The phase equilibria in the FeS–XS and MnS–XS (X: Ti, Nb and V) pseudo-binary systems were investigated by using an X-ray diffraction and electron probe micro analyzer. In the FeS–TiS and FeS–VS systems, a mono-sulfide with the NiAs structure form a complete solid solution, while two-phase separation of the mono-sulfide with the NiAs structure is observed in the FeS–NbS system. In all MnS–XS systems, two-phase region of a Mn-rich mono-sulfide and X-rich mono-sulfide exists widely. Solubility of each elements in the Mn-rich mono-sulfide and X-rich mono-sulfide is small, except that of Mn in Nb-rich mono-sulfide.

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Solubility of sulfur in Fe–V and Fe–Nb alloys was experimentally determined using a diffusion couple technique. Solubility product of VS and NbS in ferrite (α) and austenite (γ) phases were determined as log(mass%V)(mass%S)_α=4.76−10100/T, log(mass%V)(mass%S)_γ=4.90−11000/T and log(mass%Nb)(mass%S)_γ=4.70−10500/T in the temperature range from 1523 to 1573 K. A thermodynamic analysis was also carried out to evaluate the formation energy of VS and NbS. The estimated formation energy of VS and NbS are ΔG_VS^sulfide=−263100+61.0T (J/mol) and ΔG_NbS^sulfide=−260800+68.4T (J/mol), respectively.

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A thermodynamic analysis of the Fe–Nb–P ternary system has been carried out using the CALPHAD method. Among the three binary systems present in this ternary phase diagram, the phase equilibria in the Nb–P binary system, on which very few studies have been reported, were thermodynamically analysed. The thermodynamic properties of various phosphides and of a bcc solid solution obtained from first-principles calculations were utilized in this analysis to compensate for the lack of available experimental data. By applying these procedures, a highly plausible Nb–P binary phase diagram was established over the entire composition range. The thermodynamic descriptions of the Fe–Nb and Fe–P binary systems were taken from previous studies. The thermodynamic parameters of the Fe–Nb–P ternary system were evaluated based on experimental data for the phase boundaries and estimated thermodynamic properties of the ternary phosphides obtained using first-principles calculations. The calculated phase equilibria were in good agreement with the available experimental data. From the calculated results, we confirmed that the ternary phosphide, FeNbP, took part in equilibria with most of the binary phosphides.

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It is important to study the complex deoxidation equilibrium of molten iron in Ti–Mg–Al system from the view point of inclusion control. The equilibrium experiments between molten iron and TiO_X–MgO–Al₂O₃ slag and the thermodynamic calculation on the complex deoxidation are conducted at 1973 K in the present study. The liquid phase region of TiO_X–MgO–Al₂O₃ system in equilibrium with molten iron is clarified at 1973 K. The equilibrium compounds which are coexisted with the slag on the liquidus curve in the system are identified to be Mg₂TiO₄ and MgAl₂O₄. The equilibrium relation between the deoxidation products (Mg₂TiO₄ or MgAl₂O₄) and the composition of solute elements in steel is investigated, and the conditions that Mg₂TiO₄ forms instead of MgAl₂O₄ nor Al₂O₃ are examined in the complex deoxidation of Ti–Mg–Al system. When the aluminum content of molten iron is under 4 mass ppm, Mg₂TiO₄ forms over the wide concentration range. The concentration range of MgAl₂O₄ formation widens as the aluminum content of molten iron increases. It is necessary to increase Mg content and to decrease Al content in order to form Mg₂TiO₄ in the Ti–Mg–Al complex deoxidation of molten iron in the range Ti<0.01 mass%. However, it is difficult in the range of Ti>0.01 mass% to form Mg₂TiO₄.

