A Microstructural Study of Compressive Plastic Pre-Strain Effects on Creep Damage Behaviour of Type 316H Stainless Steel

Compressive plastic pre-strain induced at room temperature in type 316H stainless steel, significantly influences the tensile, creep deformation and crack growth behaviour of the material. It is known that the material is hardened after pre-strain to 8% plastic strain and thus exhibits little or no plasticity during loading of uniaxial or creep crack growth (CCG) tests. In addition pre-compression (PC) has been found to reduce the creep rupture time, creep ductility and accelerate creep crack growth rates compared to as-received (AR) (i.e. uncompressed) material. In order to understand pre-straining effects on mechanical behaviour of 316H, optical and scanning electron microscopy (SEM) studies have been performed on uncompressed and 8% pre-compressed material. Samples have been examined in three orientations (i.e. parallel and perpendicular to the pre-compression direction). Furthermore, the influence of cold pre-compression on local creep damage formation ahead of the crack tip on interrupted CCG tests on AR and PC material has been studied. The results are discussed in terms of intergranular and transgranular damage caused by the compression process and the importance of microstructural changes on the mechanical behaviour of the material in long term tests.