Low-oxygen high-cleanliness powder metallurgy high-temperature bearing steel and preparation method thereof

Abstract

The invention relates to low-oxygen high-cleanliness powder metallurgy high-temperature bearing steel and a preparation method thereof. The invention relates to low-oxygen high-cleanliness powder metallurgy high-temperature bearing steel. The bearing steel comprises the following chemical components in percentage by weight: 1.20%-1.70% of C, 3.0%-5.0% of Cr, 9.5%-12.0% of Mo, 1.50%-2.50% of V, 5.0%-7.0% of W, 0.02%-1.0% of Ni, 0.02%-1.0% of Co, 0.02%-1.0% of Nb, 1t of P and the balance of Fe. 0.005%, S: lt; 0.005%, O: lt; 0.005%, N: lt; 0.008%, H: lt; 0.0001%, and the balance being Fe. The method has the beneficial effects that the oxygen content of the powder metallurgy steel can be controlled to be lt; and meanwhile, introduction of impurities of refractory materials during smelting in the powder manufacturing process is avoided, and high cleanliness of the refractory materials is guaranteed. In addition, through alloying design of Nb and the like and powder metallurgy preparation, carbides in the high-carbon high-alloy steel are refined, and the structure uniformity is improved. And the comprehensive mechanical property of the high-carbon high-alloy steel is improved in two aspects of refining a carbide structure and ultra-low oxygen and high cleanliness.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to a low-oxygen, high-cleanliness powder metallurgy high-temperature bearing steel and a preparation method thereof. Background Art

[0002] With the development of aviation industry, medical equipment and other equipment, the service temperature of bearings is getting higher and higher, which puts higher requirements on the heat resistance of bearing steel. As the key load-bearing components of aircraft, bearing steel is required to maintain high strength and hardness at high temperatures. The service temperature of high-temperature bearing steel reported so far is generally below 500℃, which is difficult to meet the service requirements at a high temperature of 600℃.

[0003] In addition, high-temperature-resistant bearing materials generally contain high contents of alloying elements such as C, Mo, W, and V, which are prone to form large particles and network eutectic carbides. Traditional ingot forging and smelting lead to component segregation and uneven organization, which are difficult to eliminate in subsequent forging heat treatment. Large particle carbides and component segregation will seriously affect the fatigue life of the material. Powder metallurgy technology can significantly improve the component segregation, organizational uniformity and elimination of large particles and network carbides in the preparation process of high-carbon and high-alloy materials. After alloy steel is atomized and powdered, the oxygen content in the powder steel will increase. At present, the oxygen content of domestic industrial powder is 100-200ppm. Conventional water atomization powder (oxygenation>500ppm), vacuum gas atomization powder (VIGA, oxygenation>200ppm) and vacuum induction electrode gas atomization (EIGA, oxygenation>200ppm), the increase in oxygen content leads to an increase in oxide inclusions, which reduces the cleanliness of steel and thus affects the fatigue life of steel.

[0004] In summary, the motivation for the invention is to develop high-temperature bearing steel with a temperature resistance of 600°C and low-oxygen, high-hardness, high-cleanliness, powder metallurgy high-temperature bearing steel and its preparation method. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a high-temperature bearing steel with a temperature resistance of 600°C, low oxygen content, high hardness, high cleanliness, powder metallurgy high-temperature bearing steel and its preparation method, which has good high-temperature hardness, toughness, and high cleanliness.

[0006] The present invention provides a low-oxygen, high-cleanliness powder metallurgy high-temperature bearing steel, and its technical solution is:

[0007] A low-oxygen, high-cleanliness powder metallurgy high-temperature bearing steel, wherein the chemical composition range of the bearing steel is as follows by weight: C: 1.20%-1.70%, Cr: 3.0%-5.0%, Mo: 9.5%-12.0%, V: 1.50%-2.50%, W: 5.0%-7.0%, Ni: 0.02%-1.0%, Co: 0.02%-1.0%, Nb: 0.02%-1.0%, P: <0.005%, S: <0.005%, O: <0.005%, N: <0.008%, H: <0.0001%, and the balance is Fe.

