Abstract The effect of temperature on tensile and cyclic deformation is studied on SAE 1045 and SAE 4140 commercial steels. Tensile and low cycle fatigue (LCF) tests were performed at room temperature and 250°C. For a temperature of 250°C, an induction heating system was used during the tests. The temperature of the specimen was homogenized 600 s before testing. The tension-compression LCF tests were carried out at total strain amplitudes of ± 0.6%, ± 0.8%, and ± 1.0%. The Coffin-Manson-Basquim model was used to predict the LCF properties of steels. Scanning electron microscopy was used to evaluate the microstructure and the fracture surface. The fracture surfaces of samples tensile tested at room temperature and 250°C were similar. For fatigue testing, the surfaces obtained were also similar with regions of fatigue crack initiation and propagation, and rupture. A crack initiation near the surface was observed for the LCF specimens. Dynamic strain aging and recovery influenced the tensile and fatigue results, for example, the number of reversals to failure decreased for the fatigue test performed at 250°C. For fatigue tests performed at strain of 0.6% in the SAE 1045, the stress increased by 65% at 250°C when compared to testing at room temperature. Consequently, the number of reversals was reduced by 58%. 104 414 steels (LCF 250C C 250 60 tensioncompression tension compression 06 0 6 08 8 0.8% 10 1 1.0% CoffinMansonBasquim Coffin Manson Basquim propagation rupture specimens results example 0.6 65 Consequently 58 58% 41 25 0.8 1.0 0. 5 4 2 1.

ABSTRACT The complicated combined impacts of multiple parameters that affect the cutting process might make it challenging to describe burrs generated during face milling operations. The objective of the work is to study the influence of turning parameters such as depth of cut, spindle speed, and feed on three output performances such as machining time, surface roughness, and burr height. The three turning input parameters and three output turning performances are considered for machining three different materials, such as stainless steel, low-carbon steel, and high-carbon steel. The experimental design is planned as per the box-behnken design for six types of materials. Tungsten carbide is utilized as a cutting tool for all turning operations. Output parameters like machining time, burr height, and surface roughness are calculated. Machined (turned) samples are studied under the influence of a scanning electron microscope (SEM) for burr formation. Surface roughness is measured by the surface roughness meter, and machining time is calculated by the CNC machine itself. ANOVA is used to investigate and optimize machining parameters influence on output performances. The mathematical model for three output performances, such as machining time, burr height, and surface roughness, has been developed using response surface methodology. operations cut speed height materials steel lowcarbon low carbon highcarbon high boxbehnken box behnken turned (turned SEM (SEM formation meter itself methodology

Guanine was investigated as a potential green corrosion inhibitor to API 5L X65 carbon steel in HCl 0.1 mol.dm-3 solution, at pH = 2.0, under hydrodynamic conditions using electrochemical, weight loss and Raman spectroscopy experiments. Cyclic voltammetry and potentiodynamic polarization curves suggested that Guanine does not change the metal/solution interface appreciably and weight loss tests confirmed the low inhibition efficiency (IE) of Guanine in protecting the X65 steel in this corrosive medium. An IE = 22% was determined after 48 h of exposure, a value lower than that reported in the literature on the mild steel/Guanine/HCl system. Raman spectroscopy was employed to gain insight on the nature of the steel/Guanine interaction and the results pointed out to a weak physisorption of the molecule, thus explaining the very low IE values obtained. L X X6 01 0 1 0. mol.dm3 moldm3 moldm mol.dm 3 mol dm mol.dm- solution 20 2 2.0 electrochemical experiments metalsolution metal (IE medium 22 4 exposure steelGuanineHCl system steelGuanine molecule obtained dm3 2.

Abstract The effect of graphene oxide (GO) on the concrete quality and the corrosion resistance of carbon steel reinforcement was evaluated. The concrete mix was calculated at a ratio of 1: 1.86: 2.14: 0.46 (cement: sand: gravel: water); the dosages of GO were 0.03 wt.% and 0.05 wt.% and the superplasticizer (PC) concentration was 0.6 wt.% concerning the cement mass. Compressive strength tests (7, 28, and 91 days), water absorption tests, determination of voids index (WATIDVI), ultrasonic pulse velocity (UPV) testing, and optical microscopy analysis were carried out. All concrete samples showed excellent compactness and low porosity. Open circuit potential measurements and linear polarization resistance (LPR) were performed during 15 cycles of partial immersion and drying of concrete in a 3.5 wt.% NaCl solution. A beneficial effect of 0.03 wt.% of GO addition on the corrosion resistance of the reinforced concrete was identified in the saline medium and the corrosion inhibition efficiency obtained was 79.3%. (GO evaluated 1 1.86 186 86 2.14 214 2 14 046 0 46 0.4 (cement sand gravel water) 003 03 0.0 wt wt. 005 05 PC (PC 06 6 0. mass 7, 7 (7 28 9 days, days , days) WATIDVI, WATIDVI (WATIDVI) UPV (UPV testing out porosity LPR (LPR 35 3 5 3. solution 793 79 79.3% 1.8 18 8 2.1 21 04 4 00 ( (WATIDVI 79.3 1. 2. 79.

