CN111074148B

CN111074148B - 800 MPa-level hot stamping axle housing steel and manufacturing method thereof

Info

Publication number: CN111074148B
Application number: CN201811221253.6A
Authority: CN
Inventors: 刘刚; 张华伟; 王巍; 陆敏
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2018-10-19
Filing date: 2018-10-19
Publication date: 2022-03-18
Anticipated expiration: 2038-10-19
Also published as: DE112019005199T5; CN111074148A; KR102495857B1; KR20210045464A; WO2020078472A1

Abstract

The invention discloses 800 MPa-grade hot stamping axle housing steel which comprises the following chemical elements in percentage by mass: c: 0.15 to 0.21%, Si: 0.30-0.80%, Mn: 1.75-2.10%, Nb: 0.015 to 0.040%, Ti: 0.020 to 0.060%, B: 0.0015-0.0030%, and Al: 0.005-0.015%, Ca: 0.0004 to 0.001%, N: 0.001 to 0.004%, and the balance of Fe and other inevitable impurities. In addition, the invention also discloses a manufacturing method of the 800 MPa-grade hot stamping axle housing steel, which comprises the following steps: (1) smelting and casting; (2) heating; (3) rolling: controlling the reduction rate of the last rolling pass to be more than 15%; the finishing temperature is 820-900 ℃; (4) and (3) cooling: and cooling in three sections after rolling.

Description

800 MPa-level hot stamping axle housing steel and manufacturing method thereof

Technical Field

The invention relates to steel grade and a manufacturing method thereof, in particular to axle housing steel and a manufacturing method thereof.

Background

The axle housing is used as a key bearing part of an automobile, has higher requirements on safety, and needs to meet strict component fatigue performance, namely for the axle housing steel, the requirements on stable performance, low-temperature impact resistance and good weldability of a steel plate are met, and meanwhile, segregation and inclusions are strictly controlled.

At present, special axle housing steel products are lacked in China, the hot stamping axle housing steel in China is mainly common C-Mn structural steel such as 16Mn, Q345C, Q420C, Q460C and the like, and the strength of the C-Mn steel after hot stamping is further reduced, for example, the yield strength of the Q460C after hot stamping is reduced to about 400 MPa.

Chinese patent document with publication number CN104213019A, publication date 2014 12 months 17 days, entitled "600 MPa grade automobile axle housing steel and production method thereof" discloses 600MPa grade automobile axle housing steel and production method thereof. According to the technical scheme disclosed by the patent document, the contents of V and N elements are controlled, rolling and cooling are controlled, and finally the 600 MPa-grade hot-rolled strip steel for the automobile axle housing is obtained.

Chinese patent publication No. CN103422020A, published as 2013, 12 months, and 4 days entitled "a steel plate for a press-welded axle housing and a manufacturing method thereof" discloses a steel plate for a press-welded axle housing and a manufacturing method thereof. In the technical solution disclosed in this patent document, the strength of the steel sheet after hot stamping is improved by comprehensively adding elements such as Nb and V, and the low-temperature toughness and fatigue property of the steel sheet after hot stamping are improved by comprehensively controlling elements such as Ti and Al, thereby finally obtaining a strength steel sheet of 600MPa level.

Based on the above, it is desired to obtain a high-strength axle housing steel which can reach the strength level of 800MPa, and meanwhile, the steel plate has good plasticity and fatigue performance, so that the steel plate is more suitable for manufacturing axle housings.

Disclosure of Invention

One of the purposes of the invention is to provide 800 MPa-level hot stamping axle housing steel which can reach the strength level of 800MPa, has good plasticity and fatigue performance and is very suitable for manufacturing axle housings.

In order to achieve the aim, the invention provides 800 MPa-grade hot stamping axle housing steel which comprises the following chemical elements in percentage by mass:

c: 0.15 to 0.21%, Si: 0.30-0.80%, Mn: 1.75-2.10%, Nb: 0.015 to 0.040%, Ti: 0.020 to 0.060%, B: 0.0015-0.0030%, and Al: 0.005-0.015%, Ca: 0.0004 to 0.001%, N: 0.001 to 0.004%, and the balance of Fe and other inevitable impurities.

