The microstructure and thermal plasticity of the semi-solid M2 high speed steel billets prepared by cooling slope method have been investigated. The results indicate that the microstructure and thermal plasticity of the high speed steel billet can be effectively improved by the semi-solid processing as a result of the elimination of serious carbide segregation in the billet and the transformation of developed dendrite into fine round equiaxed grain. Meanwhile

the eutectic carbide in the semi-solid billets is lower and thinner than that of ones in conventional billets

and it exhibits not the developed network structure in the conventional billets but discontinuous net structure

which can result in the improvement of the thermal plasticity and the more uniform distribution of carbide in the semi-solid billets after forged. However

the desirable thermal plasticity temperature interval still is 900

1

200 ℃ in the condition of uniaxial stress.