A Comparison of Measurement and Modelling of Plastically Induced Residual Stresses in a 316H and a Weld 347 Stainless Steel

Neutron diffraction measurements on two types of stainless steel have been carried out on Compact Tension (CT) specimens containing plastically induced residual stresses at the blunt notch root. The materials were a type 316H stainless steel parent material and a type 347 stainless steel weld material. The former exhibited a high creep ductility of ∼25% and the latter exhibited brittle behaviour under operating conditions with less than 10% creep ductility. The work is based in part on an ongoing collaborative effort by the Versailles Agreement on Materials and Standards, Technical Working Area, VAMAS TWA 31 Committee working on ‘Crack Growth of Components Containing Residual Stresses’. The objective of this paper is to examine how residual stresses and/or prior straining and subsequent relaxation at high temperature (550 °C for 316H and 650 °C for 347 weld) contribute to creep crack initiation and growth in the two steels. Elastic/plastic/creep finite-element results and neutron diffraction measurements are presented for the CT specimens before and after elevated temperature exposure. The results suggest that the mechanical induced normalised stresses and strains profiles ahead of the crack tip are insensitive to material, however the relaxation response of the materials appear to be dependent on the creep behaviour and ductility. Localised cracking in the plastically deformed material has been observed in both materials due to the redistribution of the residual stress field and associated creep deformation at elevated temperature.