The design principle of each chemical element in the 800 MPa-level hot stamping axle housing steel is as follows:

c: in the 800 MPa-grade hot stamping axle housing steel, carbon plays a role in solid solution strengthening, the strength of lower bainite can be improved by adding C, and in addition, the C can also react with Fe in the air cooling process of axle housing hot stamping to form Fe3C in dispersion distribution, so that the strength of a steel plate after hot stamping is improved. However, if the mass percentage of C is too high, weldability of the steel sheet is not favorable. Therefore, in the 800 MPa-grade hot stamping axle housing steel, the mass percent of C is controlled to be 0.15-0.21%.

Si: in the 800 MPa-grade hot stamping axle housing steel, Si can inhibit cementite from precipitating at high temperature, so that the formation of lower bainite is facilitated, and meanwhile, Si can enable fine cementite particles to be formed in a steel plate, so that the strength of the lower bainite is improved. However, too high content of Si is disadvantageous in weldability of the steel sheet. Therefore, the mass percent of Si is controlled to be 0.30-0.80% in the technical scheme of the invention.

Mn: in the technical scheme of the invention, the addition of a certain content of Mn element is beneficial to promoting the formation of lower bainite, and Mn can play a certain solid solution strengthening role in the lower bainite structure. In addition, the addition of Mn is also beneficial to forming thinner ferrite or bainite during hot stamping of the steel plate, thereby being beneficial to improving the strength of the steel plate after hot stamping. However, too high content of Mn is disadvantageous to the weldability of the steel sheet. Therefore, the mass percentage of Mn in the 800 MPa-grade hot stamping axle housing steel is 1.75-2.10%.

Nb: for the 800 MPa-grade hot stamping axle housing steel, trace Nb in the steel plate reacts with C to form fine NbC particles in the controlled rolling and controlled cooling stage, so that the steel plate structure is favorably refined, and the strength, the plasticity and the toughness of the steel plate can be improved. Further, NbC precipitates in the lower bainite structure, and a strong precipitation strengthening effect can be produced. In addition, NbC can also refine austenite grains in the hot stamping heating stage, and the strength of the axle housing steel plate after hot stamping is improved. However, when the Nb element content is too high, NbC particles are large, and the effect of suppressing the austenite grain growth is rather weak. Therefore, the mass percent of Nb in the 800 MPa-grade hot stamping axle housing steel is controlled to be 0.015-0.040%.

Ti: in the technical scheme of the invention, Ti element reacts with C to form TiC particles with the diameter of several nanometers to dozens of nanometers in the phase transformation process from austenite to ferrite after rolling the steel plate, so that the precipitation strengthening effect is generated, and particularly, finer interphase precipitation can be generated within the range of 680-730 ℃. In addition, the TiC fine particles can inhibit the growth of austenite grains in the hot stamping heating stage, so that the hot stamped tissue is refined, and the hot stamped strength of the axle housing steel plate is improved. However, when the content of Ti element is too high, it is easy to react with N to form micron-sized cubic TiN large particles, which deteriorates the toughness and fatigue property of the steel plate. Therefore, the mass percentage of Ti in the 800 MPa-grade hot stamping axle housing steel is controlled to be 0.020-0.060%.

B: in the 800 MPa-grade hot stamping axle housing steel, a trace amount of B can promote the formation of bainite, however, when the content of B element is too high, the problem of B brittleness is easily caused, and the impact toughness of the steel plate is deteriorated. In addition, trace B element is beneficial to promoting the formation of thinner bainite and improving the strength of the steel plate in the hot stamping stage of the axle housing. Therefore, the mass percent of B in the 800 MPa-grade hot stamping axle housing steel is controlled to be 0.0015-0.0030%.

Al: for the 800MPa class hot stamping axle housing steel, Al is taken as an important deoxidizer, and more than 0.02 percent of Al is usually added. However, in consideration of the strict requirement of the axle housing steel on the fatigue property, the oxide chain inclusions of Al need to be controlled, and therefore, the Al content is controlled in a lower range. Therefore, the mass percent of Al in the 800 MPa-grade hot stamping axle housing steel is controlled to be 0.005-0.015%.

Ca: for the 800 MPa-grade hot stamping axle housing steel, trace Ca element can play a role of a purifying agent in the steel smelting process, so that the toughness and the fatigue property of the steel are improved; meanwhile, the Ca treatment can improve the shape of MnS inclusions and prevent the formation of elongated MnS inclusions. However, a Ca content exceeding 0.001% tends to form a large-sized Ca compound, which may adversely deteriorate toughness and fatigue performance. Therefore, the mass percentage of Ca in the 800 MPa-grade hot stamping axle housing steel is controlled to be 0.0004-0.001%.

