阅读说明：本技术 一种屈服强度355MPa级桥壳钢生产方法 (Production method of axle housing steel with yield strength of 355MPa ) 是由 温利军 薛越 李�浩 王国海 张满全 徐建东 杨文海 赵超 于 2021-08-10 设计创作，主要内容包括：本发明公开了一种屈服强度355MPa级桥壳钢生产方法,通过合适的冶炼、连铸、加热、轧制、除鳞工艺,生产出了机械性能和表面质量良好的屈服强度355MPa级桥壳钢。钢板机械性能优良,钢板的屈服强度在385MPa～440MPa之间,抗拉强度在530～570MPa之间,延伸率在26％～29％之间,-40℃冲击功在172J～226J之间。钢板表面质量良好,没有麻坑、凹坑、重皮等缺陷,表面颜色基本一致,色差小。(The invention discloses a production method of 355 MPa-grade yield strength axle housing steel, which produces 355 MPa-grade yield strength axle housing steel with good mechanical property and surface quality through proper smelting, continuous casting, heating, rolling and descaling processes. The steel plate has excellent mechanical property, the yield strength of the steel plate is between 385MPa and 440MPa, the tensile strength of the steel plate is between 530MPa and 570MPa, the elongation of the steel plate is between 26 percent and 29 percent, and the impact energy at minus 40 ℃ is between 172J and 226J. The steel plate has good surface quality, no defects of pits, heavy skin and the like, basically consistent surface color and small color difference.)

1. A production method of axle housing steel with yield strength of 355MPa is characterized by comprising the following steps: the method comprises the following steps:

1) carrying out RH furnace treatment on the molten steel, wherein the treatment time is not less than 15 minutes under the condition that the vacuum degree is not more than 112 Pa;

2) controlling the superheat degree of molten steel at 16-29 ℃ during casting, and carrying out continuous casting by adopting electromagnetic stirring and soft reduction, wherein the electromagnetic stirring frequency is 6.2Hz, the current is 290A, the reduction positions are 6, 7 and 8 sections, and the reduction amount is 2.5mm, 2.4mm and 2.3 mm;

3) a heating process: in order to ensure certain compression ratio and slab quality, a continuous casting slab with the thickness of 250mm and the width of 1600mm is selected for production, a stepping heating furnace is adopted for slab heating, the tapping temperature of the continuous casting slab is 1223-; when the plate blank is heated in the heating furnace, the moving speed of the movable beam for supporting the plate blank is 1.2 m/min; the residual oxygen content of the waste gas of the heating furnace is controlled between 1 percent and 2 percent;

4) the steel plate rolling forming process comprises the following steps: replacing the newly ground working roll by the finishing mill before rolling the seed; and (3) performing two-stage controlled rolling after the slab is heated: the initial rolling thickness of the first stage is the thickness of a plate blank, the initial rolling temperature of the first stage is 1213-1233 ℃, the final rolling temperature of the first stage is more than or equal to 1000 ℃, the single-pass reduction rate during high-temperature elongation rolling of the first stage is more than or equal to 13%, the rolling speed of the first stage is 1.4-2.9 m/s, and the biting speed is 1.2 m/s; the initial rolling thickness of the second-stage steel plate is 3 times of the thickness of the finished steel plate, the initial rolling temperature of the second-stage steel plate is 930-960 ℃, the final rolling temperature of the second stage is 830-860 ℃, the biting speed of the second stage is 1.5m/s, and the second-stage steel plate is rolled for 6 passes, wherein the first pass is idle, the scale is removed before a frame machine is used during idle, and the second pass and the rest passes are rolled after the idle machine swings for 7-11 seconds;

5) the descaling process during steel plate rolling comprises the following steps: the descaling pressure is not less than 20MPa, and odd-number pass descaling is performed during the first-stage rolling; during the second stage of rolling, descaling in the first pass and the second pass;

6) during the production period of the axle housing steel, roller bed cooling water behind the roughing mill and in front of and behind the finishing mill is closed;

the thickness of the steel plate is 16mm, and the steel plate is produced on a wide and thick plate rolling mill.

2. The method for producing axle housing steel with the yield strength of 355MPa according to claim 1, is characterized in that: the axle housing steel comprises the following chemical components in percentage by weight: c: 0.14 to 0.17 percent; si: 0.16-0.26%; mn: 1.35-1.45%; 0.014 to 0.026% of Nb; 0.008-0.015% of Ti; p is less than or equal to 0.015 percent; s is less than or equal to 0.004 percent; ca: 0.0010-0.0026%; and Als: 0.018-0.034%; the balance of iron and unavoidable impurities.

