Effect of Plasticity on Creep Deformation in Type 316H Stainless Steel

The creep life and deformation behaviour of high-temperature steels can be significantly affected by the prior plastic loading. This effect is partly due to the generation of intergranular strains from the grain-scale elastic and plastic anisotropic deformation during plastic loading. This paper investigates the effect of these plasticity generated intergranular strains on the subsequent creep strain accumulation behavior in type 316H stainless steel. An in-situ synchrotron diffraction experiment was conducted at 550°C, where the sample was loaded incrementally to different magnitudes of plastic strain, followed by a displacement-controlled stress relaxation dwell at each of this stage. The lattice strains of 4 grain families were measured during these stages. It was found that the intergranular strains generated during the plastic deformation significantly affect the relative magnitude of creep strain accumulation in different grain families. A subtle but significant difference has been observed between the creep intergranular strain accumulation behavior and the plastic intergranular strain accumulation behavior in different grain families which can be used to interrogate the validity of any micromechanical models’ formulation for creep and plastic deformation. The macroscopic stress relaxations measured from the experiment were compared with the prediction from a novel crystal plasticity based micromechanical model developed in our group. A good overall match was found between the experiment and the model regarding the magnitude of stress relaxation after various level of plasticity. The experiments have demonstrated that the model requires further development to accurately predict the rate of stress relaxation and the micro scale lattice strain evolution during creep.