Formation of α-γ-α Transformation Texture in Sheet Steel

Abstract

For the purpose of investigating the formation mechanism of the texture which is developed by ferrite (α)→austenite (γ)→ferrite (α) transformation, the effects of heating and cooling rates during phase transformation and specimen thickness on the transformation texture have been studied by using an extra low carbon sheet steel with the initial texture of {111}.
The results obtained are summarized in the following:
(1) A weak {100} and {111} texture was formed in the surface layer of the specimen transformed by rapid heating and rapid cooling.
(2) By rapid heating and subsequent slow cooling, a texture with {110} orientations and orientations 20-30 deg shifted away from {100} was obtained in the surface layer.
(3) Slow heating and slow cooling produced a distinct {100} texture in the surface layer.
(4) There was a marked difference in texture between surface and midsection of thick specimen: In the midsection, the texture similar to that described in (1) was formed, independent of the heating and cooling rates. While, the specimen surface exhibited the texture as mentioned in (1) to (3) on each condition.
(5) Those results were consistently explained on the assumptions that the orientation relationship between bcc and fcc follows the Kurdjumov-Sachs relation, and that during a slow progress of α→γ→α transformation the orientation change proceeds preferentially by operation of such variants that generate a larger elastic work in the normal direction of a sheet surface.