Composition and protective ability of rust layer formed on weathering steel exposed to various environments

The compositional change of rust (corrosion products) layer formed on weathering steel exposed to atmosphere with different amount of air-borne sea salt particles in Japan have been investigated by the X-ray diffraction method. The mass ratio (α/γ) of crystalline α-FeOOH to γ-FeOOH, in the rust layer formed on the weathering steel exposed in an industrial environment, increases with an increase in exposure duration. The α/γ is closely related to the corrosion rate in environments when the amount of air-borne salt is less than 0.2 mg NaCl/dm²/day (2.31 × 10⁻⁷ g NaCl/m²/s). However this is not the case in seaside environments with a higher amount of air-borne salts. The mass ratio (α/γ^∗) of crystalline α-FeOOH to the total mass of γ-FeOOH, β-FeOOH and Fe₃O₄, in the rust layer formed on the weathering steel is related to the corrosion rate even in seaside environments certainly more than 0.2 mg/dm²/day (2.31 × 10⁻⁷ g/m²/s) of air-borne salt particles. When the α/γ^∗ is more than 1, a higher corrosion rate more than 0.01 mm/year (3.17 × 10⁻¹³ m/s) is not observed. The α/γ^∗ is a protective ability index of rust formed on weathering steel.     

In-depth distribution of rusts on a plain carbon steel and weathering steels exposed to coastal-industrial atmosphere for 17 years

In-depth distribution of rusts on two weathering steels and a plain carbon steel exposed to atmosphere for 17 years under a bridge at a coastal + industrial region in Japan were studied. In the rust layer on all specimens, α-FeOOH, β-FeOOH, γ-FeOOH, Fe₃O₄ and so-called amorphous rust were found. Within rust layers, there were thick parts and thin parts, which were finely and complicatedly distributed on steels. Among these rust species, α-FeOOH was dominant on all specimens. α-FeOOH appeared almost homogeneously through the rust layer. Its concentration was higher on weathering steels than on plain carbon steel. β-FeOOH was found mainly at thick parts and was scarce at thin parts of rust layers. Concentration of α-FeOOH was higher and that of γ-FeOOH was lower on weathering steels than on plain carbon steel. Amorphous rust was located at the bottom of the rust layer irrespective of steel types. Concentration of magnetite was negatively correlated with concentration of β-FeOOH.     

Corrosion resistance and mechanical properties of low-alloy steels under atmospheric conditions

The corrosion resistance and mechanical strength of four newly developed low-alloy steels (LAS) were compared with a carbon steel (SS400) and a weathering steel (Acr-Ten A) using a laboratory-accelerated test that involved cyclic wet/dry conditions in a chloride environment (5 wt.% NaCl). The new LAS were designated 1605A, 1605B, 1604A, and 1604B. After 72 cycles of cyclic corrosion tests, the susceptibility of the steels to corrosion could be listed in the following order based on their weight loss (from high to low): SS400 > Acr-Ten A > 1604B ? 1604A > 1605B ? 1605A. The change in mechanical properties by corrosion was the least for SS400, Acr-Ten A was second, and effects of corrosion on the mechanical properties of the other four low-alloy steels were similar. Finally, the characteristics of the rust layers on each LAS sample were observed by SEM, and analyzed by FTIR and EPMA. The results indicated that most of the rust layers on the test steels were composed of a loose outer rust layer and a dense inner rust layer. The outer rust layer of each steel was composed of α-FeOOH, γ-FeOOH, magnetite (Fe₃O₄), H₂O, and amorphous ferric oxyhydroxide (FeO_x(OH)_3−2x, x=0-1), while the inner rust layer was composed mainly of Fe₃O₄ with a little α-FeOOH. In addition, it was apparent that the copper and chromium alloying additions were enriched, respectively, at the rust-layer/substrate interface and in the rust layers. Finally, combining the results of the accelerated tests and the rust layer analysis showed that low-alloy steels, such as 1605A and 1605B, have better weathering steel properties than Acr-Ten A for use in the humid and salty weather.     

