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Stellite 12: Composition, Properties, and Uses

In the world of advanced materials, Stellite 12 stands out as a remarkable cobalt-chromium alloy, renowned for its exceptional wear and corrosion resistance, as well as its ability to perform under high temperatures. Whether you’re in the timber industry seeking durable saw tips, in the beverage industry looking for reliable control plates, or involved in high-temperature applications, understanding the composition, properties, and uses of Stellite 12 can provide significant advantages. This alloy’s unique blend of cobalt, chromium, and tungsten, among other elements, grants it superior hardness and strength, making it indispensable in various industrial applications. Dive into the intricate details of Stellite 12 as we explore its chemical makeup, mechanical properties, and diverse applications that make it a go-to solution for enduring performance in challenging environments.

Introduction

Overview of Stellite 12

Stellite 12 is a well-known cobalt-based alloy, highly regarded for its outstanding wear and corrosion resistance, as well as its performance in high-temperature environments. Originally developed for challenging environments, Stellite alloys are now essential in many industries because of their robust properties.

Significance of Stellite 12

Stellite 12 is designed to provide an ideal balance of hardness and toughness. With a higher carbon content than other Stellite alloys, Stellite 12 offers improved wear resistance while still being ductile enough for various uses. The unique makeup of Stellite 12 enables the formation of hard carbides, greatly enhancing its durability and effectiveness in abrasive conditions.

Industrial Relevance

Industries like metal processing, power generation, and chemical processing often use Stellite 12 for its ability to withstand extreme wear and tear. Stellite 12 is ideal for components in harsh environments because it retains its strength and structure at high temperatures.

Applications and Uses

Stellite 12 is widely used to make industrial knives, saw tips, valve components, and more. It is especially valuable in situations where ongoing mechanical stress and corrosion would damage other materials.

Using Stellite 12, industries can boost equipment lifespan and efficiency, cut maintenance costs, and increase overall reliability.

Composition

Detailed Chemical Composition

Stellite 12 is a durable cobalt-based alloy designed to perform well under extreme conditions. The typical composition of Stellite 12 includes a variety of elements that contribute to its outstanding properties. Cobalt forms the base of Stellite 12, constituting approximately 27-32% of the alloy. Cobalt helps the alloy stay strong in high temperatures and corrosive environments.

Chromium (Cr)

Stellite 12 contains 7.5-9.5% chromium, which improves hardness, wear resistance, and corrosion resistance. Chromium significantly contributes to the alloy’s ability to resist corrosion, particularly in oxidizing environments, by forming a protective oxide layer on the surface.

Tungsten (W)

Tungsten content in Stellite 12 ranges from 1.4-1.7% for hardfacings and 1.7-2.0% for castings. Tungsten increases the alloy’s hardness and strength at high temperatures, allowing Stellite 12 to maintain its integrity in high-temperature applications.

Carbon (C)

Carbon helps form hard carbides that make the alloy wear-resistant. The carbon content in Stellite 12 is between 1.7-2.0%, contributing to its exceptional wear resistance and hardness in abrasive conditions.

Other Elements

In addition to the primary elements, Stellite 12 contains smaller quantities of other elements such as Nickel (Ni), Iron (Fe), Silicon (Si), and Manganese (Mn). These elements, though present in minor amounts, contribute to the overall properties of the alloy:

  • Nickel: Improves toughness and corrosion resistance.
  • Iron: Provides additional strength and hardness.
  • Silicon: Enhances oxidation resistance and helps form a protective oxide layer.
  • Manganese: Acts as a deoxidizer and improves toughness.

Comparison with Other Stellite Alloys

To understand Stellite 12’s unique advantages, let’s compare it with other Stellite alloys like Stellite 6 and Stellite 1.

Stellite 6

Stellite 6 is another popular cobalt-based alloy known for its excellent wear resistance and corrosion resistance. However, Stellite 12 has a higher carbon content than Stellite 6, which provides better wear resistance but slightly less toughness. Stellite 6 is ideal for applications needing a balance of wear resistance and toughness.

