B loss in melt mainly occures in B addition followed by alloying process,next at melt holding during smelting and pouring.The B content can be rationally controled with enhancing deoxidation and coverage.B trends towards surface coagulation at melt holding during pouring. w （B） =0.013% can refine greatly as cast microstructure,with occurence of needle like and block like phase in high magification while no needle like phases occur in lower B content.It is founded that the block like phase consits of a rich in B coumpound with As and other inpurities by DEX.Melt strongly erodes silica sand lining.