The hardenability of white cast iron represents a critical fundamental property, as its level directly dictates the engineering application value of this material, thus remaining an indispensable research direction. The microstructure of the Fe-Cr-B white cast iron, hardenability curves, and CCT curves were analysed to discuss the hardenability issues when boron was added in extremely high amounts. The results show that the addition of boron mostly results in the formation of borides, and its content in the matrix is extremely low. The presence of a small amount of boron in the matrix is beneficial to the hardenability of the material, enabling the matrix to transform into martensite in the as-cast state. End quenching experiments and determination of the CCT curve also confirmed that Fe-Cr-B white cast iron has excellent hardenability. The content of boron in the matrix is calculated via molecular dynamics, and its content is at the 1×10-4％ level. Within this content range, boron is beneficial to the hardenability of Fe-Cr-B white cast iron.