Journal of Iron and Steel Research International最新文献

In response to the new mechanism of direct vortex melting reduction of vanadium–titanium magnetite, the reaction control mechanism and the migration regularity of valuable components in the process of direct melting reduction were investigated using kinetic empirical equation by fitting and combining with X-ray diffraction, X-ray fluorescence, scanning electron microscopy, energy-dispersive spectrometry, and optical microscopy. The results show that iron reduction is controlled by the mass transfer process of (FeO_x) in the slag, while vanadium reduction is controlled by both the mass transfer of (VO_x) in the slag and the mass transfer of [V] in the molten iron, and the slag–metal interfacial reaction is the only pathway for vanadium reduction. The reduction of iron and vanadium is an obvious first-order reaction, with activation energy of 101.6051 and 197.416 kJ mol⁻¹, respectively. Increasing the vortex rate and reaction temperature is beneficial to improving the reaction rate and reduction efficiency. The mineral phase variation of iron and vanadium in the slag during the reduction process is Fe₂O₃ → Fe₃O₄/FeV₂O₄ → FeTiO₃ and FeV₂O₄ → MgV₂O₅; titanium in slag is mainly in the form of Mg_xTi_3−xO₅ (0 ≤ x ≤ 1) and CaTiO₃. As the reaction time went on, the molar ratio (n_Ti/n_Mg) in Mg_xTi_3−xO₅ (0 ≤ x ≤ 1) and the Ti₂O₃ content in the slag gradually went up, while the area proportion of Mg_xTi_3−xO₅ (0 ≤ x ≤ 1) went up and then down, and the porosity of the slag and the grain size of Mg_xTi_3−xO₅ (0 ≤ x ≤ 1) got smaller.

Sub-rapid solidification has the potential to enhance the columnar structure and the magnetic property of electrical steels. However, research on the hot deformation behavior of sub-rapid solidified non-oriented electrical steel, particularly at varying strain rates, has yet to be fully understood. The effect of thermal compression on the microstructure and mechanical properties of 3.15 wt.% Si non-oriented electrical steel strips produced through a strip casting simulator was systematically investigated. The findings reveal that increasing the deformation temperature enhances grain recrystallization, while the peak stress decreases with higher temperature. Furthermore, a lower strain rate favors dynamic recrystallization and reduces thermal stress. It can be seen that sub-rapid solidification can effectively reduce the thermal activation energy of non-oriented electrical steel, and the thermal activation energy is calculated to be 204.411 kJ/mol. In addition, the kinetic models for the dynamic recrystallization volume fraction of the studied 3.15 wt.% Si non-oriented electrical steel were established.

To enhance the corrosion resistance and electrical conductivity, the surface of 316L stainless steel was modified by the ion implantation of Mo. By investigating various accelerating voltages and implantation doses, it was found that the corrosion resistance of stainless steel was enhanced by 50%–80% and the surface conductivity by 15%–28% at most. The minimum stabilized current density is 0.72 μA/cm². This is due to the formation of a Cr and Mo riched modified layer on the surface of the stainless steel. Mo oxides synergize with Cr oxides in the form of a solid solution to enhance the corrosion resistance of passivation films on the stainless steel surface. The optimum parameters were Cr in the proportion of 6%–8% and Mo in the proportion of 4%–5%.

The microstructure evolution and bainitic transformation of an Fe–0.19C–4.03Mn–1.48Si steel subjected to near-M_s austempering treatment were systematically investigated by combining dilatometer, X-ray diffraction, and electron microscopy. Three additional austempering treatments with isothermal temperatures above M_s were used as benchmarks. Results show that the incubation period for the bainitic transformation occurs when the medium Mn steel is treated with the austempering temperature above M_s. However, when subjected to near-M_s isothermal treatment, the medium Mn steel does not show an incubation period and has the fastest bainitic transformation rate. Moreover, the largest volume fraction of bainite with a value of 74.7% is obtained on the condition of near-M_s austempering treatment after cooling to room temperature. Dilatometer and microstructure evolution analysis indicates that the elimination of the incubation period and the fastest rate of bainitic transformation are related to the preformed martensite. The advent of preformed martensite allows the specimen to generate more bainite in a limited time. Considering bainitic ferrite nucleation at austenite grain boundaries and through autocatalysis at ferrite/austenite interfaces, a model is established to understand the kinetics of bainite formation and it can describe the nucleation rate of bainitic transformation well when compared to the experimental results.

Iron ore pellets, as one of the main charges of blast furnaces, have a greater impact on the CO₂ emission reduction and stable operation of blast furnaces. The isothermal reduction behavior of the pellets obtained from a Chinese steel plant was studied in the gas mixtures of CO and N₂. The results showed the reduction process is divided into two stages. The reduction in the initial stage (time t ≤ 40 min) is cooperatively controlled by internal diffusion and interface chemical reactions with the activation energy of 30.19 and 16.67 kJ/mol, respectively. The controlling step of the reduction in the final stage (t > 40 min) is internal diffusion with the activation energy of 34.60 kJ/mol. The reduction process can be described by two equations obtained from kinetic calculations. The reduction degree can be predicted under different temperatures and time, and the predicted results showed an excellent correlation with the experimental results. The reduction mechanisms were confirmed by the analysis of the scanning electron microscope equipped with an energy dispersive spectrometer and optical microscope.

