Steel Surface Research Articles

Dual surface-modification by oleic acid and epoxy-based silane coupling agent providing cerium oxide nanoparticles as additive in pentaerythritol oleate with improved high-temperature adsorption performance and tribological properties

An epoxy-based silane coupling agent (KH560) was grafted onto the surface of oleic acid-modified cerium oxide (CeO2-OA) nanoparticles in order to improve the competitive adsorption ability of the anti-wear additives in ester oils and simultaneously hinder the additive desorption owing to thermal disturbance under high-temperature condition. The as-prepared oleic acid-epoxy silane co-modified cerium oxide (CeO2-OA/E) nanoparticles were characterized. The effect of temperature on the adsorption behavior of trityl phosphate (TCP, a commercial high-temperature antifriction agent), CeO2-OA and CeO2-OA/E in PETO was studied using a dissipative quartz microbalance. Their tribological properties as the additives in pentaerythritol oleate (PETO), a polar ester base oil, were evaluated with a four-ball machine and a ball-on-block friction and wear tester; and their tribomechanism was explored with respect to their adsorption behavior on rubbed steel surfaces at elevated temperatures. It was found that the secondary surface-capping of CeO2-OA by the KH560 silane coupling agent resulted in great increases in the surface potential (from 54 mV to 396 mV) and thermal stability as well (the thermal decomposition temperature rose from 185 °C to 254 °C). Among the tesetd lubricant additives, CeO2-OA/E exhibited the highest adsorption mass, because of the highest surface potential the chemisorption ascribed to the epoxy group of the silane coupling agent. Particularly, CeO2-OA/E added in PETO exhibited better friction reduction and anti-wear properties at 150 °C than CeO2-OA and TCP, because CeO2-OA/E added in PETO formed tribofilm composed of CeO2 and SiO2 with excellent thermal stability as well as friction-reduction and antiwear effects through stable chemical adsorption and tribochemical reaction at elevated temperatures.

Protective Effects of Small Molecular Inhibitors on Steel Corrosion: The Generation of a Multi-Electric Layer on Passivation Films

The durability of reinforced concrete structures is significantly influenced by the effectiveness of small molecular inhibitors in preventing the corrosion of steel reinforcements. In a concrete environment, the passive film on steel bars serves as a critical protective component. In this study, a molecular dynamics (MD) simulation is used to study the inhibition mechanism of chloride ions by common corrosion inhibitors (2-Amino-2-thiazoline) in concrete in an excess chloride solution. The results reveal that inhibitors adsorb onto the steel surface primarily through van der Waals forces, with more than 90% of the adsorption occurring vertically. Despite this strong adsorption, inhibitors alone do not form a protective film. In the presence of chloride ions, which frequently penetrate concrete, the coverage rate of inhibitors on the steel surface decreases from 74% to 64%. Nevertheless, inhibitor molecules still provide substantial protection in chloride-rich concrete environments. Further analysis indicates that inhibitor molecules inhibit chloride ions in two ways. Corrosion inhibitor molecules actively desorb from the steel surface to capture chloride ions and prevent them from approaching. Additionally, inhibitors form a multi-electron layer on the steel surface to enhance passive film protection and hinder chloride ion diffusion through Coulombic interactions.

Optimization of defects and high temperature corrosion resistance of laser cladding FeCrAl coatings: Influence of process parameters

To enhance the surface quality and high-temperature corrosion resistance of FeCrAl coatings further, a laser cladding technique was employed to deposit Fe-13Cr-7Al coatings on the surface of 12Cr1MoV heat-resistant steel. The study investigated the influence of laser power, scanning speed, and powder feed rate on the quality and high-temperature corrosion resistance of the Fe-13Cr-7Al coatings. Utilizing 25 orthogonal experiments, coatings were prepared and evaluated through high-temperature corrosion tests to explore the corrosion resistance and mechanisms microstructural analysis of the coatings, including their elemental distribution and corrosion mechanisms, was conducted using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The optimal parameter combinations for laser cladding coatings were discussed. The results indicated that the coating quality was optimal within specific ranges of parameters (laser power 1875–2250 W, scanning speed 33–44 mm/s, powder feed rate 12–18 g/min); deviations outside these ranges led to issues such as incomplete coverage or coating detachment from the substrate. The structure of the laser cladded Fe-13Cr-7Al coatings consisted of columnar grains and α-Fe phase. In high-temperature corrosion testing, the coatings exhibited superior corrosion resistance compared to the substrate, with nearly twice the corrosion resistance variation observed under different process parameters. This study provides a scientific basis for optimizing laser cladding process parameters of Fe-13Cr-7Al coatings, demonstrating that precise control of process parameters significantly enhances the high-temperature corrosion resistance of coatings, thereby opening new possibilities for improving material performance in high-temperature applications.

