Medium manganese steels are a grade of the third generation of advanced high strength steels (AHSS) that combine ductility, high strength and toughness for crashing resistance, determining characteristics for application in the automotive industry. During processing these steels are subjected to a hot and cold rolling followed by intercritical annealing in the field of austenite and ferrite phases. On the other side, the warm rolling processing is capable to reduce costs and operating time due to a single operation. The aim of this work was to follow, along warm rolling, the microstructure evolution. This aim was realized by optical and scanning electron microscopy analysis, X-ray diffraction, Vickers microhardness and EBSD technique in an 8Mn-0.08C steel. A very refined and deformed microstructure in warm-rolled condition was obtained, with a higher volume fraction of retained austenite without hot-rolled as previous processing step, which result in high tensile strength and total elongation. The texture shows a greater intensity of the α-fiber components as a function of higher strain in this thermomechanical processing.

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The ferritic stainless steel type 430 stabilized with Nb, with and without annealing after hot rolling, was cold rolled and subjected to isothermal annealing at temperatures 650, 700 and 750°C for times ranging between 10 to 86400 s. The recrystallization kinetics was evaluated by JMAK model through microhardness measurements and KAM and GOS parameters. The Avrami exponent data indicate the occurrence of an unidimensional grain growth due only to high angle boundaries migration, with values ranging between 0.9 and 1.2. The nucleation rate and grain growth decreased continuously with time. The evolution of the texture was analyzed via EBSD analysis by ODF maps. The steel recrystallization is based on combination of ON and SG theories, due to presence of {111}<121>, {554}<225> and {111}<112> related to γ fiber. The rotated cube component, feature of the hot rolled steel, decreased with annealing time.

Abstract

ResumoOs aços com médio teor manganês são uma classe da terceira geração de aços avançados de alta resistência (AHSS), combinam propriedades mecânicas como ductilidade e resistência mecânica e são assistidos pelo efeito TRIP, características determinantes para sua aplicação na indústria automobilística. Convencionalmente, tais ligas são produzidas por meio de laminação a quente e a frio, seguidas de recozimento intercrítico. No entanto, o trabalho a morno têm ganhado interesse com o intuito de reduzir custos e tempo operacionais. O objetivo deste trabalho foi comparar a influência da laminação a quente e a morno por meio de análises de microscopia óptica, eletrônica de varredura, difração de raios x, microdureza Vickers e técnicas de EBSD em um aço 8Mn-0,08C. Observou-se uma microestrutura mais refinada e deformada no material laminado a morno com um maior percentual de austenita retida, o que derivou uma menor dureza. Na amostra laminada a quente, o valor médio de dureza evidenciou uma microestrutura martensítica de baixo teor de carbono. Em relação à textura verificou-se uma maior intensidade de componentes da fibra α na amostra laminada a morno devido a um maior grau de encruamento neste processamento termomecânico. Palavras-chave: Aço médio manganês; Efeito TRIP; Laminação a quente; Laminação a morno. HOT AND WARM ROLLING EFFECT IN MICROSTRUCTURE, HARDNESS AND TEXTURE OF A MEDIUM MANGANESE STEEL AbstractMedium manganese steels are a grade of the third generation of advanced high strength steels (AHSS) that combine mechanical properties such as ductility and tensile strength, determining characteristics for application in the automotive industry. Conventionally, these steels are subjected to a hot and cold rolling followed by intercritical annealing. However, the warm rolling acquire interest in order to reduce costs and operating time. The aim of this study it is to compare the influence of hot and warm rolling by optical and scanning electron microscopy analysis, X-ray diffraction, Vickers hardness and EBSD in a 8Mn-0,08C steel. A refined and deformed microstructure in warm-rolled sample was observed, with a higher volume fraction of retained austenite, which derived a lower hardness. In the hot-rolled sample, the average hardness value revealed a martensite with a low carbon content microstructure. The texture shows a greater intensity of the α fiber components in warm rolled to warm due to higher strain in this thermomechanical processing.