20SiMn水轮机顶盖铸钢件断裂原因分析

Analysis of the Fracture Reason of A Castig Used for A Hydraulic Turbine Head Cover

对重约 10t的水轮机顶盖铸钢件的断裂事故进行分析 ,从铸钢件本体断裂部位取料制样 ,通过成分分析、拉伸和冲击试验、脆性转变温度测定、显微组织观察和扫描电子显微镜微观断口分析 ,确定了裂纹萌生的位置、扩展过程和微观断裂机制 ,评定了顶盖铸钢件的冶金质量、铸造及热处理工艺 ,解释了断面的各种特征。指出 :在高的内应力作用下 ,由冒口缺陷处萌生裂纹 ,导致顶盖发生冷脆断裂。提出了改进措施保证了新顶盖的浇铸成功。

The fracture of a casting used for a hydraulic turbine head cover is analyzed. All samples are made from the fracture surface below the raisings of the casting. Different tests are carried out, including chemical analysis, tensile and impact tests, measurement of FATT 50%, observation of mocro structure and fractography with optical microscope and SEM. The position of the original crack, and process of the crack growth and micro fracture mechanism are determined. The metallurgic quality of the casting and the technology of casting and heat treatment are studied. All features on the fracture surface are reasonably explained. The crack originated from the faults on the surface beow the raising of the casting and grew rapidly, finally led to cool brittle fracture due to high residual stress. The new casting is manufactured successfully according to the technology suggested in this paper.