The effect of the liquid/gas interfacial energy on the drain sink formation height has been studied using both mathematical and physical modeling. Initially, the mathematical model predictions of the drain sink formation height were compared with data from physical modeling, representing a situation with a low interfacial energy. The agreement was found to be good. Thereafter, mathematical modeling was done to evaluate the drain sink formation height at higher interfacial energies. In addition, an analytical expression was derived for the prediction of the drain sink formation height. The calculations using this equation were found to align well with both the experimental data as well as the numerical predictions. This analytical equation is suitable to use for determination of the drain sink formation height as function of the liquid/gas interfacial energy, liquid density, outlet radius and outlet length. In order to demonstrate its industrial usefulness the equation was used to predict drain sink formation heights for steel in a system with geometrical dimensions relevant for steel production. It was found that an increased interfacial energy lowered the drain sink formation height severely for small outlets, low-density fluids and short outlet lengths. In real plant practice, the predictions with the analytical equation yield that the effect of steel/argon interfacial energy decreases the predicted drain sink formation height by approximately 10% compared to if the interfacial energy was neglected.
Dissection investigation of blast furnace hearth was made at Kokura No. 2 Blast Furnace (2nd Campaign). Before blow-out, tracer response test was carried out in order to estimate the molten iron flow in hearth, and the measured data indicated that the depth of “effective” flow region of molten iron was extremely shallow. According to the result of the dissection investigation, the deadman was floating in hearth, and deadman coke was considerably degraded. Therefore, the poor permeability of the deadman is supposed to cause a downsize in the flow space of molten iron, which coincides with the prediction through the tracer response test. The numerical method to estimate the boundary shape of the deadman was developed by means of evaluating the stress field of the deadman in hearth. The calculated result was in reasonable agreement with the observed shape of deadman. In addition, based on the data obtained by analyses of the boring samples, the thermal equilibrium erosion shape of hearth refractory was evaluated by numerical simulation, and a good agreement to the observed shape was found.
The objective of this paper is to analyze the particle behavior at a bell-less top of blast furnace by using Discrete Element Method. The effect of chute angle on the flowing behavior or the particle segregation was discussed. The particles in the chute are centrifuged by the chute rotation with moving toward the outlet. The most of the smallest particles are pressed up against the chute side wall, while the larger ones stay at the outside of clustered particles due to the particle size segregation. The specific charged mass at charging area increases with increasing the number of charges, and the distribution of charged mass spreads toward the center of blast furnace, because the particles slide downward along with the slope of heap. The coke particles are pressed toward the center of blast furnace by the subsequently charged sintered ore particles with increasing the number of charges. The large collapse of coke layer is seen after 16 times charging under 36.9° and 43.1° in chute angle. It is found that the chute angle affects not only the particle segregation but also the collapse of coke layer strongly.
The kinetic study of the nitrogen dissolution into the molten steel was investigated by an isotope exchange technique. The effects of O, S, C, B, and Mn addition on surface reaction have been considered at 1873 K. Experimental results show that the rate determining step of nitrogen dissolution into molten Fe–O–S alloys would be dissociation reaction and the rate constant on bare surface of the liquid steel (k0) is 3.84×10−5 (mol/cm2·s·atm). The adsorption coefficients for oxygen, sulfur, and boron which were applied the dissociation determining model were calculated to be KO=120, KS=65, and KB=0.9, respectively. In case of manganese addition, the rate constant can be increased with increasing the content of manganese. It seems that rate constant of bare surface of Fe–Mn alloy should be affected by addition of manganese.
Conservation equations for mass and momentum with a two equation k–ε model are solved for the continuous phase along with a discrete phase particle modeling (representing gas bubbles) in the RH degasser to predict the circulation flow rate of water in a scaled down model and then the numerical solution has been extended to the real plant case for the prediction of steel circulation flow rate in the actual RH vessel. The prediction of the circulation flow rate of water from the present numerical solution matches reasonably well with that of the experimental observation, taking into account various uncertainties those have been imbedded in the numerical model. RH operation for multi up legs and single down leg for a water model shows that the circulation flow rate falls with the number of up legs and there is an optimum number of down legs for which the circulation flow rate is the maximum for the case of a single up leg. For the actual RH operation in plant it was seen that the circulation flow rate increases with the increase in snorkel diameter and snorkel immersion depth (SID). However, it is apparent that there is existence of optimum SID for maximum circulation flow rate. For different down leg immersion depth the circulation flow rate in the RH depends heavily on the up leg immersion depth. The actual RH operation of the plant for the multi up leg and down leg cases was found to be exactly similar in nature to that of the water model cases.
