预应力钢SWRH82B Φ12.5 mm盘条异常断口分析和工艺改进

SWRH82B钢主要用于高强度、低松弛预应力混凝土结构用钢丝和钢绞线,要求有良好的塑性。邢钢生产的Φ12.5mm SWRH82B钢（/%:0.79~0.86C,0.15~0.35Si,0.60~0.90Mn,≤0.030P,≤0.030S,0.17~0.50Cr）在拉拔过程中出现异常断裂。对异常断口进行金相分析,发现盘条心部存在明显的网状碳化物,而对应的铸坯中心碳偏析指数为1.16。通过优化280mm×325mm坯连铸工艺,拉速由原0.5m/min提高至0.7m/min,增加轻压下工艺（1~5辊,2mm,3.5mm,3.5mm,4mm,2mm）,使铸坯中心碳偏析指数由1.16降至1.08,V形偏析明显改善,盘条断面收缩率由原35%提高至39%,不合格品率显著降低。

An Analysis on Abnormal Fracture of Φ12.5mm Coil of Pre-stressed Steel SWRH82B and Process Improvement

The steel SWRH82B is mainly applied to high strength, low relaxation pre-stressed steel wire and strand for concrete structure, required better plasticity. The abnormal fracture of Φ12. 5mm coil of steel SWRH82B (/%: 0.79~0.86C, 0.15~0.35Si, 0.60~0.90Mn, ≤0.030P, ≤0.030S, 0.17~0.50Cr) produced at Xingtai steel occurs in cold-drawn process. By metallographic analysis on abnormal fracture of coil it is found that there is obvious network of cementite in center of coil, and the center carbon segregation index of corresponding casting bloom is 1.16. With optimizing 280mmx325mm bloom casting process including increasing casting speed from original 0.5m/min to 0.7m/min and adding soft reduction process ( No1~No5 roll, 2mm, 3.5mm, 3.5 mm, 4mm and 2mm) , the center carbon segregation index of casting bloom decreases from 1.16 to 1.08, the V-shaped segregation improves obviously, the reduction of area of steel coil increases from original 35% to 39% , and nonqualified rate of steel decreases markedly.