Influence of chemical composition and heat treatment condition on impact toughness of 15Cr ferritic creep resistant steel

Abstract

Influences of chemical compositions, heat treatment and microstructure on impact toughness of 15Cr ferritic steel have been investigated. Charpy impact values of the furnace cooled steels were lower than 15 J/ cm2 at room temperature independent of chemical compositions. Drastic improvement in impact toughness has been attained by controlling the carbon and nitrogen contents, by the addition of nickel and by the increase in cooling rate after annealing. However, the effect of nickel on impact toughness strongly depends on carbon and nitrogen contents. Improvement in impact toughness of the 15Cr ferritic steel has not been explained by individual microstructural factors of grain size, distribution of precipitates, volume fraction of martensitic phase. It has been supposed that the increase in Charpy impact toughness of the 15Cr ferritic steel was attained by improvement in toughness of ferrite matrix itself.