Improvement in Quality and Yield of the Low Alloy Steel Ingot Casting Through Modified Mould Design

The internal quality and yield in 4 ton steel ingot of 40cmd8 grade was studied by comparing its solidification in a square cross-section mould with a slender rectangular cross-section mould, using FEM simulation. The model predicted various solidification aspects like fluid flow, thermal and solidification profiles, mushy zone, local solidification time, porosity and piping for both the molds. The convective flow of the molten metal during solidification showed higher velocity in square ingot than rectangular ingot under similar conditions due to lower surface area to volume ratio that affected the heat transfer in the rectangular ingot. Higher amount of air gap between the ingot and the mould was formed in rectangular ingots. Lower microsegregation as measured in terms of local solidification time was observed in rectangular ingot. Based on microstructure parameters such as thermal gradient and rate of solidification, it was found that the square ingot had more equiaxed zone than rectangular ingot. The rectangular ingot solidified at a faster rate and showed more propensity for core porosity than the square ingot. The ingot yield was improved by 3.6% through mould shape modification from square to rectangular. Model was validated to limited extent by carrying out a typical experiment with square mould.     

VAR法熔炼Ti-3Al-2.5V的工艺研究

本文讨论了Ti-3Al-2.5V合金铸锭的研制过程、主要熔炼工艺参数的选择依据及铸锭成份的均匀性、杂质元素(N,O)的控制要点,探讨了研制工艺条件对铸锭组织结构的影响。     

换底锭模的设计与生产

阐述了开发新型锭模的必要性和换底锭模的创新设计思路，扼要介绍了换底锭模的生产方法及其使用效果。设计的换底锭模由锭模本体和活动组件两大部分组成。该模优势：易损坏的部位可以更换；应用于铁合金浇注可比常规产品延长使用寿命5倍以上；单位铁水消耗的锭模费用可降低75％。     

On the development of a three-dimensional transient thermal model to predict ingot cooling behavior during the start-up phase of the direct chill-casting process for an AA5182 aluminum alloy ingot

The control of the heat transfer during the start-up phase of the direct-chill (DC) casting process for aluminum sheet ingots is critical from the standpoint of defect formation. Process control is difficult because of the various inter-related phenomena occurring during the cast start-up. First, the transport of heat to the mold is altered as the ingot base deforms and the sides are pulled inward during the start-up phase. Second, the range of temperatures and water flow conditions occurring on the ingot surface as it emerges from the mold results in the full range of boiling-water heat-transfer conditions—e.g., film boiling, transition boiling, nucleate boiling, and convection—making the rate of transport highly variable. For example, points on the ingot surface below the point of water impingement can experience film boiling, resulting in the water being ejected from the surface, causing a dramatic decrease in heat transfer below the point of ejection. Finally, the water flowing down the ingot sides may enter the gap formed between the ingot base and the bottom block due to butt curl. This process alters the heat transfer from the base of the ingot and, in turn, affects the surface temperature on the ingot faces, due to the transport of heat within the ingot in the vertical direction. A comprehensive mathematical model has been developed to describe heat transfer during the start-up phase of the DC casting process. The model, based on the commercial finite-element package ABAQUS, includes primary cooling via the mold, secondary cooling via the chill water, and ingot-base cooling. The algorithm used to account for secondary cooling to the water includes boiling curves that are a function of ingot-surface temperature, water flow rate, impingement-point temperature, and position relative to the point of water impingement. In addition, a secondary cooling algorithm accounts for water ejection, which can occur at low water flow rates (low heat-extraction rates). The algorithm used to describe ingot-base cooling includes both the drop in contact heat transfer due to gap formation between the ingot base and bottom block (arising from butt curl) as well as the increase in heat transfer due to water incursion within the gap. The model has been validated against temperature measurements obtained from two 711×1680 mm AA5182 ingots, cast under different start-up conditions (nontypical “cold” practice and nontypical “hot” practice). Temperature measurements were taken at various locations on the ingot rolling and narrow faces, ingot base, and top surface of the bottom block. Ingot-based deflection data were also obtained for the two test conditions. Comparison of the model predictions with the data collected from the cast/embedded thermocouples indicates that the model accounts for the processes of water ejection and water incursion and is capable of describing the flow of heat in the early stages of the casting process satisfactorily.     

