Influences of Strain Rate on Plastic Deformations and Martensitic Transformation Behaviors of 304 Stainless Steels

To investigate the plastic deformation behaviors and martensitic transformation rules of 0.5 mm thick 304 stainless steels at room tcmperature, uniaxial tensile tests were conducted at five differcnt strain ratcs of 0.000 67 s_1, 0.002 s_I, 0.01 s~], 0.1 s_I and 1.0 s_1, with subscqucnt X-ray diffraction(XRD) analysis for phasc analysis. The results revcal a notable incrcasc in yield strength with rising strain rate, indicating strain rate strengthening effects. Additionally, duc to plastic work Converting into heat during tensile processes, martensitic transformation was inhibited, resulting in a slight tensile strength reduetion. Below a true strain of 0.27, work hardening rates decrease under var-ying strain ratcs. Howcvcr, beyond this threshold true strain, significant secondary hardening oecurs 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 modcl to characterize secondary hardening during tensile processes across different strain rates. The improved Johnson-Cook model achieves high aecuraey in predicting rheological stress changes, with deviations of 3.23%, 3.42%, 4.13%, 4.09%, and 5.14% respectively compared to experimental values, effec-tivcly capturing the secondary hardening stage at various strain ratcs. © 2024 Chinese Mechanical Engineering Society. All rights reserved.