What Is 718H Mold Steel?
718H mold steel is a premium pre-hardened plastic mold steel developed from the P20 steel family. By adding nickel to the alloy composition, 718H achieves better hardness uniformity, improved toughness, superior polishing performance, and enhanced dimensional stability compared with standard P20 steel.
Supplied in a pre-hardened condition of 32–36 HRC, 718H can be machined directly without additional heat treatment. This helps reduce manufacturing lead times, minimize distortion risks, and lower overall production costs.
Because of its excellent balance of machinability, wear resistance, polishability, and dimensional stability, 718H is widely used for precision plastic molds in the automotive, electronics, medical, and consumer goods industries.
Quick Overview of 718H Mold Steel
| Property | Value |
|---|---|
| Steel Type | Pre-Hardened Plastic Mold Steel |
| Typical Hardness | 32–36 HRC |
| Main Advantage | Excellent polishability and dimensional stability |
| Equivalent Grade | DIN 1.2738 / P20+Ni |
| Heat Treatment | Not required for most applications |
| Surface Finish | Mirror polishing achievable |
| Suitable Applications | Precision plastic injection molds |
| Machinability | Good |
| Wear Resistance | Better than P20 |
| Toughness | Excellent |
Key Properties of 718H Mold Steel
Excellent Hardness Uniformity
One of the most important advantages of 718H is its consistent hardness throughout the steel block. Unlike conventional P20 steel, which may show hardness variations in large sections, 718H maintains uniform mechanical properties from surface to core.
This helps ensure consistent mold performance, reduced wear, and improved dimensional accuracy during long production runs.
Superior Polishing Performance
718H is produced with a clean microstructure and low impurity content, making it an excellent choice for molds requiring high-quality surface finishes.
With proper polishing procedures, the steel can achieve mirror finishes suitable for:
- Transparent plastic products
- Cosmetic packaging
- Consumer electronics housings
- Medical plastic components
Outstanding Dimensional Stability
The addition of nickel improves the steel’s internal structure and reduces deformation during machining and production.
This makes 718H particularly suitable for:
- Deep cavity molds
- Thin-wall plastic parts
- Large mold blocks
- Complex mold geometries
Good Wear Resistance
Compared with standard P20 steel, 718H provides improved wear resistance and longer service life, especially in high-volume production environments.
High Toughness
718H offers excellent toughness and crack resistance, helping molds withstand repeated injection cycles and mechanical stresses without premature failure.
Good Weldability
The steel can be repaired through welding with relatively low distortion, making maintenance and mold modification more efficient and economical.
Chemical Composition of 718H Mold Steel
The typical chemical composition of 718H mold steel is shown below.
| Element | Content (%) | Function |
|---|---|---|
| Carbon (C) | 0.35–0.45 | Provides hardness and strength |
| Chromium (Cr) | 1.80–2.10 | Improves wear resistance and hardenability |
| Nickel (Ni) | 0.90–1.20 | Enhances toughness and hardness uniformity |
| Molybdenum (Mo) | 0.15–0.25 | Improves dimensional stability |
| Manganese (Mn) | 1.30–1.50 | Supports machinability and hardening |
| Silicon (Si) | 0.20–0.40 | Increases oxidation resistance |
| Phosphorus (P) | ≤0.020 | Controlled to reduce brittleness |
| Sulfur (S) | ≤0.010 | Maintained at low levels for polishing quality |
The nickel addition is the primary difference between 718H and conventional P20 steel, providing enhanced toughness and improved structural consistency.
718H Mold Steel Hardness
718H is typically supplied at a hardness range of 32–36 HRC.
This hardness level provides an ideal balance between:
- Machinability
- Wear resistance
- Dimensional stability
- Mold service life
Compared with P20 steel, which is usually supplied at 28–32 HRC, 718H offers improved durability while remaining easy to machine using standard CNC and EDM processes.
Does 718H Mold Steel Require Heat Treatment?
In most applications, no additional heat treatment is required.
718H is supplied in a pre-hardened condition and is designed to be machined directly into molds.
Benefits of using pre-hardened 718H include:
- Reduced manufacturing time
- Lower production costs
- Less risk of distortion
- Stable mechanical properties
- Improved dimensional accuracy
Additional quenching and tempering are generally not recommended, as they may negatively affect dimensional stability and surface quality.
718H Mold Steel Equivalent Grades
718H is known under several equivalent or comparable grade designations worldwide.
| Standard | Equivalent Grade |
|---|---|
| DIN | 1.2738 |
| AISI | P20+Ni |
| ASSAB | 718H |
| GB | 3Cr2NiMo |
| Application Category | Plastic Mold Steel |
Is 718H the Same as P20?
No.
718H is an upgraded version of P20 steel that contains additional nickel. While both are pre-hardened mold steels, 718H offers:
- Better hardness consistency
- Higher toughness
- Improved polishability
- Better dimensional stability
- Longer mold life
For precision molds and large mold blocks, 718H is generally the preferred choice.
