热轧钢材氧化及表面质量控制技术的发展及应用

热轧钢材表面质量是生产控制的重要指标之一,越来越受到重视。热轧钢材表面氧化铁皮的结构、厚度受氧化热力学、动力学及固相反应的影响,氧化铁皮的结构、高温力学行为和物理特性直接影响其去除效果。钢材的化学成分设计,以及热轧生产过程中加热、轧制和冷却过程中氧化铁皮的去除与控制,直接决定了最终产品氧化铁皮的厚度和结构,从而决定了其表面质量控制效果。热轧钢材表面氧化控制技术已经开始在表面缺陷控制、不同深加工方式钢材的氧化层设计、减量酸洗和免表面处理等方面得到了应用。为了充分挖掘该技术的潜力,还要根据热轧产品的用途进行深度的研究与开发。     

钢材表面氧化铁皮结构演变机理与应用控制技术研究进展

从氧化铁皮机械除鳞、钢材表面红色氧化铁皮(红锈)、热轧钢材表面抗腐蚀氧化层、热轧无酸洗钢材表面镀锌及氧化铁皮抗摩擦磨损等方面阐述了氧化铁皮应用控制机理。结合当前市场需求与已有控制技术,指出了未来关于氧化铁皮研究的主要发展方向。     

新一代热轧板带材表面氧化铁皮控制技术的现状与进展

热轧板带材作为海洋、交通、能源等行业的支柱性原材料,力学性能与尺寸精度一直是衡量其质量的最重要指标。然而随着相关行业的转型升级,对其表面质量也提出了严苛的要求,导致大量钢材产品由于表面不过关被降级或判废。由于钢材的氧化在热轧过程中贯穿始终,并受到合金元素及诸多工艺参数的交互影响,很难实现结构、厚度、均匀性的精准控制。尽管前期围绕着“黑皮钢”,已经开发出了一些氧化铁皮的控制方法,但仅局限于强度较低、厚度较薄的汽车结构钢。为此,东北大学轧制技术及连轧自动化国家重点实验室开发了新一代热轧板带材表面氧化铁皮控制技术,其研发与应用全面提升了我国热轧钢材产品的表面质量。目前,所生产的系列高表面质量产品已达到了国外企业对钢材表面质量的苛刻要求,成功助力我国钢铁行业产品结构的转型升级。     

新一代热轧板带材表面氧化铁皮控制技术的现状与进展

热轧板带材作为海洋、交通、能源等行业的支柱性原材料，力学性能与尺寸精度一直是衡量其质量的最重要指标。然而随着相关行业的转型升级，对其表面质量也提出了严苛的要求，导致大量钢材产品由于表面不过关被降级或判废。由于钢材的氧化在热轧过程中贯穿始终，并受到合金元素及诸多工艺参数的交互影响，很难实现结构、厚度、均匀性的精准控制。尽管前期围绕着“黑皮钢”，已经开发出了一些氧化铁皮的控制方法，但仅局限于强度较低、厚度较薄的汽车结构钢。为此，东北大学轧制技术及连轧自动化国家重点实验室开发了新一代热轧板带材表面氧化铁皮控制技术，其研发与应用全面提升了我国热轧钢材产品的表面质量。目前，所生产的系列高表面质量产品已达到了国外企业对钢材表面质量的苛刻要求，成功助力我国钢铁行业产品结构的转型升级。     

双相不锈钢2205表面缺陷剖析

采用金相及扫描电镜观察了双相不锈钢2205的热轧表面缺陷,测量了实验室模拟气氛下双相不锈钢2205在不同温度和时间下的氧化增重并对氧化铁皮结构进行了观察。分析后认为双相不锈钢热轧时的表面裂纹是由于轧制时氧化铁皮破裂、基体组织被挤出形成的。     

去除氧化铁皮的新方法介绍

氧化铁皮是热轧钢带较常见的一种产品质量缺陷,不但影响到轧制效率,而且是形成产品表面缺陷的主要原因,对氧化铁皮进行研究十分必要。文章阐述了加热过程中氧化铁皮的形成原因、影响因素、种类和组成,对目前常用的高压水去氧化皮方法进行了介绍。结合节能环保的社会要求,着重介绍了表面生态酸洗法对扁平材热轧过程中形成的氧化铁皮的良好去除效果。     

