Development And Application Of Oxide Scale Thickness And Structure Evolution Models Of Hot Rolled Strip

With the rapid development of China's manufacturing industry,the requirement for surface quality of hot rolled steel products in iron and steel enterprises has been raised rapidly.Therefore,surface quality is becoming a more and more important indicator to estimate product quality by iron and steel enterprises because of user's "zero tolerance" attitude toward surface quality of steel products.Moreover,production of high surface quality products is based on the accuracy control technology of oxide scale thickness and structure,which aims to realize the dynamic tracking of the evolution process of the thickness and structure of oxide scale based on the prediction model of oxide scale thickness and structure,and ultimately to achieve the precise control of oxide scale thickness and structure.Based on this,oxide scale thickness evolution model during hot rolling process,temperature field model and oxide scale phase structure transformation during cooling process after coiling were studied,and oxide scale thickness and structure prediction software was developed,which was applied in the production of hot rolled low carbon steel with high surface quality.The research contents of this paper are as follows:(1)Oxidation kinetics model under complex anisothermal condition was established in this work to realize oxide scale thickness prediction of hot rolled strip steel.Combining with the characteristics of actual rolling conditions,parameters such as descaling efficiency and the coefficient of variation of oxide scale density were introduced into the nonisothermal oxidation kinetics model.As a result,the thickness prediction model suitable to hot rolling process was established.Finally,the prediction results showed that the thickness of oxide scale increased continuously during heating and cooling process,while decreased during descaling and rolling.The predicted result of oxide scale thickness was in good agreement with the measured one.(2)In order to predict the scale structure of hot rolled strip,the finite difference method was used to establish the temperature field model during the cooling process after coiling.The predicted results of the model showed that predicted values of the temperature at different positions on the surface of the coil during the cooling process were close to the measured one.In the direction of width,the highest and lowest temperature point was in the middle and edge position of the coil,respectively.In the radius direction,the highest temperature point moved towards the inner surface of the coil and the lowest point was in outside surface.The temperature gradient of the cross section of the coil increased first and then decreases,and the temperature at the corner of the cross section of the coil was the lowest at the same time.(3)Aiming at problem that there is no numerical models for predicting the scale structure,the eutectoid phase transformation kinetics model of FeO under isothermal conditions was established based on JMAK equation and isothermal phase transformation experiment.The eutectoid transformation kinetics model for FeO under continuous cooling and process after coiling was established by combining Scheil additive rule.The prediction results showed that the volume fraction of eutectoid structure in FeO layer decreased with the increase of cooling rate and the incubation period of eutectoid transformation becomed shorter under continuous cooling conditions.In addition,the volume fraction of eutectoid structure increased with the increase of coiling temperature,and the volume fraction of eutectoid structure in the edge of coil after cooling to room temperature was less than that in the center.(4)The software for calculating the temperature field and predicting the morphology of oxide scale in the whole rolling process had been developed,which was proved to have a high prediction accuracy by The measured data of oxide scale thickness in industrial production.The process optimization strategy of "high temperature and fast rolling" was put forward to solve the problem that oxide scale of hot rolled low carbon steel were unreasonable controlled,and the thickness of oxide scale decreases and the volume fraction of eutectoid structure in oxide scale increases after optimizing the process.