TWI Industrial Member Report Summary 288/1985
By R H Leggatt
A study has been made of the effects of postweld heat treatment (PWHT) on residual stress levels in submerged-arc welds in a 50mm thick C-Mn-Nb-Al parent steel. Measurements were made of the surface and internal residual stresses in the welds after the application of PWHT at different temperatures and hold times, and for repeated PWHT cycles. Supporting measurements were made of the relaxation properties of all-weld metal tensile specimens using isothermal and anisothermal stress relaxation test procedures. The stress relaxation tests showed that the weld metal was more resistant to stress relief and that its relaxation properties were more variable than for typical C-Mn parent steels. The maximum longitudinal residual stresses were up to 50N/mm2 greater than the upper bound of the weld metal stress relaxation data for corresponding PWHT procedures, whilst the maximum transverse residual stresses were fairly low and were insensitive to the heat treatment conditions. The results suggest that residual stresses parallel to the welding direction after PWHT may be significantly greater than those predicted to occur using currently accepted methods.