AISI 8620 Case-Hardening Alloy Steel: Carburizing Grade for Gears, Pins & Automotive Components
ASTM A304 / ASTM A322 / SAE J404 · Published: 2026-05-31 · Updated: 2026-05-31
AISI 8620 is the most widely used low-carbon nickel-chromium-molybdenum case-hardening (carburizing) alloy steel. Its low carbon content (0.18-0.23%) provides a tough, ductile core that resists fatigue crack initiation while the carburized case...
AISI 8620 is the most widely used low-carbon nickel-chromium-molybdenum case-hardening (carburizing) alloy steel. Its low carbon content (0.18-0.23%) provides a tough, ductile core that resists fatigue crack initiation while the carburized case (0.8-1.2% carbon after carburizing, 58-62 HRC after quench and temper) provides a hard, wear-resistant surface. This core-toughness + case-hardness combination is essential for gears, camshafts, piston pins, roller bearings, and automotive transmission components that experience high contact stress (Hertzian) at the surface combined with bending and torsional fatigue through the cross-section. The nickel addition (0.40-0.70%) improves core toughness and hardenability compared to plain carbon carburizing grades (1018, 1020).
Quick Facts
| Category | Alloy Steel |
| Standard | ASTM A304 / ASTM A322 / SAE J404 |
| Density | 7.85 g/cm³ |
| Yield Strength | Core: 385 MPa (56 ksi) after carburize + harden + temper |
| Tensile Strength | Core: 635 MPa (92 ksi) after carburize + harden + temper; Case: 58-62 HRC (carburized) |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| EN 20NiCrMo2-2 | Compare |
| DIN 1.6523 | Compare |
| JIS SNCM220 | Compare |
| GB 20CrNiMo | Compare |
| BS 805M20 | Compare |
Related Materials
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Frequently Asked Questions
How does 8620 compare to 9310 for aerospace gearing?
8620 is the automotive/industrial gear standard; 9310 (3.0-3.5% Ni) is the aerospace gear standard. 9310 provides: (1) higher core hardenability for larger section sizes (Jominy hardenability at J10 approximately 38 HRC for 9310 vs 28 HRC for 8620); (2) superior core fracture toughness at equal case depth — critical for helicopter transmission gears where failure is catastrophic and non-redundant; (3) better fatigue resistance in the 10⁷-10⁹ cycle regime (very-high-cycle fatigue — relevant to helicopter main rotor transmissions). 8620 is approximately one-third the cost of 9310 and is the appropriate choice for automotive, industrial gearboxes, and non-aerospace applications where 9310's extreme performance is not required. For commercial aircraft landing gear actuation gears, 8620 is acceptable; for helicopter main transmission planetary gears, 9310 or premium aircraft-quality 8620 (AMS 6277, VAR remelted) is specified.
References & International Standards
- ASTM International. Standard Specifications for Steel & Metal Alloys. astm.org
- International Organization for Standardization (ISO). Metallic Materials — Cross-Reference Database. iso.org
- American Iron and Steel Institute (AISI). Steel Grade Designations & Equivalents. steel.org
- European Committee for Standardization (CEN). EN Steel Standards & Numbering System. cencenelec.eu