The distribution of TiN inclusions in 200 mm x 1 260 mm cast slab of ultra-pure ferrite stainless steel B439M (/%： 0.01C

0.40Si

0.25Mn

0.020P

0.001S

17.50Cr

0.15Ni

0.20Ti

0.0080N

0.0040N) has been studied by automated scanning electro microscope Aspex. Results show that due to decrease in cooling rate from surface to inside of cast slab during solidifying process

lots of small size ( average 1. 26 μm) TiN inclusions form at edge of slab width

while at 1/4 of width and center of slab

from narrow side surface to 1/4 of thickness and from 1/4 of thickness to center of thickness the TiN nucleation rate decrease

the amounts of TiN inclusions decrease and size of TiN increases. It is obtained by kinetics analysis that the size of TiN inclusion increases with decreasing cooling rate coincides well with the distribution regulation of TiN inclusions in cast slab.