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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 interstitialstrain 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.

International audience; Martensite is a major constituent of Fe-C alloys. Its metastable body-centered tetragonal structure provides high tensile strength to martensitic steels. Recent experiments highlighted the benefit of large solute carbon content to the strength and ductility of the so-called virgin martensite obtained by sub-zero quench. The results suggest a significant contribution of the elastic and anelastic deformation of the martensite crystals to the rheology of these alloys. In order to shed light on the influence of carbon content on the anelastic response, we investigated theoretically the behavior of solute carbon during Snoek relaxation. Thanks to a linear-response approach, we obtained analytical formulae of the atomic mobilities and the thermodynamic affinities, from which the relaxation strength and time were derived. We unravel the unexpected decrease of the relaxation strength and time when solute carbon content is increased. Relaxation kinetics is explained at the atomic scale by an indirect mechanism of carbon migration in martensite, at variance with ferrite. We emphasize the onset of non-linear effects when the applied stress is high.

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.

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.

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.

International audience; Snoek relaxation in bcc crystals is the delayed strain response to an applied stress resulting from the interaction of the interstitial atoms with the stress field. It is responsible for the Snoek peak observed in internal friction measurements of ferrite. However, although martensite is carbon supersaturated, several authors denied the possibility of Snoek relaxation in bct-martensite. We investigated this matter by means of Monte Carlo simulations and mean-field thermo-kinetic modeling. Our results show that Snoek relaxation does occur in bct-martensite. The computed Snoek profiles of temperature-dependent and frequency-dependent internal friction exhibit unexpected features: both peak height and peak temperature decrease when the carbon content is increased. We explain this behavior in the frame of the linear-response approximation. Our theoretical predictions are in qualitative agreement with experiments.

Boronizing is a thermochemical treatment performed to produce hard and wear-resistant surface layers. In order to control the process and obtain boride layers with the desired properties, it is very important to know how the boronizing parameters and the chemical composition of the treated steel affect the boronizing. The aim of the present study is to investigate the influence of carbon content in carbon steels, boronizing temperature, and boronizing duration on the growth kinetics of boride layers. For this purpose, three carbon steels (C1y5, C45, and C70W2) were boronized in solid medium. The experimental results show that there is a linear relationship between the carbon content and the activation energy values, and between the carbon content and the frequency factors. In addition, a statistical analysis was performed to determine the contribution of each factor. The ANOVA showed that boronizing temperature has the highest effect on the boride layer thickness, followed by the boronizing duration, while the carbon content of the steel has the least effect on the boride layer thickness. Based on a regression model, an empirical equation was derived to estimate the thickness of the boride layer on carbon steels as a function of carbon content, boronizing temperature, and duration.

The rust layer formed on carbon steel exposed to natural marine and urban-continental envi-ronments for up to 50 years was studied. Mineralogical phase composition of the rust layer was evaluated by X-ray diffraction (XRD), akaganeite, goethite, lepidocrocite, magnetite, and amorphous phases were identified. Morphological characterization of the specimens was performed using scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) microanalysis. Mechanical stress generated during the formation of the oxide causes exfoliation-induced breakout of the rust layer. Volume variation generated by structural transformations and crystallization pressure (Δp) of the crystalline phases were analyzed to assess the mechanical stress on the rust and a linear relationship was found between the molar volume expansion ratio coefficient (α) and the Δp param-eter. The highest Δp was yielded by goethite (374.99 MPa), while akaganeite presented the highest α value (3.29)., D.M. Bastidas, J. Ress, U. Martin and J. Bosch acknowledge funding from The University of Akron, Fellowship Program FRC-207367.

Приведены математические модели зависимости относительной удельной деформирующей силы, создаваемой пуансоном, и соотношения высот выдавленных стенок от размеров детали, построенные по результатам экспериментального исследования выдавливания сдвоенных втулок из стали 10. Показана возможность оценки стойкости пуансонов при выдавливании заготовок из различных сталей. Экспериментально доказано наличие самоцентрирования выдавливающего полость пуансона при двухканальном течении металла заготовки. Продемонстрировано увеличение стойкости пуансонов при объединении выдавливаемых втулок в комбинированные детали., Based on the results of an experimental study of the extrusion of twin bushings from steel 10 mathematical models of the dependence of the relative specific deforming force created by the punch and the ratio of the heights of the extruded walls on the dimensions of the part are given. The possibility of evaluating the resistance of punches when extruding billets from various steels using the constructed models is shown. The existence of self-centering of the extruding cavity during the two-channel flow of the metal of the workpiece in the extrusion process of twin bushings is experimentally proved. Increase of the resistance of punches by combining extruded bushings is demonstrated.