Explanation of the effect of high chloride concentration on the critical pitting temperature of stainless steel

We correlate the effect of high chloride concentration on the critical pitting temperature (CPT) of type 316L stainless steel with its effect on the critical pit solution chemistry as determined by the artificial pit technique. It is shown that the change in CPT with bulk chloride concentration (0.5-9 mol kg⁻¹) can be correlated with a change in the ratio of C^∗/C_s, where C^∗ is the critical dissolved alloy cation concentration to sustain pitting, and C_s is the solubility of FeCl₂ at the pit surface. A complicating factor is that natural pits can only grow with C^∗ = C_s at the lower chloride concentrations, but can grow without the salt film at very high chloride concentrations; this transition is believed to occur close to 5 or 6 m bulk chloride concentration. The dependence of C_s on bulk chloride concentration is given a new interpretation based on a common-ion effect operating within an altered local chemistry with complexation.     

Corrosion behavior of steel under wet and dry cycles containing Cr ion

The corrosion behavior of mild steel has been investigated during the wet and dry cyclic transitions containing Cr³⁺ ion added as sulfate in order to gain a better understanding of the influence of Cr on the atmospheric corrosion of steels. The corrosion rate during drying is greatly suppressed by the existence of Cr³⁺ ion in the electrolyte covered with the surface. Lower corrosion rates are observed during drying even if the surface have been polarized to negative potentials below −200 mV_SHE during the wet corrosion conditions in which the surface-covered electrolyte contains Cr³⁺ ion. This corrosion behavior is identical to the case of Cr-containing steel for the wet and dry cyclic transitions without the addition of Cr³⁺ ion. The composition of rust layer after the wet and dry cyclic transitions is composed of α-FeOOH, γ-FeOOH and Fe_3−δO₄ for both cases of non-Cr³⁺ and Cr³⁺-containing condition, and no significant difference in the mass fraction of the above rust substances between two conditions is observed by means of Mössbauer spectroscopy. The only difference in the rust layer is that the rust formed under the wet and dry cyclic transitions containing Cr³⁺ ion contains a certain amount of Cr near the steel/rust interface. Those results suggest that the role of Cr during the wet and dry cyclic transitions is the inhibition of the rust reduction and the formation of Fe²⁺-state intermediate by the existence of Cr in the rust layer. This can lead to the inhibition of the oxygen reduction during drying.     

Characterization of the rust formed on weathering steel exposed to Qinghai salt lake atmosphere

The product formed on weathering steel exposed to salt lake atmosphere for 12 months was investigated by X-ray diffraction (XRD), infrared transmission spectroscopy (IRS), scanning electron microscopy (SEM), electron probe micro analyzer (EPMA) and electrochemical techniques. The rust was mainly composed of β-FeOOH, Fe₈(O,OH)₁₆Cl_1.3 and a little γ-FeOOH. Amorphous δ-FeOOH was only on skyward surface. The rust layer suppressed anodic reaction and facilitated the cathodic reaction. The very small value of rust resistance R_r in this work indicated that the rust had poor protective ability. Cl element was rich in the whole rust layer and played an important role in accelerating the corrosion of weathering steel in salt lake atmosphere.     

Corrosion resistance of the Dhar iron pillar

The corrosion resistance of the 950-year old Dhar iron pillar has been addressed. The microstructure of a Dhar pillar iron sample exhibited characteristics typical of ancient Indian iron. Intergranular cracking indicated P segregation to the grain boundaries. The potentiodynamic polarization behaviour of the Dhar pillar iron and mild steel, evaluated in solutions of pH 1 and 7.6, indicate that the pillar iron is inferior to mild steel under complete immersion conditions. However, the excellent atmospheric corrosion resistance of the phosphoric Dhar pillar iron is due to the formation of a protective passive film on the surface. Rust analysis revealed the presence of crystalline magnetite (Fe_3−xO₄), α-Fe₂O₃ (hematite), goethite (α-FeOOH), lepidocrocite (γ-FeOOH), akaganeite (β-FeOOH) and phosphates, and amorphous δ-FeOOH phases. The rust cross-section revealed a layered structure at some locations.     

