CN113957347B

CN113957347B - 590 MPa-grade thick-specification axle housing steel for cold stamping and preparation method thereof

Info

Publication number: CN113957347B
Application number: CN202111242969.6A
Authority: CN
Inventors: 崔凯禹; 李正荣; 汪创伟; 叶晓瑜; 张开华; 胡云凤
Original assignee: Pangang Group Panzhihua Iron and Steel Research Institute Co Ltd
Current assignee: Pangang Group Panzhihua Iron and Steel Research Institute Co Ltd
Priority date: 2021-10-25
Filing date: 2021-10-25
Publication date: 2022-07-22
Anticipated expiration: 2041-10-25
Also published as: CN113957347A

Abstract

The invention discloses 590 MPa-level thick axle housing steel for cold stamping and a preparation method thereof, belonging to the technical field of hot continuous rolling plate and strip production. The 590 MPa-grade axle housing steel for cold stamping comprises the following chemical components in percentage by mass: 0.07-0.10% of C, 0.05-0.10% of Si, 1.50-1.60% of Mn, less than or equal to 0.020% of P, less than or equal to 0.008% of S, 0.030-0.040% of Nb0.07-0.10% of V, 0.010-0.015% of N, 0.015-0.050% of Als0.015, and the balance of Fe and inevitable impurities. The manufacturing method comprises the steps of smelting the chemical components of the 590 MPa-level thick-specification axle housing steel for cold stamping into a plate blank, and sequentially heating, rough rolling, finish rolling, coiling and cooling the plate blank to obtain the 590 MPa-level thick-specification axle housing steel for cold stamping. The yield strength of the product is more than or equal to 460MPa, the tensile strength is more than or equal to 590MPa, the elongation after fracture is more than or equal to 20 percent, and the impact energy KV2 at the full-size temperature of minus 40 ℃ is more than or equal to 80J, so that the problem of higher production cost of the existing high-strength axle housing steel can be effectively solved.

Description

590 MPa-grade thick-specification axle housing steel for cold stamping and preparation method thereof

Technical Field

The invention belongs to the technical field of production of hot continuous rolled plate strips, and relates to 590 MPa-grade thick axle housing steel for cold stamping and a preparation method thereof.

Background

With the development of the Chinese automobile industry, the demand of the automobile steel is gradually increased, and the performance requirements of the automobile steel are higher and higher. The axle housing is one of the main components of an automobile chassis system, and is used for supporting a vehicle frame, and meanwhile, a speed reducer, a differential mechanism, a transmission device for driving wheels and the like are arranged in the axle housing, so that the axle housing is required to have sufficient strength, good stamping forming performance, good welding performance and the like. The manufacturing process of the automobile axle housing is mostly adopted before the automobile axle housing is manufactured, but the manufacturing process of the cast axle housing is complex, the production efficiency is low, heavy and high in cost, and the manufacturing process of the axle housing which is formed by stamping the hot rolled steel plate into the half axle housing and then welding has the advantages of high production efficiency, light weight and low cost, so that the hot rolled steel plate stamping and welding axle housing becomes the development direction of the existing automobile axle housing manufacturing.

The existing stamping process of the stamping and welding axle housing is divided into hot stamping and cold stamping processes. The hot stamping process is adopted, so that the energy consumption is increased, the production cost is higher, and the mechanical property of the steel plate is reduced after the hot stamping, so that the strength is possibly lower than a required value; and the cold stamping process has higher requirements on the cold forming performance of the steel plate.

2018, 12 months, 28 days and CN109097702A disclose high-strength axle housing steel with good fatigue performance and welding performance and a preparation method thereof, wherein the steel comprises the following chemical components in percentage by weight: 0.04-0.07% of C, 0.05-0.15% of Si, 1.30-1.60% of Mn, less than or equal to 0.013% of P, less than or equal to 0.004% of S, 0.045-0.070% of Nb, 0.010-0.020% of Ti, less than or equal to 0.003% of N, 0.010-0.030% of Alt, 0.001-0.002% of O, less than or equal to 0.007% of Ti-2 xO-3.4 xN, and the balance of Fe and inevitable impurities. The tensile strength of the steel is more than or equal to 600MPa, and good fatigue performance and welding performance are realized through strict control of chemical components and rolling and cooling control processes, but the production control difficulty is increased.