Resumen En esta investigación se estudió la afectación del ambiente sobre la corrosión del acero al bajo carbono, en una región tropical de la zona central de Costa Rica, con el objetivo de establecer la variación de la velocidad de corrosión en función del ángulo de exposición. Para tal fin se colocaron probetas a diferentes ángulos (0°,30°,45°,60° y 90°), en tres estaciones a lo largo del Valle Central; asimismo se midieron los parámetros medioambientes como humedad, tiempo de humectación, temperatura y la presencia de contaminantes atmosféricos, como los sulfatos y los cloruros. Como principales resultados se determinó que el acero presentó un aumento lineal de la corrosión con la disminución del ángulo con respecto a la horizontal, así mismo la corrosión es uniforme en ángulos menores a 60 grados, presentando corrosión parcial en ángulos elevados, en especial para caras protegidas. La corrosividad se ubica en un nivel urbano leve tipo C2, según la normativa ISO.

Abstract In this research, the effect of the environment in a tropical region of central Costa Rica on the corrosion of low carbon steel was studied, with the objective of establishing the variation of the corrosion rate as a function of the exposure angle. For this purpose, specimens were placed at different angles (0°, 30°, 45°, 60° and 90°) in three stations along the Central Valley; environmental parameters such as humidity, wetting time, temperature and the presence of atmospheric pollutants, such as sulfates and chlorides, were also measured. As main results it was determined that the steel presented a linear increase of corrosion with the decrease of the angle with respect to the horizontal, likewise the corrosion is uniform in angles less than 60 degrees, presenting partial corrosion in high angles, especially for protected faces. Corrosivity is at a mild urban level, type C2, according to ISO standards.

Hybrid casting is a new fabrication concept that can reduce costs and production time of large tools, such as stamping tools for the automotive industry. In this work, we analyzed a hybrid material composed of a high chromium cast iron (HCCI) and a low carbon steel (WCB). SEM analyses indicate that the interface is free of non-metallic inclusions and porosities. The metallurgical bonding between alloys is confirmed by the diffusion of chromium and carbon from HCCI to WCB. Vickers microhardness, EDS and XRD confirmed the presence of M7C3 carbides in the HCCI and at the interface. One set of the samples was submitted to regular quenching in calm air and tempering, while another set was additionally submitted to subzero quenching before tempering. In both cases, a slight reduction of the HCCI hardness and an increase of the interface hardness were observed. The subzero treatment was effective to reduce the amount of retained austenite at the HCCI and limiting its hardness reduction. WCB microstructure and hardness showed no significative change, making it an ideal material to use with HCCI in hybrid casts. The results showed that is possible to produce bimetallic reliable components for industrial applications by means of hybrid casting. industry work (HCCI . (WCB) nonmetallic non metallic porosities microhardness MC M C M7C tempering cases observed change casts (WCB

Abstract The cold roller die process increases the tensile strength and decreases the ductility of steel wire. Annealing heat treatment is applied to restore mechanical properties, but this is a costly process. This research shows that it is possible to control the mechanical properties of ultra-low carbon steel wire inducing the Bauschinger effect and relieving residual steel stresses. The present study uses several pulleys to promote and control the Bauschinger effect magnitude through alternated cyclic bending. A Completely Randomized Design, a regression study, and the Akaike Information Criterion were used to understand the relationship between the quantity and diameter of pulleys and the influence on the magnitude of the Bauschinger effect. Statistical models showed that it is possible to have a maximum increase of 103% in uniform elongation and a maximum decrease of 14% in yield strength. An interaction between the factors studied in controlling the Bauschinger effect magnitude was confirmed. ultralow ultra low stresses bending Design 103 14 confirmed 10 1

