Stabilization of ferritic stainless steel ASTM 409, for use in automobile exhaust systems, is increasingly in demand, due to higher exhaust gas temperatures. Ti is one of the most commonly used elements. However, high concentrations cause problems during steel casting; however, stabilization with Ti and Nb represents a good alternative. The present study aims to investigate the effect of adding Nb on the microstructure, texture, and forming properties of Ti-stabilized ferritic steels. The results demonstrated that Nb-addition leads to a more deformed microstructure after hot rolling with the strongest {110}〈001〉 Goss component. In the deformed state, the steels displayed the α-fiber, but 11CrTi+Nb steel showed a more intense γ-fiber. After annealing, Nb-addition led to an increase in the γ-fiber and in average normal coefficient of anisotropy (R). Thus, it was demonstrated that the dual stabilization (Ti+Nb) of the ferritic steel was responsible for improving the recrystallization texture and forming proprieties.

O principal objetivo desse trabalho foi estudar o fenômeno de Delayed Cracking, em aços inoxidáveis austeníticos, quando foram, severamente, deformados em operações de estampagem. Durante a conformação, a austenita desses aços se transformou em martensita e a fração volumétrica dessa fase apresentou variação em relação à altura da parede do copo e à composição química dos aços. O cobre é um elemento de liga que foi capaz de tornar o aço menos sensível ao fenômeno de Delayed Cracking pela inibição da transformação martensítica. Gradientes de martensita ao longo da parede dos copos embutido e reembutido foram determinados para um aço inoxidável austenítico convencional e um com maior quantidade de cobre em sua composição química. Os efeitos desse gradiente sobre o fenômeno de Delayed Cracking também foram analisados.

The main objective of this work was to study the Delayed Cracking Phenomenon in metastable austenitic stainless steels when they were significantly deformed by deep drawing. During the forming operations, the austenite of these steels has transformed substantially to martensite. The volume fraction of this phase has changed with the cup height and chemical composition. Copper is an alloying element able to turn the steels less prone to the cracking by inhibiting the martensitic transformation. Martensite gradients throughout the drawn and redrawn cups wall were determined for one conventional and a copper-added austenitic stainless steel and their effects on the Delayed Cracking Phenomenon were evaluated.