And the fatigue strength decreased markedly after one month's exposure to atmosphere.(2) The fatigue life of SS 41 specimen, subjected to repeated wetting with 3% NaCl and drying under superimposed wave, became very short when the stress of the second wave was very small.This arises from the double effects of corrosion and superimposed wave.(3) The corrosion fatigue test on 13% Cr-Mo steel under varing stress in 3% NaCl showed that the fatigue life decreased extremely as compared with the corrosion life under constant stress.
In order to improve the corrosion resistance of MCFC separator, a new coating was made by combination of ion plating and heat treatment. The corrosion resistance of coating was investigated by electrochemical corrosion tests in a molten carbonate and MCFC single cell tests. The composition of coating was analyzed by means of EPMA and XRD. The characteristics required for the wet seal area of separator such as the flatness of surface were discussed.The results obtained are as follows:(1) Through the plating of Al layer on stainless steel and the heat treatment under a particular condition, the multi-layer coating having aluminum oxide phase at the outer side and Al-Cr-Ni diffusion alloy phase at the inner side is obtained.(2) The morphology of the coating film is affected by the thickness of Al layer plated on stainless steel.(3) Corrosion resistance in a molten carbonate environment is dependent on the composition of the oxide layer.
The corrosion fatigue tests in city water were carried out on precipitation hardening stainless steel, SUS630, variously heat treated (H1075, H1025, and H900), which was manufactured by three different melting processes (air, double and triple melting process). The results obtained are as follows.The corrosion fatigue strength of all H1075 specimens manufactured by three melting processes decreased compared with fatigue strength in air. The triple melted H1075 specimen showed the highest value of corrosion fatigue strength, followed by the double melted and air melted specimens in the descending order. This result seemed to be connected with the maximum size of inclusions in the specimens.As for the triple melted specimens subjected to different heat treatments, the H1025 specimen showed the highest value of corrosion fatigue strength and the H900 and H1075 specimens were about the same.
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