Cyclic Corrosion Test Research Articles

Preparation and Testing of Anti-Corrosion Properties of New Pigments Containing Structural Units of Melamine and Magnesium Cations (Mg2+)

This paper deals with the properties and testing of newly prepared organic pigments based on melamine cyanurate containing magnesium or zinc cations depending on their composition and anticorrosive properties in model coatings. Organic pigments based on melamine cyanurate with Mg2+ in the form of a complex differing in the ratio of melamine and cyanurate units were prepared. Furthermore, a pigment based on melamine citrate with magnesium cation Mg2+, a pigment based on melamine citrate with magnesium cation, and a pigment based on melamine cyanurate with zinc cation were prepared. The properties of Mg-containing organic pigments were also compared with those of selected magnesium-containing inorganic oxide-type pigments. The above-synthesized pigments were characterized by inductively coupled plasma-optical emission spectroscopy, elemental analysis, scanning electron microscopy, and X-ray diffraction. In addition, the basic parameters that are indicative of the applicability of the pigments in the binders of anti-corrosion coatings were determined. The anti-corrosive properties of the tested pigments were verified after application to the epoxy-ester resin-based paint binder in three different concentrations: at pigment volume concentrations of 0.10%, 0.25%, and 0.50%. The anticorrosive effectiveness of pigmented organic coatings was verified by cyclic corrosion tests in a salt electrolyte fog (NaCl + (NH4)2SO4) in an atmosphere containing SO2 and by the electrochemical technique of linear polarization. Finally, the effect of the structure of the pigments on the mechanical resistance of the organic coatings was investigated. The results obtained showed that the new organic pigments exhibit anticorrosive properties, and at the same time, differences in performance were found depending on the structure of the pigments tested. Specifically, the results of cyclic corrosion tests and the electrochemical technique of linear polarization clearly demonstrated that synthesized pigments of the organic type based on melamine cyanurate containing magnesium or zinc cations ensure the anti-corrosion efficiency of the tested organic coatings. The highest anti-corrosion efficiency was achieved by the system pigmented with synthesized melamine cyanurate with magnesium cation (C12H16MgN18O6), whose anti-corrosion efficiency was comparable to the anti-corrosion efficiency of the tested inorganic pigment MgFe2O4, which was prepared by high-temperature solid-phase synthesis. In addition, these organic coatings achieved high mechanical resistance after being tested using the most used standardized mechanical tests.

Roles of grain refinement in the rust formation and corrosion resistance of weathering steels

Weathering steels with different grain sizes (20.0 µm, 3.8 µm, and 0.6 µm) were prepared through a combination of cold-rolling and heat-treatment processes. Their corrosion behaviors were investigated using wet/dry cyclic corrosion tests in 3.5 wt% NaCl solution. The results indicate that grain refinement has a positive effect on the rust layer formation. It accelerates the formation of a more stable, compact, and protective rust layer, along with enhanced enrichment of alloying elements (Cr, Ni, and Cu) as oxide compounds within the rust layer. Moreover, grain refinement shows promise in inhibiting non-uniform corrosion and the formation of "deep-and-narrow" corrosion pits.

Structure and Protectiveness of Rust Layers Grown on Low-Alloyed Steels Under Cyclic Wet/Dry Corrosion Tests

