Microstructure and residual stresses of laser remelted surfaces of a hot work tool steel

This paper deals with a systematic metallurgical analysis of laser remelted surfaces on the hot work tool steel 1.2343 (AISI: H11). There are novel techniques using laser remelting for polishing surfaces using a constant laser beam power or for structuring surfaces using a modulated laser power. Basic properties, e. g. residual stresses, retained austenite, micro-stresses, microstructure, chemical composition and micro-hardness of the remelted near-surface layers are analyzed for different sets of procedural parameters such as laser power, laser beam diameter and number of repetitions. A carbon depleted area was found close to the remelted zone. The surface residual stresses tend from tensile to compressive and the content of retained austenite is lower when increasing both laser beam diameter and laser power. The formation of surface residual stresses is explained by a combination of shrinkage stresses and transformation stresses. The residual stresses tend from tensile to compressive with increasing number of repetitions, which can be explained by a preheating effect. A linear correlation between the measured surface hardness and the peak half width acquired by X-ray diffraction was found.