CN111471938B - Carbide bainite-free steel for electric automobile gear and production method thereof - Google Patents
Carbide bainite-free steel for electric automobile gear and production method thereof Download PDFInfo
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Abstract
The invention discloses carbide bainite-free steel for electric automobile gears and a production method thereof, wherein the steel comprises the following chemical components in percentage by weight: c: 0.20 to 0.25 wt%, Si: 1.70-1.85 wt%, Mn: 1.35-1.55 wt%, Al: 3.1-3.9 wt%, P is less than or equal to 0.01 wt%, S is less than or equal to 0.01 wt%, Mo: 0.1 to 0.14 wt%, Cr: 0.7-0.9 wt%, Nb: 0.05 to 0.07 wt%, and the balance of Fe and inevitable impurities. The invention creatively introduces the carbide-free bainite steel, adopts a brand-new high-silicon and aluminum-containing component system and a production process, comprehensively renovates the component system and the metallographic structure of the gear steel, provides a brand-new solution for the development of the new generation of gear steel, and realizes the quality-free treatment and the approximately deformation-free pioneering result of the gear steel.
Description
Technical Field
The invention relates to gear steel and a production method thereof, belongs to steel (long material) for automobile parts and a production method thereof, and particularly relates to carbide bainite-free steel for electric automobile gears and a production method thereof.
Background
Compared with the traditional automobile, the electric automobile cancels systems such as an engine, a clutch, a speed changer, exhaust and the like, adopts a brand-new electric driving mode, and is a new environment for serving parts: high speed and large torque, the data shows that the rotating speed and the torque of the motor exceed 3 times of those of the traditional automobile engine, and the service environment of parts is severer.
Along with the rapid rise of the manufacturing industry in China, particularly the vigorous development of the automobile industry in China, China has become the first world of gear manufacturing, and the continuous development of the gear industry greatly drives the demand of gear steel. The application range of the gear steel is wide, the gear steel is used in vehicles manufacturing industries such as cars, trucks, passenger cars, agricultural vehicles, motorcycles and the like, and is also used in railways, ships and engineering machinery, so that the gear steel is a core component manufacturing material for ensuring safety.
The gear is a precise mechanical part, generally needs to be forged and machined into teeth and then carburized and quenched, and the manufacturing and assembling precision of the gear has great influence on vibration, noise and the service life of gear teeth. When the gear works, the gear is affected by various stresses such as impact force, contact stress, pulsating bending stress, friction force and the like of variable load for a long time, and is also affected by various factors such as machining precision, assembly precision, grinding of external hard particles and the like, and is a part which is easy to damage, so that the gear steel for manufacturing the gear is required to have higher obdurability, fatigue strength and wear resistance.
At present, gear steel is mainly medium-low carbon alloy steel, in order to improve the strength, hardness and wear resistance of teeth, formed gear parts need to be subjected to quenching and tempering treatment (high-temperature carburization and quenching), the process flow is long, the energy consumption is high (data shows that the gear quenching and tempering process cost accounts for more than 30% of the part processing cost), heat treatment process parameters (heating temperature, time, carburizing process and other factors) directly influence the performance of the gears, and the controlled deformation (the martensite is formed by quenching and the volume expansion causes macroscopic deformation) is difficult to control in the heat treatment, so that the quality of the gears is further restricted. Therefore, there is an increasing demand for more excellent, less expensive, and environmentally friendly gear steels.
In recent years, new bright spots appear in the development of high-performance steel, and the most revolutionary discovery is the carbide-free bainite steel (also called super bainite steel, nano bainite steel and the like) discovered by Bhadeshia et al in 2004, the structure of the carbide-free bainite steel consists of slender bainite ferrite and carbon-rich film-shaped residual austenite in an alternating mode, the ferrite in the bainite structure and a parent phase are in a semi-coherent relationship, and the high strength of the steel is determined by the fine grain structure brought by low-temperature transformation, the fine structure in the ferrite and high-density dislocation; the residual austenite belongs to a face-centered cubic structure, has a plurality of sliding systems, can relieve stress concentration, belongs to a soft phase, and obviously improves the toughness of the carbide-free bainite steel.
