Efeito da adição de Al e C na evolução microestrutural e no comportamento mecânico de aços austeníticos de baixa densidade com alto teor de Mn

Abstract

Low-density steels are advanced materials that are being developed mainly for the automotive industry to reduce the structural weight of cars. The most common studied compositions comprise FeMnAlC variations, in which both the chemical composition and processing route influence the final microstructure. Most of the studies involving the austenitic low-density steels is related to the evaluation of the mechanical properties focusing on the induced plasticity mechanisms. The objective of this thesis is to evaluate the effect of Al and C additions on the microstructural evolution and mechanical behavior of high-Mn austenitic low-density steels. Five systems with different C and Al additions were studied: Fe-36%Mn, Fe-36%Mn-2.5%Al, Fe-36%Mn-5%Al, Fe-33%Mn-5%Al-0.3%C e Fe-30%Mn-5%Al-0.6%C (weight%), in which for the alloys varying the C content, the stacking fault energy (SFE) was kept constant. Theoretical models to predict the SFE, the critical resolved shear stress for the TWIP effect, and the yield stress were used. The SFE of one alloy was determined experimentally through the partial dislocations distance. The ingots were produced by spray forming followed by mechanical processing and heat treatment. It was observed that the aluminum is not effective as carbon to increase the yield stress of the alloy. Only the alloys with C additions presented deformation twins, even though they presented the highest SFE values. The alloy without Al and C additions (lowest SFE in this work) did not presented deformation twins when deformed at room temperature, but at -100°C those structures could be observed after the tensile test. It can be pointed out that mechanisms which anchored the dislocations are important to the occurrence of the TWIP effect in high-Mn low-density steels.