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Mikako Takeda Hitoshi Kushida Takashi Onishi Masao Toyama Fujio Koizumi Shinji Fujimoto 《Oxidation of Metals》2010,73(1-2):1-13
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. 相似文献
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Although oxide scale has significant influence on surface quality of hot-worked products, deformation of the scale during hot working has not been understood sufficiently. The authors propose an experimental technique to observe the scale as hot-worked using glass coating, in this study. Immediately after hot rolling at 1273 K, glass powder was sprinkled over a mild steel sheet. The glass coating suppresses further oxidation and separation of the scale from the steel. Scanning electron microscopy revealed that the scale deforms uniformly if the reduction is small (r < 20%). If the reduction is high (r > 30%), steel is extruded through cracks in the scale to the outermost surfaces. The friction between the rolls and the sheet decreases with increasing scale thickness when the scale does not deform uniformly. 相似文献
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1.~nonNUInericalmodellingbythefiniteelement(FE)methodhasbecomeaneffectiveandeconomyicmeansforsimulatingmetalfoeingprocesses.However,accuratemodellingdemandsthecorrectdefinitionandinputsofthedataforthethermalandphysicalpIDPertiesoftheworkpieceandtoolmaterials,theboUndaryconditionsattheworkpiece--toolinterfaceandinotherareas,inadditiontoappropriatemeshgenerationandnumericalsolutions.Althoughmostofthematerialdataareavailable,thedataforinterfacialheattransferandfrictionconditions,Whichhavesubst… 相似文献
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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。 相似文献
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针对热轧表检仪不能有效识别的片状、条状、山水画状、边部粗糙酸洗氧化铁皮缺陷,介绍了其形貌特征,对热轧工艺中的影响因素进行了分析和排查,得到了缺陷的形成原因。回炉板坯重复入炉加热,氧化铁皮的生成量将会增加,容易造成酸洗后片状氧化铁皮缺陷。除鳞水压力、喷射角度、喷射面重叠量及除鳞道次对二次氧化铁皮破除能力不足时,容易产生酸洗后条状、山水画状氧化铁皮缺陷。同时,粗轧工作辊轧制公里数较长、中间坯温度过高也会对山水画状氧化铁皮缺陷有一定的影响。热轧带钢终轧或卷取温度较高,薄规格带钢板形较差时,会造成酸洗后带钢边部粗糙氧化铁皮缺陷。为此,对板坯加热工艺、粗轧及除鳞工艺、精轧及层冷工艺进行了优化,大大降低了酸洗板氧化铁皮缺陷的发生率,提高了产品表面质量。 相似文献
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通过化学分析、SEM、X-ray分析等方法,探讨了用于双金属锯带的锯条体用冷轧钢带表面缺陷的形成机制。结果表明:1)在钢带样品的表面有一层12μm厚的氧化层,该氧化层是以Fe3O4为主的复合型氧化物。氧化层中有许多龟型裂纹,一部分从基体剥离形成麻点,另一部分鼓起但仍与基体相连形成鱼鳞状起皮;2)在氧化层与基体之间,有7μm厚的过渡区,该过渡区为氧化脱Cr、Mn、C区;3)钢带样品经球化退火形成的球状碳化物,主要存在于钢带的基体中,少量存在于过渡区,极少量存在于氧化层;4)这些氧化层及过渡区是在钢带热轧和/或球化退火过程中形成的,在其后的冷轧工序中被压入过渡区。 相似文献
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An investigation was conducted into the cracking phenomenon occurring during the cold rolling of lightweight steel plates. Four steels of varying C contents were fabricated and steel plates containing C contents of 0.5wt% or higher were cracked during the initial stage of the cold rolling. The steels were basically composed of ferrite grains and -carbides in a band shape, but the volume fraction and thickness of κ-carbide band increased as the C content increased. Microstructural observation of the deformed region of fractured tensile specimens revealed that deformation bands were homogeneously formed in wide areas of ferrite matrix in the steels containing C contents of 0.3 wt% or lower, while κ-carbide bands were hardly deformed or cracked. In the steels containing high C contents of 0.5 wt% or higher, on the other hand, microcracks were initiated mostly at fine proeutectoid ferrite located within κ-carbide bands, and were grown further to coalesce with other microcracks to form long cracks. To prevent the cracking, thus, the proeutectoid ferrite should be minimized by the hot rolling in the (α+γ) two phase region. As practical methods, the content of C below 0.5% or Al above 5% was suggested to expand the (α+γ) phase region. 相似文献