Stellite 1

Stellite 1 has an even higher carbon content than Stellite 12, translating to superior wear resistance but reduced toughness. Stellite 1 is typically used in applications where maximum wear resistance is required, and the material can withstand less mechanical shock.

Summary of Key Differences

Stellite 12 has higher carbon content than Stellite 6, offering better wear resistance but slightly less toughness. Compared to Stellite 1, it provides a good balance of wear resistance and toughness, making it suitable for a wide range of applications. Understanding the composition and comparison of Stellite 12 with other Stellite alloys allows for informed decisions in selecting the right material for specific industrial applications.

Properties

Physical Properties

Stellite 12 is known for its diverse physical properties, making it ideal for high-performance applications across various industries. Its density is around 8.53 g/cm³ (0.308 lb/in³), contributing to its strength and durability. With a melting range of 1200°C to 1365°C (2192°F to 2489°F), Stellite 12 maintains its structural integrity and performance at high temperatures.

Mechanical Properties

Stellite 12 is particularly valued for its hardness, tensile strength, yield strength, and elongation. Typically, Stellite 12 has a hardness of 40-51 HRC (Rockwell Hardness) or 435-590 HV (Vickers Hardness), thanks to the formation of durable carbides. Its high tensile and yield strengths allow it to withstand significant mechanical stress without deforming. While moderately ductile, Stellite 12 can absorb mechanical shocks effectively.

Corrosion Resistance

Stellite 12 is highly resistant to corrosion, especially in high-temperature oxidizing environments, due to its high chromium content. In seawater, Stellite 12 resists pitting and crevice corrosion, making it suitable for marine applications.

High-Temperature Performance

Stellite 12 performs well at temperatures above 1000°C, with optimal performance up to 700°C, essential for power generation and chemical processing.

Wear Resistance

Known for exceptional wear resistance, Stellite 12’s high carbide content protects against abrasive and adhesive wear.

Summary of Key Properties

Key properties include a density of 8.53 g/cm³, a melting range of 1200-1365°C, hardness of 40-51 HRC, optimal high-temperature performance up to 700°C, high wear resistance, and excellent corrosion resistance.

Uses and Applications

Industrial Knives for Cutting Various Materials

Stellite 12 is a popular choice for industrial knives due to its excellent wear resistance and ability to maintain a sharp edge in extreme conditions. These knives are essential in industries such as food processing, paper, and textiles, where they must cut through tough materials without losing performance.

Saw Tips in the Timber Industry

Saw tips made from Stellite 12 are highly valued in the timber industry for their durability and resistance to abrasion and high temperatures. This ensures that saw blades remain effective for longer periods, reducing downtime and maintenance costs associated with frequent replacements.

Control Plates in the Beverage Industry

In the beverage industry, Stellite 12 is used for control plates because of its outstanding corrosion and wear resistance. This is crucial for machinery exposed to acidic liquids, ensuring precision and durability over time.

Pump Vanes, Bearing Bushes, and Narrow-Neck Glass Mold Plungers

Stellite 12 is also used in pump vanes and bearing bushes, where high wear resistance and toughness are essential. Additionally, it’s used in narrow-neck glass mold plungers, which need to withstand high temperatures and abrasive conditions without deforming.

Hardfacing of Engine Valves, Pinch Rollers, and Rotor Blade Edges

Hardfacing engine valves with Stellite 12 extends their lifespan by providing superior wear and corrosion resistance, which is crucial for the automotive and aerospace industries. Pinch rollers in metal-processing also benefit from this alloy’s wear resistance, and it is used on turbine rotor blade edges for its high-temperature and erosion resistance.

High-Temperature Properties

Temperature Stability

Stellite 12 is known for its remarkable temperature stability, retaining its mechanical properties even at high temperatures. This alloy reliably performs at temperatures up to 700°C, and in certain applications, can withstand temperatures beyond 1000°C. This high-temperature stability makes Stellite 12 ideal for environments with significant thermal stress.

