A New Method for CET Position Determination of Continuous Casting Billet Based on the Variation Characteristics of Secondary Dendrite Arm Spacing

High-end steel products play an essential role in economic development and infrastructure projects. Nowadays, continuous casting is an important production process of high-end steel products due to higher efficiency and lower energy consumption. However, the quality and properties of end products, such as steel billets, bloom, and bar, will be affected by internal segregation defects, which are closely related to solidification structure characteristics. In the research on the solidification structure characteristics of billets, the columnar to equiaxed transition (CET) determination is of great significance to determine equiaxed crystal zones and the quality control of continuous casting billets. In this work, the secondary dendrite arm spacing (SDAS) of typical dendrites was measured and analyzed using the actual solidification structure of continuous casting billets and the mutation of SDAS during the solidification process from the billet surface to the center was found. Combined with the two-dimensional temperature field numerical model of the billet cross section, it can be seen that the CET will affect the heat transfer process in the billet and this will be reflected as the mutation of SDAS in typical dendrites. This work proposed a new method for the quantitative determination of CET in the continuous casting billets based on this mutation, and the starting position of the maximum SDAS increase rate is determined as the starting position of the CET. The CET positions calculated using the new method correspond to changes in the thermal gradient and growth rate in the billet, and are consistent with the positions of the actual solidification structure morphology transformations, which prove the effectiveness of this method.

Automated summary

High-end steel products are important for economic development and infrastructure projects. Continuous casting is an important production process for these products, but internal segregation defects can affect their quality and properties. This study focuses on the determination of columnar to equiaxed transition (CET) in the solidification structure of continuous casting billets. By measuring and analyzing the secondary dendrite arm spacing (SDAS), the researchers found a mutation of SDAS during the solidification process. Based on this mutation, they proposed a new method for quantitatively determining CET in continuous casting billets.