While extensive research has focused on the agglomeration of Al (Formula presented.) O (Formula presented.) inclusions in low-carbon, Al-killed steels, the behavior of non-Al (Formula presented.) O (Formula presented.) inclusions in Si- and Si/Mn-killed steels remains poorly understood—despite their widespread industrial use and importance for steel cleanliness. This study investigates the in situ agglomeration of semisolid Al–silicate inclusions in Si-killed steel using high-temperature confocal scanning laser microscopy. Particle velocity, acceleration, and attractive forces at the steel/argon interface were measured directly. A modified capillary interaction model, based on the Kralchevsky–Paunov framework, was applied to calculate interparticle forces and showed good agreement with experimental results. Compared to Al (Formula presented.) O (Formula presented.) inclusions in Al-killed steel, Al–silicate inclusions exhibited significantly weaker attractive forces (10 (Formula presented.) to 10 (Formula presented.) N) and a shorter interaction range (∼34 µm), indicating a lower tendency to agglomerate. These findings highlight key differences in inclusion behavior between steel types and confirm the model's applicability to semisolid systems.

In this study, the kinetics of melting hydrogen-direct reduced iron (H-DRI) and commercial-direct reduced iron (C-DRI) reduced by natural gas, in EAF slags containing 20 to 30 pct FeO at 1873 K, were investigated. The melting behavior of DRI pellets in the slag was visualized using X-ray fluoroscopy. There were fundamental differences between H-DRI and C-DRI melting and reacting with slag. (1) Considerable CO gas was generated during the melting of C-DRI due to the reaction of C and FeO, while there was no gas evolution from H-DRI melting due to the absence of carbon. (2) The stirring effect caused by the CO bubbles during C-DRI melting significantly improved the heat transfer by convection, and it accelerated melting and reaction kinetics; therefore, the rate of C-DRI melting was much faster than that of H-DRI. (3) The generated CO resulted in slag foaming, i.e., intensive slag foaming was observed during the melting of C-DRI pellets, whereas no slag foaming was observed during the melting of H-DRI pellets. (4) Slag’s FeO content impacted the rate of DRI melting; increasing slag’s FeO content from 20 to 30 wt pct, which shortened the melting duration of H-DRI pellets from 148 seconds to 120 seconds. The investigation demonstrated the key role of C content in DRI during DRI melting and future EAF operation with H-DRI.

Ironmaking is a crucial step for integrated steelmaking, which consumes a significant amount of energy and is the main CO₂ emission source for the whole steelmaking industry. In the Netherlands, Tata Steel, previously known as Koninklijke Hoogovens and Corus, runs an integrated steel plant and produces high-quality flat steel with more than 100 years of history (since 1918). TU Delft, the oldest technical university in the Netherlands with over 180 years of history, holds the education and research program in process metallurgy, to support the technology innovations in the metallurgical industry. Close cooperation between TU Delft and Tata Steel in process fundamentals and technology developments has a long history. This paper focuses on the cooperation in the recent 25 years from the new millennium in ironmaking research: from the blast furnace (BF) process, the “HIsarna” smelting reduction, to the future H₂-based technologies. Tata Steel has its own R&D center, focusing more on applied research to support production now and in the future. The research at TU Delft focuses more on the process fundamentals and supports process optimization and new process development. Long-term and continuous industry-academic-national funding schemes with the assistance of Materials Innovation Institute (M2i) are instrumental in supporting the academic industry alliance. Joint EU-funding applications as partner pair is another cooperation path. A recently awarded 8-year program as part of the Dutch national growth funds: Growing with Green Steel (GGS) is a good example, where the H₂-based ironmaking is an important part of the program. The paper will highlight the flagship projects in ironmaking technologies: BF cohesive zone simulation, nut-coke in BF, suspension pre-reduction and H₂-enrichment in HIsarna, H₂-based direct reduction, as well as the industrial decarbonization technology pathways. It is believed that fundamental research with a long-term funding scheme will facilitate a more rapid green transition of the steelmaking industry.

