Volume-averaged modeling of multiphase solidification with equiaxed crystal sedimentation in a steel ingot

Macrosegregation is a critical factor that limits the mechanical properties of materials.The impact of equiaxed crystal sedimentation on macrosegregation has been extensively studied,as it plays a significant role in determining the distribution of alloying elements and impurities within a material.To improve macrosegregation in steel connecting shafts,a multiphase solidification model that couples melt flow,heat transfer,microstructure evolution,and solute transport was established based on the volume-averaged Eulerian-Eulerian approach.In this model,the effects of liquid phase,equiaxed crystals,columnar dendrites,and columnar-to-equiaxed transition(CET)during solidification and evolution of microstructure can be considered simultaneously.The sedimentation of equiaxed crystals contributes to negative macrosegregation,where regions between columnar dendrites and equiaxed crystals undergo significant A-type positive macrosegregation due to the CET.Additionally,noticeable positive macrosegregation occurs in the area of final solidification in the ingot.The improvement in macrosegregation is beneficial for enhancing the mechanical properties of connecting shafts.To mitigate the thermal convection of molten steel resulting from excessive superheating,reducing the superheating during casting without employing external fields or altering the design of the ingot mold is indeed an effective approach to control macrosegregation.

Control of Equiaxed Crystal Ratio of High Carbon Steel Billets by Circular Seam Cooling Nozzle

A circular seam cooling nozzle and its online control system have been developed to reduce the center segregation in high carbon steel billets by decreasing the superheat of the molten steel and improving the equiaxed crystal ratio based on the numerical results. An industrial experiment has been carried out on a 150 mm× 150 mm caster to investigate the effect of the circular seam cooling nozzle on the superheat removal of the molten steel. The results show that the circular seam cooling nozzle can be used to control the casting temperature in a closed loop control system. The online control system can be effectively adapted to the variation of operating parameters. The casting lasts about 4 h and about 400 t steel is successfully produced in a continuous operation. The removal of about 14 ℃ superheat and the improvement of approximate 10% equiaxed crystal ratio can be achieved by the newly developed circular seam cooling nozzle.

Solidification structure simulation and casting process optimization of GCr15 bloom alloy

Based on the solidification heat transfer model and CAFÉmodel,the solidification structure of GCr15 bloom alloy was studied.Using nail shooting and acid etching experiments,the solidification models were verified.The secondary dendrite arm spacing(SDAS)model of GCr15 was obtained by simulation calculation and metallographic observation.With the increase of casting speed,the SDAS,equiaxed crystal ratio(ECR)and average grain size increase.With the rise of superheat,the SDAS increases in the 20-70 mm of thickness and decreases in the 80-160 mm of thickness.The ECR decreases and the average grain size increases with the increase of superheat.With the increase of specific water flow,both the SDAS and ECR decrease.The minimum average grain size is obtained when the specific water flow is 0.20 L·kg^(-1).The central carbon segregation index is reduced from 1.11 to 1.075.

Effect of Refrigerant on Solidification Structure of Steel

By the solidification experiment of a medium carbon steel with refrigerant added.the effect of refrigerant on solidification structure of steel was studied.The results clearly show that refrigerant can increase the ratio of equiaxed crystal,fine grains and decrease central porosity and segregation.