The chemical identification method of stainless steel

Stainless steel, it is to point to weak corrosive medium such as air, steam, water resistance and acid, alkali, salt and other chemical etching medium corrosion of the steel, also called acid-proof stainless steel. Stainless steel itself because of its corrosion resistance, high temperature resistant, wear resistant features, in our country focus on the development of energy, petrochemical, electric power, mining and other fields will be more active to play its role. Products include stainless steel flanges and stainless steel pipe fittings.
About the stainless steel chemical identification method has the following kinds:
1, magnetic test, magnetic test method is the most primitive of the most common difference between austenitic stainless steel and ferritic stainless steel of the most simple way to austenitic stainless steel, nonmagnetic steel but after cold work under big pressure will be mild magnetic, and pure chromium steel and low alloy steel are strong magnetic steel.
2, nitric acid test points that stainless steel is a striking feature of nitric acid and dilute nitric acid have inherent corrosion resistance, this performance make it can easily distinguish from most other metals or alloys, but high carbon type 420 and 440 steel in nitric acid test is a little corrosion, when meet with nitric acid was immediately non-ferrous metal corrosion, dilute nitric acid on carbon steel has strong corrosive.
3, copper sulfate spot test, the copper sulfate test is quick to distinguish between ordinary carbon steel and the easiest way of all types of stainless steel, the use of the concentration of a solution of copper sulfate is 5% – 10%, before the point tests, test area should be thoroughly remove oil and other impurities, cloth or soft grinding polishing and grinding machine, small area, and then try the droplets to burnish, ordinary carbon steel or iron within a few seconds can form a layer of metal copper surface, and test the surface of the stainless steel is not produced copper precipitation or display the color of copper.
4, sulfuric acid test, acid immersion stainless steel can make a distinction between 302 and 304 and 304 and 316. Sample trimming should pass fine grinding, and then in the volume concentration of 20% ~ 20%, the temperature of 60 ~ 66 ℃ in sulfuric acid cleaning and passivation for half an hour, the volume concentration of the sulfuric acid solution was 10%, when heated to 71 ℃, 302 and 304 in solution in stainless steel corrosion was quickly and produce a large number of air bubbles, sample in some kind of black, the 316 and 317 stainless steel sample was from corrosion or corrosion slow (not have bubbles), test does not change color within 10 ~ 15 minutes. If at the same time test specimen with a known component is used to compare similar words, can make the experiment more accurate.

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