- 學位論文
鎳鉻鉬合金鋼表面共滲鋁鉻之包覆擴散處理
Simultaneous Aluminizing and Chromizing of Ni-Cr-Mo Alloy Steels by Pack Cementation.
摘要
本研究以包覆擴散法於750°C以下，對中碳鎳鉻鉬合金鋼(JIS-SNCM439)進行共滲鋁、鉻反應，藉由控制包括：一階段或二階段處理溫度、處理時間、滲鋁劑含量之鋁鉻粉末配比、及活化劑含量等條件之控制，調整鍍膜處理中含鋁氯化物之蒸氣壓，以避免鍍膜生成含鋁量過高的脆性鐵鋁介金屬化合物，同時微量的鉻固溶於此合金中，有益於提升鋼材的室溫抗腐蝕性。 本研究成功的於中碳鎳鉻鉬合金鋼表面製備出FeAl或Fe3Al低鋁含量之鐵鋁介金屬化合物，並可於其中固溶1∼5 wt.%的Cr，依實驗參數的不同，其鍍膜厚度介於7.5∼43 μm之間，其厚度隨持溫時間及溫度上升，但當持溫時間達到六小時以上時，鍍膜表面開始形成孔洞、並析出碳化鉻，此後的膜厚成長速度大幅降低。 滲鋁劑中鋁含量愈高則鍍膜生成相中之鋁含量也愈高，當活化劑添加高於3 wt.%時，在鍍膜末期，活化劑傾向與鍍膜表面中的鋁產生反應，因此對鍍層的增長並無助益。本實驗的處理條件中，以3 wt.%NH4Cl與85/15的鉻鋁比例包覆擴散，進行一階段的750°C處理，持溫2小時所產生的鍍膜，具有最佳的耐磨性以及抗腐蝕性質組合。
並列摘要
In this study, pack cementation process is employed to simultaneously aluminize and chromize the Ni-Cr-Mo alloy steels at temperatures below 750°C. Different treatment temperature and time, concentration of activator, and Cr/Al ratio in the powder pack are controlled to avoid the formation of high Al containing Fe-Al intermetallic compounds which are brittle at room temperature. This study successfully deposited low Al content Fe-Al intermetallic compounds, FeAl or Fe3Al, on Ni-Cr-Mo alloy steel surface. The coatings also contain 1-5 wt.% of Cr. The thickness of coatings range from 7.5 to 43 μm which depend on treatment temperature and time. In cases when treatment time lasts over six hours, pores and chromium carbides form in the coatings which also reduce the growth rate significantly. Aluminum concentrations in the coatings increase with the aluminum content of the powder packs. No more than 3 wt.% of NH4Cl activator should be used, as the activator can compete with the steels to react with aluminum on steel surface in later stage of pack cementation process. In this study, combinations of good corrosion resistance and wear properties are obtained in samples deposited using powder packs of 3 wt.% NH4Cl and 12 wt.% Cr/Al=85/15 for treatment at 750°C.