换热器浮头盖SA453螺柱断裂失效分析

某批换热器在浮头盖装配时高强螺柱前后出现两次断裂现象，通过现场调查、化学成分、力学性能、宏观断口、金相观察、结构应力计算及螺柱制造工艺调查等方法，对其断裂原因进行综合分析。结果表明：螺柱和螺母咬合在一起的应力集中是致使最大剪应力超过材料的抗剪强度、导致螺柱扭断的主要原因，最大等效应力明显大于抗拉强度，致使断裂处材料因其高强度而表现出脆性断裂；热处理工艺执行不到位是造成螺柱断裂的次要原因，是螺柱批量生产中堆积装炉热处理的不规范操作所致；螺柱经真空回火热处理后提高了力学性能和硬度，规范紧固件装配操作过程后，满足了使用要求。

Failure Analysis about Fracture of SA453 Bolts of Floating Head Cover on Heat Exchanger

The high strength blots were twice fractured during assembling floating head cover of . heat exchanger. The analysis on fieldwork, chemical composition, mechanical property, macrofractrue, metallographic, structure stresses calculation and fabrication process were carried out on the fractured blots to find the reason of fracture. The results showed that the main reason both of first and second blot fracture is the maximum torsion stress of bolts exceed the elastic limit of material under torsioning. It is because the screw thread of bolt gnaws into the screw thread of nut and tightens together so that induces stresses concentration and maximum stress. The maximum equivalent stress is exceeds the tensile strength of material in evidence, and the fracture section exhibits a brittle as its high strength of material. Halfway on heat treatment process is secondary causation, because bolts were nonstandard stacked in furnace during heat treatment. The fracture of bolt is exceptional and contingency. Rehandling of vacuum tempering heat treatments was improved the mechanical properties and hardness of blots. After standard manipulation to assemble bolt and nor, it is meet the requirement of operation.