High-hardenability carburizing-free bearing steel and preparation method thereof

Abstract

The invention provides high-hardenability carburizing-free bearing steel and a preparation method thereof, and belongs to the technical field of bearing steel. The high-hardenability carburizing-free bearing steel provided by the invention comprises the following chemical components in percentage by mass: 1.2 to 1.3 percent of C, 0.1 to 0.5 percent of Si, 0.2 to 1.0 percent of Mn, 1.5 to 5.0 percent of Cr, 0.02 to 1.5 percent of Ni, 0.8 to 3.0 percent of Al, 0.01 to 1.5 percent of Mo, 0.01 to 0.3 percent of V, 0.002 to 0.01 percent of Nb, 0.002 to 0.05 percent of Re, 0.001 to 0.02 percent of B, less than or equal to 50ppm of N, less than or equal to 6ppm of O, less than or equal to 0.01 percent of S, less than or equal to 0.01 percent of P and the balance of Fe. Through the microalloying design of Nb and V, the toughness of the material is improved; by adding a proper amount of B and strictly controlling the contents of O and N, the hardenability of the material is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of bearing steel, and particularly relates to a high hardenability carburizing-free bearing steel and a preparation method thereof. BACKGROUND

[0002] New energy electric vehicles are driven by electric motors, and the torque is usually transmitted to the wheels through a speed reduction mechanism driven by the electric motor. Compared with traditional internal combustion engine vehicles, the new energy electric vehicles have a higher transmission ratio of the speed reduction mechanism and a more harsh service environment, and thus require high speed, low noise and long service life of the bearing. In addition, from the perspective of lightweight design, reducing the size of the shaft can achieve lightweight of the vehicle body, but will cause an increase in the speed of the bearing, and the service life of the bearing has become a key factor restricting the lightweight design of the new energy electric vehicles.

[0003] At present, the materials for manufacturing the bearings of new energy electric vehicles mainly include GCr15 and carburized 20CrNiMo steel. In order to improve the wear resistance and contact fatigue life, carburization is usually performed on the basis of 20CrNiMo steel or GCr15 steel. However, there are the following problems in the carburization process of GCr15 bearing steel or 20CrNiMo steel: ①Long-time carburization leads to an increase in energy consumption and cost, and also increases the emission of greenhouse gases during the carburization process; ②The carburization organization is non-uniform, which causes the existence of coarse carbides in the organization, significantly reduces the toughness of the bearing and causes noise; and ③The carbon content is only increased in a certain depth of the surface layer, and the hardenability of the material still mainly depends on the composition of the matrix material, which will cause the problem of insufficient hardenability of the bearing with a thick cross-sectional size, and lead to insufficient service life of the bearing. Therefore, how to improve the bearing steel to improve the toughness and hardenability has become a technical problem to be solved in the field. SUMMARY

[0004] The application aims to provide a high hardenability carburizing-free bearing steel and a preparation method thereof. The bearing steel provided by the application has excellent toughness and hardenability.

[0005] In order to achieve the above-mentioned application purposes, the application provides the following technical solutions: The application provides a high hardenability carburizing-free bearing steel, and the chemical components include, in terms of mass percentage, C 1.2-1.3%, Si 0.1-0.5%, Mn 0.2-1.0%, Cr 1.5-5.0%, Ni 0.02-1.5%, Al 0.8-3.0%, Mo 0.01-1.5%, V 0.01-0.3%, Nb 0.002-0.01%, Re 0.002-0.05%, B 0.001-0.02%, N≤50ppm, O≤6ppm, S≤0.01%, P≤0.01% and the balance of Fe.

[0006] Preferably, the chemical composition comprises, in percentage by mass: C 1.25~1.3%, Si 0.2~0.4%, Mn 0.3~0.9%, Cr 2.0~4.0%, Ni 0.1~1.4%, Al 0.9~2.0%, Mo 0.1~1.4%, V 0.1~0.2%, Nb 0.005~0.01%, Re 0.01~0.04%, B 0.002~0.008%, N≤50ppm, O≤6ppm, S≤0.01%, P≤0.01% and the balance of Fe.

[0007] The application further provides a preparation method of the high hardenability carburizing-free bearing steel. (1) smelting raw materials to obtain an alloy melt; (2) die casting or continuous casting the alloy melt obtained in the step (1) to obtain a casting blank; (3) rolling or forging the casting blank obtained in the step (2) to obtain a blank; (4) heat treating the blank obtained in the step (3) to obtain the high hardenability carburizing-free bearing steel.