[0008] A method for preparing low-oxygen and high-cleanliness powder metallurgy high-temperature bearing steel comprises the following steps:

[0009] Step 1: The bearing steel master alloy is melted by vacuum induction method, and the ingot is cast to obtain a high-purity master alloy with low oxygen content and high cleanliness; the impurity element content in the alloy meets the following standards: P: <0.005%, S: <0.005%, O: <0.001%, N: <0.008%, H: <0.0001%;

[0010] Step 2: The high-purity master alloy is heat treated or directly peeled and the riser is cut off to obtain a high-cleanliness master alloy;

[0011] Step 3: Prepare the alloy steel into electrode samples, and use the rotating electrode atomization powder making method to prepare high-purity alloy powder. After the powder is sieved, a high-purity metal powder of bearing steel with a purity of 0 to 200 μm is obtained. The alloy powder is packaged in a cylindrical sleeve and heated at 500 ° C and 1×10 -3 The high-temperature vacuum degassing treatment is carried out under high vacuum of 10000 Pa for more than 20 hours, and then the package brazing is sealed to ensure no leakage and air leakage; then the powder package hot isostatic pressing sintering is carried out; the hot isostatic pressing sintering process is that the package is heated with the furnace at a pressure of 110-160MPa and 1080-1200℃ for 1-5 hours, and then the temperature is controlled and cooled to below 500℃ at a rate of <40℃ / h, and then air-cooled to obtain a dense hot isostatic pressing sintered steel billet;

[0012] Step 4: Remove the steel billet jacket, heat the hot isostatically pressed steel billet to 1200°C for insulation, and then use one or more deformation equipment such as a forging hammer, a press or a rolling mill to forge or hot roll the billet, and the forging temperature range is 1180-900°C; obtain a new high-temperature powder bearing steel forging material with a compression ratio of 3-10, and achieve the refinement and homogenization of carbides and matrix structures;

[0013] Step 5: After forging, the bar is annealed. The annealing process is to heat at 840-900℃ for 1-4h, then cool to 550℃ at a rate of <20℃ / h, air cool, and surface polish after annealing to obtain powder high-temperature bearing steel bar; after annealing, the hardness of the high-temperature bearing steel is ≤340HBW, and the impurity element content in the alloy meets the following standards: O<0.005%, N:<0.008%, H:<0.0001%.

[0014] Furthermore, the heat treatment process of the high temperature bearing steel is to keep it at 1150°C to 1220°C for 0.5 to 1 hour, then oil quench, and then keep it at 500 to 600°C for 1 to 2 hours and temper it 2 or 3 times.

[0015] Furthermore, in step 2, the heat treatment process of the master alloy is: annealing treatment or forging treatment + annealing treatment;

[0016] The annealing process is: heating at 700-900℃ for 5-8h, then cooling to below 400℃ at a rate of <40℃ / h, and air cooling;

[0017] The forging + annealing process is as follows: the forging process is: heating and keeping at 1050-1200°C for 1-6h, forging in the temperature range of 1200-900°C to obtain the forging master alloy; then heating and keeping at 700-900°C for 5-8h, then cooling to below 400°C at a rate of <40°C / h, and air cooling.

[0018] Furthermore, in step 4: the hot isostatically pressed steel billet is heated to 1200° C. and kept at this temperature for 6 hours before being forged or hot rolled.

[0019] The main functions of the above chemical elements are as follows:

[0020] C: Main strengthening element, produces interstitial solid solution strengthening, and forms carbides together with Cr, W, Mo, V, and Nb alloy elements. Too high C content will lead to serious macrosegregation, increase the unevenness of carbides and hot isostatic pressing solidification sintering, which is not conducive to the densification of hot isostatic pressing billets and the uniformity of the structure, wear resistance, fatigue performance, etc. of the finished steel. Low C content will make the number of carbides insufficient, fail to achieve the expected strengthening effect, and reduce the high temperature hardness and fatigue performance of the steel. In order to ensure that the steel has sufficient high temperature precipitation strengthening and high temperature hardness, the C content is controlled at 1.20% to 1.70%.

