Preparation method of stainless bearing steel

Abstract

The invention relates to a preparation method of stainless bearing steel, belongs to the field of alloy steel, and solves the problem that the bearing steel obtained by the existing preparation method has insufficient comprehensive properties such as high-temperature hardness, wear resistance, corrosion resistance, toughness and machinability. The preparation method of the stainless bearing steel comprises the following steps: S1, material preparation: selecting raw materials according to component requirements of a target alloy; the target alloy is high-carbon high-chromium molybdenum vanadium alloy steel; s2, smelting and pouring: smelting and pouring the raw materials to form a steel ingot; s3, forging is conducted, specifically, the steel ingot is machined into a pre-forged piece through forging treatment; and S4, heat treatment after forging is conducted, specifically, the pre-forged piece is subjected to heat treatment procedures including annealing, quenching and high-temperature tempering, and the bearing steel is obtained. According to the preparation method, the bearing steel is superior to existing bearing steel in comprehensive performance of high-temperature hardness, wear resistance, corrosion resistance, toughness, machinability and the like.

Description

Technical Field

[0001] The invention relates to the technical field of alloy steel, and in particular to a method for preparing stainless bearing steel. Background Art

[0002] With the development of high-end equipment, the operating temperature of bearings is getting higher and higher, and the load is getting larger and larger. The bearings are required to have a maximum contact stress of more than 4000MPa, an operating temperature of more than 400℃, good corrosion resistance and service life, etc. Especially in the high-temperature oil-free lubrication state (dry friction or solid lubrication state), the bearing material is also required to have high wear resistance.

[0003] Commonly used stainless bearing steels are mainly high-carbon and high-chromium bearing steels G95Cr18 or G102Cr18Mo (440C). After quenching and tempering, the room temperature hardness is not less than HRC58, and it has good wear resistance and corrosion resistance. However, its high temperature hardness at 400°C is not more than 52HRC, which cannot meet the use requirements of high temperature and high load bearings.

[0004] In order to improve the high temperature resistance of bearings and reduce the heating of bearings themselves, a high temperature stainless bearing steel Cr14Mo4 (440CMOD) with increased (Mo) content has been developed at home and abroad. Its heat resistance has been greatly improved, and the maximum operating temperature has reached above 400°C, but its wear resistance is still insufficient. Moreover, Cr14Mo4 steel is a high-carbon, high-chromium, and high-molybdenum alloy steel. It is easy to generate coarse eutectic ledeburite structure (eutectic carbide) during traditional smelting and solidification, which reduces the corrosion resistance and fatigue performance of the material.

[0005] As high-end equipment places increasingly stringent requirements on bearings' temperature resistance, wear resistance, corrosion resistance and other performance requirements, traditional bearing steel preparation methods and their products have been unable to meet these growing usage standards. Summary of the invention

[0006] In view of the above analysis, the present invention aims to provide a method for preparing stainless bearing steel to solve the problem that the bearing steel obtained by the existing preparation method has insufficient comprehensive performance in high temperature hardness, wear resistance, corrosion resistance, toughness and processability.

[0007] The objective of the present invention is achieved through the following technical solutions:

[0008] The present invention provides a method for preparing stainless bearing steel, comprising the following steps:

[0009] S1. Material preparation: selecting raw materials according to the composition requirements of the target alloy; the target alloy is high-carbon, high-chromium, molybdenum, and vanadium alloy steel;

[0010] S2. Smelting and pouring: smelting and pouring the raw materials to form steel ingots;

[0011] S3, forging: through forging treatment, the steel ingot is processed into a pre-forged part;

[0012] S4, post-forging heat treatment: the pre-forged parts are subjected to heat treatment processes including annealing, quenching, and high-temperature tempering to obtain the bearing steel; wherein the quenching temperature T 42 = 1100-1150°C, the high temperature tempering temperature T 45 =450℃~574℃.

[0013] Furthermore, in step S4, between the quenching and high temperature tempering, a low temperature treatment is also included, and the temperature of the low temperature treatment is T 44 =-68℃~-78℃.

[0014] Furthermore, the quenching and low temperature treatment also include low temperature tempering, and the temperature of the low temperature tempering is T 43 =100~200℃.

[0015] Further, in step S4, the main step of annealing includes: annealing the pre-forged piece at a temperature T 411 ≤600℃ furnace loading, austenitizing and isothermal spheroidizing.

[0016] Furthermore, the austenitizing temperature T 412 =870-910℃.

[0017] Furthermore, the main steps of the isothermal spheroidization include: cooling the pre-forged piece at a cooling rate CR 4a ≤90℃ / h down to T 413a =680-720℃, and then cool down at a rate of CR 4b ≤30℃ / h down to T 413b =510-550℃ then air-cooled.

[0018] Furthermore, in step S3, before the forging process, a pre-forging heat treatment is also included; the main steps of the pre-forging heat treatment include: high-temperature diffusion, low-temperature soaking, and eutectic carbide decomposition;

[0019] Wherein, the high temperature diffusion temperature T 301 = 1180-1220°C, the temperature of the low temperature soaking is T 302 =980-1020℃, the temperature of decomposition of eutectic carbide is T 303 =1140-1180℃.

[0020] Furthermore, before the high temperature diffusion, preheating is also included, and the preheating temperature T 300 =700-800℃.

[0021] Furthermore, in step S3, after the forging treatment, a microstructure refinement heat treatment is also included; the main steps of the microstructure refinement heat treatment include: (a) preheating to 880-920°C and keeping warm; (b) heating to 1100-1140°C and keeping warm, and then oil cooling; (c) cooling to 130-170°C for tempering; (d) heating to 504-544°C and keeping warm, and then oil cooling.

[0022] Further, in step S1, the target alloy composition requirements are C: 1.0-1.5%, Cr: 14.00-16.00%, Mo: 3.5-4.5%, N: ≤0.03%, V: 1.0-1.5%, Si: 0.20-0.50%, Mn: 0.1-0.6%, P≤0.015%, S≤0.010%, and the remainder is Fe and unavoidable impurities.

[0023] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0024] (1) The present invention optimizes the microstructure of high-carbon, high-chromium, molybdenum and vanadium alloy steel by optimizing the quenching and high-temperature tempering process parameters, thereby significantly improving the comprehensive performance of the prepared bearing steel. Specifically, compared with the bearing steel prepared by the existing method, the bearing steel prepared by the present method shows better performance in terms of hardness, especially high-temperature hardness, wear resistance, corrosion resistance and fatigue resistance. For example, through a suitable quenching temperature, the carbide can be fully dissolved, so that enough C, Cr, Mo, and V elements are dissolved in the matrix, thereby improving the hardness of the bearing steel material. Through a suitable high-temperature tempering temperature, a secondary hardening phenomenon is generated, which promotes the precipitation of high-temperature carbides containing Mo, thereby improving the hardness and temperature resistance of the material. In addition, by controlling the temperature of quenching and high-temperature tempering, the alloy elements dissolved in austenite and the amount of residual austenite can be effectively regulated, thereby achieving the purpose of optimizing the key properties of bearing products including wear resistance, corrosion resistance, fatigue resistance, etc.

[0025] (2) In some preferred embodiments, during the heat treatment stage after forging, by introducing low temperature treatment, the residual austenite is decomposed, and by precisely controlling the alloying elements dissolved in the austenite and their content, the key properties of the bearing product, such as wear resistance, corrosion resistance and fatigue resistance, can be effectively optimized. The low temperature treatment process also helps to improve the dimensional stability of the product, ensuring the reliability and long life of the bearing in various applications.

[0026] (3) In some preferred embodiments, for the heat treatment process after forging, introducing a low-temperature tempering step is important for eliminating thermal stress and preventing crack formation, especially when manufacturing bearing products with complex structures. This step is particularly critical for ensuring product quality. In addition, reducing defects such as cracking caused by stress can also help further improve the comprehensive performance of bearing products, including hardness and temperature resistance, wear resistance, corrosion resistance and fatigue resistance.

[0027] (4) In some preferred embodiments, during the heat treatment process after forging, the furnace is first loaded at a relatively low temperature for heat insulation to achieve preheating, which can effectively avoid stress concentration and reduce the risk of cracking. For materials with poor thermal conductivity such as high-carbon, high-chromium, molybdenum and vanadium alloy steel, this step is also very important for ensuring product quality. In addition, reducing defects such as cracking caused by stress not only improves the overall quality of bearing products, but also further enhances their comprehensive performance, including hardness, temperature resistance, wear resistance, corrosion resistance and fatigue resistance.

