焊接热循环及峰值温度对C-HRA-2镍基合金组织演变的影响

Effect of Welding Thermal Cycle and Peak Temperature on Microstructure of C-HRA-2 Nickel-Based Alloy

摘要:

通过焊接热模拟方法得到了C-HRA-2镍基合金在不同一次峰值温度（T_p1=1150，1250，1350 ℃）和二次峰值温度（T_p2=850，950，1050，1150，1250，1350，1450 ℃）下的焊接热影响区（HAZ），研究了峰值温度和热循环次数对C-HRA-2合金HAZ微观组织演变的影响，并测试了其显微硬度。采用光学显微镜、扫描电镜和透射电镜对HAZ的微观结构和碳化物进行表征。结果表明，在T_p1=1150 ℃的HAZ中，可观察到沿晶界析出的细小的M₂₃C₆碳化物。在T_p1>1250 ℃的HAZ中，在晶界附近发现由于成分液化而导致的γ基体与M₂₃C₆碳化物组成的微观结构。当T_p2在1050~1250 ℃，可在HAZ中的晶界附近观察到与在T_p1=1150 ℃的HAZ中类似结构的碳化物，这是由T_p1和T_p2间基体中Cr的固溶度差值导致的。在T_p2>1250 ℃的HAZ中，在晶界附近可观察到与在T_p1=1250 ℃的HAZ中类似的熔融态微观组织。随着T_p2的升高，显微硬度出现很大程度的起伏，在T_p2=1250 ℃的试样显微硬度要稍高于母材硬度，这是因为晶界附近出现的碳化物起到了晶界强化作用。

Abstract:

The welding heat-affected zone (HAZ) of C-HRA-2 nickel-based alloy under various primary peak temperatures (T_p1=1150, 1250, and 1350 °C) and the secondary peak temperatures (T_p2=850, 950, 1050, 1150, 1250, 1350, and 1450 °C) was obtained by welding thermal simulation. The effect of peak temperature (T_p) and thermal cycling times on the evolution of simulated HAZ microstructure of C-HRA-2 alloy was investigated. The microhardness of simulated HAZs was measured. The HAZ microstructure and carbide were characterized by the optical microscope, scanning electron microscope, and transmission electron microscope. Results show that the fine M₂₃C₆ carbides appear along the grain boundaries in the simulated HAZ with T_p1=1150 °C. For HAZs with T_p1>1250 °C, the γ matrix bonded with M₂₃C₆ carbides appears near the grain boundaries due to component liquefaction. When T_p2 is 1050–1250 °C, the carbides similar to those in HAZ with T_p1=1150 °C can be observed near the grain boundaries due to the difference in the solid solubility of Cr in the matrix obtained at T_p1 and T_p2. In HAZ with T_p2>1250 °C, the melted microstructure similar to that with T_p1=1250 °C can be observed near the grain boundaries. The microhardness fluctuates significantly with increasing the T_p2. The microhardness of specimen with T_p2=1250 °C is slightly higher than that of the base material, because of the grain boundary strengthening effect of the carbides near the grain boundaries.