Dissolution kinetics of CaO·2Al₂O₃ (CA₂) particles in a synthetic CaO–Al₂O₃–SiO₂ steelmaking slag system have been investigated using the high-temperature confocal laser scanning microscope. Effects of temperature (i.e., 1500, 1550, and 1600 °C) and slag composition on the dissolution time of CA2 particles are investigated, along with the time dependency of the projection area of the particle during the dissolution process. It is found that the dissolution rate was enhanced by either an increase in temperature or a decrease in slag viscosity. Moreover, a higher ratio of CaO/Al₂O₃ (C/A) leads to an increased dissolution rate of CA₂ particle at 1600 °C. Thermodynamic calculations suggested the dissolution product, i.e., melilite, formed on the surface of the CA₂ particle during dissolution in slag with a C/A ratio of 3.8 at 1550 °C. Scanning electron microscopy equipped with energy dispersive X-ray spectrometry analysis of as-quenched samples confirmed the dissolution path of CA₂ particles in slags with C/A ratios of 1.8 and 3.8 as well as the melilite formed on the surface of CA₂ particle. The formation of this layer during the dissolution process was identified as a hindrance, impeding the dissolution of CA₂ particle. A valuable reference for designing or/and choosing the composition of top slag for clean steel production is provided, especially using calcium treatment during the secondary refining process.

As a result of the global transition towards green steel production, integrated steel plants are optimizing the existing processes and/or adopting new steelmaking methods to minimize their carbon footprint. These adjustments affect desulfurization conditions and requirements. The present study examines how the desulfurization is impacted for both hot metal and liquid steel across three routes: the traditional blast furnace (BF) - basic oxygen furnace (BF-BOF) with increased scrap ratio, the direct reduced iron (DRI) - electric arc furnace (EAF) with varying scrap to DRI ratios, and the DRI - electric smelting furnace (ESF) - BOF. This work discusses challenges and possible solutions for each route.

The dissolution process of CaO·2Al₂O₃ (CA2) particles in CaO-SiO₂-Al₂O₃ steelmaking slags was in situ investigated at 1550 °C. To better understand the role of particle porosity in dissolution kinetics, the particles with two different porosity levels, i.e., 0.08 and 0.20 were used in this study. The porosity (φ) and surface area of CA2 particles were characterized through X-ray Computed Tomographic Imaging (XCT), and the surface area ratio (f(φ)) between the porous and full dense particles was expressed as f(φ)=0.9398e5.9498φ. The obtained results indicated that an increase in the porosity from 0.08 to 0.20 led to an increase in the average dissolution rate from 0.35 to 0.59 μm/s. Moreover, the motion of CA2 particles during the dissolution process was observed, suggesting its importance to include in the modeling approach. A novel mathematical model was developed to predict the dissolution time of inclusion particles by incorporating both the motion and porosity of particles. This model was validated against the existing literature data and aligned well with the current experimental findings. The model predictions demonstrated that the dissolution time of CA2 particles was decreased with an increase in the velocity and porosity of particles and concentration difference of dissolving species between particle–slag interface and molten slag (∆C), and a decrease in slag viscosity.

The dissolution kinetics and mechanisms of solid calcium aluminate inclusions (CaO∙2Al₂O₃ (CA2) and CaO∙6Al₂O₃ (CA6)) in CaO-Al₂O₃-SiO₂-(MgO) metallurgical slags at 1550 °C were investigated using high temperature confocal laser scanning microscopy (HT-CLSM). The effects of slag viscosity, CaO/Al₂O₃ (C/A) ratio, and MgO content on the dissolution time of CA6 and slag MgO content on that of CA2 particles were examined by tracking the time dependent changes of particle projection areas. The obtained results showed that the dissolution kinetics of CA2 and CA6 particles was enhanced by an increase in slag MgO content. Moreover, increasing C/A ratio of slag or decreasing slag viscosity improved the dissolution rate of CA6 particles. Post dissolution analysis using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDS) combined with thermodynamic calculations revealed the dissolution paths of CA6 particles in slag S3 with C/A ratio 3.8 and S6 with 8.0 wt% MgO, where the dissolution time is out of expectation. It was found that an intermediate solid layer melilite formed around the undissolved CA6 particle in slag S3 with C/A ratio 3.8, reducing its dissolution rate. Conversely, the formation of randomly dispersed intermediate solid products around the undissolved CA6 particle in slag S6 with 8 wt% MgO did not impend their dissolution rate. Finally, based on the obtained findings, two distinct dissolution mechanisms were proposed advancing the understanding of solid inclusion dissolution in metallurgical slags. The findings obtained from this study aim to provide new insights to further improve steel cleanliness for a longevity of the product service life.

In this study, different existing methods to remove alloyed and coated copper from steel are summarized, compared, and discussed. None of these methods have been scaled up industrially so far. Characterization of industrial steel scrap will indicate in which forms and quantities copper is present. Based on environment, economics and process efficiency, the most promising techniques will be selected for further investigation. The study will then focus on ways to bring the process efficiency to the level required for industrial application, by better understanding of thermodynamic limits and the reaction kinetics. Possible removal of other undesired elements from the scrap will be taken into account as well.