AISI 8620 Alloy Steel is a low-carbon nickel–chromium–molybdenum (Ni–Cr–Mo) alloy steel specifically engineered for case-hardening applications. It develops a very hard, wear-resistant surface through carburizing or carbonitriding while maintaining a tough, shock-resistant core.
This combination makes 8620 one of the most widely used steels for gears, shafts, cam components, and heavy-duty automotive and industrial parts where surface durability and internal toughness are equally critical.
Chemical Composition
| Element | Content (%) | Role in Performance |
|---|---|---|
| Carbon (C) | 0.18 – 0.23 | Enables carburizing |
| Nickel (Ni) | 0.40 – 0.70 | Improves toughness & fatigue strength |
| Chromium (Cr) | 0.40 – 0.60 | Increases hardenability & wear resistance |
| Molybdenum (Mo) | 0.15 – 0.25 | Improves fatigue & high-stress performance |
| Manganese (Mn) | 0.70 – 0.90 | Strength & deoxidation |
| Silicon (Si) | 0.15 – 0.35 | Ferrite strengthening |
| Phosphorus (P) | ≤ 0.035 | Controlled impurity |
| Sulfur (S) | ≤ 0.040 | Controlled impurity |
| Iron (Fe) | Balance | Base metal |
Microstructure & Metallurgy
• Annealed condition: Ferrite–pearlite structure (excellent machinability)
• Carburized surface: High-carbon martensite with carbides
• Core structure: Low-carbon tempered martensite or bainite
• Nickel enhances core toughness and crack resistance
• Chromium and molybdenum improve case depth and wear resistance
Mechanical Properties
Core Properties (After Carburizing + Quenching + Tempering)
| Property | Typical Value |
|---|---|
| Tensile Strength | 850 – 1,050 MPa |
| Yield Strength | 650 – 850 MPa |
| Elongation | 15 – 25% |
| Core Hardness | 28 – 35 HRC |
| Impact Toughness | Excellent |
Surface Properties (Case-Hardened)
| Property | Typical Value |
|---|---|
| Surface Hardness | 58 – 62 HRC |
| Case Depth | 0.5 – 2.0 mm (controlled) |
| Wear Resistance | Very High |
Heat Treatment Capabilities
• Annealing – Improves machinability and ductility
• Normalizing – Grain refinement and uniform properties
• Carburizing – Hard, wear-resistant surface layer
• Carbonitriding – Enhanced fatigue and surface hardness
• Quenching & tempering – Strength–toughness balance
• Stress relieving – Dimensional stability after machining
Machinability & Weldability
✔ Very good machinability in annealed condition
✔ Good weldability with preheating and post-weld stress relief
⚠ Welding after case hardening is not recommended
Available Forms
✔ Bars (round, square, flat, hex)
✔ Plates & sheets
✔ Forgings (shafts, gears, rings)
✔ Tubes & pipes
✔ Billets & blooms
✔ Precision-machined components
Standards & Equivalent Grades
| Standard | Equivalent |
|---|---|
| AISI / SAE | 8620 |
| ASTM | A29, A322 |
| EN | 20NiCrMo2-2 |
| DIN | 1.6523 |
| BS | 805M20 |
| JIS | SNCM220 |
Applications
Automotive: Transmission gears, axles, pinions, camshafts
Industrial Machinery: Gearboxes, couplings, bearings
Oil & Gas / Mining: Heavy-duty shafts, drilling components
Construction Equipment: Drive systems, load-bearing gears
Why Choose AISI 8620 Alloy Steel
AISI 8620 is the industry benchmark for case-hardened components requiring high surface wear resistance, excellent fatigue life, and a tough internal core. Its Ni–Cr–Mo alloy system ensures long service life and dependable performance in demanding automotive, industrial, and heavy-engineering applications.