[0008] Preferably, the step (3) further comprises heating the casting blank before rolling or forging.

[0009] Preferably, the heating comprises heating to 600℃ for t1, then heating to 900℃ for t2, and then heating to 1200~1250℃ for 1~5h; t1=workpiece thickness (mm)×0.5~1.0min / mm; t2=workpiece thickness (mm)×1.0~1.5min / mm.

[0010] Preferably, the heating rate to 600℃ is ≤1℃ / min, and the heating rate to 900℃ is ≤0.8℃ / min.

[0011] Preferably, the rolling in the step (3) has a rolling start temperature of 1100~1160℃, a rolling end temperature of 850~920℃, a rolling ratio ≥5, and a rolling ratio ≥1.5 in the temperature range of 930~980℃.

[0012] Preferably, the forging in the step (3) has a forging start temperature of 1100~1160℃, a forging end temperature of 850~920℃, and a forging ratio ≥5.

[0013] Preferably, the heat treatment in the step (3) comprises spheroidizing annealing, oil quenching and tempering in sequence.

[0014] Preferably, the spheroidizing annealing is heating from room temperature to 700-720 DEG C for 1-2 hours, then heating to 750-770 DEG C for 0.5-1 hour, then heating to 780-810 DEG C for 6-10 hours, then heating to 720-740 DEG C for 0.5-1 hour, and finally heating to 650-675 DEG C, and then discharging and air cooling.

[0015] The application provides a high hardenability carburizing-free bearing steel, which comprises the following components in percentage by mass: C 1.2-1.3%, Si 0.1-0.5%, Mn 0.2-1.0%, Cr 1.5-5.0%, Ni 0.02-1.5%, Al 0.8-3.0%, Mo 0.01-1.5%, V 0.01-0.3%, Nb 0.002-0.01%, Re 0.002-0.05%, B 0.001-0.02%, N≤50ppm, O≤6ppm, S≤0.01%, P≤0.01% and Fe as the balance. The application can effectively refine the grains, improve the toughness of the material and avoid the problem of insufficient toughness of the carburizing bearing by Nb and V micro-alloying design. The hardenability of the material is improved by adding appropriate B and strictly controlling the contents of O and N, the hardness of the bearing is improved, and thus the wear resistance and the contact fatigue resistance are improved. The experimental results show that the hardenability of the high hardenability carburizing-free bearing steel provided by the application is 4.3mm higher than that of the GCr15 bearing steel under the same test conditions, and is improved by 47.8%. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The microstructure diagram of the blank in Example 1; Figure 2 The microstructure diagram of the carburizing-free bearing steel prepared in Example 1; Figure 3 The hardenability curves of the carburizing-free bearing steel prepared in Example 1 and the GCr15 bearing steel of Comparative Example 1; Figure 4 The microstructure diagram of the blank in Example 2; Figure 5 The microstructure diagram of the carburizing-free bearing steel prepared in Example 2; Figure 6 The hardenability curves of the carburizing-free bearing steel prepared in Example 2 and the GCr15 bearing steel of Comparative Example 1; Figure 7 The microstructure diagram of the blank in Example 3; Figure 8 The microstructure diagram of the carburizing-free bearing steel prepared in Example 3; Figure 9 The hardenability curves of the carburization-free bearing steel prepared in Example 3 and the GCr15 bearing steel of Comparative Example 1 were prepared. DETAILED DESCRIPTION

[0017] The present application provides a high hardenability carburization-free bearing steel, the chemical composition of which comprises, in percentage by mass, C 1.2-1.3%, Si 0.1-0.5%, Mn 0.2-1.0%, Cr 1.5-5.0%, Ni 0.02-1.5%, Al 0.8-3.0%, Mo 0.01-1.5%, V 0.01-0.3%, Nb 0.002-0.01%, Re 0.002-0.05%, B 0.001-0.02%, N≤50ppm, O≤6ppm, S≤0.01%, P≤0.01%, and the balance of Fe.

[0018] The high hardenability carburization-free bearing steel provided by the present application comprises, in percentage by mass, C 1.2-1.3%. As an embodiment, the percentage by mass of C can be 1.21%, 1.22%, 1.23%, 1.24%, 1.25%, 1.26%, 1.27%, 1.28%, or 1.29%. In the present application, C is a key element in bearing steel that determines hardness and wear resistance, which ensures that the steel has high hardness and wear resistance by forming a hypereutectoid structure.

