Effect of steel composition on failure of oxide scales in tension under hot rolling conditions

The differences in failure of oxide scales formed on mild, Si‐Mn, Mn‐Mo and stainless steels were investigated using a high‐temperature tensile test technique over the range of test parameters near to the hot rolling conditions at entry into the roll gap. Temperature, strain and strain rates were 783 – 1200 °C, 2.0 – 5.0 % and 0.2 – 4.0 s^?1 respectively. The scale thickness was maintained within 5 – 250 μm. Mild steel has the highest oxidation rate throughout the temperature range. A slightly thicker scale for the Mn‐Mo steel compared with Si‐Mn steel was observed. The stainless steel has shown the highest resistance to oxidation. Although through‐thickness cracks and sliding were competitive mechanisms for oxide scale failure for the mild steel, the other steel oxides failed only by through‐thickness cracking or were delaminated over the whole temperature range 783 ‐ 1200 °C. Modelling based on the finite‐element method was applied for better understanding of the micro‐events both during uni‐axial tension and just before contact with the rolls. The part of the model related to oxide scale failure has been upgraded taking into account experimental evidence concerning differences in scale failure, due to the steel chemical content, which were observed in the hot tensile tests.     

Influence of oxide scales on heat transfer in secondary cooling zones in the continuous casting process,part 1: heat transfer through hot-oxidized steel surfaces cooled by spray-water

For the cooling of steels in the continuous casting process it is necessary to know the heat transfer from the solidifying strand to the cooling water to enable calculation of the secondary cooling zone. Previous investigations have only determined this variable for non-oxidizing metallic surfaces. For many steels cast in practice, however, the formation of oxide layers prevents a direct transfer of the previous results. In the present research the influence of the oxide layers on the heat transfer has been investigated for spay-water cooling. Results have shown that heat transfer in the range of stable film boiling is determined for a constant spray-water temperature in the same way as for non-oxidizing metals, i.e. using the water mass flux density ·_s only. The changed surface qualities resulting from the oxide formation cause the Leidenfrost temperature, however, to shift considerably to higher values.     

Theoretical consideration on composite oxide scales and coatings

The present paper discussed some fundamental aspects on composite oxide scales and coatings for protection of alloys from high temperature oxidation, the related thermodynamic conditions, special mechanical characteristics and a sealing mechanism. It was proposed that the oxide scales and coatings with a composite structure should possess superior mechanical properties than that with a single phase oxide. It also showed that the Al2O3 scales or coatings doped with Y2O3 and ZrO2 (or YSZ)-Al2O3 composite coatings possessed superior properties at high temperatures. In such composite oxide scales and coatings, the fracture resistance of the scales was increased by the toughening effect, the thermal stress was decreased owing to the increase of thermal-expansion coefficients, and Al2O3 phase could seal the alloy substrate well. In addition, the kinetic equation of thermal growth oxide on alloy covered with composite oxide coatings was derived.     

氧化物冶金工艺对EH36钢HAZ组织性能的影响

设计了Ti- Ca和Ti- Mg两种氧化物冶金脱氧工艺的EH36实验钢来考察粗晶热影响区的组织性能和冲击韧性。结果表明,两种处理工艺的实验钢热模拟后的焊接热影响区内都有大量细小的晶内针状铁素体产生;与Ti- Ca脱氧工艺相比,采用Ti- Mg脱氧工艺的实验钢,焊接热影响区中针状组织更加明显,夹杂物的类型也更加复杂,同时Ti- Mg复合脱氧工艺在焊接热循环中能够更好地钉扎奥氏体晶界。-40℃的冲击数据表明,Ti- Mg脱氧工艺处理后的实验钢HAZ冲击性能优于Ti- Ca处理工艺。     

双相不锈钢2205热轧钢带氧化铁皮显微分析

 应用OM、SEM、XRD技术,分析研究了双相不锈钢2205热轧钢带氧化铁皮显微结构特征,这是决定钢带酸洗效果的本质因素之一。结果表明：热轧后钢带表面氧化铁皮存在大量的裂纹以及局部伴有氧化铁皮部分脱落,有利于酸洗;氧化铁皮厚度一般为10 μm左右,但是存在局部区域氧化层增厚以及氧化铁皮向基体内部的嵌入;氧化铁皮中含有难以酸洗的铁橄榄石（Fe2SiO4）和尖晶石结构的Cr2O3·FeO等物相,增加了钢带表面氧化铁皮酸洗去除的难度。     

