Improvements developed in an electric furnace design for the production of refined ferromanganese (low carbon ferromanganese), using the Nodal Wear Model (NWM), are detailed in this paper. Likewise, the NWM can be used as an instrument which is able to simulate situations that have not yet been carried out on industrial scale and to predict, for example, the performance of the electric furnace lining, under operational conditions that could form a cold wall/bottom. Finally, the NWM has been applied to simulate and predict (refractory repair consumption) the operations of patching or hot repair during the furnace campaign.
Wetting phenomena have occupied an important position in the field of high temperature metal processing for a long time. The difficulties encountered in the high temperature experiments—especially the separation of one effect from another—have frustrated efforts to achieve a full understanding of the dynamic wetting phenomena which are present in many metallurgical applications. In this work the sessile drop method is used to study the effect of reactive gases on the dynamic wetting angle of a binary iron–carbon mixture on a ceramic substrate. The use of such a mixture enables the effect of dynamic gas–liquid reactions to be separated from the solid–liquid interactions. An experiment performed with SO2, O2 and N2 gases at 1773 K proved that liquid surface tension can drop dramatically but the changes in wetting angle are only minor ones. It is also noted that the relative change in the volume of the droplet can give information about carbon boil and collapsing surface tension phenomena upon comparison with changes in the wetting angle of the droplet.
Three-dimensional numerical computations for a single bubble rising in a liquid metal within a rectangular enclosure in a uniform vertical magnetic field are carried out. In this study, the bubble shape, the velocity field and the electric current density field interact with one another under the influence of the vertical magnetic field. This is a triple simultaneous problem. The pressure and the electric potential fields are obtained with an iterative procedure by the HSMAC method. The numerical results exhibit that the rising velocity of the bubble for the range of Hartmann number 0<Ha<75 is slightly larger than that of Ha=0 because of the drag reduction due to suppression effect on flow separation behind the bubble. On the other hand, the bubble rising velocity decreases monotonously with the increase in the Hartmann number for Ha>75 owing to deceleration effect on the fluid flow by the magnetic field. The bubble elongates in the direction of the uniform magnetic field because of the modification of the pressure distribution by the Lorentz force.
In order to gain a better understanding of deoxidation phenomena, there is a need to develop a model that could involve mass transfer, nucleating and growth kinetics of inclusion to simulate unhomogeneous state at the initial stage of Al deoxidation process. Based on the computation of the model for steel droplet with aluminum at center, it is found that the reaction zone between aluminum and oxygen in liquid steel is located in a limited zone at a certain fixed time and it is moved from center to outmost with the time going. For the zone besides the deoxidizer, i.e. aluminum, the supersaturation degree SO is very high at first, and then is decreased quickly, and the main part of oxygen in steel is absorbed by nucleation. In the other side, for the outmost zone, the main part of oxygen in steel is absorbed by growth of inclusion and the growth of inclusion lasts for longer time than that of inner zones.
Mineral changes of Philippine and Indonesia nickel lateritic ores during the sintering and the mineralogy of their sinter were studied in present work. A laboratory scale sintering pot was used to prepare the sinter samples. Thermo-gravimetric (TG) tests, differential thermal analysis (DTA), and X-ray diffraction (XRD) experiments were carried out to understand the mineral change of laterites. These measurements indicate that chlorite (Fe,Mg,Al)3(Si,Al)2O5(OH)4 and serpentine Mg21Si2O28(OH)34H2O are the primary phases, while FeO(OH) and (Fe,Mg,)3Si4O10(OH)2 are the minor phases in both Philippine and Indonesia nickel laterite. The XRD, scanning electron microscope (SEM), and energy dispersive spectrometer (EDS) were used to analyze the sinter samples; the results demonstrate that olivine (Mg,Fe)2SiO4 is the main bonding phase in both Philippine and Indonesia laterite sinters, and spinel MgFe2O4 is also found as the solid bonding phase in the Philippine laterite sinter.
Japanese cypress was carbonized partly at maximum carbonization temperatures TC, max=823, 1073 and 1273 K in order to obtain semi-charcoal with some residual volatile matter (V.M.). The semi-charcoal obtained at TC, max=823 K retained much V.M., mainly H2. Then, the semi-charcoal composite pellets have been prepared and reduced at reduction temperature TR=1073, 1173 and 1273 K in N2 gas atmosphere. Fractional reduction F (%) after 60 min of the carbon composite pellet using semi-charcoal particle with the size of 63–75 μm at TC, max=823 K was 19% at TR=1073 K and 40% at TR=1173 K, and was higher than any other pellets. Fractional reductions F (%) of the semi-charcoal composite pellets at TC, max=823, 1073 and 1273 K were over 90% for 60 min at TR=1273 K. The reducibility of semi-charcoal composite pellets was did not depend on residual V.M. at TR=1273 K. On the other hand, fractional reduction F (%) of the semi-charcoal composite pellet at TC, max=1073 K using semi-charcoal with the particle size of 23–35 μm was 38% for 60 min at TR=1173 K, and was higher than any other pellets using semi-charcoal with the particle sizes of 63–75 and 105–150 μm. As the size of semi-charcoal particle decreased, the reduction of iron oxide was much enhanced at TR=1173 K.
