阅读说明：本技术 一种控制热成形后强度下降的桥壳钢及其制备方法、桥壳 (Axle housing steel for controlling strength reduction after hot forming, preparation method thereof and axle housing ) 是由 惠亚军 吴科敏 田志红 李飞 陈斌 刘锟 李秋寒 周娜 曹杰 肖宝亮 牛涛 杜 于 2020-06-09 设计创作，主要内容包括：本发明涉及一种控制热成形后强度下降的桥壳钢及其制备方法、桥壳,属于钢铁冶炼与轧制技术领域,本发明提供的控制热成形后强度下降的桥壳钢由如下质量分数的化学元素组成：C：0.26-0.30％；Si：0-0.1％；Mn：1.8-2.2％；P：≤0.010％；S：≤0.005％；Al：0.02-0.05％；V：0.01-0.03％；N：0-0.003％；其余为Fe及不可避免的杂质；该桥壳钢板的屈服强度大于600MPa,抗拉强度大于700MPa,延伸率大于20％,板形与表面质量优,热成形后的屈服强度大于550MPa,抗拉强度大于650MPa,并具有优异的表面质量的效果。(The invention relates to axle housing steel for controlling strength reduction after hot forming, a preparation method thereof and an axle housing, belonging to the technical field of steel smelting and rolling, and the axle housing steel for controlling strength reduction after hot forming comprises the following chemical elements in percentage by mass: c: 0.26 to 0.30 percent; si: 0 to 0.1 percent; mn: 1.8 to 2.2 percent; p: less than or equal to 0.010 percent; s: less than or equal to 0.005 percent; al: 0.02-0.05%; v: 0.01 to 0.03 percent; n: 0 to 0.003 percent; the balance of Fe and inevitable impurities; the yield strength of the axle housing steel plate is more than 600MPa, the tensile strength is more than 700MPa, the elongation is more than 20%, the plate shape and the surface quality are excellent, the yield strength after hot forming is more than 550MPa, the tensile strength is more than 650MPa, and the axle housing steel plate has an excellent surface quality effect.)

1. The axle housing steel for controlling strength reduction after hot forming is characterized by comprising the following chemical elements in percentage by mass: c: 0.26 to 0.30 percent; si: 0 to 0.1 percent; mn: 1.8 to 2.2 percent; p: less than or equal to 0.010 percent; s: less than or equal to 0.005 percent; al: 0.02-0.05%; v: 0.01 to 0.03 percent; n: 0 to 0.003 percent; the balance of Fe and inevitable impurities.

2. An axle housing steel for controlling strength drop after hot forming according to claim 1, wherein the microstructure of said steel is ferrite and pearlite, and the average grain size of said ferrite is 5.0 to 10.0 μm.

3. The axle housing steel for controlling strength drop after hot forming according to claim 1, wherein said microstructure contains nano-sized precipitates having an average particle diameter of 1 to 50 nm.

4. An axle housing steel for controlling strength drop after hot forming according to claim 1, wherein said steel has a thickness of 10-18 mm.

5. A method for producing an axle housing steel for controlling strength reduction after hot forming, for producing the steel of any one of claims 1 to 4, comprising the steps of:

smelting molten iron to obtain a continuous casting slab, wherein the continuous casting slab comprises the following chemical elements in percentage by mass: c: 0.26 to 0.30 percent; si: 0 to 0.1 percent; mn: 1.8 to 2.2 percent; p: less than or equal to 0.010 percent; s: less than or equal to 0.005 percent; al: 0.02-0.05%; v: 0.01 to 0.03 percent; n: 0 to 0.003 percent; the balance of Fe and inevitable impurities;

heating and preserving heat of the continuous casting plate blank;

carrying out rough rolling on the heated and heat-preserved continuous casting plate blank to obtain an intermediate plate blank;

performing finish rolling on the intermediate plate blank to obtain strip steel;

carrying out laminar cooling on the strip steel and coiling to obtain a hot rolled steel coil;

and cooling the hot rolled steel coil to room temperature, and then coiling to obtain the axle housing steel with reduced strength after the hot forming.

6. The manufacturing method according to claim 5, characterized in that the temperature of the continuous casting slab after the heating and the keeping warm is 1100-1150 ℃.

