Journal of Iron and Steel Research International最新文献

Against the background of “carbon peak and carbon neutrality,” it is of great practical significance to develop non-blast furnace ironmaking technology for the sustainable development of steel industry. Carbon-bearing iron ore pellet is an innovative burden of direct reduction ironmaking due to its excellent self-reducing property, and the thermal strength of pellet is a crucial metallurgical property that affects its wide application. The carbon-bearing iron ore pellet without binders (CIPWB) was prepared using iron concentrate and anthracite, and the effects of reducing agent addition amount, size of pellet, reduction temperature and time on the thermal compressive strength of CIPWB during the reduction process were studied. Simultaneously, the mechanism of the thermal strength evolution of CIPWB was revealed. The results showed that during the low-temperature reduction process (300–500 °C), the thermal compressive strength of CIPWB linearly increases with increasing the size of pellet, while it gradually decreases with increasing the anthracite ratio. When the CIPWB with 8% anthracite is reduced at 300 °C for 60 min, the thermal strength of pellet is enhanced from 13.24 to 31.88 N as the size of pellet increases from 8.04 to 12.78 mm. Meanwhile, as the temperature is 500 °C, with increasing the anthracite ratio from 2% to 8%, the thermal compressive strength of pellet under reduction for 60 min remarkably decreases from 41.47 to 8.94 N. Furthermore, in the high-temperature reduction process (600–1150 °C), the thermal compressive strength of CIPWB firstly increases and then reduces with increasing the temperature, while it as well as the temperature corresponding to the maximum strength decreases with increasing the anthracite ratio. With adding 18% anthracite, the thermal compressive strength of pellet reaches the maximum value at 800 °C, namely 35.00 N, and obtains the minimum value at 1050 °C, namely 8.60 N. The thermal compressive strength of CIPWB significantly depends on the temperature, reducing agent dosage, and pellet size.

MgO participates in all stages of sintering, pelletizing, and blast furnace ironmaking, and synergistically optimizing the distribution of MgO in ferrous burden can effectively enhance the interaction within the ferrous burdens and optimize the softening–melting properties of the mixed burden. Magnesium-containing pellets mixed with low-MgO sinter or mixed with high-MgO sinter in the blast furnace ferrous burden structure have opposite softening–melting performance laws. When the structure of the ferrous burden is magnesium-containing pellets mixed with low-MgO sinter, the magnesium-containing pellets can enhance the interaction of the ferrous burden in the process of softening–melting, which can optimize the composition of the slag phase and improve the slag liquidity. When the structure of the ferrous burden is magnesium-containing pellets mixed with high-MgO sinter, the magnesium-containing pellets weaken the interaction of the ferrous burden in the process of softening–melting, increase the content of the high melting point solid-phase particles in the slag, lead to an increase in the viscosity of the slag and difficult separation of the slag and iron, and decrease the permeability of the charge layer. Therefore, to ensure good permeability of the mixed burden, the following measures are suggested: optimizing the MgO distribution of the ferrous burden, reducing the MgO content of the sinter to 1.96 wt.%, increasing the MgO content of the pellets to 1.03–1.30 wt.%, controlling the MgO/Al₂O₃ ratio of the mixed burden within 1.15–1.32, narrowing the position of the cohesive zone, and maintaining an S value (permeability index) of approximately 150 kPa °C.

Ultrafine iron powder is widely used due to its excellent performance. Hydrogen reduction of fine-grained high-purity iron concentrate to prepare ultrafine iron powder has the advantages of low energy consumption, pollution-free, and low cost. The hydrogen reduction of high-purity iron concentrates, characterized by the maximum particle size of 6.43 μm when the cumulative distribution is 50% and the maximum particle size of 11.85 μm when the cumulative distribution is 90% while the total iron content of 72.10%, was performed. The hydrogen reduction could be completed at 425 °C, and the purity of ultrafine iron powders was more than 99 wt.% in the range of 425–650 °C. Subsequently, the effect of reduction temperature on various properties of ultrafine iron powder was investigated, including particle morphology, particle size, specific surface area, lattice parameters, bulk density, and reaction activity. It was found that the reaction activity of the iron powders prepared by hydrogen reduction was much higher than that of the products of carbonyl and liquid phase synthesis. Below 500 °C, the reduced iron powders were nearly unbound, with a small particle size and a low bulk density. The particles had a porous surface, with a specific surface area as high as 11.31 m² g⁻¹. The crystallization of reduced iron powders was imperfect at this time, the amorphization degree was prominent, and the interior contained a high mechanical storage energy, which had shown high reaction reactivity. It was suitable for catalysts, metal fuels, and other functionalized applications.

