With technological advances in the several areas of knowledge, the constant search for materials with characteristics that meet certain applications has been growing, especially in the chemical and petrochemical industries, where materials capable of withstanding the conditions of corrosion in aggressive environments are required. The aim of this paper was to analyze the influence of the alloy element molybdenum on the microstructure and the resistance to corrosion of two duplex stainless steels identified as A (with molybdenum) and B (without molybdenum), after solution-treated under the following conditions: heating at 1100ºC for 30, 120 and 240 minutes. The steels were characterized by SEM, EDS, DRX and microhardness. The rise in solution treatment time fostered an increase in the volumetric fraction of the ferrite phase, in both steels. The solution treatment at 1100ºC for 120 minutes, for steels A and B, provided good resistance to pit corrosion, as well as the development of a passivating film in the solution of lithium chloride (120,000 ppm of chloride ions).
Sigma phase leads to deterioration of corrosion resistance of super duplex stainless steels (SDSS) and its volume fraction increases as the time which the materials is exposed in determined temperature increases. In the present study, the effect of the short aging time on the formation of the sigma phase and on the corrosion behavior of UNS S32520 SDSS at 3.5% sodium chloride solution was evaluated using microstructural characterization, linear potentiodynamic polarization curve and electrochemical impedance spectroscopy. The results indicated that the SDSS sample solution-treated at 1150ºC and aged at 850ºC for 5 min may improve the corrosion resistance in comparison with the as-received and solution-treated conditions, due to the better partition of the elements Cr, Mo and dissolution of certain amount of sigma phase in the microstructure. However, results also showed that when SDSS solution-treated at 1150ºC is aged at 850ºC with the aging time slightly superior (10 min), the precipitation of sigma phase increases leading to a rapid deterioration of the corrosion resistance of the material.
The objective of this work was the conformation of ribbons from Sn3Zn alloy and Sn pure, using the melt-spinning fast cooling technique, in order to investigate the applicability as biomaterial. The ribbons were coated with 1% poly-caprolactone (PCL) and subsequent incorporation of silver nanoparticles (NPAg). In the uncoated ribbon was observing a surface roughness due of agglomerate caused by rapid solidification. In the ribbon coated with PCL and NPAg incorporation, it was observed that these compounds adhered to the ribbon. X-ray diffraction analysis showed no ribbons amorphization. The analysis by differential scanning calorimetry, indicated that the Sn3Zn ribbon had a lower melting temperature (198.1°C) than the Sn ribbon (228.7°C). The microhardness of Sn3Zn ribbon was 13.38 HV and Sn ribbon was 11.00 HV, both for the face without contact with the cooling wheel. In the bioactivity assays, performed in simulated body fluid medium, all samples showed apatites formation after four weeks of testing.
Titanium is used in orthopedic and orthodontic implants because it has good corrosion resistance and excellent biocompatibility. Thus, studies seek to obtain a coating to improve the adhesion between the bone and the implant, by modifying the metal’s surface. The objective of this work was to biomimetically coat C.P. Ti with hydroxyapatite doped with silver nitrate, a component with antimicrobial properties, coating the metallic-ceramic composite with a polycaprolactone polymer film, which is known by generate improved implant-tissue interaction, and reducing postoperative complications from bacterial infections. The characterization of the material demonstrated the existence of the coating overall surface of the metallic substrate. The results obtained from the bacterial culture tests with Staphylococcus aureus showed that nitrate was effective in reducing the amount of live bacteria present in the supernatant, as well as those adhered to the surface of the material. In addition, the polymeric coating did not prevent the release of the bactericidal agent, not interfering in the effect there.
This study aimed to investigate the effects of difference in nickel content and the tempering temperatures on the corrosion resistance in 13Cr2Ni0.1C and 13Cr1Ni0.15C steels. Results showed that passive film in 13Cr2Ni0.1C steel is formed more quickly at the lowest and highest tempering temperature (650°C and 750°C) but the lowest tempering temperature (650°C) showed better resistance to corrosion pitting. There was passive film formation and pitting corrosion in all tempering temperatures of the 13Cr1Ni0.15C steel and changes in tempering temperature does not significantly alter polarization curves, showing similar behavior to steel 13Cr2Ni0.1C tempered at 650°C.
The thermal treatments employed in alloys are essential to obtaining desired microstructures and corrosion resistance properties. In this paper the low carbon martensitic steel 13Cr4Ni0.2C with different tempering temperatures was studied using potentiodynamic polarization technique in synthetic marine environment, in order to evaluate the effect of the tempering temperature on the steel corrosion resistance in an environment that simulates the conditions of use in oil and gas production. Microscopy results showed differences in the microstructure of tempered steel at low (620°C) and high (770°C) temperatures, indicating the appearance and extending of martensite laths with increasing temperature. Polarization tests showed that tempering temperature located between 620°C and 710°C indicated passive film formation and tempering temperatures of around 620 °C showed better resistance values to pitting corrosion.
