Drastic improvement in mechanical properties and weldability of 316L stainless steel weld joints by using electromagnetic vibration during GTAW process

Abstract

In this study, the influence of applying electromagnetic vibration during welding on the microstructural transformations, mechanical properties, and hot-cracking susceptibility in 316L stainless steel welding joints have been investigated. For this purpose, sheets of 6 mm thick were welded using Gas-Tungsten Arc Welding (GTAW). During welding, electromagnetic vibrations with voltages of 0, 20 and 40 V were applied to the weld pool in contact with welding. Afterwards, in order to investigate the microstructure of different zones in the weld joint, optical and scanning electron microscopes (SEM) were carried out. In order to investigate the mechanical properties of weld joints, tensile, Charpy impact, and Vickers microhardness tests were carried out. Then, to study the fracture mode of joints after that tensile test, the fracture surfaces of the joints are investigated using SEM. In order to investigate the hot-cracking susceptibility of the 316L stainless steel weld joints, the longitudinal Varestraint test was carried out. Microstructural observations showed that increasing the electromagnetic vibration during welding process decreases the number and length of columnar dendrites in the weld metal and shifts the microstructure from columnar to fine equiaxed dendrites. Also, it was revealed that the microstructure of weld metal included austenite grains with grain-boundary delta ferrite. Increasing electromagnetic vibration during welding process results in a reduction of delta ferrite in the weld metal; and, also increases the extent of an unmixed zone. Mechanical tests reveal that increasing magnetic vibration during welding process results in drastic increases in mechanical properties including yield strength, toughness, and the hardness of welding joints. The results of longitudinal Varestraint tests show that increasing electromagnetic vibration during welding process results in decreasing the hot-crack susceptibility in the 316L stainless steel welding joints. Also, the analysis of fracture mode shows that increasing the electromagnetic vibration voltage during GTAW process results in a more ductile fracture with deeper dimples in the 316L stainless steel weld joints.