CN100535161C - Shaped steel having excellent fire resistance and method for producing same - Google Patents

Abstract

The present invention provides a shaped steel, such as an H-shaped steel, which is excellent in fire resistance, in which a flange portion has a strength ratio of 50% or more, a yield ratio of 80% or less, and an impact strength of charpy impact test at 0 ℃ of 100J or more, in which the strength ratio is (0.2% proof stress at 600 ℃)/(yield strength at room temperature), and a method for producing the shaped steel. The section steel comprises (in weight percent (%): c: 0.03-0.15; mo: 0.1-0.6; v is less than or equal to 0.35 and N: 0.002-0.012, and the balance being iron and residual impurities, wherein the mole fraction (x) of deposits of alloy carbides and alloy carbonitrides at 600 ℃ is 0.3% or more, and the ratio (y) of the mole fraction of deposits of alloy carbides and alloy carbonitrides at 300 ℃ to the mole fraction of deposits of alloy carbides and alloy carbonitrides at 600 ℃ is 2.0 or less.

Description

Shaped steel with excellent fire resistance and preparation method thereof

technical field

The present invention relates to a new type of steel, such as H-shaped steel, I-shaped steel, angle steel, channel steel, etc., which is used as a building material, has a low yield ratio and has excellent toughness and fire resistance, and also relates to the preparation of the shaped steel method.

Background technique

In March 1987, Japan enacted legislation on "New Regulations for Designing Fire-Resistant Buildings". Since then, refractory steels have been realized, which guarantee high strength at high temperatures, which have no or only minimal refractory packaging.

With regard to shaped steel, many techniques for securing the fire resistance of steel have been proposed in accordance with this trend. For example, it is proposed to secure strength at high temperature such as 600° C., such as strength and yield ratio, by utilizing a technique of precipitation strengthening of Mo-based carbides.

For example, JP-A-9-104944 proposes a refractory shaped steel using deposition strengthening technology and oxide metallurgy technology. Oxide metallurgy is a technique that can control the amount of oxides obtained by deoxidizing dissolved oxygen in steel using Ti, B, and Mg. Oxide metallurgy has the following effects.

During the preparation of section steel, different parts of the section steel are subjected to finish rolling at different temperatures and different cooling rates, resulting in inhomogeneity in the shape of the steel section, resulting in uniformity defects in the microstructure of the steel section. The lack of uniformity of the microstructure, such as the inhomogeneity of the grain size, leads to the inhomogeneity of the mechanical properties of the steel section.

The flange part, especially the fillet part where the flange part and the web part meet (see Figure 1), has less strain after rolling than other parts and needs to be processed at a higher temperature.

In sections of shaped steel (eg H-shaped steel), there will be about 150°C difference in finishing temperature between the three parts of fillet, 1/4 flange and web (see Figure 1). The different mechanical properties of the parts due to the difference in the rolling temperature of the parts should be eliminated.

The dependence of the formation of the microstructure during hot rolling on the final temperature can be reduced by dispersing transformation nuclei, such as titanium oxide, into the ferrite grains and thereby accelerating the transformation of the grains. This results in a homogeneous/homogeneous fine-grained microstructure, ie uniformity of mechanical properties. Furthermore, the particles of the microstructure are not only homogenized, but also fine-grained, which results in increased toughness.

The inventors of the present invention have conducted extensive research to provide a shaped steel, such as an H-shaped steel, which has a low yield ratio and is excellent in toughness and fire resistance, and provides a method for producing the shaped steel. During extensive research, the present inventors realized the following possible technical problems.

First of all, when using oxide metallurgy to produce shaped steel with excellent refractoriness, complex steps are required for the method, especially for pouring slabs, billets, ingots, slabs close to mesh, ingot iron, etc. . These complex steps include oxygen content control before Ti addition as well as after Ti addition. These steps reduce the productivity and increase the production cost of the section steel.

Further, the deposition strengthening technology contributes to the fire resistance of the section steel, such as the strength and yield ratio at high temperature. However, in the case of using Mo-based carbides mainly containing Mo ₂ C, such carbides are solidly dissolved in steel in the temperature range of 600-650° C. if these components are within specific ranges. The contribution to the strength of the steel provided by precipitation strengthening with alloy carbides and alloy carbonitrides may thus disappear.

The effect of deposition strengthening depends on the amount of deposited alloy carbonitrides. Alloy carbonitrides include alloy carbides and alloy carbonitrides. Note that one or more metals may be present with carbides or carbonitrides. That is, here, alloy carbides refer to metal carbides other than iron carbide. Hereinafter, the amount of deposition will be expressed as the mole fraction of the sediment, which may also be referred to simply as "the mole fraction of the sediment". The amount of deposition depends on temperature. Also, this temperature dependence is affected by other factors such as the carbon content of the steel and thermodynamic properties based on the type of alloy carbides and alloy carbonitrides, among others.

