 20 μm or more. (Refer to the upper left of Fig. 2)
The average width of the region of 13.0 mass% or more of Cr in the precursor region is preferably a narrow width from the interface between the alloy material A and the steel material B to the steel material B side, and Cr adjacent to the Cr is 10. The average width of the region of 0% by mass or more and less than 13.0% by mass is preferably thicker. When Cr is diffused from the alloy material A to the steel material B, the average width of the region of 13.0 mass% or more and Cr is generally 10.0 mass% or more and less than 13.0 mass% by the diffusion of Cr. These relationships are contradictory, as both of the average widths of the regions become thicker. The inventors have found that it is possible to maintain and optimize the Cr concentration of both having the contradictory relationship so as to correspond to heat treatment at a temperature of 600 ° C. to 800 ° C. for 5 minutes to 6 hours after hot rolling. .
The method of heat treatment for forming the precursor region is not particularly limited as long as the above temperature and time can be managed. The precursor region may be formed by performing batch annealing after hot rolling. It may keep warm at the time of winding after hot rolling, and may form the above-mentioned precursor field. At this time, for example, when the winding temperature is low, the temperature is maintained for a sufficient time calculated from the diffusion of Cr. Conversely, when the winding temperature is high, the temperature of the winding coil can be controlled by forced cooling to form the precursor region. Besides, there is also a means of keeping the temperature high enough to diffuse Cr including the outer side by attaching a heat insulating cover or the like in consideration of the fact that in the actual production, the outer side of the coil is easily cooled down.

Thereafter, the hot rolled clad steel plate is further cold-rolled to form a cold rolled clad steel plate. This cold rolling is to bring the α-Fe phase of the alloy material A into contact with the γ-Fe phase of the steel material B (when performing heat treatment for transformation). This is because in order to form a new seed on the steel material B using the original seed of the alloy material A, it is necessary that the two phases be in contact with each other. Before cold rolling (see the upper left of Fig. 2), if the width of the region of 13.0 mass% or more of Cr in the precursor region is 30 μm or less on average, contact of both phases is possible by cold rolling, If the width of the region is more than 30 μm, the contact between the two phases is likely to be insufficient. If this width is 20 μm or less, more areas can be brought into contact, which is more preferable. If this width is 10 μm or less, it is more preferable because a larger area can be brought into contact.

The steel sheet B in the obtained cold rolled clad steel plate is heated to a temperature above the temperature at which the α-Fe phase transforms to the γ-Fe phase to 1300 ° C. or lower, and then cooled to transform the γ-Fe phase to the α-Fe phase Heat treatment. By this, it is possible to stably obtain an excellent α-Fe {222} plane integration degree, and to manufacture a steel plate excellent in corrosion resistance and workability with a high yield.
Here, a region of 10.0% by mass or more and less than 13.0% by mass of Cr in the precursor region before cold rolling (see the upper left of FIG. 2) is Cr. An α-Fe phase of 0% by mass or more is an important area for forming a stabilized new species (see the lower right of FIG. 2). That is, the region of 10.0% by mass or more and less than 13.0% by mass of Cr is the γ-Fe phase at high temperature, and the α-Fe phase only by the remaining at least 3.0% by mass of Cr being increased by the thermal diffusion of Cr. Is stabilized. Therefore, if the width of this region is 5 μm or more on average, new seeds can be stably formed with a width of 5 μm or more on average by the heat treatment after the above-described hot rolling. If this width is less than 5 μm, it becomes difficult to stabilize new species at an average width of 5 μm or more. If the width of this region is 10 μm or more on average, it is more preferable because new species can be stably formed with a width of 10 μm or more on average. If the width of this region is 20 μm or more on average, it is further preferable because new species can be more stably formed on a width of 15 μm or more on average.
By forming new seeds with a width of 5 μm or more on average, the crystal orientation of the steel material B is stabilized following the new seeds. If the new species have an average width of 10 μm or more, the crystal orientation is more stabilized. The crystal orientation is further stabilized if the new species have an average width of 15 μm or more.
If the lower limit value of Cr in the precursor region (see the upper left in FIG. 2) is less than 10.0 mass%, the entire region is increased to 13.0 mass Cr in the α-Fe phase stabilization range. More Cr needs to be diffused to form new species and more time is needed to stabilize as new species. Since the disorder of the orientation of the crystal orientation as a new seed is generated during this time, the lower limit value of Cr of the precursor region is set to 10.0 mass%.

In the steel plate manufactured in this manner, Cr of alloy material A, which is an αFe single phase component system, diffuses into steel material B, which is an α-γ transformation component system that is an αFe phase that is an αFe phase at normal temperature. And an average width of 5 μm or more from the interface of the steel material B to the steel material B side, and Cr of the diffusion layer becomes 13.0 mass% or more and stabilizes as a new seed.

In the conventional processes of Patent Documents 6, 8, 9 and the like, the precursor regions can not be formed. In particular, in a hot-rolled clad steel sheet, the average width of the region of 10.0 mass% or more and less than 13.0 mass% can not be 10 μm or more, so Cr of 13.0 mass% or more in the clad steel sheet The average width of the new seed area can not be stably 5 μm or more.

In the conventional process of Patent Document 4, a Cr coating is used as a simple source of Cr, so if the Cr content of the steel plate is less than 3.0%, the {222} plane accumulation degree can be stably made 60% or more. It can not be written. On the other hand, in the present invention, since the alloy material A is used not only as the source of Cr but also as the original seed, if the steel material B is the α / γ transformation system, it does not depend on the Cr concentration, 60% The above-mentioned αFe {222} plane integration degree can be stably obtained.
From the viewpoint of stable manufacturing, the smaller the variation in the degree of integration of the αFe {222} plane, the higher the manufacturing stability (yield), which is preferable. According to the present invention, the variation in the degree of accumulation of αFe {222} plane can be 7% or less, more preferably 4% or less, still more preferably 2% or less, and high manufacturing stability (yield) can be obtained. it can.
Unless otherwise noted, the variation in αFe {222} accumulation in the present invention is {(maximum value−minimum value) / average value} × 100 (%) using the integration degree measured by cutting out 9 locations from the sample. It is derived by the following formula.

