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A Concise Guide to Common Injection Mould Steels

2026-01-05 15:07:29 Injection Mould
Injection mould steel is core to mould lifespan, product quality and production efficiency. Its selection directly impacts benefits and competitiveness. Varying in hardness, wear resistance, polishability and corrosion resistance, it must match product material (e.g., ABS, PP, PVC, PC), production volume, appearance requirements and moulding process. This guide outlines common types, key characteristics, industry-recognized parameters, applications, selection methods and usage notes.

1. Classification & Core Characteristics

Common injection mould steels fall into four categories, each with clear industry standards:

1.1 Pre-Hardened Mould Steel (Standard Moulds, Easy Machining)

Pre-hardened before delivery, no post-heat treatment needed, ideal for small-to-medium batches:

  • P20: HRC 28-32, good machinability. For common plastics (ABS, PP), ≤500,000 shots (appliance casings, electronics).

  • 718 (Modified P20): HRC 30-35, better polishability (Ra≤0.4μm). For precision moulds, ≤800,000 shots (high-end appliance panels).

  • 718H: HRC 33-38, stable performance. For high-precision complex moulds, ≤1,000,000 shots (automotive interior parts).

injection mould

1.2 Mirror-Finish Mould Steel (High-Gloss/Transparent Products)

  • NAK80: HRC 38-42, mirror polish (Ra≤0.01μm), no heat treatment. For transparent plastics (PC, PMMA), ≤800,000 shots (phone casings, lenses).

  • S136H: HRC 30-35, corrosion-resistant, mirror polish (Ra≤0.02μm). For mild corrosive/high-gloss plastics, ≤1,000,000 shots.

1.3 Wear-Resistant Mould Steel (High-Volume/Wear-Resistant Plastics)

  • H13: HRC 52-56 after heat treatment, wear/heat-resistant. For high-volume (≥1,000,000 shots) & glass fiber-reinforced plastics (automotive parts).

  • SKD61 (Equiv. H13): HRC 50-54, balanced performance. For high-temperature plastics (PPS, LCP), ≥1,200,000 shots.

1.4 Corrosion-Resistant Mould Steel (Corrosive Plastics)

  • S136: HRC 48-52 after heat treatment, acid/alkali-resistant. For PVC, POM, ≤1,000,000 shots (pipe fittings).

  • 420SS: HRC 50-55, stainless steel, low cost. For low-volume corrosive/food-contact plastics, ≤500,000 shots.

2. Selection Guide

  • By Material: P20/718 (common); NAK80/S136H (transparent); S136/2083 (corrosive); H13/SKD61 (wear-resistant filled).

  • By Volume: P20/420SS (small, ≤500k); 718/NAK80 (medium, 500k-1M); H13/SKD61 (large, ≥1M).

  • By Appearance/Precision: P20 (general); 718H (high precision); NAK80/S136H (mirror).

  • By Budget: P20 (economic); 718 (cost-effective); NAK80 (high-end); H13 (high-volume).

injection mould

3. Usage Notes

  • Machining: Pre-hardened steels (P20,718,NAK80) machined directly; H13/S136 follow heat treatment (H13: quenching 1020-1050°C, tempering 580-620°C).

  • Polishing: Mirror steels use fine paste, coarse-to-fine process; clean debris timely.

  • Maintenance: Clean corrosive moulds (S136,2083) post-use, apply anti-rust oil; inspect high-volume moulds (H13,SKD61) for wear.

  • Verification: Request material certificates and hardness reports when purchasing.

4. Conclusion

Select injection mould steel to match product features, volume and precision, balancing performance and cost. Master core parameters and application scenarios, follow selection and maintenance norms to extend mould life and ensure stable quality. Refine selection based on mould complexity and process parameters; consult experts if needed.

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