High-carbon chromium bearing steel bearing isothermal bainite quenching heat treatment process

Abstract

The application discloses a high-carbon chromium bearing steel bearing isothermal bainite quenching heat treatment process, and belongs to the technical field of bearing processing and manufacturing. The application mainly solves the problem of poor toughness of bearings caused by the existing high-carbon chromium bearing steel bearing heat treatment process. The main features of the application are as follows: step one, preheating: preheat the high-carbon chromium bearing steel bearing workpiece in spheroidizing annealing organization; step two, austenitizing: perform austenitizing process treatment on the preheated high-carbon chromium bearing steel bearing workpiece; step three, salt bath quenching: perform salt bath quenching process treatment on the high-carbon chromium bearing steel bearing workpiece subjected to the austenitizing process treatment, so that the workpiece is converted into the medium temperature zone after passing through the C curve nose tip, and bainite organization is obtained. The application has the characteristics of forming bainite organization on the surface of the bearing inner ring, improving the fracture strength and impact resistance of the bearing, and is mainly used for the heat treatment of commercial vehicle axle guide bearings.

Description

Technical Field

[0001] This invention belongs to the field of bearing processing and manufacturing technology, and specifically relates to an isothermal bainitic quenching process for high carbon chromium bearing steel bearings. Background Technology

[0002] Commercial vehicle axle guide bearings generally bear large impact loads and have high requirements for fracture strength. Most domestically produced automotive bearings use high-carbon chromium bearing steel, and there are generally two heat treatment processes: (1) conventional martensitic quenching and tempering heat treatment process, which forms a hard and brittle martensite structure with high hardness but poor toughness; (2) carburizing quenching and tempering heat treatment process, which is mainly used to improve the fatigue performance of bearings. Compared with carburizing quenching and tempering process, bainitic quenching process is relatively simple.

[0003] CN 110106323 A discloses a method for isothermal quenching heat treatment of medium carbon bearing steel, which involves normalizing, spheroidizing annealing, bainitic quenching and low-temperature tempering to obtain a composite structure of lower bainite and martensite, which has high hardness, wear resistance, good toughness and good fatigue life.

[0004] CN 110106323 A discloses a method for isothermal quenching of GCr15SiMn steel bearing rings. GCr15SiMn has strong hardenability, and the effective wall thickness of the bearing rings can be increased to about 40mm, thereby expanding the application range of GCr15SiMn steel in the manufacture of bearing rings and reducing the manufacturing cost of bearings.

[0005] CN 10874085 A discloses a bainitic quenching process for small (outer diameter 50-80mm) thin-walled bearing rings made of GCr15 steel, which enables such products to undergo bainitic quenching on a bainitic production line and effectively controls the deformation rate of the rings after heat treatment.

[0006] Currently, there are relevant patents for the bainitic quenching process of bearing steel, but there are no reports of this heat treatment process being applied to automotive guide bearings made of high-carbon chromium bearing steel. Summary of the Invention

[0007] The purpose of this invention is to provide a method for isothermal bainitic quenching heat treatment of high carbon chromium bearing steel bearings, so that after isothermal quenching, a composite structure of lower bainite and martensite is obtained, and the degree of deformation can be effectively controlled and good fracture toughness can be obtained, so as to meet the fracture toughness requirements of commercial vehicle guide bearings under heavy impact load conditions.

[0008] The technical solution of this invention is: an isothermal bainitic quenching heat treatment process for high-carbon chromium bearing steel bearings, characterized by the following process steps:

[0009] Step 1, Preheating:

[0010] The high-carbon chromium bearing steel bearing workpiece with spheroidized annealing structure will be preheated.

[0011] Step 2, austenitization:

[0012] The preheated high-carbon chromium bearing steel bearing workpieces are subjected to an austenitizing process.

[0013] Step 3, salt bath quenching:

[0014] The high-carbon chromium bearing steel bearing workpieces treated with the above austenitizing process were subjected to salt bath quenching to obtain bainitic structure.

[0015] The technical solution of the present invention includes the following process steps:

[0016] Step 1, Preheating:

[0017] The high-carbon chromium bearing steel bearing workpiece with spheroidized annealing structure is preheated at a temperature of 480-520℃ for 8-12 minutes.

[0018] Step 2, austenitization:

[0019] The preheated high-carbon chromium bearing steel bearing workpieces are subjected to an austenitizing process. First, they are heated to 760-800℃ and held for 8-12 minutes, with a carbon potential of 1.0%. Then, they are heated to 820℃-830℃ for 38-42 minutes and held for 28-32 minutes, with a carbon potential of 1.0%.

