Journal of Iron and Steel Research International最新文献

The production of ferroalloys is a resource-intensive and energy-consuming process. To mitigate its adverse environmental effects, steel companies should implement a range of measures aiming at enhancing the utilization rate of ferroalloys. Therefore, a comprehensive ferroalloy model was proposed, incorporating a prediction model for alloying element yield based on case-based reasoning and support vector machine (CBR–SVM), along with a ferroalloy batching model employing an integral linear programming algorithm. In simulation calculations, the prediction model exhibited exceptional predictive performance, with a hit rate of 96.05% within 5%. The linear programming ingredient model proved effective in reducing costs by 20.7%, which was achieved through accurate adjustments to the types and quantities of ferroalloys. The proposed method and system were successfully implemented in the actual production environment of a specific steel plant, operating seamlessly for six months. This implementation has notably increased the product quality of the enterprise, with the control rate of high-quality products increasing from 46% to 79%, effectively diminishing the consumption and expenses associated with ferroalloys. The reduced usage of ferroalloys simultaneously reduces energy consumption and mitigates the adverse environmental impact of the steel industry.

The effect of Zr on the microstructure and mechanical properties of 304 stainless steel joints brazed with Ag–Cu fillers was studied. The incorporation of Zr had little effect on the solid–liquid phase line of the fillers, and the melting temperature range of the fillers was narrowed, which enhanced their fluidity and wettability. The presence of Zr in the form of heterogeneous particles augmented the nucleation rate during solidification, transforming the intermittently distributed gray-black coarse dendrites into cellular crystals. This structural transformation led to fragmentation and refinement of the microstructure. The dissolution of Zr into Ag and Cu promoted the transformation of low-angle grain boundaries to high-angle grain boundaries (HAGBs), hindering crack propagation. Zr element in the brazing seam led to grain refinement and increased density of grain boundaries. The grain refinement could disperse the stress, and HAGBs could resist the dislocation movement, improving the joint strength. The results display that when Zr content was 0.75 wt.%, the maximum strength was 221.1 MPa. The fracture occurred primarily at the brazing seam, exhibiting a ductile fracture.

The GH4720Li alloy is one of the most widely used precipitation-strengthened nickel-based superalloy. However, systematic study about effect of strain rate on the plastic deformation behavior of GH4720Li alloy at intermediate temperature is lacking. The evolution of the tensile properties and plastic deformation mechanism of GH4720Li alloy with the strain rate at 650 °C were systematically studied with the help of transmission electron microscopy analysis. The results show that the tensile strength of the alloy increases and the plasticity decreases with the increase in strain rate. When the strain rate is 5 min⁻¹, the tensile strength of the alloy is 1448 MPa and the tensile plasticity is 18%. As the strain rate increases from 0.05 to 0.5 min⁻¹, the size and morphology of the primary γ′ phase of the alloy remain unchanged, with an average size of about 1.8 μm. However, when the strain rate further increases to 5 min⁻¹, the average size of the primary γ′ phase increases to 2.5 μm. In addition, the increase of strain rate has no significant effect on the size and distribution of secondary and tertiary γ′ phases. As the strain rate increases from 0.05 to 5 min⁻¹, the deformation mechanism of alloy gradually evolved from dislocation slip and twin to dislocation slip, indicating that the plastic deformation mechanism of the alloy presents a high strain rate sensitivity at 650 °C.

Laboratory experiments and thermodynamic calculations were performed to investigate the interfacial reactions between the MgO–C refractory and the steel with and without the lanthanum (La) addition. Following a reaction time of 50 min, a reaction layer comprised MgO and CaS with a thickness of 30 μm was observed at the interface between the La-free steel and refractory. The MgO layer was observed in La-bearing steel after just 10 min of reaction. The addition of La to the steel accelerated the formation of the MgO layer. As the reaction time increased, a La-containing layer was formed at the La-bearing steel/refractory interface. This La-containing layer progressed through stages from La₂O₂S + La₂O₃ → La–Ca–O–S → La–Ca–O → La–Ca–Al–O. Furthermore, the evolution of oxide inclusions in the La-free steel followed the sequence of MgO⋅Al₂O₃, Ti–Ca–Al–O and Ti–Mg–Al–O → MgO·Al₂O₃ and MgO with increasing the reaction time. In contrast, the sequence for the La-bearing steel was: La₂O₂S and La₂O₃ → La₂O₂S and La–Ti–Al–Mg–O → La–Ti–Al–Mg–O, MgO and MgO·Al₂O₃. The average penetration depth of the La-bearing steel into the refractory was notably lower than that of the La-free steel, revealing that the incorporation of rare earth element La in steel exhibits a significant inhibitory effect on the penetration of molten steel into the MgO–C refractory.

Laser oscillating welding of 2205 duplex stainless steel was performed using Ni interlayer as filler material. The influence of stirring effect caused by laser oscillating and Ni addition in the behavior of molten pool and the microstructure evolution was investigated. The results shows that Ni addition decreased the ratio of chromium equivalent and nickel equivalent in the molten pool and accelerated the austenitic transformation. The austenite/ferrite ratio was regulated, and the precipitation of nitrides was suppressed in the weld seam. The stirring effect caused by the oscillating beam facilitated the uniform distribution of Ni elements within the molten pool, promoting the formation of the homogeneous microstructures in the weld seam. With increasing the thickness of Ni interlayer, both the dimension and the peak temperature of molten pool decrease, further increasing the cooling rate and refining the grain size. When the thickness of Ni interlayer was 50 μm, the austenite/ferrite ratio in the weld seam was close to 1:1, and the grain size reached the minimum value. The tensile strength and ductility of the welded joint using Ni interlayer with thickness were 774 MPa and 25%, respectively, significantly improving the mechanical properties of 2205 duplex stainless steel joint welded without Ni addition.

