A solid-state joining approach to manufacture of transition joints for high integrity applications

Manufacture of a transition hybrid coupling from two different steels, medium carbon S355J2 and stainless 316L, has been demonstrated using two different solid-state joining routes, forge welding (FW) and rotary friction welding (RFW). An additional manufacturing route, electron beam welding (EBW), was also employed in investigating its feasibility for such application. Mechanical and microstructure properties of the final components manufactured from the three different routes have been compared. Finite element (FE) analysis was utilised to determine optimal geometries for the FW and the RFW preform rings and identify optimal parameters for both processes. Of the three manufacture routes, the FW produced an instant diffusion-like bond with a single forging stroke on a 2100T screw press with the thinnest weld interface and most uniform hardness distribution at either side of the joint. The RFW part, manufactured on a 125T RFW machine, also exhibited a very thin weld interface, yet slightly thicker compared to the FW case, with small variations in the hardness distribution at either side. The EBW produced markedly thicker weld interface compared to the two solid-state routes. The EBW part exhibited significant variation in hardness distribution across the weld exhibiting peak hardness in the weld indicating requirements for a post-weld heat treatment (PWHT). Both the FW and the RFW process routes exhibited very uniform micro-hardness and microstructures across the weld interface in contrast with the EBW process in as-manufactured condition.