Research On The Control Technology With Inter-pass Cooling Process Under Ultra-fast Cooling

The plate is an important iron and steel material supporting the development of the national economy and social development.The rising demand and the new requirements of the plate kinds,properties,product rate,energy saving,production process,production costs etc have been put forward.At the same time,plate production has a series of problems.Due to the core quality defects of the slab and the limit of rolling reduction,it results in coarse grains in product core and instability mechanical properties.Also the production efficiency is low and it is difficult to guarantee the quality.In view of the above problems,this paper based on the national key project "Research and application of high strength,large size,easy welding marine steel"(2016YFB0300601)and the Central University funded project "The internal defects evolution mechanism of high gradient temperature rolling under ultra-fast cooling"(L1507020).The study is carried out based on the control technology with temperature-deformation coupling.This paper uses the method of finite element numerical simulation and rolling experiments to study jet impingement heat transfer in high temperature,the effect of cooling process during rolling and temperature gradient rolling process on the temperature distribution and deformation.This study enriches the heat transfer and conduction theory for cooling plate with high temperature.The influence of cooling and rolling parameters on deformation behavior of temperature gradient rolling are mastered.And it provides a theoretical support and basic guarantee for the industrial application of the temperature gradient rolling.The works are listed as follows:(1)Based on the review of the research progress and related literature of control rolling and control cooling technology domestic and abroad,this paper summarized the heat transfer law,temperature distribution and the deformation characteristics of temperature gradient rolling.It provides a theoretical basis for the study of heat transfer and temperature-deformation coupling of temperature gradient rolling.(2)The basic heat transfer characteristics and main influencing factors of single jet impingement in high temperature phase are studied with laboratory cooling platform.The distribution of heat exchange area,the rule of rewetting,the heat flux,the peak value of heat flux and so on are obtained.The effects of flow rate and inclination angle on the rewetting behavior and temperature distribution were explored.Through cooling the plate with different thickness with instant cooling equipment,the law of internal temperature variation and heat conduction are obtained.(3)The finite element analysis software DEFORM is used to establish cooling model during passes.The influences of plate thickness,heat transfer coefficient,air cooling time,water cooling time and cooling path on the variation of temperature field are analyzed.The influences of various parameters on the cooling velocity distribution,temperature distribution,temperature gradient distribution,core-surface temperature difference and low temperature layer thickness are given.(4)The numerical analysis method is established for the coupling analysis of the cooling and rolling,and the effect of cooling technology,pass reduction rate,cooling technology during passes and reduction rate distribution on the deformation of plate are studied.The results show that the temperature gradient establishing by using the method of interval cooling,temperature gradient establishing at the beginning of the rolling,arranging the temperature gradient at heavy reduction can help improving the deformation in the center and deformation permeability of temperature gradient rolling.(5)Based on the numerical simulation result of temperature gradient rolling,this paper has designed single-pass and multi-pass temperature gradient rolling experiments with instant cooling equipment,compared with constant temperature rolling.It is found that the increase of the temperature gradient is favorable to the increase of the deformation and deformation permeability.In the process of temperature gradient rolling,a cooling during rough rolling helps improving the deformation in the center better,and the rolling force increases little.A cooling during finish rolling helps improving the deformation in the center,and the deformation uniformity of the plate is better but the rolling force increases a lot.(6)According to the experimental results above,the mathematical model and control system of the instant cooling system are developed by our team based on the heat transfer law of jet impingement cooling meeting the requirements of cooling control.