Abstract
In order to investigate the effect of the combined addition of W, Nb and V with B on the creep strengthening of high Cr ferritic heat resistant steel, the creep tests and the microstructural observation of crept specimen were carried out. The effect of adding B on the creep strengthening was discussed. In based steel and V free steel, the short time creep strength increases with adding B. In W free steel and Nb free steel, however, the short time creep strength of B adding steel is similar to that of B free steel. In based steel, W free steel and Nb free steel, the long term creep strengthening by adding B occurs. The suppression of microstructural recovery by adding B dose not occur in short time crept specimen of W free steel. It is suggested that the addition of B contributes to the creep strengthening through two mechanisms. One is the long term creep strengthening by stabilizing precipitates such as M23C6, Laves phase. And another is the short time creep strengthening by refining of MX, increasing the latent creep resistance and synergetic effect of alloying elements.
