Solidification Process And Structure Evolution Of Ingot With Electromagnetic Feeding-cold Core Composite Casting

Ingot is widely used in various industries such as national defense,nuclear energy,petrochemical industry,and aerospace.The foundry industry plays an important role in our national defense power and economic development.However,Solidification defects still restrict the development of casting industry.Therefore,it is necessary to constantly improve and develop ingot solidification control technology to produce high-quality casting products.In order to solve the problem that the shrinkage cavity and columnar crystal overgrowth in the traditional ingot,a new method is proposed to improve the solidification process of large ingot.The electromagnetic feeding mechanism and solidliquid composite mechanism will apply to improve the structure;it forms a new casting method called “Electromagnetic Feeding-Cold Core Composting Casting”.The noncontact heating method is used to extend the cooling time of the metal in the riser,and the solid-liquid composite casting method was used to change the heat transfer of the ingot,improve the solidification structure,and inhibit the growth of columnar crystals.In this paper,six cold core ingots controlled by electromagnetic feeding are prepared.The perspectives of preheating temperature,superheat of molten steel,power and time of electromagnetic feeding are designed.The influences of the above factors on the solidification microstructure evolution of the ingot were analyzed,and the microstructure distribution and microstructure evolution of the electromagnetic feeding cold core ingot were systematically studied.The CAFE model in the Pro CAST was used to simulate the growth of the grains according to the temperature change curve and solidification microstructure morphology obtained from the thermal experiments.The experimental results show that the cooling rate of the molten metal in the riser is significantly delayed,and the yield of the metal increased.However,it is noteworthy that the higher electromagnetic feeding power and the longer time will cause the cold core to be scoured by the superheated metal liquid for a long time,it will lead to excessive melting of the cold core at the riser.The cold core breaks the traditional heat transfer.The cold core and the crucible become the way of heat conduction in the metal liquid.When the metal contact with cold core,small grains grow on the cold core.The hot hydrochloric acid etching treatment of the cold ingot with electromagnetic reinforcement mechanism,it is obvious that the macroscopic solidification structure is divided into the following areas: the solid-liquid compound area,the free growing area,the directional growing area and the equiaxial crystal area,which account for 1.44 %,33.60 % and 64.96 % of the total volume of the ingot,respectively.It is different from the dendrite distribution of the traditional ingot.The microstructure of interfaces in different areas is observed in combination with the microstructure of solidification organization.The electromagnetic feeding mechanism can effectively improve the feeding capacity.The solid-liquid composite can satisfy the requirements of metallurgical composite,refine grain structure,and increase the proportion of equiaxial grain in the ingot.Through numerical simulation methods,it can be seen that the preheating temperature of the cold core increases from 25 ? to 850 ?,the grains increase from 902 to 1175,and the equiaxed grain rate also increases from 56.8 % to65.6 %.When the superheat of metal liquid increases from 30 ? to 70 ?,the number of grains decreases from 1143 to 892,and the equiaxed grain rate also decreases from65.4 % to 58.4 %.The results indicate that the higher preheating temperature of the cold core and the lower superheat of the metal liquid can both reduce the supercooling degree of the solidification front,inhibit the growth of columnar grains and promote the growth of equiaxed grains.