The method of producing a clad steel plate of the basic form (i) including the step of forming a precursor region of a new kind described above, and the clad steel sheet of the above (ii) having a texture different from the basic form A method of manufacturing a clad steel plate having a layer area as well as a D layer as an intermediate layer and / or an X layer as an outermost layer will be described. The description of the parts common to the basic aspect is omitted.

[(I) Method for producing a steel sheet having an αFe phase {222} plane integration degree of 60% or more and 100% or less in the inner layer region]
This method relates to the manufacture of a clad steel plate having excellent corrosion resistance and workability as a base, and on the surface of a steel material B having a low Cr concentration which is an α-γ transformation system composition, Cr which is an α single phase system composition An alloy material A having a high concentration is disposed and rolled to obtain a rolled clad steel plate having a different Cr concentration in the thickness direction, and finally a heat treatment is performed to obtain a clad steel plate.
Hereinafter, the steps will be described in order.

(Preparation of alloy material A and steel material B)
First, a steel material B for clad central layer having a thickness of 0.6 to 300 mm and containing Cr and having the composition of the α-γ transformation component system which is the α phase at normal temperature is prepared. Steel B contains, by mass%, 0% ≦ Cr <13.0%, C ≦ 0.0800%, P ≦ 0.040%, S ≦ 0.0300%, N ≦ 0.2000%, and further necessary Depending on the content, either or both of 0.1% ≦ Ni <1.0% and 0.10% ≦ Mn <1.00% may be contained, and the balance may be Fe and impurities.
In addition, as the alloy material A for the cladding surface layer, Cr is contained in excess of the Cr concentration of the steel material B for the cladding central layer, and contains C, P, S, N, Si, Mn, and further optionally Al, Ga, Mo And Nb, Sn, Ti, V, W, Zn, Ni, Cu, Co, B, Ca, Ta, and Mg containing at least one or more ferrite forming elements, the balance being Fe and impurities, α An alloy material having a thickness of 0.1 to 40 mm made of a single phase composition is prepared. The alloy material A contains 13.8 mass% or more of Cr.
The steel material B for the cladding central layer and the alloy material A for the cladding surface layer can be manufactured by applying generally known melting, hot rolling, and the like.

Then, a clad material is produced in which the steel material B for clad central layer is sandwiched between the alloy material A for clad surface layer. Bonding of the layers can be sufficiently achieved by hot rolling this clad material as it is, heat treating it, and cold rolling, but if the pressure between layers of the clad material is a reduced pressure atmosphere, bonding of the layers becomes more preferable. This clad material is subjected to 50% to 95% hot rolling to form a hot-rolled clad steel plate and held at a temperature of 600 ° C. or more and 800 ° C. or less for heat treatment of 5 minutes or more and 6 hours or less (see FIG. 1 (a))) The cold rolled clad steel plate is obtained by cold rolling this hot rolled clad steel plate at a rolling reduction of 30% or more (see the state of FIG. 1 (b)). In the state of FIG. 1A, Cr is diffused from the steel material A to the steel material B by hot rolling and subsequent heat treatment, and a precursor region is formed in the steel material B. In FIG. 1 (b), the width of the precursor region is narrowed by cold rolling. The rolling reduction at this time may be selected according to the thickness of the clad steel plate to be obtained. The upper limit of the rolling reduction is about 98% due to the restriction of the rolling mill. In cold rolling after clad hot rolling, a {111} texture can be formed at least in the surface layer portion by setting the cold rolling ratio in the range of about 30% to about 98%. The present invention is characterized in that the clad material is hot-rolled and heat-treated to form a precursor, and it is produced only by cold rolling or warm rolling without hot-rolling and heat treatment. Also, there were many cases where the surface integration degree originally obtained by the present invention was not obtained even under the same conditions as the total draft and the heat treatment conditions described later.

Thus, the central layer has the composition of the α-γ transformation component system having a relatively low Cr concentration corresponding to the steel material B, and the surface layer has a relatively simple α concentration having a Cr concentration corresponding to the alloy material A. It is the composition of the phase system.

(Formation of surface area, transition area and inner layer area)
Heat treatment is performed to cool the obtained cold rolled clad steel plate by heating to a temperature of A3 point or more and 1300 ° C. or less of the steel material B and cooling, and after cooling, it has a plurality of regions having different compositions in the thickness direction. A steel plate is obtained in which the {222} plane integration degree is increased to the steel plate central region.

In the heating and holding process of the heat treatment, Cr is further diffused from the region corresponding to the alloy material A into the region corresponding to the steel material B.
At this time, the steel sheet is recrystallized in the temperature raising process up to the point A3, but at this time, at least the α-Fe crystal grains having the {111} orientation are formed in the alloy material A and are inherited to the precursor region. (Refer to the state in FIG. 1 (c)) {In the region corresponding to the steel material B, Cr and the like from the region corresponding to the alloy material A are alloyed to form a high Cr region (the Cr concentration exceeds 13.0 mass%) That is, in the precursor region, it becomes an α single phase component and does not undergo γ transformation, and {111} oriented grains preferentially grow as the temperature of the steel plate rises (see the state of FIG. 1 (c)).

