Heat treatment process for improving tempering stability of GCr15 bearing ring

Abstract

The application discloses a heat treatment process for improving the tempering stability of a GCr15 bearing ring, and belongs to the technical field of metal heat treatment. The process comprises three core steps of pretreatment, quenching treatment and tempering treatment in sequence: the pretreatment adopts high-temperature temperature control oil cooling at 920-940 DEG C combined with 770-780 DEG C speed control spheroidizing annealing, realizes carbide dispersion refinement, and the spheroidizing organization grade is not greater than 2; the quenching adopts a three-stage step-up heating process, gradually reduces the heating rate to reduce the thermal shock, and obtains uniform and fine martensite organization; and the tempering adopts long-time heat preservation at 175-185 DEG C and then furnace slow cooling, and fully eliminates the quenching stress. The GCr15 bearing ring treated by the process has a hardness of not less than 61HRC after 250 DEG C heat preservation for 3-5h, a hardness of not less than 59HRC after 300 DEG C heat preservation for 3-5h, and a martensite grade of 3, can significantly improve the tempering stability and service reliability under the medium and high temperature working conditions, and is suitable for batch production of high-end precision bearing rings.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology, and more specifically, to a heat treatment process for improving the tempering stability of GCr15 bearing rings. Background Technology

[0002] GCr15, a typical grade of high-carbon chromium bearing steel, possesses high hardness, high wear resistance, and excellent contact fatigue performance. It is a core material for manufacturing precision bearing rings and is widely used in key equipment fields such as rail transit traction motors, new energy vehicle drive motors, high-end machine tool spindles, and wind turbine gearboxes. With the development of equipment towards higher speeds, heavier loads, and greater integration, bearing rings are subjected to the coupled effects of alternating contact stress and medium-to-high temperature environments during long-term service. Hardness decay, microstructure transformation, and dimensional accuracy deterioration have gradually become core factors restricting the service life and operational reliability of bearings. Therefore, tempering stability has become a key indicator for evaluating the heat treatment quality of high-end bearing rings.

[0003] Currently, the conventional heat treatment route for GCr15 bearing rings in the industry is mainly "forging blank - spheroidizing annealing pretreatment - quenching - low-temperature tempering". Spheroidizing annealing often employs normalizing combined with isothermal spheroidizing, quenching typically involves direct heating to the austenitizing temperature followed by oil cooling, and tempering usually involves short-term holding at 160-180℃ followed by air cooling. This type of process can meet the hardness and wear resistance requirements of bearing rings under normal operating conditions, providing fundamental technical support for large-scale production in the bearing industry.

[0004] However, under medium- and high-temperature service conditions, existing processes still have significant shortcomings: First, conventional spheroidizing annealing pretreatment has limited ability to refine and disperse carbides, making it difficult to fully break up the coarse carbides left after forging. The spheroidization grade is generally level 3 or higher, with uneven carbide size and large distribution dispersion. This not only leads to poor uniformity of the matrix structure after quenching but also accelerates carbide aggregation and coarsening during subsequent high-temperature tempering, accelerating the decrease in hardness. Second, conventional quenching processes often use a single rate to rapidly heat to the austenitizing temperature, resulting in a large temperature difference between the inside and outside of the bearing and significant thermal shock. This easily causes coarse grains and fluctuations in the content of retained austenite, reducing the thermal stability of the matrix structure. Third, the tempering stability of bearings treated by existing processes is insufficient. The hardness usually drops below 61 HRC after holding at 250℃, and is generally below 58 HRC after holding at 300℃, which is difficult to meet the long-term service requirements of high-speed motors and bearings under high-temperature conditions.

[0005] Therefore, developing a heat treatment process that can refine the carbide structure, improve the thermal stability of the matrix, and significantly enhance the ability to retain high-temperature hardness in GCr15 bearing rings is a technical problem to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a heat treatment process that significantly improves the ability of GCr15 bearing rings to retain high-temperature hardness.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a heat treatment process for improving the tempering stability of GCr15 bearing rings, comprising the following steps: Pretreatment: The forged GCr15 bearing ring blank is heated to 920-940℃ in the furnace at a heating rate of 10-20℃ / min, held for 40-50min, and then oil-cooled, with the oil exit temperature not lower than 300℃; then heated to 770-780℃ in the furnace at a heating rate of 10-20℃ / min, held for 4-6h, and then cooled to below 600℃ at a cooling rate of 60-80℃ / h, and finally air-cooled to room temperature before exiting the furnace. Further, in step (1), the temperature is raised to 920-930℃ at a heating rate of 10-15℃ / min, held for 40-45min, and then oil-cooled; during the spheroidizing holding stage, the temperature is raised at a rate of 10-15℃ / min, held for 4-5h, and then cooled to below 600℃ at a rate of 60-70℃ / h.

