When it comes to materials that excel in extreme environments, Stellite™ alloys stand out among some of the most reliable and durable options available. Kennametal Stellite provides reliable, proven, precision-engineered wear protection material solutions that people have trusted for more than 100 years. In this blog, we'll explore the key aspects of Stellite alloys, how they differ from other materials and why they are so effective in challenging environments.
Stellite 101: Understanding Wear Resistance, Corrosion and High-Temperature Alloys
What Are Kennametal Stellite™ Alloys?
Kennametal Stellite is a family of cobalt-based alloys known for their exceptional resistance to wear, corrosion, and high temperatures, making them suitable for harsh conditions. The key ingredient in Stellite alloys is cobalt (Co), which forms the base metal matrix. This is alloyed with other elements like chromium (Cr), tungsten (W), molybdenum (Mo), nickel (Ni), and others to enhance the material’s performance. Kennametal Stellite alloys come in a variety of compositions, each tailored to specific applications.
They can be broadly categorized based on their intended use: wear-resistant, high-temperature, and corrosion-resistant.
Breaking Stellite Alloys Down to its Composition
1. Wear-Resistant Kennametal Stellite Alloys: These alloys are designed to handle mechanical wear and abrasion. Their chemical composition generally includes:
Common Alloys: Stellite 1, Stellite 3, Stellite 6, Stellite 12 and Stellite 20
2. High-Temperature Kennametal Stellite Alloys: These alloys are formulated to perform under extreme heat, retaining their hardness and strength even at elevated temperatures. Their composition typically includes:
Common Alloys: Stellite 21, Stellite 25, Stellite 31, Stellite 188, Stellite 250
3. Corrosion-Resistant Kennametal Stellite Alloys: These alloys are engineered to withstand harsh, corrosive environments. Their composition typically features:
Common Alloys: Stellite 21, Stellite 209 and Stellite 306
Exploring the Key Factors Behind Kennametal Stellite’s Exceptional Performance
What makes Stellite alloys so effective in extreme environments? The answer lies in their unique crystalline structure and the synergy between their alloying elements.
- Cobalt Matrix: The cobalt in Stellite alloys is primarily responsible for the material’s ability to withstand high temperatures. Cobalt exists in two crystal structures: face-centered cubic (FCC) and hexagonal close-packed (HCP). At room temperature, cobalt typically adopts the FCC structure, which provides a good balance of strength and ductility. At elevated temperatures, the material can transition to the HCP phase, which absorbs energy and helps reduce wear and damage.
- Carbide Formation: The hard carbide phase in Stellite alloys, formed by elements like tungsten, molybdenum and chromium, enhances the alloy’s wear resistance. These carbides are stable at high temperatures and help maintain the alloy’s hardness even under harsh conditions. This carbide formation is one of the primary reasons Stellite alloys excel in resisting abrasive wear.
- Chromium for Corrosion Resistance: The high chromium content in many Stellite alloys contributes to their excellent oxidation and corrosion resistance. Chromium forms a protective oxide layer on the surface of the alloy, shielding it from corrosive agents. Additionally, cobalt alloys have superior sulfidation resistance compared to nickel-based alloys, thanks to the higher melting point of cobalt sulfides and their lower sulfur diffusivity.
- Solid Solution Strengthening: Stellite alloys are also strengthened through solid solution strengthening, where elements like tungsten and molybdenum are dissolved into the cobalt matrix. This increases the material’s hardness and resistance to wear, making it particularly suitable for high-stress environments.
Stellite Outperforms Other Materials in Wear, Corrosion and High Temperatures
While there are other alloys that can resist wear, high temperatures, or corrosion, Kennametal Stellite alloys combine all three properties in a way that most other materials cannot. For instance, stainless steel may be effective in corrosion-resistant environments but falls short in wear-resistance. Nickel-based alloys are excellent at high temperatures but do not offer the same level of wear resistance as Stellite. White cast iron can resist abrasive wear but is not suitable for high-temperature or corrosive applications. Kennametal Stellite alloys outperform many other materials when at least two of these three factors—wear, corrosion, and high temperatures—are involved.
Meeting the Demands of Extreme Environments with Advancements in Stellite Alloys
Stellite alloys have evolved to meet the growing demands of various industries, with recent advancements like the Stellite 700 series and SF alloys. Kennametal Stellite continues to innovate, collaborating with customers to create tailored solutions for specific wear, corrosion and high-temperature challenges.
Proven as a cornerstone material, Stellite excels in extreme wear, high-temperature, and corrosive environments. Its unique composition makes it ideal where other alloys fall short, delivering reliable results for high-performance applications.