Synergistic mixture of the Dactyloctenium aegyptium extract and KI as an environment friendly and highly efficient corrosion inhibitor for steel in 0.5 M HCl

To prevent steel from corroding in HCl solution, a cost-effective inhibitor of Dactyloctenium aegyptium and KI is presented. UV–Vis, infrared spectroscopy, and scanning electron microscopy analysis are used to undertake a comprehensive experimental evaluation of the inhibitors and their interactions with the steel. The optimum concentration of the Dactyloctenium aegyptium extract (DAE) with the maximum corrosion protection efficacy is found via electrochemical measurements. The bioactive constituents of the DAE such as Tricin, Vanillic acid, p-hydroxybenzaldehyde, and p-hydroxybenzoic acid conferred a maximum inhibition efficiency of 95.7 % at 800 ppm. The inhibitory activity of its ethanolic extract increased with increasing concentration. Further various adsorption isotherm models including Langmuir, Temkin and Frendluich were used to understand the adsorption of the DAE on the metal surface. The DFT based investigations show that the active constituents of the DAE are highly polarized, soluble in aqueous solution and adsorb on the steel surface efficiently.

Shielding against erosion: Exploring the effectiveness of pre-erosion surface corrosion inhibitors

This study investigates the corrosion inhibition effect and adsorption process of two imidazoline corrosion inhibitors, HEIE and TDEI, on pre-eroded X65 steel surfaces. Analysis of weight loss and electrochemical measurements suggests that the irregular structure of pre-eroded surfaces may impede the uniform adsorption of corrosion inhibitors, resulting in reduced effectiveness pre-erosion. Particularly, at a 30° angle of pre-erosion, corrosion inhibition efficacy is observed to be at its lowest. The corrosion inhibition rates of HEIE and TDEI on X65 steel surfaces are found to be 11.9 % lower under pre-eroded conditions at a 30° angle compared to non-eroded surfaces at the same angle. Molecular dynamics (MD) simulations support these findings, indicating that TDEI exhibits lower energy bandgap values and more negative adsorption energies (Eads) compared to HEIE, aligning with experimental results. Moreover, TDEI demonstrates a smaller diffusion coefficient for corrosive agents than HEIE, suggesting stronger adsorption efficiency and a more pronounced protective effect. Study of the corrosion inhibition effect on pre-eroded surfaces provides new ideas and methods for improving protective measures.

Construction of hard BCC phases FeCrVMnTix wear-resistant high-entropy alloy coatings enhanced by solid solution of Ti elements

To address the complex working conditions encountered by 1Cr13 ferritic/martensitic steel during operation, it is imperative to develop high-entropy alloys (HEAs) protective coatings with enhanced friction resistance. In this work, guided by the valence electron concentration criterion, we constructed a single-phase body-centered cubic (BCC) structure with high hardness. This was achieved through the introduction of titanium (Ti), which has a significantly different atomic radius compared to other elements. FeCrVMnTix (x = 0, 0.5, 1.0, 1.5, and 2.0) coatings were fabricated on 1Cr13 steel surfaces using laser cladding techniques, and the microstructure, mechanical properties, and wear-resistance properties of Ti-doped HEA coatings were investigated. The results reveal that the FeCrVMnTix coatings are comprised of a BCC solid solution. Increasing Ti content refined the dendritic structure of the coatings, enhancing the Vickers hardness from 4.35 GPa to 8.27 GPa and the Young's modulus from 232.6 GPa to 273.2 GPa. Additionally, the wear rate decreased from 3.07 × 10−5 mm3·N−1·m−1 to 4.94 × 10−6 mm3·N−1·m−1. Notably, the FeCrVMnTi2.0 coating demonstrated excellent wear resistance that can be attributed to the solid solution strengthening effect of Ti. These findings underscore the pivotal role of Ti in enhancing the wear resistance of the coatings.

