The paper clarifies the effect of a galvanizing coating on the fatigue stre
ngth of a ferritic steel. Depending on experimental conditions and on the m
icrostructure of the coating, a reduction in fatigue strength is observed e
specially when the coating is thick. Cracks in the galvanizing coating rapi
dly form under cyclic loading and then propagate into the steel substrate.
This completely modifies the distribution of crack lengths. Very short crac
ks are not observed in the steel when galvanized. It is shown that the prop
agation of a crack in the substrate from the coating is only possible when
the crack completely crosses the coating. By assimilating the coating thick
ness to a crack in the steel substrate, the fatigue resistance of hot-dip g
alvanized steel can be predicted using the Kitagawa-Takahashi diagram.