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Inclusion behavior like nucleation, diffusional growth, coagulation and removal in steel refining are complicated process, whereas mathematical simulation makes it possible to describe each behavior in detail. Many works have been performed in respect of the individual mechanism of inclusion behavior. However, the whole behavior is not clearly understood yet, and especially, an experimental evaluation of combined phenomena has not been carried out sufficiently until now. In this study, a cold model experiment of bubble flotation accompanied by coagulation of polystyrene particle in an electrolyte solution has been conducted in an agitated vessel under turbulent flow condition. In addition, an empirical equation of bubble flotation in a turbulent flow has been proposed from observed results of the water model experiment. This empirical equation has been combined with the population balance equation on particle coagulation, and removal rates have been predicted. Furthermore, a correction has been adopted in the population balance equation proposed by Nakaoka et al. Resultantly, a linear coupling model with bubble flotation and coagulation has been verified its applicability to a prediction of time dependence of particle number density and size distributions under various conditions.

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The direct detection of inclusions first became possible for electronically conducting fluids following the development of the LiMCA (Liquid Metal Cleanliness Analyzer) technique. The principle of this technique is based on the R.P.T. (Resistive Pulse Technique), or E.S.Z. (Electric Sensing Zone) method, for counting, and sizing, inclusions in liquids. Its application to steel melts is now studied theoretically, in order to help in the understanding and analysis of in-situ experimental measurements of inclusion size and frequency distributions in steel plant processing operations.
In developing the theoretical model for this technique, a three-step strategy was used to explore physical events that take place within the electric sensing zone, as an inclusion passes through. First, a multiphase flow model was required, in which events that can take place during the passage of the inclusion through the sensor's ESZ were considered. Inclusion trajectories and transit times were predicted using a particle momentum equation. For this, Newton's Second Law of motion was solved, in which the mass and instantaneous acceleration of the particle was balanced against the sum of the various forces acting on the particle/inclusion, during its passage through the ESZ. The forces summed included Stokes's drag, fluid acceleration, particle acceleration with added mass, gravitational and, in particular, the external self-conducting electromagnetic force induced by passing a heavy direct current through the ESZ of an electronically conducting liquid.
In the second step of this theoretical analysis, a numerical potential-integral method was conceived in order to calculate local changes in electrical resistance within an ESZ of variable geometry, and variable location of a traversing particle. This new approach was compared to alternative analytical and numerical estimates of changes in ESZ resistivity with a second phase particle within it, which neglects the effects of radial position of the particle.
In the third and final step in the present analysis, parabolic, fluted, and cylindrical ESZ's were selected, and the influence of fluid properties, ESZ dimensions, electric currents, and the inclusion's properties (electrical conductivity, density, size, shape, etc.), were investigated to determine how these various parameters affect the resistive (or voltage) pulses generated during the passage of an inclusion through the ESZ.

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Solid or molten oxides are considered to act as nucleation sites during continuous steel casting. The influence of the kind of oxide crystal and atmospheric oxygen partial pressure on the degree of undercooling and contact angle of pure molten iron on oxide substrates was measured by the sessile drop method. On Al₂O₃ and MgAl₂O₄ substrates, we found that the change in the degree of undercooling was dependent on the existence of a reaction layer and its thickness. On an MgO substrate, since no reaction layer formed, the degree of undercooling was small and was governed by the lattice misfit parameter. The equilibrium contact angle of a molten iron drop on the FeAl₂O₄ layer formed between the Al₂O₃ substrate and drop was about 100°; a similar contact angle was obtained on MgAl₂O₄. The contact angle on MgO changed during observation due to the evaporation of Mg.

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A microsegregation solidification model has been extended for an individual droplet falling through a stagnant gas during the atomization process. Assuming a uniform temperature within the droplet, the model takes into account nucleation undercooling and equiaxed growth of the dendritic and eutectic microstructures until complete solidification.¹⁾ It predicts the temperature evolution and the chemical segregation within the droplet in terms of the percent of the dendritic and eutectic microstructures. Extensive experiments have been performed on Al–Cu droplets using the impulse atomization technique. The distribution of phases, cell spacing and segregation have been quantified earlier.^2–4) It has been reported that the amount of eutectic in the droplets falls below the equilibrium prediction as the alloy composition increases. Successful comparison between the model results and the experiments leads to the conclusion that eutectic undercooling and eutectic recalescence play a very important role in the final percent of eutectic in the droplets.

