Qualitative Sorting Tests for Stainless Steels

਍ഀ These tests are intended for rapid, inexpensive and ਍ഀ usually non-destructive and on-site sorting ਍ഀ of grades of stainless steel. They are particularly useful for sorting products ਍ഀ when, for example, ਍ഀ bars of grades 304 and 303 have been accidentally stored together, or grade 304 ਍ഀ and 316 sheet ਍ഀ offcuts mixed.

਍ഀ ਍ഀ Limitations

਍ഀ These tests are extremely useful, but it is important ਍ഀ to realise that they have limitations; they ਍ഀ cannot sort one heat from another of the same grade, and there is no easy way of ਍ഀ sorting ਍ഀ certain grades from each other. For instance, it is not possible to readily sort ਍ഀ 304 from 321, 316 ਍ഀ from 316L or 304 from 304L. The  Molybdenum spot test therefore indicates ਍ഀ that a piece of steel ਍ഀ contains Mo, but does not alone indicate 316 .... in the absence of other ਍ഀ knowledge the steel ਍ഀ could be 316L, 2205 or 904L etc. It is possible to use tests in combination, so ਍ഀ an item that is ਍ഀ shown to contain Mo, and also to be attracted to a magnet is possibly grade ਍ഀ 2205, and unlikely ਍ഀ to be either 316L or 904L. But is it 444 or 18-2?

਍ഀ ਍ഀ Some Other Options

਍ഀ The simple tests described in this Note may assist in grade ਍ഀ identification and product sorting. ਍ഀ Other, more complex tests can also be carried out; these can involve several ਍ഀ chemical reagents, ਍ഀ hardness tests or checking response to heat treatment. Proprietary kits can be ਍ഀ purchased to ਍ഀ carry out some of these tests. In most cases, however, if these simple tests are ਍ഀ not sufficient to ਍ഀ identify the product it is best to have a full spectrometric analysis carried ਍ഀ out by a competent ਍ഀ laboratory. Another option is the use of portable analysis equipment, based on ਍ഀ spark emission or ਍ഀ X-ray fluorescence spectroscopy. This quite sophisticated equipment is used for ਍ഀ some PMI ਍ഀ (Positive Material Identification) testing wherein items are 100% checked for ਍ഀ correct ਍ഀ composition; this is sometimes a requirement of end users, particularly in the ਍ഀ petrochemical or ਍ഀ oil and gas project areas.

਍ഀ ਍ഀ There are other less common qualitative spot tests ਍ഀ available. A manganese spot test is available ਍ഀ with specific relevance in sorting “200-series” Cr-Mn-(Ni) austenitic stainless ਍ഀ steels from the ਍ഀ more usual Cr-Ni “300-series” grades such as 304. The 200-series steels are ਍ഀ non-magnetic and ਍ഀ otherwise indistinguishable from the 300-series, but do have some reduced ਍ഀ properties and have ਍ഀ considerably less value as scrap.

਍ഀ ਍ഀ Although this Tech Note is ਍ഀ primarily aimed at sorting of stainless steels, some of the tests are ਍ഀ also relevant to sorting carbon and low alloy steels. The sulphur spot test is ਍ഀ equally relevant to ਍ഀ sorting free-machining carbon steels (eg 1214 or 12L14) from low-sulphur ਍ഀ alternative grades (eg ਍ഀ M1020, 1045 or 4140).

਍ഀ ਍ഀ Prevention

਍ഀ The need for these sorting tests can be reduced if original ਍ഀ product identification is retained. ਍ഀ Product colour codes, tags and stickers, and stamped or stencilled ਍ഀ Batch/Heat/Grade markings ਍ഀ should be retained as much as possible. All product distributed by Atlas ਍ഀ Specialty Metals has this ਍ഀ identification, in line with requirements of our ISO 9001 quality system. Atlas ਍ഀ also colour code ਍ഀ many steel products, generally in accordance with the Australian Standard AS/NZS ਍ഀ 4496 – 1997 ਍ഀ “Recommended practice for the colour coding of steel products”.

਍ഀ Magnetic Response

਍ഀ ਍ഀ What Can Be Sorted ਍ഀ ਍ഀ

਍ഀ Austenitic (300 Series) stainless steels from other steels. ਍ഀ All other steels are attracted to a ਍ഀ magnet, including all the ferritic, duplex, martensitic and precipitation ਍ഀ hardening stainless ਍ഀ steels. The only other non-magnetic steels are the austenitic 13% manganese ਍ഀ steels (eg ਍ഀ “P8”).

਍ഀ ਍ഀ 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 ਍ഀ bending, forming, drawing or rolling. Stress relieving at cherry-red heat will ਍ഀ remove this ਍ഀ response due to cold work, but this stress relief may sensitise 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. ਍ഀ Even although duplex grades have only half the amount of the magnetic ferrite ਍ഀ phase ਍ഀ compared to fully ferritic grades such as 430, the difference in “feel” of a ਍ഀ manual test is ਍ഀ unlikely to be enough to enable sorting duplex steels from ferritic, martensitic ਍ഀ or precipitation ਍ഀ hardening grades.

਍ഀ Welds in austenitic stainless steels are also usually ਍ഀ slightly magnetic due to a deliberate ਍ഀ inclusion of a small percentage of ferrite in the austenitic deposit. The % ਍ഀ ferrite can be ਍ഀ measured by the amount of magnetic response, and special instruments are ਍ഀ available for this.

਍ഀ ਍ഀ 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 ਍ഀ 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.

