Material Selection for Large-Diameter Core Pins
Key Takeaway: For large-diameter pins ø20+ mm, toughness trumps hardness. Switch from SKH51 to SKD61 to avoid thermal fatigue cracking. For corrosive resins at large diameters, use STAVAX ESR. See the full material guide for all steel comparisons.
Material Selection by Diameter
| Pin Diameter | Recommended Material | Hardness | Rationale |
|---|---|---|---|
| ø3–12 mm | SKH51 (M2) | HRC 60–62 | Standard — max wear resistance, adequate toughness |
| ø12–20 mm | SKH51 or SKD61 | HRC 60–62 or 48–52 | Application-dependent — wear vs toughness priority |
| ø20–30 mm | SKD61 (H13) | HRC 48–52 | Toughness priority — resist thermal fatigue |
| > ø30 mm | SKD61 or pre-hardened | HRC 48–52 or 38–42 | Thermal gradient management critical |
Thermal Fatigue in Large Cross-Sections
During each injection cycle, the pin surface heats rapidly (contact with molten resin at 200–350°C) while the core remains cooler. This temperature difference creates cyclic thermal stress. In SKH51 (high hardness, moderate toughness), this stress can initiate heat-check cracks — a network of fine surface cracks that eventually propagate to fracture.
SKD61's superior toughness and thermal conductivity dissipate thermal stress more effectively, making it the preferred material for large cross-sections that experience significant thermal gradients.
Decision Framework
- Wear is primary concern (abrasive resin, ø ≤ 20 mm) → SKH51
- Breakage/cracking is primary concern (large ø, thermal cycling) → SKD61
- Corrosion is primary concern (PVC, POM, any ø) → STAVAX ESR
- Combined large ø + abrasive resin → SKD61 base + TiCN coating for surface hardness
Frequently Asked Questions
SKH51 or SKD61 for large core pins?+
ø12–20 mm: either based on application. ø20+ mm: SKD61 preferred — its toughness prevents thermal fatigue cracking in larger cross-sections.
Why does pin diameter affect material choice?+
Larger cross-sections have greater thermal gradients during heat treatment and service. SKH51 can develop micro-cracks; SKD61 tolerates thermal stress better.
STAVAX ESR for large-diameter pins?+
Suitable when corrosion resistance is needed. Otherwise SKD61 provides better toughness at the same hardness level for non-corrosive applications.
Related
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✓ SKH51, SKD61, STAVAX in stock✓ Sizes up to ø50 mm✓ MOQ 1 piece