海水飞溅区Ni-Cu-P钢的锈层和耐点蚀性能研究

在海水飞溅区对实验室冶炼的Ni-Cu-P钢、含Cu低合金钢和碳钢进行660 d的挂片实验,评价Ni-Cu-P钢的耐蚀性能;采用Fourier变换红外(FTIR)光谱、电感耦合等离子体原子发射光谱(ICP-AES)、电子探针(EPMA)、SEM和EDAX等技术,分析3种钢表面的锈层特征.结果表明,Ni-Cu-P钢表现出比...     

Atmospheric corrosion of hot and cold rolled carbon steel under field exposure in Saudi Arabia

Carbon steel (hot and cold rolled) specimens have been exposed to the action of different atmospheres at 20 test sites distributed in Saudi Arabia and was investigated in terms of environmental factors such as average temperature, average relative humidity and deposition rates of atmospheric pollutants (Cl⁻ and SO₂). Applying the standard ISO 9223 norm aggressiveness of the atmospheres corresponding to 0the different test sites has been determined. Calculations of corrosion rates were made via loss of weight and characterization of the corrosion products formed on samples has been carried out by means of X-ray diffraction (XRD). The major constituent of the rust formed in marine and marine-industrial environment is goethite (α-FeOOH). These samples also show the presence of a large proportion of lepidocrocite (γ-FeOOH) and small amounts of ferrihydrite and maghemite (γ-Fe₂O₃). In the case of urban and rural samples goethite is the major constituent of corrosion layers. The rust formed under the urban environment also contains large amounts of ferrihydrite and in a lesser proportion, of goethite and maghemite.     

Role of zinc compounds on the formation, morphology, and adsorption characteristics of β-FeOOH rusts

To simulate the corrosion of galvanized steel in marine zone, β-FeOOH was prepared by aging the FeCl₃ solutions containing ZnCl₂ and zinc rusts such as ZnO and zinc hydroxychloride (Zn₅(OH)₈Cl₂·H₂O:ZHC). Adding ZnCl₂, ZnO, and ZHC inhibited the crystallization and particle growth of β-FeOOH and the inhibitory effect was in order of ZHC ≈ ZnO > ZnCl₂. The adsorption of H₂O and CO₂ was suppressed by adding ZnCl₂, ZnO, and ZHC. These results imply that the rust formed on galvanized steel in marine environment is more compact, amorphous, and hydrophobic in nature which may lead to improve the corrosion resistance.     

The corrosion of Fe3Al alloy in liquid zinc

A systematic study of the isothermal corrosion testing and microscopic examination of Fe₃Al alloy in liquid zinc containing small amounts of aluminum (less than 0.2 wt.%) at 450 °C was carried out in this work. The results showed the corrosion of Fe₃Al alloy in molten zinc was controlled by the dissolution mechanism. The alloy exhibited a regular corrosion layer, constituted of small metallic particles (diameter: 2-5 μm) separated by channels filled with liquid zinc, which represented a porosity of about 29%. The XRD result of the corrosion layer formed at the interface confirmed the presence of Zn and FeZn_6.67. The corrosion rate of Fe₃Al alloy in molten zinc was calculated to be approximately 1.5 × 10⁻⁷ g cm⁻² s⁻¹. Three steps could occur in the whole process: the superficial dissolution of metallic Cr in the corrosion layer, the new phase formation of FeZn_6.67 and the diffusion of the dissolved species in the channels of the corrosion layer.     