The unconsumed fine coke and pulverized coal in BF dust (gravitational dust and bag dust of hop pocket) under different PCI rates in BF at Capital Steel Co. was investigated in this paper. By means of microscopic and chemical analysis the percentage of unconsumed fine coke and pulverized coal were determined. It has been found that with increasing of PCI rate all the amount of BF dust at BF, carbon mass fraction, unconsumed fine coke and pulverized coal in BF dust increase. The amount of unconsumed pulverized coal in BF dust is about 5 to 7 kg/tHM less than that of fine coke at PCI rate between 135 to 200 kg/tHM. Under PCI rate of 200 kg/tHM, utilization factor of pulverized coal could reach over 98.52%. However at PCI rate of 190 kg/tHM the amount of unconsumed fine coke was increased suddenly and has reached about 10 kg/tHM in BF dust. This result indicates that under high PCI rate the worn coke in BF increased quickly, which results in the decreasing the permeability in the cohesive zone and lower part of BF. The quality of coke should be improved for increasing of the PCI rate in BF at Capital Steel Co.
The objective of the present study is the optimization of the ladle stirring operation through a multiphase mathematical model and an analogue physical model. Four cases were considered using one and two argon injection inlets with different configuration, where the multiphase steel/slag/argon system was simulated numerically in Three-Dimensional Unsteady State conditions and a water/oil/air system for the physical model was considered. The Volume of Fluid (VOF) model was employed to simulate numerically the interaction among the phases considering the surface tensions. The simulation results were evaluated by a fluidynamics analysis of the systems and by a numerical prediction of three important operation parameters: mixing time, lining refractory wear and slag opening. The implementation of two argon inlets did not reduce the mixing time; however, the slag layer opening was decreased in a 30%, and the refractory wear in terms of the skin friction coefficient value was also decreased in a 63%. These results confirm that it is imperative to consider, for numerical simulation, the three phases present during ladle operations.
In order to improve the efficiency of the desulfurization process utilizing the mechanical stirring method, the effect of flux dispersion on the hot metal desulfurization reaction was investigated in 1/8-scale water model and 70 kg-scale hot metal experiments. Flux dispersion behavior is divided into three stages, i.e., “non-dispersion,” “transition,” and “complete dispersion.” The desulfurization rate increases remarkably from the “non-dispersion” to the “complete dispersion” stage, corresponding to the change in the condition of particle dispersion. The relationship between the impeller position and the vortex depth is defined as the dispersion index, I. When the dispersion index was over 1, complete dispersion occurred in water model experiments, and the apparent rate constant increased remarkably in hot metal experiments. The observed diameter of the desulfurization slag was 1.4 mm, which is in good agreement with the calculated value, 1.55 mm. This means that fine desulfurization flux aggregates immediately after the addition of the flux. In order to increase desulfurization efficiency, it is important to control this particle aggregation.
A great number of research articles on the physical and mathematical modelling of tundish operation have been reported in the literature. Mazumdar and Guthrie1) summarized a large portion of these in a review article in ISIJ published in 1999. Because of the growing importance of tundish metallurgy and stringent demands regarding steel quality, a lot of further work has been done on tundish technology from1999 till date. This review summarizes the basics of physical modelling, mathematical modelling and the work of different researchers around the globe in the last decade i.e. 1999 to 2009. Current trends in research have been reviewed and critiqued.
In the present work a meshless method called Finite Point Method (FPM) is developed to simulate the solidification process of continuously cast steel bloom in both primary and secondary cooling region. The method is based on the use of a weighted least-square interpolation procedure. A transverse slice of bloom as it moves with casting speed is considered as computational domain and two dimensional heat transfer equation is solved in the computational domain. The present work is verified by the comparison of the surface temperature simulated by both FPM (as the present method) and finite volume method (FVM) as a usual method. Furthermore the solidified shell thickness simulated by the present FPM is compared with the solidified shell measured on a breakout bloom. In the secondary cooling region, the surface temperatures simulated by the FVM and measured by the thermovision machine are applied to validate the surface temperature simulated by the present FPM. The results reveal that the present FPM could be used successfully for the thermal analysis of the steel bloom to determine the temperature field and solidified shell thickness.
