Structure and specific features of strain hardening upon extension of a hot-rolled nitrogen-bearing austenitic–martensitic 27Kh15AN3MD2 steel

Abstract

The microstructure and the static tensile stress–strain curve of a hot-rolled nitrogen-bearing austenitic–martensitic corrosion-resistant 27Kh15AN3MD2 steel have been studied. It is found that the curve has three straight line portions with different slopes at strains of 2–4.3% (portion I), 4.3–13.8% (portion II), and 13.8–19.5% (portion III). The intersection of the straight lines in portions I and II corresponds to the onset of the γ → α transformation at a strain of 4.3%. It is shown that strain-hardening coefficient dσ/dε of the steel in portion II is significantly larger than that in portions I and III. Insignificant twinning and fragmentation of martensite crystals are observed after extension by 2%. A 25% strain leads to significant twinning intensity, refinement, and an increase in the martensite content to 90%.