Abstract In this study, the influence of heat input on the mechanical properties and microstructure of welded joints in ASTM A572 grade 50 steel using the GMAW process and 90Ar-10CO2 shielding gas was investigated. Process parameters were varied between 20-30 V and 230-250 A, which were adjusted aiming to obtain spray transfer together producing two heat inputs with a 10% difference between them. Visual inspection, tensile tests, microhardness scans, measurements of the width of the heat-affected zone (HAZ), and metallography were performed. The experimental measurements were complemented by calculating the continuous cooling transformation (CCT) diagram of the steel from its chemical composition. The results showed that discontinuity-free and visually acceptable welded joints were obtained. The microstructure of the fusion zone was primarily composed of acicular ferrite, and the HAZ contained a mixture of bainite, pearlite, and ferrite as calculated by the CCT diagram. No statistically significant variations were observed in the microhardness measurements, with the highest value (240 MHV) obtained in the fusion zone. The width of the HAZ varied proportionally with the heat input, while no significant differences were found in the stress results as a function of the heat input. study A A57 5 90Ar10CO2 ArCO 90Ar 10CO2 Ar CO 90Ar-10CO investigated 2030 20 30 20-3 230250 230 250 230-25 10 them inspection tests scans heataffected affected HAZ, , (HAZ) performed (CCT composition discontinuityfree discontinuity free bainite pearlite 240 (24 MHV A5 90Ar10CO 10CO 203 2 3 20- 23025 23 25 230-2 1 (HAZ 24 (2 2302 230- (

ABSTRACT Due to its combination of high mechanical properties, good formability, and low production cost, steel is a key material with potential for improvement in the metallurgical industry. Based on these conditions, this research evaluated the influence of material composition and incomplete austenitization parameters on the final metallurgical and mechanical properties of high-strength microalloyed steels after cooling in a medium with high severity. The applied cycle was based on the intercritical thermal treatment of microalloyed steels with niobium (Nb) and titanium (Ti) to increase the mechanical resistance and guarantee the tenacity of the material. An experimental study was carried out testing three intercritical temperatures, 806 °C, 775 °C, and 740 °C, with subsequent cooling in polymeric solutions in water. The studies showed that the intercritical temperature variation directly contributed to the difference in the second phase microstructure present in the samples. The heat treatment findings resulted in a microhardness of 434.2 HV0.01, characterizing the low-carbon martensite. The presence of a matrix consisting of ferrite and a second phase of low-carbon martensite promoted the typical behavior of dual phase steel. In the x ray diffraction, the presence of retained austenite was not evidenced, indicating the efficiency of the cooling rate. The experiments confirmed the influence of different engineering parameters and intercritical treatment on the mechanical properties. The study enriches the current knowledge about the development of variables for the development of dual phase steel from microalloying elements. formability cost industry conditions highstrength strength severity Nb (Nb Ti (Ti temperatures 80 C °C 77 74 water samples 4342 434 2 434. HV001 HV HV0 01 HV0.01 lowcarbon carbon diffraction evidenced rate elements 8 7 43 HV00 0 HV0.0 4 HV0.

Abstract The Western Central Valley (WCV) of Costa Rica is an area of interest, due to its high concentration of population and economic activity, presenting itself as a tropical monsoontype atmospheric basin (AB), with well-defined climatic seasons (dry and rainy). The present study proposes the assessment of low carbon steel (CS) atmospheric corrosion, based on ISO 9223 (2012) and associated standards. A general analysis of the atmospheric basin effect was initially performed on these data, followed by the basic modeling of air pollutants and meteorological parameters. The WCV is an area of low contamination, which corresponds to a C2 or C3 category, according to ISO 9223. It mainly shows significant climatic seasons (dry and rainy) effects on the initial corrosion rates, but obtaining similar annual corrosion results for them. The ISO 9223 annual atmospheric corrosion model overestimated the actual obtained corrosion values, whereas linear or logarithmic models gave better results, especially when time and/or time of wetness (TOW) were considered as variables.

ABSTRACT The study of molecules extracted from natural products is becoming increasingly important for the evaluation of different properties such as antioxidant or corrosion inhibitor. The present work presents the computational studies carried out to evaluate mainly three polyphenolic molecules, such as catechin, quercetin and gallic acid, in their potential antioxidant activity, as well as the possible interactions with an iron substrate simulating its cubic crystalline structure centered on the body. The polyphenolic molecules were studied by computer simulation using Density Functional Theory (DFT). They were optimized by the Gaussian 09 software, by the Density Functional Theory (DFT) calculations, with the B3LYP functional (three hybrid parameters of the Becke and Lee-Yang-Para functional) and the set of bases 6-31G. The Vesta software was used to design the iron unit cell. Chemcraft software was used to construct a network of iron cells simulating a low carbon steel surface. Spartan software was used to calculate the Mulliken charge density distribution of the polyphenolic molecules. In the computational calculations, the energetic gaps of the molecules of gallic acid (-4.71 eV), catechin (-4.30eV) and quercetin (-3.73Ev) will be compared.

