Oxidation behavior of interstitial free steel: The defining role of substrate crystallographic texture

Abstract

The oxidation kinetics of interstitial free (IF) steel were shown to differ remarkably, by more than one order of magnitude, with the crystallographic texture of the metallic substrate. More specifically, γ-fiber or ND||<111> grains oxidized preferentially and provided epitaxial or pseudo-epitaxial growth of the corresponding oxide grains. Below 843K, the initial magnetite (Fe3O4) grains had a ∼45°<001> epitaxial orientation relationship with all the substrate ferrite grains. Specimens oxidized at temperature > 843K, on the other hand, had a pseudo-epitaxy: ND||<111> metallic-substrate grains generated ND||<001> pro-eutectoid magnetite. In both cases, the oxide grains growing from ND||<111> ferrite had more dislocations and higher tensile residual stresses. They also had more magnetite and less hematite. It was proposed that the oxide phase growing from ND||<111> ferrite grains, with higher dislocation content, has faster ionic diffusion. Faster diffusion in the magnetite also appeared to reduce the protective (lower ionic diffusion) outer hematite layer. A combination of these two generated thicker oxide layers on the ND||<111> ferrite grains.