ZHAN Lihua1, 2, ZHAO Shuai1, YANG Youliang1, 2, CHANG Zhilong3
To investigate the plastic deformation behaviors and martensitic transformation rules of 0.5 mm thick 304 stainless steels at room temperature, uniaxial tensile tests were conducted at five different strain rates of 0.000 67 s-1, 0.002 s-1, 0.01 s-1, 0.1 s-1 and 1.0 s-1, with subsequent X-ray diffraction(XRD) analysis for phase analysis. The results reveal a notable increase in yield strength with rising strain rate, indicating strain rate strengthening effects. Additionally, due to plastic work converting into heat during tensile processes, martensitic transformation was inhibited, resulting in a slight tensile strength reduction. Below a true strain of 0.27, work hardening rates decrease under varying strain rates. However, beyond this threshold true strain, significant secondary hardening occurs under low strain rates, which is attributed to the internal martensitic transformation.To address this phenomenon, the Olson-Cohen equation was integrated into the traditional Johnson-Cook model to characterize secondary hardening during tensile processes across different strain rates. The improved Johnson-Cook model achieves high accuracy in predicting rheological stress changes, with deviations of 3.23%, 3.42%, 4.13%, 4.09%, and 5.14% respectively compared to experimental values, effectively capturing the secondary hardening stage at various strain rates.
