Ever wondered what makes 8620 alloy steel a go-to choice for tough, hardworking parts? Whether you’re planning a demanding project or simply curious about steel grades, understanding how to use 8620 alloy steel can make all the difference in performance and durability.
This article breaks down everything you need to know—from its standout qualities to expert tips on handling and treating it. Get ready to discover practical guidance and insights to help you get the most from this versatile material.
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What is 8620 Alloy Steel?
8620 alloy steel, often called AISI 8620 or SAE 8620, is a low-alloy steel known for its excellent toughness, high strength, and impressive wear resistance. It’s famous in engineering, automotive, and industrial applications, particularly for parts that require both surface hardness and a tough core. This steel gets its versatility from its unique mix of elements, making it an ideal choice for processes like carburizing and heat treatment.
Chemical Composition and Key Properties
The secret behind 8620 steel’s popularity lies in its balanced chemical composition:
- Carbon (0.18-0.23%) – Offers a good mix of strength and machinability.
- Chromium (0.40-0.60%) – Adds hardness and corrosion resistance.
- Nickel (0.40-0.70%) – Increases toughness and strength.
- Molybdenum (0.15-0.25%) – Enhances wear resistance and hardenability.
- Manganese, Phosphorus, Sulfur, Silicon – Present in smaller amounts to help refine structure and machinability.
Notable Mechanical Properties
- Tensile Strength: Typically 570 – 900 MPa (depending on condition)
- Yield Strength: 400 – 650 MPa
- Hardness: Up to 62 HRC after carburizing
- Excellent machinability and weldability
- High core toughness even after surface hardening
How to Process 8620 Alloy Steel
The way you process 8620 alloy steel depends on the intended application. Here’s a breakdown of the key steps and methods:
1. Machining
8620 alloy steel is relatively easy to machine in its normalized or annealed condition. You can perform:
- Turning
- Milling
- Drilling
- Tapping
Best Practices for Machining
- Use sharp tools with proper coolants
- Prefer carbide or high-speed steel (HSS) tools
- Adjust speeds and feeds to minimize tool wear
- Anneal before machining for large or complex components
2. Heat Treatment
Heat treatments bring out the desired mechanical properties in 8620 steel. The process often involves:
a. Annealing
- Heat to 830-850°C (1525-1560°F)
- Hold for a suitable period (based on section size)
- Furnace cool slowly to refine the grain and soften the steel
- Purpose: Makes the steel easier to machine
b. Normalizing
- Heat to 870°C (1600°F)
- Air cool afterward
- Purpose: Refines grain structure to improve strength and toughness
c. Hardening (Carburizing + Quenching)
This is where 8620 shines! Carburizing adds carbon to the surface for superior wear resistance.
- Heat at 900-950°C (1650-1750°F) in a carbon-rich environment
- Soak for the required time (depends on depth needed)
- Quench in oil to harden the case
- Purpose: Achieve a hard, durable surface (case) and tough core
d. Tempering
- After quenching, temper at 150-200°C (300-400°F)
- Hold for 1-2 hours
- Purpose: Reduce brittleness while maintaining surface hardness
3. Welding
You can weld 8620 alloy steel, but precautions are necessary:
- Preheating (around 150-300°C) helps avoid cracking
- Post-weld heat treatment may be needed to relieve stress and maintain properties
- Use compatible filler materials (like low-alloy electrodes)
4. Surface Hardening by Carburizing
For parts subjected to high surface stress, like gears:
- Carburize the part to introduce extra carbon into the surface.
- Harden by quick cooling (quenching).
- Temper to achieve a tough core with a hard, wear-resistant surface.
5. Finishing
After heat treatment and machining, you may require:
- Grinding for tight tolerances and a smooth finish
- Polishing to reduce friction or for aesthetic reasons
- Surface coatings for added corrosion protection
Key Benefits of Using 8620 Alloy Steel
- Strong and Tough Core: Bears loads and withstands impact.
- Hard, Durable Surface: Resists wear, perfect for gears and shafts.
- Machinability: Easy to shape and cut when annealed or normalized.
- Versatility: Can be heat-treated or surface hardened to different specs.
