Characterization of ultrafine grain tungsten carbide tool and its wear investigation in friction stir welding of HSLA steel

In this work, cemented carbides with different cobalt content were developed by using medium and ultrafine tungsten carbide grains. The GGI, (Cr3C2), was added in small amount (0.5 wt. %) to restrict the grain growth. The effect of particle size, reinforcement content and sintering temperature on metallography, densification and mechanical properties is investigated. At 1680 degrees C, Co phase was uniformly distributed at WC interface by particle rearrangement and resulted in fully dense microstructure. The fine particle enhanced the sintering rate due to large specific surface area and surface energy. The developed tool was used to join 4 mm thick high strength low alloy steel plates without severe wear and degradation of the tool. Tool oxidation and interface degradation associated to extreme tribological welding condition is observed.