Wear Resistance

Stellite 12 stands out for its superior wear resistance, even at high temperatures, thanks to its high carbide content from elements like chromium and tungsten. This makes it ideal for applications with constant friction and wear, like cutting tools and industrial machinery.

Corrosion Resistance

Stellite 12 offers excellent corrosion resistance, particularly in high-temperature environments, due to its high chromium content forming a protective oxide layer. This makes it particularly useful in industries like power generation and chemical processing, where components face corrosive agents at high temperatures.

Hardness and Toughness

Stellite 12 typically has a hardness of 40 to 50 HRC on the Rockwell scale. With a hardness of 40 to 50 HRC on the Rockwell scale, Stellite 12 balances toughness to resist brittle fracture with exceptional wear resistance. The presence of carbon, chromium, and tungsten forms hard carbides, ensuring the alloy maintains its hardness and integrity under thermal stress.

Applications in High-Temperature Environments

Stellite 12 is widely used in various high-temperature applications due to its robust properties, including:

  • Power Generation: Components like turbine blades and vanes, which need to withstand high temperatures and corrosive environments.
  • Chemical Processing: Equipment parts like valve seats and bearings exposed to high temperatures and aggressive chemicals.
  • Metal Processing: Tools and dies that operate at elevated temperatures and require high wear resistance for precision and durability.

Summary of High-Temperature Advantages

Stellite 12’s ability to maintain mechanical properties, resist wear and corrosion, and retain hardness at high temperatures makes it invaluable for demanding industrial applications. These properties ensure components made from Stellite 12 perform reliably, reduce maintenance needs, and enhance the efficiency and longevity of industrial equipment.

Comparison with Other Alloys

Stellite 12 vs. Stellite 6

Stellite 12 and Stellite 6 are cobalt-based alloys with distinct compositions and properties, each suited for different applications.

Composition

  • Stellite 12: Contains higher levels of tungsten (8-10%) and carbon (1.8-2.4%), enhancing its hardness and wear resistance, along with a high chromium content (28-32%) for excellent corrosion resistance.
  • Stellite 6: Has lower tungsten and carbon content, resulting in less hardness and wear resistance but better impact resistance. Its chromium content is slightly lower, providing good but not exceptional corrosion resistance.

Properties

  • Wear Resistance: Stellite 12’s greater carbide content gives it higher wear resistance, ideal for severe abrasive and adhesive wear applications. Stellite 6, while still wear-resistant, is better suited for less extreme conditions.
  • Corrosion Resistance: Both alloys provide good corrosion resistance, but Stellite 12 excels in high-temperature oxidizing environments due to its higher chromium content.
  • Hardness: Stellite 12 typically ranges between 40-50 HRC, while Stellite 6 is usually below 40 HRC. This makes Stellite 12 harder but slightly less tough.
  • High-Temperature Performance: Stellite 12 can maintain its mechanical properties at temperatures exceeding 1000°C, whereas Stellite 6 is less effective at high temperatures due to its lower tungsten content.

Applications

  • Stellite 12: Stellite 12 is used in turbine blades, cutting tools, and valve components where high wear and corrosion resistance are critical.
  • Stellite 6: Preferred for applications requiring good wear resistance with better impact and cavitation resistance, such as pump vanes and bearing bushes.

Stellite 12 vs. Stellite 1

Stellite 12 and Stellite 1 are both designed for high wear resistance, but Stellite 1 offers even higher wear resistance at the expense of toughness.

Composition

  • Stellite 12: Contains 50-60% cobalt, 28-32% chromium, 8-10% tungsten, and 1.8-2.4% carbon.
  • Stellite 1: Features an even higher carbon content, enhancing its wear resistance but making it more brittle. It also contains higher fractions of hard carbides.

Properties

  • Wear Resistance: Stellite 1 exceeds Stellite 12 in wear resistance, suitable for extremely harsh conditions.
  • Corrosion Resistance: Both alloys offer excellent corrosion resistance, but Stellite 12 is more balanced in terms of wear resistance and toughness.
  • Hardness: Stellite 1 is harder, often exceeding 50 HRC, but this increased hardness can lead to brittleness.
  • High-Temperature Performance: Stellite 12 is more versatile in high-temperature applications, maintaining its properties over a broader range of temperatures.

