Oxide scale distribution on 700 MPa grade high strength steel coils rolled by CSP process

Oxide scales on the surface of 700 MPa grade high strength steel produced by CSP process were studied in this paper. It is found that along the length direction of the coil, the oxide scales on the head and the middle mostly consist of magnetite-iron eutectoid, but the oxide scale on the tail is a double-layered structure with the outer layer of Fe₂O₃ and the inner layer of Fe₃O₄. Along the width direction of the coil, the oxide scale is thick at the edge, and it thins as far away from the edge. The percentage of Fe₂O₃ and Fe₃O₄ phase decreases and the proportion of magnetite-iron eutectoid increases from the edge to the width center. When the distance is over 300 mm apart from the edge the oxide scale entirely consists of magnetite-iron eutectoid. In comparison with SPHC steel produced by CSP, the oxide scale thickness of 700 MPa grade high strength steel produced by CSP is less sensitive to strip thickness.