If titanium is so strong why isn’t it used instead of steel for buildings?
Somewhere along the way, Hollywood has latched on to titanium as being the ultimate, strongest, hardest, highest temperature metal. It’s not.
Titanium and its alloys are a nice “medium” set of alloys with properties generally between aluminum alloys and steels, with overlap. The best aluminum alloys are stronger than the weakest commercially pure titanium grades. The best titanium alloys exceed quite a few steels in strength (including common construction grades of steel), but the strongest steels leave titanium alloys in the dust.
Steels are always stiffer (Young’s Modulus) than titanium. Steels are frequently harder than titanium alloys, and can be much, much harder. Steels can be stronger than titanium. Steels of equivalent strength to titanium alloys can be tougher (high fracture toughness). Construction steels can also be welded with much less preparation and shielding gas than titanium alloys.
There are three key points about titanium versus steel for buildings:
- Cost. Cheap carbon steels used in construction may be pennies per pound. Titanium is a fairly expensive material, usually headed toward tens of dollars per pound depending on the alloy.
- Commercially pure grade 2 titanium (rather “meh” stuff) costs about $50 per pound.
- You can buy entire 10-foot steel I-beams for the price of a 1-square foot titanium panel.
- For $50 a pound, I can buy some truly exceptional steels that will outperform titanium.
- Any titanium has half the stiffness of any steel. Stiffness, or Young’s modulus, says how far a material will stretch when stress is applied. For a steel and a titanium alloy of equal strength given equal loads, the titanium will always bend and stretch twice as far as the steel.
- Cost. (This needed to be said again.)
There are also numerous secondary points.
- Steels are often easy to weld, shape, carve, and drill. Titanium alloys usually need specialty welding processes, is less conducive to forging and rolling, and needs specialty machining and drilling techniques. (Not because titanium is hard and strong, but because it’s smeary and gummy.)
- I can buy 100,000 tons of steel for a skyscraper or dam or highway without trouble because global steel production is approaching 2 billion tons per year. In 2018, raw titanium sponge production reached a record of 255,000 tons, mostly for specialty customers (like the chemical industry) who could afford $50 a pound for titanium’s properties. Trying to meet the needs of a building boom in a big city, let alone China, is impossible for the titanium industry.
- Steels also tend to be harder than titanium alloys, which may be advantageous.
- And so on.
Titanium only truly rules in movies. Elsewhere, it’s an overrated specialty alloy with some useful niche applications.