2016, 12, 21 and 21 CN106244919A disclose a low-alloy high-strength steel for punching axle housings and a production method thereof, wherein the steel plate comprises the following chemical components in percentage by mass: 0.14 to 0.18 percent of C, 0.20 to 0.40 percent of Si, 1.45 to 1.60 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.015 percent of S, 0.038 to 0.045 percent of Nb, 0.05 to 0.10 percent of V, 0.015 to 0.030 percent of Ti, less than or equal to 0.0050 percent of N, 0.035 to 0.050 percent of Als, and the balance of Fe and inevitable impurity elements. The tensile strength of the product is 600-650MPa, but the high-content Nb, V and Ti elements are added, so that the alloy composition is complex and the alloy cost is high.

Disclosure of Invention

The invention aims to solve the technical problem that the production cost of the existing high-strength axle housing steel is high.

The technical scheme adopted by the invention for solving the technical problem is as follows: the 590 MPa-level thick-specification axle housing steel for cold stamping comprises the following chemical components in percentage by mass: 0.07 to 0.10 percent of C, 0.05 to 0.10 percent of Si, 1.50 to 1.60 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.008 percent of S, 0.030 to 0.040 percent of Nb, 0.07 to 0.10 percent of V, 0.010 to 0.015 percent of N, 0.015 to 0.050 percent of Als, and the balance of Fe and inevitable impurities.

The carbon equivalent CEV of the axle housing steel for the cold stamping with the thick specification is less than or equal to 0.39 percent, and the welding crack sensitivity index Pcm is less than or equal to 0.19 percent.

The thickness of the axle housing steel for the thick cold stamping is 8-14mm, the yield strength is more than or equal to 460MPa, the tensile strength is more than or equal to 590MPa, the elongation after fracture is more than or equal to 20%, the 180-degree bending test D is 2a, the full-size impact power KV2 at minus 40 ℃ is more than or equal to 80J, and the vertical bending fatigue life of a part is more than or equal to 80 ten thousand times.

The preparation method of the 590MPa thick axle housing steel for cold stamping comprises the following steps: smelting the chemical components of the axle housing steel for cold stamping according to 590 MPa-level thick specification into a plate blank, wherein the chemical components comprise, by mass, 0.07-0.10% of C, 0.05-0.10% of Si, 1.50-1.60% of Mn, less than or equal to 0.020% of P, less than or equal to 0.008% of S, 0.030-0.040% of Nb, 0.07-0.10% of V, 0.010-0.015% of N, 0.015-0.050% of Als, and the balance of Fe and inevitable impurities; and sequentially heating, rough rolling, finish rolling, coiling and cooling the plate blank to obtain the 590MPa thick axle housing steel for cold stamping.

The heating temperature is controlled to be 1200-1240 ℃, and the heating time is controlled to be 190-400 min.

The rough rolling adopts 6-pass rolling, the reduction of each pass is controlled to be more than or equal to 19 percent, the full-length scale removal of odd passes is carried out, and the thickness of the plate blank after the rough rolling is 53-57 mm.

The finish rolling adopts 7-pass rolling, the start rolling temperature of the finish rolling is controlled to be less than or equal to 1030 ℃, the finish rolling temperature is controlled to be 830-870 ℃, cooling water is added between more than or equal to 3 frames, and the reduction rates of the three frames are respectively controlled to be more than or equal to 17 percent, more than or equal to 13 percent and more than or equal to 10 percent.

The coiling temperature was 550-590 ℃.

The cooling adopts a front-section cooling mode to carry out laminar cooling, and the cooling rate is 20-40 ℃/s.

An axle housing is made of the 590 MPa-grade thick axle housing steel for cold stamping.

The beneficial effects of the invention are: according to the invention, a certain amount of Nb and V elements are added to exert the effects of fine grain strengthening and precipitation strengthening, the structural uniformity of thick-specification products in the thickness direction is improved, the product strength is ensured, and meanwhile, the good forming performance of the products is realized, the carbon equivalent and the welding crack sensitivity index are reduced by controlling the contents of C, Si and Mn elements, and the weldability of the products is improved.

