不?鋼被廣泛地運用在工業上，其具有獨特的強度和耐腐蝕性質。藉 由鹽浴處理使氮和氧原子擴散到不?鋼基底，形成氧化鐵、氧化鉻和氮化 物提高表面硬度以利耐磨性。 本研究中，準備304，430 和17-4 PH 三種型號不?鋼，予以0.5〜2 小時，溫度450〜650oC 鹽浴處理(硝酸鈉(50 wt%)與硝酸鉀(50 wt%)混合結 晶鹽)。待實驗完成後，我們使用OM，SEM 和XRD 來觀察並研究熱合氧 化膜。不?鋼的氧化膜厚度隨鹽浴溫度和時間增加而增厚。碳化鉻的形成 會影響氧化膜的生長速率。在鹽浴處理過程中，碳與鉻相互反應形成碳化 鉻堆積於晶界上並阻礙鐵原子擴散到表面。當持溫時間達1.5 小時，氮化 鉻形成導致氧化膜表面粗糙度增加而光澤度降低。 利用CIE L * a * b *色度儀分析熱合氧化膜的色彩度。當氧化膜中的 氧化鉻增多時，表面量測的a *值，由+a*往-a*減少。在高溫鹽浴處理時， 形成的氧化鐵(Fe2O3 )產物容易分佈於氧化膜表面，導致氧化膜的顏色由灰 色轉變成紫色。氧化膜的顏色會受到熱成形層中存在的鐵、鉻和氧的影響。 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.
