WO2011062152A1 - Austenite stainless steel sheet and method for producing same - Google Patents

Abstract

Disclosed is an austenite stainless steel sheet for springs, which exerts both high strength and excellent moldability, and which has a chemical composition comprising 0.01 to 0.15% of C, 3.0% or less of Si, 3.0% or less of Mn, 10.0 to 30.0% of Cr, 4.0 to 20.0% of Ni, and 0.4% or less of N, the remainder being Fe or impurities, wherein the austenite content (γs) (%) of the surface of the steel sheet and the austenite content (γc) (%) of the plate thickness center is (γs+γc)/2≤55 and γs/γc≥0.1, and the remainder has a metal structure which is mainly a strain-induced martensite structure.

Description

Austenitic stainless steel sheet and manufacturing method thereof

The present invention relates to an austenitic stainless steel sheet and a method for producing the same, and more specifically to an austenitic stainless steel sheet for a spring having both high strength and excellent formability and a method for producing the same.

For spring materials used as leaf springs, mainsprings, housings, disc springs, dome switches, etc. in electronic equipment, nuclear facilities, automobile parts, etc., high strength to realize material thinning and a predetermined product shape Therefore, excellent moldability for processing into a sheet is required.

The material that has been applied to these uses so far has been SUS301 (AISI301) stainless steel belonging to metastable austenitic stainless steel. SUS301 stainless steel is transformed into hard work-induced martensite in the deformed part during cold working, so that high strength can be obtained relatively easily and local deformation is caused by the TRIP (transformation-induced plasticity) effect. Since it is suppressed, excellent moldability can also be obtained. Such spring materials are disclosed, for example, in Patent Documents 1 to 3 below.

In Patent Document 1, C: 0.03% or less (in the present specification, “%” for chemical composition means “mass%” unless otherwise specified), Si: 1.0% or less, Mn: 2 0.5% or less, Ni: 4.0 to 10.0%, Cr: 13.0 to 20.0%, N: 0.06 to 0.30%, S: 0.01% or less, O: 0.0. 007% or less, M value = 330− (480 × C) − (2 × Si) − (10 × Mn) − (14 × Ni) − (5.7 × Cr) − (320 × N) is 30 The above-described stainless steel having excellent formability is disclosed.

In Patent Document 2, C: 0.08% or less, Si: 3.0% or less, Mn: 4.0% or less, Ni: 4.0 to 10.0%, Cr: 13.0 to 20.0 %, N: 0.06 to 0.30%, O: 0.007% or less, and the M value is 40 or more, and stainless steel excellent in spring characteristics and fatigue characteristics of the processed part is disclosed. .

In Patent Document 3, C: 0.03% or less, Si: more than 1.0%, 3.0% or less, Mn: 4.0% or less, Ni: 4.0 to 10.0%, Cr: 13. Molding workability, including 0 to 20.0%, N: not more than 0.30%, S: not more than 0.01%, O: not more than 0.007%, and the M value is in the range of 30 to 100 Stainless steel with excellent fatigue properties is disclosed.

In all of the stainless steels disclosed in Patent Documents 1 to 3, cold rolling after hot rolling is performed at a rolling rate of 50% or more, and then fine uniform recrystallized grains having an average crystal grain size of 10 μm or less are generated. Thus, it is manufactured by subjecting it to a comparatively low temperature and short-term finish annealing and finally temper rolling. That is, all of these are intended to obtain a predetermined strength characteristic by utilizing crystal grain refining, which is a strengthening mechanism with a small deterioration of formability. However, in recent years, the strength required for the spring material has been improved, and the stainless steel disclosed in Patent Documents 1 to 3 sometimes lacked the strength required for the product.

Patent Document 4 below discloses a high-strength spring material based on SUS301L having a low C and a high N, specifically, C: 0.03% or less, Si: 1.0% or less, Mn: 2.0% And having a chemical composition including Cr: 16.0 to 18.0%, Ni: 6.0 to 8.0%, N: 0.25% or less, Nb: 0 to 0.30%, and Refining with a reduction ratio of 30% or more to stainless steel having a structure consisting of 50% or more and less than 100% recrystallized grains with an average grain size of 5 μm or less, and an unrecrystallized portion exceeding 0% and 50% or less. A stainless steel having a double phase structure of martensite and the remaining austenite or a martensite single phase structure with an area ratio of 40% or more obtained by rolling is disclosed.