Based on the two-pass differential temperature rolling bonding method, the effects of prefabricated steel/aluminum composite panel temperature on interface characteristics and microstructure properties were investigated through experimental analysis and finite element simulations. When the temperature exceeds 400 °C, the effective preparation of the steel–aluminum transition joint can be achieved, and with the increase in temperature, the interface shear and pull-off strength of the steel–aluminum transition joint exhibits an initial decrease followed by an increase. Both the interface shear and pull-off fractures are in 1060 aluminum matrix. As the temperature increases, the size of the average grain in 1060 aluminum matrix increases and then decreases. When the temperature reaches 550 °C, the comprehensive performance of the prepared steel–aluminum transition joint is the best, with the interface shear strength of 77 MPa and the interface pull-off strength of 153 MPa, exceeding the bonding strength of the explosive compounding method. There are no pinholes, wrinkles, or cracks in the lateral bending matrix and the interface.

The corrosion behavior of Ti–6Al–2Zr–1Mo–1V (TA15) alloy fabricated through selective laser melting (SLM) technology and traditional wrought technology in hydrochloric acid solutions was investigated using electrochemical testing and surface characterizations, including electron backscattered diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy analyses. The results showed that both types of TA15 alloy underwent spontaneous passivation reactions in HCl solution, and with the increase in HCl concentration, the surface of SLM-TA15 sample exhibited larger and deeper pits. In comparison to SLM-TA15 sample, the pits on the wrought-TA15 sample were shallower and the surface was more uniform. Analysis of the passive current density, breakdown potential, and electrochemical impedance revealed that the corrosion resistance of both alloys decreased as the concentration of HCl increased, and SLM sample exhibited poorer corrosion resistance compared with the wrought sample. Analysis of Mott–Schottky test curves and calculation of passive film thickness indicated that the passive film of wrought-TA15 sample was superior to that of SLM-TA15 sample.

The effects of niobium on the high-temperature oxidation resistance of austenitic stainless steel were systematically investigated. Two austenitic stainless steels with different Nb contents were prepared and exposed to air at 850 °C for 200 h. Results show that Nb positively affects the high-temperature oxidation resistance of austenitic stainless steels. The matrix organization of austenitic stainless steels with added niobium does not change, while the austenitic grain size is significantly refined, and it also promoted the release of internal stresses in the oxide film, which in turn improved the integrity of the oxide film and adhesion to the substrate. In addition, with the addition of Nb element, a large number of Nb(C, N) particles are diffusely distributed in the matrix. Nb(C, N) phase distributed in the matrix and the niobium-rich layer formed by the diffusion of niobium into the interface between the metal matrix and the oxide film during the high-temperature oxidation process effectively prevents the diffusion of iron into the outer layer and enhances the oxidation resistance at high temperatures.

The steel belt roasting process has the advantages of low cost, small footprint, and high thermal efficiency, making it widely used in the smelting of ferroalloys such as ferrochrome, ferromanganese, and ferroniobium. However, its application in preparing iron ore oxidized pellets has not been sufficiently explored. The optimal thermal process conditions for magnesium-containing oxidized pellet preparation by steel belt roasting machine were investigated based on the roasting properties of high-magnesium iron concentrate and typical iron concentrate. The results indicate that, for the blending scheme of 70 wt.% high-magnesium iron concentrate and 30 wt.% typical iron concentrate, the appropriate preheating temperature for pellets is 950–975 °C and the suitable roasting temperature is 1250–1275 °C, during which the compressive strength of pellets can exceed 2500 N pellet⁻¹. During the steel belt roasting process, SO₂ is primarily released in the preheating zone, and the maximum exhaust gas temperature in the roasting zone can reach 637 °C. High-temperature sulfur-containing exhaust gas causes oxidation corrosion, sulfide corrosion, and deformation of the steel belt. To enhance the steel belt longevity, it is recommended to appropriately reduce the wind velocity in the preheating zone and roasting zone, while also decreasing the ratio of pellet bed height to hearth layer height. By adopting the system of “low wind velocity, thin pellet bed, fast steel belt speed,” the exhaust gas temperature can be reduced to 463 °C. The prepared pellet maintains a compressive strength of 2607 N pellet⁻¹ and exhibits excellent metallurgical properties.

The correlation between the microstructure, properties, and strain partitioning behavior in a medium-carbon carbide-free bainitic steel was investigated through a combination of experiments and representative volume element simulations. The results reveal that as the austempering temperature increases from low to intermediate, the optimal balance of properties shifts from strength–toughness to plasticity–toughness. The formation of fine bainitic ferrite plates and bainite sheaves under low austempering temperature (270 °C) enhances both strength and toughness. Conversely, the wide size and shape distribution of the retained austenite (RA) obtained through austempering at intermediate temperature (350 °C) contribute to increased work-hardening capacity, resulting in enhanced plasticity. The volume fraction of the ductile film-like RA plays a crucial role in enhancing impact toughness under relatively higher austempering temperatures. In the simulations of tensile deformation, the concentration of equivalent plastic strain predominantly manifests in the bainitic ferrite neighboring the martensite, whereas the equivalent plastic strain evenly spreads between the thin film-like retained austenite and bainitic ferrite. It is predicted that the cracks will occur at the interface between martensite and bainitic ferrite where the strain is concentrated, and eventually propagate along the strain failure zone.