This study develops a finite element-based numerical model to analyze the swelling behavior of coal particles during pyrolysis. The model incorporates volatile matter release, gas diffusion, viscoelastic deformation of the coal matrix, and internal bubble pressure to reproduce realistic deformation. Simulations on single coal particles revealed non-uniform swelling, with expansion concentrated in the central region where the matrix is thinner and softer, and suppressed near the particle edges due to higher stiffness. To evaluate the influence of coal properties, the model was applied to various coal types. The results showed clear differences in swelling behavior depending on volatile content and rheological properties. Coals with higher plasticity and volatile yield exhibited earlier and more pronounced expansion, while non-caking coals showed limited swelling and high internal pressure due to their high viscosity. This indicates that both volatile generation characteristics and the temperature-dependent mechanical properties of the coal matrix play key roles in determining swelling behavior. The proposed model provides a useful tool for quantitatively evaluating deformation mechanisms in coal particles and may contribute to the optimization of pore structure in coke manufacturing for ironmaking applications.

Reducing the greenhouse gas emissions from steel production can be done through direct reduction inside a shaft furnace using hydrogen gas as a reductant, generating water as an off gas. The temperature varies along the height of the shaft furnace, and studying the non-isothermal reduction is therefore necessary. In this work, industrial hematite pellets were non-isothermally reduced in a vertical tube furnace. Different gas mixtures containing water and hydrogen were used for reduction. The reduction gas used contained water vapor contents of 5%, 10%, and 20%, respectively, and the remaining gas was hydrogen. The experimental setup was carefully designed for the reductions to be carried out under well-controlled experimental conditions. It was clear that the water present in the reduction gas significantly decreased the reduction rate, especially at the lower temperatures. Moreover, the onset temperature of reduction was increased to around 525°C when water was present, compared to 450°C when pure hydrogen was used. Water contents above 5% lead to a low-rate stage at reduction degrees between 0.11 to 0.15. The low-rate stage ended when the wüstite phase became stable, changing the mechanism of reduction, which altered the chemical reaction rate. The reduction rate was less affected by water when the heating rate increased, since an increasing heating rate led to the reduction occurring at a higher temperature. Finally, the present study showed that the kinetics of non-isothermal reduction, using different water vapor contents, are very different from isothermal reduction.

This study systematically investigates the optical texture evolution of laboratory heat-treated coke under varying temperatures (1100–1500°C) and atmospheres (N₂/CO₂), with findings validated through comparative analysis of coke specimens (including feed coke and tuyere coke) from industrial blast furnaces (BFs). The effects of heat-treatment temperature, gasification reaction, radial position of lump coke, alkali loads, particle size degradation, and effective volumes of BFs on optical texture were quantitatively analyzed. The results demonstrated that under the N₂ atmosphere, the proportion of isotropic textures increased from 32.5% to 41.2% with increasing temperature, while anisotropic textures decreased. Under the CO₂ atmosphere, the Optical Texture Index (OTI) also decreased from 144.0% to 124.8%. This indicates a tendency of coke optical texture to transform from anisotropy to isotropy at high temperatures. Notable differences exist in the radial distribution of the optical texture of tuyere coke. Specifically, the optical texture in the outer edge regions of the lump coke is more significantly influenced by the conditions inside the blast furnaces BFs. Smaller particle sizes in tuyere coke correlated with higher alkali metal content and lower anisotropy. Furthermore, a declining trend in the OTI of tuyere coke was observed with an increasing effective volume of BFs, decreasing from 146% to 109%, suggesting a potential correlation between effective volume of BFs and the OTI of coke. These findings provide critical insights into the evolution of coke optical texture and the degradation mechanisms of coke in high-temperature zones of BFs.

The permeability index directly influences the gas-solid equilibrium within blast furnace, affecting the reduction reactions and overall furnace operation. Accurate prediction of permeability index remains challenging due to the system inherent complexity, time delays, and noise interference. This research proposes a hybrid TCN-GRU deep learning framework enhanced by variational mode decomposition (VMD) and error compensation (EC) correction for permeability index. First, a multi-stage feature selection method combining LightGBM and Spearman’s rank correlation analysis identifies key predictor variables while addressing time-lag effects. The permeability index series is then decomposed into intrinsic mode functions (IMFs) via VMD to mitigate non-stationarity. Each IMF is modeled using a TCN-GRU architecture that captures multi-scale temporal dependencies through dilated causal convolutions and recurrent gating mechanisms. To further refine results, prediction errors from IMF components are recursively fed back into the model for error compensation. Tested on production data from a steel plant in Southern China, the framework demonstrates exceptional performance in one-hour-ahead permeability index prediction, achieving a RMSE of 0.201, a R² of 0.965, and a remarkable hit rate of 98.039% within ±0.5 error margin. Crucially, it maintains strong multi-step prediction capability, delivering considerable hit rates for two-hour and three-hour predictions. These results underline the model’s ability to handle complex blast furnace dynamics, providing a robust tool for proactive process optimization. This approach advances intelligent ironmaking by enabling precise permeability index prediction, supporting energy conservation, and enhancing operational stability in industrial applications.

