| Summary: | 博士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 93 === The effect of heat treatment atmosphere on the scale formation and pickling performance of 410 and 316(Cu) stainless steels (SSs) was investigated.
The experimental results indicate that the scale formed on 410 SS in the moist air was the most difficult to remove, while descaling was easy when the stainless steel was annealed in a reducing atmosphere (10% H2 + N2). The composition and microstructure of the oxides formed during annealing strongly affected the descaling performance.
The scales formed on annealed 410 SS were composed mainly of (Cr, Fe)3O4 and Cr2O3. After molten salt treatment, only Fe3O4, was detected on top of the substrate. Potential decay was noticed during pickling in sulfuric acid, which was associated with the scale removing process. Furthermore, the activation time (τ) required to complete the descaling decreased with increasing concentration and temperature of sulfuric acid.
Water vapor was detrimental to the pickling of 410 SS, while the presence of water vapor in the heat treatment atmosphere enhanced the descaling efficiency of 316(Cu) SS. From TGA results, the oxidation rate of 316(Cu) SS was accelerated in wet air as compared to that in dry air. In addition, a significant breakaway oxidation occurred, resulting in substantial weight gain, as the 316(Cu) SS was oxidized in moist air at temperatures above 950℃. The scaling behavior of 316(Cu) SS in wet air at 1030℃ could be divided into two stages based on the alteration of the oxidation rate. In each stage, the scale on 316(Cu) SS exhibited a different structure and morphology.
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