Enhancing the ductility and toughness of advanced high-strength steels is essential for the wide range of promising applications. The retained austenite (RA) is a key phase due to the austenite-to-martensite transformation and its transformation-induced plasticity effect. It is commonly accepted that slow RA-to-martensite transformation is beneficial to ductility; therefore, the RA fraction and stability should be carefully controlled. The RA stability is related to its morphology, size, carbon content, neighboring phase and orientation. Importantly, these factors are cross-influenced. It is noteworthy that the influence of RA on ductility and fracture toughness is not consistent because of their difference in stress state. There is no clear relationship between fracture toughness and tensile properties. Thus, it is important to understand the role of RA in toughness. The toughness is enhanced during the RA-to-martensite transformation, while the fracture toughness is decreased due to the formation of fresh and brittle martensite. As a result, the findings regarding to the effect of RA on fracture toughness are conflicting. Further investigations should be conducted in order to fully understand the effects of RA on ductility and fracture toughness, which can optimize the combination of ductility and toughness in AHSSs.

Reticulated ceramic foam filters provide an effective way to purify molten steel by removing non-metallic inclusions. We proposed a novel strategy to improve the purification performance of Al₂O₃-based ceramic filters by using microporous corundum–spinel raw materials to replace dense raw materials. Three kinds of Al₂O₃-based ceramic filters fabricated from dense α-Al₂O₃ micro-powder or microporous corundum–spinel powder were selected to carry out the immersion tests with molten steel. On the one hand, the higher surface roughness of the filter skeleton prepared from microporous raw materials increased the adsorption capacity of skeleton surface on inclusions in molten steel. On the other hand, the higher apparent porosity and larger pore size of the filter skeleton were more beneficial to the penetration of molten steel in the micropores of skeleton. The reaction process at the solid–liquid interface also improved the wettability of the interface between skeleton and molten steel, resulting in a larger penetration depth and a better adsorption effect on the inclusions. In summary, the novel Al₂O₃-based ceramic filter prepared with microporous corundum–spinel powder and addition of 5 wt.% nano-Al₂O₃ powder reduced the total oxygen content of the steel from 40.2 × 10⁻⁴ to 12.7 × 10⁻⁴ wt.% by 68.4% and the Al content from 0.46 to 0.18 wt.% by 60.9% after immersion test, presenting the most excellent purification performance on molten steel.

Developing deNO_x catalysts with lower activity temperatures range significantly reduces NH₃ selective catalytic reduction (SCR) operating costs for low-temperature industrial flue gases. Herein, a novel FeVO₄/CeO₂ catalyst with great low-temperature NH₃-SCR and nitrogen selectivity was synthesized using a dipping method. Characterization techniques such as X-ray diffraction, Raman spectroscopy, specific surface and porosity analysis, H₂ temperature-programmed reduction, NH₃ temperature-programmed desorption, X-ray photoelectron spectroscopy, and the in situ diffused reflectance infrared Fourier transform spectroscopy were used to investigate the catalytic mechanism. An appropriate addition for FeVO₄ in the catalyst was 5 wt.% from the results, and the active substance content reached the maximum dispersal capacity of the carrier. The NO_x conversion exceeded 90%, and the nitrogen selectivity was more than 98% over this catalyst at 200–350 °C. The activity was kept at 88% after 7.5 h of reaction at 200 °C for 7.5 h in 35 mg m⁻³ SO₂ gas. The remarkable deNO_x activity, nitrogen selectivity, and sulphur resistance performances are attributed to the low redox temperature, the abundance of medium-strong acid and strong acid sites, the sufficient adsorbed oxygen, and the superior Fe²⁺ content on the surface. The Langmuir–Hinshelwood mechanism was observed on the FeVO₄/CeO₂ catalyst in the NH₃ selective catalytic reduction of NO_x.

