Creep resistance and structural stability of low-alloy CrMo and CrMoV steels

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 degrees C. In 2.25Cr-1Mo steel such a strong favourable effect is discernible only at lower temperatures up to about 525 degrees C. The beneficial effect of Mo on the CRS of the low alloy CrMoV steels was found only when Mo concentration was up to about 0.5%. Further increasing of CRS is possible by raising vanadium content up to stoichiometric ratio V:C. The precipitation strengthening of CrMoV steels is ruled by V4C3 or V(C,N) while in CrMo steels Mo2C, respectively Mo2C and Cr7C3 are the principal precipitation strengthening particles. The dimensional stability of particles precipitating in CrMoV steel is much higher than those in CrMo steel.