Experimental and Numerical Analysis of Residual Stresses in Similar and Dissimilar Welds of T91 and Super304H Steel Tubes

Abstract

Residual stress distribution and its magnitude varies across the weldment, contributing to many catastrophic failures. Moreover, it is challenging to reliably measure residual stresses, considering a particular technique. Therefore, the present investigation aims to examine residual stresses in similar (T91-T91) and dissimilar (T91-Super304H) welds before and after post-weld heat treatments (PWHT), using non-destructive methods (sin2ψ and cos α) and SYSWELDS simulations. For a similar weld, the peak tensile residual stresses near to fusion line reached ~ 238 MPa (as per sin2ψ method) and ~ 258 MPa (as per cos α method), which is ~ 48% of yield stress (520 MPa) of T91 steel. Alternatively, for the case of dissimilar welds, peak tensile residual stresses of ~ 518 MPa and peak compressive residual stresses of ~ 290 MPa were observed at the fusion line of the T91 side and Super304H side, respectively. Dissimilar welds show relatively high residual stresses with significant deviation across weldment due to varying thermal coefficients of expansion/contraction resulting from dissimilar metal joints. Hence, PWHTs were performed to decrease the magnitude of peak residual stresses and their deviation across weldment to enhance the life of welded joints. For instance, the peak tensile residual stresses decreased from ~ 258 to ~ 120 MPa after 775 °C—30 min PWHT condition in similar welds. Similarly, for dissimilar welds, post-weld normalizing and tempering (PWNT) at 1050 °C—30 min followed by 760 °C—60 min condition was found to decrease the residual stresses from ~ 518 to ~ 70 MPa, which is a significant reduction achieved due to austenitizing.