Scale Structure Developed on the IF Steel Surface through Hot Rolling

摘要

The scale structure that developed on hot rolled steel has been visualized by electrochemical etching. The results obtained from this investigation are; 1. The scale developed under the standard hot mill operation has a "layer by layer structure" and it well matched with the predicted structure which has been widely accepted except for the bottom layer. 2. The layer by layer structure is From the scale's top surface > Fe2O3 / Fe3O4 / FeO / Fe3O4 (Fe2O3) > to the substrate steel surface. 3. The first layer was found to be the porous Fe2O3. The second layer found to be polycrystalline Fe3O4, the third layer was also polycrystalline FeO and the bottom layer was Fe3O4 4. The coiling temperature showed a strong influence on the first layer (Fe2O3 ) and the bottom layer of the scale. On the fourth layer, Fe3O4 changes to Fe2O3. 5. Under the high coiling temperature, the second layer and the fourth layer were connected to each other by channels of Fe3O4. Around the channel, Fe2O3 was found. 6. The channel has a crevice at its center, which may contribute to the supply of oxygen to the bottom layer of scale.