Carbon steels are widely used in various infrastructures due to their superior mechanical properties in addition to low cost, but the mechanical properties can be deteriorated when steels are corroded. It is well-known that the weathering steels where small amounts of alloying elements such as Cu, Cr, Ni, Si and Mn are included form compact protective rust layers during the long-term exposure to atmospheric environment, resulting in superior corrosion resistance. However, as some of the alloying elements such as P that are effective to improve the atmospheric corrosion resistance of carbon steel cause segregation in the solidification process during welding, the amounts of such alloying elements have been strictly limited. The segregation of additive elements can be suppressed in stir friction welding, so-called FSW, in which metallic materials are joined in a solid state, leading to the assumption that the restrictions on the types and amounts of alloying elements can be reduced when FSW is applied instead of conventional welding. In the present work, the structure and corrosion resistance of rust layers formed on various low-alloyed steels designed for FWS are evaluated. Ingots of various low-alloyed steels including Al and P, both of which have been proved to be effective to improve the atmospheric corrosion resistance of carbon steel, were prepared using a high-frequency vacuum induction furnace. The ingots were hot-rolled at 1273 K into a plate with the thickness of approximately 2 mm and then cut into specimens with the dimension of 20 mm × 30 mm. All specimens were subjected to a laboratory cyclic corrosion test according to SAE J2334 which simulates a severe coastal atmosphere environment. In the SAE J2334 test, the specimens were kept for 6 h in a tightly sealed box where the temperature and relative humidity (R. H.) were controlled at 323 K and 100%, respectively (humid stage). Then the specimens were immersed in an aqueous solution containing 0.5 mass% NaCl, 0.1 mass% CaCl2 and 0.075 mass% NaHCO3 for 15 min. (immersion stage), followed by holding for 17h 45 min. in the sealed box at 333 K and 50%R. H. (dry stage). These three stages were repeated up to 30 cycles. After the cyclic corrosion test, rust layers on the specimens were characterized with X-ray diffraction and elemental distributions in the rust layers were evaluated with energy-dispersive spectroscopy. The corrosion current density was estimated from extrapolating Tafel slopes in polarization curves measured for the specimens subjected to the cyclic corrosion test. In XRD measurements for the specimens after 30 cycles of the cyclic corrosion test, peaks derived from α-FeOOH, β-FeOOH, γ-FeOOH and Fe3O4 were found. The fraction of the components in rust layers grown on the specimens was estimated, providing the fractions: 30-50% of α-FeOOH, 20-40% of β-FeOOH, 4% of γ-FeOOH and 30-50% of Fe3O4. Among the components, the fraction of α-FeOOH which is well-known as protective rust increased with increasing the addition of Al and P in specimen. Furthermore, it was found from EDS analysis on the cross-sections of the specimens that Al and P were distributed in the rust layers formed on the specimens in which Al and/or P were included. This indicates that Al and P can be related to the imcreased fraction of α-FeOOH in rust layers. The corrosion current density decreased with increasing the amounts of Al and P in the specimens, implying that Al and P improved the protectiveness of rust layers, that is, the increased corrosion resistance of low-alloyed steels. Similar trend was found in the corrosion rate estimated by the weight-loss method. These beneficial effects of Al and P are attributed to the increased fraction of protective α-FeOOH in rust layers.

Predicting Galvanic Corrosion of Aluminum Using Accelerated Laboratory Electrochemical Experiments

Aluminum (Al) alloys are the most commonly used non-ferrous metals (approximately 25 million tons per year) for various technical applications and is the second most commonly used metal alloy after steel. Al alloys are also used in combination with other metals or materials to get specific desirable properties for applications such as transportation, construction, electrical appliances, and consumer goods. However, a system of dissimilar materials can lead to potential corrosion problems such as galvanic and crevice corrosion. In this work, atmospheric galvanic corrosion of Al alloy was predicted by combining electrochemical techniques and accelerated laboratory corrosion tests. Three different galvanic couples were analyzed where 6061-T6 Al alloy was coupled with a passivating metal (304 stainless steel), noble metal (copper), and a carbon fiber-reinforced polymer matrix composite (CFR PMC). The galvanic current flowing between the anode and cathode was measured using the zero-resistance ammeter (ZRA) technique in the humidity-chamber setup, cyclic corrosion test chamber following a modified GM9540P cycle, and an outdoor exposure test site. Electrolytes with varying amounts of chloride contents were used to simulate different atmospheric conditions. Four separate equations based on Faraday's law were developed to calculate the corrosion rate in grams per meter square per day (gmd) by relating the time of wetness (TOW) to the galvanic current measured from the accelerated laboratory experiments. The total exposure time was divided into wet periods (Twet) and dry periods (Tdry). The surface morphology of Al samples from the galvanic couples was studied using a scanning electron microscope (SEM), and elemental surface analysis was conducted using energy-dispersive X-ray Spectroscopy (EDXA). Figure 1

An analysis on spatial properties of corroded surface of weathering steel by different environmental conditions

ABSTRACT This study examined the spatial characteristics of the corroded surface of weathering steel by different environmental conditions to evaluate the applicability of two accelerated corrosion tests. Two types of weathering steel were subjected to the two accelerated corrosion tests for 28, 84, and 168 days. The same materials were also exposed at two separate locations for 180 and 365 days of atmospheric exposure tests. The corrosion behavior of the weathering steel was investigated by spatial statistical analysis. The analysis suggested that the spatial properties of the corrosion of weathering steel experimented in the early stage of both accelerated corrosion tests were close to those obtained in the atmospheric exposure tests. Furthermore, the corroded surfaces experimented under the ISO 16539 Method B accelerated corrosion test demonstrated a closer resemblance to the corroded surfaces of weathering steel in real corrosion environments compared to those derived from the Cyclic Corrosion Test Method A.

