2022 Volume 108 Issue 7 Pages 405-416
The laser-quenching-induced heat-affected zone (HAZ) of carbon steel was nano-mechanically and sub-micro-structurally characterized. Ferrite–pearlite-structured JIS G 4053 SCM440 specimens were laser-irradiated at 275, 260, or 240 W. The specimens were mechanically characterized by nano-indentation, and the micro-structures were observed with scanning electron microscopy (SEM). The HAZ consisted of various phases and micro-structures, including auto-tempered martensite, as-quenched martensite, martensite containing undissolved cementite, and the original ferrite–pearlite. The region and fraction of the HAZ micro-structures depended on the distance from the sample surface and the laser power. The nanohardness of the martensite structures varied widely presumably depending on the thermal history and local carbon content. In particular, the hardness of the martensite containing the undissolved cementite could be interpreted in terms of the solute carbon content estimated based on the area fractions of the undissolved cementite and precipitated carbide, as observed in the binarized SEM images. The thermal history was theoretically simulated to ensure that the micro-structures and associated hardness values were reasonable.