[0028] (5) In some preferred embodiments, during the heat treatment process after forging, the austenitizing temperature in the annealing process is precisely controlled to achieve partial dissolution of carbides, followed by isothermal spheroidizing treatment, and precise control of the temperature and the heating or cooling rate to ensure that the hardness after annealing does not exceed 269 HBW. This appropriate hardness is beneficial to improving the final comprehensive performance of the bearing steel.

[0029] (6) In some preferred embodiments, by introducing a heat treatment step before forging, the microstructure uniformity of the steel ingot can be significantly improved, its strength and toughness can be enhanced, and thermal stress can be effectively reduced. This improvement in strength and toughness not only improves the processability during forging, but also reduces the risk of defects such as cracking, thereby ensuring product quality, which is important for improving the overall quality and overall performance of the final bearing product.

[0030] (7) In some preferred embodiments, in the forging process, by introducing a structure refinement heat treatment after forging, the carbides and matrix structure can be further refined, and the inclusions, carbides and matrix structure can be refined and homogenized. For example, the particle size of the carbides can be less than 38 μm (for rods with a diameter of less than 40 mm), and the grain size can reach level 8 or above, thereby further improving the comprehensive properties of the bearing steel, such as contact fatigue life, toughness and hardness, and reducing internal defects.

[0031] (8) In some preferred embodiments, based on the preparation method of the present invention, by finely controlling the alloy composition, the comprehensive performance of the bearing steel in terms of high temperature hardness, wear resistance, corrosion resistance and fatigue resistance can be further optimized, surpassing the bearing steel produced by the traditional preparation method.

[0032] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0034] Figure 1 It is a process curve diagram of heat treatment before forging of an embodiment of the present invention;

[0035] Figure 2 It is a graph of annealing process in post-forging heat treatment of an embodiment of the present invention;

[0036] Figure 3 The surface corrosion morphologies of the test steels of the embodiments and comparative examples of the present invention under different neutral salt spray corrosion times; (a) to (c): Embodiment 2; (d) to (f): Comparative Example 1. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0038] Under the background of existing technology, the comprehensive performance of traditional bearing steel in terms of high temperature hardness, wear resistance and corrosion resistance still needs to be improved. Through in-depth research, the inventors found that the bearing steels currently on the market, such as high temperature resistant type, stainless steel type and high carbon chromium type, still have obvious room for optimization in the preparation process, especially in the forging and heat treatment process. In view of the poor overall performance of existing bearing steel materials in practical applications, especially in high temperature / high load / corrosive environments, the inventors started from the preparation process and proposed a series of innovative optimization measures, aiming to significantly improve and enhance the comprehensive performance of bearing materials in various working conditions, especially under more harsh conditions.

[0039] The present invention provides a method for preparing stainless bearing steel, comprising the following steps:

[0040] S1. Material preparation: selecting raw materials according to the composition requirements of the target alloy; the target alloy is high-carbon, high-chromium, molybdenum, and vanadium alloy steel;

[0041] S2. Smelting and pouring: smelting and pouring the raw materials to form steel ingots;

[0042] S3, forging: through forging treatment, the steel ingot is processed into a pre-forged part;

[0043] S4, post-forging heat treatment: the pre-forged parts are subjected to heat treatment processes including annealing, quenching, and high-temperature tempering to obtain the bearing steel; wherein the quenching temperature T 42 = 1100-1150°C, the high temperature tempering temperature T 45 =450℃~574℃.

[0044] Compared with the prior art, the present invention optimizes the microstructure of high-carbon, high-chromium, molybdenum, and vanadium alloy steel by optimizing the quenching and high-temperature tempering process parameters, thereby significantly improving the comprehensive performance of the prepared bearing steel. Specifically, compared with the bearing steel prepared by the existing method, the bearing steel prepared by the present method shows better performance in comprehensive performance such as hardness, especially high-temperature hardness, wear resistance, corrosion resistance, and fatigue resistance. For example, through a suitable quenching temperature, the carbide can be fully dissolved, so that enough C, Cr, Mo, and V elements are dissolved in the matrix, thereby improving the hardness of the bearing steel material. Through a suitable high-temperature tempering temperature, a secondary hardening phenomenon is generated, which promotes the precipitation of high-temperature carbides containing Mo, thereby improving the hardness and temperature resistance of the material. In addition, by controlling the temperature of quenching and high-temperature tempering, the alloy elements dissolved in austenite and the amount of residual austenite can be effectively regulated, thereby achieving the purpose of optimizing the key performance of bearing products including wear resistance, corrosion resistance, and fatigue resistance.

[0045] Specifically, the forging process in step S3 includes upsetting and drawing the blank and controlled forging and controlled cooling. Preferably, before the forging process, it also includes pre-forging heat treatment. Preferably, after the forging process, it also includes microstructure refinement heat treatment.

[0046] In some embodiments, step S3 includes the following steps:

[0047] S30, heat treatment before forging;

[0048] The main steps of the pre-forging heat treatment include: high-temperature diffusion, low-temperature soaking, and eutectic carbide decomposition; preferably, preheating is also included before the high-temperature diffusion.

[0049] S31, upsetting and drawing the blank and controlled forging and controlled cooling;

[0050] S32: Heat treatment for microstructure refinement.

[0051] In some embodiments, in step S30, the preheating temperature T 300 =700-800°C, the high temperature diffusion temperature T 301 = 1180-1220°C, the temperature of the low temperature soaking is T 302 =980-1020℃, the temperature of decomposition of eutectic carbide is T303 =1140-1180℃.

[0052] In some embodiments, the pre-forging heat treatment in step S30 specifically includes the following steps:

[0053] S300, preheating: heat the steel ingot to T 300 =700-800℃ and keep warm; preferably, the holding time t 300 =(0.8-1.2)min×D, D is the ingot diameter, in mm; more preferably, T 300 =730-770℃,t 300 =(0.9-1.1)min×D.

[0054] S301, high temperature diffusion: heat the steel ingot to T 301 = 1180-1220°C and keep warm; preferably, the holding time t 301 ≥15h; for example: t 301 15h~20h.

[0055] S302, low temperature uniform heating: cool the steel ingot to T 302 = 980-1020°C and keep warm; preferably, the holding time t 302 ≥3h; for example: t 302 =3h~6h.

[0056] S303, eutectic carbide decomposition: the ingot is heated to T 303 = 1140-1180°C and keep warm; preferably, the holding time t 303 ≥ 2 hours; for example, t 303 =2-4h.

[0057] It should be noted that the above-mentioned step S30 pre-forging heat treatment and its preferred implementation mode have a positive effect on further improving the comprehensive performance of the steel ingot, especially the strength, toughness and performance stability;

[0058] (1) The function of step S300 includes: reducing thermal stress and preventing the steel ingot from cracking; the principle is: for the steel ingot described in S2, i.e., high-carbon, high-chromium, molybdenum, and vanadium alloy steel, due to its poor thermoplasticity, the cast steel ingot obtained by pouring has certain structural unevenness and fishbone-shaped carbides. If the heating speed is too fast, for example, directly rising to the temperature of high-temperature diffusion, the temperature difference between the inside and outside of the steel ingot is large, which is easy to cause excessive thermal stress and cracking. The preheating step S300 can make the temperature inside and outside of the steel ingot uniform, and no phase change occurs when it is below AC1, so that the steel ingot does not generate large internal stress.

[0059] (2) The functions of step S301 include: improving the toughness and performance stability of the bearing steel material; the principle is: through high-temperature diffusion, P, S and other metals that are easy to segregate and have low melting points are evenly distributed.

[0060] (3) The functions of step S302 include: improving the plastic toughness of the bearing steel material; the principle is: low-temperature soaking can prevent the steel ingot from being coarse and uneven in structure, thereby improving the uniformity of the structure during subsequent forging and post-forging heat treatment.

[0061] (4) The function of step S303 includes: improving the strength and toughness of the bearing steel material; the principle is: decomposing the coarse fishbone-shaped eutectic carbides into short rod-shaped fine carbides.

[0062] In some embodiments, the specific steps of step S31 include:

[0063] S311, Upsetting and drawing the billet: First, upset the steel ingot to 1 / 3 to 1 / 2 of the original height, and then draw it out;

[0064] S312, controlled forging and controlled cooling: the forging temperature is maintained at T 312 =950-1050℃, the final forging temperature is not less than 900℃, and after forging, the steel is sent to an annealing furnace for annealing to obtain a pre-forged piece. More preferably, T 312 =980-1020℃.

