JOM最新文献

Vanadium–titanium magnetite (VTM) typically exhibits poor bed consolidation and unfavorable mineral-phase development during sintering. Oxygen-enriched sintering improves thermal conditions, accelerates oxidation kinetics, and optimizes the mineral-phase assemblage. This study evaluated the effects of oxygen enrichment applied during the heating stage, the cooling stage, and across the full process on VTM-sinter performance. Infrared thermography, X-ray diffraction (XRD), reflected-light mineral microscopy, and field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy (FE-SEM/EDS) were used to relate oxygen-potential distributions to mineralogy and metallurgical properties. Oxygen enrichment during heating narrowed the combustion zone, concentrated the heat flux, and accelerated liquid-phase formation, yielding a sintering productivity (utilization coefficient) of 2.37 t/(m²·h). It also promoted the formation of dense, acicular silico-ferrite of calcium and aluminum (SFCA), strengthening the bonding phase and thereby improving sinter strength and the low-temperature reduction-degradation index (RDI). By contrast, oxygen enrichment during cooling or throughout the process increased perovskite (CaTiO₃), produced skeletal hematite (Fe₂O₃), and induced microcracking and porosity, thereby weakening the bonding phase and worsening RDI. Overall, oxygen enrichment confined to the heating stage was the most effective strategy for simultaneously improving VTM-sinter quality and process efficiency.

In this study, the Inconel625-Ni60-Ni60/25%WC gradient coating (In625-Ni/WC GC) was prepared by adding a transition layer and changing the ratio of WC-reinforcing phase by the design method of laser cladding on Cr12MoV steel. The microstructure, wear resistance, and impact fracture behavior of GC were investigated. The results showed that the In625-Ni/WC GC had better internal metallurgical bonding properties without obvious defects. The surface phases of GC did not change significantly. The In625 layer was mainly composed of coarse columnar grains. The Ni/WC layer was mainly composed of fine dendritic and eutectic structures. The accumulation of heat from multi-layer deposition and limited diffusion at the interface between the In625 layer and Ni60 layer caused the upper Ni/WC layer to tend toward grain coarsening. The average friction coefficient and wear rate of In625-Ni/WC GC were 10.78% and 20.17% higher than those of the Ni/WC GC, respectively. The wear surface showed abrasive wear and slight adhesive wear. Notably, the impact toughness value of the DGC increased by 145.41%, and the fracture of the GC exhibited a composite fracture morphology in which cleavage fracture and ductile fracture coexisted. The fracture morphology of the In625 layer as the ‘softened region’ was dominated by dimples.

The continuous enrichment of phosphorus in the double slag steelmaking process affects the structure and properties of steelmaking slag. In this study, the effect of P₂O₅ on the structure and transport property of CaO-SiO₂-P₂O₅-FeO melts was investigated by molecular dynamics calculation. The results indicate that, with the increase of P₂O₅ content, the Ca-O bond length increased and the Fe-O bond length decreased, the Si-O and P-O bond lengths fluctuated around 1.61 Å and 1.54 Å, respectively, and the [SiO4]^4- and [PO4]^3- tetrahedral structures exhibited stability. The proportions of FO and BO decreased from 25.10% and 23.10% to 13.70% and 19.60%, respectively, while the proportion of non-bridging oxygen increased from 51.90% to 66.70%, and the aggregation degree of the system showed a decrease tendency. As the P₂O₅ content increased, the self-diffusion coefficient of Fe²⁺ ions increased significantly from 7 × 10⁻⁶ Ų/ps to 1.42 × 10⁻⁴ Ų/ps, P⁵⁺, O²⁻, and Ca²⁺ ions also showed an increasing trend, whereas Si⁴⁺ showed no significant change. Concurrently, the structural aggregation of the system decreased.

