Nondestructive potentiostatic etching technique for the detection and quantification of preexisting plastic strain in austenitic stainless steel

Nondestructive testing (NDT) of preexisting plastic strain with high accuracy and low heat-to-heat variation is important for ensuring the integrity of structural components. In the present study, a potentiostatic etching technique (IN HNO3 at -600 mVscE, 308 K [35 °C] for 20 min) was developed for NDT of plastic strain in austenitic stainless steel. It was found that the dissolution rate of the alloy is strongly dependent on crystallographic orientation with the developed potentiostatic etching condition, and the potentiostatic etching condition was employed to visualize slight and local disarray of crystal structure caused by plastic deformation. Using this etching technique, preexisting plastic strain in austenitic stainless steel can be detected and quantified based on the density of etched deformation twins for samples strained at room temperature. It was also found that preexisting plastic strain in austenitic stainless steel that was deformed at 523 K (250 °C) could be detected and quantified using the etched slip line density. Over the temperature range of straining from 303 to 373 K (30 to 100 °C), the etched deformation twin density drastically decreased as temperature was increased. This result indicates a notable slip-twinning transition in SUS316NG over the temperature range of 303 to 373 K (30 to 100 °C). This technique was also found to have high sensitivity and low heat dependency in detection of preexisting strain.