冷作工具鋼經固體粉末滲氮後之耐磨性研究

Abstract

本研究主要是在探討固體粉末滲氮法之特性，研究固體粉末滲氮應用於冷作工具鋼SKD11、SKH51、DC53時，對其耐磨性的影響。以不同的滲氮溫度和時間實施滲氮，探討此氮化法的處理條件對氮化層的顯微組織、硬度分布、含氮量分布及耐磨性的影響，進而了解固體粉末滲氮法的最佳實用條件，並和傳統 氣體滲氮法作比較，以了解兩者之間的不同之處。由實驗結果得知，固體粉末滲氮具有下列特點︰ 1.為了使表層有效硬化且得到較緻密的化合物層，500~550℃為此固 體粉末滲氮法之最佳滲氮溫度。 2.鋼料經固體粉末滲氮後，其化合物層較緻密，使用上不易破碎或 剝離，在應用上不需另行後續處理將化合物層磨除。 3.鋼料在480℃以上經固體粉末滲氮後即有硬化效果，隨著滲氮溫度 的提高和滲氮時間的增長，耐磨性皆有明顯的提升，可依使用需 求，做適當的調整，使模具或零件等產品達到最高的效益。其 中，以550℃左右進行滲氮者，耐磨性最佳。但在600℃處理者， 其化合物層較鬆散且亦會出現孔洞，再加上氮化物變得粗大，導 致表層硬度無法提升，試片所能承受的磨耗荷重和滑動距離有 限，故實用性較差。 4.在480~500℃實施固體粉末滲氮，由於滲氮溫度低不易產生變形， 適用於精密模具或零件，且短時間內即有硬化效果，對於耐磨性 有顯著之提升。 5.經固體粉末滲氮後，其化合物層除了有氮原子滲入外，亦有碳原 子滲入，雖然滲氮層不如傳統氣體滲氮來得厚，但此混合的化合 物層具有較佳之韌性，可有效提升耐磨性，此點和軟氮化有類似 之處。

The purpose of this study is to understand the characteristics of solid nitriding. The effect of solid nitriding on the wear resistance of cold working tool steel such as SKD11, SKH51 and DC53 will be discussed in this article. The above steel sample was nitrided at various temperatures for different time. Then, the microstructure, hardness distribution, nitrogen contents and wear resistance of the nitrided layer was examined for each solid nitriding condition. Moreover, above experimental data was compared with those of conventional NH3 gas nitriding. The results were summarized as follows: 1.In order to obtain an effective surface hardness and the more dense compound layer, the temperature ranging from 500℃ to 550℃ was the optimal temperature for the solid nitriding. 2.The compound layer of steel after the solid nitriding was rather dense and not easy to crack or spall off. It is not necessary to remove the layer by grinding before application. 3.The steel has hardening effect as long as the solid nitriding temperature over 480℃. The wear resistance of nitrided layer increases with increasing nitriding temperature or time. The dies and machine parts should be nitrided under appropriate conditions depending on their application reguirement. Besides, the wear resistance of the nitrided layer was the best for the steel nitrided at 550℃. As to the steel nitrided at 600℃, the holes will appear in the compound layer and nitrides will become coarse. Therefore, both the surface hardness and the wear resistance will decrease. 4.The nitriding at low temperature 480℃~500℃ was not easy to produce deformation, so this method could be applied to the precision machine parts. 5.The compound layer of solid nitriding was permeated with not only nitrogen but also carbon. Although the nitrided layer was not as thick as that of the gas nitriding, the compound layer had better toughness and wear resistance.This point was similar to Tufftriding.