抽锭电渣重熔718塑料模具钢板坯锭的新工艺

针对大型塑料模具毛坯电渣锭凝固过程中产生疏松和偏析等缺陷,从改变大型钢锭凝固条件角度出发,试图将大圆钢锭改为等截面面积的扁锭,同时采用双极串联供电控制渣池的温度场,以达到提高钢锭凝固质量的目的.本文介绍了采用双极串联、T型结晶器,抽锭电渣重熔工艺生产了0.32 m×2.0 m×4.0 m的718塑料模具钢板坯工业试验,重熔板坯锭的检验结果表明,板坯锭成分、低倍等凝固质量显著提高.     

Heat-flow-based analysis of surface crack formation during the start-up of the direct chill casting process: Part II. experimental study of an AA5182 rolling ingot

The flow of heat during the start-up of the direct chill (DC) casting process has been studied with the aim of determining the factors that make this phase of the process prone to face crack generation. Measurements have been made on an AA5182 rolling ingot instrumented with embedded thermocouples placed at key locations in the vicinity of the ingot face near its base. The resulting temperature data have been input to a two-dimensional (2-D) inverse heat-transfer model, developed in part I of this two part study, in order to calculate heat fluxvs surface temperature curves in the direct water impingement regime. The findings indicate that the flow of heat is influenced by changing surface morphology and water flow conditions during the start-up phase. A finite element based simulation of the cast start, employing the calculated flux/surface temperature relations, reveals that the ingot shell at the point of water contact reaches a maximum thickness early in the casting process. The location of this maximum was found to coincide with the position where surface cracks are routinely found to initiate. Further, this maximum was found to also coincide with position at which the rate of deflection of the base of the ingot (“butt-curl”) begins to slow. Based on the heat-flow analysis, it is believed that the face cracks form due to an excessive shell thickness during transient start-up conditions and that their occurrence could be reduced by an optimal combination of water flow rate and casting speed during start-up.     

Control of the secondary cooling in continuous casting during nozzle replacement

The cooling and solidification of a continuous-cast ingot in transient casting conditions are studied by simulation. The influence of the method of controlling the secondary cooling on the thermal state of the ingot is shown. Different approaches to the control of the coolant flow rates in various operations are compared.     

电渣重熔炉电极熔化速度对重熔过程的影响

建立了重熔钢锭的数学模型,确定了材料的物理边界条件,采用有限差分法对电渣重熔钢锭凝固过程的非稳态模型进行了求解,研究了电极熔化速度与准稳态熔池深度的关系.     

改进钢锭断面形状提高厚板成材率的变形实验

简述了钢锭断面形状对厚板成材率的作用。着重阐述模拟舞阳钢铁公司４２００ｍｍ厚板轧机的轧制工艺条件，轧制８．０ｔ镇静钢扁锭，采用正交设计法确定钢锭断面最佳尺寸。得到了在确定轧制工艺条件下，正确确定最佳钢锭断面尺寸的正交回归数学模型。在本实验最佳断面形状的锭型与合适的工艺相匹配下，厚板成材率约提高５．２７６％，边部切损率约降低３．６３５％。     

Effect of different thermomechanical processing on structure and mechanical properties of electron beam melted niobium