Regarding the carbon content, if the C content in the steel is sufficient compared with the content of metal elements, such as Mo, Ti, V, Nb, Cr, and can form alloy carbonitrides, the deposition amount of alloy carbonitrides will decrease with temperature And increase. This is because when the temperature of the steel decreases, the C content that can form deposits increases with the decrease of the carbon content of the solid dissolved (existing as a solid solution) in the ferrite.

Therefore, if the C content is high and the mole fraction of deposits of alloy carbides and alloy carbonitrides is excessively increased, the strength and yield ratio at room temperature will be excessively increased even under the same thermal conditions such as the same temperature decrease.

EP-A-0347156 discloses a method for producing a structural steel having excellent fire resistance and low yield ratio, the steel including 0.005-0.10% of V as an optional element. EP-A-1026275 discloses high strength high toughness rolled steel sections containing 0.04-0.10% V.

Contents of the invention

From this technical analysis, the present inventors have realized that: i) preferred alloy carbides and alloy carbonitrides not only have thermodynamic stability, but also have solid dissolution in steel at reheating temperature but at temperatures such as 600-650 The property of not dissolving solids at ℃, and ii) alloy carbides and alloy carbonitrides, which can be dissolved at one time during reheating and then deposited during cooling of hot rolling, which can be effectively used for deposition strengthening .

After intensive studies, the present inventors realized that it is preferable to properly control the mole fraction of deposits of alloy carbides and alloy carbonitrides in the high temperature range and room temperature range, and it is preferable to determine the composition of steel in consideration of the following issues.

(i) suppressing the mole fraction of deposits of alloy carbides and alloy carbonitrides in the room temperature range to prevent excessive increase in strength and yield ratio at room temperature; and (ii) obtaining deposits of alloy carbides and alloy carbonitrides Specific mole fraction of the compound in order to obtain sufficient strength in the high temperature range.

In view of the above problems, the present inventors designed various alloy carbides and alloy carbonitrides and found that the amount of deposits of alloy carbides and alloy carbonitrides can be reduced by making the alloy carbides and alloy carbonitrides capable of forming The amount (content) of metal elements such as Mo, Ti, V, Nb, Cr and C and N is properly balanced to control. It was found that thermodynamic properties can be controlled by properly balancing the amounts (contents) among metal elements.

More specifically, in the case where Mo-based alloy carbides such as Mo ₂ C are the main component of the deposit, it can be completely dissolved in solid form in the temperature range of 600-650°C, through the formation of alloy carbides and alloy carbonitrides. The contribution of deposition strengthening to steel strength disappears. However, it was found that the use of MCN-type alloy carbonitrides, which are more stable than M ₂ C-type alloy carbides in the high-temperature range, partially replaces Mo-based alloy carbides (i.e., MCN-type alloy carbonitrides phase with M ₂ C-type alloy carbides An increase in the specific deposition amount, where "M" stands for a metal other than iron) solves the above problems very effectively.

That is, V is added to partially replace Mo to form alloy carbonitrides instead of Mo-based alloy carbides, and by properly balancing the additions of V, Nb, and Mo, it is possible to control the beneficial Production of Alloy Carbonitrides.

When referring to phrases such as "room temperature," this generally refers to a temperature in the range of about 0°C to about 30°C. Note, however, that data at 300°C may be representative of data at room temperature. This is due to the fact that the amount of deposits of alloy carbides and alloy carbonitrides increases very little between room temperature and 300°C. Moreover, the deposits of these alloy carbides and alloy carbonitrides measured in the present invention are mainly produced between 300°C and 600°C. This is due to the fact that, as the temperature approaches room temperature, the diffusion of solid dissolved elements, such as metal elements, carbon and nitrogen, in the steel is extremely reduced in terms of deposition behavior. More specifically, the equilibrium state of deposition remains almost unchanged between room temperature and 300 °C. Therefore, in the description of the present invention, the deposition state at a temperature of 300° C. may also be representative at room temperature. Furthermore, the inventors have chosen a temperature of 600°C as a suitable "high temperature" for determining or evaluating certain mechanical properties, as well as the amount of deposits of alloy carbides and alloy carbonitrides. However, the "high temperature" is not limited to 600°C and may include other suitable temperatures.

The object of the present invention is to provide a new type of steel, such as H-shaped steel, which is used as a building material, which has a low yield ratio and excellent toughness and fire resistance, and a method for preparing the same. This object can be realized by the following section steel and its preparation method.

