Effect Of Isothermal Holding And Controlled Cooling On Formation Of Oxide Scale In Wire Cord Rods

Oxide scale is inveitable in the process of steel production. The wire cord rod willbe scratched and fractured as oxide scale on the surface of it is residual. In addition, themould will be damaged and its service life reduces. In order to improve the mechanicaldescaling of the oxide scale on the surface of the wire cord rod, the amount of FeO,Fe3O4and Fe2O3must be controlled. Considering from the actual production, layinghead temperature and cooling rate were easy to be controlled.The experiment ofisothermal holding time and cooling rate were conducted in this paper and weexplored the morphology, microstructure and thickness of oxide scale with isothermalholding time and cooling rate.The bond energy of the strongest chemical bonds in FeO, Fe3O4and Fe2O3crystalswere firstly calculated by the empirical electron theory of solid and molecules (EET). Itis found by comparison that the energy of the strongest chemical bonds and difficulty ofmechanical descaling increase in the order of FeO, Fe3O4and Fe2O3.Secondly, some samples of80-grade wire cord rod were heated to900℃and heldin air for1,5,8,12and16minutes. other samples were isothermally held at900℃before cooled to room temperature at4,12and4-12℃/s. The structures of oxide scalein wire cord rod, determined by laser raman spectroscopy, are composed of FeO, Fe3O4and little Fe2O3. The morphology and thickness of oxide scale as well as themicrostructures of rod substrate were analyzed by a metalloscope. The results indicatethat cracks or holes occurred in oxide scale formed at900℃during holding stage except1and5minutes due to CO and CO2gases generated in oxide scale. The layer of FeOthickens dramatically with increasing holding time and leads to thickening in totalthickness of oxide scale, meanwhile proeutectoid Fe3O4precipitates in FeO layer. Thethickness of FeO and total oxide scale layers are reduced with increasing cooling rate, and the amount of sorbite in substrate is increased. The oxide scale and microstructuresin wire rod, formed at the cooling rate of12℃/s, are beneficial to mechanical descalingand cold drawing.