某45钢锻造卸扣在使用过程中发生了断裂。通过化学成分分析、断口分析、金相检验和力学性能测试等方法对断裂卸扣和未断裂卸扣进行了对比分析。结果表明：锻造过热产生的表面微裂纹和粗大组织是卸扣发生断裂的原因，卸扣的承载能力和塑性变形能力下降，在外力作用下裂纹不断扩展最终导致脆性断裂。

Fracture of 45 steel forged shackle occurred during service. Comparative analysis of fractured and non-fractured shackles was carried out through chemical composition analysis, fracture analysis, metallographic examination, mechanical property testing and so on. The results show that surface microcracks and coarse microstructure caused by forge overheating were the reasons for fracture of shackle, which reduced loading capacity and plastic deformation capacity of the shackle. Under the external force, the cracks expanded continuously and ultimately led to brittle fracture.