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A Cellular Automaton (CA) -Finite Difference (FD) coupling model was developed to analyze the evolution of solidification microstructure and the columnar-to-equiaxed transition (CET) in Al–Si alloy. Kobayashi's microsegregation equation was adopted to describe the solute diffusion in solid phase, and a “decentred square” growth algorithm with coordinate transformation was performed to describe the grain growth and the entrapment of neighbor cells. Through the examination on the effects of operation parameters and nucleation parameters on solidification morphologies, it was found that the length of columnar grains is controlled by the dendrite tip growth kinetics, and that the width of columnar grains is controlled by the implicit relationship between nucleation density and cooling rate at ingot surface. It was also found that the size of equiaxed grains is controlled by the competition of the nucleation and the grain growth. With the controllability of nucleation density in the bulk of liquid for equiaxed grain size, the nucleant and the nucleation density in actual Al–Si alloy were estimated. Both of the CET criteria based on the solidification path by CA-FD coupling model and the one based on the curves of critical temperature gradient conditions by Hunt's model were strongly dependent on nucleation undercooling and Si concentration. A good agreement was obtained between these two.

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The dendrite tip growth kinetics in the flow field and the decentred quadrilateral growth algorithm for describing the evolution of grain growth are combined in Cellular Automaton model to predict the deflective growth of dendrites inclined toward upstream direction. The influences of flow intensity, cooling rate (or solidification rate), nucleation density at ingot surface on the deflective growth of dendrites are discussed. The increase of flow intensity dominantly forces the dendrites to grow in upstream direction; on the contrary, the increases of nucleation density at ingot surface and cooling rate suppress slightly this deflective growth. The relations predicted among deflection angle, flow intensity and solidification rate for Al–Si alloy and Al–Cu alloy show the same tendency as that in Okano et al.'s empirical expression deduced from experiments on steel. The deflection angle predicted for Al–Cu alloy fits well with previous experimental results.

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The multi-phase field method and CALPHAD (calculation of phase diagram) are applied to the study of the equiaxed solidifications in the Al–Ti–B and Al–Si–Ti–B systems by coupled with thermodynamic and diffusion databases. In these calculations, recalescence phenomenon is considered on the basis of the latent heat, and a plot of the seed density-radius distribution is obtained by calibration with experimental data. The calculated solidified-grain sizes are in quantitative agreement with the experimental measurements for various hypoperitectic compositions.

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In this paper, the effect of particle pinning on grain boundary motion is investigated by phase-field modeling. In general, the kinetics of grain growth in multicrystalline materials is determined by the interplay of curvature driven grain boundary motion and the balance of interfacial tension at the vertices of a grain boundary network. A comprehensive way to treat both effects in one model is given by the phase-field approach. The specific feature of the multiphase-field model used for this investigation is its ability to treat each grain or phase boundary with its individual characteristics, together with a thermodynamic coupling which allows a sound treatment of phase transformation, e.g. the formation of precipitates of a second phase.
The pinning effect itself is simulated on the nanometer scale resolving the interaction of individual inert or reactive precipitates with a curved grain boundary. From these simulations an effective pinning force is deduced, and a model for a driving force dependent grain boundary mobility is formulated accounting for the pinning effect in the grain growth simulation on the mesoscopic scale. These simulations demonstrate how particle pinning leads to much slower growth kinetics and a different grain morphology with higher boundary curvatures in the stationary state. Finally, an increase of the pinning force due to a changing particle density, e.g. during heat treatment, is shown to result in a transition between normal and abnormal grain growth before grain coarsening is inhibited completely.

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It is well known that the large-scale inclusions in steel act as the destruction starting point of the material. The labor is extremely necessary for investigating the maximum inclusions that have been distributed in the matrix of a large volume. The statistics of extreme value method is an excellent technique that can be applied for that case. When a material such as steel is opaque to visible light, the electron beam, and so on, the evaluation of the internal inclusions as three-dimensional (3D) information is presumed from the two-dimensional (2D) information observed under a microscope in respect of sample cross section. It is expected that this presumption error margin is large. It is almost impossible to verify 2D data by 3D one in a real material because the true value is uncertain, especially concerning the information of the tail of the size distribution. The purpose of the present work is to offer statistical information necessary to presume 3D characteristic value from 2D measurement data with respect to the maximum extreme value. The simulation whose 3D characteristic value is already-known is effective to this. Some 3D size distributions such as the exponential, log-normal, pseudo-normal, and Rayleigh distribution is set here, and how the 2D maximum extreme-value distribution (MED) changes into the measured number of sections is shown. The result gives a number of sections necessary to gather data with few error margins directly. Further, some findings of the relation between 3D-MED and 2D-MED are given. The overarching point is a type of the MED and conversion of the dimension.

