EFFECT OF THE BLANK SURFACE CONDITIONS ON THE QUENCHING BEHAVIOR OF A HIGH THICKNESS 22MNB5 STEEL IN PRESSHARDENING PROCESS
EFEITO DA CONDIÇÃO SUPERFICIAL DO BLANK NO COMPORTAMENTO DE TÊMPERA DO AÇO 22MNB5 DE ELEVADA ESPESSURA NO PROCESSO DE CONFORMAÇÃO A QUENTE
João Henrique Corrêa de Souza, Diego Tolotti de Almeida, Vanessa Fischer da Silveira Fischer
Abstract
act Weight reduction in commercial vehicles is increasingly gaining importance, following an already well established trend in the modern car structures. However, the production of high thickness structural components using 22MnB5 steel requires a more profound knowledge of the effect of increased heat and cycle time on the quality of the final martensitic microstructure. The identification of new process parameters offers additional possibilities to control and stabilize the manufacturing process. In this study, the influence of the surface condition of 22MnB5 steel samples with 8.0 mm thickness on the mechanisms that characterize heat transfer by contact is discussed, as is the correlation of this parameter in the characterization of the martensitic transformation and hardness profile. For this, the test specimens with three different surface conditions (natural, ground and polished) were heated to austenitization temperature, and subsequently processed in an experimental tool provided with cooling channels. Through the results of the metallographic analysis and hardness profile, it was verified that the cooling rate is affected by the superficial condition of the specimens, as well as the resulting martensitic microstructure. Higher austenitization temperatures promote austenite grain growth and, thus, deteriorate properties such as toughness and crack propagation resistance.
Keywords
Resumo
A redução de peso em veículos comerciais está ganhando cada vez mais importância, seguindo uma tendência já bem estabelecida nas estruturas modernas de carros. No entanto, a produção de componentes estruturais de alta espessura usando aço 22MnB5 requer um conhecimento mais profundo do efeito do aumento do calor e do tempo de ciclo na qualidade da microestrutura martensítica final. A identificação de novos parâmetros de processo oferece possibilidades adicionais para controlar e estabilizar o processo de fabricação. Neste estudo, a influência da condição superficial de amostras de aço 22MnB5 com 8,0 mm de espessura nos mecanismos que caracterizam a transferência de calor por contato é discutida, assim como a correlação deste parâmetro na caracterização da transformação martensítica e do perfil de dureza. Para isso, os corpos de prova com três condições de superfície diferentes (natural, retificado e polido) foram aquecidos até a temperatura de austenitização e, posteriormente, processados em uma ferramenta experimental provida de canais de resfriamento. Através dos resultados da análise metalográfica e do perfil de dureza, verificou-se que a taxa de resfriamento é afetada pela condição superficial dos corpos de prova, bem como a microestrutura martensítica resultante. Temperaturas mais altas de austenitização promovem o crescimento de grãos de austenita e, assim, deterioram propriedades como tenacidade e resistência à propagação de trinca.
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Referências
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