An industrial experiment was conducted at a certain steel plant in China to compare and analyze the effects of Ca treatment and Mg–Ca treatment on inclusions in 45MnVS non-quenched and tempered steel. Through scanning electron microscopy-energy dispersive scanning analysis of the morphology and composition of inclusions, as well as Aspex quantitative analysis of their quantity, type and size, the formation mechanism of MnS–oxide (MnS inclusions with oxide cores) was intensively studied. The influence of sulfide morphology on the impact properties of steel was also analyzed. The results show that the quantity percentage of spindle-shaped sulfides in Ca-treated steel is 19.99%, and that in Mg–Ca-treated steel is 35.38%. Compared with Ca-treated steel, there are more MnS–oxide inclusions in Mg–Ca-treated steel. Controlling the content of Ca and Mg in the oxide core of MnS–oxide inclusion above 10 wt.% and the area ratio below 5 would contribute to the formation of spindle-shaped inclusions after rolling. The mismatch between MnS and oxides decreases with the increase in MgO content in the oxides, which is beneficial to nucleation and precipitation of MnS with this type of oxides as the core. Under the same deformation conditions, the size of sulfide does not affect its aspect ratio. Under the experimental conditions, the inclusion containing a certain amount of MgO can enhance its sulfur capacity, facilitating the formation of composite sulfides. The transverse impact energy of Ca-treated steel is 25.785 J, and that of Mg–Ca-treated steel is 32.119 J. Compared with the traditional Ca-treatment, Mg–Ca treatment can increase the number of spindle-shaped sulfides in the steel, thereby improving the transverse impact toughness of the steel and reducing the anisotropy of the mechanical properties of the material.

The corrosion behaviour of zinc–aluminium–magnesium-coated steel in a simulated polluted marine atmospheric environment was investigated. Therefore, an indoor ageing acceleration test was carefully designed by simulating a polluted marine environment. The objective was to in-depth investigate the corrosion mechanism of Zn–Al–Mg-coated steel exposed to a simulated polluted marine environment. The experiments were carried out by scanning electron microscopy for micro-morphological characterization, X-ray diffraction, electrochemical impedance spectroscopy and electrodynamic polarization curves for the aged samples. The analysis of the results obtained after an indoor accelerated ageing test shows that Zn–Al–Mg coatings generate insoluble Zn₅Cl₂(OH)₈·H₂O and Zn₄SO₄(OH)₆ during the corrosion process, which hinders the diffusion of corrosive substances into the substrate, and the insoluble substances are structurally dense and thus inhibit further corrosion. Therefore, this effectively inhibits the occurrence of further corrosion, and thus, Zn–Al–Mg coating can significantly extend the service life of Zn–Al–Mg-coated steel.

The service life of a blast furnace depends largely on the degree of damage to the carbon brick in the hearth. Carbon brick and ramming material in the hearth of a 1780 m³ blast furnace after shutdown were sampled and investigated. It was found that the substances in the cracks of the carbon brick near and above the taphole were ZnO and Zn₂SiO₄, whereas the substances in the cracks of the carbon brick below the taphole were ZnS. The reaction of Zn with CO, SiO₂, and FeS generates ZnO, Zn₂SiO₄, and ZnS, resulting in volume expansion, which is an important reason for the cracking of carbon brick. Simultaneously, several obvious Zn vapor flow channels were found in the ramming material, through which Zn vapor could enter the carbon brick, causing damage to the carbon brick. Increasing the compactness of the ramming material is beneficial to preventing Zn vapor from entering the carbon brick through the voids in the ramming material, reducing the destructive effect of Zn on the carbon brick and further extending the service life of the blast furnace.

ZrO₂-strengthened porous mullite insulation materials were prepared by foaming technology utilizing ZrSiO₄ and Al₂O₃ as primary materials and Y₂O₃ as an additive. The effects of Y₂O₃ contents on the phase composition, microstructure, mechanical properties, and heat conductivity of the porous mullite insulation materials were investigated. A suitable Y₂O₃ content could promote phase transition of monoclinic ZrO₂ (m-ZrO₂) to tetragonal ZrO₂ (t-ZrO₂), reduce pore size, and improve the strengths of as-prepared specimens. The cold crushing strength and bending strength of as-prepared specimens with a 119 µm spherical pore size using 6 wt.% Y₂O₃ were 35.2 and 13.0 MPa, respectively, with a heat conductivity being only 0.248 W/(m K).