The Fe-Ti-N mater alloy was prepared through the in-situ reaction of nitrogen gas with the Fe-Ti melt.Scanning electron microscope results show that the particles uniformly distributed in the iron matrix were TiN.The deliberately prepared Fe-Ti-N master alloy was employed for the 409L ferritic stainless steel in an attempt to refine the as-cast solidification structure.It was found that the effectiveness of Fe-Ti-N master alloy on refining of the as-cast 409L ferritic stainless steel was affected by addition level,holding time and melts temperature.It was found that the average equiaxed grain size decreased from 1 503μm to 303μm,the proportion of equiaxed grain zone increased from 14%to 100%with increasing the Fe-Ti-N master alloy addition level to 2.5%.The proportion of equiaxed grain decreased from 85%to 4%as the solidification temperature increased from 1 803 K to 1 883 K.When the holding time reached to 8min,the solidification structures of 409L ferritic stainless steel show extreme points in the proportion of equiaxed grain.It is clear that the grain refining efficiency gradually fade away with the increasing of the holding time at the very beginning.However,when the holding time continues to increase and exceeds the extreme point, the grain refining efficiency of the Fe-Ti-N master alloy recovered to a certain degree.The experimental results mentioned above have been analyzed in terms of thermodynamics.Under appropriate conditions,the Fe-Ti-N master alloy used for grain refinement of the solidification structure of 409L ferritic stainless steel may have good prospects for industrial applications.
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