某批次办公椅在往复耐久性试验中发生椅背断裂失效。采用断口观察、化学成分分析、硬度测试、夹杂物检测、金相检验、扫描电镜和能谱分析，对办公椅椅背中内置弹簧的断裂原因进行了分析。结果表明：弹簧的表面硬度分布不均匀，表面有脱碳现象，近表面有夹杂物；这些缺陷破坏了基体的连续性，在椅背往复耐久性试验中，产生了疲劳断裂源；在多重应力作用下裂纹快速扩展，最终弹簧发生疲劳断裂。

During the reciprocating durability test of a batch of the office chairs, the chair backs fractured to failure. By means of fracture analysis, chemical composition analysis, hardness testing, inclusion inspection, metallographic inspection, scanning electron microscope (SEM) and energy spectrum (EDS) analysis, the reasons why internal springs of office chair backs fractured in reciprocating durability test were analyzed. The results show that:the hardness distribution of the spring surface was uneven, and there were surface decarburization on surface and the inclusions in subsurface; these defects destroyed the continuity of the matrix, leading to the crack source during reciprocating durability test; the cracks propagated rapidly under the multiple stress condition, and finally fatigue fracture occurred to the springs.