Addressing the threat of global climate change is an urgent priority for all industries. The Paris Agreement set the global long-term goal of carbon neutral by 2050 for all member countries. As the steel industry occupies approximately 7.2% of the total global greenhouse-gas emissions, innovative technologies that build upon or move beyond the past developments are desired to reach this long-term goal. Various zero carbon technologies have been proposed for the steel industry. This review focuses on the current state of the steel industry from the perspective of long-term targets and pathways for the future. The design of an optimal ironmaking process for low carbon and decarbonization is discussed from a technological perspective, considering comprehensive consistency with sustainability in the steel industry. In particular, perspectives on the hydrogen-based ironmaking process using renewable energy for carbon direct avoidance and smart carbon usage are described.

The preparation of glass microbeads by gas quenching of blast furnace slag is an effective way to achieve efficient recovery and resource utilization of the residual heat from blast furnace slag. However, due to the high viscosity and easy crystallization of blast furnace slag, there are problems such as low bead formation rate, opaque glass microbeads, and poor chemical stability. MnO tempering agent was developed, and the influence of MnO on the crystallization behavior and rheological properties of the tempered slag was analyzed. The evolution law of the crystallization phase of the tempered slag was clarified, and a viscosity-crystallization coupling control method conducive to the bead formation of blast furnace slag was proposed. The results show that during the isothermal process, when the MnO content in the tempered slag is in the range of 0.17–12.24%, with the increase of its content, the initial crystallization temperature and the amount of crystal precipitation gradually decrease, effectively inhibiting the precipitation of crystals. However, when the MnO content exceeds 12.24%, the excessive MnO increases the activity of the easily precipitated phase, and the initial crystallization temperature increases instead. Therefore, when the MnO content in the tempered slag is 12.24%, the crystallization ability is the weakest, and the glass phase content is the highest. In the continuous cooling process, when the MnO content in the tempered slag is 12.24% and the cooling rate exceeds 3°C/s, the tempered slag completely solidifies into a glassy state.

Depending on the operational conditions inside a direct reduction shaft furnace, e.g., ingoing gas temperature, feeding rate of material, and gas composition, the outgoing material will differ. This study investigates how the heating rate affects the reduction during pure hydrogen reduction of commercial iron ore pellets. As expected, the reduction rate increased with increasing heating rate. The heating rate also significantly affected the microstructure evolution inside the pellet. Inside the hydrogen direct reduced pellets, the iron had two appearances: (1) porous iron containing small and numerous intragranular pores, or (2) dense iron with larger but fewer intragranular pores. The pellet reduced with the slowest heating rate consisted of only porous iron, while the faster heating rates comprised porous and dense iron. The amount of dense iron gradually increased with increasing heating rate and was found to start forming at a temperature of around 668°C. The solid iron aggravated the mass transfer through the product layer and decreased the total reaction rate. This led to an expanded spread of the reaction zone as the heating rate increased. Through this work, it was also shown that insignificant reduction took place below a temperature of 450°C. Lastly, the microstructure that evolved during the non-isothermal reduction vastly differs from the microstructure formed during isothermal reduction. Consequently, an effective diffusivity and thermal conductivity that varies with time and temperature must be considered when optimizing the shaft furnace reactor.

The injection of pulverized coal into blast furnaces has alleviated the demand for metallurgical coke, and co-injection technology combining natural gas and pulverized coal with high oxygen enrichment has the potential to further reduce coke use and hence CO₂ emissions. This work presents a steady-state operational model for the co-injection of natural gas and pulverized coal into blast furnaces developed based on mass and energy balance. With the support of industrial data from the commercial blast furnace, the matching relationship between natural gas rate, pulverized coal injection rate, and oxygen enrichment is quantitatively examined under the constraints of raceway adiabatic flame temperature and top gas temperature. The effect of natural gas rate on coke rate and CO₂ emission reduction is investigated. The results show that increasing natural gas injection rate, lower pulverized coal rate and higher oxygen enrichment maintains a constant raceway adiabatic flame temperature and coke rate. Under the optimal operating conditions, the pulverized coal, coke rate, and CO₂ emissions are reduced by 30.2%, 7.3% and 6.2%, respectively. The model and its results are expected to be helpful for a better understanding co-injection of natural gas and pulverized coal into blast furnaces, as well as contribute to reducing coke rate, pulverized coal rate, and CO₂ emissions.

