The Mechanism of Phase Transformation in Thermally-Grown FeO Scale Formed on Pure-Fe in Air

The isothermal phase transformation behavior of thermally grown oxide scale of FeO, which was formed on Fe at 700 °C in air for 16 min, was investigated at 320, 450, 500, 520, and 560 °C in air. The phase transformation of FeO was found to consist of four transformation modes: (1) growth of outer Fe₃O₄ layer; (2) precipitation of Fe₃O₄; (3) formation of magnetite seam; and (4) eutectoid decomposition of FeO. The transformation was always completed by the eutectoid decomposition at all temperatures in the present study; however, the proportion of transformation mode (1) and (2) strongly depended on temperature. At higher temperatures growth of the outer Fe₃O₄ layer initially predominates, but the precipitation of Fe₃O₄ controls the initial transformation at lower temperature before the eutectoid reaction. The eutectoid reaction was found to be initiated by Fe nucleation from Fe-saturated FeO. Fe saturation in FeO was due to growth and/or precipitation of Fe₃O₄ and formation of the magnetite seam layer, which acts as a diffusion barrier for Fe inward diffusion into Fe substrate. It was proposed that these transformation modes, growth and/or precipitation of Fe₃O₄ and magnetite seam formation, are necessary to begin the eutectoid reaction, i.e., completion of FeO scale transformation.     

贝氏体表面浮凸及其形成机制

将3mm厚的工业用60Si2Mn、60Si2CrV和22MnCrNi钢试样抛光后在真空炉中加热到1100℃奥氏体化,保温40min,炉冷。不经浸蚀,分别采用QUANTA-400环境扫描电镜、Nanofrist-1000扫描隧道显微镜和光学显微镜观察试样,发现,贝氏体相变过程中产生了表面浮凸,表面浮凸为“帐篷形”（“A”型）,并认为贝氏体表面浮凸的产生,是由于过冷奥氏体转变为贝氏体时比体积增大,且试样表面层体积膨胀不均匀造成的。     

铝合金6061焊缝气孔形成机理的研究

进行了铝合金的氩气保护焊接试验,对采用TIG焊接铝合金板时产生的气孔形貌及其机理进行分析,研究了影响气孔产生的因素,并提出了防止气孔的有效措施。     

超薄热带氧化铁皮生成分析及消除措施

本文对超薄热带生产过程中氧化铁皮生成原因进行了分析讨论,对设备和工艺情况做了介绍,针对唐钢超薄热带的生产实际提出了相应的消除措施,改善了带钢表面质量。     

The Role of Oxygen Uptake and Scale Formation on the Embrittlement of Vanadium Alloys

Vanadium alloys are of interest in fusion energy systems, however, their environmental durability is a major concern. Specimens of V–4Cr–4Ti were exposed to air and oxygen (10⁵,Pa), low pressure (10^–3–10^–6 Pa) oxygen and high purity He environments (10⁵–10¹ Pa) it at 500–700°C in order to characterize the surface oxide, determine oxidation kinetics and quantify effects on mechanical properties at 25 and 600°C. At low oxygen pressures (P_{O_2}.10^–5 Pa), linear reaction kinetics were measured for exposures up to 2000 hr and the data were used to develop a mathematical expression for the oxidation rate as a function of temperature and oxygen pressure. At higher pressures, linear–parabolic reaction kinetics were associated with high oxygen uptake and the formation of an external oxide layer. Room-temperature and 600°it C tensile ductility was reduced by these exposures, but specimens which formed an external oxide were found to retain some tensile ductility after exposure. However, similar specimens with an external oxide that were subsequently annealed for 2000 hr at 700°C became severely embrittled demonstrating that a surface oxide will not prevent degradation of this refractory alloy. Exposures in He were performed to determine the effect of total gas pressure on oxygen uptake.Dedicated to the Memory of Jackson H. DeVan.     

