ALPHA-PHASES ANNEALING IN ULTRA LOW-CARBON SHEET STEELS(GAMMA AND GAMMA)

alpha+gamma and gamma phases annealing in Ti and Nb-added ultra low-ca rbon sheet steels with and without Mn, P, and/or Cr has been investiga ted. In high-strength steels with Mn, P and/or Cr, BH increases as the annealing temperature increases, whereas YP-El after aging at 100 deg rees C for one hour clearly decreases. It is speculated that the coexi stence of BH and nonaging properties stems from the high dense disloca tion introduced into ferrite matrix by gamma-->alpha transformation. I n contrast, YP-El in mild steel without Mn, P, and/or Cr increases as BH increases because dislocation density in net high enough to provide nonaging property. In mild steel, r-value distinctly decreases and te xture is randomized by gamma phase annealing, while r-value increases and {111} component develops by intercritical annealing. On the contra ry, in high-strength steel, recrystallization texture developed in alp ha phase is assumed to be inherited even after alpha-->gamma-->alpha t ransformation takes place. Apparently, variant is distinctly selected when at least gamma transforms into alpha in high-strength sheet steel s. The variant selection in gamma-->alpha transformation is speculated to be caused by residual stress introduced by alpha-->gamma transform ation.