AISI 304不銹鋼低溫氣體滲氮與電漿拋光之研究

Study on Low-temperature Gas Nitriding and Plasma Polishing of Stainless Steel AISI 304

吳冠霆(Kuan-Ting Wu)

指導教授 ： 陳永傳

國立臺灣大學/工學院/機械工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201602712

摘要

AISI 304不銹鋼是沃斯田鐵系不銹鋼中，受到普遍使用的鋼種，由於富含鉻、鎳元素，其表面形成緻密的氧化膜，保護內部，因此具有優秀的耐腐蝕能力。然而同時具有硬度低、容易磨損的問題，且不能透過熱處理改善其耐磨性，一般使用固溶處理強化表面。
本研究實驗以鹽酸蒸氣對AISI 304不銹鋼試片進行活化處理，去除表面氧化膜；並以經過預分解的氨氣進行低溫氣體滲氮，在試片表面固溶氮原子以增強硬度。活化處理與低溫氣體滲氮處理會分別因為腐蝕與晶格膨脹等因素造成表面粗糙度增加，因此本研究再實驗以電漿拋光處理改善表面粗糙度。電漿拋光是將試片連接正極，並使用低濃度、低汙染的拋光液，通以高電壓與高電流密度，在試片表面產生電漿蒸氣層，造成輝光放電而達到拋光效果的拋光技術。本研究主要實驗結果如下：
(1) 滲氮時間較長、滲氮溫度較高，所得的滲氮層厚度較大。滲氮層中具有高濃度的固溶氮以及高硬度值，可改善不銹鋼硬度低的問題，但滲氮溫度太高會降低不銹鋼的耐蝕性。
(2) 拋光液溫度較低、電流密度較大，拋光效率較高。電漿拋光時拋光液也會對試片造成腐蝕，當拋光效率大於腐蝕速率，可得到均勻的拋光表面。
(3) 拋光時間較長，所得到試片表面粗糙度較低，但到了一定程度後不再有明顯變化。
(4) 透過足夠的拋光效率，可在短時間內改善滲氮層的表面粗糙度，並留有一定厚度的滲氮層。

關鍵字

電漿拋光 ； 低溫氣體滲氮 ； 活化處理 ； 沃斯田鐵系不銹鋼

並列摘要

AISI 304 stainless steel is one of the commonly-used steel among austenitic stainless steel. This stainless steel has excellent corrosion resistance thanks to its high concentration of chromium and nickel. The surface is coated with a passive film that helps protect the steel from oxidation. However, it shows low hardness because of its austenite phase, and it can not be strengthened with heat treatment such as quenching, giving rise to drawbacks such as being prone to wear, scratches, and abrasion. Thus, the method of solid solution strengthening is often used to improve the hardness of
AISI 304.
This study aims to strengthen the surface of austenitic stainless steel, and reduce the surface roughness. The experiments are divided into three parts: activation treatment, low temperature gas nitriding, and plasma polishing. In order to remove the oxidation film on the surface, the specimens will go through activation treatment using HCl gas in high temperature for a short period of time. After the treatment, the surface hardness is strengthened by low temperature gas nitriding. Having been through the processes above, the surface will become rougher due to side effects like etching and lattice expansion. In order to reduce the surface roughness, the method of plasma polishing is studied in the third part. Plasma polishing is a polishing method by treating the specimen as the positive electrode. The specimen will be immersed in low concentration electrolyte, and applied with hundreds of voltages. Then, the surface would become polished when the plasma film is formed in appropriate conditions. The main results of the experiments are:
(1) With longer time span and higher temperature of gas nitriding, the nitrided layer grows thicker. The nitrided layer contains rich nitrogen and high hardness. However, overheating would cause a decrease of corrosion resistance.
(2) With lower temperature and higher current density of plasma polishing, the polishing efficiency becomes higher. The surface will become uniform when the polishing efficiency is higher than corrosion rate.
(3) The surface roughness is reduced when the polishing time is increased, but the roughness would maintain at a certain level after polished for a long time.
(4) With adequate polishing efficiency, the surface roughness could be reduced in a short period of time while maintaining enough thickness of nitrided layer.

並列關鍵字

plasma polishing ； low temperature gas nitriding ； activation treatment ； austenitic stainless steel

參考文獻

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