Study on cup forming of copper-containing austenitic stainless steel at low temperatures

Based on a systematic study of the cup-forming process of copper-containing austenitic stainless steel at low temperatures (−140 °C), combined with macro-mechanical response and microstructural characterization, this paper reveals the low-temperature deformation behavior and mechanisms of this material. The study indicates that the low-temperature environment significantly increases the material’s forming limit (cup-drawing value IE reaches 13.45 mm, an increase of 0.67 mm compared to room temperature), but simultaneously enhances deformation resistance (the peak load increased from 31.39 kN at room temperature to 62.24 kN), demonstrating the typical effects of low-temperature strengthening. Microstructural analysis revealed a gradient distribution of plastic strain: the cup-forming center region (S4) exhibited the most concentrated strain, characterized by high dislocation density, dense deformation twin networks, and nanoscale lamellar structures, while the edge region (S1) showed minimal strain; The texture strength transitions from firm rolled texture at the edge (extreme density of 4.79) to weak random texture at the center (extreme density of 0.09), reflecting the randomization of grain orientation caused by the activation of multiple slip systems under biaxial tensile stress. The deformation mechanism is dominated by the synergistic effects of twinning (TWIP effect) and strain-induced martensitic transformation (SIMT), with the martensite volume fraction increasing gradually from S1 to S4 (nearly complete transformation at S4), and plate-like martensite aligned along the direction of maximum shear stress. Transmission electron microscopy confirmed the segregation of the copper element near dislocation lines, which enhances local work hardening by obstructing dislocation movement. Additionally, the copper-containing design suppresses premature phase transformation in low-strain regions, thereby improving austenite metastability. This study elucidates the deformation behavior of copper-containing austenitic stainless steel under low-temperature complex stress conditions, providing a theoretical basis for optimizing forming processes of precision components in extreme environments (e.g., bioenergy and aerospace industries).