Residual Stress Distribution in Friction Stir Welded ODS Steel Measured by Neutron Diffraction

The residual stress distributions in oxide dispersion-strengthened steel plates, joined by Friction Stir Welding, have been mapped using neutron diffraction. The measured stress maps were interpreted in terms of the temperature profiles measured for welds using three different tool traverse speeds. The largest peak longitudinal tensile stresses, ~1200 MPa, were found in the weld produced using the fastest tool traverse speed, and corresponds to relatively high cooling rates. A reduction in tool traverse speed yields a significant decrease in tensile residual stresses in the thermo-mechanically affected zone of the welds, but also causes higher peak temperatures during welding. The transverse residual stresses were not found to be affected by the tool traverse speed and were significantly lower in magnitude than the longitudinal stresses. Additionally, the torque profiles measured during welding increased with the amount of material stirred and therefore correlated with the width of the thermo-mechanically affected zone of the welds.