ER70S-6盘条拉拔断裂原因分析

焊接用ER70S-6盘条在拉拔过程中断裂,细拉钢丝断口以杯锥状为主,粗拉钢丝断口以斜茬状为主。对φ1.2mm钢丝杯锥状断口进行扫描电镜分析,试样心部存在大量马氏体组织,马氏体与基体之间产生大量的显微裂纹。对盘条金相组织进行观察,盘条心部存在马氏体,表面出现全脱碳层,且脱碳后的晶粒尺寸较大。对斜茬状断口金相组织进行观察,裂纹与钢丝表面约呈45°角,裂纹源位于表面。分析表明,ER70S-6盘条中的锰、硅含量较高,造成铸坯凝固过程中中心缩孔处合金元素正偏析,盘条轧制后形成异常组织。采用合理的浇铸温度、拉坯速度、冷却水量等,降低缩孔级别,减轻中心偏析,提高钢坯内部质量,保证成分均匀稳定,控制轧制时的尺寸精度和轧制张力,能够有效降低焊丝拉拔断裂次数。

Cause analysis of ER70S-6 wire rod drawing fracture

ER70S -6 wire rod for welding breaked while drawing. The fracture of small diameter is cup-cone type. The fracture of large diameter is inclined stubble type. The cup-cone fracture of diameter 1.2 mm steel wire was analyzed by using SEM, large martensite structure existed in sample core, large microcracks occurred between martensite and matrix. Wire rod metallurgical structure was observed, martensite existed in wire rod core, complete decarburization occurred in surface, and grain size was large after decarburization. The metallurgical structure of inclined stubble type was observed, cracks and steel wire surface existed 45°angle, crack origin lay in surface. Analysis showed that the content of manganese, silicon in ER70S - 6 wire rod was higher than normal which caused alloy element of central shrinkage positive segregation in casting blank solidification process, abnormal structure occurred after wire rod was roiled. To adopt reasonable casting temperature, casting speed, amount of cooling water and so on, to reduce shrinkage level, to lessen central segregation, to improve interior quality of casting blank, to assure compositions even and stable, to control dimensional precision and rolling tension while in rolling, welding wire drawing breakage can be reduced effectively.