Friction stir welding of a high carbon steel

A high carbon steel joint, S70C (0.72 wt.% C), was successfully friction stir welded without any pre- or post-heat treatment. There are two methods for obtaining proper joint properties. The first method is to decrease the peak temperature to below A1 and the other is to decrease the cooling rate to less than the lower critical cooling rate. It was proved that friction stir welding enables us to properly control the cooling rate and peak temperature, which was impossible using traditional welding.