A kind of high temperature resistant and wear resistant stainless bearing steel and preparation method thereof

Abstract

The present invention relates to a heat-resistant and highly wear-resistant stainless bearing steel and a preparation method thereof, which belongs to the field of alloy steel and solves the problem that the bearing steel and the bearing steel obtained by the preparation method in the prior art have insufficient comprehensive properties such as high-temperature hardness, wear resistance and corrosion resistance. A heat-resistant and highly wear-resistant stainless bearing steel comprises 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 remainder is Fe and unavoidable impurities. The present invention realizes that the comprehensive performance of the bearing steel in high-temperature hardness, wear resistance, corrosion resistance and other properties is superior to the existing bearing steel.

Description

Technical Field

[0001] The invention relates to the technical field of alloy steels, and in particular to a heat-resistant and highly wear-resistant stainless bearing steel and a preparation method thereof. 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] In response to the above problems, it is urgent to develop a new type of high-temperature stainless bearing steel and its preparation method to obtain ultra-high cleanliness and high uniformity high-temperature resistant, high-wear resistant and corrosion-resistant bearing materials to meet the ever-increasing requirements for the temperature resistance, wear resistance and corrosion resistance of high-end equipment bearings. Summary of the invention

[0006] In view of the above analysis, the present invention aims to provide a heat-resistant and highly wear-resistant stainless bearing steel and a preparation method thereof, so as to solve the problem that the bearing steel and the bearing steel obtained by the preparation method in the prior art have insufficient comprehensive properties such as high-temperature hardness, wear resistance and corrosion resistance.

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

[0008] The invention provides a heat-resistant and highly wear-resistant stainless bearing steel. The chemical composition of the bearing steel comprises, by mass percentage, 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 inevitable impurities.

[0009] Furthermore, the contents of the four elements P, S, O and N must satisfy: P+S+O+N≤0.010%.

[0010] Furthermore, the contents of the three elements Cr, Mo and V must satisfy: Cr+Mo+V-7.5%≥12%.

[0011] Furthermore, 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 addition amount of the MgNi alloy is 0.01-0.03% based on the mass of the bearing steel.

[0012] Furthermore, the carbon equivalent Ceq of the bearing steel is 5.15-5.35, Ceq=C+(Cr+Mo+V) / 5+Mn / 6+Si / 15.

[0013] Furthermore, the Cr, Mo, and V satisfy the relationship: I=0.6×Cr+0.5×Mo+2.5×V, and 13.9<I<14.3.

[0014] The present invention also provides a method for preparing the bearing steel as described above, comprising the following steps:

[0015] S1. Material preparation: Select raw materials according to the composition requirements of the target alloy;

[0016] S2. Smelting and pouring: smelting and pouring the raw materials to form steel ingots;

[0017] S3, forging: through forging treatment, the steel ingot is processed into a pre-forged part;

[0018] S4, post-forging heat treatment: the pre-forged parts obtained by forging are subjected to heat treatment processes including annealing, quenching, low-temperature treatment and high-temperature tempering to obtain the bearing steel; wherein the quenching temperature is 1100-1500°C, and the low-temperature treatment temperature is -68~-78°C.

[0019] Furthermore, in step S4, the high temperature tempering temperature is 450°C to 574°C.

[0020] Further, in step S4, the number of high temperature tempering is ≥2 times.

[0021] Furthermore, in step S4, between the quenching and the low temperature treatment, low temperature tempering is also included, and the temperature of the low temperature tempering is 100-200°C.

[0022] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0023] (1) The present invention ensures the excellent performance of the bearing steel material in terms of high temperature hardness, wear resistance and corrosion resistance by rationally selecting the main alloying elements of the bearing steel and controlling their content within an appropriate range. At the same time, by strictly controlling the content of impurity elements at a low level, the strength and toughness of the bearing steel material are further improved, thereby improving its fatigue resistance. Compared with several typical types of existing bearing steels: high carbon chromium type, stainless type, high temperature type, and carburized type, the present invention optimizes the chemical composition to achieve a synergistic effect of various alloying elements, thereby showing significant superiority over existing bearing steels in terms of the comprehensive performance of high temperature hardness, wear resistance, corrosion resistance and fatigue resistance.

