含鉻硬質被覆層工具鋼在1N硫酸水溶液之耐蝕性

Corrosion Resistance of Three Selected Chromium-based Coatings on Tool Steel in 1N H2SO4 Solution

本研究以電鍍、PVD及熱反應擴散表面改質處理法，在JIS SKD61工具鋼表面被覆工業用硬鉻、氮化鉻及碳化鉻，部份完成表面改質之試片並施以鈍化處理，再利用恆電位儀進行1N H2SO4水溶液中之極化曲線分析，以了解不同改質處理及改質層經鈍化處理對腐蝕性質的影響。實驗結果說明：鍍硬鉻因裂紋不能提昇SKD61在1 N H2sO4水溶液之抵抗，氮化鉻及碳化鉻則可大幅提昇耐蝕能力。20 vol% HNO3鈍化處理對硬鉻及氮化鉻被覆層有負面影響，對碳化鉻層則有正面之改善。掃瞄式電子顯微鏡觀察改質層的腐蝕型態，說明鍍硬鉻因裂紋易誘發剝落，造成腐蝕電流大幅成長；而氮化鉻則有孔洞現象，也會提昇腐蝕速率。極化分析後碳化鉻被覆層表面，不論鈍化與否，均能維持平坦狀態且無明顯孔洞，在所有測試試片中耐蝕性質最優異。

Optical and scanning electron microscopies, microhardness measurment and electrochemical polarization test were carried out in this study to evaluate the corrosion resistance of a JIS SKD61 (AISI H13) tool steel coated with a variety of chromium-based coatings, including hard chromium, chromium nitride (CrN) and chromium carbide (CrC) using electroplating, cathodic arc plasma deposition and thermal reaction diffusion, respectively. Half of these coated samples were further passivated and their corrosion properties were examined and compared to those without the passivation treatment. The results showed that the coatings of CrN and CrC can effectively improve the corrosion resistance of SKD61 specimens in a sulfuric acid solution, while the hard chromium coating showed a negative influence on the corrosion resistance of the SKD61 specimen due to the cracking of the hard chromium coating. The passivation treatment can further improve the corrosion resistance of CrC coated SKD61 specimen but degraded the corrosion resistance of CrN or hard chromium coated specimens.