Applications

  • Stellite 12: Stellite 12 is ideal for various industrial applications, including cutting tools, valves, and high-wear components.
  • Stellite 1: Used in specialized applications requiring maximum wear resistance, such as aerospace and power generation components subjected to extreme conditions.

Unique Advantages and Disadvantages

Stellite 12

  • Advantages: Stellite 12 offers a balanced mix of wear resistance, toughness, and high-temperature performance, making it suitable for many applications.
  • Disadvantages: While highly wear-resistant, it is not as tough as Stellite 6 and not as wear-resistant as Stellite 1.

Stellite 6

  • Advantages: Better impact and cavitation resistance, making it suitable for applications involving less severe wear but requiring greater toughness.
  • Disadvantages: Lower hardness and wear resistance compared to Stellite 12, limiting its use in extremely abrasive conditions.

Stellite 1

  • Advantages: Stellite 1’s superior wear resistance makes it ideal for demanding applications.
  • Disadvantages: Increased brittleness due to higher hardness, limiting its use in applications where impact resistance is critical.

Manufacturing and Availability

Forms of Stellite 12

Stellite 12 comes in several forms to meet different industrial needs and manufacturing processes:

  • Rod and Castings: Used for machining custom parts and producing complex shapes and large components that need wear resistance.
  • Electrode: Used in welding to deposit Stellite 12 on other surfaces, improving their properties.
  • Wire: Utilized in welding techniques like Gas Tungsten Arc Welding (GTAW) and Plasma Transferred Arc (PTA) welding.

Standards and Specifications

Stellite 12 adheres to multiple international standards, ensuring high quality and performance across various applications:

  • ASTM B-564 and AMS 5387: Specifications for nickel alloy forgings and cobalt-chromium-tungsten alloys, respectively.
  • AWS A5.21 ERCoCr-A: Specification for welding rods and electrodes made from cobalt alloys.
  • ISO 9001: Ensures consistent quality in manufacturing processes.
  • AS9100: Aerospace industry quality standards.
  • REACH: Compliance for safe use of chemicals in manufacturing.

Suppliers and Availability

Stellite 12 is supplied by various reputable companies worldwide, available in different forms and specifications to meet industry needs:

  • Deloro Stellite and Kennametal: Leading suppliers offering a wide range of Stellite 12 products, including powders, rods, and castings.
  • H.C. Starck: Specializes in high-performance materials, including Stellite alloys.

Manufacturing Processes

Advanced processes ensure the high quality and performance of Stellite 12:

  • Powder Metallurgy and Casting: Producing fine powders for additive manufacturing and creating complex shapes by casting molten Stellite 12.
  • Machining: Using specialized tools to shape Stellite 12 into precise components.
  • Welding and Powder Sizes: Stellite 12 is used in welding to enhance surfaces and is available in various powder sizes for different applications.

Welding and Machining Considerations

Welding

  • Preheating, controlled cooling, and using the GTAW process help prevent issues like cracking and porosity.

Machining

  • Use carbide or diamond-tipped tools, lower cutting speeds, and adequate cooling to manage heat and maintain accuracy.

Stellite 12’s versatility and adherence to strict standards make it a reliable choice for numerous industrial applications, ensuring high performance and durability in demanding environments.

Frequently Asked Questions

Below are answers to some frequently asked questions:

What is the chemical composition of Stellite 12?

Stellite 12 is a cobalt-based alloy with the following chemical composition: Cobalt (Co) 50-60%, Chromium (Cr) 28-32%, Tungsten (W) 8-10%, Carbon (C) 1.8-2.4%, Nickel (Ni) less than 3%, Iron (Fe) less than 3%, and Silicon (Si) less than 2%. This specific composition imparts Stellite 12 with its distinctive properties, such as high wear resistance, excellent high-temperature performance, and superior corrosion resistance.

