The effect of nine solute elements on the dislocation substructures developed during high temperature creep in a 25Cr-35Ni austenitic steel was investigated by TEM at steady state stage at 900 and 1000°C, and was discussed in terms of the frictional stress obtained in the previous works.
Unlike usual understanding, subgrain size does not seem to be an important substructural parameter which determines the creep resistance. The increase in dislocation density with increasing in solute content was correlated well with the increase in the frictional stress, irrespectively of the kinds of solute elements. The temperature dependence of the dislocation density became larger with the addition of solute elements, and the temperature and stress dependences of the dislocation density were the same as the temperature and stress dependences of the frictional stress. The relationship between the logarithm of dislocation density and that of normalized frictional stress can be represented by a single straight line, irrespectively of temperatures and the kinds and amounts of solute elements.
The results conclusively demonstrate that the increase in the frictional stress yielding the increase in creep resistance due to the addition of solute elements corresponds directly to the increase in the dislocation densities.