帘线钢等温和控冷过程氧化铁皮的形成

制备了80级帘线钢盘条在900℃空气等温5、8、12和16min以及900℃等温后分别以4、12和(4+12)℃/s的冷速冷却形成的氧化铁皮。用激光拉曼光谱仪确定了氧化铁皮是由FeO层、Fe3O4层和极少量的Fe2O3层组成。用金相显微镜观测了氧化铁皮的形貌、各层厚度和钢基体的显微组织。结果表明:由于氧化铁皮中产生了CO和CO2气体,900℃空气等温形成的氧化铁皮,除5min的样品外,都出现不同程度的裂缝或孔洞;随等温时间的延长,FeO中不断析出先共析Fe3O4,FeO层的急剧增加导致氧化铁皮总厚度增加。随冷速的提高,FeO层及氧化皮总厚度减少,钢基体中索氏体含量增多。以12℃/s冷却形成的氧化铁皮和基体组织,既有利于机械剥壳,又有利于盘条冷拉拔。     

氧化物冶金在大线能量焊接用钢中的应用

 为了分析氧化物冶金钢中不同类型夹杂物的形核能力及其对大线能量焊接性能的提升效果，对Ti Ca、Ti Mg试验钢进行了模拟焊接热循环并利用氧化物冶金技术实现了不同钢种的工业化生产。结果表明，在1 400 ℃峰值温度等温30 s后，Ti Mg复合夹杂物可有效钉扎奥氏体晶界移动，并在后续冷却过程中作为形核质点诱导针状铁素体形核。为了保持氧化物冶金技术所需的氧含量，建立了转炉Si Mn预脱氧加Ti Mg脱氧的优化工艺路线。采用新技术冶炼的钢种具有200 kJ/cm气电立焊性能。-40 ℃下HAZ冲击韧性达到200 J，焊接接头内观察到大量针状铁素体板条组织。     

Formation of aluminum oxide scales in sulfur-containing high temperature environments

A model alloy consisting of Fe-18 wt pct Cr-6 wt pct Al was used to study the formation of α-aluminum oxide under various oxygen (1 to 10⁻²⁰ atm) and sulfur (10⁻¹³ to 10⁻⁶ atm) partial pressures at 900 °C. Acoustic emission results indicate that at constanti,e2051-01 (10⁻²⁰ atm) the oxide scale became much more resistant to isothermal cracking with increasing sulfur potentials. In addition, adherence of the oxide scale to the alloy was also enhanced and the oxidation rates increased with increasing sulfur potentials. Using inert palladium markers, the diffusion processes in the growing aluminum oxide scale were studied. In environments where oxygen was the only oxidant present, the results indicated that inward oxygen diffusion is the predominant scale growth mechanism. In contrast, oxides grown in sulfur containing environments revealed a drastic change of the marker position, indicating that the oxide growth occurred predominantly by outward aluminum ion diffusion. Oxide scale morphologies are shown using scanning and transmission electron microscopy. formerly a Graduate Student of Chemical Engineering and Materials Science Department of The University of Minnesota     

Vapor phase reduction of chromic oxide in an Ar-H2 Rf Plasma

The reduction of chromic oxide in an rf Ar-H₂ plasma was studied with a new experimental system, the process being carried out entirely in the vapor phase. The products were collected along the reactor length and analyzed by chemical methods as well as by SEM, X-ray, and IR absorption techniques. Temperatures in the reaction zone were measured by means of spectroscopic techniques. A diffusion model for the build-up of wall-deposited constituents is discussed. Vapor phase plasma reduction of Cr₂O₃ proved to be much more effective in comparison to both thermal decomposition and heterogeneous reduction.     

S32101双相不锈钢热轧中厚板氧化铁皮显微分析

摘要：采用EPMA、WDS和XRD对S32101双相不锈钢中厚板表面氧化铁皮显微结构进行研究，同时采用称重法测定出氧化增重曲线。结果表明：S32101双相不锈钢氧化铁皮厚度分布不均匀，氧化增重的平方值与氧化时间基本成直线关系。氧化铁皮外层物相为Fe2O3和Fe3O4，内层物相主要为FeCr2O4，局部区域存在MnCr2O4和NiCr2O4。结合热力学计算，得出了S32101双相不锈钢氧化铁皮形成的过程。     

