A novel method of laser surface hardening treatment inducing different thermal processing condition for Thin-sectioned 100Cr6 steel

Abstract Hardness, microstructure and residual stresses induced on the engineered steel surface have a significant effect on the manufacturing process and the life time of the components. In the present work, these are analysed on laser-treated layer obtained on 100Cr6 bearing steel surface involving different thermal processing conditions. Prior to laser surface hardening treatment, the steel was spheroidized and hardened and tempered with resulting microstructure comprising of globular carbides in the matrix of martensite and retained austenite. A 20-mm wide diode laser beam was employed with a fixed peak laser power in both continuous wave and pulsed wave modes. Additionally, the treatment was carried out with an arrangement to induce fluid contact beneath the workpiece to enhance the heat transfer coefficient. Results indicated maximum improvement in hardness (1050–1100 HV) and compressive residual stress (−630 ± 20 MPa) with retention of core properties on treated surface processed with pulsed-wave mode under fluid contact owing to formation of refined microstructure constituting refined globular carbides (alloy nano-carbides) and retained austenite in martensite matrix. The extent of increase in compressive residual stress and treated layer microhardness was found to depend on the extent of martensite refinement and alloy nano-carbides dispersed in the matrix. Sliding wear tests conducted in both unlubricated and lubricated conditions indicated gradual improvement in wear resistance of the treated surface with increase in cooling rate governed by the thermal processing condition employed with conventionally hardened and tempered one being lowest and laser processed with pulsed wave mode under fluid contact being highest. Apparently, the laser treated surface processed with pulsed-wave mode under fluid contact exhibited reduction in friction coefficient with retention of core properties as compared to untreated counterpart.