Structural-phase state and microhardness of reduced-activation 12-% chromium ferritic-martensitic steel after thermomechanical processing with deformation at 1000 °C and 1100 °C

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Abstract

Russian 12-% chromium ferritic-martensitic EK-181 steel (RUSFER-EK-181 Fe–12Cr–2W–V–Ta–B) is a promising structural material for power plants. This paper investigates the effect of thermomechanical processing with plastic deformation in the austenitic region at 1000 °C and 1100 °C on the structural and phase state of EK-181 ferritic-martensitic steel and its microhardness value. The results of the study demonstrated that under these thermomechanical processing conditions, a microstructure forms characterized by martensitic laths, fine plates of cementite and retained austenite, as well as MX-type carbonitride particles (M – V, Ta, Ti; X – C, N). Under high-temperature tempering (720 °C, 1 h), the thermomechanically processed steel exhibits coarsening of structural elements, a reduction in dislocation density, and precipitation of M23C6 carbides (M – Cr, Fe, Mn, W). Meanwhile, MX carbonitrides exhibit high thermal stability and retain their sizes. After tempering, cementite and retained austenite were not detected. A decrease in the deformation temperature leads to an increase in crystal lattice microdistortions and a reduction in coherent scattering regions. The obtained results were compared with the microstructural characteristics of the studied steel after conventional heat treatment (CHT). It was demonstrated that plastic deformation in the austenitic region ensures a reduction in the average size of prior austenite grains by 2 times, martensitic laths by 1.5 times, and M23C6 particles by 2 times compared to the CHT condition. Furthermore, higher dislocation densities and crystal lattice microdistortion values are observed. After thermomechanical processing with deformation at 1000 °C and 1100 °C, microhardness values reach 4.6 GPa and 3.9 GPa, respectively. Subsequent high-temperature tempering reduces microhardness to 2.8 GPa and 2.9 GPa, respectively. These microhardness values after thermomechanical processing and tempering are 10 % higher than values achieved after conventional heat treatment.

About the authors

Valeria V. Osipova

National Research Tomsk State University;
Institute of Strength Physics and Materials Science of Siberian Branch of RAS

Author for correspondence.
Email: lera.linnik.1999@mail.ru
ORCID iD: 0000-0001-8975-1553

postgraduate student of Chair of Physics of Metals, research engineer at the Laboratory of Materials Science of Shape Memory Alloys

Russian Federation, 634050, Russia, Tomsk, Lenin Prospekt, 36; 634055, Russia, Tomsk, Akademichesky Prospekt, 2/4

Nadezhda A. Polekhina

Institute of Strength Physics and Materials Science of Siberian Branch of RAS

Email: nap@ispms.ru
ORCID iD: 0000-0001-9076-5469

PhD (Physics and Mathematics), Senior Researcher at the Laboratory of Materials Science of Shape Memory Alloys

Russian Federation, 634055, Russia, Tomsk, Akademichesky Prospekt, 2/4

Igor Yu. Litovchenko

Institute of Strength Physics and Materials Science of Siberian Branch of RAS

Email: litovchenko@ispms.ru
ORCID iD: 0000-0002-5892-3719

Doctor of Sciences (Physics and Mathematics), Associate Professor, Chief Researcher at the Laboratory of Materials Science of Shape Memory Alloys

Russian Federation, 634055, Russia, Tomsk, Akademichesky Prospekt, 2/4

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