What Steel to Use for EVA Injection Molds

EVA is a low-viscosity, lightweight, and widely used polymer for foamed products, packaging, seals, and daily necessities. Although EVA is not highly corrosive, long-term production and foam molding impose requirements on wear resistance, polishability, and thermal stability of mold steel. Choosing the right steel directly affects mold life, product appearance, and processing cost. The following is a complete and practical selection guide for EVA injection molds.

Main Steel Selection (By Application Scenario)

General Economic Type

P20 (3Cr2Mo) is the most widely used pre-hardened steel at HRC 28–32. It requires no further heat treatment, machines easily, and costs moderately, making it ideal for molds under 500,000 cycles. 718H is an upgraded version with higher purity and hardness uniformity at HRC 32–36, suitable for medium-to-large molds with 500,000 to 1,000,000 cycles. NAK80 is a pre-hardened mirror steel at HRC 38–42 with excellent polishability for high-gloss EVA products.

High-Performance Long-Life Type

S136 (4Cr13) is stainless steel with high corrosion resistance and superior polishability. After quenching, it reaches HRC 48–52 and is widely used for food-grade, medical-grade, and humid-environment EVA molds. H13 (SKD61) is hot-work steel with outstanding thermal fatigue resistance and wear resistance, ideal for EVA foam molding and high-wear applications.

Simple and Low-Volume Molds

45# carbon steel is low-cost and easy to machine, suitable for test molds and small-batch production. Aluminum alloy 6061/7075 offers excellent thermal conductivity and fast machining, often used for rapid prototyping, but has low wear resistance and is not suitable for mass production.

Key Selection Principles

Choose steel based on production volume: P20 for small batches, 718H/NAK80 for medium batches, and S136/H13 for high-volume molds. Choose based on surface requirements: standard appearance uses P20/718H; high-gloss uses NAK80/S136. Choose based on working conditions: H13 for foaming and abrasive materials; S136 for corrosive and humid environments. Mold bases typically use S50C, while cavities and cores use selected mold steels.

Recommended Combinations

For general EVA products, P20 or 718H provides the best cost performance. For high-gloss and clean products, NAK80 or S136 ensures excellent surface quality. For foamed or filled EVA, H13 improves durability. For rapid development, aluminum molds shorten lead time and reduce cost.

Summary

The selection of EVA injection mold steel should match production volume, appearance requirements, and service environment. Conventional molds benefit most from P20 and 718H. High-gloss and clean applications require NAK80 or S136. High-volume and foam molds rely on H13 for long life. Low-cost options such as 45# steel and aluminum are suitable for trial and small-batch production. Proper steel selection balances mold life, processing cost, and product quality to support stable and efficient EVA molding.