Effect of metal active-gas welding technology on microstructure and properties of welding joint of NM400 steel

By adjusting welding technology parameters,metal active gas(MAG)welding experiments were performed for NM400 steel plate.The microstructure observations for different zones on welding joints were conducted;the size of heat-affected zone(HAZ)as well as the mechanical properties for welding joints were measured.The results show that with the welding heat input increasing,the width of HAZ increases and microstructures including widmanstatten and bainite structures became coarse.The increase in the welding heat input is responsible for the decrease in micro hardness and tensile properties of welding joints.