When the steel plate is further heated and maintained at a temperature of A3 or more and 1300 ° C. or less of the steel material B, the central layer region which is not the α single phase component is transformed from the α phase to the γ phase.
When the holding time is lengthened, the region of the α single phase composition spreads toward the center of the steel sheet and the region which is the γ phase transforms again to the α phase with the diffusion of Cr. When transforming from the γ phase to the α phase, transformation is performed in such a manner that the {111} orientation among the crystal orientations of the adjacent α grains is preferentially taken over. As a result, the {222} plane integration degree of the inner region is greatly increased as the holding time is extended. (Refer to the status in Fig. 1 (d))

Thereafter, when the steel sheet is cooled, the γ phase in the inner region is transformed to the α phase. Also in this case, transformation is performed in such a manner that the {111} orientation among the crystal orientations of the α grains is preferentially inherited from the new species (ie, the new species in the precursor region) formed in the adjacent steel material B. For this reason, the {222} plane integration degree increases even in the steel plate inner region where the Cr concentration is not so high. Since the cooling is performed from the surface of the steel sheet and a temperature gradient is generated in the thickness direction, transformation occurs from the surface side of the steel sheet toward the central layer, and {111} oriented grains develop as a columnar coarse structure toward the central layer of the steel sheet . As a result, after cooling, a high {222} plane integration degree is obtained in the steel sheet center layer (see the state of FIG. 1 (e)).
Finally, a region (surface region) having a relatively high Cr concentration and a low {222} plane integration degree and a relatively fine crystal structure is formed on the surface of the steel sheet, and at the same time, the steel sheet center side A region (inner layer region) having a relatively low Cr concentration, a high {222} plane density, and a relatively coarse crystal structure is formed. The transition region is formed between the surface layer region and the inner layer region, and the Cr concentration decreases from the surface layer region to the inner layer region.

In this method, the region corresponding to the surface layer region is formed using an alloy material A having a relatively high Cr concentration and a uniform concentration distribution. Therefore, the surface region (mainly the surface and the surface after the heat treatment is stopped by stopping the diffusion of Cr before the diffusion of Cr from the region corresponding to the alloy material A to the inside of the region corresponding to the steel material B reaches the surface layer of the clad steel plate. The region where the uniform concentration distribution of the original alloy material A remains in the vicinity) is 1 μm or more in the thickness direction of the uniform region of the Cr concentration such that the variation of the Cr concentration is within ± 3.0 mass%. To exist in the width of

In the above heat treatment, it is preferable that the temperature rising rate for raising the temperature to point A3 be 0.1 ° C./sec or more and 500 ° C./sec or less. At a temperature rise rate in this range, {111} oriented grains for causing the above-mentioned action are efficiently formed.
The holding temperature after the temperature rise is A3 or more and 1300 ° C. or less. As described above, if it is not A3 point or more, the effect of further increasing the {222} plane accumulation degree by utilizing the transformation from γ phase to α phase upon cooling can not be used. It is not preferable that heating at a temperature exceeding 1300 ° C. not only saturates the effect but also deteriorates the shape of the product steel sheet after cooling.
The holding time may start cooling immediately after reaching the holding temperature (substantially holding for 0.01 seconds or more). There is no particular upper limit on the holding time, but if it exceeds 600 seconds, not only the heat treatment cost increases but also the influence on the characteristics is saturated.
The cooling rate is preferably 0.1 ° C./sec or more and 500 ° C./sec or less. When cooled in this temperature range, preferential growth of {111} oriented grains in the transformation from γ phase to α phase during cooling of the central layer effectively takes place, and orientation to {222} plane orientation progresses more.

In the above, although the Cr layer or the alloy material A for the clad surface layer is described as one layer on one surface, the concentration distribution of the surface layer region finally formed on the steel sheet surface layer by using multiple layers with different components. It is possible to freely control the crystal structure and the crystal orientation. Even in such a case, the effects of the present invention can be obtained as long as the surface layer region and the transition region adjacent thereto do not deviate from the definition of the present invention.

[(Ii) A method of manufacturing a steel plate having a structure in which grains having an average particle diameter of 50 μm or less exist in the thickness direction of the inner layer region in the steel plate of (i)]
In this method, in the same manner as in method (i), after obtaining a clad steel sheet which has undergone heat treatment (heat treatment at a temperature of A3 or more and 1300 ° C. or less) for transformation, cold rolling and The heat treatment of No. 2 forms fine recrystallized grains over the entire steel sheet while maintaining the high {222} plane integration degree formed by the first heat treatment.
These will be sequentially described below.

(Preparation of cold rolled clad steel plate from alloy material A and steel material B)
The steel material B and the alloy material A similar to the steel material B for the clad central layer prepared with the steel plate of the above (i) and the alloy material A for the clad surface layer are prepared.
Then, a clad material is produced in the same manner as the above (i). The clad material is subjected to 50% to 95% hot rolling and heat treatment for precursor formation to form a hot rolled clad steel plate (see the state of FIG. 3 (a)). Cold rolling is performed at a rate of 30 to 98% to obtain a cold rolled clad steel sheet (see the state of FIG. 3 (b)).
In this way, a cold-rolled clad steel sheet is obtained in which the central layer has the composition of the α-γ transformation component system having a relatively low Cr concentration and the surface layer has a composition of an α single phase system having a relatively high Cr concentration. (Refer to the state in Fig. 3 (b))

(Preparation of intermediate steel plate by first heat treatment)
The obtained clad steel plate is subjected to a first heat treatment for heating and cooling the steel material B to a temperature of A3 or more and 1300 ° C. or less, similarly to the case of (i) above, As shown in FIG. 3 (c) and (d), the {111} oriented grains are grown toward the inside of the region corresponding to the steel material B (see FIGS. 3C and 3D). Refer to the state of 3 (e)).
In the heat history passing through the point A3 in the present method, control of temperature rise, retention and cooling is effective for control of crystal orientation, and in the present method is also controlled in the same manner as in the production of the steel plate of (i) above. Can provide desirable effects.

By the first heat treatment, similarly to the case of (i), a region having a relatively high Cr concentration on the surface layer side of the steel plate, a low {222} plane integration degree, and a relatively fine crystal structure is formed At the same time, a region with a relatively low Cr concentration and a high {222} plane density and a relatively coarse crystal structure is formed on the steel sheet center side (see the state of FIG. 3 (e)). .
As in the case of (i), the above behavior should be adjusted with respect to Cr concentration, crystal structure and crystal orientation in the same way as general steel materials, based on the knowledge of diffusion, recrystallization and grain growth that a person skilled in the art has Is easy.

