In plastic injection mold manufacturing, mold steel plays a major role in product quality, mold lifespan, cooling efficiency, and production cost.

Different products require different types of mold steel.
For example, a simple household product mold may use P20 steel, while high-speed production molds or engineering plastic molds may require H13 or S136 steel.

Choosing the correct steel is not only about hardness. It also affects:

• Mold durability

• Surface finish

• Production cycle time

• Maintenance cost

• Long-term production stability

This article explains the most commonly used steels for injection molds and how to select the right one for your project.

Common Types of Injection Mold Steel

1. P20 Steel — The Most Common Choice

HRC≈28–32HRC \approx 28\text{–}32HRC≈28–32

P20 steel is one of the most widely used materials in plastic injection mold manufacturing.

It is pre-hardened steel with good machinability and relatively low cost.

Advantages

• Easy to machine

• Cost-effective

• Suitable for medium production volume

• Short mold manufacturing cycle

Disadvantages

• Average wear resistance

• Limited polishing quality

• Not ideal for glass fiber materials

Typical Applications

• Plastic chair molds

• Paint bucket molds

• Household product molds

For many standard chair molds, P20 steel is still a practical and economical option.

2. 718 / 2738 Steel — Popular for Export Molds

718 steel, also known as DIN 2738, is an upgraded version of P20 steel.

Compared with P20, it offers better polishing performance and improved toughness.

Features

• Better surface finish

• Higher hardness

• More stable in mass production

• Better resistance to deformation

Common Applications

• Office chair molds

• Stackable chair molds

• Automotive plastic molds

Many export mold manufacturers prefer 718 steel because it balances mold life and production cost well.

. H13 Steel — For High-Speed and High-Wear Production

HRC≈48–52HRC \approx 48\text{–}52HRC≈48–52

H13 is a hot-work tool steel with excellent thermal resistance and wear resistance.

Advantages

• Long mold lifespan

• High hardness

• Excellent heat resistance

• Suitable for fast injection cycles

Typical Applications

• Thin-wall molds

• Engineering plastic molds

• High-cavitation molds

H13 steel is more expensive and more difficult to machine, but it performs very well in demanding production environments.

4. S136 Steel — Stainless Mold Steel

S136 is commonly used for molds that require corrosion resistance and high polish quality.

Advantages

• Excellent rust resistance

• Mirror polishing capability

• Good wear resistance

Common Applications

• Food containers

• Medical products

• Transparent plastic parts

For factories operating in humid environments, S136 can help reduce rust problems and maintenance costs.

5. NAK80 Steel — Excellent Surface Finish

NAK80 is widely known for its polishing performance.

Features

• Pre-hardened steel

• Good engraving capability

• Excellent mirror finish

Applications

• Cosmetic packaging

• Transparent products

• High-gloss plastic components

If product appearance is very important, NAK80 is often selected.

ow to Choose the Right Mold Steel

Different mold projects require different steel solutions.

For General Plastic Products

Recommended steel:

• P20

• 718 / 2738

These steels provide good cost performance for standard production.

For Long Mold Life

Recommended steel:

• H13

• 2344

These materials offer better wear resistance and are suitable for large production volumes.

For High Polish Surface

Recommended steel:

• S136

• NAK80

These steels are suitable for transparent or glossy products.

For Glass Fiber Materials

Recommended steel:

• H13

• 2344

Glass fiber materials can wear mold surfaces quickly, so higher hardness steel is necessary.

What Steel Is Used for Plastic Chair Molds?

Plastic chair molds are usually large molds with relatively high production volumes.

Commonly used steels include:

• P20

• 718 / 2738

Some high-end chair molds may also use:

• H13 inserts

• Beryllium copper cooling inserts

These materials help improve cooling efficiency and extend mold life.

Why Mold Steel Matters

Many buyers focus only on mold price, but mold steel directly affects production performance.

Better steel can improve:

• Mold lifespan

• Product quality

• Production stability

• Cooling performance

• Maintenance efficiency

Although high-quality steel increases the initial mold cost, it can reduce long-term production expenses.

Conclusion

There is no single “best” steel for injection molds.

The correct choice depends on:

• Product material

• Production quantity

• Surface finish requirements

• Mold structure

• Budget

For standard plastic molds, P20 and 718 steel are widely used.
For high-speed or high-wear production, H13 and S136 are more suitable.

Before starting a mold project, it is important to discuss steel selection with the mold manufacturer to balance cost, performance, and mold lifespan.

FAQ

What is the most common steel for injection molds?

P20 steel is one of the most commonly used mold steels because it is economical and easy to machine.

Is H13 better than P20?

H13 offers better hardness and wear resistance, but it is more expensive than P20.

What steel is used for chair molds?

Most plastic chair molds use P20 or 718 steel.

Why is S136 steel used?

S136 provides excellent corrosion resistance and polishing quality, making it suitable for food and medical products.

Does mold steel affect production efficiency?

Yes. Mold steel affects cooling performance, mold life, maintenance frequency, and production stability.