The hot deformation behavior of selected non-alloyed carbon steels was investigated by isothermal continuous uniaxial compression tests. Based on the analysis of experimentally determined flow stress curves, material constants suitable for predicting peak flow stress σp, peak strain εp and critical strain εcrDRX necessary to induce dynamic recrystallization and the corresponding critical flow stresses σcrDRX were determined. The validity of the predicted critical strains εcrDRX was then experimentally verified. Fine dynamically recrystallized grains, which formed at the boundaries of the original austenitic grains, were detected in the microstructure of additionally deformed specimens from low-carbon investigated steels. Furthermore, equations describing with perfect accuracy a simple linear dependence of the critical strain εcrDRX on peak strain εp were derived for all investigated steels. The determined hot deformation activation energy Q decreased with increasing carbon content (also with increasing carbon equivalent value) in all investigated steels. A logarithmic equation described this dependency with reasonable accuracy. Individual flow stress curves of the investigated steels were mathematically described using the Cingara and McQueen model, while the predicted flow stresses showed excellent accuracy, especially in the strains ranging from 0 to εp.

In the present investigation, the effect of main parameters for the development of parts in production such as feed rate and depth were evaluated, obtaining the machining costs depending on the characteristics of the material. The machining process used was that of turning in pieces with carbon steels and cast iron as the base material, varying the feed rate in a range between 0.2mm/tooth and 0.8mm/tooth and the depth between 1mm and 4mm allowing important parameters to be determined such as cutting speed and machine operating conditions to obtain a good final finish without affecting the surface of the piece and in production time required to optimize costs.

FEMS - (Federation of European Materials Societies), Ausforming has been found to be an alternative to the common isothermal treatment which allows to obtain nanobainite. By deforming austenite right before bainitic transformation takes place, austenite strength increases, leading thus to more refined microstructures. However, the anisotropy introduced by deformation has been found to play an important role on bainite transformation. The dilatometric signal during the isothermal step can be significantly altered and the ferrite plates have been found to be highly ordered in some cases. This phenomenon has been associated with the selection of crystallographic variants during the transformation, although a deeper study is still necessary. In this study, three different ausforming treatments have been performed, some of them have presented the previously mentioned phenomenon. Crystallographic analyses have been performed in all cases by means of EBSD and XRD, identifying the reason why such anisotropy effects are only present in some of the cases.

Environmentally assisted cracking (EAC) is a very complex process that develops in materials that involve combining actions of environment and tensile loading. Crack initiation is the least explored stage and is not clearly defined. For this paper, current knowledge of crack initiation mechanisms was reviewed for three types of commercial structure materials exposed to high-temperature (HT) water coolants of power plants, namely ferritic low-alloy (LAS) and carbon (CS) steels, austenitic stainless (AS) steels, and nickel-based alloys. Physicochemical microprocesses engaged in the two earliest phases of the mechanism, the precursor and the incubation phases, are rather specific for each of these materials. In the latter, the slow growth phase, the crack development process passes into a sequence of repeating steps where the specific key microprocesses persist.

Проведено теоретичні розрахунки фізико-хімічних умов процесу дифузійного насичення вуглецевих сталей азотом, вуглецем та хромом в умовах низького тиску в середовищі хлору. Визначено ймовірний фазовий склад в результаті дифузійного насичення. Встановлено температурний інтервал існування карбідів та нітридів. Визначено основні ймовірні конденсовані та газові фази, що утворюються в результаті насичення вуглецевих сталей вуглецем, азотом та хромом. Проаналізовано, як змінюється кількість конденсованої та газової фаз залежно від зміни температури процесу дифузійного насичення. Теоретично встановлено, що в результаті нанесення захисного покриття основними конденсованими фазами будуть два нітриди хрому CrN, Cr2N та карбід хрому Cr3C2. Встановлено температурний інтервал існування основних зміцнюючих фаз. Проаналізовано системи з вмістом кисню. Відзначається утворення оксидів хрому в газовому стані. Визначено, що на першій та заключній стадіях насичення (початкові та кінцеві температури процесу насичення) основною фазою, що містить хром, є карбід хрому та майже повна відсутність нітриду Cr2N. Температура 1300 К – оптимальна температура, при якій утворюється комплексне покриття нітрид-карбід хрому. Таке поєднання шарів захисного покриття буде мати оптимальні властивості з точки зору захисту від зносу та корозії. Theoretical calculations of physical and chemical conditions of the process of diffusion saturation of carbon steels with nitrogen, carbon and chromium in the conditions of low pressure in the chlorine environment are carried out. The probable phase composition as a result of diffusion saturation is determined. The temperature interval for the existence of carbides and nitrides was established. The main probable condensed and gas phases that are formed as a result of saturation of carbon steels with carbon, nitrogen and chromium are identified. It is analyzed how the number of condensed and gas phases changes depending on the temperature of the diffusion coating process. It is theoretically established that two chromium nitrides CrN and Cr2N and chromium carbide Cr3C2 will be the main condensed phases as a result of deposition of the protective coating. The temperature interval for the existence of the main strengthening phases is established. Systems with oxygen content are analyzed. The formation of chromium oxides in the gas state is noted. It is determined that in the first and final stages of saturation (the initial and final temperatures of the saturation process), the main chromium-containing phase is chromium carbide and the almost complete absence of Cr2N nitride. The temperature of 1300 K is the optimum temperature at which a complex chromium carbide-nitride coating is formed. This combination of protective coating layers will have optimum properties in terms of wear and corrosion protection.

