8620 Alloy Steel Castings: An In-Depth Analysis of Properties and Industrial Applications

8620 alloy steel castings are a prominent choice in various industries due to their outstanding combination of toughness, strength, and ductility. Known formally as AISI 8620, this alloy steel is a low-carbon nickel-chromium-molybdenum grade. The well-balanced chemical composition of 8620 steel makes it highly versatile, offering superior surface hardness when heat treated, while maintaining a soft, flexible core.

The adaptability of 8620 alloy steel allows it to be used in applications requiring a good balance of strength and wear resistance. To learn more about alloy castings, please read our article on alloy steel castings here, where you can find useful information such as common grades, properties, processes, and applications.

This article will explain the characteristics that make AISI 8620 a popular material for castings, along with its heat treatment processes and widespread industrial applications.

Before we delve into this article, I’d like to briefly introduce ourselves. Taiyuan Simis Investment Casting Co., Ltd is a Chinese professional investment casting manufacturer with more than 40 years of metal casting experience. We have a dedicated investment casting workshop for providing alloy steel casting services, including 8620 alloy steel castings.

AISI 8620 Steel International Equivalents

8620 alloy steel, also recognized under the AISI 8620 standard, holds a significant position in the international metals market due to its widespread usage and adaptability in various applications.

8620 alloy steel is not only known in the United States under the American Iron and Steel Institute (AISI) system but also recognized worldwide with different designations. In Europe, it is commonly referred to as 21NiCrMo2 under the DIN standard in Germany or 20NCD2 in France. The British Standard identifies it as 805M20. This alloy steel is also recognized in China as 20CrNiMo under GB standard.

Country/Region	Standard	Designation
USA	AISI/SAE	8620
Europe	EN/DIN	21NiCrMo2 (DIN), 20NiCrMo2-2 (EN)
United Kingdom	British	805M20
France	AFNOR	20NCD2
Japan	JIS	SNCM220
International	ISO	20NiCrMo2-2
China	GB	20CrNiMo

Chemical Composition of AISI 8620 Steel

8620 alloy steel castings are known for their excellent balance of toughness, strength, and ductility, a result directly tied to their specific chemical composition. We will break down its chemical elements and explain the role and impact of each element.

Breakdown of Chemical Elements

The primary constituents of 8620 steel include iron as the base, with notable percentages of nickel, chromium, and molybdenum.

• Carbon (C): 0.18% to 0.23%
• Manganese (Mn): 0.70% to 0.90%
• Chromium (Cr): 0.40% to 0.60%
• Nickel (Ni): 0.40% to 0.70%
• Molybdenum (Mo): 0.15% to 0.25%
• Silicon (Si): 0.15% to 0.35%
• Phosphorus (P): 0.035% max
• Sulfur (S): 0.040% max

Composition table and the Roles of Elements for AISI 8620 Steel

Element	Percentage	Role in 8620 Alloy Steel
Carbon (C)	0.18% – 0.23%	Adds hardness and strength, while maintaining ductility
Manganese (Mn)	0.70% – 0.90%	Enhances hardenability and tensile strength
Chromium (Cr)	0.40% – 0.60%	Increases corrosion resistance and hardenability
Nickel (Ni)	0.40% – 0.70%	Improves toughness and ductility at low temperatures
Molybdenum (Mo)	0.15% – 0.25%	Boosts strength and thermal stability
Silicon (Si)	0.15% – 0.35%	Acts as a deoxidizer and strengthens steel
Phosphorus (P)	Up to 0.035%	Kept low to avoid brittleness and reduce toughness
Sulfur (S)	Up to 0.040%	Minimized to avoid reducing impact toughness

8620 Steel Mechanical Properties

8620 alloy steel castings are highly regarded for their mechanical properties, similar to those of AISI 4340 alloy steel, including tensile strength, hardness, and other vital traits. Please see the table below that provides an analysis of these properties and explores how they impact the alloy’s performance in various environmental conditions.

Property	Value Range or Typical Value	Impact on Performance
Tensile Strength	530 to 680 MPa (77,000 to 98,000 psi)	Enables use in medium to high-stress applications, providing strength for heavy-duty operations.
Hardness	143 HB (Pre-heat treatment)	Allows for surface wear resistance when hardened, suitable for moving parts with frequent contact.
Elongation	Approx. 22%	Offers good ductility, crucial for applications requiring deformation resistance without fracturing.
Impact Toughness	High	Provides durability against sudden or cyclical impact loads, essential for automotive and machinery parts.
Corrosion Resistance	Moderate, can be enhanced with coatings	Ensures suitability for mildly corrosive environments, protecting against moisture-induced degradation.