7. The method as claimed in claim 5, wherein the outlet temperature of the rough rolling is 950-1050 ℃, and the thickness of the intermediate slab is 55-60 mm.

8. The production method according to claim 5, wherein the finish rolling finish temperature of the finish rolling is 780-810 ℃.

9. The method as claimed in claim 5, wherein the cooling rate is 10-15 ℃/s, and the coiling temperature is 600-650 ℃.

10. An axle housing made from the steel of any of embodiments 1-4.

Technical Field

The invention relates to the technical field of steel smelting and rolling, in particular to axle housing steel for controlling strength reduction after hot forming and a preparation method thereof.

Background

The axle housing is used as a structure for mainly supporting the load of the automobile, and the research on light weight is one of the problems of a great deal of research. The total mass of a common non-disconnected drive axle, a hub, a brake and a brake drum accounts for about 3.5-5% of the total mass of the car, and the proportion of the drive axle is larger for a heavy truck.

The drive axle of medium and heavy trucks is generally formed by stamping a steel plate with the thickness of 14mm-18mm, and has higher requirements on the drawing forming performance, the welding performance and the fatigue performance of materials; because the steel is limited by stamping equipment and generally formed by adopting a hot stamping process, steel for hot stamping axle housings at home and abroad is generally replaced by plain carbon steel or girder steel, the problems of poor hot processing performance, poor surface quality, high rejection rate, unstable product quality and the like are caused, particularly, the strength is seriously reduced after hot forming, the performance difference between axle housing finished products and plates is huge, and the lightweight of the axle housing and the improvement of the bearing capacity of the whole automobile are seriously limited.

The hot stamping process requires that the steel plate is heated to 840-900 ℃ in a medium frequency induction furnace, then stamping is carried out, and air cooling is carried out after stamping. The hot stamping process has the advantages of small forming pressure, high dimensional precision and good fatigue performance, thereby being widely applied. Due to the fact that the material performance is not familiar, most users only carry out factory inspection on the steel plate, the mechanical property of the steel plate after hot stamping is greatly reduced, and the mechanical property of the steel plate after hot stamping is far lower than a required value. For example, when the 510L axle housing is manufactured, after hot stamping, the yield strength is reduced by 149MPa, and the tensile strength is reduced by 162MPa, so that the performance can not meet the requirement that the tensile strength is larger than or equal to 510 MPa; when the axle housing is manufactured by adopting Q460C, after hot stamping, the yield strength is reduced by 124MPa, and the tensile strength is reduced by 158MPa, so that the performance can not meet the requirement that the tensile strength is greater than or equal to 580 MPa.

Due to the obvious reduction of the strength, the performance of the finished axle housing is obviously lower than the designed strength, so that the bearing capacity is insufficient, the safety is reduced, and the phenomenon of truck bridge breakage occurs in severe cases. For this reason, it is important for automobile manufacturers to control the rate of strength reduction after thermoforming. A plurality of products are developed for the steel for the axle housing in China, but the influence of the final hot forming process on the strength is rarely considered, wherein the patent with the application number of 201410432234.3 discloses '600 MPa-grade automobile axle housing steel and a production method thereof', hot rolled strip steel for the 600 MPa-grade automobile axle housing is produced by adding higher V, N element content and controlling the accurate rolling and cooling control process, and various mechanical property indexes of the hot formed rear axle housing above 800 ℃ can be ensured. However, the patent adds higher V/N alloy, so that the cost is higher, the process control window is narrower, and the surface quality problem is more frequent.

Disclosure of Invention

In view of the above problems, the present invention has been made to provide an axle housing steel for controlling strength reduction after hot forming, a method of manufacturing the same, and an axle housing, which overcome or at least partially solve the above problems.

The embodiment of the invention provides axle housing steel for controlling strength reduction after hot forming, which comprises the following chemical elements in percentage by mass: c: 0.26 to 0.30 percent; si: 0 to 0.1 percent; mn: 1.8 to 2.2 percent; p: less than or equal to 0.010 percent; s: less than or equal to 0.005 percent; al: 0.02-0.05%; v: 0.01 to 0.03 percent; n: 0 to 0.003 percent; the balance of Fe and inevitable impurities.

Optionally, the microstructure of the steel is ferrite and pearlite, and the average grain size of the ferrite is 5.0-10.0 μm.