[0021] Cr: The Cr content in high carbon and high temperature bearing steel is preferably about 4wt%, which can effectively improve the wear resistance and hardenability of the steel. In addition to a small amount of Cr existing in M6C and MC carbides, Cr will also form a large amount of M6C with Fe and Cr as the main alloying elements during the spheroidizing annealing process. 23C6 carbides, and promotes these carbides to be almost completely dissolved in austenite during the quenching and heating process, thereby enhancing the alloying of austenite and improving the hardenability of steel. Therefore, the Cr content is controlled at 3.0% to 5.0%.

[0022] Mo: Mo is the most important alloying element for improving the strength and hot hardness of high-temperature bearing steel. Together with microalloying elements such as Nb and V, it produces nano-precipitation strengthening, greatly improving the strength and hardness of steel, reducing or inhibiting the temper brittleness caused by other elements, improving toughness, and improving the stability of carbides at high temperatures. The Mo content is controlled at 9.5% to 12.0%.

[0023] W can form (W, Fe) with Fe and C in high speed steel 23 C6 and (W, Fe)6C, two special carbides with high hardness and high wear resistance, are one of the most important hard phases for improving the high temperature hardness and wear resistance of high temperature steel. W can increase the decomposition temperature of martensite during tempering after quenching and delay the aggregation of decomposition products, so that the steel can still maintain extremely high hardness at a temperature of 600°C, even if the alloy steel has red hardness. The primary carbide of tungsten formed by powder metallurgy high-speed steel is relatively small in size, and further processing can effectively avoid the reduction of plasticity; when W is solid-dissolved in the high-speed steel matrix, it can effectively improve the tempering stability of the steel. The W content is controlled at 5.0% to 7.0%.

[0024] V: Vanadium is an important strong carbide forming element, which can form stable and fine MC type carbides during tempering. In addition, together with Mo and Nb, it can form composite carbides with high thermal stability, thereby improving the mechanical properties of high temperature steel such as hardness, wear resistance, red hardness and cutting performance. When the V content is less than 1%, due to the low V content, the red hardness and wear resistance of high speed steel are also low, and the secondary hardening effect is not good. When the V content is higher than 3%, the grindability is poor, resulting in high grinding process costs in subsequent processing. The V content is controlled at 1.50% to 2.50%.

[0025] Ni: Nickel can improve the hardenability and tempering stability of steel, reduce the sensitivity of steel to notches, and improve its fatigue performance. The Ni content should be controlled at 0.02-1.00%.

[0026] Co: Cobalt can replace iron in a small amount and enter M6C carbide, increase the nucleation rate of secondary carbide precipitation during tempering, promote the precipitation of martensite secondary carbide, refine the carbide particle size, and increase tempering hardness; Co can also improve the red hardness of high-speed steel, but the cost of Co is high, which will increase the cost of steel, so it is suitable to add it in the form of microalloying to refine the precipitation of secondary carbides and improve stability. The Co content should be controlled at 0.02-1.00%.

[0027] Nb: It is an important microalloying element. Together with Mo and V, it produces a large amount of nano-precipitation, thereby refining the structure and improving the strength. At the same time, Nb also increases the stability of austenite, improves the hardenability of steel, and improves the uniformity and consistency of steel structural performance. However, the cost of Nb is high, which will increase the cost of steel, so it is suitable for microalloying. The Nb content should be controlled at 0.05-1.00%.

[0028] The implementation of the present invention includes the following technical effects:

[0029] The low-oxygen, high-cleanliness powder metallurgy high-temperature bearing steel of the present invention can control the oxygen content of the powder metallurgy steel to an ultra-low oxygen content of <0.005%, while avoiding the introduction of refractory inclusions during smelting during the powder making process, thereby ensuring its high cleanliness. In addition, the carbides in the high-carbon, high-alloy steel are refined and the uniformity of the structure is improved through alloying design such as Nb and powder metallurgy preparation. Compared with the prior art, the comprehensive mechanical properties of high-carbon, high-alloy steel are improved in terms of both refined carbide structure and ultra-low oxygen and high cleanliness, which is of great value for the preparation of high-carbon, high-alloy steel with high purity and high uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the annealed microstructure diagram of the low-oxygen, high-cleanliness powder metallurgy high-temperature bearing steel of Example 1 of the present invention.

