In the present study, the neural network approach was applied for the estimation of sulfide capacities (Cs) in binary and multi-component melts at different temperatures. The calculated results obtained using neural network computation were plotted against the experimental values for comparison comparative purposes. Besides, iso-sulfide capacity contours on liquid regions of some ternary melt phase diagrams were generated and plotted by using neural network model results. It was found that calculated results obtained through neural network computation agree very well with the experimental results and more precise than those of some models.
Solid state calcium ferrite formation reactions between different kinds of iron oxides and CaO under various PO2 at 1273 K have been investigated. The calcium ferrite formation rates are evaluated by using thermogravimetric method. The phase identification and quantification of calcium ferrites in the experiment have been carried out by using X-ray diffraction method (the Rietveld method). It has been found that intermediate calcium ferrite phases of CaFe2O4 and CaFe3O5 are formed prior to the Ca2Fe2O5 formation when Fe2O3 and Fe3O4 are used as a starting iron oxide, respectively. When starting from wüstite, intermediate calcium ferrite phases are not formed. The rates of Ca2Fe2O5 formation are found to be different depending on the starting reactant iron oxide phases. The Ca2Fe2O5 formation rate from wüstite is faster than that from Fe3O4, and that from Fe3O4 is faster than that from Fe2O3. It is also found that the Ca2Fe2O5 formation rate starting from Fe3O4 decreases with pO2, but that starting from wüstite is independent from pO2.
In order to carry out the de-sulfurization of liquid Fe, solid CaO is usually used as a flux, but some of solid CaO particles are not melted into molten slag, and all CaO are not always used for the refining. We have investigated how to use the solid CaO directly and efficiently for the above refining processes. Solid CaO particles have small capillary tubes from their surface to inside. When a molten slag is wetted with solid CaO, the molten slag containing some impurities such as CaS and P2O5 is expected to penetrate into those capillary tubes. Although chemical reactions in solid phase are generally believed to be very slow due to slow diffusion in solid phase, those impurities are absorbed in solid CaO rapidly by capillary force and they are removed from molten steels. We named this refining process as Capillary Refining. In the present paper, we have tried to apply capillary refining to de-sulfurization of liquid Fe and carbon-saturated liquid Fe by using molten CaO–Al2O3 and CaO–SiO2–MgO–Al2O3 slags.
The carbide capacity of the CaO–SiO2–MnO slag, which is the main system produced during Mn alloys processes, through the wide composition region has been measured at 1773 K to understand the effective slag composition on the solubility of carbon in molten slags during SiMn production processes. The carbide capacity is strongly affected by slag composition and this tendency can be reasonably estimated by employing the activity of lime and the activity coefficient of CaC2 as a thermodynamic factors affecting carbide capacity. Considering the high concentration of MnO during SiMn smelting process, the lime to silica ratio of 0.8 (±0.1) is recommended in view of high ability of carbon dissolution. The carbide capacity of the CaO–SiO2–MnO slag can be expressed as a linear function of the activity of lime and the optical basicity. The carbide capacity of the CaO–SiO2–MnO slag increases more significantly than the sulfide capacity does as the basicity of the slag increases.
The chlorination and evaporation behaviors of Zn in the ZnO–Fe2O3–CaCl2 system was studied by gravimetry from 1173 to 1323 K and the effects of carrier gas flow rate, temperature and the initial Zn content of specimen on the chlorination rate were investigated. Moreover, thermodynamic calculation was carried out. Fe and Zn were separated because Zn was selectively chlorinated by CaCl2 from ZnO–Fe2O3 system and volatilized as ZnCl2 while Fe remained as oxide in chlorinated residue. From the chemical analyses, it was clarified that the volatilization of ZnCl2 mainly cause the weight loss of specimen. Based on these results, the chlorination mechanism and kinetic model were discussed. The weight change of specimen was expressed as a function of reaction time reasonably well by assuming the first order reaction with respect to presumed ZnCl2. Apparent activation energy of chlorination reaction, calculated from obtained reaction rate constants for various initial Zn contents, was in the range between 107 and 172 kJ/mol. It is considered the rate determining step of chlorination is chemical reaction, such as the reaction between ZnO and CaCl2, or the interfacial evaporation of ZnCl2 from the specimen.
Sinters were produced in the pilot plant using four different ore mixtures with varying proportions of iron ores, fluxes and coke. All the resulting sinters were characterised by chemical and granulometric analysis, degradation testing during reduction in the blast furnace (RDI test), cold resistance testing (Tumbler test), reducibility testing, determination of softening and melting temperatures, and determination of the sinter structure by electron microscopy. The obtained result allow for the establishment of better operation conditions to manufacture sinters.