[0065] In some embodiments, the main steps of the microstructure refinement heat treatment in step S32 include the following steps (a) to (b) in sequence;

[0066] (a) Preheat to 880-920°C and keep warm;

[0067] (b) heating to 1100-1140°C and keeping the temperature, then oil cooling;

[0068] (c) cooling to 130-170°C for tempering;

[0069] (d) Raise the temperature to 504-544°C and keep it warm, then oil cool.

[0070] In some embodiments, step (a): preheating the pre-forging to T 321 =880~920℃ and keep warm for t 321 =(0.8-1.2)min×D, D is the pre-forging diameter, in mm; preferably, T 321 =890~910℃,t 321 =(0.9-1.1)min×D.

[0071] In some embodiments, step (b): heating the pre-forging to T 322 = 1100~1140℃ and keep warm, holding time t322 ≥1h, then oil cooling; preferably, T 322 =1110~1130℃,t 322 1-3h.

[0072] In some embodiments, step (c): cooling the pre-forging to T 323 = Tempering at 130-170℃, tempering time t 323 ≥1h; preferably, T 323 =140~160℃,t 323 1-3h.

[0073] In some embodiments, step (d): heating the pre-forging to T 324 =504~544℃ and keep warm, holding time t 324 ≥2h, then oil cooling; preferably, T 324 =514~534℃,t 324 For 2-4h.

[0074] Preferably, before step (d), steps (b) and (c) are repeated 1-3 times.

[0075] Preferably, after step (d), step (d) is repeated 1-4 times.

[0076] It should be noted that in the forging process of step S3, by combining upsetting and drawing, controlled forging and controlled cooling, and microstructure refinement heat treatment, the carbides and matrix microstructure can be further refined, and the inclusions, carbides, and matrix microstructure can be refined and homogenized. For example, the particle size of the carbides can be less than 35 μm (for rods with a diameter of less than 40 mm), and the grain size can reach level 8 or above, thereby further improving the comprehensive properties of the bearing steel such as contact fatigue life, toughness, and hardness, and reducing internal defects.

[0077] Preferably, in step S4, between the quenching and the high temperature tempering, a low temperature treatment is also included, and the temperature of the low temperature treatment is T 44 =-68℃~-78℃.

[0078] Further preferably, the quenching and low temperature treatment further include low temperature tempering, and the temperature of the low temperature tempering is T 43 =100~200℃.

[0079] In some embodiments, step S4 includes the following steps:

[0080] S41, annealing;

[0081] S42, quenching; the quenching temperature is 1100-1150°C;

[0082] S43, low temperature tempering; the temperature of the low temperature tempering is 100-200°C;

[0083] S44, low temperature treatment; the temperature of the low temperature treatment is -68 to -78°C;

[0084] S45, high temperature tempering; the temperature of high temperature tempering is 450℃~574℃.

[0085] Preferably, in step S4, the main step of annealing includes: subjecting the pre-forged piece to a temperature T 411 ≤600℃ furnace loading, austenitizing and isothermal spheroidizing.

[0086] In some embodiments, in step S41, the main steps of annealing include:

[0087] S411, preheating: pre-forging at temperature T 411 ≤600℃ furnace loading and protection; illustratively,

[0088] T 411 =450℃, 500℃, 550℃.

[0089] S412, austenitizing: the austenitizing temperature T 412 = 870-910 ° C; the main steps of austenitizing include: heating the pre-forged piece to T 412 = 870-910°C and keep warm; preferably, the holding time t 412 ≥2h; further, t 412 2h~4h.

[0090] S413, isothermal spheroidization: The main steps of the isothermal spheroidization include: 4a ≤90℃ / h down to T 413a =680-720℃, and then cool down at a rate of CR 4b ≤30℃ / h down to T 413b = 510-550℃ and then air-cooled. Preferably, it is reduced to T 413a And keep warm, the insulation time t 413a ≥12h; further, the insulation time t 413a =12-14h.

[0091] It should be noted that the above steps S411-S413 and their preferred implementation methods have a positive effect on further improving the comprehensive performance of bearing steel, especially preventing cracking and improving strength and toughness.

[0092] (1) The preheating function of step S411 includes: preventing cracking; the principle is: for the steel ingot described in S2, i.e., high-carbon, high-chromium, molybdenum, and vanadium alloy steel, due to its poor thermal conductivity, by charging the ingot into the furnace at a temperature not higher than 600°C, thermal stress concentration can be avoided and the risk of cracking can be reduced.

[0093] (2) The functions of austenitization in step S412 and isothermal spheroidization in step S413 include: ensuring that the annealing hardness is ≤ 269 HBW; the principle is: high temperature austenitization dissolves part of the carbides. The steel of the present invention mainly contains eutectic carbides, that is, primary carbides. The purpose of isothermal spheroidization is to form pearlite structure in the matrix, thereby softening the material and making the hardness no more than 269 HBW, which is convenient for subsequent machining of the blank, and after quenching and tempering heat treatment, the hardening reaches the performance requirements.

[0094] In some embodiments, the main steps of quenching in step S42 include: heating the pre-forged piece to a quenching temperature T 42 = 1100-1150°C and keep warm, then oil cool; preferably, the holding time t 42 ≥60min; further, T 42 =1110~1130℃, insulation time t 42 =60-90min, more preferably, T 42 =1115~1125℃.

[0095] In some embodiments, the main steps of low temperature tempering in step S43 include: cooling the pre-forged piece to T 43 = 100-200°C and keep warm, then air cool; preferably, T 43 =130~170℃, insulation time t 43 ≥60min; more preferably, T 43 =140~160℃,t 43 =60-90min.

[0096] In some embodiments, the main steps of the low temperature treatment in step S44 include: cooling the pre-forged piece to T 44 = -68℃~-78℃ and maintain, then air cool; preferably, T 44 =-71℃~-75℃, holding time t 44 ≥60min; more preferably, T 44 =-72℃~-74℃, t 44 =60-90min.

[0097] In some embodiments, the main steps of high temperature tempering in step S45 include: heating the pre-forged piece to T 45 = 450℃~574℃ for tempering; preferably, T 45=490~540℃; tempering time t 45 ≥2h; preferably, tempering 2 or more times, for example, tempering 2-7 times, each tempering time t 45 =2-4h.

[0098] It should be noted that the above steps S42-S45 and their preferred implementations have a positive effect on further improving the comprehensive performance of bearing steel, especially ensuring high hardness and temperature resistance and reducing stress;

[0099] (1) The function of step S42 includes: ensuring sufficient hardness; the principle is: the carbide is fully dissolved, so that sufficient C, Cr, Mo, and V elements are dissolved in the matrix, thereby improving the hardness of the bearing steel material.

[0100] (2) The function of step S43 includes: preventing cracks from occurring; the principle is: the steel ingot described in S2, i.e., high-carbon, high-chromium, molybdenum, and vanadium alloy steel, has poor thermal conductivity and large thermal stress after oil cooling, and the thermal stress can be removed by low-temperature tempering.

[0101] (3) The effects of step S44 include: low residual austenite and high dimensional stability; the principle is: low temperature treatment causes the residual austenite to decompose.

[0102] (4) The functions of step S45 include: ensuring hardness and temperature resistance; the principle is: high temperature tempering produces secondary hardening phenomenon and precipitates high temperature carbides containing Mo, thereby improving the hardness and temperature resistance of the material.

[0103] It should be noted that after the post-forging heat treatment in step S4, the room temperature hardness of the obtained bearing steel is ≥HRC60, and the high temperature hardness at 400°C is ≥HRC58.

[0104] In some embodiments, the main steps of step S2 include:

[0105] S21, smelting and casting the raw materials in S1 through a vacuum induction furnace to obtain an electrode rod;

[0106] S22. The electrode rod obtained in S21 is used as a raw material, and further smelted and cast in a vacuum consumable furnace to obtain a vacuum consumable steel ingot.

