Micro-Macro Modeling of Continuous Cast Steel to Simulate the Effect of Casting Velocity and Pouring Temperature on Copper Segregation

One of the most serious problems in using recycled scrap for steel production is the occurrence of surface hot shortness during hot deformation due to the presence of copper in scrap. Copper causes surface hot shortness by liquid embrittlement. Therefore, the amount of the liquid copper-enriched phase penetrating into the grain boundaries should be identified in order to keep its effects within acceptable limits. In this regard, understanding the mechanism of segregation during solidification of steel is essential. This paper attempts to demonstrate micro-macro modeling of continuous cast steel to simulate the effect of casting velocity and pouring temperature on copper segregation. First, the temperature profiles at different times were determined using a finite element (macro) model and a segregation (micro) model based on Giovanola-Kurz approach is coupled with the macro model. It is necessary to couple the heat flow calculations from the macro model and the segregation calculations from the micro model because the rate of latent heat liberation is affected by the solute redistribution process, while the solute redistribution process depends on the cooling rates. As the casting velocity and pouring temperature strongly affect the solidification of continuous cast steel, they were chosen as the variables in this study. It is hoped that this study will enable the optimization of these variable to minimize the segregation of copper. This paper also demonstrates that by decreasing casting velocity and pouring temperature of a steel billet during continuous casting, solid-liquid interface moves faster to the center of the billet and there is less chance for diffusion of the residual elements in steel. Therefore, the chance of hot shortness of copper in the steel increases.

Suppression of Surface Hot Shortness Caused by Copper during Hot Rolling

Since copper content in steel causes hot shortness, it is important to understand copper behaviour during high-temperature oxidation, in order to control the precipitated copper. This study examines copper distribution during the oxidation of steel. From the oxidation tests, it is shown that precipitated copper existing in the scale/steel interface is absorbed into the magnetite layer or evaporates into the atmosphere. Then, a proposed method to suppress hot shortness is tested by oxidation-tensile tests at high temperature and is proven to be effective.