Effect of low-cycle fatigue on acoustic birefringence in austenitic steel AISI 321

This paper presents the results of a study of the effect of low-cycle fatigue on acoustic birefringence in austenitic stainless steel AISI 321 at test temperature 20 and 60$^\circ$C. A model was proposed, which represents acoustic birefringence of entire material as the sum of two separate components for soft matrix of austenite and hard inclusions of $\alpha'$-martensite. Changes in acoustic birefringence caused by deformation of austenite and martensitic transformation under fatigue were compared using calculations based on the data obtained earlier for uniaxial tension of the same steel. The kinetics of changes in acoustic birefringence of austenite was analyzed with and without taking into account the effect of martensitic transformation. The results have practical importance for the development of ultrasonic techniques for nondestructive evaluation of the state of metastable austenitic steel.