20钢渗氮表面500℃盐浴渗铬层微观组织结构研究

Microstructure of the Composite Chromized Layer on 0.2wt% Steel after 500℃ Salt-bath Chromizing

20钢经离子渗氮后在500℃下进行盐浴渗铬,采用金相显微镜、X射线衍射仪、扫描电镜及高分辨透射电镜研究渗铬层的组织结构,并选取1 h,5 h和12 h不同渗铬保温时间的样品来探讨渗铬时间对渗铬层的组织结构的影响.结果表明,在500℃下盐浴渗铬能获得铬的化合物层,其表面相主要为CrN,β-(Cr,Fe)2(N,C)1-x相,且随着渗铬时间的延长β相增多且出现Cr7C3相.在500℃下粒径复合盐浴渗铬12 h得到的化合物层晶粒细小并存在纳米晶.化合物层中CrN晶粒较完美可长大至几百个纳米,而Cr7C3相晶粒内出现许多孪晶或层错.

Plain low-carbon steel with 0.2 wt % carbon （steel 20）was first treated with plasma nitri- ding and then was processed by salt bath chromizing at 500 ℃ for lh, 5hs and 12hs, respectively. The mi- crostructure of chromized layers was studied by means of optical microscopy, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results have shown that the chromized layer consists of CrN, β-（Cr, Fe） 2 （N, C）1-x By prolonging the chromizing time, the amount of β-phase on the surface layer increases and Cr7C3 phase can appear on the surface. The chromized layer formed at 500 ℃ for 12 h contains both sub-micron CrN grain area and nano-material area. The fine CrN grains can grow up to hundreds of nanometer,when there are a lot of twins or/and stacking faults in the Cr7C3 grains.