The study of volumetric wearing of PCBN/W-Re composite tool during friction stir processing of pipeline steels (X70) plates

Abstract

Friction stir welding is a solid-state joining/processing technique that offers high strength and productivity, resulting in a microstructure similar to hot working cycles. However, high melting temperature metals such as steels cause excessive wear over welding tools, representing a significant economic issue. Most studies conducted in steels have used polycrystalline cubic boron nitride (PCBN) and W-Re composite tools, which offer a combination of high strength and hardness at high temperatures, along with high-temperature stability. However, even those tools are susceptible to tool wear. In the present study, experimental data was collected during friction stir processing of X70 grade pipeline steel plates, using W-Re and PCBN composite tools under well-controlled conditions. Profilometry and optical microscopy were used to quantify the volume loss at the welding tool due to the number of plunges and the welded distance. Torque and transverse force at the welding tool and the welded bead width were measured and related to the wear process. Tool contamination in boron-nitrogen particles and dissolved tungsten was identified at the stir and hard zones, more substantial at the latter.