汽轮机高压内缸螺栓断裂分析及监督探讨

Fracture Analysis and Supervision Discussion on the Bolt of a Turbine High-pressure Inner Cylinder

某电厂汽轮机高压内缸20Cr1Mo1VNbTiB钢制螺栓发生断裂,通过无损检测、宏观检查、化学成分分析、微观组织分析、硬度检验、力学性能检验等方法对断裂原因进行分析,并且针对20Cr1Mo1VNbTiB钢制螺栓的监督检验提出相关建议。结果表明:螺栓本身包含原始的大颗粒夹杂物缺陷,同时内部的渗碳体和碳化物分解与合金元素在晶界聚集,使得材料的冲击韧性下降;在交变载荷的长期作用下,裂纹在螺纹第一丝牙处萌生并沿晶界扩展,导致螺栓断裂。

To solve the problem of the fracture of a 20CrlMolVNbTiB steel bolt of high-pressure inner cylinder in a power plant steam turbine,analyses were conducted on the fracture reason from the aspects of non-destructive testing,macroscopic examination,chemical composition analysis,microstructure analysis,hardness testing and mechanical property testing,while corresponding suggestions were proposed for the supervision and inspection of 20CrlMolVNbTiB steel bolts.Results show that,the bolt contains the original large particle inclusions from the manufacturing process,while the decomposed internal cementite and carbide aggregate with alloy elements at the grain boundary,which leads to the decrease of impact toughness of material.The crack from the first thread propagates along the grain boundary under the long-term action of alternating load,which finally leads to the fracture of the bolt.