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Test |
What Can Be Sorted |
Method |
Precautions |
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Magnetic Response |
Austenitic (300 Series) stainless steels from other steels. All other
steels are attracted to a magnet, including the ferritic, duplex,
martensitic and precipitation hardening stainless steels. The only other
non-magnetic steels are the austenitic manganese steels (eg “P8”). |
Note response, if any, when a permanent magnet is brought close to the
steel. |
Some austenitic grades, particularly 304, are attracted when cold
worked, eg by bending, forming or rolling. Stress relieving at
cherry-red heat will remove this response due to cold work. This stress
relief may sensitize the steel and should not be performed on an item
which is later to be used in a corrosive environment. A full anneal is
acceptable, however. |
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Nitric Acid Reaction |
Stainless steels from non-stainless steels. |
1. Place a piece of the steel in strong nitric acid (20% to 50%) at room
temperature, or a drop of the acid on a cleaned surface of the steel.
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. Stainless steels are not affected. Compare result with
standards.
4. Wash samples thoroughly afterwards. |
Wear safety glasses. Strong nitric acid attacks skin and is very
corrosive. Handle carefully. Use minimum quantities. Wash off
immediately if skin contact occurs. Do not breathe brown fume. |
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Molybdenum Spot Test (Mo) |
Stainless steels which contain significant Molybdenum from those which
do not. The most common use is to sort 304 from 316, but the following
grades also contain sufficient Mo to give a positive response to this
test: 316, 316L, 317, 317L, 444, 904L, 2205, "6-Mo" grades, 4565S and
all “super duplex” grades (e.g. S32760 / Zeron 100 / S32750 / 2507 /
S32550 / Alloy 255 / S32520 / UR52N+). Other similar grades with
deliberate Molybdenum additions will also respond. |
1. Clean the steel surface; use abrasive paper, and if necessary
degrease and dry.
2. Use "Decapoli 304/316" solution – shake well, then place one drop on
the steel.
3. Place similar drops on standard 304 and 316 samples.
4. Darkening of the yellow drop in 2 to 4 minutes indicates significant
Mo. Compare with indications on standard samples.
5. Wash or wipe samples clean. |
Avoid contact of test solution on skin, and particularly eyes. Wash off
immediately if contacted. Reliable results only obtained if samples all
the same temperature and freshly cleaned. Avoid very low sample
temperatures. Some Heats of "Mo-free" stainless steels, such as 304,
contain enough Mo to give a slight reaction. Standard comparison samples
must be used. |
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Sulphur Spot Test (S) |
Steels (stainless and plain carbon) containing at least 0.1% Sulphur, ie
free machining grades. (eg S1214, S12L14, 303, 416, 430F), from non-free
machining steels. Ugima 303 contains high sulphur (the same as standard
Type 303) so will give a positive reaction, but Ugima 304 and Ugima 316
have the same low sulphur contents as their standard (non-Ugima)
equivalents, so will not give positive reactions. |
1. Clean the steel surface; use abrasive paper, and if necessary
degrease. A flat area is preferred.
2. Prepare standard samples in the same way, eg known CS1020 and S1214,
or 304 and 303.
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 5 sec.
5. A dark brown stain indicates significant sulphur. Compare with
indications from standard samples.
6. Wash samples thoroughly. |
Wear safety glasses. Avoid contact of acid with skin and eyes. Wash
immediately if contacted. Reliable results depend on good contact with
the paper, and consistent time of contact. Standard comparison samples
must be tested in conjunction with the unknown samples. |