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This paper investigates the effect of de-oxidation inclusions on micro-structure evolution in low-carbon steels. Low carbon (0.07 wt%), high Mn (0.9 wt%) steel in a Al₂O₃ or MgO crucible was deoxidized by adding either aluminum (0.05 wt%) or titanium (0.05, 0.03 or 0.015 wt%) in a 400 g-scale vacuum furnace, and cast in a Cu mold at cooling rates between 2.0–6.0 K/s. These cast samples were re-melted and cooled at various cooling rate, 1 through 100 K/s in the hot-stage of a conforcal laser scanning microscope (CSLM) in order to investigate the effect of cooling rate.
Oxide inclusion sizes in all the Ti-killed steels were smaller and inclusion densities higher than those in the Al-killed steel. In Ti-killed steel, inclusion size and densities increased with increasing the oxygen content, inclusion size decreased and their densities increased with increasing the cooling rate.
A Confocal Scanning Laser Microscope (CSLM) was used to study the differences in solid state micro-structural evolution between the Ti-killed and theAl-killed samples. The growth of austenite grains were studied under isothermal conditions and it was found that both grain-boundary mobility and final grain size were lower in the Ti-killed sample than for the others. With regards to austenite decomposition, during continuous cooling from a comparable austenite grain structure, the resulting austenite decomposition structure was finer for the Ti-killed sample due to a higher Widmanstätten lath density due to precipitation at. The inclusion size was found to have a significant effect on both austenite grain size and austenite decomposition structure. Different orientations of ferrite precipitates originating at inclusions were observed in the Ti-killed samples. The highest lath concentration was obtained for the sample that had the smallest average inclusion size rather than the sample with highest density of sub micro-meter inclusions.

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A fine-grained microstructure yields the optimum combination of strength and toughness of steel. Moreover refinement of the as-cast structure can reduce the tendency for hot-cracking during forging and rolling. This paper describes how small inclusions can be used to control the microstructure of steels. These small inclusions (dispersoids) are oxides, sulfides, nitrides and carbides which are in the 1 μm size range and capable of promoting grain refinement during solidification by a process of epitaxial nucleation or in the solid state through intragranular nucleation of ferrite. Such particles are sufficiently small to be harmless from a toughness point of view, but at the same time large enough to act as potent nucleation sites during phase transformation. The dispersoids can either be created by balanced additions of strong oxide and sulfide forming elements to an impure steel melt or be added directly into the liquid steel through a specially designed master alloy containing the nucleating particles. In both cases it is possible to manipulate the steel microstructure in a positive direction, but the latter method, involving the use of a master alloy, has probably a wider industrial application.

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In the present investigation the phase relations within the Ce–Al–Fe–S system have been clarified, using a combination of optical microscopy and WDS microprobe analyses. As a starting point high-purity charge materials of cerium, aluminium and FeS₂ are melted and superheated to about 2000°C within small tantalum crucibles inside a dedicated laboratory furnace filled with cleaned argon. The phases detected in the as-solidified samples were CeS, Ce₃Al, Fe₂Ce and γ-Ce, along with Ce₂O₂S, which is an undesirable microconstituent in CeS-based grain refiners. It is concluded that FeS₂ can be used as a sulphur source for addition up to about 4 wt% sulphur. At higher levels the Fe–Ta interaction becomes so vigorous that tantalum no longer acts as an inert refractory metal and wetting becomes a major problem. In contrast, aluminium is an essential alloying element in the sense that it prevents the grain refiners from disintegrating in contact with air due to internal oxidation of free cerium by promoting the formation of Ce₃Al.

