The recent rapid acceleration of the green transformation trend has become a major challenge that shakes the very foundation of the steel industry. This is in response to the activation of the Paris Agreement regarding so-called climate change issues and Japan's government's declaration of carbon neutrality.

It is difficult to achieve the lofty goal of carbon neutrality attained merely through conventional energy-saving and CO₂ reduction efforts. Instead, there is a need to invest vast amounts of energy to reduce CO₂, leading to the emergence of initiatives known as “increase energy and costs to reduce CO₂” The ratio of this increased energy and increased costs has become significantly high and is becoming unacceptable, which may result in some regions where industrial activities during the transition period may not be feasible before breakthroughs in technology through inventions are completed. This report reviews the trends regarding climate change response in the iron resource process from 2015 to the present and discusses the future direction of research and development in the Japanese steel industry.

This paper describes the high-efficiency technologies that have been implemented in Japan over the past 15 years in the blast furnace, sintering, and coke making process, respectively, that lead to CO₂ reduction. In addition, recent Research and Development efforts for future carbon neutralization were introduced. In 2021, Japanese steel companies launched their own carbon neutral conversion plans. The future view can be summarized as follows. (1) companies will accelerate their global expansion in response to shrinking domestic steel demand; (2) ironmaking processes will change and diversify in pursuit of carbon neutrality, and integrated optimization, including melting processes, will advance; (3) processes will diversify in response to resource inferiority; and (4) Accelerating labor-saving and automation to cope with a shrinking domestic workforce. Against this backdrop, technological development is expected to become increasingly important, and Japan needs to lead the world in pig iron making technology with its unique technological development. In parallel with these industrial implementations, the scientific backbone has been built through outcomes of ISIJ Type I/II Joint Research Committees and their special issues in Tetsu-to-Hagané and ISIJ International. Together, these “two wheels” have advanced: (i) blast furnaces via DEM-informed burden/charging, mixed-coke and RCA, CPS-based operation guidance, and industrial NG/COG/H₂ tuyere injections; (ii) sintering via MEBIOS/RF-MEBIOS and energy-saving REMO-tec; and (iii) cokemaking via defect-origin strength control and biomass-derived carbon resources that preserves CSR while enabling high reactivity. Transition routes—FERRO-COKE, COURSE50/Super COURSE50, carbon-recycling blast furnaces, and high-rate HBI charging—now define practical operating windows linking raw-material properties to permeability, reactions, and dripping behavior.

This review provides an overview of the development history of primary refining and related technologies as environment-conscious steelmaking processes in Japan since 2000, and discusses future prospects. For impurity removal in molten iron pretreatment, the application of mechanical stirring (KR) methods to desulfurization processes was expanded, and the powder injection method was applied to KR. For dephosphorization treatment, improved phosphorus removal efficiency was achieved through slag composition optimization, intermediate slag removal technology in converters, and powder top blowing. For high-efficiency converter operation, high-speed blowing technology has been applied, utilizing lance nozzles that suppress spitting. While the focus has been on achieving an environment-conscious steelmaking process by efficiently managing these core production processes, there is a recent trend toward also concentrating on slag treatment and slag recycling, which correspond to the ‘veins’ of the process. Furthermore, the remarkable advances in data science technology in recent years are increasingly being applied to the steelmaking process. As the diversification of iron sources, including molten iron, scrap, and direct reduced iron, is anticipated, we look forward to the creation of innovative, environmentally harmonious steelmaking processes suited to this new era through industry-academia collaboration.

This report discusses the operation and technological advancements and prospects of electric arc furnaces (EAF) steelmaking that use scrap as a raw material, which have been attracting atten-tion in the development aimed at achieving global carbon neutrality. It has been 120 years since the development of EAF, and it has achieved various advancements to realize high productivity, energy efficiency and operational stability during the growing application of EAF steelmaking. (For example: Ultra-High-Power operations, utilization of oxygen and fossil fuels, waste heat re-covery technologies, etc.) Furthermore since the year 2000, many advanced and fur-ther-developed technologies have emerged to improve the efficiency of auxiliary fuels and elec-tricity. (For example: Exhaust gas analysis device, STARQ, Consteel, ECOARC, Quantum, etc.) In the future, there is a possibility that the scrap situation will change, and we need to devel-op electric arc furnace technology while considering those changes. And in addition to changes in raw materials, we must overcome the challenges of responding to the increasing quality of prod-ucts and ensuring high productivity. Therefore, I believe it is necessary to collaborate not only with steel manufacturers but also with surrounding companies and research institution such as universities to further develop technology together.