热轧时钢铁材料高温氧化铁皮的研究进展

钢在热轧过程中发生氧化反应产生大量氧化铁皮,这不仅浪费钢铁资源而且影响其表面质量和耐蚀性,有效地控制氧化铁皮的厚度和结构是迫切需要解决的问题。本文主要从钢中的合金元素和热轧工艺两方面入手,介绍了钢在不同热轧条件下产生氧化铁皮的形态结构和形成机理。重点介绍了合金元素和终轧温度、卷取温度及冷却速度对氧化铁皮的厚度和结构的影响,并对各种条件下氧化铁皮的显微结构和厚度进行了分析,从而能够对氧化铁皮的生成和其引起的各种表面缺陷进行有效的控制。     

连退板表面白线缺陷成因和控制措施

针对首钢连退板表面白线缺陷问题,能谱分析发现白线缺陷内为海绵铁颗粒,且截面观察发现缺陷存在一定的压入深度,得出该缺陷是热轧卷表面的氧化铁皮压入所致。通过应用在线表检系统对问题卷表面进行反查,发现白线缺陷的热轧卷表面主要有3种类型氧化铁皮缺陷形貌,即条带状铁皮缺陷、西瓜皮状铁皮形貌、热轧机架共振造成轧辊氧化膜脱落形成的麻点形貌。针对此情况,对热轧工艺、轧辊氧化膜控制方法及热轧除鳞系统提出了优化措施,降低了连退板白线缺陷的产生。     

卷曲温度对热轧510L带钢氧化铁皮腐蚀行为的影响

通过热模拟、暴露试验、扫描电镜和电化学阻抗测试等方法和设备研究了卷曲温度对热轧510L带钢表面氧化铁皮耐腐蚀性能的影响。结果表明,在适当高于600℃的温度卷曲可以改善热轧510L带钢表面氧化铁皮的结构,提高氧化铁皮的致密性,有效阻碍腐蚀性介质的渗透,增强氧化铁皮对基体金属的保护作用,从而提高热轧510L带钢在储运期间的耐大气腐蚀性能。     

中铬铁素体不锈钢高温氧化行为及热轧粘辊机理

采用热重法研究了中铬铁素体不锈钢的高温氧化行为,测定出不同温度条件下的氧化增重曲线,其氧化增重符合抛物线规律,由于溶质铬元素的选择性氧化形成致密的氧化层阻碍离子扩散造成实验钢的氧化激活能较高为560 k J/mol。通过氧化铁皮表面形貌观察,在氧化铁皮表面生成部分异常长大的突起铁-铬尖晶石相,并随着氧化温度升高,有增多和长大趋势。当氧化温度为1100℃时,氧化铁皮出现了分层,氧化铁皮最外层为富铁的氧化物(Fe O和Fe3O4为主),将突起铁-铬尖晶石相包裹住。结合热轧粘辊实验结果表明,突起的铁-铬尖晶石容易划伤轧辊表面形成裂纹源,在后续循环轧制过程中急剧的冷热循环和轧制变形,促进了裂纹形成和扩展,为热轧粘辊提供了形核地点。高温轧制促进表面富铁的氧化物的生成,消除突起铁-铬尖晶石相可有效的降低热轧粘辊。     

Corrosion behavior of 9-12% Cr ferritic-martensitic steels in supercritical water

As important structural materials for advanced power plants, the corrosion of 9-12% Cr ferritic-martensitic steels exposed to both high-temperature water and supercritical water (SCW) was studied using a variety of characterization techniques. Exposure temperature and time showed significant effects on the surface morphologies, oxide scale thickness, and oxide constituents. The steels approximately followed near-parabolic oxidation kinetics in the SCW conditions. The inner spinel layer was found to be porous with a size of tens of nanometers independent upon the exposure temperature and time. High temperature accelerated the formation of a large amount of pores in the outer magnetite layer.     

