Revealing the cryogenic-temperature toughness and deformation mechanisms in high manganese austenitic steels

Abstract

High-Mn austenitic steels are promising structural metallic materials for cryogenic-temperature industries due to their good properties and economy. In this work, the cryogenic-temperature toughness and deformation mechanisms were revealed by Charpy impact testing and checking the microstructural characteristics in deformed Fe-(13– 30) Mn C steels. The results show that all studied steels showed good toughness at room temperature (i.e., 293 K), while an appropriate γ SFE level was essential for their low temperature toughness at 77 K. The plastic deformation mechanisms depended on stacking fault energy and accumulated strain or dislocation density levels simultaneously. Twinning-induced plasticity (TWIP) mechanism was found for the three studied steels at 293 K, which was beneficial for good Charpy impact toughness. Enhanced TWIP mechanism was found at 77 K owing to the decreased γ SFE values. Meanwhile, both strain-induced ε HCP martensite and α' BCC martensite were indicated in Fe-13Mn-0.9C steel, and few ε HCP martensite was examined in Fe-22Mn-0.9C steel. The α' BCC martensite was generally nucleated from prior strain-induced ε HCP martensite. The cryogenic-temperature toughness would deteriorate remarkably when strain induced α' BCC martensite was introduced or mechanical twins were delayed. The statistical dislocation densities in Fe-13Mn-0.9C steel were found to accumulate faster than Fe-22Mn-0.9C steel and Fe-30Mn-1.0C steel, especially at 77 K. And a full nonadditive strengthening mechanism between dislocations and varies obstacles were observed in the deformed steels. • The cryogenic-temperature toughness and deformation mechanisms in Fe-(13– 30) Mn C austenitic steels were revealed. • The temperature dependent Charpy impact energies showed special correlations with the stacking fault energies. • The plastic deformation mechanisms were the close functions of both stacking fault energies and accumulated dislocations. • The cryogenic-temperature toughness would deteriorate with strain induced α ' BCC martensite or delayed mechanical twins. • A full nonadditive strengthening mechanism between dislocations and varies obstacles were observed in the deformed steels.