A liga Ti-6Al-4V apresenta excelentes propriedades mecânicas, baixa densidade, alta dureza e resistência à corrosão. Entretanto, tratamentos superficiais como a nitretação por plasma são amplamente utilizadas para melhorar a resistência a fadiga desta liga. O objetivo deste trabalho foi tratar termoquimicamente a liga Ti-6Al-4V por meio da nitretação por plasma a fim de verificar a sua influência nas propriedades de fadiga e comparar os resultados obtidos com as não nitretadas. Este tratamento superficial foi realizado com o objetivo de retardar a etapa de nucleação da trinca. A nitretação por plasma foi realizada em temperaturas em torno de 720°C por 4 horas, numa atmosfera de N2, Ar e H2 (5:5:1). Foi realizado um tratamento térmico nas amostras para se obter a microestrutura de Widmanstätten. A temperatura usada foi de 1050°C por 30 minutos. A caracterização microestrutural das amostras nitretadas e não nitretadas foi realizada usando difração de raios X (DRX), microscopia óptica (MO), e microscopia eletrônica de varredura (MEV). Os resultados da difração de raios X das amostras nitretadas mostram a presença de fases: α, β, ε-Ti2N, e δ-TiN e nas amostras não nitretadas as fases α e β. Essas análises revelaram a presença de uma superfície rica em nitretos seguida de uma zona de difusão com nitrogênio na matriz. A rugosidade superficial foi estudada, e foi observada um aumento na rugosidade de 61% após a nitretação. Os testes de fadiga foram realizados em uma máquina de ensaios flexo rotativa, com uma razão de carregamento R=-1 . Os resultados obtidos mostraram que as propriedades de fadiga foram melhoradas após a nitretação por plasma, retardando a etapa de nucleação de trinca. The Ti-6Al-4V alloy presents excellent mechanical properties, low density, high toughness and corrosion resistance. However, surface treatments like plasma nitriding are widely used to improve the fatigue resistance of this alloy. Therefore, the aim of this work was to treat thermochemically Ti-6Al-4V alloy by means of plasma nitriding to verify its influence in fatigue properties and compare the results with the untreated ones. This surface treatment was performed with the purpose of retards the crack initiation. The plasma nitriding was performed in temperatures around 720°C for 4 hours, with a gas atmosphere N2, Ar and H2 (5:5:1). A heat treatment was made in the samples to obtain a Widmanstätten microstructure. The temperature used was 1050°C for 30 minutes. Microstructural characterizations of nitrided and non-nitrided samples were carried out using X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). The XRD results of the nitrided sample showed the presence of the α, β, ε-Ti2N, and δ-TiN phases. These analyses revealed a surface layer rich in nitrides on the surface, followed by a diffusion layer of nitrogen in the matrix. The surface roughness was compared between the nitrided and non-nitrided layer, and it was observed that the roughness increased 61% after the plasma nitriding. Fatigue tests were performed in a rotating bending testing machine with a stress ratio (R=-1). The results obtained in fatigue tests showed that the fatigue properties were improved after plasma nitriding, retarding the crack initiation.

Os experimentos com refletores nucleares de material pesado foram realizados no reator IPEN/MB-01 utilizando-se chapas de aço inoxidável, de aço carbono ou de níquel, num total de 32 chapas de cada material, inseridas adequadamente na face oeste do núcleo do reator. As chapas têm cerca de 3 mm de espessura. A largura e comprimento axial foram suficientes para cobrir todo o núcleo ativo do reator. Tais experimentos foram realizados com cada tipo de material refletor individualmente. Para cada etapa de colocação de chapas foram efetuadas medidas da reatividade devido à inserção destas no núcleo; bem como da posição crítica das barras de controle com BC1 e BC2 igualmente retiradas. Pôde ser observado que o aumento da absorção de nêutrons e consequente diminuição da moderação de nêutrons dominaram toda a física do problema quando foram inseridas poucas chapas de material refletor (cerca de 5 chapas para o aço inoxidável e aço carbono, e 3 chapas no caso do níquel). Na sequência, a reflexão de nêutrons tornou-se importante superando a absorção neutrônica; a reatividade aumentou até ultrapassar a situação sem chapa (excesso de reatividade zero) obtendo-se um acréscimo (ganho líquido) de reatividade com as 32 chapas inseridas (cerca de 162 pcm no caso do aço inoxidável, 37 pcm para o aço carbono e 295 pcm para o níquel). Portanto, observou-se que o núcleo refletido tornou-se mais reativo do que o núcleo sem material refletor. Resultados experimentais inéditos de medidas de reatividade foram obtidos com refletores de níquel. No que concerne a esse tipo de experimento não existe experimento similar na literatura internacional ao realizado no reator IPEN/MB-01. A análise teórica empregando o MCNP-5 e a biblioteca de dados nucleares ENDF/B-VII.0 evidenciou os aspectos físicos de absorção e reflexão de nêutrons nas chapas de material refletor considerados; entretanto apresentou uma discrepância quando a reflexão de nêutrons rápidos domina o fenômeno físico do transporte de nêutrons. Essas tendências foram encontradas independentemente do tipo de refletor pesado empregado nos experimentos. Experiments with heavy-material nuclear reflectors were performed in the IPEN / MB-01 reactor using stainless steel, carbon steel or nickel plates, in a total of 32 plates of each material, properly inserted in the western face of the reactor core. The plates are about 3 mm thick. The axial width and length were sufficient to cover the entire active core of the reactor. Such experiments were performed with each type of reflective material individually. For each step of placement of plates were made measures of reactivity due to the insertion of these in the core; as well as the critical position of the BC1 and BC2 control rods also removed. It could be observed that the increase in neutron absorption and consequent decrease in neutron moderation dominated the whole physics of the problem when a few reflective material plates were inserted (about 5 plates for stainless steel and carbon steel and 3 plates for nickel). Subsequently, neutron reflection has become important overcoming neutron absorption; the reactivity increased until it exceeded the situation without plate (excess of zero reactivity) obtaining an increase (net gain) of reactivity with 32 inserts inserted (about 162 pcm in the case of stainless steel, 37 pcm for carbon steel and 295 pcm for nickel). Therefore, it was observed that the reflected core became more reactive than the core without reflective material. Unpublished experimental results of reactivity measurements were obtained with nickel reflectors. As for this type of experiment, there is no similar experiment in the international literature compared to the IPEN/MB-01 reactor. The theoretical analysis using the MCNP-5 together with nuclear data library ENDF/B-VII.0 evidenced the physical aspects of neutron absorption and reflection in the reflective material plates considered; however, it presented a discrepancy when the reflection of fast neutrons dominates the physical phenomenon of the transport of neutrons. These trends were found independently of the type of the heavy reflector employed in the experiments.

