CORRELATION BETWEEN CREEP-BEHAVIOR AND SUBSTRUCTURE OF A HEAT-RESISTANT FERRITIC CR-STEEL

The creep behaviour of a ferritic steel in a coarse- and a fine-grained structural condition was investigated to evaluate deformation mechanisms and dislocation structures. Power-law creep and exponential creep was found. For the coarse-grained material the transition between these two mechanisms is given by a relation between creep rate epsilon-s and diffusion coefficient D of about epsilon-s/D almost-equal-to 10(13) m-2. Simultaneously, the dislocation structure changes. For the fine-grained material the transition between creep mechanisms is no longer predicted by the formula presented above. Nevertheless the transition between the creep mechanisms which is determined from a change in stress dependence of creep rate is accompanied by a change in dislocation structure, too.