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This paper aims to analyze the high temperature (200°C) corrosion behavior of 2205 duplex stainless steel in acidizing stimulation solution containing hydrochloric acid (HCl) and acetic acid.

The corrosion rate of 2205 duplex stainless steel in all kinds of acid solutions was calculated through immersion tests and electrochemical test. The corrosion product composition is analyzed by X-ray diffraction analysis. The element composition and element distribution before and after corrosion were analyzed by an X-ray energy spectrometer. The corrosion morphology of the steel surface was observed by a scanning electron microscope. Both static and dynamic corrosion experiments were carried out at 200°C.

The results show that 2205 duplex stainless steel has excellent corrosion resistance in low to high concentration acetic acid solutions, but increasing the concentration of Cl⁻ in acetic acid solution will accelerate the corrosion rate. Low concentration HCl solution can cause serious corrosion to 2205 duplex stainless steel. The system of HCl and acetic acid will produce a synergistic effect on corrosion of 2205 duplex stainless steel and accelerate the corrosion. Sb₂O₃ is a good corrosion inhibitor synergist for high-temperature acidizing stimulation solution.

The amount of HCl that is used in acidizing stimulation is usually determined by the dissolution effect of the acid on the rocks, but for ultra-high-temperature reservoirs, the amount of HCl should be based on reducing the corrosion of oil and gas wells.

The purpose of this paper is to supplement the scant previous investigations on the corrosion behaviour of 2205 and 2507 duplex stainless steels in selected organic acids containing chloride additions.

Microstructural examination of the alloys was first carried out, after which the corrosion behaviour of the alloys in citric, oxalic, formic and acetic acids containing chloride additions at varying temperatures was studied using electrochemical techniques.

The alloy 2507 material had a larger grain size than did the alloy 2205 sample. The corrosion resistances of the alloys generally are highest in acetic acids and lowest in citric acid. The addition of chloride had a pronounced effect on their corrosion resistance. Alloy 2507 generally exhibited higher corrosion resistance in all of the acids than alloy 2205, with the exception of acetic acid at room temperature. The 50:50 ratio of ferrite to austenite composition, as revealed by phase compositional analysis, indicated no significant possibility for galvanic corrosion between the phases. This suggests that the corrosion behaviour of the alloys is controlled by their grain sizes and chemical compositions.

Although the corrosion behaviour of duplex stainless steels in some organic acid media has been reported, this investigation covers the major organic acids not previously reported. Since in real industrial systems a mixture of both organic and minerals acids/salts may typically exist, investigations of the combined effect of chloride ions with the organic acids reported in this paper typify real industrial operations. The paper thus provides a basis for material selection for the application of 2205 and 2507 in industrial systems where organic acids are mostly used.

This paper aims to study the effect of current density of hydrogen charging on the semiconductor properties and pitting initiation of 2205 duplex stainless steel (DSS) passivation film.

In this work, the 2205 DSS is pre-hydrogenated and passivated. Then, the passivation film is tested by electrochemical impedance method, Mott–Schottky curve method and dynamic potential scanning method. The influences of hydrogen on the properties of the passivation film and the corrosion behavior of the matrix were studied by analyzing the curves obtained in the electrochemical test. The surface of the passivation film after pre-hydrogenation and anodic polarization was observed by using the ultra-depth three-dimensional microscopy and the scanning electron microscope. The integrity, density and corrosion morphology of the passivation film were studied and discussed.

With the increase of the hydrogen current density, the growth of the passivation film is hindered, the concentrations of donor and acceptor in the film are increased, the conductivity of the passivation film increases. In the anodic polarization, the dimensional passive current density increases with the increase of the hydrogen current density, and the pitting potential is reversed, the more likely the sample is pitting. In general, hydrogen hinders the formation of the passive film on duplex stainless steel, which increases the concentration of point defects in the passive film. Finally, the passive film is easy to crack and pitting.

The performance of passive film is an important condition to influence the corrosion behavior of stainless steel. However, little research has been done on the effects of hydrogen on the electrochemistry and pitting sensitivity of 2205 DSS passivation films. The effect of hydrogen on semiconductor properties and pitting initiation of 2205 DSS passivation film is needed to be investigated.

To find out the optimum heat treatments to recover the microstructural changes of stainless steel alloys.

A total of four alloys were used in this study: two duplex stainless steel (DSS) alloys type 2304 and 2205, super DSS (SDSS) type 2507 and austenitic stainless steel alloy type 316 L. The alloys were heated to different temperatures, 750, 850, 950 and 1,050°C, for three different times, 10 min, 1 and 4 h.

