The effect of the inclination angle of the columnar dendrite on the microsegregation during directional solidification of a model alloy, i.e., Al-3 mass% Cu alloy, was investigated using two-dimensional quantitative phase-field simulation. The extent of the microsegregation was characterized by the fraction of the eutectic region in the as-cast microstructure. It was found that the microsegregation significantly decreases as the average value of the primary arm spacing increases for each inclination angle. In addition, the microsegregation decreases as the inclination angle increases. These behaviors are mainly ascribed to the change of shape of last-solidified liquid related to contribution of back diffusion for different values of the primary arm spacing and inclination angle. Furthermore, the degree of microsegregation was well-predicted from the inclination angles and primary dendrite arm spacings. This suggests the possibility that the microsegregation can be simply predicted from inclination angles and primary dendrite arm spacings.

We developed an improved Satou mold that can intentionally generate macrosegregation via bridging of the solidification structure and solidification shrinkage flow. Herein, macrosegregation can be achieved in a relatively small mold with an inner dimension of 30 mm^T × 50 mm^W × 190 mm^H. Casting experiments were conducted on a Al–10mass%Cu alloy using this mold. The obtained samples were analyzed in detail by evaluating the 3D morphology of the macrosegregation by X-ray CT imaging, analyzing the microstructure and composition at the cross-section by SEM/EDX, observing the macrostructure, and visualizing the temperature and solid-fraction distributions at the cross-section using linear interpolation of the temperature measurement points. Channel-shaped positive segregation with a length of approximately 50 mm was generated along the sample’s center line in the height direction. X-ray CT imaging at a voxel size of 10 µm and microstructural and composition analyses by SEM/EDX helped clearly observe the 3D morphology of the channel-shaped positive segregation region. The average composition of this positive segregation region was 35.12 mass%Cu, corresponding to the eutectic composition of the Al–Cu alloy. From the observation of the macrostructure and the visualization of the temperature and solid-fraction distributions at the cross section, we could confirm the formation of bridging by the isosurface of the solid fraction. From these evaluation and analysis results, the formation mechanism of macrosegregation driven by bridging and solidification shrinkage flow was clarified. We confirmed that casting experiments using the improved Satou mold can serve as an effective benchmark for macrosegregation formation.

In the industrial steel manufacturing process, such as continuous casting and ingot casting, macrosegregation occurs due to the effect of bridging and contraction flow during the middle and end periods of solidification. Since the macrosegregation results in a nonuniform structure and eventually cracks, there has been a demand for technological development that does not cause macrosegregation in the casting process. In this study, model experiments using the medium-carbon steel cast with a laboratory-scale local-chilled mold at different superheating have been carried out to investigate the relationship between solidified structure and macrosegregation occurred by local bridging during casting. The morphology of shrinkage porosities and dendrite structures was observed. The concentrations of the alloying elements were analyzed for macrosegregation by an electron probe micro-analyzer. Chill plates successfully formed the columnar dendrite bridging area and the columnar dendrite shell in the sample with high superheating. During solidification, the negative pressure of the region below the bridging increased, and the concentrated contraction flow flowed into the bottom of the large shrinkage porosity. Finally, V segregation was formed in the bridging area, large shrinkage porosities remained below the bridging area, and point-like or band-like positive macrosegregation occurred in the interdendritic region between columnar dendrites and equiaxed dendrites below the bridging. In comparison, a lower casting temperature increased the grain density and formed shrinkage porosities that were smaller in size but larger in number and more dispersed.

Prediction and control of a macrosegregation of cold tool steel in a large scale ingot is very important. In order to investigate macrosegregation behavior of 8Cr type tool steel (Fe-1C-8Cr-2mass%Mo), model ingots which have a steel chill ring in the middle region of a mullite mold with two different diameters were prepared. 8Cr steels were cast into the molds, thereafter 5 kg and 30 kg ingots were made. In both sizes of the ingot, the dendrite arm spacings in the chill rings were finer than other region which indicate the chill ring induced relatively rapid cooling than other region, results in inhomogeneous solidification. An enriched solute concentration was observed near the center of the chill ring where the top of the shrinkage cavity. The macrosegregation profiles were similar in both ingots, however the segregation ratio of the larger ingot was larger than in the small ingot. Computational simulations were also carried out and the solidification profiles of each ingot was investigated. The result shows that in smaller ingot, the duration time after the mushy zone formed to closure is shorter than in larger ingot. At every liquid fraction, the permeability for the larger ingot is higher than those of the smaller ingot, which suggests that suction of concentrated liquid phase from the upper region of chill through the mushy zone in the chill center is more preferabliy occur in the larger ingot.