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针对河北钢铁股份有限公司唐山分公司1 700 mm生产线生产热轧酸洗带钢时氧化铁皮压入缺陷严重的问题,分析了缺陷产生的根本原因是带钢化学成分中Si含量较低,精轧时产生的三次氧化铁皮压入带钢表面而致。同时,试验分析了Si含量对氧化铁皮起泡行为的影响。结果表明:低硅钢(w(Si)<0.03%)在900~1 100 ℃范围内氧化铁皮生长迅速,极易起泡、破裂,易产生月牙形氧化铁皮压入缺陷;此外,氧化铁皮过厚、破裂易导致工作辊氧化膜剥落,粗糙辊面易造成氧化铁皮、氧化膜压入缺陷。为此,提出了采用“低温快轧”的措施,可避免该缺陷的产生。 相似文献
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Kyungzoon Min Kisoo Kim Sung Kyu Kim Doh-Jae Lee 《Metals and Materials International》2012,18(2):341-348
An oxide layer, which developed on the surface of a commercial hot rolling mill, was examined by forcibly stopping the roller
between mill stands during activity. Liquid quartz was sprayed on the strip to prevent further oxide layer growth during cooling
after stopping the hot-rolling mills. Then the thickness and shape of the oxide layer was examined in a cross-sectional view
using an optical microscope. The thickness of the oxide layer increased through the 1st and 2nd passes of hot rolling, and then decreased through successive rolling, because the thickening rate by growth is larger than
the thinning rate by deformation in high temperature. The temperature distributions of the oxide layer as well as the strip
were predicted using the thermo-mechanical finite element method. As thermal conductivity of the oxide layer is low, the temperature
deviation of the oxide layer increases and average temperature decreases as the thickness of the oxide layer increases, suggesting
the increased formation of surface defects. With these results, a new cooling device was installed between the hot rolling
mills to decrease the surface temperature and the thickness of the oxide layer, resulting in improved surface quality of the
strip. 相似文献
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This study addresses the surface changes of three commercial steels (a low alloy ferritic 10CrMo9-10 steel, a Nb-stabilized austenitic AISI347 steel, and a high alloy austenitic Sanicro 28 steel) by comparing the oxide scale thicknesses, chemical compositions, and surface morphologies of samples after pre-oxidation at 200, 500 and 700 °C with different exposure times (5 and 24 h) under humid or dry conditions. With all three steels, the oxide scale thickness increased as functions of temperature and exposure time, the effect of temperature being more prominent than the effect of exposure time. The presence of water resulted in thicker oxide scales at the studied low alloy ferritic steel, whereas in the two austenitic steels, the presence of water increased chromium diffusion to the oxide scale rather than the scale thickness. The oxide layers characterized and analyzed in this paper will be further studied in terms of their abilities to resist corrosion by exposing them under corrosive conditions. The results regarding the corrosion resistance of the steels will be published in a sequel paper. 相似文献
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《CIRP Annals》2020,69(1):265-268
Rolled sheets may turn up or down after passing the roll gap. The curling occurs under asymmetric conditions, e.g., different roll speeds, diameters, frictions, etc. Even under apparently symmetric conditions, the curling incidentally occurs in hot rolling. In this study, low carbon sheets with controlled upper and lower oxide scale were hot-rolled with 15% reduction in thickness. The rolled sheets always curled toward the side with thin oxide scale and that severe curling occurred when upper and lower oxide scales deformed differently. It is concluded that surface oxide scale is a hidden factor to cause curling in hot steel rolling. 相似文献
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首钢现行工艺下IF钢热卷铁皮厚度达到10 μm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。 相似文献
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热轧钢筋在运输和储存过程中其表面会产生锈蚀,影响钢筋的使用及外观质量。分析了钢筋表面锈蚀产生的原因,利用扫描电镜和电子背散射衍射技术,对比了轧后空冷、气雾冷却和穿水冷却工艺下钢筋的抗锈蚀性能,分析了不同冷却工艺对热轧钢筋表面氧化铁皮厚度和结构的影响。结果表明:钢筋表面锈蚀与其表面氧化铁皮厚度、结构和完整性有关,与空冷及穿水冷却相比,气雾冷却工艺通过优化冷却路径,可以获得厚度为10~20 μm、主要由FeO+Fe3O4构成的致密复合氧化铁皮,能够对钢筋基体起到保护作用,从而能够延缓钢筋表面生锈,并降低生产成本。 相似文献