[0024] (2) In some preferred embodiments, by further controlling the upper limit of the content of impurity elements, the lower limit of the content of Cr, Mo, and V, adding Mg element and controlling its content range, the range of carbon equivalent, and Cr, Mo, and V satisfying a certain relationship, the comprehensive performance of the bearing steel material in terms of high temperature hardness, wear resistance, corrosion resistance, fatigue resistance, etc. can be further improved.

[0025] (3) Based on the advantages of the alloy chemical composition in the present invention in improving the comprehensive performance, the present invention also provides a corresponding bearing steel preparation method to ensure that its advantages in comprehensive performance can be realized and maintained in the final product, thereby providing solid process support for the application of bearing steel. In particular, for post-forging heat treatment, a quenching and tempering process including "low temperature treatment" is adopted to decompose the residual austenite, which has a positive effect on improving the comprehensive performance of bearing steel and improving dimensional stability by optimizing the microstructure.

[0026] (4) In some preferred embodiments, for post-forging heat treatment, the comprehensive performance of the bearing steel can be further improved by controlling the temperature and number of high-temperature tempering. By adding low-temperature tempering, thermal stress can be effectively removed and the risk of stress cracking of the bearing product can be reduced, thereby further improving the comprehensive performance of the bearing product.

[0027] 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

[0028] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. In the entire drawings, the same reference symbols represent the same components;

[0029] Figure 1 It is a process curve diagram of heat treatment before forging of a preparation example of an embodiment of the present invention;

[0030] Figure 2 It is a graph of annealing process in post-forging heat treatment of a preparation example of an embodiment of the present invention;

[0031] Figure 3 The surface corrosion morphologies of the test steels of the preparation examples and comparative examples of the embodiments of the present invention under different neutral salt spray corrosion times; (a) to (c): Preparation Example 1-1; (d) to (f): Comparative Example 1. DETAILED DESCRIPTION

[0032] 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.

[0033] Under the background of existing technology, the comprehensive performance of traditional bearing steel in terms of high temperature hardness, wear resistance, corrosion resistance, fatigue resistance, etc. 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 design of alloy composition and preparation process, especially in the heat treatment process. In view of the problem that the overall performance of existing bearing steel materials is poor in practical applications, especially in high temperature / high load / corrosive environments, the inventors started from the two aspects of alloy composition design and preparation process, and proposed a series of innovative optimization measures, aiming to improve the comprehensive performance of bearing steel materials in various working conditions, especially under more harsh conditions.

[0034] In the first aspect, the present invention provides a heat-resistant and highly wear-resistant stainless bearing steel. The chemical composition of the bearing steel includes, by mass percentage, 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 remainder is Fe and unavoidable impurities.

[0035] The design idea of ​​the chemical composition of the bearing steel of the present invention is: through the alloying design of C, Cr, Mo and V, the main alloying elements of the steel of the present invention 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.

[0036] Specifically, the functions and proportions of the elements of the present invention are as follows:

[0037] 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%.

[0038] 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%.

[0039] 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%~4.25%; for example, the Mo content is 3.80%, 3.85%, 3.90%, 3.95%, 4.00%, 4.05%, 4.10%, 4.15%, 4.20%; further, the Mo content is 4.00%~4.25%; further, the Mo content is 4.00%~4.18%.

[0040] 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%.

[0041] 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%; for example, N≤0.003%, N≤0.002%, N≤0.0015%, and N≤0.001%.

[0042] Si and Mn: Based on the above main element designs such as heat resistance, corrosion resistance, and high hardness, Si and Mn elements can be appropriately added to further improve the hardness and hardenability of steel, but excessive Si and Mn content will affect the heat resistance and corrosion resistance, so Si: 0.20~0.40%, Mn: 0.30~0.60% are required. 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%.

[0043] At the same time, in order to ensure the hot and cold processing and fatigue properties of steel, the 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%.

[0044] Compared with the prior art, the present invention ensures the excellent performance of the bearing steel material in terms of high temperature hardness, wear resistance and corrosion resistance by rationally selecting the main alloying elements of the bearing steel and controlling their content within an appropriate range. At the same time, by strictly controlling the content of impurity elements at a low level, the strength and toughness of the bearing steel material is further improved, thereby improving its fatigue resistance. Compared with several typical types of existing bearing steels: high carbon chromium type, stainless type, high temperature type, and carburized type, the present invention optimizes the chemical composition to achieve a synergistic effect of various alloying elements, thereby showing significant superiority over existing bearing steels in terms of the comprehensive performance of high temperature hardness, wear resistance, corrosion resistance and fatigue resistance. Specific optimization measures include:

[0045] (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.