Tensile Strength and Hardness

The combination of high tensile strength and adjustable hardness through heat treatment allows AISI 8620 castings to perform well in environments that subject them to mechanical stress and wear. This is particularly useful in gears and other moving parts where both impact resistance and surface durability are necessary.

Elongation and Impact Toughness

The ductility and toughness of 8620 steel make sure that it can withstand dynamic stresses and shocks common in automotive and industrial machinery applications. These properties are beneficial for operating in cold environments, where materials are typically more prone to brittleness.

Corrosion Resistance

While not as high as that of some stainless steels, the corrosion resistance of 8620 can be enhanced through protective coatings and surface treatments, thus making it perfectly suitable for use in mildly corrosive environments such as those exposed to moisture.

Casting Processes for 8620 Alloy Steel

8620 alloy steel is adaptable to various casting techniques, each bringing unique advantages to the production of complex components.

Investment Casting

Investment casting is renowned for its ability to produce components with exceptional precision and excellent surface finish. This method is especially advantageous for AISI 8620 as it allows for the creation of complex, intricate shapes that would be costly or impossible to achieve with other casting methods. The process also minimizes the need for secondary machining, saving time and reducing material waste. At SIMIS, we provide custom investment casting services, offering great flexibility in size, structure, treatments, tolerances, and more.

Sand Casting

Sand casting is a viable method for manufacturing large 8620 steel parts due to its low tooling costs and flexibility in mold and core design. This method is advantageous for its ability to handle high-volume production without compromising the structural integrity of the cast parts. It’s exceptionally fit for creating large, rugged components that require robust mechanical properties.

Sand casting can also be useful for casting small to medium-sized 8620 steel components from specialized production systems such as the DISAMATIC line, which can achieve amazing efficiency for high-volume production. However, components produced by sand casting typically have a rougher surface finish compared to those produced by investment casting, and it may not be suitable for casting complex 8620 parts with intricate internal cavities. If you’re interested in the comparison between sand casting and investment casting, you can find the article here.

Shell Mold Casting

Shell mold casting provides a higher degree of accuracy and a smoother surface finish than traditional sand casting. This process benefits 8620 alloy steel components by producing finer details and better surface quality, reducing the need for extensive surface finishing. It is quite effective for medium to high volume production, therefore making it an economical choice for parts requiring a good balance between dimensional precision and production efficiency when produced in large quantities.

8620 steel parts produced by the shell mold casting process generally have better surface smoothness compared to those produced by sand casting, but not as great as those from investment casting. You can read the comparison article here to learn more about the differences between shell mold casting and investment casting.

Lost Foam Casting

Lost foam casting is known for its ability to create complex parts with minimal machining and finishing required. For 8620 alloy steel, this method is highly useful because it allows for the production of very intricate designs that would be difficult or extremely costly to achieve with other methods. The process is also noted for its environmental benefits, as it generates less waste and uses fewer resources, thus providing a more sustainable option for detailed component fabrication.

Heat Treatments

Heat treatment processes are almost always critical for enhancing the mechanical properties of 8620 alloy steel castings, allowing them to meet specific application requirements.

Carburizing (Case Hardening)

This treatment is ideal for increasing the surface hardness of 8620 steel while retaining its tough interior. The steel is heated in the presence of a carbonaceous material, which allows carbon to diffuse into the surface, significantly enhancing its hardness and wear resistance.

Annealing

Used to reduce hardness, increase ductility, and relieve internal stresses, annealing involves heating the steel to a specific temperature before slowly cooling it. This makes the steel easier to machine or form.

Normalizing

By heating 8620 steel to a temperature slightly above its critical point and then air cooling it, normalizing helps to refine the grain structure, enhance toughness, and improve uniformity in mechanical properties.

Quenching and Tempering

This treatment enhances the strength and hardness of the steel. The steel is quenched from a high temperature to create a hard martensitic structure and then tempered at a lower temperature to reduce brittleness.

Surface Treatments of 8620 Alloy Steel Castings

Surface treatments are applied to 8620 alloy steel castings to enhance their corrosion resistance and durability, extending their usability and performance in harsh environments.

Powder Coating

This involves applying a dry powder of polymer resin, which is then cured under heat to form a skin-like protective and decorative coating on the steel surface. It provides a durable, corrosion-resistant finish that is more resistant to chipping, scratching, and other wear than other finishes. Ideal for parts that require high visual appeal and long-lasting surface protection against environmental factors.

Nitriding

This process diffuses nitrogen into the steel’s surface to create a hard, wear-resistant case without the need for quenching, minimizing distortion. It increases surface hardness and significantly enhances fatigue resistance and corrosion resistance, especially against oxidizing environments. This makes it suitable for high-precision components in engines and machinery.

Chromizing

By diffusing chromium into the surface, chromizing provides excellent resistance to oxidation and corrosion, particularly at high temperatures. It offers superior corrosion resistance and high-temperature oxidation resistance, ideal for parts exposed to aggressive chemical environments or high temperatures, such as in aerospace and automotive engines.