[0019] The high hardenability carburization-free bearing steel provided by the present application further comprises, in percentage by mass, Si 0.1-0.5%. As an embodiment, the percentage by mass of Si can be 0.2%, 0.3%, 0.31%, 0.4%, or 0.43%. In the present application, Si can improve the hardenability of the bearing steel, ensuring uniform hardening of the material after heat treatment.

[0020] The high hardenability carburization-free bearing steel provided by the present application further comprises, in percentage by mass, Mn 0.2-1.0%. As an embodiment, the percentage by mass of Mn can be 0.3%, 0.4%, 0.5%, 0.52%, 0.6%, 0.7%, 0.75%, 0.8%, 0.9%, or 0.97%. In the present application, Mn can improve the hardenability of the bearing steel, ensuring uniform hardening of the material after heat treatment.

[0021] The chemical composition of the high hardenability carburizing-free bearing steel provided by this invention, by mass percentage, also includes 1.5-5.0% Cr. As one embodiment, the mass percentage of Cr can be 1.53%, 1.6%, 1.65%, 1.72%, 2.0%, 3.0%, 3.5%, 4.0%, or 4.5%. In this invention, the Cr significantly improves the hardenability of the bearing steel by refining austenite grains and forming carbides, resulting in a uniform high-hardness microstructure.

[0022] The chemical composition of the high hardenability carburizing-free bearing steel provided by this invention, by mass percentage, further includes 0.02-1.5% Ni. As one embodiment, the mass percentage of Ni can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, or 1.4%. In this invention, the Ni promotes uniform oil quenching, enhances the steel's resistance to fatigue, and reduces the tendency to overheat.

[0023] The chemical composition of the high hardenability carburizing-free bearing steel provided by the present invention, by mass percentage, further includes 0.8-3.0% Al. As one embodiment, the mass percentage of Al can be 0.85%, 0.9%, 1.0%, 1.5%, 1.7%, 2.0%, 2.5%, or 2.8%. In the present invention, the Al can prevent the formation of network carbides.

[0024] The high hardenability carburizing-free bearing steel provided by this invention, by mass percentage, further comprises 0.01-1.5% Mo. As one embodiment, the mass percentage of Mo can be 0.02%, 0.03%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, or 1.4%. In this invention, Mo significantly improves the hardenability of the steel by refining the grain size, resulting in a uniform microstructure and higher overall strength after heat treatment.

[0025] The chemical composition of the high hardenability carburized-free bearing steel provided by this invention, by mass percentage, further includes 0.01-0.3% V. As one embodiment, the mass percentage of V can be 0.02%, 0.03%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.15%, 0.18%, 0.2%, 0.22%, 0.24%, 0.26%, or 0.28%. In this invention, the V effectively refines the grains, improves the material's toughness, and effectively avoids the problem of insufficient toughness in carburized bearings.

[0026] The high hardenability carburized-free bearing steel provided by this invention, by mass percentage, further comprises 0.002-0.01% Nb. As one embodiment, the mass percentage of Nb can be 0.0025%, 0.003%, 0.004%, 0.005%, 0.006%, 0.007%, 0.008%, or 0.009%. In this invention, the Nb effectively refines the grains, improves the material's toughness, and effectively avoids the problem of insufficient toughness in carburized bearings.

[0027] The chemical composition of the high hardenability carburizing-free bearing steel provided by this invention, by mass percentage, further includes 0.002-0.05% Re. As one embodiment, the mass percentage of Re can be 0.0025%, 0.003%, 0.004%, 0.005%, 0.006%, 0.007%, 0.008%, 0.009%, 0.01%, 0.02%, 0.03%, or 0.04%. In this invention, Re improves low-temperature toughness and resistance to brittleness by altering the dislocation structure.

[0028] The high hardenability carburizing-free bearing steel provided by this invention, by mass percentage, further comprises 0.001-0.02% B. As one embodiment, the mass percentage of B can be 0.002%, 0.003%, 0.004%, 0.005%, 0.006%, 0.007%, 0.008%, 0.009%, 0.01%, or 0.015%. In this invention, B improves the hardenability of the material, increases the bearing hardness, thereby improving wear resistance and contact fatigue resistance.