In most cases, the slag used in hot metal dephosphorization is saturated with dicalcium silicate (C2S) and contains two phases—solid C2S and liquid. It is known that C2S and tricalcium phosphate (C3P) form a solid solution over a wide range of composition. The distribution ratio of P2O5 between the solid solution and the liquid slag phase has been reported to be very high. In order to determine the maximum possible concentration of P2O5 in the solid solution, the distribution ratio of P2O5 in slag containing a high concentration of P2O5 was measured in this study, and the influence of MgO and MnO on the distribution ratio was also investigated. CaO–SiO2–Fe2O3 slag containing up to 18% P2O5 was melted at 1873 K and then cooled to 1673 K at a rate of 10 K/min. During cooling, the solid solution of C2S and C3P precipitated from the liquid slag. A linear relationship, which was independent of the lime/silica ratio and P2O5 content, was found to exist between the distribution ratio of P2O5 and the T·Fe content. On the contrary, the concentration of P2O5 in the solid solution was strongly influenced by the lime/silica ratio and P2O5 content. If the P2O5 content was high enough and the T·Fe content was controlled to show the high distribution ratio, the concentration of C3P in the solid solution can be increased to 100%. No significant change was observed in the distribution ratio upon the addition of MgO and MnO.
A method is proposed for the prediction of surface crack formation in continuous casting, based on reduction of area (RA) functions measured by the tensile test. From the RA values a critical strain is deduced which is then compared with the strain developed in the surface of the strand. The latter is computed with a thermo-mechanical model. There is the fundamental difference in the tensile test and in continuous casting that in the first the deformation is carried out under conditions of constant temperature (T) and strain rate whereas in the second, temperature and strain rate are transients. For the application of the RA(T) function to the transient conditions a procedure is used that is known from the computation of continuous transformation diagrams from isothermal transformation diagrams (Scheil procedure) and from the computation of fatigue strength of machine parts. That is the strain developed in the strand surface during a time increment is weighted by division through the critical strain for rupture at the conditions existing during the time increment, and the weighted strains are then added up. Rupture occurs when the sum, or integral, attains a certain value. The method is applied to the prediction of transverse cracks on the slab surface of aluminum deoxidized carbon steel.
Determination of best combination of current and frequency of an electromagnetic stirrer (EMS) of a billet caster is of prime importance for ensuring good internal, surface as well as subsurface quality of billets. In the present study, this optimization of current and frequency values is achieved very efficiently using image processing techniques. The EMS currents and frequency are varied between 240–300 A and 3–5 Hz respectively during casting and corresponding billet samples are collected. Samples are also collected from beginning, middle and end of casting heats in order to asses the influence of tundish superheat. The samples thus collected are scanned using ultrasonic C-scanner to get the full color image of samples. The grabbed images are processed and analysed using Matlab Image Processing Toolbox in RGB color space. Finally, data of various defects as obtained from image processing, in each grades of steel are compared for determining the best combination of EMS parameters. It has been found that length of equiaxed zone increases significantly with increasing EMS current up to 280 A, almost for all close casting grades. Increasing EMS current beyond 280 A increased the length of equiaxed zone marginally but chances mould powder entrapment at the surface of the billet and erosion of submerged entry nozzle is more. Central shrinkage number of subsurface and central crack also reduced significantly up to 280 A EMS current. Marginal improvement in billet quality is also observed when 3 Hz EMS frequency is used but the improvement in the quality is not significant.
