过热对HP40Nb炉管微观组织和力学性能的影响

Effect of overheating on the microstructures and mechanical properties of HP40Nb furnace tube

将铸态HP40Nb合金在1050,1100,1150℃下分别热处理了100 h和200 h,模拟炉管在实际服役过程中的过热情况。使用光学显微镜(OM)、扫描电子显微镜(SEM)和X射线衍射仪(XRD)对原始材料和过热材料进行了微观组织表征和物相分析,并对碳化物的含量和形态进行了定量分析,此外还测试了过热前后材料的室温和高温拉伸性能。结果表明,HP40Nb合金原始铸态组织中的析出相为M_(7)C_(3)和NbC,过热后材料的组织为M_(23)C_(6)和NbC。过热材料晶内弥散分布了大量二次碳化物;过热温度越高,晶界和晶内的碳化物粗化程度越高。随着过热温度的升高,HP40Nb合金的室温抗拉强度和屈服强度呈现先增大、后减小的趋势,室温延伸率呈现先急剧减小、后缓慢减小的趋势,高温屈服强度和抗拉强度逐渐减小,高温延伸率逐渐增大。晶内二次碳化物的含量和晶界碳化物的粗化程度是影响HP40Nb合金力学性能的重要因素。

The as-cast HP40Nb alloy was heat treated at 1050,1100 and 1150℃for 100 h and 200 h,respectively,to simulate the overheated microstructures of the furnace tube in actual service.The optical microscope(OM),scanning electron microscope(SEM)and X-ray diffractometer(XRD)were used to characterize the microstructures and phases of the original and overheated alloys,and the content and form of the carbide were analyzed quantitatively.In addition,the tensile properties at room temperature and high temperature of the alloy before and after overheating were determined.The results show that the precipitated phases in the original as-cast microstructures of HP40Nb are M_(7)C_(3)and NbC carbides,while the microstructures of the alloy after overheating treatment are M_(23)C_(6)and NbC carbides.A large amount of secondary carbides are dispersed and distributed in the matrix after overheating treatment.The higher the overheating temperature,the higher the degree of coarsening of carbides on crystal boundary and in the matrix.With the increase of overheating temperature,the tensile strength and yield strength of HP40Nb alloy at room temperature firstly increase and then decrease,and the elongation at room temperature first decreases sharply and then decreases slowly.The yield strength and tensile strength at high temperature decrease gradually,while the elongation at high temperature increases gradually with the increase of overheating temperature.The content of secondary carbides in the matrix and the coarsening extent of carbides on the crystal boundary are the key factors affecting the mechanical properties of HP40Nb alloy.