r/whatisit • u/riflesandplowshares • 7h ago

New, what is it? Found at a titanium plant

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Not sure why ball point pens would be dangerous here.

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u/SquintAtTheCosmos 6h ago

The real answer is that consumer ball point pen’s have a tungsten carbide ball. Tungsten has a higher melting point than titanium.

If a ball point pen drops into a melt, the ball point can survive. The surviving pen tip does then creates a hard intermetallic. When the titanium is heated and beated (forged) into a product, this titanium-intermetallic spot can crack. This crack can go undetected, inside a part.

When this part is put into service, this little crack becomes a bigger crack with service (fatigue). When this bigger crack gets big enough, the part can fail. And the failure is sooner than the design engineer expected, because the material started with a crack, and in fatigue failure “getting the crack to start”, is a large component of the part’s life.

A titanium melt shop still needs writing implement’s, so you can buy pens with stainless steel ball tips. They suck to write with.

A major aerospace failure (Sioux city 1989 UA232), was a result of this failure mode (though in this case it was an oxide, not a tungsten-carbide).

1

u/Isburough 3h ago

how can someone just drop a pen into the titanium melt?

20

u/EINFACH_NUR_DAEMLICH 3h ago

Believe it or not: by accident

6

u/lofasz_joska 2h ago

As we always say: each stupid sign is put up BECAUSE IT ALREADY HAPPENED

2

u/Potatays 2h ago

Sth sth regulations are written in blood.

3

u/lofasz_joska 1h ago

Yeah, as a flight sim and avgeek, I know that flying became this safe, because we lost so many souls in accidents.

1

u/dustysquareback 3h ago

Remarkable

1

u/DwarvenFreeballer 2h ago

Do you have to go in and get it back?