Thermomechanical Modelling for Refractory Lining of a Steel Ladle Lifted by Crane

Numerical methods can be applied on metallurgical processes like engineering design of a steel ladle. In this study, the thermomechanical behaviour of refractory lining of a steel ladle which is lifted by a crane was investigated. To simulate this behaviour coupled heat transfer – structural analysis was made by using FEM (Finite‐Elements‐Method). For these calculations a two‐dimensional, an axially symmetrical geometric model and a FE‐model of a steel ladle with wear lining consisting of MgO‐C brick in the slag zone and castable MgO‐Al₂O₃–spinel in the working zone were created. Thermal stresses, hydrostatic pressure, gravity of molten steel and slag and refractory lining were used as boundary conditions. The results gained from the calculations showed that the maximum total displacements were observed at the bottom lining of the ladle.     

MgO–C bricks for BOF linings

Abstract

MgO–C brick linings have become standard in basic oxygen furnaces (BOFs) all over the world. Developments in the refractory technology for BOFs over the last few years and their impact on the lifetime and performance of refractory linings are presented. These developments comprise optimised shapes for the lining of BOF and steel fibre reinforced MgO–C bricks. Optimised shapes with double wedges lead to a smooth inner surface of the refractory lining and fewer stresses and refractory consumption. Stainless steel fibre reinforced MgO–C bricks have proven to be the ultimate choice for scrap impacts or other areas with ultra high mechanical loads. They have brought down refractory wear in these particular areas significantly. Moreover, typical lining patterns of different zones in a BOF and the development of the raw material grades (MgO grades and graphite) for refractories as well as the development of lining lifetimes over the last years are discussed.     

550 m~3高炉鹅颈管热态修复施工

对某铁厂2#高炉鹅颈管内衬修复进行了总结。通过采用鹅颈管内支模板,使用灌浆料热态下快速恢复耐材内衬的方式,恢复了鹅颈管原有耐材内衬,降低了管壳的表面温度,确保了高炉的安全运行,为其他高炉鹅颈管耐材内衬破损后热态下快速修复提供可借鉴的经验。     

Interaction between molten steel and different kinds of MgO based tundish linings

Abstract

Interactions between the molten steel and the refractory linings are of fundamental importance for the steelmaking industry. During the casting process, the steel cleanliness can be made worse because of the reoxidation of the molten steel in contact with the atmosphere and/or other sources of oxygen (refractories, top slag, etc.). In the industrial trial periods, four tundish refractory linings (preformed boards, two kinds of gunning materials and dry vibrating material, all MgO based refractories) were used in order to evaluate the interactions between the refractories and the molten steel. Owing to the small dimension of the tundish (5 ton) used in the continuous casting at Villares Metals SA, after casting, the chilled steel was cut in order to show, in a single section, the stopper, submerged entry nozzle, MgO ramming and the working refractory lining. Cross-sections of samples from the steel/refractory interface were investigated by electron probe microanalysis (EPMA). Four major aspects were observed at the steel/refractory interface: steel infiltration into the tundish refractory lining, mainly in the gunning materials; a steel oxidised layer formed at the steel/refractory lining interface; formation of a spinel layer between steel and tundish working refractory lining; and many particles were found in the steel phase, near to the steel/refractory interface, being a potential source of non-metallic inclusions.     

转炉“生铁块渣补”应用实践

在转炉生产中,提高炉衬的使用寿命对提高生产率、炉龄、钢产量、钢水质量及降低耐火材料消耗、增加经济效益有重要意义。分析了影响转炉炉衬寿命的主要因素,利用生铁块渣补技术解决了兑铁水、加废钢对炉衬的冲刷及机械磨损,减少了炉料的使用量和停炉的补炉时间,解决了生产与护炉之间的矛盾。该技术的应用,使转炉炉况明显好转、炉龄由11000炉提高到15000炉,耐材消耗降低30％,为炼钢进一步提升产能和经济技术指标开辟了一条新路。     

宝钢连铸中间包热状态测试与分析

连铸中间负愉钢水温度是炼钢生产过程的重要工艺参数之一,影响该参数的因素很多,通过对宝钢炼钢部60t中间包的包衬热状态进行测试,分析了包衬蓄热状况对中间包钢水温度的影响。     

Residual stresses and their effects on deformation

Residual stresses induced by thermal expansion mismatch in metal-matrix composites are studied by three-dimensional (3-D) elastic-plastic finite element analyses. Typically, the stress-free state is 150 to 300 K above room temperature. The coefficient of thermal expansion of the matrix is 3 to 5 times larger than that of the ceramic inclusion, resulting in compressive stresses of order 200 MPa in the inclusions. Both compressive and tensile stresses can be found in the matrix. Since the stress may exceed the matrix yield strength near the particles, plastic flow occurs. The authors find a significant influence of this flow on the elastic and plastic properties of the composite. The calculated residual strains in TiC particles due to thermal expansion mismatch and external loads compare well with recent neutron diffraction experiments (Bourkeet al.) The present work is the first reported three-dimensional analysis of spherical inclusions in different arrays (simple cubic (sc) and face-centered cubic (fcc)) that permit a study of particle interactions.     

