Fluid flows have proved to be an integral part of many metallurgical processing operations. Metal, slag, and gas flows invariably affect the viability, effectiveness, and efficiency, of our reactor vessels. The performance characteristics of our blast furnaces and steelmaking vessels, such as BOF's, OBM's, ladles, tundishes, and the moulds of continuous casting machines, are all strongly influenced by such flows. Similarly, liquid metal quality and cast micro-structures, are also bound up with the way fluids have flowed and interacted. In all these aspects, the rapid evolution in our techniques and abilities to mathematically and physically model single and multi-phase flows and their attendant heat and mass transfer processes, have contributed significantly to our understanding, and ability, to control and improve these metallurgical processing operations, and to develop new and better processes. The evolution and application of computational fluid dynamics (CFD) over the past four decades has been particularly impressive. The author's many fine Japanese graduate students have made very valuable contributions to this new field of research for Process Metallurgists, as well as to the founding and scientific support of the McGill Metals Processing Centre, MMPC, following their return to Japan.
A computational model based on mass transfer and thermodynamic data as well as kinetic information from the industrial AOD process has been created in order to simulate the nitrogen content of the stainless steel melt as a function of blowing time. The model uses Butler's equation to calculate the reaction area available for nitrogen transfer between the steel and gas bubbles. Thermodynamic driving force is calculated as a function of temperature as well as stainless steel melt and gas compositions. According to the study effective surface area for nitrogen transfer achieved its maximum as well as thermodynamic driving force is also high during the 1st stage (absorption). During desorption effective reaction surface area is only approximately 7–9%. Typical initial nitrogen contents were about 400 ppm whereas the maximum values of 1000–1500 ppm were achieved before nitrogen argon switch-point. Simulations showed that desorption rate of nitrogen is low and final nitrogen contents below 400 ppm's are very difficult to be achieved economically. According to the simulations model predicts final nitrogen content of stainless steel melt after AOD process with 50 ppm accuracy.
A mathematical model has been developed to predict the dissolution rate of added fluxes such as lime and dolomite as a sub-model of an overall kinetic model of top-blown oxygen steelmaking process. The calculation of dissolution rates included dimensionless analysis technique as well as the evolution of gas generated due to decarburization reaction during the blowing process. The progress of flux dissolution and the amount of slag generated were predicted as a function of saturation concentration of CaO and MgO in the slag, CO gas flow rate and the physical properties of slag throughout the blow. The results from the model were consistent with the plant data from the study of Cicutti et al. The influences of variations in solid particle size and flux addition rate on flux dissolution were also investigated. It has been shown in this study that the amount of flux dissolved in oxygen steelmaking process is accelerated if the addition rate of flux is increased or if the size of flux particle is decreased.
Al–O equilibria in molten Fe–Al alloys were experimentally investigated. Molten steel with varying Al content (0.01–10 mass%) was equilibrated with a pure Al2O3(s) crucible at 1873 K in an Ar atmosphere with 3 vol% H2. The oxygen content of steel with Al content higher than 1.0 mass% was found to be much lower than that found in previous works, while the oxygen content for Al content less than 1 mass% was found to be slightly higher, resulting in a smaller equilibrium constant. The interaction parameters as well as the equilibrium constant of the Al–O equilibria in molten steel at 1873 K were reevaluated in the present study. The equilibrium for the Al deoxidation of molten steel was well represented up to 10.0 mass% Al using the reevaluated parameters.
Phase equilibria of the MnO–MnS, MnO–SiO2–MnS, and MnO–Al2O3–MnS systems under low oxygen partial pressure have been experimentally investigated for the temperature range of 1200 to 1500°C using equilibration and quenching techniques. Equilibrium phases were analyzed by Scanning Electron Microscope, Electron Probe X-ray Microanalysis (EPMA), and Differential Thermal Analysis (DTA). Phase diagrams were successfully constructed for the systems investigated. A ternary compound in the MnO–SiO2–MnS system was observed at 1200°C and 1250°C. No ternary compound or solid solution was observed in the MnO–Al2O3–MnS system. The results of the present study were critically compared with the results reported previously.
