铬和镍对中碳钢渗硼层组织和生长动力学的影响

Effects of Cr and Ni on microstructure and kinetics of boride layers on medium carbon steels

为研究中碳钢中铬、镍合金元素对渗硼层组织和渗硼动力学的影响,对40钢、40Cr和40CrNi钢在880、910和940℃分别进行3、5、7、9 h的粉末渗硼,用光学显微镜、扫描电镜观察了渗层的组织形貌,对渗层进行了EDS和XRD分析。结果表明,渗硼层组织为锯齿状,Cr和Ni合金元素对渗层锯齿状结构的尖锐度略有影响。铬、镍合金元素均匀分布于硼化物层中,渗层物相组成中除了大量的Fe2B相外,还有少量的FeB相及Cr2B、Ni2B和Fe。动力学研究表明,40钢、40Cr和40CrNi的渗层厚度与渗硼时间均呈抛物线关系,渗硼扩散激活能分别为147、243和256 kJ/mol。

The solid powder boriding was carried out on 40,40 Cr and 40 CrNi steel substrates at 880,910 and 940 ℃ for 3,5,7 and 9 h,respectively.The effects of Cr and Ni alloying elements on microstructure of boride layers and the boriding kinetics were investigated.The microstructure of the boride layers was observed by optical microscope and SEM.The chemical composition and element distribution of boride layers were analyzed by EDS and XRD.The results show that the boride layers on the substrates have sawtooth morphology and the Cr,Ni alloying elements have a little effect on the formation of sawtooth morphology in the boride layers.Furthermore,the Cr and Ni alloying elements are homogenously distributed in the boride layers.The boride layers mainly consist of Fe2 B phase and a little FeB,Cr2 B,Ni2B and Fe.The results of the boriding kinetics shows that the thickness of boride layer has a parabola relationship with the processing time,while the activation energies of boriding on 40,40 Cr and 40 CrNi steel are about 147,243 and 256 kJ /mol,respectively.