The correlation between yielding behavior and precipitation in ultra purified ferritic stainless steels

Cold rolled sheets of a ultra purified ferritic stainless steel were annealed either by being slowly cooled from 950 °C or being rapidly cooled to room temperature from the intermediate holding at 750 °C. The former exhibited substantial Lüders elongation during tensile testing, while the later showed continuous yielding behavior. In the slowly cooled sheet, both Nb(C, N) and (Fe, Cr)2Nb have been formed, and no (Fe, Cr)2Nb could be observed in the rapidly cooled sheet. The fast growth of (Fe, Cr)2Nb is believed to have caused local depletion of Nb atoms around fine NbC particles, resulting in their dissolution and having carbon atoms released for the formation of the Cottrell atmosphere. These results have been confirmed by the internal friction measurements and thermodynamic calculations.