Impact of a multi-step heat treatment on different manufacturing routes of 18CrNiMo7-6 steel

Effect of an optimized multi-step heat-treatment routine on conventional (machining from wrought bar stock) and alternate manufacturing routes (hot forging and cold rotary forging) for producing flat cylindrical shaped machine drive components from 18CrNiMo7-6 steel was investigated. The microstructure and mechanical properties of the final component manufactured using these three different routes were analysed using optical microscopy, electron backscatter diffraction (EBSD), hardness testing, electro-thermal mechanical testing (ETMT) and rotary bending fatigue testing (RBFT) before and after implementing the multi-step heat-treatment. It was found that the multi-step heat-treatment transformed the as-received microstructure into the tempered martensitic microstructure, improving hardness, tensile and fatigue properties. The heat-treatment produced desired properties for the components manufactured by all three different routes. However the cold rotary forging, which is the most material utilizing route over the others, benefited the most from the optimized heat treatment.