The prior art searches and analyzes: the gear steel is mainly fixed in GB/T3077, GB/T5216 or AISI, EN and other standards or subjected to component fine adjustment, and the hot-rolled structure of the gear steel is as follows: ferrite + pearlite; tissue after tempering: the tempered martensite contains usually 0.15 to 0.50% of C and contains a certain amount of Cr, Ni, Mo, V, W, etc. The Chinese patent publication No. CN106967931 discloses 20Cr2Ni4 gear steel and a production process thereof, wherein the mass percentage of Mo is adjusted to 0.15-0.30% on the basis of traditional components so as to meet the requirements of users on hardenability, grain size, heat strength and the like. The Chinese patent with publication number CN100569983 discloses a preparation method of Cr-Mn-Ti gear steel, and in consideration of the angle of ensuring the strength and the fatigue limit of the gear steel, the patent regulates the Ti content in the traditional 20 CrMnTiH% to be down-regulated to 0.01-0.038%. Chinese patent publication No. CN109972024 discloses a steel for a gear steel bar, a preparation method thereof and a preparation method of the steel bar, and the steel bar comprises the following chemical components: 0.17 to 0.24 percent of C, 0.85 to 1.07 percent of Mn, 0.19 to 0.30 percent of Si, 0.98 to 1.10 percent of Cr, 0.05 to 0.10 percent of Mo, 0.15 to 0.25 percent of Ni, 0.01 to 0.05 percent of Al, less than or equal to 0.02 percent of P and less than or equal to 0.02 percent of S. The Chinese patent publication No. CN108531804 discloses an aluminum killed gear steel and a sulfide morphology control method thereof, wherein the aluminum killed gear steel comprises the following chemical components: 0.15 to 0.25 percent of C, 0.40 to 1.60 percent of Mn, 0.05 to 0.40 percent of Si, 0.8 to 2.0 percent of Cr, 0 to 0.60 percent of Mo, 0 to 2.00 percent of Ni, 0.015 to 0.06 percent of Al, less than or equal to 0.015 percent of P, 0.015 to 0.040 percent of S, 0.005 to 0.040 percent of Te,0.008 to 0.015 percent of [ N ], lessthan or equal to 0.0015 percent of T.0 and less than or equal to 0.25 percent of Cu. At present, all the patent documents of the gear steel aim at the improvement of the existing products or processes, and the problems of obdurability and deformability of the gear steel are not fundamentally solved through quenching and tempering in the production.
Disclosure of Invention
The invention aims to overcome the defects of high energy consumption of a quenching and tempering process, difficult control of quenching and heat treatment deformation and the like commonly existing in the conventional gear steel, the invention introduces the carbide-free bainite steel, adopts a brand-new high-silicon and aluminum-containing component system and a production process, comprehensively reforms the component system and the metallographic structure of the gear steel, provides the carbide-free bainite gear steel for the electric automobile and a production method thereof, and realizes the pioneering results of no quenching and tempering and almost no deformation of the gear steel. The silence and the service life of the gear prepared by the steel exceed 45CrNiMoVA, so that the energy consumption and the cost of a user are reduced. In addition, a brand new metallographic structure, namely carbide-free bainite, wherein the residual austenite serving as a soft phase generates a TRIP effect under the action of stress to form martensite and reduce the generation of cracks (the microstructure can realize self-repair of microcracks through phase transformation), so that the strength of a stressed area is increased, the crack expansion is inhibited, and the service life of the gear is obviously prolonged. Meanwhile, as the problem of quenching deformation does not exist (no quenching and tempering process), the overall dimension of the gear can be accurately controlled, the silence of the gear is improved, the stress condition is improved, and a series of advantages are brought.
In order to achieve the purpose, the invention designs carbide bainite-free steel for gears of electric automobiles, which comprises the following chemical components in percentage by weight: c: 0.20 to 0.25 wt%, Si: 1.70-1.85 wt%, Mn: 1.35-1.55 wt%, Al: 3.1-3.9 wt%, P is less than or equal to 0.01 wt%, S is less than or equal to 0.01 wt%, Mo: 0.1 to 0.14 wt%, Cr: 0.7-0.9 wt%, Nb: 0.05 to 0.07 wt%, and the balance of Fe and inevitable impurities
Further, the steel for the gear comprises the following chemical components in percentage by weight: c: 0.22 to 0.25 wt%, Si: 1.80-1.85 wt%, Mn: 1.45-1.55 wt%, Al: 3.5-3.9 wt%, P is less than or equal to 0.01 wt%, S is less than or equal to 0.01 wt%, Mo: 0.12 to 0.14 wt%, Cr: 0.8-0.9 wt%, Nb: 0.06 to 0.07 wt%, and the balance Fe and inevitable impurities.
