Influence of variation of energy per unit length on mechanical-technological properties of ultra-high-strength steel 22MnB5 in the laser beam welding process

Abstract

Abstract Ultra-high strength steel 22MnB5 with 1.5 mm thickness was laser beam butt welded under varied welding parameters such as focal diameter, welding speed and beam power. The ultra-high strength material is softened by the laser beam welding process due to tempering in the heat-affected zone, which causes a loss in tensile strength and hardness compared to the base material. The influence of softening on the mechanical-technological properties was investigated. Hardness profiles of welded specimens were examined and tensile tests with digital image correlation were carried out. The digital image correlation showed the area in which the strain was concentrated as well as the location of fraction initiation. The microstructure was examined using micrographs and scanning electron microscopy images; the composition of the structure was subjected to X-ray diffraction. Dilatometry was used to map the individual areas of the heat-affected zone with respect to temperature and hardness. An increase in the energy per unit length influenced the width of the heat-affected zone and thus, the width of the softened zone. It was not possible to exert influence on the depth of hardness drop. The tensile strength, however, increased due to the narrower width of the softened zone.