The microstructural investigations showed that 2205 and 2507 behaved similarly in recovering their microstructures, especially in terms of the ferrite:austenite ratio within specific heat treatments and changing the hardness values. The results indicated that the microstructure of both alloys started to change above 750°C, the largest changes were shown at 850 and 950°C as the lowest ferrite content (FC%) was recorded at 850°C for both alloys. However, the microstructures of both alloys started to recover at 1,050°C. The reduction in the hardness values was attributed to the formation of new ferrite grains, free of residual stresses. On the other hand, the microstructure of the alloy type 2304 was stable and did not show large changes due to the applied heat treatments, similarly for austenitic alloy except showing chromium (Cr) carbide precipitation.

Finding the exact heat treatments, temperature and time to recover the microstructural changes of DSS alloys.

Duplex stainless steel is composed of equal amounts of austenite and ferrite, which has excellent corrosion resistance and strength. However, after the metal was welded, the ratio of austenite and ferrite in the joint is unbalanced, and secondary phase precipitates are produced, which is also an important cause of pitting corrosion in the joint.

This paper aims to study the mechanical and corrosion behavior of welded joints, by adjusting the welding parameters of laser hybrid welding, dual heat sources are used to weld 2205 duplex stainless steel. The two-phase content of different parts of the welded joint is measured to study the influence of the ratio of the two-phase on the mechanical and corrosion properties of the joint.

The ratio of austenite and ferrite in different welded joints has an obvious difference, and from top to bottom, the austenite content decreased gradually, and the ferrite content increased gradually. The harmful phases are precipitated in the middle and lower part of the joint. The strength of welded joints is slightly lower than that of base metal. At the same time, the fracture analysis shows that some ferrite phases are affected by the precipitate in the grain and produce quasi-cleavage fracture. The corrosion results show that the corrosion resistance of the welded joints is lower than that of the base metal, and the concentration of chloride ions affects the corrosion resistance.

In this paper, the authors use the influence of different welding processes on the two-phase ratio of the joint to further study the influence of the microstructure on the corrosion resistance and mechanical properties of the weld.

This paper aims to reduce the cost, limit the time and increase raw material source availability, coral aggregate seawater concrete (CASC) composed of coral, coral sand, seawater and cement can be widely used for the construction of ports, levees, airports and roads to achieve practical engineering values. However, the naturally porous coral structure and abundant Cl⁻ in the seawater and coral lead to extremely severe reinforcement corrosion for CASC. It is well known that Cl⁻ is the main cause of reinforcement corrosion in the marine environment. Therefore, it is necessary to research the reinforcement corrosion of CASC in the marine environment.

In this study, linear polarization resistance was adopted to test the linear polarization curves of reinforcement in CASC with different exposure times. E_corr, R_p, I_corr and V_corr were calculated according to the weak electrochemical polarization theory and Stern–Geary formula. The effects of concrete cover thickness, exposure time, reinforcement types and inhibitor on reinforcement corrosion in CASC were analysed. The reinforcement corrosion degradation rule was determined, which provided theoretical support for the durability improvement, security assessment, service life prediction and service quality control of CASC structures in marine islands and reef engineering.

The corrosion resistance was enhanced with increased concrete cover thickness, and the concrete cover thickness for organic new coated steel should be at least 5.5 cm to reduce the reinforcement corrosion risks in CASC structures. The corrosion resistance of different types of reinforcements followed the rule: 2205 duplex stainless steel > 316 stainless steel > organic new coated steel > zinc-chromium coated steel > common steel. In the early exposure stage, the anti-corrosion effectiveness of the calcium nitrate inhibitor (CN) was superior to that for the amino alcohol inhibitor (AA). With the extension of exposure time, the decreasing rate of anticorrosion effectiveness of CN was higher than that of AA.

Reinforcement corrosion of CASC in a marine environment was studied. Concrete cover thickness, exposure time, reinforcement type and inhibitor influenced the reinforcement corrosion were investigated. New technique of reinforcement anti-corrosion in marine engineering was proposed. Possible applications of CASC in marine engineering structures were suggested.

This study aims to assess the performance of SAF 2205 duplex stainless steel against pure wear, tribo-corrosion, corrosion and the synergism between wear and corrosion. The effect of plasma nitriding conducted at low temperature (380°C) on SAF 2205 steel was analyzed.

Three systems were used for assessing the synergism between wear and corrosion: tribo-corrosion – wear tests conducted using the micro-scale abrasion test, performed under a slurry of alumina particles containing 3.5% NaCl; pure wear – tests conducted using the previous system but isolated in a glovebox with a 99% N2 atmosphere; and cyclic polarization under 3.5% NaCl solution. A hard nitrided layer of 3 µm thickness was characterized using X-ray diffraction, presenting expanded austenite.

The wear mode after micro-scale abrasion tests changed in the absence of an oxygen atmosphere. During pure wear, a mixed mode was identified (rolling + grooving), with the grooving mode more intense for the untreated steel. For tribo-corrosion tests, only rolling wear was identified. For all cases, the nitrided samples presented less wear. The corrosion results indicated a higher repassivation potential for the nitrided condition.