N: for the 800 MPa-grade hot stamping axle housing steel, the N element is required to be controlled in a narrow range. The trace N element can react with Ti to form TiN particles, so that the growth of austenite grains can be effectively inhibited during welding and hot stamping, a welding heat affected zone and a structure after hot stamping are refined, and the strength, the low-temperature toughness and the fatigue performance of the heat affected zone and a hot stamping steel plate are improved. However, when the N content is too high, the TiN particles formed are too large, which may deteriorate the low temperature toughness and fatigue property of the steel sheet. Therefore, the mass percent of N in the 800 MPa-grade hot stamping axle housing steel is controlled to be 0.001-0.004%.

In the embodiment of the present invention, the other inevitable impurity elements include P, S and O. P, S and O are both inevitable harmful impurity elements in steel materials, which are not beneficial to the steel performance, for example, P is easy to generate cold brittleness problem as an impurity element; s is easy to react with Mn to generate MnS inclusions, which is not beneficial to the fatigue performance in steel; o reacts readily with Al to produce Al₃O chain inclusions are detrimental to fatigue properties in steel. Therefore, the lower the content of P, S and O in the steel, the better, but in view of the economical efficiency of steel smelting costs, the mass percentage of the above-mentioned inevitable impurity elements is controlled within a certain appropriate range, and when the inevitable impurity elements are controlled within the appropriate range, the harmful effects of the inevitable impurity elements can be minimized, thereby not significantly adversely affecting the steel properties.

Further, in the 800 MPa-grade hot stamping axle housing steel of the present invention, the other inevitable impurities satisfy at least one of the following: p is less than or equal to 0.015 percent, S is less than or equal to 0.0020 percent, and O is less than or equal to 0.003 percent.

Further, in the 800 MPa-grade hot stamping axle housing steel, the relevant elements also meet the following requirements: the Ti/N is more than or equal to 5, which is beneficial to keeping enough Ti element to react with C to form TiC precipitation strengthening by controlling the Ti/N to be more than or equal to 5.

Furthermore, in the 800 MPa-grade hot stamping axle housing steel, the microstructure of the steel is ferrite and fine lower bainite, wherein the phase proportion of the ferrite is 5-10%.

Further, in the 800 MPa-grade hot stamping axle housing steel, the width of the lower bainite lath is less than 300 nm.

Furthermore, in the 800 MPa-grade hot stamping axle housing steel, nano-scale TiC interphase precipitates are formed in the ferrite, and the grain diameter of more than 70% of the TiC interphase precipitates in the ferrite is less than 30 nm. This is because, in the present case, the finer the precipitate particles are, the better the precipitation strengthening effect is.

Furthermore, in the 800 MPa-grade hot stamping axle housing steel, the yield strength is more than or equal to 800MPa, the tensile strength is more than or equal to 900MPa, and the elongation percentage A is₅₀More than or equal to 22 percent and more than or equal to 60J of impact energy at the temperature of minus 20 ℃.

Further, in the 800MPa class hot stamping axle housing steel, the grades of various types of non-metallic inclusions are below 1.0, the sum of the grades of all the non-metallic inclusions is controlled below 3.0, and the 800MPa class hot stamping axle housing steel does not have long-strip-shaped inclusions.

In the scheme, the requirement of the axle housing steel on the fatigue performance is considered, so that the grade of the nonmetallic inclusion can be controlled to be not more than 1.0 grade, the grades of all the nonmetallic inclusions are comprehensively controlled to be below 3.0 grade, and the formation of long-strip-shaped inclusions is inhibited at the same time, so that the performance of the 800 MPa-grade hot stamping axle housing steel is improved.

Correspondingly, the invention also aims to provide a manufacturing method of the 800 MPa-grade hot stamping axle housing steel, the 800 MPa-grade hot stamping axle housing steel obtained by the manufacturing method can reach the strength grade of 800MPa, and meanwhile, the plasticity and fatigue performance of the 800 MPa-grade hot stamping axle housing steel are good, so that the 800 MPa-grade hot stamping axle housing steel is very suitable for manufacturing axle housings.

In order to achieve the purpose, the invention provides a manufacturing method of the 800 MPa-grade hot stamping axle housing steel, which comprises the following steps:

(1) smelting and casting;

(2) heating;

(3) rolling: controlling the reduction rate of the last rolling pass to be more than 15%; the finishing temperature is 820-900 ℃;

(4) and (3) cooling: cooling the steel plate to 680-730 ℃ at the speed of 80-200 ℃/s, and air-cooling for 5-7 s; then cooling the steel plate to 360-450 ℃ at the speed of 30-70 ℃/s; and then coiling or air cooling to room temperature.

