Effect of Scale Microstructure on Scale Adhesion of Low Carbon Sheet Steel

For industrial purposes, the adhesion control of secondary scale on hot rolled steel sheet is important. A basic study was carried out to clarify the effect of scale microstructure on the scale adhesion of low carbon steel (0.03%C-0.2%Mn). When scale of FeO (about 8μm thickness) was generated at 800°C and transformed by continuous cooling from 250~600°C to 200°C, the scale transformed from 400°C showed good adhesion. The scale consisted of magnetite seam from the steel substrate, lamellar structure of magnetite and α-Fe, and magnetite layer from the scale surface. The orientation analysis by TEM showed the relationship {110}Fe // {100}Fe3O4, Fe // Fe3O4, and the lattice strain was calculated as 4%. On the other hand, FeO/Fe substrate showed the relationship {100}Fe // {110}FeO, Fe // FeO, and 25% lattice strain was calculated. It is considered that the adhesion of scale should be affected by the lattice strain, thus Fe3O4/Fe substrate showed better adhesion than FeO/Fe substrate. The temperature of FeO formation also affects the scale adhesion through the extent of Fe super saturation in FeO.