Research And Application Of The Plate Temperature Homogeneity Under The Ultra Fast Cooling Condition

Based on the newly added ultra fast cooling project in one domestic 4300mm plate production line, the research object of this paper is the plate temperature homogeneity under the ultra fast cooling condition. The works of this investigation is mainly focus on the developing of the plate temperature field model, the control strategies of the temperature homogeneity, the designing and application of the ultra fast cooling automatic control system and the adaptability of the temperature homogeneity control strategies during the cooling process. Applying the developed model, strategies and control system into one domestic 4300mm plate production line, the mass production of high-grade steel under the ultra fast cooling condition was firstly realized in our homeland. On this basis, the possibility and the adaptability of performing the temperature homogeneity control between the rough rolling and the finishing rolling and during the cooling process after rolling were analyzed and researched. Therefore, the concept of using the additional cooling system to control the plate temperature homogeneity during the rolling process was proposed. The main contents and results are as follows:(1)Due to the larger temperature gradient between the plate surface and the center under the ultra fast cooling condition, in order to improve the simulation accuracy, the influence of the temperature gradient must be considered during the process of developing the temperature model under the ultra fast cooling condition. So, based on the heat transfer principle, a new temperature model for the plate ultra fast cooling process was developed by using the finite element method. The material property inside an element varying with the temperature was considered in this model by the introduction of the unit specific heat interpolation function. To satisfy the accuracy and real-time requirements of the online model, the method of refined layer by layer was used to discrete the thick direction with intensive surface, sparse center, the variable bandwidth storage method was used to storage the data, the variable step-size model was also used to adjust the time-step dynamically. Based on these method, an on-line computation code of the proposed model is developed in the programming environment of Microsoft Visual C++6.0.(2)Based on the thermo-elastic-plastic constitutive equation coupled with the phase transformation, the coupling simulation of temperature-organization-deformation during the plate cooling process was carried out by using the Deform software. The simulation result shows that the calculated temperature and the calculated organization of the plate after cooling are in excellent agreement with the measured temperature data and the measured metallurgical structure. On this basis, the flatness varying tendency during the uneven cooling process in plate thick direction and width direction was analyzed. For the unsymmetrical cooling from top and bottom surface, the plate will warp to the rapid cooling surface and hence the whole plate shape is become shipshape. While the edge-wave will be easily formed if the plate edge in the width direction was overcooled, because that the deformation is mainly occurred at the plate edge area under this condition. This investigation provides a theoretical support for the on-site adjustment of the plate flatness.(3)The temperature homogeneity in plate length direction during the ultra fast cooling process was investigated. The idea of the micro-acceleration for each sample has been put forward in this paper. So, the optimization speed model for the run out table was established and the harmony relationship between the whole and the sample was demonstrated by the mathematical induction. The temperature homogeneous control problem of the uneven temperature distribution in plate length direction which was formed before the plate entering into the water was effectively solved and the high-precision control for the plate full-length stop cooling temperature was also realized by this model.(4)Based on the demand of cooling homogeneity and control, the new generation automatic control system for plate cooling after rolling has been designed. The State Key Laboratory of Rolling and Automation named it as ADCOS-PM (Advanced Cooling System for Plate Mill). The water supply mode of the ultra fast cooling was developed by using the water-tower of the quench machine as a stabilizer. By using this water supply mode, the mass production requirements of the NG-TMCP (New Generation TMCP) have been satisfied. Based on the cooling mode to switch the system, the seamless combination of the new-added ultra fast cooling system and the primitive ACC system was achieved by using the "first-in first-out" queue storage technology and storage time-limiting technology. Therefore, the newly added ultra fast cooling system and the original ACC system was organized to the new generation ADCOS-PM.(5)Based on the excellent cooling homogeneity of ADCOS-PM, the low-cost and reduction job has been carried out in one domestic plate production line during the high grade steel production process. For instance, the composition V is cancelled during the production of X70 pipeline steel by using the NG-TMCP. During the production of Q690, the traditional TMCP+Q+T process has been substituted by the NG-TMCP+T process.(6)In order to reduce the adjustment load of the cooling system after rolling and to ensure the homogeneity and the stability requirements of plate quality, the concept of performing the temperature homogeneity pre-control between the rough rolling and the finishing rolling and the cooling process after rolling was proposed. What’s more, the possibility and the adaptability of this concept were verified by the theoretical analysis and the numerical simulation. The simulation results shows that the deviation between the average temperature in plate width direction after cooling and its average value is less than ±15℃, while the deviation between the temperature in plate length direction and its target stop cooling temperature is less than ±10℃. That means to say, the high-precision control of the plate temperature homogeneity during the rolling process can be realized by this method. This will greatly reduce adjustment load of the cooling system after rolling. What’s more, it will play an important role for obtaining the product with high temperature homogeneity and high performance homogeneity, improving the stability of the product performance, reducing the cutting loss (head cutting, tail cutting and edge cutting) and improving the yield.This paper focus on the systematic study of the plate temperature homogeneity under the ultra fast cooling condition, the advanced cooling system for plate mill has been developed. The developed system has strong practicability, which can satisfy the control requirements of the plate temperature homogeneity for the new generation TMCP. The results have been successfully applied in the actual production control of the new generation plate cooling process after rolling in one domestic 4300mm plate production line. The industrial application shows that the ADCOS-PM is running stability. The high-precision control of the plate temperature homogeneity has been achieved by the ADCOS-PM. As part of research results, some conclusions have been award the fist prize of science and technology by the people’s government of Beijing in 2012. It has created enormous economic benefits for the enterprises. Based on this, the exploratory research and the prospective study on the pre-control of the temperature homogeneity during the rolling process were carried out. It has laid a solid foundation for realizing the high-precision control of the whole line temperature homogeneity during the plate production, obtaining the product with homogeneity temperature and organization and improving the process stability.