EVALUATION OF STRENGTH IN PRE-DEFORMED AUSTENITIC STAINLESS STEEL USING NONLINEAR ULTRASONIC WAVE

The different strengths induced by the different deformation modes for 304 austenitic stainless specimens were measured by using nonlinear ultrasonic wave technique. Results showed that nonlinear ultrasonic parameter increased with the increasing yield strength of 304 austenitic stainless steel induced by the tensile deformation,asymmetrical cyclic deformation and early symmetrical cyclic deformation. A power-law relation was proposed between nonlinear ultrasonic parameter and yield strength according to the dislocation string model of acoustic nonlinearity and the theory of flow stress of metallic material. The measured data was fitted by the power-law relation,and then the sensitivity coefficient of nonlinear ultrasonic parameter to strength λ under the condition of tensile deformation,asymmetrical cyclic deformation and symmetrical cyclic deformation was found to be 3. 27 × 10-7,6. 91 × 10-6 and 1. 95 × 10-5,respectively. Microstructures analysis indicates that the differences of the three sensitivity coefficient λ might be due to the different evolution mechanism of dislocation structures and the content of martensite in different deformation conditions.