Microestrutura, textura e propriedades de estampagem de aços inoxidáveis ferríticos estabilizados ao titânio e ao nióbio após processos de laminação a quente, a frio e recozimento

Abstract

The influence of texture and microstructure of hot rolled coil on the texture, microstructure, mechanical and stamping properties after cold rolling and annealing for a niobium stabilized ferritic stainless steel and a niobium and titanium stabilized one was evaluated. The samples were taken after hot rolling with a thickness of 4mm and were cold rolled with 85% reduction and then industrially annealed. The microstructural evolution was also evaluated during recrystallization after cold deformation, subjecting the materials to rapid heating and cooling cycles at temperatures of 600°C, 700°C, 750°C and 800°C. After the hot rolling step, the steel stabilized with niobium presented a recrystallized microstructure on the surface and only recovered in the center of the thickness, and in this region the texture presented high alpha and gamma fiber fractions. The bi stabilized steel after hot rolling showed a microstructure of coarser grains, recrystallized and with a more random texture along the thickness. After cold rolling, the steel with niobium showed more pronounced alpha fiber textures. By analyzing the softened fraction during the evaluation of the evolution of the recrystallization of the two steels, it was noticed the effect of niobium in delaying this phenomenon, associated with higher fractions with orientations {001} // DN, which also showed influence in delaying the recrystallization due to the low energy accumulated during cold rolling deformation. After final annealing in an industrial area, steel with niobium showed more unfavorable relationships between the fraction of γ fiber and fiber θ when compared to bi stabilized steel, obtaining a ratio of 4.62 for steel with niobium to and 7, 74 for bi stabilized steel and consequently lower values of 𝑅̅ were obtained, being 1.43 and 1.82 respectively. For stamping tests, the LDR value was more favorable for bi-stabilized steel due to the direct relationship of the result with 𝑅̅.