Influence of cooling bed temperature on microstructural, mechanical properties and surface quality of high-strength seismic-resistant rebar

High-strength seismic-resistant rebar is essential in construction engineering, yet balancing its strength, plasticity, seismic resistance, and surface quality poses challenges. This research explores niobium-vanadium-nitrogen composite reinforced steel, examining how cooling bed temperature affects its microstructure, mechanical properties, and surface quality using advanced microscopy techniques. The research reveals that the steel's microstructure primarily consists of ferrite and pearlite. As cooling bed temperatures decrease, both the proportion and colony size of pearlite, along with ferrite size, show a declining trend. Specifically, reducing the cooling bed temperature from 1100 °C to 900 °C results in a decrease in yield strength, tensile strength, and tensile-to-yield strength ratio by 6 MPa, 27 MPa, and 0.03, respectively. Meanwhile, elongation after fracture, total elongation at maximum force, and strength-ductility balance improve by 3.8%, 1.5%, and 1.93%, respectively. At a cooling bed temperature of 1100 °C, significant blistering occurs on the steel surface. Significant blistering at 1100 °C vanishes at 1000 °C and 900 °C, with diminished silicon enrichment in the surface oxide scale. A cooling bed temperature of 1000 °C ± 20 °C is recommended for optimal performance. This study provides a temperature control strategy for the properties of high-strength seismic-resistant rebar rated at 650 MPa and above, contributing valuable insights to the field of advanced construction materials.

Inhibitory Effect of Fennel Fruit Essential Oil and Its Main Component Anethole of Corrosion on Steel Plates in 1 M HCL

Corrosion worldwide causes large losses of metal, which is why various ways are being sought to slow it down. The aim of this study was to investigate the inhibitory effect of fennel fruit essential oil (Foeniculum vulgare Mill.) and its main component anethole. The inhibitory effect of three different concentrations of the fennel essential oil and anethole (1.0 mL/L, 1.5 mL/L, and 2.5 mL/L) in a solution of 1 M HCl at 298 K for 6 h on a sheet of low-carbon steel was investigated. The inhibitory effect was established using gravimetric methods evaluating weight loss, corrosion rate, and inhibition efficiency, as well as electrochemical methods. In gravimetric studies, the inhibition effect of the inhibitors fennel essential oil and isolate anethole at a concentration of 2.0 mL/L was 70.85% and 45.86%, respectively. The anodic polarization curve data at 298 K demonstrate that the anethole and fennel essential oil adsorption on the metal surface creates a barrier that hinders hydrogen ions’ access and prevents them from being reduced on the steel surface’s cathode sites. Fennel essential oil acting as a mixed type-inhibitor can replace synthetic organic substances and could become an alternative to be used as environmental corrosion inhibitors.

Behavior of Retained Austenite and Carbide Phases in AISI 440C Martensitic Stainless Steel under Cavitation

In this work emphasis was given to determine the evolution of the retained austenite phase fraction via X-ray diffractometry technique in the as-hardened AISI 440C martensitic stainless steel surface subjected to cavitation for increasing test times. Scanning electron microscopy results confirmed the preferential carbide phase removal along the prior/parent austenite grain boundaries for the first cavitation test times on the polished sample surface during the incubation period. Results suggest that the strain-induced martensitic transformation of the retained austenite would be assisted by the elastic deformation and intermittent relaxation action of the harder martensitic matrix on the austenite crystals through the interfaces between both phases. In addition, an estimation of the stacking fault energy value on the order of 15 mJ m−2 for the retained austenite phase made it possible to infer that mechanical twinning and strain-induced martensite formation mechanisms could be effectively presented in the studied case. Finally, incubation period, maximum erosion rate, and erosion resistance on the order of 7.0 h, 0.30 mg h−1, and 4.8 h μm−1, respectively, were determined for the as-hardened AISI 440C MSS samples investigated here.

Role of sodium citrate in electrochemical behavior of reinforcing steel exposed to carbonated alkali-activated fly ash contaminated with chloride ions

Alkali-activated fly ash (AAFA) is considered as a promising alternative to ordinary Portland cement (OPC). However, the lack of calcium hydroxide in AAFA leads to an increased susceptibility to carbonation, thereby resulting in a decreased alkalinity of pore solutions in AAFA and significantly impacting the stability of steel passive films. To improve the corrosion resistance of steel in carbonated AAFA environments, sodium citrate was used as an environmentally-friendly corrosion inhibitor with three carboxylate groups. In this context, the corresponding electrochemical behavior of steel exposed to carbonated AAFA solutions with different concentrations of citrate was studied. In spite of the detrimental effect on the initial passivation behavior, sodium citrate was found to effectively improve the corrosion resistance to chloride attack for steel owing to a synergistic inhibition effect of adsorption film and precipitates on the steel surface. In addition, the correlation of citrate concentration and inhibition mechanism in carbonated AAFA solutions was revealed.