Among the refractory metals and alloys, niobium and niobium alloys are used in variety of high temperature applications ranging from light bulbs to rocket engines because of its high melting and boiling point, lower density, good ductility at room temperature and high corrosion resistance. In this paper the effects of different thermomechanical processing on structure and mechanical properties of electron beam melted niobium ingot was investigated. The correlation among the different processing conditions and microstructure as well as mechanical properties have been investigated using optical microscope, SEM, UTM and microhardness testing. The results show that the cold forging response of EB melted ingot was very poor, where as oxidation resistant coated ingot and ingot sealed in evacuated stainless steel jacket were successfully forged at 900 °C. The cast and hot forged EBM niobium ingot was cold rolled without any intermediate annealing. The hot forged, cold rolled and annealed niobium sheets exhibit better strength as compared to cold rolled and annealed niobium sheets. The mechanical properties of all the niobium sheets processed by using different processing conditions are superior to the properties specified by ASTM standard.     

A numerical simulation of the D.C. continuous casting process including nucleate boiling heat transfer

The steady-state thermal problem associated with the direct-chill continuous casting of A6063 aluminum cylindrical ingots is solved using the numerical finite element technique. Excellent correlation is demonstrated between the numerical model and experimental data from ingots cast at two different speeds. By application of the model, effective heat transfer coefficients are calculated as a function of vertical position on the outside surface of the ingot. It is shown that direct application of these coefficients to the modeling of different casting situations will produce substantial errors in the region in which heat transfer is by nucleate boiling. Using theories of nucleate boiling with forced convection and film cooling, a method is developed to calculate the external boundary conditions in the submold region of the ingot, thus making it possible for the first time to define explicitly all of the thermal boundary conditions associated with this casting configuration. These theories are incorporated into the numerical model, and a subsequent simulation shows excellent agreement with experimental data from a third ingot.     

热顶设计对镍基高温合金铸锭收缩孔隙的影响

为减轻缩孔缺陷以降低铸锭头部切除率进而提高铸锭成材率,通过数值模拟研究了热顶高度和热顶预热温度对铸锭收缩孔隙率的影响。对ø350 mm×3 200 mm的高温合金铸锭进行纵向剖切来验证模拟精确性,并结合试验测试和反算法确认了合理的铸锭与锭模界面换热系数,阐明了热顶最优设计方案。试验结果表明,不采用加热冒口时,铸锭缩孔达到1 400 mm并在铸锭中下部出现严重的疏松缺陷。通过有限元数值模拟,验证了镍基高温合金铸锭中心疏松形成条件。过高的热顶高度和预热温度会加剧中心疏松,相反会降低铸锭缩孔高度。因此,为全面控制这两个缺陷,设定ø350 mm高温合金铸锭最佳热顶高度和预热温度为600 mm和900 ℃,这一标准已成功用于优化ø350 mm高温合金铸锭生产。     

钢锭中硫化物偏析的研究

对钢锭凝固过程进行实测和计算机凝固模拟计算，研究了钢锭凝固时的偏析问题，结果表明凝固模拟计算是预测分析大型钢锭凝固进行的有效手段。由此，通过凝固冷却条件能预测钢锭中产生偏析的可能性，并进一步寻求减少和消除偏析的方法。     

A Simple Model of the Mold Boundary Condition in Direct-Chill (DC) Casting of Aluminum Alloys

An accurate thermofluids model of aluminum direct-chill (DC) casting must solve the heat-transfer equations in the ingot with realistic external boundary conditions. These boundary conditions are typically separated into two zones: primary cooling, which occurs inside the water-cooled mold, and secondary cooling, where a film of water contacts the ingot surface directly. Here, a simple model for the primary cooling boundary condition of the steady-state DC casting process was developed. First, the water-cooled mold was modeled using a commercial computational fluid dynamics (CFD) package, and its effective heat-transfer coefficient was determined. To predict the air-gap formation between the ingot and mold and to predict its effect on the primary cooling, a simple density-based shrinkage model of the solidifying shell was developed and compared with a more complex three-dimensional (3-D) thermoelastic model. DC casting simulations using these two models were performed for AA3003 and AA4045 aluminum alloys at two different casting speeds. A series of experiments was also performed using a laboratory-scale rectangular DC caster to measure the thermal history and sump shape of the DC cast ingots. Comparisons between the simulations and experimental results suggested that both models provide good agreement for the liquid sump profiles and the temperature distributions within the ingot. The density-based shrinkage model, however, is significantly easier to implement in a CFD code and is more computationally efficient.     