Recently, the reduction in the amount of the CO2 emission has become an important issue. It is important to increase the reactivity of iron sources used in a blast furnace to decrease of CO2 emission. Therefore, the carbon composite iron ore agglomerates are significant. The production experiments of a new agglomerate named CIS (Carbon Included Sinter), where green balls were granulated by a model pan pelletizer were carried out using pot tests. The reduction of produced CIS with CO–CO2 gas mixture were examined, and were compared with that of ordinary sinter ore. Also, the softening and melting property tests of 50% CIS–50% sinter mixed layer were carried out and compared with the results using 100% sinter layer. The results are summarized as follows: (1) A new agglomerate, which an anthracite particle was surrounded by a shell with the same components as ordinary sinter ore, was produced by sintering pot test. (2) When CIS was reduced by CO–CO2 gas mixture at 1273 K, the degree of reduction achieved 80% in 120 min, even though ordinary sinter ore achieved less degree of reduction. (3) 250 g CIS–250 g ordinary sinter ore packed bed achieved 1/3 maximum pressure drop of 500 g ordinary sinter ore packed bed in the softening-melting property test.
Enhancement of reactivity of the burden in the blast furnace can decrease the reducing agent of blast furnace. Besides high reactivity coke, the carbon iron ore composite is considered to be a typical high reactivity burden that can control the thermal reserve zone temperature. Since the reactivity of biomass char is much higher than that of coke, the use of carbon iron ore composite with biomass char will be favorable for decreasing the reducing agent. In the present study the reaction and reducing behavior of the carbon iron ore composite with biomass char were investigated. The gasification rate of biomass char was measured in CO2 atmosphere, and the reaction rate equation of that was derived. The microscopic structure change of biomass during carbonization was experimentally analyzed. According to the experimental results, the reduction of the composite begins at about 550°C in an inert gas atmosphere, and it is much lower than the composite with coke. Analysis of the reaction of carbon iron ore composite was carried out with the reaction model of the carbon iron ore composite based on a lumped system, in which the reaction rate of biomass char and iron ore were installed. The reaction model shows that the biomass char can improve the reduction behavior of the carbon iron ore composite especially in the lower temperature region. Moreover, the influence of gas atmosphere and the optimum structure of the composite were investigated by the model calculation to estimate the optimum condition of the composite in the blast furnace.
Using the sessile drop approach, interfacial reactions taking place in the slag/carbon region were investigated at 1550°C in a horizontal tube furnace under inert atmosphere (1 L/min Ar). In this study, waste rubber tyres were blended with metallurgical coke, already used as injectant in electric arc furnace (EAF) steelmaking, in different proportions. Off gas analyses and physicochemical properties of the slag have been evaluated and correlated with the carbon/slag interactions. The gaseous emissions from metallurgical coke showed lower concentrations in comparison to the emissions from the coke–rubber blends. With an increase of rubber in the blend, gaseous emissions were enhanced. Significant carbon/slag interactions occurred when coke/rubber blends were used, with associated iron oxide reductions within the slag phase. Higher gas entrapment in the slag was also observed when the rubber partially replaced the coke. High levels of gas generation leads to increased likelihood of convective transport of reactants and products from the carbonaceous material surface due to evolution of gases as a result of slag/carbon interactions. The oxides present in the ash partially dissolve the molten slag, modifying the slag composition. The results have been discussed and correlated with the hydrogen, ash and sulphur contents of the carbonaceous residues as well as with the dynamic changes in slag composition. This study highlights significant differences in the carbon/slag interactions of coke/rubber blends with EAF slag, compared to interaction of coke with the same slag.
In recent years, much attention has been paid to determining not only the composition, but also the inclusion characteristics from liquid steel samples extracted from a ladle or a tundish. Here, a crucial point is that the steel sampler is filled and solidified without changing the inclusion characteristics that exist at steel making temperatures. Therefore, one of the first steps to investigate is the flow pattern inside samplers during filling in order to obtain a more in-depth knowledge of the sampling process. In this paper, this is done using physical modeling of a lollipop-shaped sampler. More specifically, particle image velocimetry was employed to capture the flow field and calculate the velocity vectors during the entire experiment. The filling rate at the pin part of the sampler was varied during the experiments. It was found that due to the geometry change at the transition from the inlet pin to the body part of the sampler, the flow is very chaotic at the initial filling stage. Furthermore, vortexes are formed in the water sampler vessel during all the fillings and the height of the vortex center varies with the filling rate. Overall, it was found that the flow patterns in the lollipop-shaped sampler vessel can be characterized into three distinct flow regions: the upper vortexes region, the lower horizontal flow region and the middle nozzle flow region.
