An Electron Microscopy Study of Vein-like Grain Boundary Microstructure in Nitrocarburized Low Carbon Steels  

作　　者：Wanglin Chen Cuilan Wu Jianghua Chen Aigui He 

机构地区：[1]Center of High Resolution Electron Microscopy,College of Materials Science and Engineering,Hunan University

出　　处：《Journal of Materials Science & Technology》2013年第7期669-672,共4页材料科学技术（英文版）

基　　金：supported by the National Basic Research Program of China(No.2009CB623704);the National Natural Science Foundation of China(Nos.51071064 and 51171063);the Nature Science Foundation of Hunan Province(Grant No. 09JJ6002);Instrumental Innovation Foundation of Hunan Province(No.2011TT1003);the Aid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province

摘　　要：The coarsened grain boundaries （GBs） with vein-like morphology frequently appear in the nitrogen diffusion layer of nitrocarburized carbon steels. The electron probe X-ray microanalysis shows that such vein-like GBs are rich in nitrogen and carbon atoms. Transmission electron microscopy and scanning electron microscopy further reveal that the coarsened GBs consist of γ＇-nitrocarbide （Fe4（C,N）） and ε-nitrocarbide lamellas that are formed during nitrocarburizing due to high nitrogen concentration at GBs. It is shown that many of {111}〈112〉 micro twins exist in the γ＇-phase lamellas and thin ε-phase slices prefer to nucleate at their twin boundaries with the orientation relationship of {0001}ε//{111}γ＇. Upon growing large γ＇-Iamellas may become faceted and thin ε-Iamellas may grow thicker and become the main portions in the vein-like GBs. The microstructure evolution occurring in the vein-like GBs can be depicted as： α ＋ [N]/[C] → ＋ [C,N] →ε-nitrocarbides.The coarsened grain boundaries （GBs） with vein-like morphology frequently appear in the nitrogen diffusion layer of nitrocarburized carbon steels. The electron probe X-ray microanalysis shows that such vein-like GBs are rich in nitrogen and carbon atoms. Transmission electron microscopy and scanning electron microscopy further reveal that the coarsened GBs consist of γ＇-nitrocarbide （Fe4（C,N）） and ε-nitrocarbide lamellas that are formed during nitrocarburizing due to high nitrogen concentration at GBs. It is shown that many of {111}〈112〉 micro twins exist in the γ＇-phase lamellas and thin ε-phase slices prefer to nucleate at their twin boundaries with the orientation relationship of {0001}ε//{111}γ＇. Upon growing large γ＇-Iamellas may become faceted and thin ε-Iamellas may grow thicker and become the main portions in the vein-like GBs. The microstructure evolution occurring in the vein-like GBs can be depicted as： α ＋ [N]/[C] → ＋ [C,N] →ε-nitrocarbides.

关 键 词：Nitrocarburizing Grain boundary γ＇-Fe4（C N） e-Nitrocarbide 

分 类 号：TG142.1[一般工业技术—材料科学与工程]