Date:         Thu, 31 Dec 1998 08:01:45 EST
Reply-To:     PaoloD1455@AOL.COM
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Paolo Damiani <PaoloD1455@AOL.COM>
Subject:      Re: How to tell if it is stainless steel pipe? (careful,
              I'm technobabbling)
Comments: To: vanagon@vanagon.com
Content-type: text/plain; charset=US-ASCII

In a message dated 12/30/98 10:21:23 PM Eastern Standard Time, jag@CS.YALE.EDU
writes:

<< So intuitively could you say that ferritic or austenitic depends on
 wether the magnetic domains are randomly or coherently oriented, and
 that orientation can be disturbed either by adding more chromium etc.
 to the alloy or by heat treating. However I'm puzzled since it seems to
 me that a rapid cooling like after welding will cause random orientations
 and hence be non-magnetic, not like you say mildly magnetic.
  >>
Martin,

Actually the magnetic properties depend on whether the crystal structure is
FCC (face centered cubic) or BCC (body centered cubic). Austenite is a solid
solution of iron and carbon (or in our case nickel). Ferrite is BCC.

Austenite typically does not exist below approximately 730 deg C. It is
stabilized by the presence of nickel in the case of a stainless steel and
forms a metastable solution. If this is disturbed by less than optimal
cooling, other Fe-C phases form all of which are BCC and magnetic.

Welding cooling rates, however, are very geometry, mass and welding method
dependent. Needless to say, there are gradients across the weld and into the
base metal, such that a variety of "heat treatments" occur unless carefully
cooling is controlled or the piece is then heat treated. Needless to say, I'm
fairly certain that your pipe didn't get this attention.

This is a rather sticky metallurgical situation, but there is tons of work out
there on heat effects on SS. I've been out of the metallurgy business for
about four years now so I'm rather... please forgive this pun!... rusty.

For your purposes, I don't think that vinegar will be quite aggressive enough
to let you know which stainless steel you do or don't have.

So, in the interest of Vanagon cameraderie, I propose the following:

Take that clean file I told you about. File off some metal from an area which
won't cause functional damage to your hardware. Place this material onto a
piece (about 1" long) of double sided tape, and stick it to a piece of paper.
Write something to the effect "Here are the metal filings we have
discussed..." . Fold it carefully and place it in an envelope and mail it to
me, making sure that your name and return address are visible so I don't toss
it with all the junk mail I get everyday.

I'll go down to the old lab and rev up the ol' SEM, and we'll have you an
analysis with which can torture the vendor if they are lying. We can report
the results to the listmembers and be heralded as crusading investigative
reporters.

It's the least the private sector can do for academia.

So, if you want, send it to:

Paolo Damiani
Actual address removed
from list posting

I assume that you like technology and are not a "Ted K" type (Metal filings
ONLY in the letter). I'll get you the results by e-mail asap.


Paul