Efeito da deformação a frio e recozimento sobre a microestrutura, textura e propriedades mecânicas de um aço baixo C contendo 17%Mn

Abstract

Steels containing high Mn, Si and Al have a great formability combined with a high mechanical strength. This excellent mechanical performance occurs due to twinning, TWIP effect (Twinning Induced Plasticity), or martensitic transformation, called TRIP effect (Transformation Induced Plasticity). Currently, the ductility and formability are two important parameters in external automotive components manufacture, due to favoring of drawing and providing greater safety for passengers in eventual collisions. This study evaluated the microstructure and crystallographic texture, as well as the influence of these parameters on the mechanical behavior of a TRIP/TWIP steel containing 17% Mn. The stacking fault energy for this material is 14.5 mJ/m2, indicating the occurrence of martensitic transformation and twinning as deformation mechanisms. It was checked that phase transformation kinetics is favored by a longer cooling time. TRIP effect was assumed to enhance the hardening ability due to the martensitic transformation. When ' martensite reverts into shearing occurs together with diffusion mechanism. Austenite reversion is more effective and faster at higher temperatures and when it has greater stored energy from deformation. This process completes at 700°C regardless of the cold deformation amount in cold rolling. It was also proved that the martensitic transformation occurs in two steps ' and that ' martensite tends to be the major phase with the deformation increasing. The misorientations at phase boundaries were shown to be corresponding to Kurdjumov-Sachs (K-S) orientation relationship between austenite and martensite and to ShojiNishiyama (S-N) between martensite and austenite. Texture results proved that the reversion of austenite occurs without simultaneously recrystallization once the Cube component was not observed in annealed samples until 700ºC. As annealing proceeds, Goss component tends to give place to Brass in austenite. This fact is beneficial because it becomes {332}<113> in martensite after phase transformation and could promote good formability as well as high strength and toughness to the material.