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The present study focused on demonstrating the versatility of the slurry deposition technique to produce aluminide coatings to protect components from high-temperature corrosion in a broad temperature range, from 400 to 1400 °C. This is a simpler and low-cost coating technology used as an alternative to CVD and pack cementation, which also allows the coating of complex geometries and offers improved and simple repairability for a lot of industrial applications, along with avoiding the use of non-hazardous components. Slurry aluminide coatings from a proprietary water-based-Cr6+ free slurry were produced onto four different substrates: A516 carbon steel, 310H AC austenitic steel, Ti6246 Ti-based alloy and TZM, a Mo-based alloy. The resulting coatings were thoroughly characterised by FESEM and XRD, mainly so that the identification of microstructures and appropriate phases was reported for each coating. The importance of surface preparation and heat treatment as key parameters for the coating final microstructures was also evidenced, and how those parameters can be optimised to obtain stable intermetallic phases rich in Al to sustain the formation of a protective Al2O3 oxide scale. These coating systems have applications in diverse industrial environments in which high-temperature corrosion limits the lifetime of the components. [ABSTRACT FROM AUTHOR]

Keeping recruitment of green and cost-effective solutions for environmental challenges in view, the current work was designed to solve the problems related to metal corrosion in the aqueous phases of crude oil in chemical industries. Green materials can play an important role in protecting metals from this corrosion. Hence, the green anti-corrosion material based upon gossypol derivate is suggested to solve the above problems. The electrochemical characteristics were appraised by cyclic voltammetry, electrochemical impedance spectroscopy, potentiodynamic polarization, and electrochemical noise methods. The thermodynamics were studied by gravimetric analyses. The surface morphology was scrutinized using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Density functional theory and molecular dynamic simulations were exploited in theoretical analyses. The gossypol derivate is green, non-toxic, more efficient, non-volatile, and chemically stable anti-corrosion material for gas and oil industries. Carbon steel corrosion simulated in aqueous phases of crude oil (NaCl solutions (1.0 M) saturated with H2S and CO2) was maximally prohibited by forming a protective layer of binaphthalene. Its protection degree is 96.71% (at 100.0 mg/L/0.107 mM). The gossypol ring is a suitable core for preparing the next modification materials to protect against corrosion. The rigid adsorption progressed mainly via hydroxyl functional moieties. Compared to the inhibition behavior of the neutral form of gossypol, the optimized protonated form causes a greater inhibition. A gossypol derivate showed excellent anti-corrosive efficiency as a green inhibitor. [ABSTRACT FROM AUTHOR]

The paper presents the results of non‐destructive testing examinations, metallographic tests and risk assessment of degradation related to corrosion of amine regeneration unit in a desulphurisation system. Intensive corrosion resulting from acid gases environment upon water condensation causes perforation of the pipeline. Detailed analysis reveals cracking related to the mechanism of wet H2S. Hydrogen penetration, resulting from the wet H2S process, causes a decrease in mechanical properties of steel and an increase in hydrogen content inside steel. Corrosion results mostly from high stream velocity, the presence of acid gases (with high ammonia content), the presence of amine and low stream temperature. [ABSTRACT FROM AUTHOR]

Hereditary modification is based on the effect of structural heredity, which is considered from the standpoint of nanostructured crystallization of casting alloys. The mechanism of hereditary modification of carbon steels and cast irons is nanostructured and is determined by the stability of the crystallization centers of microcrystals of the δ-phase, austenite and eutectic graphite, which is inversely proportional to the concentration of oxygen dissolved in the melts. This concentration increases with increasing overheating and/or dwell time of melts, which reduces the efficiency of hereditary modification of carbon steels and cast irons. [ABSTRACT FROM AUTHOR]

Abstract—The pipes of the gas distribution network of the city of Minsk after operation for 50 years have been investigated. The main defects of the pipes are found to be surface defects having formed during their production, and the corrosion damage to the pipe surface is associated with a violation of the continuity of waterproofing. On the whole, the structure of the pipes meets the requirements for grade 20 and 10 steels, including those of the basic standards (GOST 8233–56, 5639–82, 5640–68, 1778–70). The mechanical properties of the metal in pipeline sections without damage meet the requirements for carbon steels. The stress level is below the yield strength. In the absence of external mechanical actions, the preservation of the air tightness of the insulation coating can be considered a sufficient sign of extending the service life of the gas pipes. [ABSTRACT FROM AUTHOR]