Deoxidation is a key process in refining liquid steel and enhancing its cleanliness. O removal from the melt is typically achieved by adding elements with a high affinity for O, such as Al, Si, or by adjusting a specific Mn/Si ratio in the melt. In the production of high-Si steels, precise knowledge of the equilibrium between the liquid metal and solid silica (SiO₂) becomes increasingly important. In the present study, a CALPHAD-based thermodynamic model for Si deoxidation in liquid Fe was developed, covering the full composition range from pure liquid Fe to pure liquid Si, including the O saturation limit. The Gibbs energy of the ternary Fe–Si–O liquid phase was formulated using the Modified Quasichemical Model (MQM) in the pair approximation, which accounts for strong interactions among Fe, Si, and O. Comparisons with experimental data demonstrated an excellent agreement in predicting the liquid/SiO₂(s) equilibrium within the temperature range of 1550–1650°C. Modeling the deoxidation equilibria in this ternary system can aid in refining the model description in binary Fe–Si liquid. The model predicted a pronounced “deep minimum” in O solubility. It was in agreement with an experimental approach reported by Shibaev et al. (https://doi.org/10.2355/isijinternational.45.1243) and with another thermodynamic approach by Cho and Kang (https://doi.org/10.1007/s12613-023-2766-7). The present assessment can be incorporated into CALPHAD databases for applications in steelmaking and liquid metal processing.

To investigate the impact of deoxidizer addition sequence on the cleanliness of Al-killed and S-containing steel Cf53, adding Al ingots followed by SiCaBa alloys (A-SCB scheme) and adding SiCaBa alloys followed by Al ingots (SCB-A scheme) during converter tapping were conducted in industrial trials. Through systematic sampling and SEM-EDS analysis, the chemical composition of steel and slag, as well as the characteristics (type, size, and quantity) of non-metallic inclusions were compared. Industrial trials reveal the differences in T.O and T.Al contents, along with inclusion quantities during LF refining of the both schemes. The A-SCB scheme produces more Al₂O₃ and MgO–Al₂O₃ inclusions during LF refining, while the SCB-A scheme results in more CaO–MgO–Al₂O₃ inclusions. Both schemes mainly generate CaS-bearing inclusions in casting billets, while the size of inclusions in A-SCB scheme is larger than those in SCB-A scheme. Thermodynamic analysis reveals that adding SiCaBa alloys first acts as a pre-deoxidation step, enhancing alloying effects of subsequent Al ingots addition, thus SCB-A scheme achieves a higher Al yield. Variations in T.Al, T.O content, and inclusion evolution during LF refining are influenced by the composition and oxidation potential of refining slag. In the vacuum degassing treatment and tundish casting, the T.Ca and T.S contents in steel, and molten steel temperature significantly affect the inclusion evolution. Ultimately, altering the deoxidizer addition sequence influences Al yield, but has limited effect on steel cleanliness. This study provides a practical guidance for optimizing deoxidizer addition sequence for Cf53 steel and elucidates the mechanism via thermodynamic analysis.

Three-way servovalve controlled cylinder (TSCC) is the main method used in hydraulic automatic gauge control (HAGC) system of rolling mill, which generally only foucus on the screw-down speed of HAGC cylinder under load resistance. However, with the development of plan view pattern control and variable gauge rolling, the lifting-up speed of HAGC cylinder is required to be as high as the screw-down speed. At present, high frequency response and large flow servovalves or even double servovalves in parallel are usually used to achieve high lifting-up speed, resulting in a substantial increase in equipment cost. In this paper, the nonlinear mathematical models of the TSCC and four-way servovalve controlled cylinder (FSCC) are firstly established, and the steady-state speed equations of the two methods are derived. Then, the steady-state speed of the two methods with different HAGC cylinder sizes under different load conditions is compared and analyzed, and it is proved that FSCC has obvious advantages in lifting-up speed. Finally, simulation experiments of variable gauge rolling on a 1050 mm cold-rolling mill are carried out. In the rolling process of transition zone where the roll gap increases, the FSCC has higher control precision and wider dynamic adjustment ability, which is more conducive to improving rolling speed, production efficiency and shape quality.