A new type of Austempered Ductile Iron (ADI) containing free carbides in its microstructure, called Carbidic ADI (CADI), has been purposely designed for applications requiring high levels of abrasion resistance, but still keeping impact toughness. Nevertheless, wear resistance is strongly dependent on the tribosystem, and this is clearly noticed for the abrasive wear mechanism. In earlier investigations, the authors used the low stress abrasion condition imposed by the ASTM G 65 standard for laboratory tests. Therefore, this study is intended to evaluate CADI wear resistance by means of field trials under different abrasion conditions. Apart from the additional laboratory tests indicated by the ASTM G 65 standard, two CADI prototype parts were evaluated: screw segments for animal food extruders, whose abrasion severity is considered of low stress type (similar to that imposed in the laboratory), and wheel loader bucket edges, whose abrasion severity is considered of high stress type. The results gathered have demonstrated that CADI behaves satisfactorily under low stress abrasion conditions, though performance is poor under high stress conditions. To justify the differences in wear behavior, the worn surfaces were studied by microscopy, and also scratch tests were performed in order to evaluate the interaction between the abrasive particles and the microstructure. It was found that the good performance is obtained when the groove size is smaller than the average carbide size, and that under this condition abrasion resistance increases with the increase in the carbide content and hardness. Contrarily, when the groove size is greater than that of carbides, the performance is impoverished with the increase in the carbide content.
A mathematical model of the continuous casting process, which explicitly incorporates the presence of slag, molten steel, heat transfer through the mould walls, and shell solidification, is presented. The model is based on the solution of the Navier–Stokes equations for the multiphase slag–steel–air system under transient conditions, including tracking of the interface between these phases. The use of an extremely fine mesh (100 μm) in the meniscus region allows, for the first time, the direct calculation of liquid slag infiltration into the shell-mould gap. Elsewhere, a coarser mesh is used to capture the influence of the metal flow on the overall solution. Predictions are compared with prior, cold model experiments and high temperature mould simulators. Excellent agreement was found for features such as slag film development and heat flux variations during the oscillation cycle. Furthermore, predictions of shell thicknesses and heat fluxes for a variety of simulated casting speeds are also in good agreement with plant measurements. These findings provide an improved fundamental understanding of the basic principles involved in slag infiltration and solidification inside the mould and how these affect key process parameters, such as powder consumption and shell growth. These parameters have a decisive effect on the formation of oscillations marks and transverse cracks, which are a major source of defects in the casting practice.
Cooling curve of sample surface of ultra low carbon steel at initial stage of solidification was measured using a new temperature measurement system that consisted of a two-dimensional optical pyrometer and a chill plate which was made of transparent sapphire glass. The presence of recalescence phenomena was observed on the measured cooling curve of ultra low carbon steel sample and the recalescence temperature existed in the range of peritectic transformation temperature as well as low carbon and middle carbon steel samples. The difference of temperature at each measured point of a sample surface was very small until the temperature reached the recalescence temperature, but the difference of temperature became larger after recalescence because the thermal deformation of solidifying shell seemed to be generated. From experimental results for tensile strength and density during solidification, these values changed depending on the phase and the change of values between δ phase and γ phase was large. As the unevenness of solidified shell was generated by deformation accompanying peritectic transformation and the degree of unevenness could be arranged by both temperature ranges, there was a difference of tensile strength and difference of density during peritectic transformation.
The formation of σ phase was investigated in Fe–Cr–Ni–Mo alloys with high nitrogen content. The amounts of the σ phase are correlated with the calculated δ-Fe values. The Md-PHACOMP (Phase Computation) method, which takes into consideration the effect of nitrogen and carbon content as well as microsegregation at the interdendritic region, can predict the σ precipitations. The numerical methodology for a multi-phase-field model can be also applied to σ phase formation by δ to (γ+σ) transformation.
The effect of substrate dissolution in brazing CP-Ti and Ti-15-3 using Ti–15Cu–15Ni filler metal has been performed in the experiment. Microstructures of infrared brazed joints are strongly related to dissolution of substrate during brazing. For the 1800 s brazed CP-Ti specimen, the depletion of Cu and Ni from the braze alloy into substrate cause eutectoid transformation of β-Ti into lamellar Ti2Cu and α-Ti. In contrast, dissolution of Ti-15-3 substrate into the molten braze during infrared brazing results in the 1800 s brazed zone alloyed with V, stabilizing the β-Ti to room temperature.