(Formation of surface region, transition region and inner layer region by second heat treatment)
Next, after cold-rolling the clad steel plate after the first heat treatment, the temperature within the α phase of the composition of the steel material for cladding center B (that is, the temperature at which the steel material does not transform to the γ phase) and the recrystallization temperature A second heat treatment of heating to the above temperature is performed to form a final surface layer region and an inner layer region. The transition region is a region which is formed between the surface layer region and the inner layer region and in which the Cr concentration decreases from the surface layer region to the inner layer region.
The steel plate is recrystallized in the heating process of this heat treatment. At that time, the crystal grains take over the orientation before recrystallization and recrystallize, maintaining the surface accumulation degree before recrystallization or becoming an improved recrystallized structure (see the state of FIG. 3 (g)).
As a result, the surface layer region and the inner layer region have a structure in which the {222} plane accumulation degree of the αFe phase is 50% or more and 100% or less.
Furthermore, although fine equiaxed grains are formed in the surface layer region and the inner layer region, it is desirable that the grain diameter be adjusted to 50 μm or less by adjusting the cold rolling ratio and the heating temperature.
Although the diffusion of Cr occurs with the second heat treatment, it does not affect the formation of the texture.

Cold rolling performed before the second heat treatment preferably has a rolling reduction of 50% or more, although it depends on the heating temperature. If the rolling reduction is less than 50%, it will be difficult to inherit the previous texture and to recrystallize. In order to efficiently carry out recrystallization at a low heating temperature, a rolling reduction of 70% or more is more desirable.
In the second heat treatment, the heating temperature is at least the recrystallization temperature of the steel plate B1 and at the A3 point or less at which the α-γ transformation does not occur, in order to cause recrystallization in at least the central region.

Also in the second heat treatment, it is easy to adjust the cold rolling ratio and the heating temperature to finally obtain the Cr concentration, the crystal structure and the crystal orientation of the steel sheet of the present invention based on the knowledge that a person skilled in the art usually has.
The grain refining treatment of crystal grains by the combination of cold rolling after the first heat treatment and the second heat treatment may be performed only once after the first heat treatment, or may be performed twice or more.

In the above, although the Cr layer or the alloy material A for the clad surface layer is described as one layer on one surface, the concentration distribution of the surface layer region finally formed on the steel sheet surface layer by using multiple layers with different components. It is possible to freely control the crystal structure and the crystal orientation. Even in such a case, the effects of the present invention can be obtained as long as the surface layer region and the transition region adjacent thereto do not deviate from the definition of the present invention.

[Production of a clad steel plate having a D layer]
A steel material B for clad central layer and an alloy material A for clad surface layer similar to those prepared in the production of the steel plate of the above (i) are prepared.
Next, a film D of an Fe-based alloy containing at least one or more ferrite forming elements of Al, Ga, Mo, Nb, Si, Sn, Ti, V, W, Zn on one surface or both surfaces of the steel material B for cladding central layer A cladding material formed by laminating the cladding surface layer alloy material A and the cladding core layer steel material B such that the film D is in between, or a cladding surface layer steel material with the cladding surface layer alloy material A A clad material (with the film D being located between the alloy material A and the steel material B as a result) laminated so as to sandwich B is produced.

As in the case of the steel plate of (i) or (ii) above, this clad material is subjected to heat treatment for cold rolling, heat treatment for forming a precursor, and cold rolling, and then heat treatment for transformation to form a film A ferrite forming element is diffused from the portion corresponding to D to both side regions, and Al, Ga, Mo, Nb, Si, Sn, Ti, V, W, Zn are formed on the steel material inner side of the region of uniform Cr concentration. A clad steel plate having a D layer containing at least one or more ferrite forming elements and having a thickness of 0.05 μm or more is manufactured.
As in the case of the steel plate of (ii), this clad steel plate is subjected to a single treatment of a combination of cold rolling and a second heat treatment in which the temperature is higher than the recrystallization temperature and lower than the A3 point. It can be done multiple times.

In addition, the method of attaching the ferrite forming element for forming the film D is, as described in Patent Document 4, various methods such as plating, rolling clad method, dry process such as PVD and CVD, and powder coating. The method can be adopted. Further, by setting the adhesion thickness to 0.05 μm or more and 1000 μm or less, the action of the above-mentioned ferrite forming element can be effectively used.

[Production of a clad steel plate having an X layer]
A steel material B for clad central layer and an alloy material A for clad surface layer similar to those prepared in the production of the steel plate of the above (i) are prepared.
Furthermore, 16.0% ≦ Cr ≦ 26.0%, 6.0% ≦ Ni ≦ 22.0%, C ≦ 0.1500 by mass% on one side or both sides of the clad steel sheet as the outermost layer of the clad steel sheet %, P ≦ 0.045%, S ≦ 0.0300%, N ≦ 0.4000%, Si ≦ 5.000%, Mn ≦ 10.00%, Mo ≦ 4.000%, Cu ≦ 2.50% , Remainder: Cladding material formed X layer which is Fe and impurities and laminated like XA-B, X-A-B-A-X (as a result, as outermost layer of alloy material A and steel material B Make the X layer).

As in the case of the steel plate of (i) or (ii) above, this clad material is subjected to heat treatment for cold rolling, heat treatment for precursor formation, and cold rolling, and then heat treatment for transformation, A clad steel plate having an X layer as a surface layer is manufactured. The X layer is clad together in the step of cladding the steel plate (alloy material A and steel material B) of the above (i) or (ii).
As in the case of the steel plate of (ii), this clad steel plate is subjected to a single treatment of a combination of cold rolling and a second heat treatment in which the temperature is higher than the recrystallization temperature and lower than the A3 point. It can be done multiple times.

As mentioned above, although the basic aspect and the aspect which changed a part of those, etc. were explained about the present invention, the following explains the present invention in more detail with an example.

Hereinafter, an embodiment will be shown with the following configuration.

