罩退冷轧薄规格IF钢横向性能波动原因及控制

针对罩退冷轧薄规格IF钢产品横向性能波动大的问题,系统分析了带钢宽度不同位置的性能、组织、化学成分差异特点,以及从冶炼、热轧、酸轧到退火等不同工序下的碳含量变化情况。结果表明:性能异常带钢边部强度和碳含量明显高于中部,屈服强度差值可达89 MPa,带钢宽度方向碳含量不一致是导致横向组织变化及性能波动的主要原因;而横向性能波动主要产生于退火工序,因为酸轧工序残留在带钢表面的乳化液在罩退过程中发生裂解,随着退火温度的升高,裂解后的碳与氢气反应生成CH₄,当退火温度超过700 ℃时,CH₄再分解出活性碳吸附于带钢表面从而产生渗碳现象,最终由于带钢横向增碳不均而导致性能波动。通过增加400 ℃保温平台、降低退火温度、降低退火升温速度、增加吹氢流量、降低酸轧卷取张力等改进措施,显著提高了带钢横向性能的均匀性。

Causes and controls of transverse properties fluctuation of cold rolled thin gauge IF steel strip in batch annealing

Aiming at the problems of large transverse properties fluctuation of cold rolled thin gauge IF steel strip in batch annealing, the differences in properties, microstructure and composition of the strip at different positions along the width direction were systematically analyzed as well as the carbon content changes under different process conditions from smelting, hot rolling, pickling to annealing. The results show that the strength and carbon content at the edge of the strip with transverse properties fluctuation are significantly higher than those in the middle region, and the difference in yield strength reached 89 MPa. The inconsistency of carbon content in the width direction of the strip is the main reason for the change of transverse microstructure and the fluctuation of transverse properties. The annealing process causes transverse properties fluctuation. Because the emulsion remaining on the surface of the strip in the pickling process is cracked during the batch annealing process. As the annealing temperature increases, the cracked carbon reacts with hydrogen to generate CH₄. When the annealing temperature exceeds 700 ℃, the activated carbon decomposed by CH₄ is adsorbed on the surface of the strip, resulting in carburization. Finally, the properties fluctuation is caused by the uneven transverse carbonization of the strip. By the improvement measures of adding a 400 ℃ heat holding platform, reducing the annealing temperature, reducing the annealing heating rate, increasing the hydrogen blowing flow and reducing the coiling tension of acid rolling, the uniformity of the transverse properties of the strip is significantly improved.