Vacuum carburizing and quenching process of 15CINi4MoA steel cross shaft

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The cross shaft is an important part of the cross-shaped universal joint shaft. The material is often made of 15CINi4MoA steel. The final vacuum heat treatment process is vacuum carburizing and quenching. Because the Ni content (mass fraction) of the material is as high as 4%~4.5%, Ni and Fe can Infinite solid solution, expanding the austenite region, is the main alloying element for forming and stabilizing austenite, it will reduce the martensite transformation end temperature Mf point to below room temperature, and a considerable amount of retained austenite will remain after quenching, plus After carburizing, the austenite carbon concentration of the carburized layer is very high, reaching 0.7%~0.9%, and the high carbon content will also increase the amount of retained austenite. Therefore, there is a large amount of retained austenite in the quenched structure. Austenite is a phase with very low hardness, which will lead to a decrease in hardness, so that the hardness of the cross shaft after carburizing and quenching can only reach about 55HRC. The journal of the cross shaft is directly assembled with the bearing roller, and the hardness of the bearing roller is usually above 60HRC. Due to the low hardness of the cross shaft, the cross shaft is often quickly worn by the high hardness bearing roller, resulting in surface peeling failure.

In order to improve the carburizing and quenching hardness of the cross shaft, the common method is to add a cryogenic treatment process after vacuum carburizing and quenching, so that the retained austenite continues to transform into martensite, reducing the amount of retained austenite and increasing the amount of martensite, thereby increasing the hardness. However, the cost of cryogenic treatment is higher and the cryogenic time is longer.

After the cross shaft is vacuum carburized and quenched, induction quenching is performed on one of the journals, and the ferrule is continuously heated. After the cross shaft is vacuum carburized and quenched and tempered at a low temperature, its surface structure is high-carbon tempered horse. In this state, secondary quenching is carried out, and quenching cracks are prone to occur. In order to solve this problem, induction quenching adopts self-cooling for cooling.

15CINi4MoA steel cross-axis vacuum carburizing quenching and induction quenching can effectively increase the surface hardness of the workpiece to about 60HRC, and improve the overall hardness gradient value, increase the depth of the hardened layer, and improve the metallographic structure of the hardened layer.

Vacuum carburizing and quenching plus induction hardening process is used in the repair of 15CrNi4MoA steel cross shaft, which is more convenient and cost-effective than re-carburizing and quenching.

Equipment selection: The RVGQ series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment of tooling and molds. The good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum carburizing furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.