Test high speed steel M2 ( % : 0. 85C

5. 92W. 4. 74Mo

3. 86Cr

1. 84V) was melted by 25kg vacuum induction furnace and ingot was cast bv sand mould. The effect of 0 ~ 1. 3% Al on stiucture of as-cast steel has been studied. Results showed that added 0. 6% Al was available to fine the ledeburite network and improve the distribution of carbides in steel ； while added excessive amount of Al (1. 3% ) promoted the formation of a great lot of acicular carbide eutectoid-transformed from δ ferrite in primary grain. Al promoted the  M

2

C carbide translbrnied from curved rod-like to straight lamella-like in which the alloy element content increased. Compared with lamellar M

2

C

the rod-like M

2

C easily decomposed short rod-like and granular carbides favorably to improve the morphology of carbide in steel.