STATIC RECRYSTALLIZATION OF AUSTENITE AND STRAIN-INDUCED PRECIPITATION KINETICS IN TITANIUM MICROALLOYED STEELS

Using torsion tests and applying the back extrapolation method the recrystallized fraction of austenite was measured at two strains (0.20 and 0.35) and several temperatures in three Ti microalloyed steels. Graphical representation of the activation energy vs the inverse of the temperature makes it possible to determine the static recrystallization critical temperature (SRCT) of each steel as a function of the strain. With the results obtained, a model was constructed for the recrystallized fraction both at temperatures above and below the SRCT, and this, together with other equations already published, permits calculation of the residual strain and austenite grain size which the steel is expected to have at the end of rolling and before the gamma --> alpha transformation. Graphs of the recrystallized fraction vs time show the kinetics of strain induced precipitation and PTT diagrams (precipitation-time-temperature) were constructed for the three steels. It is noted that the degree to which the strain affects the precipitation kinetics decreases as the titanium content of the steel is increased.