Calcium vanadate (CaV₂O₆), a new product of vanadium precipitation, was obtained from vanadium slag by sodium roasting-water leaching and calcium precipitation. The separation behavior of vanadium and silicon in vanadium slag during sodium roasting and water leaching was systematically studied, and micro-morphology and valence migration behavior of vanadium and Fe in vanadium slag, roasting slag, and residue were revealed. The Na₂CO₃ was added to the vanadium slag at 20% mass fraction, roasted at 790 °C, and kept for 120 min, the roasted sample was added to the deionized aqueous solution with a liquid-solid ratio of (L/S) 5mL/g, and then heated at 90 °C for 60 min, 89.54% vanadium and 1.96% chromium were extracted. Sodium carbonate tends to combine with vanadium to form sodium vanadate, while silicon is easy to combine with Fe and Na to form acmite (NaFeSi₂O₆). When the molar ratio of N (Ca/V) is 0.6 and CaO, is added to adjust the pH of vanadium leaching solution to 6.7 ± 0.1 and precipitate 90 min at 90 °C, vanadium is precipitated in the form of CaV₂O₆ with a purity of 95.69%, under these conditions, the precipitation ratio is 95.03%.

Cr/low-carbon steel surface composites were prepared by aqueous solution co-deposition and high-temperature solid-state diffusion technology, and the macro rule of the solid-state diffusion of chromium on the surface of low-carbon steel was analyzed. The molecular dynamics (MD) method was used to simulate and calculate the diffusion process of the Cr/Fe interface, and the macro and micro diffusion mechanisms were analyzed. The results show that the diffusion of the chromium in iron is the combined action of the temperature, crystal structure and lattice distortion, and the diffusion coefficients of chromium in α-Fe and γ-Fe have little difference. The vacancy diffusion mechanism of the first adjacent transition is the main diffusion mode. In practice, chromium atoms diffuse along the grain boundaries of the low-carbon steel matrix and provide pinning at the grain boundaries to prevent grain growth. The simulation law is in good agreement with the experimental law. The variation law of the average diffusion coefficient of chromium atoms with temperature is obtained. The diffusion rate of chromium in the bcc crystal structure is obviously higher than that in the fcc crystal structure. In the same crystal structure, the diffusion coefficient of chromium increases with the increase in temperature. However, in the lattice transition temperature region, the diffusion coefficient of chromium gradually decreases with the increase in temperature until the end of the transformation.

The effective diffusion of Cu in Fe is the key to forming a stable transition layer between copper and low-carbon steel, but it is seriously affected by several factors, especially temperature, and the diffusion of Cu can only be completed at high temperatures. In order to analyze the diffusion coefficient of Cu in low-carbon steel under high temperatures, and to obtain the best diffusion temperature range of Cu in steel, the electrodeposition method was used to prepare the diffusion couple of copper and low-carbon steel, which would be annealed under different temperatures for 6 h; meanwhile, the MD models were also used to analyze the diffusion behavior of Cu in Fe at different temperatures. The results show that the diffusion of Cu in low-carbon steel could be realized by high-temperature annealing, and as the temperature increases, the thickness of the Cu/low-carbon steel transition layer shows an increasing trend. When the annealing temperature is between 900 °C and 1000 °C, the thickness of the transition layer increases the fastest. The results of the MD models show that, when the temperature is in the phase transition zone, the main restrictive link for the diffusion of Cu in Fe is the phase transition process of Fe; additionally, when the temperature is higher, the main restrictive link for the diffusion of Cu in Fe is the activity of the atom.

The automotive industry’s rapid expansion has made the development of lightweight, high-strength automotive steels essential for both energy efficiency and emission reduction. Among these materials, Fe-Mn-Al-C steel has drawn considerable interest due to its favorable combination of low density and high strength. This research examines the impact of Nb alloying (with Nb content of 0% and 0.5%) and solution treatment on the microstructure and mechanical properties of cold-rolled Fe-28Mn-10Al-C low-density steel. Various methods were employed, including Thermo-Calc thermodynamic simulations, the Olson–Cohen model, X-ray diffraction (XRD), metallographic microscopy, room-temperature tensile testing, and scanning electron microscopy (SEM). The findings demonstrate that Nb alloying significantly refines the austenite grain structure of the Fe-28Mn-10Al-C steel, improving both strength and ductility in comparison to the 0Nb steel. After solution treatment at 1050 °C for 30 min, the cold-rolling-induced defects are effectively removed, leading to a substantial increase in elongation at fracture (38.14–44.45%) and an ultimate tensile strength exceeding 900 MPa. As the solution treatment temperature increases, the austenite grains coarsen, and the number of twins increases, while yield strength and ultimate tensile strength decrease. However, there is a notable enhancement in ductility, with the material exhibiting a ductile fracture mechanism. These results offer valuable insights and a theoretical foundation for further improving the mechanical properties of Fe-Mn-Al-C low-density steels.

Research on improving the corrosion resistance of carbon steel has become a hot topic in the iron and steel field in recent years. Copper plating on the surface of carbon steel is considered an effective means to improve its corrosion resistance, but the copper-plated carbon steel material prepared by this method has the problems of poor abrasion resistance, easy delamination of copper layer and similar issues, which affect the service performance of the copper-plated carbon steel material. To solve this problem, a new type of material whose surface is copper and the copper element is gradually diffused into carbon steel was developed by a plating-diffusion method, which is defined as a copper-carbon steel gradient material. Carbon steel with a copper plated surface and the Cu-Fe/carbon steel gradient material with 80% Cu content on the surface were prepared by the same method. The cross-sectional microstructure and composition of different samples were analysed, and the corrosion behaviors of samples in 3.5% NaCl solution were studied by the linear polarization curve method and electrochemical impedance spectroscopy. The cross-sectional microstructure result shows that the diffusion of copper in carbon is mainly carried out along its grain boundary, and the diffusion of copper will inhibit the growth of grains during heat treatment. As shown in the results of corrosion behaviors, there is no pitting corrosion in the corrosion process of all samples, as well as the stable passive film. All samples showed active dissolution. Compared with carbon steel, the corrosion potential of the Cu/carbon steel gradient material becomes more positive from −600 mV to −362 mV, the corrosion current density decreases from 53.0 μA/cm² to 30.6 μA/cm² and the radius of electrochemical impedance spectroscopy enlarges while the corrosion resistance is improved, and the corrosion resistance is mainly obtained by its surface copper layer. The corrosion resistance of Cu-Fe/carbon steel gradient material is lower than that of Cu/carbon steel gradient material, while it is still better than carbon steel, and it shows a clear passivation trend during corrosion. Therefore, the copper/carbon steel gradient material can significantly improve the corrosion resistance of carbon steel. Even after the surface copper layer is destroyed, the gradient material can protect the matrix and improve the service life of the material.