Overview
SAE/AISI 8620 Steel is a low-carbon nickel-chromium-molybdenum alloy steel specifically developed for carburizing and case hardening applications. It combines a hard, wear-resistant surface with a tough, ductile core, making it one of the most widely used steels for gears, shafts, pinions, and drivetrain components.
Compared with SAE 4140 and SAE 4340, SAE 8620 offers lower core strength but significantly better performance in case-hardened applications due to its excellent carburizing characteristics.
SAE 8620 is widely used in:
- Automotive Gears
- Transmission Components
- Pinions
- Camshafts
- Crankshafts
- Bearings
- Industrial Machinery
- Aerospace Components
Because of its outstanding case-hardening capability and dimensional stability, 8620 is one of the most popular gear steels worldwide.
Material Specification
| Property | Value |
|---|---|
| Material Designation | SAE/AISI 8620 |
| Standard | ASTM A29 / SAE J404 |
| UNS Number | G86200 |
| Material Family | Nickel-Chromium-Molybdenum Alloy Steel |
| Density | 7.85 g/cm³ |
| Magnetic Property | Magnetic |
| Standard Forms | Bar, Plate, Forgings, Tube, Gear Stock |
Chemical Composition
| Element | Content (%) |
|---|---|
| Iron (Fe) | Balance |
| Carbon (C) | 0.18–0.23 |
| Nickel (Ni) | 0.40–0.70 |
| Chromium (Cr) | 0.40–0.60 |
| Molybdenum (Mo) | 0.15–0.25 |
| Manganese (Mn) | 0.70–0.90 |
| Silicon (Si) | 0.15–0.35 |
| Phosphorus (P) | ≤0.035 |
| Sulfur (S) | ≤0.040 |
The alloy combination provides excellent hardenability, toughness, and carburizing response.
Mechanical Properties
Annealed Condition
| Property | Value |
|---|---|
| Tensile Strength | 530–680 MPa |
| Yield Strength | 350–480 MPa |
| Elongation | 20–30% |
| Hardness | 140–200 HB |
| Elastic Modulus | 205 GPa |
Quenched & Tempered Condition
| Property | Value |
|---|---|
| Tensile Strength | 700–1000 MPa |
| Yield Strength | 550–850 MPa |
| Elongation | 12–20% |
| Hardness | 22–35 HRC |
Carburized Condition
| Property | Value |
|---|---|
| Surface Hardness | 58–64 HRC |
| Core Hardness | 25–40 HRC |
| Wear Resistance | Outstanding |
| Impact Toughness | Excellent |
Physical Properties
| Property | Value |
|---|---|
| Density | 7.85 g/cm³ |
| Melting Point | 1425–1540°C |
| Thermal Conductivity | 43 W/m·K |
| Electrical Resistivity | 0.22 μΩ·m |
| Thermal Expansion Coefficient | 11.8 × 10⁻⁶/K |
| Specific Heat Capacity | 475 J/kg·K |
Corrosion Resistance
| Environment | Performance |
|---|---|
| Indoor Environment | Good |
| Dry Atmosphere | Good |
| Outdoor Environment | Moderate |
| Humid Environment | Moderate |
| Marine Environment | Poor |
| Chemical Environment | Poor |
SAE 8620 is not corrosion resistant and generally requires surface protection.
Recommended surface treatments:
- Carburizing
- Black Oxide
- Zinc Plating
- Electroless Nickel Plating
- Hard Chrome Plating
- Phosphate Coating
- QPQ Treatment
Weldability
| Welding Process | Rating |
|---|---|
| TIG Welding | Good |
| MIG Welding | Good |
| Arc Welding | Good |
| Resistance Welding | Good |
| Spot Welding | Good |
Because of its low carbon content, SAE 8620 offers better weldability than many alloy steels.
For critical applications:
- Preheating Recommended
- Stress Relief Recommended
Machinability
| Process | Rating |
|---|---|
| CNC Turning | Excellent |
| CNC Milling | Excellent |
| Drilling | Excellent |
| Grinding | Excellent |
| Threading | Good |
| Broaching | Excellent |
Machinability Comparison
| Material | Machinability |
|---|---|
| 1018 | Excellent |
| 8620 | Excellent |
| 4140 | Good |
| 4340 | Good |
| 9310 | Good |
8620 is commonly machined before carburizing and final grinding.
