Thermal shock cycling experiments are conducted in this paper to explore the effects of extreme conditions on the corrosion rate, surface morphology, and corrosion products of both Q345R (carbon-manganese steel) and 347H (UNS S34709) in KNO3-NaNO2-Na2CO3 mixed molten salt. Scaning electron microscopy, energy dispersive spectroscopy, x-ray diffraction (XRD), and other methods are used to characterize morphologies and microstructures of the samples obtained under the static and cyclic corrosion conditions. The experimental results showed that the corrosion products of the 347H sample are mainly FeCr2O4, Fe3O4, Fe2O3, and NaFeO2, while those of the Q345R sample only include Fe3O4, Fe2O3, and NaFeO2. Besides the thermal cycling operation's effects on the electrochemical corrosion process of metals in the molten salts, Na2CO3 addition in the molten salt is also proven to be a key factor affecting the corrosion process and further altering both phase constituent and proportion in the corrosion layer. Especially, the experiment discloses that Na2CO3 also should be responsible for the surface corrosion morphology transition of the corroded sample due to its ability to enhance the inhomogeneous distribution of the corrosion rate on the sample surface. In addition, in comparison with the Q345R steel, the 347H steel has been proven to be more sensitive to the cycled heat-treatment. Further analyses on the XRD data suggest that several reasons, including reduction of Cr2O3& FeCr2O4, increment of brittle NaFeO2 and Fe2O3 phase in the scale resulting from the cycled operation, and discrepancy in thermal property resulting from the complex phases in the scale, etc., can be used for explaining the weakened corrosion behaviors of the 347H steel in the molten salt used in experiments.
This study aims to evaluate the hot corrosion resistance of a novel NiCrMoAlSi cladding layer compared to conventional Inconel 625 under a K2SO4-55 at% ZnCl2 salt film at 650 degrees C and 700 degrees C, elucidating the role of Al and Si in enhancing protective oxide scale formation. Inconel 625 and NiCrMoAlSi cladding layers were prepared via laser cladding and subjected to 100-h hot corrosion tests under a deposited salt film. Mass loss measurements, x-ray diffraction, and scanning electron microscopy-energy dispersive spectorsopy were used to analyze corrosion products, scale morphology, and elemental distribution. The NiCrMoAlSi cladding layer exhibited significantly lower mass loss (2.63 mg/cm2 to 6.43 mg/cm2) than Inconel 625 (27.05 mg/cm2 to 27.52 mg/cm2), due to a dense, multilayered oxide scale enriched with Cr and Al externally and Si internally. In contrast, Inconel 625 formed porous oxides and a Cr/Fe dissolution zone, leading to severe corrosion degradation.
During steel processing, surface treatment often fails to meet the Sa2.5 standard or higher, sometimes requiring manual rust removal. Even after manual cleaning, rust products frequently remain on the steel surface, severely compromising the performance of traditional anticorrosion coatings. In this study, we grafted phytic acid onto the molecular chain of epoxy resin through chemical synthesis to produce a composite resin with rust conversion capability and determined optimal synthesis parameters. The water absorption rate and electrochemical impedance spectroscopy data indicate that although the addition of modified resin increases a coating's hydrophilicity, the resin enhances the degree of cross-linking and reacts with the rust layer, forming a new shielding layer and improving the coating's overall corrosion resistance. The coating with a 20% modified resin exhibited the best corrosion resistance.
In this paper, the microstructure evolution of Cr16Mn8NiMoN metastable austenitic stainless steel under gradient tensile deformation with strain ranging from 10% to 40% was systematically investigated, and its influences on microstructural transformation and corrosion resistance were further analyzed. The results indicate that the tensile specimen with 20% deformation is in the critical state of microstructural transformation. Dislocation proliferation, strain-induced martensite formation, and grain refinement collectively reduce the corrosion resistance of the metastable austenitic stainless steel. Compared with the degradation of corrosion resistance at 30% strain, the decline in corrosion resistance at 20% strain is mainly attributed to the increased surface energy difference, higher fraction of strain-induced martensite, and a larger number of low-angle grain boundaries. With the increase of strain, the variation of pitting nucleation sites is closely correlated with the rise in dislocation density and the growth of strain-induced martensite. Based on the above correlation, grain boundary misorientation is identified as a potential key microstructural parameter, which may play an important role in multifactor coupling. This study provides an important theoretical basis for the precise optimization of the strength and corrosion resistance synergistic performance of metastable austenitic stainless steel via deformation processes.
W18Cr4V high-speed steel is the core material for woodworking cutting tools, and its corrosion-induced failure in acidic wood media is the primary cause of shortened tool service life. Existing studies have mostly focused on macroscopic corrosion behavior characterization, while quantitative elucidation of microscale corrosion initiation mechanisms and dynamic pit propagation processes remains insufficient. This study systematically clarifies the entire corrosion failure process of W18Cr4V steel in acetic acid media by combining electrochemical experiments and multiphysics numerical simulations. First, potentiodynamic polarization tests and static immersion experiments were conducted to determine the corrosion kinetic parameters of W18Cr4V steel in acetic acid solutions with concentrations ranging from 1% to 20%. The results show that the material exhibits typical active corrosion characteristics, and the corrosion rate shows a significant nonmonotonic dependence on acetic acid concentration: it increases first and then decreases with increasing concentration, reaching a peak at 15% concentration. On this basis, a two-dimensional microgalvanic corrosion model containing the Fe matrix and WC carbide phases was constructed. In the model, the Fe-Cr-V-W multicomponent substitutional solid solution matrix was simplified as a pure iron phase, based on the fact that Fe accounts for over 70 wt% and its oxidation reaction dominates the dissolution behavior. The simulation results quantitatively reveal the microgalvanic effect during the corrosion initiation stage, showing that corrosion preferentially nucleates at the interphase boundaries between WC carbides and the matrix due to electrochemical activity differences, with the local current density at the boundaries reaching 3-5 times the average current density of the matrix. Furthermore, an axisymmetric pit propagation model based on the level set method was established to reveal the evolution law of the occluded microenvironment inside pits. It is found that, contrary to the common perception of self-acidification inside pits in traditional strong acid systems, the consumption rate of H+ by the cathodic hydrogen evolution reaction is much higher than the production rate of H+ by Fe2+ hydrolysis in this acetic acid system, leading to local alkalization inside the pits. Meanwhile, the increase in local conductivity caused by ion enrichment forms an autocatalytic positive feedback loop, driving the rapid deep propagation of pits. Finally, the reliability of the simulation model was verified from three dimensions: macroscopic trend, microscopic morphology, and chemical composition through surface topography and component analysis of static immersion experiments. The "initiation-propagation" progressive corrosion model established in this study can provide a theoretical basis for corrosion life prediction and protective design of woodworking cutting tools.
