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Gear steel high temperature carburizing process

The carburizing process is a traditional manufacturing process for service parts to obtain high hardness surfaces and strong toughness matching the core. The purpose is to improve the load-bearing capacity and service life of the parts, and ensure that the carburized parts have high load-bearing capacity, good impact resistance, contact resistance, Due to its strong bending fatigue ability, high surface hardness, and good wear resistance, the carburizing and quenching process has become the mainstream process for surface strengthening of key components. However, conventional carburizing has problems such as long process cycle, high energy consumption, and high labor intensity, which seriously affects production efficiency and becomes a bottleneck in the gear manufacturing process. In order to solve the above problems, it is necessary to carry out research on high-temperature carburizing technology. Preliminary research results show that when the carburizing temperature is increased to 1050°C, the carburizing diffusion coefficient increases by 7 times, significantly shortening the carburizing process time and improving the carburizing process efficiency.

20Cr2Ni4A steel is a high Cr and Ni carburized alloy steel. Due to its high strength, good toughness, resistance to contact fatigue and good anti-gluing ability, it has become the material of choice for gears in heavy-duty vehicle transmission systems. The high-temperature carburizing test equipment uses SIMUWU vacuum carburizing furnace. The process conditions are to use high temperature and high carbon potential for carburization under controlled atmosphere conditions. The diffusion temperature is higher than the strong penetration temperature to facilitate the diffusion of high-concentration carbon-rich atmosphere. The carburizing gas uses propane (CH) and N. After carburizing, the oil is cooled to a certain temperature, and high-temperature tempering is performed after the oil cooling process is completed in order to continue the decomposition of residual austenite. After high-temperature tempering, air cooling is performed, and then secondary heating oil quenching is performed. Using the principle of recovery and re-hardening, the temperature is raised to 860 °C for quenching after isothermation at 750 °C to refine the austenite grains and meet the particle size requirements. After the vacuum quenching process is completed, low temperature tempering at 180°C is performed. In order to compare carburizing processes, conventional carburizing process tests were also conducted at the same time. The conventional carburizing process is carburizing at 930°C → high temperature tempering at 650°C → secondary heating oil quenching at 860°C → low temperature tempering at 180°C.

High temperature carburizing process conclusion
1) After high-temperature carburizing heat treatment, the structure of the carburized layer of 20Cr2N4A steel is tempered martensite, dispersed carbide particles and a small amount of retained austenite. The hardness and carbon concentration gradient of the carburized layer change relatively slowly, and the effective hardened layer is deep. Reaching 2.0~2.4mm (at 550 HV), the surface hardness of the carburized layer is 58~62HRC, the austenite grain size can reach about 8 levels, and the sample verification indicators meet the technical requirements of the carburizing process.
2) When the effective hardened layer depth is (2.2±0.2)mm, the process time required for conventional carburizing of 20Cr2Ni4A steel is 26 h, while the process time required for high-temperature carburizing is only 20.5h, which shows that high-temperature carburizing can Improve carburizing efficiency by more than 20%.