应用金相、X射线衍射和微区成分分析研究了20钢经离子氮化后在不同温度渗铬(复合渗铬)所得渗铬层的显微组织及其生成机制。不同温度复合渗铬层的表面层均由CrN(fcc)，－Cr2N(hcp)和－(Cr, Fe)(bcc)组成，其中 －(Cr, Fe)的含量随渗铬温度提高而减少。在复合渗铬过程中，原先的氮化白亮层发生扩散反应相变, 生成复合渗铬白亮层，而扩散层中的相变主要是析出/共析转变，生成'氮化物析出带和/或一种类似珠光体的（+')共析反应带。
The morphology and formation mechanism of the microstructure of the composite ion-nitrided plus chromized layers obtained at various chromization temperatures in a plain low-carbon steel (steel 20) were investigated using metallography, X-ray diffraction and microanalysis. It was found that the surface zone of the composite--chromized layers obtained at various temperatures was composed of the phases in which the fractiondecreased with increasing the chromization temperature. During chromization of the nitrided layer, the diffusion-controlled reaction transformation occurred within the white (compound) layer of the former nitrided layer, forming a white composite-chromized layer. Meanwhile, the precipitation/eutectoid reaction took place in the transition (diffusion) zone of the nitrided layer during air cooling from a chromization temperature at or above 580℃, resulting in the formation of nitride precipitate zone and/or an eutectoid zone similar to the pearlitic structure.
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