[0107] In some embodiments, step S21 specifically includes:

[0108] S211, preparation stage: according to the composition requirements described in step S1, the main alloy elements of Fe, Cr, Mo and V are added into a vacuum induction furnace, and vacuum is drawn; preferably, the vacuum degree in the furnace is reduced to below 5 Pa, for example, vacuum is drawn for 5-15 minutes;

[0109] S212, melting stage: electric melting, melting the charge by induction heating in a vacuum environment;

[0110] S213, refining stage; preferably, the vacuum degree is maintained at ≤5Pa, and the refining time is ≥45 minutes;

[0111] S214, alloying stage: according to the composition requirements described in step S1, Si, C, and Mn are added into a vacuum induction furnace for deoxidation;

[0112] S215, pouring stage: transferring the molten metal from the vacuum induction furnace to the mold for pouring to form an electrode rod;

[0113] S216, cooling stage: after the casting is completed, the electrode rod needs to be cooled in a controlled environment; illustratively, it is hood-cooled or pit-cooled, and after leaving the pit, it is promptly sent for annealing and finishing. Preferably, the hood-cooling or pit-cooling time is ≥ 48h.

[0114] In some embodiments, S214, the alloying stage, further includes adding MgNi alloy into the vacuum induction furnace. Preferably, the amount of MgNi alloy added is 0.01-0.03% based on the total mass of the bearing steel raw material.

[0115] In some preferred embodiments, in step S22, during the smelting process using a vacuum consumable furnace, the melting rate of the vacuum consumable furnace is controlled to be ≤10kg / min, and the vacuum degree is 0.13-1.33Pa. The vacuum consumable steel ingot obtained in step S2 needs to be cooled in a controlled environment; illustratively, hood cooling or pit cooling, and after leaving the pit, red annealing and peeling and finishing are carried out in time. Preferably, the hood cooling or pit cooling time is ≥48h.

[0116] In some embodiments, during the smelting and pouring process described in step S2, the contents of impurities P, S, O, Cu, and Ni in the steel are controlled by the following steps respectively:

[0117] (1) Controlling P content: including but not limited to vacuum degassing;

[0118] (2) Controlling the S content: including but not limited to, during vacuum induction melting, by adding C element in batches, the melt can be desulfurized to a large extent under ultra-high vacuum conditions;

[0119] (3) Controlling the O content: including but not limited to vacuum degassing;

[0120] (4) Control the Cu (copper) content: Select raw materials with lower Cu content for smelting, and use the high volatility coefficient of Cu element in the vacuum consumable process to further volatilize and reduce it.

[0121] Optionally, in step S1, the target alloy composition requirements are C: 1.0-1.5%, Cr: 14.00-16.00%, Mo: 3.5-4.5%, N: ≤0.03%, V: 1.0-1.5%, Si: 0.20-0.50%, Mn: 0.1-0.6%, P≤0.015%, S≤0.010%, and the remainder is Fe and unavoidable impurities.

[0122] The microstructure of the high-carbon, high-chromium, molybdenum, and vanadium alloy steel obtained by the above preparation method is martensitic matrix + residual carbides + residual austenite; the maximum size of the carbides is not more than 35μm; the grain size is not less than level 7. This structure is conducive to significantly improving the comprehensive properties of high-carbon, high-chromium, molybdenum, and vanadium alloy steel, including high-temperature hardness, wear resistance, corrosion resistance, etc. For example, the martensitic matrix provides high strength and hardness, the residual carbides increase the wear resistance of the material, and the residual austenite helps to improve the toughness and corrosion resistance of the material; the fine carbide distribution helps to improve the wear resistance and strength of the material, and at the same time, the fine carbides are also conducive to maintaining the toughness of the material and avoiding the increase of brittleness caused by excessive carbides. In some embodiments, the properties of the bearing steel prepared by the present invention are as follows: room temperature hardness ≥HRC60, high temperature hardness at 400°C ≥HRC58; relative wear resistance measured by pin-disc wear test ≥1.08, average weight loss measured by ball-block wear test ≤0.22 mg; partial uncorroded areas exist after 96 hours of neutral salt spray test, which is better than the existing G102Cr18Mo stainless bearing steel.

[0123] In order to further improve and enhance the comprehensive performance of bearing materials under various working conditions, especially under relatively harsh conditions, the present invention further optimizes the alloy composition.

[0124] In some preferred embodiments, the target alloy composition is C: 1.10-1.20%, Cr: 14.00-15.00%, Mo: 3.75-4.25%, N: ≤0.004%, V: 1.10-1.30%, Si: 0.20-0.40%, Mn: 0.30-0.60%, P≤0.008%, S≤0.002%, Cu≤0.20%, Ni≤0.25%, O≤0.0015%, and the balance is Fe and unavoidable impurities.

[0125] It should be noted that the design ideas of the alloy components in the above preferred embodiments are as follows:

[0126] Through the alloying design of C, Cr, Mo and V, the main alloying elements of the invention steel are formed to ensure the high temperature hardness, wear resistance and corrosion resistance of the bearing steel, wherein the C content is controlled mainly to obtain ultra-high hardness and excellent wear resistance. Specifically, in the preferred implementation, the role and proportion of each element are as follows:

[0127] C is an austenite stabilizing element and a carbide forming element, which plays a role in martensite solid solution strengthening and precipitate dispersion strengthening. The higher the C content, the higher the martensite hardness and wear resistance after quenching, but too high a C content will reduce the toughness and corrosion resistance of the steel, so the C content should be controlled at 1.10% to 1.20%; for example, the C content is 1.12%, 1.14%, 1.16%, and 1.18%.

[0128] Cr is the main element of the corrosion-resistant alloying design of stainless steel. Its solid solution content must reach more than 12.5% ​​to ensure the corrosion resistance of steel. It is also an element that improves the hardenability and hardenability of steel. As the Cr content increases, the corrosion resistance and hardenability of steel improve, but too high Cr content will promote the formation of high-temperature ferrite and affect the type and size control of carbides in steel. Therefore, 14% ≤ Cr ≤ 15% is required; illustratively, the Cr content is 14.2%, 14.4%, 14.6%, and 14.8%. Further, Cr is 14.6-15.0%.

[0129] Mo is a ferrite-forming, solid solution strengthening, carbide and carbonitride-forming element, and is also the main element for improving heat resistance and corrosion resistance. Mo forms carbides with C and precipitates during high-temperature tempering to produce secondary hardening to improve the heat resistance of steel; Mo increases the density of the passive film on the surface of steel and improves the ability to resist pitting corrosion. However, if Mo is too high, ferrite will easily appear, reducing the strength and toughness of steel. Mo should be controlled at 3.75% to 4.25%; illustratively, the Mo content is 3.80%, 3.85%, 3.90%, 3.95%, 4.00%, 4.05%, 4.10%, 4.15%, and 4.20%; further, the Mo content is 4.00% to 4.25%; further, the Mo content is 4.00% to 4.18%.

[0130] V is a strong carbide-forming element, which has the functions of refining grains, forming VC high-temperature carbides, and improving the strength and heat resistance of steel. However, excessive V affects the toughness and processing properties of steel, so V is controlled at 1.10-1.30%; for example, the V content is 1.15%, 1.20%, 1.22%, 1.25%, 1.27%; further, the V content is 1.20-1.30%.

[0131] N is an austenite stabilizing element, and is also a martensite solid solution strengthening and precipitation strengthening element. The more N content, the higher the strength, hardness and corrosion resistance of the steel. However, the solid solubility of nitrogen in martensitic steel is very low. Increasing the N content too much will increase the difficulty of smelting and other preparations, increase the residual austenite content, and reduce the dimensional stability of the bearing. In addition, too high a N content will produce more nitride inclusions, which have an adverse effect on the comprehensive performance of the bearing steel, especially in terms of fatigue life and crack generation. Therefore, the N content should be controlled at no more than 0.004%; illustratively, N≤0.003%, N≤0.002%, N≤0.0015%, N≤0.001%.

[0132] Si and Mn: Based on the above main element design of heat resistance, corrosion resistance, high hardness, etc., Si and Mn elements can be appropriately added to further improve the hardness and hardenability of steel, but too high Si and Mn content will affect the heat resistance and corrosion resistance, so Si: 0.20-0.40%, Mn: 0.30-0.60%. For example, the Si content is 0.25%, 0.27%, 0.30%, 0.32%, 0.35%; further, the Si content is 0.22%-0.38%. For example, the Mn content is 0.35%, 0.40%, 0.42%, 0.45%, 0.47%, 0.50%, 0.52%, 0.55%, 0.57%; further, the Mn content is 0.42%-0.60%.

