Experimental insight into the cyclic softening/hardening behavior of austenitic stainless steel using ultrasonic higher harmonics

MOE Key Laboratory of Pressurized System and Safety, School of Mechanical and Power Engineering, East China University of Science and Technology - Shanghai 200237, PRC

^(a) fzxuan@ecust.edu.cn

Received: 8 September 2014
Accepted: 3 November 2014

Abstract

The correlation of cyclic hardening/softening behavior of 304 stainless steel (SS) was investigated using nonlinear ultrasonic wave technique. Results reveal that primary hardening leads to the increase of acoustic nonlinearity, while secondary hardening causes the reverse tendency. This distinct phenomenon is governed by two competitive mechanisms: in the primary-hardening stage, the ascended acoustic nonlinearity is related to the increase of planar dislocation structures. While in the second-hardening stage, the decrease of acoustic nonlinearity is partly caused by the development of cell structures. In addition, the deformation-induced martensitic transformation also contributes to the increase of acoustic nonlinearity under higher stress amplitudes.