Revised Weld Residual Stress and Creep Damage Assessments

Reheat cracking is a brittle inter-granular type of cracking that occurs in some types of stainless steel welds that have not been post-weld heat treated. It is caused by the accumulation of small creep strains that accompany the relaxation of the weld induced residual stresses. Because relaxation processes produce small creep strains, reheat cracking can occur only if creep ductility is low. Sufficiently low ductilities arise if there is a combination of three factors, susceptible material, operation in the susceptible temperature range and stress triaxiality. The current method used to predict the extent of the zone where reheat cracking can initiate in Type 316H steel weldments is based on continuum damage mechanisms using specially developed material models. In this work more advanced methods have been developed. These methods have been applied to welded specimens manufactured from Esshete 1250. These specimens are described as 'Borland' specimens and have been used to study reheat cracking in stainless steel welds. The advanced methods include an improved plasticity model that incorporates combined isotropic and kinematic hardening as well as a two phase annealing function. A number of simulated thermal soak conditions were performed, with a reheat cracking initiation model employed to predict the development of creep damage. This paper details the methodology of the improved welding simulation, its influence on the prediction of reheat cracking and a comparison to previous simulations using existing methods.