Effect of solute Mo, W and dispersoid carbonitride on high temperature creep of ferritic steels

摘要

The creep behaviour of alpha iron and its solid-solution Fe-Mo and/or W alloys and Fe-Mo and/or W with MX alloys was investigated at temperature of 600℃ (0.48 T{sub}m, T{sub}m: the melting temperature) under stress of 30 to 120 MPa. The results showed that the creep curves of these alloys were similar to those observed for ferritic steels. The minimum creep rate of ε{sub}(min) for solid-solution Fe-Mo and/or W alloys was three orders of magnitude lower than ε{sub}(min) in alpha iron. Also ε{sub}(min) for Fe-Mo and/or W with MX alloys was five orders of magnitude lower than ε{sub}(min) in alpha iron. By the dispersed MX particles the stress exponent of, n, increased to 11, while it was 7 in alpha iron. The observed substructure revealed that sub-boundaries with well-knitted dislocations were always formed and the subgrain size in steady state was inversely proportional to the applied stress. The subgrain size and the dislocation density within subgrains during creep decreased unequivocally with strain, while the misorientation of subgrains increased with strain. The rate of refinement for the subgrains of these alloys, however, was dependent on the solute Mo and W its concentration and the dispersed MX particles. It is suggested that creep of these alloys is controlled by the mobility of dislocations in the subgrains and sub-boundaries under the present experimental condition, though the subgrains are refined due to creep.