1. Color recognition
The surface color of the pickled stainless steel is white and bright. The color of chromium-nickel stainless steel is as white as jade; the color of chromium stainless steel is white, slightly gray, and the luster is also weak; the color of chromium-manganese nitrogen stainless steel is similar to chromium-nickel stainless steel, but the color is lighter.
The surface color of non-pickling stainless steel: chromium-nickel steel is brown-white, chromium steel is brown-black, and chromium-chromium-manganese steel is black (these three colors refer to the colors with heavier oxidation). The surface color of cold-rolled unannealed chromium-nickel stainless steel is silver-white and reflective.
2. Use magnets to identify
Magnets can be used to differentiate between the two types of stainless steel. Because chromium stainless steel can be attracted by magnets in any state. Chromium-nickel stainless steel is generally non-magnetic in the annealed state; some will become magnetic after cold working. However, manganese-rich steels with higher manganese content are non-magnetic. The magnetism of chromium-nickel-nitrogen stainless steel is relatively complex: some are non-magnetic, some are magnetic, some are non-magnetic on the vertical surface, and are magnetic on the lateral surface. Therefore, although magnets can basically distinguish between chromium stainless steel and chromium-nickel stainless steel, they cannot correctly distinguish some steel types with special properties, let alone specific grades or types of stainless steel.
3. Identification of copper sulfate
Remove the oxide layer on the steel, drop a drop of water and wipe it with copper sulfate. If it does not change color after friction, it is usually stainless steel; if it turns purple, it may be one of two results: 1) If it is non-magnetic, it is high manganese steel; 2) If it is magnetic, it is usually ordinary steel or low manganese steel alloy steel.
For steel types with special properties, the following three methods can be used to identify them.
4. Identification of grinding sparks
Grinding spark identification is to grind stainless steel on a grinder and observe sparks. For example, if the sparks are streamlined and the knots are dense, it is high manganese steel or manganese nitrogen steel with higher manganese content; if there are no knots, it is chromium steel or chromium-nickel stainless steel.
5. Annealing identification
If the cold-worked chromium-nickel stainless steel is magnetic, you can verify it in two ways: take a small piece, burn it until red, and then 1) cool it naturally; 2) put it in water. In general, the magnetism will be significantly reduced or completely lost after annealing. However, some chromium-nickel stainless steels, such as Cr18Ni11Si4AlTi steel and Cr21Ni5Ti steel, are magnetic even in the hot working state because they contain more ferrite elements and a considerable part of their internal structure is ferrite.
6. Chemical qualitative identification
Chemical qualitative identification is a method to identify whether magnetic stainless steel contains nickel. The method is to dissolve a small piece of stainless steel in aqua regia, dilute the acid with clean water, add ammonia, and then gently inject the nickel reagent. If there is red fluffy material floating on the surface of the liquid, it means that the stainless steel contains nickel. If there is no red fluff, it proves that there is a lack of nickel in the stainless steel. Since the content of nickel in stainless steel is relatively low, only a few percent, its content is not easy to sense or determine. Generally, multiple standard sample experiments are required to determine its content.
