Effect of Cooling Rates on the Local—Overall Morphology Characteristics of Solidification Structure at Different Stages for High Carbon Steel

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.

Simulation and Experimental Study on the Effect of Superheat on Solidification Microstructure Evolution of Billet in Continuous Casting

“…The change of superheat mainly affects the growth of columnar crystals and the formation of equiaxed crystal regions. In the case of low superheat, the grain growth may be more random, resulting in a more uniform grain orientation distribution in the final billet, leading to a more dense equiaxed grain [30]. At the same time, a lower superheat may produce a relatively uniform texture.…”

Design of High Mn Fe-Mn-Al-C Low Density Steels for Additive Manufacturing

“…The size of the domain dendrites, known as the secondary dendrite arm spacing (SDAS), is frequently associated with the cooling rate [247,248]. This is because the SDAS represents the region where liquid is commonly trapped during the solidification process, and consequently, it is linked to micro-segregation [249,250]. The correlation between the SDAS and the cooling rate is commonly expressed by equation 1.5, wherein λ 2 represents the SDAS measured in micrometers (µm), Ṫ denotes the cooling rate measured in Kelvin per second (K/s), and the constants a and b are specific to the material.…”