This study has analyzed the growth and removal mechanisms of Al₂O₃, MgO, MgAl₂O₄, ZrO₂, SiO₂, and Ti₃O₅ inclusions in molten steel formed through the addition of various deoxidizing elements by dividing them into single inclusions and cluster inclusions resulting from the agglomeration of these inclusions with a focus on the kinetics. Additionally, we have evaluated the maximum particle diameter of cluster inclusions from both thermodynamics and agglomeration force perspectives to examine the agglomeration properties and mechanisms of various inclusions. The growth mechanism of various single inclusions, measuring several micrometers in diameter and suspended in molten steel, is governed by Ostwald ripening with collision agglomeration due to Brownian motion and turbulent stirring. Contrarily, cluster inclusions with diameters of 10 µm or more float in molten steel agglomerate with suspended single inclusions. Depending on the inclusion type, they also agglomerate with other clusters along their floating path, growing larger and undergoing floating separation. Furthermore, the agglomeration strength of various inclusions in molten steel follows the order MgO < Ti₃O₅, SiO₂ < MgAl₂O₄ < ZrO₂ < Al₂O₃. The kinetic mechanism of agglomeration growth is explained in a unified manner by the interparticle interactions of agglomeration force driven by cavity bridge forces.

This study focuses on the warpage behavior in strip rolling, particularly on the formation of shear bands, that potentially give reasonable account of the warpage behavior. Rolling experiments and rigid-plastic finite element analyses were conducted to clarify the effect of each factor on the equipment one and the material one to the control of warpage, yielding the following results:

(1) As the experimental and analytical conditions, two asymmetrical rolling factors adopted together, strip entering the roll-bite with an angle ±8°, and a single roll driven condition. As a result, direction of warpage is determined by the shape factor Γ (contact arc length / thickness). Γ ≤ 1.6; direction of warpage is mainly influenced by the strip's inclination. Γ ≥ 1.9; direction of warpage is mainly influenced by the driving conditions. The strip's inclination significantly affects the shear stress distribution and the form of shear bands, especially when Γ ≤ 1.6. On the other hand, the driving conditions of rolls have a greater influence when Γ ≥ 1.9.

(2) To investigate the effect of work hardening index (n value) of the rolled material on the warpage behavior, single driven rolling experiments and analyses were conducted using materials with different n values. N value of the rolled material affects the concentration of shear bands, which in turn influences the warpage behavior. A larger n value, i.e. great work hardening material that tends to broad the strain concentration, results in lower concentration of shear bands, and smaller warpage curvature.

Micro-yielding occurs during macro-yielding in the steel, or polycrystalline material. In this phenomenon, some grains start to transform preferentially at lower strain, or the steel has preferentially deformed grains. However, this phenomenon has mostly been studied in uniform-grained steel so that the effect of duplex-grains is not clear. In this study, preferentially deformed grains during micro-yielding in duplex-grained austenitic steel are investigated. Rotation angle of every grain as deformation is analyzed with SEM-EBSD. Every preferential deformed grain has no trend for grain size and Schmid factor separately. In case grains which are in contact with a preferential grain have larger size and larger/smaller Schmid factor than it, it may be affected by around grains into deforming (Case I). On the other hand, in case grains which are in contact with a preferential grain has smaller size than it, it has larger size and larger Schmid factor (Case II).

We attempted to improve the strength–ductility balance in tempered martensite steel using multi-objective Bayesian optimization. The martensite steels were tempered at two stages, and fine and coarse cementite particles were mixed. Water-quenching rather than furnace-cooling between the first and second temper stages provided a better balance of strength and ductility. Moreover, the strength–ductility balance was also improved by tempering at a low temperature in the first stage and a high temperature in the second stage, rather than tempering at a high temperature in the first stage and a low temperature in the second stage. Based on these experimental results, multi-objective Bayesian optimization was used to further improve both tensile strength and total elongation. The strength–ductility balance that is better than the experimental results was achieved with a minimal number of optimization times. Additionally, machine learning suggested that it is crucial to control the average aspect ratio of cementite particles to less than 1.8 and the size of coarse cementite particles to less than 2.0 μm in order to improve the strength–ductility balance.

This study investigated the fundamental aspects of signal enhancement in arc-plasma-assisted laser-induced breakdown spectroscopy (AP-LIBS), as a crucial step towards its potential application for enhanced real-time compositional analysis in electric arc furnaces (EAF). By superimposing a sustained arc discharge with nanosecond laser pulses on molten iron, AP-LIBS achieved significant signal enhancement compared with conventional LIBS. Spatiotemporal characterizations revealed that the enhancement was most pronounced in the peripheral plasma region, characterized by larger plasma size and longer lifetime in AP-LIBS setups. The enhancement factor η, defined as the ratio of AP-LIBS signal intensity to the sum of individual arc and laser-induced plasma intensities, exceeds 10 for most emission species. Spatial distribution analyses show increased emission intensities at greater distances from the laser spot in AP-LIBS, in contrast to the decay observed in standard LIBS. Temporal analysis demonstrated extended high-intensity periods for AP-LIBS compared to the rapid decay in conventional LIBS techniques. The spatiotemporal behavior of the enhancement factor varies significantly among the emission species, thereby providing insights into complex plasma dynamics. Elements with low vapor pressure and ionic species generally exhibited higher enhancement, whereas elements with high vapor pressure exhibited limited enhancement, indicating minimal additional evaporation effects for high vapor pressure element. These findings provide valuable insights into plasma generation and maintenance mechanisms in AP-LIBS, suggesting its potential for improved sensitivity in elemental analysis for electric arc furnace applications.