Anomalous temperature dependence of oxidation kinetics during steam oxidation of ferritic steels in the temperature range 550-650 °C

The oxidation behavior of a number of selected ferritic steels in a simulated steam environment at temperatures between 550 and 650 °C was studied. In the prevailing test gas, some of the studied 9-12% Cr steels tended to exhibit an anomalous temperature dependence of the oxidation behavior. This means, that the oxidation rates do not steadily increase with increasing temperature. At higher temperatures, some of the studied steels tend to form a very thin and protective oxide scale whereas at lower temperature rapidly growing, less-protective oxides are being developed. The anomalous temperature dependence is related to differences in chromium distribution in the inner part of the oxide scale. The effect is observed for steels with intermediate-Cr contents (∼10-12%) whereas steels with either lower or higher Cr contents exhibit an increasing oxidation rate with increasing temperature.     

晶粒尺寸对耐热钢在高温水蒸汽中的氧化行为的影响

从氧化动力学、氧化膜相组成及微观结构方面,研究了晶粒尺寸对18Cr-8Ni耐热钢在700 ℃下的高温水蒸汽中氧化行为的影响。结果表明：晶粒细化提高了耐热钢的抗水蒸汽氧化性能,降低了其氧化增重,推迟了失稳氧化的发生;晶粒细化改变了耐热钢氧化膜的微观结构,减小了“弹坑”区的尺寸且促进了“弹坑”区与合金界面上富Cr氧化物层的形成;晶粒细化对耐热钢抗水蒸汽氧化性能的改善主要归因于其对氧化物的形核和Cr向氧化膜/合金界面扩散的促进作用。     

Influence of Oxidation Temperature and Cr Content on the Adhesion and Microstructure of Scale on Low Cr Steels

Descalability of steels during hot rolling processes is essential in order to maintain the surface quality of steel products, because the remaining scale can be impressed into the steel, producing surface defects. Therefore, a quantitative evaluation of scale adhesion at high temperature is needed in order to find suitable heating conditions for hot rolling processes that promote the formation of scale that easily detach. Round bar shape specimens of low Cr steels were oxidized in a fuel combustion environment, and then compressed at high temperature to detach the scale. The area fraction of the remaining scale was evaluated by image analysis. Under a thick outer oxide scale, a thin continuous inner oxide layer, which consisted of Cr and Si oxides, strongly adhered to the substrate, resulting in poor descalability. On the other hand, if this inner scale changed into a discontinuous layer with a porous FeO layer beneath, the descalability improved. It was found that scales with greater descalability formed on steels containing less Cr and for oxidation at higher temperatures.     

氧化时间及铬含量对Fe-Cr钢高温氧化行为的影响

为了测定不同氧化时间以及铬含量对高温条件下钢材表面氧化铁皮组织和厚度的影响,将Fe-5Cr钢与Fe-10Cr钢在1000 ℃空气条件下氧化60~180 min,采用增重法绘制其氧化动力学曲线,并利用光学显微镜、能谱仪和X射线衍射仪对氧化铁皮的断面形貌和物相进行研究。结果表明,两试验钢氧化初期为“气-固”反应,中后期为“气相-氧化铁皮-固相”反应。两试验钢氧化铁皮结构均由外氧化层、内氧化层和内氧化区域组成。当氧化时间为180 min时,Fe-10Cr钢检测到了内氧化物Cr₂O₃。空气中氧元素向内扩散与基体中铬元素发生反应生成内氧化物Cr₂O₃,再与氧化铁皮层中的FeO发生固相反应生成尖晶石结构产物FeCr₂O₄。随着氧化时间的增加,由于内氧化物Cr₂O₃不断受到内氧化层的包裹而转为外氧化,内外氧化的转变使得基体不断被腐蚀,氧化铁皮厚度不断增加。     

