超_超_临界汽轮机汽缸紧固螺栓高温蠕变断裂研究

第27卷第29期中国电机工程学报V ol.27 No.29 Oct. 2007

2007年10月Proceedings of the CSEE ©2007 Chin.Soc.for Elec.Eng. 文章编号：0258-8013 (2007) 29-0080-04 中图分类号：TH140 文献标识码：A 学科分类号：470⋅30

超(超)临界汽轮机汽缸紧固螺栓高温蠕变断裂研究

徐鸿1，郑善合1，MAILE Karl2

(1．华北电力大学电站设备状态监测与控制教育部重点实验室, 北京市昌平区 102206；

2．斯图加特大学国家材料测试中心，斯图加特70569, 德国)

Research on Creep Rupture of Fastening Bolts of Ultra-supercritical Steam Turbine

Cylinder Case at High Temperature

XU Hong1, ZHENG Shan-he1, MAILE Karl2

(1. Key Laboratory of Condition Monitoring and Control for Power Plant Equipment of Ministry of Education,

North China Electric Power University, Changping District, Beijing 102206, China;

2. State Material Testing Institute, University Stuttgart, Stuttgart 70569, Germany)

ABSTRACT: Nickel based alloy will become one of the most common material of ultra-supercritical steam turbine cylinder case fasteners in future. It is important to study creep damage of bolts for ultra-supercritical generating units performance safely and service. Creep rupture experiments of Nimonic 80A uniaxial specimen and hollow bolts at 550 °C and different stress were carried out. Creep damage model was improved by inducting strain threshold value based on Norton-Bailey- Kachanov creep model, which was more exact to describe creep process. Creep behaviors of hollow bolt were simulated by ABAQUS based on reworking improved creep damage model of subroutine. It is indicated that creep rupture of hollow bolt is not taking place at screw thread where the stress concentrated, but taking place at the position of screw shaft. A good coincidence comparing the result calculated according to the theoretical model presented with finite element calculation can be observed.

KEY WORDS: ultra-supercritical steam turbine; fastening bolt; creep at high temperature; creep damage model; strain threshold value; rupture

摘要：超(超)临界汽轮机汽缸以镍基超高温合金作为紧固件材料，螺栓蠕变损伤的研究对超(超)临界机组的安全运行及维修具有重要意义。对镍基合金Nimonic 80A进行了550 ℃不同应力下单轴及空心螺栓的蠕变实验，引入应变阈值，结合Norton-Bailey-Kachanov蠕变方程，改进了蠕变损伤模型，模型能更准确描述蠕变全过程；修改有限元软件ABAQUS 子程序，模拟了空心螺栓的蠕变过程。结果表明，空心螺栓蠕变断裂并不是在应力集中的螺纹处，而是在螺杆处，有限元计算结果与实验结果吻合较好。

关键词：超(超)临界汽轮机；紧固螺栓；高温蠕变；蠕变损伤模型；应变阈值；断裂0 引言

亚临界机组紧固件材料多用强化的12%Cr系耐热钢，随着超(超)临界机组蒸汽参数的提高，其高温紧固件所用材料[1-4]也发生了改变。镍基合金由于成本比较高，一般在蒸汽温度高于593℃或满足一定设计要求时使用。美国、日本、欧洲等制造的超(超)临界机组的紧固螺栓有的使用镍基合金[5-7]。Nimonic80A(NiCr20TiAl)是镍基超高温合金的一种，本文对Nimonic80A合金材料进行了单轴及螺栓在550℃下的蠕变实验。汽轮发电机组汽缸紧固螺栓失效机理包括疲劳、蠕变、疲劳蠕变交互作用和松弛，在机组稳定负荷下，可以认为螺栓只受蠕变作用，本文主要对螺栓的高温蠕变损伤进行了研究。

普遍认为蠕变损伤的进展是由于材料内部微孔洞或微裂纹的合并和增长[8-9]。Kachanov[10]和Rabotnov[11]在Norton蠕变法则的基础上用损伤变量D来描述蠕变损伤，提出有效应力[12]概念，认为材料内部微观缺陷使材料的有效承载截面面积减小，从而造成蠕变第三阶段应变速率上升(如图1)，实验研究表明蠕变第一阶段、第二阶段金属晶粒只发生错位，晶粒脱离发生在蠕变第三区。Norton蠕变模型[13]只能描述蠕变过程的第一、第二阶段，不能描述蠕变第三阶段，Kachanov蠕变模型[14-15]计算结果也不能很好与实验结果吻合。Lemaitre- Chaboche[16-17]和Cock-Ashby[18]用微结构对蠕变进行了分析。本文在Kachanov蠕变模型的基础上引