Comparison of Hardness and Residual Stresses in Multiline Laser Surface Hardening and Induction Hardening

This study investigates the differences between induction hardening and multiline laser surface hardening processes on AISI 4140 quenched and tempered steel to facilitate process selection based on resulting material properties. The microstructures, hardness, and residual stress profiles resulting from the two processes were analyzed, revealing different characteristics. Induction hardening demonstrates rapid processing and uniform hardening but exhibits negative aspects such as edge effects and depth limitations. In contrast, multiline laser surface hardening offers adaptability to different geometries. Due to tempering effects, a layered microstructure was noted with lower hardness in previously processed areas. Favorable compressive residual stresses were measured in the center of the induction-hardened sample, while tensile residual stresses were measured for the multiline surface-hardened sample. This study sheds light on the strengths and limitations of these two surface hardening techniques, providing insight into the selection of optimal processes for enhancing material properties.