振动激发金属液形核过程的传热研究

Research on Heat Transfer in the Process of Liquid Metal Nucleation Stirred by Vibration

为了提高铸坯凝固组织的均匀性,减轻宏观偏析,提出了振动激发金属液形核技术,其传热机理是为了促进形核,需要确保晶核发射器棒体表面温度控制在金属液的固、液相线之间,为此开展了传热计算及模拟试验研究。通过试验可知,在气冷条件下,棒体表面因冷却强度不够而无法产生大量的细小晶粒;而在水冷条件下,棒体表面因与钢液间的过冷度太大而迅速结壳,达不到向钢液连续弹射晶粒的目的。通过气雾冷却条件下的传热研究,在气流量为65 m3/h,水雾加湿量为3 kg/h的气雾冷却条件下,与棒体表面接触的钢液能够获得26℃以上的过冷度,因此棒体表面迅速形成大量的晶核而且不会结壳,进而可使晶粒被连续不断地弹射至金属液中,成为凝固过程中等轴晶的形核核心,促进铸坯凝固组织的均匀化。

In order to improve the uniformity of slab solidification structure and reduce macro-segregation,liquid metal nucleation technology stirred by vibration has been proposed.Its heat transfer mechanism was that temperature of the crystal nucleus generator surface should be controlled between liquidus and solidus of the metal treated to induce nucleation.Therefore,the heat transfer calculation and simulation experiments have been carried out.The results show that,in the air-cooled condition,the cooling intensity of crystal nucleus generator surface was too weak to obtain a large number of small grains,while in the water-cooled condition,the cooling intensity of crystal nucleus generator surface was so strong that the coagulation cove grew very fast,thus it was difficult to achieve the goal expected.Through heat transfer studies under the aerosol cooling,when the gas flow rate was 65 m3/h and the amount of mist humidifier was 3 kg/h,the molten steel degree of undercooling in contact with the crystal nucleus generator surface could be more than 26 ℃.A large amount of rods of nuclei could nucleate rapidly and would not crust under this case,thus the grain could be continuously ejected into the molten metal and become the nuclei of equiaxed grain in process of solidification.This promotes the homogenization of the slab solidification organization.