In the manufacturing method of the 800 MPa-level hot stamping axle housing steel, a small amount of ferrite and fine lower bainite tissues can be obtained by the sectional cooling control and the medium-temperature coiling, so that the finally obtained steel plate has the yield strength of more than or equal to 800MPa, the tensile strength of more than or equal to 900MPa, the elongation A50 of more than or equal to 22 percent and the impact energy at the temperature of minus 20 ℃ of more than 60J.

Wherein, the rolling reduction of the last rolling is controlled to be more than 15 percent in the step (3); the finishing temperature is 820-900 ℃, so that enough deformation can be accumulated before austenite is transformed to bainite, and the formation of a thinner bainite structure is promoted. The rolling temperature is too low, so that the high-temperature phase change of ferrite is easy to occur, and the strength of steel is reduced; the deformation accumulated in the austenite is recovered when the rolling temperature is too high, which is not beneficial to refining the structure after the phase transformation.

In the step (4), the steel plate is firstly cooled to 680-730 ℃ at a cooling speed of 80-200 ℃/s in order to be rapidly cooled to a ferrite forming temperature range, and then air-cooled for 5-7s to form 5-10% of ferrite. At the high temperature of 680-730 ℃, fine TiC particles are generated and precipitated when austenite is transformed to ferrite. And then rapidly cooling the steel plate to a lower temperature of 360-450 ℃ at a cooling speed of 30-70 ℃/s, and coiling or air-cooling to room temperature, wherein in the step, rapid cooling is used for inhibiting continuous phase transformation of ferrite, and cooling to 360-450 ℃ is used for coiling or air-cooling to form a fine lower bainite structure, and meanwhile, heat preservation at a lower temperature is beneficial to inhibiting continuous growth of precipitate particles.

Further, in the manufacturing method of the 800 MPa-grade hot stamping axle housing steel, in the step (2): heating the casting blank in a furnace at 1180-1270 ℃, and preserving heat for more than 1.5 hours after the core of the casting blank reaches the temperature.

In the scheme, the casting blank is heated in a furnace at 1180-1270 ℃, heat preservation is carried out after the core of the casting blank reaches the temperature, and the heat preservation time is more than 1.5h, so as to ensure that alloy elements are fully dissolved in the solution. When the heating temperature exceeds 1270 ℃, austenite grains excessively grow to cause the intercrystalline bonding force to weaken, and cracks are easy to generate during rolling; in addition, when the heating temperature exceeds 1270 ℃, the surface of the billet is easily decarburized, which adversely affects the mechanical properties of the final steel.

The 800 MPa-grade hot stamping axle housing steel and the manufacturing method thereof have the advantages and beneficial effects as follows:

the 800 MPa-grade hot stamping axle housing steel is excellent in strength, impact, fatigue, welding and the like, inclusions influencing fatigue are controlled through reasonably optimized alloy design, such as rolling control, sectional cooling, coiling in a medium temperature range or air cooling to room temperature, so as to control the formation of required ferrite and fine lower bainite, and be beneficial to the formation of nano-scale precipitate particles in the ferrite, and finally the 800 MPa-grade hot stamping axle housing steel realizes high plasticity, namely A, the yield strength grade of 800MPa is realized, and simultaneously the 800 MPa-grade hot stamping axle housing steel realizes high plasticity₅₀Not less than 22 percent, and has good low-temperature impact property and welding property.

In addition, the 800 MPa-grade hot stamping axle housing steel specially controls components and inclusions which may influence the fatigue performance of the steel plate, is favorable for improving the fatigue performance of the steel plate, and is favorable for inhibiting the growth of austenite and refining the final structure in the axle housing hot stamping process, so that the steel plate has higher strength after hot stamping.

In addition, the technical scheme of the invention obtains a small amount of ferrite and a fine lower bainite structure by controlling the content of elements such as Ti, B and the like and matching with controlled rolling and controlled cooling, improves the plasticity and fatigue property of the steel plate and is very suitable for manufacturing axle housings.

Drawings

FIG. 1 is a metallographic structure diagram of an 800MPa class hot stamped axle housing steel of example 2.

FIG. 2 is a metallographic structure diagram of the 800MPa class hot stamped axle housing steel of example 3.