Applications of 718H Mold Steel
Consumer Electronics Molds
718H is commonly used for:
- Smartphone accessory housings
- Power bank cases
- Bluetooth speaker shells
- Charger enclosures
- Precision electronic components
Its excellent surface finish capabilities make it ideal for visible plastic parts.
Automotive Plastic Molds
Typical applications include:
- Dashboard components
- Interior trim parts
- Air vent housings
- Lamp frames
- Electronic control module covers
The steel’s dimensional stability supports consistent quality during high-volume production.
Medical Plastic Molds
718H is frequently selected for:
- Syringe components
- Medical connectors
- Disposable medical devices
- Healthcare plastic products
The material provides smooth cavity surfaces and reliable production consistency.
Cosmetic Packaging Molds
Manufacturers often use 718H for:
- Cosmetic containers
- Beauty product packaging
- Transparent plastic bottles
- Premium consumer packaging
Its polishing performance helps achieve excellent visual quality.
Large and Complex Plastic Molds
718H performs exceptionally well in:
- Deep cavity molds
- Multi-cavity molds
- Large mold bases
- Thin-wall plastic parts
- Complex curved surfaces
Its hardness uniformity remains stable even in large cross-sections.
Machining Guidelines for 718H Mold Steel
CNC Machining
Recommended machining parameters include:
- Cutting speed: 60–100 m/min
- Feed rate: 0.12–0.25 mm/rev
- Depth of cut: 1.5–3 mm
Coated carbide tools are recommended for optimal performance and tool life.
EDM Processing
718H offers stable EDM performance and produces a relatively uniform discharge surface, reducing subsequent polishing requirements.
Polishing
A typical polishing sequence includes:
240 → 600 → 1200 → 3000 grit abrasives followed by diamond paste polishing.
Proper polishing can achieve mirror-quality surfaces suitable for transparent plastic products and cosmetic packaging molds.
Texture Etching
The fine and uniform microstructure of 718H supports:
- Leather textures
- Matte finishes
- Decorative patterns
- Fine etched surfaces
Excellent texture consistency can be maintained throughout the mold cavity.
Welding Repair
For repair welding:
- Use matching welding consumables
- Preheat to 150–200°C
- Control cooling rates carefully
These practices help reduce residual stress and prevent cracking.
718H vs P20 vs NAK80
Choosing the right mold steel depends on mold complexity, surface finish requirements, production volume, and budget.
| Property | P20 | 718H | NAK80 |
|---|---|---|---|
| Hardness | 28–32 HRC | 32–36 HRC | 38–42 HRC |
| Toughness | Good | Excellent | Good |
| Polishing Performance | Good | Excellent | Excellent |
| Dimensional Stability | Good | Excellent | Excellent |
| Wear Resistance | Moderate | Good | Very Good |
| Machinability | Excellent | Good | Moderate |
| Material Cost | Low | Medium | High |
When to Choose P20
- General-purpose molds
- Lower production volumes
- Budget-sensitive projects
When to Choose 718H
- Precision plastic molds
- High-gloss surfaces
- Complex mold structures
- Multi-cavity molds
- Large mold blocks
When to Choose NAK80
- Optical components
- Ultra-mirror surface requirements
- Premium appearance parts
- Long production runs
For most medium- and high-end plastic mold projects, 718H offers the best balance between performance and cost.
Frequently Asked Questions About 718H Mold Steel
What is the hardness of 718H mold steel?
718H is typically supplied at 32–36 HRC.
Is 718H better than P20?
For precision molds, yes. 718H provides better toughness, hardness uniformity, polishing performance, and dimensional stability than standard P20 steel.
Can 718H achieve a mirror finish?
Yes. With proper polishing procedures, 718H can achieve mirror-quality surfaces suitable for transparent plastic parts and cosmetic packaging molds.
Does 718H require heat treatment?
No. It is supplied pre-hardened and can usually be machined directly without additional heat treatment.
What is the equivalent grade of 718H?
Common equivalents include DIN 1.2738 and P20+Ni.
Conclusion
718H mold steel is one of the most widely used pre-hardened steels for precision plastic mold manufacturing. Compared with conventional P20 steel, it provides superior toughness, improved hardness uniformity, better polishing performance, and enhanced dimensional stability.
Whether you are producing automotive components, consumer electronics, medical devices, cosmetic packaging, or other high-precision plastic products, 718H offers a reliable and cost-effective solution that delivers consistent quality and long mold service life.
Looking for High-Quality 718H Mold Steel?
KUTU supplies certified 718H mold steel with custom cutting, rough machining, and technical support. Our engineering team can help you select the most suitable steel grade based on mold size, surface finish requirements, production volume, and budget.
Contact us today for a free quote and the latest 718H material datasheet.
718H (Premium P20+Ni Grade) High Polishing Plastic Mold Steel Plate Pre-Hardened – KUTU