Stellite: Definition, Properties, Grades, and Applications

Stellite is a silver-white metal known for its wear resistance, corrosion resistance, and high-temperature oxidation resistance, making it highly valued. Its unique properties have led to widespread applications across various industries including aerospace, automotive, medical, and chemical.

Stellite exists in several grades and alloys, each offering distinct properties tailored for specific applications. This article defines stellite, describes its origins and features, discusses its different grades and alloys, and explores its applications.

What is Stellite?

Stellite is a cobalt-based alloy, typically exhibiting a silver-white or gray luster. Also known as cobalt-chromium-molybdenum alloy, it is broadly categorized into two types: Co-Cr-Mo alloys, often used for cast products, and Co-Ni-Cr-Mo alloys, typically (hot) forged for precision machining. It is renowned for its hardness, providing excellent resistance to wear, corrosion, and high-temperature oxidation. Common applications of Stellite alloy include cutting tools and aerospace applications, valves and valve seats, automotive parts, as well as applications in energy and chemical industries.

What is the Origin of Stellite?

In 1907, American Elwood Haynes invented Stellite alloy based on the principle that the structure, from room temperature to the melting point, can largely rely on carbide strengthening with elements C, W, Cr, and Co to stabilize. This alloy, primarily composed of cobalt, chromium, and tungsten, appears silver-white after cooling with a brilliant metallic luster akin to stars. The name Stellite derives from the Latin word for stars, "Stella," reflecting its sparkling appearance. Haynes later trademarked stellite.

What is Stellite Made of?

Stellite alloy is primarily composed of cobalt, with significant amounts of nickel, chromium, tungsten, and small quantities of molybdenum, niobium, tantalum, titanium, lanthanum, and occasionally iron as alloying elements.

How is Stellite Made?

High-purity cobalt and other alloying elements such as chromium, molybdenum, nickel, and possible strengthening materials are selected. These materials are then melted and mixed at high temperatures to ensure uniform alloy composition. The chemical composition and crystal structure are carefully controlled. The alloy is shaped into desired dimensions and forms through casting or hot working processes.

Early Stellite alloys were produced using non-vacuum melting and casting techniques. Later alloys, like Mar-M509 alloy, which contain more reactive elements like zirconium and boron, are produced using vacuum melting and vacuum casting techniques.

What are the Key Features of Stellite?

The properties and characteristics of Stellite vary depending on the grade and specific alloy, but here are some general features:

Wear Resistance: Exhibits high hardness, effectively resisting wear, particularly suitable for wear-resistant applications in high-temperature and high-pressure environments. Widely used in tools, valves, etc.

High Temperature Resistance: Maintains dimensional stability in high-temperature environments, preventing deformation, suitable for aerospace and chemical applications.

Excellent Hardness: Typically exceeds 40 HRC and can reach over 60 HRC, providing significant advantages in wear resistance, cutting, and impact resistance. Widely used in cutting tools, wear-resistant parts, etc.

Corrosion Resistance: Chromium, cobalt, and other elements impart excellent corrosion resistance, capable of resisting various chemical corrosion and high-temperature gas erosion. Widely used in aerospace and chemical industries.

High Fatigue Resistance: Demonstrates good mechanical properties, maintaining high performance under repeated stress conditions, ideal for applications requiring high reliability and durability (structural components).

High Strength: Its unique alloy structure enables it to withstand high loads and impact forces, playing a crucial role in high-strength applications.

What are the Common Grades of Stellite?

Stellite alloys, as a special engineering material, are now widely used. They exhibit excellent performance in high temperature resistance, wear resistance, erosion resistance, and corrosion resistance. However, the specific properties vary among different grades. Typical grades of Stellite alloys include: Stellite 1, Stellite 4, Stellite 6, Stellite 8, Stellite 12, Stellite 20, Stellite 21, Stellite 31, Stellite 100.

1. Stellite 1 or UNS R30001

Stellite 1, also known as UNS R30001, contains approximately 30.5% Cr, 12.5% W, 2.4% C, and other elements. Due to its high content of C and W, it exhibits the highest hardness and excellent wear resistance. Grade 1 is typically used for applications such as valve seats, bearings, and cutting edges.

