Influence of different welding methods on mechanical properties and microstructure of laser welded joints of ultra-high strength armored steel

Austenitic and ferritic stainless steel welding wires are often used in MAG process of armored steel, which greatly reduces tensile strength and hardness of welded joints, meanwhile, causes local softening of heat-affected zone, and reduces protective performance of armored vehicles. In order to meet strength and hardness protection requirements of welded joints with ultra-high strength armored steel, laser welding process of ultra-high strength armored steel was studied in this paper, which included four welding methods, MAG, laser self-fusion welding, laser wire filler welding and laser-arc hybrid welding. Performance indicators of tensile, bending and hardness of welded joints and microstructure of welded joints were studied. The result showed that weld of laser welded joints was composed of coarse lath martensite, and microstructure of MAG weld was made up of ferrite and granular bainite. For laser welding and MAG, quenched coarse grain zone was composed of both coarse acicular martensite, quenched fine-grain zone was made up of fine acicular martensite, and incomplete quenched zone consisted of mixed microstructure of martensite and ferrite. Tensile strength and hardness of laser welded joints were much higher than those of MAG joints. Tensile strength of laser welded joints could reach more than 90% of base metal, and hardness was about 82% of base metal, which greatly improved safety of protective vehicle. However, bending strength of laser welded joints was lower than that of MAG joints. Regardless of face bending or back bending, bending samples of laser welding usually were broken when bending angle was between 10°～30°, which was much lower than bending angle 90° (not broken) of bending samples of MAG, thus limited its usage scenarios.