热扩散法电镀黄铜珠光体钢丝湿式拉拔断丝研究

Study on necking fracture of brass-coated steel wire produced by heat diffusion electroplating during wet drawing

为找出电镀黄铜钢丝湿拉发生颈缩断丝的原因,通过扫描电镜、能谱仪以及X射线衍射仪分析了湿式拉拔正常和异常的钢丝的微观组织和镀层物相,并用拉伸试验机检测了其力学性能。结果发现,2种镀黄铜钢丝的微观组织均为伪共析珠光体,未发现异常的先共析铁素体和球化渗碳体,二者力学性能也无明显差异。湿拉异常的镀黄铜钢丝的镀层中,β-黄铜相的质量分数高达24%,是湿拉正常钢丝的6倍。当镀黄铜钢丝的微观组织和力学性能良好时,镀层中过多的硬脆β-黄铜相是导致湿拉出现颈缩状断口的重要原因。通过在规定温度下对异常钢丝镀层重新做热扩散处理,可使湿拉断丝率从5.0次/t下降至0.1次/t。

To find out the cause of necking fracture during wet drawing of brass-plated steel wires, their microstructures and coating＇s phases in cases of normal and abnormal wet drawing were studied by scanning electron microscope, energy-dispersive spectrometer, and X-ray diffractometer, and their mechanical properties were tested by tensile testing machine. The results showed that the microstructures of both brass-plated steel wires are pseudo-eutectoid pearlite, no abnormal proeutectoid ferrite or spherical cementite are found, and there is no distinctive difference in mechanical properties between them. The mass fraction of β-brass phase is up to 24% in the coating of the brass-plated steel wire abnormally wet drawn, which is 6 times as large as that in the coating of normally drawn steel wire. The excessive mass fraction of hard and fragile β-brass phase in the coating is the key factor that leads to necking fracture, while the microstructure and mechanical properties of brass-plated steel wire are fine. The wire fracture rate is reduced from 5.0 times per ton to 0.1 time per ton during wet drawing by redoing heat diffusion treatment of the abnormal steel wire at a specified temperature.