55SiCr弹簧钢盘条异常断裂原因分析

Abnormal fracture analysis of 55SiCr spring steel wire rods

从生产现场中发现部分55SiCr弹簧钢盘条在仓库存储的过程中发生异常断裂。对断裂试样进行了断口宏微观形貌、化学成分、显微组织、力学性能、硬度与氢含量的分析以及电化学充氢验证试验,以找出断裂原因。结果表明:55SiCr弹簧钢盘条断裂试样的化学成分符合行业标准,其抗拉强度为2030 MPa,断面收缩率为38%,硬度平均值为615. 3 HV0. 3,符合技术要求。其异常断裂为应力状态下的氢致开裂,断裂起源点在试样表面的划伤缺陷处,该处在弹簧钢盘卷状态下具有较高的应力集中,容易诱导氢在此处聚集;断裂起源处呈沿晶断裂形貌,自起源点向内不断延伸,继而出现准解理与韧窝特征,裂纹扩展路径与试样所受应力方向垂直。现场发生断裂的试样中含有较少的氢含量,这是由于氢在室温下的逸出所致。

Abnormal fracture of some 55 SiCr spring steel wire rods are often found during the warehouse storage. The fractured specimens were studied by macroscopic and microscopic analysis,chemical composition analysis,mechanical properties testing,hardness testing,hydrogen content testing,and electrochemical hydrogen charging tests under the condition of the stress to find out the cause of the fracture.The results show that the chemical composition of the 55 SiCr spring steel wire rod fractured specimen complies with industry standards. Its tensile strength is 2030 MPa,the reduction in area is 38%,and the average hardness is 615. 3 HV0. 3,conforming to the technical requirements. The abnormal fracture of the steel is hydrogen-induced cracking under stress conditions,originated at scratch defect on the specimen surface. The fracture origin place has a high stress concentration in the coiled state of the spring steel and it is easy to induce hydrogen gathering,where shows an intergranular fracture morphology after fracture. Extending inward from the point of origin,the quasicleavage and dimple features also appear,and the crack propagation path is perpendicular to the direction of the stress on the specimen. The specimens broken at the site contain less hydrogen content,which is due to the escape of hydrogen at room temperature.