Hardening Mechanisms of 12% Chromium Ferritic-Martensitic Steel EP-823

• Published in: Steel in translation Vol. 52; no. 12; pp. 1135 - 1141
• Main Authors: Almaeva, K. V., Litovchenko, I. Yu, Polekhina, N. A., Linnik, V. V.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.12.2022; Springer Nature B.V
• Subjects: Chemistry and Materials Science; Chromium; Deformation; Dislocation density; Dispersion hardening; Dual phase steels; Ferrite; Ferritic stainless steels; Grain boundaries; Heat treating; Heat treatment; High temperature; Machining; Martensite; Martensitic stainless steels; Materials Science; Molybdenum; Thermomechanical treatment; Yield strength; Yield stress; hardening mechanisms; grain boundary hardening; high-temperature thermomechanical treatment; ferritic-martensitic steel EP-823; solid solution hardening; dispersion hardening; dislocation hardening; substructural hardening
• ISSN: 0967-0912; 1935-0988
• DOI: 10.3103/S0967091222120026

Based on experimental data on microstructure parameters of the reactor heat-resistant high-chromium (12% Cr) ferritic-martensitic steel EP-823, the main factors responsible for its strength properties have been identified. An analysis of the hardening mechanisms of this steel after processing is carried out according to the modes that provide a different level of its strength properties. Traditional heat treatment (THT) and advanced modifying high-temperature thermomechanical treatment (HTMT) are considered. The main mechanisms of steel hardening, regardless of the processing mode, are: dispersed hardening with nanosized particles of the MeX type ( Me = V, Nb, Mo; X = C, N) according to the Orowan mechanism; grain-boundary hardening by high-angle boundaries of martensitic blocks and ferrite grains; substructural hardening by low-angle boundaries of martensitic lamellae; dislocation hardening due to the increased density of dislocations. The HTMT mode, which includes hot deformation in the austenitic region, leads to a significant modification of the structural-phase state of steel relative to THT: a decrease in the average sizes of martensite blocks and lamellae, as well as ferrite grains, an increase in the dislocation density and the volume fraction of nanosized particles of the MeX type. In this case, the corresponding contributions to the value of the yield strength of steel from grain boundary, substructural and disperse hardening increase in comparison with THT by 1.2, 1.3, and 1.8 times. The relative contributions of the considered hardening mechanisms to the yield strength of ferritic-martensitic steel EP-823 are discussed. It is shown that the closest to the experimental yield strength values after the two studied machining modes are obtained by using the Langford-Cohen model to estimate the value of substructural hardening.