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Keywords:

  • C + N steels;
  • mechanical properties;
  • TWIP Steels

Abstract

New developed (20–30)Mn12Cr(0.56–0.7)CN TWIP steels developed from thermodynamic calculations exhibit great mechanical properties, such as high strength (1800 MPa UTS), deformability (80–100% elongation), toughness (300 J ISO-V), and impact wear resistance equivalent to that of Hadfield steel. In addition, they exhibit corrosion resistance by passivation in aqueous acidic media. Microstructure examination by SEM and EBSD at different degrees of deformation reveals that twinning takes place and is responsible for the high cold-work hardening of the steels. Stacking fault energy measurement of three different developed steels locates them in the range of 30–40 mJ m−2, being highly dependent on the N and Mn contents. Measurements carried out with digital image correlation indicate that at room temperature dynamic strain aging or Portevin–LeChatelier effect takes place. Measurements of impact toughness indicate that the steels have ductile to brittle transition at cryogenic temperatures as a consequence of the effect of nitrogen on the deformation mechanisms, resulting in a quasi-cleavage fracture along the {111} planes at −196°C.