Duplex stainless steels (UNS S32205, UNS S32750) are used in various environments. The potentiodynamic polarization tests were conducted at 30 ℃ in order to study the electrochemical corrosion behaviors of duplex stainless steels under different seawater concentrations (fresh water, seawater, mixed water). The results of Tafel analysis in seawater showed that UNS S32205 and UNS S32750 had the highest corrosion current densities at 6.12 × 10^-4 mA/cm² and 5.41 × 10^-4 mA/cm², respectively. The pitting potentials of UNS S32205 and UNS S32750 were comparable to or higher than the oxygen evolution potential in fresh water, mixed water, and seawater. The maximum damage depths and surface damage ratio caused by pitting corrosion increased with chloride concentration. The synergy effect of molybdenum and nitrogen enhances the concentration of Mo, Ni, and Cr at the interface of the metal-electrolyte. In particular, in the case of nitrogen, NH₃ and NH₄⁺ are formed to compensate for the pH drop in the pitting region, thereby strengthening the repassivation of the film. The excellent corrosion resistance of UNS S32750 is attributed to the strengthening effect of the chromium oxide film due to the presence of molybdenum and nitrogen.

Due to its good corrosion and heat resistance with excellent mechanical properties, 304L stainless steel is commonly used in the fabrication of spent nuclear fuel dry storage canisters. However, welds are sensitive to stress corrosion cracking (SCC) due to residual stress generation. Although SCC resistance can be improved by stress relieving the weld and changing the chloride environment, it is difficult to change corrosion environment for certain applications. Stress control in the weld can improve SCC resistance. Ultrasonic shot peening (USP) needs further research as compressive residual stresses and microstructure changes due to plastic deformation may play a role in improving SCC resistance. In this study, 304L stainless steel was welded to generate residual stresses and exposed to a chloride environment after USP treatment to improve SCC properties. Effects of USP on SCC resistance and crack growth of specimens with compressive residual stresses generated more than 1 mm from the surface were studied. In addition, correlations of compressive residual stress, grain size, intergranular corrosion properties, and pitting potential with crack propagation rate were determined and the improvement of SCC properties by USP was analyzed.

Recently, hot rolled galvanized steel is widely used in automotive parts. As the paradigm of the automotive market has changed from fossil fuel vehicle to electric vehicle, the automotive industry needs more high-strength steels to reduce weights of automobiles. However, because high-strength steel contains high solute carbon, it is expected to have a risk of stretcher-strain on the surface due to dislocation trapping by solute [C] and [N]. Generally, galvanized steel is supposed to pass through a furnace around the temperature of Zinc pot to increase material temperature. Otherwise, the inhibition layer could not be formed. However, solute carbon and nitrogen are volatile enough to move around the furnace temperature. Moreover, the ratio of ferrite phase and precipitated Fe3C can be variable, resulting in yield point elongation related to the stretcher strain. Furthermore, the quality of the galvanized surface can be affected by a high temperature of the furnace. Although a relatively hot rolled galvanizing line furnace has a lower temperature than an annealing line furnace, it can affect various quality aspects. In other words, this paper aims to determine how these phenomena appear concerning furnace temperature.

Hot-dip Zn-Mg-Al coatings have a complex microstructure consisting of Zn, Al, and MgZn₂ phases. Its crystal structure depends on alloy content and cooling rates. Microstructure and corrosion resistance of these coatings might be affected by heat treatment. To investigate effect of heat treatment on microstructure and corrosion resistance of Zn-Mg-Al coatings, Zn-1.5%Mg-1.5%Al coated steel was heated up to 550 ℃ at a heating rate of 80 ℃/s and cooled down to room temperature. At above 500 ℃, the ternary phase of Zn-MgZn₂-Al was melted down. Only Zn and MgZn₂ phases remained in the coating. Heat- and non-heat-treated specimens showed similar corrosion resistance in Salt Spray Test (SST). When a Zn-3.0%Mg-2.5%Al coated steel was subjected to heat treatment at 100 ℃ or 300 ℃ for 200 h and compared with GA and GI coated steels, the microstructure of coatings was not significantly changed at 100 ℃. However, at 300 ℃, most Al in the coating reacted with Fe in the substrate, forming a Fe-Al compound layer in the lower part of the coating. MgZn₂ was preferentially formed in the upper part of the coating. As a result of SST, Zn-Mg-Al coated steels showed excellent corrosion resistance, better than GA and GI.

Zn-Mg-Al alloy hot-dip galvanized steel sheet has high corrosion resistance. Compared to conventional Zn coating with the same coating thickness, the high corrosion resistance Zn-Mg-Al coating is more corrosion-resistant. Various coating compositions are commercially produced and applied in diverse fields. However, these steel sheets typically contain up to 3 wt% magnesium. In recent years, there has been a growing demand for higher corrosion resistance in harsh corrosive environments. Therefore, variations in Mg and Al contents were investigated while evaluating primary properties and performance. As a result, we developed new alloy-coated steel with ultra-high corrosion resistance. A Zn-5 wt%Mg-Al coated steel sheet was evaluated for its corrosion resistance and various properties. As the amount of Mg added increased, the corrosion loss tended to decrease. The corrosion resistance of the coated steel sheet in a particular composition, the Zn-5 wt%Mg-Al coating sheet, was about 1.5 to 2 times higher than that of the conventional Zn-3 wt%Mg-Al coating sheet. Ultimately, this ultra-high corrosion-resistance coated steel sheet will provide a robust solution to conserve Zn resources and contribute to a low-carbon society.

