Strain effect on microstructural properties of SUS 304L joint by PAW plus GTAW

JIS SUS 304L stainless steel was joined by a combination welding process of plasma arc welding and gas tungsten arc welding (PAW+GTAW). Then pre-strain treatment on 304L welded joint of 9 % was carried out using uniaxial quasi-static tensile at room temperature. Effect of strain on microstructure evolution in joint was analyzed by field emission scanning electron microscope (FESEM) and on mechanical properties was also studied. The results indicated that the pre-strain rate of 304L joint showed inhomogeneity including 3 % in the weld metal and 13 % in the heat-affected zone (HAZ), which induced martensitic transformation occurring in HAZ. Tensile strength of the joint increased from 700 MPa as welded to 804 MPa after pre-strain treatment at room temperature, and it reached 1700 MPa from 1480 MPa as welded at low temperature of -196 degrees C. Impact energy in the HAZ was the least among the whole 304L weld, but it was still 94 J at -196 degrees C after pre-strain. The fracture morphology showed large numbered of cleavage steps with elongated parabolic dimples.