1Cr18Ni9Ti管道焊缝金属疲劳短裂纹萌生与早期扩展  

Initiation and Early Propagation of Short Fatigue Cracks on Weld Metal of 1Cr18Ni9Ti Pipes

作　　者：赵永翔[1] 杨冰[1] 高庆[1] 

机构地区：[1]西南交通大学,机械工程研究所,成都610031

出　　处：《核动力工程》2003年第2期127-132,共6页Nuclear Power Engineering

基　　金：国家自然科学基金(50075073);全国优秀博士学位论文作者专项资金;四川省青年科技基金(2000-14-458)项目

摘　　要：复型研究了1Cr18Ni9Ti管道焊缝金属的疲劳短裂纹萌生与早期扩展特点。结果表明,有效短裂纹萌生于与管道内外表面一致的试样表面局部区域中delta铁素体与基质的界面。早期扩展具有显著微观结构效应特征,最大障碍尺度约为40μm,与焊缝金属特征微观组织结构——柱状晶中富delta铁素体带间距离一致。该尺度范围,由于强微观结构约束,短裂纹密度较高并逐渐增加;尺度不规则扩展,直到若干较长短裂纹发生合并形成导致试样失效的主导短裂纹。这一过程通常称为“微观结构短裂纹(MSC)”阶段。主导短裂纹及其发展路径上的短裂纹对疲劳损伤做出直接贡献,可分别称为“主导有效短裂纹(DESFC)”和“有效短裂纹(ESFCs)”。为描述该阶段不规则行为,有必要引入尺度等于ESFCs尺度均值的虚拟裂纹即MSC阶段DESFC的概念。该阶段DESFC尺度恒定增加,扩展率恒减小。Initiation and earl propagation of the short fatigue cracks on weld metal of 1Cr18Ni9Ti pipes are studied with a replicating techniques. Nineteen smooth hourglass shaped specimens are observed. Results reveal that the effectively short cracks are always initiated from the delta ferrite bounds inlaid in the material matrix in the local weakest zone of specimen surface. This zone is located in one of districts on the specimen surface, which is orientated in accordance with the inner or outer surface of pipe. Early propagation of the cracks has a significant character of micro-structural effects. The maximum micro-structural barrier size is 40 μm, which agrees with the distance between the neighboring rich delta ferrite bounds in the characterized microstructure of weld metal, i.e. the columnar grain structure. Within the size range, density of the cracks is higher and increases gradually. The cracks grow irregularly till a coalescence occurs between some longer cracks to form a dominant short crack which will finally result in failure of the specimens. This process is generally referred as micro-structural short crack (MSC) stage. The dominant crack and the cracks on the growth path of dominant crack contribute directly to fatigue damage and thus, are referred appropriately as a dominant effectively short fatigue crack (DESFC) and effectively short fatigue cracks (ESFCs), respectively. A virtual crack which size is equal to the average size of the ESFCs, the DESFC in the MSC stage, should be introduced to describe the irregular behavior. The crack size increases steadily and its growth rate decreases constantly in the stage.

关 键 词：疲劳 短裂纹 萌生 微观结构效应 管道 焊缝金属 

分 类 号：TG405[金属学及工艺—焊接] TL341[核科学技术—核技术及应用]