Measurements of Residual Stresses in 316 Stainless Steel Weldments

Neutron diffraction measurements have been performed to quantify the residual stresses distributions in austenitic type 316 stainless steel Manual Metal Arc (MMA) weldment sections, which are similar to those used in creep crack growth testing. Measurements have been taken along the expected crack path in these samples to determine the influence of residual stresses on high temperature crack growth. The influence of EB welding extension pieces onto the weldments sections, in order to increase specimen size, and sample cutting for compact tension specimen manufacture are also examined. Similar stress distributions have been measured in nominally identical MMA weldments sections, where peak stresses of up to 120 MPa have been shown. The effects of the EB weld used to attach extension pieces to the weldments sections dominate over the MMA weldments residual stress distributions in these samples, and increases the peak stresses by up to a factor of three. Significant stress relaxation takes place during compact tension specimen manufacture, and in addition creep strain accumulation will further relax these residual stresses. Residual stress effects are therefore considered to only influence the creep crack initiation period in short-term creep crack growth tests. However, in long-term creep crack growth tests, the residual stresses may also influence subsequent creep crack growth behaviour.