Currently, steel products are manufactured by continuous casting or large-sized ingot casting, and macrosegregation that occurs during the manufacturing process significantly impacts product quality in terms of cracks and deterioration of mechanical properties. To clarify the principle of casting defects, such as shrinkage porosity and macrosegregation due to the formation of bridging of the columnar dendrite of the medium-carbon steel, in this experiment, a laboratory-scale local-chilled mold in which the middle part was forcedly cooled was designed to cause bridging, shrinkage porosities, and macrosegregation. Enough risers were also designed to simulate realistic gravity casting as much as possible. The solidification structure morphology was observed, concentration analysis of alloying elements was performed, and the effect of bridging on macrosegregation was investigated. Solidification proceeded preferentially from the chill plate, and the bridging was formed successfully at a high casting temperature. The high casting temperature condition could cause bridging, but large shrinkage porosities would be formed as well. On the contrary, the lower casting temperature condition could increase the grain density and form shrinkage porosities that are smaller in size but larger in number and more dispersed, compared with the case cast with no chill plate mold. Due to the formation of bridging, macrosegregation was formed, and the difference between positive and negative segregation was increased from the longitudinal center of the sample.

The closure of large voids, whose thickness-to-void-height ratio exceeds 0.2, in S10C steel plates during hot rolling was investigated to determine whether hydrostatic integration (Q-value) can be used to predict the closing behavior of large voids. The steel plates with an open void along the rolling (RD), transverse (TD), and normal (ND) directions were hot rolled at 1000 and 1300°C with a target rolling reduction of 10% at each pass until 40% total target reduction. It was found that the effect of temperature on the closing behavior was negligibly small. RD and TD voids were almost entirely closed at a reduction of 40%, whereas ND voids could not be closed. The width of RD void was almost linearly decreased with reduction increase. TD void were closed at a lower reduction ratio than RD void. The thickness above and below the void was compressed after rolling in RD void but less reduced in TD void, which is presumable reason of the earlier closure of TD void. The FE analysis clarified that the void volume over initial volume (V/V₀) of the voids could be expressed as a function of the Q-value in the case of RD and TD voids. However, the closure behavior of the ND void cannot be expressed by the Q-value. These results indicate that the Q-value can be used to predict the closure of large voids in the RD and TD during rolling, although it cannot be used if the void shape is elongated in the compression direction.

A magnetic field can suppress liquid metal motion and this function is used as an electromagnetic brake in a continuous casting process in the steel industry. Thus, the magnetic field has the potential to reduce macro-segregation, and the electromagnetic braking effect should be clarified under the uniform and gradient magnetic field conditions because the magnetic field must non-uniformly distribute in a large size casting machine. This was experimentally examined in this study. A liquid tin was flowed in the packed bed filled with copper balls or alumina balls as a model of the liquid-solid coexisting phase. As the results, the friction factor for the alumina packed bed and the copper packed bed agreed with that calculated by the Ergun equation under the no-magnetic field condition. By imposing the magnetic field, the friction factor increased, especially for the copper packed bed. That is, the electromagnetic braking effect in the case of the copper packed bed was stronger than that in the case of the alumina packed bed. This is similar to the Hartmann flow theory. The electromagnetic braking effect under the uniform magnetic field condition and that under the gradient magnetic field condition were similar in the case of the alumina packed bed while the former was larger than the latter in the case of the copper packed bed. The oxidation of the copper balls in the packed bed may affect the electromagnetic braking effect.

Owing to the worldwide growth of aging population, the biomedical materials, such as implantation materials, are greatly demanded in these decades. Shape memory alloys (SMAs) and superelastic (SE) alloys, whose shape deformation could be manipulated by controlling the stress and temperature applied, are considered as promising materials to practice the biomedical applications. In this article, the β-Titanium (β-Ti) alloys were chosen for their high biocompatibility and appropriate shape deformation behaviors. First, Gold (Au) element was chosen as the tailoring element to functionalize the β-Ti alloys for its high X-ray contrast, which is a crucial prerequisite for the biomedical materials. Second, to impose the phase transformation temperature to be around the human body temperature, various transition metals were examined and introduced into the Ti-Au-based alloys. Based on the screening results of the transition metals, chromium (Cr) was determined to be the addition element. To further enhance the X-ray contrast and biocompatibility as well as conduct the fine-tune of phase stability of the Ti-Au-Cr-based alloys, Tantalum (Ta), which possesses high X-ray contrast and excellent biocompatibility, was served as the fourth element in this system and its addition concentration was optimized. Besides to the selection of the elements, the annealing temperature and annealing time length were both investigated to optimize the transformation temperature, phase stability, and microstructures. It was found that the Ti-4Au-5Cr-5Ta alloy, which was annealed at 1073 K for 1.8 and 3.6 ks performed a room temperature superelasticity, showed almost 100% shape recovery upon unloading.