The 590 MPa-grade thick-specification axle housing steel prepared by the components and the preparation method has good uniformity of the structure in the thickness direction; the yield strength is more than or equal to 460MPa, the tensile strength is more than or equal to 590MPa, the elongation after fracture is more than or equal to 20 percent, the 180-degree bending test D is 2a, the full-size-40 ℃ impact power KV2 is more than or equal to 80J, and high strength, excellent plasticity, bending property and low-temperature impact toughness are realized; the axle housing steel disclosed by the invention is subjected to a bench test, the vertical bending fatigue life of a part is more than or equal to 80 ten thousand times, and excellent fatigue performance is realized.

The alloy designed by the invention has simple components and low alloy cost; meanwhile, the smelting process parameter control designed by the invention is easy to realize, the production method is simple, the alloy components are well matched with the rolling and cooling control process, the smelting difficulty is low, the production cost is reduced, and the method is suitable for large-scale production. The product of the invention has excellent comprehensive performance, is suitable for the cold stamping forming process of the automobile axle housing, and has good application prospect.

Drawings

FIG. 1 shows a typical thickness direction edge structure of 590MPa grade thick specification axle housing steel for cold stamping prepared in example 1 of the present invention;

FIG. 2 shows a typical thickness direction 1/4 structure of 590MPa grade thick cold stamping axle housing steel prepared in example 1 of the present invention;

FIG. 3 shows a typical thickness direction core structure of 590MPa grade thick specification axle housing steel for cold stamping prepared in example 1 of the present invention.

Detailed Description

The technical solution of the present invention can be specifically implemented as follows.

The 590 MPa-level thick-specification axle housing steel for cold stamping comprises the following chemical components in percentage by mass: 0.07-0.10% of C, 0.05-0.10% of Si, 1.50-1.60% of Mn, less than or equal to 0.020% of P, less than or equal to 0.008% of S, 0.030-0.040% of Nb, 0.07-0.10% of V, 0.010-0.015% of N, 0.015-0.050% of Als, and the balance of Fe and inevitable impurities.

The reason for designing the components of the 590 MPa-grade thick-specification axle housing steel for cold stamping is as follows:

c has the effect of solid solution strengthening, can be combined with Nb and Ti to form carbide precipitation particles, can realize the effects of fine grain strengthening and precipitation strengthening, improves the carbon content and is beneficial to improving the strength, but too high carbon content can form more coarse and brittle carbide particles in steel and is not beneficial to plasticity and toughness, too high carbon content can form a segregation zone in the center of a steel plate and is not beneficial to bending property formability, and too high carbon content increases welding carbon equivalent and welding crack sensitivity index and is not beneficial to welding processing, so the invention designs C to be 0.07-0.10%.

Si has higher solid solubility in steel, is beneficial to thinning rust layer tissues, reduces the integral corrosion rate of the steel and improves the toughness, but the excessive content can cause difficult descaling in rolling and can also cause the reduction of welding performance, so the invention designs Si to be 0.05-0.10%.

Mn has a strong solid solution strengthening effect, can obviously reduce the phase transition temperature of steel, refines the microstructure of the steel, is an important toughening element, but is easy to generate casting blank cracks in the continuous casting process when the content of Mn is excessive, can cause the core component segregation of a steel plate, and can also reduce the welding performance of the steel, so that the Mn is designed to be 1.50-1.60%.

P and S elements can generate adverse effects on the structure performance of the steel plate, the plasticity and low-temperature toughness of the steel can be obviously reduced due to the over-high content of P, and the performance of the steel can be deteriorated due to sulfide inclusion formed by S, so that P is less than or equal to 0.020% and S is less than or equal to 0.008% by the design of the invention.

Nb can pin austenite grain boundaries to prevent grain growth, and finally refine grains, which is beneficial to improving impact toughness, but the fine grain reinforcement enables yield strength to rise more obviously, which leads to yield ratio rising, and the Nb content is too high, which increases production cost, so that the invention designs Nb 0.030-0.040%.

The V element is dissolved in austenite in a solid mode, so that static and dynamic recrystallization in the thermal deformation process can be inhibited, the non-recrystallization area of austenite is expanded, the strain amount in the non-recrystallization area in the finish rolling process is increased, the transformation from austenite to ferrite is promoted, and ferrite grains are refined. Meanwhile, V and C, N are combined to form a tiny carbonitride pinning crystal boundary, so that recrystallization is delayed, austenite crystal grain growth is inhibited, fine grain strengthening and precipitation strengthening effects are generated, and the welding performance is improved. The content of N element in the steel is increased, which is beneficial to the precipitation of a second phase of V, but the content of N is too high, which increases the aging tendency, cold brittleness and hot brittleness of the steel and damages the welding performance and cold bending performance of the steel, so the invention designs V0.07-0.10% and N0.010-0.015%.