This paper presents a model for the hot rolling scheduling problem (HRSP), which is derived from the actual steel production. The model is characterized by some new features, such as the rolling length of the consecutive slabs with the same width, temperature jump between adjacent slabs. The warm up part is a minor part of a turn and is usually ignored, but it affects directly the product quality. Therefore, besides the slab sequence in the staple material section, we also consider the slab sequence in the warm up material section. These features make the solution methodology more difficult. Therefore, two hybrid strategies are proposed to determine good approximate solutions for this complicated problem. The first one (CT_ACO) is a hybrid strategy based on the solution construction mechanism of ant colony optimization (ACO) with cyclic transfers (CT). The second one (CT_SS) is to hybridize scatter search (SS) and CT neighborhood search. Moreover, we design a decision support system in which two algorithms have been embedded for the HRSP. The most popular feature of the system is the architecture of component management, which allows us to modify easily some components according to the practice situation. The computational experiments show that CT_ACO is superior to general ACO, and CT_SS is also better than SS in terms of solution quality. The CT_ACO method and CT_SS have more potential for improvement to solve the HRSP compared with the current scheduling method, and the CT_ACO generates slightly better quality solutions than CT_SS algorithm.
One of the important qualities of a cold-rolled steel sheet is the surface texture, which is obtained by imprinting a dull-roll surface texture. It is controlled by actual operation data and experiences, because the mechanism of the surface imprinting has not been clarified because of the complexity of elastic–plastic deformation of the rolled sheet in temper rolling. In this paper, surface imprinting is investigated in temper rolling as dry rolling of a 4-high rolling mill. Temper rolling experiments for as-annealed low-carbon steel strips and as-annealed high-carbon steel strips were conducted in the range of 1 to 11% reductions. Electric-discharged dull rolls and shot-dull rolls were employed. Surface microstructures of temper rolled strips were observed directly, as well as surface textures in terms of the arithmetical mean deviation of the assessed profile (Ra), material ratio curves, and probability densities applied to compare the surface imprinting. As a result, the electric-discharged dull roll shows better surface imprinting than the shot-dull roll. The peak part of the roll surface is more easily imprinted on the steel sheet to form the valley part when the electric-discharged dull roll is used than when the shot-dull roll is used.
Dynamic recrystallization behavior of twin roll cast low carbon steel strip was investigated in this paper in an attempt to provide guiding deformation parameters for the on line hot rolling. As cast strip was reheated and soaked with austenite grain size similar to the width level of the as cast columnar structure. Tensile test was used and the deformation temperature is in the range of 900 to 1100°C and the strain rates are 0.01, 0.1 and 1 s−1. Activation energy and stress exponent were determined by regression to be 306 kJ/mol and 4.69 respectively. The ratio of critical strain to the peak strain εc/εp is 0.65, and that of critical stress to the peak stress σc/σp is 0.92. Dependence of the peak strain εp on the initial grain size D0 and Zener–Hollomon parameter Z is εp=9.1×10−4×D00.48Z0.13. Kinetics of the dynamic recrystallization and the recrystallized grain size was predicted using models published. The as cast coarse austenite will be dramatically refined after complete dynamic recrystallization under low deformation temperature and slow strain rate according to the predicting results.
Resistance spot welding (RSW) is one of the most widely used processes in sheet metal fabrication. Although used in mass production for several decades, RSW has a major problem of inconsistent quality from weld to weld, which results from both the complexity of basic process as well as from various process conditions, noise and errors. There have been a number of investigations on monitoring and controlling the resistance spot welding of low carbon steel by using dynamic resistance, but those for stainless steel are limited because the dynamic resistance has descent property. Dynamic resistance curve in spot welding for low carbon steel has a typical shape: the resistance drops sharply at the beginning, and then rises; before the current is terminated, the resistance starts to drop, which results in a peak. Unlike low carbon steel, dynamic resistance for stainless steel decreases rapidly at the beginning and then decreases at a reducing rate. The objective of this research is to explore the effects of various process conditions in spot welded stainless steel on quality by using dynamic resistance. The process conditions studied in this research are chosen to be the most often observed in production, such as variations of welding parameters, edge weld, small weld spacing, poor fitup and axial misalignment. A series of experiments will be conducted to research how process conditions affect the dynamic resistance. The results show that dynamic resistance responds well to the variations of process conditions and can serve as an important indicator of weld quality.
