Friction Stir Welding of Steels Using a Tool Made of Iridium‐Containing Nickel Base Superalloy

An addition of Ir to Ni base super alloy can increase the high temperature strength. An Ircontaining Ni base superalloy produced through a process of rapid solidification casting, solution heat treatment and subsequent aging was found to exhibit a compressive strength greater than 500 MPa at 1000°C, which suggested it would be a suitable material to use in a friction stir welding (FSW) tool for high-softening-temperature materials, such as stainless steels and carbon steels. Precision tilt casting of this Ir-containing Ni base superalloy into a copper mold followed by appropriate heat treatment, resulted in tools with a fine γ/γ’ microstructure containing intergranular carbides. These tools were subsequently proven capable of producing welds on AISI 304 stainless steel and ultrahigh carbon steel without large deformation or severe wear.