The effect of Al on mechanical properties and microstructures of Fe-32Mn-12Cr-xAl-0.4C cryogenic alloys

The effect of Al addition (0–3 wt%) on tensile properties and microstructures of Fe-32Mn-12Cr-xAl-0.4C cryogenic alloys were investigated at temperatures ranging from −196 to 250 °C. The Al is an austenite stabilizer suppressing the formation of the strain induced ɛ-martensite, while it behaved as a δ-ferrite stabilizer when added to 3 wt%. The Fe-32Mn-12Cr-0Al-0.4C alloy showed the strain induced ɛ-martensite after tensile deformation at −196 °C. Deformation twins were observed in deformed cryogenic alloys except Fe-32Mn-12Cr-2Al-0.4C alloys at temperatures ranging from −196 to 25 °C. The formation of both the deformation twins and the strain induced ɛ-martensite enhanced the tensile elongation by retarding local necking. The Fe-32Mn-12Cr-(0,1,3)Al-0.4C alloys exhibited elongation peaks within a temperature range forming the deformation twins. As the stacking fault energy increases with increasing Al content, the elongation peak shifted to lower temperature with increasing Al content in Fe-32Mn-12Cr-xAl-0.4C alloy. The continuous formation of strain induced phases, deformation twins and ɛ-martensite, up to a large strain was important to increase the tensile elongation of Fe-32Mn-12Cr-xAl-0.4C cryogenic alloys.