2. Stellite 4 or UNS R30004

Stellite 4, containing 30% Cr, 14% W, 1% C, and other elements, is a cast alloy suitable for machining. It features high hardness, wear resistance, and high temperature resistance, making it suitable for applications requiring superior wear resistance. Stellite 4 is commonly used in the manufacturing of cutting tools, wear parts, and high-temperature components.

3. Stellite 6 or UNS R30006

Stellite 6, also known as UNS R30006, contains approximately 29% Cr, 4% W, 1.15% C, along with small amounts of Ni, Fe, Si, Mn, and Mo. With lower C and W content, Stellite 6 offers a balanced combination of wear resistance and toughness. It exhibits excellent high temperature resistance and oxidation resistance, making it the most widely used grade. Stellite 6 is commonly employed in the manufacture of cutting tools, wear parts, and high-temperature components such as nozzles and turbine blades.

4. Stellite 8 or UNS R30008

Stellite 8, containing 27% Cr, 6% Mo, 2% Ni, 0.2% C, and other elements, is a low-carbon alloy strengthened with molybdenum, nickel, and other elements. While it exhibits low hardness at room temperature, its hardness increases after cooling. It possesses excellent high-temperature corrosion resistance, thermal shock resistance, high strength, and ductility, with elongation typically ranging from 8% to 10% at room temperature. Stellite 8 is machinable and commonly used in applications such as gas turbine blades, brass casting molds, and extrusion dies.

5. Stellite 12 or UNS R30012

Stellite 12, also known as UNS R30012, contains 29.5% Cr, 8.25% W, and 1.4% C. With moderate levels of C and W, it is considered an intermediate alloy between Stellite 6 and Stellite 1. It exhibits moderate hardness, better wear resistance, and high temperature resistance compared to Stellite 6. Stellite 12 is commonly used in the manufacturing of high-temperature and high-pressure valves, saw teeth, and spiral push rods.

6. Stellite 20 or UNS R30020

Stellite 20, also known as UNS R30020, contains 32.5% Cr, 17.5% W, and 2.5% C. With a high carbon content of up to 2.5% and over 30% carbides in its structure, this grade exhibits strong wear resistance and corrosion resistance. It has a high hardness of up to 52 HRC and is typically used in casting or as hardfacing material for coatings. Stellite 20 is utilized in applications such as bearing sleeves, rotary seal rings, wear plates, and work rests for centerless grinding machines.

7. Stellite 21 or UNS R30021

Stellite 21, also known as UNS R30021, contains 27.5% Cr, over 5.5% Mo, 0.25% C, and other elements. With Mo strengthening and low carbon content, Stellite 21 is a cobalt-chromium alloy that exhibits lower hardness at room temperature and increased hardness after cooling. It offers good high-temperature corrosion resistance, wear resistance, and overall mechanical properties. Stellite 21 is suitable for hardfacing various hot forging dies and is commonly used in the production of turbine blades, various fluid valves, and valve seats.

8. Stellite 31 or UNS R30031

Stellite 31 is a non-magnetic alloy containing 25% Cr, 10% Ni, 7% W, 0.3% C, and small amounts of other elements. It has a relatively low coefficient of thermal expansion, making it ideal for applications requiring dimensional stability. With a hardness range of 35-45 HRC, it is suitable for cutting parts. Stellite 31 also exhibits strong thermal shock resistance and is primarily used for engine components, valve parts, bearings, and extrusion dies.

9. Stellite 100 or UNS R30100

Stellite 100 is the hardest alloy in the Stellite family, with a hardness greater than 61-66 HRC. It also exhibits high hot hardness, maintaining around HRC 45 at 800°C, and exceptional resistance to abrasive wear. It possesses good corrosion resistance but is difficult to machine. This type of alloy is specifically designed for metal cutting applications and is commonly used in the manufacturing of cutting tools such as blades and milling cutters.

What are the Main Properties of Stellite?

Some of the physical and chemical properties of stellite are listed below:

Density: Stellite has a density ranging approximately from 8.5 to 9.5 g/cm³.

Color: Stellite exhibits a silver-white or gray luster.

Strength: The strength of stellite depends on its grade and the concentration of alloying elements. Stellite alloys can achieve a tensile strength in the range of 1100-1500 MPa, with yield strength typically between 800-1100 MPa, showing high strength characteristics.

Wear Resistance: Stellite features high tensile yield strength, hardness, and excellent fatigue resistance, making it highly durable with a long expected service life.