Residual Stress Measurement and Fatigue Crack Growth Prediction after Cold Expansion of Cracked Fastener Holes

The cold expansion technique is often used to introduce beneficial compressive stress at fastener holes, and can be used for remedial work where cracks already exist. In this paper, results are presented showing the effect of preexisting cracks on the residual stress field produced by cold expanding a fastener hole, and on subsequent fatigue crack growth. The effect on the residual stresses was experimentally evaluated in two ways: indirectly, in terms of retained expansion and directly, by measurement of the stresses using the X-ray and neutron diffraction techniques. The retained expansion ratio showed that cold expansion is more sensitive to the existence of precracks at lower levels of applied interference, and the inlet and outlet faces have different behavior. The stress measurements showed that preexisting cracks reduce the compressive residual stresses more on the mandrel inlet face than on the outlet face and in the middle of the specimen. The effect on fatigue crack growth rates was modeled using a linear-elastic fracture mechanics approach. It was found that cold expansion of a hole containing a preexisting crack longer than 1 mm introduces little benefit for subsequent fatigue crack growth behavior.     

Thermal and thermomechanical evaluations of channel induction furnace applying strong insulation containing lightweight aggregates

Monolithic materials with a strong thermal insulating effect are required by the foundry industry for further energy savings, meanwhile possible premature wear of refractory linings caused by over-insulation should be avoided. A monolithic insulating material containing lightweight aggregates possessed strong thermal insulation and was proposed to replace the traditional insulating material made of chamotte currently used in a channel induction furnace. To evaluate the new lining concept, creep of the working lining was considered in the finite element modelling and followed the classical von Mises creep model, which was defined with the Norton–Bailey strain hardening creep equation. The results showed that the lightweight design of the insulating lining reduces the heat loss from the steel shell and material consumption. Moreover, the thermomechanical loads in the refractory linings and steel shell remain within a reasonable range when compared with the currently in-use refractory lining concept.     

中温中压容器用钢13MnNiMoR的热变形行为研究

为制定中温中压容器用钢13MnNiMoR的热加工工艺提供理论依据并实现其工业化生产,利用单道次热压缩模拟实验研究了变形温度(900~1150℃)和应变速率(0.01~1s~(-1))对其热变形行为的影响.结果表明:当应变速率低于0.1s~(-1)时,新晶粒有足够的时间进行形核和长大,奥氏体容易发生动态再结晶;当变形温度降低或应变速率增加时,实验钢在变形过程中主要发生动态回复,流变应力也随之提高.基于测定的流变应力曲线,通过拟合得到实验钢在热变形时的应力指数为4.29,动态再结晶激活能为319kJ/mol,据此建立了13MnNiMoR钢在高温变形时的热加工方程.     

Service Life Predictions for Hot Bulk Forming Tools

Hot bulk forming tools are subject to high thermal and mechanical alternating loads which can induce the formation of fatigue cracks in the highly stressed regions of the tool. It this way, premature tool failure occurs with which increased tool costs are associated. It is therefore vitally important to calculate the tool life output during the process design to improve the efficiency. Thermomechanical fatigue tests using the hot‐working tool steel X38CrMoV5‐3 are carried out as the basis for service life predictions in order to characterise the material behaviour subject to cyclic loading. In the tests, the thermal and mechanical loads operating in the tool steel during a forging process are reproduced. In this way, a strain controlled S‐N curve is determined for a specific temperature interval by varying the applied mechanical load. Thus it is possible to consider the damage mechanisms in the material, which operate during the forming process, for computing the service life. Based on the experimentally determined strain controlled S‐N curve, the computation of a fatigue failure is carried out for a practical example with tool fracture. By comparing the material's experimentally determined load carrying capacity with the loading computed by employing the elastic‐plastic material behaviour, the number of forging cycles is ascertained up to incipient cracking. The simulation model introduced here permits an improved prediction of the fatigue crack formation by integrating the cyclic material behaviour subject to similar conditions found in the forging process.     

