72A帘线钢线材冷拔笔尖状断裂分析和改进工艺措施

Analysis on Pencil-Tip Shaped Fracture of Cord Steel 72A during Cold Drawing and Improvement of Process

72A帘线钢线材拉丝笔尖状断裂的推动力,为拉拔时的不均匀变形。心部粗大的先共析铁素体和粗片状渗碳体易形成粗拉时的裂纹源;中心偏析产生的裂纹多出现在中拉工序。控制连铸坯中心碳偏析指数≤1.1,采用相变前≥15℃/s快冷,相变区600～620℃近似等温的控冷策略,获得先共析铁素体含量≤0.8%,索氏体率达90%的均匀组织,基本杜绝了72A线材直拉时笔尖断裂的产生。

Un-homogeneity of deformation is the driving force on pencil-tip shaped fracture of cord steel 72A during cold drawing. The coarse proeutectoid ferrite and thicker cementite lamella at center of wire are source of crack during rough drawing; and the crack produced by center segregation often occurs during middle-drawing. With controlling center carbon segregation index of cast billet ≤1. I, using ≥15 ℃/s quick cooling process before phase transformation, controlling cooling at phase transformation zone 600 - 620 ℃ similar isothermal transformation to obtain proeutectoid ferrite content ≤0. 8% , uniform sorbite structure being up to 90% , the pencil-tip shaped fracture of 72A steel wire during straight-line drawing is basically avoided.