Effect of spot continual induction hardening on the microstructure of steels: Comparison between AISI 1045 and 5140 steels

Spot continual induction hardening (SCIH) is a surface heat treatment process, which can strengthen more than one small area or relative large area on complicated component surface. In order to investigate the difference between AISI 1045 and 5140 steels on the microstructure and mechanical properties after SCIH, the microstructure, microhardness and residual stresses with different process parameters were analyzed. The results showed that there was only martensite in hardened area of AISI 5140 steel specimens while a mixture of martensite and pearlite was found in hardened area of AISI 1045. The domain size of both materials in {110} diffraction direction in hardened area was smaller than matrix area and decreased with the increasing of inductor feed velocity. The hardness distributions on the surface and in depth of AISI 5140 were more uniform than that of AISI 1045 due to the alloy element chromium, which can delay the transformation from austenite to pearlite. The surface compressive stress in hardened area decreased and tensile stress in transitional area increased with the increasing of feed velocity in both material conditions. The achieved results indicate that the SCIH with relatively low feed velocity is more suitable for improving the mechanical properties of both materials.