Water Vapour Effects on FeO Scale Growth: Differences Between Iron and Steel

High purity iron and a low carbon, low silicon steel were oxidised at temperatures of 800–1,200 °C, in atmospheres of N₂–H₂–H₂O and N₂–O₂–H₂O. Scales of wüstite grew at low oxygen potentials, and of FeO/Fe₃O₄/Fe₂O₃ at high oxygen potentials, both according to parabolic kinetics after an initial transient period. The iron and steel behaved similarly in the O₂/H₂O gases, but not in H₂/H₂O, where the steel oxidised much more slowly than the iron. The rate for steel increased with $ p_{{H_{2} O}} $ at fixed $ p_{{O_{2} }} , $ but for iron was almost independent of $ p_{{H_{2} O}} , $ whilst rates for both metals increased with $ p_{{O_{2} }} $ at fixed $ p_{{H_{2} O}} $ . These results are discussed using point defect models involving hydroxyl anions and cation vacancies. Scaling rates in O₂/H₂O also increased with $ p_{{H_{2} O}} , $ a result attributed to gas phase transport within oxide pores which were present in the scales, but absent in wüstite grown in H₂/H₂O.     

Increase in Pressure Loss and Magnetite Formation in a Benson Boiler

Abstract

Mechanisms causing corrosion in the steel evaporator tubes and increasing the pressureloss in the Benson boiler was investigated both at Mannheim Power Station, and on tubesamples and pressure loss behaviour of other boiler plants.

In the water phase area and above a certain velocity the outer coarsely crystalline magnetite layer formed shows a ripple-like surface structure. This type of roughness produces a high flow resistance. It is considered that the process by which the magnetite forms generates aporous inner layer; diffusion of hydronyl and ferrous ions occurs through the pores causing the rapid stress-free deposition of a firmly adherent oxide layer. Crystallisation of magnetite under certain conditions of turbulent flow and erosion create the ripple structure.     

铝青铜气孔形成机理及消除措施

通过热力学计算及分析得出,高温铜液与环境中的水蒸气反应是铝青铜铸件形成针孔的主要原因,并提出了为消除针孔可采用的工艺措施。     

铜铸件针孔形成机理及消除措施

纯铜铸件具有非常好的导电、导热性能,广泛用来制造高炉风嘴、顶吹纯氧转炉炼钢用的氧气喷头、电炉的电极夹头、连续铸造用的结晶器和结晶轮等.由于这些产品的铜含量要很高,熔炼过程中需要严格控制杂质元素的含量;并且纯铜铸件极易产生析出性气孔,也叫针孔,它的特征是均匀分布于铸件内、呈圆点状.     

含Cr低合金钢的CO2腐蚀产物膜形成及机理研究进展

针对含Cr低合金钢石油专用管的CO₂腐蚀产物膜,介绍了CO₂腐蚀产物膜的形成机理,总结了含Cr低合金钢的CO₂腐蚀产物膜的影响因素,其中包括Cr含量、温度、CO₂分压、pH值、腐蚀时间、Cl^-浓度、流速等对其腐蚀产物膜的影响,并对腐蚀产物膜的结构与成分进行总结,归类了缓蚀剂对含Cr低合金钢石油专用管的保护办法,以期为今后含Cr低合金钢的CO₂腐蚀产物膜的研究提供借鉴。     

贝氏体相变机制与块状转变

应用JEM-2010高分辨电镜和Quanta-400型环境扫描电镜,运用试验与综合分析的方法,研究了纯铁的块状转变和钢中的贝氏体相变.通过对相变的形核、长大,贝氏体亚单元和组织的形成的综合研究和分析,认为贝氏体相变与块状转变存在亲缘关系.依靠随机涨落,形成贫碳区,贝氏体铁素体在贫碳的奥氏体中形核.Fe原子和替换原子通过热激活跃迁、界面扩散或切变等方式,重复产生亚单元.在亚单元边界处的富碳奥氏体中析出碳化物,或成为残留奥氏体.贝氏体相变机制具有过渡性,即切变-扩散整合机制.     

Synthesis and ageing effect in FeO nanoparticles: Transformation to core-shell FeO/Fe3O4 and their magnetic characterization

This paper reports the magnetic properties of partially oxidized FeO nanoparticles (NPs) prepared using thermal decomposition of iron acetylacetonate at high temperature. X-ray diffraction (XRD) analysis confirmed that the resulting NPs comprise a mixture of wüstite and magnetite phases, which are subsequently confirmed using high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) pattern. Magnetic properties were investigated using vibrating sample magnetometer (VSM), which exhibit superparamagnetic (SPM) behavior at room temperature. Alternatively, below 200 K, a large exchange bias field has been observed in field cooled mode whose magnitude increases with the decrease in measuring temperature attaining a maximum value of ∼2.3 kOe at 2 K accompanied by coercivity enhancement (∼3.4 kOe) and high field of irreversibility (>50 kOe). The results are discussed taking into account the role of interface exchange coupling on the macroscopic magnetic properties of the nanoparticles.     

