Correlation between microstructure and mechanical properties of reduced activation modified F-82H ferritic martensitic steel

Abstract

Metallurgical characterisation of modified F–82H steel was carried out. Microstructural studies together with mechanical testing were conducted on the steel in the as received state and after thermal aging in the temperature range 300–600°C for periods up to 5000 h. In addition, precipitate development during creep tests at 600 and 650°C was studied. During thermal aging, the general microstructure of the steel (tempered martensite with M₂₃C₆ precipitates) remained stable up to 500°C. However, at 550 and 600°C, in addition to the M₂₃C₆ carbides, Laves phase and precipitates with intermediate composition between carbides and Laves phase were observed. In terms of mechanical properties, the F–82H modified steel exhibited the same values of hardness, ultimate tensile stress and 0.2% proof stress, and similar creep rupture strength, regardless of the material condition studied. In contrast, aging treatments at 550 and 600°C caused a significant decrease in impact properties, essentially attributable to the Laves phase precipitation.