DEVELOPMENT OF LOW ALLOY AND 9-12 CHROMIUM STEELS

摘要

The purposeful development of low alloy steels for elevated temperature service started early after the First World War, when some steels with low Mo and Cr contents were developed. In the 0.5Cr-0.5Mo-0.3V steel a pronounced effect of proof stress at room temperature on the creep rupture strength (CRS) in 10~5 hours is still in evidence at relatively high temperature up to 575 ℃.In 2.25Cr-lMo steel such a strong favourable effect is discernible only at lower temperatures up to about 500 ℃. The beneficial effect of Mo on the CRS of the low alloy CrMoV steels was found only when Mo concentration was up to 0.5%. The creep strength of 9-12% Cr ferritic steels is effected by the precipitation and solid solution strengthening. The precipitation strengthening is ruled by M_(23)C_6 and especially by vanadium nitride. Further increasing of CRS is possible by raising nitrogen content.