Exploring the adsorption of 4,4’-[oxalylbis(imino)]bis(2-hydroxybenzoic acid) layer at steel/biogasoline interface by the combined electrical-optical-simulation approach

Reactions at the steel/biogasoline interface trigger the adsorption of 4,4’-[Oxalylbis(imino)]bis(2-hydroxybenzoic Acid) (ODA) layer on the steel surface, thereby activating a mechanism that inhibited the early reactions. Exploring the conditionally deposited ODA layer requires a combined approach, including electrical, optical, and simulation techniques to track the film development and coating characteristics over time, and with the assistance of atomic force microscopy, quantum chemistry (DFT), and molecular dynamics (MD) simulations to reveal the adsorption mechanism of the ODA layer at steel/biogasoline interface. The four experimental ODA concentrations were conducted, related to the simulated un-coverage, undersaturated-, saturated-, and oversaturated-coverage model of the adsorbate on the adsorbent. The EC-RS data examines surface compositions and their distribution, coating/solution interface, and coating/substrate adhesion by, respectively, Raman spectroscopy (RS), electrochemical impedance spectroscopy (EIS), and current density—potential (I-V) scan. Namely, RS pointed out that an organic layer was established when ODA was added to the simulated biogasoline. EIS results revealed insulator behaviors of the ODA layer at the solid–liquid interface, limiting the charge transfer between the steel substrate and the biogasoline. I-V results showed an increase in surface current density and a decrease in surface polarization resistance of the coating with the rise in ODA concentration. The AFM morphology profile verified the degradation of the sample’s surface when exposed to biogasoline and the minimization of surface damage by ODA addition through adsorption. The simulation findings revealed that the adsorption of ODA on steel preferred physisorption, reaching the most stable state at a specified temperature and ODA concentration. The adsorption mechanism follows the Generalized Langmuir isotherm. The adsorbate (ODA molecules) can produce a transition phase with the steel substrate surface, which modifies the surface thermodynamic characteristics. The combined electro-optical-simulation technique can be applied to investigate various surface phenomena (reactions, catalyzes, adsorption). It especially helps to understand the protective mechanism of inhibitors in different media.

Effect of Crevice Size on Crevice Corrosion of N80 Carbon Steel in CO2-Saturated NaCl-HAc Solution.

The effect of crevice size on the crevice corrosion of N80 carbon steel was investigated by electrochemical measurements and surface analysis in a CO2-saturated NaCl-HAc solution. The N80 carbon steel exhibits a high susceptibility to crevice corrosion in this environment, which can be initiated immediately without an induction period for specimens with crevice sizes of 100 μm, 300 μm, and 500 μm. Typically, crevice solutions become more acidic during crevice corrosion; however, in this study, the crevice solution became alkaline, resulting in galvanic corrosion between the inner and outer steel surfaces and leading to severe crevice corrosion. The pH levels of the crevice solution for specimens with 100 μm and 300 μm crevice sizes are similar, but both are notably higher than that of the specimen with a 500 μm crevice size. As a result, there is no significant difference in the crevice corrosion phenomenon between specimens with 100 μm and 300 μm crevice sizes, but it is more severe than in the specimen with a 500 μm crevice size.

Study on the Scale and Corrosion Inhibition Effect of Curcumin‐Based Novel Polymers

AbstractThe curcumin‐malic acid‐aspartic acid polymer (PCMA) as a new water treatment agent was prepared by solid phase synthesis of curcumin, malic acid and aspartic acid. The static scale inhibition experiments showed that PCMA can inhibit CaCO3 and CaSO4 scale formation by 100.0 % and had excellent scale inhibition effect under various experimental conditions. The mechanism of action of PCMA was obtained by X‐ray diffraction, scanning electron microscope and molecular dynamics simulation. Electrochemical test showed that PCMA is an anodic corrosion inhibitor that achieves 93.1 % corrosion inhibition by forming a protective film on the surface of Q235 carbon steel. Besides, fluorescence spectra proved that PCMA has stable fluorescence intensity.

