Surface energy controlled α-γ-α transformation texture and microstructure character study in ULC steels alloyed with Mn and Al

Abstract

In this article, an ultralow-carbon steel grade alloyed with Mn and Al has been investigated during α-γ-α transformation annealing in vacuum. Typical texture and microstructure has evolved as a monolayer of grains on the outer surface of transformation-annealed sheets. This monolayer consists of < 100 > //ND and < 110 > //ND fibre, which is very different from the bulk texture components. The selective driving force is believed to reside in the anisotropy of surface energy at the metal-vapour interface. The grain morphology is very different from the bulk grains. Moreover, 30-40% of the grain boundary interfaces observed in the RD-TD surface sections are tilt incoherent < 110 > 70.5° boundaries, which are known to exhibit reduced interface energy. Hence, the conclusion can be drawn that the orientation selection of surface grains is strongly controlled by minimization of the interface energy; both metal/vapour and metal/metal interfaces play a roll in this.