Analysis of stainless steel surface characterization treated in salt bath treatment
| Autor: | Chi-Fan Chen, 陳啟帆 |
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| Rok vydání: | 2010 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 98 Stainless steel is widely used in industry due to its unique properties in strength and cor rosion resistance. Stainless steel treated by salt bath could introduce nitrogen and oxygen atoms to diffuse into matrix forming i ron oxide and chromium oxide and nitride as well to enhance the surface hardness for wear resistance. In the present study, three types of stainless steel, 304, 430 and 17-4 PH stainless steel were prepared and treated in NaNO3 (50 wt%) and KNO3 (50 wt%) salt bath for 0.5~2 hours at 450~650oC. After experiment, we observed and examined the thermally formed oxide layer by OM, SEM and XRD. The thickness of thermal ly- formed layer on s tainless steel was increased with increasing salt bath temperature and time. The growth rate of oxide films was affected by the formation of chromium carbide. Carbide interacted with chromium that formed on grain boundary to hinder the iron atoms diffusion to surface during salt bath treatment. When the immersion time reached 1.5 hours, the chromium nitride formed leading to increasing oxide film roughness but reducing glossiness. The CIE L*a*b* colorimeter were used to analyzed the surface color saturate. The measured a* value was decreased from positive toward negative as increasing chromium oxide in oxide films. The Fe2O3 that was the product from high salt bath temperature likely di stributed over oxide film surface led the surface color of films to transform from gray to purple. The variation of surface color was affected by existing of iron, chromium and oxygen complex oxide in the thermally- formed layer. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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