Recrystallization and precipitation behavior during the hot deformation of Nb-Ti microalloyed steels

Abstract

Constant strain rate compression tests at the temperature 900∼1100 °C and the strain rate 10−3∼20 s−1 and the interpass time 300∼1000 s of double stage interrupted tests were carried out for a microalloyed steel containing 0.024 % Nb, 0.016 % Ti, 1.39 % Mn and 0.15%C, to investigate its dynamic (DRX), static (SRX) and metadynamic recrystallization (MDRX) and precipitation behavior. Softening curves were determined by the offset method and back extrapolation method. It was found that the SRX and MDRX process have different Avrami exponent n and apparent activation energy Q. For the former n=1, Q=359 kJ/mol, while for the later n=0.57, Q=259 kJ/mol. Influences of temperature, prestrain and strain rate on the kinetics of SRX process were discussed and a mathematical model was furtherly constructed. Finally, the precipitation-time-temperature (PTT) curve was determined by the stress relaxation tests, and the influence of precipitation on the SRX process was also discussed. Direct microstructural evidence for precipitation during and after deformation was obtained by transmission electron microscopy.