620℃汽轮机用CB2钢高温时效过程组织与析出相演变分析  

Microstructure and Precipitation Phase Evolution of CB2 Steel Used For 620℃Steam Turbine During High Temperature Long-term Aging

作　　者：田晓[1] 李芳草 徐慧 李太江[1] 李益民[1] TIAN Xiao;LI Fang-cao;XU Hui;LI Tai-jiang;LI Yi-min(Xi'an Thermal Power Research Institute Co.,Ltd.,Xi'an 710051,China;Xi'an Yitong Thermal Technology Service Co.,Ltd.,Xi'an 710048,China)

机构地区：[1]西安热工研究院有限公司,西安710051 [2]西安益通热工技术服务有限责任公司,西安710048

出　　处：《汽轮机技术》2022年第3期236-240,共5页Turbine Technology

基　　金：中国华能集团公司总部科技资助项目(HNKJ18-H05)。

摘　　要：为获得长时服役过程中CB2钢的组织演变规律和老化特征,研究了CB2钢在620℃高温时效过程中显微组织和析出相的演变行为。结果表明:CB2钢在高温时效过程中显微组织仍为回火马氏体,板条形态清晰、位错密度未见明显下降,组织稳定性良好,供货态中析出的M_(23)C_(6)碳化物大量弥散分布在马氏体板条边界、原奥氏体晶界,在时效过程中尺寸无明显增大,时效8000h后仍在200nm以内,这是CB2钢保持良好高温强度的重要原因。CB2钢高温时效过程中微观组织的变化主要表现为Laves相的析出和长大,它依附于M_(23)C_(6)碳化物优先形核析出并以吞噬机制长大,随时间延长颗粒尺寸呈线性增大、不断粗化,这是造成CB2钢时效脆化的重要原因。In order to obtain the microstructure evolution and aging characteristics of CB2 steel during long-term service,this paper studied the evolution behavior of microstructure and precipitated phases of CB2 steel during high temperature aging at 620℃.The results show that during the high temperature aging process,the microstructure of CB2 steel is still tempered martensite,the shape of the lath is clear,the dislocation density does not decrease significantly,and the microstructure stability is superior.In the supply state,a large amount of M_(23)C_(6) carbide precipitates distributes in the boundary of martensite lath and the grain boundary of original austenite.There is no significant increase in size of M_(23)C_(6) during the aging process,and it is still within 200nm after aging for 8000h,which is an important reason for CB2 steel to maintain superior strength at high temperature.The change of the microstructure of CB2 steel during high temperature aging is mainly manifested as the precipitation and growth of Laves phase,which is preferentially nucleated and precipitated by M_(23)C_(6) carbides and grows by a phagocytic mechanism.With the extension of time,the particle size of the Laves phase linearly increases and continuously coarsens,which is an important reason for the aging embrittlement of CB2 steel.

关 键 词：CB2铸钢 高温时效 力学性能 微观组织 M_(23)C_(6)碳化物 LAVES相 

分 类 号：TK265[动力工程及工程热物理—动力机械及工程]