The titanium scrap that cannot go back where it came from

Aerospace machining turns most of a titanium forging into swarf, so secondary supply exists in volume — but specification, not volume, decides which market it can be sold into.

Pending review

A loose heap of tightly coiled bright metal turnings tangled on a stained concrete floor, some straw-coloured from heat and some clean silver. — Illustrative artwork: machining turnings of the kind produced as scrap in metal manufacturing. Not a facility, equipment or material connected to this project. · Illustration · Osmond Hub

The short version

Making an aerospace titanium part mostly consists of removing titanium. The scrap that results is real, clean, alloyed metal in large quantities — and where it can go next is decided by specification rather than by how much of it there is. Some returns to the titanium industry; some leaves for the steel industry as ferrotitanium and never comes back. Those are two different markets, and treating them as one secondary supply is the commonest error in reading this material. Why aerospace titanium scrap ends up in steel covers the recovery mechanism — how much is lost in machining, why the aerospace door is narrow, and what the trade's vocabulary means. This article takes that as given and asks the question that follows it: what the resulting stream is worth as supply.

The volume is not in doubt

The peer-reviewed figure for how much of a forging survives to become a part is unflattering and consistent. One study of aerospace machining waste gives a typical buy-to-fly ratio for such components as "approximately 9:1"(opens in a new tab), and notes examples where up to 95% "of an expensive titanium alloy forging is machined away and disposed of"(opens in a new tab). A national-laboratory report puts the same thing as a mass loss, and states it twice, in two places and on two bases — once as an upper bound, once as a typical case. That accounting, with the buy-to-fly range from three further sources, belongs to Why aerospace titanium scrap ends up in steel.

Both figures above carry their hedges — typical, approximately, up to — and both describe the same physical situation. The secondary stream in titanium is not a trickle from end-of-life products decades hence. Most of it is generated the same week the part is made.

What decides where it can go

The constraint is not collection. It is what a melter is permitted to put in the furnace.

FAA guidance for premium quality titanium rotating engine components sets out that charge materials "should be composed of only approved raw materials, such as sponge, master alloys, elemental additions, titanium oxide, and recycled material (where permitted)"(opens in a new tab) — and the parenthesis is where this article lives. Its recycled-material section then limits by form. In general, "only turnings should be permitted to be directly recycled in multiple VAR processed premium quality titanium alloy"(opens in a new tab). Bulk weldables "should be prohibited for use in multiple VAR processed material, except when previously melted (consolidated) by an approved CHM process"(opens in a new tab). Finer material — grinding products, dust and sludge — is prohibited outright, and the failure mode the whole scheme is built against, the high density inclusion whose presence in a single indication condemns a heat, is set out in Why aerospace titanium scrap ends up in steel.

Note the register: this is advisory guidance, written in should, and the operative specifications for any given engine belong to its manufacturer. But the shape of the restriction is clear, and it is not a percentage. It is a rule about physical form, cleanliness and inspectability.

The question a melter asks about scrap is never how much there is. It is what shape it came in, and what got into it on the way.

Chemistry does the rest

The second constraint is what melting can and cannot fix. As PNNL states it, the melting process "removes most volatile impurities but cannot separate out the nonvolatile metal impurities"(opens in a new tab). Oxygen in particular travels with the metal, and the working response is dilution: current recycling approaches "require that Ti scrap be diluted with ~50% fresh Ti sponge to manage oxygen content"(opens in a new tab) — a laboratory's account of practice rather than a written limit, and hedged with its own approximation.

How little it takes to fall outside a specification is worth seeing concretely. In the study cited above, the swarf was "out of specification against the 0.08% carbon, 0.20% oxygen, and 0.05% nitrogen stated in ASTM B381-13" because it exceeded "the oxygen level requirement by 0.01%"(opens in a new tab) — one hundredth of a percentage point, on one element, in one particular sample.

So the stream splits, and the split is the market story

USGS's last published breakdown of where American titanium scrap actually went shows the two destinations side by side: about 45,000 tons of titanium scrap metal was consumed in 2020 — "35,000 tons by the titanium industry, 8,000 tons by the steel industry, less than 500 tons by the superalloy industry, and the remainder in other industries"(opens in a new tab), the figure carrying USGS's own about and less than.

The steel destination is not a lesser form of the same market; it is a different market. USGS's yearbook records that ferrotitanium "usually is produced by induction melting of titanium scrap with iron or steel but may be produced through the aluminothermic reduction of ilmenite"(opens in a new tab), and that in the steel industry titanium "was used for deoxidation, grain-size control, and control and stabilization of carbon and nitrogen content"(opens in a new tab) — consumed as a chemical additive, in tonnages a mill decides on its own grounds. It also notes that a significant quantity of titanium "in the form of ferrotitanium, scrap, and sponge was consumed in the steel and nonferrous alloy industries"(opens in a new tab) — a sentence that attaches no figure of its own to that quantity.

Read as supply, that produces a specific conclusion, and it is ours rather than any source's: secondary titanium displaces primary sponge only in the segments whose specifications will accept it, and in every other segment it is not competing supply at all — it has left for an unrelated market where its titanium content is a reagent. A market analysis that adds the two together and calls the result recycled titanium supply has counted material that can never come back.

One further caution belongs with those figures. The current editions do not publish the split at all: the titanium-industry figure is withheld and the steel, superalloy and other-industry figures are not available (usgs_ti26), a sentence quoted in full in Why aerospace titanium scrap ends up in steel. The most useful number in this subject is one nobody currently publishes — which is why the 2020 breakdown above is carrying so much of the weight here.

Related

Why aerospace titanium scrap ends up in steel (Sustainability · Recycling) — the recovery mechanism this article takes as given: machining loss, the HDI rule and the trade's vocabulary
Recycling Technology — the processes that determine what a stream can become
Supply & Demand — the primary balance this stream competes inside
Processing Capacity — the melting and qualification steps that gate re-entry
Titanium/Rutile — the primary production this stream returns to, or does not