Automotive injection moulds cover a wide range of parts, from very large bumper and dashboard tools to high-gloss interior trim and transparent lighting components. Because these moulds have different dimensions, surface requirements and resin systems, there is no single universal automotive plastic mould steel.
A practical automotive mould steel shortlist often includes P20 / 1.2311 Mould Steel, 1.2738 Mould Steel, 1.2316 Mould Steel and NAK80 Plastic Mould Steel. Each solves a different tooling problem.
Start With the Automotive Part, Not the Grade Name
| Automotive Component | Primary Mould Requirement | Practical Grade Direction |
| Bumper / large fascia | Large section, toughness, machining efficiency | 1.2738 or P20 family |
| Dashboard / door panel | Large mould, texture, dimensional stability | 1.2738 / P20 |
| General interior trim | Machinability and balanced cost | P20 |
| High-gloss decorative trim | Polishability and surface consistency | NAK80 |
| Headlamp / transparent optical parts | Polishing + corrosion resistance | 1.2316 or high-cleanliness polishing grade |
| Corrosive or flame-retardant resin parts | Corrosion resistance | 1.2316 |
P20 / 1.2311 for General Automotive Injection Moulds
P20 / 1.2311 Mould Steel remains a strong general-purpose choice because it is supplied in a machinable pre-hardened condition and provides balanced strength, toughness, weldability and cost. It is useful for automotive interior moulds and other tools where extreme corrosion resistance or optical-level polishing is not required.
The main advantage is manufacturing efficiency. Eliminating a full final hardening operation for a large mould can reduce process complexity and distortion risk. For cost-sensitive, medium-demand applications, that practical benefit can be more valuable than selecting a premium grade with properties the part does not need.
1.2738 for Large Bumper, Dashboard and Exterior Moulds
1.2738 Mould Steel is particularly relevant to large and extra-large plastic moulds. Its pre-hardened condition, toughness and through-section performance make it well suited to automotive bumpers, dashboards, door panels, grilles and other large parts.
As mould thickness and width increase, consistency through the block becomes more important. A large mould also represents substantial machining value, so internal soundness, hardness uniformity and dimensional stability should be specified as purchasing requirements rather than assumed.
1.2316 for Corrosion-Sensitive and Optical Automotive Parts
1.2316 Mould Steel is a corrosion-resistant pre-hardened mould steel that becomes relevant when plastics or additives can create a corrosive moulding environment. It is also useful where good polishability and clean cavity surfaces matter, including automotive lighting and selected transparent parts.
If a mould spends significant maintenance time on rust, pitting or repeated cavity repolishing, a corrosion-resistant material can lower lifecycle cost even if its initial price is higher.
NAK80 for High-Gloss Interior and Premium Surface Parts
NAK80 Plastic Mould Steel is positioned toward high-end precision moulds requiring mirror polishing, fine texture reproduction and stable pre-hardened performance. It can be valuable for visible interior components, decorative trims, display-related housings and premium surface parts where the mould cavity directly determines perceived product quality.
NAK80 should not automatically replace P20 or 1.2738 in a large structural mould. Its value is strongest where high surface quality and precision justify the premium material.
Resin Selection Changes Mould Steel Requirements
Automotive plastics may contain glass fibre, flame retardants, fillers or other additives. Glass-filled materials increase abrasive wear, while corrosive decomposition products can increase the need for corrosion resistance. Before final material selection, the mould maker should review the exact resin specification instead of relying only on the component name.
Large Automotive Moulds Require More Than a Grade Certificate
- Uniform pre-hardened hardness across the full block.
- Controlled internal quality and ultrasonic inspection where required.
- Appropriate machining allowance.
- Straightness, flatness and dimensional tolerance.
- Heat number and material traceability.
- Confirmed polishing or texturing requirement.
- Welding and repair plan for long-service moulds.
Practical Automotive Mould Steel Selection
Use P20 as an economical general-purpose baseline. Move toward 1.2738 when mould size, toughness and large-section consistency become more important. Select 1.2316 when corrosion resistance is part of the service requirement. Consider NAK80 when mirror finish, fine texture or premium surface quality is a major product requirement.
| RFQ Tip: For automotive projects, compare the product data for P20 / 1.2311 Mould Steel, 1.2738 Mould Steel, 1.2316 Mould Steel and NAK80 Plastic Mould Steel before finalizing the mould material specification. |
Frequently Asked Questions
What steel is commonly used for automotive bumper moulds?
P20-family steels and 1.2738 are commonly considered. 1.2738 becomes especially relevant for large sections requiring good toughness and dimensional stability.
Which mould steel is suitable for automotive headlamp parts?
For transparent or corrosion-sensitive components, a polishable corrosion-resistant grade such as 1.2316 may be considered depending on the exact optical and resin requirements.
Is NAK80 suitable for automotive interior moulds?
Yes, particularly for high-gloss, precision or finely textured visible parts where surface quality is a major requirement.
Is P20 enough for every automotive mould?
No. P20 is a strong general-purpose option, but large moulds, corrosive resins and optical/high-gloss surfaces may justify different grades.
