[en] Highlights: • SR correlated with deformation under CFI in RAFM steels. • Stress relaxation directly related to plastic strain accumulated, inversely to CFI life. • Optimum combination of W and Ta best for CFI life. • RAFM steels demonstrated compressive dwell sensitivity. • SR tends toward constant value at long hold. - Abstract: The aim of this work is to understand the effect of varying tungsten and tantalum contents on creep–fatigue interaction (CFI) behavior of reduced activation ferritic–martensitic (RAFM) steels. Increase in W improved CFI life. Effect of changing Ta and W upon the resultant CFI life seems to be interrelated and an optimum combination of both W and Ta works out to be the best for CFI life. Stress relaxation obtained during application of hold can be a useful parameter to relate deformation and damage in the RAFM steels.