304 / 316 SS etchant recommendations?

Joe

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Nov 30, 2001, 1:22:08 PM11/30/01

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Can anybody recommend a non-electrolytic etchant for grain boundaries in
304 / 316 stainless steels? I would normally use an electrolytic oxalic
acid etch, but my specimen geometry makes electrolytic etching difficult.

Has anybody experimented with Sodium Metabisulfite etchants in these
stainless steels?

Thanks for the bandwidth

-Joe Skaggs

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Kai Lorcharoensery

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Nov 30, 2001, 6:01:40 PM11/30/01

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I like 60 vol% HNO3 in water most. It doesn't reveal too many twins.
Great for grain boundaries. Unfortunately, it is electrolytic.

Beraha suggested a few metabisulfite etchants (immersion). He
pre-etched samples with 25% nital for 10 sec but I wish to live longer
so I never tried at that concentration. From my experience with plain
carbon steel and Fe-Ni alloys, a pre-etch with 2% nital about 10 sec
works fine. Here are what I found in his book.

Beraha no. 4
15-35 g sodium metabisulfite in 100 ml of water.

Beraha no.9a
Stock solution: 20 vol% of 35+% HCl in water
Mix 100 ml of stock solution with 0.5 - 1 g of potassium metabisulfite.

Metabisulfite works by depositing an anodic film on austenite or
ferrite. Thus, grain boundaries are revealed by constrast rather than
chemical attack. Sometimes, it's hard to see.

Good luck
Kai

=====================Quote===================
Joe wrote:

Has anybody experimented with Sodium Metabisulfite etchants in these
stainless steels?

==============================================

Michael Featherby

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Nov 30, 2001, 10:06:20 PM11/30/01

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Try glyceregia (nitric, hydrochloric and glycerin). Wing the ratios if you
can't find them anywhere (I forget, I usually use oxalic!)

D Deuchar

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Dec 1, 2001, 10:01:05 AM12/1/01

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I generally use nitric & hydrochloric acid in water. It is not as good as
the glycerin based etches on some materials, and can tend to pit the surface
on some samples, but saves getting hold of glycerin. I get the best results
with concentrations that take 5-10 minutes to give an etch.

"Michael Featherby" <mfea...@san.rr.com> wrote in message
news:3C084981...@san.rr.com...

Edward D. Vojcak

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Dec 3, 2001, 9:43:13 AM12/3/01

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Joe <schaefe...@earthlink.net> wrote in message news:<Xns9169729C880CBsc...@207.217.77.25>...

> Can anybody recommend a non-electrolytic etchant for grain boundaries in
> 304 / 316 stainless steels? I would normally use an electrolytic oxalic
> acid etch, but my specimen geometry makes electrolytic etching difficult.
>
> Has anybody experimented with Sodium Metabisulfite etchants in these
> stainless steels?
>
> Thanks for the bandwidth
>
> -Joe Skaggs

Have you tried Marbles'? 10g Copper sulfate in 50 ml Hydrochloric Acid
50 ml Water, can use hot.

Ed Vojcak

Joe

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Dec 3, 2001, 11:17:48 AM12/3/01

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Joe <schaefe...@earthlink.net> wrote in
news:Xns9169729C880CBsc...@207.217.77.25:

> Can anybody recommend a non-electrolytic etchant for grain boundaries in
> 304 / 316 stainless steels? I would normally use an electrolytic oxalic
> acid etch, but my specimen geometry makes electrolytic etching difficult.
>
> Has anybody experimented with Sodium Metabisulfite etchants in these
> stainless steels?
>
> Thanks for the bandwidth
>
> -Joe Skaggs
>

Thanks to Ed and others for the suggestions. I'll probably try the
Marble's first (since I have the copper sulfate already), and if that
doesn't work out, I'll try the glyceregia afterwards. I'll let you all
know how it works out.

Regards,
Joe

Leonard Brick

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Dec 3, 2001, 4:56:14 PM12/3/01

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What about my good friend Mr. Vilella's (ASTM # 80)? This works well
with 21-2 and 21-4 SS. Contains picric acid which I think may be
restricted in some states.

edp...@megsinet.net (Edward D. Vojcak) wrote in message news:<21080484.0112...@posting.google.com>...

Daniel Senter

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Dec 7, 2001, 1:04:13 PM12/7/01

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Be careful using the Marbles....

I've used it on 301 302 and 316 grades and found it to be very aggressive!

Only a few seconds submersion seemed to heavily etch my samples (hot rolled
plate)

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