大型圆台钢锭定向凝固的数值模拟

利用大型软件CFX建立大型圆台钢锭凝固过程温度场的数学模型，分析讨论了不同换热条件对钢锭凝固进程的影响。     

20kg铝锭铸造机组脱模的研究

针对目前20kg铝锭铸造机组生产中脱模率低的问题,对影响脱模的因素进行了全面的分析,提出了多项改进措施,通过实践证明,脱模率达到了99%以上,另外推导出了脱模机构动力学方程。     

Mathematical model of the thermal processing of steel ingots: Part I. Heat flow model

A two-dimensional mathematical model has been developed to predict stress generation in static-cast steel ingots during thermal processing with the objective of understanding the role of stress generation in the formation of defects such as panel cracks. In the first part of a two-part paper the formulation and application of a heat-flow model, necessary for the prediction of the temperature distribution which governs thermal stress generation in the ingot, are described. A transverse plane through the ingot and mold is considered and the model incorporates geometric features such as rounded corners and mold corrugations by the use of the finite-element method. The time of air gap formation between mold and solidifying ingot skin is input, based on reported measurements, as a function of position over the ingot/mold surface. The model has been verified with analytical solutions and by comparison of predictions to industrial measurements. Finally, the model has been applied to calculate temperature contours in a 760×1520 mm, corrugated, low-carbon steel ingot under processing conditions conducive to panel crack formation. The model predictions are input to an uncoupled stress model which is described in Part II. B. G. THOMAS, formerly a Graduate Student at the University of British Columbia     

MC系列模铸保护渣的研究

本文介绍了MC系列模铸保护渣的广泛适应性和良好的使用效果。分析了该系列保护渣的特性,阐述了以电厂灰和硅灰石为基料,采用复合配碳,适当调整熔剂材料的种类和配比,使保护渣成分设计合理、理化性能优良、融熔结构稳定,按钢种、锭型和浇铸工艺的不同,实现保护渣系列化的理论依据和研究实践。     

大规格纯钛铸锭脱氧现象及对策

利用真空自耗电弧炉进行了大规格纯钛铸锭的工业生产,研究并分析Ф1040 mm大规格高氧含量纯钛铸锭的底部脱氧现象和氧元素均匀性的问题。纯钛铸锭底部脱氧的原因是海绵钛中的Mg与添加剂TiO₂在一次铸锭熔炼时反应引起的。采用真空自耗电弧炉对梯度加氧自耗电极进行两次熔炼,结果表明:通过梯度加氧的方式可以有效解决纯钛铸锭脱氧的问题,并显著改善纯钛铸锭氧元素成分均匀性,使生产出的Ф1040 mm高氧含量纯钛铸锭头部、尾部氧含量的偏差控制在0.011%范围内。     

金银分析实验室银废液中银的回收方法探讨

金银实验室实验后产生大量的废银夜。采用氯化钠沉淀废液中的银,得到的氯化银沉淀渣同还原剂铁粉、熔融剂碳酸钠、助熔剂玻璃粉及硼砂按一定比例进行配料,经马弗炉高温熔炼,获得银锭,从而建立一种从废液中回收银的方法。分别以铁粉、淀粉、面粉和碳粉为还原剂进行了比对试验,结果表明铁粉还原效果最佳。还对还原剂、熔融剂、助熔剂用量及熔融时间进行了探讨,结果表明,取30 g氯化银沉淀渣,加入60 g碳酸钠、15 g铁粉、10 g硼砂及60 g玻璃粉,在马弗炉中1 100 ℃熔炼20 min,可较好的回收银锭。按照实验方法得到的银锭,银的回收率可达99.73%,银锭的纯度为99.35%。