This study investigates the nonlinear evolution of rust layers on weathering steel in a simulated tropical marine atmosphere. Seven critical time points (24, 72, 168, 288, 360, 480, and 720 h) were identified using electrochemical impedance spectroscopy, and changes in rust layer morphology, composition, and distribution were analyzed. In the early stage (0-72 h), a single-layer rust formed, consisting of a mixture of five phases: alpha-FeOOH, gamma-FeOOH, (3-FeOOH, gamma-Fe2O3, and Fe3O4. During the metastable stage (168-288 h), the rust layer began to stratify, forming an inner layer adjacent to the steel substrate, composed of alpha-FeOOH and Fe3O4. Between 360 and 480 h, the rust layer further differentiated into four distinct zones: an inner rust layer, a valley zone rich in all five phases, an outer rust layer, and an outermost layer consisting of gamma-FeOOH. After 480 h, the stable stage, a stable, protective rust structure was established. The improved weatherability at later stages is attributed to the valley's disappearance and the inner layer's thickening enriched in stable alpha-FeOOH.

The effect of silty sand in the corrosion of N80 carbon steel with pre-corroded FeCO3 films under CO2-saturated liquid-solid two-phase flow conditions was investigated using a small-scale loop corrosion apparatus. The preformed FeCO3 film substantially reduces the corrosion rate by impeding the transport of corrosive species. In contrast, complete removal of the FeCO3 film exposes the Fe3C phase, which enhances micro-galvanic coupling with ferrite and accelerates the active dissolution of the steel. The interaction between silty sand and the FeCO3 film exhibits a dual effect: on the one hand, it compromises the integrity and compactness of intact films, thereby increasing porosity and accelerating corrosion. On the other hand, it adsorbs onto partially damaged regions and becomes embedded within surface pores, blocking active dissolution sites and reducing the corrosion rate. Moreover, the embedded silty sand particles promote the growth of corrosion product films, which further hinder ion transport. Overall, both the FeCO3 film and silty sand deposition exhibit corrosion-inhibiting effects, but the continuous and compact FeCO3 film provides more effective protection compared to silty sand alone.

This study explores the influence of robot weaving width on the microstructure and mechanical properties of 4043 aluminum alloy thin-walled components fabricated using cold metal transfer (CMT)-based wire arc additive manufacturing (WAAM). Thin-wall structures composed of 20 layers were deposited using weaving widths of 4 mm, 6 mm, and 8 mm. As the weaving width increased, the microstructure evolved from coarse lath-like dendrites to finer dendrites. The phase composition remained consistent across all samples, consisting of Al and Si. Mechanical testing in both the travel (X) and building (Z) directions, along with hardness profiling through the wall height, revealed that a 6 mm weaving width achieved an optimal balance between structural refinement and mechanical performance. This condition also minimized anisotropy in mechanical performance. In contrast, at 8 mm, ductility decreased, and fracture surface at building (Z) direction exhibited mixed ductile-brittle fracture mode. These findings demonstrate that robot weaving width is a useful parameter in optimizing the WAAM-CMT process. A properly selected weaving width can enhance deposition efficiency without compromising material integrity, offering a practical approach for the rapid and reliable fabrication of large-scale aluminum alloy components.

This study investigates the influence of impact angles on the corrosion behavior of 5Cr steel in a CO2-silty sand environment through hydrodynamics analysis. The primary cause of degradation in 5Cr steel is the combined effect of the mechanical damage to the corrosion product film by silty sand particles and corrosive environment. The severity of damage to the corrosion product film on the 5Cr steel surface caused by silty sand particles at different impact angles, from highest to lowest, is 45 degrees, 90 degrees, and 0 degrees. At an impact angle of 45 degrees, the silty sand exerts equal tangential and normal stresses on the corrosion product film, compromising its integrity and requiring more Cr(OH)3 for repair and stabilization, resulting in the most severe localized pitting corrosion. At impact angles of 0 degrees and 90 degrees, the silty sand exerts only tangential stress and normal stress on the corrosion product film, respectively. The imbalance between normal and tangential stresses at these angles results in shallower and more limited removal of corrosion products, making the destructive effect less significant than at a 45 degrees impact angle.

The effect of low-energy mechanical impact exerted by silty sand on the evolution of corrosion product film on N80 carbon steel was investigated using a small-scale flow loop apparatus. Silty sand exhibited a dual effect on the film development. During the early corrosion stage, its adsorption on the steel surface reduced the corrosion rate, promoted the nucleation and growth of FeCO3 within the inner layer, and contributed to the stabilization of a protective film. In contrast, silty sand disrupted the film integrity in the later stage, resulting in severe localized corrosion and an overall increase in corrosion rate.