- Weldability: Can be joined, with the right precautions.
Common Uses and Applications
You’ll find 8620 steel in industries needing a balance of toughness and surface hardness:
- Automotive components (gears, crankshafts, camshafts, pinions, axle shafts)
- Heavy equipment (bushings, rollers, sprockets)
- Oil and gas (valves, couplings)
- Aircraft parts
- Power transmission parts
Challenges and Considerations
While 8620 is versatile, there are points to keep in mind:
- Requires precise heat treatment for optimal properties—improper procedures can lead to undesired hardness or brittleness.
- Surface carburizing is time-consuming and requires controlled environments.
- May require specialized equipment for large or complex parts.
- Welding-related cracking if you skip pre-or post-heat treatment.
- Not corrosion-resistant: For harsh environments, consider a coating or an alternative alloy.
Practical Tips and Best Practices
- Order in the state suited to your needs: Annealed for easy machining; as-hot-rolled for forging; pre-hardened for ready-to-use components.
- Work with qualified heat treaters: Heat treatment quality dramatically impacts performance.
- Design for case depth: Specify the required hardness depth for your application, especially for load-bearing components.
- Factor in potential distortion: Carburizing, quenching, and hardening may cause minor dimensional changes—plan your machining sequence accordingly.
- Use appropriate lubricants and coolants: Helps prevent tool wear during machining.
- Inspect for cracks and distortion after hardening, particularly in thin or complex shapes.
Cost Tips When Purchasing and Shipping 8620 Steel
- Buy standardized sizes: Standard bars or billets are more economical than custom cuts.
- Order in bulk to save: Larger quantities often lead to lower per-unit costs.
- Consider shipping weight: Alloy steels are heavy; minimize costs by consolidating orders.
- Request local sourcing or suppliers: Reduces shipping expenses and lead times.
- Factor in additional processing: Machining and heat treatment add to the total cost—sometimes it’s more cost-effective to buy parts pre-machined or pre-hardened.
A Quick Comparison: 8620 Alloy Steel vs. Other Alloy Steels
- Compared to 4140 or 4340: 8620 offers easier carburizing and better combination of case-and-core hardness
- Compared to carbon steel: 8620 is significantly tougher and better for parts that need both durable surfaces and strong cores
- Compared to stainless steel: 8620 is less corrosion resistant but offers much higher surface hardness after treatment
Summary: Why Choose 8620 Alloy Steel?
In a nutshell, 8620 alloy steel stands out for its combination of toughness, wear resistance, and versatility. Whether you need automotive gears, heavy-duty bearings, or custom machine components, its ability to be tailored via heat treatment makes it a smart, reliable choice. Thanks to its machinability and weldability, you’ll find it manageable to work with, provided you use proper processes and precautions.
Frequently Asked Questions (FAQs)
1. What is the main advantage of 8620 alloy steel?
The biggest advantage of 8620 steel is its ability to develop a hard, wear-resistant surface while retaining a core that stays tough and ductile. This makes it ideal for components like gears and shafts that face heavy use and high loads.
2. Can I weld 8620 alloy steel?
Yes, you can weld 8620 steel. However, it’s important to preheat the steel before welding (usually to 150–300°C) and perform post-weld heat treatment where possible. This reduces the risk of cracking and maintains the steel’s properties.
3. How hard can 8620 steel get after heat treatment?
After carburizing and quenching, the surface of 8620 steel can reach hardness levels up to approximately 62 HRC. The core will remain significantly softer and tougher, preventing brittleness.
4. Is 8620 alloy steel corrosion resistant?
8620 steel is not classified as a corrosion-resistant alloy. For increased protection in corrosive environments, it’s advisable to use coatings, plating, or select a stainless steel instead.
5. What are common alternatives if 8620 is not available?
Popular alternatives include 4140, 4340, and 9310 alloy steels. The choice depends on required properties—4140 for high strength, 4340 for extra toughness, and 9310 for superior case hardenability.
By understanding 8620 alloy steel’s composition, properties, and best practices, you’ll be well-equipped to take advantage of everything this versatile material has to offer for your engineering or manufacturing needs.