Abstract: Heat treatment of a camshaft with a large ratio of length and diameter for a type of intelligent diesel engine is difficult to produce, and need special technology to deal with. In order to find a solution for this, a series of equipment including multi-purpose furnace, vacuum tempering furnace, pit type carburizing furnace, cryogenic box, pit type furnace, straightening machines and other equipment was used on the base of key technics analysis. The production practice indicates that the camshaft with a high hardness, good microstructure and high mechanical properties, and less distortion can be produced by the processes of cleaning, stop-off coating and drying, preheating, carburizing and high temperature tempering and alignment, stress relieving in vacuum, machining, hardening, cryogenic treatment, and tempering. It is pointed out that multiple cycle carburizing with high and low carbon potential in turn in multi-purpose furnace has more obvious advantages than the traditional two stages carburizing, such as higher carburizing speed, better carbide morphology, higher hardness, flatter hardness gradient, shorter carburizing time, and higher production efficiency. The heat treatment process scheme of this part is adopted, and the final processed specimens fully meet the requirements of users.

Key words: 18CrNiMo7-6 steel, camshaft, hardness, heat treatment distortion, microstructure