Al is added into steel to play a role in deoxidation, and the steel quality can be improved, but the content of Al is too high, and nitrogen oxide is easy to precipitate at austenite grain boundary to cause the generation of casting blank cracks, so that the invention designs Als 0.015-0.050%.

The thickness of the thick axle housing steel is 8-14mm, the yield strength is more than or equal to 460MPa, the tensile strength is more than or equal to 590MPa, the elongation after fracture is more than or equal to 20%, the 180-degree bending test D is 2a, the full-size-40 ℃ impact power KV2 is more than or equal to 80J, and the vertical bending fatigue life of the part is more than or equal to 80 ten thousand times; the carbon equivalent CEV is less than or equal to 0.39 percent, the welding crack sensitivity index Pcm is less than or equal to 0.19 percent, and the weldability is good.

The preparation method of the 590 MPa-level thick axle housing steel for cold stamping comprises the following steps: smelting the chemical components of the axle housing steel for cold stamping according to 590 MPa-level thick specification into a plate blank, wherein the chemical components comprise, by mass, 0.07-0.10% of C, 0.05-0.10% of Si, 1.50-1.60% of Mn, less than or equal to 0.020% of P, less than or equal to 0.008% of S, 0.030-0.040% of Nb, 0.07-0.10% of V, 0.010-0.015% of N, 0.015-0.050% of Als, and the balance of Fe and inevitable impurities; and heating, rough rolling, finish rolling, coiling and cooling the plate blank in sequence to obtain the 590 MPa-level thick axle housing steel for cold stamping.

The slab is heated in order to homogenize the cast structure and the component segregation and simultaneously dissolve the alloying elements in solid, but the problems of burning loss, overheating, overburning and the like can occur when the heating temperature is too high and the heating time is too long, so the heating temperature is preferably controlled to be 1200-1240 ℃ and the heating time is preferably controlled to be 190-400 min.

Enough deformation is required to be achieved in rough rolling to ensure austenite recrystallization, austenite grains are refined, mixed crystal tissues are prevented from appearing, iron scales can be fully removed in rough rolling descaling, and the problem of surface quality caused by pressing of the iron scales is avoided; if the intermediate slab thickness is too large, the rough rolling deformation amount may be insufficient and the finish rolling load increases, and if the intermediate slab thickness is too small, the finish rolling deformation amount may be insufficient. Therefore, the rough rolling is preferably performed by 6 passes, the reduction of each pass is controlled to be more than or equal to 19 percent, the odd pass is subjected to full-length descaling, and the thickness of the plate blank after the rough rolling is 53-57 mm.

After finish rolling, the three stands are basically rolled in an austenite non-recrystallization region, austenite grains which are rolled in the recrystallization region and refined to a certain degree can be flattened and elongated by adopting large deformation rate, the grain boundary area of austenite in unit volume is increased, and simultaneously a large amount of deformation zones and high-density dislocation can be generated in the grains, so that the ferrite nucleation rate is improved, and fine grain structures are obtained after phase transformation; if the initial rolling temperature of finish rolling is too high, the deformation of the non-recrystallization region of austenite in the finish rolling process is insufficient, and the structure refinement is not facilitated; cooling water between the racks is opened, so that the cooling speed of the strip steel in the finish rolling process can be increased, the rolling speed is increased on the basis of ensuring the finish rolling temperature, the difference between the finish cooling temperature of the laminar cooling section and the coiling temperature is reduced, and the product performance is ensured; if the finishing temperature is too low, the difference between the finishing temperature and the initial rolling temperature is too large, so that the cooling speed in the finish rolling process is too high, the risk of rolling of a plurality of racks in a two-phase region after finish rolling exists, and the comprehensive performance of a product is poor; if the finishing temperature is too high, the deformation of the unrecrystallized area is insufficient, which is not beneficial to the refining of the final structure. Therefore, preferably, the finish rolling adopts 7-pass rolling, the rolling temperature of the finish rolling is controlled to be less than or equal to 1030 ℃, the finishing temperature is controlled to be 830-870 ℃, cooling water is added between frames with the rolling reduction rate of more than or equal to 3, and the rolling reduction rate of the three frames is controlled to be more than or equal to 17 percent, more than or equal to 13 percent and more than or equal to 10 percent respectively.

