Large diameter seamless steel magnetic test is the easiest way to distinguish annealed austenitic stainless steels and ferritic stainless steels. Non-magnetic austenitic stainless steel, but after a large reduction will have a mild cold magnetism; and pure chromium steel and low alloy steels are ferromagnetic steel. A significant feature points nitrate test stainless steel tube is concentrated nitric acid and dilute nitric acid which has inherent corrosion resistance. Such properties make it can easily be distinguished from most other metals or alloys. However, high carbon steel type 420 and 440 points during nitric acid test is slightly corroded, non-ferrous metals will immediately encounter concentrated nitric acid corrosion. And dilute nitric acid has a strong corrosive to carbon steel. Copper sulfate point test is the easiest way to quickly distinguish between ordinary carbon steel and stainless steel of all types. The concentration of copper sulfate solution is used for 5 to 10%. Before point test, the test area should be thoroughly remove grease or impurities, and polished with a small area Polishing cloth, then use copper sulfate solution drip drip bottle area to clean up after. 

Ordinary carbon steel or iron in a few seconds to form a layer of copper metal surface, and the surface of stainless steel or copper precipitation is not generated to display the color of copper. Sulfuric acid immersion test can stainless steel tube 302 and 304 with 316 and 317 to distinguish. Trimming of the sample should be finely ground, and then the volume concentration of 20 to 30%, temperature 60 ~ 66 ℃ nitric acid (specific gravity 1.42) and a half hours in the cleaning and passivation. Volume of test solution is a sulfuric acid concentration of 10%, when heated to 71 ℃ .302 and 304 steels immersed in this hot solution was rapidly etched and produce a large number of bubbles, the samples darkened within minutes; 316 and 317 steels and The sample is not subject to corrosion or reaction is very slow (no bubbles), the sample does not change color within 10 to 15 minutes. If large diameter seamless steel specimens tested simultaneously with a known composition to approximate comparison, make the test more accurate.