Selecting a mould steel requires more than comparing hardness.
Plastic resin, mould size, expected cycles, surface finish, corrosion conditions and machining requirements all influence the correct material.
For this reason, there is no single “best mould steel grade” for every injection mould.
Common Plastic Mould Steel Grades
| Grade | Key Advantage | Typical Application |
|---|---|---|
| P20 | Cost-effective and machinable | General injection moulds |
| 1.2312 | Excellent machinability | Large/general moulds |
| 1.2738 | Toughness and large-section performance | Automotive moulds |
| 1.2316 | Corrosion resistance | PVC, medical, optical |
| NAK80 | Mirror polishing and precision | High-gloss products |
P20
P20 remains one of the most widely recognised plastic mould steel families.
Its major advantage is balanced performance.
Pre-hardened supply reduces the need for final hardening, allowing mould makers to machine material directly.
Suitable applications include:
- Appliance housings
- Consumer products
- Automotive trim
- General injection moulds
- Industrial plastic components
1.2312
1.2312 is valued particularly for machinability.
It is useful when a mould contains substantial machining or complex cavities and production efficiency matters.
1.2738
1.2738 is commonly considered for large and extra-large plastic moulds.
Applications include:
- Automotive bumpers
- Dashboards
- Door panels
- Grilles
- Large appliance housings
Its suitability for larger sections makes it particularly relevant to automotive tooling.
1.2316
When corrosion becomes a concern, the mould steel selection changes.
1.2316 provides considerably stronger corrosion resistance than general-purpose P20-type materials.
It is commonly considered for:
- PVC
- Corrosive engineering plastics
- Medical moulds
- Pharmaceutical packaging
- Optical products
- Automotive lighting
NAK80
NAK80 targets a different problem: extremely high surface finish.
Typical applications include:
- Light guides
- Optical covers
- Cosmetic packaging
- High-gloss appliance panels
- Premium consumer electronics
- Fine-textured parts
Choose by Failure Mechanism
A simple mould selection rule is:
Wear → wear-resistant steel
Corrosion → corrosion-resistant steel
Large mould → high toughness and good through-section properties
Mirror finish → clean, highly polishable steel
Fast mould production → machinable pre-hardened steel
Resin Matters
Materials containing glass fibre can increase abrasive wear.
PVC and some flame-retardant materials can increase corrosion concerns.
Transparent components increase the importance of polishing and material cleanliness.
That means the same mould steel should not automatically be specified across every resin family.
Production Volume Matters
For prototypes or limited production, machining economy may dominate.
For long production runs, buyers should consider:
- Wear resistance
- Dimensional stability
- Maintenance
- Downtime
- Repair frequency
The cheapest steel per kilogram is not necessarily the lowest-cost mould material over its complete service life.
Information Required for Mould Steel Selection
Send:
- Plastic resin
- Mould dimensions
- Expected production quantity
- Surface finish
- Texture requirement
- Required hardness
- Corrosion environment
- Required steel grade
- Inspection requirement
This information creates a much stronger basis for material selection than simply asking for “mold steel.”
FAQ
What is the most common plastic mould steel?
P20-type pre-hardened mould steels are widely used for general injection mould manufacturing.
What mould steel is suitable for large automotive moulds?
1.2738 is commonly considered for large automotive tooling.
Which mould steel is corrosion resistant?
1.2316 is an important option for corrosion-sensitive plastic mould applications.
Which mould steel is best for mirror polishing?
NAK80 is widely associated with high-polish precision mould applications.
