H13钢550℃复合渗铬工艺研究

Study on Complex Chromizing at 550℃ for H13 Steel

通过光镜、扫描电镜、X射线能谱仪、X射线衍射仪和AUTOLAB电化学工作站研究了H13钢在540～560℃离子渗氮8h再进行550℃低温盐浴复合渗铬后的表层相组织结构的转变。在550℃复合渗铬6h后CrN化合物层平均厚度为5μm,化合物层的显微硬度为1500HV。渗铬层主要由最外层的CrN、中间的扩散层和内部剩余的氮化物层组成。内部的氮化物层会随渗铬时间的延长而消失,转变的过程为ε-Fe2N!γ′-Fe4N!α-Fe。获得高硬度和强耐腐蚀性的表面层是由于生成了大量的细小的CrN晶粒。

The phase microstructure transformations of H13 steel subjected by plasma nitriding at 540-560℃ for 8 h, followed by a salt bath thermoreactive deposition and diffusion （TRD） chromizing process at 550 ℃ were investigated by means of optical microscopy, scanning electron microscopy（SEM）, X-ray energy dispersive spectroscopy （EDS）, X-ray diffi-action and electric chemistry of AUTOLAB. The results show that a CrN compound layer with an average thickness of 5 μm and an average microhardness of 1 500 I-IV is formed in the prior plasma nitrided compound layer by low-temperature chromizing at 550 ＂C for 6 h. The chromized coating consists of three sub-layers, i.e. namely the outer CrN layer, the intermediate diffusional layer and the inner residual nitrided compound layer, the prior nitrided compound layer with the inner sub-layer is vanishing as the chromizing time prolonging. The transformation course is ε-Fe2N→γ＇-Fe4N→α-Fe. The high hardness and corrosion-resistant of the chromized coating are attributed to a large amount of the fine CrN grains on the surface of compound layer.