CHARACTERIZATION OF ELECTRON BEAM WELDED 17-4 PH STAINLESS STEEL

The Canadian Department of National Defence (DND) currently has a requirement for a fully automated captive trajectory system (CTS) with six degrees of freedom, all of which are to be motorized, to study the movement of stores (such as missiles) during carriage/release testing of F-18 and other military aircraft in the National Research Council (NRC) trisonic blowdown wind tunnel. In the CTS, one of the joints providing linear motion is designed and fabricated with a linkage (telescoping inner strut (TIS)) in two halves, split along its neutral plane, to allow machining of the internal geometry. To support the dynamic, kinematic and aerodynamic loads induced, the two halves must be welded together while maintaining high tolerances on the inner geometry. The designed weld areas on the neutral plane require a penetration of 17.1 mm from each face in 17-4 precipitation hardening (PH) martensitic stainless steel (SS). Using conventional joining techniques, such as tungsten inert gas TIG welding, the fabrication of a thick section requires a V groove joint design and multiple passes to achieve the required penetration. However, exposure to a substantial heat input through this process renders large weld and heat affected zones on either face of the strut as well as distortion of the component, which poses considerable difficulties for assembly and motion. The application of a high energy density technique, namely electron beam (EB) welding, was utilized to penetrate the thick section with a single pass, while minimizing the weld region, heat affected zone (HAZ) and distortion of the strut (low heat input).