Biomaterials are effective alternatives for tissue substitution, including the bone tissue, since they do not pose risks of transmission of diseases or immune rejection. Nowadays, there is an interest in new materials capable of being associated with other substances which favor bone formation, especially natural biopolymers, in particular chitosan, which may present a potential for repairing bone defects and forms films that adhere to metal surfaces. Titanium, despite being a material greatly employed in implants because of its excellent physical properties, does not present bioactive characteristics, making it necessary to use methods of surface modification to enhance its biological response, favoring bone formation. This work aims at studying commercially pure titanium (cp-Ti) coating with chitosan using the biomimetic method and the evaluation of the effects of process variables as substrate surface conditions. Subsequently, the incorporation of AgNO3 was studied and its effects on corrosion resistance were evaluated. To evaluate the coating process, several tests were conducted, such as scanning electron microscopy, X-ray diffraction and infrared spectroscopy. From the results obtained, the efficacy of the chitosan film in inhibiting the corrosion of the metals is concluded, which was the target of this study, thus justifying its use for osseointegration and in several implants.
Heart diseases affect part of world population and generally involves the functioning of valves. Valves replacement is the most common treatment and the choice between synthetic or natural/biological implants depends on several factors. Synthetic implants have greater durability, whereas biological ones are more biocompatible. This work proposes the use of polymeric coating on titanium metal surface to increase implant biocompatibility. Poly-caprolactone (PCL) has demonstrated greater efficacy for biomedical applications due to its biocompatibility. It can easily form films and coat surfaces. Titanium discs were submitted to alkaline and thermal treatments and coated with 1%PCL and 1%PCL+TiO2. For both conditions, PCL crystals were found in titanium coated surface (SEM and EDX) and X-ray diffractogram confirmed PCL coating. Infrared Spectroscopy spectra showed both PCL and TiO2 characteristic peaks. Moreover, corrosion resistance of coated disc has considerably increased, proving the effectiveness of PCL as coating material and its potential application in cardiac valves.
The formation of intermetallic phases alters the properties of duplex stainless steel and is therefore a crucial factor in its performance. For example, the formation of sigma phase in duplex steel increases its brittleness and decreases its corrosion resistance because this phase consumes chromium and molybdenum in solid solution, thus leading to the depletion of these elements in the matrix. This study investigated the corrosion resistance of as-cast SAF 2205 duplex stainless steel after solution annealing treatment at 1100 °C for 240 minutes, under varying cooling rates. The objective was to evaluate the correlation between cooling condition, microstructural changes and corrosion resistance based on cyclic potentiodynamic polarization and double loop electrochemical potentiokinetic reactivation (DL-EPR) measurements. The results revealed a significant reduction in the corrosion resistance of a slowly cooled sample, which presented an increase in the degree of Cr (Qr / Qa) depletion resulting from the formation of sigma phase.
AbstractPrimarily, tempering is used in martensitic stainless steels with low carbon in order to change their mechanical properties. However, it also modifies the corrosion properties; usually depending on the temperature and duration of the heat treatment. This work investigated the impact of tempering on the corrosion of 13Cr4Ni0.02C and 13Cr1Ni0.15C (% weight) steels. Samples were tempered at 650º, 700º and 750ºC, characterized by optical microscopy and cyclic anodic polarization tests in a synthetic marine environment. The results showed differences in the microstructure of the 13Cr4Ni0.02C tempered samples, which changed from lath to lamellar with precipitates in the prior austenite grain boundaries. On the other hand, tempering did not affect the 13Cr1Ni0.15C microstructure. The anodic polarization tests showed that the pitting potential of the 13Cr4Ni0.02C samples decreased with the tempering temperature increasing. Similar values of pitting potential were found with the 13Cr1Ni0.15C tempered samples, which were lower than the 13Cr4Ni0.02C samples after tempering. It shows that even though the corrosion resistance of the 13Cr4Ni0.02C reduces when the tempering temperature was increased, it is better than that presented by 13Cr1Ni0.15C.
