RECRYSTALLIZATION OF AUSTENITE AFTER DEFORMATION AT HIGH-TEMPERATURES AND STRAIN RATES - ANALYSIS AND MODELING

Double-hit compression tests were performed on low-carbon steels containing various combinations of niobium, boron, and copper over a wide range of temperatures and strain rates pertinent to hot rolling. The kinetics of static recrystallization are characterized in terms of the mean flow stresses, which lead to more accurate results than alternative methods. The fractional softening defined by the mean flow stress method was first corrected for adiabatic heating using a simple procedure. Appropriate expressions are given for the recystallization kinetics as a function of predeformation, temperature, and strain rate. Particular attention is paid to the effect of preloading strain rate on recystallization kinetics. It is shown that there is a one order of magnitude increase in softening rate when the strain rate is increased by two orders of magnitude. Thus, simple extrapolations of laboratory data determined at conventional strain rates to high-speed mill conditions are likely to be inaccurate.