The synergism was more positive for the nitrided sample than for the untreated one, which can be considered for surface treatments of duplex stainless steels in practical applications.

A detailed description of wear mechanisms showed a significant change in the presence of oxygen atmosphere, a new approach for isolating pure wear.

The aim of this paper was to investigate the effect of strain rate on microstructure and corrosion behavior of 2205 duplex stainless steel, after high-temperature compression tests.

The specimens were prepared using a Gleeble3800 thermo-simulation machine over a range of temperatures from 850 to 1,250°C and strain rates from 0.005 to 5 s−1, and the corresponding flow curves and deformation microstructure obtained were further analyzed. To evaluate the effect of strain rate on corrosion behavior, potentiodynamic polarization tests and double-loop electrochemical potentiodynamic reactivation (DL-EPR) were used to characterize the electrochemical performance.

Compared with strain rate of 0.5 s−1, the worst corrosion resistance behavior from the potentiodynamic polarization test results after deformation at 0.005 s−1 was attributed to more austenite (γ) and ferrite (δ) grain boundaries or δ/γ phase interface formation due to the better effect of γ dynamic recrystallization (DRX) or δ dynamic recovery (DRV). Increasing strain rate to 5 s−1 lowered the corrosion resistance, due to the increase in dislocation density. At the low strain rate of 0.005 s−1, the susceptibility to intergranular corrosion (IGC) was comparatively high after deformation at 1050 and 1150°C with more γ/γ grains and δ/γ phase boundary formation, which was lowered with the strain rate increase to 0.5 s−1, due to suppressing effect of γ DRX.

The paper provides the scientific basis for the practical application of hot working of 2205 duplex stainless steel.

There are obvious differences in corrosion resistance of different 2205 welding joints with different ratios of austenite and ferrite, from the top to the bottom, the austenite content decreased gradually while the ferrite increased. In each region of welded joint, the pitting resistance number of ferrite is higher than that of austenite; pitting corrosion is more likely to occur in austenite phase first on the top region of the weld and in the secondary phase precipitates on the other regions of the weld. The fluctuation of the ratio of austenite and ferrite has a great influence on performance of passive film in 3.5 per cent NaCl solution.

To study the corrosion behavior of welded joint, the samples were obtained by laser hybrid welding. Pitting corrosion was studied in different area of welded joint. The Mott–Schottky curves of welded joints were measured to study the passive film on the different welded joint area.

Due to the difference of heat input and the limit of filler depth of the wire, the microstructure of duplex stainless steel laser welding joint has obvious difference in the thickness direction. In addition, there will be harmful secondary phase (such as chromium nitride and σphase) precipitates in the lower part of the joint. For the welded joint, the corrosion resistance decreases with the increase in the difference of the microstructure. Pitting corrosion usually takes the two phases as the nucleation point and grows up. The surface of 2205 duplex stainless steel laser hybrid welding joint cannot form a complete passive film in 3.5 per cent NaCl solution, and the more the ratios of austenite and ferrite deviate from equilibrium position (50:50), the worse the performance of passive film is.

In this paper, the authors attempt to establish the correlation between the semiconductor electronic properties of passive film and the difference of microstructures and the component in a joint welded by laser hybrid welding. The effect of passive film on the corrosion resistance of the weld was further investigated.

Coral aggregate seawater concrete (CASC) is a new type of lightweight aggregate concrete that is becoming widely used in reef engineering. To investigate the corrosion behavior of different kinds of rebar in CASC exposed to simulated seawater for 0-270 d, the electrochemical techniques, including linear polarization resistance (LPR) technique and the electrochemical impedance spectroscopy (EIS), were used in the present work.

The electrochemical techniques, including LPR technique and the EIS, were used in the present work.

Based on the time-varying law of linear polarization curves, self-corrosion potential (E_corr), polarization resistance (R_p), corrosion current density (I_corr), corrosion rate (i), and the characteristics of EIS diagrams for different types of rebar in CASC, it can be found that the anti-corrosion property of them can be ranked as epoxy resin coated steel > 2205 duplex stainless steel (2205S) > 316 L stainless steel (316 L) > organic coated steel > ordinary steel. Additionally, the linear regression equation between R_p and charge transfer resistance (R_ct) was established. Finally, the EIS corrosion standard of rebar was established from the LPR corrosion standard, which provides a direct standard for the EIS technique to determine the condition of rebar in CASC.

The linear regression equation between polarization resistance and charge transfer resistance was established. And the EIS corrosion standard of rebar was established from the LPR corrosion standard, which provides a direct standard for the EIS technique to determine the condition of rebar in CASC.