Understanding the mechanisms of intergranular corrosion in 2024 Al alloy at the polycrystal scale

This paper provides a new insight into the understanding of the susceptibility to intergranular corrosion (IGC) of 2024 Al alloy. Whatever the exposure conditions, coincidence site lattice high-angle grain boundaries (CSL HAGBs) slightly contributed to IGC damage because of their low contribution to the cumulative length of GBs. Low-angle grain boundaries (LAGBs) showed intrinsic susceptibility to corrosion initiation almost similar to random HAGBs and lower susceptibility to IGC propagation. However, cyclic corrosion tests promoted both corrosion initiation and propagation at LAGBs. This was mostly due to the trapping of corrosion-induced hydrogen in the core of the dislocations defining the LAGBs.

Formation of Composite Coatings of Layered Double Hydroxide Particles and Hydroxide Gel by Electrophoretic Deposition on Mg Alloy and Corrosion Resistance

To improve the corrosion resistance of Mg alloys, composite coatings of layered double hydroxide intercalated with carbonate (LDH-CO3, hydrotalcite) particles and magnesium and aluminum hydroxide gel were formed on AZ31 Mg alloy by electrophoretic deposition (EPD) using the LDH-CO3 suspension with Mg(NO3)2 and Al(NO3)3 in total of 1.25–125 mmol/L. Wet-dry cyclic corrosion tests were performed for the coated specimens after ultrasonication. LDH-CO3 particle-rich layer and magnesium and aluminum hydroxide gel-rich layer almost alternately piled up to form a composite layer. The hydroxide gel adhered the particles together and to the substrate. At the bottom of the composite layer, flake-shape LDH-structured substance densely covered the substrate surface. The coverage and thickness of the composite layer increased from sub-micrometers to 30 µm with an increase of Mg and Al ion concentrations of the suspension. By ultrasonication, parts of the composite layer delaminated to expose the LDH-structured substance layer, while the coverage by the remaining composite layer increased with an increase of Mg and Al ion concentrations. The LDH-CO3 particles and hydroxide gel composite coatings prevented corrosion initiation even in the areas where the LDH-structured substance layer was exposed.

Effect of Ca and Sb on the Corrosion Resistance of E690 Steel in Marine Atmosphere Environment

This study investigates the impact of Ca and Sb elements on the corrosion resistance of E690 steel in a simulated marine environment. Electrochemical testing and dry/wet cyclic corrosion testing were conducted on prepared E690 steel specimens. The eroded specimens’ microstructure was observed under a scanning electron microscope, and the inclusion morphology was analyzed using an energy-dispersive spectrometer (EDS). The simulating liquid was designed to emulate the severe marine atmospheric environment in Xisha. Results showed that the addition of Ca and Sb elements effectively enhances the corrosion resistance of E690 steel in the simulated marine environment. The corrosion rates of E690 steel specimens with Ca and Sb additions were lower than those without, and the corrosion morphology was more uniform. These findings suggest that the addition of Ca and Sb elements can improve the corrosion resistance of E690 steel in simulated marine environments and have potential for use in marine engineering applications.

New Accelerated Corrosion Test Method Simulating Atmospheric Corrosion of Complex Phase Steel Combining Cyclic Corrosion Test and Electrochemically Accelerated Corrosion Test.

The automobile industry commonly uses cyclic corrosion tests (CCTs) to evaluate the durability of materials. However, the extended evaluation period required by CCTs can pose challenges in this fast-paced industry. To address this issue, a new approach that combines a CCT with an electrochemically accelerated corrosion test has been explored, to shorten the evaluation period. This method involves the formation of a corrosion product layer through a CCT, which leads to localized corrosion, followed by applying an electrochemically accelerated corrosion test using an agar gel electrolyte to preserve the corrosion product layer as much as possible. The results indicate that this approach can achieve comparable localized corrosion resistance, with similar localized corrosion area ratios and maximum localized corrosion depths to those obtained through a conventional CCT in half the time.

