Contrasting effects of Si on high-temperature deformation behavior and room-temperature strength in V-microalloyed 10Mn-18Cr stainless steels

Two MnCr stainless steels (0.17C-10Mn-18Cr-xSi-1V-0.25N, wt.%) with varying Si contents (x=0.4 and 2.2 wt. %) were designed with a stacking fault energy of 35 mJ/m2 to activate the TWIP effect. The high-temperature deformation behavior and room-temperature (RT) tensile properties were investigated to explore the impact of Si in both high and RT regimes. The high-temperature behavior of the steels was assessed using hot-rolled plates through compression tests at temperatures ranging from 950 to 1100 degrees C and strain rates from 0.01 to 10 s-1. Hot deformation processing maps were established to identify the safe and unstable deformation zones. The RT tensile properties were evaluated through uniaxial tensile tests of fast-heating (FH) annealed cold-rolled sheets at temperatures ranging from 800 to 1200 degrees C for 3 min. Microstructural analysis of the hot-rolled and FH annealed structures was conducted using electron backscatter diffraction and laser scanning confocal microscopy, and precipitation was characterized by transmission electron microscopy. The findings demonstrated that MnCr-V steel with higher Si content (2.2 wt.%) had reduced hot-deformation resistance and lower activation energy for deformation (477 kJ/mol) compared to its lower Si counterpart (507 kJ/mol). This can be attributed to the soft ferrite phase within the austenite during elevated temperature tests. Conversely, the RT tensile properties exhibited an opposite trend, with the high Si steel showing increased yield strength (YS) and Ultimate tensile strength (UTS) compared to the low Si steel. This improvement is due to solid solution strengthening from Si, precipitation strengthening from V(C,N) particles, and a fine-grained recrystallized structure resulting from short annealing. For instance, after a FH process at 1000 degrees C for 3 min, the YS, UTS, and total elongation values were 665 MPa, 980 MPa, and 40 %, respectively, for the low Si steel, while the high Si steel achieved values of 715 MPa, 1045 MPa, and 30 %, respectively. Mechanical twinning was evident in both materials.