National University of Science and Technology “MISIS”, Moscow, Russia:

L. M. Kaputkina, Dr. Phys.-Math., Prof., Chief Researcher, e-mail: kaputkina@mail.ru
A. N. Svyazhin, Dr. Eng., Prof., Chief Researcher, e-mail: svyazhin@misis.ru
I. V. Smarygina, Cand. Eng., Associate Prof., e-mail: smarygina.inga@yandex.ru
V. E. Kindop, Cand. Eng., Deputy Head of Science Department, e-mail: vk@misis.ru

Alloying by nitrogen has a strong effect on the whole complex of steel properties. Joint alloying by nitrogen and copper increases apparently austenite stability and decreases the beginning temperature of martensite transformation. The steels alloyed by copper and nitrogen also elevate their resistance to pitting and microbiological corrosion. The conducted investigation was based on laboratorial steel melting with pure charge materials. Mechanical properties have been determined during testings for single-axial static extension at the temperature values +100 °C, +20 °C, –100 °C, –175 °C, and for impact bending at the temperature values +100 °C, +20 °C, –100 °C, –196 °C. Presence of ferromagnetic phase has been defined after testings via magnetometrical method. Equilibrium phase diagrams of the investigated steels have been calculated using Thermo-Calc program, critical nitrogen concentration values NKP excluding forming of nitrogen bubbles during crystallization have been determined, as well as temperature values MH, MD30 of the beginning of martensite transformation and parameter of pitting corrosion resistance (PREN). The results of testings at different temperatures have been visualized and analyzed in the kinds of deformation diagrams, non-magnetic properties, low temperatures of the beginning of martensite transformation MH, MD30. It is concluded based on these results that austenite of steels Cr19Mn10Ni6Mo2N is stable in thermal and deformation conditions at rather high deformation degree. Additional alloying by copper (up to 2%) of nitrogen steel Cr₁₉Mn₁₀Ni₆Mo₂N has a small effect on its mechanical properties, but increases its austenite stability (via lowering of the temperatures of the beginning of martensite transformation MH, MD30), eliminates forming of δ-ferrite in crystallization and rises pitting corrosion resistance, increasing PREN parameter. Austenite of classic stainless steels Cr₁₈Ni₉N and Cr₁₈Ni₉ has insufficient mechanical stability at negative temperatures, thereby these steels can be used for non-deformed products at the temperatures below –70 °C, because forming of deformation martensite in these steels is possible.

The research was financially supported by the RF Ministry of education and science (unique agreement identification RFMEFI57514X0071).

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