How Many Methods To Identify Stainless Steel?

In the case of unknown steel grade (number), we can use simple tools to determine whether it is stainless steel and which type of stainless steel it belongs to based on the inherent physical and chemical properties of the product (including whole materials, leftovers, waste materials, and other physical objects). It should be pointed out that sensory identification cannot distinguish specific steel (grade) numbers, and can only basically distinguish chromium stainless steel, chromium nickel stainless steel (SUS304, 304), and chromium manganese nitrogen stainless steel (200 series). The identification method is as follows:
1. Identification of color: Identify the changes in color of stainless steel before and after pickling:
type
After pickling
Not pickled (when oxidation is severe)
Chromium nickel stainless steel
Silver white with jade color
Brownish white in color
Chromium stainless steel
The color is white, slightly gray, and the light is weak
Brownish black in color
Chromium manganese nitrogen stainless steel
Similar to chrome nickel stainless steel, slightly lighter
Black in color
2. Identification with copper sulfate
The method is to remove the oxide layer on the steel, add a drop of water, wipe with copper sulfate, and if it does not change color after wiping, it is generally stainless steel; If it turns purple red: non magnetic is high manganese steel, while magnetic is generally ordinary steel or low alloy steel.
3. Identification with iron absorption stone
Magnets can basically distinguish between two types of stainless steel. Because chromium stainless steel can be attracted to magnets in all states; Chromium nickel stainless steel is generally non magnetic in the annealed state, but some may have magnetism after cold working. But high manganese steel with high manganese content is non magnetic; The magnetic properties of chromium nickel nitrogen stainless steel are more complex: some are non magnetic, some are magnetic, and some are non magnetic in the longitudinal plane and magnetic in the transverse plane. Therefore, although magnets can basically distinguish between chromium stainless steel and chromium nickel stainless steel, they cannot correctly distinguish some special steel grades, let alone specific steel grades.
For steel grades with special properties, we also need to adopt the following three methods for identification.
1. Grinding identification
Grinding identification involves grinding stainless steel on a grinder and observing its sparks. If the spark is linear and has many dense knots, it is a high manganese steel or manganese nitrogen steel with high manganese content; If there are no knots, it is chromium steel or chromium nickel stainless steel.
2. Identification by annealing method
If the chromium nickel stainless steel used for cold working has magnetism, a small piece can be burned red in the fire to allow it to cool naturally or placed in water (annealing). Generally, after annealing, the magnetism will significantly weaken or disappear. However, some chromium nickel stainless steels, such as Cr18Ni11Si4AlTi steel and Cr21Ni5T, contain a considerable amount of ferrite due to the high content of ferrite elements in the steel. Therefore, even in the state of hot working, there is magnetism.
3. Chemical qualitative identification
Chemical qualitative method is a method of identifying whether nickel is present in magnetic stainless steel. The method involves dissolving small pieces of stainless steel in aqua regia, diluting the acid solution with clean water, adding ammonia to neutralize, and then gently injecting nickel reagent. If there is a red fluffy substance floating on the liquid surface, it indicates that stainless steel contains nickel; If there is no red fluffy substance, it indicates that there is no nickel in stainless steel. However, due to the low nickel content in stainless steel, which is usually only a few percent, the nickel content is not easily exposed or determined, and it generally requires multiple experiments with standard samples to master.