Feasibility of underwater friction stir welding of HY-80 steel

Abstract

The purpose of this thesis is to determine the feasibility of underwater friction stir welding (FSW) of high-strength; quench and temper low carbon steels that are susceptible to hydrogen-assisted cracking (HAC). The specific benefits of underwater FSW would be weld repairs of ship and submarine control surfaces and hulls without the need for drydocking and extensive environmental control procedures. A single tool of polycrystalline cubic boron nitride (PCBN) in a Tungsten-Rhenium binder was used to conduct three bead-on-plate FSW traverses, approximately 40 inches in length on 0.25 inch HY-80 steel. The first traverse was a dry weld and the second and third traverse were wet (underwater) welds, all conducted at a combination of 400 revolutions per minute and 2 inches per minute. The wet welds were conducted for the purpose of assessing the HAC susceptibility of the process.