The invention of alloys has paved the way for stronger, more durable substances that can withstand the harshest environments. Just like steel alloys rely on the best components of iron and carbon, Stellite coatings merge the beneficial properties of cobalt, chromium, tungsten and sometimes carbon to serve up superior wear, corrosion, and heat resistant surfaces. Stellite coatings can be found everywhere from hardfacing parts to valve seats. Industries like manufacturing, processing, and oil and gas select these coatings to help combat extreme heat, oxidation, and erosion. While Stellite coatings offer many advantages, it’s important to consider the specific requirements of each application to determine whether this cobalt-chromium alloy is the best fit.

What is Stellite Coating?

There are many different types of Stellite coatings. One of the most popular and widely used is Stellite 6. Like other Stellites, Stellite 6 is a cobalt-based alloy. The composition of this particular coating tends to be as follows: 27–32% chrome, 4–6% tungsten, 1–2% carbon, 3–4% nickel, 1–2% silicon, and 3–4% iron. Due to the unique nature of its alloying, Stellite 6 has incredible hardness and wear resistance, with hardness values ranging from 36–45 HRC on the Rockwell scale and 380–490 HV on the Vickers scale. This alloy can be applied via traditional welding, PTA, laser clad, or HVOF thermal spray processes. 

Is Stellite 6 Coating Right for My Project?

Stellite coatings can be utilized in both powder and wire form and are widely used for valve seats, poppet valves, pump shafts, turbine blades, and tools subjected to severe abrasion or corrosion. Due to Stellite 6’s hardness, it remains a strong option for parts or components needing protection from mechanical and chemical degradation over a wide temperature range. Other components that can benefit from Stellite 6’s exceptional wear, scratch, and abrasion resistance include impellers, saw teeth, and bearings.

How to Apply Stellite 6 Coating

This durable coating offers the advantage of multiple application processes. Generally, Stellite 6 can be applied through a welding process such as PTA or via HVOF thermal spray. Many times, HVOF Stellite 6 coatings are selected due to the fact that their application process will not change the properties of the base metal, which can occur during welding. Stellite 6 applied through HVOF can prevent distortion due to temperature change; however, the end product will be more brittle. The welded form of Stellite 6 is common in valves due to the metallurgical bond, which allows it to absorb impact from the seating of the valve without cracking.

Pros and Cons of Stellite 6 Coating

When determining whether to use Stellite 6, make sure you know the positives and negatives of this ultra-tough alloy. Industries ranging from mining to aerospace reach for Stellite 6 to repair and refurbish components due to the following properties:

• Extreme Hardness: Owing to its carbide structure, Stellite 6 can retain hardness up to 932° F (500° C) and can be a superior alternative to both stainless steel or electroless nickel plating.

• Excellent Corrosion Resistance: Stellite 6’s hardness allows for a coating that can resist corrosion and oxidation even at extreme temperatures. Its electrical resistivity also makes it a suitable choice for environments such as power or mineral processing plants.

• Low Porosity: Stellite 6 coatings create an effective barrier that prevents water, chemicals, and salts from seeping in, helping to avoid corrosion, surface breakdown, and premature part failure.

• High Bond Strength: Industrial equipment is often subject to vibrations, extreme temperature fluctuations, and cyclic stresses. When applied via thermal spray, Stellite 6 provides unparalleled bond strength and ensures valves, pumps, and turbines are able to carry their intended load. 

• Diverse Applications: Every industry and part requires specific coating needs, Stellite 6 offers the advantage of being able to be applied via traditional welding or through more advanced techniques such as HVOF or laser cladding. For example, hydroelectric power plants depend on Stellite 6 and HVOF application to protect turbine runners from routine cavitation.

• Nonmagnetism: Another positive attribute of Stellite 6’s cobalt structure is its nonmagnetism, which makes it a desirable choice for nonmagnetic applications needed in chemical processing, aerospace, or even pharmaceutical manufacturing. 

However, Stellite 6 may not be a suitable option for all parts. Disadvantages of choosing this coating can include:

• High Upfront Cost: Since Stellite 6 is a specialized alloy, the initial cost of the material and application process can be high. Nonetheless, this cost can be amortized over time thanks to its ability to extend component life, reduce downtime, and increase reliability.

• Requires Precise Grinding: As a result of its extreme hardness, both the grinding and machining of Stellite can be difficult and requires precision. 

• Diminished Ductility: The integral strength and hardness of Stellite 6 means it can exhibit less ductility, and its performance might be sub-optimal when faced with high-impact or extreme shock loading conditions.

• Risk of Cracking & Thermal Distortion: If applied through traditional welding methods, Stellite 6 is at risk for brittleness, cracking, and distortion or damage to the underlying base material. 

HTS Coatings has a long history of leveraging the standout properties of Stellite 6 for our clients. Whether we are coating components to be acid resistant or extending the service life of a gate valve, we’ve found that Stellite 6 coatings combine the best of both metallurgical and mechanical properties. As a result, Stellite 6 forges a formidable shield against surface attacks and other damage. 

Interested in learning more about our Stellite 6 capabilities or application methods? Contact us today to see how we work wonders with this exceptional cobalt-based alloy.