This paper proposed an innovative electrochemical method for copper recovery from spent sulfide slag (Na₂S–FeS–Cu₂S), generated during copper removal from iron-based melts. It aims to reduce the high decopperization agents’ consumption caused by low copper distribution ratio during the copper removal process, address the cost issues by recycle of slag and recovery of copper, and expand the application potential of the emerging copper removal method using the sulfide slag systems. The feasibility of electro-recovery of copper is verified by cyclic voltammetry tests and potentiostatic electrolysis experiments. The results show that in the Na₂S–FeS–Cu₂S melt, although copper cannot be reduced alone without reducing iron, rough separation can be achieved by controlling the temperature. The current efficiency of Cu⁺ reduction in the molten sulfide is about 9.1% due to electronic conduction in the sulfide melt, which needs further improvement. The slag treated by the innovative electrochemical process can be reused, as the XRD results show that it has a similar composition to the primary slag unused.

High-temperature H₂ reduction and melting experiments were conducted to extract metallic Fe from lunar regolith simulant. Differences in the recovery of metallic Fe with the addition of oxides were investigated in terms of the wettability at the interface between molten slag and liquid Fe. Ilmenite, albite, and Na₂O·xSiO₂ compounds were used as additive oxides. The effect of wettability on Fe recovery is discussed by evaluation of the contact angle obtained by calculations of surface tension and interfacial tension. The results confirmed that wettability is a major factor affecting coalescence of Fe particles in these slags.

During the solidification process, the precipitation of inclusions is inevitable due to micro-segregation, especially AlN and MnS in TWIP steel. In order to reasonably control the precipitation of inclusion, the cooling rate as an important factor in the casting process was studied through the unidirectional solidification experiments. The combined analyses using ASEM-EDS, EPMA and optical microscope revealed that the number density of precipitated inclusion decreased along the solidification direction with the decrease of the solid fraction. The number density of Al₂O₃, which existed in the liquid alloy was basically stable. On the contrary, the number density of MnS decreased and that of AlN increased with the increasing of cooling rate. Moreover, in the early stage of the solidification (f_s<0.1), the order of Al concentration curve slope was 0.58 K/s >0.38 K/s >0.1 K/s due to the entrapment of precipitated AlN by the solid-liquid interface moving relatively fast. Temperature was the main factor to affect the AlN precipitation and the particles were precipitated at the early stage of the solidification process. AlN inclusions can become the core to form the composite particles and have the positive effect on fining grains.

To obtain the formation characteristics of melting slag-iron in cohesive zone of hydrogen rich blast furnace (BF), the phase composition of primary slag, the variation of slag amount and the mechanism of metal iron carburizing under different atmosphere conditions were analyzed. The results showed that: The hydrogen-rich operation in BF changes the formation of primary slag and the carburizing behavior of metal iron in the cohesive zone. After hydrogen enrichment in gas, the amount of primary slag decreases. The wustite decreases, however, the primary slag absorbs CaO and Al₂O₃ to form the monticellite, hortonolite and magnesium rosaceite. With the increase of hydrogen enrichment ratio φ(H₂), the high melting point material (2CaO·SiO₂) began to crystallize out, and the melting point of primary slag gradually increase, coupled with the substantial reduction of slag content, which may lead to the “Drying” phenomenon of primary slag in hydrogen-rich blast furnace. The hydrogen-rich operation of blast furnace changes the contact mode between the iron charge and coke from surface contact to point contact in the cohesive zone, which reduces the carburizing rate of metal iron in cohesive zone so that the content of [C] and [S] in the dripping molten iron decreases accordingly. The formation of high melting point material in the primary slag and the blockage of the carburizing process of metal iron lead to the increase of the droplet temperature of slag-iron, which makes the blast furnace’s cohesive zone move down and thinner.

Image analysis was performed on the analytical objects constructed by X-ray computed tomography images of coke with anthracite as low swelling and softening-melting coal to evaluate the pore structure three-dimensionally. The sphericity of the pores was calculated based on the volume and surface area of the pores. Tracers were inserted into all anthracite particles to distinguish coke matrices derived from anthracite from those derived from coking coal. This is the first success in identifying coke matrices derived from coking coal and those derived from other carbon source. The sphericity of pores in the surrounding area of the coke matrix derived from anthracite and the area without coke matrix derived from anthracite was extracted from the analytical object. The surrounding area of the coke matrix derived from anthracite contained more low-sphericity pores compared to the area without coke matrix derived from anthracite. This may be due to the free expansion of the coking coal in the surrounding area of the anthracite since the anthracite does not soften or expand during carbonization. The coking coal expanded excessively to fill the voids between the particles, resulting in the bubbles bursting and generating connected pores.

