In the context of supersonic oxygen jets impinging on the bath surface, understanding the gas-bath interaction mechanism is of paramount importance for optimizing lance design in the converter for steelmaking process. This study employs a coupled VOF model and realizable k-ε turbulence model to simulate the gas/metal/slag turbulent flow in a 180 t converter for exploring the essential aspects such as cavity, stirring dead zone, slag-metal splash, and kinetic energy distribution. To validate the model reliability, the numerical results are compared with experimental measurement. The results indicate that: the shear stress from the deflected oxygen jet induces surface waves in the cavity, propagating from its edge to the converter wall. The total splashing volume of the metal and the slag is minimal at a nozzle inclination angle of 14°, while the mass ratio of entrained molten iron in the splash is lowest at an inclination angle of 18°. The slag kinetic energy typically accounts for approximately 30% of the total kinetic energy of the bath. Remarkably, the slag layer, equipped with 4 nozzles and an inclination angle of 14°, demonstrates the most efficient utilization of the molten bath stirring energy, constituting an impressive 34.03% of the total kinetic energy. Moreover, a larger characteristic cavity depth expedites local circulation motion while diminishing the overall stirring performance in the bath. These findings provide valuable insights into the behavior of multiple supersonic oxygen jets in the converter, furnishing essential information for process optimization and design in the steelmaking industry.

Since 10 million tons of steelmaking slag, which contains a few percent of phosphorus, are annually produced, the phosphorus amount in the slag is equivalent to the annual import volume of phosphorus rock in Japan. Therefore, the steelmaking slag is attracting attention as a potential phosphorus resources. Phosphorus-concentrated slag obtained by the dephosphorization reaction between high phosphorus hot metal and oxidizing slag at high temperature contains phosphorous comparable to that of phosphorus rock. However, because of high FeO concentration, it is difficult to use for phosphorus resources directly. In this work, the effects of pH, acid type and leaching method on the dissolution behavior of phosphorus from P-concentrated slag were investigated. As a result, phosphorus dissolution progressed at lower pH, and was promoted by the addition of citric acid, which is known as a chelate former. When nylon mill pot stirring with citric acid and alumina mill pot stirring with nitric acid were compared to impeller stirring, respectively. By combining nylon mill pot stirring and citrate leachate, phosphorus dissolution was accelerated, because the slag was pulverized during stirring and a formation of insoluble metal-phosphate was inhibited by the formation of complex ion between leached metal cation and citrate. When the slag was leached with alumina mill pot while controlling pH by nitric acid, the phosphorus dissolution ratio lowered since phosphorus ion and aluminum ion, which is supplied by the dissolution of pot and crushing ball during leaching, constructed secondary products with low solubility along with other dissolved ions.

In this study, influence of crystal structure and chemical composition for Silico-Ferrite of Calcium and Aluminum (SFCA) on its reducibility are examined. Eight types of powder samples containing SFCA and SFCA-I were prepared using chemical reagents by the heat treatments in air. The samples were heated up to 800°C in the different atmospheres of CO–CO₂–H₂–H₂O systems. The reducibility of the samples was evaluated using the peak intensity ratio identified by XRD before and during the reduction experiment. The intensity of SFCA peak is not decreased up to 700°C in CO–CO₂ atmosphere, whereas the intensity become weak in CO–CO₂–H₂–H₂O atmosphere. The intensity of SFCA-I peak is decreased above 500°C in all atmospheric condition and the reduction reactions are enhanced by the addition of H₂–H₂O gas. Decrease in intensity of SFCA peak is independent of Fe composition, whereas that of SFCA-I is decreased with decreasing Fe concentration. The difference in reducibility is attributed to the difference in the crystal structure of multi-component CF. SFCA and SFCA-I are composed of pyroxene and spinel units. Since the pyroxene unit contains more gangue minerals than spinel unit, it implies that the pyroxene unit shows low reducibility than the spinel units. Since SFCA-I contains more the spinel units than SFCA, SFCA-I is easily reduced than SFCA.

Using the X-ray diffraction (XRD) patterns collected on the products of laboratory furnace experiments performed on a synthetic iron ore sinter mixture with composition 77.36% Fe₂O₃, 14.08% CaO, 3.56% SiO₂ and 5.00% Al₂O₃, it is demonstrated that the previously reported Fe-rich SFCA phase has the same crystal structure as triclinic SFCA-III. Therefore, the four principal members of the silico-ferrite of calcium and aluminium (SFCA) family are SFCA, SFCA-I, SFCA-II, and SFCA-III. In addition, using XRD patterns collected for sinter strand and pot-grate sinter samples supplied as part of a sinter analysis round robin the presence of the SFCA-III phase in industrial sinter is confirmed for the first time, with important implications for sinter characterisation and research.

