The United States is the earliest country in the tool steel for plastic mold steel, P to represent the main, divided into five categories. ◆ Carburized plastic mold steel: P1, P2, P3, P4, P5, P6. Low carbon content of this type of steel, mainly the United States early and extrusion molding method, requiring good cold plasticity, high extrusion performance, surface hardening carburizing to improve the surface hardness, long service life. Low-carbon core can quench the deformation of the smallest. ◆ Conditioning plastic mold: P20, P21. P20 plastic mold in a large amount, has become the main body, most of the pre-hardened state to use. ◆ Medium carbon alloy tool steel for thermosetting plastic mold. H13 steel, and L2 and S7, O1 and A2 are also applications. The characteristics of this category are: (1) The basic is a secondary hardening of the steel, 500-600oC when the heat strength is good. (2) high chromium, atmospheric corrosion is good. (3) excellent hardenability, suitable for large modules. ◆ stainless steel for corrosion-resistant plastic mold, the main steel No. 420,414 L, 440,416.
◆ aging steel is aging treatment and access to high performance. There are two kinds, one is P21 low-carbon Ni-A1 age-hardening steel; the other is 18Ni martensitic aging steel. The latter is a carbon-free, high-purity, high-strength, high-toughness material for the aerospace industry. For mechanical properties, dimensional accuracy, finish and corrosion resistance are demanding plastic mold. Selection of plastic mold steel: thin-walled plastic box, the production volume in less than 100,000, with P20, P21 pre-hardened (HB250 ~ 300), corrosive with 414L. Ordinary plastic mold with high life, with P6 or P20, after hardened by a carburizing hardness HRC54-58; plastic parts is not too large, available O1, S7. Corrosive with 420. Non-high temperature thermosetting mold P6, P20 after carburizing and quenching use. Corrosive 420. High temperature thermosetting plastic mold with H13 and S7 or carburizing steel P4. These high chromium have good resistance to tempering and high temperature oxidation resistance.