Ultrasonic Characterization of Strain Hardening Behavior in AISI 316L Austenitic Stainless Steel

The present work is aimed at characterizing the strain hardening behavior of AISI 316L austenitic stainless steel using ultrasonic velocity measurements. For this purpose, microstructural studies and ultrasonic velocity measurements were carried out on the samples deformed to different levels of strain at room temperature. Strikingly, the ultrasonic velocity-strain plot of the alloy exhibited a three-stage behavior that was similar to the strain hardening rate-strain response of the alloy. At strains lower than about 0.06 (stage A), a falling regime of velocity was observed that was related to the increase of dislocations density. This stage was followed by a stage of a nearly constant velocity (stage B). The initiation of this stage was concurrent with the onset of deformation twinning in the microstructure. Beyond a strain of about 0.2, the second falling regime of velocity (stage C) was developed. The occurrence of this stage was attributed to the difficulty of new twins formation with an increasing strain.