Multi-walled carbon nanotubes – zinc in commercial acrylic sealant as a coating for anticorrosive protection system in metallic building structures

Corrosion protection is a matter of primary importance. In this regard, different methods have been explored to improve the protection of vulnerable areas of metallic structures with the aim of maintaining the homogeneous distribution of the protective layer and reducing cracks that allow the entry of corrosive agents. In this study, coatings with Multi-Walled Carbon Nanotubes and Zinc (MWCNTs-Zn), synthesized by the chemical vapour deposition method, in a commercial acrylic sealant were tested to protect welds. The coatings were produced with three different MWCNTs-Zn ratios (80:20; 50:50; 20:80) and applied to welded joints. The tested samples, characterized by SEM and XRD, showed a good dispersion of the MWCNTs tubular structure surrounding the Zn lamellar structure. In addition, the coatings exhibited a particle size range from 29 to 352 nm, which acted as a barrier against the corrosive medium, improving the anticorrosive performance. Electrochemical techniques and accelerated tests at different ages showed that these coatings offer an effective protective barrier. The samples were subjected to an accelerated corrosion test during 336 h, the 50:50 MWNTCs-Zn ratio presented better results than the 80:20 ratio (icorr and Rcorr , ∼50% lower in the cyclic corrosion test and 27% lower in the salt spray test).

Cover Picture: Materials and Corrosion. 3/2023

Cover: There are concerns about the acid of refrigerant oils (inside piping) and corrosion by the salts in seawater (outside piping) for industrial piping. Corrosion-resistant characteristics of various aluminum alloys were investigated by accelerated degradation tests with changing storage conditions, such as temperature and atmosphere. The results from immersion tests in a refrigerant and cyclic corrosion tests (intermittent cycles between salt mist and drying) proved that aluminum alloys can be used for refrigerant piping. More detailed information can be found in: Seiji Uchiyama, Satoshi Uemura, Koji Hiraoka, Yuji Kimura, Shiro Seki, Corrosion and degradation behavior of aluminum and copper refrigerant piping, Materials and Corrosion 2023, 74, 344.

Microstructural, Corrosion, and Mechanical Characterization of Friction Stir Welded Al 6022-to-ZEK100 Mg Joints

Friction stir welded (FSW) aluminum–magnesium lightweight vehicle joints have gained significant interest due to their high strength-to-weight ratio. In this work, the corrosion resistance of this material is analyzed through electrochemical tests, which include open circuit potential (OCP) inspection and potentiodynamic polarization (PD) scanning. Weight loss measurements tested the corrosion rate of the FSW weld through cyclic corrosion testing (CCT) according to the standard SAEJ 2334. Mechanical properties were also investigated, including lap-shear strength, micro- and nano-hardness mapping, and true stress–strain curves as a function of local processing history. The electrochemical results indicate that the center weld zone’s corrosion property stays between the two base alloys. Indentation-based testing demonstrated that the weld zone behaves differently from base alloys. Lap shear strength surprisingly did not drop much even after eight weeks of cyclic corrosion tests, indicating that the joint did not allow any ingress of the electrolyte.

Accelerated Corrosion Test Based on ISO 16539 for Life Prediction of Carbon Steel in Tropical Coastal Areas

The developments of accelerated corrosion tests have been focused on the cyclic corrosion test with an improved correlation with the field corrosion behavior. This study applied ISO 16539 to simulate the tropical coastal environment in Thailand. ISO 16539 method B with 0.1 g-salt/m2 correlated well with Rayong (C2) exposure data. A method for calculating salt deposition and testing period was derived by interpolation and extrapolation of the simulated test results that were calibrated with the field-test database for Rayong (C2) and Phangnga (C4), Thailand. This work enables the application of ISO 16539 in life prediction for carbon steel exposed to the tropical coastal climate with sulfur dioxide deposition rate less than 13 (mg/m2/d: mmd) and chloride ion deposition rates greater than 10 mmd.

Effect of Proportions of Γ and Iron–Zinc Solid Solution Phases on the Corrosion Prevention Performance of Mixed Coating Layers on Heated Galvannealed Steel Sheets

Coating layers having different ratios of a Γ phase to an Fe–Zn solid solution phase were produced on galvannealed steel sheets by heat treatment. The corrosion prevention characteristics of these layers were then investigated using combined cyclic corrosion test, electrochemical measurements and analyses of corrosion products. A coating layer with a larger proportion of the Γ phase showed better corrosion prevention properties along with a smaller corrosion mass loss. The Γ phase exhibited a sacrificial corrosion protection effect with regard to both the Fe–Zn solid solution and the steel substrate while the Fe–Zn solid solution showed a sacrificial corrosion protection effect on the steel substrate. The corrosion products formed from the Γ phase comprised Zn5(OH)8Cl2·H2O, Zn5(CO3)2(OH)6, ZnO and various amorphous compounds, while the Fe–Zn solid solution generated Zn-containing ferrihydrite and amorphous compounds. The presence of Zn evidently stabilized the ferrihydrite and delayed the formation of crystalline iron oxyhydroxide based on comparisons with corrosion products formed on cold-rolled steel sheets. These effects improved the corrosion prevention performance of the Fe–Zn solid solution. The zinc-based corrosion products formed from the Γ phase provided even better corrosion prevention performance by delaying the formation of crystalline iron oxyhydroxide and were also themselves resistant to reduction.