[0046] (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.

[0047] (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 can exhibit 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.

[0048] 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%.

[0049] 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.

[0050] 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 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.

[0051] 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.

[0052] 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.

[0053] 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 balance is Fe and unavoidable impurities.

[0054] The structure of the bearing steel of the present invention is martensite matrix+residual carbide+residual austenite; the maximum size of the carbide is not greater than 35 μm, and the grain size is not less than 7 levels.

[0055] The performance parameters of the bearing steel of 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 area exists after 96 hours of neutral salt spray test, which is better than the existing G102Cr18Mo bearing steel.

[0056] In a second aspect, the present invention further provides a method for preparing the bearing steel as described above, comprising the following steps:

[0057] S1. Material preparation: Select raw materials according to the composition requirements of the target alloy;

[0058] Exemplarily, the raw material is a high-purity metal or alloy including Fe, Cr, Mo, V, C, Si, and Mn;

[0059] S2. Smelting and pouring: smelting and pouring the raw materials to form steel ingots;

[0060] S3, forging: through forging treatment, the steel ingot is processed into a pre-forged part;

[0061] S4, post-forging heat treatment: performing heat treatment steps including annealing, quenching, low temperature treatment, and high temperature tempering on the pre-forged parts to obtain the bearing steel.

[0062] Based on the advantages of the alloy chemical composition in the present invention in improving the comprehensive performance, the present invention also provides a corresponding bearing steel preparation method as above, ensuring that its advantages in comprehensive performance can be realized and maintained in the final product, thereby providing solid process support for the application of bearing steel. In particular, for post-forging heat treatment, a quenching and tempering process including "low temperature treatment" is adopted to decompose the residual austenite, and by optimizing the microstructure, it has a positive effect on improving the comprehensive performance of bearing steel in terms of high temperature hardness, wear resistance, corrosion resistance, fatigue resistance, etc., as well as improving dimensional stability.

[0063] Specifically, step S3 includes the following steps:

[0064] S30, pre-forging heat treatment; the main steps of the pre-forging heat treatment include: preheating, high-temperature diffusion, low-temperature soaking, and eutectic carbide decomposition;

[0065] S31, upsetting and drawing the blank and controlled forging and controlled cooling;

[0066] S32: Heat treatment for microstructure refinement.

[0067] 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 decomposition temperature of the eutectic carbide is T 303 =1140-1180℃.

[0068] In some embodiments, the pre-forging heat treatment in step S30 specifically includes the following steps:

[0069] 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 diameter of the steel ingot, in mm; more preferably, T 300 =730-770℃, t 300 = (0.9-1.1)min×D.

[0070] S301, high temperature diffusion: heat the steel ingot to T 301 = 1180-1220℃ and keep warm; preferably, the holding time t 301 ≥15h; for example: t 301 15h~20h.

[0071] S302, low temperature uniform heating: cool the steel ingot to T 302 =980-1020℃ and keep warm; preferably, the holding time t 302 ≥3h; for example: t 302 =3h~6h.

[0072] S303, eutectic carbide decomposition: the ingot is heated to T 303 = 1140-1180℃ and keep warm; preferably, the holding time t 303 ≥ 2 hours; for example, t 303 =2-4h.

[0073] 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;

[0074] (1) The function of step S300 includes reducing thermal stress and preventing cracking of the steel ingot. The principle is that 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.

[0075] (2) The functions of step S301 include: improving the strength, 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.

[0076] (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.

[0077] (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.

[0078] In some embodiments, the specific steps of step S31 include:

[0079] 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;

[0080] 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 hot forging is sent to the annealing furnace for annealing to obtain a pre-forged piece. More preferably, T 312 =980-1020℃.

[0081] In some embodiments, the main steps of the microstructure refinement heat treatment in step S32 include the following steps (a) to (b) in sequence;

[0082] (a) Preheat to 880~920℃ and keep warm;

[0083] (b) Heating to 1100~1140℃ and keeping warm, then oil cooling;

[0084] (c) Cooling to 130~170℃ for tempering;

[0085] (d) Raise the temperature to 504~544℃ and keep it warm, then oil cool.

[0086] In some embodiments, step (a): preheating the pre-forging to T 321 =880~920℃ and keep warm, the holding time is 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.

