738H Steel: Is It the Right Choice for Your Mold Tooling Needs?

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When selecting steel for mold bases or plastic injection molds, 738H steel often stands out as a popular and reliable option. But how does it compare to alternatives like P20 or 718? And is it suitable for your specific manufacturing requirements? In this article, we’ll explore the key properties, common uses, advantages, and potential limitations of 738H steel to help you make an informed decision.

What Is 738H Steel?

738H steel is a pre-hardened chromium-molybdenum-nickel alloyed tool steel. It is widely used in the mold-making industry for its well-balanced mechanical properties, good machinability, and corrosion resistance. Its composition is similar to 718 steel, but it offers slightly different characteristics at a more competitive cost.

Some basic properties of 738H steel include:

Hardness range: 30 to 34 HRC

Tensile strength: around 1000 MPa

Density: approximately 7.85 grams per cubic centimeter

Thermal conductivity: about 25 watts per meter-kelvin at room temperature

Why Do Manufacturers Choose 738H Steel?

At various stages of product development and production, different priorities arise. Here’s how 738H steel supports decision-making across these stages:

1. Early Stage: Comparison with Other Mold Steels

Manufacturers often compare 738H steel with other common materials like P20, 718, and NAK80. Here’s a simplified comparison:

Compared to P20, 738H offers better corrosion resistance and slightly higher hardness.

Compared to 718, it is more cost-effective but with slightly lower polishability.

Compared to NAK80, 738H is more affordable and easier to machine but doesn’t achieve the same high-gloss polish or hardness levels.

Conclusion: 738H steel strikes a solid balance between performance and price, making it ideal for general-purpose plastic molds that don’t require ultra-high polish or extremely long mold life.

2. Design Stage: Machinability of 738H Steel

738H steel is delivered in a pre-hardened condition, which means it does not require post-machining heat treatment. This saves time and cost. Its machinability is rated as good, and it works well with carbide tools. For best results, a cutting speed of 60 to 80 meters per minute is typically recommended.

3. Production Stage: Performance in Real-Life Applications

738H steel performs well in medium-volume production molds, typically supporting up to 500,000 cycles under proper conditions. Its corrosion resistance, thanks to elements like nickel and chromium, makes it a better choice than P20 in environments with water cooling or high humidity.

Common uses include:

Injection molds for consumer electronics

Automotive interior parts

Home appliance components

Medium-complexity, multi-cavity molds

Thermal Resistance

738H steel can handle moderate molding temperatures and performs well up to around 250 degrees Celsius. However, if your application involves high-temperature plastics like PEEK or PSU, you might consider switching to a higher-grade tool steel such as H13.

When to Avoid 738H Steel

While 738H is versatile, it may not be the best choice in the following scenarios:

Molds with extremely high production volumes (more than one million shots)

Parts that require high-gloss or optical finishes

Applications involving high wear or very high temperatures

In such cases, steels like 718 or H13 are better suited due to their higher durability and resistance properties.

Recommendations for Mold Designers and Buyers

738H steel is ideal for:

Medium-volume production molds

Applications needing moderate corrosion resistance

Scenarios where cost efficiency and reliable performance are both important

To enhance wear resistance, you can also consider surface treatments such as nitriding.

Final Thoughts: Is 738H Steel Right for You?

If you’re looking for a steel that offers good machinability, reasonable hardness, moderate corrosion resistance, and a competitive price, 738H is an excellent choice for general mold applications.

However, if your needs involve optical finishes, extreme wear resistance, or high-heat applications, you should look into alternatives like NAK80, 718, or H13.

Whether you’re designing molds for consumer products, automotive parts, or electronics, understanding the strengths and limitations of 738H steel can help you make smarter, more cost-effective decisions. If you're unsure, consult with your mold maker or steel supplier to match the material to your exact requirements.