The Ni–ZnFe₂O₄ (Ni_xZn_1−xFe₂O₄, x = 0.4–0.7) spinel was synthesized using Zn²⁺ extracted from electric arc furnace dust (EAFD), nickel chloride hexahydrate, and Fe³⁺ extracted from iron scale as raw materials. The zinc was selectively extracted from EAFD using CaO roasting followed by NH₄Cl solution leaching. The ferric ion was leached from iron scale using HCl solution as acid lixiviant. The experimental results demonstrate a high level of efficiency in the extraction of zinc, with a rate of 97.5%, and the leaching rate of ferric ion is 96.89%. The composition of the leaching solution is primary zinc and iron with low calcium, which is beneficial to the preparation of spinel ferrite. The influence of Ni content (x) and calcination temperature on the synthesis and magnetic properties of Ni_xZn_1−xFe₂O₄ compounds was investigated by X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. The results revealed that both Ni content and calcination temperature significantly affect the synthesis and magnetic properties of spinel Ni_xZn_1−xFe₂O₄. Under the conditions of Ni content set at x = 0.6, calcination temperature of 1100 °C, and a duration of 2 h, a spinel Ni_xZn_1−xFe₂O₄ with high saturation magnetization (M_s = 65.7 A m² kg⁻¹) and low coercivity (H_c = 0.056 A m⁻¹) was obtained.

The effect of rolling schedules on the ridging resistance of ultra-thin ferritic stainless steel (FSS) 430 foil was evaluated by studying the microstructure and texture. The results show that specimens processed with three-pass cold rolling under the reductions of 40%, 40% and 31%, respectively, exhibit improved ridging resistance owing to the microstructural refinement and the texture structure optimization. A nearly 40% reduction of ridging height can be achieved using the proposed rolling schedule compared to the other two rolling schedules. In addition, the effect of annealing temperature after cold rolling on the ridging resistance of FSS 430 foil is also found to be crucial, and an optimal annealing temperature of 900 °C is obtained for FSS 430 foil with high ridging resistance. Overall, the improvement in the ridging resistance of FSS 430 foil can be attributed to the reduction in the fraction of {001}<110> and {114}<110> components by optimization of the rolling and annealing processes.

MnAl rare-earth-free permanent magnets exhibit excellent advantages from economic and resource perspectives, which have attracted extensive attentions in recent decades. We reported the evolution in phase formation and intrinsic magnetic properties of τ-phase in binary MnAl alloys with the variation in Mn:Al ratios. Ferromagnetic τ-phase can be generated within the compositional range of Mn_50+xAl_50−x (x = 1–8), and pure τ-phase can only be obtained in the alloys with x = 4–7. With Mn:Al ratio increasing, saturation magnetization M_s and magnetocrystalline anisotropy constant K₁ are gradually weakened due to the incremental antiferromagnetic Mn-1d atoms, but Curie temperature of τ-phase is gradually increased induced by the strengthened d−d hybridization of Mn_1a−Mn_1d. An attempt of doping traces of Ti was carried out in order to eliminate the negative antiferromagnetic interaction derived from Mn-1d atom. Ti atoms tend to occupy 1d sites and replace the Mn-1d atoms due to the relatively fewer valence electrons compared with Mn, resulting in the reduction in Mn_1a−Mn_1d antiferromagnetic interactions, which is demonstrated by the higher M_s of Mn_55−yAl₄₅Ti_y (y = 1) than that of Mn₅₅Al₄₅. However, with further substitution of Mn by Ti, unfavorable κ-phase is unavoidably generated. Finally, the occupation preference and the corresponding influences on local magnetic interactions as well as the magnetizations of the different alloying atoms including interstitial element C, 3d atoms Ti, Co and Cu, and main-group element Ga are systematically summarized, in order to offer the guidance of designing MnAl permanent magnets with ideal magnetic properties.

The vacuum diffusion bonding method was used to introduce Al foil as the middle layer, and 6061 aluminium alloy was vacuum diffusion bonding together. The typical microstructure characteristics and mechanical properties of 6061/Al/6061 welded joints were studied in detail, the effects of process parameters and Al intermediate layer on the microstructure and mechanical properties were revealed, and the diffusion bonding mechanism of 6061/Al/6061 welded joints was described. Al foil middle layer welded joint had the best performance at the temperature of 540 °C, the holding time of 120 min, and the welding pressure of 4 MPa. The bonding ratio is 95.91%, the shear strength is 79 MPa, and the deformation rate is 8.05%, and the introduction of Al intermediate layer improves the element distribution and microstructure, so that the bonding ratio of the welded joint is increased by 10.86%, the shear strength is increased by 5.55 MPa, and the deformation rate is reduced by 1.58%. The fracture morphology has typical ductile fracture characteristics.

The electromigration reliability on Sn–10Bi solder joints is investigated and the performance is tried to be improved with trace Zn addition in solder by depressing the growth of interfacial intermetallic compounds (IMCs) under electromigration. The electromigration test was realized on Cu/solder/Cu linear specimens at a current density of 1.0 × 10⁴ A/cm² with different stressing time. It was found that Bi atoms in Cu/Sn–10Bi/Cu solder joint were driven towards anode side under current driving force and then accumulated at anode interface with current stressing time increasing. The thickness and growth rate of Cu₆Sn₅ IMCs at anode interface were obviously larger than those at cathode side due to polarity effect. The addition of 0.2 wt.% Zn inhibited the migration of Bi atoms during the electromigration process, and the composition of interfacial IMCs was transformed into Cu₆(Sn, Zn)₅, which played as a diffusion barrier to effectively reduce the asymmetric growth of IMCs and the consumption of Cu substrate during electromigation.