The effect of frequency on the fatigue strength and patterns of fracture surfaces of Cr-Mo cast steel were investigated in fresh water and also in water Containing sodium nitrite inhibitor at 88°C.
The fatigue strength in fresh water at 88°C had no fatigue limit and became markedly low at low frequency, 170cpm, in the long term tests. The fatigue strength in fresh water containing sodium nitrite inhibitor had no effect on frequency and had the same level of fatigue limit as that in air. In the long term tests, it was found that sodium nitrite inhibitor was stable and was effective for the inhibition of corrosion fatigue failure at any frequency. Fracture surfaces in fresh water were of an intergranular pattern in the crack initiation area, and of a plain and brittle pattern in the crack propagation area. However, the effect of frequency on patterns of fracture surfaces was not clear. Intergranular facets were partially observed in the crack initiation area, and ductile striations were observed clearly in the crack propagation area on fracture surfaces in fresh water containing inhibitor, which were of the same patterns as those in air. From the observation of fracture surfaces, it was found that sodium nitrite inhibitor was very effective for the inhibition of corrosion fatigue failure.
