Avaliação das propriedades mecânicas de um aço dual-phase
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Citações na Scopus
Tipo de produção
Trabalho de Conclusão de Curso
Data
2023
Autores
Morais, Amanda Falcari
Orientador
Magnabosco, Rodrigo
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Texto completo (DOI)
Palavras-chave
dual-phase,propriedades mecânicas,austenitização parcial,dual-Phase steel,mechanical properties,partial austenitizing
Resumo
Este projeto teve por objetivo avaliar as propriedades mecânicas e microestrutura de um aço dual-phase produzido em laboratório, verificando seu desempenho para uma possível aplicação estrutural na indústria automobilística, para a qual se espera principalmente boas ductilidade e resistência mecânica. Através do ThermoCalc© foram objetivadas amostras com frações volumétricas de martensita de 32,8%, 40,0% e 51,1% considerando três temperaturas diferentes de austenitização parcial, 728°C, 745°C e 765°C. Foram realizados ensaios de tração, ferritoscopia, dureza, metalografia e Difração de Raios-X (DRX) nas amostras após o tratamento térmico, a fim de analisar as propriedades mecânicas. Foi verificado que o limite de resistência e limite de escoamento apresentaram maiores valores com o aumento de temperatura. A dureza das amostras, assim como os valores de limite de escoamento e resistência, aumentou na presença de maiores teores de martensita por ser uma fase mais dura e resistente. O módulo de elasticidade mostrou valores não muito condizentes com a teoria, descartando-se a possibilidade de influência da austenita retida, assim, sendo proposto uma mudança no método de determinação do módulo. O alongamento uniforme dimunui na presença de maior fração volumétrica de martensita enquanto o alongamento total se mantém praticamente constante, os quais sofrem influência da homogeneidade de distribuição da ferrita nas amostras. O aumento da estricção é justificado pelo maior teor de austenita retida na estrutura e refino do tamanho de grão da ferrita. A análise por DRX apresentou apenas picos de ferrita que, por sua vez, engloba a microestrutura martensítica, além de não evidenciar picos de austenita, indicando que a austenita retida, está presente provavelmente com tamanho diminuto entre as ripas de martensita. A ferritoscopia comprovou a presença de austenita retida com teores pequenos de 1,7%, 5,2% e 8,8%, crescente com a temperatura de tratamento, sendo influenciada pela composição química (principalmente o elemento carbono), que afeta diretamente as temperaturas de transformação martensíticas (Ms e Mf). Com o auxílio do ImageJ© foi notado que as frações volumétricas de martensita objetivadas (32,8%, 40,0% e 51,1%) não foram atingidas (64,9%, 85,1% e 92,3%) provavelmente porque o tempo no patamar isotérmico não foi suficiente para formação da fração de equilíbrio de ferrita.
This project aims to evaluate the mechanical properties and microstructure of a dual-phase steel produced in laboratory, verifying its performance for potential structural applications in the automotive industry, focusing mainly on good ductility and mechanical strength. Using ThermoCalc©, samples with volumetric fractions of martensite at 32.8%, 40.0%, and 51.1% were targeted, considering three different temperatures for partial austenitizing: 728°C, 745°C, and 765°C. Tensile testing, ferritoscopy, hardness testing, metallography and X-ray diffraction (XRD) analyses were carried out on the samples after the heat treatment to analyze their mechanical properties. It was observed that the ultimate tensile strength (UTS) and yield strength (YS) showed higher values with increasing temperature. Sample hardness increased with higher martensite content, as well as UTS and YS, due to martensite's greater hardness and strength. The modulus of elasticity exhibited values that were not entirely consistent with theory, ruling out the possibility of retained austenite influence. Therefore, a proposed modification in the module determination method is suggested. Uniform elongation decreased with a higher volumetric fraction of martensite, while total elongation remained relatively constant; both were influenced by the homogeneity of ferrite distribution in the samples. The increase in necking was attributed to the higher content of retained austenite in the structure and the refinement of ferrite grain size. XRD analysis revealed only ferrite peaks, the same found for the martensitic microstructure, without indicating austenite peaks. This suggests that the retained austenite is probably present in a very small size between the martensite laths. Ferritoscopy confirmed the presence of retained austenite at small levels of 1,7%, 5,2%, and 8,8%, increasing with the treatment temperature, and it was influenced by the chemical composition, mainly carbon content, which directly affects martensitic transformation temperatures (Ms and Mf). Using ImageJ©, it was found that the targeted volumetric fractions of martensite (32,8%, 40,0%, and 51,1%) were not achieved (64,9%, 85,1%, and 92,3%), likely due to insufficient isothermal holding time for the formation of the equilibrium fraction of ferrite.
This project aims to evaluate the mechanical properties and microstructure of a dual-phase steel produced in laboratory, verifying its performance for potential structural applications in the automotive industry, focusing mainly on good ductility and mechanical strength. Using ThermoCalc©, samples with volumetric fractions of martensite at 32.8%, 40.0%, and 51.1% were targeted, considering three different temperatures for partial austenitizing: 728°C, 745°C, and 765°C. Tensile testing, ferritoscopy, hardness testing, metallography and X-ray diffraction (XRD) analyses were carried out on the samples after the heat treatment to analyze their mechanical properties. It was observed that the ultimate tensile strength (UTS) and yield strength (YS) showed higher values with increasing temperature. Sample hardness increased with higher martensite content, as well as UTS and YS, due to martensite's greater hardness and strength. The modulus of elasticity exhibited values that were not entirely consistent with theory, ruling out the possibility of retained austenite influence. Therefore, a proposed modification in the module determination method is suggested. Uniform elongation decreased with a higher volumetric fraction of martensite, while total elongation remained relatively constant; both were influenced by the homogeneity of ferrite distribution in the samples. The increase in necking was attributed to the higher content of retained austenite in the structure and the refinement of ferrite grain size. XRD analysis revealed only ferrite peaks, the same found for the martensitic microstructure, without indicating austenite peaks. This suggests that the retained austenite is probably present in a very small size between the martensite laths. Ferritoscopy confirmed the presence of retained austenite at small levels of 1,7%, 5,2%, and 8,8%, increasing with the treatment temperature, and it was influenced by the chemical composition, mainly carbon content, which directly affects martensitic transformation temperatures (Ms and Mf). Using ImageJ©, it was found that the targeted volumetric fractions of martensite (32,8%, 40,0%, and 51,1%) were not achieved (64,9%, 85,1%, and 92,3%), likely due to insufficient isothermal holding time for the formation of the equilibrium fraction of ferrite.