Technical Field

The invention relates to the field of hot rolling, in particular to a production method of axle housing steel with yield strength of 355 MPa.

Background

The axle housing is one of the main components of the vehicle, supports the frame and its subsequent overall weight, and is also a component of the vehicle drive train. The automobile axle housing is used as a main body part of an axle and is a key part for ensuring the normal running of an automobile and meeting the service life, so that the automobile axle housing has higher requirements on the strength, the toughness, the fatigue resistance and the like. At present, axle housings of medium and heavy-duty automobiles are produced by hot stamping and forming by using hot rolled steel plates with the thickness of 12-20 mm in a large quantity, so that the steel plates are required to have good plasticity. After the axle housing is manufactured, the surface of the axle housing needs to be subjected to corrosion prevention treatment, so that the steel plate needs to have good surface quality. Good surface quality requires that the surface of the steel plate cannot have surface defects such as pits, heavy skin, cracks and the like, and the color of the surface of the whole steel plate is consistent. The axle housing steel has high requirements on mechanical property and surface quality, so the production difficulty is high, particularly when a wide and thick plate rolling mill is adopted for production.

The patent publication No. CN 109097702A of 'high-strength axle housing steel with good fatigue property and welding property and a preparation method thereof' provides a production method of the axle housing steel. The axle housing steel produced by the method has good welding performance and fatigue performance. But the method needs the steel plate to be rapidly cooled after rolling, the cooling rate of the steel plate is high, the requirement on the capability of cooling equipment is high, the final cooling temperature is low, the shape is difficult to control, and meanwhile, the method is suitable for the production of a continuous rolling unit.

The patent publication No. CN 110205559A 'axle housing steel with excellent surface quality and tensile strength more than or equal to 510MPa and a production method thereof' provides a production method of the axle housing steel. The axle housing steel produced by the method has good surface quality. However, the method needs rapid cooling after the steel plate is rolled, the final cooling temperature of the steel plate is required to be low, the plate shape is difficult to control, and meanwhile, the method is suitable for production of a continuous rolling unit.

The patent publication No. CN 110079740A, "a high-toughness hot-rolled 530 MPa-grade automobile cold stamping axle housing steel plate and a manufacturing method thereof" provides a production method of axle housing steel. The toughness of the axle housing steel produced by the method is good, but the method does not relate to the surface quality control of the steel plate.

Disclosure of Invention

The invention aims to provide a production method of 355 MPa-grade axle housing steel with good surface quality of a steel plate, consistent color of the whole steel plate and excellent mechanical property.

In order to solve the technical problems, the invention adopts the following technical scheme:

the invention relates to a production method of axle housing steel with yield strength of 355MPa, which comprises the following chemical components in percentage by weight: c: 0.14 to 0.17 percent; si: 0.16-0.26%; mn: 1.35-1.45%; 0.014 to 0.026% of Nb; 0.008-0.015% of Ti; p is less than or equal to 0.015 percent; s is less than or equal to 0.004 percent; ca: 0.0010-0.0026%; and Als: 0.018-0.034%; the balance of iron and inevitable impurities; the method comprises the processes of smelting, continuous casting, heating, rolling and cooling, and specifically comprises the following steps:

1) in order to ensure a certain compression ratio and slab quality, a continuous casting slab with the thickness of 250mm and the width of 1600mm is selected.

2) And carrying out RH furnace treatment on the molten steel, wherein the treatment time is not less than 15 minutes under the condition that the vacuum degree is not more than 112 Pa.

3) The thickness of a continuous casting billet is 250mm, the superheat degree is controlled to be 16-29 ℃ during molten steel casting, electromagnetic stirring and soft reduction are adopted during continuous casting, the electromagnetic stirring frequency is 6.2Hz, the current is 290A, the reduction positions are 6, 7 and 8 sections, and the reduction amount is 2.5mm, 2.4mm and 2.3 mm.

4) A heating process: the method is characterized in that a continuous casting slab with the thickness of 250mm is adopted for production, a stepping heating furnace is adopted for slab heating, the tapping temperature of the continuous casting slab is 1223-. The moving speed of the movable beam for supporting the plate blank when the plate blank is heated in the heating furnace is 1.2 m/min. The residual oxygen content of the waste gas of the heating furnace is controlled between 1 percent and 2 percent.