Slag foaming in an electric arc furnace (EAF) is examined using a mathematical model of the EAF to compute the CO generation rate and slag chemistry and laboratory measurements of the foam index. The foam height limited by either the foam stability or from the amount of slag present was computed for a high productivity furnace using relatively large amounts of pig iron, carbon and oxygen. It was found that for this case the foam is usually simply limited by the amount of slag in the furnace. The effects of the amounts of pig iron, carbon, oxygen and slag were determined. As the amount of carbon as pig iron, coke and coal and oxygen are reduced, the foam height is limited by the CO generation rate and is reduced. The foam decreases towards the end of the process due to lower CO generation rates.
The computational efficiency and accuracy of the phase-field simulation of the dendritic solidification of Fe–0.5mass%C alloy are investigated for the original model, a model incorporating the reduced interface method and a model incorporating the antitrapping current method. By performing two-dimensional simulations, it was found that the model incorporating the antitrapping current method can accurately determine the growth velocity with a calculation time of about 20% of that of the other two models. Also the comparison of concentration profiles among the three models shows that the antitrapping current method provides the most effective way of suppressing the anomalous interface effect caused by the thin-interface limit condition. By performing three-dimensional simulations, it was also shown that the growth velocities calculated by the model incorporating the antitrapping current method are in good agreement with those predicted by the LKT model.
Fluid flow phenomenon in Centrifugal Flow (CF) tundish is investigated using water modeling and numerical simulation techniques. The effect of the dam spacing and rotation speed on the flow structure has been analyzed in detail. Results reveal that the bias flow, originating from the rotary outflow, leads to the formation of transversal circulation behind the dam. Such transversal flow can effectively diminish the conventional dead volume. Meanwhile, small dam spacing helps to produce a large-scale transversal circulation, and thus the prolonged flow path and relatively low velocity results in an increased plug volume. With the increase of dam spacing, the intensity of transversal circulation decreases and the increased fluid velocity causes a minished plug volume. The highest ratio of plug to dead volume is obtained under the dam spacing when transversal circulation is strongest. Furthermore, under lower magnetic intensities, the weaker fluid momentum leads to relatively large dead volume. With the increasing of magnetic intensity, the fluid mixing becomes better. However, much larger magnetic intensity will lead to decreased ratio of plug to dead volume. Therefore, a medium rotation speed (around 30 r/min) should be recommended.
The configuration of a tundish for a two-strand horizontal continuous caster was designed and optimized using water modeling, mathematical modeling and industrial trials. Five designs were studied: the original tundish without flow control devices, the tundish with a turbulence inhibitor at the bottom, the tundish with a deep inlet launder and a tilted dam at the end of the inlet launder, the tundish with two dams with holes, and the tundish with a shallow inlet launder and a high dam in the main chamber. Water modeling was used to measure residence time and investigate dead zone fractions and fluid flow patterns. In the mathematical modeling, fluid flow, heat transfer and inclusion motion and removal were calculated. In industrial trials, the total oxygen, nitrogen pick-up, and inclusions in steel samples taken from the tundish and the billets were analyzed. The results indicated that the tundish with an inlet launder and a dam either at the end of the chamber or in the main chamber was the best design.
It is well known that boron (B) addition to steels can cause difficulties during continuous casting. The difficulty includes surface cracks, internal half-way cracks as well as centerline problems on the cast products. In severe cases, a breakout can occur during casting of B-bearing steels. According to the studies of the effect of boron on the pseudo-binary phase diagrams of Fe–B alloys at various carbon levels by the authors, it was found that the addition of boron introduces the possibility of steel initially completely solidifying followed by a retrograde melting phenomenon in all C contents below 1%. This retrograde melting phenomenon will most likely occur at interdendritic regions and grain boundaries at temperatures approaching 1350°C. The remelt liquid will be retained down to temperatures approaching 1100°C. The retention of this low melting point phase during casting is believed to be the primary cause of casting difficulties of the B-bearing commercial products. In order to confirm the modeling study of the phase diagrams and the finding of the remelting phenomenon, Confocal Scanning Laser Microscope (CSLM) studies were carried out for “in-situ” observation. These studies not only confirmed the existence of the retrograde-melting phenomenon at temperatures below 1200°C, but also revealed that severe segregation of B in steel could cause the existence of liquid phase down to at least 1350°C even in steels bearing as little as 10 ppm B. The present paper will summarize the observation results.
