淬回火弹簧钢丝中心裂纹涡流探伤及成因分析

Eddy current testing and cause analysis of central crack of quenched and tempered spring steel wire

2.80 mm 55SiCr淬回火弹簧钢丝在涡流探伤时出现异常信号,经检测确认为中心裂纹。通过金相显微镜、显微硬度计、扫描电镜及EDS线扫描等方法,分析了弹簧钢偏析行为和中心裂纹的产生机理,通过探伤参数的调整测试,实现了对本批材料的涡流探伤工业化检测。结果表明,弹簧钢连铸过程中形成了中心区域局部较严重的Si偏析,并遗传至弹簧钢线材。Si偏析形成的偏析条带致使线材冷拔时形变能力严重不协调,造成钢丝拉拔过程中局部形成中心裂纹;当钢丝规格较小,涡流探伤渗透深度能够达到钢丝中心时,可以识别钢丝的内部缺陷,且电流频率越低,激发信号越高。

Diameter 2.80 mm 55SiCr quenched and tempered spring steel wire appeared abnormal signal during eddy current inspection,which was confirmed as central crack by testing.The segregation behavior and mechanism of central crack of spring steel were analyzed by means of metallographic microscope,microhardness tester,scanning electron microscope and EDS line scanning.The eddy current testing of this batch of materials was realized by adjusting testing parameters.Results show that severe Si segregation occurs in central region of spring steel during continuous casting and is inherited to spring steel wire rod.The segregation band formed by Si segregation results serious disharmony of deformation capacity of wire during drawing,which leads to formation of local central crack in process of wire drawing.When size of steel wire is small and penetration depth of eddy current inspection can reach center of steel wire,the internal defects of steel wire can be identified,and the lower current frequency,the higher excitation signal.