There are at least a dozen alloy
variations in the inconel family, with differing mechanical properties. I
have never heard of H-25 alloy; but presumably a variation of 625. Perhaps
not the best choice for properties, but is one of the more weldable. Hard to
find fatigue data on the alloys, but many, including 625 work-harden (related
to fatigue failure) quite rapidly making them difficult to machine.
I don’t know which alloy was used
for my manifold/muffler, but the guy that made it for me got the material from
Boeing. He thought it was 694 or 718; both of which are more common in
the aerospace industry. Just playing with a scrap it seemed to be quite
malleable at room temperature. What ever it is, he did a very nice job of
welding and it is doing nicely on my engine at 120 hours.
I’d agree; at 1500F the best bet
is 321 SS. At 1700F I’d go with inconel to avoid stress corrosion;
but even then with thick walls, low stress, 321 can work.
Al
-----Original Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Greg Ward
Sent: Thursday, July 24, 2008 2:41
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: exhaust
building
It (H-25) fatigues early at lower
temps. That's why all the Nascar types have stopped using it,
because they run around 1500 deg. or so, and got tired of spending about 5
times the money for header failures.
----- Original Message -----
Sent: Thursday,
July 24, 2008 11:55 AM
Subject: [FlyRotary]
Re: exhaust building
Iconel, on the
other hand is overkill. It lives at 2000+
degrees, and doesn't like it at
lower temps, and will degrade, plus it's very
expensive.
Brad;
Yes,
inconel tolerates temps of 2000+, but explain what is “and
doesn't like it at
lower temps”. That sounds strange to me.
Al G