Effect of carbon concentration on melting behavior of steel scraps in hot metal baths

To reveal the intricate mechanisms underlying the melting and dissolution processes of scraps in the iron ladle, the melting characteristics of three carbon steels with different C concentrations at the bath temperatures of 1623 and 1723 K were studied. Upon immersing scraps into the molten metal, the liquid metal immediately froze around the submerged parts of scrap cylinders. Whereafter, the solid shell completely melted at both bath temperatures after the immersion time of 5 s. The maximum thickness of solidified steel shells significantly decreased with increasing the bath temperature. The findings also suggested that the melting rate of scrap cylinder exhibited a positive correlation with the C concentration in the scrap and the bath temperature. Quantitatively, the mass transfer coefficients of C for the low carbon (0.18 wt.%), medium carbon (0.32 wt.%), and high carbon (0.61 wt.%) concentrations in the scrap cylinders at 1723 K were determined by a kinetic model, which were 8.78 × 10⁻⁵, 9.57 × 10⁻⁵ and 10.00 × 10⁻⁵ m s⁻¹, respectively, and those corresponding values decreased to 3.87 × 10⁻⁵, 4.49 × 10⁻⁵ and 3.54 × 10⁻⁵ m s⁻¹ at 1623 K. However, there was little difference observed among the heat transfer coefficients of hot metal for the three carbon steels, which were estimated to have an average value of 16.36 and 18.82 kW m⁻² K⁻¹ at the experimental temperatures of 1623 and 1723 K, respectively. The results from the experiments and mathematical models showed good consistency at both bath temperatures, providing feasible guidance for efficient melting of steel scraps in the iron ladle.