極低炭素鋼のα+γ 2 相域およびγ単相域焼鈍

概要

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α+γ and γ phases 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℃ 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.
社団法人日本鉄鋼協会の論文
1994-01-01