400MPa盘条钢筋性能异常原因分析及控制

针对昆钢400MPa盘条钢筋生产过程中出现的屈服强度及断后伸长率偏低、同卷盘条力学性能不稳定等问题,取样进行了化学成分、金相显微组织、断口形貌及夹杂物检验分析。结果表明:屈服强度及断后伸长率偏低的主要原因为试样金相显微组织出现8%～30%的粒状贝氏体,粒状贝氏体质量分数30%的试样断口形貌表现为脆性断裂,钢筋塑韧性差;同卷盘条力学性能不稳定的主要原因为冷却速度不同造成金相组织中贝氏体质量分数不同。针对上述情况,炼钢采取出钢全程底吹氩及渣洗工艺,轧钢采取降低精轧及吐丝温度(精轧入口温度控制为870～890℃、吐丝温度控制为840～870℃)、减弱斯太尔摩控冷强度、增加辊道速度等措施,消除了400MPa盘条钢筋性能异常情况。

Reason analysis and control of abnormal performance for 400 MPa ribbed bars coil

In view of lower elongation and yield strength,unstable mechanical performance for 400 MPa ribbed bars coil in WuKun steel Co.Ltd.,chemical composition,microstructure,morphology of fracture and inclusions were analyzed by sampling.The results show that main reason of lower elongation and strength for 400 MPa ribbed bars coil is emergence of abnormal microstructure for bars coil,the content of granular bainite is 8 %-30 %,fracture of specimen with 30 % bainite shows brittle,ductility and toughness of ribbed bars is bad;the main reason of unstable mechanical performance for same coil samples is that the bainite content of microstructure is different due to different cooling rates.According to above-mentioned reasons,slag rinsing and bottom blowing argon during tapping process were carried out in steel-making.In addition,reducing of finishing temperature（controlled at 870-890 ℃） and spinning temperature（controlled at 840-870 ℃）,weakening of controlled-cooling of Stelmor,increasing of roller speed,etc.were carried out in steel-rolling.As a result,the abnormal performance of 400 MPa rebars coil was eliminated.