Ni-based superalloy as a potential tool material for thixoforming of steels

Abstract

Semisolid processing, already a well established manufacturing route for the production of intricate, thin walled aluminium and magnesium parts with mechanical properties as good as forged grades, faces a major challenge in the case of steels. The tool materials must withstand complex load profiles and relatively higher forming temperatures for thousands of forming cycles for this near-net shape process to be attractive for steels on an industrial scale. The potential of a Ni-based superalloy, Inconel 617, reported to exhibit superior thermal fatigue resistance in demanding tooling applications, was investigated. The response to thermal cycling of this alloy at high temperatures was compared with that of X38CrMoV5 hot work tool steel widely used in the manufacture of conventional forging dies. The favourable thermophysical properties of the latter were completely negated by its limited temper resistance, while the Inconel 617 alloy responded to thermal cycling by the usual heat cracking mechanism.     

热轧钢材免酸洗还原退火热镀锌技术进展

介绍了热轧钢材免酸洗还原退火热镀锌的主要技术进展，从钢材氧化铁皮的精细化控制技术入手，结合氧化铁皮退火还原和热浸镀锌过程中各个控制环节的研究成果，进行了氧化铁皮的精细化控制、氧化铁皮高效还原以及基于免酸洗还原退火的热镀锌等关键技术的开发，并进行试制生产。试制结果表明，采用免酸洗工艺生产的热浸镀锌板表面质量良好，锌层延展性优良，能够满足使用要求，同时大幅降低吨钢成本，能够创造更大的经济效益。     

Growth Rate,Microstructure and Phase Composition of Oxide Scales for Three Typical Steels in Simulated Continuous Casting Process

Growth rate,microstructure and phase composition of scale layer formed during oxidation in 56%H2O-9%O2-N2 and following continuous cooling in ambient air were experimentally investigated by means of optical microscopy,scanning electron microscopy(SEM),energy-dispersive spectroscopy(EDS)and X-ray diffraction(XRD)for45,20 CrMnTi and TTS443 Msteels respectively,to examine the effects of strand surface temperature and steel composition on the scale formation in simulated continuous casting process.The growth rates were found to be approximately parabolic and the calculated activation energy of TTS443 Msteel is much higher than those of the two other steels.For 45 and 20CrMnTi steels,the scale layers were looser and a distinct gap formed at the scale-substrate interface at higher strand surface temperature.The dominant phases within the scale were iron oxides except for FeO·Cr2O3phase simultaneously existing in the oxide scale of 20 CrMnTi steel.On the other hand,the scale layer formed on TTS443 Msteel was compact and tightly attached to the steel surface.At both lower and higher strand surface temperature,iron oxide was main phase in external layer of the scale,while chromia was dominant in inner layer with an appreciable Cr enrichment.     

轧制工艺对高强耐候钢表面氧化铁皮的影响

某钢铁企业开发铁道用高强耐候钢Q550NH,生产中存在的主要问题为钢卷表面存在大面积红锈状氧化铁皮及柳叶状氧化铁皮压入缺陷.通过采取调整在炉时间、除鳞道次、粗轧出口温度、热卷箱模式等轧制工艺参数,研究了高强耐候钢表面氧化铁皮解决方法.通过提高粗轧出口温度,红锈状氧化铁皮消失;控制粗轧出口温度,缩短在炉时间,增加除鳞道次...     

Thixocasting Steel Hand Tools using Al2O3‐coated Steel and Molybdenum Dies

Forging is state‐of‐the‐art for producing hand tools on an industrial scale. Due to high demands on the stiffness and the fracture toughness, high‐strength forging steels are used to provide cavity‐free components with high mechanical load capacity. Moreover, forging is a cost‐effective mass production process but, in spite of all its advantages, it has its limitations, e.g. in the freedom of designs. However, because of the extreme thermal loading (particularly with regard to permanent moulds) and the frequently unavoidable casting defects, hand tools are not cast. By means of thixocasting steel, technical difficulties can be reduced and new options are provided which allow the manufacturing of components with much higher complexity than that using forging. Through near‐net shape production, manufacturing steps and costs can be reduced. Furthermore, steels, which are difficult to forge but nonetheless have high potential for specific applications (such as high strength or corrosion resistant steels), can also be processed. In cooperation with industrial partners, X39CrMo17 stainless steel size 17 combination spanners were thixocast. Forming dies were designed and optimized by simulation, the hot forming X38CrMoV5 tool steel as well as the molybdenum alloy TZM were selected as the tool alloys. The dies were treated by a plasma nitriding process and subsequently coated with crystalline Al₂O₃ protective coatings by plasma‐enhanced chemical vapor deposition (PECVD). During the experiments, combination spanners were successfully cast in the semi‐solid state. Cast parts were heat‐treated to enhance the components' toughness, which was subsequently measured by Charpy impact and tensile tests.     