What are the physical and mechanical properties of Stellite 12?

Stellite 12 is known for its impressive physical and mechanical properties. It has a density of 8.53 g/cm³ and a melting range between 1200-1365°C. Its thermal conductivity is approximately 14.6 W/m·K, and its electrical resistivity is 98 μ-ohm·cm. Mechanically, Stellite 12 exhibits a hardness ranging from 45-51 HRC and 435-590 HV. The tensile strength for castings is about 740 MPa, while HIP-consolidated forms can reach up to 1200 MPa. The yield strength (0.2% offset) for castings is 580 MPa, and for HIP-consolidated forms, it is 900 MPa. Elongation is less than 1% for castings and around 2% for HIP-consolidated forms. Additionally, the elastic modulus is approximately 226 GPa for castings and 208 GPa for HIP-consolidated forms. These properties make Stellite 12 an excellent choice for applications requiring high wear resistance, corrosion resistance, and performance at elevated temperatures.

How does Stellite 12 compare to other Stellite alloys?

Stellite 12 is distinguished from other Stellite alloys primarily by its chemical composition and resulting properties. Compared to Stellite 6, Stellite 12 has a higher hardness and wear resistance due to its increased carbon and tungsten content, making it more suitable for applications involving severe abrasive and adhesive wear. It also maintains excellent mechanical properties at high temperatures up to 700°C, comparable to other Stellite alloys but slightly superior in certain high-temperature environments. Stellite 1, on the other hand, has higher resistance to low-angle erosion and severe sliding wear but may not balance hardness and toughness as effectively as Stellite 12. Overall, Stellite 12 offers a unique combination of wear resistance, high-temperature performance, and balanced hardness, making it ideal for demanding industrial applications such as cutting tools and hardfacing.

What are the typical applications and uses of Stellite 12?

Stellite 12 is primarily used in applications requiring high wear, corrosion, and heat resistance. Typical uses include industrial knives for cutting materials such as carpets, plastics, paper, and synthetic fibers; saw tips in the timber industry; and control plates in the beverage industry. It is also utilized for pump vanes, bearing bushes, and narrow-neck glass mold plungers. In the oil and gas sector, Stellite 12 is used for hardfacing engine valves and other components exposed to abrasive and corrosive environments. Additionally, it finds applications in high-temperature settings like turbine blades and pinch rollers, as well as in marine environments for parts like propellers and pump shafts.

How resistant is Stellite 12 to wear, corrosion, and high temperatures?

Stellite 12 is highly resistant to wear, corrosion, and high temperatures due to its specific chemical composition. The high content of chromium and tungsten forms hard carbides that significantly enhance its wear resistance, making it suitable for applications that experience heavy abrasion and adhesion. Its hardness ranges from 40-51 HRC, contributing to its durability in high-wear environments.

In terms of corrosion resistance, Stellite 12 performs exceptionally well, particularly in oxidizing environments. The chromium in the alloy forms a protective oxide layer that prevents extensive corrosion, making it effective in seawater and chloride solutions where it primarily corrodes by pitting rather than uniform mass loss.

Regarding high-temperature performance, Stellite 12 can maintain its mechanical properties even at temperatures exceeding 1000°C. This stability is due to the cobalt and chromium content, which ensures that the alloy retains its hardness and wear resistance at elevated temperatures. Consequently, Stellite 12 is ideal for use in high-temperature applications such as engine valves and turbine components.

Can Stellite 12 be used in extreme environments?

Yes, Stellite 12 can be used in extreme environments. Its composition, primarily consisting of cobalt, chromium, and tungsten, provides exceptional wear resistance, high-temperature stability up to approximately 1000°C, and excellent corrosion resistance. These properties make Stellite 12 ideal for demanding applications such as industrial knives, saw tips, valves, pump vanes, and components in power generation and chemical processing industries. Its ability to maintain performance in harsh conditions, including high wear, high temperatures, and corrosive environments, underscores its suitability for extreme applications.

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