The stainless steel disclosed in Patent Document 4 is formed into a metal structure including a work-induced martensite structure by temper rolling, and then formed into a predetermined shape and further subjected to an aging treatment, whereby fine chromium-based martensite is formed. Nitride is deposited. By utilizing the precipitation strengthening at that time, the strength can be increased without adding a new process.

JP-A-4-214484 JP-A-5-279802 Japanese Patent Laid-Open No. 5-117813 Patent No. 4321066

However, in order to reduce the size of the product and improve its performance, the spring material is still required to have higher strength and improved formability. For this reason, even the stainless steel disclosed in Patent Document 4 may not fully satisfy the performance required for the latest products.

In one aspect, the present invention provides C: 0.01 to 0.15%, Si: 3.0% or less, Mn: 3.0% or less, Cr: 10.0 to 30.0%, Ni: 4. It contains 0 to 20.0%, N: 0.40% or less, has a chemical composition consisting of the balance Fe and impurities, and has an austenite amount γs (%) in the steel plate surface portion and an austenite amount in the center portion of the steel plate thickness. Austenitic stainless steel characterized in that γc (%) satisfies (γs + γc) / 2 ≦ 55 and γs / γc ≧ 0.10, and the balance mainly has a metal structure which is a work-induced martensite structure. It is a steel plate.

Here, the austenite amount γs (%) of the steel plate surface portion means the volume ratio (%) of austenite contained in the region (referred to as the steel plate surface portion) from the outermost surface of the steel plate to a depth position of 10 μm in the plate thickness direction. To do. On the other hand, the austenite amount γc (%) at the center of the plate thickness is an area (plate) from the surface of one side of the steel plate cut to half the original plate thickness by mechanical polishing and chemical polishing to a depth position of 10 μm in the plate thickness direction. It means the volume ratio (%) of austenite contained in the thickness center portion).

In the austenitic stainless steel sheet of the present invention, the chemical composition is replaced with a part of Fe,
1) At least one of Mo: 3.0% or less and Cu: 3.0% or less, and / or 2) Ti: 0.50% or less, Nb: 0.50% or less, and V: 1.0% or less One or more selected from the group consisting of
Can further be included.

From another aspect, the present invention provides a cold rolled annealed material by cold rolling and annealing the obtained hot rolled steel sheet after hot rolling the steel material having the above chemical composition. A method for producing an austenitic stainless steel sheet, characterized by subjecting an annealed material to temper rolling at a rolling reduction (%) / 10 pass or more.

In the above method, it is preferable that the cold rolled annealed material before temper rolling has an average austenite grain size of 5 μm or less.
The present invention provides an austenitic stainless steel plate having both high strength and excellent formability and a method for producing the same.

Explanatory drawing which shows an example of the process which the austenitic stainless steel plate which concerns on this invention receives after temper rolling. Explanatory drawing which shows an example of the relationship of the distribution of the thickness direction of the austenite amount after temper rolling, and a moldability. Explanatory drawing which shows a moldability evaluation method.

The present invention will be described in more detail with reference to the accompanying drawings.
The austenitic stainless steel sheet according to the present invention is a cold-rolled steel sheet subjected to temper rolling. As shown in FIG. 1, this austenitic stainless steel sheet is subjected to a forming process after temper rolling, and then subjected to an aging treatment as necessary to obtain products (eg, various springs) and Is done.

The inventor considered that by increasing the content of C, which is a solid solution strengthening element, the work-induced martensite structure generated by temper rolling is strengthened, and the strength of the steel can be increased. The above-described problem of insufficient strength can be solved by superimposing the strengthening of the martensite phase by increasing the C content and further the precipitation strengthening utilizing Cr ₂ N.