Rapid iron melting initiation and molten slag separation which take place in carbon composite iron ores are quite interesting phenomena, but their mechanisms have not been established yet. Since the size of carbonaceous material and iron ore particles is tiny in carbon composite iron ores, molten slag can dynamically play a critical role in the iron melting initiation and the slag separation. The behavior of the molten slag was clarified by direct observation of phenomena occurring in a simplified carbon composite agglomerate sample (iron disk–slag particle–graphite or coke particle) via a confocal laser scanning microscope combined with an image furnace. It was found that the molten slag wetting induced the iron melting initiation by attracting graphite or coke to iron and the molten slag separation took place with iron melting propagation. However, the high content of coke ash could suppress the iron melting initiation. In addition, the mechanism of molten slag separation from Fe–C melt was verified by phase field modeling.
Flows of solid particles and air in a model blast furnace have been simulated using Distinct Element Method (DEM) for the particles and Finite Difference Method for the numerical analysis of Navier–Stokes equations with the interaction terms between the air and the particles. The flow of solid particles, the air flow, the raceway and the packing fraction distribution are presented. The raceway depth, the diameter of particle inflow area and the raceway height which quantitatively represent a raceway are also presented and compared with the experimental data (CAMP-ISIJ, 16 (2003)). The fairly good agreement obtained by the comparison indicates that our simulation results are sound and the simulation results would represent the flow mechanisms of the solid particles and the air in the model blast furnace, and the simulation method that the Lagrangian motion of particles and the Eulerian motion of the air are simultaneously solved is a useful tool for predicting the flow fields of particles and the gas in a blast furnace. Unsteady state solutions of these flows suggest that dynamical characteristics in the model blast furnace are unstable and fluctuate, and that an unusual phenomenon would happen under some conditions even in the small scale model blast furnace.
Ninety-five percent bulk mixing times were determined experimentally in water models (D=0.30 m and D=0.60 m respectively) of a 140 T industrial ladle fitted with dual ‘plugs’ (located diametrically opposite at mid bath radius position) in the presence of an overlying, second phase liquid. Experiments were conducted to investigate the influences of gas flow rate, liquid depth, thickness of the upper phase liquid together with the latter's physical properties on mixing time. Within the range of variables studied, it is observed that besides gas flow rate, liquid depth and vessel radius, thickness of the upper phase liquid has the most significant bearing on mixing times. In contrast, considerably less pronounced effect of density and viscosity on mixing was noted. Dimensional analysis and regression of the experimental data show that 95% bulk mixing times in slag covered, dual plug fitted ladles can be described, in terms of relevant dimensionless groups, via:
in which, Q is the gas flow rate, L is the depth of liquid, R is the vessel radius, ΔL is the thickness of the overlying liquid, ρL is the density of the bulk liquid and νs is the kinematic viscosity of the upper or slag phase. Mixing correlations applicable to slag covered, dual plug fitted ladle and its slag free counterpart were found to bear striking similarity. This, as a possibility, suggests that embodying an additional factor, (<6(ΔL/L)0.3νs0.033(Δρ/ρL)−0.044) into a mixing correlation applicable to a slag free, gas stirred ladle, a correlation for an equivalent slag covered system can be derived. The hypothesis has been tested against axi-symmetrical gas stirred ladle system and towards this, relevant experimental measurements, mixing correlations etc. reported on such systems were applied. These suggest that 95% bulk mixing time in slag covered, axisymmetrical ladles can indeed be predicted reasonably well embodying the aforementioned addition factor into an existing correlation applicable to an equivalent slag free system.
Thermal stress simulations by the finite element method (FEM) are widely used to analyze refractory damage caused by mechanical factors. Issues studied by FEM simulation of refractories include joint conditions, and friction between refractories. The static friction coefficient and dynamic friction coefficient between MgO–C refractories with various surface conditions were measured. And the effects of joint conditions and friction force on the thermal stress analysis of the refractory lining in the barrel and cone of the converter were investigated numerically. The results are summarized as follows. (1) The friction coefficient between refractories that had various surface conditions was measured. As a result, a static friction coefficient of 0.52 and a dynamic friction coefficient of 0.42 were obtained for the friction working between the surfaces of baked MgO–C refractories. (2) It is necessary to consider friction force in the thermal stress analysis because local abnormal increases in stress occur, corresponding to large displacement of the bricks. Considering the situation of wear brick in operation, it was appropriate to apply for the value of baked brick as a friction coefficient. (3) The effect of the joint conditions used here, which were contact element, gap element, and anisotropy of mechanical property, on the results of calculations of thermal stress by FEM was comparatively smaller than that of friction force when friction force was considered. If the logic of displacement and stress transmission on two bricks is considered, contact element is appropriate from the viewpoint of stress transmission.