Online crown calculations are essential for effective shape control of hot-rolled strip steel, the accuracy of which is often limited by modeling assumptions and the complexity of operating conditions. Model parameters significantly influence calculation accuracy, requiring process engineers to make regular adjustments based on their experience. As customization, small batch sizes, and multiple specifications become mainstream in production and supply modes, reliance on manual experience is increasingly insufficient. This paper aims to enhance the accuracy of online crown calculations for hot-rolled strip steel. Initially, based on the mechanism model incorporating gain coefficients and formula derivation, a relational expression between the gain coefficients for each stand in the tandem rolling mill group and the final crown is established, transforming the discrete issue of correcting influential factors into a unified problem of solving gain coefficients, thus improving correction efficiency. To ensure the reliability of the estimated results, three forms of constructing the constraint equation are compared: no constraint, limiting the proportional crown difference, and proportional exit crown. Utilizing rolling production data, two parameter estimation methods—normal linear regression and robust regression—are explored to determine the gain coefficients. Results indicate that combining the constraint based on proportional exit crown and robust regression will provide more reliable gain coefficients and significantly enhances the accuracy of online crown calculations, improving precision by over 50% compared with the model before correction.

Although the instrumented Taylor impact (ITI) test has been extended to measure the unknown mechanical behavior of pure aluminum at ultra-high-speed impact, it remains uncertain whether the important assumption that internal force distributes linearly in certain regions holds for other materials. Hence, in this work, pure iron, whose deformation behavior at ultra-high-speed impact remains unknown due to the speed limitations of existing methods, is introduced into the ITI test to verify the assumption and attempt to evaluate its mechanical behavior. The assumption is verified using the digital image correlation (DIC) method. Unlike the pure aluminum specimen, the assumption holds for a relatively longer time period in the case of pure iron. According to the experimental results, a previously uncaptured high frequency component in the impact force wave is newly discovered using a polyvinylidene fluoride (PVDF) film instead of a strain gauge. Hence, the impact force wave should be measured using a PVDF film rather than a strain gauge. The shock wave is observed for the first time in the ITI test using a pure iron specimen. Additionally, a previously unreported opposite pulse in the impact force wave was newly observed in the ITI test, implying that the magnetic properties of the material might have changed.

In the cold sheet rolling process of steel, the deformation of the steel sheet and friction between the roll and steel sheet lead to the generation of iron fines. When steel is mass produced, the generation of iron fines can cause pollution. When the base oil is hydrolyzed under catalysis by iron fines and heat, hydrolyzed products, such as fatty acids, can react with iron fines to form iron soap, which is the major component of scum. The generation of scum decreases the emulsion stability of the rolling oil coolant, and its accumulation inside the cold rolling mill causes dirt. Therefore, it is important to understand the factors that affect the generation of iron fines.

In this study, experiments were conducted to compare the generation of iron fines under different rolling and lubricant conditions in an experimental rolling mill. The amount of iron fines generated increased with the number of rolling passes at the same reduction in thickness. However, after considering the increase in the rolling distance, the amount of iron fines generated per unit rolling length was similar. The amount of iron fines generated increased as the surface roughness of roll increased, emulsion concentration increased, emulsion temperature decreased and base oil viscosity increased. The results show that the rolling and lubricant conditions can be changed to establish an evaluation method to develop a new rolling oil for achieving low generation of iron fines and good surface cleanliness after cold rolling.

The metastable Fe₅₀Mn₃₀Cr₁₀Co₁₀ (at.%) high-entropy alloy (HEA) integrates the principles of HEA and transformation-induced plasticity (TRIP), resulting in an exceptional combination of tensile strength and ductility. However, the inherently low yield strength restricts its application as a structural material. In this study, 50% warm rolling at 573 K was employed as a straightforward and cost-effective thermomechanical processing strategy to fabricate metastable Fe₅₀Mn₃₀Cr₁₀Co₁₀ HEA with enhanced yield strength while retaining large ductility. The mechanical responses and deformation behaviors of the metastable HEA were examined using room temperature tensile tests, along with postmortem X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) analyses. Compared to the fully recrystallized counterparts, the warm-rolled specimens exhibited a threefold increase in yield strength while retaining substantial uniform elongation. The warm rolling treatment increased the mechanical stability of the austenitic phase against stress-assisted γ-ε martensitic transformation, shifting the yielding mechanism from martensitic transformation to dislocation slip, thereby enhancing the yield strength. Moreover, warm rolling completely suppressed the athermal γ-ε martensitic transformation even at 77 K, while the strain-induced γ-ε martensitic transformation remained pronounced at room temperature, contributing to the alloy’s high strength and large ductility.