Corrosion Evaluation of Body in White Bimetallic Joints

Abstract This scientific article deals with cyclic corrosion testing of bimetallic joints in order to describe the influence of different surface treatment as a protection against galvanic corrosion on bimetallic materials. Multi-material body parts joined with advanced manufacturing technologies are used to achieve the required car properties. Metallic materials have different values of electronegativity and joining increases the risk of corrosion. Different types of coatings are used to prevent galvanic corrosion, but each increases investments and costs. Galvanic corrosion affects the lifecycle of the car. Cyclic corrosion testing provides replicable results to estimate the range of corrosion in a real environment. Test specimens from different materials were riveted and treated with various surface treatments. The method and design of samples preparation is unique and reflects the reality more than current methods. It has not yet been published in any literature. The corrosion test was performed for 6 weeks. Samples were subjected to a salt mist with temperatures of 25 °C and 50 °C, wetting and drying phases. The samples were evaluated according to the standard EN ISO 4628-1:2016. Microscopic and energy-dispersive analysis were performed. Tests have shown considerable galvanic corrosion on uncoated samples. On the samples with ecoated surface galvanic corrosion was not recorded.

Corrosion and degradation behavior of aluminum and copper refrigerant piping

AbstractMany types of refrigerant piping use copper alloys because of such alloys' high workability, thermal conductivity, and weatherability. However, copper is the 25th most abundant element in Earth's crust (as indicated by its Clark number: a relatively low value, ca. 0.01). Therefore, there is concern about depletion, if emerging countries and new devices such as electric vehicles use large quantities of copper. Recently, we have focused on aluminum as a lightweight metal, which is 4th place in terms of Clark number (ca. 7.6). Refrigerant piping also uses aluminum in air conditioning equipment; thus, practical applications are available. Aluminum alloys used as material for piping also contain other elements such as manganese, silicon, magnesium, copper, and iron. Regarding practical use for pipework, long‐term evaluation (more than 20 years) by corrosion is necessary. Therefore, in this study, we investigated the corrosion‐resistant characteristics of various aluminum alloys by accelerated degradation tests with changing storage conditions, such as temperature and atmosphere. In general, the corrosion of the piping materials depends on the contact atmosphere and differs between inside (refrigerant) and outside (e.g., air) piping. Specifically, there are concerns about the acid of refrigerant oils (inside piping) and corrosion by the salts in seawater (outside piping). The results from immersion tests in refrigerant and cyclic corrosion tests (intermittent cycles between salt mist and drying) proved that aluminum alloys can be used for refrigerant piping in the same way as copper materials.

(Digital Presentation) The Role of Mg in Cut-Edge Corrosion Protection of 55 Mass% Al-Zn-Mg Coated Steel Under a Wet-Dry Cyclic Condition

Pre-painted hot-dip 55 mass% Al-Zn coated steel sheets are widely used as a building material due to their superior corrosion resistance. In consideration of its long-term service, a pre-painted hot-dip 55 mass% Al-Zn-2 mass% Mg coated steel sheet with enhanced corrosion resistance has been developed in recent years.1 It has been shown that the addition of 2 mass% Mg not only reduced the corrosion rate by 1/3 but also inhibited the delamination of organic paints from the cut-edge. As yet, however, the role of Mg in the cut-edge corrosion protection of the 55 mass% Al-Zn-2 mass% Mg coated steel has not been completely clear. In this study, we focused on the influence of Mg-containing corrosion products on the electrochemical properties of the coating layer and the steel substrate. Hot-dip 55 mass% Al-Zn-2 mass% Mg-1.6 mass% Si and 55 mass% Al-Zn-1.6 mass% Si coated steel sheets were used in this study. The Al-Zn-Mg coating layer is composed of Al-rich, Zn-rich, and Mg-Si phases. Our previous study has reported that for the Al-Zn-Mg coating layer, the Zn-rich phase preferentially dissolves during the initial process of cut-edge corrosion.2 In addition, Mg also preferentially dissolves from the Mg-Si phase in the Al-Zn-Mg coating layer. The wet and dry cyclic corrosion test showed that the formation of the Zn-based corrosion products at the cut-edge for the Al-Zn-Mg coated steel was more inhibited than that for the Al-Zn coated steel. In addition, the sacrificial corrosion protection ability of the Al-Zn-Mg coated steel was higher than the Al-Zn coated steel. It was found that the dense corrosion products including Mg were formed on the steel substrate at the cut-edge for the Al-Zn-Mg coated steel 1 hour after the onset of the corrosion test. The Mg-containing corrosion products slightly reduced the cathodic current for the oxygen reduction reaction, and this is thought to be one of the factors for the improved cut-edge corrosion resistance.1) N. Shimoda, Y. Morimoto, Y. Kubo, S. Fujii, and S. Shiragaki, Galvatech 2015 Proceedings, 802 (2015).2) S. Tokuda, I. Muto, Y. Sugawara, M. Takahashi, M Matsumoto, and N. Hara, Corros. Sci, 129, 126 (2017).

