Prediction of stress relaxation and stress relief cracking in SEN testpieces

Abstract

A computer model has been described for the prediction of stress relaxation and stress relief cracking (in coarse grained, heat affected zone microstructure) during the heating period of a simulated post-weld heat treatment in four-point bend single edge notched (SEN) testpieces. Stress relaxation by plastic deformation was calculated from isothermal creep strain rate data. The two main mechanisms of stress relief cracking were considered, i.e. higher temperature, intergranular microvoid coalescence and lower temperature, low ductility intergranular fracture. Existing theoretical models for ‘creep cavitation’ were used to estimate crack growth by the intergranular microvoid coalescence mechanism. An experimental relationship between crack propagation rate, stress intensity, and temperature was derived for the estimation of crack growth by the low ductility intergranular fracture mechanism. A comparison was made between the model predictions and experimental results from a recently developed, reheat cracking assessment test which employs SEN specimens. The model was found to predict the major features of stress relaxation and stress relief cracking with reasonable accuracy for three 2·25Cr–1Mo steel alloys considered. Practical application of the model to the quantitative assessment of reheat cracking in actual weldments was discussed.