[0020] Step 3, salt bath quenching:

[0021] The high-carbon chromium bearing steel bearing workpieces treated with the above austenitizing process are subjected to salt bath quenching. The quenching temperature is 220-240℃, the quenching time is 12-15min, the holding time is 28-32min, the quenching medium is 50%KNO3+50%NaNO2, and the salt bath stirring frequency is 40Hz.

[0022] The technical solution of the present invention includes the following process steps:

[0023] Step 1, Preheating:

[0024] The high-carbon chromium bearing steel bearing workpiece with spheroidized annealing structure is preheated at a temperature of 480-490℃, 490-510℃ or 510-520℃ for a time of 8-9min, 9-11min or 11-12min.

[0025] Step 2, austenitization:

[0026] The preheated high-carbon chromium bearing steel bearing workpieces are subjected to an austenitizing process. First, the workpieces are heated to 760-770℃, 770-790℃, or 790-800℃, with holding times of 8-9 min, 9-11 min, or 11-12 min, and a carbon potential of 1.0%. Then, they are heated to 820℃-830℃ for 38-39 min, 39-41 min, or 41-42 min, with holding times of 28-29 min, 29-31 min, or 31-32 min, and a carbon potential of 1.0%.

[0027] Step 3, salt bath quenching:

[0028] The high-carbon chromium bearing steel bearing workpieces treated with the above austenitization process are subjected to salt bath quenching. The quenching temperature is 220-230℃ or 230-240℃, the quenching time is 12-13min, 13-14min or 14-15min, the holding time is 28-29min, 29-31min or 31-32min, the quenching medium is 50%KNO3+50%NaNO2, and the salt bath stirring frequency is 40Hz.

[0029] The technical solution of this invention includes the following process steps:

[0030] Step 1, Preheating:

[0031] The high-carbon chromium bearing steel bearing workpiece with spheroidized annealing structure is preheated at a temperature of 510℃ or 500℃ for 10 minutes.

[0032] Step 2, austenitization:

[0033] The preheated high-carbon chromium bearing steel bearing workpieces were subjected to an austenitizing process. First, they were heated to 780℃ and held for 10 minutes, with a carbon potential of 1.0%. Then, they were heated to 820℃-830℃ for 40 minutes and held for 30 minutes, with a carbon potential of 1.0%.

[0034] Step 3, salt bath quenching:

[0035] The high-carbon chromium bearing steel bearing workpieces treated with the above austenitizing process are subjected to salt bath quenching. The quenching temperature is 220-240℃, the quenching time is 12-15min, the holding time is 30min, the quenching medium is 50%KNO3+50%NaNO2, and the salt bath stirring frequency is 40Hz.

[0036] In the technical solution of the present invention, the preheating in step one is carried out in a preheating furnace; the austenitization in step two is carried out in the rear chamber of a heating furnace or an isothermal quenching heat treatment device; and the salt bath quenching in step three is carried out in the quenching tank of an isothermal quenching heat treatment device.

[0037] The high-carbon chromium bearing steel bearing workpiece described in the technical solution of this invention is a high-carbon chromium bearing steel bearing ring.

[0038] The technical solution of the present invention also includes:

[0039] Step 4, Tempering:

[0040] The high-carbon chromium bearing steel bearing workpieces that have undergone salt bath quenching are subjected to tempering in a continuous tempering heat treatment production line. The tempering temperature is 160℃-180℃ and the tempering time is 120-180min.

[0041] The technical solution of this invention involves cleaning the high-carbon chromium bearing steel bearing workpiece after the tempering process.

[0042] The technical solution of this invention involves cleaning the high-carbon chromium bearing steel bearing workpiece after salt bath quenching.

[0043] The high-carbon chromium bearing steel bearing workpiece described in the technical solution of this invention is cleaned in a cleaning equipment.

[0044] The present invention has the following positive effects:

[0045] First, this invention is mainly used to improve the NJ308EVX2 guide bearing of the 440 axle of Dongfeng Dana Axle Co., Ltd., to meet the fracture toughness and strength requirements of automotive guide bearings.

[0046] Secondly, compared to martensitic quenching and tempering, isothermal bainitic quenching heat treatment forms lower bainite. Bainitic structure has higher wear resistance and better toughness than martensitic structure of the same hardness.

[0047] Third, because the transformation of bainite is slow rather than instantaneous martensite, the structural stress is smaller throughout the process, the dimensional expansion difference in the diameter direction of the sample is smaller, and the dimensional change is more concentrated, which helps to reduce the difficulty of pre-deformation control in subsequent grinding. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the microstructure of the bearing ring after isothermal bainitic quenching according to an embodiment of the present invention. Detailed Implementation

[0049] The present invention will be further described in detail below with reference to specific embodiments.