Failures in welded joints constitute a challenge that requires a scientific approach due to its phenomenological essence. This work determines the causes of failure in welded joints of a piping system, which were carried out with the SMAW process. Visual inspection, tension tests of the base material, chemical analysis by optical emission spectrometry as well as macrograph and metallography of the welded joint were carried out to a sample extracted from the damaged area using a cooled disc. In conclusion, we can say that the cause of failure has its origin in the poor procedure applied when welding, although other factors such as mechanical fatigue or an inappropriate design could also have been present. [ABSTRACT FROM AUTHOR]

Q235 carbon steel is a commonly used engineering material, but its application in marine environments is limited by its susceptibility to corrosion, especially localized corrosion that can lead to material perforation. Effective inhibitors are crucial to addressing this issue, particularly in acidic environments where localized areas become increasingly acidic. This study reports the synthesis of a new imidazole derivative corrosion inhibitor and evaluates its effectiveness in corrosion inhibition performance using potentiodynamic polarization curve and electrochemical impedance spectroscopy techniques. High-resolution optical microscopy and scanning electron microscopy were employed for surface morphology analysis. Fourier-transform infrared spectroscopy was used to explore the protection mechanisms. The results demonstrate that the self-synthesized imidazole derivative corrosion inhibitor offers an excellent corrosion protection performance for Q235 carbon steel in a 3.5 wt. % NaCl acidic solution. This inhibitor can provide a new strategy for carbon steel corrosion protection. [ABSTRACT FROM AUTHOR]

In this study, Oregano (Origanum vulgare) leaf essential oil was studied as an environmental-friendly anticorrosion agent for carbon steel in aggressive hydrochloric acid. The corrosion inhibition of O. vulgare was characterized by surface morphology, electrochemical, weight loss, theoretical and computational methods. It was found that the highest inhibition performance of O. vulgare was 85.64% at 2 g/l in 1 M HCl. The results of Langmuir isotherm and adsorption thermodynamics investigation demonstrated that the O. vulgare inhibitor adsorbed on the metal surface by the formation of rigid covalent bonds. The adsorption and inhibition centers of the selected inhibitor were studied by the computational methods, resulting in that the hydroxyl functional groups and benzoyl rings are mainly responsible for the high inhibition efficiency. [ABSTRACT FROM AUTHOR]

Abstract The effect of carbon doping contents on the microstructure, hardness, and corrosion properties of heat-treated AISI steel grades of plain carbon steel was investigated in this study. Various microstructures including coarse ferrite-pearlite, fine ferrite-pearlite, martensite, and bainite were developed by different heat treatments i.e. annealing, normalizing, quenching, and austempering, respectively. The developed microstructures, micro-hardness, and corrosion properties were investigated by a light optical microscope, scanning electron microscope, electromechanical (Vickers Hardness tester), and electrochemical (Gamry Potentiostat) equipment, respectively. The highest corrosion rates were observed in bainitic microstructures (2.68–12.12 mpy), whereas the lowest were found in the fine ferritic-pearlitic microstructures (1.57–6.36 mpy). A direct correlation has been observed between carbon concentration and corrosion rate, i.e. carbon content resulted in an increase in corrosion rate (2.37 mpy for AISI 1020 to 9.67 mpy for AISI 1050 in annealed condition).

The electrospark deposition (ESD) technique is a low-heat-input process that has great potential for coating applications and the restoration of damaged high-value parts. Carbon steels are commonly used as a substrate material for ESD coatings. However, we demonstrated that carbon steels could be used successfully as the electrode tool for the ESD process. Furthermore, ESD coatings commonly have a high as–deposited roughness. In view of this, in order to reduce the roughness of the ESD coatings, electrodeposition as a tool to alter surface morphology was investigated. Hence, the micro-leveling power of several electrolytes for Ni, Fe-W, Fe, and Cr electrodeposition were evaluated. The maximum leveling effect was detected for Ni electroplated from the Watts electrolyte. Thus, the novel hybrid coatings based on an ESD layer and a subsequent layer of electrodeposited Ni were obtained. ESD layers were obtained by using the following electrode tools as anodes: several types of carbon steels (St20, St30, and St45), alloys T15K6 (WC + TiC + Co), CuNiZn; and NiCr. The morphology and structure of the obtained hybrid coatings with an electrodeposited Ni top-layer was analyzed and compared to ESD coatings from the point of view of their wear and corrosion behavior. The wear rate of the novel ESD coatings based on carbon steels was comparable with coatings obtained using the NiCr electrode tool. Moreover, for all the studied cases, the corrosion resistance of the hybrid coatings was higher than for their ESD counterparts and close to electrolytic chromium. [ABSTRACT FROM AUTHOR]

