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It is important to realize the transformation behavior of wüstite, because it greatly affects the final structure of the oxide layer and the surface quality of steel products. In the present study, the transformation behaviors of the wüstite layer are examined under nearly-oxygen-free conditions in order to simulate the cooling processes after the hot rolled strip is coiled. As the single phase wüstite is prepared at 950 °C, the 460 °C transformed oxide layer is composed of a mixture of iron and magnetite formed through eutectoid reactions. For the 750 °C-fabricated wüstite, only magnetite is observed after transformation, without iron precipitates, and residual wüstite. It is speculated that the unusual transformation behavior of the low-temperature-made wüstite results from the pseudo-structural intermediate phase transformation between wüstite and magnetite. This pseudo-structure is a pre-transformed wüstite and contains various concentrations of ferrous ion, which is determined by the fabrication conditions. During the hot strip mill process, wüstite is produced continuously from finish mill to laminar flow sections and culminated at 570 °C. Consequently, the final eutectoid transformation below 570 °C is dominantly controlled by the surface temperature ranging from 750 to 950 °C for low carbon steel. [ABSTRACT FROM AUTHOR]

In the present study, the reduction behaviors of red scale and the galvanization behaviors on the reduced red scale region are investigated on the Si and Mn based dual phase steel. The experiments are conducted using an Iwatani simulator. After annealing in 30 vol% H 2 at 800 °C for 120s, most of red scale can be reduced to iron but some residual FeO and SiO 2 still exist at the scale/substrate interface. By microstructure analyses after they have been galvanized, Fe, Mn and Si oxides and pure iron are observed at the interface. Fe/Zn alloy is strongly attached to the FeO contained particles from the reduced oxide scale. It indicates that zinc can be selectively coated on the oxide which can be reduced more easily. A significant factor in the galvanizing of these steels has been determined to be the oxidation state of the alloying elements. The galvanization reactions taking place at the bath/substrate interface will be discussed. [ABSTRACT FROM AUTHOR]