Nb and Prior Microstructure Effects on Induction Hardening Response of 1060 Steel

Induction hardening is used to improve the hardness and fatigue strength of steel parts to allow higher performance with smaller parts. This project examines the influence of the starting microstructure and microalloy additions on the transformation to austenite during heating and to martensite during quenching. Specimens of two 1060 steels containing 0.03 wt pct Al or 0.016 wt pct Nb were evaluated using a dilatometer by heating at a rate of 200°C/s to 850°C and 950°C, holding for times ranging from 0 to 16 seconds, and quenching with He. Changing from a ferrite-pearlite to a martensitic initial microstructure lowered the M_s temperature by 50 to 70 ^oC and lowered the hardness by 10 to 15 HV. Nb increased hardness by 20 HV and heating conditions influenced results by 40 ^oC and 25 HV. Specimens were evaluated by Scanning Electron Microscopy to track changes in austenite grain size and cementite dissolution.