[0031] Figure 2 This is the annealed microstructure diagram of the low-oxygen, high-cleanliness powder metallurgy high-temperature bearing steel of Example 2 of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be described in detail below in conjunction with embodiments and drawings. It should be pointed out that the described embodiments are only intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0033] The present invention has developed a new low-oxygen and high-cleanliness powder metallurgy high-temperature bearing steel through alloying design of C, Si, Mn, Cr, Mo, V, Nb, W, Co, Ni, etc. The steel is mainly used in the field of high-carbon and high-alloy bearing steel. With the guarantee of scientific preparation method and heat treatment process, the new high-temperature powder bearing steel has the characteristics of higher strength and good toughness.

[0034] Example 1

[0035] The preparation method of the low-oxygen high-cleanliness powder metallurgy high-temperature bearing steel of this embodiment comprises the following steps:

[0036] Step 1: According to the ratio of each element in the alloy, high-purity alloy raw materials are used for mixing, and the raw material ratio is C: 1.20% ~ 1.70%, Cr: 3.0% ~ 5.0%, Mo: 9.5% ~ 12.0%, V: 1.50% ~ 2.50%, W: 5.0% ~ 7.0%, Ni: 0.02% ~ 1.0%, Co: 0.02% ~ 1.0%, Nb: 0.02% ~ 1.0%, and the balance is Fe. The master alloy is melted by vacuum induction method, and 100 kg of alloy steel casting rods are prepared in a 50 kg vacuum induction furnace. The casting rods should have low oxygen content and high cleanliness, P: <0.005%, S: <0.005%, O: <0.001%, N: <0.008%, H: <0.0001%.

[0037] Step 2: After the cast rod is heated and kept at 860°C for 6 hours for softening annealing, it is cooled to below 400°C at a rate of <40°C / h and air-cooled to obtain a high-purity master alloy rod.

[0038] Step 3: Prepare the alloy steel into electrode samples and perform rotary electrode atomization powder making (PREP) to obtain high-purity alloy powder. The powder is sieved in a sealed box to obtain high-purity alloy steel powder with a size of 0 to 200 μm. The oxygen content of the metal powder is required to be less than 0.005%. The alloy steel powder is packaged in a cylindrical package and heated at 500°C and 1×10 -3 The hot isostatic pressing process of the invention steel is required to heat the casing with the furnace at a pressure of 120MPa and a high temperature of 1130℃ for 3h, and then cool it to below 500℃ at a rate of <40℃ / h and air cool it to obtain a dense hot isostatic pressing sintered billet of the invention steel.

[0039] Step 4: After the steel billet is removed from the jacket and heated to 1200℃ for heat preservation, the hot isostatically pressed steel billet can be forged or hot rolled using deformation equipment such as forging hammers, presses, and rolling mills. The forging temperature range is 1180-900℃. A new type of high-temperature powder bearing steel forging material with a compression ratio of 3-10 is obtained. The carbide and matrix structure are refined and homogenized.

[0040] Step 5: After forging, the bar is annealed, heated at 860℃ for 4h, then cooled to 550℃ at a rate of <20℃ / h, air-cooled, and surface polished after annealing to obtain powder high-temperature bearing steel bar. The hardness of powder high-temperature bearing steel is required to be ≤340HBW, O<0.005%, N:<0.008%, H:<0.0001%.

[0041] Then, chemical analysis, structure and hardness samples were taken from the bars, and room temperature hardness and high temperature hardness properties were measured after quenching and tempering. The chemical composition results are shown in Table 1.

[0042] Table 1 Chemical composition of bearing steel of Example 1 (wt.%)

[0043]

[0044] The heat treatment method of the sample is as follows:

[0045] Quenching: 1190℃, keep warm for 30min, oil cooling;

[0046] Tempering: 560℃, keep warm for 1 hour, air cool. Temper twice.

[0047] Attached Figure 1 This is the quenching and tempering structure diagram of the test steel.

