Influence of cooling rate on the structure and formation of oxide scale in low carbon steel wire rods during hot rolling

In the present work, oxide scale formed on low carbon steel during conventional wire rod rolling (similar to 1.4 degrees C s(-1) cooling rate after laying head temperature, LHT, at 900 degrees C) was investigated. The gamma-alpha Fe transformation temperature of the grade was determined using thermomechanical simulator. Subsequently, the formation of FeO type scale was engineered through modification in cooling rate (similar to 1.4 degrees C s(-1) at 900 degrees C LHT till 750 degrees C and subsequently 8 degrees C s(-1) till reformer tub). The oxide scale formed after hot rolling was characterized using Raman spectroscopy and optical metallography. It was observed that the scale on wire rods produced through conventional cooling practices contained magnetite (Fe3O4) and hematite (Fe2O3) predominantly between the steel substrate and wustite layer, whereas a uniform wustite (FeO) layer with less transformed magnetite and proeutectoid magnetite was found on the wire rods with modified cooling practices. The modified cooling strategy at Stelmor conveyor showed a reduction in scale by 15% over conventional cooled wire rods. The increase in the tensile strength was minor (similar to 4 MPa) with the enhanced cooling rate. (c) 2005 Elsevier B.V. All rights reserved.