Heat Treatment
Annealing
| Parameter | Value |
|---|---|
| Temperature | 815–870°C |
| Cooling Method | Furnace Cool |
Normalizing
| Parameter | Value |
|---|---|
| Temperature | 870–925°C |
| Cooling Method | Air Cool |
Carburizing
| Parameter | Value |
|---|---|
| Temperature | 900–950°C |
| Case Depth | 0.5–2.5 mm |
| Surface Hardness | 58–64 HRC |
Quenching
| Parameter | Value |
|---|---|
| Temperature | 815–845°C |
| Cooling Medium | Oil |
Tempering
| Parameter | Value |
|---|---|
| Temperature | 150–650°C |
| Purpose | Toughness Adjustment |
Carbonitriding
| Property | Value |
|---|---|
| Surface Hardness | 58–65 HRC |
| Wear Resistance | Excellent |
International Equivalent Grades
| Standard | Equivalent Grade |
|---|---|
| SAE/AISI (USA) | 8620 |
| ASTM (USA) | ASTM A29 Grade 8620 |
| UNS | G86200 |
| GB/T (China) | 20CrNiMo |
| EN (Europe) | 21NiCrMo2 |
| DIN (Germany) | 1.6523 |
| JIS (Japan) | SNCM220 |
| ISO | 21NiCrMo2 |
Available Forms
| Product Type | Availability |
|---|---|
| Round Bar | Yes |
| Flat Bar | Yes |
| Alloy Plate | Yes |
| Forgings | Yes |
| Gear Blanks | Yes |
| Mechanical Tube | Yes |
| Ground Bar | Yes |
| Precision Shaft Stock | Yes |
Typical Applications
Gear Manufacturing
- Spur Gears
- Helical Gears
- Planetary Gears
- Gear Shafts
Automotive Industry
- Transmission Gears
- Differential Components
- Pinions
- Drive Components
Aerospace Industry
- Landing Gear Parts
- Gear Systems
- Structural Components
Industrial Machinery
- Couplings
- Spline Shafts
- Drive Components
- Mechanical Assemblies
Bearing Industry
- Bearing Races
- Bearing Components
- Wear Parts
Agricultural Equipment
- Gear Systems
- PTO Components
- Transmission Parts
Manufacturing Characteristics
| Manufacturing Process | Rating |
|---|---|
| CNC Turning | Outstanding |
| CNC Milling | Outstanding |
| Gear Hobbing | Outstanding |
| Carburizing | Outstanding |
| Carbonitriding | Outstanding |
| Precision Grinding | Excellent |
| Forging | Excellent |
| QPQ Treatment | Excellent |
Advantages
Excellent Carburizing Performance
One of the best steels for case hardening.
Tough Core Structure
Maintains impact resistance after carburizing.
Outstanding Wear Resistance
Excellent for gears and transmission components.
Good Machinability
Easy to machine before heat treatment.
Excellent Fatigue Resistance
Ideal for cyclic loading applications.
Cost Effective
More economical than aerospace-grade alloy steels.
Limitations
Lower Core Strength Than 4140 or 4340
Designed primarily for case-hardening applications.
Limited Corrosion Resistance
Requires protective coatings.
Heat Treatment Required
Maximum performance depends on carburizing.
Not Ideal for Through-Hardening Applications
Better suited to surface-hardened components.
Comparison with Other Alloy Steels
| Property | 8620 | 9310 | 4140 | 4340 | 20CrNiMo |
|---|---|---|---|---|---|
| Carbon Content | Low | Low | Medium | Medium | Low |
| Carburizing Ability | Outstanding | Exceptional | Moderate | Moderate | Outstanding |
| Core Toughness | Excellent | Outstanding | Excellent | Outstanding | Excellent |
| Gear Applications | Excellent | Exceptional | Good | Good | Excellent |
| Cost | Moderate | High | Moderate | High | Moderate |
Comparison with Engineering Materials
| Material | Yield Strength | Surface Hardness | Wear Resistance |
|---|---|---|---|
| SAE 8620 | 550–850 MPa | 58–64 HRC | Outstanding |
| SAE 9310 | 700–1100 MPa | 60–65 HRC | Exceptional |
| SAE 4140 | 655–1200 MPa | 58 HRC | Excellent |
| SAE 4340 | 740–1600 MPa | 60 HRC | Outstanding |
| 17-4PH Stainless | 860–1170 MPa | 44 HRC | Good |
| 20CrNiMo | 550–850 MPa | 58–64 HRC | Outstanding |
Available Surface Finishes
Raw Finishes
- Annealed Finish
- Normalized Finish
- Machined Finish
- Ground Finish
Protective Finishes
- Carburized Finish
- Carbonitrided Finish
- Black Oxide
- Zinc Plating
- Electroless Nickel Plating
- QPQ Treatment
Decorative Finishes
- Powder Coating
- Spray Painting
- Electrophoretic Coating (E-Coating)
Frequently Asked Questions (FAQ)
What is SAE 8620 steel?
SAE 8620 is a nickel-chromium-molybdenum alloy steel specifically designed for carburizing and case-hardening applications.
What is SAE 8620 used for?
Typical applications include:
- Gears
- Pinions
- Transmission Components
- Bearing Parts
- Aerospace Components
- Industrial Machinery
What is the difference between SAE 8620 and SAE 4140?
| Property | SAE 8620 | SAE 4140 |
|---|---|---|
| Carbon Content | Lower | Higher |
| Carburizing Ability | Better | Moderate |
| Core Strength | Lower | Higher |
| Gear Applications | Better | Good |
What is the difference between SAE 8620 and 20CrNiMo?
SAE 8620 and Chinese 20CrNiMo are generally considered equivalent grades and are interchangeable in most engineering applications.
Is SAE 8620 suitable for gears?
Yes. SAE 8620 is one of the most commonly used gear steels in the automotive and industrial sectors.
Can SAE 8620 be carburized?
Yes. It is specifically designed for carburizing and case hardening.
What hardness can SAE 8620 achieve?
- Carburized Surface: 58–64 HRC
- Carbonitrided Surface: 58–65 HRC
Why is SAE 8620 widely used in transmission systems?
Because it combines:
- Hard Wear-Resistant Surface
- Tough Core
- Excellent Fatigue Resistance
- Good Machinability
- Cost Efficiency
making it ideal for gears and drivetrain components.
Can SAE 8620 be welded?
Yes. Due to its low carbon content, it offers good weldability compared with many alloy steels.
Does GCNOV provide custom manufacturing services for SAE 8620?
Yes. GCNOV provides:
- CNC Turning
- CNC Milling
- Gear Manufacturing
- Gear Hobbing
- Carburizing
- Carbonitriding
- Precision Grinding
- QPQ Treatment
- Prototype Development
- Low-Volume Production
- Mass Production