Effects of Prior Microstructure and Induction Hardening Recipe on Surface Residual Stress in a 0.6 wt pct C Steel

Specimens of a 0.6 wt pct C steel with an as- hot rolled pearlitic microstructure and a quenched and tempered martensitic microstructure were machined into 15.9 mm diameter test specimens and induction hardened to an effective case depth of 3 mm using peak surface temperatures of 850 ^oC and 1050 ^oC. Vickers micro-hardness profiles verified the effective case depths. The case hardened microstructures were evaluated using light optical and scanning electron microscopy. Surface residual stresses before and after tempering at 176 ^oC were measured by x-ray evaluation at depths up to 1.4 mm. Specimens exhibited compressive surface stresses in the range of 200 MPa to more than 450 MPa. The relationships between prior microstructure and induction hardening process with the surface microstructure and the amount of surface compressive residual stress are presented and discussed.