FIG. 3 is a scanning metallographic structure diagram of the 800MPa class hot stamped axle housing steel of example 2.

FIG. 4 is a scanning metallographic structure diagram of the 800MPa class hot stamped axle housing steel of example 3.

FIG. 5 schematically shows typical inclusion size, morphology and distribution for an 800MPa class hot stamped axle housing steel of example 1.

FIG. 6 schematically shows typical inclusion size, morphology and distribution for the 800MPa class hot stamped axle housing steel of example 2.

FIG. 7 schematically shows typical inclusion size, morphology and distribution for an 800MPa class hot stamped axle housing steel of example 3.

FIG. 8 schematically shows typical inclusion size, morphology and distribution for an 800MPa class hot stamped axle housing steel of example 4.

Detailed Description

The 800MPa class hot stamped axle housing steel and the manufacturing method thereof according to the present invention will be further explained and illustrated with reference to the drawings and the specific examples, which, however, should not be construed to unduly limit the technical scope of the present invention.

Examples 1 to 6

Table 1 shows the mass percentages of the chemical elements in the 800MPa class hot stamped axle housing steels of examples 1-6.

TABLE 1 (wt%, balance Fe and unavoidable impurities other than P, S and O)

The 800MPa class hot stamped axle housing steels of examples 1-6 were prepared using the following procedure (see Table 2 for specific process parameters):

(1) smelting and casting: smelting according to the mass percentage of the chemical elements listed in the table 1, adopting a vacuum circuit to smelt, and then pouring the smelted molten steel into a casting blank;

(2) heating: heating the casting blank in a furnace at 1180-1270 ℃, and preserving heat for more than 1.5 hours after the core of the casting blank reaches the temperature. (ii) a

(3) Rolling: controlling the reduction rate of the last rolling pass to be more than 15%; the final rolling temperature is 820-900 DEG C

Table 2 lists the specific process parameters for the method of making the 800MPa class hot stamped axle housing steels of examples 1-6.

Table 2.

The 800MPa class hot stamped axle housing steels of examples 1-6 were tested for performance and the results are shown in Table 3.

Table 3.

Note: three columns of the-20 ℃ impact energy test results in Table 3 represent the test results for three parallel samples, respectively

As can be seen from Table 3, the 800MPa class hot stamping axle housing steels of examples 1-6 have yield strengths of 800MPa or more, tensile strengths of 900MPa or more, elongations A50 of 22% or more, and impact powers of 60J or more at-20 ℃. Therefore, the 800 MPa-grade hot stamping axle housing steel of each embodiment can reach the strength grade of 800MPa, and meanwhile, the plasticity and the fatigue performance of the 800 MPa-grade hot stamping axle housing steel are good, so that the 800 MPa-grade hot stamping axle housing steel is very suitable for manufacturing axle housings.

FIG. 1 is a metallographic structure diagram of an 800MPa class hot stamped axle housing steel of example 2. FIG. 2 is a metallographic structure diagram of the 800MPa class hot stamped axle housing steel of example 3.

As can be seen from the combination of FIG. 1 and FIG. 2, the microstructure of the 800MPa class hot stamping axle housing steel of examples 2 and 3 in the present case is ferrite + fine lower bainite, wherein the phase ratio of ferrite is 5-10%.

FIG. 3 is a scanning metallographic structure diagram of the 800MPa class hot stamped axle housing steel of example 2. FIG. 4 is a scanning metallographic structure diagram of the 800MPa class hot stamped axle housing steel of example 3.

As can be seen by combining the graphs in FIGS. 3 and 4, the TiC interphase precipitates with nanometer scale are formed in the ferrite of the 800MPa class hot stamping axle housing steel of the embodiment 2, wherein the grain diameter of more than 70% of the TiC interphase precipitates in the ferrite is below 30nm, while the lower bainite is precipitated in the 800MPa class hot stamping axle housing steel of the embodiment 3, and the width of the lower bainite lath is below 300 nm.

In addition, since the inclusions have some influence on the properties of the steel sheet, the inclusions of examples 1 to 4 of this embodiment were tested and the results are shown in fig. 5 to 8 and table 4. Wherein, FIG. 5 schematically shows the inclusion size, morphology and distribution of the 800MPa class hot stamped axle housing steel of example 1. FIG. 6 schematically shows the inclusion size, morphology and distribution of the 800MPa class hot stamped axle housing steel of example 2. FIG. 7 schematically shows the inclusion size, morphology and distribution of the 800MPa class hot stamped axle housing steel of example 3. FIG. 8 is a schematic representation of inclusion size, morphology and distribution for the 800MPa class hot stamped axle housing steel of example 4.

