Effect of Different Calcium and Magnesium Treatments on the Evolution of Nonmetallic Inclusions in AH36 Ship Plate Steel

Abstract

Comprehensive thermodynamic calculations and high‐temperature experiments are performed to systematically evaluate the effect of calcium and magnesium additions on the modification and control of inclusions in AH36 ship plate steel. The results show that Al2O3 or MgAl2O4 inclusions are formed under the casting temperature conditions. Calcium treatment modifies the inclusions into calcium aluminate, of which components partially fall into the liquidus region, and the aspect ratio and number density of inclusions became smaller, avoiding nozzle clogging, but the inclusions are easy to gather and grow up, which would affect the steel properties. Magnesium treatment modifies the inclusions into dispersed magnesium‐aluminum spinel with small size. However, the number density and aspect ratio of inclusions increase, as well as the melting points of inclusions are high, which would easily cause nozzle clogging. When calcium–magnesium synergistic treatment, with the increase of magnesium proportion, the inclusions types increased, and the liquidus area of inclusions became narrower until it disappeared. Synergistic treatment with more calcium and less magnesium (Ca2Mg1) is optimal since the inclusions were fine and diffuse, and the corresponding liquidus area of inclusions is wider than the calcium treatment.