Preparation method of superfine structure 8Cr4Mo4V bearing steel

Abstract

The invention belongs to the technical field of bearing steel preparation, and particularly relates to a superfine structure 8CrMo4V bearing steel preparation method which comprises the following steps that 1, 8Cr4Mo4V steel is subjected to forging treatment; (2) the forged 8Cr4Mo4V steel is subjected to temperature control rolling; 3, the 8Cr4Mo4V steel is subjected to isothermal quenching ultrafine treatment; and 4, the 8Cr4Mo4V steel is subjected to deep cooling and tempering treatment. Results show that the method can obviously refine original austenite grains and martensite substructures.

Description

Technical Field

[0001] The invention belongs to the technical field of bearing steel preparation, and specifically relates to a method for preparing ultra-fine structure 8CrMo4V bearing steel. Background Art

[0002] 8Cr4Mo4V steel is currently the most widely used steel for aircraft engine main shaft bearings, and fatigue performance is the main factor determining its service life. With the continuous development of aerospace technology, the service requirements of bearings are becoming more and more stringent, and at the same time, high requirements are placed on long life and high reliability, so it is necessary to break through the performance limits of bearing materials. For a long time, the improvement of the service performance of 8Cr4Mo4V steel has mainly relied on the improvement of steel purity and the refinement of primary carbides. With the development of metallurgical technology and hot processing technology, inclusions and large-sized primary carbides in steel have been effectively controlled.

[0003] The patent document with the announcement number CN11141203B discloses a method for obtaining an optimized quenching process for 8Cr4Mo4V steel. The method comprises the following steps: (1) determining a heating solution process; (2) determining the time point of the highest hardness of isothermal quenching; (3) performing a composite quenching treatment on the basis of step (2); (4) selecting an optimized composite quenching process sample; (5) subjecting the optimized composite quenching process sample obtained by step (4) to a tempering treatment at 520-550°C, 1.8-2.5h, and 3 to 4 times to obtain the final optimized heat-treated 8Cr4Mo4V steel. However, this patent technology still has the problem of insufficiently precise control, which is mainly to reduce the stress corrosion sensitivity of titanium alloy materials while ensuring that the materials have good plasticity and toughness.

[0004] Relevant studies have shown that with the refinement of inclusions and primary carbides, the coarse laths in the martensite matrix become an important factor causing fatigue crack initiation. Therefore, further refining the matrix structure of 8Cr4Mo4V steel becomes an important way to further improve its service performance. Summary of the invention

[0005] Aiming at the deficiencies of the prior art, the present invention proposes a method for preparing ultra-fine structure 8CrMo4V bearing steel.

[0006] This is achieved specifically through the following technical solutions:

[0007] A method for preparing ultrafine structure 8Cr4Mo4V bearing steel comprises the following steps:

[0008] Step 1: 8Cr4Mo4V steel is subjected to three-upsetting and three-drawing forging treatment, and the upsetting deformation amount each time is not less than 50%;

[0009] Step 2: Temperature-controlled rolling of the forged 8Cr4Mo4V steel;

[0010] Step 3: Perform isothermal quenching and ultra-fine treatment on 8Cr4Mo4V steel;

[0011] Step 4: deep cooling and tempering of 8Cr4Mo4V steel.

[0012] Furthermore, in step 2, the temperature of the temperature-controlled rolling furnace is controlled at 1100-1160°C, and the temperature control treatment is performed after the reduction reaches 30%-50% of the expected deformation amount. The final rolling is performed after the surface temperature of the bar is reduced to between 1000-1050°C, and the temperature after the final rolling is controlled at 950-1000°C.

[0013] Furthermore, in the isothermal quenching ultra-fine treatment process in step 3, the solution treatment temperature is 1090-1110°C, the holding time is 30-60min, and then the sample is taken out and placed in a salt bath furnace at 180-240°C for 30-180min, and then the sample is taken out and placed in quenching oil to cool to room temperature.

[0014] Furthermore, the deep cooling and tempering treatment process in step 4 is as follows: after the 8Cr4Mo4V steel is subjected to isothermal quenching and ultra-fine treatment, it is subjected to deep cooling treatment within 120 minutes, the deep cooling temperature is not higher than -50°C, and the constant temperature time is not less than 60 minutes. After deep cooling, tempering treatment is required, the tempering temperature is 550°C, and the constant temperature time is 2 hours. The above deep cooling and tempering treatment steps need to be repeated 3 times.