5) The rolling forming process of the steel plate with the thickness of 16mm comprises the following steps: and replacing the newly ground working roll in the pre-rolling finishing mill, and rolling 8-13 steel plates of other steel grades with the width of 2650mm before rolling the pre-rolling finishing mill. And (3) carrying out two-stage controlled rolling after the plate blank is heated, wherein the initial rolling thickness of the first stage is the plate blank thickness, the initial rolling temperature of the first stage is 1213-1233 ℃, the final rolling temperature of the first stage is more than or equal to 1000 ℃, the single-pass reduction rate during high-temperature extension rolling of the first stage is more than or equal to 13%, the rolling speed of the first stage is 1.4-2.9 m/s, and the biting speed is 1.2 m/s. The initial rolling thickness of the second-stage steel plate is 3 times of the thickness of the finished steel plate, the initial rolling temperature of the second-stage steel plate is 930-960 ℃, and the final rolling temperature of the second stage is 830-860 ℃; and the biting speed of the second stage is 1.5m/s, and the second stage performs rolling for 6 passes, wherein the first pass is idle, the frame machine is used for removing scale before the idle pass is performed, and the idle pass is performed after the idle pass is performed and the frame machine swings to be heated for 7-11 seconds, and then the second pass and the rest passes are rolled.

6) The descaling process during steel plate rolling comprises the following steps: the descaling pressure is not less than 20MPa, and odd-number passes of descaling are carried out during the first-stage rolling. And in the second stage of rolling, descaling is performed in the first pass and the second pass.

7) And during the production period of the axle housing steel, roller bed cooling water behind the roughing mill and in front of and behind the finishing mill is closed.

8) The steel plate is 16mm thick and is produced on a wide and thick plate rolling mill.

As the axle housing steel with the yield strength of 355MPa contains a certain amount of microalloy, the slab is heated at a higher temperature, and in order that Nb, Ti and the like can be fully dissolved in the slab during heating, carbon and nitride of the microalloy can be fully precipitated during subsequent rolling and cooling, so that the microstructure of the steel plate is improved. The higher heating temperature also enables the iron scale formed in the heating process of the plate blank to be easily removed, and is beneficial to controlling the surface quality of the steel plate. In order to ensure that the difference of the mechanical properties of the same steel plate is small, the surface color of the steel plate is uniform, and the plate blank is heated by adopting longer soaking time, so that the temperature of the plate blank is uniform as much as possible.

And (3) performing controlled rolling on the heated continuous casting billet in an austenite recrystallization zone and a non-recrystallization zone. The steel grade adopts two-stage controlled rolling, the first stage controlled rolling belongs to austenite recrystallization controlled rolling in a high temperature region, and the first stage adopts a rolling strategy under high pressure. The large single-pass reduction rate can enable rolling deformation to fully penetrate to the center of the steel plate, fully refine austenite grains and homogenize austenite structure, and simultaneously the high-temperature welding effect generated by rolling can eliminate the defects of looseness, microcracks and the like in the casting blank to a great extent, so that the density of the steel plate is improved, and the comprehensive performance of the material is improved; in the first stage of rolling, because the billets are thick and the temperature is reduced slowly, the steel plate is subjected to large temperature reduction after each pass of rolling by adopting low-speed rolling, so that grains can be refined to different degrees after each pass of rolling, and finally, the aim of fully refining austenite grains is fulfilled; the rolling speed difference between the head and the tail of the steel plate and the plate body can be reduced by adopting a larger biting speed during rolling so as to reduce the temperature difference between the head and the tail of the steel plate and the plate body when the steel plate is rolled. Because the steel plate can generate iron scale in the rolling process and influence the uniformity of the surface color and the surface quality of the steel plate, the scale removal needs to be strengthened during the first-stage rolling, the requirements of the shape and the surface quality of the steel plate are comprehensively considered, and the scale removal is carried out once every other pass during the first-stage rolling. The higher finish rolling temperature required in the first stage is to fully ensure that the start rolling temperature in the second stage meets the requirement.

