基于氧化特性分析的IF钢连退麻点缺陷产生机理

Analysis of the pitting scale defect formation mechanism of IF steel based on its high temperature oxidation characteristics

首钢现行工艺下IF钢热卷铁皮厚度达到10μm以上,边部铁皮略薄,中部铁皮较厚,随着卷取温度的升高,铁皮厚度增加且对应酸洗时间延长;不同卷取温度下的热卷酸洗后均发现小麻坑缺陷。本文利用差热分析手段研究了IF钢的高温氧化机理,发现IF钢抗氧化性低,随温度升高铁皮增厚明显,精轧区间以FeO铁皮结构为主,在1 150℃左右发生明显的内氧化,界面形成大颗粒氧化质点。综合分析得出:IF钢带钢连退后麻点缺陷产生的主要机理为热卷的铁皮较厚,热轧过程压入钢板表面所致。为此,提出了控制措施,即降低热轧过程温度,改变层冷模式,加大精轧用水量,提高精轧轧制速度,降低冷轧酸洗速度等,有效减少了麻点缺陷的发生概率。

The scale thickness of hot rolled IF steel strip was above 10μm,and it was thicker at the center and thinner at both sides of the strip.The scale thickness was increased with enhancing coiling temperature which resulting in longer pickling time.As the pitting scale defect during continuous annealing process was observed on the strip surface with different coiling temperatures,the oxidation mechanism of IF steel was studied by differential thermal analysis.The results showed that the low resistance property to oxidation of IF steel was caused by high thickening speed with increasing temperature.The scale structure was mainly composed of FeO in the finish rolling stage.The internal oxidation was observed around 1 150 ℃ with large oxidized particles on the interface between scale and basal steel.Accordingly,the pitting scales was mainly induced because of thicker scale during hot rolling process,then impressed on the strip surface.Therefore,several measures were proposed to reduce the incidence rate of the pitting scale defect,such as decreased hot rolling temperature,changed layer cooling model,increased cooling intensity during finish rolling stage,reduced pickling speed during cold rolling stage,and so on.