Atomic Ionic-scale Mechanism on Inclusion Modification by Calcium Treatment in the Electroslag Remelting Process Based on Ion and Molecule Coexistence Theory and Molecular Dynamics Simulation

Abstract

In the course of industrial electroslag remelting (ESR), large-size Ca–Al–Mg–O nonmetallic inclusions were prone to form in 4Cr13 die steels and will deteriorate mechanical properties and service life seriously. In order to reveal the underlying mechanism, this work delves into the origins of Ca–Al–Mg–O inclusions in 4Cr13 die steel, establishing a correlation between inclusion characteristics and ESR slag composition. Utilizing molecular dynamics simulations, this work examines the CaO–Al₂O₃–CaF₂–SiO₂–MgO slag system, analyzing slag microstructure and the mean square displacement of Ca²⁺ ions. Combining the ion and molecule coexistence theory (IMCT), it was demonstrated that the key factor determining the total calcium (T.Ca) content and large-size Ca–Al–Mg–O inclusions in ESR steel is the concentration of free Ca²⁺ ions in the slag. In addition, a model for calculating free Ca²⁺ ions concentration in slag has been formulated based on IMCT. This model elucidates the influence of CaF₂ and CaO on the concentration of free Ca²⁺ ions in slag. The empirical data facilitated the development of a modified slag composition with reduced CaF₂ content, aiming to lower the T.Ca content in steel and reduce the quantity and size of Ca–Al–Mg–O inclusions. These hypotheses have been verified through a series of laboratory and industrial trials. This is crucial for optimizing the ESR slag composition and enhancing the metallurgical quality of ESR steels.