If the coiling temperature is too low, the cooling rate during laminar cooling is too high to cause abnormal structure generation, and the coiling temperature is too high to cause coarse grains to cause deterioration of the overall properties of the finished product, so that it is preferable that the coiling temperature is 550-.

The laminar cooling section adopts front section cooling, thereby can realize great super-cooling degree and make final structure refine, is favorable to simultaneously precipitating tiny dispersed second phase, strengthens fine grain strengthening and precipitation strengthening effect. Therefore, it is preferable that the laminar cooling is performed in a front stage cooling mode at a cooling rate of 20 to 40 ℃/s.

The technical solutions and effects of the present invention will be further described below by practical examples.

Examples

The invention provides two groups of examples adopting the design components and the preparation method of the invention, and provides two groups of comparative examples. The chemical compositions of examples 1-2 and comparative examples 1-2 are shown in Table 1.

TABLE 1 chemical composition/%, of examples and comparative examples

The specific preparation methods of examples 1-2 and comparative examples 1-2 are as follows:

examples 1 to 2: smelting according to data in the table 1 to obtain a plate blank, and processing the plate blank, wherein the method specifically comprises the following steps: the heating temperature is 1200-1240 ℃, and the heating time is 190-400 min; then, 6-pass rough rolling is carried out, the pass reduction is more than or equal to 19 percent, odd-pass full-length scale removal is carried out, and the thickness of the intermediate blank is 53-57 mm; then 7 times of finish rolling are carried out, the reduction ratios of the three racks are respectively 18%, 13% and 10%, 3 racks of cooling water are used, the start rolling temperature of the finish rolling is not more than 1030 ℃, the finish rolling temperature is 830-870 ℃, and the coiling temperature is 550-590 ℃; after rolling, laminar cooling is carried out, a front-section cooling mode is adopted, and specific process parameters are shown in table 2.

Table 2 examples 1, 2 preparation process parameters

FIG. 1 shows a typical thickness direction edge structure of 590MPa grade thick specification axle housing steel for cold stamping prepared in example 1 of the present invention; FIG. 2 shows a typical structure 1/4 in the thickness direction of 590MPa grade thick specification axle housing steel for cold stamping prepared by the embodiment 1 of the invention; FIG. 3 shows a typical thickness direction core structure of 590MPa grade thick specification axle housing steel for cold stamping prepared in example 1 of the present invention; as can be seen from fig. 1-3: the metallographic structure of the axle housing steel prepared in the embodiment 1 of the invention is ferrite plus pearlite, the structure uniformity in the thickness direction is good, and the matching performance of the controlled rolling and controlled cooling process is good.

Comparative example 1: smelting according to data in the table 1 to obtain a plate blank, adopting an RH process and carrying out Si-Ca treatment in the smelting process, controlling the continuous casting drawing speed to be 1.2m/min and the continuous casting water amount to be 4012L/min, and putting into electromagnetic stirring; and then processing the obtained plate blank, specifically: the heating temperature is 1205 ℃, the finish rolling temperature is 900 ℃, the coiling temperature is 595 ℃, laminar cooling is carried out after rolling, front-stage cooling is adopted, and indirect drawing type cooling is adopted, and the water cooling speed is 100 ℃/s.

Comparative example 2: smelting according to data in a table 1 to obtain a plate blank, and processing the plate blank obtained by smelting, wherein the method specifically comprises the following steps: the initial rolling temperature of rough rolling is 1030 ℃, the initial rolling temperature of finish rolling is 944 ℃, the final rolling temperature is 882 ℃, the reduction in the finish rolling stage is not less than 60%, cooling is not controlled after rolling, and air cooling is carried out to the room temperature.

The axle housing steels for cold stamping prepared in examples 1 and 2 and comparative examples 1 and 2 were subjected to performance tests, and the test results are shown in table 3.

