MICROSTRUCTURAL CHANGES OF IF STEELS DURING HOT STRIP ROLLING

The hot deformation behavior of three interstitial free (IF) containing Ti and/or Nb under strip or plate rolling was investigated by means of multi-pass torsion tests. All the tests were carried out at a strain rate of 2 s^-1 . Three types of strip rolling schedules (they differed only with respect to the number and total strain of finishing passes) and one type of plate rolling were employed. Under strip rolling conditions the effects of total finishing pass strain and first finishing pass temperature was investigated. The plate rolling schedule was used in order to determine the three critical hot deformation temperatures, i.e., Tnr, Ar3 and Ar1. The results indicate that, under strip rolling conditions, static recrystallization is responsible for the high degree of interpass softening in the early passes of rolling. During the final passes, dynamic recrystallization occurs to a degree that depends on the composition of the steel, the total finishing strain and the temperature.