Novas classes de aços inoxidáveis martensíticos, com baixo teor de carbono, têm sido desenvolvidas, para atender, principalmente, às necessidades do segmento da indústria do petróleo. Contudo o seu uso tem sido restrito pelo fato de ser um desenvolvimento recente e muitas de suas propriedades ainda são motivos de investigação. Nesse trabalho, foram determinados os valores das temperaturas inicial e final da transformação austenítica e as temperaturas de início e fim da formação martensítica, para a liga 13Cr2Ni0,1C, através de ensaios dilatométricos com resfriamento contínuo. Com base nesses resultados, foram obtidas as condições otimizadas dos tratamentos térmicos de têmpera e revenido. A caracterização microestrutural das ligas na condição de bruta fusão foi realizada por microscopia ótica observando-se uma matriz martensítica com a presença de ferrita delta.
New classes of martensitic stainless steels, with low carbon levels, have been developed aiming to meet the needs of the petroleum industry segment. However, their use has been restricted due to the fact it is a recent development and many of its properties are still under investigation. This work determines the values of initial and final temperatures for the austenitic transformation and the initial and final temperatures of martensitic formation for alloy 13Cr2Ni0,1C, by means of dilatometric tests under continuous cooling. Based on these results the optimized conditions for quench and temper heat treatments were obtained. The microstructural characterization of the alloys under coarse fusion condition was carried out by optical microscopy and the presence of delta-ferrite in the martensitic matrix was observed.
O concreto armado tem cada vez mais despertado interesse científico e tecnológico, principalmente no que se refere a sua melhoria e inovação, seja pela utilização de novos materiais ou pelo estudo da corrosão para evitar a deterioração das estruturas. Dessa forma, têm-se intensificado os estudos da corrosão em concreto armado, sendo que a maior dificuldade está em detectar o início da corrosão na armadura. Uma das causas de degradação do concreto armado e sua posterior corrosão da sua armadura é a sua exposição a ambientes industriais. Assim, é necessário melhorar o desempenho das estruturas, prevendo a vida útil e conhecendo as formas de prevenção para minimizar o processo corrosivo. Há métodos de controle da corrosão do aço, como a incorporação de inibidores no concreto, como o molibdato de sódio, que é um inibidor anódico e não poluente tóxico. Nesse trabalho, foi avaliada a eficiência do molibdato de sódio, nas concentrações de 0, 1, 2 e 4% em relação à massa de cimento, empregando espectroscopia de impedância eletroquímica, simulando uma atmosfera ácida como agente agressor. A concentração de 4% do inibidor foi a mais eficiente.
The reinforced concrete has more and more arisen scientific and technological interest concerned mainly to its innovation and improvement either by the utilization of new materials or by the study of corrosion to avoid structure deterioration. In that way, the study of corrosion in reinforced concrete has been intensified but the biggest difficult is to detect the beginning of the corrosion in the steel. One of the reasons of the reinforced concrete degradation and afterwards the corrosion in the steel is its exposition to industrial environments. Thus, it is necessary to improve the performance of the structures, foreseeing its useful life and knowing the manners of prevention to minimize the corrosive process. There are methods to control the corrosion of the steel as the annexation of concrete inhibitors such as the sodium molybdate, an anodic inhibitor and not a toxic pollutant. In this work the efficacy of the sodium molybdate was evaluated with concentrations of 0, 1, 2 and 4% related to the cement mass, employing the electrochemistry impedance spectroscopy, simulating an acid atmosphere as an aggressive agent. The concentration of 4% in the inhibitor was the most efficient.
O controle dos ciclos térmicos, nos tratamentos térmicos de têmpera e revenido, nos aços inoxidáveis martensítico do tipo 13Cr5Ni0,02C, é essencial para se obter boa resistência mecânica associada à resistência à corrosão, principalmente em equipamentos para a extração de petróleo. Corpos-de-prova foram austenizados por três horas a 1025°C, com posterior têmpera ao ar e água e revenido a 680ºC por 10 horas e resfriados ao ar. Um segundo grupo de corpos-de-prova foi tratado, termicamente, nas mesmas condições, porém foi realizado alívio de tensão a 150ºC por 1 hora e resfriado ao ar. O revenimento aumenta, substancialmente, a tenacidade e a ductilidade e, em alguns casos, sem redução substancial da resistência mecânica. A elevada dureza e resistência da martensita revenida está relacionada à alta relação de área entre os contornos de cementita e da matriz, pois estas agem como barreiras à movimentação das discordâncias, durante a deformação plástica. Dessa maneira, a matriz que é dúctil, é reforçada pela cementita.