Sodium modification is an effective approach for enhancing the properties of bentonite and reducing its usage in pellets. However, due to limited research, the relationship between the physicochemical properties of bentonite and its green ball properties remains unclear, and the optimal degree of modification for bentonite has rarely been discussed. Therefore, this paper proposes a novel research idea: to exploring the correlation between the five most commonly used indexes for evaluating the physicochemical properties of bentonite (water absorption, methylene blue index, swell capacity, colloid index, and cation exchange capacity) and the most frequently used evaluation indexes for assessing green ball performance (drop strength), in order to determine the optimal degree of sodium modification of bentonite for pellets. The response surface methodology was employed in this paper to investigate the quantitative relationship between the five indexes and the green ball drop strength. The results demonstrate that when the drop strength of the green ball reaches its optimal level, the five commonly used indicators of bentonite are as follows: water absorption is 545.27%, methylene blue index is 22.94 g/100 g, swell capacity is 72.36 ml/g, colloid index is 35.95 ml/g, and cation exchange capacity is 68.93 mmol/100 g. Under these conditions, it has been the predicted value for green ball drop strength is determined to be 12.88, which exceeds the maximum value in the experimental conditions by 48.05%. The study determined the optimal degree of sodium modification for bentonite in pelletizing, providing valuable guidance for optimizing the properties of bentonite.

The main function of the converter furnace lining was to provide a durable container for the high-temperature molten bath. During the steelmaking process, the occurrence of melting corrosion led to the destruction of the furnace lining structure and a subsequent change in the shape of the furnace. Hence, the dynamic condition of the molten bath was altered. In this paper, both water experiment and numerical simulation have been adopted to analyze the flow field characteristic of molten bath by various oxygen lance parameters, in both the initial and late stages of the furnace lining structure of a top-blowing converter. The results revealed the late furnace lining structure improved the average velocity of the molten bath, thereby reducing the mixing time and volume of the low-velocity dead zone, comparing with the furnace lining structure. In the late furnace lining structure, the larger furnace diameter expanded the impaction area of the molten bath, resulting in an enhanced contact area between the liquid slag and the molten steel. Consequently, the FeO in the liquid slag rapidly reacted with the C element in the molten steel, leading to a decrease in the fluidity of the liquid slag and a decline in dephosphorization efficiency. Based on the results generated by water experiment and numerical simulation, two types of new oxygen lances were investigated in the industrial application research. Subsequently, it was determined that the new oxygen lance with an inclination angle of 12.3° was deemed suitable for the 35t top-blowing converter.

As for steelmaking process such as basic oxygen furnace (BOF) and electric arc furnace (EAF), slag foaming consists of introducing gas bubbles into molten metal and slag by chemical reaction. In the case of the BOF process, excessive foaming is over the converter capacity, a phenomenon called “slopping”. Slopping reduces yield and equipment lifespan and increases production time. It is therefore important to control slag foaming properly. In previous studies by other investigators, the jet from top lance in BOF process effectively suppresses slag foaming. However, it is not obvious which mechanism of the jet from top lance is effective to suppress slag foaming, and its quantitative effect has not been reported. To clarify the relationship between slag foaming and the jet from top lance, the effects of the number of nozzle holes and lance height on the slag foaming were investigated by using a converter-shaped water-model device and test converter. The experimental results indicated that slag foaming height decreased as the number of nozzle holes increased. Also, slag foaming height changed instantly with the change in lance height, e.g., slag foaming height decreased as lance height increased, and vice versa. The foaming suppression mechanism of the jet from top lance is the entrainment of foaming slag into the jet. Consequently, slag foaming model that takes the effect of the jet from top lance into account is proposed. And it enables to predict the change in slag foaming height with time.

In this study, to elucidate the agglomeration mechanism of various inclusions in molten steel based on their interfacial chemical interactions, the agglomeration forces exerted between the solid-phase oxides of MgO, MgAl₂O₄, ZrO₂, SiO₂, and TiO₂ in molten steel, in addition to those between the reference material Al₂O₃ have been measured directly. We experimentally verified for the first time that the agglomeration force due to the cavity bridge force in molten steel acts in a relatively stable manner between all solid-phase oxides that are difficult to wet with molten steel. Furthermore, this force decreased with increasing O concentration in molten steel, which is attributed to the interfacial activation effect caused by the adsorption of oxygen at the interface between the oxides and molten steel. The agglomeration properties of various oxide inclusions in the deoxidized molten steel were further evaluated from the perspectives of both agglomeration force and thermodynamics. Quantitative analysis indicated easy agglomeration of oxide inclusions in the order MgO < TiO₂ < SiO₂ < MgAl₂O₄ < ZrO₂ < Al₂O₃. A comparative evaluation of the agglomeration and external forces acting on the oxide inclusions in molten steel suggests that any oxide inclusion in the deoxidized state forms cavity bridges and agglomerates and retains that state under intense molten steel flow. However, these agglomerated inclusions may separate again under a molten steel flow at a high O concentration. The extent of separation depends primarily on the type of oxide used.