[0015] Beneficial effects:

[0016] The present invention aims at the demand for improving the performance of 8Cr4Mo4V bearing steel and the problem of fatigue cracks initiating in the matrix structure. The core invention content is to refine the original austenite grains and martensite substructures of 8Cr4Mo4V steel through large deformation forging, temperature-controlled rolling and isothermal quenching ultra-fine treatment, and finally achieve the purpose of improving the fatigue performance of 8Cr4Mo4V steel. Specifically, the coarse carbides are fully broken and the structure is homogenized through three-ton and three-draw forging deformation, which lays a good foundation for subsequent temperature-controlled rolling; the grain size of 8Cr4Mo4V steel is then regulated through temperature-controlled rolling. The grain size of 8Cr4Mo4V steel after rolling should not be greater than grade 8.0, and the austenite grains should be evenly distributed, and mixed crystals are not allowed; the solution treatment temperature is then controlled at 1090-1110°C to dissolve the carbides while preventing the excessive growth of the austenite grains; isothermal quenching is performed in step 3 to generate A small amount of bainite structure plays the role of dividing the original austenite grains and refining the martensite structure. The austempering temperature should be controlled between 180-240℃. If the temperature is too high, it will easily lead to coarse bainite structure. If the temperature is too low, the bainite phase transformation incubation period will be too long. After the warm quenching, the sample should be oil-cooled to room temperature to produce sufficient martensite phase transformation. The deep cryogenic treatment in step 4 should be carried out within 120 minutes after quenching. Its purpose is to promote the transformation of residual austenite to martensite and prevent austenite stabilization.

[0017] The present invention is different from the traditional isothermal quenching process. The main purpose of the isothermal quenching in the present invention is to divide the original austenite grains through bainite phase transformation, so as to refine the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The metallographic photograph and EBSD photograph of the structure of 8Cr4Mo4V steel prepared by the existing 8Cr4Mo4V steel preparation process;

[0019] Figure 2 The metallographic photograph and EBSD photograph of the 8Cr4Mo4V steel structure prepared in Example 1;

[0020] Figure 3 Metallographic photographs and EBSD photographs of the 8Cr4Mo4V steel structure prepared in Example 2. DETAILED DESCRIPTION

[0021] The specific embodiments of the present invention are further described in detail below, but the present invention is not limited to these embodiments, and any improvement or substitution based on the basic spirit of the present embodiment still falls within the scope of protection required by the claims of the present invention.

[0022] Existing 8Cr4Mo4V steel preparation process:

[0023] (1) 8Cr4Mo4V steel consumable ingots are smelted by double vacuum industry and subjected to high temperature homogenization annealing;

[0024] (2) After high-temperature homogenization annealing, the 8Cr4Mo4V steel is charged into the furnace and heated to 1130 to 1180°C. After being kept at this temperature for 10 hours, it is taken out of the furnace for forging. The forging process is three upsetting and three drawing. The size of the forged bar is a square bar or round bar with a side length or diameter between 90 and 200 mm. After forging, the bar is cooled to a black skin state and then spheroidized annealing or stress relief annealing is performed. The spheroidized annealing or stress relief annealing process is carried out according to the process commonly used for high-speed steel.

[0025] (3) After forging, the bar is slowly heated to 1100-1160°C, and after being fully kept warm, it is rolled out of the furnace. After the deformation reaches 30%-50% of the total deformation, the bar is temperature-controlled, and the bar is cooled to between 1000-1050°C for final rolling. The temperature after final rolling is controlled at 950-1000°C. After rolling, the bar is air-cooled to a black skin state for spheroidizing annealing or air-cooled to room temperature and then reheated for spheroidizing annealing;

[0026] (4) Sampling the rolled bars after spheroidizing annealing to make samples or parts. This process is rough machining, and appropriate machining allowance is reserved;

[0027] (5) After rough processing, the sample or component is slowly heated to 1190-1100℃ in the furnace for solution treatment. According to the size of the sample or component, the appropriate heating rate and holding time (30-60min) are selected.

[0028] (6) The solution treated sample is placed in a salt bath furnace at 180-240°C for 30-180 min. After the salt bath, the sample is cooled to room temperature with oil;

[0029] (7) After oil cooling, take out the sample and perform deep cooling treatment within 120 minutes, cool it with the furnace, the deep cooling temperature is not higher than -50℃, and the constant temperature time is not less than 60 minutes. After deep cooling, heat it to room temperature and then perform tempering treatment. The tempering temperature is 550℃ and the constant temperature time is 2 hours. The above deep cooling and tempering treatment steps need to be repeated 3 times.

[0030] The microstructure of 8Cr4Mo4V steel prepared by this process is shown in Figure 1 , the width of the martensite lath bundle is about 1.25μm.

