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• 2026/7/3

Stainless Steel vs Tool Steel: Meto Tells You Which One to Use for Preform Molds

Introduction: The Steel Decision

When you buy a preform mold, one of the most important decisions is the steel. The steel determines how long the mold will last, how consistent the preforms will be, and how much maintenance the mold will need.

Two main categories of steel are used for preform molds: tool steel and stainless steel. Tool steel provides excellent wear resistance at a reasonable cost. Stainless steel provides corrosion resistance at a higher cost.

This article explains the differences between tool steel and stainless steel for preform molds. It shows when to use each type. It helps you choose the right steel for your application.

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Part 1: Tool Steel for Preform Molds

Tool steel is the traditional choice for preform molds. It is strong, tough, and wear resistant. It can be heat treated to high hardness.

The most common tool steel for preform molds is H11, also known as 1.2343. This is a chromium hot work steel. It contains chromium, molybdenum, and vanadium. It provides good wear resistance and toughness at high temperatures.

Another tool steel used is H13, also known as 1.2344. It is similar to H11 but with slightly different alloy composition. It provides slightly better toughness but lower wear resistance than H11.

Tool steel is hardened to 48 to 52 HRC. This provides excellent wear resistance for the neck finish area. The steel holds its dimensions well. It resists deformation under high clamping and injection pressures.

Tool steel is less expensive than stainless steel. For virgin PET applications, it is the most economical choice.

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Part 2: Stainless Steel for Preform Molds

Stainless steel is used when corrosion resistance is needed. The most common stainless steel for preform molds is 420, also known as 1.2083. This is a martensitic stainless steel. It contains 13 to 17 percent chromium. The chromium forms a passive oxide layer that resists corrosion.

Stainless 420 can be hardened to 48 to 52 HRC. This provides wear resistance comparable to tool steel. It can be polished to a mirror finish. This is important for cosmetic applications.

Another stainless steel used is 1.2316. This is a higher alloy stainless steel with better corrosion resistance than 1.2083. It is used for aggressive rPET applications.

Stainless steel costs more than tool steel. But it is necessary for rPET, PCR, and corrosive applications.

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Part 3: Corrosion Resistance Difference

Corrosion resistance is the biggest difference between tool steel and stainless steel.

Tool steel contains chromium, but not enough to form a passive layer. It rusts when exposed to moisture and acids. PET degradation byproducts include acetic acid and other corrosive compounds. These attack tool steel surfaces.

When tool steel corrodes, the surface becomes rough. The roughness transfers to the preform. The preform surface is no longer smooth. For clear bottles, this is unacceptable.

Stainless steel resists corrosion. The chromium oxide layer protects the steel from acid attack. The surface remains smooth. The preform remains clear.

For virgin PET, corrosion is minimal. For rPET and PCR, corrosion is a serious problem. Stainless steel is required for rPET applications.

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Part 4: Wear Resistance Comparison

Wear resistance is comparable between H11 and 420 stainless at the same hardness.

Both steels can be hardened to 48 to 52 HRC. At this hardness, both resist abrasive wear from PET flow. The neck finish threads and sealing surfaces remain within tolerance for millions of cycles.

H11 has better wear resistance at very high temperatures. Its alloy content provides better hot hardness. For very fast cycle applications, H11 may have a slight advantage.

420 stainless has adequate wear resistance for most preform applications. The difference is small enough that it rarely affects mold life.

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Part 5: Polishability Comparison

Surface finish affects preform clarity and release.

420 stainless polishes very well. It can achieve a mirror finish of Ra 0.05 to 0.1 microns. This is why it is used for cosmetic and high clarity applications.

H11 also polishes well, but not as well as 420 stainless. It can achieve Ra 0.1 to 0.2 microns. This is sufficient for most water and beverage bottles.

For high clarity bottles where preform clarity is important, 420 stainless is preferred. For standard bottles, H11 is sufficient.

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Part 6: Price Comparison

Tool steel is significantly less expensive than stainless steel.

For a 32 cavity preform mold, H11 steel costs approximately 50,000 US dollars. 420 stainless steel costs approximately 60,000 US dollars. The stainless mold is approximately 20 percent more expensive.