[0050] Example 1:

[0051] A cylindrical roller guide bearing NJ308EVX2JTB-KC, material: GCr15 steel, outer diameter φ51 mm. Before heat treatment, the workpiece has a spheroidized annealing structure and is required to be austempered. The heat treatment performance meets the technical requirements for bearing parts in GB / T34891-2017 standard.

[0052] The austempering process for the ring of the cylindrical roller guide bearing includes the following steps:

[0053] Step 1, preheating:

[0054] The preheating step is completed in a preheating furnace. The preheating temperature is 500°C and the holding time is 10 min.

[0055] Step 2, austenitization:

[0056] Austenitization is carried out in the heating chamber of an austempering heat treatment equipment. The bearing ring is heated to 780°C, held for 10 min, and the carbon potential is 1.0%. Subsequently, it is heated to 820°C - 830°C, heated for 40 min, held for 30 min, and the carbon potential is 1.0%.

[0057] Step 3, salt bath quenching:

[0058] Salt bath quenching is carried out in the quenching tank of an austempering heat treatment equipment. The temperature is 240°C, the quenching time is 12 - 15 min, the holding time is 30 min, the quenching medium is 50% KNO3 + 50% NaNO2, and the stirring frequency of the salt bath is 40 Hz. After passing through the nose of the C curve, it is transferred to the isothermal transformation in the medium temperature zone to obtain a bainite structure. After the salt bath quenching is completed, the surface of the bearing ring is cleaned, which is completed in a cleaning machine.

[0059] Figure 1 It is a schematic diagram of the surface layer structure after the austempering treatment of the workpiece in Example 1, meeting the technical requirements for the austempered bearing parts in GB / T34891-2017 standard.

[0060] Table 1 shows the results of dimensional inspection, metallographic inspection and hardness inspection of the bearing ring of the workpiece in Example 1 after heat treatment, all of which meet the quality technical requirements of the parts. Using the GB / T34981-2017 standard, for the bainite grade, the fifth level diagram, less than level 1 is qualified.

[0061] Table 1 Inspection Results of the Austempered Process of the Workpiece in Example 1 after Heat Treatment

[0062]

[0063] Example 2:

[0064] Model 32213 tapered roller guide bearing, material: GCr15 steel, outer diameter φ51 mm, the workpiece has a spheroidized annealed structure before heat treatment, and bainitic quenching is required. The heat treatment performance meets the technical requirements for bearing parts in GB / T34891-2017 standard.

[0065] The isothermal bainitic quenching process for tapered roller guide bearing rings is the same as the isothermal bainitic quenching process for cylindrical roller guide bearing rings in Example 1.

[0066] Table 2 Comparison of deformation results of the two processes for the part in Example 2

[0067]

[0068] Table 2 compares the deformation of the parts prepared by isothermal quenching of bainitic material and conventional quenching and tempering of martensitic material in Example 2. 30 samples were taken. The data in Table 2 show that after isothermal quenching of bainitic material, the expansion along the diameter direction of the part is greater than that after quenching and tempering. Furthermore, due to the different quenching and cooling methods, the range of outer diameter expansion is better than that of conventional martensitic quenching and tempering, which facilitates the subsequent grinding allowance and ensures the dimensional accuracy after grinding.

[0069] A flange fracture test was performed on the bearing of Example 1 using a YWA-2000 testing machine. An axial load was slowly applied to the bearing at a speed of 10 KN / S until the inner ring of the bearing fractured. The test load value at the time of bearing fracture was recorded.

[0070] Table 3 compares the fracture toughness of the parts prepared in Example 1 with that prepared using conventional martensitic quenching and tempering. Three sets of samples were prepared for each process. After bainitic quenching, the average maximum axial force at bearing fracture increased from 124.3 KN to 152.7 KN. The fracture toughness of the parts heat-treated using the process of this invention is higher than that of the parts prepared using conventional martensitic quenching and tempering, which can effectively improve the fracture toughness value of bearings.

[0071] Table 3 Comparison of fracture test results of the parts manufactured under two processes in Example 1

[0072]

[0073] This invention applies this process to the heat treatment of automotive guide bearing rings to improve their fracture toughness and increase their fracture strength.

