Numerical Simulation Of Solidification Process Of Ferritic Stainless Steel Under Vibration Conditions

Ferritic stainless steel is a resource-saving material and may replace expensive austenitic stainless steel.However,the defects of wrinkles and even cracks,which are easy to form during the rolling process,reduce the product yield rate of the rolled ferritic stainless steel sheets.So its wide industrial applications are limited.Improving the ratio of equiaxed grain structure in continuous casting process is an effective way for ferritic stainless steel to eliminate the above forming defects.Based on the technology of crystal nucleation and detachment from a chilling-solid surface with vibration,the coupling action method of mechanical vibration and heterogeneous nucleation has been presented to control the solidification microstructure of ferritic stainless steel.A chilling ferritic stainless steel generator with TiN layer was selected,exerting vibration to the generator may promote the chill crystals to break off and translate equiaxed grains.Vibration can also break TiN particles to deposit into the melt and become effective nucleating centers.As a high-temperature thermoforming process,the interactions of temperature field and velocity field during the solidification of ferritic stainless steel are very complex,and they affect directly the nucleation and growth of equiaxed grains.It is difficult to obtain scientific results by real time observation and measurement.Therefore,the numerical simulation of solidification process is necessary and it has important scientific significance.In this paper,a finite element software FLUENT was selected and a two-dimensional model was established to simulate the temperature field,velocity field and the path of TiN particles in the melts along the parallel and perpendicular to vibration direction under 600 Hz,700Hz and 800 Hz.The results show that the temperature field is heterogeneous with three different frequency of vibration.The average temperature gradient parallel(Y axis)and perpendicular(X axis)to vibration direction amplifies with vibration time but decreases with the increase of the vibration frequency.The shell on the chilling surface of the generator begins to grow along the vibrating direction and spreads to both sides,a closed shell forms eventually perpendicular to the vibration direction.The time of crusting prolongs with the increase of the vibration frequency,and the longest crusting time is 9.620 s under the vibration frequency of 800 Hz.The velocity field distribution of the melt flows out of the vibration direction and break up on the other side of the chilling generator,convection begins to form around the circular mold wall.The flow velocity increases with the increase of the vibration frequency,and the maximum velocity perpendicular to the vibration direction can reach 1.989 m/s under the vibration frequency of 800 Hz.Melt fluidity perpendicular to the vibration direction is better than that along the vibration direction.The path of Ti N particles in the melts is almost similar to the melt flow.With the increase of vibration time,the concentration of TiN particles in the melts gradually increases and distribute in the whole mold finally.TiN particles tend to cluster along the perpendicular direction of vibration.Considering the temperature gradient,crusting time and the concentration distribution of TiN particles,the optimum vibration frequency is 800 Hz.