[0029] The chemical composition of the high hardenability carburizing-free bearing steel provided by this invention, by weight percentage, also includes N ≤ 50 ppm. This invention strictly controls the N content, improving the hardenability of the material, increasing the bearing hardness, and thus improving wear resistance and contact fatigue resistance.

[0030] The chemical composition of the high hardenability carburizing-free bearing steel provided by this invention, by weight percentage, also includes O ≤ 6 ppm. This invention strictly controls the O content, improving the hardenability of the material, increasing the bearing hardness, and thus improving wear resistance and contact fatigue resistance.

[0031] The chemical composition of the high hardenability carburizing-free bearing steel provided by this invention, by mass percentage, also includes S ≤ 0.01%. In this invention, S is a harmful element, and by reducing its content, the hardenability of the bearing steel can be further improved.

[0032] The chemical composition of the high hardenability carburizing-free bearing steel provided by this invention, by mass percentage, also includes P ≤ 0.01%. In this invention, P is a harmful element, and by reducing its content, the hardenability of the bearing steel can be further improved.

[0033] The chemical composition of the high hardenability carburizing-free bearing steel provided by this invention, by weight percentage, also includes the balance Fe. In this invention, the Fe is a matrix element.

[0034] This invention, through Nb and V microalloying design, can effectively refine grains, improve material toughness, and effectively avoid the problem of insufficient toughness in carburized bearings; by adding an appropriate amount of B and strictly controlling the O and N content, the hardenability of the material is improved, the bearing hardness is increased, thereby improving wear resistance and contact fatigue resistance.

[0035] This invention reduces the original austenite grain size and subsequent pearlite clusters and lamellar spacing by adding V and Nb. During spheroidizing, the carbides have more nucleation sites, resulting in finer and more dispersed carbide particles. VC and NbC carbides effectively reduce the austenite grain size before oil quenching. Simultaneously, the uniformly distributed carbide particles dissolve evenly during heating, yielding fine martensite and uniformly distributed carbide particles, thus effectively reducing bearing noise during operation. By adding B and strictly controlling the O and N content, hardenability can be effectively improved, making it suitable for manufacturing bearing rings or rolling elements with larger thicknesses.

[0036] The carburized bearing steel provided by this invention has a higher hardness than GCr15, and its wear resistance and contact fatigue resistance are better than GCr15. The pearlite clusters are refined to below 15μm, and there are no network carbides at the grain boundaries.

[0037] This invention also provides a method for preparing the high hardenability carburization-free bearing steel described in the above technical solution, comprising the following steps: (1) The raw materials are smelted to obtain an alloy melt; (2) The alloy melt obtained in step (1) is subjected to die casting or continuous casting to obtain a billet; (3) Roll or forge the billet obtained in step (2) to obtain a billet; (4) Heat treat the billet obtained in step (3) to obtain high hardenability carburizing-free bearing steel.

[0038] Unless otherwise specified, the present invention does not have any special limitations on the source of the raw materials used, and commercially available products or well-known preparation methods familiar to those skilled in the art can be used.

[0039] This invention involves smelting raw materials to obtain an alloy melt. The smelting process is not specifically limited, as long as the harmful element content in the alloy melt is controlled to N ≤ 45 ppm and O < 6 ppm.

[0040] After obtaining the alloy melt, the present invention performs die casting or continuous casting on the alloy melt to obtain a casting billet.

[0041] The present invention does not impose any special limitations on the operation of the die casting or continuous casting, and die casting or continuous casting familiar to those skilled in the art can be used.

[0042] After obtaining the cast billet, the present invention rolls or forges the cast billet to obtain the billet material.

[0043] In this invention, the process of heating the billet before rolling or forging preferably includes raising the temperature to 600°C and holding for t1, then raising the temperature to 900°C and holding for t2, and then raising the temperature to 1200~1250°C and holding for 1~5 hours; where t1 = workpiece thickness (mm) × 0.5~1.0 min / mm; and t2 = workpiece thickness (mm) × 1.0~1.5 min / mm. Heating the billet before rolling or forging in this invention allows for a more uniform distribution of various alloying elements and provides better hot deformation capability.

[0044] In this invention, the heating rate to 600°C is preferably ≤1°C / min; the heating rate to 900°C is preferably ≤0.8°C / min.