The equilibrium internal oxidation of CMnSi TRIP steel at intercritical annealing temperatures in a +3°C dew point N2+10%H2 atmosphere was investigated by means of high resolution transmission electron microscopy of cross-sectional samples. The experimental conditions are considered to lead to the selective internal oxidation of Mn and Si. The intercritical annealing however resulted in the formation of three types of isolated particles on the surface: 200–340 nm size single crystal MnO oxide particles, crystalline 30–60 nm size xMnO·SiO2 (1≤x≤4) and amorphous α-xMnO·SiO2 (0<x<0.9) oxide particles. A thin 25–35 nm film of crystalline xMnO·SiO2 (1≤x≤2) was present between these particles. Thin discontinuous transition oxide layers with a thickness of 25–55 nm were formed between the MnO particles and the Fe matrix. The composition of this xMnO·SiO2 layer varied from 1≤x≤2 for crystalline xMnO·SiO2 to 0<x<0.9 for amorphous α-xMnO·SiO2. In the subsurface region, two distinct types of internal oxidation zones were observed. In the first internal oxidation zone, within the 1 μm range below the surface, fine ferrite grains with a grain size of ~550 nm were observed. Crystalline xMnO·SiO2 (1≤x≤2) oxide particles with a diameter of 80–250 nm were present in this internal oxidation zone. In the second internal oxidation zone, from 1 to 4 μm below the surface, the ferrite grain size was about 4 μm, and similar to the grain size in the bulk. Inter-granular amorphous α-SiO2 particles, 180–300 nm in diameter, and an extensive, apparently continuous, grain boundary network of amorphous α-SiO2 were observed in this second internal oxidation zone. The observed oxide distribution is related to the difference in selective oxidation behavior of the main alloying elements Si and Mn and very likely due to the difference in their diffusivities, oxide stability and oxide solubility during intercritical annealing. The decarburization of the matrix during annealing in a high dew point atmosphere is also likely to play a role. The observed selective oxidation is relevant for the continuous galvanizing of high strength steels. It is expected that the presence of a thinner oxide film is less likely to prevent the formation of the inhibition layer and the wetting of the steel surface by the liquid Zn during hot dip galvanizing. Operation of the annealing furnace at a higher dew point during the processing of Si-bearing steels such as conventional CMnSi TRIP steel may therefore lead to a decrease of galvanizing surface defects.
In order to establish the necessary conditions for producing high strength hot-dip Zn galvanized steel sheets for automotive use on a Continuous Galvanizing Line (CGL), a thermodynamic calculation of the selective oxidation behavior of Si, Mn-added high strength steel sheets was introduced, assuming a model in which an equilibrium is reached locally at the outermost surface layer of the steel sheet. The applicability of that model is confirmed by comparison with experimental results. Both the calculated chemical potential diagram for an Fe–Si–Mn–O system and an isothermal pseudo ternary phase diagram for an FeO–SiO2–MnO system, explain the reaction path of the selective oxidation behavior in 1 mass% Si and 0.01–3.01 mass% Mn-added steel. As this simulation model demonstrates good agreement with experimental results, this thermodynamic calculation is extremely appropriate for prediction of the surface oxidation behavior of Si, Mn-added high strength steel sheets. The transition from selective surface oxidation to internal oxidation can be explained by considering the oxygen flux in the oxidation film and the effect of the selective surface oxides on the inward diffusion behavior of oxygen. By thermodynamic calculation of the suppression condition of SiO2 film formation, which deteriorates the molten Zn wettability of the surface of annealed sheets, a process control model for industrially stable production of high strength hot-dip Zn galvanized steel sheets with arbitrary chemical compositions is proposed. Based on this research, a comprehensive surface control technology for high strength steel sheets is established.