According to the present invention, through a specific process such as hot rolling cast steel containing specific components to form alloy carbides and alloy carbonitrides mainly containing V and Mo in an appropriate amount, excellent strength at high temperature and excellent mechanical properties at room temperature can be obtained. Performance steel, such as H-beam. According to the present invention, "cast steel" includes slabs, ingots, slabs, nearly mesh-shaped slabs, ingot iron, and the like.

Description of drawings

FIG. 1 shows the position where a test piece (sample) is taken from an H-shaped steel 1 . The first position is the central area of the flange 2 in the thickness direction (1/2 t ₂ ) and the distance from the end of the flange 2 in the flange width direction to 1/4 of the total flange width (B) one quarter (1 /4B) location. The second position is the central area (1/2 t ₂ ) of the flange 2 in the thickness direction and the half (1/2B) position of the total flange width (B) in the flange width direction (rounded portion 4 ). The third position is the central area (1/2 t ₁ ) of the web 3 in the thickness direction and half (1/2H) of the total web height (H) in the flange width direction.

Fig. 2 (a) is an example containing 0.35% V of the present invention, showing the total mole fraction of the deposit (being the sum of the M ₂ C type alloy carbide mole fraction and the MCN type alloy carbonitride mole fraction) and A graph of the relationship between temperature, where _M2C -type alloy carbides partially include V and Nb as solid solutions and MCN-type alloy carbonitrides include V and Nb as main components, and partially include Mo as solid solutions. The vertical axis of Fig. 2(a), Fig. 2(b) and Fig. 3 is the mole fraction of deposits of alloy carbide, alloy carbonitride and the sum of alloy carbide and alloy carbonitride.

Fig. 2(b) is a graph showing the relationship between the total mole fraction of the deposit and temperature, similar to Fig. 2(a), where the V content is 0.22%.

Fig. 3 shows the relationship between temperature and the respective mole fractions of deposits of the sum of M ₂ C type alloy carbides, MCN type alloy carbonitrides and M ₂ C type alloy carbides and MCN type alloy carbonitrides using conventional methods relationship diagram. Note that the conventional method neither considers the mole fraction of alloy carbide and alloy carbonitride deposits at 600 °C, nor considers the mole fraction of alloy carbide and alloy carbonitride deposits at 300 °C and alloy carbide Any method in which the ratio of the mole fractions of deposits of metal and alloy carbonitrides at 600°C is 2.0 or less.

Detailed ways

The present invention is described more specifically below. The elements contained in the shaped steel of the present invention are described below. In this specification, the percentage "%" represents "% by weight".

C is an element that can increase the strength of steel. From the viewpoint of sufficient strength of structural steel, the content of C is 0.03% or more. C also has an effect on the toughness of the base steel, the weld crack resistance and toughness in the heat-affected zone (HAZ). From the standpoint of these properties, the content of C is 0.15% or less. Therefore, the content of C is 0.03-0.15%.

Si functions as a deoxidizer (or oxygen scavenger) in the steelmaking process and also affects the strength of the steel. From the viewpoint of sufficient strength of structural steel, the content of Si is 0.05% or more. Si also affects the toughness in the HAZ since an excess of Si produces a hardened structure of M-A (Martensitic-Austenitic) composition, which destroys the toughness in the HAZ. Based on this, the content of Si is 0.5% or less. Therefore, the content of Si is 0.05-0.50%.

Mn is an element capable of improving the strength and toughness of a mother phase. From this point of view, the content of Mn is 0.4% or more. Mn also has an effect on crack resistance and toughness in the HAZ. From the standpoint of these properties, the content of Mn is 2.0% or less. Therefore, the content of Mn is preferably 0.4-2.0%.

Mo is an element capable of forming Mo-based alloy carbides. In the present invention, it is considered that the shape steel has excellent strength at room temperature and high temperature due to alloy carbide deposition of Mo. In order for the shape steel to have sufficient strength at high temperature, the content of Mo is 0.1% or more. Mo also improves the hardenability of steel. Excessive Mo impairs the toughness of steel and HAZ because the hardenability increases excessively. From the viewpoint of these properties, the content of Mo is 0.6% or less. Therefore, the content of Mo is 0.1-0.6%, preferably 0.2-0.4%, more preferably 0.2-0.3%.

V is an element capable of forming alloy carbonitrides, and contributes to the deposition strengthening of steel. In the present invention, when V is used together with Mo, V can be solidly dissolved in M ₂ C alloy carbide mainly containing Mo to form ((Mo, V) ₂ C). Furthermore, V can dissolve Mo solid in an alloy carbonitride of M(C,N) mainly containing V to form ((Mo,V)(C,N)).