[0133] At the same time, in order to ensure the hot and cold processing and fatigue properties of steel, low melting point and impurity elements such as P, S, Cu, Ni, and O are controlled at the following levels: P≤0.008%, S≤0.002%, Cu≤0.20%, Ni≤0.25%, O≤0.0015%.

[0134] Compared with the prior art, the present invention improves the forging and heat treatment processes, finely controls and optimizes the microstructure and uniformity of the bearing steel, thereby significantly improving its comprehensive performance. On this basis, by finely controlling the alloy composition, the overall performance of the bearing steel in terms of high temperature hardness, wear resistance, corrosion resistance and fatigue resistance can be further optimized, making its comprehensive performance surpass that of the bearing steel prepared by the traditional method.

[0135] (1) By appropriately increasing the carbon (C) content, reducing the nitrogen (N) content and controlling the contents of other elements such as Cr, Mo, V, Si, and Mn within a suitable range, the high-temperature hardness and wear resistance of the bearing steel material are significantly improved, solving the problem that the high-temperature hardness and / or wear resistance of the bearing steel in the prior art is still insufficient.

[0136] (2) By appropriately reducing the nitrogen (N) content and strictly controlling the impurity elements at a low level, the fatigue resistance of the bearing steel material is further improved, especially reducing the initiation and propagation of fatigue cracks under long-term high loads, ensuring its reliability and long life under various working conditions, especially under high loads.

[0137] (3) By appropriately reducing the nitrogen (N) content in the bearing steel material, controlling the content of other elements such as C, Cr, Mo, and V within an appropriate range, and strictly controlling the impurity elements at a low level, the bearing steel exhibits better toughness, plasticity, and processability during the preparation process, thereby reducing the probability of stress cracking or other defects, improving the yield rate, and facilitating industrial-scale application and reducing costs.

[0138] In some preferred embodiments, the contents of the four elements P, S, O, and N must satisfy: P+S+O+N≤0.010%. By controlling the upper limit of the sum of the contents of P, S, O, and N, the thermoplasticity and toughness of the bearing steel material can be further improved, the generation of inclusions such as oxides, nitrides, or sulfides can be reduced, and the strength, toughness, and fatigue properties of the material can be improved. Furthermore, Cu≤0.01%; Ni≤0.15%.

[0139] In some preferred embodiments, the content of the three elements Cr, Mo and V must meet the following requirements: Cr+Mo+V-7.5%≥12%. Phase analysis shows that when the bearing steel alloy system of the present invention is in the use state, i.e., the quenched and tempered state, part of the Cr, Mo and V elements are dissolved in the matrix, and the other part mainly forms M with C. 23 C6 type, its chemical formula is usually expressed as (Fe, Cr, Mo, V) 23 C6, for example: (Fe0.379Cr0.473Mo0.090V0.058) 23 C6 carbide; Cr, Mo and V elements dissolved in the matrix play a role in solid solution strengthening and form a passivation film to improve corrosion resistance. To ensure sufficient corrosion resistance and solid solution strengthening, the three elements of Cr, Mo and V preferably meet the following requirements: Cr+Mo+V-5%-2%-0.5% is 12% and above.

[0140] In a preferred embodiment, the chemical composition of the bearing steel also includes: Mg, which is added in the form of MgNi alloy during the preparation process, and the amount of the MgNi alloy added is 0.01-0.03% based on the mass of the bearing steel. By adding Mg to the alloy system (which is added to the alloy system in the form of MgNi alloy during smelting), the performance of the bearing steel can be further optimized and the processability can be improved; specifically, the addition of a suitable amount of Mg can improve the microstructure of the material, such as refining cast carbides, improving the thermoplasticity and ductility of the bearing steel material, reducing the difficulty of processing, improving processing efficiency, reducing defects and improving the yield rate.

[0141] In some preferred embodiments, the carbon equivalent Ceq of the bearing steel is 5.15-5.35, Ceq = C + (Cr + Mo + V) / 5 + Mn / 6 + Si / 15. By optimizing the range of carbon equivalent (Ceq), the bearing steel material of the present invention exhibits better toughness and processability during the preparation process, and achieves an optimized balance in terms of wear resistance, high temperature hardness, corrosion resistance and fatigue performance, thereby significantly improving the overall performance.

[0142] In some preferred embodiments, in the chemical composition of the bearing steel provided by the present invention, the Cr, Mo, and V satisfy the relationship: I = 0.6 × Cr + 0.5 × Mo + 2.5 × V, and 13.9 < I < 14.3. Further controlling these three elements to satisfy the above relationship can significantly improve the overall performance, for example: achieving an optimized balance in terms of wear resistance, high temperature hardness, corrosion resistance, and fatigue resistance.

[0143] In some preferred embodiments, the chemical composition of the bearing steel includes: C: 1.13-1.17%, Cr: 14.60-14.90%, Mo: 4.05-4.15%, V: 1.23-1.27%, Si: 0.25-0.35%, Mn: 0.45-0.55%; N: ≤0.004%, P≤0.008%, S≤0.002%, Cu≤0.20%, Ni≤0.25%, O≤0.0015%, and the remainder is Fe and unavoidable impurities.

[0144] The performance parameters of the bearing steel obtained by the present invention are as follows: room temperature hardness ≥HRC60, high temperature hardness at 400°C ≥HRC58; relative wear resistance measured by a pin-disc wear test ≥1.08, average weight loss measured by a ball-block wear test ≤0.22 mg; partial uncorroded areas exist after 96 hours of a neutral salt spray test, which is superior to the existing G102Cr18Mo stainless bearing steel.

[0145] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and comparative examples.

[0146] Example 1

[0147] S1. Material preparation: prepare high-purity raw materials according to the following element ratios by mass percentage: C: 1.10%, Cr: 14.00%, Mo: 3.75%, V: 1.10%, Si: 0.20%, Mn: 0.30%, and the balance is Fe;

[0148] S2. Smelting and pouring: Use vacuum induction furnace + vacuum consumable furnace to smelt and pour the prepared raw materials to form steel ingots;

[0149] Specifically, according to the alloy composition ratio of S1, the main alloy elements of Fe, Cr, Mo, and V are added to a vacuum induction furnace, vacuumed, electrically melted, and refined for 45 minutes; Si, C, and Mn are added to the vacuum induction furnace for deoxidation; casting is performed to form an electrode rod, and the electrode rod is hood-cooled for 48 hours; the electrode rod is used as a raw material, and a vacuum consumable furnace is used for further smelting and casting. The melting rate of the vacuum consumable furnace is controlled at 10kg / min, and the vacuum degree is ≤1.33Pa to obtain a vacuum consumable steel ingot. The vacuum consumable steel ingot is pit-cooled for 48 hours, and after leaving the pit, it is promptly red-sent for annealing and then peeled and finished to obtain a vacuum consumable steel ingot;

[0150] S3, forging;

[0151] Upsetting and drawing: first upset the steel ingot to 1 / 3 of the original height and then draw it to obtain the billet after billeting; controlled forging and controlled cooling: forge the billet after billeting, keep the forging temperature between 950-1050℃, the final forging temperature is not less than 900℃, and send it to the annealing furnace for annealing after forging.

[0152] S4, heat treatment after forging;

[0153] (1) Annealing; austenitization: The pre-forged part is heated to T 412 = 870℃ and keep warm, holding time t 412 = 2h; Isothermal spheroidization: The pre-forged piece is cooled at a rate of CR 4a =90℃ / h down to T 413a = 680℃ and keep warm, holding time t 413a = 12h, then cool down at a rate of CR 4b =30℃ / h down to T 413b =510℃ and then air-cooled;

[0154] (2) Quenching: Heat the pre-forging to the quenching temperature T 42 = 1110℃ and keep warm, holding time t 42 For 60min, then oil cool;

[0155] (3) High temperature tempering: Heat the pre-forging to temperature T 45 =450°C for tempering to obtain the bearing steel.

[0156] Example 2

[0157] The difference between this embodiment and embodiment 1 lies in step S4; the remaining steps and parameters are substantially the same as those of embodiment 1. Specifically, in step S4, low temperature treatment is further included between the quenching and high temperature tempering.

[0158] The cryogenic treatment comprises: cooling the pre-forged piece to T 44 =-68℃ and keep t 44 = 60min, then air cool.

[0159] Example 3

[0160] The difference between this embodiment and embodiment 2 lies in step S4; the remaining steps and parameters are substantially the same as those of embodiment 2. Specifically, in step S4, low-temperature tempering is further included between the quenching and the low-temperature treatment.

