热处理对蒸汽发生器用国产690合金管显微组织和显微硬度的影响

Effects of Heat Treatment on the Microstructure and Microhardness of Domestic Alloy 690 Tube in Steam Generator

为改善蒸汽发生器常用国产690合金管的抗微动磨损性能,通过实验研究不同的热处理条件对合金显微组织和显微硬度的影响规律.首先,对690合金管进行固溶处理和TT处理(也称脱敏处理),以改变690合金管的晶粒平均直径和晶界碳化物形貌;然后用光学显微镜观察晶粒平均直径的大小,用场发射扫描电子显微镜观察晶界碳化物的形貌;最后,用显微硬度计分别测量690合金管基体和晶界的显微硬度.结果表明:对于国产690合金管,当固溶处理温度为1080℃时,晶界的碳化物未完全溶解,基体的显微硬度低于晶界;当固溶处理温度达到1090℃后,晶界的碳化物完全溶解进入基体;升高固溶处理温度和延长处理时间,晶粒平均直径会增大,基体和晶界的显微硬度都会降低,并且基体的显微硬度高于晶界的显微硬度.对固溶处理后的国产690合金管进行TT处理时,晶界碳化物尺寸和间距都随着TT处理温度升高和处理时间的延长而增大,晶界碳化物逐渐变得离散;基体的显微硬度基本不变并低于晶界,晶界的显微硬度在TT处理温度715℃、时间5 h都会出现一个峰值.研究表明,通过固溶处理可调整690合金管的晶粒度,TT处理获得不同的晶界碳化物形貌,进一步影响材料的显微硬度,进而可能改善材料在蒸汽发生器中应用的抗微动磨损性能.

To improve the fretting wear resistance of domestic alloy 690 tubes commonly used in steam generators,the effects of different heat treatment conditions on the microstructure and microhardness of the alloys were studied.First,an alloy 690 tube was treated by solution treatment and thermal treatment(TT)to change the average grain diameter and intergranular carbides morphology.Then,the average grain diameter was observed by an optical microscope,and the intergranular carbides morphology was observed by field-emission scanning electron microscopy.Finally,the microhardnesses of the matrix and grain boundary of the alloy 690 tube were measured by a microhardness tester.The results indicate that for the domestic alloy 690 tube,when the solution treatment temperature was 1080℃,the intergranular carbides partially dissolved into the matrix,and the microhardness of the matrix was lower than that of the grain boundary.When the solution treatment temperature reached 1090℃,the intergranular carbides completely dissolved into the matrix.With an increase in the solution treatment temperature and time,the average grain diameter increased,and the microhardnesses of the matrix and the grain boundary both decreased;in addition,the microhardness of the matrix was higher than that of the grain boundary.When the solution-treated domestic alloy 690 tube was subjected to TT,the intergranular carbides size and spacing increased with the increase of the TT temperature and time,and then the intergranular carbides gradually became discrete.The microhardness of the matrix was basically constant and lower than that of the grain boundary.The grain boundary microhardness reached its peak when the TT was at 715℃for 5 h.This study shows that the grain size of the alloy 690 tube can be adjusted by solution treatment;different intergranular carbides morphology can be obtained by TT;and these further affect the microhardness of the material,which may improve the fretting wear resistance of the material in steam generator applications.