FB2转子钢在长期热时效中的组织变化

Evolution of Microstructure during Long-term Aging of FB2 Steel Used for Turbine Rotors

利用EBSD与BSE分析方法研究FB2转子用钢在长期热时效过程中微观组织的变化,重点研究晶界比例变化、M_(23)C_6与L_(aves)相析出长大行为及材料硬度的变化。研究结果发现,从原始态到650℃18 000 h,FB2钢微观组织中小角度晶界与大角度晶界的比值略有增加,马氏体板条没有明显的回复现象。随着时效时间的延长,M_(23)C_6颗粒的平均尺寸先增加后逐渐趋于稳定;时效时间超过1 000 h后,出现了形状不规则的L_(aves)相,且L_(aves)相颗粒的平均尺寸一直稳定增加。随时效时间延长,FB2钢的硬度先急剧下降,后改为缓慢下降并逐步趋于稳定。时效时间超过1 000 h后,M_(23)C_6颗粒尺寸增加的趋势与硬度值下降的趋势基本保持一致。随着时效时间的延长,在析出相的相界附近应变增大,马氏体板条界处的应变有所减弱,整体组织的应变有所增加。

The variation of the microstructure of FB2 rotor steels during long-term thermal aging is studied with analysis methods EBSD and BSE. The study focused in the boundary proportion variation, M_（23）C_6 and L_（aves）phase precipitation and material hardness variation. The results show that from initial state to 650 ℃/18 000 h, the ratio of low angle to high angle boundaries increases slightly and the obvious recovery of martensite lath does not take place. With increasing aging time, the mean size of M_（23）C_6 grains increases firstly and then gradually tends to be stable. L_（aves）phase has been found in the specimens after exposure at 650 ℃ for 1 000 h, and have irregular shape, hose size keeps steady growth. There is a remarkably decreases in hardness during the early stage of long-term aging and then begins a slow deline, finally achieves stability. After aged at 650 ℃ for 1 000 h, the trend of decreasing in hardness accords very well with the trend of increasing in size of M_（23）C_6. With increasing aging time, on the vicinity of phase interfaces, the degree of strain increases, but at the vicinity of martensite lath boundaries in decreases, and the degree of strain for whole microstructure increases.