It is well known that the addition of boron to steels can cause difficulties during continuous casting, including surface cracks and internal cracks of the cast products. In severe cases, breakout and slab breakage can occur.
Studies on the effect of boron on Fe-B alloys pseudo-binary phase diagrams at various carbon levels found that small addition of boron introduces the possibility of so-called retrograde melting, i.e., upon cooling, the steel initially completely solidifies and then remelts at segregated interdendritic regions and grain boundaries at temperatures approaching 1200 oC. This phenomenon is the primary cause of casting difficulties of B-bearing products.
To confirm the theoretical work on the finding of retrograde melting phenomenon, Confocal Scanning Laser Microscope studies were carried out for “in-situ” observation. These studies revealed the existence of the retrograde melting phenomenon in commercial B-bearing steels at temperatures below 1200 oC. The present paper summarizes the results.