Phosphating

This chemical process coats the steel with a layer of phosphate crystals that helps to reduce friction and improve paint adhesion, useful for parts that require subsequent painting. While not significantly improving corrosion resistance on its own, phosphating enhances paint adhesion and reduces wear by providing a more durable paint layer, beneficial for parts that are painted for additional corrosion protection or aesthetic purposes.

Painting

Applying paint to 8620 steel not only improves its appearance but also serves as a barrier against corrosion and environmental damage. This is largely beneficial for components used in visible areas or in harsh environments where additional protection is needed.

Applications of AISI 8620 Alloy Steel Castings

Due to its strength, toughness, and ductility, AISI 8620 alloy steel is an excellent material for a wide range of applications in various industries.

Railway

8620 steel is used to manufacture a variety of railway components due to its ability to withstand dynamic loads and varying environmental conditions. These components include couplings, bearings, center plates, yokes, bogie side frames, axle boxes, and adapters. The alloy’s high fatigue resistance and toughness also make it very practical for brake components, where reliability and safety under stress are uncompromisable. With these important attributes, 8620 steel is one of the most frequently used material for critical railway applications, supporting both the structural integrity and operational safety of rail vehicles.

Automotive

The automotive sector relies heavily on 8620 steel for creating gears and shafts in transmissions and engines, thanks to its excellent strength and wear resistance, which are crucial for durability and long-lasting performance. Additionally, pinions, crankshafts, and shifter forks are made from 8620 alloy steel to take advantage of its strength and toughness. These components benefit from the alloy’s ability to endure the stresses of engine and transmission operations, maintaining reliable performance under demanding conditions. This makes AISI 8620 a fundamental alloy grade for various critical components within the automotive industry.

Oil and Gas

In the oil and gas industry, 8620 steel is extensively used in the manufacture of drilling equipment parts, such as drill collars, gears, and cross coupling cable protectors, which must withstand high impact and abrasive environments. Additionally, pump casting parts benefit greatly from the corrosion resistance and strength of 8620 steel, notably components like submersible pump impellers and pump housings that are exposed to corrosive substances. These applications showcase the alloy’s ability to perform reliably in the demanding and harsh conditions typical of oil and gas extraction and processing, ensuring durability and longevity of essential equipment.

Mining and Construction

8620 steel is quite prominent in mining and construction for producing excavator teeth, which require durability and impact resistance for digging hard materials. Drive sprockets, another critical component for machinery in this industry, utilize the wear resistance and strength of 8620 steel components to ensure operational reliability and longevity. Similar to 8620 steel castings, high-manganese steel is also a highly viable material for mining and construction industry due to its amazing wear resistance and strength, check out our article for manganese steel castings for more information.

Agriculture

In agriculture industry, 8620 steel is widely used to produce gearboxes for machinery, as it can handle heavy loads and resist wear under tough conditions. It is also utilized in making chains, sprockets, plow blades, and combine parts for agricultural equipment, benefiting from the alloy’s toughness and strength to withstand variable loads and harsh environmental factors. These components are pivotal for the efficient and reliable operation of farm machinery, allowing it to perform optimally in the demanding world of agricultural production where durability is indispensable.

Industrial Machinery

For industrial machinery, AISI 8620 is chosen for machine frames that support heavy operations without compromising performance. It is also used in load-bearing parts, gear reducer housings, and worm gear housings, where its high strength-to-weight ratio is vital for maintaining safe and efficient machine operation. These components benefit from the alloy’s ability to handle significant stress and load, in turn making it perfect for critical applications in machinery that requires durability and reliability under constant use. The versatility of 8620 steel is evident in the manufacturing of robust and long-lasting industrial machinery components.

Conclusion

The importance of AISI 8620 alloy steel castings cannot be understated in various industries due to their excellent toughness, strength, and ductility. This alloy is commonly used in applications ranging from automotive components to heavy machinery in agriculture and construction, proving its adaptability and reliability. The ability to tailor 8620 steel through various heat and surface treatments to meet specific needs underscores its fundamental role in engineering and manufacturing.

As demands for higher performance materials grow, the significance of 8620 alloy steel is expected to increase. Taiyuan Simis Investment Casting Co., Ltd strives to provide the highest quality possible to all our clients.

We have an advanced testing and inspection system that includes X-ray, spectrometer, and CMM. Our custom casting services can offer incredible value to our clients, featuring our advanced production system, which includes our massively improved silica sol casting technique and automation. Moreover, our extensive metal casting experience can help clients achieve difficult, costly projects with relative ease and significant cost savings without ever compromising on quality. Get in touch with us today to discuss your next AISI 8620 casting project.