Stellite 3 is a high-carbon cast cobalt-chromium-tungsten alloy and one of the oldest, hardest members of the numbered Stellite family (UNS R30001 / R30103). Its nominal chemistry - roughly 30.5% chromium, 12.5% tungsten, and 2.3% carbon, cobalt balance - places it among the most carbide-dense grades Kennametal currently publishes, alongside Stellite 1 and Stellite 20. That high carbon and tungsten content builds a dense chromium/tungsten carbide network that gives Stellite 3 excellent abrasion and solid-particle erosion resistance and strong metal-to-metal wear resistance, including good galling resistance when mated with other Stellite alloys.

The trade-off for that wear performance is brittleness: Kennametal's own technical data describes Stellite 3 as "nearly impossible to hardface crack-free" and notes it "withstands very little impact." Hardness runs 48-63 HRC depending on processing, among the highest of the standard numbered grades, with a comparatively modest tensile strength of about 551 MPa reflecting that low ductility/toughness.

No AMS specification is published for Stellite 3 in Kennametal's current data sheet. Given its extreme hardness and crack sensitivity, Stellite 3 is normally applied as a hardfacing overlay or investment casting for severe abrasion/erosion service - valve trim, wear plates, and similar components - rather than produced as machinable wrought stock.

Stellite 3 is one of the most difficult Stellite grades to machine by conventional cutting, driven primarily by its carbide volume fraction rather than bulk hardness alone. At 2.3% carbon and 12.5% tungsten, the alloy's microstructure is dominated by a dense network of hard chromium/tungsten carbides in the cobalt matrix - carbides that behave as an embedded abrasive against any cutting edge, driving rapid, often unpredictable flank wear.

Like other cobalt-base alloys, Stellite 3 has low thermal conductivity that concentrates cutting heat at the tool edge, and it retains hardness at elevated temperature rather than softening the way many steels do at higher speed. At 48-63 HRC bulk hardness - among the highest of any material covered in this library - the cutting edge is under continuous, severe mechanical load throughout the cut, and the alloy's low toughness (Kennametal notes it is "nearly impossible to hardface crack-free" and withstands very little impact) means both the workpiece and the tool edge are prone to chipping under interrupted or shock loading.

Because of this combination, Stellite 3 is frequently finished by grinding in production rather than by turning or milling. Where cutting is required, extremely conservative speeds, sharp positive-rake ground carbide edges, maximum rigidity to avoid any impact loading, and continuous flood coolant are essential; tool life will generally run shorter and less predictable than on any other alloy in this library's Stellite/Haynes-Stellite group.