Degradation of nickel-bonded tungsten carbide tools in friction stir welding of high carbon steel

Rapid tool degradation poses a critical challenge for joining of high carbon steels using friction stir welding (FSW) despite its ability to provide sound and defect-free welded joints. Tools of tungsten carbide with nickel binder phase (WC-Ni) are potential alternatives as they exhibit good strength and toughness. A detailed examination on the wear and consequent damage of WC-Ni tools for FSW of steels is reported in this work. The results show that the longevity of the WC-Ni tools is improved at relatively higher welding speed and lower tool rotational speed during FSW of high carbon steels. In contrast, higher tool rotational speeds and lower welding speeds result in higher rate of heat generation and elevated temperature leading to adhesion wear and oxidation of the tools. In FSW of typical 3-mm-thick high carbon steel plates, a tool rotational speed of 300 rpm and welding speed of 150 mm min⁻¹ resulted in the minimum tool wear and allowed the use of a single tool up to 1000 mm without any significant damage.