【作者】 杨晓东；

【导师】 陈登福；

【作者基本信息】 重庆大学 ， 冶金工程， 2010， 硕士

【摘要】 连铸过程中,铸坯的传热及受力状况与铸坯的最终质量密切相关。因此,应用数学方法分析铸坯的温度及应力场对连铸生产具有重要的现实意义。论文针对某钢厂直弧型板坯连铸机部分钢种生产过程中铸坯角部和内部裂纹缺陷问题,以该铸机的基本结构和工艺参数作为基础,根据该厂直弧型板坯连铸机的铸坯具体的凝固传热和受力的边界条件,构建二维温度与应力的有限元模型。论文中分别分析板坯连铸过程中二维横向和纵向的凝固传热,并应用非稳态热传导方程对铸坯的传热进行分析。在MSC.Marc中有限元传热分析求解采用加权残差的Galerkin方法。凝固传热模型中考虑了热物性参数的非线性变化,以及由于钢液引起的强制对流边界条件。在二维温度场的基础上,考虑了高温下的铸坯材料非线性力学行为、铸坯与夹辊的接触状态、钢水静压力的影响,运用由屈服应力和硬化模量决定的冯米塞斯屈服准则,分别建立了板坯的二维横向和纵向的热弹塑性应力模型。有限元模型采用单元边长比接近于1的高精度四边形单元划分网格。基于MSC.Marc?有限元商业软件的温度和弹塑性分析相结合的方式对模型求解,其中的非线性分析采用具有很好收敛性的牛顿瑞佛森法求解。凝固传热计算得到了二维横向特定夹辊位置下铸坯断面温度场,以及铸机整个纵断面的铸坯温度场。选取结晶器出口断面,凝固前期弯曲过渡段和中后期的矫直段在三个拉速下的温度场进行分析。结果表0明凝固前期结晶器和足辊段冷却水量不合理是造成连铸坯角部纵裂纹的主要原因。弯曲矫直段铸坯的温度场应结合铸坯的高温力学性能制定适宜的目标温度,避免铸坯微裂纹的生成或加剧扩展。在温度场的计算结果上,计算分析了连铸过程中铸坯坯壳内的等效应力伴随凝固过程的变化情况,内外弧等效应力变化规律,以及夹辊与坯壳间接触受力情况。结果表明弯曲过渡段外弧前部和矫直段内弧后部等效应力值在各自区域内最大。在低拉速下的二冷前期,弯曲过渡段的铸坯容易在内外弧的角部产生较大的应力集中区域,随着凝固的进行,应力集中区域会沿铸坯宽面向内推移。论文中对横向二维应力模型的固定约束的接触处理方式进行了评估。结果表明在横向二维应力模型中,固定约束和加载法向接触力两种方式的等效应力结果相当。同时将横向与纵向二维应力模型在铸坯宽度方向中心线位置的等效应力值进行对比,分析表明纵向应力模型分析连铸过程铸坯整体受力情况具有优势。更多还原

【Abstract】 In the continuouse casting process,the Thermal-Mechanical behavior of casting slab has an important impact on the final product quality. Therefore, the application of mathematical analysis of the temperature and stress field of slab,which has important practical significance in continuous casting production. This paper direct internal and corner crack defects of some steel grades in the vertical-bending slab caster production process, base on the basic structure of the ccaster and process parameters, According to strand solidification heat transfer and force boundary conditions under the vertical-bending slab caster in the plant, construct two-dimensional temperature and stress finite element model.In the paper, analysis of solidification heat transfer in the slab continuous casting process of horizontal and vertical two-dimensional section respectively,and application of non-steady state heat conduction equation in slab heat transfer analysis, Finite element analysis of heat transfer in MSC.Marc used Galerkin method of weighted residuals. The influence of liquid steel caused forced convection boundary conditions and thermal properties of nonlinear changes,were taken into consideration in the solidification heat transfer model.Based on two-dimensional temperature field, consideration of the impact of nonlinear mechanical behaviour of slab at the high temperature , the contact state between slab and roller, the static pressure of liquid steel, used of the yield stress and hardening modulus determined Von Mises yield criteria, were established two-dimensional horizontal and vertical section thermal elastic-plastic stress model of slab.Finite element model mesh use the high-precision rectangular unit which aspect ratio close to 1. The solve combines temperature and elastic-plastic analysis based on the commercial Finite elements method system Msc.marc?, in which a very good use of nonlinear analysis of convergence of Newton-Rafson method was applied.Calculations of Solidification heat transfer have been given two-dimensional horizontal section temperature field under particular roll position,and the longitudinal section temperature field of the overall slab caster., Analysis of the temperature fields at the cross section of mold, bending transition zone at the earlier stage of solidification and Straightening zone at the later stage of solidification three zones in the three different drawing speed. The results show that the longitudinal cornercracks is main caused by an unreasonable amount of cooling water at mold and the foot roller zone.The appropriate objectives temperature of strand at bending and straightening zone should be combined with high-temperature mechanical properties of strand , to avoid cracks formation or worsening cracks expand of slab.Base on the Temperature field calculation results, analysis of the equivalent stress changes inner strand shell associated with solidification , both inner and outer side of the slab variation of equivalent stress distribution, as well as the contact load state between slab and roller.The results show that outer side of the slab at bending transition zone and inner side of the slab at straightening zone have maximum equivalent stress. Prophase of secondary cooling zone under low drawing speed,Both inside and outside the slab in the corner have a greater stress concentration area at bending transition zone, the stress concentration area will be move inward along with the solidification progresses.Assessment of fixed constraint of contact approach in the horizontal two dimensional stress model, Results show that calculations are consistent with Normal contact force load approach.Contrast the equivalent stress value of slab centre line across the width between horizontal and vertical two dimensional stress model , Results show that application of the vertical two dimensional stress model analysis of the Force of the overall slab has more advantages.更多还原