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2026年1月23日
6 Most Common Injection Mold Steels: A Comprehensive Selection Guide
When developing an injection mold, selecting the right steel is a critical decision that balances tool life, production cost, and part quality . Different plastic resins—especially those with corrosi
When developing an injection mold, selecting the right steel is a critical decision that balances tool life, production cost, and part quality. Different plastic resins—especially those with corrosive or abrasive properties—demand specific steel grades.
Choosing the right material ensures your mold withstands the rigors of mass production while staying within budget. Below is a detailed analysis of the 6 most widely used mold steels in the industry.
1. P20 Steel (Pre-hardened General Purpose Steel)
Domestic Grade: 3Cr2Mo
P20 is the "workhorse" of the industry, ideal for medium-to-low complexity molds and moderate production volumes.
- Core Characteristics:
- Pre-hardened: Delivered at 30-35 HRC, eliminating the need for secondary heat treatment and preventing dimensional deformation.
- Excellent Machinability: High CNC milling and EDM efficiency. Polishing can reach #2000-#4000 grit.
- Moderate Durability: Good toughness for impact resistance, though wear resistance is standard.
- Best For: General plastics like ABS, PP, PE, PS, and PC.
- Applications: Household goods (bottle caps, toys), automotive interiors, and appliance housings.
- Mold Life: Approx. 100,000 to 300,000 shots.
2. 718H Steel (Premium Pre-hardened Steel)
Domestic Grade: 3Cr2NiMo
718H is an upgraded version of P20. The addition of Nickel (Ni) ensures superior hardness uniformity and a finer internal structure.
- Core Characteristics:
- High Uniformity: Pre-hardened to 35-40 HRC, offering better resistance to deformation than P20.
- Superior Polishability: Can achieve a semi-mirror finish (#6000-#8000 grit).
- Enhanced Strength: Better fatigue resistance, making it suitable for large or multi-cavity molds.
- Best For: Reinforced plastics (PA+GF, PBT) and high-gloss products.
- Applications: Precision electronic connectors, automotive light housings, and high-gloss home appliance panels.
- Mold Life: Approx. 300,000 to 500,000 shots.
3. NAK80 Steel (High-Precision Mirror Steel)
NAK80 is a high-performance, pre-hardened steel specifically designed for high-gloss and optical-grade applications.
- Core Characteristics:
- Top-Tier Mirror Finish: Can be polished to #10000-#15000 grit ($Ra \le 0.01 \mu m$), perfect for optical clarity.
- No Heat Treatment Needed: Delivered at 40-42 HRC, ensuring excellent dimensional stability for intricate designs.
- Great EDM Surface: Leaves a uniform finish after electrical discharge machining.
- Best For: Transparent plastics like PMMA (Acrylic), Transparent PC, and COP.
- Applications: Camera lenses, light guides, cosmetic packaging, and premium automotive grilles.
- Mold Life: Up to 500,000 to 1,000,000 shots.
4. H13 Steel (Hot-Work Tool Steel)
Domestic Grade: 4Cr5MoSiV1
H13 is engineered for extreme environments involving high temperatures and rapid thermal cycling.
- Core Characteristics:
- Extreme Heat Resistance: Maintains structural integrity at 500-600°C. Excellent resistance to thermal cracking (heat checking).
- High Hardness: Post-heat treatment hardness reaches 48-52 HRC.
- Toughness: Exceptional impact resistance for high-stress mold structures.
- Best For: High-temperature engineering plastics (PEEK, PEI, PPS, LCP) and glass-fiber reinforced resins.
- Applications: Automotive engine covers, 5G antenna covers, medical surgical tools, and heavy-duty industrial parts.
- Mold Life: Over 1,000,000 shots.
5. S136 Steel (Corrosion-Resistant Stainless Steel)
Domestic Grade: 4Cr13
S136 is the premier choice for corrosive plastics and products requiring medical-grade cleanliness or high-gloss finishes.
- Core Characteristics:
- Superior Corrosion Resistance: High Chromium (13.6%) content protects against corrosive resins (PVC, flame retardants) and humid environments.
- Optical Polishability: Reaches #8000-#12000 grit, suitable for transparent parts.
- High Hardness: Heat-treated to 48-52 HRC for excellent wear resistance.
- Best For: Corrosive plastics (PVC, V0-rated ABS) and medical-grade materials.