This study examines the possible substitution of sustainable basalt fibers for traditional glass fibers. The epoxy matrix has been reinforced with basalt or glass wovens, and hybrid or non-hybrid composites were fabricated via the hand lay-up/compression molding technique. The developed composite systems were characterized by thermal conductivity analysis, scanning electron microscopy (SEM) and mechanical tests. The impacts of various stacking sequences on these specifications have also been investigated. Notwithstanding an insignificant alteration in overall thickness, composites that integrate one or multiple basalt fabrics demonstrate enhanced thermal conductivity coefficients and reveal superior resistance to tensile stresses. An increase in the number of glass wovens contributes to elongation at break but decreases the ultimate tensile strength of the composite system. The deteriorative effect of flexural and compressive forces is exacerbated by an increase in the number of basalt fibers. Hybridization promotes the production of more slender composite systems characterized by reduced thermal conductivity coefficients, but it also leads to handling composite systems with unpredictable strain characteristics.

Oscillating laser technology demonstrates effectively effective improvement in coating formability and microstructure refinement. This study fabricates tungsten carbide (WC)/Stellite 6 composite coatings on high-chromium cast iron BTMCr20 using circular oscillating laser cladding to examine the effects of WC content (0–30 wt.%) on the microstructure and mechanical properties. Results indicate that laser oscillation induces mechanical stirring that enhances molten pool convection, effectively inhibiting WC particle settling and maintaining uniform distribution even at 30 wt.% WC. In addition to the inherent grain refinement effect of the oscillating laser, the increasing WC content provides additional heterogeneous nucleation sites, leading to further microstructural refinement. This resulted in a reduction of the average grain size by approximately 40% compared to the coating without WC, which is attributed to the presence of reinforcing phases such as W₂C, Fe₇W₆, and Cr₇C₃. Microhardness and wear resistance improve linearly with WC content, reaching 613 HV_0.2 and 2.17 × 10⁻⁴ mm³ wear volume at 30 wt.% WC. The wear mechanism transitions from mixed abrasive-adhesive to predominantly abrasive wear. Impact toughness peaks at 10.59 J/cm² with 20 wt.% WC, attributed to synergistic grain refinement, dispersed carbides, and ductile γ-Co phase. These findings provide valuable guidance for microstructural control in particle-reinforced laser-clad coatings.

Slag basicity is a critical factor that determines the operational stability and efficiency of separation between metal and slag in metallurgical processes. In this study, the effect of basicity on the melting separation process of reduced Hongge vanadium titanomagnetite pellets was systematically investigated. The results show that the increase of basicity promote the separation of slag and metal, and increase the recovery rates of iron, vanadium, and titanium in the metallic phase. However, excessive basicity led to a decrease in the recovery rate of TiO₂ in the molten titanium slag. With the increase of basicity, the melting temperature of the molten titanium slag demonstrated an initial decrease followed by an increase, and the slag viscosity decreased. Furthermore, the diffraction peak intensity of anosovite weakened, while the diffraction peak intensity of pyroxene was enhanced and the diffraction peak of perovskite appeared. Except for the presence of metallic iron particles in the molten titanium slag with a basicity of 0.4, only the matrix phase and Ti-rich phases were observed under other basicity conditions.

Large-diameter thick-walled LSAW pipes are widely used in the transportation of oil and gas at sea. However, the bending forming of medium-thick plates is prone to produce crack defects. In this paper, an extended study on crack prediction for bending forming of medium-thick plates is carried out. An improved theoretical crack prediction model considering the neutral layer offset is proposed, aiming to improve the bending crack prediction accuracy of medium-thick plates. The improved Lemaitre ductile fracture criterion integrates the effect of large plastic strain accumulation on damage and investigates the effect of neutral layer offset on strain. With 7075-T6 aluminum alloy as the object, verified by theoretical calculation, DEFORM finite element simulation and macro–micro experiments, the neutral layer offset is 0.6–0.7 mm when cracks initiate. The Lemaitre ductile fracture criterion threshold, C, at the time of experimental (C = 11.46) is compared with theoretically ( C = 11.9), and its relative error is 3.6%. The influence of the neutral layer offset on the accuracy of strain and crack prediction was verified. This criterion effectively improves crack prediction accuracy, provides theoretical support for optimizing the bending process of high-strength aluminum alloy medium-thick plates in marine engineering and aerospace fields.