At this time, if the amount of work-induced martensite is small and a large amount of austenite remains, a predetermined strength cannot be obtained. Therefore, the average value of the austenite amount γs (%) of the steel plate surface portion and the austenite amount γc (%) of the center portion of the plate thickness, that is, the value of (γs + γc) / 2 (hereinafter, this value is referred to as the average austenite amount). 55 or less. γs and γc are as defined above.

The present inventor has also considered that the control of the distribution of the austenite amount in the thickness direction is effective in order to improve the formability which decreases with increasing strength. FIG. 2 is an explanatory diagram showing an example of the relationship between the distribution in the thickness direction of the austenite amount after temper rolling and the formability.

As shown in FIG. 2, even if the average austenite amount after temper rolling is the same, the formability can be greatly improved by changing the distribution of the austenite amount after temper rolling in the thickness direction. . Specifically, by increasing the amount of austenite remaining on the steel sheet surface after temper rolling, a work-induced martensitic transformation occurs in the steel sheet surface part that undergoes the greatest deformation during the subsequent forming process, and a sufficient TRIP effect is exhibited. Thereby, excellent moldability is obtained.

Furthermore, when this austenitic stainless steel is subjected to an aging treatment, fine Cr ₂ N precipitates around a martensite phase having a small N solid solubility limit, so that aging strengthening can also be utilized. Thus, the austenitic stainless steel according to the present invention can have both high strength and excellent formability.

On the other hand, the processing heat generation of the steel sheet in temper rolling increases as the rolling reduction per pass increases, so the surface temperature of the steel sheet cooled by rolling oil is significantly lower than the temperature at the center of the plate thickness. As the amount of martensite generated on the steel sheet surface during rolling in the next pass is significantly increased, the amount of austenite on the steel sheet surface portion is greatly reduced.

That is, when the temper rolling is performed with a small number of passes as in the conventional method, the amount of austenite remaining on the surface of the steel sheet is significantly smaller than the amount of austenite remaining in the center of the sheet thickness, and the austenite during the subsequent forming process Thus, sufficient TRIP effect accompanying the processing-induced martensitic transformation cannot be obtained, and moldability is lowered.

On the other hand, the amount of austenite remaining on the steel sheet surface after temper rolling can be increased by increasing the number of passes of temper rolling and reducing the reduction amount per pass to suppress heat generation. Thereby, distribution of the thickness direction of the austenite amount desirable for the subsequent forming process can be achieved.

Specifically, the austenite amount γs (%) at the surface portion of the steel sheet after temper rolling and the austenite amount γc (%) at the center portion of the plate thickness satisfy the condition of γs / γc ≧ 0.10. When the direction distribution is achieved, a sufficient TRIP effect is exhibited in the steel plate surface portion that is most greatly deformed during the subsequent forming process, and the formability is improved.

Even if the number of passes in temper rolling is increased and the amount of reduction per pass is reduced, the temperature of the steel plate surface portion is lower than that of the plate thickness center portion, so that the steel plate surface portion is martensitic compared to the plate thickness center portion. It is inevitable that the amount produced is higher and therefore the amount of austenite is smaller. However, it has been found that if the amount of austenite at the steel plate surface portion is 1/10 or more of the amount of austenite at the center of the plate thickness, formability sufficient for practical use is ensured.

As explained above, the present invention is based on the fact that “the martensite phase is strengthened by increasing the C content and the precipitation strength strengthening by Cr ₂ N is superposed and the distribution of the austenite content in the thickness direction is optimized. Based on the technical idea that an austenitic stainless steel sheet that satisfies the requirements as a material for spring parts that are reduced in size and weight can be obtained.

Next, the chemical composition, metal structure and manufacturing method of the austenitic stainless steel sheet according to the present invention will be described.
(1) Chemical composition C: 0.01 to 0.15%
C is a solid solution strengthening element and is extremely effective for strengthening the martensite phase generated by cold working, so the C content is set to 0.01% or more. However, if the amount of C is excessive, coarse carbides are produced in the production process and formability and corrosion resistance deteriorate, so the C content is set to 0.15% or less. The C content is desirably 0.03% or more.