PurposeThis study aims to address the urgent need for accurate prediction of the long-term corrosion performance of low-alloy steel in tropical marine atmospheric environments and to quantify the effects of environmental factors and steel composition on corrosion.Design/methodology/approachThis study compared the predictive accuracy of four machine learning algorithms: Support Vector Regression, Multi-Layer Perceptron, Random Forest and Extreme Gradient Boosting (XGBoost). Subsequently, the best-performing XGBoost model was interpreted using SHapley Additive exPlanations (SHAP) and Accumulated Local Effects (ALE) to quantitatively assess the influence of features on corrosion.FindingsThe XGBoost model demonstrated the best predictive accuracy on the independent dataset and showed good generalization ability (R-2 = 0.841, MAE = 5.37 mu m/a). SHAP and ALE quantified the influence of features and revealed the nonlinear threshold effects of features on corrosion.Originality/valueThis study provides insights into the long-term prediction of the corrosion performance of low-alloy steel and the formulation of targeted, condition-responsive corrosion prevention strategies.

Based on the dissolution and redeposition characteristics of Cu in H 2 SO 4 solution, this study examines the impact of sulfuric acid patination treatment on the weatherability of Cu‐containing weathering steel in the simulated tropical marine atmosphere. Results reveal that acid treatment improves the protective properties of the rust layer by inducing more Cu to participate in rust layer formation and causing a layered distribution of Cu in rust layers, which reduces the rust layer defects, increases the content of α‐FeOOH, reduces rust particle size, increases the diffusion resistance to corrosive species, and enlarges the thickness of the protective rust layer.

The effects of flow velocity and silty sand on CO2 corrosion of N80 carbon steel were studied using a small flow loop. Silty sand does not change the electrochemical characterization of corrosion but reduces the corrosion rate of steel. Under the low flow velocity, silty sand embeds in the sample surface, reducing active area for iron dissolution and delaying the formation of FeCO3 in corrosion product layer. At medium and high flow velocity, silty sand erodes the sample surface, and wall shear stress damages the integrity of the corrosion product layer, but do not lead to greater corrosion rate.

This study discusses the comparative weatherability of three microstructures of ferrite, ferrite + bainite, and bainite, obtained by controlling the rolling and cooling processes of a well-established weathering steel by adding 3 wt

The passivation performance of the selective laser melted Inconel 718 alloy after tempering treatments was investigated, and the underlying mechanism for the improved passivation film protectiveness was explored. The dislocation reversion and the mitigated segregation of Nb, Mo and Ti at Laves and δ phases decreased the storage energy of lattice distortion were critical factors for the formation of more protective passivation film in chloride-containing solutions. The film formation rate increased after tempering, presenting the increased electric field strength and the decreased dissolution rate accordingly, as well as for the point defect diffusion coefficient and the oxygen vacancy flux therein.

The study focused on constructing a machine learning model, considering the interaction of alloying elements on corrosion resistance of low alloy steels in the marine atmospheric environment. Spearman's analysis was applied, and the relationship between alloying element and corrosion rate was evaluated based on random forest (RF) importance and Shapley additive explanation (SHAP) analysis. The prediction performance of the six models (RF, multilayer perceptron (MLP), ridge regression (RR), K-nearest neighbor regression (KNN), logistic regression (LR), and support vector machine (SVM) was compared by using the preferred dominant elements as input variables. Afterwards, a high-precision corrosion rate prediction model based on RF was constructed. Finally, the generalizability of the model was demonstrated using 10 lines of steel corrosion data from several new marine atmospheric environments.

This study determined the range of Cl- concentrations that enable the formation of protective rust layers in simulated tropical marine atmosphere by examining the corrosion of weathering steel. The steel exhibited good weatherability in atmospheres with 0.5 to 2.0 wt.% NaCl. Chloride ion influenced rust layer protection by altering phase distribution and defect structure. In the Cl-free environment, the rust layer was loose and lacked protection due to the low degree of corrosion during the limited experimental period. Excessive Cl- increased beta-FeOOH content and compressed alpha-FeOOH distribution, raising internal stresses and compromising the protective properties of rust layer.

