Effect of precipitation on recrystallization in microalloyed steels

Abstract

The progress of precipitation in undeformed austenite containing 0.018%Nb was determined by means of a mechanical testing technique. This technique is based on the influence of dynamic precipitation on the strain to the peak in the flow stress observed during isothermal compression testing at a constant true strain rate. The results obtained over the temperature range 875 to 1025°C lead to precipitation kinetics which are some what faster than those reported previously. A modification of this method was used to measure the precipitation rate in austenite containing 0.035%Nb which was given a prestrain of 5% in the temperature range 885 to 925°C. These results indicate that precipitation in deformed austenite is at least one order of magnitude faster than precipitation in undeformed austenite. A related method was employed to determine the rate of precipitation during deformation. This was observed to be a further order of magnitude faster than precipitation in deformed austenite. The retarding effect of Nb addition on the rates of both static recovery and static recrystallization is discussed, and it is concluded that a significant part of the retardation is due to the presence of Nb in solution. Furthermore, the results indicate that the occurrence of carbide precipitation can retard static recrystallization only when recrystallization is already sufficiently retarded by the solute additions to prevent its initiation prior to the beginning of the precipitation process.