Peculiarities of the solidification mechanism of steel after Nd:YAG long-pulse laser welding

ABSTRACTThe hot cracking problem encountered when 1 mm thick stainless steel sheets are seam welded using a long pulse Nd:YAG laser is studied. Cracks are observed only in regions where the primary austemte was formed in the coolingphase, depending on it amount in the weld. The initiators of cracks were found between the heat affected zone and basemetal as a band of segregate. High repetition rates decrease the crack formation at constant average power and weldingspeed. The primary austemte dendrites are strongly influenced by cooling rate. Melt thickness increases with pulse energywhen pulse duration and repetition rate are kept constant. The optimum focus position was approximately 0.5 mm belowthe level of the workpiece front face and produced good quality seam welds.Keywords: laser welding, long pulse Nd:YAG laser, solidification structure. 1. INTRODUCTION Fusion welding is one major fabrication process where the laser has found a large field of applications. Production rate and yield, welding of materials with different melting points in inaccessible areas and different environments through