Characterization of the hot deformation behavior of a Ti-22Al-25Nb alloy using processing maps based on the Murty criterion

Isothermal compression testing of Ti-22Al-25Nb alloy was carried out at deformation temperatures between 940 and 1060 °C with strain rate between 0.001 and 10 s⁻¹, and a height reduction of 50%. The hot deformation behavior of Ti-22Al-25Nb alloy was characterized based on an analysis of the stress-strain behavior, kinetics and the processing map, for obtaining optimum processing windows and achieving desired microstructures during hot working. The constitutive equation was established, which described the flow stress as a function of the strain rate and deformation temperature. The apparent activation energies were calculated to be 788.77 kJ/mol in the α₂ + β/B2 + O phase region and 436.23 kJ/mol in the α₂ + B2 phase region, respectively. Based on Dynamic Material Model and the Murty instability criterion, the processing map for the Ti-22Al-25Nb alloy was constructed for strain of 0.6. The map exhibits a stable domain for the temperature range of 940-1060 °C and strain rate range of 0.001-0.1 s⁻¹ with two peaks in power dissipation of 51 and 56%, occurring at 940 °C/0.001 s⁻¹ and 1060 °C/0.001 s⁻¹, respectively. One is associated with lamellar globularization, and the other displays a phenomenon of recrystallization. Therefore, the desired processing condition of the Ti-22Al-25Nb alloy is 940 °C/0.001 s⁻¹ in the α₂ + β/B2 + O phase field. Moreover, the material also undergoes flow instabilities at strain rates higher than 1 s⁻¹. This instability domain exhibits flow localization and adiabatic shear bands which should be avoided during hot processing in order to obtain satisfactory properties.     

Magnetic property based characterization of rust on weathering steels

The characterization of rusts on weathering steels is important in understanding the origin of their corrosion resistance. Rust consists of several phases, e.g. α-, β- and γ-FeOOH, which are anti-ferromagnetic with different Neél temperatures. Rust on so-called advanced weathering steel containing 3 wt.% Ni [H. Kihira, A. Usami, K. Tanabe, M. Ito, G. Shigesato, Y. Tomita, T. Kusunoki, T. Tsuzuki, S. Ito, T. Murata, in: Proc. Symp. on Corrosion and Corrosion Control in Saltwater Environments, Honolulu, 1999, The Electrochemical Soc., pp. 127-136] contains in addition a ferrimagnetic spinel phase [M. Kimura, H. Kihira, Y. Ishii, T. Mizoguchi, in: Proc. 13th Asian-Pacific Corrosion Control Conference, Osaka, 2003; M. Kimura, H. Kihira, N. Ohta, M. Hashimoto, T. Senuma, Corros. Sci., this volume; M. Kimura, N. Ohta, H. Kihira, Mater. Trans. JIM, in press]. The nanostructure of real rust cannot be elucidated satisfactorily only with conventional analytical methods such as X-ray diffraction, because of the complex mixture of phases with fine and imperfect crystallites. Because of the short range of the super-exchange coupling between Fe ions in a solid, the magnetic properties can give information on local configurations even in the absence of perfect crystalline coherence. Therefore, the magnetic properties of rust samples were investigated in detail using a Superconducting Quantum Interference Device (SQUID) magnetometer and Mössbauer spectroscopy. SQUID magnetometry is effective to determine the quantity of the ferrimagnetic phase. The temperature dependence of the Mössbauer spectrum gives information about not only the fractions of the phases but also the distribution of grain volume, V, in each phase according to the super-paramagnetic relaxation effect. This approach has been applied to rust of conventional [T. Okada, Y. Ishii, T. Mizoguchi, I. Tamura, Y. Kobayashi, Y. Takagi, S. Suzuki, H. Kihira, M. Ito, A. Usami, K. Tanabe, K. Masuda, Jpn. J. Appl. Phys. 39 (2003) 3382] and advanced weathering [H. Kihira, A. Usami, K. Tanabe, M. Ito, G. Shigesato, Y. Tomita, T. Kusunoki, T. Tsuzuki, S. Ito, T. Murata, in: Proc. Symp. on Corrosion and Corrosion Control in Saltwater Environments, Honolulu, 1999, The Electrochemical Soc., pp. 127-136] steels.The grains of the rust formed on advanced weathering steel have clearly bimodal Gaussian distributions of volume with peaks at V ≈ 5 × 10⁻²⁴ m³ and V ≈ 16 × 10⁻²⁴ m³ in α-FeOOH and β-FeOOH phases. The outer layer has grains of γ-FeOOH which are an order of magnitude smaller. The inner layer, in contrast, has a continuous distribution of grain volume, consistent with the formation of a continuous densely packed thin protective rust layer which prevents further corrosion.     

