17-4PH推靠器螺钉断裂失效机理研究

Study on Fracture Failure Mechanism of 17-4PH Propeller

17-4PH材质的推靠器采用同样材质的内沉头六方孔螺钉进行紧固连接,螺钉主要承受剪切力。在测井作业中,螺钉发生断裂。文章从断口微观与宏观形貌、硬度、金相、夹杂物、微区能谱、化学成分、人为断口形貌等方面,分析螺钉失效机理。试验测试结果发现,螺钉材质化学成分合格,硬度值低于标准要求下限,基体存在夹杂物,金相组织为马氏体+带状高温铁素体,铁素体的存在破坏基体连续性,造成硬度与力学性能下降,宏观断口与微观断口形貌有明显的疲劳断裂特征,据此推断螺钉失效机理为剪切应力造成的疲劳断裂。

The 17-4PH eccentering ailll is fastened with the inner countersunk head hexagonal hole screw(17-4PH),which mainly bears shear force.During logging operation,the screw broke.In this paper,the failure analysis of the broken focuses on aspects of micro and macro morphology,hardness,metallography,inclusions,micro energy spectrum,chemical composition and artificial fracture morphology.According to the test results,the chemical composition of the screw material is qualified,while its hardness value is lower than the lower limit of the standard requirements,and there exist inclusions in the matrix.The metallographic structure is martensite and high-temperature ferrite,and the existence of ferrite destroys the continuity of the matrix.As a result,the hardness and mechanical properties decline.The fatigue fracture characteristics in the micrograph shows that the failure mechanism of the screw is fatigue fracture caused by shear stress.