High Temperature Resistance: Stellite has a thermal expansion coefficient of approximately 12-14 µm/m·K (in the range of 20-100°C), displaying good thermal stability. It can maintain mechanical properties at high temperatures (up to approximately 1200°C) and resist high-temperature oxidation.

Corrosion Resistance: Stellite exhibits excellent resistance to common corrosive media such as sulfuric acid, hydrochloric acid, and sodium bicarbonate, maintaining stable mechanical properties while also resisting oxidation at high temperatures.

What are the Applications of Stellite?

Based on the characteristics of Stellite, careful selection of grades according to technical requirements is essential to achieve optimal comprehensive performance. Here are some applications of stellite:

Aerospace

Stellite alloys are ideal materials for aerospace due to their high temperature resistance, corrosion and oxidation resistance, and ability to withstand extreme environments. They are commonly used in manufacturing engine components, turbine blades, combustion chamber parts, exhaust valves, etc.

Automotive

Due to its wear resistance and high temperature resistance, Stellite is used in automotive manufacturing for parts such as engine components and turbocharger parts to enhance durability and mechanical performance. Its application in automotive industry is somewhat limited due to its higher cost compared to other materials, but its use may expand with advancing automotive technologies.

Energy

Stellite's excellent wear resistance, corrosion resistance, and high temperature resistance make it suitable for manufacturing components used in oil and natural gas extraction equipment (e.g., drill bits, pump bodies) and for components in thermal and nuclear power plants, ensuring energy safety, efficiency, and reliability.

Chemical Industry

Stellite can resist corrosion from strong acids, alkalis, oxidizers, and reducers, making it suitable for manufacturing various reactors, vessels, and pipelines used to handle and store corrosive chemicals. Common applications include pumps, valves, heat exchangers, and other corrosion-resistant components, enhancing safety and efficiency in chemical production.

Mechanical Industry

Stellite, known for its excellent wear resistance, high temperature resistance, and impact resistance, is widely used in manufacturing cutting tools such as turning tools, milling cutters, drills, reamers, and taps. It maintains sharpness during high-speed and heavy-duty cutting operations and under high temperature conditions, thereby extending the life of the tools.

Medical

Stellite is renowned for its outstanding wear resistance, corrosion resistance, and high temperature resistance, making it suitable for manufacturing surgical tools, blades, durable components in medical equipment, orthopedic tools, and joint replacement components. While Stellite alloys generally exhibit good biocompatibility, potential risks such as cobalt ion release and allergic reactions need to be considered in certain applications.

These applications highlight Stellite's versatility and importance across various industries.

What are the Limitations of Stellite?

Low Ductility: Stellite alloys exhibit poor ductility, often leading to brittleness and susceptibility to fracture under impact loads. Therefore, they are not suitable for use in components that require resistance to impact loads.

Hard to Machine: Stellite has high hardness, making it challenging to machine. Advanced equipment and techniques are required for machining, resulting in higher processing time and costs.

High Cost: The production process of stellite is complex and involves high-purity cobalt and other precious metals, making its cost significantly higher compared to other materials such as stainless steel.

FAQs

What are the Benefits of Stellite?

Stellite alloys exhibit excellent hardness and wear resistance, maintaining sharpness and durability over prolonged use. They demonstrate outstanding resistance to various chemicals and corrosive environments, remain stable at high temperatures, and possess high strength.

What is the Color of Stellite?

Stellite alloys are typically gray or silver-gray in color. This color is primarily determined by the cobalt-based alloy composition, often resembling the appearance of stainless steel or chrome steel.

What are the Most Commonly Used Grades of Stellite?

The most commonly used Stellite grades include Stellite 1, Stellite 6, Stellite 12, and Stellite 21. These correspond to low-carbon, medium-carbon, high-carbon cobalt-chromium-tungsten alloys used in casting and welding applications. The deposited layers exhibit excellent corrosion resistance, heat resistance, and wear resistance, maintaining these properties even at high temperatures up to 800°C.

Summary

This article introduces stellite, explaining what stellite is and its characteristics, and discusses various applications of Stellite. If you would like to learn more about stellite, please contact us.

DEK is a global custom parts manufacturer, providing high-quality services to customers across various industries worldwide. If you are interested in starting a new Stellite project with us, we welcome you to explore our machining stellite services. You will receive a satisfactory response!