Still further, the steel for gears comprises the following chemical components in percentage by weight: c: 0.24 wt%, Si: 1.82 wt%, Mn: 1.50 wt%, Al: 3.6 wt%, P: 0.006 wt%, S: 0.007 wt%, Mo: 0.13 wt%, Cr: 0.85 wt%, Nb: 0.065 wt%, and the balance of Fe and inevitable impurities.
Still further, the rolling performance of the steel for the gear reaches: tensile strength of 1700 MPa-1850 MPa, yield strength of 1500 MPa-1650 MPa, elongation after fracture of 10% -30%, reduction of area of 45% -60%, and impact energy of 45J-65J.
The invention also provides a production method of the steel for the electric automobile gear without the carbide bainite, the method is to smelt according to the chemical components according to the traditional smelting method to obtain the steel for the electric automobile gear without the carbide bainite in the microstructure, wherein,
1) in the casting blank process, after being heated by a heating furnace, controlled rolling and controlled cooling are carried out: the temperature of the finish rolling stage is controlled between 850 ℃ and 950 ℃, and 3-6S is adopted-1The final rolling temperature is less than or equal to 850 ℃ when the final rolling of 10% of deformation is carried out;
2) and (4) placing the rolled finished product in a slow cooling pit, wherein slow cooling is more than or equal to 24 hours.
The relevant working mechanism of the invention is as follows:
c: carbon is an important constituent element in steel, and has the most significant influence on the strength and plasticity of the gear steel. The method is different from the prior art, adopts an ultra-low carbon component system innovatively, and changes the current situation that the traditional gear steel mainly depends on the carbon content to improve the strength. The carbon content of the invention is 0.20-0.25 wt%.
Si: silicon is a strengthening element in steel and can inhibit the formation of carbides, promote the formation of carbide-free bainite, and generate high temperature on the meshing surface of a gear in operation, so that softening resistance is needed, and the content of Si is also needed to be increased. Therefore, comprehensive analysis shows that the Si content of the invention is controlled to be 1.70-1.85 wt%.
Mn: proper amount of manganese can improve the strength and hardenability, and lath bainite with small size can be obtained; in addition, manganese and sulfur are combined to generate MnS, so that the harm of sulfur is reduced, but the overhigh manganese can increase the overheating sensitivity of steel, so that crystal grains are easy to grow during heat treatment. The Mn content of the invention is controlled to be 1.35-1.55 wt%.
Al: the aluminum plays a main role in inhibiting the formation of carbides and promoting the formation of carbide-free bainite, is a key element in a component system, can obviously shorten the bainite phase transition time, and shortens the conventional phase transition process which needs several hours or even several days to meet the requirements of industrial production, but the overhigh aluminum pair causes difficulty in smelting and continuous casting. The invention Al: 3.1 to 3.9 wt%.
P, S: phosphorus and sulfur are harmful elements in the steel, phosphorus is easy to produce cold brittleness, sulfur is easy to produce hot brittleness, and further the processing conditions of steel wire drawing and heat treatment are deteriorated, so the content of the phosphorus and the sulfur needs to be reduced as much as possible. The invention has P less than or equal to 0.01 wt% and S less than or equal to 0.01 wt%.
Mo: the bainite area is enlarged, the bainite structure is favorably obtained, the mechanical property of the gear steel can be improved, but Mo belongs to a noble metal, and the use cost is higher, so that the comprehensive consideration of Mo: 0.1 to 0.14 wt%.
Cr: the austenite matrix is strengthened, the hardenability and the uniformity are improved, the high-temperature creep resistance of the gear is improved, and the Cr: 0.7 to 0.9 wt%.
Nb: nb has a promoting effect on carbide-free bainite transformation and can significantly refine grains during hot rolling dynamic recrystallization, but excessive Nb can cause NbCN coarse particles, lose the effect of refining grains and be harmful to the fatigue life of the gear steel. The invention Nb: 0.05 to 0.07wt percent.
Rolling process (at 850-950 deg.C for 3-6S-1The final rolling temperature is less than or equal to 850 ℃ when the final rolling of 10% of deformation is carried out; after rolling, placing the finished product in a slow cooling pit, wherein slow cooling is more than or equal to 24 h): the transformation of carbide-free bainite can be accelerated according to low temperature and small deformationAnd the transformation time of the carbide-free bainite is obviously shortened, so that the carbide-free bainite structure with the lath width of about 200nm is obtained to improve the toughness.
