Influence of N-content on microstructure and mechanical properties of PMIG welding joints of high nitrogen steel

To meet high quality welding requirement of high nitrogen austenitic stainless steel components, the steel is welded by PMIG welding with 307Mo weld wire. By adjusting the shielding gas composition, the jointswith different N-content are obtained, and the influence of N-content on microstructure and mechanical properties of joints is investigated. The experimental results indicate thatif the N-content of the weldmetal is lower than 0.24%, the solidification mode is FA and the microstructure is austenite and skeletal ferrite. The higher N-contentin the weldmetal, the less ferrite in it and a lower microhardness will be got. When the N-content of the weldmetal is higher than 0.30%, the solidification mode is A and the microstructure is single austenite. The austenite dendrites become progressive coarse and the microhardness become higher while there is a higher nitrogen level.No nitrides can be found in the weld joints. The nitrogen pore will increase when the N-content of the weld metal ishigher. The higher N-content in the weld also can benefit the toughness, but if the N-content is too high, nitrogen pores can damage the toughness of the weld.