Deformation mechanisms for a new medium-Mn steel with 1.1 GPa yield strength and 50% uniform elongation

A new medium-Mn steel was designed to achieve unprecedented tensile properties, with a yield strength beyond 1.1 GPa and a uniform elongation over 50%. The tensile behavior shows a heterogeneous deforma-tion feature, which displays a yield drop followed by a large LAlders band strain and several Portevin-Le Chatelier bands. Multiple strain hardening mechanisms for excellent tensile properties were revealed. Firstly, non-uniform martensite transformation occurs only within a localized deformation band, and ini-tiation and propagation of every localized deformation band need only a small amount of martensite transformation, which can provide a persistent and complete transformation-induced-plasticity effect dur-ing a large strain range. Secondly, geometrically necessary dislocations induced from macroscopic strain gradient at the front of localized deformation band and microscopic strain gradient among various phases provide strong heter-deformation-induced hardening. Lastly, martensite formed by displacive shear trans-formation can inherently generate a high density of mobile screw dislocations, and interstitial C atoms segregated at phase boundaries and enriched in austenite play a vital role in the dislocation multipli-cation due to the dynamic strain aging effect, and these two effects provide a high density of mobile dislocations for strong strain hardening. (c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

A new medium-Mn steel with unprecedented tensile properties has been designed, demonstrating a yield strength beyond 1.1 GPa and a uniform elongation over 50%. Multiple strain hardening mechanisms, including non-uniform martensite transformation, geometrically necessary dislocations, and dynamic strain aging effect, contribute to the excellent tensile properties.