[0048] Table 2 Hardness at room temperature and high temperature

[0049]

[0050]

[0051] Table 3 Example Powder Steel Inclusion Rating

[0052]

[0053] Example 2

[0054] The preparation method of the low-oxygen high-cleanliness powder metallurgy high-temperature bearing steel of this embodiment comprises the following steps:

[0055] Step 1: According to the ratio of each element in the alloy, high-purity alloy raw materials are used for mixing, and the raw material ratio is C: 1.20% ~ 1.70%, Cr: 3.0% ~ 5.0%, Mo: 9.5% ~ 12.0%, V: 1.50% ~ 2.50%, W: 5.0% ~ 7.0%, Ni: 0.02% ~ 1.0%, Co: 0.02% ~ 1.0%, Nb: 0.02% ~ 1.0%, and the balance is Fe. The alloy steel ingot melted by 200kg vacuum induction + vacuum consumable method has ultra-low oxygen content and high cleanliness. The impurity element content in the alloy meets the following standards: P: <0.005%, S: <0.005%, O: <0.0008%, N: <0.008%, H: <0.0001%.

[0056] Step 2: After the ingot is heated and kept at 1200℃ for 6 hours, it is forged at a temperature range of 1150-900℃ to obtain a master alloy bar with high cleanliness. The bar is softened and annealed at 860℃ for 6 hours.

[0057] Step 3: After annealing, electrode samples are prepared and rotary electrode atomization powder (PREP) is performed to obtain high-purity alloy powder. The powder is sieved in a sealed box to obtain high-purity alloy steel powder with a size of 0 to 150 μm. The oxygen content of the metal powder is required to be less than 0.005%. The alloy steel powder is packaged in a cylindrical package and heated at 500°C and 1×10 -3 The high temperature vacuum degassing treatment is carried out under high vacuum of 10000 Pa for 20 hours, and then the brazing sealing is carried out to ensure that there is no leakage and air leakage. Then the powder encapsulation hot isostatic pressing sintering is carried out. The hot isostatic pressing process of the invention steel is required to heat the encapsulation with the furnace at a pressure of 150MPa and a high temperature of 1160℃ for 3 hours, and then cool to below 500℃ at a rate of <40℃ / h and air cool to obtain the dense hot isostatic pressing sintered billet of the invention steel.

[0058] Step 4: After the steel billet is removed from the jacket and the hot isostatically pressed steel billet is heated to 1200℃ and kept for 6 hours, it can be forged or hot rolled using deformation equipment such as forging hammers, presses, and rolling mills. The forging temperature range is 1180-900℃. A new type of high-temperature powder bearing steel forging material with a compression ratio of 3-10 is obtained. The carbide and matrix structure are refined and homogenized.

[0059] Step 5: After forging, the bar is annealed, heated at 860℃ for 4h, then cooled to 550℃ at a rate of <20℃ / h, air-cooled, and surface polished after annealing to obtain powder high-temperature bearing steel bar. The hardness of the powder high-temperature bearing steel bar after annealing is required to be ≤340HBW, O<0.005%, N:<0.008%, H:<0.0001%.

[0060] Then, chemical analysis, structure, hardness and tensile impact specimens were taken from the bars, and the room temperature and high temperature mechanical properties were measured after quenching + tempering. The chemical composition results are shown in Table 4.

[0061] Table 4 Chemical composition of bearing steel in Example 2 (wt.%)

[0062]

[0063] The heat treatment process of the sample is as follows:

[0064] Quenching: 1200℃, keep warm for 30min, oil cooling;

[0065] Tempering: 540℃, keep warm for 1 hour, air cool. Temper 3 times.

[0066] Figure 2 The annealing structure and quenching and tempering structure diagram of the test steel.

[0067] Table 5 Hardness of bearing steel at room temperature and high temperature in Example 2

[0068]

[0069] Table 6 Inclusion rating of bearing steel in Example 2

[0070]

[0071] Table 7 Room temperature tensile and unnotched impact toughness of bearing steel of Example 2

[0072]

