STELLITE® alloy 1

STELLITE-Alloy1

Introduction to Stellite Alloys

Stellite alloys are a group of cobalt-chromium ‘super-alloys’ consisting of complex carbides in an alloy matrix predominantly designed for high wear resistance and superior chemical and corrosion performance in hostile environments. The combination of Cobalt and Chromium also results in an extremely high melting point making them perfect for a range of intriguing applications from extreme cutting tools to hot section alloy coatings in gas turbines. They may also contain molybdenum or tungsten and a small amount of carbon to offer even greater performance for specific applications.

The Stellite range of alloys were first developed by Elwood Haynes in the early 1900s as an alternative for cutlery that was susceptible to staining. Stellite is a trademarked name of the Deloro Stellite Company, now part of the Kennametal group.

Stellite alloys are non-magnetic and typically associated with high corrosion resistance and as with many alloys, they are adaptable and can be refined for a range of specific applications. Due to their incredibly hard material properties, Stellite alloys are inherently difficult and often expensive to machine therefore some very precise casting and grinding machining methods are often employed.

The carbides present in the Co-Cr-W-based stellite alloys are of chromium-rich M7C3 type. The trademark owners of Stellite claim that Stellite 6 is the most widely used of their range of Stellite alloys, offering a proven industry standard for general-purpose wear resistance, and high mechanical and chemical perfromance in hostile environments.

Typical Chemical Properties of Stellite Alloys

There are several types and variations of stellite superalloys containing varying levels of: titanium, silicon, sulfur, phosphorus, molybdenum, manganese, chromium, carbon, boron, aluminium, iron, nickel and cobalt in different quantities. Most of the stellite alloys contain four to six of these elements. The Carbon content (and hence carbide volume) of a Stellite alloy is incredibly influential on the materials performance. Therefore, it is possible to group Stellite alloys as follows:

High carbon – designed for high wear applications
Low carbon – for high temperature uses
Low carbon / higher Chromium to combat corrosion

Chromium is also an extremely important component of Stellite alloys, not only does it offer its high corrosion resistant properties to the alloy but it is also the predominant carbide former and it provides strength (as a solute) in the alloying matrix.

Typical Chemical composition of stellite 1:

ElementsContent
Cobalt, Co57%
Chromium, Cr28 – 32%
Tungsten, W11 – 13%
Carbon, C2 – 3 %
Silicon, Si1.20%
Iron, Fe1%
Nickel, Ni1%
Other1.50%

Mechanical Properties of Stellite 1 Alloy

The mechanical properties of stellite 1 are displayed in the table below:

PropertiesMetricImperial
Density8.69 g/cm30.314 lb/in3
Hardness, Rockwell C50-5850-58
Tensile strength1195 MPa173 ksi
Yield strength1050 MPa152 ksi
Modulus of elasticity230 GPa33.4×106 psi
Elongation at break<1%<1%

Manufacturing Processes of Stellite Alloys

Stellite alloys are produced by a range of different processes or methods including wrought or hot forging, hardfaced deposit, powder metal and casting depending on teh final appication.  Stellite is more difficult to machine and grind than steel, and hence requires high performance processing equipment and specialized machining tools. Due to its incredible toughness Stellite is often machined by grinding rather than cutting.

Currently Stellite base material is rolled into bar, sheet and plate forms. During forming, the size and orientation of the matrix in the alloy is optimized, so that the material achieves higher strength than traditional cast material. The alloy is then cut into blanks of different sizes, which are then processed into finished parts.

Stellite Alloy Applications

Some of the major applications of stellite include the following:

Saw teeth, hardfacing, and acid-resistant machine parts
Poppet valves, valve seats and exhaust valves of internal combustion engine
M2HB machine gun and machine gun barrels
Medical applications including manufacturing of artificial hip joints, other bone replacements and cast structure of dental prosthesis
Turning tools for lathes

Reviewed by Nick Gilbert

References

Alloy Compositions and Product Forms – Google Books
Stellite 1 Alloy – Kennametal Stellite
Temperature-Dependence of Hardness and Wear Resistance of Stellite Alloys – S. Kapoor, R. Liu, X. J. Wu, M. X. Yao