Análise da influência do processamento termomecânico na microestrutura, propriedades mecânicas e textura cristalográfica de um aço 0,08C-8Mn

Abstract

Medium manganese steels are a third generation class of advanced high strength steels (AHSS) that combine mechanical properties such as ductility, mechanical strength and fracture toughness, determining characteristics for application in the automotive industry. The conventional processing route involves hot rolling followed by cold rolling and intercritical annealing, resulting in an ultrafine microstructure with a high-volume fraction of retained austenite with adequate stability so that during the deformation it becomes martensite due to the TRIP effect. Warm rolling appears as an alternative route to produce these alloys being able to reduce costs and operational time by applying only one processing step. In this context, the aim of this work is to investigate the influence of thermomechanical processing parameters on microstructure and mechanical properties in a 0.08C-8Mn steel by two distinct routes. In the conventional processing route different intercritical annealing times and temperatures were studied, to isolate the condition that exhibited the highest volume fraction of retained austenite among those studied. Scanning electron microscopy, backscattered electron diffraction, X-ray diffraction and hardness tests were carried out on both routes. For a comparative analysis between the condition of greater retained austenite volume fraction after annealing and warm rolling, analyzes were performed by EDS, transmission electron microscopy and tensile tests. Comparatively, the two conditions resulted in an ultrafine microstructure, with considerable volume fractions of retained austenite. However, a slightly larger fraction as well as a more heterogeneous austenite morphology, resulted from the warm rolling process, which may be associated with a higher hardening rate. The texture analysis, in general, indicates the predominance of the characteristic components of the deformed material, as well as the predominance of high angle grain boundaries, associated with the high dislocation density.