Solid solutions in Fe-C, Fe-N, Nb-O, Ta-O or W-C systems consist of a body-centered lattice containing C, N or O interstitials in octahedral sites. Among these systems, carbon-supersaturated iron has a major industrial interest. At low temperature, it can be found in the form of ferrite (bcc-Fe) or martensite (bct-Fe and bco-Fe). Based on a mean-field elasto-chemical model of the interstitial–strain interaction, we investigated numerically the thermodynamic stability of the three possible crystal forms. The phase stability depends not only on temperature and solute carbon content but also on the mechanical stress state of the crystal. We computed phase diagrams mapping the equilibrium phase and orientational variant as function of the components of the stress tensor. These maps are intended to help understanding the spatial distribution of orientational variants in martensite nano-crystals and in Cottrell atmospheres around dislocations. [ABSTRACT FROM AUTHOR]

In quenched Fe-C (C: 0.0∼2.0 wt.%) binary alloys, the body-centered cubic (BCC) {112}-type twin structure (density, size and morphology) in martensite was investigated by means of transmission electron microscopy (TEM). In the samples quenched to room temperature, the twin density increased as the carbon content increased. In the carbon-free or pure iron sample, no twin structure was observed. In high carbon martensite, a high density of twins could be seen with twin thickness of 1 nm–2 nm, which is of the scale of the smallest α-Fe grain. The twin density variance is discussed based on a detwinning process, which occurs upon cooling. The twin, as an initial product of martensitic transformation, would experience a higher temperature auto-tempering process in low carbon alloys than in high carbon samples. A noticeable detwinning process takes place in low carbon alloys and results in a low density of twins observed at room temperature. Martensite starting (Ms) temperature plays a crucial role in the detwinning or auto-tempering effect on the twins.

The review is devoted to the state-of-the-art views on the microstructure evolution in structural and tool carbon steels during the surface severe plastic deformation (SPD). The main focus is on the effects of the nanocrystallization in the near-surface area of the low-carbon steel (C 0.05–0.2%), medium-carbon steel (C 0.35–0.65%), and high-carbon steel (C 1.0–1.5%). It is reviewed the following advanced surface SPD methods for the metal surfaces in recent years: an ultrasonic impact peening (UIP), high-frequency impact peening (HFIP), air blast shot peening (ABSP), surface mechanical attrition treatment (SMAT), and laser shock peening (LSP). Microstructure evolution before and after SPD is studied by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The effects of the SPD parameters on the nanocrystalline modification of such main phase components of the carbon steels as ferrite, pearlite and cementite are analysed. The atomic mechanism of the nanocrystallization is presented. The strain-hardening effect induced by SPD is demonstrated by the data of the near-surface microhardness profiles.

The effect of carbon doping contents on the microstructure, hardness, and corrosion properties of heat-treated AISI steel grades of plain carbon steel was investigated in this study. Various microstructures including coarse ferrite-pearlite, fine ferrite-pearlite, martensite, and bainite were developed by different heat treatments i.e. annealing, normalizing, quenching, and austempering, respectively. The developed microstructures, micro-hardness, and corrosion properties were investigated by a light optical microscope, scanning electron microscope, electromechanical (Vickers Hardness tester), and electrochemical (Gamry Potentiostat) equipment, respectively. The highest corrosion rates were observed in bainitic microstructures (2.68–12.12 mpy), whereas the lowest were found in the fine ferritic-pearlitic microstructures (1.57–6.36 mpy). A direct correlation has been observed between carbon concentration and corrosion rate, i.e. carbon content resulted in an increase in corrosion rate (2.37 mpy for AISI 1020 to 9.67 mpy for AISI 1050 in annealed condition). [ABSTRACT FROM AUTHOR]