RESUMEN El estudio de biomoléculas extraídas a partir de productos naturales está cobrando cada vez más importancia en la evaluación de diferentes propiedades tales como las antioxidantes, aquellas que tienen la capacidad de inhibir la corrosión. El presente trabajo muestra los estudios computacionales realizados para evaluar principalmente tres moléculas polifenólicas, como son la catequina, la quercetina y el ácido gálico en su potencial efecto antioxidante, así como las posibles interacciones ante un sustrato de hierro que simula su estructura cristalina cúbica centrada en el cuerpo. Las moléculas polifenólicas fueron estudiadas mediante simulación computacional utilizando la teoría de la densidad funcional (DFT). Fueron optimizadas por el software Gaussian 09, por los cálculos del Estudio de Teoría Funcional de la Densidad (DFT), con el funcional B3LYP (tres parámetros híbrido de funcional Becke y Lee-Yang- Para) y conjunto de bases 6 -31G. Para el diseño de la celda unitaria de hierro se utilizó el software Vesta. Para la construcción de una red de celdas de hierro que simularía una superficie de acero de bajo carbono se utilizó el software Chemcraft. Para los cálculos de distribución de densidad de cargas de Mulliken de las moléculas polifenólicas se utilizó el software Spartan. En los cálculos computacionales se obtuvieron los gaps energéticos de las moléculas de ácido gálico (-4.71eV), catequina (-4.30eV) y quercetina (-3.73Ev).

ABSTRACT This work aims to study the fracture mechanisms of a low carbon laminated steel under different biaxial stress states employing a universal testing machine with an Arcan type device. The chosen material was an AISI/SAE 1020 steel, A specific butterfly specimen geometry was designed with the aid of finite element simulations to concentrate critical stresses at the center of its neck. The Arcan device can change the specimen's orientation regarding the machine loading axis, generating different biaxial stress states. Tests were carried out on pure tension (0°), combined stress with a predominance of shear stress (60°), and pure shear (90°). An evident deformation was observed in the microvoids generated in the specimens at 60° and 90°, orienting them in the direction of the shear stress, favoring their coalescence, and decreasing their mechanical resistance. Although no apparent difference was observed between the failure surface morphologies of the specimens loaded at 60° and 90°, an evident difference was observed concerning the sample at 0° due to the dominant presence of shear stress.

RESUMEN Este trabajo presenta un estudio de los mecanismos de fractura de un acero laminado de bajo carbono cuando es sometido a distintos estados de carga biaxial. Para la realización de los ensayos mecánicos se empleó un dispositivo tipo Arcan que se acopla a las mordazas de la máquina universal de ensayos y permite cambiar la orientación de la probeta respecto al eje de aplicación de la fuerza vertical, generando un estado de esfuerzo plano que varía desde la tensión uniaxial hasta el cortante puro, pasando a través de diferentes estados de esfuerzos combinados. Se eligió un acero AISI/SAE 1020 y se diseñó, con la asistencia de simulaciones de elementos finitos, una probeta mariposa cuya geometría específica concentra los esfuerzos críticos en el centro de su cuello. Se realizaron ensayos a tensión pura (0°), esfuerzo combinado con predominancia de esfuerzo cortante (60°) y cortante puro (90°). Se observó una clara deformación en los microvacíos generados en las probetas a 60° y 90° orientándolos en la dirección del esfuerzo cortante, favoreciendo su coalescencia y disminuyendo su resistencia mecánica. Aunque no se observó una diferencia apreciable en la morfología de la superficie de falla en las probetas a 60° y 90°, debido a la presencia predominante del esfuerzo cortante, sí se observa una clara diferencia con respecto a morfología de la probeta a 0°.

For the first time, the influence of gas mixture on first damage resistance of a plasma nitrided DIN 18MnCrSiMo6-4 bainitic steel was investigated. Samples were nitrided at 500 °C with three different N2-H2 gas mixtures, containing 5, 24, and 76 vol.% N2. Samples were characterized concerning the resulting roughness, microstructure, compound layer’s phase composition, residual stresses in the diffusion zone, and surface hardness. Tribological ball-on-flat tests were carried out in reciprocal mode using zirconia as ball material for friction coefficient and the compound layer resistance until the first damage. The test results were evaluated statistically by analysis of variance (ANOVA). As the amount of nitrogen in the gas mixture decreases, the ε-Fe2-3(C)N content in the compound layer decreases. A γ’-Fe4N monophasic compound layer was achieved at 5 vol.% N2 gas mixture. The diffusion zone as expected presented compressive residual stresses with the highest values near the surface. In the tribological tests, better results were obtained for 5 and 24 vol.% N2 in the gas mixture as higher amounts of γ’-Fe4N were formed. The 76 vol.% N2 gas mixture led to a brittle behavior, due to the biphasic compound layer (γ’-Fe4N and ε-Fe2-3(C)N) with a predominant content of ε-Fe2-3(C)N.