Study on microbiologically influenced corrosion of HSLA-65 steel

In the current study, the corrosion behavior of HSLA-65 steel was investigated in a simulated marine environment inoculated with P. aeruginosa. In the electrochemical measurements, the negative shift in OCP, lower values of corrosion potential, pitting potential, and increased corrosion current density of the HSLA-65 steel in the biotic medium signified its low corrosion resistance in the presence of P. aeruginosa. The observation of the surface morphology revealed biofilm formation on the steel surface in the P. aeruginosa-inoculated culture medium, which significantly accelerated the pitting corrosion of the steel. The pit observed on the steel surface in the biotic medium was about 3.9 times deeper than in the sterile medium. In addition, the weight loss of the steel in the biotic medium was about 2.4 times higher compared to that in the sterile medium. These findings suggest that the P. aeruginosa biofilm significantly accelerated the corrosion of HSLA-65 steel in the simulated marine environment.

Development of a pressure-, velocity-, and acceleration-dependent phenomenological friction model using experimental data of sliding tests between 11 polymers and stainless steel

This paper experimentally investigates the frictional behavior between stainless steel and 11 polymers. Particularly, the dependence of the friction coefficient on the sliding velocity, pressure, and acceleration is quantified. The novelty of this work lies in quantifying the acceleration-dependent nature of friction, correlating it to the well-documented Stick-Slip effect. The experimental setup consisted of two parallel stiff steel beams, one above the other, with a separation of 95 mm, and steel surfaces welded at the inner sides for sliding the polymers. Cylindrical polymer pads were placed between the stainless-steel surfaces and connected to a dynamic actuator to apply the displacement protocol. The protocol consisted of consecutive nominally constant-velocity ramp cycles covering velocities from 1 mm/s to 300 mm/s (with 20 mm/s increments). An additional vertical force was applied with a hydraulic actuator to reach nominal pressures in the polymers between 5 and 80 MPa. The results showed that the friction coefficient depends on the velocity, pressure, and acceleration of the motion, and a phenomenological model on these three variables is proposed. The velocity dependence can be represented through a logarithmic relationship, while the pressure dependence is through an exponential decay relationship. The acceleration dependence was represented through a linear relationship, which could capture the stick-slip effect. Overall, this work contributes to a better understanding of friction for seismic isolation systems. Since friction is the main source of energy dissipation in such structures, the proposed model will allow a higher accuracy in predicting variables of interest during the dynamic analyses of seismically isolated structures with frictional systems.

Research on micro-arc oxidation method based on passivation layer on non-valve metal low-carbon steel surface

In this study, a method for preparing micro-arc oxidation (MAO) coatings on the surface of non-valve metal low-carbon steel based on a passivation layer is proposed. Microstructure and elemental composition of the surface and cross-section were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS). Micro-scratch tests, tribological tests and electrochemical corrosion tests were conducted. Compared to MAO coatings, coatings obtained by pre-passivation treatment exhibit fewer surface micropores with smaller pore sizes, and both wear resistance and corrosion resistance are enhanced. In summary, the method for preparing MAO coatings based on the passivation layer on the surface of low-carbon steel provides feasible approach to improving the drawbacks of low-carbon steel.

Effect of peening with fine iron-sulfide particles on the rotating bending fatigue properties of low alloy steel and formation of iron-sulfide layer

Low alloy steels were subjected to peening with fine iron sulfide particles (FeS-peening) under ambient conditions to transfer a layer of such particles, which can improve seizure resistance and sliding properties, and thus enhance the fatigue characteristics of the steel. This process was performed without the use of aqueous Na2S2O3 and the specimens were assessed using electron probe microanalysis and rotating bending fatigue tests. Treated specimens exhibited higher fatigue limits as a result of high degree of compressive residual stress generated on the steel surface. The effects of residual stress on the fatigue limit were quantitatively investigated using a modified Goodman diagram. Sample cross-sections were observed using electron backscattered diffraction, which confirmed that FeS-peening formed fine surface grains. Grain refinement was determined to be at least partly responsible for the improved fatigue properties of the steel following FeS-peening.

Biomass of Anthonotha macrophylla leaf extract as a mild steel acid corrosion inhibitor: Experimental and theoretical study

This study investigated weight loss and electrochemical impedance spectroscopy (EIS) to explore the inhibition potential of Anthonotha macrophylla leaf extract (AME) on mild steel corrosion in 0.5 M H2SO4 medium. The result shows that the highest inhibition efficiency of 90.47 % at 303 K and 80.02 % at 333 K were obtained. At temperatures of 303 K and 333 K, it was discovered that the corrosion rate decreased as the concentration of the AME inhibitor rose from 0.1 g/L (7.73×10−4gcm−2hr−1) to 0.5 g/L (2.27×10−4 gcm−2hr−1). The result of the EIS measurement is in consistent with that of the weight loss method. Adsorption isotherms portrayed that Tempkin and Freundlich's adsorption isotherms were obeyed. Calculated values of Ea, ∆Hads and ∆Gads suggested a physical adsorption mechanism. FTIR, SEM-EDX, and XRD measurements revealed that the AME inhibitor efficiently shields the mild steel surface from further corrosion attack by inducing the formation of passivated film on the mild steel surface. The calculated quantum parameters correlated with experimental results, thus, AME can be used as an alternative inhibitor for the protection of mild steel against corrosion.

