Microstructural analysis as the indicator for suitability of weld repairing of the heat resistant Cr - Ni steel (original) (raw)
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Revista de Metalurgia
El efecto del calor de entrada sobre el comportamiento a la fractura de la zona afectada por el calor recalentada en uniones soldadas multipasos de acero ASTM A633 fue evaluado mediante la prueba de impacto, fractografía, microscopia electrónica de barrido y procesamiento digital de imágenes. Los resultados de impacto indicaron una reducción en la energía Charpy como función de la velocidad de alimentación de alambre, lo cual se confirmó mediante fractografias después del procesamiento digital de imágenes que mostraron una reducción en la fracción volumétrica de microhoyuelos en la fractura dúctil acompañada del incremento en la rapidez de alimentación, favoreciendo la fractura frágil con facetas de clivaje transgranular conteniendo marcas de rio. La fracción mínima de microhuecos y el tamaño más largo de facetas mostrando un mayor número de patrones de rio fueron encontrados a la máxima rapidez de alimentación de 200 mm·s-1. La microestructura heterogénea de la zona afectada por el...
Microestrutura e propriedades mecânicas do aço AISI 1016 calibrado processado por ECAP
Universitas scientiarum, 2014
Low carbon cold drawn steel was deformed using equal channel angular pressing to evaluate its mechanical properties and microstructure, while assessing the possibility of improving properties beyond the cold drawn process. We used low carbon cold drawn steel with a composition of 0.16% C, 0.8% Mn, 0.2% Si, 0.02% P, 0.012% S and Fe balance. The process was carried out at room temperature and four passes at route Bc with a deformation of ~0.6 in each pass. Using scanning electron microscopy and x-ray diffraction, we evaluated the evolution of the structure before and after deformation as well as the mechanical properties of microhardness and tensile strength. A slight increase in the mechanical properties occurred when the number of passes was increased. There were changes in the original ferritic-pearlitic structure with the refinement of ferrite grains and pearlite deformation.
A Microstructural and Fractographic Study on the Failure of a Drive Shaft
Journal of Failure Analysis and Prevention, 2011
As in the case of implants, the increase of the life expectancy and of the risk of accidents, thus causing a higher incidence of surgeries, has led to an increased use of surgical instruments. The reliability of these instruments, used in applications of considerable responsibility, depends on the characteristics of the materials, as well as on the conditions of manufacture. Using some techniques such as optical microscopy, scanning electron microscopy, and hardness tests, this work has as purpose the identification of the possible causes of failure of surgical torch meters used for dental implants fixation, trying to correlate with the microstructural characteristics of the austenitic and martensitic stainless steels used in their manufacture. The results thus obtained allowed the identification of the main causes of the failure, primarily related to microstructural heterogeneities which resulted from inadequate heat treatment and with the presence of non-metallic inclusions, which favored brittle fracture and corrosion.
Microstructural Analysis of Failure in Building Materials
Scanning Electron Microscopy "SEM" provide valuable tools to identify microstructural differences in materials due to ageing, aggressive environmental exposures and loading. Image processing technique has been applied on several SEM micrographs to provide information on the extent of damage in the surfaces of the microstructure; it measures the area of micro-voids on the surface. Analysis has shown that lime mortar materials were the main building materials used in many heritage buildings due to the ease of production and application. However due to long exposure the lime mortar develop failure in the mode of cracks, crumbling and erosion of the materials. Steel sections were also deteriorated due to environmental exposure combined with loading. Therefore, to understand how various materials degraded with time, it is important to analyze the microstructural changes supplemented with measurement of the area of damages in the form of micro-voids. SEM micrographs revealed loose microstructures in damaged lime mortar materials and uniform and dense microstructures in protected and durable materials. The void fraction of the damaged steel section due to load and exposure was found to be 0.0003.
Fractography of sintered iron and steels
The processing technology of sintered steels cannot avoid typical microstructural discontinuities such as pores and their agglomerates and prior particle, interface and interphase boundaries, which all influence initiation, growth, and propagation of cracks when the sintered microstructure is mechanically loaded. Fracture paths and fracture resistance are shown to be related to details of the complex, frequently inhomogeneous, microstructures comprising, ferrite, austenite, upper and lower bainite, martensite, pores and weak interfaces. All these have characteristic fracture resistance properties resulting in, frequently combinations of, dimple rupture, cleavage, intergranular and interparticle failure micromechanisms. Keywords: fracture in metals, fractography of sintered iron and steels INTRODUCTION Metals fail in many different ways and for different reasons. The main purpose of microfractography is to determine how and why a component fails -it means to determine a mode of failu...
A Mathematical Model to Predict Microstructure of Heat-Treated Steel
Journal of Materials Engineering and Performance, 2007
The dual effects of chemical composition and cooling rate on microstructural evolution were theoretically simulated extending the Johnson-Mehl equation for non-isothermal pro-eutectoid ferrite transformation kinetics incorporating the effect of supercooling (DT) as well as for isothermal pearlite transformation kinetics assuming the exponent on time 'nÕ to vary inversely with time as, n = p/t m , for case carburized steel quenched in oil. Carbon concentration profile of steel carburized at 930°C for 10 h was theoretically computed by solving the FickÕs diffusion equation. The cooling curves from surface to core were generated for typical 20.32 and 15.6 mm diameter steels using FEM package (ANSYS) for oil quenching, water quenching, and air cooling. The effect of varying carbon concentration from surface to core was incorporated in the heat transfer equations while generating cooling curves, at different case depths (surface, 0.31, 0.558, 1.239, and 3.469 mm). The cooling curves for oil quenching were superimposed on the published TTT diagrams of the steels of corresponding carbon content and using the empirical equations the evolution of different microconstituents, e.g., ferrite, pearlite, and martensite from the parent austenite phase were computed for the carburized 20.32 and 15.6 mm diameter steel samples. These steel samples were also case carburized experimentally at 930°C for 10 h followed by oil quenching. The theoretically predicted case depth of 3.469 mm matched closely with the experimentally observed value. Microstructural studies were done on inverted microscope and quantitative image analyzer at different case depths/nodal points. Microhardnesses were also measured at case depths from 0.1 mm to center of the samples at selected areas to identify the different phases. The experimentally observed microstructures matched well with the theoretically predicted evolution of microconstituents.
Este trabalho investiga as causas que levaram à fratura de um dispositivo prolongador. O componente faz parte de um conjunto de fixação de punções e machos de um equipamento para compactação de pós metálicos. A análise identificou mecanismos macro e microscópicos através de análise da superfície de fratura. Foram adotadas técnicas de caracterização como análise visual, ensaio de dureza Rockwell C, análise metalográfica e microscopia eletrônica de varredura. Os resultados indicam que a trinca iniciou na região próxima à superfície, devido à uma fragilização do material. A falha resultou em nucleação de trincas intergranulares no material. À medida que a trinca avançou, o micromecanismo de fratura alterou para fratura frágil por clivagem, até a ruptura final da peça.