Dendrite growth simulations have been performed to analyze Columnar-to-Equiaxed Transition (CET) of δ-ferrite dendrite structure triggered by fine particles of a primary Ti(C, N) crystal. The CET position estimated by Hunt's criterion and the present simulation indicated that the existence of a large number of the Ti(C, N) particles gives rise to the CET of the dendrite structure even in the vicinity of the mold wall under the present casting condition. Furthermore, the capability of the Ti(C, N) leading to the CET was discussed in the light of the different number of Ti(C, N) particles and the different thickness of cast ingot. It was shown that a sufficient number of Ti(C, N) leads to the formation of fully equiaxed dendrite structure irrespective of the ingot thickness.
A coupled mathematical model on fluid flow, heat and solute transport, and inclusion transport is developed to investigate turbulent flow, solidification, and inclusion collision-growth in the slab continuous caster. The behaviors of inclusion and solute in the steel belong to mass transfer phenomena, but inclusion transport is different from solute transfer in the liquid phase zone, mush zone and solid phase zone. In the continuous caster, turbulent collision and Stokes collision, which are the major factor causing inclusions to coalescence, have been taken into account in the mathematical model. All these differential equations have the same basic structure and can be solved by the same numerical method. Influenced by the fluid flow, the temperature, carbon element and inclusion in the molten steel have similar spatial distribution as the fluid flow in the continuous caster. Their spatial distribution can be divided into the upper and lower recirculation zones, but their distributions have their own characteristics. Near the center of the recirculation zones, the temperature of molten steel and the characteristic inclusion concentration and the characteristic inclusion number density are lower, but the carbon concentration and the inclusion size are greater. Due to the interaction between the movement of solidified shell and the downward flow, a small corner-vortex appears near the meniscus. The initial solidified shell forms near the meniscus, so there is a few of indigenous inclusions with small size in the initial solidified shell.
In this study, the effects of chemical composition and process parameters on the tensile strength of hot strip mill products were modeled by Artificial Neural Network (ANN). A good performance of network was achieved when compared with the experimental data taken from Mobarakeh Steel Company (MSC). Moreover, the relative importance of each input variable was evaluated by sensitivity analysis. The results are evaluated based on metallurgical phenomena of steels. Therefore, it is proposed that, this model can be employed as a guide to predict the final mechanical properties of commercial low carbon steel products.
A novel near net-shape layer-by-layer welding technique—Shaped Metal Deposition (SMD)—using Tungsten Inert Gas (TIG) welding was employed to produce components from a 308 stainless steel wire. This technique is meant to fabricate metal components for rapid prototyping or for reparation of components when no additional tooling is available. The mechanical properties of components prepared by this novel route have to be known before application, since they do not necessarily coincide with the properties of components derived from conventional fabrication methods. The component exhibits a microstructure composed of austenite and vermicular δ ferrite with the predominance of austenite. Neither the structure nor the mechanical properties are dependent on the height of the component. The mechanical properties are comparable to those of components prepared by conventional techniques.
The influence of the thermal cycle and austempering treatment on the mechanical behavior of a 0.56C–1.43Si–0.58Mn–0.47Cr (wt%) steel has been investigated. The thermal cycle consisted of heating the steel to 800°C or 900°C, in the intercritical and austenitic region respectively, fast cooling down to 600°C or 400°C, followed by 300 s hold. After austempering the materials were cooled at different rates and then submitted to tensile testing. The total elongation of 15–20% and tensile strength of 1300–1400 MPa were reached after heating to 900°C and transformation at 400°C. The strain-induced austenite transformation to martensite during the plastic deformation (Transformation Induced Plasticity Effect) is responsible for this combination of high strength and ductility. Silicon acts to stabilize the austenite during austempering. However, the stabilized austenite can be transformed and the microstructure modified, resulting in the formation of others constituents such as bainitic ferrite, upper bainite and martensite.
The crystallographic orientation relationships that are active during the transformation of austenite to bainite are studied for two TRIP steels by means of Electron BackScatter Diffraction (EBSD). A detailed evaluation of about 360 retained austenite grains and their BCC neighbours was performed. Three relationships were considered, namely Kurdjumov–Sachs, Nishiyama–Wassermann and Pitsch. It was found that the majority of the austenite grains had at least one neighbour that could be related with one of the three orientation relationships. The Kurdjumov–Sachs relationship appeared to be dominant and no strong indication for variant selection could be retrieved from the studied data. It was, however, also demonstrated that some precautions need to be made since a clear distinction between the evaluation of a small region of the microstructure and conclusions made for the complete material is necessary.