Si: 3.0% or less Si is a solid solution strengthening element and contributes to increasing the strength of steel and is also used as a deoxidizing material during melting. However, if the Si content is excessive, coarse Si compounds are produced during the production process, and these coarse Si compounds cause deterioration of hot workability and cold workability. For this reason, Si content is 3.0% or less, Preferably it is 2.8% or less.

Mn: 3.0% or less Mn is used as a deoxidizer during melting. Further, Mn is an austenite stabilizing element and is contained in an appropriate amount in consideration of balance with other elements. However, if the Mn content is excessive, a coarse Mn compound is produced in the production process, and the coarse Mn compound becomes a starting point of destruction, and the moldability deteriorates. Therefore, the Mn content is 3.0% or less, and desirably 2.8% or less.

Cr: 10.0 to 30.0%
Cr is a basic element of stainless steel, and by containing 10.0% or more, Cr has an effect of forming a passive film on the surface of the steel material to enhance corrosion resistance. Further, when the steel is aged, it precipitates as fine Cr ₂ N, thereby contributing to improvement of the strength of the steel. However, since Cr is a ferrite-forming element, if the Cr content is excessive, δ-ferrite is generated at a high temperature, and the hot workability of the steel is significantly deteriorated. Therefore, the Cr content is 10.0% or more and 30.0% or less, and desirably 12.0% or more and 25.0% or less.

Ni: 4.0 to 20.0%
Ni is a basic element of austenitic stainless steel, and in order to stably obtain an austenitic phase having an excellent strength-ductility balance at room temperature, 4.0% or more of Ni is contained. However, if the Ni content is excessive, the austenite phase becomes too stable and the processing-induced martensitic transformation is suppressed, so that high strength cannot be obtained. Therefore, the Ni content is 4.0% or more and 20.0% or less, and preferably 4.5% or more and 18.0% or less.

N: 0.40% or less N, like C, is a solid solution strengthening element and contributes to improving the strength of steel. Also, upon aging of the steel, even by precipitation as fine Cr ₂ N, which contributes to increasing the strength of steel. However, if the N content is excessive, it becomes easy to induce ear cracks during hot working. Therefore, the N content is 0.40% or less, preferably 0.05% or more and 0.30% or less.

The austenitic stainless steel according to the present invention may further contain the following optional additive elements as necessary.
One or both of Mo: 3.0% or less and Cu: 3.0% or less Mo and Cu are elements that contribute to increasing the strength of the steel sheet by precipitating fine intermetallic compounds during aging treatment. , May be included as necessary. However, if the Mo content or the Cu content is excessive, δ ferrite is likely to be generated at a high temperature, and the hot workability may be remarkably deteriorated due to precipitation at the grain boundaries. Therefore, both the Mo content and the Cu content are 3.0% or less, and desirably both are 2.8% or less.

One or more selected from Ti: 0.5% or less, Nb: 0.5% or less, and V: 1.0% or less Ti, Nb and V are fine carbides or nitrides in the manufacturing process. Since it contributes to the increase in strength of the steel sheet by precipitation strengthening, it may be contained as necessary. However, if the content of these elements is excessive, coarse carbides and nitrides are formed, which become the starting points of fracture during deformation and significantly deteriorate the moldability. Therefore, Ti content and Nb content shall be 0.5% or less, and V content shall be 1.0% or less. Desirably, the Ti content and the Nb content are 0.4% or less, and the V content is 0.8% or less.

The balance other than those described above is Fe and impurities. Typical impurities include P: 0.05% or less, S: 0.03% or less, and the like.
(2) Metal structure [Austenite distribution in the thickness direction]
As a result of performing various tests, the inventor has found that the austenite amount γs (%) of the steel sheet surface portion and the austenite amount γc (%) of the center portion of the sheet thickness satisfy the following expressions (1) and (2), It has been found that an austenitic stainless steel sheet having both high strength and formability can be obtained when the balance is mainly a work-induced martensite structure.

