Microstructure and Properties of Laser Surface Melted AISI 316L Stainless Steel

The present study aims to understand the influence of laser parameters (applied power density and scan speed) on microstructure, surface mechanical (microhardness and wear resistance), and electrochemical (corrosion resistance) properties of AISI 316L stainless steel following laser surface melting (LSM), conducted using a 6.6 kW continuous wave diode laser with the applied power density and scan speed ranging from 58.98 to 88.46 W/mm2 and 20 to 80 mm/s, respectively. Detailed characterization included microstructure investigation, composition analysis, phase determination, and assessment of wear and corrosion resistance. The melt zone microstructure mainly comprises dendrites with the secondary arm spacing systematically varying with laser parameters. With increase in laser power density, cumulative lattice strain, dislocation density, and residual stress increased. The relationship between these properties and scan speed is just the opposite. Microhardness of the melt zone varied between 180 and 336 VHN, with higher values obtained either at higher laser power density or lower scan speed. Similarly, wear volume and wear rate after LSM also vary with the laser parameters. Detailed microstructural analysis of the worn surface was carried out to study the mechanism of wear. Interestingly, LSM recorded a corrosion resistance better than that in as-received conditions which systematically varies with the LSM parameters. Orientation imaging by electron backscattered diffraction analysis suggested that LSM with 88.46 W/mm2 power density and 20 mm/s scan speed developed a lower area fraction of high-angle grain boundaries and orientation mismatch and, hence, offered highest corrosion resistance in a 3.56 wt.% NaCl solution.