The price difference comes from the material cost and the machining. Stainless steel is harder to machine than tool steel. It requires specialized cutting tools and slower speeds.

The additional cost must be justified by the need for corrosion resistance.

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Part 7: Life Comparison

Mold life depends on the application.

For virgin PET, H11 and 420 stainless have similar life. Both can achieve 5 to 7 million cycles with proper maintenance. H11 has excellent resistance to thermal fatigue for long production runs.

For rPET or PCR, H11 life is significantly shorter. Corrosion causes pitting and surface roughness. Life is typically 2 to 3 million cycles.

For rPET or PCR, 420 stainless life is 5 to 7 million cycles. The corrosion resistance prevents pitting. The surface remains smooth.

For corrosive applications, stainless steel lasts 2 to 3 times longer than tool steel.

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Part 8: Surface Treatments

Both tool steel and stainless steel can be surface treated to extend life.

H11 can be plasma nitrided. Nitriding adds a hard surface layer of 65 to 70 HRC. Wear resistance increases significantly. Life can extend to 7 to 8 million cycles. Nitriding does not improve corrosion resistance. It may even reduce it.

420 stainless can also be nitrided, but nitriding reduces corrosion resistance. The chromium is tied up in nitrides. The passive layer is weakened. For rPET applications, nitriding is not recommended.

PVD coatings such as TiN and CrN can be applied to both steels. These coatings provide wear resistance and corrosion protection. They are expensive. They are typically reserved for extreme applications.

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Part 9: Application Decision Guide

Use this guide to choose the right steel.

Choose H11 tool steel for virgin PET with low to medium rPET content under 20 percent, standard water and beverage bottles, price sensitive projects, applications where corrosion is not a concern, and standard cycle times.

Choose 420 stainless steel for rPET or PCR content over 20 percent, juice and acidic product bottles, cosmetic and high clarity bottles, applications requiring mirror finish, and aggressive processing conditions.

For applications between 20 and 40 percent rPET, either steel may work. Test both to see which performs better with your specific material.

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Part 10: Customer Examples

A water bottler in Southeast Asia uses virgin PET. They chose H11 tool steel. The mold has run 6 million cycles with no corrosion. The lower cost was the right choice.

A juice bottle producer in Europe uses 50 percent rPET. Their H11 tool steel molds pitted at 2.5 million cycles. They switched to 420 stainless steel. The mold has run 4 million cycles with no corrosion. The stainless mold lasts longer.

A cosmetic bottle producer in North America requires high clarity preforms. They chose 420 stainless steel. The mirror finish gives their preforms the clarity they need.

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Part 11: Meto Steel Standards

Meto uses H11 for standard virgin PET preform molds. All H11 steel is certified. Vacuum heat treatment is performed in house. Double tempering is standard. Hardness is 48 to 52 HRC on every cavity. Nitriding is optional.

Meto uses 420 stainless for rPET and cosmetic preform molds. All 420 stainless steel is certified. Vacuum heat treatment is performed in house. Double tempering is standard. Hardness is 48 to 52 HRC on every cavity. Surface finish is Ra 0.1 microns or better.

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Part 12: Practical Tips

If you are switching to rPET, change your steel. H11 will corrode. 420 stainless is recommended.

If you are using rPET and do not see corrosion yet, monitor closely. Corrosion starts slowly and accelerates.

If you need mirror finish for clarity, choose 420 stainless. H11 cannot achieve the same finish.

If you are price sensitive and use virgin PET, choose H11. It provides the best value.

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Part 13: Conclusion

The choice between tool steel and stainless steel depends on your material and application.

H11 tool steel is the right choice for virgin PET and low rPET applications. It provides excellent wear resistance at a reasonable cost.

420 stainless steel is the right choice for high rPET, PCR, and cosmetic applications. It resists corrosion and provides mirror finish.

Meto can help you choose the right steel for your application. We consider your material, volume, and quality requirements. We provide a recommendation that balances cost and performance.

Do not use tool steel for rPET. You will pay for it in shorter mold life and higher maintenance.

Do not use stainless steel for virgin PET. You will pay more than you need to.

Choose the right steel. Save money. Run longer.

Contact Meto today to discuss your preform mold steel requirements. Tell us your material and production volume. We will recommend the right steel for your application.