Recycling phosphorus from phosphorus-containing wastes and byproducts is a promising secondary phosphorus resource. Steelmaking slag is generated in large quantities as a byproduct of the iron and steelmaking industry, and contains phosphorus that could be a possible secondary phosphorus resource. Phosphorus can be extracted from slag into aqueous solution; however, the phosphorus concentration is generally lower than other elements, causing a problem for phosphorus recovery. In this study, bipolar membrane electrodialysis was applied to separate and recover phosphorus from solution. The reaction and performance of phosphorus recovery were investigated. The effect of initial phosphorus concentration, volume ratio, and electric potential on recovery process was determined. Ion adsorption on an anion-exchange membrane during the initial stages and ion competition between H₂PO₄⁻ and OH⁻ in the later stages are the main factors affecting the extraction efficiency. In this study, the maximum concentration ratio achieved was 2.46, and the minimum phosphorus concentration in treated solution was 3.64 mg/L, which is under the Japanese effluent standard. In general, bipolar membrane electrodialysis has good potential for concentrating and recovering phosphorus from aqueous solution.

An inclusion compound of Ca₁₂Al₁₄O₃₃ has been reported as a solid oxide having high sulfide capacity. Towards better understanding of the substitution reaction of S²⁻ for clathrated O²⁻ in Ca₁₂Al₁₄O₃₃, in this study, the inclusion compounds were equilibrated under fixed O₂/S₂ partial pressure ratios at 1573 K. It was founded that the sulfide capacity of solid Ca₁₂Al₁₄O₃₃ was higher than that of the homogeneous CaO–Al₂O₃ liquid and decreased with an increase in the sulfur content. When the sulfur-substituted inclusion compound was regarded as the Ca₁₂Al₁₄O₃₃–Ca₁₂Al₁₄O₃₂S solid solution, the Ca₁₂Al₁₄O₃₃ and Ca₁₂Al₁₄O₃₂S activities exhibited Raoultian behaviors. Furthermore, the standard Gibbs energy change for the following substitution reaction was determined.

Ca₁₂Al₁₄O₃₃+(1/2)S₂(gas)=Ca₁₂Al₁₄O₃₂S+(1/2)O₂(gas)

ΔG^∘=68.2 kJ⋅mol^-1 at 1573 K

In order to achieve a low-carbon operation of the blast furnace, it is important to promote not only the reduction of iron oxides but also the carburizing and melting of reduced iron. In this study, the use of highly reactive carbon-iron oxide composite was focused on. The effect of chemical species of silicon oxides which are main components of ash in coal and gangue minerals in iron ores on the carburizing and melting phenomena of iron was examined in detail. The silicon transfer to metallic iron was also thermodynamically investigated under the condition with low carbon activity in iron.

The composites prepared by hematite reagent, carbonaceous materials and silicon oxides such as SiO₂, CaSiO₃ and Ca₂SiO₄ having different SiO₂ activity were heated up to 1300°C under inert gas flow. The reduction, carburization and melting behaviors were examined.

The silicon concentration of the reduced iron in the composite with high SiO₂ activity was high, while the carbon concentration was low. It was thermodynamically confirmed that silicon transfer precedes carburization of iron in the reduced carbon-iron oxide composite under high SiO₂ activity condition.

