Abstract
α+γ andγphases annealing in Ti and Nb-added ultra low-carbon sheet steels with and without Mn, P, and/or Cr has been investigated.
In high-strength steels with Mn, P and/or Cr, BH increases as the annealing temperature increases, whereas YP-El after aging at 100°C for one hour clearly decreases. It is speculated that the coexistence of BH and nonaging properties stems from the high dense dislocation introduced into ferrite matrix by γ→α transformation. In contrast, YP-El in mild steel without Mn, P. and/ or Cr increases as BH increases because dislocation density in not high enough to provide nonaging property.
In mild steel, r-value distinctly decreases and texture is randomized by γ phase annealing, while r-value increases and {111} component develops by intercritical annealing. On the contrary, in high-strength steel, recrystallization texture developed in α phase is assumed to be inherited even after α→γ→α transformation takes Place. Apparently, variant is distinctly selected when. at least γ transforms into α in high-strength sheet steels. The variant selection in γ→α transformation is speculated to be caused by residual stress introduced by α→γ transformation.
