Plastic deformation in 316LN stainless steel – characterization of deformation microstructures

The effects of irradiation, test temperature, and strain on the deformation microstructures of a 316LN stainless steel have been investigated using a disk-bend method and transmission electron microscopy. Deformation microstructure changed progressively from a dislocation network dominant to a large stacking fault/twin band dominant microstructure with increasing radiation dose and with decreasing test temperature. Also, an increased strain level enhanced the propensity of deformation twinning. Since the stress was considered to be a key external parameter controlling deformation mechanism in 316LN austenitic stainless steel, the equivalent stress level was estimated for the examined surface of the disk sample. It was possible to categorize the deformation microstructures in terms of the equivalent stress range. A key conclusion is that the austenitic material will deform by forming bands of large stacking faults and twins when the stress exceeds a critical equivalent stress level of about 600 MPa by any of several possible strengthening measures: irradiation, increasing strain level, and decreasing test temperature.