Abstract The purpose of this research is to investigate the effect of heat treatment parameters on the tool life and surface roughness of dual phase steel. Optimization of machining parameters (cutting speed, feed and depth of cut) is carried out for the machinability tests on medium carbon low alloy steel. Taguchi’s method of design is used to carry out machinability tests. Analysis of variance (ANOVA) is carried out to determine the relative contribution of machining parameters on tool life and surface roughness. Microstructure analysis is carried out to ascertain the machining behavior of the steel. Results have shown that, depth of cut and cutting speed are the most significant factors contributing on the variation of the tool life and surface roughness. Optimized machining parameters are calculated in order to obtain higher tool life and lower surface roughness value.

RESUMO Os materiais compósitos de base cimentícia, incluindo pasta de cimento, argamassa e concreto, são os materiais mais comumente utilizados na construção civil. No entanto, a sua natureza frágil, elevada dureza, baixa resistência à tração e propensão às fissuras são fatores-chave que comprometem a durabilidade e resultam em altos custos de manutenção das estruturas. Materiais de reforço como barras de aço, fibras de aço, fibras de carbono, fibras de vidro e polímeros foram extensivamente aplicados em concretos nos últimos anos. Embora estes materiais possam melhorar bastante a tenacidade do concreto, solucionando bem os defeitos que ocorrem na micro escala inerentes aos materiais cimentícios, as fraturas nestes materiais persistem. Os nanomateriais (como nanosílica, nanotubos de carbono e derivados do grafeno) podem atuar complementarmente às fibras tradicionais, reforçando ainda mais os materiais cimentícios fibrosos, por meio dos mecanismos de restrição à iniciação e à propagação das fissuras na escala nanométrica, bem como disponibilização de uma área de superfície específica extremamente elevada para interação com os produtos de hidratação do cimento. Dentre os nanomateriais, o óxido de grafeno (OG) apresenta um enorme potencial para aplicação nos compósitos cimentícios. Neste trabalho foram realizados ensaios com adição de OG produzido e patenteado no CTNano/UFMG em pastas de cimento classe CP-III-RS-40. Objetivou-se avaliar as propriedades mecânicas de pastas de cimento com adição de OG, nos teores de 0,03% e 0,05%. Dentre os teores de adição analisados, o teor de 0,05%OG permitiu a obtenção dos melhores resultados aos 28 dias de cura. Foram obtidos aumentos de 19,40%, 16,86%, 27,37% e 21,55% no módulo de elasticidade, resistência à tração na flexão, tenacidade à fratura e energia de fratura, respectivamente. Diante destes resultados, pode-se inferir que o OG tem potencial para ser aplicado na construção civil, visando a melhoria das propriedades mecânicas e parâmetros de fratura de pastas de cimento.

ABSTRACT Cement-based composite materials, including cement paste, mortar and concrete, are the most commonly used materials in civil construction. However, its brittle nature, high hardness, low tensile strength and propensity to cracking are key factors that compromise durability and result in high maintenance costs for structures. Reinforcement materials such as steel bars, steel fibers, carbon fibers, glass fibers and polymers have been extensively applied to concrete in recent years. Although these materials can greatly improve the toughness of concrete, solving well the defects that occur in the micro scale inherent to cementitious materials, the fractures in these materials persist. Nanomaterials (such as nanosilica, carbon nanotubes and graphene derivatives) can act as a complement to traditional fibers, further reinforcing fibrous cementitious materials, through mechanisms that restrict the initiation and propagation of cracks at the nanometer scale, as well as providing an extremely high specific surface area for interaction with cement hydration products. Among the nanomaterials, graphene oxide (GO) has an enormous potential for application in cementitious composites. In this work, tests were carried out with the addition of GO produced and patented at CTNano/UFMG in cement pastes class CP-III-RS-40. The objective was to evaluate the mechanical properties of cement pastes with the addition of GO, at the levels of 0.03% and 0.05%. Among the addition levels analyzed, the content of 0.05%GO allowed to obtain the best results at 28 days of curing. Increases of 19.40%, 16.86%, 27.37% and 21.55% were obtained in the modulus of elasticity, flexural tensile strength, fracture toughness and fracture energy, respectively. In view of these results, it can be inferred that GO has the potential to be applied in civil construction, aiming the improvement of the mechanical properties and fracture parameters of cement pastes.