Formula (1): (γs + γc) / 2 ≦ 55
Formula (2): γs / γc ≧ 0.10
First, as shown in Equation (1), the average austenite amount, which is the average value of the austenite amount γs at the surface portion of the steel sheet and the austenite amount γc at the central portion of the plate thickness, is 55% or less, and the balance is mainly high-strength work-induced martensite. High strength steel can be obtained by sighting. The average austenite amount is desirably 50% or less, more desirably 45% or less, still more desirably 40% or less, and most desirably 35% or less. The lower limit of the average austenite amount is not particularly specified, but if the austenite is extremely small, a sufficient TRIP effect may not be obtained on the surface of the steel sheet during the forming process, so it is preferably 5% or more, more preferably 7 More than 5%.

Next, as shown in Formula (2), the ratio of the austenite amount γs of the steel sheet surface portion to the austenite amount γc at the center portion of the plate thickness (γs / γc ratio) is set to 0.10 or more, thereby forming the plate. Even on the steel sheet surface that is sometimes subjected to the greatest deformation, the TRIP effect accompanying the work-induced martensitic transformation of austenite is sufficiently exhibited, and excellent formability is obtained. The γs / γc ratio is desirably 0.2 or more, more desirably 0.3 or more, still more desirably 0.5 or more, and most desirably 0.6 or more.

In the present invention, when the austenite amount at the steel plate surface portion and the austenite amount at the plate thickness center portion satisfy both the expressions (1) and (2), both high strength and excellent formability can be achieved. .

The balance other than austenite of the metal structure mainly consists of a processing-induced martensite phase. This work-induced martensite is generated by temper rolling a steel sheet annealed after cold rolling. Therefore, the austenitic stainless steel sheet of the present invention is a temper rolled material.

“Consisting of mainly processing-induced martensite phase” means that processing-induced martensite accounts for 50% by volume or more of the balance other than austenite. In the austenitic stainless steel sheet manufactured according to the method of the present invention described later, the metal structure is substantially austenite and work-induced martensite, and the other phases are fine precipitates (carbide, nitride, carbonitride). Etc., but the amount is slight. A complete martensitic single phase structure with γs = γc = 100% is outside the scope of the present invention.

As described above, since the amount of austenite is greater in the center of the plate thickness than in the surface portion of the steel plate, even in the austenitic stainless steel plate according to the present invention in which the amount of austenite of the steel plate surface portion is increased, γs <γc (ie, γs / Γc <1).

Crystal grain size of austenite grains before temper rolling: 5 μm or less Refinement of crystal grains is known as a strengthening method in which the deterioration of the ductility of the steel is small, and is also an effective strengthening method in the stainless steel targeted by the present invention It is. In addition, by reducing the crystal grain size and increasing the density of the crystal grain boundaries, there is an effect of dispersing the strain concentrated on the grain boundaries during the molding process and suppressing the generation of cracks. Therefore, in the present invention, it is desirable that the crystal grain size of the austenite grains of the steel sheet (cold-rolled annealed material) before temper rolling be 5 μm or less.

(3) Manufacturing method According to the present invention, after hot rolling the steel material having the above-described chemical composition, the obtained hot-rolled steel sheet is cold-rolled and annealed to obtain a cold-rolled annealed material. The austenitic stainless steel sheet according to the present invention described above can be manufactured by subjecting the cold-rolled annealed material to temper rolling at a rolling reduction (%) / 10 or more passes.

Hot rolling, cold rolling and annealing may all be performed according to conventional methods. The cold rolling is preferably performed about 1 to 3 times so that the total rolling reduction is about 30 to 90%, and annealing is performed when a predetermined total rolling reduction is obtained. Multiple passes of cold rolling and annealing can be repeated. It does not specifically limit regarding the frequency | count of the cold rolling pass implemented before temper rolling.

When the total rolling reduction ratio of the cold rolling is increased and the austenite grain average grain size of the cold rolled annealed material used for the next temper rolling is made a fine metal structure of 5 μm or less, the formability becomes particularly good. Therefore, it is preferable.