The addition of Ca is a useful method to control the shape of sulfides in steel. In this paper, in order to identify growth behavior of MnS on CaO–MgO–Al₂O₃ oxides in steel, based on two heats of Al-killed Ca-treated resulfurized steel, the characteristics of duplex (Ca,Mn)S inclusions in bars and blooms were observed and analyzed. It is found that there are three types of duplex (Ca,Mn)S inclusions with CaO–MgO–Al₂O₃ core oxides, named as Type-C, Type-MC and Type-M, respectively. In bar, Type-C behaves circular shape, Type-MC behaves spindle shape, and Type-M behaves long strip shape. From Type-C to Type-M, CaO or MgO content in core oxides decreases, Al₂O₃ content in core oxides increases, sizes of core oxides decrease, and the area ratios of wrapping sulfides and core oxides increase. Growth of MnS on CaO–MgO–Al₂O₃ oxides are influenced by the sizes and compositions of oxides. MnS inclusions are easier to grow on CaO–MgO–Al₂O₃ oxides with smaller sizes, lower CaO content, lower MgO content or higher Al₂O₃ content. In order to obtain more spindle-shaped duplex (Ca,Mn)S inclusions, appropriate compositions of core oxides are 5–20% CaO, 5% MgO and 75–90% Al₂O₃, and appropriate sizes of core oxides are 1–3 µm.

The flow control devices (FCD) play an important role to realize the best metallurgical performance of the tundish. An integrated workflow for designing a single-strand tundish equipped with FCD is presented in this paper. Mean age theory was applied to predict the spatial mean age distributions in the tundish. Melt change efficiency (MCE) was used as a key measure to characterize the tundish’s mixing performance. Taguchi method was employed to optimize the design factors, i.e. geometrical parameters of the FCD. The fluid flow and mixing of materials were analyzed based on the numerical simulations of a developed computational fluid dynamics (CFD) model. Compared to the residence time distribution (RTD) method, the mean age theory shows advantages in both numerical accuracy and efficiency. In addition, the size and location of undesired mixing zones can be easily identified which is essential for tundish design. The developed workflow that combined the CFD-Taguchi method and mean age theory can be used as an efficient tool for wide industrial applications.

This paper is the first of a series of papers on the roughness characteristics of the burden surface in the blast furnace. The measurement method of the burden surface roughness texture is described, and the overall roughness characteristics of the burden surface are studied from a statistical point of view. This study focuses on two typical granularized burden materials, coke and sintered ore, which present four kinds of burden particles under two individual particle sizes. Simulated cold-state burden belts proportional to the practical burden radial sectors were stacked in a pilot plant. An RGBD camera was used to measure the simulated burden belt surfaces to obtain the surface texture details. Four corresponding digital elevation models of the burden belts were obtained through data processing. The root mean squared height, skewness, kurtosis, and spatial autocorrelation function are selected as statistical indexes. The obtained digital elevation models were counted. The results show that all four kinds of burden surfaces are Isotropic-Rough-Surface. In addition, the height distributions of the rough burden surface are close to the Gaussian distribution. Also, the spatial autocorrelation functions of the coke and large-sized sintered ore burden surfaces are close to the Gaussian function form. And lastly, the spatial autocorrelation function of the small sintered ore burden surface is close to the exponential function form.

In twin-roll strip casting process, the height of the liquid level (LH) directly affects the casting stability and quality of strip. High accuracy and quick LH detection are essential for LH stability control. In this paper, an LH detection technique based on computer vision was introduced, involving an easy calibration method and an efficient image processing method. It only requires the cameras to observe three different width whiteboards for camera calibration. To realize the highly precise and quick LH detection, a pseudo boundary caused by complicated casting process was emphasized and corresponding solutions were proposed. The application results show that the proposed method could achieve high precise and quick processing of LH detection, and the detection deviation can be controlled within ±2 mm of the target LH. Based on real-time LH detection, it could realize stable casting and minimize thickness deviation affected by LH fluctuation.

In automotive industry, it is well known that cracks which are promoted by liquid metal embrittlement (LME) can occur during the resistance spot welding (RSW) of zinc-coated advanced high-strength steels (AHSS). The coating type is supposed to be one of the factors impacting LME susceptibility. Recently, Zn–Al–Mg coating is gaining increasing focus because of its enhanced corrosion resistance compared to traditional Galvanized (GI) coating. However, there is a lack of research on assessing the influence of this coating on LME susceptibility. In this study, the LME susceptibility of Zn–Al–Mg and GI coated advanced high strength steels with similar microstructure and strength are compared by hot tensile tests and RSW. The results show that Zn–Al–Mg coated samples present a more significant ductility loss than that of GI coated ones in hot tensile test, and also there are more LME cracks with large length occur in Zn–Al–Mg coated RSW joints, indicating that Zn–Al–Mg coatings have a higher LME sensitivity. The high temperature phase evolution analysis results show that Fe–Zn intermetallic compounds formed in two coatings are different, indicating that there are lower level of Fe–Zn alloying reactions in Zn–Al–Mg coating. The inadequate Fe–Zn reactions potentially facilitate the direct contact between liquid Zn and steel substrate, leading Zn–Al–Mg coating to a higher LME susceptibility.

