Performance Evaluation of Surface-Activated Solid-State Welding for ASTM A992 Structural Steel

This paper presents the results of a pilot study to evaluate a solid-state welding technology, called surface activated solid-state (SASS) welding, for joining structural steel members. SASS welding does not require bulk melting of base metals and can be readily automated to produce high quality joints free from volumetric flaws and without extensive operator training. In addition, this welding process is performed instantly over a plane, in contrast to sequentially along lines as in arc welding; consequently, the former achieves much higher production rates than the latter. Butt-welded joints constructed from A992 steel were SASS welded and subjected to a series of mechanical tests and metallurgical evaluations. Coupon test results indicate that the SASS-welded joints can overmatch the tensile strength and match the ductility of the base metal. However, in the as-welded condition, SASS-welded joints did not display sufficient notch toughness for use in demand critical applications. A metallurgical study of these joints suggests that coarse prior austenite grains, brittle secondary phases, and the texture of grain boundary ferrite at or near the joint interface were possible causes. Notch toughness of SASS welds was significantly improved by post-weld heat-treatment, particularly at temperatures higher than $A{c}_3$, which were observed to homogenize the microstructure across the weld joint, refine ferrite grains, and produce purely reconstructive phase transformation products (i.e., polygonal ferrite + pearlite). The improvement in notch toughness is believed to be a result of these microstructural changes.