There are the following 5 types of common plastic mold steel:

1.Corrosion-resistant type

 

Uses: mainly used in the production of materials such as polyvinyl chloride, polystyrene, ABS plus flame-retardant resin, which will decompose corrosive gases.

 

Grades: Typical grades of corrosion-resistant plastic steels commonly used abroad are martensitic stainless steel and precipitation hardening stainless steel, such as STSAX (4Cr13) and ASSAB~8407 of ASSAB company in Sweden. Common domestic are high-carbon high-chromium corrosion-resistant steels such as 1Cr17Ni2 martensitic stainless acid-resistant steel, 0Cr16Ni4Cu3Nb precipitation hardening stainless steel, etc.

 

2.Tempering type

 

The quenched and tempered type refers to the quenching and tempering process after the mold is processed to make the mold performance better. There are three main categories:

Carbon steels such as 45 and 55

 

Uses: Suitable for molds with simple shapes or low precision requirements and short service life.

40CrMo, 42CrMo.

 

Uses: the former has good low-temperature impact toughness and low notch sensitivity, suitable for making medium-sized molds; the latter belongs to high-strength steel, and has a high fatigue limit, good low-temperature impact resistance, suitable for manufacturing large size requiring certain strength and toughness , Medium-sized plastic mold.

38CrMoAl, 5CrNiMo.

 

Uses: The former is suitable for plastic molds of PVC and PC. The latter is mainly used for molds with high temperature and high wear resistance requirements, such as thermosetting plastic molds.

 

3. Age hardening type

 

Uses: Age hardening type is mainly used to manufacture high-precision, complex cavity plastic molds, which is expensive. There are two categories of maraging steel and precipitation hardening steel.

 

Grades: Typical grades are newly developed low-cobalt, cobalt-free, low-nickel maraging steel and MAST maraging steel.

 

Among them, the low-cobalt, non-cobalt, low nickel maraging steel, the hardness of the tempered steel is about 30HRC, and the hardness after aging treatment can reach 38-42HRC. MAST maraging steel has a hardness of 28-32HRC after solid solution and 48-52HRC after aging. The steel has high toughness, small changes in aging size, and good welding performance.

 

4. Carburizing type

 

 

Uses: Carburized steel has low hardness and good plasticity after annealing, and can be formed by cold extrusion.
Grades: Typical grades are 8416 in Sweden and P2 and P4 in the United States.

 

Chemical composition: The carburized plastic mold steel has a low carbon content, and the element Cr is often added. At the same time, appropriate amounts of Ni, Mo, V are added to improve the hardenability and carburizing ability. After annealing, the response should be ≤100HBS.

 

5. Pre-hard type

 

Uses: The pre-hardened type is a mold steel developed to avoid deformation of large and medium-sized precision molds after heat treatment and to ensure the accuracy and performance of the molds.

 

Brand: The pre-hardened plastic mold steels listed in the national standard are only 3Cr2Mo (P20) steel and 3Cr2MnNiMo.

 

Chemical composition: It is pre-conditioned and has a hardness of 30-40HRC. This type of steel is generally low-carbon alloy steel with a carbon content of 0.35%-0.65%. Commonly used alloy elements are Cr, Ni, Mn, V, etc. To improve its machinability, S, Ca, etc. are added.

 

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