਍ഀ ਍ഀ Tips & Traps

਍ഀ Grease or similar contaminants will prevent the acid ਍ഀ contacting the steel surface, so the ਍ഀ surfaces should be clean – use detergent or an organic solvent to remove these ਍ഀ contaminants. Surface oxide layers such as mill scale will also interfere … ਍ഀ these should be ਍ഀ filed or ground off, or removed by pickling. ਍ഀ Very lean stainless steels, such as AtlasCR12 and other 12%Cr grades, are not ਍ഀ totally ਍ഀ immune from nitric acid attack. They can show some minor reaction, but much less ਍ഀ violently ਍ഀ than on a carbon or low alloy steel.  ਍ഀ If the product being tested is not stainless steel there is likely to be ਍ഀ significant attack and ਍ഀ hence a significant change in  appearance. Carry out the test on a surface ਍ഀ where any ਍ഀ appearance change can be tolerated.

਍ഀ ਍ഀ Safety Precautions

਍ഀ Consult the MSDS for nitric acid and follow directions. ਍ഀ Personal protective equipment should be ਍ഀ used as directed. Strong nitric acid attacks skin and is very corrosive. Use ਍ഀ minimum quantities. ਍ഀ Wash off immediately if skin contact occurs. Do not breathe brown fume.

਍ഀ Molybdenum (Mo) Spot Test

਍ഀ ਍ഀ What Can Be Sorted

਍ഀ 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 and ਍ഀ all “super duplex” grades (e.g. S32760, S32750, S32550, S32520). ਍ഀ Other similar grades with deliberate Molybdenum additions will also respond.

਍ഀ ਍ഀ 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 ਍ഀ indications on the known 304 and 316 samples.

਍ഀ ਍ഀ 5. Wash or wipe samples clean.

਍ഀ ਍ഀ Tips & Traps

਍ഀ Reliable results only obtained if samples all the same ਍ഀ temperature and freshly cleaned. Avoid ਍ഀ very low sample temperatures. Standard comparison samples and test samples must ਍ഀ be at the ਍ഀ same temperature. ਍ഀ Some Heats of “Mo-free” stainless steels, such as 304, contain enough Mo to give ਍ഀ a slight ਍ഀ reaction; up to about 0.5% is not unusual. Standard comparison samples must be ਍ഀ used.

਍ഀ ਍ഀ Safety Precautions

਍ഀ Consult the MSDS for the product and follow directions. ਍ഀ Avoid contact of test solution on skin, ਍ഀ and particularly eyes. Wash off immediately if contacted.

਍ഀ Sulphur (S) Spot Test

਍ഀ ਍ഀ What Can Be Sorted

਍ഀ Free machining grades of stainless and plain carbon steels, ਍ഀ which typically contain about ਍ഀ 0.25-0.35% sulphur (eg 1214, 12L14, 303, 416, 430F), from non-free machining ਍ഀ steels, ਍ഀ which typically contain up to 0.03% sulphur. ਍ഀ Ugima 303 contains high sulphur (the same as standard Grade 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.

਍ഀ ਍ഀ Method

਍ഀ ਍ഀ 1. Clean the steel surface; use abrasive paper, and if ਍ഀ necessary degrease. A flat area is ਍ഀ preferred.

਍ഀ 2. Prepare standard high and low sulphur samples in the ਍ഀ same way, eg known M1020 and ਍ഀ 1214, 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 10 seconds.

਍ഀ 5. A dark brown stain indicates significant sulphur. ਍ഀ Compare with indications from standard ਍ഀ samples.

਍ഀ ਍ഀ 6. Wash samples thoroughly.

਍ഀ ਍ഀ Tips & Traps

਍ഀ 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. This ਍ഀ test also shows the distribution of sulphur across the tested section, which is ਍ഀ useful in some ਍ഀ cases.

਍ഀ ਍ഀ Precautions

਍ഀ Consult the MSDS for sulphuric acid and follow directions. ਍ഀ Wear personal protective equipment ਍ഀ as directed. Avoid contact of acid with skin and eyes. Wash immediately if ਍ഀ contacted. ਍ഀ This "Tech Note" is the first of a series of brief notes covering technical ਍ഀ matters related to the ਍ഀ selection, application, fabrication and use of special steels. It is hoped that ਍ഀ these notes will be ਍ഀ of assistance to all those with an interest in special steels. Copies are freely ਍ഀ available to all in ਍ഀ the engineering community. To obtain further copies of this or other Tech Notes ਍ഀ please ਍ഀ contact your Atlas representative or office.

਍ഀ ਍ഀ ਍ഀ Stainless Steel |਍ഀ ਍ഀ Pitting ਍ഀ Crevice Corrosion | ਍ഀ Corrosion Directory |਍ഀ ਍ഀ Cleaning ਍ഀ Stainless steel |਍ഀ ਍ഀ L & H ਍ഀ Grades of Stainless Steels |਍ഀ ਍ഀ Metal ਍ഀ Corrosion |Copper ਍ഀ Pipe Corrosion |਍ഀ ਍ഀ Galvanic Corrosion ਍ഀ | ਍ഀ What is Corrosion | ਍ഀ ਍ഀ Metal castings https: |਍ഀ ਍ഀ Basic welding  Introduction to welding |਍ഀ ਍ഀ Chemical properties of copper |਍ഀ ਍ഀ Online chemistry dictionary

਍ഀ ਍ഀ Reference & Further Information

਍ഀ ਍ഀ Atlas Specialty Metals Technical Handbook, available from ਍ഀ the Atlas website.

਍ഀ Material Safety Data Sheets for each of the test products.

਍ഀ ਍ഀ This article is taken from: ਍ഀ ਍ഀ Atlas Specialty Metals  ਍ഀ Tech Note : "Qualitative Sorting Test for Steels"