The high temperature oxidation behavior of the electroslag remelting (ESR) process of welded 30CiNiMo8 billets electrode is investigated. High-temperature oxidation experiments are conducted to clarify the scale formation kinetics for the model. The steel is heated at 700–1200°C under a 21% oxygen atmosphere. The oxidation kinetics of the steel follow a parabolic law, with the oxidation rate equilibrium constant lnK = −23.801×1/T+17.866 and apparent activation energy ΔE_a = 197.88 J/mol. The temperature distribution on the electrode surface is obtained by measurement and fitted vertically and horizontally. The temperature increases exponentially with the electrode height, and the temperatures on the surface cross-section are inconsistent. Finally, the oxidation weight gain model is established by applying the isothermal oxidation kinetics model, the Arrhenius equation, and the Simpson formula. The amount of FeO_x carried into the slag under the industry experiment is 58.68 mg/s with the content of FeO as 65 wt%, which is established by the EDS and EBSD of the scale, and 4.77 g of aluminum addition into the slag pool every 5 minutes is suggested to reduce the FeOx potential when using four 160×160 mm welded billets electrode with a descending speed as 1.19×10⁻⁴ m/s.

To improve the quality of steel production, it is important to understand the behavior of bubbles rising in a liquid metal under a horizontal magnetic field (MF). However, such behavior has not been fully experimentally evaluated because of the limitations of existing experimental methods. In this study, a two cross-sectional ultrasonic tomography (UT) method was developed and used to measure the 3D motion of bubbles in a cylindrical container with an inner diameter of 50 mm. We conducted UT measurements alternately at the upper and lower measurement cross-sections of the container using the developed method, with a measurement interval of 2 ms in each cross-section. The applicability of this system was evaluated by measuring the 3D behavior of bubbles in a gallium alloy under different MF strengths. When no MF was applied or the MF strength was lower, the directions of the velocity vectors were randomly distributed. However, they aligned in the direction of the flow channel with an increase in the MF strength. With an increase in the flow rate, that is, as the distance between the bubbles decreased, the velocity oscillations of the bubbles perpendicular to the MF direction were greater than those parallel to the MF direction at higher MF strengths. Consequently, the distribution of the bubble-passing positions at the cross-section was slightly more spread in the direction perpendicular to the MF than in the parallel direction. These results demonstrate the effectiveness of the developed method in evaluating the 3D behavior of rising bubbles in a liquid metal.

In this study, the solidification path and crack sensitivity of high‑manganese austenitic cryogenic steel (HMACS) were studied based on DSC and directional solidification experiments. DSC experiment explored the solidification mode with the result that the solidus of the steel is 1342°C and the liquidus is 1400°C. Subsequently, the relationship between solid fraction and temperature of HMACS was analyzed by DSC and directional solidification experiment with a pulling velocity of 5 µm/s. Based on this relationship, the brittleness temperature range of HMACS and its crack sensitivity were analyzed. The results suggest that the high crack sensitivity of HMACS is primarily due to its broad brittleness temperature range. Furthermore, according to the directional solidification experiments with different pulling velocities, the solidification cracks and microporosities of HMACS during the brittleness temperature range were also characterized and analyzed by using thermal stress calculations. All results express that the high crack sensitivity of HMACS is primarily due to its broad brittleness temperature range. This leads to the solidification structure experiencing a longer brittle period, resulting solidification cracks and microporosities defects during the liquid-to-solid transition.

Accurate measurement of the position and shape of the blast furnace (BF) burden surface (BS) is crucial for automated and intelligent BF control. The detection method based on key points of BS can improve the accuracy of radar BS detection in challenging environments with strong interference, ensuring long-term detection accuracy stability across long maintenance intervals. However, transferring a successfully applied detection model from the original BF to a new target BF requires sufficient sample collection in the target BF and model retraining. In practical scenario, data collection is often constrained by plenty of factors like time, space, and personnel. Thus, reducing the number of samples needed for retraining, or implementing model transfer based on small samples, can significantly boost BS detection efficiency. This paper proposes a Conv-Adapter Transfer Net (CATNet) designed for the transfer problem of key point detection models in BFBS and small sample scenarios. The CATNet adopts a newly designed parallel Conv-Adapter transfer module, a small-scale deep learning network with a minimal parameter quantity. Compared to fine-tuning the entire backbone model with a large number of parameters, retraining this transfer module requires far less training data. Therefore, CATNet is more suitable for model transfer in small sample scenarios. The experimental results demonstrate that the CATNet can exhibit strong transfer capability and higher prediction accuracy than the commonly used pretrain-finetune method in small sample scenarios, thereby enhancing the efficiency of model transfer across different BFs.

