摘要
针对S355GD-M带钢氧化铁皮过厚且边部与中部存在色差的问题,对其升温加热过程中的氧化铁皮进行了原位观察,并对不同卷取温度下带钢冷却后表面氧化铁皮结构转变进行了实验研究。结果表明:S355GD-M板坯试样在升温加热过程中氧化铁皮的生长分为沿晶界生长、致密生长、疏松生长、聚合纵向生长、稳定生长几个阶段,在氧化的开始时期,试样表面没有氧化产物的覆盖,基体中的Fe原子与O2充分接触,由于基体内晶界处的能量较高,氧化产物优先于晶界处形核,随着温度的进一步升高,晶界处完全被氧化产物覆盖,氧化反应向非晶界处进行直到试样表面完全被致密的氧化产物覆盖,此时氧化产物最外层与O_(2)接触的部分氧浓度最高,FeO被氧化为Fe_(2)O_(3)和Fe_(3)O_(4),并开始纵向生长;随着卷取温度的降低,共析组织的比例呈现出先增加后逐渐减少的趋势;而随着冷速的降低,共析组织的比例逐渐增加。根据实验结果绘制出了氧化铁皮中FeO结构转变的CCT曲线,发现其符合C曲线规律,鼻尖温度在500℃左右。根据原位观察的实验结果,温度越高,氧化铁皮的生长越快,减小氧化铁皮厚度的有效策略就是避免带钢在高温阶段长时间停留,通过降低开轧温度、提高终轧温度、提高带钢的轧制速度等策略,有效减少了带钢在高温下的停留时间,达到减薄氧化铁皮厚度的目的。氧化铁皮的结构差异主要来源自由于带钢不同位置冷却速度的不同,而根据FeO共析相变的实验结果,对带钢的卷取制度进行了调整,将卷取温度设定在鼻尖温度附近,降低了带钢边部及中部氧化铁皮的结构差异。经过工艺优化,S355GD-M带钢表面氧化铁皮厚度约为12μm,带钢边部和中部的氧化铁皮结构均由Fe_(3)O_(4)+FeO+共析组织组成,带钢表面的色差缺陷得到了明显改善,实现了热轧产品表面质量的提升。
To solve the problem of thick oxide scale and color variation between edges and center of S355GD-M strip,in-situ observations were conducted on oxide scale formation during the heating,and experimental studies were performed on the structural transformation of surface oxide scale after strip cooling at different coiling temperatures.Results indicate that oxide scale on S355GD-M slab surfaces during heating progresses through several stages:intergranular growth,dense growth,loose growth,aggregated longitudinal growth,and stable growth.At the beginning of oxidation,the specimen surface is not covered by oxidation products,allowing Fe atoms in the substrate to fully contact O2.Due to higher energy at grain boundaries within the substrate,oxidation products nucleate preferentially at grain boundaries.As temperature further increases,grain boundaries become fully covered by oxidation products,and the oxidation reaction proceeds toward non-grain boundary regions until the specimen surface is completely covered by dense oxidation products.At this time,the outermost layer of oxidation products in contact with O_(2) exhibits the highest oxygen concentration,where FeO is oxidized to Fe_(2)O_(3) and Fe_(3)O_(4) and begins longitudinal growth.As the coiling temperature decreases,the proportion of eutectoid structure first increases and then gradually decreases.Conversely,as the cooling rate decreases,the proportion of eutectoid structure gradually increases.Based on experimental results,a CCT curve for the FeO structural transformation within the iron oxide scale was plotted,revealing compliance with the C-curve pattern,with a nose temperature around 500℃.Based on in-situ observation results,higher temperatures accelerate iron oxide scale growth.An effective strategy to reduce iron oxide scale thickness is to minimize the strip's prolonged exposure to high temperatures.By lowering the starting rolling temperature,increasing the finishing rolling temperature,and raising the strip rolling speed,the high-temperature dwell time was effectively reduced,achieving the goal of thinning the oxide scale.The structural differences in oxide scale primarily result from varying cooling rates across different strip locations.Based on experimental results of FeO eutectic phase transformation,the coiling system was adjusted by setting the coiling temperature near the nose tip temperature,thereby reducing structural variations between the strip edges and center.Following process optimization,the thickness of the oxide scale on the surface of S355GD-M strip reached about 12μm.Both the edge and center regions exhibited an oxide scale structure composed of Fe_(3)O_(4)+FeO+eutectic phase.This significantly improved surface color defects,enhancing the surface quality of the hot-rolled product.
作者
张昭
李积鹏
谯德高
杨华
刘惊宇
郑国升
曹光明
ZHANG Zhao;LI Jipeng;QIAO Degao;YANG Hua;LIU Jingyu;ZHENG Guosheng;CAO Guangming(Jiuquan Iron and Steel(Group)Co.,Ltd.,Jiayuguan 735100,China;State Key Laboratory of Digital Steel,Northeastern University,Shenyang 110819,China)
出处
《轧钢》
北大核心
2025年第6期29-36,共8页
Steel Rolling
基金
国家重点研发计划项目(2022YFB3304800)
兴辽英才计划项目(XLYC2203186)
辽宁省科技专项项目(2022JH25/10200001)。
关键词
高温氧化行为
原位观察
FeO共析相变
卷取温度
氧化铁皮
色差缺陷
high-temperature oxidation behavior
in-situ observation
FeO eutectoids phase transformation
coiling temperature
oxidation scale
color difference defect