Hot-dip 55%Al–Zn alloy coated steel sheet has superior corrosion resistance both on flat panel and near shear cut edge in various atmospheric environments. However, the corrosion often occurs near the shear cut edge in continuous wet conditions, for example, NaCl solution spray test (SST, JIS Z2371), and this has been explained by galvanic model. In this paper, it is clarified that the corrosion near shear cut edge is suppressed by artificial sea water and its second ingredient, MgCl2. To make clear the corrosion mechanisms on MgCl2 suppression of the corrosion near shear cut edge, the measurement of cathodic polarization curve on the Fe electrode after the corrosion test using a AZ/Fe/AZ galvanic electrode, the estimation of corrosion products by numerical analysis in consideration of the substances migration and the precipitation reactions, and the analysis of corrosion products by FT-IR spectroscopy were conducted. As a result, in the galvanic condition, it is clarified that Mg(OH)2 precipitates on the Fe exposed cut edge. Moreover, the corrosion near shear cut edge is suppressed by the effect of the cathodic reaction suppression of Mg(OH)2.
The austenite of the Hadfield type manganese steels (1.0–1.4% C; 12–14% Mn), even though able to be hardened by impact, explosion, etc., is very ductile, tough and deformable, so that the industrial parts made with this material often suffer important geometric deformations during service. To minimize this problem, it is necessary to reinforce the austenitic matrix with hard, microscopic and dispersed ceramic particles, such as TiC, in order to increase the austenite stiffness while maintaining its toughness. Indeed, the development of a liquid metallurgy process enabling the reinforcement by means of the addition of the ceramic material to the molten metal in the melting furnace would become an important advance in this field. Nevertheless, these ceramic products are prone to the coalescence and have poor wettability by the molten bath, so that, their yield and the subsequent property improvement is very low. These disadvantages are solved if the ceramic particle is a complex carbide (TiMo)C bonded by metallic Fe, having a masteralloy of the Fe(TiMo)C type made by self-propagated high temperature synthesis (SHS). After that, its addition to the liquid austenitic manganese steel, the pouring of the mix (steel+carbides), its solidification, for example in sand molds, and the subsequent heat treatment (solution annealing and rapid quenching) produces composite castings or parts composed by an austenitic matrix and discrete carbide (TiMo)C particles inserted in it. This paper describes the process required to fabricate such a material and its characteristics.
The use of charcoal as a fuel and reductant in ironmaking and steelmaking in place of fossil fuel-based carbon sources has been assessed from both an environmental and economic point of view. Life cycle assessment methodology has been used to indicate potential reductions in greenhouse gas emissions resulting from charcoal substitution rates up to 100% in the integrated, direct smelting and mini-mill routes for steelmaking. The results indicated that based on typical costs of charcoal and coal, charcoal is not competitive with coal in the steelmaking applications considered. However, the introduction of a carbon trading scheme or carbon taxes can be expected to improve the competitiveness of charcoal compared to coal. Based on a long-term price of $US90/t for metallurgical coal, a carbon tax in the order of US$30–35/t CO2 would be required with the direct smelting and integrated routes for the overall charcoal and coal costs to be roughly equal, including a charcoal electricity co-product credit. However, if the recent increase in price of metallurgical coal is sustained for an extended period of time, the required carbon tax rate would fall to about US$18/t CO2.
In ironmaking and steelmaking processes, dehydration technology is often recognized to be a key process for the successful operation. That is not an exception in recycling process of valuable elements such as Fe, Ni, Cr and so on by reducing the wasted materials including dust, scales and sludge, generated in each steel works. This investigation basically focused on the availability of microwave technique for dehydration stage of sludge generated in a stainless steel mill. Actually sludge is well-known as a wasted resource difficult to be dehydrated. Unless dehydration of such resource is successful, some problems with slow heating and/or burst of briquettes may arise. In this study, prior to the industrial studies, dehydration experiments of goethite were performed. The results showed that the microwave treatment could heat up the specimen directly from inside of specimen while being heated from the outside by the electric furnace. Thus the dehydration ratio resulted higher in the microwave irradiation, indicating the benefit of the microwave treatment. Thereafter the microwave technique was tried for dehydration of industrial sludge. Consequently, the effectiveness of microwave treatment was confirmed because 34 mass% weight-loss after the microwave treatment corresponded to the complete dehydration while 7 mass% weight-loss after heating in a conventional electric furnace. If application to industrial practice is realized, it is expected that the problems brought by the conventional way will be hopefully solved to prevent burst of agglomerations.