Effect of surface-active elements on the wetting behavior and surface tension of steels: Assessing sessile drop and maximum bubble pressure techniques

This study investigates the influence of surface-active elements (Si, S, and B) on the surface tension (σ) and wetting behavior of molten steels and provides a direct comparison between the Maximum Bubble Pressure (MBP) and Sessile Drop (SD) measurement techniques. High-silicon electrical steels (ES) (3 - 6 wt% Si) and Mn-B steels (WS) with controlled B and S contents were examined at 1500 - 1650 °C. The results show that the increasing Si content decreases both σ and contact angle, enhancing the wettability on MgO. ES steels exhibit a characteristic parabolic temperature (T) dependence of σ, attributed to Si-O interactions and surface oxidation effects. In WS steels, S reduces σ, and the T coefficient becomes increasingly positive with rising S content. B displays an ambiguous effect: MBP measurements show a slight σ reduction with increasing B, whereas SD measurements indicate the opposite trend. Steel infiltration into porous MgO affects the contact line, causing reduced wetting angles and deviations in SD σ values. Across all compositions and temperatures, SD consistently yields higher σ values than MBP. This discrepancy is primarily linked to surface depletion of volatile species (Mn and S) during SD experiments, while the continuous surface renewal in MBP minimizes compositional changes. The findings demonstrate that both alloy chemistry and measurement technique significantly influence the determined interfacial properties. Overall, this work provides a comprehensive assessment of how surface-active elements govern wetting and σ in steel-MgO systems and highlights methodological considerations essential for interpreting high-temperature interfacial measurements in steelmaking research.