Understanding the ultrafine substructure in freshly formed Fe-C martensite is the key point to reveal the real martensitic transformation mechanism. As-quenched martensite, whose transformation temperature is close to room temperature, has been investigated in detail by means of transmission electron microscopy (TEM) in this study. The observation results revealed that the freshly formed martensite after quenching is actually composed of ultrafine crystallites with a grain size of 1–2 nm. The present observation result matches well with the suggestion based on X-ray studies carried out one hundred years ago. Such nanocrystals are distributed throughout the entire martensite. The whole martensite shows a uniform contrast under both bright and dark field observation modes, irrespective of what observation directions are chosen. No defect contrast can be observed inside each nanocrystal. However, a body-centered cubic {112}<111>-type twinning relationship exists among the ultrafine α-Fe grains. Such ultrafine α-Fe grains or crystallites are the root cause of the fine microstructure formed in martensitic steels and high hardness after martensitic transformation. The formation mechanism of the ultrafine α-Fe grains in the freshly formed martensite will be discussed based on a new γ → α phase transformation mechanism. [ABSTRACT FROM AUTHOR]

The precipitation behavior and transformation mechanism of cementite in low‐ and medium‐carbon steels (0.04–0.5% C) after hot rolling are studied using ultrafast cooling (UFC) technology. The results show that the carbon concentration and stop‐cooling temperature are the primary factors influencing the precipitation behavior of nanoscale cementite. It is found that 1) the pearlite grows discontinuously, and the nanoscale cementite is dispersed and precipitated in the 0.17% C and 0.33% C steels cooled by UFC from 953 to 873 K without the addition of microalloys, and 2) the yield strength increases gradually with decreasing UFC stop temperature. The discontinuous growth state of cementite is attained when ferrite and pearlite formation occurs alternately and competitively on the α/γ interface forefront. The growth length of ferrite when vα is equal to vp decreases significantly with the increase in carbon concentration. Moreover, the difference between the ferrite growth length and pearlite lamellar spacing decreases with the decreasing transformation temperature. The moderate carbon concentration and lower stop‐cooling temperature are more conducive to breaking up the continuity of the pearlite growth. This study of the transformation behavior of degenerate pearlite under continuous cooling conditions is more instructive for actual production. [ABSTRACT FROM AUTHOR]

The adoption of the ultrafast heating (UFH) process has gained much attention in the last few years, as the green energy and minimization of CO2 emissions are the main aspects of contemporary metal science and thermal treatment. The effect of ultrafast heating (UFH) treatment on carbon steels, non-oriented grain (NGO) electrical steels, and ferriticor austenitic stainless steels is reported in this review. The study highlights the effect of ultrarapid annealing on microstructure and textural evolution in relation to microstructural constituents, recrystallization temperatures, and its effect on mechanical properties. A strong influence of the UFH process was reported on grain size, promoting a refinement in terms of both prior austenite and ferrite grain size. Such an effect is more evident in medium–low carbon and NGO steels than that in ferritic/austenitic stainless steels. A comparison between conventional and ultrafast annealing on stainless steels shows a slight effect on the microstructure. On the other hand, an evident increase in uniform elongation was reported due to UFH. Textural evolution analysis shows the effect of UFH on the occurrence of the Goss component (which promotes magnetic properties), and the opposite with the recrystallization g-fiber. The recovery step during annealing plays an important role in determining textural features; the areas of higher energy content are the most suitable for the nucleation of the Goss component. As expected, the slow annealing process promoted equiaxed grains, whereas rapid heating promoted microstructures with elongated grains as a result of the cold deformation. [ABSTRACT FROM AUTHOR]

This study analyzes the microstructural aspects of 35 and U8 carbon steels subjected to deforming cutting using metallographic analysis and scanning electron microscopy. X-ray phase analysis shows that the amount of retained austenite after deformation cutting (DC) is much greater than that after bulk quenching of steels of the same composition. Possible causes of the inhibition of martensitic transformation in steels during DC are considered. [ABSTRACT FROM AUTHOR]

Q235 carbon steel is a commonly used engineering material, but its application in marine environments is limited by its susceptibility to corrosion, especially localized corrosion that can lead to material perforation. Effective inhibitors are crucial to addressing this issue, particularly in acidic environments where localized areas become increasingly acidic. This study reports the synthesis of a new imidazole derivative corrosion inhibitor and evaluates its effectiveness in corrosion inhibition performance using potentiodynamic polarization curve and electrochemical impedance spectroscopy techniques. High-resolution optical microscopy and scanning electron microscopy were employed for surface morphology analysis. Fourier-transform infrared spectroscopy was used to explore the protection mechanisms. The results demonstrate that the self-synthesized imidazole derivative corrosion inhibitor offers an excellent corrosion protection performance for Q235 carbon steel in a 3.5 wt. % NaCl acidic solution. This inhibitor can provide a new strategy for carbon steel corrosion protection.

