Abstract: The surface transversal cracks occur on steel 65Mn (/%： 0.65C, 0.24Si, 1. 00Mn, 0.014P, 0.006S) 2.5mm X 10mm flat wire cold-drawn and rolled by φ6.5mm Coil. With analysis on defects it is obtained that due to casting billet surface carburization the abnormal structure of carbide block with strip distribution forms on coil surface, and in cold-drawing process the micro cracks form at abnormal structure and in flat-rolling process the micro cracks develop and combine to macro cracks. During casting process the liquid entraps enriched carbon layer of mold flux led to casting billet local surface carburization. With improving the 150 mm X 150 mm billet casting process including decreasing liquid surface fluctuating extend from original 7~8 mm to 3~4 mm, increasing depth of immersion nozzle from 70~80 mm to 90~100 mm, optimizing viscosity of mold powder from 0.35 Pa ·s to 0.40 Pa ·s and decreasing casting speed from 2.1~2.4 m/min to 2.1~2.2 m/min, the ratio of surface cracks of steel 65Mn flat wire decreases from original 2.33% to 0.

摘要： 由65Mn钢（/%:0.65C，0.24Si，1.00Mn，0.014P，0.006S）Φ6.5mm盘条冷拔和轧制的2.5mm×10mm扁钢丝出现表面横裂现象。通过对缺陷分析，得出由于铸坯表面增碳，使盘条表面形成条带状分布的块状碳化物的异常组织，并在冷拔过程中异常组织处形成微裂纹，在轧制压扁阶段，微裂纹扩展、合并形成宏观裂纹。连铸过程中钢液卷入保护渣富碳层会造成连铸坯局部表面增碳。通过改进150 mm×150 mm方坯连铸工艺，即液面波动由7~8 mm降低3~4 mm,浸入式水口插入深度由70~80 mm增至90~100 mm，保护渣粘度由0.35Pa·s优化成0.40Pa·s，连铸拉速由2.1~2.4m/min降至2.1~2.2m/min，65Mn扁钢丝的表面横裂纹率由原来的2.33%降至0。

关键词: 65Mn钢, 150mmx150mm连铸坯, 2.5 mm X 10 mm扁钢丝, 横裂, 表面增碳, 异常组织, 工艺改进