沃斯田鐵系不銹鋼之低溫氣體滲碳氮化之研究

Study on Low-temperature Gas Carbonitriding of Austenitic Stainless Steel

鄭愉宏(Yu-Hong Jheng)

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(2014年)

https://doi.org/10.6342/NTU.2014.11298

摘要

沃斯田鐵系不銹鋼表面有一層富含Cr2O3且結構極為緻密的鈍化膜，能夠保護內部且有效隔絕外界環境，但也會阻礙C、N原子的滲入，因此必須先透過活化處理將不銹鋼表面的Cr2O3鈍化膜去除，才能實施低溫氣體滲碳氮化來達到不銹鋼表面硬化的目的。
本研究活化處理為利用高純度氮氣加上鹽酸蒸氣為活化氣氛，能在數分鐘內去除不銹鋼表面的鈍化膜，而且在大氣中放置多天還能進行低溫滲碳氮化處理。
本研究氣體滲碳氮化的滲碳氣氛採用氮氣加上木精分解氣，滲氮氣氛則用氨氣，不銹鋼試片經過活化處理與適當條件的低溫滲碳氮化處理後，主要實驗結果如下：
1.AISI 316L不銹鋼經低溫滲碳氮化後會產生雙層硬化層(滲氮層SN與滲碳層SC)，不論滲碳與滲氮的先後順序，滲氮層一定在外，而滲碳層一定在內、且與滲氮層鄰接。
2.AISI 316L不銹鋼在430℃下進行低溫滲碳氮化時，N會將C往內推擠，若持溫時間增長，容易析出碳化物，而先滲碳再滲氮時，N會將滲碳層往內推擠，進而形成滲氮層，若先滲氮再滲碳時，C會跨越滲氮層，往內形成滲碳層。
3.滲氮層硬度高於滲碳層，而滲碳層的硬度介於滲氮層與基材之間，可以補償滲氮層與基材之間的硬度落差。
4.若總處理時間一定，AISI 316L不銹鋼經同時低溫滲碳氮化處理後，其硬化層厚度與耐蝕性均優於先滲碳再滲氮者或先滲氮再滲碳者。

關鍵字

沃斯田鐵系不銹鋼 ； 活化處理 ； 鈍化膜 ； 低溫氣體滲碳氮化 ； 滲碳與滲氮先後順序

並列摘要

Austenitic stainless steel has a thin layer of Cr2O3 passive film on the surface, which not only can protect the inside material from corrosion but also hinder the penetration of carbon atoms and nitrogen atoms. Therefore, the Cr2O3 passive film on the surface should be removed by activation treatment before proceeding the low-temperature gas carbonitriding of austenitic stainless steel.
It was found that using the mixture of high purity nitrogen and hydrochloric acid vapor as activation atmosphere can remove the passive film in a few minutes, and the activated specimen still can be performed carbonitriding after placed in the air for several days.
In this research, the mixture of nitrogen and methanol dissociation gas was used as carburizing atmosphere and the ammonia was used as nitriding atmosphere. After the stainless steel is activated and then carbonitrided in a low temperature, the results are as follows:
1.After the low-temperature carbonitriding, AISI 316L stainless steel forms duplex hardened layers (nitrided layer and carburized layer). No matter what the sequential order of the carburizing and nitriding is, the outer layer always is the nitrided layer, which adjoins the carburized layer.
2.The carbon is pushed toward the inside by the nitrogen when the AISI 316L stainless steel is carbonitrided under the temperature of 430℃. Carbides(Fe3C) are precipitated easily if the processing time is getting longer. If carburizing is conducted first and then nitriding, the nitrogen will push the carburized layer toward the inside to form the outer nitrided layer. On the contrary, if nitriding is conducted first and then carburizing, the carbon will pass through the nitrided layer to form the inner carburized layer.
3.The hardness of the carburized layer is lower than that of the nitrided layer, so the hardness disparity between the hardened layer and the substrate can be decreased.
4.For a given processing time of AISI 316L stainless steel, the hardened layer thickness and corrosion resistance of the low-temperature carbonitriding are superior to those of pre-carburizing/post-nitriding treatment and pre-nitriding/post-carburizing treatment.

並列關鍵字

Austenitic stainless steel ； Activation treatment ； Passive film ； Low-temperature gas carbonitriding

參考文獻

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