Table 3 results of performance testing of examples and comparative examples

Note 1: the bending pressure head diameter D and the sample thickness a;

note 2: the impact test adopts a three-quarter size sample; the impact test temperature of the examples was-40 ℃ and the impact test temperature of comparative example 1 was 0 DEG C

As is apparent from Table 3, the strength and elongation after fracture of examples 1 and 2 were comparable to those of comparative examples 1 and 2, the bending properties were good, the impact toughness was higher than that of comparative example 2, and the fatigue properties were comparable to those of comparative example 1. However, the content of Nb in the comparative example 1 is high, and Ti, N and O elements are strictly controlled, so that the smelting process is difficult and the cost is high; compared with the comparative example 2, the content of C, Si is high, the weldability of the material is reduced, and meanwhile, the Ti element with higher content is added, so that the alloy cost is increased.

According to the embodiment and the comparative example, the 590MPa thick-specification axle housing steel for cold stamping is developed, the high strength, the good plasticity and bending property, the excellent forming property, the excellent welding property and the excellent fatigue property of the product are realized through reasonable alloy components and production process design, the production method of the product is simple, the alloy cost is low, the comprehensive performance is excellent, and the 590MPa thick-specification axle housing steel is suitable for the cold stamping forming process of the automobile axle housing and has good application prospect.

Claims

1.590 MPa level thick specification axle housing steel for cold stamping, its characterized in that, its chemical composition is according to the mass percent: 0.07 to 0.10 percent of C, 0.05 to 0.10 percent of Si, 1.50 to 1.60 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.008 percent of S, 0.030 to 0.040 percent of Nb, 0.07 to 0.10 percent of V, 0.010 to 0.015 percent of N, 0.015 to 0.050 percent of Als, and the balance of Fe and inevitable impurities;

the preparation method of the 590 MPa-level thick-specification axle housing steel for cold stamping comprises the following steps: smelting the chemical components of the 590 MPa-grade thick axle housing steel for cold stamping into a plate blank, wherein the chemical components comprise, by mass, 0.07-0.10% of C, 0.05-0.10% of Si, 1.50-1.60% of Mn, less than or equal to 0.020% of P, less than or equal to 0.008% of S, 0.030-0.040% of Nb, 0.07-0.10% of V, 0.010-0.015% of N, 0.015-0.050% of Als, and the balance of Fe and inevitable impurities; heating, rough rolling, finish rolling, coiling and cooling the plate blank in sequence to obtain 590MPa thick axle housing steel for cold stamping;

the rough rolling adopts 6-pass rolling, the reduction of each pass is controlled to be more than or equal to 19 percent, the full-length scale removal of odd passes is carried out, and the thickness of the rough-rolled plate blank is 53-57 mm;

the finish rolling adopts 7-pass rolling, the start rolling temperature of the finish rolling is controlled to be less than or equal to 1030 ℃, the finish rolling temperature is controlled to be 830-870 ℃, cooling water between frames is used for more than or equal to 3, and the reduction ratios of the three frames are respectively controlled to be more than or equal to 17 percent, more than or equal to 13 percent and more than or equal to 10 percent;

2. The axle housing steel for 590 MPa-grade thick-gauge cold stamping according to claim 1, characterized in that: the carbon equivalent CEV is less than or equal to 0.39 percent, and the welding crack sensitivity index Pcm is less than or equal to 0.19 percent.

3. The axle housing steel for 590MPa grade thick specification cold stamping according to claim 1, characterized in that: the thickness is 8-14mm, the yield strength is more than or equal to 460MPa, the tensile strength is more than or equal to 590MPa, the elongation after fracture is more than or equal to 20 percent, the 180-degree bending test D =2a, and the full-size impact power KV at minus 40 DEG C₂More than or equal to 80J, and the vertical bending fatigue life of the part is more than or equal to 80 ten thousand times.

4. The axle housing steel for 590 MPa-grade thick-gauge cold stamping according to claim 1, characterized in that: the heating temperature is controlled to be 1200-1240 ℃, and the heating time is controlled to be 190-400 min.

5. The axle housing steel for 590MPa grade thick specification cold stamping according to claim 1, characterized in that: the coiling temperature is 550-590 ℃.

6. An axle housing, its characterized in that: the 590 MPa-grade thick-gauge axle housing steel for cold stamping according to any one of claims 1 to 3.