| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 91 === The purpose of this study is to investigate the effects of alternative air/N2 atmospheres on the hot corrosion behavior of four commercial steels (SB450, STPA24, STPA26 and 430SS) with NaCl deposit. Corrosion tests carried out at 850℃ with a const flow-rate of 600 mL/min. In the air atmosphere, the results showed that the metal loss decreased with increasing chromium content and the SB450 has the greatest metal loss among four alloys studied. The scales formed on A24 and SB450 were triple layer consisting of Fe2O3, Fe3O4, and FeO from the outer to the inner layer. The outer layer scale of A24 was always fragile while the inner layer showed laminated structure which parallel led to the surface of the steel. The high-Cr-content alloys (A26 and 430SS) formed an outer layer of iron oxide and an inner layer of chromina. The low-Cr-content alloys (A24 and SB450) exist FeO in the test temperature through the observation of quenched specimen, but it disappear after air-cooling. In the N2 atmosphere, oxychlorination was not occurred, and all specimens only had slight metal loss. The chromina merely formed on the high chromium content alloys (A26 and 430SS) due to the low dissociation pressure of oxygen.
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