| Austenitic stainless steel-strain hardening technology is widely used in pressure vessel manufacturing for nuclear power plants and chemical plants. Material strength can be improved by using this method, so as to achieve safety, save raw materials and reduce energy consumption.304 austenitic stainless steel is the most common material for industrial equipment. Deformation induced martensite, dislocation and other microstructures jointly achieve its strain-hardening. Therefore, microstructure detection method is particularly important for understanding material mechanical properties during deformation. Recent studies show that nonlinear ultrasonic wave technique can be used for characterizing materials, and as a nondestructive testing method, it should be well explored.In order to explore the function between nonlinear ultrasonic parameter and material microstructure changes during plastic deformation, interrupted uniaxial tensile tests were taken under -70℃,25℃ and 300℃, and samples with different martensitic content were then tested by ultrasonic wave. According to ultrasonic testing results, ultrasonic nonlinear parameter is proportional to plastic strain under the same temperature, and the growth rate of nonlinear parameter becomes much higher under lower temperature. By transmission electron microscopy, electron backscatter diffraction and other micro-analysis, microstructure evolution of 304 austenitic stainless steel during plastic deformation is detail analyzed, including dislocation growth, formation of dislocation cell, changes of stacking fault and twinning, development of shear bands and martensitic transformation nucleation and growth process. It’s confirmed that more intense phase transformation at lower temperature leads to the increase of nonlinear parameters growth rate. By fitting the power function between bcc-martensitic (a’) content and nonlinear parameter, effect of martensite on ultrasonic wave can be evaluated. |
PDF Full Text Request