Taking full account of the complex mechanism of the continuous annealing furnace (CAF) production process and the difficulty in establishing an accurate mathematical model, this paper adopts a quantum particle swarm optimization (QPSO) algorithm to optimize the parameters of the radial basis function (RBF) neural network which used to predict the model of strip temperature in CAF. Firstly, to improve the accuracy of modeling, the input and output variables of RBF neural network model prediction are determined by analyzing the mechanism model of the heating section of the CAF and the factors affecting the strip temperature. Secondly, due to the trial and error method used for parameter selection in RBF neural network, which results in low work efficiency and difficulty in selecting the optimal value, the QPSO algorithm is introduced to search for the optimal solution. Furthermore, to avoid encountering local optimal issues and improve searching performance, an improved QPSO algorithm that combines the characteristics of generalized opposition-based learning and differential evolution is proposed. Finally, by collecting the production site data of a large-scale CAF, experiments are carried out to verify the effectiveness of the proposed methods.

Dual-phase (DP) steels are advanced high-strength steels used in automotive design. To achieve optimal mechanical properties the control of phase transformations during processing is paramount, e.g. for hot-rolled DP steels a desired ferrite fraction is required to form during run-out table cooling. Thus, sensor technologies such as laser ultrasonics (LUS) are of considerable interest that can in-situ monitor ferrite formation. In this study, the ferrite formation kinetics in a laboratory DP steel were measured by LUS during stepped cooling treatments which were designed to simulate the cooling paths on the run-out table in hot strip mills. LUS measurements were first validated with well-established dilatometry measurements during continuous cooling. For the stepped cooling tests, the fractions transformed obtained from the ultrasonic velocity changes agree with the ferrite phase fractions as characterized by ex-situ metallography. Further, the velocity changes are described by the JMAK approach using parameters that are consistent for the austenite-to-ferrite transformation in low-carbon steels.

To understand the interdiffusion of alloying elements in the α-Fe phase of the Fe–Cr–Mo and Fe–Cr–Si ternary systems, interdiffusion coefficients are determined. The main ( and , i: Cr and j: Mo or Si in the present study) and cross ( and ) interdiffusion coefficients in the ternary systems were determined by the Whittle–Green method. From main interdiffusion coefficients in the ternary systems at 1073 K, the average value of was approximately 1.5 times higher than that of in the Fe–Cr–Mo system, while the average value of was 1.8 times higher than that of in the Fe–Cr–Si system. From the values of the ternary systems, Si has an accelerating effect than Mo on Cr diffusion in the α-Fe phase. Increasing the ratio of the Mo to Cr concentration has a suppressing effect on the respective Cr and Mo interdiffusion flux within the α-Fe phase. Increasing the concentration ratio of Mo to Cr suppresses the effect of Mo and Cr on the respective Cr and Mo interdiffusion fluxes within the α-Fe phase. Considering the temperature dependence, the Mo diffusivity is more sensitive than the Cr diffusivity. The cross interdiffusion coefficients, and , are positive and the values are insignificantly different in the Fe–Cr–Mo system, while and were negative. This study is beneficial to understand microstructure evolution in ferritic stainless steels at high temperatures.

The effects of alloying elements on the bainite transformation behaviors were investigated for Fe-0.3N and Fe-0.3N-1M (M: Si, Cr, Mn, Mo) (mass%) alloys. Nitrogen (N) was introduced into austenite by gas nitriding and subsequent isothermal holding were employed at 500°C. Bainitic ferrite starts to form from the austenite grain boundaries in all alloys. Bainite structure changed from nitride-free bainite (B-I type) to bainite accompanying film-like nitride precipitation between bainitic ferrite (B-II type) with increasing holding time in Fe-0.3N alloy. The transformation kinetics was retarded by addition of all the alloying elements investigated, resulting in larger retained austenite fraction after subsequent cooling to room temperature. The retardation was significant with Cr and Mn addition.

Quantitative evaluation of energy dissipation calculated from the interfacial N concentration showed that the effect of additive elements was small at short holding times. In this region, the dissipation due to the interfacial friction and the transformation strain were dominant. Whereas the effect of alloying elements appeared as the interface velocity decreased with increasing holding time.