Optionally, the microstructure comprises a nanoscale precipitated phase with an average particle size of 1-50 nm.

Optionally, the thickness of the steel is 10-18 mm.

Based on the same inventive concept, the embodiment of the invention also provides a preparation method of the axle housing steel for controlling the strength reduction after the hot forming, which is used for preparing the axle housing steel for controlling the strength reduction after the hot forming and comprises the following steps:

smelting molten iron to obtain a continuous casting slab, wherein the continuous casting slab comprises the following chemical elements in percentage by mass: c: 0.26 to 0.30 percent; si: 0 to 0.1 percent; mn: 1.8 to 2.2 percent; p: less than or equal to 0.010 percent; s: less than or equal to 0.005 percent; al: 0.02-0.05%; v: 0.01 to 0.03 percent; n: 0 to 0.003 percent; the balance of Fe and inevitable impurities;

heating and preserving heat of the continuous casting plate blank;

carrying out rough rolling on the heated and heat-preserved continuous casting plate blank to obtain an intermediate plate blank;

performing finish rolling on the intermediate plate blank to obtain strip steel;

carrying out laminar cooling on the strip steel and coiling to obtain a hot rolled steel coil;

and cooling the hot rolled steel coil to room temperature, and then coiling to obtain the axle housing steel with reduced strength after the hot forming.

Optionally, the temperature of the continuous casting slab after heating and heat preservation is 1100-.

Optionally, the outlet temperature of the rough rolling is 950-.

Optionally, the finish rolling finishing temperature of the finish rolling is 780-810 ℃.

Optionally, the cooling rate is 10-15 ℃/s, and the coiling temperature is 600-650 ℃.

Based on the same inventive concept, the embodiment of the invention also provides an axle housing which is made of the axle housing steel for controlling the strength reduction after hot forming.

One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

the axle housing steel for controlling strength reduction after hot forming provided by the embodiment of the invention adopts chemical elements with reasonable proportion, and obtains a microstructure which is easy to flatten and has obviously reduced mechanical property reduction rate after hot forming through reasonable hot rolling process design, so that the axle housing steel has good plate shape quality, still has high mechanical property after heat treatment, and simultaneously, subcutaneous microcracks and red iron scales do not exist on the surface of the produced axle housing steel. Wherein, the lower tapping temperature is the guarantee of fine austenite structure, and the follow-up controlled rolling and controlled cooling process is used for obtaining smaller ferrite grains. The key measure for ensuring the uniformity and fineness of ferrite at a lower finishing rolling temperature, the key measure for ensuring the ferrite structure at a higher coiling temperature and the improvement of the plate shape quality by the ferrite structure. Therefore, the difficulty that thick-specification and high-strength steel is not suitable for flattening is effectively solved, the contribution of solid solution strengthening is unchanged after hot forming, the grain size after forming and a certain amount of nano-scale precipitates are ensured to be precipitated by controlling the original ferrite structure size, the contribution of fine crystal strengthening and precipitation strengthening is improved, so that the aim of improving the strength after hot forming is fulfilled, the yield strength of the steel plate is more than 600MPa, the tensile strength is more than 700MPa, the elongation is more than 20%, the plate shape and the surface quality are excellent, the yield strength after hot forming is more than 550MPa, the tensile strength is more than 650MPa, and the effect of excellent surface quality is achieved.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.

FIG. 1 is a metallographic structure of an axle housing steel for controlling a decrease in strength after hot forming in example 1 of the present invention.

Detailed Description

The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.

Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.

In order to solve the technical problems, the general idea of the embodiment of the application is as follows:

the embodiment of the invention provides axle housing steel for controlling strength reduction after hot forming, which comprises the following chemical elements in percentage by mass: c: 0.26 to 0.30 percent; si: 0 to 0.1 percent; mn: 1.8 to 2.2 percent; p: less than or equal to 0.010 percent; s: less than or equal to 0.005 percent; al: 0.02-0.05%; v: 0.01 to 0.03 percent; n: 0 to 0.003 percent; the balance of Fe and inevitable impurities.

The design principle of each chemical element is as follows:

c: c is one of the most economical strengthening elements in steel. If the C content is too high, the desired weldability and toughness cannot be ensured. If the carbon content is too low, the contribution value of solid solution strengthening is affected. Therefore, comprehensively considered, the content of C in the steel is controlled to be 0.26-0.30%.

