Microstructure and mechanical properties of same-material and dissimilar laser-arc hybrid welded joints of high grade silicon steel

Objective The aim is to investigate the microstructure and performance of normalizing non-oriented high grade silicon steel V19 alloy of same-material and dissimilar (Q235A) laser-arc hybrid welded joint to provide guidance for formulating laser welding and rolling process for high grade silicon steel. Methods The microstructure and mechanical properties of welded joints are analyzed and compared using techniques such as electron backscatter diffraction, scanning electron micrcscope and tensile testing. Results The results show that obvious microstructure differences are found between the same-material and dissimilar welded joints. The weld of same-material welding is mainly composed of ferrite columnar crystal, while the weld of dissimilar joint is composed of ferrite and pearlite. The microstructure of heat affected zone on the V19 side of same-material and dissimilar welding is less affected by heat input and basically consistent with the base metal. The heat affected zone on the Q235A side of dissimilar welding can be divided into three kinds of zone, such as coarse grain area, fine grain area and microstructure non-uniform area, due to different heat input. The hardness of the welds is higher than that of the heat affected zone for the same-material and dissimilar welding. More stable hardness distribution on the weld is found for dissimilar welding. The tensile strength of the same-material welded joints is 9.3% higher than that of the dissimilar welded joints, but the dissimilar welded joints have better uniform plastic deformation ability than same-material welded joints. The tensile fracture mode of the same-material welded joints is cleavage transgranular fracture, while the dissimilar welded joint is ductile fracture. Conclusion The dissimilar welded joints between Q235A and V19 exhibit an excellent strength-plasticity matching, whereas the welds of V19 same-material welding characterized by coarse columnar grain structure reduces plasticity and affects the stability of mechanical properties.