Effects of DBU, morpholine, and DMA on corrosion of low carbon steel exposed to steam

Effects of morpholine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and dimethylamine (DMA) on oxidation kinetics and oxide phase formation/transformation of AISI 1018 steel at 120 °C were evaluated. Low carbon steel samples were exposed to steam in an autoclave containing amine added aqueous solution at pH of 9.5 for 1, 2, 4, 6, 8, and 12 h. Control samples exposed to plain steam and amines showed the highest and lowest weight loss respectively. Fourier Transform Infrared Spectrophotometry (FTIR) showed that DBU containing steam favored formation of magnetite (Fe₃O₄) while steam with DMA formed more α and γ-FeOOH. Transformation of magnetite to hematite (α-Fe₂O₃) was fastest for morpholine. Analysis of oxides morphology was done utilizing Scanning Electron Microscopy (SEM). Oxides formed in plain or DMA containing steam exhibited acicular particles of goethite/hematite (α-FeOOH/α-Fe₂O₃) compared to DBU containing steam that showed equiaxed particles of magnetite/maghemite (Fe₃O₄/γ-Fe₂O₃). Morpholine containing steam promoted agglomeration of thin sharp platelets into coarse flakes of hematite.     

Corrosion inhibition of mild steel in hydrochloric acid solution by some double Schiff bases

The inhibition effect of four double Schiff bases on the corrosion of mild steel in 2 M HCl has been studied by polarization, electrochemical impedance spectroscopy (EIS) and weight loss measurements. The inhibitors were adsorbed on the steel surface according to the Langmuir adsorption isotherm model. From the adsorption isotherm, some thermodynamic data for the adsorption process were calculated and discussed. Kinetic parameters activation such as E_a, ΔH∗, ΔS∗ were evaluated from the effect of temperature on corrosion and inhibition processes. Quantum chemical calculations have been performed and several quantum chemical indices were calculated and correlated with the corresponding inhibition efficiencies.     

耐候钢表面锈层稳定化处理技术研究

目的解决耐候钢裸露使用初期锈液流失导致污染环境的问题。方法制备了耐候钢表面锈层稳定化处理溶液。通过周期浸润循环腐蚀试验、锈层微观分析和电化学测试等方法,研究了在模拟工业大气环境下,表面处理溶液对耐候钢锈层结构及耐腐蚀性能的影响。结果表面处理后,耐候钢的开路电位由处理前的-0.395 V降低到-0.475 V,表面快速生成一层连续致密的氧化层。加速腐蚀16 d后,耐候钢的腐蚀速率由未处理时的0.209 mg/(cm^2·d)降低到表面处理后的0.106 mg/(cm^2·d),降低了约49%;锈层的自腐蚀电位由未处理的-0.216 V提高到处理后的-0.073 V,提高了约66%,自腐蚀电流密度由未处理时的7.41μA/cm^2降低到1.58μA/cm^2,降低了约79%。随着腐蚀时间从1 d延长至16 d,处理后的耐候钢锈层中α-FeOOH的质量分数由2.96%增加到4.46%,增加了51%,γ-FeOOH的质量分数由2.06%降低到1.65%。表面处理后的耐候钢锈层中,Cu和Cr元素在锈层与基体结合处和锈层内部发生富集。结论处理溶液降低了耐候钢表面的开路电位,可使耐候钢快速生成致密且连续的锈层,锈层中Cu、Cr元素富集促进了γ-FeOOH向α-FeOOH的转化,提高了锈层电化学保护性能,降低了后期腐蚀速率,缩短了稳定化进程。     

Mechanisms of corrosion layer formation during zirconium immersion in a (Fe)-bearing glass melt

The kinetics and mechanism of pure zirconium corrosion in an iron-bearing borosilicate glass melt are investigated from 1230 to 1418 °C. The influence of immersion time and temperature on the corrosion layer morphologies is discussed. The corrosion mechanism is a multi-step process and is described using the Zr-Si-O-B phase diagram. Boron and silicon species contained in the melt are reduced at the zirconium contact and ZrSi_sB_b intermetallic compounds are formed while the Zr substrate is oxidized into ZrO_x. When the local melt fO₂ value induces the Fe⁰ precipitation, complex ZrSi_sB_bFe_f compounds are formed. The last step consists in the oxidation of ZrO_x into ZrO₂.     