[0161] The low temperature tempering includes: cooling the pre-forged piece to T 43 = 100℃ and keep warm for t 43 = 60min, then air cool.

[0162] Example 4

[0163] The difference between this embodiment and embodiment 3 lies in step S3; the remaining steps and parameters are substantially the same as those of embodiment 3. In step S3, before the blank is upset and drawn, a pre-forging heat treatment is also included.

[0164] The pre-forging heat treatment comprises:

[0165] (1) High temperature diffusion: The steel ingot is heated to T 301 = 1180℃ and keep warm, holding time t 301 =15h;

[0166] (2) Low temperature uniform heating: cool the steel ingot to T 302 =980℃ and keep warm, holding time t 302 =3h;

[0167] (3) Eutectic carbide decomposition: The ingot is heated to T 303 = 1140℃ and keep warm, holding time t 303 =2h.

[0168] Example 5

[0169] The difference between this embodiment and embodiment 4 lies in step S3; the remaining steps and parameters are substantially the same as those of embodiment 4. In step S3, before the blank is upset and drawn, a pre-forging heat treatment is also included.

[0170] The pre-forging heat treatment comprises:

[0171] (1) Preheating: Heat the steel ingot to T 300 =700℃ and keep warm, holding time t 300 =1.2min×D; D is the diameter of the steel ingot, in mm;

[0172] (2) High temperature diffusion: The steel ingot is heated to T 301 = 1220℃ and keep warm, holding time t 301 =15h;

[0173] (3) Low temperature uniform heating: cool the steel ingot to T 302 = 1020℃ and keep warm, holding time t 302 =3h;

[0174] (4) Eutectic carbide decomposition: The ingot is heated to T 303 = 1180℃ and keep warm, holding time t 303 =2h.

[0175] Example 6

[0176] The difference between this embodiment and embodiment 5 is the annealing in step S4; the remaining steps and parameters are basically the same as those in embodiment 5;

[0177] Specifically, the annealing in this embodiment includes the following steps:

[0178] a) Annealing; Preheating: Pre-forging the workpiece at temperature T 411 ≤600℃ loading furnace for protection; austenitization: heat the pre-forging to T 412 =910℃ and keep warm, holding time t 412 = 2h; Isothermal spheroidization: The pre-forged piece is cooled at a rate of CR 4a =85℃ / h down to T 413a =720℃ and keep warm, holding time t 413a = 12h, then cool down at a rate of CR 4b =25℃ / h down to T 413b =550℃ and then air-cooled.

[0179] Example 7

[0180] The difference between this embodiment and embodiment 6 is the high temperature tempering in step S4. The high temperature tempering times in this embodiment are 2 times; the other steps and parameters are basically the same as those in embodiment 6.

[0181] Example 8

[0182] The difference between this embodiment and embodiment 7 is that in step S3, after the forging treatment, a microstructure refinement heat treatment is also included; the remaining steps and parameters are basically the same as those in embodiment 7.

[0183] Specifically, the microstructure refinement heat treatment in this embodiment includes the following steps:

[0184] (a) Preheat the forging to T 321 = 880℃ and keep warm for t 321 =0.8min×D; D is the pre-forging diameter, in mm;

[0185] (b) The pre-forging is heated to T 322 = 1100℃ and keep warm, holding time t 322=1h and then oil cooling;

[0186] (c) The pre-forging is cooled to T 323 = Tempering at 130℃, tempering time t 323 =1h;

[0187] (d) The pre-forging is heated to T 324 =504℃ and keep warm, holding time t 324 =2h and then oil cool.

[0188] Example 9

[0189] S1. Material preparation: prepare high-purity raw materials according to the following element ratios by mass percentage: C: 1.10%, Cr: 14.00%, Mo: 3.75%, V: 1.10%, Si: 0.20%, Mn: 0.30%, and the balance is Fe;

[0190] S2. Smelting and pouring: Use vacuum induction furnace + vacuum consumable furnace to smelt and pour the raw materials to form steel ingots;

[0191] Specifically, according to the alloy composition ratio of S1, the main alloy elements of Fe, Cr, Mo, and V are added to a vacuum induction furnace, vacuumed for 5 minutes (vacuum degree ≤ 5Pa), electro-melted, and refined for 45 minutes. Si, C, and Mn are added to the vacuum induction furnace for deoxidation; casting is performed to form an electrode rod, and the electrode rod is hood-cooled for 48 hours; the electrode rod is used as a raw material, and a vacuum consumable furnace is used for further smelting and casting. The melting rate of the vacuum consumable furnace is controlled at 8kg / min, and the vacuum degree is ≤ 0.5Pa to obtain a vacuum consumable steel ingot. The vacuum consumable steel ingot is pit-cooled for 48 hours, and after leaving the pit, it is promptly red-sent for annealing and peeling and finishing to obtain a vacuum consumable steel ingot;

[0192] S3, forging;

[0193] S30, heat treatment before forging;

[0194] The pre-forging heat treatment comprises:

[0195] S300, preheating: heat the steel ingot to T 300 =750℃ and keep warm, holding time t 300 =1.0min×D; D is the diameter of the steel ingot, in mm;

[0196] S301, high temperature diffusion: heat the steel ingot to T 301 = 1200℃ and keep warm, holding time t 301 =15h;

[0197] S302, low temperature uniform heating: cool the steel ingot to T 302 = 1000℃ and keep warm, holding time t 302=3h;

[0198] S303, eutectic carbide decomposition: the ingot is heated to T 303 = 1160℃ and keep warm, holding time t 303 =2h.

[0199] S31. Upsetting and drawing: First, upset the steel ingot to 1 / 2 of the original height and then draw it to obtain the billet after billeting. Controlled forging and controlled cooling: Forge the billet after billeting, keep the forging temperature between 950-1050℃, and the final forging temperature is not less than 900℃. After forging, send it to the annealing furnace for annealing.

[0200] S32, microstructure refinement heat treatment;

[0201] The structure refinement heat treatment comprises the following steps:

[0202] (a) Preheat to T 321 = 900℃ and keep warm for t 321 =1.0min×D; D is the pre-forging diameter, in mm;

[0203] (b) Heating to T 322 = 1120℃ and keep warm, holding time t 322 =1h and then oil cooling;

[0204] (c) Cool down to T 323 =150℃ for tempering, tempering time t 323 =1h;

[0205] (d) Heating to T 324 =524℃ and keep warm, holding time t 324 =2h and then oil cool.

[0206] S4, heat treatment after forging;

[0207] S41, annealing; the pre-forged parts are annealed at a temperature T 411 ≤600℃ loading furnace for protection; austenitization: heat the pre-forging to T 412 = 890℃ and keep warm, holding time t 412 = 2h; Isothermal spheroidization: The pre-forged piece is cooled at a rate of CR 4a =90℃ / h down to T 413a =700℃ and keep warm, holding time t 413a = 12h, then cool down at a rate of CR 4b =30℃ / h down to T 413b =530℃ and then air-cooled;

[0208] S42, quenching: heat the pre-forging to the quenching temperature T 42 = 1120℃ and keep warm, holding time t42 For 60min, then oil cool;

[0209] S43, low temperature tempering: cool the pre-forging to T 43 = 150℃ and keep warm, holding time t 43 = 60min, then air cool.

[0210] S44, low temperature treatment: cool the pre-forging to T 44 =-73℃ and keep t 44 = 60min, then air cool;

[0211] S45, high temperature tempering: heat the pre-forging to temperature T 45 =510°C and tempered twice to obtain the bearing steel.

[0212] Table 1: High temperature hardness of bearing steel obtained in Examples 1-9

[0213]

[0214]

[0215] Table 2: Wear resistance of bearing steel obtained in Examples 1-9

[0216]

[0217] It can be seen from Table 1 and Table 2 that, while keeping the alloy composition unchanged (i.e., basically the same as Example 1), by adopting the preparation method of the present invention and its preferred implementation mode, the comprehensive properties of the bearing steel, including high temperature hardness and wear resistance, can be significantly improved. For example, the high temperature hardness at 250°C is increased from HRC59.0 to 61.8, the high temperature hardness at 350°C is increased from HRC58.0 to 61.6, the high temperature hardness at 400°C is increased from HRC57.8 to 60.2, the high temperature hardness at 450°C is increased from HRC52.9 to 58.6, and the high temperature hardness at 550°C is increased from HRC29.5 to 38.3; the relative wear resistance measured by the pin-disc wear test is increased from 1.085 to 1.122, and the average weight loss measured by the ball-block wear test is reduced from 0.23 mg to 0.16 mg.

