Abstract
The solidification characteristics of 70 steel at the stage of the superheat elimination and the liquid–solid phase transformation were analyzed at cooling rates from 10 to 150 °C/min based on a high-temperature confocal scanning laser microscope (HT-CSLM). Secondary dendrite arm spacing (SDAS) and fractal dimension (D) were used to quantitatively describe the local compactness and overall self-similar complexity of the solidification morphology. It was found that the cooling rate had a very important influence on the local and overall morphology characteristics of solidification structures. At the superheat elimination stage, the cooling rate affected the morphology of the microstructure through the dynamic structural fluctuation between the generation and disappearance of atomic clusters in the molten steel. At the liquid–solid phase transformation stage, the cooling rate affected the local morphology of the microstructure by affecting the solute diffusion rate between dendrite arms, while it affected the overall morphology by changing the concentration undercooling at the front of all solidified interfaces. The presented results show that adjusting the cooling system at the superheat elimination stage can also be an important way to control the solidified morphology of different alloys.
Highlights
Published: 16 August 2021High carbon steel tends to solidify in a wide temperature range during continuous casting due to the high C content that is prone to internal quality defects such as macrosegregation and shrinkage cavities [1,2,3,4]
The results showed that secondary dendrite arm spacing increased with increasing superheat when the cooling rate was constant
The results showed that the fractal dimension is an effective parameter to quantitatively describe the overall morphology characteristics of the solidification structure, and it changes with the change in solidification parameters
Summary
High carbon steel tends to solidify in a wide temperature range during continuous casting due to the high C content that is prone to internal quality defects such as macrosegregation and shrinkage cavities [1,2,3,4]. Macrosegregation in the casting occurs within the mushy zone. It is mainly caused by interdendritic flow, driven by thermal convection or solute convection and solidification shrinkage [5,6,7]. It is an effective way to control the formation of macrosegregation defects during the solidification of metal alloys by controlling the morphology of the structure to increase the resistance of interdendritic flow. The morphology characteristics of the solidification structure in high carbon steel are very common, which is very meaningful for similar phenomena in other alloys
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