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The inclusion of low carbon submerged arc weld metals of a Ti–B system with different aluminum contents has been studied. The inclusions contributing to acicular ferrite nucleation were multi-phase consisting of MnS, MnAl₂O₄ and amorphous phases. In the energy dispersive X-ray spectroscopy mapping analysis, inclusions were surrounded by a titanium-rich layer. This layer was analysed as Ti–O by energy disperse X-ray spectroscopy spectrum from the interface between inclusion and ferrite. The selected area diffraction pattern of inclusion surface was characterized as TiO. The acicular ferrite had Baker–Nutting orientation relationship with this TiO layer on the inclusions surface, and the lattice misfit was 3.0%. Therefore, it was supposed that the narrow TiO on the inclusion surface promotes acicular ferrite nucleation supplying low interface energy.

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The effects of non-metallic inclusions in nucleating acicular ferrite in steels during cooling from a weld or cooling from an austenitic temperature are reviewed. The influence of the acicular ferrite (AF) structure on mechanical properties of steels such as strength and toughness is briefly mentioned. The different factors affecting the formation of acicular ferrite, such as the soluble content of alloying elements in steel, cooling rate from austenitizing temperature, austenite grain size and inclusion characteristics in steel, are discussed. The mechanisms of acicular ferrite formation on non-metallic inclusions, such as reduction of interfacial energy, mismatch strain between the inclusion and ferrite/austenite, thermal strains at the inclusions and changes in matrix composition near the inclusions are also discussed. Finally, the effects of inclusion characteristics, such as size, number and composition are described and their effectiveness in nucleating acicular ferrite is discussed.

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The selection and the formation of carbide govern quality and the service life of hot steel milling rolls. Thus the microsegregation and the formation of the carbides and the graphite during the solidification have been investigated for high speed steel type cast iron and Ni-hard type cast iron. The crystallization of high speed steel type cast iron proceeds in the order of primary austenite (γ), γ+MC and γ+M₂C eutectic. On the other hand, in Ni-hard type cast iron, eutectic graphite flakes can crystallize after the formation of primary γ, and γ+M₃C eutectic by controlling the content of Ni and Si in spite of containing strong carbide formers such as Cr. As γ+carbide eutectic grows, the residual liquid among eutectic cells becomes rich or poor in carbide formers according the partition coefficient between residual liquid and eutectic cell. It is realized that the change of composition of carbide formers during the solidification is estimated with Scheil–Gulliver equation and computed phase diagrams in both of cast irons. The graphite forming tendency is also evaluated by applying the parameter, which expresses the solubility limit of carbon to the molten iron for Ni-hard type cast iron.

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An overview of the different types of precipitates in Interstitial Free High Strength (IFHS) steels has been presented. Details regarding their sequence of formation during processing, their morphologies and chemical compositions have been discussed. Correlation between precipitation and final properties has also been pointed out.

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The elements of Cu and Sn are two of the main residual impurities in steel, especially in recycled scrap steel. Sulfur is one of the main impurities in steel, and it may result in a large emission of slag and CO₂ to remove sulfur from steel. Utilization of these elements has been an important and difficult matter for metallurgist. In the present paper, the as-cast steels containing different concentrations of Cu, S and Sn are prepared in laboratory. The effect of Sn addition on sulfide precipitation is investigated and discussed with respect to the morphology, size, and composition of sulfide. The experimental results show that the addition of Sn suppresses the sulfide precipitation at high temperature, promotes more copper bearing and smaller sulfides precipitation at low temperature. On the other hand, sulfide precipitates are shown to reduce the micro-segregation degree of Sn in steel, which may be because Sn dissolves in sulfide to some extent and sulfide particles provide more interfaces for Sn to distribute.

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The effects of uniform and gradient magnetic fields on gravity segregation in Al–5wt%Cu and Al–10wt%Mg alloys are investigated. The results show that high magnetic fields can be used to control the solute distribution and thus control gravity segregation caused by the difference of physical properties such as density and magnetic susceptibility between the bulk liquid and the solute-enriched liquid. The effects of the field can be attributed to performances of Lorentz and magnetic forces.

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