High performance HSS refers to the steel with the some alloyoing element increased to high level: V (＞2.50%) or Co (≥ 4.5%) or Al(0.80~1.20%). Compared to normal high speed steel. High performace HSS can be hardened to 65~70HRC. The wear resistance and hot strength are both improved substancially. These grades can be used for tooling material for the processing of stainless steel, heat resisting steel and high strength steel. High performance HSS with about 2.5%V, its wear resistance is increased due to the high hardness of vanadium carbide, 2800HV in the steel. On the other hand, it also increases the difficulty when manufacturing the tools, especially in grinding. Typical grade of cobalt high speed steel is W2Mo9C4VCo8 (M42). Adding the cobalt in the steel can improve the hot hardness and resistance to oxidation at high temperature, it is therefore chosen to be the tool materials working at higher cutting speeds. Cobalt also plays important role in increasing martensitic transformation temperature, improving martensitic formation and precipitation of fine carbide particles in the tempering process obtaining secondary harding effect. This element can suppress the formed carbide particles growth, improving hardness and hot hardness during quenching and tempering process. High thermal conductivity of cobalt is useful to improve the tool performance in cutting. Adding cobalt into steel can reduce the coefficient of friction and improve its grindability. Aluminum high speed steel is a unique cobalt-free high performance high speed steel in China. Typical grade is W6Mo5Cr4V2Al (M2Al). Aluminum is a non-carbide forming elements, which can increase the solubility of W, Mo and other elements in steel and improving the cast microstructure. Therefore with the addition of Al into HSS, the hot strength、ductility and toughness are all increased. When cutting using Al HSS tool, the surface of tool can form aluminum oxide thin film at the high cutting temperature, which can reduce friction and helpful in chip removal. The mechanical properties and cutting performance using M2Al are similar to that of M42, while its price is much lower than M42. However, more attention should be paid to heat treatment process when using M2Al, impoper heat treatment parameters, especially improper annealing process after deformation, it will prone to mixed grain in structure and early tool failure.