Measurement of Internal Stress and Internal Resistance Resulting from Creep of Type 316H Stainless Steel

Abstract Descriptions of high temperature creep deformation often use the concept of the effective stress, which includes the presence of the internal stress. Many experimental techniques have been applied to measure the internal stress induced by creep deformation. However, there is still a debate about the validity of the measured values. This is partly because the distinction between internal stress and material internal resistance is unclear. In this paper, neutron diffraction measurements, undertaken using the spallation source at the Rutherford Appleton Laboratory, UK, are combined with in-situ loading to investigate the internal state of a Type 316H stainless steel. By undertaking measurements of the lattice strain for different grain families, before, during and after mechanical loading, the internal stress and internal resistance induced by prior creep were determined. The results show that these two parameters are important measures of the internal state, each changing during creep and influencing creep deformation rate. Additionally, internal stress is shown to be dependent on specific crystallographic planes of each grain family. The results are discussed with respect to the underlying mechanisms of creep deformation in stainless steel