By adjusting the content of V and Mo, the alloy carbide is converted into one or both of the alloy carbide with the structure of M ₂ C and the alloy carbonitride with the structure of M (C, N), and the thermodynamic basis can be adjusted appropriately. performance of the sediment. In order for this conversion to proceed efficiently, the content of V is 0.04% or more.

When an excessive amount of V is added, the amount of alloy carbonitrides will excessively increase and the toughness of steel and HAZ will be impaired. Therefore the content of V is 0.35% or less.

On the other hand, in order to ensure sufficient strength of the steel for refractory properties at 600°C, for example, it may be preferable to have a sufficient amount of alloy carbonitrides deposited in the steel. For this purpose, the content of V is 0.20% or more. Therefore, the content of V is 0.20-0.35%.

In order to obtain refractory properties, the deposition of V-based alloy carbides having a structure of M ₂ C is mainly controlled. However, it is more preferable to mainly control the formation of alloy carbonitrides having a structure of M(C,N) in order to effectively improve refractory properties. From this point of view, the content of V is 0.20% or more.

N is an element capable of forming alloy carbonitrides. In order to obtain sufficient deposits, the N content is 0.002% or more. Also, since excessive N reduces the toughness of steel, the N content is 0.012% or less. Therefore, the content of N is 0.002-0.012%.

Al acts as a strong deoxidizer (oxygen scavenger) during steel preparation. However, Al can combine with N to form AlN, which results in a reduced amount of alloy carbonitrides (deposits). Therefore, the Al content is preferably 0.01% or less.

Also, in the present invention, other optional components may be added.

Nb is an element similar to V and Ti, which can form alloy carbonitrides, such as M(C,N), and is conducive to deposition strengthening. However, when the Nb content is greater than 0.06%, it cannot further increase the strength of the steel by precipitation strengthening because the amount of alloy carbonitrides that do not dissolve at a heating temperature of 1100-1300°C before hot rolling increases.

From the viewpoint of improving strength by depositing alloy carbonitrides, the Nb content is preferably 0.02% or more. Therefore, the content of Nb is preferably 0.02-0.06%.

Ti is an element similar to Nb and V, which can form alloy carbonitrides such as M(C,N) and facilitate deposition strengthening. In the present invention, Ti is solid dissolved in an alloy carbonitride such as M(C,N), which is formed by adding V or a combination of V and Nb to form an alloy carbonitride such as (V,Ti) (C,N) or (V,Ti,Nb)(C,N). Therefore, Ti affects the stability of alloy carbonitrides at high temperature.

More specifically, alloy carbonitrides such as M(C,N) can extend thermal stability to higher temperatures when Ti is present. However, when the content of Ti exceeds 0.02%, the amount of alloy carbonitrides that cannot be solid-dissolved increases due to the heating temperature applied before hot rolling, such as 1100-1300°C, so it is not conducive to precipitation strengthening. Therefore, the content of Ti is preferably 0.02% or less.

Cr is not only an element capable of increasing the strength at room temperature and high temperature by increasing the hardenability and precipitation hardening of steel, but also an element capable of preventing grain boundaries (grain boudary) on the steel surface from being oxidized (intergranular oxidation). )), and thus elements that improve the properties of the steel surface, such as smoothness and uniformity. However, the toughness of the parent phase and the toughness in the HAZ are compromised when excess Cr is present. From this point of view, the content of Cr is preferably 0.7% or less.

Ni is an element capable of improving the toughness of the matrix. However, from the viewpoint of cost, the content of Ni is preferably 1.0% or less.

Cu is an element that can increase the strength of steel. However, when an excessive amount of Cu is present, the hardenability of the steel increases excessively, so the toughness of the steel and the toughness in the HAZ decrease. From this point of view, the content of Cu is preferably 1.0% or less.

The structures of the alloy carbides and alloy carbonitrides and the mole fractions of the deposits of the alloy carbides and alloy carbonitrides can be determined by electron microscope observation and analysis. As a simple method, a software program for calculating thermodynamic equilibrium can be used.

Regarding the software that can be used in the present invention, for example, "Thermo-Calc" (manufactured by "Thermo Calc Software, USA) can be used to calculate thermodynamic equilibrium. As a database, for example, "SSOL" can also be used for analysis. However, for The software and database in the present invention are not limited as long as the software and database are reliable.

In the present invention, when calculating the mole fraction of deposits of alloy carbonitrides, here two types of alloy carbides and alloy carbonitrides, that is, alloys representing MCN type alloy carbonitrides with a face-centered cubic structure The sum of the mole fraction of carbonitride deposits and the mole fraction of deposits of alloy carbides representing M ₂ C type alloy carbides with a Hexagonal Closed-Packed structure is defined as alloy carbide and alloy Mole fraction of carbonitride deposits. Therefore, the present inventors calculated the deposit amounts of alloy carbides and alloy carbonitrides, and calculated their sum, using the total deposit amounts of alloy carbides and alloy carbonitrides for the mole fraction of deposits. Under the calculation conditions, specific mole fractions of deposits of alloy carbides and alloy carbonitrides were evaluated for different elements and different temperatures.

