Desulphurization capacity of ladle slags for tool steels

Abstract: Steel quality is in direct correlation with the desulphurization process, meaning the removal of sulphur. A good desulphurization process greatly improves the mechanical properties among others, and is essential for obtaining higher quality steel. This study aims to evaluate and analyse the desulphurization capacity of ladle slags based on both thermodynamic and  kinetic properties. Data from six heats were provided by Uddeholm, four from steel grade B, and two from steel grade C, which were then analysed based on thermodynamic and kinetic parameters and their impact on the desulphurization capacity. This was done by calculating the maximum distribution of sulphur in the slag for thermodynamic equilibrium (LS,td), along with the measured sulphur distribution coefficient (LS,r). The results and observations obtained, although only measured over six heats, demonstrated a close relationship between LS,td  and LS,r for two of the heats, but bad correlation between the remaining four heats. The thermodynamic results indicated that the activity of oxygen greatly reduces the desulphurization capacity. They also indicated that the optical basicity of the slag affects the sulphide capacity (CS), with a high basicity favouring a higher CS. The compositions varied greatly in regards to carbon between the two given steel grades, obtaining a higher LS,td  for steel grade CS without much difference in the measured sulphur partition ratio. This could be an indicator of limiting kinetics in the ladle processing stage.