Si: si is a solid solution strengthening element. When the Si content is high, the surface quality of the strip steel is not favorable, and the weldability of the strip steel is also unfavorable. Therefore, the Si content in the steel of the present invention is controlled to 0.10% or less in a comprehensive consideration.

Mn: mn is a solid-solution strengthening element. The Mn element has larger contribution to solid solution strengthening and fine crystal strengthening, the steel grade of the invention is mainly selected by solid solution strengthening to ensure the mechanical property after hot forming, so the high Mn element content needs to be added, but when the Mn content is too high, a serious banded structure can be formed to influence the welding performance. Therefore, the Mn content is designed to be 1.8-2.2% in comprehensive consideration.

P and S: p and S are impurity elements in steel, and the P element easily causes center segregation of the steel and deteriorates the weldability and the plastic toughness of the steel; the S element is likely to form MnS inclusions with the Mn element, and deteriorates weldability and formability of the steel. Therefore, the content of P in the steel is controlled to be less than or equal to 0.010 percent and the content of S in the steel is controlled to be less than or equal to 0.005 percent by comprehensively considering the weldability and the ductility and toughness of the material.

Al: al acts as a deoxidizer during steel making. While insufficient deoxidation leads to a decrease in cold formability of the material, an excessively high Al content leads to an excessive amount of AlN inclusions in the steel, and a decrease in elongation of the material. Therefore, the Al content of the invention is controlled to be 0.02-0.05% by comprehensively considering deoxidation and cold formability.

Nb, V, Ti: nb, V, and Ti play a role of precipitation strengthening as second phase forming elements, and also have a role of suppressing recovery of austenite and grain growth of recrystallization in the hot rolling step to make the ferrite phase a desired particle size, and the second phase particles belong to a hard phase to increase the strength of the matrix. However, in the case of the hot formed axle housing steel, the second phase particles present in the strip steel are coarsened significantly during the axle housing forming heating process, and the contribution of precipitation strengthening is reduced, resulting in a significant decrease in strength, so that it is not preferable to use the Nb and Ti microalloyed element. The solid solution temperature of the V element is low, the V element can be dissolved in hot forming heating, and is precipitated again after forming to keep a fine and dispersed state, so that the contribution of precipitation strengthening is improved, and therefore, the V microalloying is selected. On the other hand, when the V element is high, the solid solution temperature is increased, the alloy is wasted, and the cost is increased. Therefore, the V content is controlled to be 0.01 to 0.03 percent in comprehensive consideration.

N: the addition of N element is likely to promote the precipitation of V and raise the solid solution temperature of V, thus being unfavorable for the re-dissolution of V during heating, and is likely to cause the precipitation during forming and unfavorable for the secondary forming because the addition of N element promotes the precipitation of V. Therefore, the lower the content of N element in steel grades, the better, and the content of N element is controlled to be less than 0.003% in consideration of steel-making cost.

As an alternative embodiment, the microstructure of the steel is ferrite and pearlite, the ferrite having an average grain size of 5.0 to 10.0 μm.

As an alternative embodiment, the microstructure contains nanoscale precipitates having an average particle size of 1 to 50 nm.

In order to ensure that the strip steel has excellent plate-shaped quality and reduce the obvious reduction of subsequent fine-grain strengthening and phase change strengthening after hot forming, thereby causing the great reduction of strength, the structure is controlled to be ferrite + pearlite, and the average grain size of the ferrite structure is ensured to be 5-10 mu m; in order to increase the contribution of the precipitation strengthening ratio, the second phase particles are mainly composed of a nano-sized precipitation phase having an average particle diameter of 1 to 50 nm.

As an alternative embodiment, the thickness of the steel is 10-18 mm.

Based on the same inventive concept, the embodiment of the invention also provides a preparation method of the axle housing steel for controlling strength reduction after hot forming, which is used for preparing the steel and comprises the following steps:

smelting molten iron to obtain a continuous casting slab, wherein the continuous casting slab comprises the following chemical elements in percentage by mass: c: 0.26 to 0.30 percent; si: 0 to 0.1 percent; mn: 1.8 to 2.2 percent; p: less than or equal to 0.010 percent; s: less than or equal to 0.005 percent; al: 0.02-0.05%; v: 0.01 to 0.03 percent; n: 0 to 0.003 percent; the balance of Fe and inevitable impurities;

heating and preserving heat of the continuous casting plate blank;

carrying out rough rolling on the heated and heat-preserved continuous casting plate blank to obtain an intermediate plate blank;

performing finish rolling on the intermediate plate blank to obtain strip steel;

carrying out laminar cooling on the strip steel and coiling to obtain a hot rolled steel coil;

and cooling the hot rolled steel coil to room temperature, and then coiling to obtain the axle housing steel with reduced strength after the hot forming.