Example 1
With respect to the 13 compositions B to E, G to J, and L to P shown in Tables 1 to 3, ingots each having a thickness of 300 mm were melted and hot-rolled to produce a steel material B for clad center. Similarly, an alloy material A for the clad surface layer having four compositions Q, R, S, and T shown in Table 4 was separately prepared. The components Q, R, S, and T have no A3 point, and have a composition of α-Fe single phase from normal temperature to high temperature.
Then, a clad material having a structure in which the steel material for clad center B was sandwiched from both surfaces by the alloy material A for clad surface layer, or a clad material in which the alloy material A and the steel material B were laminated were manufactured. The clad material was simply packed with mild steel, and the inside of the pack was evacuated to a rotary pump level. This clad material is hot-rolled at a temperature of 1,100 ° C. and a reduction of 50 to 78% so as to obtain the thickness after hot-rolled cladding shown in Table 5-1 and Table 5-2, and then immediately 60 ° C. at 730 ° C. Heat treatment was performed for a minute. Thereafter, cold rolling was performed at a rolling reduction of 60% or more to obtain cold-rolled clad steel plates having thicknesses shown in Tables 5-1 and 5-2.
As a comparison, cold rolling was performed without heat treatment after clad hot rolling (Comparative Example 2).
As a comparison, warm rolling was performed at 400 ° C. instead of hot rolling, and then heat treatment was directly performed at 730 ° C. for 60 minutes (Comparative Example 3).
The structure of the base metal portion of the obtained cold rolled clad steel sheet was observed. As a result, the main phase at normal temperature was the α-Fe phase. The surface layer region has the same thickness on both surface sides, and the numerical values in the table are the thickness on one side.
In addition, the composition, crystal orientation, and crystal grain size were also measured for each of both surface side surface regions, and the average value was evaluated.

A plurality of samples are cut out from the cold rolled clad steel plate, and heat treated by heating and cooling at a heating rate, a holding time, and a cooling rate shown in Table 5-1 and Table 5-2 to give a clad steel plate sample in the form of sheet and foil. Obtained.
The cut-out position of the sample is the width of the rolled sheet at the both ends in the rolling direction and in the vicinity of their intermediate positions from the steel sheet collected at a size of 500 mm in the rolling direction and 300 mm in the width direction from any place of the cold rolled clad steel sheet. Near both ends of the direction and near the center in the rolling width direction, there are nine locations in total.
The various characteristic values of the sample after heat treatment were measured as follows.
The sample after heat treatment was confirmed by XRD measurement to be an α-Fe single phase under all conditions.
These samples were analyzed for Cr concentration in the plate thickness direction by GDS analysis, and a region corresponding to the surface region, a region corresponding to the transition region, and a region corresponding to the inner layer region were determined. When the region corresponding to the alloy material A of the cold-rolled clad steel plate is thick, it is thinly polished with an emery paper and then GDS analysis is performed.
A surface region from the surface of the sample to a position where the Cr concentration is 95% of the Cr concentration on the surface, a transition region where the Cr concentration is 13.0 mass% or more, and a region where the Cr concentration is less than 13.0 mass% The thickness average composition and the {222} plane accumulation degree are shown in Table 5-1 and Table 5-2 for the inner layer region which is Needless to say, each numerical value is a numerical value measured according to the definition of the present invention described in the above-mentioned [Form for carrying out the invention]. The average value of the {222} accumulation degree is an average value of values at nine sample cutting positions under each condition. Further, the variation of the {222} accumulation degree is represented by {(maximum value−minimum value) / average value} × 100 (%) among nine values.

The formability was evaluated by using the ear height after deep drawing of a cylinder having a drawing ratio of 2. When cylindrical squeezing is performed from a disc having a diameter D with an inner diameter bunch of a shaped product having a diameter d, D / d is referred to as a throttling ratio. When the ear height is small, good in-plane anisotropy during molding, surface roughening resistance, and ridging resistance can be obtained. If the ear height is more than 1.5 mm, any one of the above-mentioned characteristics is inferior, and this is taken as the upper limit of the pass. The conditions of cylindrical deep drawing were as follows. That is, the punch diameter: φ50 mm, the punch shoulder R: 5 mm, the blank diameter φ100 mm, the wrinkle pressing force: 1 ton, and the coefficient of friction: 0.11 to 0.13.
Furthermore, the average r value was measured by the method described above.

The corrosion resistance was evaluated by a salt dry combined cycle corrosion test CCT (Cyclic Corrosion Test). The test consists of 100 cycles of salt spray (5% NaCl aqueous solution spray, temperature 35 ° C, 30 minutes) → drying (60 ° C, humidity 30%, 60 minutes) → wetting (40 ° C, humidity 95%, 1 hour) It is a condition that Evaluation evaluated the sample surface after 100 cycles, calculated | required the area rate of rusting, and determined it on the following references | standards. The area ratio of rusting was determined from the ratio of the area of the rusted area to the sample area by visually judging the presence or absence of rust on the sample surface after the cycle test. The plate-shaped sample was measured to have a width of about 20 to 50 mm and a length of about 30 to 100 mm, but the edge of the plate is a cut site and not a site having a high Cr concentration in the surface layer. In order to eliminate the influence of the edge, the edge was covered with a resin or the like so as not to be exposed directly to the corrosive atmosphere.
発 (very good) when there is no rust, ie, when the film retention is 100%, ○ (good) when the rusting ratio is less than 5% (95% or more and less than 100%) ((Acceptable), rusting rate of 5% or more and less than 30% (70% or more and less than 95% of film remaining rate) Δ, 30% or more rusting rate (less than 70% of film remaining rate) ). Here, ◎ (very good) in the case where the film retention rate is 100%, and 場合 (good) in the case where the rusting rate (a film retention rate of 95% or more and less than 100%) is less than 5% was accepted.

The preparation of the sample for X-ray diffraction for measuring the surface integration degree and the random intensity ratio is performed as follows.
The sample is polished to a predetermined position in the plate thickness direction by mechanical polishing or chemical polishing, and finished to a mirror surface by buffing, and then distortion is removed by electropolishing or chemical polishing, and at the same time, 1/1 of the surface region or inner layer region. 2 Adjust so that the plate thickness part becomes the measurement surface.
In addition, it is difficult to accurately set the measurement surface to a half plate thickness part, so the sample is prepared so that the measurement surface is within 3% of the plate thickness centering on the target position. do it.