The invention has the beneficial effects that:
the invention creatively introduces the carbide-free bainite steel, adopts a brand-new high-silicon and aluminum-containing component system and a production process, comprehensively renovates the component system and the metallographic structure of the gear steel, provides a brand-new solution for the development of the new generation of gear steel, and realizes the quality-free treatment and the approximately deformation-free pioneering result of the gear steel. The invention aims at the performance of 45CrNiMoVA of the existing gear steel for the electric automobile, develops the carbide bainite-free gear steel for the electric automobile and the production method thereof, and the silence, the service life and the like of the gear prepared by the steel exceed 45CrNiMoVA, thereby reducing the energy consumption and the cost of a user. In addition, a brand new novel metallographic structure, namely carbide-free bainite, takes place the TRIP effect as a residual austenite of a soft phase under the action of stress to form martensite and reduce the generation of cracks (the microstructure can realize the self-repair of microcracks through phase transformation), so that the strength of a stressed area is increased, the crack expansion is restrained, and the service life of the gear is obviously prolonged. Meanwhile, as the problem of quenching deformation does not exist (no quenching and tempering process), the overall dimension of the gear can be accurately controlled, the silence of the gear is improved, the stress condition is improved, and a series of advantages are brought.
Drawings
Fig. 1 is a carbide-free bainite microstructure.
Detailed Description
The present invention is described in further detail below with reference to specific examples so as to be understood by those skilled in the art.
Example 1
The carbide bainite-free steel 1 for the electric automobile gear comprises the following chemical components in percentage by weight: c: 0.21 wt%, Si: 1.75 wt%, Mn: 1.50 wt%, Al: 3.7 wt%, P: 0.008 wt%, S: 0.007 wt%, Mo: 0.12 wt%, Cr: 0.80 wt%, Nb: 0.065 wt%, and the balance of Fe and inevitable impurities. The method for producing the steel 1 for the electric automobile gear without the carbide bainite is to obtain the steel 1 for the electric automobile gear without the carbide bainite in the microstructure by smelting according to the traditional smelting method according to the chemical components, wherein,
1) in the casting blank process, after being heated by a heating furnace, controlled rolling and controlled cooling are carried out: performing conventional rolling according to the section and the size of the finished product of the blank, wherein the temperature of the finish rolling stage is 880 ℃, and the rolling temperature is 4S-1The final rolling with 10% deformation is carried out at the final rolling temperature of 850 ℃;
2) and (4) placing the rolled finished product in a slow cooling pit, wherein slow cooling is more than or equal to 24 hours.
The rolling performance of the steel for electric automobile gears 1 prepared in the embodiment can reach: the tensile strength is 1750MPa, the yield strength is 1550MPa, the elongation after fracture is 15%, the reduction of area is 50%, the impact energy is 55J, and various mechanical properties are comprehensively superior to those of a standard steel type 45CrNiMoVA after quenching and tempering. In addition, a brand new metallographic structure, namely carbide-free bainite, is used as a soft phase residual austenite, under the action of stress, a TRIP effect is generated to form martensite, so that the generation of cracks is reduced (the self-repair of microcracks can be realized through phase transformation of microstructures), the strength of a stressed area is increased, the crack expansion is inhibited, and the service life and the safety of the gear are obviously improved.
Example 2
The carbide bainite-free steel 2 for the electric automobile gear comprises the following chemical components in percentage by weight: c: 0.22 wt%, Si: 1.78 wt%, Mn: 1.48 wt%, Al: 3.6 wt%, P: 0.005 wt%, S: 0.007 wt%, Mo: 0.13 wt%, Cr: 0.85 wt%, Nb: 0.055 wt%, the balance Fe and inevitable impurities.
The production method of the steel 2 for the electric automobile gear without the carbide bainite is to obtain the steel 2 for the electric automobile gear without the carbide bainite in the microstructure by smelting according to the chemical components according to the traditional smelting method, wherein,
1) in the casting blank process, after being heated by a heating furnace, controlled rolling and controlled cooling are carried out: according to the section of the blank and the size of the finished productConventional rolling at 920 deg.C in the finish rolling stage and 4S-1The final rolling with 10% deformation is carried out at the final rolling temperature of 800 ℃;
2) and (4) placing the rolled finished product in a slow cooling pit, wherein slow cooling is more than or equal to 24 hours.