The exposure of carbon steel in marine atmospheres can lead in certain circumstances to the formation of thick rust layers (containing a number of compact laminas) that are easily detached (exfoliated) from the steel substrate, leaving it unprotected and considerably accelerating the corrosion process. This deterioration phenomenon is of particular concern in steel infrastructures located close to the sea (civil constructions, bridges, etc.), whose service lifetime can be extraordinarily limited. High times of wetness of the metallic surface and high chloride ion deposition rates play a decisive role in the formation of this type of rust. Research has been carried out for 1 year in eight pure marine atmospheres with annual average chloride deposition rates of 70–1906 mg Cl-/m2 day. The studied carbon steels consisted of one mild steel, one conventional weathering steel (Corten A), and one high nickel (~3 wt.%) advanced weathering steel (AWS). The paper describes the environmental conditions that lead to the formation of these thick multilaminar rust layers and presents a characterisation study of this singular type of rust using a variety of analysis techniques: scanning electron microscopy/energy-dispersive X-ray spectroscopy, X-ray diffraction, Mössbauer spectroscopy, and transmission electron microscopy/electron diffraction. The Ni-AWS shows greater resistance to the occurrence of rust exfoliation.

© 2015, The Minerals, Metals & Materials Society and ASM International. The efficacy of the conducting polymers as coating on a metallic substrate is strongly dependent on the manner how they are applied. Polypyrrole (PPy)/Ni organic–inorganic hybrid coatings were electropolymerized on commercial carbon steel (AISI 1018) by combining potentiostatic and potentiodynamic techniques. In first instance, it was analyzed the electrodeposition of PPy using a constant potential regime and cyclic voltammetry techniques evaluating different synthesis parameters such as deposition time, applied potential, and potential cycles, respectively. Thereafter, it was used a potentiostatic method to obtain PPy/Ni bilayer films. The morphological, mechanical, and adhesion properties of these films depend on the synthesis parameters. The results revealed that polypyrrole films formed by both methods provide a globular-type structure, although coatings produced by cyclic voltammetry are denser and slightly thicker than those produced potentiostatically. Ni (oxide/hydroxide) particles are capable of sealing the pores of globular PPy coatings, thus increasing the hardness of the carbon steel (CS)/PPy/Ni system. As a result of the study, we have seen that PPy/Ni bilayer films are more uniform, compact and enhanced the hardness when the PPy is obtained by cyclic voltammetry than that observed for potentiostatic approach. Specifically, when four potential cycles are used to electropolymerized pyrrole, the more convenience properties in the CS/PPy/Ni arrangement are obtained., The authors acknowledge the financial support provided by CONACYT through the 133618 and 132660 projects, SIP-IPN 2014-0992, 2014-0164, and SNI-CONACYT.

