Stress-strain response of S15C carbon steel friction welded butt joints under impact tensile loading

Stress-strain response of S15C carbon steel friction welded butt joints under impact tensile loading is determined using the split Hopkinson bar. Round tensile specimens machined from as-welded butt joints of 13-mm diameter are used in both quasi-static and impact tension tests. Friction welding is carried out using a brake type friction welding machine under fixed welding conditions. The effect of strain rate up to epsilon =700/s on the tensile stress-strain characteristics of the joint specimens and a base material (S15C carbon steel) is studied. It is shown that the flow stress for friction welded butt joints is always higher than that for the base material at low and high rates of strain, but the former are less sensitive to strain rate than the latter. Microhardness measurements are conducted to examine the extent of the heat-affected zone (HAZ) across the weld interface. The enhanced strength of joints is found to be attributed to the presence of a locally-hardened region within the HAZ.