Electrochemical and surface investigations of N, S codoped carbon dots as effective corrosion inhibitor for mild steel in acidic solution

Mild steel is a versatile, inexpensive, highly flexible, and easily weldable material widely used in construction, pipelines, transportation, shipping, and other industries. However, it is also extremely susceptible to corrosion processes under the influence of weather phenomena, posing a significant threat to society and human health. In this work, we investigated the corrosion inhibition capacity of a new type of N, S codoped carbon dots (N, S-CDs) on Q235 carbon steel in the acidic medium. The goal product was synthesized by hydrothermal method using o-phenylenediamine and amidinothiourea as precursors. Combined with electrochemistry, Fourier transform infrared (FTIR) spectroscopy, scanning electrochemical microscopy (SECM), and theoretical calculations, the inhibition properties of N, S-CDs on Q235 carbon steel in HCl solution were evaluated. The potentiodynamic polarization (PDP) curves and electrochemical impedance spectroscopy (EIS) results indicated that the corrosion inhibition efficiency reached 90.3 % and 92.4 % at 100 mg/L concentration, respectively. Indeed, the presence of N, S-CDs reduced the electric double-layer capacitance, increased the thickness of the adsorption film on the carbon steel surface, and reduced the corrosion current density, resulting in a delay of corrosion. X-ray photoelectron spectroscopy (XPS) analysis and surface characterization confirmed the successful doping of N, S and the formation of adsorption films, the Langmuir adsorption isotherm also confirmed the superior inhibition of N, S-CDs on the surface of Q235 carbon steel through physical and chemical adsorption mechanisms. At the same time, quantum chemical calculations and molecular dynamics (MD) simulations revealed its inhibition mechanism at the molecular/atomic level.

Corrosion Initiation on Reinforcing Steel with Mill Scale in Mortar

Corrosion of reinforcing steel rebar is the main cause of loss of the long-term reliability of concrete structures. When the rebar is corroded, the rust induces cracks and detachment of the cover concrete. The mill scale, a thick oxide film, is formed on the rebars when the rebar is hot rolled. The role of mill scale on the corrosion resistance of rebars in concrete has not been clarified, yet. This study studied the corrosion behavior of rebars with mill scale in mortar.The samples are commercial rebars with 19 mm diameter, which have a mill scale of several tens of micrometers in thickness. The rebars without mill scale prepared by the electrolytic polishing were used as the comparison samples. A Hyperbaric-oxygen accelerated corrosion test (HOACT) [1] was carried out using the rebars embedded in the mortar with a 5.5 mm cover thickness. To prompt the breakdown of passive film on the rebars, 2.1 M NaCl solution was mixed with the mortar. In the HOACT, pressurized oxygen gas is supplied to the sample, and the oxygen reduction reaction on the steel surface is enhanced, leading to the steel's corrosion acceleration. The oxygen pressure was 0.6 MPa and the test period was 14 days. The corrosion of the rebar with a mill scale was more significant than that without a mill scale. This result shows that the mill scale reduces the corrosion resistance of the steel rebar in concrete [2].To investigate the effect of the mill scale on the corrosion resistance of the rebar, anodic polarization measurements of the rebars with and without the mill scale were carried out in a saturated Ca(OH)2 solution containing Cl-. The pitting potential of the rebar with mill scale was more noble than that of the sample without mill scale. However, when the mill scale was scratched, the pitting potential was significantly shifted to the less noble direction, and it was below that of the rebar without the mill scale. These results show that the mill scale improves the corrosion resistance of the rebar in concrete, in contrast, the corrosion resistance of the rebar with a defective mill scale becomes even worse than that of the rebar without the mill scale [2].[1] K. Doi, S. Hiromoto, H. Katayama, E. Akiyama, J. Electrochem. Soc., 165(9), C582-C589 (2018).[2] K. Doi, S. Hiromoto, T. Shinohara, K. Tsuchiya, H. Katayama, E. Akiyama, Corrosion Science, 177, 108995 (2020).