The effect of molybdenum (Mo) contents on hardenability and precipitation behaviors in Mo–B simultaneously added steels were investigated placing a focus on high austenitizing temperature. The hardenability of 0.5% Mo - 11 ppm B steel austenitized at 1150°C was decreased compared with that austenitized at 950°C, whereas 1.0% Mo - 10 ppm B and 1.5% Mo - 9 ppm B steels were less affected by high austenitizing temperature than 0.5% Mo - 11 ppm B steel. The Fe₂₃(C, B)₆ precipitation by increasing austenitizing temperature was also revealed to be suppressed in 1.5% Mo – 9 ppm B steel. These results indicate that the improved effect of the Mo addition on hardenability by retarding the precipitation of Fe₂₃(C, B)₆ still appear in B-added steels austenitized at high temperature. Furthermore, Fe₂₃(C, B)₆ precipitation start temperature was increased in Mo–B added steels austenitized at 1150°C. This result implies that non-equilibrium B segregation mechanism during cooling from high austenitizing temperature enhances the amount of segregated B on grain boundaries leading to the promotion of the borides precipitation at high austenitizing temperature region. However, Mo is presumed to fix a part of thermal vacancies as Mo–V complex resulting in the suppression of non-equilibrium B segregation to grain boundaries during cooling, which is speculated to inhibit the Fe₂₃(C, B)₆ precipitation. Thus, the effect of Mo–B combined addition on hardenability was presumably maintained even in high austenitizing temperature region.

Medium-manganese steel that undergoes Lüders deformation exhibits good uniform elongation owing to large elongation with a yield plateau. To accurately predict the deformation behavior in engineering applications, the yield stresses of medium-manganese steel (5% Mn), exhibiting the transformation-induced plasticity (TRIP) effect were investigated during elongation under a multi-axial stress state (MSS). Compact tensile tests with real-time diameter measurements were conducted on smooth and notched, tiny round-bar specimens to evaluate the local yield stress and strain without the Lüders band propagation effect. Consequently, the true stress plateau was measured without the upper yield point for the smooth round-bar specimen, and the cross-sectional average true stress of the blunt notched round-bar specimens had the same plateau as the smooth round-bar specimen. The sharp-notched round-bar specimen exhibited a two-stage linear increase in true stress. The true stresses of the three specimens at the initial yield point were almost identical. Under the MSS, the hydrostatic stress typically increases the true stress at the initial yield point. The independence of the MSS indicates that the yield stress during elongation was independent of the shear-dominant crystal slip resistance. Finite element (FE) analysis using the Mises yield locus did not express the true stress plateau and its independence of the MSS. Additionally, the transformation rate of retained austenite was measured for mechanistic analysis; however, the TRIP effect did not contribute to this unusual independence because it started at the intermediate yield elongation stage. Thus, the stress criterion for the generation of mobile dislocations can determine yield stress.

Change in lattice defects density in bcc pure iron due to tensile deformation was quantified by using both electrical resistivity measurements and X-ray diffraction (XRD). As bcc pure irons, ultra-low carbon steel (ULCS) and interstitial free (IF) steel are used as the model specimen. Dislocation density evaluated using Williamson Hall method with XRD shows the saturation with the value of around 3.7×10¹⁵ m⁻² for ULCS and around 1.4×10¹⁵ m⁻² for IF steel after plastic strain after ~5%. Increase in electrical resistivity was observed with increasing plastic strain. Consequently, increase in vacancy concentration occurs with increasing plastic strain of around 0.3, such as, 2.6×10⁻⁵ for ULCS and 3.4×10⁻⁵ for IF steel. Additionally, the migration of carbon atoms from grain interior to grain boundary via dislocation might occur at the initial stage of plastic deformation in ULCS.

The yield-point phenomena in ferrite–pearlite duplex steels were investigated using multiscale computational simulations. In these multiscale simulations, the stress–strain relationship of the ferrite phase was characterized by an elastoplastic constitutive model considering the stress-drop behavior, and its material constants were determined by minimizing the residual error between a computational simulation and a tensile test experiment, where the yield-point phenomenon in a tensile test of ferrite steel was reproduced. Using the determined material response of the ferrite phase, finite element analyses of the ferrite–pearlite duplex microstructure were executed to scrutinize both the macroscopic material response and microscopic deformation mechanisms. Subsequently, finite element analyses of tensile tests, based on numerical results from microstructural analyses, were carried out to replicate the yield-point phenomena in ferrite–pearlite duplex steels. Consequently, the study characterized the strengthening effect of the pearlite constituent while considering microscopic heterogeneity and yield-point phenomena in the ferrite phase. The findings from the multiscale simulations underscored the necessity for a more accurate estimation of local mechanical properties in both the ferrite phase and pearlite constituent for quantitative simulations.