Fe–Cr–Co alloys are becoming important as a half-hard magnet for their novel applications, including non-contact electromagnetic brakes, because of the controllability of its magnetic hardness depending on the modulated structure formed by spinodal decomposition. However, the experimental optimization of the complicated heat-treatment process to control the microstructure significantly increases the development cost, and microstructure prediction by computational simulation is desired. In this study, we first developed the method of phase-field simulation for spinodal decomposition in Fe–Cr–Co alloy during various heat treatments, including isothermal heat treatment, multistep continuous fast and slow cooling, which allows us to conduct a simulation of spinodal decomposition under conditions close to the condition of practical heat treatment. The simulation results revealed that the morphology of the modulated structure is predominantly determined by the cooling rate and does not change significantly during the subsequent isothermal annealing process, while the difference between the concentrations of the FeCo-rich magnetic phase and the Cr-rich non-magnetic phase increases. Continuous cooling at rates higher than 140 K/h demonstrates the maximum number densities of the ferromagnetic particles of α₁-phase seemingly almost reaching saturation, which is expected to give rise to exhibiting the largest coercive force of the Fe–Cr–Co magnet. Moreover, this method can be extended to other materials for designing a modulated structure to show a desired property.

For the wall-thickness reduction of the components destined for pressurized gaseous hydrogen, widespread use of high-strength martensitic steels has long been desired. However, their strong susceptibility to hydrogen-assisted fatigue crack growth (HA-FCG) is still limiting their proactive applications. Here, we instead focused on pearlite as another potential reinforcing agent for the development of new hydrogen-compatible steels with acceptable cost performance. Fatigue crack growth (FCG) behavior of three eutectoid steels with different microstructure sizes (i.e., ferrite/cementite interlamellar spacing, colony and block sizes) and strength levels was investigated in a 90 MPa hydrogen gas, an essential evaluation when attempting to perform a defect tolerant design of the components used for high-pressure gases.

The pearlitic steels clearly exhibited the acceleration of their FCG rate in hydrogen gas up to a hundred times that in air, wherein its magnitude was greater in the material with finer microstructure and concomitant higher strength. The delamination of ferrite/cementite lamellae, which were inclined largely from the loading axis, was determined to be the primary cause of such HA-FCG in pearlitic steels. Nevertheless, the extent of FCG acceleration was minor with respect to martensitic steels. The fact was ascribed to the barrier role of the cementite platelets oriented nearly perpendicularly to the crack as well as to the geometrical retardation effects arising from the crack deflection and blanching. Ultimately, pearlite was superior to martensite from the perspective of HA-FCG resistance; besides, the superiority was more substantial as the loading rate became slower.

Aluminum cations are generally present in four-fold (^[4]Al³⁺) or five-fold coordination (^[5]Al³⁺) in aluminosilicate slags, where the concentration of ^[5]Al³⁺ varies depending on the type of charge compensator, for example, Mg²⁺ and Ca²⁺. Although it has been reported that the amount of ^[5]Al³⁺ species increases with the replacement of CaO with MgO in the CaO–MgO–SiO₂–Al₂O₃ system, the detailed mechanism underlying the change in the local structure near the aluminum cations remains unclear. Because the residual negative charge on the bridging oxygen between ^[4]Si⁴⁺ and ^[5]Al³⁺ (^[4]Si⁴⁺–O_BO–^[5]Al³⁺) is larger than that of ^[4]Si⁴⁺–O_BO–^[4]Al³⁺, it is essential to understand the positive charge contributions of alkaline-earth cations to compensate for these negative charges on the bridging oxygens. In the present study, the valence of a single chemical bond near Mg²⁺ and Ca²⁺ cations in the chosen aluminosilicate glasses was determined using a simple empirical model, which enabled calculation of the bond valence from the observed interatomic distance of near alkaline-earth cations by synchrotron X-ray total scattering. Magnesium cations had a larger average bond valence (+0.39) than calcium cations (+0.31). The difference in the positive charge contribution from Mg²⁺ and Ca²⁺ should explain the variation in the coordination number of aluminum cations.