US divided into according to the mold service condition the molding tool steel three big kinds, American Metal Academic society Tool steel Committee has listed: Cold working molding tool steel, hot work molding tool steel and plastic molding tool steel three big kinds. Among them, the cold working molding tool steel branches out 12 minor sorts, the hot work molding tool steel 9 minor sorts, the plastic molding tool steel 2 minor sorts. Each minor sort selection is decided by three primary factors: The size size and the shape complexity, the material, the durable request or the design life which processes.
　　The cold working molding tool steel divides into five groups: W group, O group, A group, D group, S group. W group of namely tool steel, some 11 aluminums, 7 ordinary tool steels, carbon amount from 0.7%-1.3%. O group of namely cold working molding tool steels (popular name oil-quenched steel), some 4 aluminums, carbon amount in 0.85-1.55%. A group namely spatially quenches the alloy cold working molding tool steel, some 9 aluminums, carbon amount from 0.5-2.25%. D group is Gao Tangao the chromium cold working molding tool steel, some 7 aluminums, carbon amount 0.9%-2.5%. S group namely bears attacks the tool steel, some 7 aluminums, carbon amount 0.4-0.6%.
　　Because the hot work mold in has under the temperature condition to work, the request material has the hot stubborn and unyielding person and the hot resistance to wear, in order to guarantee the mold the service life mold must cool, the hot cold mold can have the chap in turn, namely hot fatigue cracking, therefore the material requests to have the anti-crack ability and the heat-resistant weary performance.
　　American molding tool steel minute two big kind: molding tool steel and super hot strong alloy.
　　US is most as early as lists the plastic mold special-purpose steel country in the tool steel, expresses by P primarily, altogether divides into five kinds.
　　Cementation plastic molding tool steel: P1,P2,P3,P4,P5,P6. This kind of steel carbon amount is very low, mainly is the American early time and with the extrusion formation die making, the request cold plasticity is good, has the high extrusion performance, after the formation case hardening quenching enhances the skin hardness, the service life is long. The core section ultra low-carbon may cause when quenching the amount of deformity is smallest.
　　Quenching and tempering plastic mold: P20,P21. At present in the plastic mold the P20 amount used very is big, has become the main body, majority when pre-hard condition uses.