Claims

1. A high-carbon chromium bearing steel isothermal bainitic quenching heat treatment process for bearings used in commercial vehicle axle guide bearings, characterized in that... The process includes the following steps: Step 1, Preheating: The high-carbon chromium bearing steel bearing workpiece with spheroidized annealing structure is preheated at a temperature of 480-520℃ and held for 8-12 minutes. Step 2, austenitization: The preheated high-carbon chromium bearing steel bearing workpieces are subjected to an austenitizing process. First, they are heated to 760-800℃ and held for 8-12 minutes, with a carbon potential of 1.0%. Then, they are heated to 820℃-830℃ for 38-42 minutes and held for 28-32 minutes, with a carbon potential of 1.0%. Step 3, salt bath quenching: The high-carbon chromium bearing steel bearing workpieces treated with the above austenitizing process are subjected to salt bath quenching. The quenching temperature is 220-240℃, the quenching time is 12-15min, the holding time is 28-32min, the quenching medium is 50%KNO3+50%NaNO2, and the salt bath stirring frequency is 40Hz to obtain a bainitic structure. The bainitic structure is a composite structure of lower bainite and martensite. Step 4, Tempering: The high-carbon chromium bearing steel bearing workpieces treated by the above salt bath quenching process are subjected to tempering process in a continuous tempering heat treatment production line. The tempering temperature is 160℃-180℃ and the tempering time is 120-180min.

2. The isothermal bainitic quenching heat treatment process for high-carbon chromium bearing steel bearings according to claim 1, characterized in that... The process includes the following steps: Step 1, Preheating: The high-carbon chromium bearing steel bearing workpiece with spheroidized annealing structure is preheated at a temperature of 480-490℃, 490-510℃ or 510-520℃, and the holding time is 8-9min, 9-11min or 11-12min. Step 2, austenitization: The preheated high-carbon chromium bearing steel bearing workpieces are subjected to an austenitizing process. First, the workpieces are heated to 760-770℃, 770-790℃, or 790-800℃, with holding times of 8-9 min, 9-11 min, or 11-12 min, and a carbon potential of 1.0%. Then, they are heated to 820℃-830℃ for 38-39 min, 39-41 min, or 41-42 min, with holding times of 28-29 min, 29-31 min, or 31-32 min, and a carbon potential of 1.0%. Step 3, salt bath quenching: The high-carbon chromium bearing steel bearing workpieces treated with the above austenitization process are subjected to salt bath quenching. The quenching temperature is 220-230℃ or 230-240℃, the quenching time is 12-13min, 13-14min or 14-15min, the holding time is 28-29min, 29-31min or 31-32min, the quenching medium is 50%KNO3+50%NaNO2, and the salt bath stirring frequency is 40Hz.

3. The isothermal bainitic quenching heat treatment process for high-carbon chromium bearing steel bearings according to claim 1, characterized in that... The process includes the following steps: Step 1, Preheating: The high-carbon chromium bearing steel bearing workpiece with spheroidized annealing structure is preheated to a temperature of 510℃ or 500℃ and held for 10 minutes. Step 2, austenitization: The preheated high-carbon chromium bearing steel bearing workpieces were subjected to an austenitizing process. First, they were heated to 780℃ and held for 10 minutes, with a carbon potential of 1.0%. Then, they were heated to 820℃-830℃ for 40 minutes and held for 30 minutes, with a carbon potential of 1.0%. Step 3, salt bath quenching: The high-carbon chromium bearing steel bearing workpieces treated with the above austenitizing process are subjected to salt bath quenching. The quenching temperature is 220-240℃, the quenching time is 12-15min, the holding time is 30min, the quenching medium is 50%KNO3+50%NaNO2, and the salt bath stirring frequency is 40Hz.

4. The isothermal bainitic quenching heat treatment process for high-carbon chromium bearing steel bearings according to any one of claims 1-3, characterized in that: The preheating described in step one is carried out in a preheating furnace; the austenitization described in step two is carried out in the rear chamber of a heating furnace or isothermal quenching heat treatment equipment; and the salt bath quenching described in step three is carried out in the quenching tank of an isothermal quenching heat treatment equipment.

5. The isothermal bainitic quenching heat treatment process for high-carbon chromium bearing steel bearings according to any one of claims 1-3, characterized in that: The high-carbon chromium bearing steel bearing workpiece mentioned above is a high-carbon chromium bearing steel bearing ring.

6. The isothermal bainitic quenching heat treatment process for high-carbon chromium bearing steel bearings according to any one of claims 1-3, characterized in that: The high-carbon chromium bearing steel bearing workpieces are cleaned after the tempering process.

7. The isothermal bainitic quenching heat treatment process for high-carbon chromium bearing steel bearings according to claim 5, characterized in that: Clean the high-carbon chromium bearing steel bearing workpiece after salt bath quenching.

8. The isothermal bainitic quenching heat treatment process for high-carbon chromium bearing steel bearings according to claim 6, characterized in that: The high-carbon chromium bearing steel bearing workpiece is cleaned in a cleaning equipment.

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