钢的半固态电磁搅拌力场与组织转变

Electromagnetic Stirring Force Field and Microstructure Evolution of Semi-Solid Steel

利用自制的高熔点半固态电磁搅拌装置对60Si2Mn钢半固态电磁搅拌力场及它对组织转变的影响进行了理论分析和实验研究。结果表明:电磁搅拌功率和频率直接影响电磁搅拌力,进而对金属熔体的流动形态有明显的影响。在一定频率范围内,搅拌功率加大,搅拌力随之增加;当搅拌功率达到一定值时(5kW),继续加大搅拌功率将导致搅拌装置发热并恶化60Si2Mn钢半固态组织的转变效果。适宜的频率范围为20～50Hz。如果频率太高,屏蔽和钢熔体粘滞效应增大,将导致搅拌力下降;频率太低,涡漩电流减小,同样导致搅拌力下降。电磁搅拌力作用下的金属熔体流动形态由一个集中的大漩涡和较多的小漩涡构成。这种流动形态在宏观上可促使钢液的温度场和浓度场均匀化;微观上增加局部紊流密度,促使枝晶组织向球状组织转变。

With the help of selfmade high melt point semisolid stirring apparatus, the experimental study and theoretical analysis for the effects of stirring force field on microstructure of 60Si2Mn semisolid slurry have been conducted. The results show that stirring force increases with increasing stirring power in a certain frequency range. The greater stirring power results in increase of heat given off from apparatus and deteriorates semisolid structure evolution when the power exceeds 5 kW. The frequency range from 20 Hz to 50 Hz is suitable. The higher frequency results in increase of adhesion of steel melt, and magnetic shielding and stirring coin impedance. The lower frequency is associated with decrease of vortex current. Therefore, the higher or lower frequency causes the decrease of stirring force. The flow pattern of metal melt consists of a main concentrated vortex and many small vortexes. This flow pattern contributes to the uniform distribution of temperature field macroscopically and increases vortex density microscopically. The dendritic structure is transformed into the spherical shape by means of stirring process.