As an alternative embodiment, the temperature of the continuous casting slab after the heating and the heat preservation is 1100-1150 ℃.

The heating temperature of the continuous casting slab is 1100-1150 ℃. The heating temperature of the continuous casting slab is set according to the solid solution and precipitation condition of V in steel and the coarsening behavior of original austenite grains. When the heating temperature is low, a precipitated phase generated during continuous casting is not dissolved, and the final strength is influenced. When the heating temperature is high, austenite grains are coarsened, which affects the size of the final ferrite structure, and the desired strength cannot be secured.

As an optional embodiment, the outlet temperature of the rough rolling is 950-.

The rough rolling adopts a 1+5 mode rolling process (R1 one-pass rolling and R2 five-pass rolling), and the outlet temperature range of the rough rolling is 960-1060 ℃; the thickness range of the rough rolling intermediate billet is 55-60 mm.

As an alternative embodiment, the finishing temperature of the finish rolling is 780-810 ℃.

In order to ensure good surface quality of the strip, the surface scale of the strip is completely removed by performing a descaling operation using high-pressure water of 18MPa or more before finish rolling so as not to affect the surface quality by pressing into the surface of the strip during finish rolling.

The finishing temperature of the finish rolling is 760 and 810 ℃. When the finish rolling temperature exceeds 810 ℃, the uniformity of the ferrite phase of the obtained strip is insufficient, and the grain size of the obtained ferrite is liable to be larger than 10 μm. On the other hand, when the finishing temperature is lower than 760 ℃, the rolling enters a two-phase region for rolling, the tissue uniformity is insufficient, and the rolling difficulty is large.

As an alternative embodiment, the cooling rate is 10-15 ℃/s and the coiling temperature is 600-650 ℃.

Laminar cooling adopts a sparse cooling mode, and the coiling temperature is 600-650 ℃. After finishing rolling, the hot rolled strip steel is cooled to the temperature range of 600-650 ℃ at the speed of 10-15 ℃/s and is coiled.

The higher cooling speed, the ferrite grains are obviously refined, or bainite structures are easy to appear, so that the strength of the strip steel is too high, and the control of subsequent flattening plate shape is not facilitated; the cooling speed is too low, so that ferrite grains are easy to be abnormally coarse, and the mechanical property of the raw material is not satisfactory. The coiling temperature is the key to determine the type of hot rolled strip structure. When the coiling temperature is lower than 600 ℃, bainite structures are easy to appear, so that the phase transformation strengthening contribution is large, the strength of the raw material is high, and the control of the strength reduction rate after subsequent flattening and hot forming is not facilitated; the coiling temperature is high, the ferrite crystal grains are easy to be overlarge, and the strength of the strip steel is not ensured to meet the requirements.

Based on the same inventive concept, the embodiment of the invention also provides an axle housing which is made of the axle housing steel for controlling the strength reduction after hot forming.

The axle housing steel for controlling strength reduction after hot forming, the method for manufacturing the same, and the axle housing of the present application will be described in detail with reference to examples, comparative examples, and experimental data.

The steel of the following examples 1-4 was prepared by the following method: smelting → continuous casting heating → rough descaling → fixed width press → rough rolling → coiled sheet box → flying shear → fine descaling → fine rolling → laminar cooling → coiling, etc.;

wherein the content of the first and second substances,

1. the rough rolling adopts a 1+5 mode rolling process, R1 carries out one-pass descaling, and R2 carries out 1, 3 and 5-pass descaling;

2. before finish rolling, high-pressure water with the pressure of more than 18MPa is used for fine descaling, and iron scales on the surface of the strip steel are completely removed, so that the influence on the surface quality caused by pressing into the surface of the strip steel during finish rolling is avoided;

3. laminar cooling uses a sparse cooling mode.