This study compares the weathering performance of steel with three microstructures: ferrite, ferrite + bainite, and bainite. The rolling and cooling processes of a novel and cost-effective Ni-Mo weathering steel (WS) were manipulated to achieve these microstructures. Validation of these microstructures was performed through field exposure tests in Trat, Thailand, representing a typical tropical marine atmospheric environment. The bainitic steel exhibited better weathering resistance. After 12-month of exposure, the corrosion rates for ferritic + bainite and bainitic steels were 105.6 % and 97.9 % respectively, compared to ferritic steel. The variation in corrosion rates confirm that modifying the microstructure, with emphases on bainite, improves the WSs' resistance to atmospheric corrosion. Changes in corrosion rate mainly depend on the rust layer's adherence. Interestingly, alpha-FeOOH predominantly characterizes the rust layer on the skyward side of the samples following 12-month of exposure, while the earthward side is mainly composed of Fe3O4/gamma-Fe2O3.

The effect of substituting equal concentrations of Ni with 0.7 wt

Duplex stainless steel (DSS) hydraulic control pipelines readily form sigma phase during the heat treatment process, reducing corrosion resistance and leading to pipeline leakage and failure. This study employs various analysis methods to investigate the effect of sigma phase on the corrosion behavior of 2205 hydraulic control pipeline steel, focusing on the electronic characterization of passive film and pitting corrosion behavior. Results revealed that the sigma phase content reaches a maximum value of 13% at 850 °C within the heat treatment temperature range of 750 - 950 °C. The voltaic potential of the sigma phase is approximately 47 mV higher than the matrix, but the Cr-depleted zone around the sigma phase is about 85 mV lower than the matrix. The passive film of specimens containing sigma phase exhibits higher carrier densities and lower content of Cr(OH)3 and Cr2O3 compared to as-received specimens. The morphologies of the film show obvious groove defects, which provide a corrosion channel to the matrix. Moreover, specimens containing sigma phase exhibit higher intergranular corrosion susceptibility and lower pitting corrosion resistance. Pits preferentially nucleate and develop in the Cr-depleted zone around the sigma phase, with their quantity and size positively correlated with the sigma phase content.

The effect of silty sand on the dynamic mechanism of corrosion products formed on carbon steel in a CO2 environment containing 3.5 wt% NaCl and 0.1 wt% NaHCO3 is investigated. Silty sand has a dual effect on the corrosion products structure. First, silty sand presents on the surface, and embeds in the Fe3C network. Then, silty sand delays the FeCO3 precipitation, and changes the FeCO3 crystals growth manner and structure. Silty sand decreases active surface area, but this effect is less significant than FeCO3 precipitation. Consequently, silty sand first alleviates, then promotes general corrosion rate, while always alleviates localized corrosion.

The effect of Cr content on the corrosion behavior of Ni-Mo steel in the tropical marine atmospheric environment is systematically investigated. The increase of Cr content accelerates the aggregation and the enrichment of Ni element, and thus promotes the formation of an inner electronegative film which attracts positively charged ions including Mo6+, Mo4+, Ni2+ and Cr3+ ions, and repels negatively charged Cl- ions. Cr promotes the formation of more nano-FeOOH and the conversion of γ-FeOOH into α-FeOOH. A small amount of chromium promotes the formation of micro-pits at the initial stage, and with time, those micro-pits gradually accumulate into pieces.

The interaction between silty sand and temperature towards corrosion of carbon steel in CO2 environment is investigated. The effect of silty sand is more complicated, while the effect of temperature is more remarkable. High temperature causes a more protective corrosion products layer. Silty sand physically adsorbs on the surface and embeds in the porous Fe3C layer at 40 degrees C to slightly reduce corrosion. At 80 degrees C, silty sand delays FeCO3 precipitation and significantly increases the porosity of corrosion products layer, thus promoting corrosion. At 120 degrees C, silty sand increases the porosity and hinders the formation of Fe3O4 to accelerate corrosion.

The effect of using 1 wt% Cr instead of 1 wt% Ni on the corrosion behavior of 3 wt% Ni steel in the simulated tropical marine atmospheric environment is studied. The results show that replacing part of Ni in 3 wt% Ni steel with Cr can effectively promote the conversion of gamma-FeOOH to alpha-FeOOH during the early stages of corrosion, which facilitates the densification of the rust layer to prevent the intrusion of corrosive media. As corrosion test periods and Cl- concentration increased, the hydrolysis effect of Cr causes local acidification leading to corrosion pits develop deeper and severe local corrosion, while destroying the protective nature of the rust layer and exhibiting strong electrochemical reaction activity.