Abstract
Extra-low-carbon and extra-low-nitrogen steel has been cold rolled to 75% in reduction, and subsequently nitrogen contents of the steel have been adjusted to ≤2 ppm and 160 ppm by atmospheric reaction to the steel at 350°C. These two steels have been annealed at various temperatures at a constant heating rate, and their recrystallization behaviors have been investigated by X-ray diffraction analysis and electron microscopic observations.
In the low nitrogen steel, recrystallization starts at low temperature, initially withont any change in texture, and at the later stage of recrystallization {111} components increase. While in the high nitrogen steel, recrystallization starts at higher temperature accompanied by slight decrease in {111} components and rapid increase in {110} components. According to the electron transmission studies of the steels in the early stage of recrystallization, rotation angles between recrystallized grain and adjacent recovered matrix are relatively small for the low nitrogen steel and large for the high nitrogen steel. These observations imply that in situ recrystallization which takes place with small-angle boundary migration or annihilation is preferred in the former steel and the growth of recrystallized grain by large-angle boundary migration from heavily curved regions in deformed matrix is predominant in the latter steel.
These differences in recrystallization behavior by nitrogen content are believed to be caused by the strong interaction between dislocations and nitrogen atoms.