[0008] Quenching treatment: The pretreated ring blank is heated to 640-660℃ in the furnace at a heating rate of 10-20℃ / min and held for 20-30min; then heated to 815-825℃ at a heating rate of 10-15℃ / min and held for 20-30min; finally, heated to the quenching temperature of 845-865℃ at a heating rate of 5-10℃ / min and held for 20-30min before oil cooling. Furthermore, in step (2), the preheating stage is heated to 640-650℃ at a rate of 10-15℃ / min and held for 20-25min; the secondary preheating stage is heated to 815-820℃ at a rate of 10-12℃ / min and held for 20-25min; the austenitizing stage is heated to 845-855℃ at a rate of 5-8℃ / min and held for 20-25min before oil cooling.

[0009] Tempering treatment: The quenched ring blank is heated to 175-185℃ in the furnace at a heating rate of 10-20℃ / min, held for 3-5h, and then slowly cooled to room temperature in the furnace before being removed from the furnace. Further, in step (3), the temperature is increased to 175-180℃ at a rate of 10-15℃ / min, held for 3-4h, and then slowly cooled to room temperature in the furnace.

[0010] By adopting the above technical solution, the following technical effects are achieved: Significant carbide refinement effect: The pretreatment adopts a two-step process of "high temperature controlled oil cooling crushing + controlled speed spheroidizing annealing", which breaks down the coarse network / plate carbides after forging, and achieves uniform dispersion of carbides. The spheroidization structure grade can be controlled within the GB / T 34891 standard level 2, which improves the tempering resistance from the root of the structure, which is different from the traditional route of conventional normalizing + isothermal spheroidizing.

[0011] Uniform and stable matrix structure: The quenching adopts a three-stage stepped heating process, gradually reducing the heating rate, effectively reducing the thermal shock of the ring and the internal and external temperature difference, inhibiting grain growth, obtaining a uniform and fine acicular martensite structure, with the martensite grade stable at level 3, and the residual austenite content controllable, thus improving the thermal stability of the matrix.

[0012] Significantly improved tempering stability: The tempering process employs low-temperature long-time holding + slow furnace cooling, which fully eliminates quenching stress and inhibits premature carbide agglomeration and coarsening. Combined with the pre-treatment microstructure refinement effect, the hardness is not less than 61 HRC after holding at 250℃ for 3-5 hours and not less than 59 HRC after holding at 300℃ for 3-5 hours, which is significantly better than conventional heat treatment processes and greatly improves the service life and reliability of the bearings under medium and high temperature service conditions.

[0013] Strong industrial adaptability: All process parameters are quantifiable and repeatable, requiring no additional special equipment, and can be directly adapted to existing industrial heat treatment production lines, with good prospects for mass production applications. Attached Figure Description

[0014] Figure 1 is a schematic diagram of the heating curve of the heat treatment process of the present invention; Figure 2 shows the metallographic structure of the GCr15 bearing ring after heat treatment according to the present invention. Detailed Implementation

[0015] Reference Figures 1 to 2 The embodiments of the present invention will be further described below.

[0016] Example 1: Take the forged 6307 type GCr15 bearing ring blank and perform heat treatment according to the following steps: Pretreatment: The ring blank is heated to 940℃ in the furnace at a heating rate of 20℃ / min, held for 50min, and then oil-cooled, with the oil outlet temperature controlled not lower than 300℃; then it is heated to 780℃ in the furnace at a heating rate of 20℃ / min, held for 6h, and then cooled to below 600℃ at a cooling rate of 80℃ / h, and finally air-cooled to room temperature before being removed from the furnace.

[0017] Quenching treatment: The pretreated ring blank is heated to 660℃ in the furnace at a heating rate of 20℃ / min and held for 30min; then heated to 825℃ at a heating rate of 15℃ / min and held for 30min; finally, heated to the quenching temperature of 845-865℃ at a heating rate of 5-10℃ / min and held for 20-30min before oil cooling.

[0018] Tempering treatment: The quenched ring blank is heated to 185°C in the furnace at a heating rate of 20°C / min, held at that temperature for 5 hours, and then slowly cooled to room temperature before being removed from the furnace.

[0019] Performance testing: The microstructure and performance of the rings treated in this embodiment were tested. The spheroidized microstructure after pretreatment was rated as grade 2 according to GB / T 34891. The hardness of the quenched and tempered sample after holding at 250℃ for 3 hours was 61.8 HRC. The microstructure was acicular martensite + retained austenite, and the martensite grade was grade 3.

[0020] Example 2: Take the forged 6307 type GCr15 bearing ring blank and perform heat treatment according to the following steps: Pretreatment: The ring blank is heated to 920℃ in the furnace at a heating rate of 10℃ / min, held for 40min, and then oil-cooled, with the oil outlet temperature controlled not lower than 300℃; then it is heated to 770℃ in the furnace at a heating rate of 10℃ / min, held for 4h, and then cooled to below 600℃ at a cooling rate of 60℃ / h, and finally air-cooled to room temperature before being removed from the furnace.