[0087] In some embodiments, step (b): heating the pre-forging to T 322 =1100~1140℃ and keep warm, holding time t 322 ≥1h, then oil cooling; preferably, T 322 =1110~1130℃,t 322 1-3h.

[0088] In some embodiments, step (c): cooling the pre-forging to T 323 =130~170℃ for tempering, tempering time t 323 ≥1h; preferably, T 323 =140~160℃, t 323 1-3h.

[0089] 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.

[0090] Preferably, before step (d), steps (b) and (c) are repeated 1-2 times.

[0091] Preferably, after step (d), step (d) is repeated 1-4 times.

[0092] 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 microstructures can be further refined, and the inclusions, carbides, and matrix microstructures 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.

[0093] Specifically, step S4 includes the following steps:

[0094] S41, annealing;

[0095] S42, quenching; the quenching temperature is 1100-1150°C;

[0096] S43, low temperature tempering; the temperature of the low temperature tempering is 100~200℃;

[0097] S44, low temperature treatment; the temperature of the low temperature treatment is -68~-78°C;

[0098] S45, high temperature tempering; the temperature of high temperature tempering is 450℃~574℃;

[0099] In some embodiments, in step S41, the main steps of annealing include:

[0100] S411, preheating: pre-forging at temperature T 411 ≤600℃ furnace loading and protection; illustratively, T 411 =450℃, 500℃, 550℃.

[0101] S412, austenitizing: the austenitizing temperature T 412 = 870-910 ℃; the main steps of austenitization include: heating the pre-forged piece to T 412 =870-910℃ and keep warm; preferably, the holding time t 412 ≥2h; further, t 412 2h~4h.

[0102] 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, lower to T 413a And keep warm, the insulation time t 413a ≥12h; further, the insulation time t 413a =12-14h.

[0103] 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.

[0104] (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.

[0105] (2) The functions of austenitization in step S412 and isothermal spheroidization in step S413 include: ensuring the annealing hardness ≤ 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.

[0106] 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℃ and keep warm, then oil cool; preferably, the holding time t 42 ≥60min; further, T 42 =1110~1130℃, holding time t 42 = 60-90min, more preferably, T 42 =1115~1125℃.

[0107] In some embodiments, the main steps of low temperature tempering in step S43 include: cooling the pre-forged piece to T 43 = 100~200℃ and keep warm, then air cool; preferably, T 43 =130~170℃, holding time t 43 ≥60min; more preferably, T 43 =140~160℃, t 43 =60-90min.

[0108] 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.

[0109] 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.

[0110] 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;

[0111] (1) The function of step S42 includes: ensuring sufficient hardness; the principle is: the carbides are 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.

[0112] (2) The function of step S43 includes: preventing cracks from being generated; the principle is: for the steel ingot described in S2, i.e., high-carbon, high-chromium, molybdenum, and vanadium alloy steel, its thermal conductivity is poor, and the thermal stress is large after oil cooling, and the thermal stress is removed by low-temperature tempering.

[0113] (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.

[0114] (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.

[0115] 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.

[0116] In some embodiments, the main steps of step S2 include:

[0117] S21, smelting and casting the raw materials in S1 through a vacuum induction furnace to obtain an electrode rod;

[0118] 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.

[0119] In some embodiments, step S21 specifically includes:

[0120] 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;

[0121] S212, melting stage: electric melting, melting the charge by induction heating in a vacuum environment;

[0122] S213, refining stage; preferably, the vacuum degree is maintained at ≤5Pa, and the refining time is ≥45 minutes;

[0123] 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;

[0124] S215, pouring stage: transferring the molten metal from the vacuum induction furnace to the mold for pouring to form an electrode rod;

[0125] 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.

[0126] 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.

[0127] 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 red-feed annealing and peeling and finishing are carried out in time after leaving the pit. Preferably, the hood cooling or pit cooling time is ≥48h.

[0128] 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:

[0129] (1) Control of P content: including but not limited to vacuum degassing;

[0130] (2) Controlling the S content: including but not limited to, by adding C element in batches during vacuum induction melting, the melt can be desulfurized to a large extent under ultra-high vacuum conditions;

[0131] (3) Controlling the O content: including but not limited to vacuum degassing;

[0132] (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.

