【摘要】 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),β-Cr2N(hcp)和α-(Cr,Fe)(bcc)组成,其中α-(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γ’氮化物析出带和/或一种类似珠光体的(α+γ’)共析反应带.更多还原

【Abstract】 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 CrN (fcc), β-Cr2N (hcp) and α-(Cr, Fe) (bcc), in which the fraction of α-(Cr, Fe) decreased 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 a γ’ nitride precipitate zone and/or an (α+γ’) eutectoid zone similar to the pearlitic structure.更多还原