Detailed Diffraction and Electron Microscopy Study of Inertia-Friction-Welded Dissimilar High-Strength Steels

Abstract

A detailed characterization of two dissimilar high-strength steels, SCMV and Aermet 100, joined by inertia friction welding (IFW)—a solid-state welding technique—was undertaken using high energy synchrotron X-ray diffraction and advanced electron microscopy in order to understand the dramatic hardness variation across such a weld. It was found that the severe high-temperature deformation in the thermomechanically affected zones (TMAZs) of the weld, stabilized ordered, and nanosized FeCo zones in Aermet 100 and about 12 to 14 vol pct austenite in SCMV (Ni equivalent 9 wt pct). The ordered FeCo zones in Aermet 100 resulted in exceptionally high hardness values of 700 to 725 HV. Very close to the weld line, the TMAZ of Aermet 100 also displayed a region with about 15 vol pct austenite, while in the parent material, 8 to 9 vol pct was typically observed. No indication of martensite was found in the weld region of Aermet 100. Ferrite texture analysis at different locations within the TMAZs on either side of the weld showed that SCMV develops a very strong α-fiber texture near the weld line and, in addition, a γ-fiber texture toward the heat-affected zone (HAZ), suggesting the presence of ferrite during welding near the weld line and recrystallization further away. The ferrite texture development in the TMAZ of Aermet 100 was relatively weak, suggesting that austenite is a dominant phase in the TMAZ during IFW.