[0218] Examples 10-16

[0219] The difference between Examples 10-16 and Example 2 lies in the target alloy chemical composition requirements in step S1, and the remaining steps and parameters are basically the same as those in Example 2. The Mg element in Example 16 is introduced into the alloy in the form of an alloy of MgNi during smelting, and the amount of MgNi added is 0.01%. Table 3 shows the chemical composition of the steel ingots prepared according to the alloy element composition requirements of each example and obtained through step S2.

[0220] Table 3: Chemical composition of bearing steels of Examples 2 and 10-16 (%)

[0221]

[0222] Table 4: High temperature hardness of bearing steel obtained in Examples 2, 10-16 under the same preparation process

[0223]

[0224] Table 5: Wear resistance of bearing steels obtained in Examples 2, 10-16 under the same preparation process

[0225]

[0226] It can be seen from Tables 4 and 5 that by further optimizing the alloy composition and content, compared with Example 2, Examples 10-16 obtain better high temperature hardness and wear resistance; specifically, the hardness HRC value at 250-550°C increases, the relative wear resistance measured by the pin-disc wear test increases, and the average weight loss measured by the ball-block wear test decreases.

[0227] Comparative Example 1

[0228] The existing 8Cr4Mo4V bearing steel, by mass percentage, has the following main chemical components: C: 0.75-0.85%; Cr: 3.75-6.00%; Mo: 4.00-4.50%; V: 0.30-1.10%, Mn≤0.40%, Si≤0.35%, Ni: 0.25~0.35%, and the balance is Fe.

[0229] Comparative Example 2

[0230] The existing G102Cr18Mo bearing steel has the following main chemical components by mass percentage: C: 0.95-1.1%; Cr: 16.0-18.0%; Mo: 0.4-0.7%; Mn≤0.80%, Si≤0.80%, and the balance is Fe.

[0231] Comparative Example 3

[0232] The metallic chromium, metallic molybdenum, ferrovanadium, ferrosilicon, metallic manganese, ferrochrome nitride and raw steel (smelted and purified by EAF+LF+VOD) are prepared according to the composition of the obtained steel ingot containing C: 1.4%, Si: 0.4%, Mn: 0.3%, P: ≤ 0.015%, S: ≤ 0.010%, Cr: 15.5%, Mo: 4.2%, V: 1.4%, N: 0.03%. Except for ferrochrome nitride, metallic chromium and metallic manganese, all the raw materials are reserved. The other raw materials are added into a vacuum induction furnace and melted for 7 hours at a vacuum degree of 5Pa and an electric power of 800KW. In the first 10 minutes, since the vacuum degree is higher than 5Pa, the electric power is maintained at 300KW, and the temperature of the fully molten steel is 1550℃. Then, under industrial frequency stirring, the vacuum degree is controlled to 2Pa and the electric power is kept at 1500KW. The refining treatment is carried out at a rate of 400KW for 30min; then, sampling and analysis are carried out, and the reserved metal chromium is used for sample adjustment until the composition of the molten steel meets the requirements, and then metal manganese and ferrochromium nitride are added under stirring with argon gas to make the manganese and N contents in the molten steel meet the target contents; then the molten steel is cast into a steel ingot mold with a diameter of 410mm at a steel tapping temperature of 1560℃ and a steel tapping speed of 400kg / min, and the remaining 3 weight% of the molten steel is used to feed the steel ingot in the steel ingot mold; the steel ingot after shrinkage is cooled to 1200℃ at a speed of 25℃ / min and then broken, and then cooled for 3h until the ingot temperature is less than 800℃ and then demolded, and then put into the furnace for annealing, the annealing temperature is 870℃, and after keeping warm for 20h, it is slowly cooled to room temperature at a speed of not more than 50℃ / h to obtain an electrode for a vacuum consumable furnace.

[0233] The poorly compensated part of the obtained electrode is cut off and its surface is polished. Then it is used as the base material of the vacuum consumable furnace for remelting. The remelting conditions are: current setting value: 6700A, voltage setting value: 23.7V, melting speed setting value: 3.5kg / min, droplet short circuit time setting value: 0.25s, droplet level setting value: 8 levels, helium pressure setting value: 0Pa when the ingot weight in the crystallizer is less than 200kg, 250Pa when the ingot weight is 200-700kg, 450Pa when the ingot weight is 700-1500kg, until the ingot size is The filling is stopped, and the ingot is cooled for 3 hours until the ingot temperature is less than 800℃, then demoulded and put into the furnace for annealing at 850℃. After keeping warm for more than 15 hours, it is slowly cooled to room temperature at a speed of no more than 50℃ / h.

[0234] The air-cooled and polished steel ingot was evenly heated under the following conditions: first heated to 1150°C at a heating rate of 1.3°C / min, kept warm for 4 hours, and then sent to a 4500t press for upsetting. During upsetting, the ingot height was pressed down by 400mm, the starting upsetting temperature was 1080°C, the upsetting time was 10min, and the ingot was returned to the furnace for reheating at 1140°C for 2.5h. It was then sent to a 4500t press for a stretching for 10min, with a single-side reduction of 20mm, a starting stretching temperature of 1070°C, and a final forging temperature of 930°C until the diameter was 380mm. It was returned to the furnace for reheating at 1140°C for 2.5h, and then sent to a 4500t press for a stretching for 10min, with a single-side reduction of 30mm, a starting stretching temperature of 1070°C, and a final forging temperature of The steel is sent to a 4500t press for a drawing time of 10 minutes, with a single-sided reduction of 35mm, a starting drawing temperature of 1060℃, and a final forging temperature of 920℃, to a diameter of 270mm, and is returned to the furnace for a drawing time of 10 minutes at 1130℃ for 2.0h, and is sent to a 4500t press for a drawing time of 10 minutes, with a single-sided reduction of 40mm, a starting drawing temperature of 1060℃, and a final forging temperature of 910℃, to a diameter of 190mm, and is returned to the furnace for a drawing time of 15 minutes at 1130℃ for 2.0h, and is sent to a 1600t press (diameter forging machine) for a drawing time of 15 minutes, a starting drawing temperature of 1060℃, and a final forging temperature of 910℃, to a diameter of 100mm. Then it is placed in a 400-600℃ holding furnace for 3-5 hours, and then heated to 850℃. After being kept for more than 15 hours, it is slowly cooled to room temperature at a rate of no more than 50℃ / h to obtain a high-temperature stainless bearing steel Cr15Mo5V steel rod with a diameter of 100mm.

[0235] Comparative Example 4

[0236] Metallic chromium, metallic molybdenum, ferrovanadium, ferrosilicon, metallic manganese, ferrochrome nitride and raw steel (smelted and purified by EAF+LF+VOD) are prepared according to the following ingredients: C: 1.3%, Si: 0.4%, Mn: 0.3%, P: ≤ 0.015%, S: ≤ 0.010%, Cr: 15.5%, Mo: 4.2%, V: 1.4%, N: 0.03% in the obtained steel ingot. Except for ferrochrome nitride, metallic chromium and metallic manganese, all the other raw materials are reserved. The other raw materials are added into a vacuum induction furnace. The melting treatment is carried out for 7 hours at a vacuum degree of 5Pa and an electric power of 800KW. In the first 10 minutes, the vacuum degree is higher than 5Pa, the electric power is maintained at 300KW, and the temperature of the fully molten steel is 1550℃. Then, the vacuum degree is controlled to 2Pa, 800KW and 1500℃ under industrial frequency stirring. The electric power is 400KW for refining treatment for 30min; then, sampling and analysis are carried out, and the reserved metal chromium is used for sample adjustment until the composition of the molten steel meets the requirements, and then metal manganese and ferrochromium nitride are added under stirring with argon gas to make the manganese and N contents in the molten steel meet the target contents; then the molten steel is cast into a steel ingot mold with a diameter of 410mm at a steel tapping temperature of 1560℃ and a steel tapping speed of 400kg / min, and the remaining 3 weight% of the molten steel is used to feed the steel ingot in the steel ingot mold; the steel ingot after shrinkage feeding is cooled to 1200℃ at a speed of 25℃ / min, and then broken, and then cooled for 3h until the ingot temperature is less than 800℃, and then demolded, and then put into the furnace for annealing, the annealing temperature is 880℃, and after keeping warm for 15h, it is slowly cooled to room temperature at a speed of not more than 50℃ / h to obtain an electrode for use as a vacuum consumable furnace.

