表面氮化處理對鐵錳鋁碳合金微結構與機械性質之影響

Effects of Nitriding Treatment on the Mechanical Property and Microstructure of the Fe-Mn-Al-C Alloy

鐵錳鋁碳合金施以540℃氮化處理後，可以獲致160至200 μm不等的氮化層，其氮化層硬度可達HV1200，大幅提升鐵錳鋁碳合金的表面硬度與耐磨耗特性。然而，我們亦可發現鐵錳鋁碳合金的氮化層最表面硬度值僅約HV650左右，此部分與傳統合金鋼經氮化處理後所得之氮化層特性有明顯的差異。經由XRD與TEM顯微結構分析發現，本研究鐵錳鋁碳合金氮化層最表層除了Fe3N及Fe4N以外，還有厚度約為6~10μm的MnO氧化層，而經過此氧化層後即是氮化處理具有最佳硬度的AlN、Fe3N及Fe4N等氮化層，此種特殊氮化組織顯示鐵錳鋁碳合金中的錳含量會影響到氮化處理後的結果。經由本研究發現，錳含量的提高雖不會影響氮化層的硬度值，但卻會抑制氮化層的成長與降低氮化層厚度，此結論尚未被其他鐵錳鋁碳合金研究學者所揭示過。

When the Fe-Mn-Al-C Alloy was heat treated by gas nitriding treatment at 540℃ for 40 hours, the thickness of the nitriding layer was observed to be between 160μm to 200μm. The hardness of the nitriding layer could be raised to HV1200. The surface hardness and wear resistance of the Fe-Mn-Al-C alloy were significantly improved by gas nitriding treatment. However, we also found that the outer surface hardness value of the nitriding layer was only about HV650, which was quite different from the characteristic of the nitriding layer for the commercial nitriding alloy steel. Based on the XRD and TEM analyses, besides Fe3N and Fe4N nitrides, MnO oxide with the thickness of 6~10μm could be observed on the outer surface of the nitriding layer. The nitriding layer of the Fe-Mn-Al-C alloy was mainly comprised of Fe3N, Fe4N and AlN nitrides. This particular nitriding structure would improve the surface hardness and wear resistance of the Fe-Mn-Al-C Alloy by gas nitriding treatment. In the present study, we also found that the increase of Mn content in the Fe-Mn-Al-C alloy wouldn’t influence the maximum surface hardness value but would both inhibit the formation of nitriding layer and decrease the thickness of nitriding layer. This conclusion has not yet been revealed by other Fe-Mn-Al-C alloy researchers.