Steels have excellent mechanical properties and weldability. They are also economically producible. Thus, they are widely applied in various industries. However, they have a disadvantage in that rust can occur after a certain period of time. To compensate for this, Zn, which has excellent sacrificial corrosion resistance, can be coated on steels. With global zinc consumption increasing at the current rate, depletion is expected in the near future. Recently, POSCO has developed innovative Al-Zn-Si alloy coated steel sheets with better corrosion resistance than Zn coating. In this study, corrosion resistance, weldability, friction characteristics, and so on were evaluated compared to GI steel sheets to evaluate their applicability to automotive steel sheets. It showed excellent corrosion resistance even at a lower coating weight compared to GI steel sheet. It was also excellent in terms of galling and welding LME. Its spot welding life, electrodeposition coating, and bendability were equally excellent. This is presumed to be related to the formation of the Al-Zn-Si alloy phase at the interface of the coating layer.

The purpose of this study was to elucidate effects of a thin (tens to hundreds of nanometers) Ni-flash coating layer on hydrogen embrittlement (HE) and liquid metal embrittlement (LME) in ultra-high-strength electrogalvanized steel with a tensile strength of more than 1 GPa. Various experimental and analytical methods, including thermal desorption spectroscopy, slow strain rate testing, resistance spot welding, X-ray diffraction, and metallographic observation, were employed. Results showed that an increase in Ni target amount for flash coating resulted in a decrease in diffusible hydrogen content during electrogalvanizing, resulting in a significant decrease in HE sensitivity. Moreover, a Ni target amount of more than 1000 mg/m² drastically reduced the occurring frequency and average depth of LME. This reduction could be primarily attributed to formation of Zn-Ni intermetallic phases during the welding process that could inhibit liquefaction of intermetallic phases in the heat-affected zone. This study provides a desirable Ni target amount for Ni-flash coating on ultra-high-strength steels conducted in a continuous galvanizing line or a high-speed batch line to achieve high resistance to both HE and LME.

The corrosion behavior of high chromium white cast iron was studied in 0.5 mol dm^-3 H₂SO₄ + 0.01 mol dm^-3 HCl solution over time through electrochemical and immersion experiments. Potentiodynamic and potentiostatic polarizations revealed active-passivation transition behavior, with critical current densities observed at -0.27 V_SSE and 0.00 V_SSE, repectively. The former potential showed preferential dissolution of primary γ phases, while the latter one showed preferential dissolution of eutectic γ phases. Immersion tests showed an exponential increase in corrosion rate, with significant acceleration observed around 1000 seconds due to the onset of eutectic γ phase dissolution. Over a 24-hour immersion period, both γ phases exhibited extensive corrosion, leaving carbides largely intact. These findings elucidate distinct corrosion behaviors of high chromium white cast iron in acidic environments, providing critical insights into material performance evaluation. Understanding these mechanisms is essential for predicting the longevity and durability of materials in corrosive conditions, thereby informing better material design and application strategies.

This work examined pitting corrosion failure of a copper heat-return pipe used in a district heating system. The copper pipe was corroded with a 48% reduction in thickness due to localized corrosion on the inner surface exposed to heating water of 20 ~ 40 ℃. Fe and Si elements as corrosion products were found around pits. Cl element was also observed, which accelerated oxidation of copper inside pits. Cu₂O deposits on the pit's bottom surface decreased the pH inside the pit. X-ray diffraction analysis revealed hematite, cuprite, malachite and brochantite as corrosion products. Chemical analysis demonstrated that Fe and Si elements did not exist in the copper, supply water, or heating water, indicating that Fe and Si species might have entered into the pipe from the exterior. These results indicated that pits were initiated due to ion concentration gradient near Fe and Si species. Moreover, the interior of pits had lower pH due to Cl^- concentration and Cu₂O reactions, which accelerated the pit's growth and led to formation of pinholes. Additionally, we confirmed that the type of pitting corrosion was a complex combination of types I and II based on the HCO₃^-/SO₄^2- ratio, pH, temperature, and corrosion products.

Atmospheric corrosion poses a significant threat to durability of metallic materials and safety of structures, making precise prediction of corrosion rates crucial in industrial and engineering settings. Understanding the exact rate of corrosion is essential. However, accurate inclusion of various environmental factors that can influence atmospheric corrosion in the calculation of corrosion rate is a complex challenge. This study introduces a physics-based model that incorporates electrochemical methods and considers active surface area affected by surface contaminants to estimate atmospheric corrosion rate of carbon steel. The model can evaluate corrosion levels using key factors such as chloride deposition rate, relative humidity, and the presence of surface particles. By integrating these considerations, this model moves beyond empirical estimations, providing a more stable prediction of corrosion rate that is less susceptible to environmental variations. This model provides a robust tool for defense applications, offering precise insights into the dynamics of atmospheric corrosion that could enhance the maintenance and safety of weapon systems.

The need for efficient and sustainable energy storage solutions has emerged due to a rapidly increasing energy demand and growing concerns about environmental issues. Among various energy storage methods, lithium secondary batteries are widely used in a variety of electronic devices such as smartphones, laptops, electric vehicles, and large-scale power storage systems due to their high energy density, long lifespan, and cost competitiveness. Recently, all-solid-state batteries (ASSBs) have attracted great attention because they can reduce the risk of fire associated with liquid electrolytes. Additionally, using high-capacity alternative anodes and cathodes in ASSBs can enhance energy density. However, ASSBs that use solid electrolytes experience a degradation in their electrochemical performances due to resistance at solid-solid interfaces. These interfaces can also result in poor physical contact and the presence of products formed from chemical and electrochemical reactions. Solving this interface problem is a critical issue for the commercialization of ASSBs. This review summarizes interfacial reactions between the cathode and solid electrolyte, along with research aimed at improving these interactions. Future development directions in this field are also discussed.