Mechanism of Brittle Cracking for High-Purity Cr18Mo2 Ferritic Stainless Steel

摘要

A study has been carried out on the effect of continuous cooling with different rate from 1 200℃ on the brittleness of vacuum melted, extra-low interstitial Or18Mo2 ferritic stainless steels. The ductile-brittle transition temperature was found to be the lowest after water cooling and the highest after furnace cooling. The increase of brittleness with cooling rate decrease is attributed to the formation of more nitrides. With the increase of titanium content the ductile — brittle transition temperature increases significantly. A low transition temperature occurred in steel containing 0.18% Nb. and further increase of niobium brought about an increase of transition temperature. The transition temperature of ferritic stainless steel was raised severely by the precipitation of nitrides (Cr_2N, Cr_2Nb_2N_2 and TiN)and oxides(Al_2O_3)promoting brittle crack initiation.