Re: [PSUBS-MAILIST] protecting aluminum parts

["Adam Lawrence" <adteleka@in-tch.com>]

The knife blade was probably a matensitic stainless steel (maybe 440C) which
is an iron-chromium alloy with around 1% C and 16% Cr. Good for making
knives because higher carbon and chrome alloys, when quenched, give high
hardness. But there is a trade off, corrosion resistance is lowered because
to much chrome promotes a ferritic microstructure which is softer then a
martensitic structure.

Shooting from the hip, a greater percentage of iron would exist at the
surface of the blade, coupled with less chrome; the iron would be
selectively leached out by the salt water. The leaching wouldn't continue
subsurface because of grain orientation and possibly the saltwaters
inability to penetrate the iron free pores.



Adam




----- Original Message ----- 
From: <VBra676539@aol.com>
To: <personal_submersibles@psubs.org>
Sent: Wednesday, January 07, 2004 3:44 AM
Subject: Re: [PSUBS-MAILIST] protecting aluminum parts


> Hmmm. Maybe one of our metal guys will take a shot at that. The only thing
I
> ever did similar was replace a piece of 304 stainless in the oxygen system
on
> one of the boats when it turned to rust on a single dive. It should have
been
> 316 to start with, but we were all surprised that it rusted like that. I
> wonder if we could have polished it out and by doing so, sealed the pores
and maybe
> made it shinier and less likely to do it again? Very strange. Vance