The main application of steelmaking slag is base course material for road construction. In order to utilize slag as a base course material, it must possess the various characteristics specified in the relevant standard. Among these, the modified California Bearing Ratio (CBR) value, which evaluates performance as a base course material, is an important index in comparison with other competing materials. Although factors such as slag granularity and particle shape are expected to affect CBR characteristics and compaction properties, the particle properties and granularity of the steel slag differ depending on the refining processes in which the slag is formed. X-ray CT measurement of slag as base course material and the evaluation of effect of particle properties have not been examined until now. In this study, measurement of the internal phenomena of steelmaking slag as base course material by microfocus X-ray CT and various other measurements were carried out. This investigation revealed that the particle strength of porous particles was lower than that of dense particles regardless of the particle size, and the difference in base course bearing capacity was smaller than the difference in particle strength. Based on the mechanism by which stress propagates and an elastic finite element analysis were applied to the results obtained by X-ray CT, the stress distribution altered according to the change in the dispersion of the particle strength of each grain, and this affected the properties of the base course material, which is the integral value of the effective stress.

The purpose of this report is to compare the coating structure and corrosion mechanism of newly developed Zn-19%Al-6Mg-Si with conventional Zn–Al–Mg alloy coating Zn-11%Al-3%Mg-0.2%Si. In past papers the corrosion resistance of Zn–Al–Mg alloy coating layers was mainly discussed based on analysis methods that focus on one aspect of early corrosion stage. However, this report focuses on the changes in the corrosion mechanism until the end of the coating lifespan and picks up the factors of the coating layer that contribute to corrosion resistance.

The results of the corrosion cross section images of the Zn–Al–Mg alloy coating layer after cyclic corrosion test suggested that corrosion of the coating layer progresses selectively in each phase, which means each phase has its own electrochemical potential. Considering the differences in the corrosion mechanisms of these two coated steel sheets, it was suggested that the phase proportion of the coating layer and the unique potential determine the corrosion resistance of the coating layer.

Microstructures of lath martensite have been studied intensively to understand their effect on the mechanical properties of steels. It is, however, said that the relation between microstructural factors and mechanical properties has not been clarified yet. The plastic deformation behavior of fully lath martensitic steels has become important because they are applied to automobile body structures such as bumper reinforcement. It is, therefore, important to understand the microstructural factors that control the work-hardening behavior of fully martensitic steels. Although we could not clarify differences in microstructural factors when manganese (Mn) concentrations of steels are altered, the work-hardening of 8 mass%Mn martensitic steel is much higher than that of 5 mass%Mn martensitic steel. It was found using the digital image correlation (DIC) method, that the strain concentration due to the in-lath-plane slip deformation is more developed in 5 mass%Mn martensitic steel than 8 mass%Mn martensitic steel. Transmission electron microscope (TEM) observations revealed the existence of two types of fine twins inside laths. Long twins that are parallel to the longitude of the lath are observed both in 5 mass%Mn and 8 mass%Mn martensitic steels. Short twins that partially cross the laths, on the other hand, can only be found in 8 mass%Mn martensitic steel. Since twin boundaries are high angle boundaries, the short twins are supposed to prevent the development of in-lath-plane slip deformation. This seems to be the mechanism of higher work-hardening behavior observed in 8 mass%Mn martensitic steel.

Stress and plastic strain distributions and those partitioning behaviors of ferrite and retained austenite were investigated in the medium manganese (Mn) and the transformation-induced plasticity-aided bainitic ferrite (TBF) steels, and the martensitic transformation behaviors of retained austenite during Lüders elongation and work hardening were analyzed using synchrotron X-ray diffraction at SPring-8. The stress and plastic strain of retained austenite and volume fraction of retained austenite were remarkably changed during Lüders deformation in the medium Mn steel, implying that the medium Mn steel possessed inhomogeneous deformation at the parallel part of the tensile specimen. On the other hand, the distributions of the stress, plastic strain and volume fraction of retained austenite were homogeneous and the homogeneous deformation occurred at the parallel part of the tensile specimen at the plastic deformation regime with work hardening in the medium Mn and TBF steels. The martensitic transformation of retained austenite at Lüders deformation in the medium Mn steel was possessed owing to the application of high stress and preferential deformation at retained austenite, resulting in a significant increase in the plastic deformation and reduction of stress in the retained austenite. The martensitic transformation of retained austenite at the plastic deformation regime with work hardening was induced by the high dislocation density and newly applied plastic deformation in retained austenite in the medium Mn steel whereas the TBF steel possessed gradual transformation of retained austenite which is applied high tensile stress and moderate plastic deformation.