This paper reviews emerging ironmaking technologies aimed at decarbonizing the steel industry. While the blast furnace route remains dominant, its substantial CO₂ emissions have accelerated the development of alternative processes. The review covers direct reduction methods, including shaft furnace and fluidized bed processes, highlighting their transition toward hydrogen-based operation and integration with electric arc furnaces. Smelting reduction technologies are examined for their adaptability to low-grade ores. In addition, electrolytic ironmaking and microwave-assisted reduction are introduced as electricity-driven, carbon-free concepts, though still at pilot scale. Key commercialization challenges—raw material flexibility, energy efficiency, cost competitiveness, and infrastructure—are discussed. The paper concludes by emphasizing the importance of technological innovation, renewable energy deployment, and cross-sector collaboration to achieve carbon-neutral steelmaking.

Linear friction welding (LFW) of a Ti-5Al-2Fe-3Mo was performed to clarify the effect of applied pressure on microstructure evolution and mechanical properties, particularly focusing on cold dwell fatigue behavior. Sound joints were successfully obtained under applied pressures of 50, 300, and 550 MPa. At 50 MPa, the joint interface consisted mainly of equiaxed β grains containing acicular α phases, indicating that the welding temperature was above the β transus. In contrast, at 300 and 550 MPa, the interface exhibited retained primary α, ultrafine equiaxed α grains of about 0.1 μm or less, slightly flattened β grains of less than about 1 μm, and α/β lamellar regions, suggesting welding below the β transus. The joint interface showed significant hardening due to grain refinement, while the adjacent region exhibited additional hardening attributed to work hardening under high pressure. Tensile tests revealed that all joints fractured in the base material, demonstrating joint strength comparable to that of the base metal. In both low-cycle fatigue and cold dwell fatigue tests, the joints also exhibited base metal fracture with fatigue lives that appeared to be similar to those of the base material. Compared with Ti-6Al-4V, the present alloy showed superior resistance to creep deformation and improved cold dwell fatigue performance. These results indicate that Ti-5Al-2Fe-3Mo is a promising alternative material for high-reliability LFW joints.

Hydrogen embrittlement in high-strength steels remains a critical challenge. In the presence of hydrogen, interactions between dislocations and grain boundaries (GBs) during deformation can initiate atomic-scale disorder at GBs, which may subsequently lead to intergranular fracture. Such disorder can be regarded as damage to GBs. Machine learning interatomic potentials (MLIPs) have recently emerged as a powerful approach for atomistic simulations, enabling reliable analyses of lattice defects and the effects of alloying elements. In this study, MLIP-based molecular dynamics calculations were conducted for the Fe–H binary system to separately investigate the origin of cleavage fracture at damaged and hydrogen-segregated GBs. A damaged GB was constructed by introducing vacancies uniformly into GB with atomically flat (110) plane. Such uniform damage induced boundary roughening, promoted dislocation emission, and resulted in local damage accumulation, leading to a reduction in GB cleavage strength. It was also found that the GB behaviors during deformation differ between uniformly distributed and localized damage states. Compared with the hydrogen-segregated but undamaged (110) GB, the vacancy-induced uniform damage resulted in lower GB strength but increased fracture strain. These results suggest that the damage state of GBs, in addition to hydrogen, has a significant influence on GB strength and may serve as an additional descriptor for GB characterization.

Steel industry is responsible for approximately 13% of CO₂ emissions in Japan. Therefore, it is important to reduce CO₂ emissions from steelmaking plants. Carbon Capture and Utilization (CCU) is a technology that aims at capturing CO₂ and converting it into a variety of products such as renewable fuels, chemicals, materials, and carbonates. Among CCU technologies, carbonation, the chemical reaction of CO₂ to give carbonates, is promising for steelmaking slag, which contains high amounts of CaO as raw materials for carbonates. To improve efficiency, a new carbonation process has been developed at JFE steel. The process realizes simultaneous heat recovery and carbonation by contact between slag and CO₂. By applying this technology, potential reduction of CO₂ emissions from steelmaking processes is expected. In this study, gram-scale experiments were carried out to establish a kinetic model for carbonation. It was found that the carbonation of steelmaking slag was promoted at approximately 600 °C and at high CO₂ concentration. Moreover, slags with high specific surface area exhibited higher carbonation amount. To simulate the experimental data, kinetic model considering 2 types of carbonation sites with different reaction rate was established. The calculated carbonation amount by the model showed good agreement with gram-scale carbonation experiments. The model also showed good agreement with kilogram-scale carbonation experiments.