[Temperature rolling conditions]
In the present invention, the temper rolling is strengthened in order to make maximum use of the strengthening caused by work-induced martensite. The total rolling reduction is preferably 40% or more, more preferably 50% or more, and most preferably 60% or more. The upper limit of the total rolling reduction is not particularly specified, but is usually less than 100%, preferably 90% or less.

When strong temper rolling is performed with a small number of passes, as described above, work-induced martensite in the steel plate surface portion advances, the austenite amount in this portion decreases, and the austenite amount γc in the center portion of the plate thickness decreases. The ratio of the austenite amount γs (γc / γs ratio) ≧ 0.1 in the steel plate surface portion cannot be satisfied, and the formability deteriorates.

As a result of investigating the relationship between the number of passes during temper rolling and the austenite distribution in the sheet thickness direction, the present inventor has obtained a number of passes that gives a total reduction ratio (%) / 10 or more, as shown in Equation (3). It was confirmed that the γc / γs ratio was 0.10 or more by performing temper rolling. Therefore, temper rolling is performed with the total number of reductions (%) in temper rolling / 10 passes. For example, when the total rolling reduction of temper rolling is 65%, the number of passes is 7 or more.

Formula (3): Number of temper rolling passes ≧ Total temper rolling reduction ratio (%) / 10
Preferably, the rolling reduction in each pass of temper rolling is substantially the same. Therefore, it is desirable that the rolling reduction in each temper rolling pass is 10% or less. Increasing the number of passes unnecessarily deteriorates work efficiency, so the number of passes should be within the range from the smallest number of passes to satisfy the total reduction ratio (%) / 10 to the number of passes that is two passes more than that. Is preferred.

Table 1 shows the chemical components of the stainless steel used in this example. Steels A to F are invention steels that satisfy the components specified in the present invention, and steels G to M are comparative steels that do not satisfy the components specified in the present invention.
Table 2 shows the manufacturing conditions and test results of steel sheets manufactured using steels A to M. Steel plates 1 to 8 are steel plates that satisfy the provisions of the present invention, and steel plates 9 to 18 are comparative steel plates that do not satisfy the prescriptions of the present invention.

A steel material having the chemical composition shown in Table 1 was melted in a normal atmospheric melting furnace to obtain a 17 kg steel ingot. The steel ingot is hot rolled and annealed to form a hot rolled steel sheet having a thickness of 6.0 mm, and then cold rolled and annealed on the hot rolled steel sheet 1 to 3 times to obtain a thickness of 0.8 to A 4.0 mm cold-rolled annealed material was obtained. The cold-rolled annealed material was subjected to temper rolling with a plurality of passes, and finally a thin plate having a thickness of 0.4 mm was obtained. The temper rolling was performed under the condition that the rolling reduction rate of each pass was equal.

Using the test pieces collected from the steel sheets before and after the temper rolling, the crystal grain size, austenite amount, formability, and tensile strength were investigated by the following methods. Some steel plates were subjected to an aging treatment at 300 ° C. for 1 minute after temper rolling. The tensile strength of these steel plates was the value after aging treatment.

(Average grain size after annealing)
The crystal grain size of the austenite grain was calculated from the nominal grain size of the austenite grain from the scanning micrograph after corrosion of the cross section of the specimen taken from the cold rolled annealed material before temper rolling.

(Austenite amount)
The amount of austenite was calculated from the steel plate surface portion of the test piece collected from the temper-rolled steel plate and the plate thickness center portion surface cut by mechanical polishing and chemical polishing. For the calculation, an integrated intensity ratio obtained by X-ray diffraction measurement and a scanning micrograph after etching were used. In Table 2, the amount of austenite at the surface portion of the steel sheet is denoted by γs, and the amount of austenite at the center surface of the plate thickness is denoted by γc.

(Formability)
FIG. 3 is an explanatory view showing a formability evaluation method. A shallow drawing process as shown in FIG. 3 was applied to a 100 mm square test piece taken from the temper rolled steel sheet. After that, the corners were observed with an optical microscope, ◎ if no crack was confirmed, ○ if no continuous crack was confirmed, or if a continuous crack was confirmed, or fractured Was marked with x.

