Metallurgical and Materials Transactions B最新文献

Ti is produced by the Kroll method, mainly by carbothermic chlorination, magnesiothermic reduction, and vacuum distillation, which result in complex processes, low efficiency, and high cost. Although Ti has many excellent properties, its high production costs limit its widespread applications. There is an urgent need to develop new Ti extraction processes to reduce the cost of Ti production. In this study, we propose a new method for the direct preparation of low-oxygen Ti powder from TiO₂ using Mg as a reducing agent and the formation of CeOCl (2Mg (l) + TiO₂ (s) + 2CeCl₃ (l) = Ti (s) + 2CeOCl (s) + 2MgCl₂ (l)). First, a deoxidization experiment of Ti with Mg as a deoxidizer was conducted, and the ability of Mg to deoxidize Ti was demonstrated. At 1273 K, when the activity of CeCl₃ was 1, the oxygen concentrations of Ti-A and Ti-B were 380 and 270 ppm, respectively. Subsequently, the TiO₂ reduction experiment was conducted using Mg as the reducing agent. The results showed that MgO activity was effectively reduced by the formation of CeOCl (MgO(s) + CeCl₃(l) = MgCl₂(l) + CeOCl(s)). When the system reached the Mg/MgCl₂/CeOCl/CeCl₃ equilibrium, low-oxygen Ti powder below 1000 ppm was directly produced from TiO₂.

The research focused on the effect of graphite proportion and the incorporation of fly ash in Fe-Cu-based friction materials produced via powder metallurgy technique. Microstructural investigation of the specimens demonstrated the homogenous distribution of the secondary element (Cu), lubricant (graphite), and reinforcements (fly ash) in the matrix (Fe). A maximum density of 5.7 g/cm³ was attained for the specimens, with an overall density of 70 pct of theoretical density. FM03 specimens showed a better wear resistance of 4.7 × 10⁻⁸ g/Nm with an optimum coefficient of friction of 0.4. The specific wear rate of the conventional friction material was 97.7 pct higher than the FM03 specimens.

Graphical Abstract

The melting and motion of ferroalloys play a crucial role in the mass transfer and homogenization of molten steel in ladles. Heat transfer, melting, and solidification behavior of an alloy affect its size, thereby altering its motion within the gas-stirring ladle. This study established a heat transfer and solidification-melting model for alloy particles in high-temperature metal liquids. The computational fluid dynamics (CFD) method was used to simulate the fluid within the ladle, and the discrete element method (DEM) was employed for the alloy particles. This coupling approach elucidates the motion trajectories of different types of alloys in molten steel under flow and heat exchange, particle heating, melting, and shrinkage conditions. Furthermore, the effects of alloy size, initial alloy temperature, molten steel flow rate, and molten steel temperature on the melting behavior of different types of alloys were investigated. The results showed that the melting time exponentially increased with increasing alloy size or decreasing molten steel flow rate. Moreover, the alloy melting time decreased with increasing initial alloy temperature or molten steel temperature. The impact of these factors on the melting of FeCr, FeMn, FeSi, and Al alloys was also evaluated. Furthermore, FeSi and Al alloys added at different positions in the ladle with symmetric dual gas bottom blowing had a residence time of only 1 second in the molten steel and did not completely melt. These findings indicate that FeSi, Al, and FeCr alloys should be added at the 0.4R position in the symmetrical plane. Furthermore, the − 0.4R or − 0.2R positions are more favorable for the melting of FeMn.

