Surface Hardening of AISI 420 Stainless Steel by Using a Nanosecond Pulse Laser

Abstract

Unlike the conventional heat treatments, laser hardening process can selectively and locally harden the workpiece surface with minimum part distortion, thus making the process suitable for small or thin workpieces. To elucidate a better understanding of process performance, this paper presents an investigation of laser hardening process for AISI 420 martensitic stainless steel. A nanosecond pulse laser was used as a heat source to harden the metal surface. The effects of laser power scan overlap and scan speed on micro-hardness and case depth were experimentally examined. The results revealed that the micro-hardness of stainless steel surface increased from 242 HV to 1700 HV without any sign of surface melting. The depth of hardened layer was found to be 60-80 µm depending on laser power, scan speed and scan overlap applied. In addition, the scan overlap of 50% was recommended to lessen the deviation of micro-hardness across the laser-scanned area.