With the rapid development of hydrogen pipelines, their safety issues have become increasingly prominent. In order to evaluate the properties of pipeline materials under a high-pressure hydrogen environment, this study investigates the hydrogen embrittlement sensitivity of X70 welded pipe in a 10 MPa high-pressure hydrogen environment, using slow strain rate testing (SSRT) and low-cycle fatigue (LCF) analysis. The microstructure, slow tensile and fatigue fracture morphology of base metal (BM) and weld metal (WM) were characterized and analyzed by means of ultra-depth microscope, scanning electron microscope (SEM), electron backscattering diffraction (EBSD), and transmission electron microscope (TEM). Results indicate that while the high-pressure hydrogen environment has minimal impact on ultimate tensile strength (UTS) for both BM and WM, it significantly decreases reduction of area (RA) and elongation (EL), with RA reduction in WM exceeding that in BM. Under the nitrogen environment, the slow tensile fracture of X70 pipeline steel BM and WM is a typical ductile fracture, while under the high-pressure hydrogen environment, the unevenness of the slow tensile fracture increased, and a large number of microcracks appeared on the fracture surface and edges, with the fracture mode changing to ductile fracture + quasi-cleavage fracture. In addition, the high-pressure hydrogen environment reduces the fatigue life of the BM and WM of X70 pipeline steel, and the fatigue life of the WM decreases more than that of the BM as well. Compared to the nitrogen environment, the fatigue fracture specimens of BM and WM in the hydrogen environment showed quasi-cleavage fracture patterns, and the fracture area in the instantaneous fracture zone (IFZ) was significantly reduced. Compared with the BM of X70 pipeline steel, although the effective grain size of the WM is smaller, WM’s microstructure, with larger Martensite/austenite (M/A) constituents and MnS and Al-rich oxides, contributes to a heightened embrittlement sensitivity. In contrast, the second-phase precipitation of nanosized Nb, V, and Ti composite carbon-nitride in the BM acts as an effective irreversible hydrogen trap, which can significantly reduce the hydrogen embrittlement sensitivity.

Long-term steel reinforcement corrosion greatly impacts reinforced concrete structures, particularly in marine and coastal settings. Concrete failure leads to human casualties, requiring extensive demolition and maintenance, which represents an inefficient use of energy and resources. This study utilizes microscopic observation, atomic force microscopy (SKPM), electrochemical experiments, and XPS analysis to investigate the corrosion behavior of 500CE and 500E under identical conditions. We compared 500E with 500CE, supplemented with 0.94% Cr, 0.46% Mo, 0.37% Ni, and 0.51% Cu through alloying element regulation to obtain a finer ferrite grain and lower pearlitic content. The results indicate that 500CE maintains a stable potential, whereas 500E exhibits larger grain sizes and significant surface potential fluctuations, which may predispose it to corrosion. In addition, despite its more uniform microstructure and stable electrochemical activity, 500E shows inferior corrosion resistance under prolonged exposure. The electrochemical corrosion rate of 500CE in both the pristine and passivated states and for various passivation durations is slower than that of 500E, indicating superior corrosion performance. Notably, there is a significant increase in the corrosion rate of 500E after 144 h of exposure. This study provides valuable insights into the chloride corrosion phenomena of low-alloy corrosion-resistant steel reinforcement in service, potentially enhancing the longevity of reinforced concrete structures.

As the pace of human development in the ocean accelerates, the demand for corrosion-resistant building materials in marine engineering projects is constantly increasing. The development of high-performance corrosion-resistant materials and their mechanism research has gradually become the latest hotspot in the field of metal materials. Through cyclic dry–wet testing, electrochemical techniques, morphological characterization, and compositional analysis, this study simulated the impact of varying manganese content on weathering steel corrosion resistance in chloride environments. The results indicated that, compared to low-manganese weathering steel, the average rust layer thickness of high-manganese weathering steel increased by 22.5%. Additionally, manganese was found in the rust as MnO/MnO₂, acting as a catalyst to promote electron transfer, which led to a decrease in the α/γ* ratio in the high-manganese weathering steel, thereby accelerating the corrosion reaction.

The corrosion behaviors in chloride environment of two commercial low-alloy steel bars were studied. Through cyclic wetting tests, accelerated corrosion experiments ranging from 1 to 576 h were conducted on low-alloy bars and original bars. Techniques such as OM, SEM, EDS, AFM, and XRD were employed to characterize the corrosion emergence and expansion behaviors of these bars in a simulated marine wetting and sun exposure environment. The designed low-alloy corrosion-resistant rebar achieved a 500 MPa yield strength. In each corrosion cycle, its corrosion loss and rate were lower than those of same-strength ordinary rebars. Analysis of the rust layer’s macro and micro morphology and alloy element distribution revealed alloy elements had little effect at corrosion initiation. In later corrosion, their enrichment led to a denser rust layer, effectively blocking corrosion expansion and chloride salt infiltration. After 72 h of accelerated corrosion, the corrosion rate growth of both bars slowed. The inner rust layer’s electrochemical potential increased, and local corrosion pits turned into uniform corrosion. The inner rust layer of the rebar formed more stable chromic acid with ionic compounds, reducing corrosion sensitivity. This study offers insights into steel bar corrosion and alloy element roles, guiding the preparation of low-alloy corrosion-resistant steel bars.

In this paper, the influence of Cr element on the mechanical properties of welded joints of gas-shielded solid wire used in oil and gas long-distance pipelines was studied by means of tensile test, impact test, and hardness test, and the microstructure and crack propagation path of weld were characterized by means of an optical microscope, scanning electron microscope, and electron backscattering diffraction. The results show that with the addition of Cr, the strength and toughness of the weld are significantly improved, in which the tensile strength is increased from 607 MPa to 656 MPa, and the impact toughness is increased from 126.37 J to 223.79 J. The proportion of the ferrite side plate in the weld structure is reduced by about 20%, and the effective grain size of acicular ferrite is reduced by about 15%. The reason is that the addition of the Cr element improves the hardenability of the weld structure, inhibits the formation of the ferrite side plate, and promotes the effective refinement of acicular ferrite, which increases the proportion of high-angle grain boundaries in the weld, effectively hindering the crack propagation, improves the crack propagation work, and thus improves the strength and toughness of the weld.

This study employs microwave roasting to decompose smithsonite mineral (zinc carbonate) into zinc oxide, which then reacts with pyrite to sulfurize its surface, forming zinc sulfide. This process is beneficial for the flotation recovery of zinc oxide minerals. The surface sulfidation behavior of smithsonite under low-temperature microwave roasting conditions is examined through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and thermodynamic calculations. XRD and thermodynamic analysis indicate that smithsonite completely decomposes into zinc oxide at 400 °C. Introducing a small amount of pyrite as a sulfidizing reagent leads to the formation of sulfides on the surface of decomposed smithsonite. XPS analysis confirms that the sulfide formed on the surface is zinc sulfide. SEM analysis reveals that sulfides are distributed on the surface of smithsonite, and the average sulfur concentration increases with the pyrite dosage. Microwave-assisted sulfurization of smithsonite (ZnCO₃) was found to significantly enhance its floatability compared to conventional sulfurization methods. The optimal mass ratio of ZnCO₃ to FeS₂ is approximately 1:1.5, with the best temperature being 400 °C. These findings provide a technical solution for the application of microwave roasting in the efficient recovery of smithsonite through flotation.