[0133] Through the above preparation method, the microstructure of the bearing steel can be further optimized, and the obtained bearing steel has a structure of martensite matrix + residual carbide + residual austenite; the maximum size of the carbide is not greater than 35μm, and the grain size is not less than level 7, thereby further improving the comprehensive performance of the bearing steel.

[0134] The bearing steel obtained by the present invention has excellent comprehensive properties in terms of high-temperature hardness, wear resistance and corrosion resistance, for example: 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 bearing steel.

[0135] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and comparative examples.

[0136] A. Examples 1 to 8

[0137] The present invention provides 8 embodiments of the heat-resistant and wear-resistant stainless bearing steel, and the chemical composition thereof is shown in Table 1; Embodiments 1-8 are prepared according to the mass ratio of the main alloy elements shown in Table 1, and are smelted using a vacuum induction furnace + a vacuum consumable furnace.

[0138] Table 1: Chemical composition of bearing steel of Examples 1-8 / %

[0139]

[0140] B. Preparation examples of 8 embodiments under the same preparation process (Preparation Examples 1-1 to 8-1)

[0141] The present invention also provides preparation examples 1-1 to 8-1 of the above 8 embodiments, the difference between which is that the alloy composition requirements in step S1 are different, and the remaining steps S2-S5 are basically the same. In particular, in preparation example 8-1 of embodiment 8, 0.01% MgNi (the mass ratio of Mg to Ni is 3:7) is added in step S2; taking embodiment 1 as an example, its preparation example 1-1 includes the following steps:

[0142] 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;

[0143] S2. Smelting and pouring: Use vacuum induction furnace + vacuum consumable furnace to smelt and pour the prepared raw materials to form steel ingots;

[0144] 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;

[0145] S3, forging;

[0146] 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.

[0147] S4, heat treatment after forging;

[0148] (1) Annealing; austenitizing: Heat the pre-forged part 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;

[0149] (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;

[0150] (3) Low temperature treatment: Cool the pre-forged part to T 44 = -68℃ and keep t 44 = 60min, then air cool;

[0151] (4) High temperature tempering: Heat the pre-forging to temperature T 45 =450°C and tempered once to obtain the bearing steel.

[0152] Table 2: High temperature hardness of bearing steel obtained in 8 examples under the same preparation process

[0153]

[0154] Table 3: Wear resistance of bearing steel obtained in 8 examples under the same preparation process

[0155]

[0156] It can be seen from Table 2 and Table 3 that, under the same preparation process, by adopting the alloy composition of the present invention, excellent high temperature hardness and wear resistance can be obtained, for example, high temperature hardness ≥HRC59.0 at 250°C, high temperature hardness ≥HRC58.3 at 350°C, high temperature hardness ≥HRC58.0 at 400°C, high temperature hardness ≥HRC53.7 at 450°C, high temperature hardness ≥HRC30.1 at 550°C, relative wear resistance measured by pin-disc wear test ≥1.09, average weight loss measured by ball-block wear test ≤0.22mg. Based on the alloy composition provided by the present invention, by accurately controlling the compatibility relationship of elements and introducing Mg elements, etc., the high temperature hardness and wear resistance of bearing steel can be further improved.

[0157] C. Preparation examples of Example 1 under different preparation processes (Preparation examples 1-2 to 1-8)

[0158] The present invention also provides preparation examples 1-2 to 1-8 of embodiment 1, the difference between which is that the process conditions of steps S2 to S5 are different.

[0159] Preparation Example 1-2

[0160] The difference between this preparation example and preparation example 1-1 is step S4; the remaining steps and parameters are basically the same as those of preparation example 1-1. Specifically, in step S4, low-temperature tempering is further included between the quenching and low-temperature treatment.

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

[0162] Preparation Example 1-3

[0163] The difference between this preparation example and preparation example 1-2 is step S3; the remaining steps and parameters are basically the same as those of preparation example 1-2. 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 t302 =3h;

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

[0168] Preparation Example 1-4

[0169] The difference between this preparation example and preparation examples 1-3 is step S3; the remaining steps and parameters are basically the same as those of preparation examples 1-3. 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] Preparation Example 1-5

[0176] The difference between this preparation example and preparation example 1-4 is the annealing in step S4; the remaining steps and parameters are basically the same as those of preparation example 1-4;

[0177] Specifically, the annealing in step S4 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] Preparation Example 1-6

[0180] The difference between this preparation example and preparation example 1-5 is the high temperature tempering in step S4. The high temperature tempering times in this preparation example are 2 times; the other steps and parameters are basically the same as those in preparation example 1-5.

