根据430铁素体不锈钢的主要成分和缓冷实验条件下得到的宏观凝固组织,确定3D－CAFE模拟计算需要的枝晶尖端生长动力学系数和Gauss分布参数;采用不同的传热系数进行反复计算,通过计算得到的凝固组织与实验得到凝固组织基本相同来确定缓冷条件下模拟计算需要的传热系数.采用3D－CAFE法对缓冷、空冷和水冷条件下430铁素体不锈钢铸件凝固过程的温度场和流场进行分析,发现缓冷条件下铸件凝固过程中的温度场最均匀且固液两相区最宽, 空冷次之,水冷条件下铸件的温度场很不均匀且固液两相区最窄; 缓冷、空冷和水冷条件下,铸件的凝固速率在铸件中心位置达到最大值, 分别为2.3, 3.0和3.3 mm/s.缓冷条件下在铸件中心位置处流动速率达到最大值8.9 mm/s,空冷条件下靠近侧壁处流动速率达到最大值9.8 mm/s,水冷条件下在离侧壁3/5处流动速率达到最大值4.6 mm/s.缓冷条件下铸件的凝固组织几乎全是等轴晶, 空冷条件下只有心部有少量等轴晶,水冷条件下铸件的凝固组织由粗大的柱状晶构成.

The dendrite tip growth kinetic coefficients and Gauss distribution parameters for 3D－CAFE simulation are determined according to the main compositions of 430 ferrite stainless steel and the macrostructure forming under the experimental condition of slow cooling. Based on the repeated computation with different heat transfer coefficients, the heat transfer coefficient under slow condition is determined when the solidification structure by above simulation computation is basically the same as the experimental one under slow cooling. The temperature fields and flow fields of 430 ferrite stainless steel during the solidification process under the conditions of slow cooling, air cooling and water cooling were analyzed by use of 3D－CAFE method, respectively. The results show that the temperature field of solidification process under slow cooling condition is the most uniform and the solid－liquid region is the widest, followed by air cooling condition, while the temperature field under water cooling is quite non－uniform and the solid－liquid region is the narrowest. The maximum solidification rates are 2.3 mm/s with slow cooling, 3.0 mm/s with air cooling and 3.3 mm/s with water cooling, respectively, which are obtained in the center of the castings. The maximum flow rate is obtained in the center of casting with the value of 8.9 mm/s under slow cooling condition, and the maximum flow rate is 9.8 mm/s near the side wall under air cooling condition, while the maximum flow rate is 4.6 mm/s at the position with the 3/5 distance from the side wall under water cooling condition. The solidification structure of casting is composed of almost all equiaxed grains under slow cooling condition, and only a few equiaxed grains exist in the centre of casting under air cooling condition, while the solidification structure of casting consists of coarse columnar grains under water cooling condition.