In the case of unknown steel grade, we can use simple appliances to determine whether it is stainless steel and what kind of stainless steel it belongs to according to the inherent physical and chemical properties of commodities (including whole materials, surplus materials, scraps, etc.).
It should be pointed out that sensory identification can not distinguish specific steel grades, but can only basically distinguish chromium stainless steel, chromium-nickel stainless steel (SUS304, 304) and chromium-manganese nitrogen stainless steel (200series).
1. Identification of color: through the color changes of stainless steel before and after pickling:
Kinds.
After pickling.
Not pickled (when oxidation is serious).
Chromium-nickel stainless steel.
The color is silvery white and jade.
Be brown and white.
Chrome stainless steel.
The color white is slightly gray and the luster is weak.
Brownish black.
Cr-mn-N stainless steel.
Similar to chromium-nickel stainless steel.
Show black.
2. Identify with copper sulfate.
The method is to remove the oxide layer on the steel, put on a drop of water, wipe it with copper sulfate, and if it does not change color after rubbing, it is generally stainless steel; if it changes purplish red: the non-magnetic steel is high manganese steel, and the magnetic steel is generally ordinary steel or low alloy steel.
3. Identify with siderite.
Magnets can basically distinguish between two types of stainless steel.
Because chromium stainless steel can be attracted by magnets in the state; chromium-nickel stainless steel is generally non-magnetic in the annealed state, and some will be magnetic after cold working.
However, the high manganese steel with high manganese content is non-magnetic, and the magnetic situation of Cr-Ni-N stainless steel is more complex: some are non-magnetic, some are magnetic, some vertical planes are non-magnetic and some horizontal surfaces are magnetic.
Therefore, although the magnet can basically distinguish between chromium stainless steel and chromium-nickel stainless steel, it can not correctly distinguish some special properties of steel, let alone the specific steel grade.
For the special nature of steel, we also need to take the following three methods to identify.
1. Identification of grinding flowers.
The identification of grinding flowers is to grind stainless steel on a grinder to watch its sparks.
If the spark is streamlined and has more dense nodal flowers, it is high manganese steel or manganese nitrogen steel with high manganese content; if there is no nodal flower, it is chromium steel or chromium-nickel stainless steel.
2. Identification by annealing method.
If the cold-worked chromium-nickel stainless steel is magnetic, small pieces can be heated in fire to cool naturally or put into water (annealing). Generally speaking, the magnetic properties will be significantly weakened or disappear after annealing.
However, some chromium-nickel stainless steels, such as Cr18Ni11Si4AlTi steel and Cr21Ni5T steel, because the steel contains more ferrite elements, a considerable part of its internal structure is ferrite.
Therefore, it is magnetic even in the state of hot working.
3. Chemical qualitative identification.
Chemical qualitative method is a method to identify whether there is nickel in magnetic stainless steel. the method is to dissolve small pieces of stainless steel deeply in aqua regia, dilute the acid solution with clean water, neutralize it with ammonia water, and then gently inject nickel reagent.
If there is a red fluffy substance floating on the liquid surface, it indicates that there is nickel in the stainless steel; if there is no red fluffy substance, it is proved that there is no nickel in the stainless steel.
However, due to the low content of nickel in stainless steel, generally only a few percent, the content of nickel is not easy to reveal or determine how much, generally need to be tested with standard samples for many times before being able to grasp.