This paper presents the new experimental facility LIMMCAST which was designed for modeling fluid flow and transport processes in the continuous casting of steel. The facility operates at temperatures of 200–400°C by using the low melting point alloy SnBi. The main parameters of the facility, including the dimensions of the test sections, will be given. The resultant possibilities with respect to flow investigations in the tundish, in the submerged entry nozzle, and in the mould will be discussed. Over the period of assembling and commissioning the LIMMCAST facility, the small-scale set-up Mini-LIMMCAST was employed which uses the alloy GaInSn that is liquid at room temperatures. At this precursory facility an experimental program was started which is focused on quantitative flow measurements in the mould and in the submerged entry nozzle (SEN). The Ultrasound Doppler Velocimetry (UDV) and the Contactless Inductive Flow Tomography (CIFT) were applied to determine the flow structure within the mould. First experimental results will be presented here for a single and a two-phase flow in which argon gas bubbles were injected at the inlet of the SEN. According to the concept of the electromagnetic brake the impact of a DC magnetic field on the emergent jet flow from the SEN has been studied.
This paper investigates how the basicity and alumina content in synthetic slags influence the crystallization behavior that takes place in a heat flux simulator for mold slags. The purpose is to elucidate the variation in crystallization behavior for model slags that are expected to be glassy, partly crystalline and fully crystalline in order to correlate the changes in heat flux to the dynamic solid evolution that occurs in the simulator. Three levels of alumina content (3, 15 and 25 wt%) were chosen to investigate the heat transfer behavior through slag film which have different tendency of reaction with molten steel during continuous casting of high aluminum containing Transformation Induced Plasticity (TRIP) steels. A Confocal Scanning Laser Microscopy (CSLM) was used to develop TTT diagrams for the slags. XRD and SEM were also used to analyze the micro-structures of the crystalline phases. The measured heat fluxes through the mold slags tested were found to increase, as the crystallinity of the slag film decreased with decreasing basicity and alumina content. It was found that the crystallization temperature increased, while the incubation time for crystallization decreases with increasing basicity and alumina content. The increase in alumina content induced the precipitation of CaF2 during cooling process and hence a change in the crystalline phase from Ca4Si2O7F2 to Ca2Al2SiO7.
In as-cast structure of AISI M2 steel, the predominant type of eutectic carbides is M2C, the morphology of which has crucial influence on the distribution and dimension of carbides in final products. In the present work, the morphology and properties of M2C carbides formed at different cooling conditions have been investigated by means of optical microscope (OM), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM), X-ray diffraction (XRD) and differential thermal analysis (DTA). With increasing cooling rates, the morphology of M2C transforms from the lamellar type to the rod-like one, and the two carbides show different growing characteristics during solidification. Compared with the lamellar carbides, rod-like M2C is less stable and decomposes faster at high temperatures, accelerating the separation and spheroidization of carbides, even after hot deformation. It is concluded that the formation of rod-like M2C in cast ingots promotes homogeneous distribution and refinement of carbides in the final products, favoring the improvement of mechanical properties of high speed steels.
Molecular dynamics simulations have been performed to give an estimate on the solid–liquid interfacial properties of bcc iron, namely the kinetic coefficients and solid–liquid interfacial energy. The kinetic coefficients for different orientations were estimated from the propagation velocity of planar solid–liquid interfaces. The anisotropy of kinetic coefficients, μ, was confirmed to be μ(100)>μ(110), which is similar to the literatures using other interatomic potentials. Moreover, growing and shrinking behavior of the freestanding spherical crystal and semi-spherical crystal on the substrate in the undercooled liquid was examined. There is a critical temperature dividing shrink or growth of both the freestanding spherical crystal and semi-spherical crystal on the substrate. The solid–liquid interfacial energy was then estimated from Gibbs–Thomson relation in the critical temperature as a function of the inverse of crystal radius.