The results are shown in Tables 5-1 and 5-2.

In Inventive Example 1 to Inventive Example 31, the width of one side of the transition region adjacent to the inner layer region is 5 μm or more on average, so the variation of the {222} plane density of the αFe phase in the inner layer region is 7% or less , Excellent manufacturing stability was obtained. When the width is 10 μm or more, the variation is 4% or less, and when the width is 15 μm or more, the production stability is further improved as the variation is 2% or less.
The results of CCT in Comparative Examples 1 to 4 were acceptable, but in Comparative Example 1, the heat treatment temperature after cold rolling is lower than the A3 point temperature of the steel material B, so the {222} plane of the αFe phase in the inner layer region The degree of integration was less than 60%, and the ear height of the index of formability was higher than 1.5 mm, and sufficient processability could not be obtained.
In Comparative Example 2, since the heat treatment after clad hot rolling was not performed, the width of the transition region adjacent to the inner layer region is less than 5 μm on average, and the variation of the {222} plane integration degree of the αFe phase in the inner layer region Increased to 8.9% and the production stability decreased. In Comparative Example 3, since lamination was performed by warm rolling at 400 ° C., bonding between the alloy material A and the steel material B is not sufficient, and even if heat treatment is performed thereafter, a predetermined Cr diffusion layer can not be formed. The dispersion of the {222} plane density of the α-Fe phase was as large as 12.5% and the production stability was lowered. In addition, the {222} plane accumulation degree of the αFe phase in the inner layer region was less than 60%, the ear height of the index of formability was higher than 1.5 mm, and sufficient processability was not obtained. In Comparative Example 4, since the Cr content of the steel material B is 13% by mass or more, the α / γ transformation does not occur, and the {222} plane integration degree of the αFe phase in the inner layer region is less than 60%, which is an index of formability The height of the ear was higher than 1.5 mm, and sufficient processability could not be obtained. In Comparative Examples 1 to 4, since the random intensity ratio of {222} <112> of the αFe phase in the surface layer region and the inner layer region is less than 16%, the average r value is as low as 1.1 or less.
In the invention examples 1 to 31, the Cr concentration in the surface layer region was 13.8% by mass or more, and the width on one side of the surface layer region was 5% or more of the total thickness. Sufficient processability was obtained because the αFe {222} plane accumulation degree in the inner layer region was 60% or more and the ear height of the index of formability was 1.5 mm or less. In the invention examples 1 to 31, the random strength ratio of {222} <112> of the αFe layer in the inner layer region was larger than 16 and the average r value exceeded 2.6.

Example 2
Using the alloy material A for the clad surface layer and the steel material B for the clad central layer prepared in the same manner as in Example 1 using the materials having the compositions shown in Tables 1 to 4, the steel material B for the clad center is prepared A clad material to be sandwiched from both sides or a clad material in which alloy material A and steel material B are laminated is manufactured, and this clad material is made to have the thickness of the hot rolled clad material shown in Table 6-1 and Table 6-2. Hot rolling at a reduction of 80 to 95% at 1100.degree. C., and immediately heat treatment at 730.degree. C. for 60 minutes. Thereafter, cold rolling was performed at a reduction ratio of 35 to 60% or less to obtain cold rolled clad steel plates having the thicknesses shown in Tables 6-1 and 6-2.
As a comparison, cold rolling was performed without heat treatment after clad hot rolling (Comparative Example 7).
As in Example 1, a plurality of samples were cut out from the obtained cold-rolled clad steel plate and heat treated to obtain clad steel plate samples.

The various characteristic values of the sample after heat treatment were measured and evaluated in the same manner as in Example 1.
Ridging resistance gave a tensile strain of 15% with a tensile tester after collecting JIS No. 5 tensile test specimens in parallel with the rolling direction. The uneven height of the plate surface at the center of the parallel portion of the test specimen was scanningly measured with a contact type roughness meter in the direction perpendicular to the rolling direction to evaluate the ridging resistance. The scanning conditions were a scanning length of 10 mm, a scanning speed of 0.2 mm / sec, and a cutoff of 0.8 mm. The case where the height of the unevenness was less than 6 μm was defined as passing (○), and 6 μm or more was defined as failing (×).

The results are shown in Tables 6-1 and 6-2.
In Inventive Example 32 to Inventive Example 61, since the width of one side of the transition region adjacent to the inner layer region is 5 μm or more on average, the dispersion of the {222} plane density of the αFe phase in the inner layer region is 7% or less , Excellent manufacturing stability was obtained. When the width is 10 μm or more, the variation is 4% or less, and when the width is 15 μm or more, the production stability is further improved as the variation is 2% or less.
The results of CCT in Comparative Examples 5 to 7 were acceptable, but in Comparative Example 5, the heat treatment temperature after cold rolling is lower than the A3 point temperature of the steel material B, so the {222} plane of the αFe phase in the inner layer region The degree of integration was less than 60%, and the ear height of the index of formability was higher than 1.5 mm, and sufficient processability could not be obtained. In addition, since the particle size ratio of the inner layer region to the surface layer region was less than 1.5, sufficient ridging resistance was not obtained.
In Comparative Example 6, since the Cr content of the steel material B is 13.0% by mass or more, the α / γ transformation does not occur, and the {222} plane accumulation degree of the αFe phase in the inner layer region is less than 60%. The ear height of the index was higher than 1.5 mm, and sufficient processability could not be obtained.
In Comparative Example 7, since the heat treatment after clad hot rolling was not performed, the width of the transition region adjacent to the inner layer region becomes less than 5 μm on average, and the variation of the {222} plane integration degree of the αFe phase in the inner layer region Increased to 8.2% and the production stability decreased.
In the invention examples 32 to 61, the results of CCT passed, and sufficient processability was also obtained. Furthermore, since the αFe {222} plane accumulation degree in the inner layer region was 60% or more and the ear height of the index of formability was 1.5 mm or less, sufficient processability was obtained. In addition, since the particle size ratio of the inner layer region to the surface layer region was 1.5 or more, it was a machined surface excellent in ridging resistance.

