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Qualitative Sorting Tests for Stainless Steels | ഀ
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These tests are intended for rapid, inexpensive and ഀ
usually non-destructive and on-site sorting ഀ
ഀ
Limitations ഀ
These tests are extremely useful, but it is important ഀ
to realise that they have limitations; they ഀ
ഀ
Some Other Options ഀ
The simple tests described in this Note may assist in grade ഀ
identification and product sorting. ഀ
ഀ
There are other less common qualitative spot tests ഀ
available. A manganese spot test is available ഀ
ഀ
Although this Tech Note is ഀ
primarily aimed at sorting of stainless steels, some of the tests are ഀ
ഀ
Prevention ഀ
The need for these sorting tests can be reduced if original ഀ
product identification is retained. ഀ
Magnetic Response ഀ
ഀ
What Can Be Sorted ഀ
Austenitic (300 Series) stainless steels from other steels. ഀ
All other steels are attracted to a ഀ
ഀ
Method ഀ
Note response, if any, when a permanent magnet is ഀ
brought close to the steel. ഀ
ഀ
Tips & Traps ഀ
Some austenitic grades, particularly 304, are attracted to ഀ
a magnet when cold worked, eg by ഀ
Welds in austenitic stainless steels are also usually ഀ
slightly magnetic due to a deliberate ഀ
ഀ
Safety Precautions ഀ
No hazards associated with this test ഀ
Nitric Acid Reaction ഀ
ഀ
What Can Be Sorted ഀ
Stainless steels from non-stainless steels. ഀ
ഀ
Method ഀ
ഀ
1. Place a piece of the steel in strong nitric acid (20% to ഀ
50%) at room temperature, or a ഀ
2. Test standard samples in the same way, ie stainless and ഀ
non-stainless steel samples. ഀ
3. Non-stainless steels will quickly be attacked; a pungent ഀ
brown fume is produced. ഀ
ഀ
4. Wash samples thoroughly afterwards. ഀ
ഀ
Tips & Traps ഀ
Grease or similar contaminants will prevent the acid ഀ
contacting the steel surface, so the ഀ
ഀ
Safety Precautions ഀ
Consult the MSDS for nitric acid and follow directions. ഀ
Personal protective equipment should be ഀ
Molybdenum (Mo) Spot Test ഀ
ഀ
What Can Be Sorted ഀ
Stainless steels which contain significant Molybdenum from ഀ
those which do not. The most ഀ
ഀ
Method ഀ
ഀ
1. Clean the steel surface; use abrasive paper, and if ഀ
necessary degrease and dry. ഀ
2. Use test solution “Decapoli 304/316”, “Moly Drop 960” or ഀ
similar – shake well. ഀ
3. Place one drop on the steel of interest, and similar ഀ
drops on known 304 and 316 samples. ഀ
4. Darkening of the test drop in 2 to 4 minutes indicates ഀ
significant Mo. Compare with ഀ
ഀ
5. Wash or wipe samples clean. ഀ
ഀ
Tips & Traps ഀ
Reliable results only obtained if samples all the same ഀ
temperature and freshly cleaned. Avoid ഀ
ഀ
Safety Precautions ഀ
Consult the MSDS for the product and follow directions. ഀ
Avoid contact of test solution on skin, ഀ
Sulphur (S) Spot Test ഀ
ഀ
What Can Be Sorted ഀ
Free machining grades of stainless and plain carbon steels, ഀ
which typically contain about ഀ
ഀ
Method ഀ
ഀ
1. Clean the steel surface; use abrasive paper, and if ഀ
necessary degrease. A flat area is ഀ
2. Prepare standard high and low sulphur samples in the ഀ
same way, eg known M1020 and ഀ
3. Soak photographic paper in 3% sulphuric acid for about 3 ഀ
minutes. ഀ
4. Press the prepared steel surfaces on the face of the ഀ
photographic paper for 10 seconds. ഀ
5. A dark brown stain indicates significant sulphur. ഀ
Compare with indications from standard ഀ
ഀ
6. Wash samples thoroughly. ഀ
ഀ
Tips & Traps ഀ
Reliable results depend on good contact with the paper, and ഀ
consistent time of contact. ഀ
ഀ
Precautions ഀ
Consult the MSDS for sulphuric acid and follow directions. ഀ
Wear personal protective equipment ഀ
ഀ
ഀ
ഀ
Reference & Further Information ഀ
ഀ
Atlas Specialty Metals Technical Handbook, available from ഀ
the Atlas website. ഀ
Material Safety Data Sheets for each of the test products. ഀ
ഀ
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