Tungsten grades / Tungsten heavy alloy W-Ni-Fe

Tungsten Heavy Alloy, W-Ni-Fe

The grade most shops mean when a buyer just says "machined tungsten." Tungsten held in a nickel-iron binder, ordered to ASTM B777.

W-Ni-Fe heavy alloy is 90 to 97% tungsten by weight, bound with nickel and iron. The binder is what makes the material practical to machine: it turns a brittle refractory metal into something that shears cleanly under a cutting edge. Mills supply it against ASTM B777, which sets four classes by tungsten content and density plus minimum mechanical properties.

Property	Typical value
Density	17.0 to 18.5 g/cm³ (ASTM B777 Class 1 to 4)
Hardness	Roughly low 20s to low 30s HRC, typical
Magnetic behavior	Mildly magnetic (iron binder)
Typical tolerance	±0.01 to ±0.025 mm, tighter by grinding

Typical density

W-Ni-Fe heavy alloy runs 17.0 to 18.5 g/cm³, typical, depending on the ASTM B777 class and the mill's exact composition. That is roughly 50 to 60% denser than lead, which is why it is the usual upgrade from lead in shielding parts where space is tight.

Hardness

Heavy alloy typically falls in the low to mid 20s to low 30s HRC range as sintered and machined. It is not heat treated the way tool steel is; its hardness comes from the sintered tungsten-nickel-iron microstructure rather than a quench-and-temper process, so the hardness you get is close to what the material ships with. That sits well above untreated structural steel but well below hardened tool steel or tungsten carbide, which is why heavy alloy is chosen for density and toughness first, with moderate wear resistance as a secondary property rather than the main reason to specify it.

Magnetic or non-magnetic

Standard W-Ni-Fe heavy alloy carries mild magnetism from its iron content. For most applications this is irrelevant. If your part sits near MRI equipment, magnetic sensors or anything sensitive to stray fields, specify the W-Ni-Cu binder instead; a mill defaults to W-Ni-Fe unless told otherwise.

How it machines

Heavy alloy machines much like hard gray cast iron rather than like a difficult exotic metal. It turns, mills, drills and taps on standard CNC equipment with carbide tooling. What actually changes versus cutting steel is tool wear (the tungsten grains are abrasive, so inserts wear faster), part weight (over twice the same shape in steel, which affects workholding and fixture design) and chip handling (heavy alloy chips have scrap value and are usually collected separately). None of this needs an exotic machine, but it does need a shop that has run the material before.

Typical achievable tolerance

±0.01 to ±0.025 mm is common on turned and milled features, typical. Bores, threads and O-ring grooves are routine at these tolerances. A face or bore that needs to be tighter is usually finished by grinding after the main machining operations.

ASTM B777 classes

B777 defines four classes by minimum tungsten content and a corresponding density range, plus minimum tensile strength, yield strength and elongation. Class 1 sits at the lower end of the heavy alloy density range, around 17.0 g/cm³, and Class 4 sits at the highest, around 18.5 g/cm³, with Class 2 and Class 3 in between. Higher classes carry more tungsten and higher density, sometimes with a small tradeoff in ductility. All four classes machine in broadly the same way, closer to hard cast iron than to a difficult exotic metal; small differences in binder ratio between classes can shift tool wear and finish slightly, but a shop plans its tooling around heavy alloy versus pure tungsten first, not around the specific class.

Typical applications

Radiation shielding: collimators, shielding inserts and source containers in medical imaging and industrial radiography
Aerospace balance and counterweights for control surfaces and rotating assemblies
Oil and gas sinker bars and downhole logging weights
Motorsport and ballast counterweights where mass in a fixed envelope matters
Anti-vibration tooling, such as boring bar bodies, where mass damps chatter

Sources

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