Decomposition,Reduction and Dissolution Mechanism of Calcium Sulfate in Iron Oxide Dust Pellet

Iron oxide dust generated during oxygen blowing in the BOF process contains a high content of iron. This iron oxide dust can be used as a material of iron source in the BOF slag reduction process or as de‐siliconisation flux or dephosphorization flux of hot metal pretreatment. One of the most practical uses of iron oxide dust is recycling as a form of pellets in the BOF considering easy application and the amount that can be recycled. In the process of making iron dust pellets cement is used as a binder that contains a lot of calcium sulfate. This calcium sulfate is reduced and dissolved in the molten metal during refining in the BOF. If the oxygen content in slag and molten steel is high enough, the reduced sulfate cannot be dissolved into molten metal and it can be removed as SO_x gas. The behaviour of calcium sulfate has been studied using of 50kg high frequency induction furnace and industrial‐scale plant tests were carried out at a 300ton BOF. The results show that for low carbon steels the evaporation of decomposed sulfate increases with increasing oxygen content in the slag while for high carbon steels the decomposed sulfate is reduced into the molten metal.     

Cr含量对2.25Cr-1Mo钢蒸汽氧化性能的影响

对第四代核电主体结构材料2.25Cr-1Mo钢中铬含量对蒸汽氧化性能的影响进行了研究.完成了500 ℃/0.1 MPa下600h的高温蒸气氧化实验,并利用分析天平测量氧化增重,采用扫描电镜、X射线能谱和X射线衍射仪表征氧化膜的结构特征和物相.实验结果表明,Cr质量分数为1.99％和2.37％的实验钢氧化增重曲线都符合立...     

Continuous cooling transformation kinetics of thermomechanically worked low-carbon austenite

Continuous cooling transformation diagrams were determined for molybdenum-boron steels containing 0.24, 0.4, and 0.66 pct Mo with 0.1 pct C, and also 0.4 pct Mo with 0.2 pct C, after thermomechanically working by compressive deformation to 12, 25, and 50 pct reduction at 830°C (1525°F), as well as for the steels in the underformed condition. In underformed specimens, higher carbon or molybdenum decreased the limiting cooling rate for the avoidance of polygonal ferrite formation. The same was true for deformed specimens, although increased deformation raised the limiting cooling rates of all compositions. The limiting cooling rate for polygonal ferrite formation increased exponentially with austenite, deformation, as measured by true strain. Thermomechanical working also raised bainite start temperatures at fast cooling rates and caused small increases in martensite start temperatures.     

Thermo-oxidative ageing behavior of cerium oxide/silicone rubber

Cerium oxide/silicon rubber was prepared via mechanical blending.Mechanical and frictional properties,as well as thermal stability after thermo-oxidative ageing were investigated in this rubber composite.3D surface profilometry,scanning electron microscopy(SEM) and thermogravimetry analysis(TGA) were used to study the friction surface characteristics,friction mechanism and thermal stability,respectively.Additionally,swelling experiments were carried out to investigate the variation of crosslinking density.After thermo-oxidative ageing,the tear strength of cerium oxide/silicon rubber decreases.However,in the early ageing stage,improvements in tensile strength,elongation at break,and frictional performance are caused by crosslinking density increments.Moreover,the addition of cerium oxide remarkably improves the re-cross linking degree during ageing process,which in turn decreases the number of holes on the friction surface and endows the silicon rubber with better mechanical and frictional properties,as well as thermo-oxidative ageing resistance.     

700 MPa级别热轧高强钢氧化铁皮结构转变规律

选取700 L作为试验用典型钢种，利用高温同步热分析仪（TGA）研究了热轧过程中不同卷取温度和冷却速率条件对氧化铁皮结构转变的影响规律。实验结果表明，450～500 ℃为700 L共析转变的“鼻温”区间，此时共析转变的孕育期最短，容易发生共析转变，生成大量的共析组织（Fe+Fe₃O₄）。相较于其他成分钢种的氧化铁皮共析组织转变规律，700 L中添加的Mn、Nb、Ti元素会使晶粒细化，进而使参与反应的离子的扩散通道增加，并最终使共析转变速率发生一定的延迟，共析“C”曲线整体出现向左偏移。