Effect of deformation parameters on the
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I.
INTRODUCTION
K N O W L E D G E of the no-recrystallization temperature (T,r) is important in the design of controlled rolling schedules, because it determines the temperature below which the pancaking strain is accumulated. Avoiding the partial recrystallization that takes place in its vicinity can also help in reducing the occurrence of duplex grain structures. It is well known that the precipitation of carbonitrides during hot deformation plays an important role in retarding recrystallization, and several compression techniques have been developed for following the progress of precipitation in both austenite I~1 and ferrite t21 under isothermal deformation conditions. In the case of multipass deformation under continuous cooling conditions, the hot torsion test has been widely used to simulate industrial hot-rolling processes, t3-~j In the study described in this article, the latter kind of test was employed to investigate the effect of deformation parameters, such as the pass strain, strain rate, and interpass time, on the T,r during multipass deformation. This demonstrated that a Tnr is obtained even in the absence of precipitation but that it increases as the interpass time is decreased, in opposition to the dependence obtained when precipitation is taking place. The addition of titanium to Nb-bearing steels can influence the kinetics of Nb(C,N) precipitation and thus the kinetics of recrystallization. The undissolved TiN particles present prior to deformation can act as nucleation sites for austenite recrystallization, tlz,~3,~4~ thus leading to faster recrystallization kinetics. Fine freshly D.Q. BAI, Graduate Student, S. YUE, Associate Professor, and J.J. JONAS, Professor, are with the Department of Metallurgical Engineering, McGill University, Montreal, PQ, Canada H3A 2A7. W.P. SUN, formerly Research Associate, McGill University, Department of Metallurgical Engineering, is with the Department of Metals and Materials Engineering, The University of British Columbia, Canada. Manuscript submitted December 17, 1992.
METALLURGICAL TRANSACTIONS A
precipitated TiN particles, on the other hand, can act as nucleation sites for Nb(C,N) precipitation, which then accelerate the progress of precipitation. Two levels of titanium addition (0.007 and 0.026 wt pct) were employed to investigate this phenomenon; the results obtained enabled the influence of titanium on the precipitation of Nb(C,N) and therefore on the recrystallization of austenite to be clarified.
II.
EXPERIMENTAL MATERIALS AND PROCEDURE
A. Experimental Materials Three high-strength low-alloy (HSLA) steels, containing niobium concentrations of 0.05, 0.07, and 0.09 wt pct, were employed in this work. The chemical compositions of these steels are shown in Table I. The different combinations of niobium, carbon, and nitrogen concentration present in these steels made it possible to investigate the effect of supersaturation on the kinetics of Nb(C,N) precipitation. The as-received plates were machined into torsion specimens with gage lengths of 22.4 mm
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