If necessary, add V to partially replace Mo, because Mo tends to form Mo-based alloy carbides, which can be completely solid dissolved in steel in the temperature range of 600-650 ° C, which is not conducive to deposition at such a high temperature strengthen. Within the range of V content of 0.20-0.35% in the present invention, different mole fractions of different kinds of alloy carbides and alloy carbonitrides and deposits at different temperatures were evaluated at several temperatures, such as room temperature and high temperature. mechanical features. This was done to investigate the proper balance of C content and N content, while paying particular attention to Mo and V contained in alloy carbides and alloy carbonitrides.

It is preferred to assume that alloy carbides mainly containing Mo and in which V and/or Nb are also solid-soluble are " _M2C -type alloy carbides", and alloy carbides mainly containing V and Nb and in which Mo is solid-soluble is "MCN-type alloy carbonitrides", and the mole fractions of deposits of alloy carbides and alloy carbonitrides are estimated by calculating this thermodynamic equilibrium. Since the mole fraction of the deposit in an actual process using continuous cooling is slightly different from the mole fraction calculated above, some correction is preferred.

Mechanical properties at 600°C are preferred, especially proof stress of 0.2% for excellent fire resistance. The proof stress of 0.2% is preferably 157 MPa or more.

Varying the balance of the elements C and N used in the present invention, the performance of the section steel was evaluated within the range of the mole fraction of deposits of alloy carbides and alloy carbonitrides of 0-1.0%. It was found that the mole fraction of deposits of alloy carbides and alloy carbonitrides was necessarily 0.3% or more at 600°C.

Moreover, in order to solve the problem of excessive increase in strength and yield ratio at room temperature, the appropriate ratio of the mole fraction of deposits of alloy carbides and alloy carbonitrides, that is, the moles of deposits of alloy carbides and alloy carbonitrides Scale of fractions at 300°C and at 600°C, and suitable mechanical properties at several elevated temperatures and at room temperature. In order to simultaneously obtain suppression of excessive increase in strength at room temperature and excellent fire resistance, it was found that the following conditions must be satisfied: i) the impact strength of the Charpy impact test is 100 J or more at 0° C.; and the condition ii) is preferably satisfied The tensile strength of the flange portion is 400 MPa or more; and iii) the 0.2% proof stress at 600° C. is 157 MPa or more. Conditions i) and ii) are mainly for room temperature properties and condition iii) is mainly for fire resistance.

By varying the balance of the elements C and N used in the present invention in the presence of a V fraction in place of Mo, evaluation of the performance of steel sections in the range of mole fractions of deposits of alloy carbides and alloy carbonitrides in the range of 0-5.0% . It was found necessary that the ratio of the mole fractions of deposits of alloy carbides and alloy carbonitrides at 300°C and at 600°C was 2.0 or less.

From the above studies, deposits of alloy carbides and alloy carbonitrides with excellent properties can be newly obtained, as shown in Fig. 2(a) and (b). In Fig. 2(a) and (b), the amount of deposits of alloy carbides of the M ₂ C type containing V and Nb as a solid solution partly, the M2C type alloy carbide mainly containing V, Nb and partly containing Mo as a solid solution are shown. The amount of deposits of MCN-type alloy carbonitrides, and the sum of M ₂ C-type alloy carbides and MCN-type alloy carbonitrides.

Fig. 2(a) shows the case where the content of V is 0.35%. The mole fraction of deposits of alloy carbides and alloy carbonitrides is 0.52% at a temperature of 600°C, which is within the range of the present invention (0.3 or more). As the temperature moves from 600°C to 300°C, the mole fraction of alloy carbide and alloy carbonitride deposits increases from about 0.52% to about 0.54%. Their ratio is about 1.03, satisfying the condition of 2.0% or less of the present invention.

Fig. 2(b) shows the case where the V content is 0.22%. The mole fraction of deposits of alloy carbides and alloy carbonitrides is 0.52% at a temperature of 600°C, which is within the range of the present invention (0.3% or more). As the temperature moves from 600°C to 300°C, the mole fraction of deposits of alloy carbides and alloy carbonitrides increases from about 0.52% to about 0.59%. Their ratio is about 1.14, satisfying the condition of 2.0%.

Therefore, it was found that the above-mentioned compositional design can simultaneously achieve suppression of excessive increase in strength at room temperature and excellent fire resistance at 600°C.

