The effects of dissolved oxygen (DO), test temperature and strain rate on the stress corrosion cracking (SCC) behavior of a Fe-base shape memory alloy in high temperature pure water were determined. The tests were conducted by using slow strain rate test machine in water of 383K-563K. The shape memory alloy was found to have two types of the SCC. The one type of cracking occurred above 473K. The SCC susceptibility increased with temperature and dissolved oxygen promoted the SCC as well as the case of austenitic AISI 304 stainless steel. The other type of cracking was observed at the temperatures lower than 423K. Decreasing the test temperature and the oxygen concentration increased the SCC susceptibility. Considering from the transformation temperature of the tested alloy, the mechanism of cracking in the low temperature region is inferred to be hydrogen embrittlement.
The effect of C, Si and P on intergranular corrosion (IGC) susceptibility of Type 316 stainless steels (SS) has been studied in terms of the composition dependent IGC and the compound dependent IGC. The results obtained are as follows; (1) C increases the IGC resistance of Type 316 SS in Huey and Coriou tests by supressing the precipitation of Laves phase. However, severe IGC occures in HNO3+HF and Huey tests when the Cr depleted zone is continuously formed at grainboundaries (GB). (2) Si raises the IGC susceptibility both in Huey and Coriou tests. It is considered that Si enhances the precipitation of Laves phase at GB. (3) P also increases the IGC susceptibility both in Huey and Coriou tests by precipitating as Ni-P phosphides at GB.
Tungsten carbide bearing hard alloys have been used as rolls in the hot working process of steel. Wear corrosion of the roll surface by cooling water is a serious problem in this process. The effect of pH and Ca (II) on the corrosion of hard alloy was investigated in water at elevated temperatures. Immersion test was carried out at 100 and 150°C in the aqueous solution of pH at 3.5 to 10 and Ca (II) concentrations of 0 to 0.003 moldm-3. Analysis of the dissolved metal ions revealed that the corrosion of hard alloy was characterized by the preferential dissolution of binder alloy in acidic media and of tungsten carbide in alkaline media. The dissolution rate of tungsten carbide was markedly decreased in the solutions containing Ca (II): the corrosion inhibition has resulted from the formation of crystalline CaWO4 on the specimen. Effect of temperature, pH and Ca (II) ion on the solubility of CaWO4 was investigated. It was considered that the corrosion of hard alloy in alkaline solution was controlled by the dissolution/precipitaiton equilibrium of CaWO4.
Corrosion behavior of structural ceramics in aqueous environments, such as high-temperature high-pressure water and steam, and acidic and basic aqueous solution, are reviewed. These environments lead to three main types of chemical corrosion: dissolution of grain boundary phase, reaction of ceramic grains, and water-induced phase transformation. Corrosion resistance of structural ceramics are discussed from the microstructure resulting from ceramic processing.