【作者】 王丙兴；

【导师】 张殿华； 王君；

【作者基本信息】 东北大学 ， 材料加工工程， 2009， 博士

【摘要】 控制冷却是TMCP技术的重要组成部分,它通过改变轧后冷却条件来控制相变条件和碳氮化物析出行为从而改善钢板组织和性能。中厚板轧后多阶段冷却控制策略的研究目的在于对轧后钢板在冷却过程中的温度变化和组织演变过程进行精细控制,提高冷却均匀性,使之满足复相钢、高强钢等新产品生产的需求。本文以国家“十一五”科技支撑计划中“节约型钢材减量化轧制技术”课题为背景,结合新一代轧后快速冷却系统开发项目,针对中厚板轧后多阶段冷却控制策略进行研究。重点对冷却过程中的换热机理,温度场解析模型等理论模型以及钢板内部温度变化规律等工艺过程进行系统研究。在此基础上,开发中厚板多阶段冷却控制系统,研究高精度、均匀化冷却技术,解决工程应用实际问题,并以高强度C-Mn钢为例实现轧后多阶段冷却控制策略的应用。最后,根据最优控制理论进行了多阶段温度路径最优跟踪控制。本文主要研究内容和成果如下：(1)研究控制冷却系统的理论模型。首先,对超快速冷却和层流冷却状态下换热模型、冷却效率模型进行研究,分析得到换热系数、冷却效率随各种影响因素的变化规律。在此基础上,根据能量守恒定律回归水冷换热系数模型,获得可在线应用的数学模型。(2)采用有限元解析方法求解钢板内部温度场。根据中厚板冷却过程中的导热微分方程及其初始条件和边界条件,利用有限元法实现对钢板内部温度场的解析计算。其中,重点研究相变转变产物及其转变量的计算方法,获得相变潜热的计算模型；合理划分有限单元网格,确定迭代计算时间步长,在保障模型计算精度的同时,满足在线应用要求。以内能为基础,建立钢板平均温度的处理方法,计算结果更能真实地反映钢板平均温度变化情况。(3)分析各种冷却条件下中厚板内部温度变化规律。对钢板在各种冷却方式下钢板温度变化规律进行研究,包括空冷过程,超快速冷却及其返红过程和加速冷却及其返红过程。阐明各种因素对钢板内部温度变化影响,并揭示了钢板冷却有效厚度、平衡温差以及返红分界线的变化规律。(4)研究多阶段冷却条件下钢板工艺特点。首先,分析钢板在复合冷却方式,不同冷却模式及集管排布形式条件下的温度变化规律。其次,研究获得各种冷却策略条件下,钢板冷却速度变化规律。最后,分析指出轧后立即进行超快速冷却有利于提高钢板力学性能,而采用控制灵活的加速冷却方式,可以实现对过冷奥氏体相变的灵活控制。(5)建立多阶段冷却控制系统。结合国内某中厚板厂轧后冷却设备的具体布置形式,建立多阶段冷却控制系统,分别对其基础自动化和过程自动化功能及时序触发机制进行系统阐述。解决影响系统控制精度及冷却均匀性的关键问题,满足多阶段冷却控制的工业生产需要。深入研究多阶段冷却过程控制机理,确定各阶段冷却方式,实现超快速冷却、加速冷却过程控制,并以高强度C-Mn钢为例阐述多阶段冷却过程控制原理。(6)基于线性二次型优化算法,实现中厚板轧后多级温度路径的优化控制。以集管冷却效率、终冷温度和温度路径为目标建立中厚板轧后多级温度路径优化控制算法。对20mm厚高强船板DH36轧后多级温度路径进行工艺优化控制,实现了各个冷却阶段终冷温度和冷却速度的高精度控制,将优化结果应用于工业实验,有效避免了钢板厚向温度及组织差异过大,获得了具有理想组织性能的产品。更多还原

【Abstract】 Controlled cooling was an important part of TMCP technology by which the effect factors of phase transformation and the precipitation behavior of carbide were controlled to improve the microstructure and mechanical property of steel. Multistage cooling control was to control the phase transformation process accurately and to improve cooling uniformity so as to satisfy the need of the production of new products such as complex steel and high-strength steel etc. Based on the significant technology "Saving Type Steel Products and Its Reduced Steel Rolling Technology" of "11th Five-Year Plan" Key Technology R&D Program, the new generation cooling system was developed and the multistage cooling control stragety of hot plate was researched in this article. The mechanisms of heat transfer during accelerated cooling and ultra-fast cooling process and the analytical model for the variation of temperature inside plate were analyzed. The key technology basis for controlled cooling was researched, where the emphasis was the variation of temperature filed under different cooling strategy. Based on theoretical and technological researched, multistage cooling control system was developed. To satisfy the need of industrial application, the high-precision and uniform cooling technology was researched. Optimum control of multistage temperature profile was accomplished based on optimal control theory. The main work and results are as follows:(1) The theoretical models of the controlled cooling system were researched. First, the heat transfer between plate and coolant during the process of accelerated cooling, ultra-fast cooling and air cooling etc. were analyzed profoundly. Based on energy conservation principle, the on-line regression equation for the coefficient of heat transfer was established. (2) The finite element method to analyze temperature field was established. The differential equation and its boundary condition, initial condition to analyze thermal conduction inside hot plate were introduced. The differential equation was analyzed by the finite element method. The models for calculating latent heat during various phase transformation inside hot plate deduced from an important model of which was the transmutation product and its quota of phase transformation. The finite element mesh and time step for iterative computation were decided appropriately so that the finite element method could be used on-line with high-precision. Based on internal energy, the average temperature inside hot plate was calculated. The calculated results could reflect the variation of real average temperature.(3) The variation regular of temperature was researched for building of the multistage cooling control system. The variation regular of temperature inside hot plate under different cooling condition was researched such as accelerated cooling, ultra-fast cooling, and air cooling. The variation regulars of effective cooling thickness, balance temperature difference and red-back critical line were disclosured.(4) The technology feature of hot plate under the condition of multistage cooling was researched. Firstly, the variation regular of temperature under the combined type cooling system developed by RAL was researched. Secondly, the cooling rate was researched under different cooling strategy. Base on cooling rate, the effects of cooling method on phase transformation were analyzed. The ultra-fast cooling and the accelerated cooling were recommended to control the incubation period of phase transformation and the process of phase transformation respectively.(5) The multistage cooling control system was established to satisfy the need of industrial production of plate. Base on cooling equipment layouts of some plate plant, a multistage cooling control system was developed. The function of electric automatic control system and technology automatic control system, and trigger mechanism according to time sequence were described. The key technology to improve control accuracy and cooling uniformity of the control system was introduced. The working principle of the technology automatic control system was researched. How to select the cooling pattern and to realize the control process of ultra-fast cooling and accelerated cooling were discussed in details. The working principle of multistage cooling control system was introduced as an example to high strength C-Mn steel.(6) The optimal control based on linear quadratic was introduced to control the multistage temperature profile of hot plate. To control cooling profile with high degree of accuracy using optimal cooling efficiency, the controlled targets of performance fuction were cooling efficiency of cooling unit, finish cooling temperature and cooling profile. The finish cooling temperature and the cooling rate of 20mm DH36 of each stage were controlled with high-precision. The ideal microstructure and mechanical property of DH36 were obtained during the industrial experiment at some factory.更多还原