Mechanism of the Effect of Cr on the Low-Temperature Toughness of High-Mn Austenitic Steels
High-Mn steels with very stable austenitic structure exhibit a ductile-to-brittle transition at low temperature, which is accompanied by a change in the fracture mechanism from microvoid coalescence to intergranular fracture. Analyses by means of TEM-EDS and AES have shown that the low-temperature brittleness is caused by nonequilibrium segregation of Mn at grain boundaries. The addition of Cr greatly increases the low-temperature toughness. For the very stable, high-Mn austenitic steels, the effect of Cr cannot be explained on the basis of increased austenite stability or a change in its inhomogeneous deformation characteristic. It has been established by TEM-EDS analyses that Cr also segregates at the grain boundaries; therefore, it decreases the Mn segregation at the grain boundaries and increases the low-temperature toughness of high-Mn austenitic steels. For the 40Mn-7Cr steel, the relationship between the Cr and Mn contents at grain boundaries is: Mn = 47.99% - 0.88% Cr.
KeywordsAustenitic Steel Intergranular Fracture Manganese Austenitic Steel Nonequilibrium Segregation High Nitrogen Austenitic Stainless Steel
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