Total iron contents in iron ores have been accurately determined by JIS M 8212, in which iron ions in digested solutions of iron ores are reduced to divalent prior to redox titration. It is necessary for the iron reduction process that no reducing chemicals other than iron(II) in the decomposition solutions must not remain after the reduction with titanium(III). However, the redox reactions concerning the chemical species present in the decomposition solution has not been completely elucidated at the present time. In this paper, the redox reactions that occurred in the decomposition solution during the iron reduction in JIS M 8212 were studied by potentiometry and spectrophotometry under nitrogen atmosphere. The redox reaction of tin(II)/(IV) was very slow, causing significant effects on identifying the end point of the indicator for the iron reduction. The copper chloro-complexes were reduced with titanium(III) at a potential higher than that of indigo carmine used as a redox indicator, so that the reduced copper(I) gave a positive error to the potassium dichromate titration. The pentavalent vanadium was reduced with titanium (III) to form a complex with titanium, which also interfered with the potassium dichromate titration positively. To avoid these interferences, titanium(III) chloride was stoichiometrically added to the reaction mixture after addition of tin(II) chloride under nitrogen atmosphere so as to reduce only iron to divalent prior to the following redox titration. Combination of the proposed protocol with the potassium dichromate titration could successfully determine the iron content of certified reference materials of iron ores.

Controlling the primary recrystallization texture is important to improve the magnetic properties of grain-oriented electrical steel through secondary recrystallization. To understand the factors influencing fine precipitates on the primary recrystallization mechanism and texture formation, changes in the recrystallization behaviors with states of precipitates (extremely fine, and coarse) were investigated through cold rolling, pre-annealing, and primary recrystallization annealing in Fe-3%Si alloy with initial coarse Goss ({110}<001>) grains using EBSD and TEM. Extremely fine MnS precipitated during the recovery stage had significant effects on the suppression of further recovery and recrystallization, especially after pre-annealing at 550°C. Recrystallized Goss grains were observed after primary recrystallization annealing by nucleation and growth irrespective of the states of precipitates; however, in the steel with extremely fine precipitates, {111}<112> grains remained through primary recrystallization annealing. It is assumed that fine precipitates would inhibit the growth of Goss grains and keep {111}<112> orientation, the main orientation in the cold rolled sheet, which would indicate occurrence of continuous recrystallization.

Oxidation processes are unavoidable in continuous casting and further hot processing of steel. A deeper understanding of the occurring phenomena such as intergranular oxidation and liquid metal infiltration of grain boundaries is essential to continuously improve the quality of the products. In this study, oxidation experiments were performed with simultaneous thermal analysis for two thin slab casting and rolling applications under near-process conditions up to the point prior to the first reduction stage. The experiments were performed for two low-carbon steels contaminated with undesirable tramp elements (Cu, Sn, …). In addition, the two steels contain Silicon at different levels. The results show that for the “Endless Strip Production” process (ESP), intergranular oxidation is significantly less pronounced compared to a “Thin Slab Casting and Rolling process” with a gas-fired tunnel furnace (TSCR TF). Due to the short process time at high temperatures in the ESP process, hardly any liquid metal infiltration by copper appears. In low silicon steel, intergranular oxidation results from various oxides, and liquid metal infiltration appears simultaneously in the TSCR TF process. Furthermore, the yield loss from oxidation is significantly higher in the TSCR TF process. The change from a natural gas combustion atmosphere to a hydrogen combustion atmosphere further increases the oxidation rate and results in a higher mass loss.

The influence of MC-type carbide formation on pitting corrosion resistance in weld metal of austenitic stainless steel was investigated. The relationship between the microstructure such as carbides and element distribution, and pitting corrosion resistance of the simulated weld metal of austenitic stainless steel was studied. The addition of molybdenum improved the pitting corrosion resistance. The effect of niobium addition on the pitting resistance was negligible. However, the addition of titanium significantly reduced the pitting corrosion resistance. The addition of niobium or titanium induced the formation of MC-type carbides, such as TiC and NbC, at the cellular boundaries. The pits were mainly initiated near or at carbides. The chromium depletion zone was formed near M₂₃C₆ coexisting with TiC only in the specimen added titanium. Thus, TiC formed during solidification accelerated the chromium diffusion-associated M₂₃C₆ precipitation on TiC. The depletion zone deteriorated the pitting corrosion resistance of the titanium-containing specimen.