A heat transfer model developed under conditions analogous to industrial online quenching demonstrates enhanced relevance and applicability to real-world manufacturing processes. This research explores the heat transfer characteristics of a single nozzle jet impinging on a steel plate closely resembling industrial environments, primarily focusing on the wetted area, heat flux density, and temperature drop at different widths and depths in the wetted zone. Key experimental parameters include the initial temperature of the steel plate (T₀), jet impingement velocity (v_j), and the moving speed (v_m) of the plate. The T₀ ranges from 750°C to 450°C, v_j varies between 2 and 7 m/s; and v_m ranges from 0.07 to 0.28 m/s. Heat transfer characteristics within the wetted region strongly correlate with T₀, v_j and v_m, with the impact point exhibiting the highest sensitivity. Furthermore, the temperature drop along the depth is influenced not only by these parameters but also by the depth itself. Mathematical expressions are proposed to predict the peak heat flux density and temperature drop based on external parameters (T₀, v_j, v_m). This study deepens the understanding of heat transfer dynamics in moving jet cooling and provides a comprehensive three-dimensional perspective on jet impingement heat transfer.

The microstructural evolution and tensile properties of joints fabricated by the newly developed cold spot joining (CSJ) method were investigated using galvannealed DP 780 MPa steel sheet. The novel solid-state joining method called CSJ is proved to make the joining interface plastically deformed under high pressure and appropriate current by expelling Zn–Fe coated layer, resulting in the sound joints with strong interface. Joints exploiting CSJ method were made focusing on the effects of the pressing speed and current level. Microstructural observations of the joints revealed that the lower pressing speed increases the interface temperature. In addition, the increase in the current also increases the interface temperature. The increase in the interface temperature has a positive effect in terms of expelling Zn–Fe coated layer. The positive effect of increasing current is more significant than that of decreasing the pressing speed. The increase in temperature near the interface by increasing current promotes the removal of the Zn–Fe coating layer, resulting in plastic deformation near the joining interface. Appropriate pressure and current settings can facilitate the sound spot joints with enough tensile strength. Both tensile-shear and cross-tension tests have confirmed a plug failure in the base material region.

Boron (B) is frequently used as an additive to improve the hardenability of advanced high strength steel. Based on thermodynamical calculations, it has been reported that B in steel reacts with atmospheric N₂ during annealing at a low oxygen potential (low dew point) to form boron nitride (BN). In this study, the effect of BN formation on the steel surface on coatability during hot-dip galvanizing was investigated experimentally. B-free specimens and specimens containing 15 or 30 ppm B were annealed at various temperatures and dew points and then hot-dip galvanized. Annealed specimens were also prepared and analyzed by GD-OES, XPS, SEM-EDX and TEM-EELS to investigate oxide and nitride formation on the steel surface during annealing. As results, coatability was deteriorated as the B content in the steel and the annealing temperature increased and as the dew point decreased. These trends were not correlated with the amount of oxides, but rather, with the amount of BN formation, indicating that BN formation deteriorates coatability. Surface and cross-sectional analyses revealed that BN formed around oxides, covering the steel surface. It was suggested that this leads to deterioration of coatability because most of the steel surface is covered by BN and oxides, which are both known to have low wettability with molten Zn.

Controlling martensitic transformation behaviors in metastable austenitic steels is key to developing high-performance materials with an optimal balance of strength and ductility. When a bending load is applied during the manufacturing process, tensile and compressive loads are applied simultaneously, which can result in a transformation behavior that differs from that observed under uniaxial tensile loading due to the distributions of stress/strain and stress triaxiality. In the present study, a multimodal approach combining high-resolution X-ray nano-tomography and X-ray diffraction (XRD) was employed to investigate the martensitic transformation behavior of transformation-induced plasticity (TRIP) steel during bending tests. The martensitic transformation of austenite grains was analyzed to evaluate the effects of the grain size, grain shape, crystal orientation, and stress distribution. The transformation behavior was influenced primarily by the stress distribution, whereas the transformation rate was scattered among individual grains due to differences in grain size and shape. These variations were attributed to the effects of local stress concentrations.

