Rare Earth Low Temperature Vacuum Carburizing Process of 20CrMnTi Steel

The test was carried out on the tractor end drive driven gear made of 20CrMnTi steel, the modulus is 3.5, the number of teeth is 52, the technical requirements: the surface hardness is 58 ~ 64HRC, the core hardness is greater than 35 ~ 48HRC, the depth of the vacuum carburized layer is 0.7 ~ 1 . 1mm, furnace capacity 64 pieces/furnace. The test equipment adopts RVC vacuum vacuum carburizing furnace, uses kerosene as vacuum carburizing agent and adds self-prepared rare earth infiltrating agent, manually controls the amount of infiltrating agent, and the diameter of the dripping hole is 3mm.

1 Effect of Rare Earth Vacuum Carburizing on Microstructure
Due to the high temperature of vacuum carburizing in the conventional process, the surface structure after vacuum carburizing is mainly blocky and strip-like. If the carbon potential is not well controlled, it is easy to form network carbides; The infiltration of elements makes the surface structure obviously refined, and the morphology of carbides is fine block and granular with large dispersion.
2 Effect of Rare Earth Vacuum Carburizing on Deformation
Using the rare earth vacuum carburizing process, due to the decrease of temperature, the thermal stress is reduced, and the deformation is also reduced accordingly. The gears subjected to 10 batches of vacuum carburizing and quenching treatment by the above-mentioned process were used for comparison test to check the spline hole. According to the inspection, 640 pieces of 10 furnaces treated by conventional technology need to be pushed with a push knife to push the spline hole, and 38 pieces need to be repaired mechanically, accounting for about 6%. There are 10 pieces with holes, and 640 pieces of 10 furnaces quenched into quenching medium after rare earth vacuum carburizing are all qualified.
3 Effect of Rare Earth Vacuum Carburizing on Microstructure
Due to the high temperature of vacuum carburizing in the conventional process, the surface structure after vacuum carburizing is mainly blocky and strip-like. If the carbon potential is not well controlled, it is easy to form network carbides; The infiltration of elements makes the surface structure obviously refined, and the morphology of carbides is fine block and granular with large dispersion.
4 Effect of Rare Earth Vacuum Carburizing on Deformation
Using the rare earth vacuum carburizing process, due to the decrease in temperature, the thermal stress decreases, and the deformation also decreases accordingly. The gears that have been subjected to 10 heats of vacuum carburizing and quenching with the above process are used for comparison tests, and the spline holes are checked. The results are: The gears were inspected with process plug gauges before vacuum carburizing, and all were qualified; after vacuum carburizing, they were inspected with comprehensive plug gauges. A total of 640 pieces were processed in 10 furnaces with conventional processes. Push knives were required to push the spline holes, and 38 pieces were mechanically repaired. 640 pieces in 10 furnaces of ordinary engine oil quenched after rare earth vacuum carburizing, 10 pieces need to be pushed, and 640 pieces of 10 furnaces quenched into quenching medium after rare earth vacuum carburizing are all qualified.
5 Conclusion
(1) Under certain temperature and pressure conditions, the addition of rare earth elements can significantly speed up the vacuum carburizing process, and the structure of the carburized layer is refined, so the performance of the carburized layer is also improved.
(2) The application of rare earth vacuum carburizing and the use of RVGQ vacuum quenching furnace can further reduce deformation and improve product quality.

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