Figure 3, on the other hand, shows the results of applying the conventional method to steels whose composition is within the scope of the present invention. As shown in FIG. 3, the mole fractions of deposits of alloy carbides and alloy carbonitrides are within the range of the present invention (0.30% or more) at 600°C. However, when the temperature is moved from 600°C to 300°C, the mole fraction of the deposits of alloy carbides and alloy carbonitrides increases significantly from about 0.61% to about 1.42%. The ratio of the mole fractions of deposits at 300°C and 600°C is out of the range of the present invention (2.0 or less). Fig. 3 shows that the problem with the conventional method is that the strength at 300°C is too high. Note that the conventional method neither considers the mole fraction of alloy carbide and alloy carbonitride deposits at 600 °C, nor considers the mole fraction of alloy carbide and alloy carbonitride deposits at 300 °C and alloy Any method in which the ratio of mole fractions of carbides and alloy carbonitride deposits at 600°C is 2.0 or less.

The size of deposits such as alloy carbides and alloy carbonitrides has an effect on strength. Depending on the desired strength, the deposits are preferably fine-grained, for example, to a size of 10-1000 nm. It is preferable to perform solution treatment before hot rolling and form deposits during cooling after hot rolling, or to form deposits by keeping the temperature of the steel at about 600°C.

In the present invention, MCN-type alloy carbonitrides with temperature-dependent deposit amounts having lower stability (only in the temperature range of 300°C-600°C) and _M2C -type alloy carbides with temperature-dependent deposit amounts The ratio of the amount of deposit between is not particularly limited. However, it can be said that the ratio of deposits of MCN-type alloy carbonitrides/deposits of _M2C -type alloy carbides (hereinafter referred to as MCN/ _M2C ratio) is greater than that obtained by conventional methods. Ratio of things. For example, an MCN/M ₂ C ratio of 0.7 or more provides sufficient effect at high temperatures such as 600°C. However, the MCN/M ₂ C ratio is not decisive when the total amount of M ₂ C is reduced. In other words, an MCN/M ₂ C ratio of 0.7 or more is not a requirement for the present invention.

The reason for restricting the hot rolling process is as follows. First, the cast steel, such as slab, steel billet, steel ingot, near mesh slab, ingot iron, etc., is reheated to the range of 1100-1300°C. The reason for limiting the temperature is to ensure a temperature sufficient to enable the cast steel to be processed in the austenitic range and to fully develop the deposition by once solid dissolution of the alloy carbides and alloy carbonitrides during the hot rolling of the section steel strengthen.

After reheating, the cast steel goes through a hot rolling process. The hot rolling process basically includes a break-down process by groove rolling, intermediate rolling, and finish rolling. The intermediate rolling process may be performed by an intermediate general rolling machine including an edger rolling machine and a general rolling machine, and the finish rolling process may be performed by a general rolling machine. The above process also includes a rolling process of controlling the height of the web portion of the shaped steel using skew roll.

In the crushing process of the above-mentioned rolling process, the cast steel is rolled in the width direction by a plurality of rolls each having grooves whose bottom widths are different from each other and the bottom has a convex portion in the middle of the bottom of the groove. This ensures proper flange width and web height.

In the intermediate rolling process, the appropriate flange width is obtained by the edger and the appropriate web thickness and flange thickness are obtained by the universal rolling mill. Also in the finish rolling process, a shaped steel having a predetermined size is formed while maintaining the surface temperature of the flange portion at, for example, 800° C. or more.

The invention is preferably applicable to steel sections where the web thickness is in the range 9mm-40mm, the flange thickness is in the range 12mm-60mm, the web height is about 500mm and the flange width is in the range 200mm-500mm.

In the hot rolling process after reheating, it is preferable that the shaped steel is cooled with water at least once to 700° C. or less, and then rolled in a heat returning process, the temperature being measured at the surface of the flange portion.

As mentioned above, due to the shape of the section steel, the temperature of the fillet and flange portion is generally higher than that of the beam web portion. In order to reduce the temperature non-uniformity, the flange part is cooled with water and rolling is performed at least once during the heat supply process. Preferably, the cyclic process of cooling with water and rolling can be repeated according to the size of the steel profile and the number of rolling processes.

In the present invention, after the hot rolling process is completed, the shaped steel is naturally cooled, or rapidly cooled, for example, at least once, and then naturally cooled. During this cooling process the microstructure of the steel is fine-grained, which results in increased strength at room temperature, toughness and strength at elevated temperatures.

In the case of rapid cooling before natural cooling, the average cooling rate is preferably between 0.5-5.0 °C/s so that the microstructure can be further refined.