After the first-stage rolling is finished, the intermediate blank swings on the roller way to cool, and starts to roll when the temperature is reduced to the second-stage rolling temperature, wherein the second-stage rolling belongs to low-temperature non-recrystallization controlled rolling. The strain is generated in the crystal grains under rolling deformation through the precipitation of carbo-nitrides of Nb, Ti and the like and the pinning dislocation, and a large amount of deformation energy and phase transformation nucleation positions are accumulated in the crystal grains through multi-pass rolling and large accumulated reduction. After rolling, the steel is rapidly cooled to a lower temperature, the transformation of the gamma phase → the alpha phase is completed, and the alpha phase structure with fine grains is obtained. During the second stage of rolling, the first pass is empty, which is needed for surface descaling, and because the plate shape of the intermediate billet is generally not good, if the intermediate billet is not empty, transverse cracks and other defects are easy to appear at the tail part of the steel plate during normal descaling; the second pass of continuous descaling is to thoroughly remove the scale generated in the intermediate blank during the temperature waiting period, and the scale is not required to be removed again in the later pass because the steel plate is already thin and the temperature is low and the scale is generated slowly. Meanwhile, the first pass is idle, the pass load distribution is optimized, and the steel plate which needs to be rolled in 6 passes originally is rolled in 5 passes, so that the single-pass reduction rate is increased, and the microstructure of the steel plate is improved. During rolling, roller bed cooling water behind the roughing mill and in front of and behind the finishing mill is turned off so as to eliminate the influence of the roller bed cooling water splashing out of the roll surface and scattering on the surface of the steel plate on the surface quality of the steel plate.

Compared with the prior art, the invention has the beneficial technical effects that:

1) the invention adopts low-component design, only adopts cheap Si, Mn, Nb, Ti and other alloys, and obtains the axle housing steel with good comprehensive performance and yield strength of 355MPa grade by proper smelting, continuous casting, heating and controlled rolling processes without other special controlled cooling equipment with strong cooling capacity. The manufacturing process is simple, and the manufacturing cost of the working procedure is low.

2) The steel plate has good strength, plasticity and toughness, and the structure is fine ferrite plus pearlite. The yield strength of the steel plate is between 385MPa and 440MPa, the tensile strength is between 530MPa and 570MPa, the elongation is between 26 percent and 29 percent, and the impact energy at minus 40 ℃ is between 172J and 226J.

3) The steel plate has good surface quality, no defects of pits, heavy skin and the like, basically consistent surface color and small color difference.

Drawings

The invention is further illustrated in the following description with reference to the drawings.

FIG. 1 is a metallographic structure diagram of a steel sheet according to example 1 of the present invention;

FIG. 2 is a metallographic structure diagram of a steel sheet according to example 2 of the present invention;

FIG. 3 is a metallographic structure diagram of a steel sheet according to example 3 of the present invention.

Detailed Description

Example 1

The steel plate is produced by a wide and thick plate rolling mill, and a plate blank with the thickness of 250mm and the width of 1600mm is rolled into a 16mm thick steel plate. RH treatment is carried out on the molten steel, the time of vacuum degree below 112Pa is 15 minutes, the thickness of a continuous casting billet is 250mm, the superheat degree of the molten steel during casting is 16 ℃, the frequency of electromagnetic stirring during slab continuous casting is 6.2Hz, the current is 290A, the reduction positions are 6, 7 and 8 sections, and the reduction amount is 2.5mm, 2.4mm and 2.3 mm. The slab heating process adopts a stepping heating furnace, the moving speed of the slab supported by the movable beam when the slab is heated in the heating furnace is 1.2m/min, the tapping temperature of the slab is 1223 ℃, the heating time of the slab is 245 minutes, the heating time in the soaking section is 32 minutes, the residual oxygen content in the waste gas of the heating furnace is 1%, and the (weight percentage) chemical components of the slab are as follows: 0.14% of C, 0.16% of Si, 1.45% of Mn, 0.026% of Nb0.026% of Ti, 0.008% of P, 0.015% of S, 0.004% of Als, 0.034% of Ca, and the balance of Fe and inevitable impurities. The newly ground work rolls were replaced in the pre-rolling mill and 8 steel plates of 2650mm width of other steel grades were rolled before rolling the grade. The descaling pressure is 20MPa, and odd-number passes of descaling are carried out during the first-stage rolling; and during the second stage of rolling, the first pass is idle, the rolling is started for the second pass and the rest passes after the idle pass is finished and the rolling is swung to be heated for 7 seconds, and the descaling is carried out on the first pass and the second pass. And during the production period of the axle housing steel, roller bed cooling water behind the roughing mill and in front of and behind the finishing mill is closed. The production is carried out by adopting a wide and thick plate rolling mill. The steel plate has good surface quality, no defects such as pits and the like, and the surface color of the steel plate is basically consistent. The detailed rolling and cooling processes are shown in Table 1, and the mechanical properties are shown in Table 2.

