Effect of Vanadium and Niobium on creep strength in 10% Chromium steel analyzed by STEM-EDS

Mitsuhara, Masatoshi*; Yoshida, Yu*; Ikeda, Kenichi*; Nakashima, Hideharu*; Wakai, Takashi 

The effect of V and Nb on creep strengthening was studied in 10% Cr steels. In a steel added 0.06% V where no particles were observed in the lath, creep strength was slightly increased, indicating that it was not strengthened by particle hardening effect in the lath. Lump-shaped precipitates and film-shaped precipitates including Cr and V, which were observed on lath boundaries in the steel added V, are expected to inhibit the lath boundaries from migrating. This inhibition is the mechanism of the improvement in the steel added V. In the case of steels added Nb individually, creep strength was found to be increased by dispersion hardening due to fine precipitates in the lath. These results revealed that V and Nb have each role to improve creep strength. In steels added both V and Nb, the effect on creep strength was expressed by the sum of the effects due to each element, which were the retardation of the lath boundary migrations and the pinning of the dislocations in the lath.