[0021] Quenching treatment: The pretreated ring blank is heated to 640℃ in the furnace at a heating rate of 10℃ / min and held for 20min; then heated to 815℃ at a heating rate of 10℃ / min and held for 20min; finally, heated to 845℃ at a heating rate of 5℃ / min and held for 20min before oil cooling.

[0022] Tempering treatment: The quenched ring blank is heated to 175°C in the furnace at a heating rate of 10°C / min, held at that temperature for 3 hours, and then slowly cooled to room temperature before being removed from the furnace.

[0023] Performance testing: The microstructure and performance of the rings treated in this embodiment were tested. The spheroidized microstructure after pretreatment was rated as grade 1.5 according to GB / T 34891. The hardness of the quenched and tempered sample after holding at 300℃ for 5 hours was 59.4 HRC. The microstructure was acicular martensite + retained austenite, and the martensite grade was 3.

[0024] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A heat treatment process for improving the tempering stability of GCr15 bearing rings, characterized in that, Includes the following steps: (1) Pretreatment: The forged GCr15 bearing ring blank is heated to 920-940℃ in the furnace at a heating rate of 10-20℃ / min, held for 40-50min and then oil-cooled, with the oil outlet temperature not lower than 300℃; then heated to 770-780℃ in the furnace at a heating rate of 10-20℃ / min, held for 4-6h, then cooled to below 600℃ at a cooling rate of 60-80℃ / h, and finally air-cooled to room temperature before being taken out of the furnace. (2) Quenching treatment: The pretreated ring blank is heated to 640-660℃ in the furnace at a heating rate of 10-20℃ / min and held for 20-30min; then heated to 815-825℃ at a heating rate of 10-15℃ / min and held for 20-30min; finally heated to 845-865℃ at a heating rate of 5-10℃ / min and held for 20-30min before oil cooling. (3) Tempering treatment: The quenched ring blank is heated to 175-185℃ at a heating rate of 10-20℃ / min and held for 3-5 hours. Then it is slowly cooled to room temperature and removed from the furnace.

2. The heat treatment process for improving the tempering stability of GCr15 bearing rings according to claim 1, characterized in that, In step (1), the temperature is increased to 920℃ at a heating rate of 10℃ / min, held for 40min, and then oil-cooled; during the spheroidizing and holding stage, the temperature is increased at a rate of 10℃ / min, held for 4h, and then cooled to below 600℃ at a rate of 60℃ / h.

3. The heat treatment process for improving the tempering stability of GCr15 bearing rings according to claim 1, characterized in that, In step (1), the temperature is increased to 940℃ at a heating rate of 20℃ / min, held for 50min, and then oil-cooled; during the spheroidizing and holding stage, the temperature is increased at a rate of 20℃ / min, held for 5h, and then cooled to below 600℃ at a rate of 80℃ / h.

4. The heat treatment process for improving the tempering stability of GCr15 bearing rings according to claim 1, characterized in that, In step (2), the preheating stage is heated to 640℃ at a rate of 10℃ / min and held for 20min; the secondary preheating stage is heated to 815℃ at a rate of 10℃ / min and held for 20min; the austenitizing stage is heated to 845℃ at a rate of 5℃ / min and held for 20min before oil cooling.

5. The heat treatment process for improving the tempering stability of GCr15 bearing rings according to claim 1, characterized in that, In step (2), the preheating stage is heated to 660℃ at a rate of 20℃ / min and held for 30min; the secondary preheating stage is heated to 825℃ at a rate of 15℃ / min and held for 30min; the austenitizing stage is heated to 865℃ at a rate of 10℃ / min and held for 30min before oil cooling.

6. The heat treatment process for improving the tempering stability of GCr15 bearing rings according to claim 1, characterized in that, In step (3), the temperature is increased to 175°C at a rate of 10°C / min, held for 3 hours, and then slowly cooled to room temperature in the furnace.

7. The heat treatment process for improving the tempering stability of GCr15 bearing rings according to claim 1, characterized in that, In step (3), the temperature is increased to 185°C at a rate of 20°C / min, held for 5 hours, and then slowly cooled to room temperature in the furnace.

8. A GCr15 bearing ring, characterized in that, The bearing ring is prepared using the heat treatment process described in any one of claims 1-7; the spheroidized structure of the bearing ring after pretreatment is rated as grade 2 according to GB / T 34891 standard; the hardness of the quenched and tempered sample is not less than 61 HRC after holding at 250℃ for 3-5 hours, and not less than 59 HRC after holding at 300℃ for 3-5 hours; the microstructure is acicular martensite + retained austenite, and the martensite grade is determined to be grade 3 according to GB / T 34891 standard.

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