A new slurry-making method, called the nucleation-accelerated semi-solid slurry (NASS) method, was developed to fabricate high-quality semi-solid slurry with fine and uniform globular microstructures. The method's application to rheo-diecasting of ADC10 alloy was investigated. To enhance the heterogeneous nucleation of primary α particles in the initial stage of solidification, various types of funnels, including the pouring system in the slurry-making vessels, were designed and estimated by thermal analysis. It was found that the heterogeneous nucleation of primary α particles was closely related to the temperature–time history and the flow pattern. In the present study, the NASS method was set up based on the optimized funnel. It consisted of a specially designed conical-shaped funnel and the electromagnetic stirring (EMS) unit for artificial agitation. The conical-shaped funnel generated swirly flow pattern in the melt. This was further exaggerated by the EMS in the slurry-making vessel during the pouring stage, resulting in a copious heterogeneous nucleation. The qualities of the slurry were investigated using optical microscopy and rheo-diecasting. To study the effect of process parameters, the semi-solid slurry of ADC10 alloy was rheo-diecast using an 85-ton high-pressure die casting (HPDC) machine. Microstructural observation and hardness test were then carried out on the rheo-diecast specimens. The rheo-diecast products of the NASS method showed fine and uniform microstructures, with primary α-globules diameter averaging 39 μm and form-factor indicating a degree of globularity of 0.9. The optimized heat treatment condition for the rheo-diecast product of ADC10 alloy was achieved at the solution temperature of 490°C for 30–60 min, water quenching, and age hardening at 180°C for 7–8 h.
This article proposes a new mixing model for predicting the composition distribution in continuously cast steel during a grade transition. The transient model consists of two sub-models, one for mixing in the tundish and the other for mixing in the liquid pool of the strand. The Cho and Kim's simple tundish mixing model (which is very efficient and practical) is adopted as the present tundish model. For the mixing model in the strand, the concept of Cho and Kim's tundish model was extended to the strand. In order to verify the proposed model, plant tests were conducted on three kinds of casters (slab, bloom and thin slab caster) during the grade transition period of continuous casting under various conditions. The real grade intermixed slabs and blooms were produced and the composition distributions were measured and compared. When the proposed model was applied to several cases of the slab, bloom and thin slab casting, the numerical results were found to be in good agreement of the experimental data. These findings verify that the proposed model is capable of tracking mixing phenomena for arbitrary casters and operating conditions.
An electromagnetic shield was developed to improve the wavy meniscus profile in billet continuous casting with in-mold electromagnetic stirring (M-EMS). The characteristics of this shield were investigated through coupled simulation of the electromagnetic and the flow field. These numerical studies found that the designed shield decreases the electromagnetic force near the meniscus to 50% whereas that in the M-EMS core region is reduced about 18%. The designed shield was applied in the real billet caster with M-EMS. The imposed current was increased to compensate the reduced electromagnetic force near the M-EMS core. A close inspection of the produced billets found that the proposed shield greatly reduces the meniscus height even in the case of a stronger rotation flow in the mold.
A 0.036% Nb microalloyed steel was deformed in torsion over the temperature range 816–896°C in a 2%H2–Ar gas atmosphere. Strains of 0.5–5.0 were applied at strain rates of 0.04 and 0.4 s−1. The experimental parameters were varied in order to study the effects of strain, strain rate and temperature on the formation of ferrite by dynamic transformation (DT) at temperatures above the Ae3. The critical strain for ferrite formation by DT was 0.5 and the volume fraction formed increased with strain and slightly with strain rate. It was also observed that the applied strain has a far greater influence on the transformation than the time. Average ferrite grain sizes of 2 to 3.5 μm were produced, the size increasing with the transformation temperature and decreasing strain rate. By comparison with the behavior of plain C steels, it is evident that the addition of niobium slows the reverse transformation to a considerable degree. Two stages were detected in the reverse transformation: i) in stage I, observed during the initial 200 s of isothermal holding, the deformation-induced ferrite was fairly stable; ii) in stage II, observed after 200 s of holding, the reverse transformation began to take place, going to completion in about 400 s. The results of these experiments support the view that it is the stored energy of the ‘inhomogeneously’ distributed dislocation (i.e. those in shear bands and sub-boundaries) that provides the driving force for such “non-equilibrium” transformation.