The effect of Mn on the alloying reaction during hot-dip galvanization was investigated. The microstructure of the Fe–Zn intermetallic layers consisted of ζ, δ, and Γ phases for both pure Fe and Fe–2Mn (wt.%) alloy. The intermetallic layers grew thicker with increasing dipping time, and the growth rate of each layer was similar for both substrates. In the case of Fe–2Mn, the formation of the δ_1p phase was observed after dipping for 2 s. However, δ_1p formation was delayed for pure Fe, indicating that Mn may promote nucleation of the δ_1p phase. It is known that the δ_1p phase nucleates in the Fe-saturated ζ phase. The Fe content at the ζ/δ_1p interface was found to be lower for the Fe–2Mn alloy by electron probe microanalysis, suggesting that the supersaturation of Fe for the nucleation of δ_1p is decreased by Mn addition and Mn may stabilize the δ_1p phase. Once δ_1p became a continuous layer, the growth rates of the δ_1p layer on pure Fe and Fe–2Mn were similar. Mn could affect only the nucleation of δ_1p during the initial stage of the alloying reaction.

The mechanical properties of TRIP steels depend on heterogeneities of chemical composition and grain size in the retained γ structure, although these heterogeneities have not been characterized in detail. Therefore, in this study, we quantitatively investigate the inhomogeneous carbon concentration and grain size distribution, and its effects on the thermal stability of the retained γ in Fe-2Mn-1.5Si-0.4C (mass%) TRIP steel using FE-EPMA, EBSD, Mössbauer spectroscopy, and in-situ neutron diffraction during bainitic transformation at 673 K. In-situ neutron diffraction experiments detects high-carbon γ evolving during bainite transformation, in addition to the original γ, and the time variation of the volume fraction of high-carbon γ agrees well with the fraction of γ retained at room temperature. Williamson-Hall analysis based on peak width suggests that heterogeneity of carbon content exists even within the high-carbon γ. Compositional analysis using FE-EPMA and three-dimensional atom probe directly revealed that fine filmy γ was highly enriched with carbon compared to larger blocky γ, and the carbon content in blocky γ decreases with increasing blocky γ size. DICTRA simulation qualitatively reproduces the size dependency of carbon enrichment into γ. It was also found that γ tends to be retained at higher carbon content and smaller γ grain size since the smaller grain size directly improves thermal stability and the smaller γ size further contributes to the thermal stability via enhanced carbon enrichment.

In this paper, fatigue crack initiation and propagation properties of three structural steels with different static strength and cyclic softening behavior were evaluated and compared with the estimation results based on the local strain response. Steel C had the highest cyclic softening rate, which was 10 times that of steel A and twice that of steel B. The relationship between strain range and fatigue life in the fatigue life region shorter than 10⁵ cycles was almost the same regardless of the test steels. The fatigue crack initiation life from the notch bottom of the SENT specimen was almost the same independent of static strength and cyclic softening rate. The crack initiation life estimated from the Strain range versus fatigue life equation using the local strain response measured by DIC was roughly in agreement with the experimental results. Steel C had the highest crack opening load and the slowest fatigue crack propagation rate compared to the other two steels. The local strain range at the fatigue crack tip showed a good correlation with the fatigue crack propagation rate irrespective of the steel grade. In addition, the estimates of fatigue crack propagation rate based on the local strain response were in almost agreement with the experimental results.

The iron and steelmaking industry must focus on neutralizing CO₂ emissions. One solution involves using hydrogen as a reducing agent for iron ore. However, carbon is an essential element as primary steel is produced by refining molten carbon-saturated iron (hot metal). Ironmaking processes applying CO₂ capture and utilization have been suggested; however, they are limited to the reduction process. To satisfy the demand for primary steel production with net-zero CO₂ emissions, a new carbon recycling ironmaking process capable of producing hot metal must be considered. This study proposes a carbon recycling ironmaking process using deposited carbon-iron ore composite (CRIP-D). In the CRIP-D process, hot metal is produced by using the solid carbon recovered by reforming exhaust gas as reducing and carburizing agents. Moreover, using the recovered solid carbon, iron oxides are reduced more rapidly, and reduced iron is melted at a lower temperature than that using fossil fuel-derived carbon. This means carbon-neutral steel can be produced more efficiently than conventional ironmaking processes. Using proven technologies, following hot metal production, primary steel can be produced while minimizing the burden on the steel mills for converting equipment. Thus, true carbon-neutral primary steel is feasible using the proposed CRIP-D process.