Corrosion performance of zinc coatings containing aluminum in excess of 5% was assessed in modified salt-spray tests. X-ray diffraction studies indicated that the corrosion products consisted mainly of simonkolleite Zn5(OH)8Cl2·H2O, hydrozincite Zn5(OH)6(CO3)2, and zinc aluminum carbonate hydroxide hydrate Zn6Al2(OH)16CO3·4(H2O). The content of Zn6Al2(OH)16CO3·4(H2O) in the corrosion product increased as the aluminum content in the coatings increased. SEM-EDX analyses revealed that the microstructural features formed by the primary aluminum-rich α-phase frequently corroded first and at a faster pace than the zinc-rich β-phase in these coatings. The volume fraction and morphology of the zinc-rich β-phase existing in the coatings as degenerated eutectic are the two main factors which determine the corrosion resistance of Zn–Al coatings under development. The corrosion resistance of coatings peaked at about 12% Al in this study.
The kinetics of strain aging in cold rolled multiphase steel processed for a yield strength of 250 MPa and a tensile strength of 450 MPa (250/450 MPa grade of mechanical strength) was studied by means of aging experiments in the temperature interval from 50 to 185°C and time intervals ranging from 1 to 4915 min followed by tensile tests. The aging kinetics law was determined in terms of changes in the bake hardening value with the aging time and temperature for specimens with a tensile prestrain of 0.5%. The steel studied showed two strain aging stages, the first one between 50°C and 155°C (for times shorter than 9 min) and the second one between 125°C (for times longer than 211 min) and 185°C. The changes in the bake hardening value suggest, for the first stage, a process controlled by the locking of the dislocations in the ferrite due to the formation of clusters and/or transition carbides, such as the ε-carbide, with an activation energy close to 70 kJ/mol and following a kinetic law with a time exponent of 0.4. In the second stage, the phenomenon is controlled by tempering of martensite, particularly the precipitation of transition carbides, ε-carbide and/or η-carbide. The corresponding activation energy is approximately 130 kJ/mol and the kinetics of this stage can be described with a time exponent of 0.5.
Microstructural evolution during intercritical annealing after rapid heating of cold rolled low carbon steels was investigated by EBSD and TEM. When the specimens were heated to above the Ac1 temperature before the completion of the primary recrystallization of α and then annealed, remarkable retardation of the primary recrystallization was observed, resulting in non-uniform grain size distribution of α. Because of the retardation, subgrains formed in non-recrystallized α are not consumed by recrystallized α and are thus able to gradually grow with annealing, and finally the grain size distribution of α becomes uniform. The analysis based on the rn−r0n=kt equation has shown that the subgrain growth in non-recrystallized α from the holding period of 100 to 1000 s follows n=3, indicating that the subgrain growth is controlled by the volume diffusion of Mn at α and γ interfaces. The transition of n from 3 to 2, observed at the holding time of longer than 1000 s, may be due to the gradual disappearance of the smaller γ phase at subgrain boundaries.
Grain boundary engineering (GBE) primarily aims to prevent the initiation and propagation of intergranular degradation along grain boundaries by frequent introduction of coincidence site lattice (CSL) boundaries into the grain boundary networks in materials. It has been reported that GBE is effective to prevent passive intergranular corrosion such as sensitization of austenitic stainless steels, but the effect of GBE on transpassive corrosion has not been clarified. In the present study, a twin-induced GBE utilizing optimized thermomechanical processing with small pre-strain and subsequent annealing was applied to introduce very high frequencies of CSL boundaries into type 304 austenitic stainless steels containing different phosphorus concentrations. The resulting steels showed much higher resistance to transpassive intergranular corrosion during the Coriou test, in comparison with the as-received ones. The high CSL frequency resulted in a very low percolation probability of random boundary networks in the over-threshold region and remarkable suppression of intergranular deterioration during GBE.
A fundamental study was carried out in order to fix CO2 on slag. The electronic arc furnace reducing slag was wet-ground by a vibration ball mill under CO2 atmosphere. The effect of grinding conditions on the behavior of CO2 absorption was investigated. The rate of the absorption of CO2 under wet grinding was larger than that under dry grinding. The total amount of CO2 absorption increased with the increase in total amount of the slag and water in case that the weight ratio of the water to the slag was kept constant. The CO2 was fixed as CaCO3 and Ca4Si2O6(CO3)(OH, F)2. Any compounds of Mg were not detected by XRD after the experiment. In the early stage of grinding, the CO2 was absorbed even if the grinding was stopped. The concentration of Ca in the water was larger than the solubility of Ca(OH)2. Hence, the absorption of CO2 was determined by the surface reaction that consisted of chemical reaction and mass transfer in liquid. In the latter stage of grinding, the CO2 was not almost absorbed immediately after the grinding was stopped. The concentration of Ca in water was small. Accordingly, the absorption of CO2 was influenced by the dissolution of slag into water. The amount of the exhausted CO2 was calculated from the electronic power which was necessary for operating this experimental apparatus. The amount of CO2 absorption was larger than that of the exhausted CO2 from a solar, an atomic, a wind and a water power plant.