Laser Welding of Ultra-Fine Grained Steel SS400

The effects of laser welding on microstructure and mechanical properties of ultra-fine grained steel SS400 were studied. The plasma arc welding and MAG welding were conducted to make a comparison between these weldings and laser welding. The coarse grain heat-affected zone( HAZ) of laser welding was simulated using thermomechanical simulation machine,and the impact toughness was tested. The deep penetration laser welding produces weld of large depth and narrow width. The weld metal and HAZ of laser welding was heated and then cooled rapidly. The prior austenite grain size of coarse grain HAZ is1 /10 of that for arc welding. For laser welding,the toughness of weld metal is higher than that of base metal,and the toughness of the coarse grain HAZ of laser welding is on a level with that of base metal. Matching lower laser power with lower welding speed,the hardening tendency of the weld metal and the coarse grain HAZ can be decreased. There is no softened zone. The tensile strength of welded joint formed by laser is higher than that of base metal. The joint has good bending ductility.