[Example 3]
Using the alloy material A for the clad surface layer and the steel material B for the clad central layer prepared in the same manner as in Example 1 using the materials having the compositions shown in Tables 1 to 4, the steel material B for the clad center is prepared A clad material to be sandwiched from both sides or a clad material in which alloy material A and steel material B are laminated is manufactured, and this clad material is made to have the thickness of the hot rolled clad material shown in Table 7-1 and Table 7-2. Hot rolling at a reduction of 50 to 95% at 1100.degree. C., and immediately heat treatment at 790.degree. C. for 80 minutes.
A cold-rolled clad steel plate is prepared in the same manner as in Example 1, and a clad steel plate is obtained by carrying out a first heat treatment in which heating and cooling are performed at the heating rates and holding temperatures and times and cooling rates shown in Tables 7-1 and 7-2. Made. Next, after performing cold rolling at a rolling ratio of Table 7-1 and 7-2, a second heat treatment of heating to a heating temperature of Table 7-1 and Table 7-2 and then cooling was performed.
Various sample characteristic values after heat treatment were measured in the same manner as in Example 1.

Further, the toughness was evaluated by carrying out a metal material bending test method in accordance with JIS 2248. The test piece was processed into a width of 20 mm and a length of 60 mm, and was bent with a bending radius of 1 mm. The bent and deformed surface was observed with an optical microscope to determine whether the surface was acceptable or not. The case where wrinkles and cracks could not be confirmed is regarded as ○, and the case where wrinkles and cracks could be confirmed is regarded as x, and を was accepted and x was rejected.

The results are shown in Tables 7-1 and 2.
In Inventive Example 62 to Inventive Example 93, since the width of one side of the transition region adjacent to the inner layer region is 5 μm or more on average, the variation of the {222} plane integration degree of the αFe phase in the inner layer region is 7% or less , Excellent manufacturing stability was obtained. When the width is 10 μm or more, the variation is 4% or less, and when the width is 15 μm or more, the production stability is further improved as the variation is 2% or less.
However, in the invention examples 92 and 93,
Since the average crystal grain size of the surface layer region and the inner layer region exceeded 50 μm, sufficient toughness could not be obtained.
Invention Examples 62 to 91 passed the CCT results, and sufficient processability was also obtained. Furthermore, since the average particle diameter of the surface layer region and the inner layer region was less than 50 μm, the toughness was also excellent.
In Comparative Example 8, the average thickness of the surface layer region is less than 5% of the total thickness of the steel (the thickness / total thickness of one side of the surface region is less than 0.005), and the width of one side of the transition region adjacent to the inner layer region is an average Since it was less than 5 μm, excellent formability and excellent corrosion resistance were not obtained.

[Example 4] (Example of steel plate including D layer)
Using the materials having the compositions shown in Tables 1 to 4, an alloy material A for the clad surface layer and a steel material B for the clad central layer were produced in the same manner as in Example 1. A ferrite forming element was attached to one surface or both surfaces of the clad central layer steel material B by a method such as plating to form a film D. Al and Sn were deposited by hot-dip plating, and Mo, Nb and W were deposited by DC magnetron sputtering.
Next, the alloy material A for the clad surface layer and the steel material B for the clad central layer are combined and laminated, and cooled as in Example 1 (except that the heat treatment immediately after hot rolling was performed at 770 ° C. × 60 minutes) A rolled clad steel plate was produced, samples were produced from the cold rolled clad steel plate in the same manner as in Example 1, and these were heat-treated to produce a clad steel plate.

The obtained clad steel sheet was subjected to line analysis of the thickness section of the sample in the thickness direction by EPMA, and in addition to the area corresponding to the surface area, the area corresponding to the transition area and the area corresponding to the inner layer area The area corresponding to
Furthermore, various characteristic values of the heat-treated sample were measured and evaluated in the same manner as in Examples 1 and 2. The results are shown in Table 8-1.

In Inventive Example 94 to Inventive Example 103, since the width of one side of the transition region adjacent to the inner layer region is 5 μm or more on average, the dispersion of the {222} plane integration degree of the αFe phase in the inner layer region is 7% or less , Excellent manufacturing stability was obtained. When the width is 10 μm or more, the variation is 4% or less, and when the width is 15 μm or more, the production stability is further improved as the variation is 2% or less.
In comparison with the invention examples 95 and 95 'and the invention examples 96 and 96', respectively, the {222} plane accumulation of the αFe phase in the inner layer region with the film D compared with the case without it The variation of the degree was reduced by about 20%, and the manufacturing stability was improved.
In the invention examples 94 to 103, the Cr concentration in the surface layer region is 13.8% by mass or more, and the width on one side of the surface layer region is 5% or more of the total thickness. Sufficient processability was obtained because the inner layer region had an α {222} plane accumulation degree of 60% or more and an ear height of 1.5 mm or less as an index of formability.
The results of CCT in Comparative Examples 10 and 11 passed, but in Comparative Example 10, the heat treatment temperature is below the A3 point of the alloy material A, and the αFe {222} plane integration degree in the inner layer region is less than 60%. Since the ear height of the index of formability was higher than 1.5 mm, sufficient processability could not be obtained.
In Comparative Example 11, the width of one side of the transition region adjacent to the inner layer region was less than 5 μm on average, so the variation of the {222} plane integration degree of the αFe phase in the inner layer region increased to 9%. Further, in Comparative Example 11, the αFe {222} plane accumulation degree in the inner layer region was less than 60%, and the ear height of the index of formability was higher than 1.5 mm, so sufficient processability could not be obtained.

