Effect of the precipitation hardening on regularities of plastic deformation and fracture mode of V-alloyed high nitrogen austenitic steel

Keywords: high nitrogen steel, Fe-19Cr-22Mn-1,5V-0,3C-0,86N, austenite, precipitation hardening, σ-phase, carbonitrides, discontinuous decomposition

Abstract

Nitrogen alloying of austenitic steels increases their corrosion resistance and improves mechanical properties. During heat treatment, high-nitrogen austenitic steels tend to the precipitation hardening and the increase of strength characteristics. In the current paper, the authors studied the effect of the duration of age-hardening at the temperatures of 700 °С and 800 °С on the structure, phase composition, plastic flow behavior, and fracture mechanisms of V-alloyed high nitrogen chrome-manganese austenitic Fe-19Cr-22Mn-1.5V-0.3C-0.86N (mass %) steel. The study revealed that after water-quenching at 1200 °С, the specimens possess the high strength properties, ductility and contain large (300–500 nm) (V,Cr)(N,C) particles. Aging at temperatures of 700 °С and 800 °С facilitates complex reactions of austenite discontinuous decomposition with the Cr2N-plate formation in grains and continuous decomposition with the formation of vanadium nitride-based particles in austenite. During the long-term aging (50 h at 700 °C and 10 h at 800 °C), the intermetallic σ-phase appears in specimens. At age-hardening, the observed phase transformations cause the changes in macro- and micro-mechanism of fracture in the specimens of steel under the study. In the initial state, the specimens show mainly the ductile transgranular fracture. After age-hardening, the fracture mechanism changes into the mixed mechanism with the elements of brittle intergranular and ductile transgranular fractures. When increasing the duration of aging and implementation of complex reactions of decomposition of solid solution, the specimens are fractured by the quasi-cleavage mechanism. The specimens aged at temperatures of 700 °С and 800 °С have quite similar precipitation hardening mechanisms, though the increase in aging temperature leads to the rising of the decomposition rate of solid solution. The sequence of transformations described above and the corresponding sequence of changes in the mechanisms of steel fracture are implemented faster when increasing the aging temperature.

Author Biographies

Anastasiya S. Mikhno, National Research Tomsk Polytechnic University, Institute of Strength Physics and Materials Science of Siberian branch of Russian Academy of Sciences

student, engineer of the Laboratory of physics of structural transformations

Marina Yu. Panchenko, Institute of Strength Physics and Materials Science of Siberian branch of Russian Academy of Sciences

postgraduate student, junior researcher of the Laboratory of local metallurgy in additive technologies

Galina G. Maier, Institute of Strength Physics and Materials Science of Siberian branch of Russian Academy of Sciences

PhD (Physics and Mathematics), researcher of the Laboratory of physics of structural transformations

Valentina A. Moskvina, Institute of Strength Physics and Materials Science of Siberian branch of Russian Academy of Sciences

postgraduate student, junior researcher of the Laboratory of local metallurgy in additive technologies

Evgeny V. Melnikov, Institute of Strength Physics and Materials Science of Siberian branch of Russian Academy of Sciences

junior researcher of the Laboratory of local metallurgy in additive technologies

Sergey V. Astafurov, Institute of Strength Physics and Materials Science of Siberian branch of Russian Academy of Sciences

PhD (Physics and Mathematics), senior researcher of the Laboratory of physics of structural transformations

Elena G. Astafurova, Institute of Strength Physics and Materials Science of Siberian branch of Russian Academy of Sciences

Doctor of Sciences (Physics and Mathematics), leading researcher of the Laboratory of physics of structural transformations

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Published
2020-06-29
Section
Technical Sciences