[0181] Preparation Example 1-7

[0182] The difference between this preparation example and preparation examples 1-6 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 of embodiments 1-6.

[0183] Specifically, the microstructure refinement heat treatment in this preparation example 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 =130℃ for tempering, 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] Preparation Example 1-8

[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; pouring is performed to form electrode rods, and the electrode rods are hood-cooled for 48 hours; the electrode rods are used as raw materials, and further smelted and poured in a vacuum consumable furnace. 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, heat treatment for microstructure refinement;

[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 t 42 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 4: High temperature hardness of bearing steel obtained under different preparation processes in Example 1

[0213]

[0214] Table 5: Wear resistance of bearing steel obtained under different preparation processes in Example 1

[0215]

[0216] It can be seen from Tables 4 and 5 that, compared with Preparation Example 1-1 of Example 1, while keeping the alloy composition unchanged (i.e., basically the same as Example 1), by adopting the optimization strategy for forging, heat treatment process, etc. in the preparation method disclosed in the present invention, Preparation Examples 1-2 to 1-8 can obtain better high-temperature hardness and wear resistance, which is specifically manifested in an increase in the hardness HRC value at 250-550°C, an increase in the relative wear resistance measured by the pin-disc wear test, and a decrease in the average weight loss measured by the ball-block wear test.

[0217] D. Performance comparison between examples and comparative examples

[0218] Comparative Example 1

[0219] The main chemical components of the existing 8Cr4Mo4V bearing steel, calculated by mass percentage, include: 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.

[0220] Comparative Example 2

[0221] The existing G102Cr18Mo bearing steel, calculated by mass percentage, has the following main chemical components: 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.

[0222] Comparative Example 3

[0223] 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.

[0224] 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 at 406mm, and the ingot is cooled for 3h 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 15h, it is slowly cooled to room temperature at a speed of no more than 50℃ / h.

[0225] 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.

[0226] Comparative Example 4

[0227] 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 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.

[0228] 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 at 406mm, and the ingot is cooled for 3h 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 15h, it is slowly cooled to room temperature at a speed of no more than 50℃ / h.

[0229] 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 steel ingot was pressed down by 400mm in height, 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-sided 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-sided reduction of 30mm, the starting stretching temperature was 1070°C, and the final forging temperature was 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 sent to a 4500t press for a stretching of 10min, with a single-sided pressing amount of 30mm. The starting stretching 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 sent to a 4500t press for a stretching of 10min, with a single-sided pressing amount of 30mm, and the starting stretching 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 sent to a 1600t press (diameter forging machine) for a stretching of 15min, with a starting stretching 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.

[0230] Comparative Example 5

[0231] The difference between this comparative example and preparation example 1-1 lies in the alloy composition in step S1. The composition of the target alloy in this comparative example includes 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%, and the balance is Fe.

[0232] Comparative Example 6

[0233] The difference between this comparative example and preparation example 1-1 lies in the alloy composition in step S1. The composition of the target alloy in this comparative example includes 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%, and the balance is Fe.

[0234] Table 6: Comparison of hardness and wear resistance of Preparation Example 1-1 of Example 1 and Comparative Example 1-2

[0235]

[0236] Table 7: Comparison of corrosion resistance of Preparation Example 1-1 of Example 1 and Comparative Example 1-2

[0237]

[0238] As can be seen from Tables 6 and 7, the hardness, wear resistance and corrosion resistance of Preparation Example 1-1 of Example 1 of the present invention are better than those of Comparative Examples 1 and 2.

[0239] By comparison, the embodiments of the present invention are significantly better than Examples 3 and 4 in terms of comprehensive performance in terms of temperature resistance, hardness, wear resistance, corrosion resistance, and life. Examples 5-6 have significantly improved comprehensive performance (temperature resistance, hardness, wear resistance, corrosion resistance, and life) compared with Examples 3-4 by virtue of the preparation method of the present invention, especially the fine control of the forging and heat treatment processes after smelting and pouring. However, since the alloy composition of Examples 5-6 does not conform to the alloy composition design of the present invention, the comprehensive performance of the bearing steel obtained in Examples 5-6 is still far behind that of the embodiments of the present invention.