(Tensile strength)
The tensile strength was measured based on JISZ 2241 using a JIS-13B tensile test specimen taken from a steel sheet after temper rolling or after aging treatment. Along with the measured value, a case where the tensile strength exceeds 1500 N / mm ² is indicated as ◯, and a case where the tensile strength is not reached is indicated as ×.

Steel plates 1 to 8 in Table 2 are steel plates of the present invention and have excellent formability and high strength. Moreover, by comparing the steel plates 1 and 2, it was confirmed that particularly high strength was obtained by the precipitation of fine Cr ₂ N during the aging treatment. In addition, it was confirmed that the steel plates 3 and 4 having a crystal grain size after annealing of 5 μm or less obtained particularly high strength and excellent formability.

Steel plates 9 to 18 are comparative examples in which the chemical composition or production conditions are outside the range defined in the present invention.
Steel sheets 9 to 11 have a γs / γc of less than 0.1 and high strength is obtained, but the formability is poor. Further, when the steel plate 7 and the steel plate 10 or the steel plate 8 and the steel plate 11 are compared, the steel plates 7 and 8 have both high strength and formability, but the steel plates 10 and 11 have high strength but have poor formability. Thus, it was confirmed that even when steels having the same composition were produced at the same temper rolling ratio, the distribution of the austenite amount changed depending on the number of rolling passes, and the characteristics changed greatly.

The steel plate 12 has a C content and an N content exceeding the range of the present invention, and coarse carbonitrides are produced, so that the formability is extremely poor.
The steel plate 13 has a C content below the range of the present invention, and has a low strength even after aging treatment. Moreover, since γs / γc is less than 0.1, the moldability is also poor.

The steel sheet 14 has a Cr content and a Ni content exceeding the range of the present invention, and the average value of γs and γc exceeds 55, so that the strength is low even after aging treatment.
The steel sheet 15 has poor formability because the Cr content and Ni content are below the range of the present invention and γs / γc is less than 0.1.

The steel plate 16 has a Si content and a Mn content exceeding the range of the present invention, and the average value of γs and γc exceeds 55, so that the strength is low even after aging treatment. In addition, coarse Si compounds and Mn compounds are produced, and the moldability is poor.

The steel plate 17 has a Mo content and a Cu content exceeding the range of the present invention, and the average value of γs and γc exceeds 55, so that the strength is small even after aging treatment. In addition, coarse intermetallic compounds are produced and formability is also poor.

Furthermore, the steel plate 18 has a Ti content exceeding the range of the present invention, and coarse TiN is produced, resulting in poor formability.

Claims (5)

By mass%, C: 0.01 to 0.15%, Si: 3.0% or less, Mn: 3.0% or less, Cr: 10.0 to 30.0%, Ni: 4.0 to 20. 0%, N: not more than 0.40%, having a chemical composition composed of the balance Fe and impurities, the austenite amount γs (%) of the steel plate surface portion and the austenite amount γc (%) of the center portion of the plate thickness, An austenitic stainless steel sheet characterized by satisfying (γs + γc) / 2 ≦ 55 and γs / γc ≧ 0.10, and the balance mainly having a metal structure that is a work-induced martensite structure. The austenitic stainless steel sheet according to claim 1, wherein the chemical composition has at least one of Mo: 3.0% or less or Cu: 3.0% or less in mass% instead of part of Fe. The chemical composition may be one selected from the group consisting of Ti: 0.50% or less, Nb: 0.50% or less, and V: 1.0% or less in mass% instead of part of Fe. The austenitic stainless steel sheet according to claim 1 or 2 having two or more kinds. After hot rolling the steel material having the chemical composition, the obtained hot-rolled steel sheet is cold-rolled and annealed to form a cold-rolled annealed material, and the cold-rolled annealed material is reduced (%) / 10 The method for producing an austenitic stainless steel sheet according to any one of claims 1 to 3, wherein the temper rolling is performed with the number of passes described above. The method according to claim 4, wherein the average crystal grain size of the austenite grains of the cold-rolled annealed material before temper rolling is 5 μm or less.

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