Crystallization characteristics of two mold fluxes (%:2.54～3.0Al203 、7.34~8.35Na

2

0 、8.83～8.87F、 0.79~3.00Li

2

O)during temperature decreasing and solidifying process for≤1.3 m/min normal speed casting (mold powder  TCaO/SiO

2

=1. 19)and≥1.5m/min high speed casting (mold powder TCaO/SiO

2

=1.40) of 0.07～0. 10C hypoperitectic steel and effect of crystallization on viscosity of fluxes have been studied. It was obtained that above solidification temperature there was obvious crystallization behavior for high-speed casting flux and the main crystal phase was cuspidine (3CaO ·2SiO

2

·CaF

2

); but above solidification temperature there was no obvious cryst

allization phenomenon in normal speed casting flux. Compared with normal speed casting flux

after completed solidification the grain in high-speed   casting flux was larger with a lot of gaps between grains being favorable to increase heat resistance of flux film and decrease heat transfer in mold. Above crystallization temperature

the TCaO/SiO

2

=1.40 high speed casting flux had lower viscosity being available to lubricate the mold

and below crystallization temperature

its viscosity rapidly increased being favorable   to increase the thickness of solid film and slow down mold heat transfer.