T91钢和TP304钢对含氯盐水蒸气的抗氧化性能

为比较T91钢与TP304钢在垃圾焚烧环境中的抗氧化性能,用含有微量KCl的水蒸气气氛模拟垃圾焚烧烟气,在530,600,670℃下对材料进行了氧化试验。结果表明:在含有微量KCl的高温水蒸气条件下,经过24h后T91钢的氧化质量增加是TP304钢的5倍,表明TP304钢对于高温含Cl-水蒸气的抗氧化能力优于T91钢的;在三种温度下氧化后,T91钢和TP304钢表面生成的片状氧化物成分与金属基体的Cr含量有关,Cr含量较低的T91钢表面生成了Fe2O3,Cr含量较高的TP304表面则生成了富含Cr的(Fe,Cr)2O3,(Fe,Cr)2O3氧化层的生成是TP304钢具有更高抗氧化性的原因。     

Formation mechanism of surface scale defects in hot rolling process

Thick oxide scale on steel may result in serious surface defects on hot-worked products. Yield efficiency and productivity of processes are considerably deteriorated by formation of defects. It is highly demanded to establish a way to produce hot-worked steels free from surface defects by controlling oxide scale. The oxide scale shows various behaviors in hot rolling; (a) uniform deformation with matrix steel, (b) cracking, (c) fragmentation, (d) indentation to matrix steel, etc. Through observations using glass coating, it is found that the behavior strongly depends on the rolling temperature as well as the scale thickness before rolling. Temperature drop due to contact with cold rolls is found to cause the cracking and a major reason for the thickness dependence. It is found that the scale cracking is predictable using the estimated scale temperature and the ductile-brittle transition temperature of Wustite (FeO). Then, methodology to produce hot rolled steels without surface defects in industrial processes is presented.     

Influence of the mode of introduction of a reactive element on the high temperature oxidation behavior of an alumina‐forming alloy. Part I: Isothermal oxidation tests

Different modes of introduction of yttrium have been tested with regard to the influence on the high temperature oxidation behavior of a FeCral alloy. Y₂O₃ sol‐gel coatings, Y₂O₃ metal‐organic chemical vapor deposition (MOCVD) coatings, implanted yttrium ions and yttrium as alloying element (0.1 wt.%) in the same Fe‐20Cr‐5Al alloy were oxidized at 1100°C in air under atmospheric pressure. Whatever the mode of introduction of the reactive element, the oxidation rates were not decreased compared to the oxidation rate of the blank specimen. The observation of the oxidized surface indicated that the alumina scale largely spalled from the blank alloy. Spallation was reduced for the Y₂O₃ sol‐gel coated, the Y₂O₃ MOCVD coated alloys and the yttrium ion implanted steels. The Y‐containing alloy did not exhibit any detachment of the oxide scale, indicating the best high temperature oxidation behavior, at least from the viewpoint of scale adherence.     

High-Temperature Oxidation and Pickling Behaviour of HSLA Steels

The high-temperature oxidation behaviour of three boron-containing HSLA steels was studied at 800 and 900 °C in laboratory still-air conditions. At both temperatures, the oxidation rate of the specimens was in accordance with the parabolic rate law and was sensitive to the silicon content when they were oxidized at 800 °C. The chemical composition of the oxide scale was also influenced by the silicon content of the steel. The mechanical behaviour of the oxide scales formed at the metal–oxide interface was also different at each temperature. Finally, the pickling rate and surface quality of the steels depended on the chemical composition of the oxides that formed.     

Mo对22MnB5钢板热冲压过程中高温氧化行为的影响

针对22MnB5钢板在热冲压成形过程中易被氧化且氧化层易脱落，不仅影响工件的美观和表面质量，也会对模具造成一定磨损的问题，需研究热冲压成形钢的高温氧化行为。采用模拟试验对22MnB5和22MnMoB5钢板的高温氧化行为进行了分析。结果发现，除含Mo和不含Mo外，两种钢板在其他元素含量及工艺参数相同条件下，22MnMoB5钢板的氧化程度明显低于22MnB5钢板，这主要是因为Mo能够在基体表面富集，阻碍易被氧化元素向氧化层扩散；同时，促进Cr氧化物在基体和外氧化层间富集形成保护层，从而抑制基体被进一步氧化。