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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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Distinguishing 304 and 316 Stainless Steel
March 20, 2009
Q. I noted down a reply by, I think Goran B., some time ago to a posting with reference to a spot test to distinguish between 304 and 316, using drop-wise HCl and then SO2 solution.
Presumably the Molybdenum forms black Moly Disulfide in the 316 and not in the no-Moly 304. My problem is that I have just tried it on some EB insert material to attempt to save time waiting on wet chemical analysis, and am getting inconclusive results.
Black stains on all samples, known 304 reference samples as well.
Is there a knack to this?
Does it work best on bulk or flat samples?
Also how critical is the one drop of each?
I've tried a few times and results are confusing to say the least.
Regards,
Metallurgical Technician - Plymouth, UK
A. As you have found out, it is a poor test. You may get a better result if you use some 120 grit wet and dry carbide paper to wet sand a spot until it is quite bright and then try the test. This breaks thru the oxide layer and gives the chemicals a better chance of working. For spot testing, I normally put one drop on it and then added another drop every 20 seconds or so until I had a spot that was about 1/2" wide.
I had a poor man's battery powered set that worked a bit better on some materials than the traditional spot test. I do not remember the name of it.
- Navarre, Florida
March 23, 2009
A. I can't be 100% sure this is the same kit that was mentioned but we use a spot test kit supplied by a company in the US called Koslow.
It is reasonably effective for distinguishing between different grades of material.
- Blackwood, Gwent, UK
March 25, 2009
adv.
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