The thermal cycle control of heat treatments for the quenching and tempering of martensitic stainless steels, type 13Cr5Ni0,02C, is essential for obtaining the good mechanical resistance which is associated to corrosion resistance, mainly in equipment used in petroleum extraction. Samples were austenized during three hours at 1025°C, with posterior air and water quenching and tempering at 680ºC during 10 hours and then, air-cooled. A second sample group was heat treated under the same conditions, but a stress relief was done at 150ºC for 1 hour and then, air-cooled. The tempering increases substantially its hardness and ductility and in some cases, without substantial reduction of the mechanical resistance. The great hardness and resistance of the tempered martensite is related to the large area relation between the cementite and matrix contours, because these act as barriers to the dislocation motion during the plastic deformation. In this way, the matrix which is ductile is reinforced by the cementite.
Nas últimas décadas, foram desenvolvidas novas classes de aços inoxidáveis martensíticos, com composição química 0,01-0,1%C, 11-13%Cr e 2-6%Ni, com o objetivo de atender às necessidades das indústrias de petróleo, por apresentarem boa resistência à corrosão em ambientes de média agressividade associada à boa resistência mecânica. Contudo o seu uso tem sido restrito pelo fato de ser um desenvolvimento recente e muitas de suas propriedades ainda serem motivos de investigações. Esse trabalho estuda as transformações de fases pela técnica dilatométrica de resfriamento rápido, obtendo-se os dados para a construção das curvas de transformação tempo-temperatura-transformação (TTT), em aços inoxidáveis martensíticos fundidos e analisa a influência da adição do níquel nessas transformações. Com base nos resultados obtidos, foram selecionadas as condições dos tratamentos térmicos de têmpera e revenido. Determinaram-se os valores das temperaturas inicial (Ac3) e final (Ac1) da transformação austenítica e as temperaturas de início (Mi) e fim (Mf) da transformação martensítica por resfriamento contínuo, obtendo uma estrutura final martensítica que apresente, simultaneamente, as propriedades de resistência à corrosão e mecânicas recomendadas quando em serviço.
In the last decades, new classes of martensitic stainless steels were developed with chemical composition 0,01-0,1%C, 11-13%Cr, 2-6%Ni, with the objective of attending mainly the petroleum industry needs because they present good corrosion resistance in medium aggressive environments associated to good mechanical resistance. However, its use has been restricted by the fact of being a recent development and many of its properties are still under investigation. This work studies phase transformations by the dilatometry technique with fast cooling in order to construct the transformation time-temperature-transformation (TTT) curves in cast martensitic stainless steels and to analyze the nickel addition influence on the transformations. Based on the results the quenching and tempering conditions were selected. By continuous cooling, the austenitic transformation temperatures (Ac3) and (Ac1) and martensitic transformation temperatures (Mi) and (Mf) respectively were obtained, which provided the final martensitic structure that presents simultaneously the mechanical and corrosion resistance properties, recommended when in service.
Esse trabalho estuda a resistência à corrosão do aço inoxidável martensítico fundido em meio marinho sintético saturado com CO2 e também faz uma comparação com solução aerada. A liga foi usada na condição temperada e revenida. A corrosão foi avaliada usando a técnica de polarização potenciodinâmica cíclica. As medidas de polarização foram obtidas em meio marinho sintético com concentrações de cloreto de 20000ppm e 80000ppm na temperatura ambiente. As curvas de polarização cíclica obtidas mostram uma região de passivação definida para as condições adotadas para o ensaio, sendo possível para a identificação dos parâmetros eletroquímicos, o potencial de pite, o potencial de proteção e a susceptibilidade ao pite. Em solução saturada com CO2 e concentração de cloreto de 20000ppm, o potencial de proteção aumentou e a susceptibilidade ao pite diminuiu, em comparação com a solução aerada. Em contraste, os potenciais de pite e de proteção decresceram em solução saturada com CO2 e concentração de cloreto de 80000ppm, indicando que a resistência ao pite é influenciada por um sinergismo entre a concentração de cloreto e a solução saturada com CO2.
This work studies the corrosion resistance of the martensitic stainless steel cast in CO2-saturated synthetic seawater. A comparison is also made with an aerated solution. The alloy was used in a quenched and tempered condition. The corrosion behavior was evaluated using the cyclic potentiodynamic polarization technique. The potentiodynamic polarization measurements were taken in synthetic seawater with 20000ppm and 80000ppm chloride contents at room temperature. The obtained cyclic polarization curves show a defined passive region for the adopted test conditions making possible the identification of the electrochemical parameters: pitting potential, protection potential and susceptibility to pitting. In the CO2 saturated solution and in the 20000ppm chloride contents, the protection potential increased and the pitting susceptibility decreased in comparison with the aerated solution. In contrast, the pitting and the protection potentials decreased in the CO2 saturated solution and in the 80000ppm chloride content indicating that the pitting resistance is influenced by a synergy between the chloride concentration and the CO2 saturated solution.