Stress governs tissue phenotype at the femoral insertion of the rabbit MCL

The cells in the midsubstance portion of skeletal ligaments typically have elongated shapes, but where ligaments insert into bone the cells appear very rounded and the tissue phenotype is that of fibrocartilage. Between the midsubstance and the insertions there is a gradient in cell shape and tissue phenotype that has been hypothesized to reflect a gradient of mechanical stresses. To test this hypothesis, cell shapes (an index of tissue phenotype) were quantified in the central part of the femoral insertion of the rabbit medial collateral ligament by computer-assisted histomorphometry. Morphometric measurements were correlated with the mechanical stresses and strains in the central part of the insertion as predicted by finite element analysis. Throughout the ligament the direction of the predicted principal tensile stresses coincides with the direction of the collagen fibers which curve from the midsubstance to meet the femur at nearly right angles. Principal compressive stresses also occur within the ligament: the highest are localized near the bone; the lowest in the midsubstance. The areas with the roundest cells correspond to the areas with the highest principal compressive stresses in the model; the areas with the flattest cells correspond to the areas with the lowest compressive stresses in the model. A correlation between cell shape and mechanical stresses suggests that physiological loading of the MCL is important for the maintenance of tissue phenotype throughout this insertion. We theorize that the cells in ligament insertions adapt to the prevailing local mechanical environment.     

Spectral factors in the perception of vowel quantity in Icelandic

The aim of this study was to clarify the effect of heating rate on the development of both transient and residual stresses in investment molds. Solid, cylindrical, gypsum-based molds were modeled and theoretical calculations made of temperature distributions with a constant heating rate. These calculations used experimental thermal diffusivity data obtained with a laser flash method. The simulations calculated transient thermal stresses during heating and at the end of heating for two surface conditions: an unrestricted surface, and a surface restricted by a casting ring. The simulation model developed nonuniform strains and stresses at casting temperature; tangential stress was compressive at the surface and tensile at the mid-point for the unrestricted surface model. The surface restricted model developed compressive tangential stresses throughout the mold at the casting temperature. This resulted in significant thermal strain differences compared to the magnitudes of expansion of the mold due to heating.     

热轧带肋钢筋的负偏差轧制工艺设计及实践

以小规格热轧带肋钢筋的轧制生产实践为基础,探讨小规格热轧带肋钢筋负偏差轧制的工艺设计和实践。指出了切分轧制条件下小规格热轧带肋钢筋实施负偏差轧制的难点及注意事项。最后介绍本研究的应用效果。     

钢包内衬耐火材料的选择与使用

从耐火材料的材质、经济性、使用部位、精炼工艺、浇注工艺、耐火材料的相互作用、冶炼的钢种、吊车能力等8个方面，论述了如何选择钢包耐火材料，文章还以梅山钢厂150t钢包为例，详细介绍了耐火材料的选择及使用情况。     

Modeling of Steel-Concrete Composite Beams under Negative Bending

Negative bending moments acting in the support regions of continuous composite beams generate tensile stresses in the concrete slab and compressive stresses in the lower steel profile. As a result the mechanical behavior of these beams is strongly nonlinear even for low stress levels, due not only to the slip at the beam-slab interface, but also to cracking in the slab. Therefore, an adequate theoretical modeling should take account of the interactions between the structural steel and the concrete slab by shear connectors and also between steel rebars and concrete in tension by bond phenomenon. In this paper a model of steel and concrete composite beams subjected to negative bending is presented. It accounts for the slip occurring at both the beam-slab interface and the steel reinforcement-concrete interface. Some numerical results, obtained using a suitable numerical procedure, are discussed to show the capacity of the model.     

耐火材料对钢水纯净度影响的试验研究

通过对钢包、中间包衬层内示踪剂在浇铸过程中变化的试验分析，判断衬层耐火材料在钢水中的变化情况，分析每炉钢水对耐火材料的冲刷量及耐火材料对钢水纯净度的影响程度。从而提出减少耐火材料衬层对钢水污染的措施。     

内铸钢管水冷炉喉钢砖温度场和应力场计算

 利用数值模拟的方法研究了边缘煤气流过分发展对炉喉钢砖的影响。建立了水冷式炉喉钢砖模型,计算了其在不同煤气温度下热面的温度分布和应力差异以及水管和内部耐材表面的最高温度和最大应力。结果发现,煤气温度从500℃升高至1100℃,钢砖的热面最高温度上升约500℃,热面高温区域应力迅速增大,导致钢砖破损加剧,因此需借助布料等上部调节手段,控制边缘煤气流过分发展,防止形成边缘“管道”,确保钢砖正常、稳定地工作。     

碱性干式自流料在方坯连铸中间罐上的应用实践

为适应高效连铸和开发新品种的需要，邯钢第三炼钢厂方坯连铸中间包工作层用碱性干式自流料取代了硅质绝热板。生产实践表明，它在提高中间包使用寿命、降低钢水消耗、减少夹杂废品量、降低耐火材料消耗及降低劳动强度等方面具有明显优势。