TABLE 1 Rolling Process

TABLE 2 mechanical Properties of the Steel sheets

Example 2

The steel plate is produced by a wide and thick plate rolling mill, and a plate blank with the thickness of 250mm and the width of 1600mm is rolled into a 16mm thick steel plate. RH treatment is carried out on the molten steel, the time of vacuum degree below 112Pa is 16.5 minutes, the thickness of a continuous casting billet is 250mm, the superheat degree of the molten steel during casting is 29 ℃, the frequency of electromagnetic stirring during slab continuous casting is 6.2Hz, the current is 290A, the reduction positions are 6, 7 and 8 sections, and the reduction amount is 2.5mm, 2.4mm and 2.3 mm. Adopt marching type heating furnace during the slab heating, the walking beam holds up the translation rate of slab when the slab heats in the heating furnace is 1.2m/min, and the slab temperature of coming out of the furnace is 1243 ℃, and slab heating time is 290 minutes, and the heating time at the soaking zone is 35 minutes, and the residual oxygen volume is 2% in the heating furnace waste gas, and the (weight percent) chemical composition of slab is: 0.17% of C, 0.26% of Si, 1.35% of Mn, 0.014% of Nb0.014%, 0.015% of Ti, 0.013% of P, 0.002% of S, 0.018% of Als, 0.0026% of Ca and the balance of Fe and inevitable impurities. The newly ground work rolls were replaced in the pre-rolling mill and 13 steel plates of 2650mm width of other steel grades were rolled before rolling the seed. The descaling pressure is 20.2MPa, and odd-number passes of descaling are carried out during the first-stage rolling; and during the second stage of rolling, the first pass is idle, the rolling is started for the second pass and the rest passes after the first pass is idle and the rolling is swung to be heated for 11 seconds, and the scale removal is carried out on the first pass and the second pass. And during the production period of the axle housing steel, roller bed cooling water behind the roughing mill and in front of and behind the finishing mill is closed. The steel plate has good surface quality, no defects such as pits and the like, and the surface color of the steel plate is basically consistent. The detailed rolling and cooling process is shown in Table 3, and the mechanical properties are shown in Table 4.

TABLE 3 Rolling Process

TABLE 4 mechanical Properties of the Steel sheets

Example 3

The steel plate is produced by a wide and thick plate rolling mill, and a plate blank with the thickness of 250mm and the width of 1600mm is rolled into a 16mm thick steel plate. RH treatment is carried out on the molten steel, the time of vacuum degree below 112Pa is 17.3 minutes, the thickness of a continuous casting billet is 250mm, the superheat degree of the molten steel during casting is 25 ℃, the frequency of electromagnetic stirring during slab continuous casting is 6.2Hz, the current is 290A, the reduction positions are 6, 7 and 8 sections, and the reduction amount is 2.5mm, 2.4mm and 2.3 mm. The slab heating process adopts a stepping heating furnace, the moving speed of the movable beam for supporting the slab when the slab is heated in the heating furnace is 1.2m/min, the tapping temperature of the slab is 1236 ℃, the heating time of the slab is 274 minutes, the heating time in a soaking section is 34.5 minutes, the residual oxygen content in the waste gas of the heating furnace is 1.6 percent, and the chemical components (in percentage by weight) of the slab are as follows: 0.15% of C, 0.22% of Si, 1.38% of Mn, 0.019% of Nb0.011% of Ti, 0.012% of P, 0.001% of S, 0.024% of Als, 0.0021% of Ca, and the balance of Fe and inevitable impurities. The newly ground work rolls were replaced in the pre-rolling mill and 11 steel plates of 2650mm width of other steel grades were rolled before rolling the seed. The descaling pressure is 20.35MPa, and odd-number passes of descaling are carried out during the first-stage rolling; and during the second stage of rolling, the first pass is idle, the rolling is started for the second pass and the rest passes after the first pass is idle and the rolling is swung to be heated for 9 seconds, and the scale removal is carried out on the first pass and the second pass. And during the production period of the axle housing steel, roller bed cooling water behind the roughing mill and in front of and behind the finishing mill is closed. The steel plate has good surface quality, no defects such as pits and the like, and the surface color of the steel plate is basically consistent. The details of the rolling and cooling process are shown in Table 5, and the mechanical properties are shown in Table 6.

TABLE 5 Rolling Process

TABLE 6 mechanical Properties of the Steel sheets

The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.