Optimization Technology Of Solidification Structure Of 18CrNiMo7-6 Steel Ingot

Casting is an important foundation for supporting the national industry and plays an important role in many industries.For example,automotive manufacturing,aerospace,energy,heavy machinery and other fields have a large demand for foundry products.It is necessary to use a lot of manpower,material resources and financial resources to improve the defects in steel ingots by traditional experimental means,so numerical simulation has become an important means to optimize the quality of steel ingots.In this paper,the numerical simulation is used to analyze the possible problems in the ingot solidification process,and the influence of the pouring system structure and the casting process parameters on the quality of the ingot is simulated.The ProCAST software was used to simulate the filling and solidification process of steel ingots.The results show that the flow field of steel ingots is disordered at the initial stage of casting,and the liquid level flow in the middle and late stages is stable.Due to the existence of thermal insulation risers,the ingot solidification process can be effective feeding,so the steel ingot only have Primary shrinkage cavity.Temperature measurement was performed on the surface of steel ingots and ingot molds.According to the data obtained by temperature measurement,the heat transfer coefficient between the steel ingot and the ingot mold is inversely calculated.The interface heat transfer coefficient at the initial stage of solidification is very large,up to 5300W/(m2?K).With the opening of the air gap,the heat transfer coefficient decreases rapidly.To 150 W /(m2?K),and then slowly decrease as the cooling process.The numerical simulation of the risers of different shapes shows that the two risers can be effectively supplemented during the solidification process of the ingot,and the integrated riser is more suitable for actual production due to the advantages of easy assembly and multi-mode use;The influence of the shape and size of the mold bottom brick on the initial flow field of the casting can be seen that the hole diameter of the mold bottom brick is increased from 70 mm to 90 mm.The molten steel flow is more stable at the initial stage of casting,which can effectively reduce the possibility of slag slag.When the bottom brick is poured,it flows more smoothly than the liquid surface of the straight hole mold bottom brick.The numerical simulation of the solidification process of steel ingot under different process parameters shows that the casting temperature of molten steel is increased from 1530°C to 1590°C,the time required for complete solidification of molten steel increases,and the distance between secondary dendrite arms in steel ingot decreases.The range of the columnar crystal region increases,the range of equiaxed crystal regions decreases,and the grain size increases;the preheating temperature of the ingot mold is increased from 50°C to 250°C,the complete solidification time of the molten steel increases,and the secondary dendrites in the steel ingot The arm spacing is increased,and the variation of the columnar crystal zone and the equiaxed crystal zone in the steel ingot is not obvious.