Use of slag containing water as a lubricant in high straining rolling for ultrafine-grained steels

We investigated the possibility of using waste slag as a lubricant in high straining rolling for ultrafinegrained steels. When slag is applied as a lubricant, it might satisfy the requirement for stable biting work-pieces because slag is as stable as glass with high hardness at the biting temperatures in rolling (100-200°C). On the other hand, ordinary slag doesn't have the fluidity necessary to provide a lubricating effect at rolling temperatures of 300-400°C since its melting temperature is usually high. However, slag containing water has been targeted as a new lubricant, and we focused on lowering the glass transition temperature and the structural change of slag containing water with the aim of improving the lubricity of slag in rolling. The microstructures of slag containing water and slag that released water were observed in the present study, along with in-situ observation of water released from the surface of slag containing water were conducted after heating in a SiO₂-Na₂B₂O₃ slag system. We found that water was mainly contained in the phase formed by ions dissolved from the original slag under hydrothermal conditions, and the amount of water was dependent on the state of the phase, such as glass or crystal. It was confirmed that slag containing water could provide a lubricating effect when the water is released from the slag above the glass transition temperature because a porous structure is formed due to the water release.