According to different molding and solidification, plastic mold falls into such two types as thermoset plastic mold and thermoplastic plastic mold. The plastics, during the working of thermoset plastic molds, are solid powder materials or prefabricated blank materials, which are added into the cavity and molded through thermal pressing under certain temperature. The force pplied thereon is large, friction is also large due to the impact it is subject to; thermal mechanical load and abrasion is large. Plastics for thermoplastic plastic mold are injected or pressed into the cavity under viscous flow state, wherein the deformation resistance is relatively smaller and the heat, pressure and abrasion applied on the molds are usually not very serious. However, when solid fillers are added therein, the abrasion will increase enormous Basic requirements for the performance of plastic mold steel are as follows O High rigidity and sound abrasion resistance; surface hardness of cavity should be 30-60HRC and hardenability >55HRC, sufficient hardening dept is required and sufficient obdurability is demanded at the heart therein to avoid brittle fracture and deformation 2 Certain heat resistance and erosion resistance. Due to the generally complicated structure of plastic molds, it requires low surface roughness and high precision for the cavity and excellent technical performance should be ensured. The specific requirement is as follows O Slight deformation during heat treatment and sound hardenability 2 Sound performance for cutting processing and superior polishing property and abrasion 3 For plastic molds employing cold extrusion forming process, it requires sound cold extrusion molding ability, and to make it convenient for molding, the hardness after anneal should be low, the plasticity good, and deformation resistance small. The deformation resistance after quenching is hig Other processing properties, such as forging and jointing properties, should be fine Plastic mold parts fall into working parts and structural parts. Working parts refer to those determining the geometrical shape, dimension and precision of plastic products, and are also called molding parts or the molding section of parts, such as cavity, core, insert, molding pin and molding ring etc. Their working condition is rather complicated and the technical requirement is high, especially the surface quality of the working face of molding parts, which is the major factor influencing the appearance and quality of plastic products as well as the service life of molds Commonly-used plastic mold steel includes the following 1. Casehardened Plastic Mold Steel Casehardened steel can be provided with tough core and abrasion-resistant surface, wherein high surface hardness will be beneficial for polishing treatment. Carbon content in the casehardened steel is less than 0.25%. During heat treatment carbon element can strengthen the intensity of core. To get higher surface hardness, carbon content on the surface must be increased, whereby can be achieved through adding carbon accelerant during the course of heat treatment he ideal carbonization temperature depth is 0.6-lmm. After quenching and tempering, the surface hardness can reach HRC58-62. Since the carbonization temperature is rather high, the dimension change is bound to occur, which requires extra follow-up treatment 2. Through-hardened Plastic Mold SteelAccording to different molding and solidification, plastic mold falls into such two types as thermoset plastic mold and thermoplastic plastic mold. The plastics, during the working of thermoset plastic molds, are solid powder materials or prefabricated blank materials, which are added into the cavity and molded through thermal pressing under certain temperature. The force applied thereon is large; friction is also large due to the impact it is subject to; thermal mechanical load and abrasion is large. Plastics for thermoplastic plastic mold are injected or pressed into the cavity under viscous flow state, wherein the deformation resistance is relatively smaller and the heat, pressure and abrasion applied on the molds are usually not very serious. However, when solid fillers are added therein, the abrasion will increase enormously. Basic requirements for the performance of plastic mold steel are as follows: ① High rigidity and sound abrasion resistance; surface hardness of cavity should be 30~60HRC and hardenability ＞55HRC; sufficient hardening dept is required and sufficient obdurability is demanded at the heart therein to avoid brittle fracture and deformation. ② Certain heat resistance and erosion resistance. Due to the generally complicated structure of plastic molds, it requires low surface roughness and high precision for the cavity and excellent technical performance should be ensured. The specific requirement is as follows: ① Slight deformation during heat treatment and sound hardenability. ② Sound performance for cutting processing and superior polishing property and abrasion resistance. ③ For plastic molds employing cold extrusion forming process, it requires sound cold extrusion molding ability, and to make it convenient for molding, the hardness after anneal should be low, the plasticity good, and deformation resistance small. The deformation resistance after quenching is high. ④ Other processing properties, such as forging and jointing properties, should be fine. Plastic mold parts fall into working parts and structural parts. Working parts refer to those determining the geometrical shape, dimension and precision of plastic products, and are also called molding parts or the molding section of parts, such as cavity, core, insert, molding pin and molding ring etc. Their working condition is rather complicated and the technical requirement is high, especially the surface quality of the working face of molding parts, which is the major factor influencing the appearance and quality of plastic products as well as the service life of molds. Commonly-used plastic mold steel includes the following: 1. Casehardened Plastic Mold Steel Casehardened steel can be provided with tough core and abrasion-resistant surface, wherein high surface hardness will be beneficial for polishing treatment. Carbon content in the casehardened steel is less than 0.25%. During heat treatment, carbon element can strengthen the intensity of core. To get higher surface hardness, carbon content on the surface must be increased, whereby can be achieved through adding carbon accelerant during the course of heat treatment. The ideal carbonization temperature depth is 0.6~1mm. After quenching and tempering, the surface hardness can reach HRC58~62. Since the carbonization temperature is rather high, the dimension change is bound to occur, which requires extra follow-up treatment. 2. Through-hardened Plastic Mold Steel