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含镍合金钢高温防护涂层 制备与性能研究
Alternative TitlePreparation and Performance of High Temperature Protective Coating for Nickel-containing alloy steel
何影
Subtype硕士
Thesis Advisor叶树峰  ;  魏连启
2014-06
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword高温防护涂层   抗氧化性能   除鳞效果   表面质量   含镍合金钢
Abstract在热轧前的高温加热过程中,含镍合金钢基体表面和氧化性气氛发生反应生成一次氧化铁皮。由于Ni、Si等合金元素的选择性氧化并在界面处富集,使一次氧化铁皮具有较强的粘附性。后期的高压水除鳞系统无法完全去除这些氧化皮,导致残余氧化皮压入钢材表面,形成凹坑和麻点等表面缺陷。为了解决这些问题,本文采用涂层的方式,通过降低铁氧扩散速率以及控制合金元素在界面处的富集量,提高一次氧化皮的去除率,从而降低表面缺陷,改善产品表面质量。具体工作如下: 分析了9Ni、NM360、Fe-36Ni几种含镍合金钢的高温氧化过程及氧化皮结构,推导出导致氧化皮粘附性原因与钢基体Ni、Si初始含量有关。实验结果表明:9Ni、NM360的高温氧化行为符合抛物线定律,其扩散速率受离子穿过氧化层的扩散速率控制。此外,剖析了9Ni钢基体内由Si元素选择性氧化导致的内氧化问题。 提出了高温防护涂层的设计原则,分别从钢坯加热制度、钢材成分、热膨胀系数及相图热力学等角度对涂层组成体系进行了优选;在实验室已有研究基础上,创新选择并制备了核心功能组分含Zn溶胶,确定了提高含镍合金钢除鳞性能及减少氧化烧损的MgO基涂层体系。 针对除鳞效果及内氧化性能难以量化评价的问题,创新提出了使用测量Ni、Si富集层深度的方法评价涂层降低氧化皮粘附性效果,通过测量氧化钉长度与内氧化颗粒直径表征涂层抑制内氧化性能的表征方法。 探讨了涂层对含镍合金钢表面微量元素分布的影响。在1150℃、1200℃、1250℃加热60min的条件下,9Ni钢涂覆样较空白样Ni、Si富集层深度分别减少73.5%、80.9%和74.1%,NM360钢涂覆样较空白样富集层深度分别减少44.1%、55.1%和53.4%,防护效果良好。能谱断面元素分布结果显示,9Ni和NM360涂覆样中Si富集层消失,说明涂层有效抑制了Si元素在界面的富集。 研究了涂层提高钢坯防氧化性能的效果。在1150℃、1200℃、1250℃加热120min的条件下涂层降低9Ni钢坯氧化烧损率分别为56.0%、54.0%、50.1%,降低NM360钢坯氧化烧损率分别为52.2%、50.4%、50.9%,防护效果均达到50%以上。 利用XPS、XRD、SEM-EDX、TG-DSC等分析测试手段,讨论了核心功能组分对涂层高温下的反应过程的影响,并初步探讨了涂层高温防护机理。对比实验显示,含锌溶胶的添加可较大程度提升涂层的防氧化效果。XRD和XPS结果表明,涂层与基体的氧化物反应生成MgFe2O4,且MgFe2O4中一部分八面体位Mg2+与一部分四面体位Fe3+交换位置,使Mg2+同时占据八面体位和四面体位。涂层高温防护机理初步探讨为:一方面Mg2+、Zn2+填充FeO中阳离子空位,降低空位浓度,降低阳离子扩散速率;另一方面Mg-Fe固溶体演变生成的MgFe2O4提升了八面体扩散能垒,提高了阳离子的扩散难度,降低了阳离子的扩散速率。通过这两方面作用,涂层降低基体中Fe的氧化速率,相对的抑制了合金元素Ni、Si的选择氧化行为,减缓了富集层的生成,实现对钢基体的高温防护。
Other AbstractDuring the reheating process before hot rolling, nickel-containing alloy steel surface reacts with the oxidizing atmosphere and results in forming primary scales. As alloy element Ni/Si tend to be oxidized selectively and get concentrated at the interface, primary scales could be strongly adhesive. The hydraulic descaler cannot remove the scale completely, which would lead to serious consequence, as the remaining scale may be erased into the steel surface and form scale pits and stripes. To solve these problems, in this paper a method of wearing a protective coating is used to decrease the diffusion rate of Fe and O ion and the concentration of alloy element. As a result, primary scales attached on the steel surface can be completely removed, and the defects formed on the steel can be eliminated so that the quality of the steel can be improved. The high temperature oxidation process and scale structure of several nickel-containing alloy steel (9Ni、NM360、Fe-36Ni) are investigated, and a conclusion can be drawn that the adhesion of primary scale is relevant to the initial concentration of Ni/Si element in steel substrate. Besides, high temperature oxidation behaviors of 9Ni and NM360 follow the parabolic law, which means the oxidation rate of Fe is controlled by diffusion rate of ions. In addition, the internal oxidation occurring in 9Ni steel, which is due to preferential oxidation of element Si, is also investigated. Based on the design principal of high temperature protective coating, the selection of coating composition has been discussed from various angles, like reheating schedule, steel composition, thermal expansion coefficient and phase diagram. Based on the past lab research result, we prepared a creative MgO protective coating adding new critical component which can effectively enhance the descaling and oxidation resistance ability. A new evaluation method of coating protective effects have been proposed: evaluating scale adhesion by measuring length of Ni/Si entanglement, evaluating oxidation resistance by continuous thermal gravimetric experiment, evaluating internal oxidation resistance by SEM and metalloscope. The effect of coating lowering scale adhesion is investigated. When heating for 60min at 1150℃, 1200℃ and 1250℃, the depth of the entanglement for 9Ni coated specimens is reduced by 73.5%, 80.9% and 74.1% respectively, and the depth of the entanglement for NM360 coated specimens is reduced by 44.1%, 55.1% and 53.4% respectively. Element distribution of the cross section shows that the Si enrichment layer in 9Ni and NM360 steel has been eliminated, which proves that the coating can effectively control Si element concentration at the interface. However, the coating will only decrease 38.1% of the entanglement on Fe-36Ni, still need to be improved. The effect of coating increasing oxidation resistance is investigated. When heating for 120min at 1150℃, 1200℃ and1250℃, the metal loss for 9Ni coated specimens is reduced by 56.0%, 54.0% and 50.% respectively, and the metal loss for NM360 coated specimens is reduced by 52.2%, 50.4% and 50.9% respectively, which shows a good protection effect of the coating. The effect of coating decreasing internal oxidation is investigated. With the use of XPS, XRD, SEM-EDX and DSC-TG, we discuss the effect of the critical component on the coating reaction process and the mechanism of the protective coating under high temperature. According to the experiment result, the addition of a small quantity of zinc sol has greatly improved the oxidation resistance. XPS and XRD results show that the coating and iron oxides have reacted to form MgFe2O4. Above 900℃, some Mg2+ ions occupying at octahedral site change places with some Fe3+ ions occupying at tetrahedral site. It results in Mg2+ ions occupying at both octahedral and tetrahedral site. The protective mechanism is illustrated as following: from one aspect, Mg2+ and Zn2+ can occupy the vacancies in FeO to reduce the concentration of
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/15571
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
何影. 含镍合金钢高温防护涂层 制备与性能研究[D]. 中国科学院研究生院,2014.
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