Fe-30Mn-12Cr-xAl계 초저온 합금의 저온 기계적특성 및 미세조직

Abstract

The effects of Al addition (0-3wt%) to Fe-30Mn-12Cr-xAl cryogenic alloys on tensile properties and microstructures were investigated within temperature ranged from -196℃ to 25℃. The addition of Al increased the stability of δ-ferrite and Fe-30Mn-12Cr-3Al alloy showed the phase transition from single γ phase to γ plus δ-ferrite. The Fe-30Mn-12Cr-0Al alloy showed the deformation induced ε-martensite in deformed structure at -196℃. The deformation twins were observed in deformed cryogenic alloys except Fe-30Mn-12Cr-2Al alloy, in which the stacking fault energy of γ phase exceed about 50mJ/㎡. The formation of deformation twins during the tensile test was found to be beneficial to enhance the elongation through multiple necking. Fe-30Mn-12Cr-(0, 1, 3)wt% alloys showing deformation twins exhibited the elongation peaks between -196℃ and 25℃. The elongation peak shifted to lower temperature with increased Al content, since the stacking fault energy increases with increasing Al content. The stacking fault energies of the cryogenic alloys at temperatures showing the elongation peaks were calculated to be about 35-40mJ/㎡. The gradual formation of deformation twin during the test was found to be important to maximize the elongation.