Oxide scale behavior and rolling characteristics in hot steel rolling

Abstract

Synopsis: In hot steel rolling process, oxide layer, i.e. scale, is formed on surface by oxidation. The scale may influence friction between rolls and workpiece and affect rolling characteristics. In this study, low carbon steel sheet was inserted to a furnace at 1173K, 1273K, 1373K filled with argon. After 900 s, the atmosphere was changed to air to allow oxide scale to grow for 0, 10, 40 s. After the oxidation, the sheet was immediately rolled by 10-30% on a two-high laboratory mill. After passing the roll bite, glass powder was sprinkled over the sheet to suppress secondary oxidation. If the oxidation time is 0 s, the thin scale deforms relatively uniformly at all the three temperatures. At 1173K, if the oxidation time is 40 s, the scale is indented to the matrix steel, the interface between the scale and the matrix steel roughens apparently. At 1273K, the scale fractures and the matrix steel is extruded through cracks to outermost surface. At 1373K, the scale cracks in thickness direction, however the interface between the scale and the steel is smooth. The rolling force is not sensitive to the oxidation time at 1173K. At 1273K and 1373K, However, when the reduction is high, the force decreases with oxidation time. In these cases, the internal shear deformation decreases with oxidation time. It is supposed that thick scale tends to fracture and decreases the shear deformation by introducing relative sliding between the rolls and the matrix steel.