Re: [PSUBS-MAILIST] Post for Vance Bradley

[John Brownlee <jonnie@cobweb.scarymonsters.net>]

Hi Vance,

	Well, I grew up in a titanium household, in fact, dad's company
(then Titanium Industries or Timet or Oremet, now owned by Alleghany
Steel) made the upgrade Alvin hull years back. My father was in the metals
business, and corrosion-resistant products and pressure vessels was their
speciality. This means that, like many other members of my family, I was
indoctrinated at an early age into the wonderful world of working Ti.
Here's what I recall:

	The issue with titanium is partially the cost of the metal
(particularly with the vanadium and aluminum alloys that are often used in
the aerospace industry too), but with the advent of the Russian stocks of
Grade 5 Ti (the good stuff) this is not as much an issue as it was when
most of the metal sponge came out of Brazil and South Africa. The real
bear about Ti is that if you take the metal above the temperature it's
crystal structure changes to the 'beta' phase, it can dissolve gasses in
the metal that are present even in the minimal air-leakage you get with
most inert-gas welding and working processes. It took a long time to prep
a weld with Ti, and even longer to test it after it was cool and the inert
atmosphere can be removed. You -MUST- machine it with carbide tools, and
depending on the work sometimes work other than welding had to be done
with inert gas shielding. All these little things mean that the cost of
working Ti is in the extra labor and experience it takes to really make a
quality weld. My memory was that nuke-vessel welders were the top end, and
those who -liked- working Ti were the creme-de-la-creme and maybe a little
crazy. Their work was worth it's weight in twenty dollar bills, to steal
from the P2 thread.
	Now, I should inject that I don't know the idiosyncracies of the
high-yield Navy steels, but my most fond memory of learning to work Ti was
doing a destructive tensile test on two identical welds (if there is such
a thing but that's another matter), one with anal-retentive gas shielding,
and another with less careful shielding. The difference in strength was
almost an order of magnitude; the weld with dissolved nitrogen and oxygen
from poor shielding broke like glass!


							John

John Brownlee
Chief Systems Administrator
Scary Monsters Network
jonnie at scarymonsters dot net