In the present invention, after the above-mentioned cooling process is performed, a refractory shaped steel having the following mechanical properties can be produced. That is, for example: the strength ratio defined by (0.2% proof stress at 600° C.)/(yield strength at room temperature) is 50% or more, the yield strength ratio at room temperature is 80% or less, and 0 Charpy impact absorption energy at ℃ is 100J or more mechanical properties; flange part tensile strength at room temperature is 400MPa class (grade), 0.2% proof stress at 600℃ is 157MPa or more, and 0℃ Charpy impact absorption energy is 100J or more mechanical properties; and flange portion tensile strength at room temperature is 490MPa class, 0.2% proof stress at 600°C is 217MPa or more, and Charpy impact absorption at 0°C Can be 100J or greater mechanical properties.

Example

Embodiments of the present invention are described below. However, the conditions described in these examples are merely descriptive, and the present invention is not limited to these conditions. The present invention can be carried out under other various conditions without departing from the gist of the present invention in order to achieve the object of the present invention.

The ingots and slabs used in these examples, having the components/compositions shown in Table 1 and having the mole fractions of the deposits predetermined by equilibrium calculations at 600°C and 300°C by "Thermo-Calc", were used in the smelting process. Melting in a steel furnace and pouring ingots and billets with a thickness of about 240-300mm in a continuous casting process. In Table 1, "tr" means "undetectable" or "inevitable impurity".

The conditions of Examples "a-g" of the comparative steel are not within the scope of the present invention. The conditions of the compositions of examples "a-c" are within the scope of the invention, but the mole fractions of the deposits of alloy carbides and alloy carbonitrides at 600°C are not within the scope of the invention (0.3% and greater). As for Examples "d-g", the ratio of the mole fraction of the respective alloy carbide and alloy carbonitride deposits at 300°C to the mole fraction of alloy carbide and alloy carbonitride deposits at 600°C, namely (Mole fraction at 300°C)/(Mole fraction at 600°C) is out of the scope of the present invention (2.0 and less).

In Table 1, the ratio of the mole fraction of deposits of alloy carbides and alloy carbonitrides at 300 °C to the mole fraction of deposits at 600 °C shown in the far right column is related to the ratios obtained from the respective alloy carbides and The calculated mole fraction of alloy carbonitride deposits at 300°C and 600°C are not exactly the same. This difference is due to significant figures because the mole fractions of the respective deposits of alloy carbides and alloy carbonitrides are calculated to three decimal places rounded off.

Each cast steel is reheated to 1100-1300°C, and then goes through a hot rolling process, including the following processes, crushing process through groove rolling process; intermediate rolling process, wherein, the intermediate universal rolling machine includes edge rolling mill and general rolling mill, and the finish rolling process carried out by the general rolling mill, thereby forming H-shaped steel of predetermined size.

In the above hot rolling process, the web height of the H-beam is controlled through the rolling process using skew rolling.

H-beams are produced with a web thickness in the range of 9mm-40mm, a flange thickness in the range of 12mm-60mm, a web height of about 500mm and a flange width in the range of 200mm-500mm.

Figure 1 shows the cross-section of an H-shaped steel, which is produced by cutting the steel in the transverse direction (not longitudinal). The mechanical properties of the produced H-shaped steel were obtained by various tests using test pieces (samples). Fig. 1 shows the positions taken from the test piece (sample). The first position is the central area of the flange 2 in the thickness direction (1/2 t ₂ ) and the distance from the end of the flange 2 in the flange width direction to 1/4 of the total flange width (B) one quarter (1 /4 B) Position. The second position is the central area (1/2 t ₂ ) of the flange 2 in the thickness direction and half (1/2 B) of the total flange width (B) in the flange width direction (rounded portion 4 ). The third position is the central area (1/2 t ₁ ) of the web 3 in the thickness direction and half (1/2 H) of the total web height (H) in the flange width direction. The mechanical properties at the upper (1/4 B) position can represent the mechanical properties of the flange portion of the H-shaped steel. However, measure the mechanical properties of the above 3 positions and check the average value of the mechanical properties of these 3 positions and the value of the mechanical properties of the web portion (third position) to confirm that excessive mechanical properties with the web portion can be prevented. strengthen. That is, the ratio of the value at the web portion to the average of the three locations is calculated.

