Abstract

Four different Transformation Induced Plasticity (TRIP) – assisted steels, were manufactured from three different carbon contents (0.2, 0.3 and 0.4 wt% C) to study the evolution of their microstructure and the relationship with their mechanical properties under tensile, impact and fracture in 15 mm thick plates. TRIP Bainitic Ferrite steels were subjected to the same austenitization heat treatment and subsequent bainitization isothermal treatment. The TRIP Polygonal Ferrite steel was subjected to an intercritical annealing and subsequent isothermal bainitization treatment. All were microstructurally characterized by optical, scanning electron and atomic force microscopies, X-ray diffraction and tensile tests in a previous paper. This research is focused on the relation between the physical metallurgy aspects with the mechanical properties, including fracture toughness. All steels presented brittle behavior in different magnitudes. The results showed that with increasing carbon content, tensile strength increased, but elongation, impact toughness and fracture toughness decreased, explained by the evolution to a coarser, harder and more brittle microstructure. It was established that the generation of a bainitic – ferrite matrix microstructure of thin plates or slats with finely distributed retained austenite, would improve the fracture toughness of the material.