Influence of Rust Layers on the Corrosion Behavior of Ultra-High Strength Steel 300M Subjected to Wet–Dry cyclic Environment with Chloride and Low Humidity

The influence of rust layers on the corrosion behavior of ultra-high strength steel 300 M subjected to a simulated coastal atmosphere was investigated by corrosion weight loss, surface analysis techniques, and electrochemical methods.The results exhibit the presence of a large proportion of c-Fe OOH and a-Fe OOH and a small amount of Fe3O4 in the outer rust layer. During the wet–dry cyclic process, the bonding performance and the density of outer rust layer deteriorate with the thickness of outer rust. The inner rust layer plays a main role on protectiveness, which can be attributed to the formation of an ultra-dense and adherent rust film with major constituent of a-Fe OOH and a-Fe2O3 on the steel.     

Electrochemical and theoretical investigation on the corrosion inhibition of mild steel by thiosalicylaldehyde derivatives in hydrochloric acid solution

Inhibitory effect of three Schiff bases 2-{[(2-sulfanylphenyl)imino]methyl}]phenol (A), 2-{[(2)-1-(4-methylphenyl)methylidene]amino}-1-benznethiol (B), and 2-[(2-sulfanylphen-yl)ethanimidoyl)]phenol (C) on corrosion of mild steel in 15% HCl solution has been studied using weight loss measurements, polarization and electrochemical impedance spectroscopy (EIS) methods. The results of the investigation show that the compounds A and B with mean efficiency of 99% at 200 mg/L additive concentration have fairly good inhibiting properties for mild steel corrosion in hydrochloric acid, and they are as mixed inhibitor. All measurements show that inhibition efficiencies increase with increase in inhibitor concentration. This reveals that inhibitive actions of inhibitors were mainly due to adsorption on mild steel surface. Adsorption of these inhibitors follows the Langmuir adsorption isotherm. Thermodynamic adsorption parameters (K_ads, ΔG_ads) of studied Schiff bases were calculated using the Langmuir adsorption isotherm. Activation parameters of the corrosion process such as activation energies, E_a, activation enthalpies, ΔH^∗, and activation entropies, ΔS^∗, were calculated by the obtained corrosion currents at different temperatures. Obvious correlation was found between the corrosion inhibition efficiency and the calculated parameters. The obtained theoretical results have been adapted with the experimental data.     

Ex-situ and in-situ X-ray diffractions of corrosion products freshly formed on the surface of an iron-silicon alloy

Ex-situ X-ray diffraction measurements of a small amount of samples extracted from wet corrosion products freshly formed on a pure iron and iron-2 mass% silicon surfaces have been conducted using synchrotron radiation for clarifying the formation process of corrosion products. The results showed that γ-FeOOH was formed on the outer side of wet corrosion products formed on the surface of the pure iron by sodium chloride solution, while γ-FeOOH, α-FeOOH, Fe₃O₄, and green rusts were formed on the inner side. On the other hand, in comparison to the case of the pure iron, a significant formation of β-FeOOH was observed in the iron-silicon alloy. Influences of silicon alloying on corrosion products formed by aqueous solution containing sulfate ions were also observed. Furthermore, in-situ diffraction measurements by a conventional X-ray source were conducted for analyzing corrosion products formed on the pure iron and iron-silicon alloy surfaces by cyclic exposure to wet and dry atmospheres. The results obtained by the in-situ diffraction and ex-situ diffraction measurements on the corrosion products were consistent.