Chengjia Shang

The influence of the copper (Cu) content on the corrosion resistance of 3.5%Ni low-carbon weathering steel was investigated using periodic dry–wet cycle accelerated corrosion tests. The mechanical properties of the steels were assessed via tensile and low-temperature impact tests, while corrosion resistance was evaluated based on weight loss measurements. Surface oxide layers were characterized using three-dimensional laser confocal microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electrochemical methods. Electron probe microanalysis (EPMA) was employed to examine the cross-sectional morphology of the oxide layer after 72 h of accelerated corrosion tests. The results indicate that the solution state of Cu increased the strength of 3.5%Ni steels but significantly damaged the low-temperature toughness. As the Cu content increased from 0.75% to 1.25%, the corrosion rate decreased from 4.65 to 3.74 g/m² h. However, when there was a further increase in the Cu content to 2.15%, there was little decrease in the corrosion rate. With the increase in the Cu content from 0.75% to 2.15%, the surface roughness of 3.5%Ni weathering steel after corrosion decreased from 5.543 to 5.019 μm, and the corrosion behavior was more uniform. Additionally, the α/γ protective factor of the oxide layer of the surface layer increased from 2.58 to 2.84 with an increase in the Cu content from 0.75% to 1.25%, resulting in the oxide layer of the surface layer being more protective. For 1.25%Cu steel, the corrosion current density of rusted samples is lower (ranging from 1.2609 × 10⁻⁴ A/cm² to 3.7376 × 10⁻⁴ A/cm²), and the corrosion potential is higher (ranging from −0.85544 V to −0.40243 V). Therefore, the rusted samples are more corrosion resistant. The Cu in the oxide layer of the surface layer forms CuO and CuFeO₂, which are helpful for increasing corrosion resistance, which inhibits the penetration of Cl⁻.

This study investigates the relationship between recrystallization behavior and second-phase precipitation in Nb-V microalloyed steel during the rough rolling stage through thermal simulation experiments. The effects of deformation amount and temperature on austenite recrystallization were analyzed, alongside thermodynamic and kinetic calculations to assess the influence of Nb-V microalloying on second-phase precipitation. The results show that both the deformation amount and temperature significantly affect recrystallization, with Nb-V steel exhibiting more pronounced grain refinement compared to Nb steel. Significant differences in the type, morphology, and size distribution of second-phase precipitates were observed, with Nb-V steel primarily precipitating (Nb, V)C, while Nb steel only precipitates NbC. The average size of second-phase particles in Nb-V steel (10.60 nm) is smaller and more uniformly dispersed than in Nb steel (33.85 nm). Thermodynamic and kinetic analyses indicate that Nb-V microalloying accelerates second-phase precipitation kinetics. Moreover, second-phase particles hinder grain-boundary motion during recrystallization, with their effect surpassing that of Nb and V solid-solution atoms. These findings enhance the understanding of Nb-V composites in refining austenite grain size and promoting second-phase precipitation, providing valuable insights into the design and processing of high-performance microalloyed steels.