The strengthening mechanism of ausforming in martensitic steels is believed to be due to the inheritance of dislocations in austenite by the subsequently transformed martensite. However, no studies to date have quantified the dislocation density before and after ausforming. In this study, the dislocation densities of Fe-5%Mn-C alloys were analyzed, and the relationship between hardening by ausforming and dislocation accumulation, as well as the effect of carbon on this relationship, were investigated. The hardness of ausformed martensite increased with the ausforming reduction in austenite, and the strengthening effect of ausforming increased with the addition of carbon. Similarly, the dislocation density of ausformed martensite increased with the ausforming reduction in austenite, and the dislocation accumulation by ausforming increased with the addition of carbon. Because the hardness of the ausformed martensite follows the Bailey–Hirsch relationship, the strengthening mechanism owing to ausforming could be explained by dislocation strengthening. To understand the dislocation accumulation process during ausforming, the dislocation density of austenite immediately after ausforming was measured by in-situ heating neutron diffraction. Consequently, the dislocation density of the ausformed austenite was not dependent on the carbon content, indicating that dislocations are not inherited in carbon-free steels. By contrast, in steels with sufficient carbon content, not only are dislocations inherited but additional dislocations are introduced during martensitic transformation.

The effect of nitrogen introduced by solution nitriding on microstructure and mechanical properties of modified 9Cr-1Mo (Gr. 91) steel at room temperature was investigated. The nitrogen concentration at the sample surface was 0.164 wt% and nitrogen diffused at least 5000 µm after solution nitriding heat treatment at 1200°C for 48 hours. The martensite with a small amount of MX carbonitride with cF8 structure and retained austenite was formed on 100 µm from the sample surface. The Cr₂N phase with hP9 structure containing V, Nb and Mo and Cr₂₃C₆ phase with cF116 structure precipitated by tempering. Solute nitrogen improved the hardness, yield strength, ultimate tensile strength and uniform elongation. However, the nitride formation did not contribute to the improvement of hardness and decreased yield strength and ultimate tensile strength. It suggests that the contribution of solid solution strengthening by Cr, V, Nb and Mo is larger than that of precipitation strengthening by nitride at room temperature.

The effects and mechanisms of various alloying elements on the characteristics of Ni-based alloys have not yet been systematically investigated, despite the widespread application of such alloys in diverse domains. To address this gap, in this study, we investigated the effects of the substitutional alloying elements, specifically Fe, Cr, Mo, and Mn, on the lattice expansion, mechanical properties, hydrogen diffusivities, and solubilities of Ni. These elements led to both austenite lattice expansion and strengthening. We measured hydrogen diffusivities under high-pressure hydrogen environments (100 MPa) and desorption at constant temperatures. Notably, all the examined alloying elements reduced the hydrogen diffusivity of Ni in the order: Mn < Mo ≈ Fe < Cr. The effects of alloying cannot be simply explained by lattice expansion or strengthening but are attributed to increased activation energy for hydrogen diffusivity. We also assessed the hydrogen solubility through thermal desorption analysis (TDA) after exposure to high-pressure hydrogen (100 MPa). Except for Fe, alloying elements increased hydrogen solubility in the order: Cr < Mo ≈ Mn. These effects are attributed to changes in the activation energy of hydrogen solubility. Additionally, TDA spectra for almost all the alloys, simulated based on the temperature dependence of hydrogen diffusivity, indicated that hydrogen diffusion through the face-centered cubic lattice remained unaffected by hydrogen trapping.

Microtensile tests combined with crystal plasticity finite element simulations were performed on a single-packet structure of a nano-bainite steel. The steel microstructure consisted of bainitic ferrite and retained austenite, and its constituents were formed according to the Nishiyama–Wassermann crystallographic orientation relationship. The single-packet specimens exhibited plastic anisotropy in their yielding behavior, similar to those of lath martensite and upper bainite. The deformation-induced transformed martensite variants demonstrated high kernel average misorientation values owing to the introduction of a large number of dislocations, and these crystallographic orientations were similar to those of the adjacent bainite variants, in which the slip system with the highest Schmid factor was nearly parallel to the transformation system. A numerical analysis incorporating a crystal plasticity constitutive model that accounted for the martensitic transformation closely represented experimental stress–strain responses, demonstrating the effectiveness of the proposed method. When applied to polycrystalline structures, multiaxial stress distributions promoted martensitic transformations, leading to significant strain hardening. Assuming a high austenite strength in the analysis model, the strength increased owing to the bainitic matrix, whereas strain hardening was limited because of the suppressed martensitic transformation. In contrast, assuming low-strength austenite in the model, the yield stress was slightly reduced while the martensitic transformation was enhanced, which resulted in pronounced strain hardening and a high tensile strength. These findings suggest that the incorporation of low-strength austenite within a high-strength matrix can optimize the balance between strength and ductility.