Metallurgical and Materials Transactions B最新文献

Supersonic coherent jets are widely in practice in steelmaking processes including electric arc furnaces (EAF). Injecting oxygen through such coherent jets plays a vital role in enhancing the liquid gas mixing and reaction rates leading to boosting energy efficiency. Several experiments and numerical simulations have been carried out to understand the physical phenomenon of the coherent jets and to predict the behavior of the jets. However, the research on pollutant formation in the coherent jets for steelmaking is limited. As the industry transitions toward reducing emissions, prediction of pollutant formation is crucial. This numerical study analyzes both methane shrouding coherent jets and hydrogen shrouding coherent jets and predicts the NO_x (oxides of nitrogen) formation. It has been found that NO concentration dominates over N₂O and NO₂ and has the highest concentration around the jet. Although the NO concentration reaches as high as 1070 ppm at high-temperature region around the jet, it remains below 225 ppm along the fuel inlet axis. Also, it has found that the NO_x concentrations increase along the radial direction up to (1.5{text{De}}) from the jet central line and gradually decreases, whereas the NO concentration peaks at (15{text{D}}_{{text{e}}}) along the jet axis in the downstream direction.

Spent lithium-ion batteries (SBs) are important sources of valuable and critical raw materials. An integration of battery recycling with well-established primary processes for metals production has many advantages. In this work, the recycling of two battery scrap fractions obtained from mechanical pretreatment was integrated with a Ni-slag cleaning process at laboratory scale. Graphite from SBs acted as the main reductant, and the reduction behavior of major and trace elements was investigated as a function of time at 1350 °C. Major CO and CO₂ concentrations, as well as minor amounts of SO₂, NO₂, CH₄, and C₂H₄, were detected in the off-gas line. The evolution of gases took place within the first minutes of the experiments, which indicated that metal oxide reduction reactions as well as decomposition of the organic binders both happened very rapidly. This result is in line with the analytical results obtained for the slag phase, where the most significant metal oxide reduction was observed to take place within the first 5 to 10 minutes of the experiments. The distribution coefficient values for Co and Ni between metal alloy and slag as well as between matte and slag showed no significant differences when battery scrap fractions with different compositions were used. The addition of Ni-concentrate in the starting mixture resulted in increasing recoveries of Ni and Co, as well as improved settling of the matte phase.

The copper alloy components are produced using the process of thixotropic extrusion and subsequently subjected to annealing at temperatures ranging from 500 °C to 600 °C for 2 hours. The liquids islands exist inside the solid phases, and the primary phases consist of α-Cu, Cu41Sn11, and Cu3P phases of thixotropic extruded copper alloy. The average grain size initially declines and subsequently increases as the annealing temperature rises. The segregation is improved, and the average grain size is fined of thixotropic extruded copper alloy by annealing at 550 °C for 2h. The impact of texture on mechanical properties can be ignored due to negligible preferred orientation is formed following annealing. The tensile strength and elongation of thixotropic extruded copper alloy are improved after annealing at 550 °C for 2h, resulting in the highest values of 449.8 MPa and 19 pct, respectively.

To investigate the effect of TiO₂ in refining slag on the nonmetallic inclusions in Ti-bearing Al-killed steel, industrial studies are conducted with and without TiO₂ addition in refining slags. It is found that a suitable addition of TiO₂ (around 5 pct) can improve the fluidity of the slag. When using TiO₂-containing slag, the Ti content in steel increases to 72 ppm after LF refining due to [Ti]-[O] equilibrium, and the yield of Ti-Fe alloy also climbs from 86.5 to 96.3 pct in RH refining even with a lower addition amount. The inclusions generally transform from Al₂O₃ into solid MgO-Al₂O₃ and even liquid CaO-Al₂O₃ inclusions. Although a small amount of TiO_x is generated in inclusions at the middle stage of LF refining due to the effect of TiO₂-containing slag, solid MgO-Al₂O₃ inclusions are still the dominant inclusions in steel after RH refining. Therefore, the suitable addition of TiO₂ does not evidently influence the evolution of inclusions. As a result, it can hardly weaken the removal efficiency of inclusions, while the cleanliness of steel is in fact improved. Lower total oxygen and nitrogen contents are obtained, and the number density of inclusions decreases from 31.7 mm⁻² to 25.0 mm⁻².