In the 1980s, three ambitious international programmes on atmospheric corrosion (ISOCORRAG, ICP/UNECE and MICAT), involving the participation of a total of 38 countries on four continents, Europe, America, Asia and Oceania, were launched. Though each programme has its own particular characteristics, the similarity of the basic methodologies used makes it possible to integrate the databases obtained in each case. This paper addresses such an integration with the aim of establishing simple universal damage functions (DF) between first year carbon steel corrosion in the different atmospheres and available environmental variables, both meteorological (temperature (T), relative humidity (RH), precipitation (P), and time of wetness (TOW)) and pollution (SO₂ and NaCl). In the statistical processing of the data, it has been chosen to differentiate between marine atmospheres and those in which the chloride deposition rate is insignificant (

The prolonged exposure of carbon steel in marine atmospheres with high chloride deposition rates and long times of wetness of the metallic surface leads to the formation of thick multilayered rust. The present work proposes an accelerated cyclic laboratory test based on immersion (4.2 min) in a 3.5% NaCl solution followed by drying (12 min) under infra-red lamps in the laboratory atmosphere. The carbon steel corrosion process is thus accelerated, giving rise to the generation of thick rust layers in relatively short times. The rust phases and the structure of the rust layers formed offer a good approximation to the multilayered rust formed in marine atmospheres. The study includes a gravimetric evaluation of the magnitude of corrosive attack and a characterisation of the rust phases and corrosion layers formed using XRD, optical microscopy and SEM.

This study studied the phase transformations occurring at different continuous cooling rates in an air hardening steel used in the rock-crushing industry. Samples of this steel were submitted for calorimetric testing using the differential scanning calorimetry (DSC) technique. In the experimental run, the samples were heated at the rate of 0.33 °C/s from 50 to 1050 °C and equilibrated at this temperature for 900 s, then cooled at seven different cooling rates between 0.05 and 0.5 °C/s. For all the cooling rates, the DSC traces of the samples showed a first exothermic peak at about 500 °C and for samples cooled at rates higher than 0.15 °C/s, a second exothermic peak at about 295 °C was observed. From the microstructural investigations carried out by light microscopy (LM) and scanning electron microscopy (SEM), it was observed that all the samples after DSC treatment were characterized by the presence of bainite. In the samples cooled at rates higher than 0.15 °C/s, martensite was also detected. Comparing the results of DSC and SEM, it was concluded that the first peak at 500 °C corresponds to the austenite -> bainite transformation, while the second peak at 295 °C corresponds to the austenite -> martensite transformation. The experimentally determined bainite and martensite start temperatures were compared to the values derived from a number of well-known empirical equations.

The morphological structures displayed by iron oxides present a very wide range of shapes and sizes, reflecting to a large extent the growth environment where the iron has been exposed. However, the structure of the rust phases formed on carbon steel in atmospheric exposure includes many imperfections, and real component structures appear to diverge from the ideal crystallographic structure of typical iron oxides. Rigorous information on the morphology of the rust phases formed in atmospheric exposure is very scarce, and there are even fewer studies of analytical information on the chemical compounds corresponding to these rust morphologies. The aim of this paper is to advance this field using scanning electron microscopy (SEM)/micro-Raman spectroscopy to perform a more direct and rigorous characterization of the main rust phases. The equipment used consists of a fully integrated confocal Raman microscopy module, which includes an optical video microscope and a high-resolution XY stage on top of the SEM main stage. Correlation between the SEM images and Raman images is achieved by overlaying the video and SEM images of the sample itself. The study consists of a micro-Raman characterization of the morphologies most commonly observed for the main rust phases: lepidocrocite (γ-FeOOH), goethite (α-FeOOH), akaganeite (β-FeOOH), and magnetite (FeO)., The authors gratefully acknowledge the financial support for this study from the Ministry of Science and Innovation of Spain (CICYT-MAT2008-06649).

This work analyses the corrosion mechanisms of carbon steel when exposed to marine atmospheres with very different chloride ion deposition rates. Two extreme situations are described, characterized by a >consolidated rust layer> (at relatively low atmospheric salinities), formed by a diffusion-controlled corrosion mechanism in which the reduction of dissolved oxygen in the aqueous film deposited on the metal is the predominant cathodic reaction, and an >exfoliated rust layer> (at high atmospheric salinities), where the cathodic reaction of hydrogen evolution becomes important, notably accelerating the corrosion process. The research has employed a range of near-surface and bulk sensitive analytical techniques (SEM/EDS, μXRD, and SEM/μRaman) to characterize the corrosion products and rust layers formed., The authors gratefully acknowledge the financial support for this study from the Ministry of Science and Innovation of Spain (CICYT-MAT2008-06649). They would also like to thank the Spanish Meteorology Agency (AEMET) for the data provided on meteorological parameters in the study area.

The scientific literature contains very little knowledge on the morphology of the different rust phases formed upon exposure of carbon steel to the atmosphere. In recent years this topic has attracted the attention of many researchers working on atmospheric corrosion, but the various morphologies seen in microscopic observations and reported in many publications lack a rigorous characterisation and identification in terms of the rust phases that give rise to them. The aim of this paper is to advance in this respect with a dual purpose: firstly to try to make a classification of the numerous different types of morphologies seen in the microscopic observation of rusts formed on carbon steel exposed to marine atmospheres, and secondly to identify some of these morphologies, perhaps the most common, using the powerful SEM/Micro-Raman spectroscopic technique. This work distinguishes several main types of morphology: globular, acicular, laminar, tubular and toroidal, and the variants existing within each group. The rust phases most commonly found are the oxyhydroxides lepidocrocite, goethite and akaganeite and the iron oxide magnetite., The authors gratefully acknowledge the financial support for this study from the Ministry of Science and Innovation of Spain (CICYT-MAT2008-06649). The authors would like to express their gratitude to the companies ENEL and GAS NATURAL-FENOSA for the facilities provided and for allowing the location of the corrosion stations at Cabo Vilano wind farm (Camariñas, Spain).

