Microestrutura e textura dos aços inoxidáveis ferríticos ASTM 439 e ASTM 430estabilizado ao nióbio: influência nas propriedades mecânicas e de estampagem

Abstract

A comparison of the influence of microstructure and texture on mechanical properties and drawability between the niobium stabilized ferritic stainless steel type ASTM 430, 430Nb, and the niobium titanium stabilized ferritic stainless steel type ASTM 439 was performed. Thin sheets of these two steels, produced and provided by the siderurgical company Aperam South America, were cold rolled and annealedin a process similar to that one which occurs in an industrial scale. The annealing was interrupted in five different temperatures aiming texture and microstructural characterization in different stages of recrystalization. All the samples were characterized by optical microscopy, Vickers microhardness and Electron Backscatter Diffraction (EBSD). The annealed samples were analyzed through Swift test and tensile test to evaluate mechanical properties and drawability while the precipitateswere characterized by scanning electron microscopy. The steel 430Nb showed smaller grain size, which lead to a greater yield stress. Regarding drawability, the steel ASTM 439 presented better results through a higher normal anisotropy coeficient, R, and higher Limit Drawing Ratio (LDR) due to higher proportion of texture componentsbelonging to fiber and a minor proportion of components belonging to the and fibers compared to 430Nb steel. These results are presented and discussed in terms of the characteristics of precipitates and crystallographic texture developed in the recrystallization of both steels.