[0045] In this invention, the initial rolling temperature is preferably 1100~1160℃; the final rolling temperature is preferably 850~920℃; the rolling ratio is preferably ≥5, and the rolling ratio in the temperature range of 930~980℃ is preferably ≥1.5. As one embodiment, the initial rolling temperature can be 1110℃, 1120℃, 1130℃, 1140℃, or 1150℃; the final rolling temperature can be 860℃, 870℃, 880℃, 890℃, 900℃, or 910℃; and the rolling ratio in the temperature range of 930~980℃ can be 2. By limiting the rolling process parameters within the above range, this invention effectively refines the grains, improves the material's toughness, and effectively avoids the problem of insufficient toughness in carburized bearings.

[0046] In this invention, the initial forging temperature is preferably 1100~1160℃; the final forging temperature is preferably 850~920℃, and the forging ratio is preferably ≥5. As one embodiment, the initial forging temperature can be 1110℃, 1120℃, 1130℃, 1140℃, or 1150℃; the final forging temperature can be 860℃, 870℃, 880℃, 890℃, 900℃, or 910℃. By limiting the forging process parameters within the above ranges, this invention effectively refines the grains, improves material toughness, and effectively avoids the problem of insufficient toughness in carburized bearings.

[0047] After rolling or forging is completed, the present invention preferably cools the product obtained by rolling or forging to obtain a billet.

[0048] In this invention, the cooling is preferably rapid cooling to below 700°C followed by slow cooling to room temperature; the rapid cooling rate is preferably ≥1.5°C / s; the slow cooling rate is preferably ≤0.5°C / s.

[0049] After obtaining the billet, the present invention performs heat treatment on the billet to obtain high hardenability carburizing-free bearing steel.

[0050] In this invention, the heat treatment preferably includes spheroidizing annealing, oil quenching, and tempering performed sequentially. The heat treatment described above enables the bearing steel to exhibit superior wear resistance and contact fatigue properties compared to carburized bearings.

[0051] In this invention, the spheroidizing annealing is preferably carried out by heating from room temperature to 700-720°C for 2-3 hours and holding for 1-2 hours, then heating to 750-770°C for 0.5-1 hour and holding for 0.5-1 hour, then heating to 780-810°C for 0.5-1 hour and holding for 6-10 hours, then cooling to 720-740°C for 1-3 hours and holding for 0.5-1 hour, and finally cooling to 650-675°C for 1-3 hours, followed by air cooling after removal from the furnace.

[0052] The present invention does not impose any special limitations on the heating rate and cooling rate, as long as the specified temperature is reached within a specified time.

[0053] In one implementation, the spheroidizing annealing can be performed by heating from room temperature to 700°C for 2 hours and holding for 1 hour, then heating to 750°C for 0.5 hours and holding for 0.5 hours, then heating to 790°C for 8 hours and holding for 1 hour, then cooling to 720°C for 1 hour and holding for 1 hour, and finally cooling to 675°C for 1 hour, followed by air cooling after removal from the furnace. Alternatively, the process can be performed by heating from room temperature to 710°C for 2.5 hours and holding for 1.5 hours, then heating to 760°C for 1 hour and holding for 0.8 hours, then heating to 800°C for 9 hours and holding for 0.8 hours, then cooling to 730°C for 1 hour, and finally cooling to 670°C for 2 hours, followed by air cooling after removal from the furnace.

[0054] In this invention, the oil quenching is preferably performed by heating the spheroidized annealed workpiece to 840~860℃ and holding it at that temperature for 0.5~5 hours. This invention does not impose any specific limitation on the heating rate, as long as the specified temperature is reached.

[0055] In one embodiment, the oil quenching can be performed by heating the spheroidized annealed workpiece to 850°C and holding it at that temperature for 1 hour.

[0056] In this invention, the tempering treatment is preferably performed by holding at 160~240℃ for 1.5~3 hours and then air-cooling. As one embodiment, the tempering treatment can be performed by holding at 200℃ for 2 hours and then air-cooling, holding at 240℃ for 2 hours and then air-cooling, or holding at 160℃ for 2 hours and then air-cooling.

[0057] This invention improves wear resistance and contact fatigue performance by controlling the process parameters of spheroidizing annealing, oil quenching, and tempering within the above-mentioned range.

[0058] Existing carburizing processes take anywhere from several hours to tens of hours, leading to increased costs. This invention avoids the carburizing process, significantly shortens the production cycle, and effectively reduces production costs.

