Tool performance evaluation of friction stir welded shipbuilding grade DH36 steel butt joints

Tool wear is a key issue in the friction stir welding of high strength materials like steel-, titanium-, and nickel-based alloys. The wear assessment is an important aspect for developing or modifying the existing tool materials and tool designs. In this study, two different grades of tungsten carbide tools, i.e., tool A (WC-6 wt.% Co) and tool B (WC-10 wt.% Co), were used to join DH36 steel plates. Pre- and post-welded tungsten carbide tools were characterized using different techniques like microstructure analysis, weight measurement, profile measurement, and X-ray diffraction phase analysis. It was observed that the degradation mechanisms strongly depend on the tool material composition and welding conditions. During this study, tool A was degraded by intergranular failure caused by the separations of tungsten carbide grains which promoted further cracks inside the tool. Different degradation mechanisms such as adhesion, abrasion, crack initiation, diffusion, and oxidation were observed for tool B. Progressive wear in tool B was strongly affected by the process temperatures. Minimum wear was observed at low rotational speed and high traverse speed.