What are the special methods for identifying stainless steel

Grinding pattern identification 

The method of identifying by grinding is to grind the stainless steel on a grinding wheel machine and observe the sparks. If the sparks are in a streamlined shape and have more and denser swirls, it indicates a high manganese steel or manganese-nitrogen steel with a higher manganese content; if there are no swirls, it is a chromium steel or chromium-nickel stainless steel. 

2. Annealing method identification 

The cold-worked chromium-nickel stainless steel, if magnetic, can be cut into small pieces, heated red-hot in a fire and allowed to cool naturally, or placed in water (for annealing). Generally speaking, after annealing, the magnetism will significantly weaken or completely disappear. However, for some chromium-nickel stainless steels, such as Cr18Ni11Si4AlTi steel and Cr21Ni5Ti steel, since they contain a considerable amount of ferrite elements, a considerable part of their internal structure is ferrite. Therefore, even in the state of hot processing, they still have magnetism. 

3. Chemical qualitative analysis method for identification 

The chemical qualitative method is a way to identify whether nickel is present in magnetic stainless steel. The method is as follows: Take a small piece of stainless steel and dissolve it in aqua regia. Dilute the acid solution with clean water, add ammonia to neutralize it, and then gently inject the nickel reagent. If a red fluffy substance floats on the liquid surface, it indicates that the stainless steel contains nickel; if there is no red fluffy substance, it proves that there is no nickel in the stainless steel. (However, since the nickel content in stainless steel is low, usually only a few percent, the nickel content is not easy to be revealed or determined precisely. Generally, it is necessary to conduct experiments with standard samples multiple times before one can master it.) 

The above several identification methods indicate that when using a sensory tube to identify stainless steel, not only multiple methods need to be combined for testing, but the test results can only determine the type of stainless steel, but cannot determine which alloy elements are contained in the steel and their specific contents. Therefore, it can be said that the sensory identification method is currently extremely imperfect. Some of them may be incorrect, and many physical phenomena are only known in terms of their effects but not the reasons behind them. They still need further exploration. 

The best way to accurately distinguish different types of stainless steel is to conduct in-depth investigations at relevant processing units, consult with their material managers and workers, understand the steel type used, carefully examine the steel grade marks on the steel, and review the original materials, etc. This is the fundamental method for correctly identifying the types and quality of stainless steel.