[0240] In addition, the impact toughness and fatigue properties of the bearing steel obtained in the embodiments of the present invention and its preparation examples can meet the use requirements of high-end equipment bearings in practical applications. For example, the impact toughness can at least reach a level equivalent to that of comparative examples 1 and 2.

[0241] 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 heat-resistant and highly wear-resistant stainless bearing steel, characterized in that: In terms of mass percentage, the chemical composition of the bearing steel includes 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; the contents of the three elements Cr, Mo, and V must meet the following requirements: Cr+Mo+V-7.5%≥12%; the carbon equivalent Ceq of the bearing steel is 5.15-5.35, Ceq=C+(Cr+Mo+V) / 5+Mn / 6+Si / 15; The method for preparing the bearing steel comprises the following steps: S1. Material preparation: Select raw materials according to the composition requirements of the target alloy; S2. Smelting and pouring: smelting and pouring the raw materials to form steel ingots; S3, forging: The steel ingot is processed into a pre-forged part by forging. Step S3 includes the following steps: S30, pre-forging heat treatment; the main steps of the pre-forging heat treatment include: preheating, high temperature diffusion, low temperature soaking, eutectic carbide decomposition; 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 decomposition temperature of the eutectic carbide is T 303 =1140-1180℃; S31, upsetting and drawing the blank and controlled forging and controlled cooling; S32, microstructure refinement heat treatment; the main steps of microstructure refinement heat treatment include the following steps (a) to (b) in sequence; (a) Preheat to 880~920℃ and keep warm; (b) Heating to 1100~1140℃ and keeping warm, then oil cooling; (c) Cooling to 130~170℃ for tempering; (d) Heating to 504~544℃ and keeping warm, then oil cooling; S4, post-forging heat treatment: the pre-forged parts obtained by forging are subjected to heat treatment processes including annealing, quenching, low-temperature tempering, low-temperature treatment, and high-temperature tempering to obtain the bearing steel; wherein the quenching temperature is 1100-1500°C, and the low-temperature treatment temperature is -68~-78°C; The performance parameters of the bearing steel 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.

2. The bearing steel according to claim 1, characterized in that: The contents of the four elements P, S, O and N must satisfy the following requirement: P+S+O+N≤0.010%.

3. The bearing steel according to claim 1, characterized in that: The chemical composition of the bearing steel also includes: Mg, which is added in the form of MgNi alloy during the preparation process. Based on the mass of the bearing steel, the addition amount of the MgNi alloy is 0.01-0.03%.

4. The bearing steel according to claim 1, characterized in that: The Cr, Mo and V satisfy the relationship: I=0.6×Cr+0.5×Mo+2.5×V, and 13.9<I<14.

3.

5. A method for preparing the bearing steel according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Material preparation: Select raw materials according to the composition requirements of the target alloy; S2. Smelting and pouring: smelting and pouring the raw materials to form steel ingots; S3, forging: The steel ingot is processed into a pre-forged part by forging. Step S3 includes the following steps: S30, pre-forging heat treatment; the main steps of the pre-forging heat treatment include: preheating, high temperature diffusion, low temperature soaking, eutectic carbide decomposition; 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 decomposition temperature of the eutectic carbide is T 303 =1140-1180℃; S31, upsetting and drawing the blank and controlled forging and controlled cooling; S32, microstructure refinement heat treatment; the main steps of microstructure refinement heat treatment include the following steps (a) to (b) in sequence; (a) Preheat to 880~920℃ and keep warm; (b) Heating to 1100~1140℃ and keeping warm, then oil cooling; (c) Cooling to 130~170℃ for tempering; (d) Heating to 504~544℃ and keeping warm, then oil cooling; S4, post-forging heat treatment: the pre-forged parts obtained by forging are subjected to heat treatment processes including annealing, quenching, low-temperature tempering, low-temperature treatment, and high-temperature tempering to obtain the bearing steel; wherein the quenching temperature is 1100-1500°C, and the low-temperature treatment temperature is -68~-78°C.

6. The preparation method according to claim 5, characterized in that: In step S4, the high temperature tempering temperature is 450°C to 574°C.

7. The preparation method according to claim 6, characterized in that: In step S4, the high temperature tempering is performed ≥ 2 times.

8. The preparation method according to claim 5, characterized in that: In step S4, the temperature of the low temperature tempering is 100-200°C.

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