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本文对铁碳合金表面获得铬碳化物扩散层的形成特征进行了研究。渗铬材料为石墨、普通碳钢、灰口铸铁和白口铸铁,渗铬采用粉末法。为了能够看出渗铬介质中铁含量对渗层形貌的影响,所以使用高纯度的铁粉与铬粉。渗铬工艺为;567～1100℃加热5～1500分钟。通过X线衍射测定渗层的相组成;用电子探针测定渗层中Cr与Fe的分布;用光学及电子显微镜对渗层的显微组织进行观察,电镜试样采用复型和薄膜二种。薄膜衍射法显示了M_7C_3层结构,并测定了它的晶体位向。当试样加热到正常渗铬温度时,发现在低于Ac_1温度下即已开始形成碳化物层。本文试验表明;渗层中M_3C出现与否主要取决于渗铬温度和被渗材料中的含碳量;渗铬介质中的Fe;Cr比对渗层显微组织和厚度影响很大;柱状晶粒M_7C_3层具有某种特殊的晶体学位向关系,即M_7C_3的[0001]方向垂直于扩散前沿。这些碳化物层微观组织数据都是通过薄膜透射法获得的。碳化层生长方向的确定,是我们提出碳化物层形成的扩散模型的依据。
In this paper, the formation of chromium carbide diffusion layer on the surface of iron-carbon alloy was studied. Chromizing materials for graphite, ordinary carbon steel, gray cast iron and white cast iron, chromizing powder method. In order to see the effect of iron content in the chromizing medium on the morphology of the layer, high-purity iron and chromium powders are used. Chromizing process; 567 ~ 1100 ℃ heating 5 ~ 1500 minutes. The phase composition of the layer was determined by X-ray diffraction. The distribution of Cr and Fe in the layer was measured by electron probe. The microstructure of the layer was observed by optical and electron microscopy. . The thin film diffraction method shows the M_7C_3 layer structure and its crystal orientation has been determined. When the sample was heated to normal chromizing temperature, it was found that the formation of carbide layer started below Ac_1 temperature. The experimental results show that the presence or absence of M_3C in the layer mainly depends on the temperature of the chromizing and the amount of carbon in the material being infiltrated. The amount of Fe and Cr in the chromizing medium greatly affects the microstructure and thickness of the layer. The grain M_7C_3 layer has some special crystallographic orientation relationship, that is, the [0001] direction of M_7C_3 is perpendicular to the diffusion front. These carbide layer microstructure data are obtained by the thin film transmission method. The determination of the growth direction of the carbide layer is the basis for the diffusion model that we propose to form the carbide layer.