6.5 mm的45钢盘条在拉拔到4.2mm和5.5 mm时断裂，通过扫描电镜对断口进行观察，发现引起试样发生拉拔断裂是由于表面有异常组织所致。进一步通过金相检验，发现试样在产生裂纹源的表面有异常增碳区，其中，拉拔到5.5 mm的断裂样表面还发现了金属的横向流动，通过用能谱对微区成分进行分析,确定这是一起因表面增碳引起的拉拔断裂事故。而同样是增碳，当试样不圆度超差较大时，会引起试样表面金属的横向流动，增加表面增碳造成的危害。
Fracture occurred in drawing process from 6.5 mm rod to 5.5 mm and then 4.2 mm wire. The fracture was caused by surface abnormal structure by the analysis of the fracture samples using SEM. Further metallographic examination of the samples show that carburization appeared on the sample surface where the fracture arose,and that transversal metal flow appeared on the surface of 5.5 mm fracture samples. By analyzing the microarea composition using energy spectrum, it is concluded that the fracture was caused by the surface carburization of 45 rod,and that outofroundness of 45 rod could lead to transversal metal flow on the rod surface and make the surface carburization more harmful.
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