Table 4 shows the results of the evaluation of non-metallic inclusions in the 800MPa class hot stamped axle housing steels of examples 1-6. The definition and rating method of each type of inclusion refer to the national Standard "microscopic examination method of determination Standard rating map of the content of non-metallic inclusions in Steel" (GB/T10561-2005).

Table 4.

As can be seen from fig. 5 to 8 and table 4, in the 800MPa class hot stamped axle housing steels according to examples 1 to 6, the grades of various types of non-metallic inclusions were below 1.0, the total of all non-metallic inclusions was controlled below 3.0, and the steels were free of long-strip inclusions.

In conclusion, the 800 MPa-grade hot stamping axle housing steel has the advantages that through reasonable and optimized alloy element design, the proportion among alloy elements and the level of inclusions are controlled, and meanwhile, the process is matched for controlled rolling and controlled cooling, so that a required microstructure is obtained, a small amount of ferrite and fine lower bainite are obtained, and meanwhile, a large amount of nano-scale TiC particles are formed in the ferrite, so that the final 800 MPa-grade hot stamping axle housing steel can reach the yield strength of more than 800MPa, has good plasticity, low-temperature toughness and fatigue performance, and is very suitable for high strength and weight reduction of a hot stamping axle housing.

It should be noted that the prior art in the protection scope of the present invention is not limited to the examples given in the present application, and all the prior art which is not inconsistent with the technical scheme of the present invention, including but not limited to the prior patent documents, the prior publications and the like, can be included in the protection scope of the present invention.

In addition, the combination of the features in the present application is not limited to the combination described in the claims of the present application or the combination described in the embodiments, and all the features described in the present application may be freely combined or combined in any manner unless contradictory to each other.

It should also be noted that the above-mentioned embodiments are only specific embodiments of the present invention. It is apparent that the present invention is not limited to the above embodiments and similar changes or modifications can be easily made by those skilled in the art from the disclosure of the present invention and shall fall within the scope of the present invention.

Claims

1. The 800 MPa-grade hot stamping axle housing steel is characterized by comprising the following chemical elements in percentage by mass:

c: 0.15 to 0.21%, Si: 0.30-0.80%, Mn: 1.75-2.10%, Nb: 0.015 to 0.040%, Ti: 0.020 to 0.060%, B: 0.0015-0.0030%, and Al: 0.005-0.015%, Ca: 0.0004 to 0.001%, N: 0.001-0.004%, and the balance of Fe and other inevitable impurities;

the microstructure of the 800 MPa-grade hot stamping axle housing steel is ferrite and fine lower bainite, wherein the phase proportion of the ferrite is 5-10%; the nano TiC interphase precipitates are formed in the ferrite, and the grain diameter of more than 70% of the TiC interphase precipitates in the ferrite is less than 30 nm.

2. The 800 MPa-grade hot stamped axle housing steel according to claim 1, wherein the other unavoidable impurities satisfy at least one of: p is less than or equal to 0.015 percent, S is less than or equal to 0.0020 percent, and O is less than or equal to 0.003 percent.

3. The 800MPa grade hot stamped axle housing steel according to claim 1, wherein each relevant element further satisfies: Ti/N is more than or equal to 5.

4. The 800MPa class hot stamped axle housing steel of claim 1 in which the width of the lower bainite lath is less than 300 nm.

5. The 800MPa grade hot stamping axle housing steel as claimed in claim 1, wherein the yield strength is not less than 800MPa, the tensile strength is not less than 900MPa, and the elongation A is₅₀More than or equal to 22 percent and more than or equal to 60J of impact energy at the temperature of minus 20 ℃.

6. The 800MPa class hot-stamped axle housing steel according to claim 1, wherein the grade of each type of non-metallic inclusion is below 1.0, the sum of all grades of non-metallic inclusions is controlled below 3.0, and the axle housing steel does not have long-strip-shaped inclusions.

7. The manufacturing method of the 800MPa class hot stamping axle housing steel as claimed in any one of claims 1 to 6, which comprises the steps of:

(1) smelting and casting;

(2) heating;

8. The manufacturing method of 800MPa class hot stamping axle housing steel according to claim 7,

in step (2): heating the casting blank in a furnace at 1180-1270 ℃, and preserving heat for more than 1.5 hours after the core of the casting blank reaches the temperature.