SAE8620 Carburized Steel Bearing Heat Treatment
In August 1997, our company produced 23 specifications and 67294 inch tapered bearing rings for American Rockwell Company. This is the first time that our company has used this material to mass produce bearings. In order to study the stability of bearing performance, we have carried out a comprehensive process test and achieved satisfactory results. The following only takes the IR-RHM218248 specification as an example for introduction.
1 Properties and material inspection of G20CrNiMoA steel
The chemical composition w (%) of the G20CrNiMoA steel tested is: 0121C, 0146Cr, 0168Ni, 0121Mo, 01025P, 01006S. The experimental analysis shows that the grain size is grade 6, brittle inclusions [grade 310, plastic inclusions [grade 210], and point-like non-deformable inclusions [grade 210]. The steel surface is in good condition.
2 heat treatment process
2.1 Annealing adopts forging waste heat annealing, and the final forging temperature is 970~940e,
2.2 Carburizing, quenching and tempering
The process curve of carburizing, quenching and tempering is shown in Figure 2. The cooling medium is N32 machine oil of 25~60e. During quenching, the crane is used for cooling up and down for 5 minutes, and after cooling, it is cooled in the oil tank for more than 10 minutes.
3 Test results and analysis
3.1 Annealing After annealing, the hardness is 195HB, and the organization is directional pearlite and ferrite. Due to the forging residual heat annealing, the cooling rate of the part after final forging is effectively controlled, and the formation of the Widmanstatin structure is controlled, reaching the ZBJ36001) 86 standard requirements. Bearing blank cutting performance is good.
3.2 Carburizing Direct Quenching
The quality inspection results of carburizing direct quenching are shown in Table 1. There are no coarse and reticulated carbides on the surface of the microstructure.
The analysis of the test results shows that the hardness of the core is low after carburizing and direct quenching, which is mainly caused by the large diameter of the sample and the poor cooling. Different contents of retained austenite were retained in G20CrNiMoA steel after quenching. The retained austenite content in this test is normal and will not affect the hardness after secondary quenching. Therefore, after carburizing and direct quenching, secondary quenching can be performed directly.
3.3 Secondary quenching
The hardness, hardened layer depth and microstructure test results after secondary quenching are shown in Table 2, and the microstructure of the surface layer is shown in Figure 3.
After the second quenching of the sample and the ferrule, sandblasting was carried out, and then the surface soft spots and cracks were checked by pickling, and no quality problems were found.
The surface carbon content of the finished product is required to be 0180%~1105%. The surface carbon concentration distribution curve of the sample after carburizing and secondary quenching is shown in Figure 4.
3.4 Temper resistance
The results of tempering and anti-tempering hardness test are shown in Table 3. In order to test the tempering resistance of the material after tempering, the sample is tempered again by the original tempering process, and the test is repeated at the vicinity of the original hardness. The re-examination results show that the tempering resistance is very good and can be used to manufacture rolling bearing parts.
4 Economic Benefit Analysis
The small and medium-sized carburized bearing rings produced by our company are all made of G20CrNi2MoA steel, and the purchase price is 9,000 yuan/t. This time, the bearing rings produced in the United States are made of new material G20CrNiMoA steel, and the purchase price is 8,700 yuan/t. Processing 67294 The bearing rings share 120t of steel, which can reduce the cost by 3.16 million yuan.
Through the test, it can be seen that the carburizing speed of G20CrNiMoA steel is faster than that of G20CrNi2MoA steel, and the carburizing time of each furnace can be reduced by 3 hours. 67,294 ferrules need to be carburized for 560 furnaces. The RJJ-280 carburizing furnace consumes 187 yuan per hour, which can save 3114 10,000 yuan, and the total economic benefit is 350,000 yuan.
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