The exposure of carbon steel to marine atmospheres gives rise to the formation of various corrosion products (lepidocrocite, goethite, magnetite, akaganeite, etc.) that present a wide variety of morphologies depending on the specific conditions of their formation. The literature on this topic is scarce and lacks a rigorous analytical characterization of the different morphologies seen in microscopic observation of rust surfaces under a scanning electron microscope. The research presented in this paper uses XRD and the powerful integrated SEM/Micro-Raman technique to characterize a series of morphologies commonly found in the rust that forms when mild steel is exposed to marine atmospheres. Two atmospheres with highly different chloride deposition rates (atmospheric salinity) have been considered. In the lower salinity atmosphere an adherent rust layer was formed on the steel, the outer surface of which layer exhibited a variety of SEM morphologies corresponding to lepidocrocite (mainly) and goethite. In the higher salinity atmosphere the thick rust layer formed on the steel was easily exfoliated (detached) and the morphologies on the inner surface observed using SEM were very different, corresponding mainly to akaganeite and magnetite., The authors gratefully acknowledge the financial support for this study from the Ministry of Science and Innovation of Spain (CICYT-MAT2008-06649). The authors would like to express their gratitude to the companies ENEL and GAS NATURAL-FENOSA for the facilities provided and for allowing the location of the corrosion stations at Cabo Vilano wind farm (Camariñas, Spain).

Um dos mais críticos problemas encontrados na união de materiais distintos é a formação de tensões residuais, que ocorre principalmente pelo fato desses materiais possuírem coeficientes de expansão térmica e condutividades térmicas diferentes. Neste trabalho foi estudada a técnica de soldagem laser entre o aço carbono AISI 1010 e o aço inoxidável AISI 304. Os materiais foram unidos por solda autógena de topo com um laser de Nd:YAG contínuo. O principal objetivo do estudo foi a identificação da influência dos parâmetros de soldagem, pela análise das tensões residuais na zona termicamente afetada (ZTA). Foi executado um planejamento fatorial de três fatores a dois níveis com uma réplica, em que foram variadas a potência, a velocidade de soldagem e a posição focal do feixe laser. Na superfície da amostra foram realizadas medidas de tensão residual pela técnica de difração de raios X, para estudar sua variação em função dos parâmetros investigados. O método do furo cego foi também utilizado para avaliar a tensão residual ao longo da profundidade das amostras até a profundidade de 1 mm. Além das medidas de tensão residual, os cordões de solda foram avaliados por microscopia óptica e eletrônica de varredura (MEV), que tiveram como objetivos determinar a geometria do cordão e mudanças na microestrutura, também foram feitas medidas de microdureza Vickers para se avaliar a extensão da ZTA. Para se avaliar as propriedades mecânicas da união foram realizados ensaios de tração e fadiga. O software MINITAB 15 foi utilizado para a análise das tensões residuais nas diferentes profundidades da ZTA obtidas pelo método do furo cego. Foi utilizada também a regressão estatística baseada nas diferentes influências da entrada e combinação dos fatores na tensão residual geradas nessa união. Os resultados indicam que o desenvolvimento de modelos pode prever as respostas satisfatoriamente e fornecer aos usuários um guia para definir os melhores parâmetros de união. The dissimilar materials union has the residual stress formation as one of the most critical problems, which occurs mainly because these materials have both different thermal expansion coefficients and thermal conductivities. In this study, it was investigated the laser welding technique between steels, AISI 1010 and AISI 304. The materials were joined by butt autogenous welding with a continuous Nd:YAG laser. The main objective was to identify the welding parameters influence by the residual stresses analysis in the heat affected zone (HAZ). It was executed a factorial design with three-factor at two levels with a replica, which were varied power, welding speed and focal position of the laser beam. Residual stress measurements by the diffraction of X-rays were performed on the sample surface, to study their variation as a function of the parameters investigated. The blind hole method was also used to evaluate the residual stress along the samples depth, up to depth of 1mm. Besides residual stress measurement, weld seams were evaluated by optical and scanned electron microscopy, which were aimed to determine the weld geometry and changes in the microstructure. It was also made Vickers hardness measurements to evaluate the extent of HAZ. To evaluate the mechanical properties of the union were performed tensile and fatigue test. The MINITAB 15 software was used to analyze the residual stresses obtained by the blind hole method at different depths of the HAZ. It was also used statistical regression based on both the influences different and the combination of this input factors, in the residual stress of union. The results indicate that the models can satisfactorily predict the responses and provide users a guide to better define the welding parameters.

