Microstructural characterization and mechanical behavior during recrystallization annealing of Nb-stabilized type ASTM 430 and Nb-Ti-stabilized ASTM 439 ferritic stainless steels

A comparison between the niobium-stabilized type ASTM 430, 430Nb, and niobium-titanium-stabilized ASTM 439 ferritic stainless steels with respect to their microstructure and texture at the different stages of recrystallization was performed. The annealed samples were subjected to tensile test and Swift test for evaluation of mechanical behavior and deep drawability, respectively. The heat treatment was carried out on lab-scale cold rolled sheets with 85% thickness reduction as an attempt to mimic the industrial process. Recrystallization occurred first for 430Nb steel with smaller recrystallized grain sizes, less pronounced γ-fiber texture, lower average normal anisotropy coefficient, R¯, and limit drawing ratio, LDR. On the other hand, ASTM 439 showed higher yield stress but better drawability. These results are presented and discussed based on microtexture evolution, precipitate characteristics and grain boundary character distributions.