Surface Hardening and Microstructural Evolution of High Carbon Steel By Friction Stir Processing

In this investigation, effect of single pass FSP with Varying RPM of 150, 300 and 600 at a fixed feed rate of 70 mm min-1were studied for C70 steel which is majorly used in the automotive industry. Mechanical properties such as micro hardness and tensile strength along with microstructural refinement are investigated in depth by Scanning electron microscope and optical microscope. FSP resulted in three times enhanced micro hardness in comparison to BM with 220 HV hardness. A similar result was achieved with significant increase in the UTS of FSPed sample with 1190 MPa in comparison to a low UTS of 640 MPa of BM. A relative reduction of 50% in elongation of FSPed sample was recorded in comparison to 14% of BM. Increased strength was primarily attributed to phase transformation of ferrites to marten site as a result of intense plastic deformation followed by rapid cooling thereby reducing the grain size from 20μm to 2-3μm in accordance with renowned Hall-Petch equation.