Stellite 4 is a cobalt-chromium-tungsten-carbon hardfacing alloy from the Stellite family, developed by Haynes/Kennametal Stellite for applications that demand greater wear resistance than the industry-standard Stellite 6 while still tolerating only moderate mechanical shock. It carries a nominal chemistry of 30% chromium, 14% tungsten and 1% carbon in a cobalt matrix, with small residual additions of manganese, iron, silicon and nickel. The higher tungsten and carbon content compared to Stellite 6 increases the volume of hard chromium/tungsten carbides in the microstructure, which is what drives its superior wear resistance and its extremely good high-temperature strength.

Stellite 4 also exhibits very good galling resistance at both room and elevated temperature and a notably low coefficient of friction when run against itself or against hard steels. This combination of properties makes it a common choice for hot-work tooling: dies, hot-pressing and hot-extrusion tooling for copper- and aluminum-base alloys, as well as bushings and sleeves used in zinc-aluminum hot-dip galvanizing lines. It also sees service in pumps handling corrosive or erosive media. It is registered under UNS R30404 and is typically supplied as castings or powder for hardfacing deposition.

Stellite 4 sits toward the difficult end of the cobalt-base hardfacing group. Its dense population of chromium and tungsten carbides - the same phases responsible for its wear resistance in service - are highly abrasive to cutting edges, producing rapid flank and notch wear even at conservative cutting speeds. Because it is a cast, work-hardening alloy, any rubbing or hesitation at the cutting edge (light finishing passes, dull tools, interrupted cuts) generates a hardened surface skin that is markedly tougher to cut than the bulk material, so maintaining a consistent, adequate chip load throughout the cut is essential.

The alloy's low thermal conductivity concentrates cutting heat at the tool-chip interface rather than carrying it away in the chip, accelerating crater wear on carbide tooling. Its retained strength and hardness at elevated temperature - the same trait that makes it useful in hot-work dies - means there is no useful softening effect to lean on at higher cutting speeds the way there is with steel. Rigid setups, sharp positive-rake geometries, very hard PVD/CVD-coated carbide substrates, and constant generous coolant are the standard countermeasures; CBN inserts are worth considering where cutting speed needs to be pushed well beyond what carbide can sustain.