Last updated: 2026-09-05 · 5 min read

Mold Surface Treatment — How Do Nitriding, PVD Coating and Chrome Plating Compare for Wear Resistance, Cost and Lead Time?

Nitriding: 5–30 μm diffusion layer at 500–580°C, $200–600 per mold set, 8–12 hours. PVD (TiN/TiAlN/CrN): 2–5 μm hard layer at 200–500°C, $400–1,200, 4–8 hours. Chrome plating: 5–50 μm deposit, $300–800, 6–10 hours. Each process targets a different wear mechanism — nitriding for general abrasion on P20/H13, PVD for glass-filled and high-temp resins, chrome for corrosion from PVC or halogenated flame-retardant programs.

Key Facts

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  • Nitriding forms iron nitrides (Fe₂N, Fe₃N) in a compound layer at 60–65 HRC, with a diffusion zone extending 0.1–0.5mm below. Gas nitriding causes +0.005–0.02mm growth; plasma nitriding is near-zero. Both suit P20 and H13 cores running unfilled resins above 100K shots.
  • PVD coatings 2,000–3,300 HV (vs. 800–1,000 HV for nitrided case). TiN for general use up to 600°C, TiAlN for high-temp resins (PPS, PEEK) up to 800°C, CrN for corrosive environments. Coating adds 2–5 μm uniformly to all surfaces.
  • Chrome plating (65–70 HRC) is the only treatment combining wear and corrosion resistance. Specified for PVC (releases HCl), halogenated FR resins, and medical disposables. Environmental cost: hexavalent chromium bath requires wastewater treatment.

    • Shrinkage — The dimensional reduction from mold cavity to cooled part. Amorphous resins: 0.4–0.7% (uniform). Semi-crystalline: 1.0–2.5% (directional). Mold makers apply shrinkage factor when machining cavity. Actual shrinkage varies with wall thickness, gate location and packing pressure. The related guide covers adjacent topics.

    How Do the Five Key Parameters Compare Across All Three Processes?

    Parameter Gas Nitriding PVD TiN PVD TiAlN Hard Chrome
    Surface hardness 60–65 HRC 2,000–2,200 HV 3,000–3,300 HV 65–70 HRC
    Process temperature 500–580°C 200–450°C 300–500°C 40–60°C (bath)
    Layer thickness 5–30 μm compound + 100–500 μm diffusion 2–5 μm 2–4 μm 5–50 μm
    Dimensional change +0.005–0.02mm Near-zero Near-zero +0.005–0.05mm
    Cost per mold set $200–600 $400–800 $600–1,200 $300–800

    PVD TiAlN is the hardest option at 3,300 HV and handles service temperatures up to 800°C — the right choice for PPS and PEEK molding with glass-filled grades. Gas nitriding is the most economical at $200–600 but causes slight dimensional growth that can push tight tolerances (below ±0.02mm) out of range. Chrome plating operates at near-ambient bath temperature, so there is no thermal distortion risk for complex inserts.

    Which Resin and Volume Combinations Require Each Treatment?

    1. Unfilled PP, PE, ABS, PC below 200K shots. No surface treatment needed. Base steel (P20 at 28–40 HRC) outlasts the program without measurable wear.
    2. Unfilled engineering resins above 200K shots. Gas nitriding at $300–500 extends wear life 2–3×. Cost per additional shot: $0.001–0.003.
      The default choice for ABS and PC programs above 200K.
    3. Glass-filled resins (GF15–GF50) above 100K shots. PVD TiN or TiAlN at $500–1,000 extends wear life 5–10× vs. untreated steel. GF30 PA66 at 500K shots without PVD guarantees mid-program refurbishment costing 3–5× the PVD price.
    4. Corrosive resins (PVC, halogenated FR) at any volume. Chrome plating at $400–800 prevents HCl-induced pitting on cavity steel.
      No other treatment addresses both wear and corrosion simultaneously.
    5. Above 1M shots with abrasive fill. PVD TiAlN on H13 hardened to 48–52 HRC, with re-coat at 500K shots. Total surface cost: $1,000–2,000 over the mold’s life.
      Total additional shots gained: 500K–1M.

    Gate vestige — The visible mark left on the part surface where the gate was trimmed. Edge gate: 0.5–2.0mm vestige. Pin-point gate: 0.2–0.5mm. Valve gate: 0.05–0.1mm (flush). Vestige size affects cosmetic appearance and may require secondary trimming. The related guide covers adjacent topics.

    Nitriding: $200–600, 8–12h, 60–65 HRC — unfilled resins above 200K. PVD TiN: $400–800, 4–8h, 2,200 HV — glass-filled above 100K. PVD TiAlN: $600–1,200, 4–8h, 3,300 HV — high-temp and GF30+ resins. Chrome: $300–800, 6–10h, 65–70 HRC — PVC and halogenated FR. Match the treatment to the resin, not the other way around.

  • Key parameter identified — critical variable confirmed against spec.
  • Tolerance within achievable range — commercial ±0.15mm or tighter as needed.
  • Material matched to application — resin grade selected for end-use environment.
  • Process window validated at T1 — parameters locked after first trial.
  • Inspection method defined — CMM, visual, or functional test specified.

    • Frequently Asked Questions

    Can you stack nitriding and PVD on the same mold insert?

    Yes — this is common for high-wear programs above 500K shots with glass-filled resins. The nitrided diffusion zone (60–65 HRC) supports the PVD coating and prevents it from collapsing under high contact pressure. The PVD on top provides low friction and abrasion resistance.

    Combined cost: $700–1,500 per set. The sequence is: heat treat to core hardness, nitride, then PVD coat as the final step. Do not reverse the order.

    Does surface treatment change the mold’s dimensional accuracy?

    Gas nitriding adds +0.005–0.02mm of growth — significant for tolerances below ±0.02mm. Plasma nitriding and PVD are near-zero. Chrome plating adds +0.005–0.05mm, which must be compensated in the final grinding pass.

    If the part has critical dimensions below ±0.01mm, specify plasma nitriding or PVD and flag those dimensions on the drawing so the treatment house can mask or compensate.

    Can surface treatment be reapplied after production starts?

    PVD coatings can be stripped and re-coated without affecting the base steel. Nitriding is permanent — the diffusion layer cannot be removed or reapplied. If a nitrided surface wears through, the insert must be re-cut and re-nitrided.

    Chrome plating can be stripped and re-plated 2–3 times before the insert loses too much material. Each stripping cycle removes a small amount of base steel, so track the number of re-plates per insert.

    Key Takeaways

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  • Nitriding: $200–600, 60–65 HRC — unfilled engineering resins above 200K shots.
  • PVD TiN/TiAlN: $400–1,200, up to 3,300 HV — glass-filled and high-temp resins above 100K.
  • Chrome: $300–800, 65–70 HRC — PVC and halogenated FR, the only wear+corrosion option.
  • Nitriding+PVD stacking at $700–1,500 for 500K+ shots with abrasive fill.

    • Surface treatment is one of the few modifications that can be applied after the mold is in production — if wear accelerates at 300K shots, a PVD coating can still be added without rebuilding the insert.
    But cost per shot is always lower when the treatment is specified before the first shot. Include it in the DFM review alongside steel grade and heat treatment.

    Sources: ASM Handbook Vol. 4F — Heat Treating of Steels · Oerlikon Balzers — PVD Coating Technical Guides · Society of Plastics Engineers (SPE) — Mold Wear and Surface Treatment Papers · Ionix — Plasma Nitriding Process Data Sheets · ASTM International — Surface Hardness and Wear Test Standards

    — Arthur, Tooling Engineer at aCatMould