[0237] The poorly compensated part of the obtained electrode is cut off and its surface is polished. Then it is used as the base material of the vacuum consumable furnace for remelting. The remelting conditions are: current setting value: 6500A, voltage setting value: 23.9V, melting speed setting value: 3.7kg / min, droplet short circuit time setting value: 0.27s, droplet level setting value: 8 levels, helium pressure setting value: 0Pa when the ingot weight in the crystallizer is less than 200kg, 200Pa when the ingot weight is 200-700kg, 400Pa when the ingot weight is 700-1500kg, until the ingot size is The filling is stopped, and the ingot is cooled for 3 hours until the ingot temperature is less than 850℃, then demoulded and put into the furnace for annealing at 870℃. After keeping warm for more than 15 hours, it is slowly cooled to room temperature at a speed of no more than 50℃ / h.

[0238] The air-cooled and polished steel ingot was evenly heated. The evenly heated conditions were as follows: first, it was heated to 1150°C at a heating rate of 1.3°C / min, kept warm for 4 hours, and then sent to a 4500t press for upsetting. During upsetting, the ingot height was pressed down by 400mm, the starting upsetting temperature was 1080°C, the upsetting time was 10min, and it was returned to the furnace and reheated at 1150°C for 2.5h. It was sent to a 4500t press for a stretching for 10min, with a single-side reduction of 30mm, the starting stretching temperature was 1070°C, and the final forging temperature was 930°C. When the diameter was 380mm, it was returned to the furnace and reheated at 1150°C for 2.5h. It was sent to a 4500t press for a stretching for 10min, with a single-side reduction of 30mm, the starting stretching temperature was 1070°C, and the final forging temperature was 930°C. The temperature is 930℃, to a diameter of 320mm, and then it is returned to the furnace and heated at 1150℃ for 2.5h. It is then sent to a 4500t press for a drawing for 10min, with a single-sided reduction of 30mm. The starting drawing temperature is 1060℃, and the final forging temperature is 920℃, to a diameter of 270mm, and then it is returned to the furnace and heated at 1150℃ for 2.0h. It is then sent to a 4500t press for a drawing for 10min, with a single-sided reduction of 30mm. The starting drawing temperature is 1060℃, and the final forging temperature is 910℃, to a diameter of 190mm, and then it is returned to the furnace and heated at 1140℃ for 2.0h. It is then sent to a 1600t press (diameter forging machine) for a drawing for 15min, with a starting drawing temperature of 1060℃, and a final forging temperature of 910℃, to a diameter of 100mm. Then it is placed in a 400-600℃ holding furnace for 3-5 hours, and then heated to 880℃. After being kept for more than 15 hours, it is slowly cooled to room temperature at a rate of no more than 50℃ / h to obtain a high-temperature stainless bearing steel Cr15Mo5V steel rod with a diameter of 100mm.

[0239] Comparative Example 5

[0240] The difference between this comparative example and comparative example 3 lies in the alloy composition in step S1. The composition of the target alloy in this comparative example includes: C: 1.1%, Si: 0.2%, Mn: 0.3%, P: ≤ 0.008%, S: ≤ 0.002%, Cr: 14.0%, Mo: 3.75%, V: 1.1%, N: ≤ 0.004%, Cu ≤ 0.20%, Ni ≤ 0.25%, O ≤ 0.0015%, and the balance is Fe.

[0241] Comparative Example 6

[0242] The difference between this comparative example and comparative example 4 lies in the alloy composition in step S1. The composition of the target alloy in this comparative example includes C: 1.2%, Si: 0.4%, Mn: 0.6%, P: ≤ 0.008%, S: ≤ 0.002%, Cr: 14.5%, Mo: 3.85%, V: 1.15%, N: ≤ 0.004%, Cu ≤ 0.20%, Ni ≤ 0.25%, O ≤ 0.0015%, and the balance is Fe.

[0243] Table 6: Comparison of hardness and wear resistance of Example 2 and Comparative Example 1-2

[0244]

[0245] Table 7: Comparison of corrosion resistance of Example 2 and Comparative Examples 1-2

[0246]

[0247]

[0248] It can be seen from Tables 6 and 7 that the hardness, wear resistance and corrosion resistance of Example 2 of the present invention are better than those of Comparative Examples 1 and 2.

[0249] By comparison, the embodiments of the present invention are significantly better than comparative examples 3 and 4 in terms of comprehensive performance in terms of temperature resistance, hardness, wear resistance, corrosion resistance, and life. Comparative examples 5-6 have been significantly improved in comprehensive performance (temperature resistance, hardness, wear resistance, corrosion resistance, and life) compared with comparative examples 3-4 by virtue of further optimization of the alloy composition disclosed in the present invention (the composition of comparative examples 5-6 is basically the same as that of embodiments 2 and 10 of the present invention). However, since the preparation method of comparative examples 5-6, especially the forging and heat treatment processes, do not conform to the preparation method disclosed in the present invention, the comprehensive performance of comparative examples 5-6 is still significantly lower than that of the bearing steel obtained in embodiments 2 and 10 of the present invention.

[0250] In addition, the impact toughness and fatigue properties of the bearing steel obtained in the embodiment of the present invention can meet the use requirements of high-end equipment bearings in practical applications. For example, the impact toughness can reach a level comparable to that of Comparative Examples 1 and 2.

[0251] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing stainless bearing steel, characterized in that: The following steps are involved: S1. Material preparation: selecting raw materials according to the composition requirements of the target alloy; the target alloy is high-carbon, high-chromium, molybdenum, and vanadium alloy steel; S2. Smelting and pouring: smelting and pouring the raw materials to form steel ingots; S3, forging: through forging treatment, the steel ingot is processed into a pre-forged part; S4, post-forging heat treatment: the pre-forged parts are subjected to heat treatment processes including annealing, quenching, and high-temperature tempering to obtain the bearing steel; wherein the quenching temperature T 42 = 1100-1150°C, the high temperature tempering temperature T 45 =450℃~574℃.

2. The preparation method according to claim 1, characterized in that: In step S4, between the quenching and high temperature tempering, a low temperature treatment is also included, and the temperature of the low temperature treatment is T 44 =-68℃~-78℃.

3. The preparation method according to claim 2, characterized in that: The quenching and low temperature treatment also include low temperature tempering, the temperature of the low temperature tempering is T 43 =100~200℃.

4. The preparation method according to claim 1, characterized in that: In step S4, the main steps of annealing include: annealing the pre-forged piece at a temperature T 411 ≤600℃ furnace loading, austenitizing and isothermal spheroidizing.

5. The preparation method according to claim 4, characterized in that: The austenitizing temperature T 412 =870-910℃.

6. The preparation method according to claim 5, characterized in that: The main steps of the isothermal spheroidization include: 4a ≤90℃ / h down to T 413a =680-720℃, and then cool down at a rate of CR 4b ≤30℃ / h down to T 413b =510-550℃ then air-cooled.

7. The preparation method according to claim 1, characterized in that: In step S3, before the forging process, a pre-forging heat treatment is also included; the main steps of the pre-forging heat treatment include: high-temperature diffusion, low-temperature soaking, and eutectic carbide decomposition; Wherein, the high temperature diffusion temperature T 301 = 1180-1220°C, the temperature of the low temperature soaking is T 302 =980-1020℃, the temperature of decomposition of eutectic carbide is T 303 =1140-1180℃.

8. The preparation method according to claim 7, characterized in that: Before the high temperature diffusion, preheating is also included, and the preheating temperature T 300 =700-800℃.

9. The preparation method according to claim 1, characterized in that: In step S3, after the forging treatment, a microstructure refinement heat treatment is also included; the main steps of the microstructure refinement heat treatment include: (a) preheating to 880-920°C and keeping warm; (b) heating to 1100-1140°C and keeping warm, and then oil cooling; (c) cooling to 130-170°C for tempering; (d) heating to 504-544°C and keeping warm, and then oil cooling.

10. The preparation method according to claim 1, characterized in that: In step S1, the target alloy composition requirements are C: 1.0-1.5%, Cr: 14.00-16.00%, Mo: 3.5-4.5%, N: ≤0.03%, V: 1.0-1.5%, Si: 0.20-0.50%, Mn: 0.1-0.6%, P≤0.015%, S≤0.010%, and the remainder is Fe and unavoidable impurities.

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