输变电用导线的腐蚀机理

在某输电线路工程现场用导线发生大面积腐蚀,腐蚀产物为白色胶状细颗粒。采用理化分析、试验模拟等方法对腐蚀产物及导线接触物进行分析,并探究腐蚀机理。结果表明:Cl是导致导线腐蚀的主要元素,导线中弥散分布的第二相粒子加速了腐蚀进程。据此,提出了导线在加工制造、运输存贮及使用过程中避免腐蚀的方法。     

燃烧合成焊接钢/不锈钢焊缝结构及形成机制

摘要将燃烧合成技术与传统焊接技术相结合，以Ti-Ni体系为连接材料研究了08钢/1Cr18Ni9不锈钢焊接焊缝的形成过程，探索了Ti-Ni加压燃烧合成的过程及产物的形成机制，焊缝与基体的结合行为。目的在于开发出一种新型层状金属复合材料的制备工艺。     

球磨纳米TiO2的结构转变

采用X射线衍射研究锐钛矿型纳米TiO2在高能球磨过程中及球磨后的纳米TiO2在退火过程中的结构变化。结果表现在室温常压下高能球磨诱发锐钛矿相转变为金红石相和S相。随着退火温度升高，球磨纳米TiO2粉末的晶粒逐渐长大，锐钛矿相逐渐转变为金红石相，而S相并不直接转变为金红石相而是先转变为锐钛矿相，然后由锐钛矿相转变为金红石相。与未球磨的纳米TiO2相比，高能球磨导致的晶粒细化，显微畸变以及晶格缺陷密度的增加而引起的额外储能使球磨后纳米TiO2的锐钛矿相-金红石相转变温度明显降低。     

含Ca,Si镁合金的铸态组织及其形成机制

利用金相,电子显微镜,X射线衍射仪和X射线能谱仪研究了含Ca,Si镁合金的铸态组织特征．结果表明：含Si较低的合金由镁基体及CaMgSi相组成,而含Si较高的合金由镁基体及CaMgSi和Mg2Si两种相组成．CaMgSi相呈三种不同的形态：离散块状、微细点状和针状,而本身是针状的Mg2Si则以“汉字形”团块的形态存在．根据Mg—Mg2Si—CaMgSi赝三元相图,详细讨论了铸态组织的形成机制．     

奥氏体形成机制

以T8等钢为例研究并综合分析了珠光体逆共析转变为奥氏体的过程和机制,指出,奥氏体是碳或各种化学元素溶入γ-Fe中所形成的固溶体。奥氏体在铁素体／渗碳体相界面形核,也可在珠光体领域交界处和原奥氏体晶界上形核。奥氏体以体扩散形式长大。奥氏体形核及长大过程中可同时吞噬铁素体和渗碳体,或只吞噬铁素体片长大,或吞噬铁素体较快,而吞噬渗碳体较慢,完成逆共析转变,最后剩下部分渗碳体。为减少相变积累的畸变和缓和应变能,而调整生长方向,形成了孪晶。奥氏体中存在未溶碳化物,需继续溶解和均匀化。     

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 采用光学显微镜、扫描电镜以及能谱分析等方法对低合金中厚板边部裂纹形成机制进行研究。结果表明：中厚板边部裂纹的形成是由于在轧制过程中钢板边部表层出现低温组织;变形不均匀导致边部应力集中,以钢板次表层存在的皮下气泡或颗粒状CaO-SiO2-Al2O3夹杂物为裂纹源,萌生裂纹并扩展,形成中厚板边部多处断续出现的横向应力裂纹。     

热轧带钢氧化铁皮的成因及对策

通过分析氧化铁皮的组成、结构和性质，结合宝钢集团梅山钢铁公司热轧板厂带钢氧化铁皮的现状，对氧化铁皮的形成原因进行了分析，并提出了减少带钢氧化铁皮质量缺陷的对策。