冷拉弹簧钢丝卷制断裂原因分析

Fracture Analysis of Cold-drawing Steel Wires for Spring

对冷拉弹簧钢丝卷制过程中发生断裂的原因进行分析,对其卷制工艺性的影响因素进行总结。通过扫描电镜、能谱仪、光学显微镜、显微硬度测试仪、拉伸试验机等设备对多件卷制过程中发生断裂的1Cr18Ni9Ti冷拉弹簧钢丝的断口形貌、微观组织和力学性能进行对比和分析。结果表明:冷拉弹簧钢丝的断裂模式为塑性断裂,断口形貌呈韧窝特征,断裂原因与材料的卷制工艺性有关;钢丝表面机械损伤会提供初始裂纹扩展源区,组织中的氮化物聚集会破坏材料的连续性,材料强度过高会降低材料的塑性余量,该3类缺陷均会加大钢丝的断裂倾向,给钢丝的卷制加工带来不利影响。因此,需要尽量避免材料表面缺陷、组织缺陷以及性能缺陷,以便提高材料的卷制工艺性。

The fracture cause of cold-drawing steel wires for spring during the coiling process was analyzed,and the influencing factors of the coiling process were also summarized. The fracture morphology,microstructure and mechanical property of 1Cr18Ni9Ti cold-drawing steel wires were compared and analyzed by scanning electron microscopy( SEM),energy dispersive spectroscopy( EDS),metallographic microscopy,micro-hardness testing and tensile testing. The analysis results indicate that the fracture mode is ductile fracture,the fracture morphology is mostly dimple,and the fracture cause is related to the coiling process of spring wires. The surface mechanical damage of spring steel wires promoted the initiation of the cracks,the nitride aggregation in the microstructure impaired the continuity of the material,and the higher strength lowered the ductility capacity of the material. The above-mentioned defects increased the fracture inclination of the material,exerting unfavorable influence on the spring processing. Therefore,surface defects,microstructure defects and property defects should be avoided to improve the coiling capability of the spring wires.