Effect of tin addition on the corrosion resistance of low‐alloyed steel in simulated coastal‐industrial atmosphere environment

AbstractIn simulated coastal‐industrial atmosphere, the atmospheric corrosion behavior of three different tin content low‐alloy steels has been investigated by indoor wet/dry cyclic corrosion test. The results indicate that in the early stage of atmospheric corrosion, tin addition has beneficial effect on the corrosion resistance improvement, and corrosion resistance increases as tin content increases. However, increased corrosion resistance due to tin addition does not last long. After a large amount of corrosion products are formed on the surface of the sample, the stability and compactness of rust layer are degraded by tin. Therefore, in the long‐term atmospheric corrosion process, the lower the tin content in steel, the better the corrosion resistance of steel.

INVESTIGATION OF THE EFFECT OF MULTI-LAYER COATING ON CORROSION PREVENTION PERFORMANCE FORMED BY THE APPLICATION OF SOLVENT-BASED ZINC LAMEL COATING ON ALKALI ZINC AND ALLOY ZINC COATING

Bu çalışmada, alkali çinko, çinko-nikel ve çinko-demir alaşım kaplama prosesleri ile çözücü bazlı çinko lamelli kaplama prosesi yeniden düzenlenerek bir araya getirilmiş ve iki farklı kaplama prosesinin tekil üstün özellikleri birleştirilerek üstün korozyon önleme performansına sahip ürünlerin üretilmesine olanak sağlayan yeni bir proses geliştirilmiştir. Yürütülen deneysel çalışmalar sonucunda elde edilen ve görsel uygunluk kriterini sağlayan kaplamalar kuru yapışma, su direnci, nem direnci, tuz sisi, çevrimsel korozyon ve kimyasal direnç testlerine tabi tutulmuştur. Geliştirilen yeni proses, yüksek korozyon direncine (>1000 saat tuz sis testi ve >63 döngü döngüsel korozyon testi), yüksek sıcaklık direncine (300 °C'de bir saat), kimyasal dirence ve elektriksel yalıtkanlığa sahip parçaların üretilmesini olanak sağlamıştır. Testlerden elde edilen sonuçlar otomotiv endüstrisinin beklentileriyle kıyaslanmış ve beklentilerden daha üstün özellikler elde edilmiştir.

Corrosion behavior of additively manufactured AISI 316L stainless steel under atmospheric conditions

AbstractThis study investigated the corrosion behavior of AISI 316L produced by direct energy deposition (DED). Microstructural and chemical analysis showed a homogeneous distribution of Si and Si–Mn inclusions of 0.5–1 µm and the Cr and Mo enrichment within interdendritic areas. Scanning Kelvin probe analysis of additively manufactured stainless steel highlighted a regular “striped‐like” surface potential feature with a potential gradient of 30 mV for a mean value of 0.320 ± 0.017 V versus standard hydrogen electrode. It can be related to the presence of the residual stress in the oxide film and the complex thermal history due to the fabrication process. A cyclic corrosion test simulating atmospheric conditions revealed the same corrosion properties for stainless steel fabricated by DED compared to cold rolled one. Various surface preparations of 316L were also exposed for corrosion tests. It was found that the “as‐received” and “brushed” surfaces exhibited poorer corrosion resistance due to the presence of an as‐build defective layer. However, prior passivation of brushed surface, machining, or mechanical grinding down to P1200 improve significantly the corrosion resistance.