The effects of intergranular W-rich compounds (W₆C/W₁₂C and µ phases) on the creep properties of a γ’-precipitation-strengthened, wrought Ni-Co-based superalloy were examined. Two microstructures with different intergranular precipitates (but the same volume fraction and size of intragranular γ’ precipitates) were prepared by adjusting aging conditions, leading to two distinct grain-boundary precipitation microstructures, with grain-boundaries exhibiting: (i) W-rich compounds (W₆C/W₁₂C and µ), or (ii) W-free compounds (Cr₂₃C₆ and γ’ phases, as in conventional Ni-based alloys). In compressive creep tests, lower minimum creep rate and longer 1% creep life were observed for alloys with the second grain-boundary microstructure (with Cr₂₃C₆ and γ’) than for the first grain-boundary microstructure (with W₆C/W₁₂C and µ). On the other hand, in tensile creep tests, longer creep rupture life was observed for alloys with the first grain-boundary microstructure than for the second, especially at higher stresses. Based on the grain boundary precipitation strengthening mechanism, it is suggested that the difference in compressive minimum creep rate between both microstructures can be explained by the difference in grain-boundary coverage. In tensile creep tests, the creep rate due to cavity and crack growth appears to be the dominant factor in the overall creep rate at higher stresses, consistent with Stress Assisted Grain-Boundary Oxidation (SAGBO). It appears that the grain-boundary precipitation of W₆C/W₁₂C and µ phases is more effective in suppressing SAGBO than grain-boundary precipitation of Cr₂₃C₆ and γ’.

Fatigue tests under axial loading were conducted on steel with a shallow hardened layer induced by induction hardening, and in situ X-ray stress measurements were performed to investigate the relaxation of residual stresses during fatigue. The residual stresses were relaxed owing to tensile loading and not compressive loading. The two conditions that bring about this phenomenon are (i) a high peak of tensile residual stress just below the hardened layer, and (ii) the hardened layer coinciding with the compressive residual stress field that prevents the yielding of the compressive residual stress field under compressive loading. In this case, tensile yielding occurred just below the hardened layer under tensile loading, the residual stresses are redistributed, and the compressive residual stress on the material surface is relaxed. The experimental results also showed that the fatigue fracture morphology changed depending on the residual stress relaxation behavior.

The usage of LiFePO₄ (LFP) battery cathodes for electric vehicles (EVs) has increased in recent years. Phosphorus for LFP will be required for a comparable amount of fertilizer. However, the economically minable phosphate rock mines are decreasing, and the market for phosphorus is already tight. Thus, it is urgently necessary to promote the production of LFP based on secondary phosphorus resources. In this study, the production of LFP using phosphorus recovered from steelmaking slag was investigated. After selective leaching of steelmaking slag, the phosphorus in the extract is precipitated as FePO₄ by titration with FeCl₃ at pH=3. The FePO₄ was mixed with LiOH·H₂O and glucose (C₆H₁₂O₆) and heat treated at 700°C to prepare LFP. The FeCl₃ titration amount should be controlled within 0.6 stoichiometric mole ratio of Fe³⁺ to phosphorus to avoid the Fe₃PO₇ generation. The glucose should be mixed at the mole ratio of FePO₄/C=1.0 to prevent the Fe³⁺ from being over-reduced to Fe. The other elements, Ca, Si, Mg, Al, and Mn in the slag extract, did not affect the crystallization process and the structure of FePO₄ and LFP. The present study confirmed the feasibility of using steelmaking slag as a source of phosphorus for the preparation of LFP.

Wettability between molten iron and non-metallic inclusions is an important factor, as it influences the behavior of non-metallic inclusions during secondary metallurgy. In the present study, the wettability of CaS against molten iron was investigated using the sessile drop method at 1873 K. The CaS substrate was fabricated using spark plasma sintering, achieving a high relative density of 98%. The measured contact angle of CaS against molten iron was found to be 118 degrees. This finding indicates that the wettability of CaS is poor, which contrasts with the previous report. This result will contribute to further understanding regarding the inclusions’ behavior during secondary refining processes.

Fe–Si sheet, which has {110}<001> crystal orientation (Goss-FeSi), consists of Basic domain and Lancet-comb domain. Although the geometric structures of the Lancet-comb domain have been predicted by theoretical aspects, they have not been proved by experimental studies.

In this paper, we study the Lancet-comb domain structures of a Fe–Si steel by a volume sensitive method, i.e., transparent X-ray topography (XRT). From the XRT results, we found the parallelogram structures, which is bulk structure of the Lancet-comb domain. The long side of the parallelogram forms about 55° angle to the rolling direction and the short side forms about 35° angle to the rolling direction. We assigned the long side of the parallelogram to {110} domain wall and the short side to {111} domain wall based on the geometric analysis. This Lancet-comb domain model well explains the behavior of the magnetic moments of Goss-FeSi.

https://doi.org/10.2355/isijinternational.ISIJINT-2024-260

The authors have found that the Corresponding Author, Miyuki Hayashi’s ORCID ID in the above paper is incorrect. The authors would like to correct the ORCID ID as follows:

Original ID (incorrect)

https://orcid.org/0000-0001-8098-3024

Corrected ID

https://orcid.org/0000-0001-5449-2651