Carbide and Nitride Precipitation in High Temperature Tensiled Specimens and Hot Ductility of Nb-and Ti-Containing Steel CC Slabs

Hot ductility of the Nb- and Ti-containing line-pipe steel CC slab specimens were measured under the sirain rate of 1 × 10^-3/s. Three types of precipitates were found in the fractured specimens. One was the block-shaped coarse TiN particles precipitated at high temperature. Another type was the fine dynamic precipitation products precipitated at 950~900℃ which caused remarkable ductility reduction of the steel. The third type was the co-existed precipitates formed by fine Nb precipitates nucleating and growing on TiN paricles. Compared with Nb-containing steel which contains no Ti, there was no ductility drop for Nb- and Ti-containing steel at temperature between 850℃ and A_r3 and, the γ→α transformation inside the grain matrixes proceeded faster, which both improved the ductility of the steel in the low ductility temperature Region Ⅲ.