The United States is the first in the tool steel listed in the plastic mold special steel countries, to P to express the main, a total of five categories. ◆ carburized plastic mold steel: P1, P2, P3, P4, P5, P6. This kind of steel is very low carbon, mainly in the United States early and with the extrusion molding method, requires good cold plasticity, have high extrusion performance, after carburizing quenching forming the surface to improve surface hardness, long service life. Ultra-low carbon core can make cooling deformation minimal. ◆ Tempered plastic molds: P20, P21. Currently the amount of P20 in plastic molds is large and has become the main body, most of which are used in the pre-hardened state. ◆ Medium carbon alloy tool steel is used for thermosetting plastic molds. Steel grades are H13, although L2 and S7, O1 and A2 are also used. The characteristics of this class are
(1) It is basically a secondary hardening steel with good thermal resistance at 500-600oC.
(2) High chromium content, good atmospheric corrosion.
(3) Very good hardenability, suitable for large modules. ◆ Stainless steel is used for plastic molds with high corrosion resistance requirements. The main steel grades are 420, 414L, 440, 416. ◆ Aging steel is used to obtain high serviceability after aging treatment. There are two types, one is P21 low carbon Ni-A1 aging steel;
The other type is 18Ni maraging steel. The latter is a carbon-free material, of high purity, high resistance and high toughness, used in the aerospace industry. It is used in plastic molds where high mechanical properties, dimensional accuracy, finish and corrosion resistance are required. Steel selection for plastic molds Thin-walled plastic box, production batch in less than 100.000 pieces, with P20, P21 pre-hardened (HB250~300), stronger corrosive with 414L. High life of ordinary plastic mold, with P6 or P20, by carburizing a quenching hardness in HRC54-58;
When the plastic parts are not too big, use O1, S7. When the corrosion is strong, use 420. For thermoset molds that are not high temperature, use P6, P20 after carburizing and cooling. For high-temperature thermosetting molds, use H13 and S7 steels or P4 carburized steel, which have high chromium content and good resistance to tempering and oxidation at high temperatures.