The rolling state performance of the steel 2 for the electric automobile gear prepared by the embodiment can reach: the tensile strength is 1800MPa, the yield strength is 1600MPa, the elongation after fracture is 20%, the reduction of area is 60%, the impact energy is 60J, and all the mechanical properties are comprehensively superior to those of a standard steel grade 45CrNiMoVA after quenching and tempering. In addition, a brand new metallographic structure, namely carbide-free bainite, is used as a soft phase residual austenite, under the action of stress, a TRIP effect is generated to form martensite, so that the generation of cracks is reduced (the self-repair of microcracks can be realized through phase transformation of microstructures), the strength of a stressed area is increased, the crack expansion is inhibited, and the service life and the safety of the gear are obviously improved.
Example 3
The carbide bainite-free steel 3 for the electric automobile gear comprises the following chemical components in percentage by weight: c: 0.24 wt%, Si: 1.82 wt%, Mn: 1.50 wt%, Al: 3.6 wt%, P: 0.006 wt%, S: 0.007 wt%, Mo: 0.13 wt%, Cr: 0.85 wt%, Nb: 0.065 wt%, and the balance of Fe and inevitable impurities.
The production method of the steel 3 for the electric automobile gear without the carbide bainite is to obtain the steel 3 for the electric automobile gear with the microstructure of the carbide bainite-free according to the traditional smelting of the chemical components, wherein,
1) in the casting blank process, after being heated by a heating furnace, controlled rolling and controlled cooling are carried out: performing conventional rolling according to the section and the size of the finished product of the blank, wherein the temperature of a finish rolling stage is 930 ℃, and the rolling temperature is 4S-1The final rolling with 10% deformation is carried out at the final rolling temperature of 830 ℃;
2) and (4) placing the rolled finished product in a slow cooling pit, wherein slow cooling is more than or equal to 24 hours.
The rolling state performance of the steel 3 for the electric automobile gear prepared in the embodiment can reach: the tensile strength is 1750MPa, the yield strength is 1550MPa, the elongation after fracture is 15%, the reduction of area is 50%, the impact energy is 55J, and various mechanical properties are comprehensively superior to those of a standard steel type 45CrNiMoVA after quenching and tempering. In addition, a brand new metallographic structure, namely carbide-free bainite, is used as a soft phase residual austenite, under the action of stress, a TRIP effect is generated to form martensite, so that the generation of cracks is reduced (the self-repair of microcracks can be realized through phase transformation of microstructures), the strength of a stressed area is increased, the crack expansion is inhibited, and the service life and the safety of the gear are obviously improved.
Example 4
The carbide bainite-free steel 4 for the electric automobile gear comprises the following chemical components in percentage by weight: c: 0.24 wt%, Si: 1.70 wt%, Mn: 1.43 wt%, Al: 3.8 wt%, P: 0.007 wt%, S: 0.005 wt%, Mo: 0.13 wt%, Cr: 0.87 wt%, Nb: 0.068 wt%, and the balance of Fe and inevitable impurities.
The production method of the steel 4 for the electric automobile gear without the carbide bainite is to obtain the steel 4 for the electric automobile gear with the microstructure of the carbide bainite-free according to the traditional smelting of the chemical components, wherein,
1) in the casting blank process, after being heated by a heating furnace, controlled rolling and controlled cooling are carried out: performing conventional rolling according to the section and the size of the finished product of the blank, wherein the temperature of a finish rolling stage is 870 ℃, and the rolling temperature is 5S-1The final rolling with 10% deformation is carried out at the final rolling temperature of 810 ℃;
2) and (4) placing the rolled finished product in a slow cooling pit, wherein slow cooling is more than or equal to 24 hours.
The rolling performance of the steel 4 for the electric automobile gear prepared by the embodiment can reach: the tensile strength is 1800MPa, the yield strength is 1600MPa, the elongation after fracture is 22%, the reduction of area is 48%, the impact energy is 52J, and all the mechanical properties are comprehensively superior to those of a standard steel grade 45CrNiMoVA after quenching and tempering. In addition, a brand new metallographic structure, namely carbide-free bainite, is used as a soft phase residual austenite, under the action of stress, a TRIP effect is generated to form martensite, so that the generation of cracks is reduced (the self-repair of microcracks can be realized through phase transformation of microstructures), the strength of a stressed area is increased, the crack expansion is inhibited, and the service life and the safety of the gear are obviously improved.
