摘要
采用等离子堆焊技术在 304H不锈钢上分别堆焊Stellite6 和Stellite21 钴基合金,研究了在 550～650℃不同温度下钴基合金堆焊层的显微组织和性能演变规律.利用光学显微镜、扫描电镜与电子探针对堆焊层组织形貌及结合处元素分布进行观察分析,采用显微硬度计与电化学工作站分别对堆焊层的显微硬度与耐腐蚀性能进行检测.结果表明:两种合金堆焊层组织由熔合区的平面晶、中部柱状晶及顶部的等轴晶组成.随着温度升高,堆焊合金枝晶间距略有增大,熔合处无明显元素扩散,具有良好的组织稳定性.焊态Stellite6、Stellite21 合金堆焊层的显微硬度分别为 463、365HV0.3,受热后两种合金堆焊层硬度略有降低;焊态Stellite6、Stellite21 合金堆焊层的腐蚀电流密度分别为 1.312、10.848 μA/cm2,受热后两种合金腐蚀电流密度均略增大.总体而言,在 550～650℃下两种合金均具有较高的硬度和良好的耐腐蚀性能.
Abstract
Stellite6 and Stellite21 Co based alloys were surfaced on the 304H stainless steel by using plasma surfacing,respectively.The evolution of microstructure and properties of the Co based alloy surfacing layers under 550-650℃was studied.The microstructure of the surfacing layers and element distribution at the bonding zone were observed and analyzed by optical microscope,scanning electron microscope and electron microprobe.Microhardness and corrosion resistance of the hardfacing layers were measured by microhardness tester and electrochemical workstation,respectively.The results show that the microstructure of surfacing layer of the two alloys is composed of plane crystal,columnar crystal and equiaxed crystal.With the increase of temperature,the dendrite spacing of the surfacing alloys increases slightly,there is no obvious element diffusion at the fusion zone,and it has good microstructure stability.The microhardness of the surfacing layer of Stellite6 and Stellite21 alloys in welded state is 463,365HV0.3,respectively,and the hardness of surfacing layer of the two alloys decreases slightly after heating.The corrosion current density of surfacing layer of Stellite6 and Stellite21 alloys in welded state is 1.312,10.848 μA/cm2,respectively,and the corrosion current densities of the Stellite6 and Stellite21 alloys increase slightly after heating.Generally,the two alloys have high hardness and good corrosion resistance at 550-650℃.
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