Selected formation of variants under magnetic field in a diffusional process has been investigated by using Co–50Pt (at%) and Fe–55Pd (at%) alloys exhibiting A1 (disorder)–L10 (order) transformations. A single variant of the ordered phase is obtained in these alloys by applying a magnetic field during the early stage of ordering. The lowest magnetic field required for obtaining the single variant is about 0.5 T for the Co–50Pt alloy, and 4 T for the Fe–55Pd alloy in the present heat-treatment conditions. Such a difference could be due to the relation between nucleation barrier for the formation of the ordered phase and magnetocrystalline anisotropy at the nucleation stage.
Multipass torsion tests were carried out with two eutectoid steels, one microalloyed with vanadium, using different deformation sequences. The aim of the study was to investigate the potency of vanadium in the retardation of recrystallization for accumulating strain in the austenite. The study showed that at certain deformation conditions well defined non-recrystallization temperatures (Tnr) were observed in the vanadium microalloyed steel. As a consequence, an increase in the austenite grain boundary area per unit volume (SV) was obtained which led to a refinement of the “ferrite unit” size in the pearlite.
Fatigue damage in nitrogen-strengthened austenitic steel that showed subsurface crack generation and intergranular cracking at cryogenic temperatures has been characterized using electron backscatter diffraction (EBSD) analysis. Strain gradients near grain boundaries and localized stress concentrations in grains were clearly detected. The strain gradient in the vicinity of a grain boundary accompanied a misorientation of a few degrees, and may result from co-planar dislocation arrays at the grain boundary. To reduce localized strain incompatibility at grain boundaries, fine-grained duplex microstructure was obtained through partial recrystallization. The treated material showed considerably improved high-cycle fatigue strength and more homogenous plastic deformation.
Damping behavior of Fe–16.0~28.0at%Al and Fe–23.0at%Al–2.0at%M (M=Cr, Mn, Co, Ni) in the wide strain amplitude range was examined and the damping mechanism was discussed. In Fe–Al binary single crystals, magneto-mechanical damping caused by irreversible motion of magnetic domain walls took place at low strain amplitudes. On the other hand, pseudoelasticity based on reversible motion of 1/4 ‹111› superpartial dislocations appeared in Fe–23.0at%Al single crystals which also contributed to the high damping capacity at high strain amplitudes. The effect of Cr, Mn, Co and Ni on the vibration attenuation of Fe–23.0at%Al crystals was also examined. As a result, Ni doping was found to be effective in the increase in both internal friction and yield strength of Fe–Al alloys.
To estimate the electromagnetic field circumstance of the particle-shaped material in high frequency electromagnetic field application, the penetration scale length is shown in this paper by means of micro-sized calculation model, in which the eddy current and displacement current is considered and finite element method based on jω method is used. From the calculation results, the following items are introduced. The eddy current, which is induced by external magnetic field, plays an important role, when electromagnetic field is applied to the particle-shaped materials in high-frequency. It is important that the electromagnetic field is in the high frequency domain where the side wave occurs, in order that the electromagnetic field is transmitted deeply into the particle-shaped materials. When the electrical conductivity of the particle substance of the particle-shaped materials varies, the eddy current distribution within the particle is different and the estimated penetration scale length has a peak value. In the high electrical conductivity, the eddy current has a clean circle within the particle, which flows around the external magnetic field direction. High Joule energy consumption is obtained. In the electrical conductivity at which the penetration scale length has a peak value, the eddy current flows in one-sided within the particle and small Joule energy consumption is obtained. In the low electrical conductivity, the eddy current flows in the same direction within all area of the particle, and high Joule energy consumption is obtained. The particle begins to behave like a dielectric and then the continuity of eddy current is not formed.
This paper describes the synthesis of zeolite-X from waste metals; in this synthesis, silicon sludge and Al(OH)3 from aluminum dross are separately solved in NaOH solution, leading to the generation of hydrogen, and then mixed with the desired molar ratio to synthesize zeolite-X; and residual liquid was repeatedly used as raw material to save Si and Na sources. During the synthesis, the effect of the cyclic use of residual liquid on the property of zeolite was examined and it was compared with the product synthesized from reagents of Al(OH)3, Si, and NaOH. Although the original raw materials used were industrial wastes, all products showed the same XRD patterns, Si/Al molar ratio (1.0–1.5), and BET surface area (500–600 m2/g) as the commercially available product. The use of the residual liquid increases the utilization ratio—21.4 mol% in Si and 7.8 mol% in Na—after three times of cyclic use. Inverse manufacturing of zeolite-X was experimentally validated.