[0059] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0060] Example 1 The chemical composition of the carburized-free bearing steel, by mass percentage, is: C 1.2%, Si 0.31%, Mn 0.52%, Cr 1.53%, Ni 0.02%, Al 0.85%, Mo 0.01%, V 0.1%, Nb 0.002%, Re 0.002%, B 0.005%, and the balance Fe; The method for preparing the carburizing-free bearing steel is as follows: (1) The raw materials are smelted and the harmful element composition is controlled to N 45ppm, O 5ppm, S 0.005% and P 0.01%, and then continuous casting is carried out to obtain the billet; (2) The billet obtained in step (1) is heated to 600℃ at a rate of 0.8℃ / min and held for 0.5h, then heated to 900℃ at a rate of 0.5℃ / min and held for 1h, then heated to 1200℃ and held for 1h, then rolled, and then rapidly cooled to 700℃ at a rate of 1.5℃ / s and then slowly cooled to room temperature at a rate of 0.5℃ / s to obtain the billet; wherein the initial rolling temperature is 1160℃, the final rolling temperature is 920℃, and the rolling ratio is 5; the rolling ratio in the temperature range of 930~980℃ is 2; (3) The billet obtained in step (2) is heated from room temperature to 700°C for 2 hours and held for 1 hour, then heated to 750°C for 0.5 hours and held for 0.5 hours, then heated to 790°C for 8 hours and held for 1 hour, then cooled to 720°C for 1 hour and finally cooled to 675°C for 1 hour. Then it is taken out of the furnace and air-cooled to obtain the spheroidized annealed billet. (4) The spheroidized annealed billet obtained in step (3) is held at 840℃ for 0.5h for oil quenching, then tempered at 160℃ for 2h and then air-cooled to obtain carburized bearing steel.

[0061] Comparative Example 1 GCr15 bearing steel The microstructure of the billet in Example 1 is shown in the figure below. Figure 1 As shown.

[0062] from Figure 1 It can be seen that the network carbides have been largely eliminated.

[0063] The microstructure of the carburized-free bearing steel prepared in Example 1 is shown in the figure below. Figure 2 As shown.

[0064] from Figure 2 It can be seen that the carbide particle size is significantly refined, with an average grain size of 0.55±0.35μm.

[0065] The hardenability of the carburized-free bearing steel prepared in Example 1 and the GCr15 bearing steel in Comparative Example 1 were tested, and the results are as follows: Figure 3 As shown; the test conditions and methods are as follows: the sample size is a round bar with a diameter of 25 mm and a length of 100 mm, which is heated from room temperature to 860℃ in 40 min, held at that temperature for 30 min, and then oil quenched using a 25℃ water flow.

[0066] Under the same test conditions, the hardening depth of the carburized-free bearing steel prepared in Example 1 is 4 mm higher than that of GCr15 bearing steel, which is an improvement of 44.4%.

[0067] Impact tests were conducted on the carburized-free bearing steel prepared in Example 1. The results showed that the impact toughness A of the carburized-free bearing steel was... KU 5.5 J / cm 2 The martensitic structure of GCr15 bearing steel, which is 3.8 J / cm³ after oil quenching at 850℃ and tempering at 160℃ for 2 hours, is higher than that of GCr15 bearing steel. 2 .

[0068] Example 2 The chemical composition of the carburized-free bearing steel, by mass percentage, is: C 1.25%, Si 0.43%, Mn 0.75%, Cr 1.65%, Ni 0.02%, Al 1.5%, Mo 0.01%, V 0.18%, Nb 0.0025%, Re 0.002%, B 0.01%, S 0.005%, P 0.005%, and balance Fe; The method for preparing the carburizing-free bearing steel is as follows: (1) The raw materials are smelted and the harmful element composition is controlled to N 45ppm, O 5ppm, S 0.005% and P 0.01%, and then continuous casting is carried out to obtain the billet; (2) The billet obtained in step (1) is heated to 600℃ at a rate of 0.8℃ / min and held for 1h, then heated to 900℃ at a rate of 0.6℃ / min and held for 1.5h, then heated to 1210℃ and held for 3h, then rolled, and then rapidly cooled to 700℃ at a rate of 1.8℃ / s and then slowly cooled to room temperature at a rate of 0.5℃ / s to obtain the billet; wherein the initial rolling temperature is 1160℃, the final rolling temperature is 920℃, and the rolling ratio is 5; the rolling ratio in the temperature range of 930~980℃ is 2; (3) The billet obtained in step (2) is heated from room temperature to 710°C for 2.5 hours and held for 1.5 hours, then heated to 760°C for 0.8 hours and held for 1 hour, then heated to 800°C for 0.8 hours and held for 9 hours, then cooled to 730°C for 2 hours and held for 1 hour, and finally cooled to 670°C for 2 hours. Then it is taken out of the furnace and air-cooled to obtain the spheroidized annealed billet. (4) The spheroidized annealed billet obtained in step (3) is kept at 850°C for 1 hour for oil quenching, then tempered at 200°C for 2 hours and then air-cooled to obtain carburized bearing steel.

