Several simple identification methods for 304 stainless steel

　　Several simple identification methods for 304 stainless steel:

　　1. Identify with copper sulfate

　　Remove the oxide layer on 304 stainless steel, put a drop of water, and rub it with copper sulfate. If it does not change color after rubbing, it is generally stainless steel; if it turns purple, the non-magnetic one is high manganese steel, and the magnetic one is generally ordinary steel or Low-alloy steel.

　　For steel grades with special properties, we need to adopt the following three methods for identification.

　　If the cold-worked chromium-nickel stainless steel is magnetic, it is advisable to burn a small piece in the fire and let it cool naturally or put it in water (annealing). Generally speaking, the magnetism will be significantly weakened or completely disappeared after annealing. However, some chromium-nickel stainless steels, such as Cr18Ni11Si4AlTi steel and Cr21Ni5Ti steel, contain more ferrite elements in the steel, and a considerable part of their internal structure is ferrite. Therefore, it is magnetic even in the hot-worked state.

　　Second, grinding flower identification

　　Grinding identification is to grind stainless steel on a grinder and watch its sparks. If the spark is streamlined and has more dense knots, it is high manganese steel or manganese nitrogen steel with higher manganese content; if there is no knot, it is chromium steel or chrome-nickel stainless steel.

　　3. Identification by chemical qualitative method

　　Chemical qualitative method is an identification method to identify whether nickel is contained in magnetic stainless steel. The method is to dissolve a small piece of stainless steel in aqua regia, dilute the acid solution with clean water, add ammonia water for neutralization, and then gently inject nickel reagent. If there is a red velvet substance floating on the liquid surface, it means that the stainless steel contains nickel; if there is no red velvet substance, it proves that there is no nickel in the stainless steel (but because the nickel content in stainless steel is low, generally only a few percent, the nickel content The content is not easy to reveal or determine how much, and generally can only be grasped after many experiments with standard samples).

　　The above several identification methods show that to identify stainless steel with senses, it is not only necessary to use several methods for comprehensive testing, but the test results can only determine a certain type of stainless steel, and cannot determine which alloy elements and specific contents are contained in the steel. Therefore, the method of sensory identification is currently extremely imperfect, and some may be wrong. There are still many physical phenomena that are only known but not known, and need to be further explored. The best way to correctly distinguish stainless steel grades is to conduct in-depth investigation and research, and ask relevant testing units to conduct testing and judgment. This is the fundamental method to correctly distinguish the type and quality of stainless steel.