Scripta METALLURGICA Vol. 30, pp. 73-78, 1994 Pergamon Press Ltd. et MATERIALIA Printed in the U.S.A. All rights reserved THE INFLUENCE OF TITANIUM ON THE STATIC RECRYSTALLIZATION OF HOT DEFORMED AUSTENITE AND ON INDUCED PRECIPITATION KINETICS S.F. Medina and J.E. Mancilla° Centro Nacional de Investigaciones Metahirgicas, CSIC, Av. Gregorio del Amo 8; 28040-Madrid, Spain * Universidad Aut6noma de Puebla, UAP, Rio Sabinas 6109, 72570-Puebla, Mexico (Received August Ii, 1993) (Revised September 24, 1993) Despite the fact that some of the new microalloyed steels contain titanium, few studies published deal with the influence of this element on the static recrystallization of hot deformed austenite (1-3). Furthermore very little experimental work has been carried out on the kinetics of precipitation induced by the deformation of steels containing titanium carbides. Many Nb or V microalloyed steels contain a small percentage of Ti, usually no greater than 0.025 (% wt) due to the effect it is known to have on the austenite grain refinement (4-6). After undergoing hot deformation, the static recrystallization of micro,alloyed steels is dearly divided into two separate stages: before and after the start of induced precipitation. In the first stage the curves of the recrystallized fraction against time are similar to those of non micro,alloyed steels and in the second stage the curves display a plateau, caused by the formation of precipitates which inhibit reerystallization (7-9). The chemical composition of the steel has a considerable influence on the static recrystallization kinetics and this influence can most clearly be seen on the activation energy, which appears in the expression of the parameter t0.s in Avrami's equation (10). In the first stage the activation energy is constant and in the second stage it is a function of the temperature. In both cases the static reerystallization kinetics can be mathematically modelled (8-10). The limit between the two stages comes at a point which will henceforth be described as the Static Recrystallization Critical Temperature (SRCT), or the temperature at which the inhibition of static recrystallization begins as a consequence of the induced precipitation. This work presents a study of the influence of Ti on the kinetics of static recrystallization measured at different temperatures and on the kinetics of induced precipitation. The recrystallized fraction has been measured using the method known as back extrapolation (11). It has been found that using this method the softened fraction and the recrystallized fraction are approximately equal (12). The method used has also made it possible to draw, as will be seen later, precipitation-time-temperature (PTT) diagrams, until now determined in other Nb microalloyed steels using theoretical equations (13), or using transmission microscopy (14), and discovering in this way the kinetics of the precipitation induced by the strain. The recrystallized fraction will be modelled in accordance with Avrami's equation, as its application in hot rolling is of great use (8), and whose expression is: [ X a = l-exp-0.693 (z) where %.5 is the time corresponding to a recrystallized fraction of 0.5. 73 0956-716X/94 $6.00 + .00 Copyright (c) 1993 Pergamon Press Ltd.