[0073] The low-oxygen, high-cleanliness powder metallurgy high-temperature bearing steel of the present invention can control the oxygen content of the powder metallurgy steel to an ultra-low oxygen content of <0.005%, while avoiding the introduction of refractory inclusions during smelting during the powder making process, thereby ensuring its high cleanliness. In addition, the carbides in the high-carbon, high-alloy steel are refined and the uniformity of the structure is improved through alloying design such as Nb and powder metallurgy preparation. Compared with the prior art, the comprehensive mechanical properties of high-carbon, high-alloy steel are improved in terms of both refined carbide structure and ultra-low oxygen and high cleanliness, which is of great value for the preparation of high-carbon, high-alloy steel with high purity and high uniformity.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A low-oxygen, high-cleanliness powder metallurgy high-temperature bearing steel, characterized by: The chemical composition range of bearing steel is as follows by weight percentage: C: 1.20% ~ 1.70%, Cr: 3.0% ~ 5.0%, Mo: 9.5% ~ 12.0%, V: 1.50% ~ 2.50%, W: 5.0% ~ 7.0%, Ni: 0.02% ~ 1.0%, Co: 0.02% ~ 1.0%, Nb: 0.02% ~ 1.0%, P: <0.005%, S: <0.005%, O: <0.005%, N: <0.008%, H: <0.0001%, and the balance is Fe.

2. A method for preparing low-oxygen, high-cleanliness powder metallurgy high-temperature bearing steel, characterized in that: The following steps are involved: Step 1: The bearing steel master alloy is melted by vacuum induction method, and the ingot is cast to obtain a high-purity master alloy with low oxygen content and high cleanliness; the impurity element content in the alloy meets the following standards: P: <0.005%, S: <0.005%, O: <0.001%, N: <0.008%, H: <0.0001%; Step 2: The high-purity master alloy is heat treated or directly peeled and the riser is cut off to obtain a high-cleanliness master alloy; Step 3: Prepare the alloy steel into electrode samples, and use the rotating electrode atomization powder making method to prepare high-purity alloy powder. After the powder is sieved, a high-purity metal powder of bearing steel with a purity of 0 to 200 μm is obtained. The alloy powder is packaged in a cylindrical sleeve and heated at 500 ° C and 1×10 -3 The high-temperature vacuum degassing treatment is carried out under high vacuum of 10000 Pa for more than 20 hours, and then the package brazing is sealed to ensure no leakage and air leakage; then the powder package hot isostatic pressing sintering is carried out; the hot isostatic pressing sintering process is that the package is heated with the furnace at a pressure of 110-160MPa and 1080-1200℃ for 1-5 hours, and then the temperature is controlled and cooled to below 500℃ at a rate of <40℃ / h, and then air-cooled to obtain a dense hot isostatic pressing sintered steel billet; Step 4: Remove the steel billet jacket, heat the hot isostatically pressed steel billet to 1200°C for insulation, and then use one or more deformation equipment such as a forging hammer, a press or a rolling mill to forge or hot roll the billet, and the forging temperature range is 1180-900°C; obtain a new high-temperature powder bearing steel forging material with a compression ratio of 3-10, and achieve the refinement and homogenization of carbides and matrix structures; Step 5: After forging, annealing is performed. The annealing process is heating and keeping at 840-900°C for 1-4h, then cooling to 550°C at a rate of <20°C / h, air cooling, and surface polishing after annealing to obtain powder high-temperature bearing steel bars; after annealing, the hardness of the high-temperature bearing steel is ≤340HBW, and the impurity element content in the alloy meets the following standards: O<0.005%, N: <0.008%, H: <0.0001%.

3. The method for preparing low-oxygen, high-cleanliness powder metallurgy high-temperature bearing steel according to claim 2, characterized in that: The heat treatment process of high temperature bearing steel is to keep it at 1150℃~1220℃ for 0.5~1 hour, then oil quench, and then keep it at 500~600℃ for 1~2 hours and temper it 2 or 3 times.

4. The method for preparing a low-oxygen, high-cleanliness powder metallurgy high-temperature bearing steel according to claim 2, characterized in that: In step 2, the heat treatment process of the master alloy is: annealing or forging + annealing; The annealing process is: heating at 700-900℃ for 5-8h, then cooling to below 400℃ at a rate of <40℃ / h, and air cooling; The forging + annealing process is as follows: the forging process is: heating and keeping at 1050-1200°C for 1-6h, forging in the temperature range of 1200-900°C to obtain the forging master alloy; then heating and keeping at 700-900°C for 5-8h, then cooling to below 400°C at a rate of <40°C / h, and air cooling.

5. The method for preparing low-oxygen, high-cleanliness powder metallurgy high-temperature bearing steel according to claim 2, characterized in that: In step 4, the hot isostatically pressed steel billet is heated to 1200°C and kept at this temperature for 6 hours before being forged or hot rolled.

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