Table 2 describes the results of the above tests, namely, yield strength at room temperature, tensile strength at room temperature, yield strength ratio at room temperature, Charpy impact absorption energy at 0°C (according to the 3-point average of JIS, the sample is JIS NO. 4 (actual size), with 2mm V-shaped notch), 0.2% proof stress at 600°C according to JIS A2, and ratio of 0.2% proof stress at 600°C to yield strength at room temperature, for example according to JIS NO.13A or 13B, depending on the thickness of the section steel. Regarding the Charpy impact test, the data in Table 2 represent the measured values of the fillet portion (1/2 B), which has a lower value in the Charpy impact test than any other portion of the section of the H-shaped steel. Regarding the 0.2% proof stress at 600°C, the data in Table 2 represent the measured values at the (1/4 B) position of the flange portion. The value at the (1/4 B) position represents the strength of the H-beam. For steel, there are two different classes (grades) of required strength. One is the SN400 type in which the tensile strength at room temperature is 400 MPa and greater, and the other is the SN490 type in which the tensile strength at room temperature is 490 MPa and greater. Regarding the SN400 class, examples showing strengths of about 400-520 MPa. Regarding the SN490 class, examples showing strengths of about 500-611 MPa. In Table 2, the results are described according to these classes, and in addition, the values of the mechanical properties of the web portion are calculated in relation to the average value of the 3 positions and are listed in the table.

The steel of the present invention satisfies the following conditions such as composition, mole fraction of deposits of alloy carbides and alloy carbonitrides. The mechanical properties of the steel of the present invention achieve target properties such as yield strength, tensile strength, Charpy impact absorption energy at 0°C at high temperature (600°C) and room temperature, and in particular define the strength ratio of the flange portion of the steel as The ratio of (0.2% proof stress at 600°C)/(yield strength at room temperature) and the yield strength ratio at room temperature.

Although the comparative examples have the same composition as the steel of the present invention, they do not satisfy at least one of the mechanical properties at room temperature and high temperature because they do not satisfy the deposits of alloy carbides and alloy carbonitrides of the present invention. Mole fraction requirements.

The comparative steels "c, f, g" had insufficient Charpy impact absorption energy at 0°C compared with the steels of the present invention (100J or more). The comparative steels "a, b", belonging to the SN400 class, did not reach the target value of 0.2% proof strength at 600°C, ie 157 MPa and more. The comparative steels "d, e", which belong to SN490 class, have 0.2% verification strengths at 600°C of 206, 212 MPa, respectively, which do not reach the target value of 217 MPa and greater. The intensity ratio of the comparison "d, e" did not reach the target value of 50% or more.

As described above, under the condition that the added amounts of V and Mo are properly balanced, by forming alloy carbides and alloy carbonitrides mainly composed of V and Mo, the present invention provides excellent refractoriness and has ideal properties at high temperatures. strength and mechanical properties at room temperature.

The shaped steel of the invention can be used as building material and has great industrial applicability.

All cited patents, publications, pending applications, and provisional applications referenced in this application are hereby incorporated herein.

The invention thus being described, it will be obvious that it may be varied in many ways. Such changes are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications obvious to those skilled in the art are also included within the scope of the claims.

Claims (4)

1, a kind of shaped steel comprises (weight percent (%)):

C：0.03-0.15，

Si：0.05-0.50，

Mn：0.4-2.0，

Mo：0.1-0.6，

V:0.20-0.35 and

N：0.002-0.012，

Optional Al≤0.01 that exists,

And randomly comprise the element of one or more following weight percents (%):

Ti：0.005-0.020，

Nb≤0.06％，

Cr≤0.7，

Ni≤1.0 and

Cu≤1.0，

And surplus is iron and residual impurity, wherein

Alloy carbide and the alloy carbonitride sedimentary molar fraction (x) under 600 ℃ be 0.3% or bigger and

Alloy carbide and the alloy carbonitride sedimentary molar fraction under 300 ℃ with have a M ₂C type alloy carbide is 2.0 or littler with the ratio (y) with MCN type alloy carbonitride sedimentary molar fraction under 600 ℃,

Wherein, the flange portion of described shaped steel has 50% or bigger strength ratio, 80% or the shock strength of littler yield tensile ratio and 100 J or bigger 0 ℃ of following Charpy impact test, wherein strength ratio=(600 ℃ 0.2% proof stresss) down/(yield strength under the room temperature).

2, the preparation method of shaped steel as claimed in claim 1 carries out hot rolling after reheat cast steel, comprise step:

(a) with the cast steel reheat to 1100-1300 ℃;

(b) the described cast steel of hot rolling is to form shaped steel; With

(c) after hot rolling finishes, naturally cooling or quick cooling, the described shaped steel of naturally cooling then.

3, method as claimed in claim 2, wherein said hot-rolled step comprise at least once shaped steel with being water-cooled to 700 ℃ or littler, and described temperature is in the surface measurements of the flange portion of shaped steel, and is rolling in temperature recovery process then.

4, method as claimed in claim 3, wherein said quick refrigerative step is to carry out under the average cooling rate of 0.5-5.0 ℃/s.

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