The high-nitrogen stainless bearing steel 30Cr15Mo1VN, possessing excellent tensile strength (~ 2466 MPa) and impact toughness (~ 130.3 J), was manufactured by pressurized induction melting and pressurized electroslag remelting (PIM + PESR) duplex process. Herein, the inclusion characteristics and element segregation of as-cast ingots, as well as the precipitate characteristics, retained austenite (RA) distribution were systematically investigated to clarify the effect of PESR on tensile and impact properties. Compared with PIM ingot, the lower quantity and larger spacing of inclusions in PIM + PESR ingot were beneficial to improving toughness. Besides, the dendrite segregation originating from solidification inherited to tempered steels and changed the multiphase structure and toughening mechanism. First, the lighter segregation (C, N, Cr, etc.) was induced by the high cooling rate, directional solidification, and short-time homogenization during PESR process, obtaining the higher contents of precipitates and RA in the PIM + PESR ingot. Second, the smaller precipitates and more RA were uniformly distributed in tempered PIM + PESR steel by alleviating segregation, obtaining better interface and matrix plasticity. Third, the dislocation densities of martensite and RA were increased by the greater precipitation pinning effect after PESR, and the uniform area ratios of close-packed and Bain groups were obtained, effectively inhibiting the propagation of secondary crack. Finally, the smaller strength difference between RA and martensite owing to lighter segregation after PESR, alleviated strain localization at phase interfaces and accommodated plastic deformation of matrix, thus, significantly enhancing the strength and toughness of the PIM+PESR steel.

In the current study, the aggregation of CaO-Al₂O₃ inclusions with different CaO contents at the steel/Ar interface was in situ observed using the confocal laser scanning microscope. The critical acceleration distance and attractive force during the inclusion aggregation process were measured and calculated, and effects of inclusion composition and radius on the aggregation of inclusions were analyzed. When the CaO content in CaO-Al₂O₃ inclusions in 16Mn steels increased from 3 to 51 pct, inclusions gradually changed from solid to liquid. Solid and partial liquid inclusions aggregated to form large clusters with a maximum diameter of 446.2 μm. When the CaO content in inclusions increased from 3 to 26 pct, the critical acceleration distance between inclusion pairs decreased from 104.9 to 62.1 μm, and the attractive force between inclusion pairs decreased from 1.0 × 10⁻¹⁶ N~1.0 × 10⁻¹³ N to 1.0 × 10⁻¹⁸ N~1.0 × 10⁻¹⁵ N. As the host inclusion radius increased from 5~15 to 25~35 μm, the critical acceleration distance increased from 104.9 to 166.6 μm. For liquid inclusions, when the CaO content in inclusions increased from 38 to 51 pct, the critical deceleration distance increased from 59.7 to 93.6 μm, and the repulsive force increased from 1.0 × 10⁻¹⁷ N~5.0 × 10⁻¹⁵ N to 1.0 × 10⁻¹⁷ N~1.0 × 10⁻¹³ N. The liquid inclusion overcame the repulsive force and aggregated, when the host inclusion radius was larger than 10 μm, and the initial velocity of the guest inclusion was faster than 150 μm/s. The calculated attractive force between inclusions was larger than the theoretical value calculated by Kralchevsky-Paunov model.

Although single-phase diffusion triples have been adopted successfully to deduce interdiffusivities in a much wider composition range than using diffusion couples, recent studies show that diffusion quadruples can further raise efficiency covering an even broader range of compositions than triples. In the present work, two diffusion quadruples of the fcc Co–Ni–Ta alloy system were assembled at 1473 K, allowing for a direct comparison with the former triple scheme. The composition-dependent interdiffusivities were then deduced, and mutually validated by comparing with the results calculated from the triple scheme and the traditional methods (i.e., the Sauer–Freise method and Whittle–Green method). To ensure the universality of the quadruple scheme, one diffusion quadruple was fabricated under universal preparation conditions without strict requirements of the original interfaces. By updating our two-dimensional (2D) numerical inverse scheme, the present quadruple scheme can well handle general cases with both ideal and universal original interfaces. However, since the absolute deviation is not significant and the results obtained by the quadruple scheme are fine-tuning of those from the triple scheme, both the triple and quadruple schemes are acceptable for engineering applications.

