This study investigates the work-hardening behavior of a 5 %-Mn high-strength steel sheet in a warm temperature range up to 200 °C. This study was motivated by the known strong temperature dependence of the transformation-induced plasticity (TRIP) effect in this temperature range and need for accurate work-hardening curves for finite element (FE) simulations in press-forming applications for automobiles. Conventional tensile tests with elongation measurements cannot accurately evaluate the work-hardening curves of this steel because of the nonuniform deformation caused by large Lüders elongation, which exhibits approximately 0.1 yield elongation. To overcome this challenge, we employed real-time diameter change measurements converted to true strain to assess local work-hardening at warm temperatures. Key findings include: (1) strong temperature dependence of work-hardening curves up to 100 °C due to TRIP effect suppression with optimal uniform elongation at 75 °C; (2) temperature-independent stress plateau corresponding to Lüders deformation up to 100 °C; and (3) constant fracture strain across temperatures despite significant improvements in uniform elongation. These results provide crucial insights for optimizing press-forming processes and enhancing FE simulations for medium-Mn high-strength steel sheets.

The forward rod-backward can combined extrusion test was performed to investigate the tribological properties of duplex stainless steel during cold forging in this study. Two types of duplex stainless steel and an austenitic stainless steel were employed. The specimens were coated with a MoS₂ single-bath-type environmentally friendly lubricant and oxalate and stearic acid conversion coatings. After forming, the geometries of the specimens were measured and plotted to a calibration diagram created by the finite element method to identify the Coulomb friction coefficient at the interface between a specimen and a tapered die surface. The results showed that the environmentally friendly lubricant had a lower friction coefficient for all materials. For the chemical conversion coatings, differences in friction coefficients among the materials, namely the friction coefficient of austenitic stainless steel was higher than the others were observed. This phenomenon is presumed to be due to the differing insoluble components generated during the coating process.