which steel

["asmyth" <asmyth@hsomail.com>]

Hi everyone,

I am wondering which type of steel is recommended for the pressure hull. I'm
not about to start on the hull for quite some time yet, but I am about to
make some parts that will be welded to it eventually, so I thought I'd use
the same material if possible, and this forces a decision. Obviously, this
one issue could be discussed for ever, since there are so many physical
properties to weigh, as well as price, etc.

I am not looking for an Unobtainium alloy that will take me to the Marianas
trench... just something COMMON (i.e., inexpensive and available in every
shape or size) but with a good yield strength, machinability, and
weld-ability.

My little PSUB library includes a Welding Journal article about the
construction of a K-boat. It says they used "A516, Gr.70 boilerplate steel,
welded with E7018 covered electrodes". I then found pages and pages about
A516 on Bethlehem Steel's website, which basically said this is the cats
whiskers for pressure vessels. Yet the yield strength was specified as 38K
psi. The Machinery's Handbook says common alloys like 4130 are around 46
Kpsi yield strength, and some are way higher. So what's special about A516?

No doubt I'm revealing my metallurgical ignorance, but I'd appreciate any
suggestions from someone who knows more about this!

- Alec Smyth