MECHANISMS OF HARDENING OF 12% CHROMIUM FERRITIC-MARTENSITIC STEEL EP-823

K. Almaeva, I. Litovchenko, N. Polekhina, V. V. Linnik
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Abstract

Based on experimental data on microstructure parameters of the reactor high-strength high-chromium (12 % Cr) ferritic-martensitic steel EP-823, the authors identified the main factors responsible for its strength properties. The hardening mechanisms of this steel were analyzed after processing according to the modes that provide different level of steel strength properties. Traditional heat treatment (THT) and promising modifying high-temperature thermomechanical treatment (HTMT) are considered. The main mechanisms of steel hardening, regardless of the processing mode, are: dispersed hardening by nanoscale particles of the MeX type (Me = V, Nb, Mo; X = C, N) by the Orovana mechanism; grain-boundary hardening by high-angle boundaries of martensitic blocks and ferrite grains; substructural hardening by small-angle boundaries of martensitic lamellae; dislocation hardening by increased dislocation density. HTMT mode, which includes hot deformation in the austenitic area, leads to a significant modification of the structural-phase state of steel relative to THT: a decrease in the average size of blocks and lamellae of martensite, as well as ferrite grains, an increase in the density of dislocations and the volume fraction of nanoscale particles of the MeX type. At the same time, the corresponding contributions to value of the steel yield strength from grain boundary, substructural and dispersed hardening increase by 1.2, 1.3 and 1.8 times in comparison with THT. The relative contributions of the considered hardening mechanisms to the yield strength of ferritic-martensitic steel EP-823 were discussed. The values closest to the experimental yield strength after two treatment modes studied are obtained when the Langford-Cohen model is used to estimate the magnitude of substructural hardening.
12%铬铁素体-马氏体钢ep-823的硬化机理
根据反应器高强度高铬(12% Cr)铁素体-马氏体钢EP-823的显微组织参数实验数据,确定了影响其强度性能的主要因素。根据提供不同强度性能的模式,分析了该钢加工后的硬化机理。考虑了传统的热处理方法(THT)和有发展前途的高温热处理方法(HTMT)。无论采用何种加工方式,钢的硬化主要机制是:MeX型纳米级颗粒(Me = V, Nb, Mo;X = C, N)由Orovana机制;马氏体块体和铁素体晶粒的高角度晶界硬化;马氏体薄片小角边界的亚结构硬化;位错密度增加导致位错硬化。HTMT模式,包括奥氏体区域的热变形,导致钢的结构相状态相对于THT有明显的改变:马氏体块和片层以及铁素体晶粒的平均尺寸减小,位错密度和MeX型纳米级颗粒的体积分数增加。同时,晶界硬化、亚组织硬化和分散硬化对钢屈服强度值的贡献分别是THT的1.2倍、1.3倍和1.8倍。讨论了不同硬化机制对EP-823铁素体-马氏体钢屈服强度的影响。采用Langford-Cohen模型估算子结构硬化强度时,得到的两种处理模式下最接近实验屈服强度的值。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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