The traditional melt quenching method was used to prepare new zinc boroselenite glasses in the system xSeO₂·(50 − x)ZnO·50B₂O₃ with varying SeO₂/ZnO molar ratio. X-ray diffraction patterns (XRD) have revealed an amorphous structure in glasses of up to 40 mol pct SeO₂. On the other hand, the presence of sharp diffraction peaks on the XRD spectra of samples containing 40 and 50 mol pct SeO₂ confirms a formation of some polycrystalline phases distributed in the host glass network. Based on FTIR and NMR data, the glass structure at a short-range order exhibited a similar value of the fraction of tetrahedral boron (N₄), particularly, for both samples of 0 and 5 mol pct SeO₂. In this situation, SeO₂ is as well as ZnO both played a modifier role. On the other hand, increasing SeO₂ on expense of ZnO decreases the N₄ fraction gradually. However, in SeO₂-rich glass, most of boron atoms are mainly placed in three coordinated sites in BO₃ units coordinated with SeO₄ groups. Decreasing N₄ fraction and increasing crystallization confirmed that SeO₂ operates as a glass former and mainly as a crystalline agent. The results based on the TEM of the selected area of electron diffraction patterns (EDP) agree well with the ones obtained by XRD. The diffraction patterns clearly displayed two sets of diffraction rings: one is caused by boroselenite nanocrystals and the other by zinc selenite. In contrast, a broader halo of dispersed structure, known as an amorphous structure, is present in the diffraction pattern obtained from SeO₂-free glass.

Research on intragranular acicular ferrite inclusions has demonstrated that high-melting-point oxide MgAl₂O₄ cores and composite inclusions precipitated by Ti₂O₃ adhesion can be used as effective nucleation particles in oxide metallurgy. However, the microscopic mechanism underlying this adsorption behavior remains unclear. Hence, in this study, the adsorption and polymerization mechanisms of Ti₂O₃ on the MgAl₂O₄(100)Mg- and MgAl₂O₄(111)O₃(Mg)-terminal surfaces in steel were studied using first-principles calculations based on density functional theory. The calculation based on the first principles of DFT and performed by the CASTEP code under plane wave basis set. The exchange correlation energy and correlation effects were described by generalized gradient approximation (GGA) using the Perdew–Burke–Ernzerhof (PBE) function. Spin polarization was considered in all calculation. Ultrasoft pseudopotentials (USPP) was employed to describe the electron-ion interactions. The energy cutoff for the plane wave basis was set at 620 eV in the current work. For the Brillouin zone sampling, we carried out 3 × 3 × 3 k-points mesh for MgAl₂O₄ bulk using the method of Monkhorst-Pack. A vacuum layer of 20.0 Å is added above the top surface of MgAl₂O₄ to eliminate the interaction of the normal periodic repetition of the surfaces. In all the surface calculations, the use of symmetry in bulk crystal was failed and k-point grids is set to 3 × 3 × 1. The results of this study revealed that when the most stable adsorption positions of Ti₂O₃ on the surface of MgAl₂O₄(100)Mg- and MgAl₂O₄(111)O₃(Mg)-terminal are located at T_Al and F_Mg, the adsorption energy is the highest and the most stable. The most stable adsorption configurations are located on vertical and parallel (P1) surfaces. Through comparative analysis, the best surface for Ti₂O₃ adsorption was found to be the MgAl₂O₄(111)O₃(Mg)-terminal surface, and the adsorption behavior mainly occurred on the first layer of atoms on the surface. The best adsorption configuration was P1, and the best adsorption mode occurred when Ti₂O₃ formed three rings connected in pairs with the surface and embedded in the surface of the MgAl₂O₄(111)O₃(Mg)-terminal. This study provides insights into the adsorption polymerization mechanisms of MgAl₂O₄–Ti₂O₃ complex inclusions in steel that could facilitate the fabrication of novel low-melting-point oxides and sulfides.

