采用ＳＥＭ和ｘ射线薄膜掠射装置测定了工业纯铁在Ｆｅ－Ｎ共析温度以上两段离子渗氮层的组织形态和γ’ａ两相沿渗层深度的分布。发现对应渗层的亚共析成分区存在网状分布的γ’相并构成富γ’相域；带状的ａ相区与基体邻接。这两种反常组织是由第二段降温渗氮时γ／ａ界面反向迁移所致。 SEM and X-ray film grazing device was used to measure the microstructure and the distribution of the depth of two-phase ion nitriding layer of industrial pure iron above Fe-N eutectic temperature. It is found that the sub-eutectoid composition zone corresponding to the infiltrated layer has a network-like distributed γ ’phase and constitutes a γ-rich phase region; and the band-shaped a-phase region is adjacent to the matrix. These two abnormalities are caused by the reverse migration of the γ / a interface during the second stage of nitriding.