The electrospark deposition (ESD) technique is a low-heat-input process that has great potential for coating applications and the restoration of damaged high-value parts. Carbon steels are commonly used as a substrate material for ESD coatings. However, we demonstrated that carbon steels could be used successfully as the electrode tool for the ESD process. Furthermore, ESD coatings commonly have a high as–deposited roughness. In view of this, in order to reduce the roughness of the ESD coatings, electrodeposition as a tool to alter surface morphology was investigated. Hence, the micro-leveling power of several electrolytes for Ni, Fe-W, Fe, and Cr electrodeposition were evaluated. The maximum leveling effect was detected for Ni electroplated from the Watts electrolyte. Thus, the novel hybrid coatings based on an ESD layer and a subsequent layer of electrodeposited Ni were obtained. ESD layers were obtained by using the following electrode tools as anodes: several types of carbon steels (St20, St30, and St45), alloys T15K6 (WC + TiC + Co), CuNiZn; and NiCr. The morphology and structure of the obtained hybrid coatings with an electrodeposited Ni top-layer was analyzed and compared to ESD coatings from the point of view of their wear and corrosion behavior. The wear rate of the novel ESD coatings based on carbon steels was comparable with coatings obtained using the NiCr electrode tool. Moreover, for all the studied cases, the corrosion resistance of the hybrid coatings was higher than for their ESD counterparts and close to electrolytic chromium.

The effect of cementite morphology on the crack initiation and growth path was studied using in situ electrochem-ical micro-cantilever bending (ECCB) technique under hydrogen (H) charging. Two carbon steels with lamellar cementite morphology (pearlitic microstructure) and spherical or broken lamellas cementite morphology (spheroidite microstructure), both with approximately the same carbon equivalent, were used in this study. The ECCB tests were performed in H-free and two H charging steps with −1050 mV and −1550 mV charging potential versus Ag/AgCl reference electrode. The results show that both materials are resistant to crack initiation in the H-free condition while under −1050 mV charging, crack propagates through the grain boundaries in a tortuous path in spheroidite mi-crostructure and the lamellar microstructure displayed a higher strength with small cracks propagating through both the grain boundaries and the lamellas. A drastic load decrease in the load-displacement (L-D) curve happened under −1550 mV charging for both microstructures accompanied by a straight crack growth path in spheroidite microstruc-ture, independent of grain boundaries or ferrite-cementite interfaces while a competition between the shear crack growth mechanism and the interfacial cracking determines the crack growth path in the lamellar microstructure. • Cementite morphology's role on the hydrogen induced crack growth path is studied. • In low H fugacity, cementite-ferrite interface failed in spheroidite microstructure. • In pearlite microstructure few H-induced interface cracks formed, In low H fugacity. • In high H fugacity, crack grows regardless of the interfaces in S microstructure. • Interfacial cracking and shear mechanisms lead the crack in P microstructure. [ABSTRACT FROM AUTHOR]

In order to study the influence of sulfate-reducing bacteria(SRB) on the corrosion behavior of carbon steel under the corrosive working conditions in Tahe Oilfield, the tests were carried out by simulating the corrosive working conditions with a high temperature and high pressure autoclave to measure the bacteria counts, the corrosion morphology and pitting depth was analyzed with scanning electron microscope and laser scanning confocal microscope, and the corrosion rate was calculated using a weight loss method. The study found out that, under the condition of high salinity(the mass concentration of Cl- is 11.87×104 mg/L), the temperature rose from 40 ℃ to 80 ℃, and the bacteria counts reduced from 110 cells/mL to 25 cells/mL. The maximum pitting rate, 5.475 mm/a, occurred at 40 ℃, and at 60 ℃, the bacteria activity decreased and the pitting rate decreased at first and then rose with the salinity increase. Under 60 ℃ condition with high salinity, changing the partial pressure of H2S had no obvious effect on bacteria count in solution, but the pitting rate and uniform corrosion rate decreased. The study results indicate that SRB can survive under the extreme conditions of Tahe Oilfield, temperature rise and increasing of salinity may result in the decreasing of SRB concentration, but partial pressure of H2S has little influence on SRB concentration. Temperature is an important factor affecting SRB corrosion. The higher the temperature is, the slighter the pitting caused by SRB is. Additionally, increasing of salinity may affect the activity of bacteria, further weakening the pitting due to bacteria.

