THE EFFECT OF NB, V, N AND AL ON THE CREEP-RUPTURE STRENGTH OF 9-12-PERCENT CR STEEL

The creep resistance of advanced chromium steels can be significantly increased due to precipitation of very small particles of vanadium nitride VN. The solubility and precipitation of VN, Nb(C,N) and AIN in austenite and ferrite was analysed using relevant solubility products. The calculated values of nitrogen in solid solution were used for assessment of creep rupture strength of chromium steel (mean considered chemical composition, mass contents in %: 0.18 C; 10.5 Cr; 1.0 Mo; 0.2 V; 0.07 Nb; 0.05 N; 0.01 Al). Increasing N mass contents from 0.03 to 0.07% leads to increasing creep rupture strength in 100 000 h at 600 degrees C of about 60%. Lowering Al mass contents from 0.045 to 0.005% produces higher creep rupture strength of about 30%.