Dynamic Plastic Deformation Mechanism of 301 Stainless Steel at Low Temperatures

Deep space exploration faces challenges from extreme temperatures and complex high-speed operating environments, placing higher demands on the low-temperature impact resistance of materials. In this study, a low-temperature Hopkinson bar impact experimental device was developed to achieve dynamic loading of materials under ultra-low temperature conditions within a vacuum liquid helium environment. The dynamic mechanical response of 301 stainless steel produced by two rolling processes was investigated under the combined effects of low temperature (30–298 K) and high strain rates (4000–5000 s⁻¹). Experimental results show that the yield strength of both materials exhibits a significant negative correlation with temperature and a positive correlation with strain rate. The unidirectionally rolled samples displayed an anomalous increase in toughness at 77 K. The study indicates that the unidirectional rolling process induces a higher content of martensitic phase, thereby endowing the material with greater strength. Microstructural characterization results reveal that the anomalies in macroscopic mechanical behavior stem from the competition of deformation mechanisms. At room temperature, the samples mainly exhibit a toughness fracture mechanism, dominated by ductile dimples, whereas at low temperatures, they transition to a brittle fracture mode, dominated by quasi-cleavage. Based on this, the Johnson-Cook constitutive model was used to fit the mechanical properties, demonstrating good consistency with the experimental results. This research provides important experimental methods and theoretical support for the dynamic strength and toughness design of metallic materials under extreme low-temperature impact conditions.