© 2015 CSIC. Basic research on marine atmospheric corrosion of carbon steels is a relatively young scientific field and there continue to be great gaps in this area of knowledge. The presence of akaganeite in the corrosion products that form on steel when it is exposed to marine atmospheres leads to a notable increase in the corrosion rate. This work addresses the following issues: (a) environmental conditions necessary for akaganeite formation; (b) characterisation of akaganeite in the corrosion products formed; (c) corrosion mechanisms of carbon steel in marine atmospheres; (d) exfoliation of rust layers formed in highly aggressive marine atmospheres; (e) long-term corrosion rate prediction; and (f) behaviour of weathering steels. Field research has been carried out at Cabo Vilano wind farm (Camarinas, Galicia) in a wide range of atmospheric salinities and laboratory work involving the use of conventional atmospheric corrosion techniques and near-surface and bulk sensitive analytical techniques: scanning electron microscopy (SEM)/energy dispersive spectrometry (EDS), X-ray diffraction (XRD), Mossbauer spectroscopy and SEM/Raman spectroscopy.., The authors gratefully acknowledge the financial support for this study from the Ministry of Science and Innovation of Spain (CICYT-MAT 2008-06649)

Mössbauer spectroscopy and X-ray powder diffraction (in selected samples) have been used to characterize corrosion products on carbon steels after atmospheric exposure to the tropical Panamanian locations of Panama and Colon, classified according to ISO 9223 as C3 and C5, respectively. Goethite (α-FeOOH) of intermediate particle size (20-100 nm), lepidocrocite (γ-FeOOH), a spinel phase consisting of non-stoichiometric magnetite (Fe3-xO4) and/or maghemite (γ-Fe2O3) and nano-sized particles were identified in the corrosion products. The spinel phase is related to short term atmospheric exposure transforms in time to other corrosion products. The corrosion resistance increased with fraction of goethite following a saturation-type behavior.Se caracterizaron los productos de corrosión de aceros al carbono expuestos a las atmósferas tropicales panameñas localizadas en Panamá y Colón, mediante el uso de la espectroscopia Mössbauer y difracción de rayos-X (en muestras seleccionadas). Las atmósferas se clasifican como C3 y C5, respectivamente, de acuerdo a la norma ISO 9223. Se lograron identificar los compuestos goethita (α-FeOOH) de tamaño de partícula intermedio (20-100 nm), lepidocrocita (γ-FeOOH), una fase de espinela consistente en magnetita no estequiométrica (Fe3-xO4) y/o maghemita (γ-Fe2O3), y nanopartículas. La fase de espinela se puede correlacionar con exposiciones cortas a la atmósfera, transformándose en el tiempo en otros productos de corrosión. La resistencia a la corrosión se incrementa con la cantidad de goethita siguiendo una conducta de saturación.

The mechanism of corrosion inhibition was searched by investigating the stability of Zn complexes of five imidazole derivatives using semiempirical methods in gas phase. The obtained results were found to be parallel to the experimental values of literature with the exception of compound 3 which is an ester.

It is known that transformation of martensite into austenite ( α ′→ γ ) can take place in the surface layer of steels treated with sufficiently intense pulses of laser, ion or plasma beams. Our present work focuses on the phase transformations in the near-surface layer of various types of steel irradiated with short (μs range) intense (5–6×10 −4 J/m 2 ) argon and nitrogen plasma pulses. The results of CEMS measurements, the pin-on-disc wear tests and SEM observations are presented.

Изложены результаты ряда экспериментов по насыщению поверхностных слоев углеродистых марок стали легирующими элементами, содержащимися в сталеплавильных шлаках, в результате их выдержки при различных температурах различные промежутки времени. The paper describes the results of several experiments on saturation of the surface layers of carbon steels with alloying elements contained in the steel smelting slags as a result of exposure at various temperatures for various time intervals. Чуманов Илья Валерьевич, доктор технических наук, профессор, заведующий кафедрой общей металлургии, Южно-Уральский государственный университет, филиал в г. Златоусте. 456209, Челябинская обл., г. Златоуст, ул. Тургенева, 16. Тел.: (3513)665829. E-mail: chiv71@susu.ac.ru. Чуманов Валерий Иванович, кандидат технических наук, профессор кафедры общей металлургии, Южно-Уральский государственный университет, филиал в г. Златоусте. 456209, Челябинская обл., г. Златоуст, ул. Тургенева, 16. Тел.: (351)3665829. E-mail: maria@zb-susu.ru. Аникеев Андрей Николаевич, аспирант кафедры общей металлургии, Южно-Уральский государственный университет, филиал в г. Златоусте. 456209, Челябинская обл., г. Златоуст, ул. Тургенева, 16. Тел.: (3513)665829. E-mail: anikeev-ml@mail.ru. Матвеева Мария Андреевна, аспирант кафедры общей металлургии, Южно-Уральский государственный университет, филиал в г. Златоусте. 456209, Челябинская обл., г. Златоуст, ул. Тургенева, 16. Тел.: (3513)665829. E-mail: 26mist26@mail.ru. I.V. Chumanov, South Ural State University, Zlatoust Branch, Zlatoust, Chelyabinsk region, Russian Federation, chiv71@susu.ac.ru, V.I. Chumanov, South Ural State University, Zlatoust Branch, Zlatoust, Chelyabinsk region, Russian Federation, maria@zb-susu.ru, A.N. Anikeev, South Ural State University, Zlatoust Branch, Zlatoust, Chelyabinsk region, Russian Federation, anikeev-ml@mail.ru, M.A. Matveeva, South Ural State University, Zlatoust Branch, Zlatoust, Chelyabinsk region, Russian Federation, 26mist26@mail.ru

Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques have been used to study passive layers anodically grown on steel rebars in an aqueous alkaline solution simulating the electrolyte of the concrete pores. Nyquist diagrams recorded by EIS at the different stabilization potentials show a diffusional tail at low frequencies. The analysis of the impedance measurements has been made by means of an equivalent circuit with a Warburg component and within the framework of the point defect model (PDM) theory. It is observed that the calculated concentration of vacancies is a function of the potential in accordance with the theoretical prediction of the PDM.

Made available in DSpace on 2014-10-09T12:52:01Z (GMT). No. of bitstreams: 0 Made available in DSpace on 2014-10-09T13:57:53Z (GMT). No. of bitstreams: 0 A difra????o de raios X e de el??trons retroespalhados, em escalas distintas, foram aplicadas para acompanhar mudan??as microestruturais em dois a??os ferr??ticos baixo carbono (2%Si e ABNT 1006), observando-se o desenvolvimento da textura nas etapas de lamina????o a frio (skin-pass) e recozimento a 760 oC. Para ambos os a??os, os resultados permitiram afirmar que o fen??meno que ocorre ap??s a lamina????o por skin-pass e tratamento t??rmico, nas condi????es deste trabalho, ?? a recristaliza????o prim??ria. A aplica????o do skin-pass criou mais discord??ncias em gr??os com baixo fator de Taylor por sofrerem mais deforma????es. Observou-se a nuclea????o e crescimento de gr??os em regi??es de grande densidade de c??lulas de discord??ncias. A presen??a do sil??cio atrasou a recupera????o favorecendo o aumento de subcontornos. N??o foi observado o crescimento anormal de gr??os, nem em fun????o da presen??a de gr??os Goss. Os contornos CSL n??o garantiram o crescimento do gr??o. N??cleos de crescimento de gr??os deram origem a gr??os com orienta????es distintas, indicando que o crescimento de gr??os n??o dependeu da exist??ncia pr??via de gr??os com as orienta????es desenvolvidas, demonstrando que o crescimento anormal de gr??os n??o est?? relacionado necessariamente com os gr??os Goss. Tese (Doutoramento) IPEN/T Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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In previous papers, several hipoeutectoide carbon steels in quenched condition showed values of Young's modulus inferior to values corresponding to tempered condition. In all cases, Young's modulus was measured by ultrasound techniques. In fact, modulus of C22E steel (EN 10083) increases from 209 GPa (quenched condition) up to 211 GPa (tempered to 650 °C); for C45E steel, modulus increases from 199 GPa to 211 GPa (tempered to 500 °C), and for C55E steel Young's modulus varies from 202 GPa to 209 GPa for tempered steel to 650 °C. The present work focuses on the microstructural characterization of these steels at different heat conditions using reflection optical microscopy and also scanning electronic microscopy and the authors propose an explanation of the modulus variation using the behaviour of the dislocations array and their interaction with solute atoms and other dislocations present in steel. En trabajos anteriores se ha constatado que varios aceros al carbono hipoeutectoides, en estado de temple, presentan valores del módulo de Young inferiores a los correspondientes en estado de revenido. En todos los casos la determinación se ha realizado mediante ultrasonidos. En concreto, para el acero C22E (EN 10083), el módulo se incrementa ligeramente desde 209 GPa (material templado) hasta 211 GPa (revenido a 650 °C), para el acero C45E el módulo aumenta desde 199 GPa hasta 211 GPa (revenido a 500 °C) y para el acero C55E el módulo varía desde 202 GPa hasta 209 GPa para el acero revenido a 650 °C. El presente trabajo se centra en la caracterización estructural de los tres aceros mencionados a los distintos estados de tratamiento térmico, utilizando las técnicas de microscopía óptica de reflexión y microscopía electrónica de barrido, y se propone una explicación de la variación del módulo a partir del comportamiento de las dislocaciones y su interacción con átomos de soluto y con otras dislocaciones.

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Made available in DSpace on 2014-10-09T12:36:19Z (GMT). No. of bitstreams: 0 Made available in DSpace on 2014-10-09T13:59:16Z (GMT). No. of bitstreams: 1 12908.pdf: 2121499 bytes, checksum: c2d2abf4d18418855c9e93a43337b8ad (MD5) Dissertacao (Mestrado) IEA/D Escola Politecnica, Universidade de Sao Paulo - POLI/USP