[Example 5] (Example of steel plate including X layer)
The SUS304 stainless steel is laminated on both sides of the combination of the alloy material A and the steel material B of the invention example 21 of the example 1 and the invention example 23 and cold rolling under the same conditions as the invention example 21 and the invention example 23 A clad steel plate was obtained (Invention Example 104, Invention Example 105). A plurality of samples were cut out from the obtained cold rolled clad steel plate in the same manner as in Example 1 and heat treated to obtain clad steel plate samples.

The various characteristic values of the sample after heat treatment were measured and evaluated in the same manner as in Example 1. However, except for evaluation of formability by deep drawing test and salt dry combined cycle corrosion test CCT measurement, the X layer of the outermost layer was removed by polishing before measurement.

The results are shown in Table 9.
In Inventive Example 104 and Inventive Example 105, since the width of one side of the transition region adjacent to the inner layer region is 15 μm or more on average, the dispersion of the {222} plane integration degree of the αFe phase in the inner layer region is 2% or less , Excellent manufacturing stability was obtained.
Moreover, in Inventive Example 104 and Inventive Example 105, the Cr concentration of the surface layer region was 13.8 mass% or more, and the width of one side of the surface layer region was 5% or more of the total thickness (not including the X layer). Since SUS304 stainless steel was laminated on the outermost layer, the results of ○ (good) in the CCT test of Inventive Example 21 and Inventive Example 23 were) (very good), and the corrosion resistance was further improved. The workability was slightly reduced compared to Inventive Example 21 and Inventive Example 23 because the αFe {222} plane accumulation degree in the inner layer region was 60% or more, but SUS304 stainless steel was laminated on the outermost layer. However, the ear height of the index of formability was 1.5 mm or less, and sufficient processability was obtained.
The average r value was approximately the same as in Inventive Example 21 and Inventive Example 23 in the random strength ratio of {222} <112> of the αFe layer in the inner layer region, but since SUS304 stainless steel is laminated on the outermost layer, Compared with invention examples 21 and 23, they slightly decreased.

INDUSTRIAL APPLICABILITY The present invention is industrially effective because it can provide a steel sheet having a high yield, excellent production stability, and excellent corrosion resistance and excellent workability by using less Cr.

Claims (10)

In a clad steel plate having a plurality of layers having different compositions in the thickness direction,
It is a laminated structure of surface layer region-transition region-internal layer region or surface layer region-transition region-internal layer region-transition region-surface region in the thickness direction,
The surface layer region is a region from the surface to a position where the Cr concentration is 95% of the Cr concentration of the surface in the plate thickness direction,
The transition region is a region from a position adjacent to the surface layer region in the thickness direction to a position where the Cr concentration is 13.0 mass% or more,
The inner layer region is a region adjacent to the transition region,
The width of the transition region is at least 5 μm on average,
The average thickness of the surface layer region is 5% or more of the total thickness of the steel plate and less than the thickness of the inner layer region,
The {222} plane accumulation degree of the αFe phase in the inner layer region is 60% or more and 100% or less,
The average composition of the surface region is mass%,
Cr ≧ 13.8%, C ≦ 0.1500%, P ≦ 0.040%, S ≦ 0.0300%, N ≦ 0.2000%, Si ≦ 2.500%, Mn ≦ 1.20% Furthermore, selectively, Al ≦ 8.000%, Mo ≦ 2.500%, Ga ≦ 3.50%, Nb ≦ 1.000%, Sn ≦ 1.800%, Ti ≦ 2.000% V ≦ 2.00%, W ≦ 6.00%, Zn ≦ 4.00%, Ni ≦ 0.6%, Cu ≦ 0.80%, Co ≦ 0.01%, B ≦ 0.01%, At least one element selected from the group consisting of Ca ≦ 0.01%, Ta ≦ 0.01%, Mg ≦ 0.01%, balance: Fe and impurities,
The average composition of the inner layer region is mass%,
0% <Cr <13.0%, C ≦ 0.0800%, P ≦ 0.040%, S ≦ 0.0300%, N ≦ 0.2000%, and optionally 0.1 % ≦ Ni <1.0%, 0.10% ≦ Mn <1.00%, Cu ≦ 0.01%, Co ≦ 0.01%, B ≦ 0.01%, Ca ≦ 0.01%, Ta A clad steel sheet comprising at least one or more elements selected from the group consisting of ≦ 0.01% and Mg ≦ 0.01%, with the balance being Fe and impurities.
The steel sheet according to claim 1, wherein the {222} plane accumulation degree of the αFe phase in the surface layer region is 60% or more.
The steel plate according to claim 1 or 2, wherein a ratio Br / Ar of the average crystal grain diameter Br of the inner layer region and the average crystal grain diameter Ar of the surface layer region is 1.5 or more.
The steel plate according to any one of claims 1 to 3, wherein a random strength ratio of {222} <112> of the αFe phase in a half thickness of the inner layer region is 16 or more.
The steel plate according to any one of claims 4 to 10, wherein the random strength ratio of {222} <112> of the alpha Fe phase in the half thickness of the surface layer area is 16 or more.
The steel plate according to any one of claims 1 to 5, characterized in that it has a texture in which grains having an average particle diameter of 50 μm or less exist in the thickness direction in the inner layer region.
Further, an X layer is provided outside the surface area,
The composition of the X layer is 16.0% ≦ Cr ≦ 26.0%, 6.0% ≦ Ni ≦ 22.0%, C ≦ 0.1500%, P ≦ 0.045%, S ≦ 10% by mass. Characterized by 0.0300%, N ≦ 0.4000%, Si ≦ 5.000%, Mn ≦ 10.00%, Mo ≦ 4.000%, Cu ≦ 2.50%, balance: Fe and impurities The steel plate according to any one of claims 1 to 6, wherein
The steel plate according to any one of claims 1 to 7, which has a form of a thin steel plate or a foil having a thickness of 0.004 mm or more and 3 mm or less.
A steel pipe manufactured from the steel plate according to any one of claims 1 to 7, having a thickness of 0.004 mm or more and 3 mm or less.
A steel container manufactured from the steel plate according to any one of claims 1 to 7, having a thickness of 0.004 mm or more and 3 mm or less.

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