Ferro tungsten density is one of the few properties of the alloy that can be predicted with confidence before a single heat is melted, because it follows directly from the proportions of the two metals it contains. The figure matters commercially as well as technically: density drives settling and dissolution behaviour in the steelmaking ladle, and it is the reason the alloy appears in ballast weights, gyro rotors and radiation shielding. This article gives the working values, shows how they are calculated, and explains what shifts a measured density away from the calculated one.
What Ferro Tungsten Consists Of
Ferro tungsten is a master alloy of tungsten and iron used to introduce tungsten into steel and cast iron. Commercial material is made by carbothermic reduction of tungsten ore concentrate in an electric furnace, with iron-bearing material charged so that the reduced tungsten dissolves in liquid iron rather than being produced as a pure metal. The result is a dense, brittle alloy that solidifies as a mixture of intermetallic phases, principally the FeW and Fe2W compounds, together with a limited amount of iron-rich matrix.
Main element: tungsten, typically 70 to 85 percent by mass in commercial grades.
Balance: iron, with small and controlled amounts of carbon, silicon, phosphorus and sulphur.
Product forms: cast lump, crushed and screened fractions, and fine powder for cored wire and briquette production.
Melting behaviour: the alloy melts over a range rather than at a single point, because the phases present differ in composition.
Typical Density Values by Grade
Because the alloy is a mixture, its density lies between the density of pure tungsten, about 19.25 g/cm³, and the density of pure iron, about 7.87 g/cm³. The mixture rule for density is not a simple weighted average of the two figures, since what is conserved is volume rather than density:
1 / ρalloy = (w(W) / ρ(W)) + (w(Fe) / ρ(Fe)), where w denotes mass fraction.
| Grade | Tungsten content | Calculated density (g/cm³) |
|---|---|---|
| FeW70 | 70 percent | 13.43 |
| FeW75 | 75 percent | 14.14 |
| FeW80 | 80 percent | 14.93 |
| FeW85 | 85 percent | 15.82 |
Calculated values therefore rise from about 13.4 to about 15.8 g/cm³ across the commercial range. Solid commercial material in the usual FeW75 to FeW80 window is normally quoted at approximately 14.0 to 15.5 g/cm³, with the calculated figure representing a pore-free alloy of exactly the stated composition. For context, plain carbon and low alloy steel sits at 7.75 to 8.05 g/cm³ and lead at about 11.34 g/cm³, so a tungsten-bearing master alloy is roughly 1.8 times as dense as steel and noticeably denser than lead.
Factors That Shift the Measured Density
A laboratory figure taken from a delivered lot rarely matches the calculated value exactly. The differences are explainable, and each one points to a property worth specifying in the purchase order:
Tungsten to iron ratio: the dominant factor. Every additional percentage point of tungsten raises the density of the alloy.
Carbon content: carbon additions lower density slightly, both because carbon is light and because carbon changes the proportion of the phases present.
Residual elements: molybdenum and other heavy residuals can substitute for tungsten and shift the result in either direction, so grades are bought against a chemistry specification rather than a nominal name.
Porosity and shrinkage: cast ingots and lumps contain voids, so a measured piece density can fall below the calculated value even when the chemistry is correct.
Entrapped slag and non-metallic inclusions: lighter than the alloy, these lower the average density and also reduce tungsten recovery in the ladle.
Bulk density of crushed lots: when the product is crushed and screened, the mass per poured volume of the packed bed is always lower than the solid density of the particles, and it depends on the size distribution and particle shape rather than on chemistry.
For that last reason a density figure is meaningless unless the basis is stated. Buyers should require that the certificate distinguishes solid particle density from bulk density, and should fix the size fraction at the same time, because a fine fraction and a coarse fraction of identical chemistry will not behave the same way in the melt.
Why Density Matters in Practice
In the steelmaking ladle and in the furnace, high density is an operational advantage. A dense addition penetrates the slag layer, reaches the liquid metal quickly and dissolves there, whereas a light addition can float, oxidise at the surface and be lost to the slag. This is why tungsten is charged as ferro tungsten rather than as oxide or as a fine powder, and why sizing is matched to the practice: lump for furnace charging, fine fractions for cored wire where a controlled addition rate is needed.
Outside the melting shop, the density of the alloy is the reason it is selected at all:
Ballast and counterweights: the highest mass in the smallest volume, for aircraft control surfaces, lift and crane counterweights, and racing applications.
Rotating inertia: gyro rotors and flywheel rims, where a compact high-density mass is required.
Radiation shielding: tungsten-bearing material offers shielding performance close to lead at a much smaller thickness, without lead's toxicity and handling restrictions.
Density gradient parts: components deliberately built with a lighter outer shell and a dense core, or the reverse, to place mass where it controls vibration or balance.
Machining and processing follow the same logic. A dense, hard and brittle alloy is slow to cut, so it is usually finished by grinding with abrasive grades suited to hard, low-ductility workpieces, and it is rarely welded. Where a finished part is required, the density figure feeds directly into weight calculations, and therefore into the size of the billet ordered.
Frequently Asked Questions
Q: What is the density of ferro tungsten?
Solid commercial material is commonly quoted at about 14.0 to 15.5 g/cm³ for tungsten contents of 70 to 85 percent. Calculated pore-free values for the same grades run from about 13.4 to 15.8 g/cm³.
Q: Why is the density of ferro tungsten not the average of tungsten and iron?
Density is mass per unit volume, so volumes combine rather than densities. The mixture rule adds the volume each component occupies, which is why the alloy is lighter than the tungsten it contains.
Q: Is ferro tungsten heavier than lead?
Yes. Lead is about 11.34 g/cm³ against roughly 14 g/cm³ or more for the alloy, which is why tungsten-bearing material is favoured for compact counterweights and shielding.
Q: Does higher tungsten content always mean higher density?
Within the FeW70 to FeW85 range, yes. Real lots can deviate if porosity, slag inclusions or heavy residual elements are present, so density is verified alongside chemical analysis.
Q: What is the difference between solid density and bulk density of ferro tungsten?
Solid density describes the material of the particle itself. Bulk density describes a packed heap of crushed product and is lower, because the voids between particles are counted in the volume.
Q: Why must ferro tungsten be crushed to a graded size?
Dissolution rate, charging method and recovery all depend on particle size. Furnace charging tolerates lump, while ladle and cored wire additions need a narrower and finer size fraction.
