The addition of boron to steel introduces the possibility ofsteel initially completely solidifying and then remelting inthe interdendritic regions at very low carbon levels. For allcarbon levels, a low melting Fe-B alloy exists as a liquiddown to around 1100°C. This liquid is found in steel with aslow as 0.0004% boron due to the boron segregation. Thepersistence of this liquid leads to hot shortness, breakouts,and other casting defects. Pseudo-binary phase diagramsfor low boron concentrations have been developed usingThermoCalc software and were confirmed using experimentaltechniques.