[0031] Example 1

[0032] (1) 8Cr4Mo4V steel consumable ingots are smelted by double vacuum industry and subjected to high temperature homogenization annealing;

[0033] (2) After high-temperature homogenization annealing, the 8Cr4Mo4V steel is charged into the furnace and heated to 1130°C. After being kept at this temperature for 10 hours, it is taken out of the furnace for forging. The forging process is three upsetting and three drawing. The size of the forged bar is a square bar with a side length of 120 mm. After forging, the bar is cooled to a black skin state and then spheroidized annealing or stress relief annealing is performed. The spheroidized annealing or stress relief annealing process is carried out according to the process commonly used for high-speed steel.

[0034] (3) After forging, the bar is slowly heated to 1100°C, and after sufficient heat preservation, it is rolled out of the furnace. After the deformation reaches 30% of the total deformation, the bar is temperature controlled and cooled to 1050°C for final rolling. The final rolling temperature is 963°C. After rolling, the bar is air-cooled to a black skin state for spheroidizing annealing;

[0035] (4) Sampling the rolled bars after spheroidizing annealing and processing them into samples or parts;

[0036] (5) After rough processing, the sample or parts are slowly heated to 1090℃ for solution treatment, and the holding time is 30min;

[0037] (6) The solution treated sample was placed in a salt bath furnace at 220 °C for 120 min. After the salt bath, the sample was cooled to room temperature with oil.

[0038] (7) After oil cooling, the sample is taken out and deep-cooled within 120 minutes, cooled with the furnace, the deep-cooling temperature is -75℃, the constant temperature time is 120 minutes, and after deep cooling, it is heated to room temperature and tempered, the tempering temperature is 550℃, the constant temperature time is 2 hours, and the above deep cooling and tempering treatment steps need to be repeated 3 times.

[0039] The metallographic photos and EBSD photos of Example 1 are shown in Figure 2 ,According to statistics, the width of the martensite lath bundle is about 0.91μm.

[0040] Example 2

[0041] Except that the isothermal time in process (6) is 180 min, the other step parameters are the same as those in Example 1;

[0042] The metallographic photos and EBSD photos of Example 2 are shown in Figure 3 According to statistics, the width of the martensite lath bundle is about 0.80μm.

[0043] Although the present invention has selected the preferred embodiments disclosed above, it is not intended to limit the present invention. Any researcher in the field can use the design parameters and contents in the above disclosed embodiments to change and modify the research scheme of the present invention without departing from the spirit and scope of the present invention. Therefore, any simple modification, parameter change and modification made to the above embodiments based on the research essence of the present invention without departing from the content of the present invention, all belong to the protection scope of the present invention.

Claims

1. A method for preparing ultrafine structure 8Cr4Mo4V bearing steel, characterized in that: The following steps are involved: Step 1: 8Cr4Mo4V steel is subjected to three-upsetting and three-drawing forging treatment, and the upsetting deformation amount each time is not less than 50%; Step 2: Temperature-controlled rolling of the forged 8Cr4Mo4V steel; Step 3: Perform isothermal quenching and ultra-fine treatment on 8Cr4Mo4V steel; Step 4: deep cooling and tempering of 8Cr4Mo4V steel.

2. The method for preparing ultrafine structure 8Cr4Mo4V bearing steel according to claim 1, characterized in that: In step 2, the temperature of the temperature-controlled rolling furnace is controlled at 1100-1160°C, and the temperature control treatment is performed after the reduction reaches 30%-50% of the expected deformation. The final rolling is performed after the surface temperature of the bar is reduced to between 1000-1050°C, and the temperature after the final rolling is controlled at 950-1000°C.

3. The method for preparing ultrafine structure 8Cr4Mo4V bearing steel according to claim 1, characterized in that: In the isothermal quenching ultra-fine treatment process in step 3, the solution treatment temperature is 1090-1110°C, the holding time is 30-60min, then the sample is taken out and placed in a salt bath furnace at 180-240°C for 30-180min, then the sample is taken out and placed in quenching oil to cool to room temperature.

4. The method for preparing ultrafine structure 8Cr4Mo4V bearing steel according to claim 1, characterized in that: The deep cooling and tempering treatment process in step 4 is as follows: after the 8Cr4Mo4V steel is subjected to isothermal quenching and ultra-fine treatment, it is subjected to deep cooling treatment within 120 minutes, the deep cooling temperature is not higher than -50°C, and the constant temperature time is not less than 60 minutes. After deep cooling, tempering treatment is required, the tempering temperature is 550°C, and the constant temperature time is 2 hours. The above deep cooling and tempering treatment steps need to be repeated 3 times.

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