Stellite 398671 226014332 2008-07-16T13:16:41Z Wizard191 935746 rmv horse note '''Stellite''' alloy is a range of [[cobalt]]-[[chromium]] [[alloy]]s designed for [[wear]] resistance. It may also contain [[tungsten]] and a small but important amount of [[carbon]]. It is a [[trademark]]ed [[name]] of the Deloro Stellite Company and was invented by [[Elwood Haynes]]<ref>[http://www.wpi.edu/News/Conf/Roundtable/Barcelona/alumni.html "The WPI International Corporate Leaders Roundtable: The Impact of Evolving Technologies on the Future of Business: Notable Achievements of Alumni of Worcester Polytechnic Institute"]. Elwood Haynes, Class of 1881.</ref> in the early 1900s as a substitute for [[flatware]] that stained (or that had to be constantly cleaned). ==Properties== Stellite alloy is a completely [[magnetism|non-magnetic]] and [[corrosion|non-corrosive]] cobalt alloy. There are a number of Stellite alloys, with various compositions optimised for different uses. Information is available from the manufacturer, Deloro Stellite, outlining the composition of a number of Stellite alloys and their intended applications. The alloy currently most suited for cutting tools, for example, is Stellite 100, because this alloy is quite hard, maintains a good cutting edge even at high temperature, and resists [[Hardening (metallurgy)|hardening]] and [[Annealing (metallurgy)|annealing]] due to heat. Other alloys are formulated to maximize combinations of [[wear resistance]], corrosion resistance, or ability to withstand extreme temperatures. Stellite alloys display astounding [[Hardness (materials science)|hardness]] and [[toughness]], and are also usually very resistant to corrosion. Stellite alloys are so hard that they are very difficult to [[machining|machine]], and anything made from them is, as a result, very expensive. Typically a Stellite part will be very precisely [[casting|cast]] so that only minimal machining will be necessary. Machining of Stellite is more often done by [[grinding machine|grinding]], rather than by cutting. Stellite alloys also tend to have extremely high [[melting point]]s due to the cobalt and chromium content. ==Applications== Typical applications include [[saw]] [[Tooth|teeth]], [[hardfacing]], and [[acid]]-resistant machine parts. Stellite was a major improvement in the production of [[poppet valve]]s and [[valve seat]]s in [[internal combustion engine]]s; by reducing wear in them, the competing slide-valve design was driven from the market. The first third of [[M60 machine gun|M60]] [[machine gun]] [[Barrel (firearms)|barrels]] (starting from the [[Chamber (weaponry)|chamber]]) are lined with Stellite. In the early 1980s, experiments were done in the [[United Kingdom]] to make artificial [[Hip (anatomy)|hip joints]] and other [[Replacement joint|bone replacements]] out of precision-cast Stellite alloys. Stellite has also been used in the manufacture of [[tool bit|turning tools]] for [[Lathe (metal)|lathes]]. With the introduction and improvements in [[tipped tool]]s it is not used as often any more, but it was found to have superior cutting properties compared to the early [[carbon steel]] tools and even some [[high speed steel|high speed steel tools]], especially against difficult materials such as [[stainless steel]]. Care was needed in grinding the blanks and these were marked at one end to show the correct orientation, without which the cutting edge could chip prematurely. While Stellite remains the material of choice for certain internal parts in industrial process valves (valve seat hardfacing), its use has been discouraged in [[Nuclear power|nuclear power plants]]. In piping that can communicate with the reactor, tiny amounts of Stellite would be released into the process fluid and eventually enter the reactor. There the cobalt would be activated by the [[neutron flux]] in the reactor and become cobalt-60, a [[Radionuclide|radioisotope]] with a five year [[half life]] that releases very energetic [[gamma ray]]s. While not a hazard to the general public, about a third to a half of nuclear worker exposures could be traced to the use of Stellite and to trace amounts of cobalt in stainless steels. Replacements for Stellite have been developed by the industry, such as the [[Electric Power Research Institute]]’s “NOREM”, that provide acceptable performance without cobalt. Since the United States nuclear power industry has begun to replace the Stellite valve seat hardfacing in the late 1970s and to tighten specifications of cobalt in stainless steels, worker exposures due to cobalt-60 have dropped significantly. ==Varieties== '''Talonite''' is an alloy similar to Stellite which has been hot-rolled and hardened in a particular way, to provide a combination of hardness, wear resistance and [[Machining|machinability]]. Not all Stellite alloys respond to this process. ==Notes== {{reflist}} ==External links== * [http://www.armstrongblue.com/Publications/msds__stellite_tips.htm Material Safety Data Sheet for stellite], includes table of compositions of individual variants *[http://www.stellite.com Deloro Stellite company website] [[Category:Cobalt alloys]] [[de:Stellite]] [[it:Stellite]] [[ja:ステライト]] [[pl:Stellite]] [[pt:Estelite]] [[ru:Стеллит]] [[fi:Stelliitti]]