The stable control of mold level is a key link in the production of high-quality continuous casting slabs. Periodic mold level fluctuation (PMLF) is common during the continuous casting process, and the abnormal PMLF has significant harmful effects on surface quality of slab. This article proposed an analysis and control method for abnormal PMLF. First, the finite impulse response (FIR) filter and fast Fourier transform (FFT) were used to remove noise interference in PMLF data and highlight the fluctuation characteristics of PMLM. Then, considering that uneven solidification has a significant impact on abnormal PMLF, the influence of chemical composition on the equilibrium Fe-C pseudo-binary diagram was calculated by Thermo-Calc software. Furthermore, roller diameter, roller spacing, casting speed, and chemical composition were chosen as the prediction indicator to predict the quality of PMLF. Random forest (RF) model shows good performance in predicting PMLF; the prediction accuracy of RF model is 92.76 pct, which is 21.39 pct higher than that of GA-BP model. Finally, the Feedforward fuzzy PID (F2FPID) controller designed in this article was used to eliminate abnormal PMLF. The average range of mold level fluctuation under the PID controller is ± 6.8 mm, while under the F2FPID controller, the average range of mold level fluctuation is ± 1.1 mm. And the F2FPID controller owns a lower overshoot of 0.48 pct and an adjusting time of 1.52 seconds, which are 94.8 pct and 59.5 pct, respectively, lower than those of the PID controller.

Strip casting casts molten steel into thin strips, enabling direct hot rolling to produce products. A typical hot stamping steel thin strip was made by a strip casting simulator under tailored casting and hot rolling temperatures. The casting strip showed improved surface quality at a higher casting temperature (1597 °C) and a lower rolling temperature (900 °C), achieving 1275 MPa tensile strength with 12.3 pct elongation due to refined austenite grains transforming to martensite.

The multi-lance top-blown converting furnace is pivotal in the converting process of molten white matte (copper content nearly 75 pct) in continuous copper smelting technology. The complex multiphase hydrodynamics and phase interaction mechanisms inherent in this furnace significantly influence converting efficiency of blister copper. This study numerically explores the intricate gas–melt flow hydrodynamics and stirring dynamics in the multi-lance top-blown converting furnace based on the OpenFOAM platform. Following model validation, this study elucidates various aspects of bath dynamics in the furnace. The findings reveal that the arrangement of multiple lances along the longitudinal axis introduces an offset effect on longitudinal momentum transfer and a superposition effect on transverse momentum transfer, unlike the single-lance blowing configuration. A linear empirical relationship between jet momentum number and length group under multi-lance top blowing is established, with a determined constant value of 3.65 for turbulent gas jet. Additionally, a strong correlation between dimensionless cavity shape index and the kinetic energy of molten slag is observed, leading to the formulation of a functional relationship equation demonstrating exponential growth: E_b = exp(− 2.81011–0.79077 ({I}_{text{cm}}) + 0.13479 ({{I}_{text{cm}}}^{2})). Moreover, both the internal flow of molten bath and the shear stress on the furnace wall exhibit a step-like periodic oscillation mode. Notably, based on the similarity observed in the main frequency peaks, a robust correlation between the two phenomena is inferred. Under conditions of small lance spacing and diameter, an increase in the cavity aspect ratio enhances momentum transfer efficiency and stirring performance of bath, but it also exacerbates erosion of the lances and the furnace. This study elucidates the multiphase mixing characteristics, phase interaction mechanisms, and furnace wall erosion patterns in a multi-lance top-blown converting furnace, providing a crucial theoretical foundation for the design, operation, and optimization of such systems.

The vacuum carbon deoxidation process via CO formation has the ability to achieve high cleanliness of nickel alloys in vacuum induction melting. In the present study, the effect of vacuum degree in melting chamber, melt temperature, and initial carbon content on deoxidation efficiency was studied. The reactions of vacuum carbon deoxidization and MgO decomposition were strongly affected by chamber pressure and melt temperature. Low chamber pressure and high melt temperature resulted in a severe MgO-crucible decomposition reaction and increased oxygen supply to molten nickel alloy, and hence, decreased the deoxidation efficiency. Therefore, moderate vacuum degree in the chamber and lower melt temperature would improve the vacuum carbon deoxidation efficiency. The reaction rates of vacuum carbon deoxidization and MgO decomposition were controlled by the mass transfer of oxygen in liquid boundary layers near the reaction interfaces. The nitrogen in molten nickel alloy could be well removed together with carbon deoxidation under the vacuum conditions in the present study. A prediction model of deoxidation and carbon loss in vacuum melting process was established to determine the optimum temperature and vacuum conditions in vacuum carbon deoxidation process.