Abstract: The longitudinal crack with 0.3 mm depth occurred in φ11.5 mm cold drawn products of low carbon high sulphur free cutting structural steel (0.07C,0.86Mn,0.06P,0.32S) to product some batches of rejection. The analysis results by sampling indicated that the rating unit of banded structure in φ14 mm cold drawing blank was up to 4 and the section reduction in cold drawn one pass was up to 32.52% which led to crack formed in cold drawing. With overheat control of molten steel during casting, finishing rolling temperature increasing to 1050 ℃ from 850 ℃ during continuous rolling of cold drawn blank, spraying cooling and 650 ℃ self tempering, the rating unit of banded structure of φ14 mm cold drawing blank decreased to less than 1.5,moreover the section reduction in cold drawn pass decreased to less than 30.5%,thereby the longitudinal crack in Φ11.5 mm Cold drawn products was avoided.

Key words: Low Carbon High Sulphur Free Cutting Steel, Banded Structure, Cold Drawing, Longitudinal Crack

摘要： 低碳高硫易切削结构钢(%:0.07C、0.86Mn、0.06P、0.32S)Φ11.5 mm冷拔材出现0.3 mm深的一次纵裂纹,造成批量废品。经取样分析表明,Φ14 mm冷拔坯(热轧材)的带状组织达4级,冷拔一次断面缩减率达32.52%,致使在冷拔过程中产生裂纹。通过控制连铸时钢水过热度,在冷拔坯连轧过程精轧温度由850℃提高到1050℃,喷淋冷却,650℃回红,使Φ14 mm冷拔坯带状组织降至1.5级以下;冷拔时一次断面缩减率降低至30.5%以下,从而避免了Φ11.5 mm冷拔材纵裂纹的产生。