- Applications: Medical syringes, food containers, optical lenses, and smartphone camera parts.
- Mold Life: 500,000 to 1,000,000+ shots.
6. 2344 Steel (Premium Hot-Work Alloy)
2344 is a high-grade Chrome-Moly-Vanadium alloy similar to H13 but often preferred for more demanding thermal cycle applications.
- Core Characteristics:
- Fatigue Resistance: Specifically optimized to prevent cracking in thin-walled or deep-cavity molds.
- High Thermal Conductivity: Helps in reducing cycle times during high-heat production.
- Hardness: Achieves 48-52 HRC with excellent toughness.
- Best For: High-temp plastics and abrasive glass-filled resins (PA66+GF).
- Applications: Large automotive parts (dashboards, bumpers), electronic housings, and high-volume thin-wall packaging.
- Mold Life: Designed for long-run production (1,000,000+ shots).
Summary: Which Steel Should You Choose?
Goal | Recommended Steel |
Low Cost / Low Volume | P20 |
Large Molds / Better Finish | 718H |
Mirror Finish / Optical Parts | NAK80 |
High Temp / High Wear (PEEK/GF) | H13 / 2344 |
Corrosive Plastics / Medical Grade | S136 |
Expert Tip: Selecting the right steel is just the first step. Proper mold maintenance and cooling channel design are equally vital to maximizing your ROI.
Mold Steel Cost-Effectiveness & ROI Analysis
Choosing a cheaper steel like P20 might save money upfront, but if your production volume is high, the maintenance and replacement costs will eventually exceed the price of a premium steel like H13 or S136.
Steel Type | Relative Cost | Hardness (HRC) | Primary Value Driver | Best Production Volume |
P20 | $ (Lowest) | 30-35 | Economy & Speed | 100k - 300k |
718H | $$ | 35-40 | Balance of finish & cost | 300k - 500k |
NAK80 | $$$ | 40-42 | Precision & Mirror Shine | 500k+ |
H13 | $$$ | 48-52 | Heat & Wear Resistance | 1M+ |
S136 | $$$$ | 48-52 | Corrosion & High Purity | 1M+ |
2344 | $$$$ (Highest) | 48-52 | High-Speed Thermal Cycles | 1M+ |
How to Choose Based on Your Project Scale
1. Low Volume / Prototyping (Up to 100k shots)
- Winner: P20
- Why: At this volume, the mold will likely become obsolete before the steel wears out. P20 is pre-hardened, meaning you skip the heat treatment phase, saving both money and time (typically 1-2 weeks off the lead time).
2. Mass Market Consumer Goods (300k - 500k shots)
- Winner: 718H
- Why: It offers a much better surface finish than P20 for a marginal price increase. If your product needs to look "premium" but isn't a high-end optical part, 718H is the sweet spot for ROI.
3. Optical & Luxury Goods
- Winner: NAK80
- Why: Even though S136 can reach a mirror finish, NAK80 is easier to machine and provides a more stable surface for intricate textures and high-transparency parts like LED lenses.
4. Engineering & Industrial Parts (High Heat/Glass Fiber)
- Winner: H13 / 2344
- Why: If you are using "tough" plastics like Nylon with Glass Fiber (PA+GF), standard steels will erode quickly. The high hardness of H13 after heat treatment ensures the "gates" and "parting lines" of your mold stay sharp for over a million cycles.
5. Medical & Food Grade (High Regulation)
- Winner: S136
- Why: This isn't just about mold life; it’s about cleanliness. S136 does not rust, meaning no rust particles contaminate your medical or food-grade parts. It also allows the mold to be stored in non-climate-controlled warehouses without degrading.
Pro-Tip: The "Hybrid" Approach
To optimize your budget, you don't have to make the entire mold out of expensive steel. Many professional toolmakers use:
- S136 or NAK80 for the Cavity/Core (the parts that touch the plastic).
- P20 or 45# Carbon Steel for the Mold Base (the structural frame).
This "Insert" strategy gives you the performance of high-end steel at a significantly lower total tool cost.
Need Expert Advice on Your Next Project?
Selecting the right mold steel is the foundation of a successful production run. At JST Mold, by we don't just build molds—we provide optimized manufacturing solutions tailored to your budget and volume requirements.
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Contact our engineering team today to ensure your project starts with the right foundation. Contact us : info@jstmold.com