Análise via microscopia óptica de um aço bainítico DIN 18MnCrSiMo6-4 austenitizado e resfriado em diferentes meios
Optical microscopic analysis of a DIN 18MnCrSiMo6-4 bainitic steel austenitized and quenched with different coolants
Cristiano José Turra, Pedro José de Castro, Antonio Figueiredo Silveira, Alexandre da Silva Rocha
Resumo
mo Aços bainíticos de baixo carbono e baixa liga produzidos por resfriamento contínuo apresentam formidável combinação de resistência mecânica e tenacidade para uma série de aplicações. O ponto chave desta interessante combinação está relacionado à microestrutura multifásica, a qual é influenciada principalmente pela composição química e parâmetros de tratamentos térmicos ou termomecânicos. O modo e a velocidade de resfriamento são parâmetros essenciais nas transformações microestruturais, e impactam no tipo, proporção e refino da microestrutura, determinando o desempenho do material. O objetivo deste trabalho foi avaliar a influência de diferentes meios de resfriamento sobre a microestrutura do aço bainítico DIN 18MnCrSiMo6-4. Amostras do material na condição de recebimento foram submetidas à austenitização e posteriormente ao resfriamento em água e óleo (têmpera), ao ar (normalização), em forno (recozimento) e em banho aquecido (austêmpera). As amostras tratadas foram caracterizadas por microscopia óptica e medições de dureza Vickers. Os resultados mostraram que o resfriamento em forno favorece a formação de ferrita, reduzindo a dureza do material, enquanto que o resfriamento ao ar não modifica significativamente a microestrutura e dureza. Já o resfriamento em banho isotérmico produz bainita granular e bainita em ripas, aumentando ligeiramente a dureza. Os resfriamentos em água e óleo formam martensita com dureza de 436 e 424 HV, respectivamente.
Palavras-chave
Abstract
Low carbon and low alloy bainitic steels produced by continuous cooling present a formidable combination of strength and toughness for various applications. The key point of this interesting combination is related to their multiphase microstructure, which is mainly influenced by chemical composition and heat treated or thermomechanical parameters. Cooling conditions and rate are the most predominant factors when regarding microstructural transformation, and impact on the resulting phases, quantity and refinement of microstructure, determining the material performance. This work aims at evaluating the influence of different cooling media over the microstructure of DIN 18MnCrSiMo6-4 steel. Steel samples in as received condition were submitted to austenitizing and subsequently cooled in water, oil (quenching), air (normalizing), in the furnace (annealing), and in heated bath (austempering). The treated samples were analyzed by Optical Microscopy and Vickers microhardness measurements. Results showed that cooling from furnace benefits ferrite formation, reducing the material hardness, while air cooling doesn’t change the microstructure and hardness significantly. In addition, cooling in heated bath produces granular bainite and lath-like bainite, slightly hardness increasing. Water and oil cooling forms martensite with hardness 436 and 424 HV, respectively.
Keywords
Referências
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Submetido em:
18/03/2020
Aceito em:
16/10/2020
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