Example 5
The carbide bainite-free steel 5 for the electric automobile gear comprises the following chemical components in percentage by weight: c: 0.24 wt%, Si: 1.80 wt%, Mn: 1.53 wt%, Al: 3.6 wt%, P: 0.007 wt%, S: 0.005 wt%, Mo: 0.14 wt%, Cr: 0.78 wt%, Nb: 0.060 wt%, the balance Fe and inevitable impurities.
The method for producing the steel 5 for the electric automobile gear without the carbide bainite is to obtain the steel 5 for the electric automobile gear with the microstructure of the carbide bainite-free according to the traditional smelting of the chemical components, wherein,
1) in the casting blank process, after being heated by a heating furnace, controlled rolling and controlled cooling are carried out: performing conventional rolling according to the section and the size of the finished product of the blank, wherein the temperature of the finish rolling stage is 880 ℃, and the rolling temperature is 4S-1The final rolling with 10% deformation is carried out at the final rolling temperature of 840 ℃;
2) and (4) placing the rolled finished product in a slow cooling pit, wherein slow cooling is more than or equal to 24 hours.
The rolling state performance of the steel 5 for the electric automobile gear prepared by the embodiment can reach: the tensile strength is 1810MPa, the yield strength is 1600MPa, the elongation after fracture is 18%, the reduction of area is 55%, the impact energy is 55J, and all the mechanical properties are comprehensively superior to those of a standard steel grade 45CrNiMoVA after quenching and tempering. In addition, a brand new metallographic structure, namely carbide-free bainite, is used as a soft phase residual austenite, under the action of stress, a TRIP effect is generated to form martensite, so that the generation of cracks is reduced (the self-repair of microcracks can be realized through phase transformation of microstructures), the strength of a stressed area is increased, the crack expansion is inhibited, and the service life and the safety of the gear are obviously improved.
Other parts not described in detail are prior art. Although the present invention has been described in detail with reference to the above embodiments, it is only a part of the embodiments of the present invention, not all of the embodiments, and other embodiments can be obtained without inventive step according to the embodiments, and the embodiments are within the scope of the present invention.
Claims (3)
1. The steel for the carbide bainite-free electric automobile gear is characterized in that: the steel for the gear comprises the following chemical components in percentage by weight: c: 0.22 to 0.25 wt%, Si: 1.80-1.85 wt%, Mn: 1.45-1.55 wt%, Al: 3.5-3.9 wt%, P is less than or equal to 0.01 wt%, S is less than or equal to 0.01 wt%, Mo: 0.12 to 0.14 wt%, Cr: 0.8-0.9 wt%, Nb: 0.06-0.07 wt%, and the balance of Fe and inevitable impurities, wherein the rolling state performance of the steel for the gear reaches: tensile strength of 1700 MPa-1850 MPa, yield strength of 1500 MPa-1650 MPa, elongation after fracture of 10% -30%, reduction of area of 45% -60%, and impact energy of 45J-65J.
2. The steel for carbide bainite-free electric automobile gears according to claim 1, characterized in that: the steel for the gear comprises the following chemical components in percentage by weight: c: 0.24 wt%, Si: 1.82 wt%, Mn: 1.50 wt%, Al: 3.6 wt%, P: 0.006 wt%, S: 0.007 wt%, Mo: 0.13 wt%, Cr: 0.85 wt%, Nb: 0.065 wt%, and the balance of Fe and inevitable impurities.
3. A production method of the steel for electric automobile gears free of carbide bainite according to claim 1, wherein the steel for electric automobile gears having a microstructure of carbide bainite is obtained by smelting according to the above chemical components according to a conventional smelting method, and the method is characterized in that:
1) in the casting blank process, after being heated by a heating furnace, controlled rolling and controlled cooling are carried out: the temperature of the finish rolling stage is controlled between 850 ℃ and 950 ℃, and 3-6S is adopted-1The deformation rate of (2) is carried out to last 10%Rolling the deformation, wherein the final rolling temperature is less than or equal to 850 ℃;
2) and (4) placing the rolled finished product in a slow cooling pit, wherein slow cooling is more than or equal to 24 hours.
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