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What's the grade of this SS ? [India]



July 21, 2010

we are into manufacturing of SS 304 18/8 AISI grade baskets.recent R/M procured showed strong magnetic response,where in small magnets even stuck onto the R/M.then we sent those(magnetic R/M) samples for chemical testing,along with NON MAGNETIC samples for comparing.to our surprise both nonmagnetic and magnetic samples showed all most the same chemical properties.(NONMAGNETIC sample: cr=18.362 ;Ni=7.651 & MAGNETIC sample: Cr=18.941 ;Ni=7.771).
now my question is
1) is this steel SS 304 grade.if not what is the grade?
2) will it rust or corrode?
3) why is this showing magnetic property?
PLEASE RESPOND IMMEDIATELY.(ASAP)

Guru Deep
plating shop - INDIA



simultaneous July 27, 2010

Unlike 316 (I think), 304 SS can become ferromagnetic from cold working - wire drawing, rolling, centerless grinding, shot blasting, heavy polishing, are some mentioned on the internet. Check this thread.
www.finishing.com/454/35.shtml

Chris Owen
- Nevada, Missouri, USA



July 27, 2010

Dear Guru Deep.

As this is a voluntary forum and even for free, you cannot expect an immediate reply. I hope the following information is useful to you, in order to widen your understanding, you should do additional research:

Summarizing:
From the composition: Yes, this is SS.
Normally the SS 3-4 is non-magnetic.
An extreme cold working or heat treatment could make is magnetic.

Yes, This can influence the corrosion properties as well.

So, If I was in your place, and till now you always received non magnetic material, I would be suspicious about this supply. Your should have a very good explanation and guarantee why it is now suddenly magnetic and that this delivery is not different in behaviour from earlier deliveries and about what happened which made it different from earlier deliveries. (Rolling, casting and heat treatment processes can have an influence on magnetic properties of this type of stainless steel)Having detected such a difference, I only would take the risk in using it for "low risk" applications after thorough testing the final product compared to the original stainless steel supplies you used and even that isn't an absolute guarantee. If it is for critical parts, you shouldn't and couldn't take a risk and of course you have to tighten your specifications as well.

There has been an earlier discussion on this topic in this forum, see:

www.finishing.com/333/03.shtml

Although not directly referring to your problem, but comparable:

www.finishing.com/112/70.shtml

For your further information (with thanks to Pat Doyle -see:
http://lists.contesting.com/_towertalk/1996-11/msg00136.html)

(What follows is copied from this site):
Stainless steel is a ferrous (iron based) alloy.
The American Society for Metals (ASM) defines
stainless steel as an alloy containing at least
10% chromium (Cr) (with or without other
elements). Few of the alloys contain more than
30% Cr or less than 50% iron (Fe). Cr is the
element that makes the stainless steel more
resistant to rusting and staining than plain
carbon or low-alloy steels. Other elements are
added to give specific properties.

There are four metallurgic categories for
stainless steel: 1) martensitic; 2) ferritic; 3)
austenitic; 4) precipitation-hardened. The most
common types found in general use are martensitic
and austenitic. I will not address the less
common types.

Austenitic stainless is non-magnetic.
Martensitic stainless is magnetic.

Nickel (Ni) is found in austenitic stainless and
is makes it non-magnetic. It has to do with the
alloy structure and where the various elements of
the alloy end up in that structure.

Martensitic is stronger and harder than
austenitic, primarily because it is heat treated.
The heat treating causes the alloy's structure to
form such that it is not magnetic.

Alloy 304 is an austenitic stainless and has the
widest range of applications and is available in a
variety of forms for exterior architectural
applications. If you encounter stainless steel,
it is most likely 304. It possesses excellent
resistance to corrosion from exposure to weather.
It is non-magnetic.

304L is a low carbon version having slightly
higher corrosion resistance. This is a good
choice if the piece is to be welded. Welding
reduces stainless steels' corrosion resistance.
Carbon will "steal" Cr to form Chromium Carbide at
welding temperatures (remember that Cr is what
makes stainless corrosion resistant).



Best regards,

Harry van der Zanden
Harry van der Zanden
- Budapest, Hungary

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