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Generally the strength of stainless austenitic steels does not live up to their good corrosion resistance. Solid solution hardening by interstitial elements is a means of raising the strength, but is used only moderately because of poor weldability, which, however, is not required in various applications. The solubility of nitrogen is high in stainless austenite of steels with 18 mass% of Cr and Mn each, but low in the melt. Carbon reveals the opposite behaviour. Instead of producing high nitrogen steels by pressure metallurgy, about 1 mass% of C+N is dissolved in the melt at ambient pressure. The new cost‐effective C+N steel reaches a yield strength of 600 MPa, a true fracture strength above 2500 MPa and an elongation above 70 %. Conduction electron spin resonance revealed a high concentration of free electrons. Thus, the ductile metallic character of the C+N steel is enhanced, explaining the high product of strength times toughness. The high interstitial content requires rapid quenching to avoid an embrittling precipitation and respective intercrystalline corrosion.

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Mechanisms of cold work hardening in three austenitic steels containing (mass%) 12Mn and 1.2C (Hadfield steel denoted as C1.2); 21Cr, 23Mn, 2Ni and 0.9N (Böhler steel P‐560 denoted as N0.9); 18Cr, 18Mn, 0.345C, 0.615N (CARNIT steel denoted as CN0.96) were studied using mechanical tension tests and TEM studies of substructure formed in the course of plastic deformation. Hadfield steel C1.2 reveals the smallest yield and ultimate stresses and elongation but the highest cold work hardening. Similar yield and ultimate stresses were obtained for steels N0.9 and CN0.96 with a higher elongation and cold work hardening for the latter. The analysis of TEM results leads to the following conclusions: Cold work hardening of the carbon steel C1.2 is mainly due to intensive twinning with rather thick twins. Localized planar slip is a feature of the substructure in the nitrogen steel N0.9 and carbon+nitrogen steel CN0.96 at strains up to 10 %, whereas twinning is involved in deformation at strains in the range of 10 to 50%. The strain‐induced ∊ martensite is rarely observed in both of these steels at strains above 30 %. The substructure and cold work hardening are discussed in terms of stacking fault energy, short‐range atomic order and binding between interstitial atoms and dislocations.