中压主汽门用20Cr1Mo1VTiB钢紧固螺栓断裂分析  

Fracture analysis of 20Cr1Mo1VTiB steel fastening bolts used for intermediate pressure main stop valve

作　　者：郑建军 樊子铭 程旭 张艳飞 石全强[3] Zheng Jianjun;Fan Ziming;Cheng Xu;Zhang Yanfei;Shi Quanqiang(Inner Mongolia Power Research Institute Branch,Inner Mongolia Power(Group)Co.,Ltd.,Hohhot Inner Mongolia O10020,China;Air Force in ShenyangFirst Military Representative Office,Shenyang Liaoning 110039,China;Shi-changxu Innovation Center for Advanced Materials,Institute of Metal Research,Chinese Academy of Sciences,Shenyang Liaoning 110016,China)

机构地区：[1]内蒙古电力(集团)有限责任公司内蒙古电力科学研究院分公司,内蒙古呼和浩特010020 [2]空装驻沈阳地区第一军事代表室,辽宁沈阳110039 [3]中国科学院金属研究所师昌绪先进材料创新中心,辽宁沈阳110016

出　　处：《金属热处理》2023年第11期293-299,共7页Heat Treatment of Metals

基　　金：内蒙古电力科学研究院2022年自筹科技项目(2022-05);内蒙古电力科学研究院2023年自筹科技项目(2023-12)。

摘　　要：在对某汽轮机组中压主汽门进行解体检修时,发现两根20Cr1Mo1VTiB钢高温紧固螺栓发生断裂失效现象。采用化学成分分析、宏观及微观形貌观察、冲击断口分析及力学性能测试等方法剖析了螺栓发生提前断裂失效的原因,并阐明了其断裂失效机理。结果表明,两根20Cr1Mo1VTiB钢高温紧固螺栓的脆性断裂现象均发生于螺母端第一扣螺纹牙底处,且与长期高温的运行工况有关。20Cr1Mo1VTiB钢高温紧固螺栓在长时高温和交变循环应力共同作用下,基体中的碳化物颗粒逐渐发生Ostwald熟化,导致其韧性降低,且于应力集中程度较高的螺母端第一扣螺纹牙底处形成蠕变孔洞,致使其发生提前断裂失效。此外,1号螺栓基体中存在的平均尺寸为5μm且呈线性分布的Ti(N,C)夹杂物,进一步降低了冲击性能,从而导致其先于2号螺栓发生断裂。由于中压主汽门整体的受力状况在1号螺栓发生脆性断裂后发生改变,进而导致冲击性能余量较小的2号螺栓随之发生脆性断裂失效。Two 20Cr1Mo1VTiB high temperature fastening bolts were found to be broken during the disassembly and maintenance of the intermediate pressure main stop valve used for a steam turbine unit.The reasons for the premature failure of bolts were analyzed by means of macro and micro morphology observation,chemical composition analysis,impact fracture analysis as well as mechanical property test,and the fracture failure mechanism was also clarified.The results show that the fracture behavior of the two 20Cr1Mo1VTiB steel high temperature fastening bolts is mainly belong to brittle fracture triggered at the bottom of the first thread,which is mainly related to the long-term high temperature operation condition.The carbide particles in the matrix of the 20Cr1Mo1VTiB high temperature fastening bolt are gradually Ostwald ripening with the combined action of long-term high temperature and alternating cyclic stress,resulting in a decrease of toughness.Besides,creep cavities are also formed at the nut end of the first thread bottom with high stress concentration,leading to premature fracture failure.In addition,the linearly distributed Ti(N,C)inclusions with average size of 5μm further lead to the reduction of impact property of the No.1 bolt,causing the fracture of No.1 bolt prior to bolt No.2.Then the overall stress condition of the intermediate pressure main stop valve is changed,which leads to brittle fracture of the No.2 bolt with a small impact property margin.

关 键 词：中压主汽门 20Cr1Mo1VTiB钢 紧固螺栓 断裂分析 夹杂物 碳化物 

分 类 号：TG146[一般工业技术—材料科学与工程]