【作者】 陈伟；

【导师】 张玉柱；

【作者基本信息】 燕山大学 ， 机械设计及理论， 2009， 博士

【摘要】 在钢铁产品的结构组成中,各种异型钢材占很重要部分。H型钢是一种经济断面型材,其一经问世就在国民经济建设的各个领域得到了广泛应用。近终形异型连铸坯是生产H型钢最理想的坯料,目前国内仅有三条异型坯连铸生产线。作为一种新型坯型,异型坯连铸技术在国内外均属刚刚起步阶段,加上异型坯截面形状比较复杂,在其生产过程中容易存在较多的内部质量和表面质量缺陷。目前科研工作者对异型坯连铸技术的研究刚刚开始,因此开展H型钢异型坯质量控制研究,从根本上查找异型坯产生相关质量缺陷的原因,并在此基础上优化改进异型坯连铸工艺技术,具有重大的经济意义和学术价值。本文以一异型坯连铸生产线为基础,从异型坯存在的表面裂纹和洁净度等质量问题入手,采用实验研究和数值模拟两种研究方法对异型坯出现相关质量问题的原因和预防措施进行了分析和探讨。其中实验研究主要是对裂纹和夹杂物以及保护渣的分析和检测,初步分析影响铸坯质量的各种因素;数值模拟是对连铸工艺过程的流场、温度场和以及夹杂物行为的跟踪模拟,通过模拟从根本上查找异型坯存在相关质量问题的根源,并提出优化异型坯连铸工艺的具体措施。主要研究工作有:(1)从异型坯生产工艺现状和轧后H型钢出现的表面裂纹入手,采用金相显微镜及扫描电镜观察了裂纹特征,根据裂纹形貌、显微成分及夹杂,统计了裂纹的类型,初步分析了表面裂纹的成因。(2)采用示踪剂追踪、系统取样、综合分析等手段开展了从转炉炼钢→中间包→结晶器→异型坯成品整个异型坯生产工序中钢的洁净度水平的跟踪分析,其中采用红外吸收法测定了各试样中氧含量;采用大样电解法和扫描电镜分析了钢中的大型夹杂物;采用金相显微镜和扫描电镜分析了钢中显微夹杂物;在以上对夹杂物的类型、来源、组成和演变规律研究基础提出了提高异型坯洁净度、减少缺陷发生率的有效措施。(3)测定分析了异型坯结晶器保护渣成分,保护渣熔化温度、熔化速度及粘度等理化指标,查找了由于保护渣问题而导致异型坯发生表面裂纹缺陷的原因,并根据测定结果和生产实际提出了保护渣性能调整建议。(4)采用有限元法对异型坯中间包内钢液三维流场及温度场进行了耦合数值模拟分析,在此基础上对中间包钢液中不同尺寸夹杂物的运动规律以及夹杂物的去除率、收集率进行了模拟计算,详细分析了中间包钢液流动行为存在的问题;并在模拟计算基础上对中间包稳流器结构进行了优化,以改善中间包内钢液流动,促进夹杂物的去除,提高钢水洁净度。(5)采用有限元法对异型坯结晶器内钢液三维流场进行了数值模拟,对异型坯结晶器弯月面的自由液面波动进行了仿真,分析了拉速、浸入式水口参数(水口的浸入深度、水口侧孔出口角度)等工艺参数对结晶器内钢液的涡心位置、冲击深度、自由液面表面流速和自由液面波高的影响规律;并在模拟计算的基础上提出了最适宜的工艺参数取值,以优化结晶器内钢液流动,促进夹杂物的去除,提高钢水洁净度。(6)采用有限元法对异型坯凝固过程的二维温度场与应力场进行了系统模拟和详细分析;通过与连铸冶金准则的对比,找出了异型坯出现表面裂纹问题的主要工艺因素;创建了应用MATLAB遗传算法工具箱函数编制多目标遗传算法(MOGA)和有限元方法(FEM)相结合的多目标优化程序,对连铸二冷各段配水量进行了多目标智能优化,以降低缺陷发生率,提高生产率。最后,在以上分析基础上综合提出了异型坯出现表面裂纹和洁净度等质量问题的原因和预防措施。研究成果在生产现场的实际应用证明,本文所建立的H型钢异型坯质量控制研究体系科学、合理、有效。更多还原

【Abstract】 In the steel products, there are some kinds of special section steel. As an economic section material, H-beam has been used in many fields of national economy development. Beam blank is the idealist strand for H-beam production. In our country, there are only three beam blank production lines. Moreover, there are more defects on /in beam blank than other common strand. Therefore, studying on the H-beam blank quality assurance system, finding the key factors causing the defects and optimizing the casting technic has great significance to the economy and science.Based on the actual production process, the paper is aimed to find the key factors causing the surface cracks and the cleanness defects of beam blank and to optimize the casting technic. There are two research methods, the one is experiment analysis, and the other is numerical simulation. The former is to test and analyze the cracks, the inclusions and the flux in the mould, and to find the preliminary factor causing defects of beam blank. The latter is to simulate the flow field, temperature field and the inclusion movement, to find the key factor causing defects and the optimum the casting technic. The main work is listed in the followings:(1)The cracks on the H-beam web were analyzed under the metalloscope, the stereoscan and the energy spectrometer. Based on the pattern and the component of the surface cracks, the cracks characteristics were analyzed and the preliminary factor causing cracks were found.(2)By the tracers tracking, sampling taking and micro analyzing the steel cleanness, the source of inclusions were analyzed from steelmaking to continuous casting. T[O] in the steel was analyzed by infra-red absorption, the large-scale inclusions were analyzed by sample-electrolyzing method and the micro inclusions were analyzed by the metalloscope and the stereoscan. The methods increasing the cleanness and decreasing the defects were brought forward based on the above analysis.(3)The physicochemical property of the flux in the mould, such as the alkalipenia, the melting speed, the melting temperature and the viscosity was measured or calculated. The weakness of the flux was find, which may cause the surface defects of beam blank. The suggestion was put forward to modify the flux based on the above analysis and actual production.(4)The 3D coupled flow field and temperature field in the tundish was simulated used the finite element method. Then, the inclusions movement, the collection rate from the outlets and removal rate of the inclusions were calculated. The shortcomings of the fluid flow in the tundish were analyzed. Moreover, to increase the cleanness of the steel, the physical dimension of turbulence inhibitor was optimized.(5)The 3D flow field and the meniscus fluctuation in the mould were simulated used the finite element method. The influences of processing parameters (such as casting speed and the nozzle parameters) on the molten steel flow (such as the location of the vortex, the steel impact depth, the velocity and fluctuation of the liquid at free surface) were analyzed. In order to increase the cleanness of the steel, the optimum spans of the processing parameters were brought forward based on the calculation.(6)A coupled 2D thermo-mechanical finite element model was developed to compute the temperature and stress/strain profile in beam blank. By comparing the calculated data with the metallurgical constraints, the key factors causing the cracks on the beam blank can be found out. In order to optimize the processing parameters, a new optimization method was developed combined MOGA and FEM based on the MATLAB toolbox functions. The heat flow density was modified in each secondary cooling zone used this optimization method.In order to increase the cleanness of beam blank and decrease the cracks on the web, a series of corresponding methods are put forward in this paper. Now, online verifying of those optimization projects have been put in practice, which can prove that those are very useful and efficient to control the actual production.更多还原