[0069] The microstructure of the billet in Example 2 is shown in the figure below. Figure 4 As shown.

[0070] from Figure 4It can be seen that the network carbides have been largely eliminated.

[0071] The microstructure of the carburized-free bearing steel prepared in Example 2 is shown in the figure below. Figure 5 As shown.

[0072] from Figure 5 It can be seen that the carbide particle size is significantly refined, with an average grain size of 0.52±0.33μm.

[0073] The hardenability of the carburized-free bearing steel prepared in Example 2 and the GCr15 bearing steel in Comparative Example 1 were tested, and the results are as follows: Figure 6 As shown; the test conditions and methods are as follows: the sample size is a round bar with a diameter of 25 mm and a length of 100 mm, which is heated from room temperature to 860℃ in 40 min, held at that temperature for 30 min, and then oil quenched using a 25℃ water flow.

[0074] Under the same test conditions, the hardening depth of the carburized-free bearing steel prepared in Example 2 was 4.2 mm higher than that of GCr15 bearing steel, an increase of 46.7%.

[0075] Impact tests were conducted on the carburized-free bearing steel prepared in Example 2. The results showed that the impact toughness A of the carburized-free bearing steel was... KU 5.8 J / cm 2 The martensitic structure of GCr15 bearing steel, which is 3.8 J / cm³ after oil quenching at 850℃ and tempering at 160℃ for 2 hours, is higher than that of GCr15 bearing steel. 2 .

[0076] Example 3 The chemical composition of the carburized-free bearing steel, by mass percentage, is: C 1.3%, Si 0.5%, Mn 0.97%, Cr 1.72%, Ni 0.02%, Al 1.7%, Mo 0.01%, V 0.22%, Nb 0.003%, Re 0.002%, B 0.015%, and the balance Fe; The method for preparing the carburizing-free bearing steel is as follows: (1) The raw materials are smelted and the harmful element composition is controlled to N 45ppm, O 5ppm, S 0.005% and P 0.01%, and then continuous casting is carried out to obtain the billet; (2) The billet obtained in step (1) is heated to 600℃ at a rate of 0.5℃ / min and held for 2 hours, then heated to 900℃ at a rate of 0.4℃ / min and held for 2 hours, then heated to 1220℃ and held for 4 hours, then rolled, and then rapidly cooled to 700℃ at a rate of 1.75℃ / s and then slowly cooled to room temperature at a rate of 0.5℃ / s to obtain the billet; wherein the initial rolling temperature is 1150℃, the final rolling temperature is 900℃, and the rolling ratio is 7; the rolling ratio in the temperature range of 930~980℃ is 5; (3) The billet obtained in step (2) is heated from room temperature to 720°C for 3 hours and held for 2 hours, then heated to 770°C for 1 hour and held for 1 hour, then heated to 810°C for 10 hours, then cooled to 740°C for 3 hours and held for 1 hour, and finally cooled to 675°C for 3 hours. Then it is taken out of the furnace and air-cooled to obtain the spheroidized annealed billet. (4) The spheroidized annealed billet obtained in step (3) is kept at 860℃ for 2 hours for oil quenching, then tempered at 240℃ for 2 hours and then air-cooled to obtain carburized bearing steel.

[0077] The microstructure of the billet in Example 3 is shown in the figure below. Figure 7 As shown.

[0078] from Figure 7 It can be seen that the network carbides have been largely eliminated.

[0079] The microstructure of the carburized-free bearing steel prepared in Example 3 is shown in the figure below. Figure 8 As shown.

[0080] from Figure 8 It can be seen that the carbide particle size is significantly refined, with an average grain size of 0.50±0.38μm.

