Research On Solidification Structure And TiN Distribution Of Incoloy 825 Alloy Under Electromagnetic Stirring

Incoloy 825 alloy is a nickel-based corrosion resistant high-temperature alloy.Traditional die casting production process has serious disadvantages such as high energy consumption and low yield.In recent years,the continuous casting technology of nickel-based corrosion resistant high-temperature alloy has become a research hotspot.However,in the process of continuous casting,Incoloy 825 alloy casting billet has serious defects such as central loose,shrinkage cavity and element segregation.Aiming at the problems existing in the continuous casting process of Incoloy 825 alloy,a new V-EMS way is adopted.This paper mainly studies the solidification structure change and TiN inclusion distribution of Incoloy 825 alloy ingot under different EMS methods by means of metallographic microscope,scanning electron microscope and energy spectrum analysis.The following conclusions are drawn:(1)The results of physical simulation experiment on the distribution and removal of inclusion in alloy liquid under the action of EMS show that:Without EMS,the inclusion is distributed uniformly along the direction of ingot height,and the area of inclusion takes up a large proportion.When EMS is applied,the removal rate of inclusion increases with the increase of the action time of EMS.The inclusion removal rate under the action of V-EMS is higher than that under the action of R-EMS at the same time.This fully indicates that the effect of V-EMS on the distribution and removal of inclusion in alloy liquid is better.(2)The results of solidification structure change of Incoloy 825 alloy ingot under the action of EMS show that:In the absence of EMS,Incoloy 825 alloy ingot has a loose shrinkage zone length of 50mm and a loose shrinkage cavity ratio of 25%.Dendritic structure is composed of large columnar crystal region and central equiaxed crystal region.The average grain size is 8.32mm,and the ratio of the central equiaxed crystal region is only 33.3%.When R-EMS is applied,the loose shrinkage zone is reduced to 15mm and the ratio of loose shrinkage cavity is reduced to 7.5%.Dendritic structure is composed of a few relatively developed columnar crystal region at the edges,cross dendritic region at the inner surface and central equiaxed crystal region.The grain size decreases to 2.03mm,and the ratio of the central equiaxed crystal area reaches 88.3%.When V-EMS is applied,the loose shrinkage zone is moved up to the riser,and the internal quality of the ingot is greatly improved.There is columnar crystal region growing in the dendritic structure.The grain size decreases to 3.04mm,and the ratio of the central equiaxed crystal area reaches 83.3%.(3)The results of macroscopic segregation of Ti elements in Incoloy 825 alloy ingot under the action of EMS show that:EMS or not,macroscopic segregation of Ti element exists in both the central cross section and longitudinal central section of Incoloy 825 alloy ingot.On the central cross section,the macrosegregation degree of Ti element decreases after EMS,and the overall uniformity of Ti element is good.On the longitudinal central section,the macrosegregation degree of Ti element after V-EMS is smaller than that without EMS and R-EMS,and the overall uniformity of Ti element is better.(4)The results of TiN inclusion distribution along the height direction of Incoloy 825 alloy ingot under the action of EMS show that;TiN inclusions are uniformly distributed without EMS.When R-EMS is applied,the area proportion of TiN inclusion gradually increases from the lower part of the ingot to the upper part.When V-EMS is applied,under the action of the large longitudinal circulation along the ingot height,the area proportion of TiN inclusion presents different distribution trends according to the distance from the single side vertical electromagnetic agitator.However,by calculating the average proportion of the inclusion area at different heights of the ingot and at different locations far and near from the single side vertical electromagnetic agitator,it can be seen that the inclusion area gradually increases from the lower part of the ingot to the upper part.To sum up,on the basis of physical simulation experiments on the distribution and removal of inclusion in alloy liquid under the action of EMS,by comparing the solidification structure change and TiN inclusion distribution of Incoloy 825 alloy ingot under different EMS ways,it can be concluded that V-EMS has played an important role in improving the internal quality of Incoloy 825 alloy ingot due to its special properties.