The article presents the results of metal science research on the influence of nitrogen and vanadium microalloying of carbon steels with a carbon content of 0.5–0.8 wt.% on the thermodynamic and thermokinetic parameters of the phase redistribution of nitrogen and vanadium, as well as the formation of ferrite-pearlite, bainite and martensite structures and their transformation during high tempering. It was shown that the dispersion of the structure formed during cooling after austenitization, as well as the decrease of the growth rate and coagulation of cementite particles are the result of dispersion of the pearlite, bainite and martensite tempering structures. The positive effect of the dispersion of structures of all levels on the improvement of the mechanical properties (yield point, impact toughness, wear resistance under sliding and rolling friction, etc.) of the steel modified by nitrogen and vanadium microalloying is noted. That provides good prospects for the effective use of steels with dispersion nitride hardening for the production of railway wheels and rails.

The review is devoted to the state-of-the-art views on the microstructure evolution in structural and tool carbon steels during the surface severe plastic deformation (SPD). The main focus is on the effects of the nanocrystallization in the near-surface area of the low-carbon steel (C 0.05-0.2%), medium-carbon steel (C 0.35-0.65%), and high-carbon steel (C 1.0-1.5%). It is reviewed the following advanced surface SPD methods for the metal surfaces in recent years: an ultrasonic impact peening (UIP), high-frequency impact peening (HFIP), air blast shot peening (ABSP), surface mechanical attrition treatment (SMAT), and laser shock peening (LSP). Microstructure evolution before and after SPD is studied by an optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The effects of the SPD parameters on the nanocrystalline modification of such main phase components of the carbon steels as ferrite, pearlite and cementite are analysed. The atomic mechanism of the nanocrystallization is presented. The strain-hardening effect induced by SPD is demonstrated by the data of the near-surface microhardness profiles. [ABSTRACT FROM AUTHOR]

Accurate corrosion predictions are vital to safe and optimised designs of marine assets. Traditional approaches, including those used to develop rule requirements, seek to use empirical regressions to model corrosion, but most are solely time-dependent. This may lead to conservative damage estimates and hence heavy and inefficient ships. To provide more accurate predictions, this paper presents an interpretable machine learning algorithm based on data fusion of ship survey and experimental measurements. The corrosion behaviour in bulk carrier ballast tanks is interpreted through a sensitivity analysis which quantifies the relationships between operational/environmental factors and the corrosion rate. The prediction accuracy is improved by a minimum of 82% when compared to the two representative empirical models, with a mean absolute error down to 0.10 mm.

Understanding the ultrafine substructure in freshly formed Fe-C martensite is the key point to reveal the real martensitic transformation mechanism. As-quenched martensite, whose transformation temperature is close to room temperature, has been investigated in detail by means of transmission electron microscopy (TEM) in this study. The observation results revealed that the freshly formed martensite after quenching is actually composed of ultrafine crystallites with a grain size of 1–2 nm. The present observation result matches well with the suggestion based on X-ray studies carried out one hundred years ago. Such nanocrystals are distributed throughout the entire martensite. The whole martensite shows a uniform contrast under both bright and dark field observation modes, irrespective of what observation directions are chosen. No defect contrast can be observed inside each nanocrystal. However, a body-centered cubic {112}-type twinning relationship exists among the ultrafine α-Fe grains. Such ultrafine α-Fe grains or crystallites are the root cause of the fine microstructure formed in martensitic steels and high hardness after martensitic transformation. The formation mechanism of the ultrafine α-Fe grains in the freshly formed martensite will be discussed based on a new γ → α phase transformation mechanism.

The effect of copper content, on the nature and roughness of the corrosion products formed on carbon steel in a synthetic brine saturated with CO2 at room temperature, was studied using a jet impact chamber tuned at different impact angles. Corrosion rate was determined by linear polarization resistance, and steels behavior was described by electrochemical impedance spectroscopy. The corrosion products formed on steel were characterized by scanning electron microscopy, electron-dispersive analysis, optical profilometry and grazing incidence X-ray diffraction. The chemical composition and morphology of corrosion products affected corrosion rate. For the different steels, Fe3C and iron oxides provided a low degree of protection. Steels with higher copper contents showed a decrease in corrosion rate due to the formation of copper oxides (CuO and Cu2O), which apparently offered a stronger physical barrier between the aggressive environment and the substrate. Small roughness of corrosion products was correlated with more compact and uniform layers of corrosion products and also to lower corrosion rates. [ABSTRACT FROM AUTHOR]