Creep relaxation of residual stresses in the heat affected zone of Type 316H austenitic stainless steel weldments

The present work extends the understanding of the role of thermo-mechanical history on the relaxation of residual stresses. Different thermo-mechanical pre-treatments have been developed and applied to an ex-service Type 316H austenitic stainless steel to produce both microstructures and residual macro-stresses typical of those in the heat affected zone (HAZ) of thick section attachment weldments, where reheat cracking has been observed during high temperature service (~550°C). The microstructures have been characterised after each step of pre-treatment. The through section residual macro-stresses have been measured by neutron diffraction. For the range of thermo-mechanical pre-treatments adopted, the relaxation of the initial residual macro-stresses have been measured following thermal exposure at a temperature of 550°C for times of 1h and 1800h. The results are discussed, based on the relaxation characteristics of the residual macro-stresses, in terms of the role of initial microstructure on the creep deformation behaviour and the susceptibility to the service reheat cracking.