[0081] The hardenability of the carburized-free bearing steel prepared in Example 3 and the GCr15 bearing steel in Comparative Example 1 were tested, and the results are as follows: Figure 9 As shown; the test conditions and methods are as follows: the sample size is a round bar with a diameter of 25 mm and a length of 100 mm, which is heated from room temperature to 860℃ in 40 min, held at that temperature for 30 min, and then oil quenched using a 25℃ water flow.

[0082] Under the same test conditions, the hardening depth of the carburized-free bearing steel prepared in Example 3 was 4.3 mm higher than that of GCr15 bearing steel, an increase of 47.8%.

[0083] Impact tests were conducted on the carburized-free bearing steel prepared in Example 3. The results showed that the impact toughness A of the carburized-free bearing steel was... KU 5.2 J / cm 2 The martensitic structure of GCr15 bearing steel, which is 3.8 J / cm³ after oil quenching at 850℃ and tempering at 160℃ for 2 hours, is higher than that of GCr15 bearing steel. 2 .

[0084] As can be seen from the above embodiments and comparative examples, the bearing steel provided by the present invention has excellent toughness and hardenability.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high hardenability, carburizing-free bearing steel, the chemical composition of which, by mass percentage, comprises: C 1.2~1.3%, Si 0.1~0.5%, Mn 0.2~1.0%, Cr 1.5~5.0%, Ni 0.02~1.5%, Al 0.8~3.0%, Mo 0.01~1.5%, V 0.01~0.3%, Nb 0.002~0.01%, Re 0.002~0.05%, B 0.001~0.02%, N≤50ppm, O≤6ppm, S≤0.01%, P≤0.01%, and balance Fe.

2. The high hardenability carburizing-free bearing steel according to claim 1, characterized in that, The chemical composition, by mass percentage, includes: C 1.25~1.3%, Si 0.2~0.4%, Mn 0.3~0.9%, Cr 2.0~4.0%, Ni 0.1~1.4%, Al 0.9~2.0%, Mo 0.1~1.4%, V 0.1~0.2%, Nb 0.005~0.01%, Re 0.01~0.04%, B 0.002~0.008%, N≤50ppm, O≤6ppm, S≤0.01%, P≤0.01%, and the balance Fe.

3. A method for preparing the high hardenability carburization-free bearing steel according to claim 1 or 2, comprising the following steps: (1) The raw materials are smelted to obtain an alloy melt; (2) The alloy melt obtained in step (1) is subjected to die casting or continuous casting to obtain a billet; (3) Roll or forge the billet obtained in step (2) to obtain a billet; (4) Heat treat the billet obtained in step (3) to obtain high hardenability carburizing-free bearing steel.

4. The preparation method according to claim 3, characterized in that, The step (3) also includes heating the billet before rolling or forging.

5. The preparation method according to claim 4, characterized in that, The heating process includes raising the temperature to 600°C and holding it at that temperature for t1, then raising the temperature to 900°C and holding it at that temperature for t2, and then raising the temperature to 1200~1250°C and holding it at that temperature for 1~5 hours. The value of t1 is calculated as: workpiece thickness (mm) × 0.5~1.0 min / mm. The t2 is calculated as: workpiece thickness (mm) × 1.0~1.5 min / mm.

6. The preparation method according to claim 5, characterized in that, The heating rate to 600℃ is ≤1℃ / min, and the heating rate to 900℃ is ≤0.8℃ / min.

7. The preparation method according to claim 3, characterized in that, In step (3), the initial rolling temperature is 1100~1160℃, the final rolling temperature is 850~920℃, the rolling ratio is ≥5, and the rolling ratio in the temperature range of 930~980℃ is ≥1.

5.

8. The preparation method according to claim 3, characterized in that, In step (3), the initial forging temperature is 1100~1160℃, the final forging temperature is 850~920℃, and the forging ratio is ≥5.

9. The preparation method according to claim 3, characterized in that, The heat treatment in step (3) includes spheroidizing annealing, oil quenching and tempering in sequence.

10. The preparation method according to claim 9, characterized in that, The spheroidizing annealing process involves heating from room temperature to 700-720℃ for 2-3 hours and holding for 1-2 hours, then heating to 750-770℃ for 0.5-1 hour and holding for 0.5-1 hour, then heating to 780-810℃ for 0.5-1 hour and holding for 6-10 hours, then cooling to 720-740℃ for 1-3 hours and holding for 0.5-1 hour, and finally cooling to 650-675℃ for 1-3 hours before air cooling.

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