The hot torsion simulator has been extensively used as a means to understand the microstructure evolution of different steel grades during hot rolling. The test is suitable to simulate ‘real’ industrial schedules as well as schedules designed to obtain information regarding the intrinsic properties of the materials. For example, it is common to apply ‘average’ schedules, in which deformation per pass, interpass time, strain rate and cooling rate are kept constant, to determine the characteristic temperatures Ar3, Ar1 and Tnr (start and finish of the austenite transformation and no recrystallization temperatures) of steels. In this work, both a ‘real’ schedule simulating a rolling schedule in a reversing mill and an ‘average’ schedule were applied to a series of Ti and Nb microalloyed steels. In general, the steels exhibited somewhat different behaviours for the different thermomechanical schedules, e.g. the pancaking temperature region is easily detectable after an ‘average’ schedule, while for the ‘real’ schedule some softening can be detected in the pancaking region, which is strongly dependent on the strain and interpass time. Moreover, the paper analyzes a new approach to stress-strain curves, which is used to better understand the sequence of events which take place during rolling and their dependence on rolling parameters.
An austenitic stainless steel plate was coated with a sheet of Ag–Cu filler alloy by using explosive energy to simplify the subsequent brazing operation. The coated specimen had a typically wavy interface, and there were no defects like void. The adhesion at the interface was retained even after heating at a temperature of more than eutectic point of the Ag–Cu binary system (1052 K), although the molten Ag–Cu alloy did not show a good wettability on the stainless steel without coating. To investigate the effect of the coating on the interfacial microstructure and the bonding strength of finally obtainable joints, two coated specimens were overlapped and then heated at 1173 K for 0.3 ks in a low vacuum. The obtained joint had a shear strength of about 200 MPa, and broke mainly within the Ag–Cu alloy after a shear test. The joint brazed with the Ag–Cu alloy was also fabricated under the same heating conditions. Its shear strength was about 90 MPa, and the fracture position was at the Ag–Cu alloy/stainless steel interface. This indicates that the substantial bond between the Ag–Cu alloy and the stainless steel, which is achieved by explosive energy, contributes to the subsequent brazing process. Additionally, a commercially pure Ti plate was used as a substrate. In this case, the advantages of the coating process could not be recognized in the finally obtained joint. It is found that the substantial bond provided by explosive energy is canceled by the formation of a reaction layer on the brazing operation.
Aluminized steel has excellent heat resistance because of the stable oxide film that forms on its surface. Thus, it is often used for parts that are required to be exposed to elevated temperature. When aluminized steel is heated to temperatures above 873 K, diffusion occurs between the plating layer and the steel substrate; as a result, the plating layer is composed of a mixture of several intermetallic compound layers. In this study, aluminized steel was heated at 873 K for various heating times. The composition of each layer formed on the surface of the specimens was analyzed by SEM-EDS, and each layer was identified by comparing the analyzed composition with an Al–Fe–Si phase diagram obtained by using Thermo-calc. The diffusion path between the aluminized layer and steel substrate was determined at 873 K. The layer formed in the middle of intermetallic layers was observed to have lower Al content than other layers. Judging from the composition of the layer, it can be inferred that it consists of a mixture of fine grains in two phases. TEM-EDS analysis indicated that this layer consisted of a mixture of Fe2Al5 and τ1 phase.
The kinetics of the (110)bcc//(111)fcc heterointerface of iron during the fcc–bcc phase transformation has been investigated by molecular dynamics simulation. The various orientation relationships (ORs) between Nishiyama–Wasserman (N–W) and Kurdjumow–Sachs (K–S) ORs, which are experimentally observed, were examined. The planar propagation of the fcc–bcc heterointerface was observed in the case of the N–W and near N–W ORs, whereas a fast needlelike growth after initial planar growth was observed in the case of the K–S and near K–S ORs. The transformation started from the matching area of the fcc and bcc lattice and followed the Bain transformation path. It was confirmed that the difference in the matching area of the fcc and bcc lattices at the interface between the N–W and K–S ORs causes the two different propagation behaviors. In addition, the distribution of the atomic stress in the system during phase transformation was examined. The residual atomic stress was distributed toward the [01̄0]bcc direction after the transformation in the case of the N–W OR. The change in the direction of the Bain deformation path during phase transformation caused a fast needlelike growth after the initial planar propagation in the case of the K–S OR.
Weldments in high-energy piping of fossil power plants are known to suffer extensive creep damage over the course of long-term operations. This damage appears in the form of macro cracks, which result from the formation and linkage of creep cavities at the grain boundaries. It has been reported that creep cavities become sintered when subjected to compressive stress at high temperatures, and, if they could be eliminated before they develop into macro cracks, it was considered that this would enable life extension of components. This paper presents a process of regenerative heat treatment for the life extension of low alloy steel weldments by means in localized high-temperature heating of deteriorated locations. It is shown that recovery of creep life is attained as a result of high temperature compression tests and heat cycles around the A3 transformation temperature.