Chromium, broadly present in metallurgical systems such as stainless steel slags and vanadium-bearing slags, tends to be in a trivalent form bound in spinel phases due to their ultrahigh stability. To explore the stability of chromium bearing spinels with different divalent cations, herein ACr₂O₄ (A=Mg, Zn, Mn) spinels were synthesized and stability-tested under both alkaline and acidic environments. X-ray diffraction (XRD) and refinement results reveal that MnCr₂O₄ exhibited the largest lattice parameters. X-ray photoelectron spectroscopy (XPS) results show that MnCr₂O₄ had the highest oxygen vacancy concentration, potentially triggering structural instability, consistent with the Fourier-transform infrared (FTIR) and Raman analyses. To further investigate the stability of ACr₂O₄ spinels in alkaline and acidic environments, we introduced CaO and SiO₂, respectively, for high temperature calcinations. XRD analyses reveal that ACr₂O₄ spinels exhibited a high instability under an alkaline condition, with an increasing degree of instability for MgCr₂O₄, ZnCr₂O₄, and MnCr₂O₄ successively. We further quantified the relationship between the oxygen vacancy concentrations and the divalent cations containing in spinels as well as the spinel stabilities under an alkaline environment. Under an acidic condition, all ACr₂O₄ spinels demonstrated a relatively strong structural stability. The understanding of formation and stability of chromium bearing spinels under different conditions could contribute to potential modifications and applications of spinels especially with regard to resource recycling in metallurgy.

Abundant low-grade nickel sulfide ore reserves hold potential as nickel resources but are hindered by high magnesium silicate content, limiting efficient utilization. The authors investigated the possibility of extracting nickel from a low-grade ultramafic nickel sulfide concentrate into ferronickel alloy. The nickel extraction study involved thermal upgrading and physical separation. Thermal upgrading efficiently concentrated nickel values from ultramafic concentrate into ferronickel alloy, achieving over 90 pct extraction with more than 40 pct nickel grade and a characteristic particle size of d₈₀=100 µm. The presence of magnesium silicate gangues in the concentrate adversely impacted the thermal extraction of nickel. Multiple thermal treatment variables have been studied to improve nickel extraction efficiency, including metallic iron addition rate, heating duration, temperature, additives, and atmosphere. The proposed solid-state thermal upgrading method avoided smelting of materials and generation of sulfur dioxide. Magnetic separation recovered approximately 85 pct of nickel in the thermal treatment products into a ferronickel concentrate at 20 pct nickel grade.

For the control of the wear amount of work rolls and replacement moment in finishing rolling, most of the traditional models are unable to accurately predict the optimal finishing wear amount and replacement moment of work roll in advance, which may lead to the disruption of the production rhythm, and even cause product quality defects. This research describes a Lévy's improved arithmetic optimization algorithm twin support vector regression (LAOA-TSVR) prediction model for wear amount of work roll and replacement moment in a finishing mill. Firstly, the research group initially employed real production data from a hot strip finishing mill to identify influential factors of wear amount of work roll through correlation analysis using SPSS. Subsequently, to validate its predictive performance, the model was compared against three classical algorithms: Back Propagation (BP), Radial Basis Function (RBF), and Support Vector Machine (SVM), confirming LAOA-TSVR's superior accuracy. Finally, the model underwent practical production testing with a dataset totaling 200 sets. The findings reveal that the model attains a 95.2 pct hit rate for predicting wear amount of work roll within ± 0.5 pct. Likewise, it achieves a 98.3 pct hit rate for predicting the replacement moment of work roll for finishing mill.

The influence of magnesium treatment on cleanliness and microstructure characteristics of as-cast high-nitrogen stainless bearing steel (HNSBS) was systematically investigated. Results manifested that as the magnesium content increased from 0.0003 to 0.0054 wt pct, the oxygen and sulfur contents in steel, along with the number density and average size of inclusions significantly decreased due to the strong thermodynamic affinity and the removal of inclusions. Meanwhile, the inclusion evolution processes were Al₂O₃ → MgO·Al₂O₃ → MgO and MnS → MgS + Mg₃N₂, and the magnesium content in HNSBS should not exceed 0.0047 wt pct to prevent the formation of deleterious Mg₃N₂ inclusion. Additionally, the secondary dendrite spacing and the area fraction of precipitates (M₂₃(C, N)₆ and M₂(C, N)) at the 1/2 radius of ingots decreased form 83 ± 25 μm and 17 pct to 63 ± 16 μm and 12 pct, respectively. The dendrite structure was refined owing to the increase in effective nucleation sites for γ-Fe provided by MgO·Al₂O₃ and MgS inclusions, as well as the enrichment of magnesium in the liquid phase at solidifying front. The area fraction and size of precipitates were reduced due to the decrease of chromium activity. The finer and more dispersed precipitates was attributed to the reduction of growth space and increase in effective nucleation sites. This work provides theoretical guidance for preventing the formation of deleterious inclusions (especially for nitrides) in high-nitrogen alloy systems and refining the microstructure of alloy systems containing M₂₃(C, N)₆ and M₂(C, N) precipitates.