Study On Process Improvement And Formation Mechanism Of Red Rust On HRB400E Wire Rod Surface

Steel in the high temperature and oxygen environment will inevitably lead to the formation of scale,and the surface red oxide scale defect generated in the Stelmor cooling process of hot-rolled wire rod will affect the product delivery and downstream users'use.In order to improve the surface quality of wire rod,the structure of oxide scale must be controlled to obtain the appropriate oxide layer structure.In this paper,HRB400E wire rod is taken as the research object.By simulating different heating and cooling processes in the laboratory,isothermal experiments and continuous cooling experiments are designed.The microstructure of scale is observed by scanning electron microscope.The temperature and cooling rate of each stage are analyzed and studied in depth.It provides reference for the control of iron oxide scale on industrial site.The research results are as follows:(1)The effect of oxidation temperature and oxidation time on the formation of scale was analyzed by oxidation kinetics experiment.The oxidation kinetic models of early and late stage were deduced.It was considered that the oxidation of steel was linear in the early stage and parabola in the later stage.The oxidation equation of HRB400E was established.(2)The results show that the thickness of scale increases with the increase of isothermal temperature,and the content ratio of FeO layer reaches the peak at 900?and 950?.When the temperature is higher than 900?,the growth of scale increases rapidly.When the temperature is below 850?,the oxidation rate is low and gentle.With the prolongation of holding time and the decrease of temperature,the FeO layer gradually disappears and the Fe₂O₃layer appears.The scale is mainly composed of Fe₃O₄.(3)The continuous cooling experiment simulated the spinning temperature and Stelmor cooling process,it is found that the proeutectoid transformation of FeO layer is the main factor causing the red rust.The more the amount of proeutectoid,the more likely the red rust defect will occur.Higher spinning temperature and lower air cooling speed will increase the number of proeutectoid transformation.When the spinning temperature is 750?and the air cooling speed is 6?/s,it can effectively inhibit the formation of proeutectoid structure and avoid the occurrence of red rust.The industrial test was carried out in the high-speed wire rod workshop.Different scale structures were formed on the surface of the wire rod by adjusting the spinning temperature and the cooling rate of Stelmor.The mechanical test and metallographic observation were carried out on the improved wire rod.The cooling process system was obtained to avoid red rust and the microstructure and properties of steel matrix met the standard requirements.