The Cobalt Family of Alloys
The family of cobalt based alloys was mostly invented by the Haynes Corp. The alloys have been tweaked through the years to suit specific purposes. The alloys are unusual in that they do not gall, they have a very low coefficient of friction, and do not lose strength until above 1100F. They are generally corrosive resistant down to a 3 PH. The nickel content has been increased in certain members of the family to increase corrosion resistance. The trademark name of “Stellite” has been sold various times and at this writing belongs to Kennametal as a registered name. The family of alloys also has ASTM or AMS specifications that cover each one. Geronimo Alloys produces the alloys under the ASTM or AMS specification and does not purchase the alloys from Kennametal or use their registered trademark name of “Stellite”.
The cobalt based alloys have a wide use in a multitude of industries to control abrasion that is exacerbated by corrosion and/or temperature. The price of these alloys is not cheap. The price for the alloy itself is almost solely determined by the market price of Cobalt. We have seen this price range from $4.00 per pound to $80.00 per pound. The other contributing cost factor is the increased forming cost. The alloys are generally very difficult to machine rapidly. Even though the cost of the part may be several 100% higher than common steel, the extended wear life may actually make the operational cost substantially less than the steel part. The alloy is often used as an overlay or cladding material. Geronimo applies them with our robotic PTA process or with TIG, MIG, or laser, whichever is the more economical or practical. Although cladding or overlay is much more economical than casting, castings have a 35% better wear life than a cladding. The tendency of the cobalt alloys to break or crack prevents the use of solid parts in many cases.
The ASTM or AMS specification for the abrasive resistant cobalt alloys does not carry a hardness requirement. There is no heat treatment requirement except for stress relieving. The reason for this is that this alloy is not changed by heat treatment. None of the properties can be changed once the alloy has solidified. These alloys, cobalt 1, cobalt 3, cobalt 4, cobalt 12, and cobalt 6, etc. get their wear resistance at the instant the alloy goes from liquid to solid in the casting process. Hardness is determined by the quantity and size of the carbides formed in the transition phase from liquid to solid. The elements of the alloy combine to produce carbides. These elements are iron, silicon, tungsten, and chromium. They combine with the carbon to form carbides. The problem is that these carbides are form in an extremely short period of time. The time is determined by the thickness of the cross section of the piece. A thicker cross section will always be softer than a thinner cross section. What happens in the transition is that the number of carbides is reduced, but the individual size of the carbides grows. The inter-granular space between carbides become larger and the hardness decreases. The carbides may become so large that the carbides are pulled out of the matrix in the finishing process. The carbides should be in the single digit thousands of an inch. We have experience carbides that measure more than .050 of an inch. Geronimo molds and pours all cobalt alloys in a manner that colds the casting as quickly as possible. The cobalt is simply the matrix that holds the carbides together. Cobalt as a matrix provides some very advantageous qualities to the alloys. The coefficient of friction is very low and the alloy does not gall. Geronimo has built bearings where the outer and inner halves run against each other. An example of the effects of the lower coefficient of friction is a pump that was originally of cast iron. The company was pumping chromium sand slurry. We replaced the pump with a cobalt based alloy to solve a wear problem. An unintended consequence was that the pump put out 15% more volume at the same speed because of the lower coefficient of friction. The lower coefficient of friction make abrasive particle slide off the alloy rather than digging in to the alloy. Geronimo has run numerous tests on wear life between the cobalt based wear resistance alloys and the nickel based alloys. In almost all application the cobalt alloys have a substantially longer life. The nickel based alloys must be “worked” hard enough to continually work harden to have any wear life. Another problem with the nickel based alloys is that they contain boron to get the hardness. Boron is a very contaminating element in a foundry.
The biggest problem with the cobalt based wear resistant alloys is their tendency to break. The more wear resistant the alloy, the higher the tendency for it to break. In the “as cast” condition, these alloys have no difference in the yield and tensile strengths. Hot working will provide some difference in the tensile and yield. Care should be taken in choosing the correct alloy so as to avoid breakage from thermal or physical shock. Geronimo’s 30+ years of experience can seriously help in this choice.
When it comes to specific needs, Geronimo Alloys is always ready to deliver. Understanding that their clients are number one and their lifeblood when it comes to business revenues, Geronimo Alloys are more than just appreciative of the business of their customers. Even more, their clients are seen as key team members in the development of the project for which they have contracted Geronimo Alloys.
Anyone in the manufacturing industry knows that being able to create the most precise materials and items is of the greatest value and necessity for each of their clients. While each customer has unique needs that they are seeking to fulfill, it is the background and experience of the professional staff of Geronimo Alloys that makes the difference through quality workmanship and attention to the most minute details. It is no wonder that they have clients in a variety of industries, including such diverse areas as food production, petrochemicals, die casting, steel mill, synthetic polymer production, and injection molding.
Since 1983, Geronimo Alloys has remained dedicated to serving the needs and desires of their clients. With a 35,000 square foot facility in Seguin, Texas, which was custom designed at the time of construction, they are ideally suited and prepared to meet the demands of any customers, from the smallest to the largest project. They are ready and willing to work 365 days out of the year and 24 hours per day, whenever necessary. In fact, they recently skipped a Super Bowl event in order to deliver the goods to one of their clients. Their philosophy is that whatever it takes to get the job done, they will do it.
This is perhaps one of the reasons that in 2014, there was not one customer return, and in 2013, only $300 in returns was requested. It is obvious that such a company is committed to meeting the needs of their clients. Whether the client needs parts built using cobalt alloys, or other materials, Geronimo Alloys will acquire the best quality raw materials in order to deliver quality products for their clients.