Views: 0 Author: Site Editor Publish Time: 2026-04-17 Origin: Site
If you’re in the injection molding industry, you know one truth well: the quality of your mold steel directly determines the lifespan of your mold, the precision of your products, and even your production efficiency. Choosing the wrong steel can lead to frequent mold repairs, poor product appearance, and unnecessary cost overruns.
Today, I’m breaking down the most commonly used injection mold steels, their suitable plastic materials, core characteristics, and the reasons behind their compatibility. No overly complex jargon—just practical, factory-tested advice to help you make the right choice.
Suitable Plastics: PMMA (Acrylic), PC transparent parts, optical components, PVC, flame-retardant nylon, medical-grade plastics, and molds used in humid environments.
Why It’s Suitable: This steel contains a high chromium content, which gives it excellent rust and corrosion resistance. Plastics like PVC and flame-retardant materials decompose into corrosive gases during molding—ordinary steel will rust and develop pitting quickly, but S136 can withstand this. Additionally, it offers top-tier mirror polishing, ensuring transparent products have no fogging or watermarks.
Key Features: High mirror finish, strong corrosion resistance, excellent polishability. After quenching, its hardness reaches HRC 48–52, leading to a long mold life. The only downside is its higher price and slightly higher processing difficulty.
Suitable Plastics: ABS, PC, high-gloss casings, cosmetic boxes, home appliance shells, and general transparent parts (non-optical grade).
Why It’s Suitable: NAK80 comes pre-hardened (HRC 38–42) from the factory—no additional quenching is needed, so you can process it directly and put it into use, saving time and cost. It polishes extremely well, achieving a high-gloss mirror effect without material lines. It also performs well in electrical discharge machining (EDM), producing beautiful textures.
Key Features: Easy to polish and process, no deformation. It has moderate rust resistance but cannot be used with PVC or flame-retardant materials. Perfect for appearance parts and high-demand casings.
Suitable Plastics: ABS, PP, PE, PS, PC, and ordinary nylon (without glass fiber).
Why It’s Suitable: Compared to P20 steel, 718H/2738 has higher purity and more uniform hardness. It won’t deform even for large or long molds, making it ideal for auto interiors and home appliance panels that require stability and consistency.
Key Features: Strong comprehensive performance and high cost-effectiveness. It polishes well and can be textured. However, it is not corrosion-resistant and not suitable for glass fiber-reinforced plastics.
Suitable Plastics: PP, PE, ABS, PS, ordinary toys, home appliance internal parts, and low-grade casings.
Why It’s Suitable: P20 is affordable, easy to cut, and has a fast delivery time. It’s the most commonly used steel for products with low to medium production volumes and general appearance requirements—perfect for small-batch production or daily-use items.
Key Features: Pre-hardened for direct use without heat treatment. Its polishing performance is average, and it has poor rust resistance. It has a moderate service life (within 300,000 mold cycles).
Suitable Plastics: PA+GF (glass fiber-reinforced nylon), PBT+GF, PPS, PEEK, LCP, and other high-temperature engineering plastics.
Why It’s Suitable: Glass fiber-reinforced plastics are extremely abrasive—ordinary steel will wear down, tilt, or deform quickly. H13/SKD61 has high high-temperature strength, excellent thermal fatigue resistance, and strong wear resistance, making it able to withstand the harsh conditions of molding high-temperature and abrasive plastics.
Key Features: High wear resistance, high toughness, and heat crack resistance. It must be quenched (HRC 48–52) before use. It has no rust resistance and is not suitable for PVC.
Suitable Plastics: PVC, POM, molds used in humid environments, food packaging, and ordinary transparent parts.
Why It’s Suitable: It has good corrosion and rust resistance—slightly lower than S136, but much more affordable. It’s a cost-effective choice for corrosion-resistant molds that don’t require a top-tier mirror finish.
Key Features: Rust-proof and polishable, with higher cost-effectiveness than S136.
Suitable Plastics: PP, PE, one-time molds, test molds, simple structural parts, and low-volume internal parts.
Why It’s Suitable: It’s extremely cheap and very fast to process. It’s only suitable for molds with the lowest requirements, such as test molds or small-batch internal parts that don’t need good appearance or long life.
Key Features: Not wear-resistant, not rust-proof, and easy to deform. Short service life, not suitable for appearance parts.
Transparent/optical/PVC products → Choose S136
High-gloss appearance, no quenching needed → Choose NAK80
Ordinary appearance, medium to large batch production → Choose 718H
Affordable, internal parts, small batches → Choose P20
Glass fiber-reinforced, high-temperature engineering plastics → Choose H13
Choosing the right injection mold steel doesn’t have to be complicated. The key is to match the steel’s characteristics with your plastic material, production volume, and product appearance requirements. If you’re still unsure which steel to use, feel free to leave a comment with your product details—I’ll help you find the perfect match!
Thanks for reading, and happy molding!
