Magnetic test is the simplest way to distinguish between annealed austenitic stainless steel and ferritic stainless steel. Austenitic stainless steel is a non-magnetic steel, but it will be slightly magnetic after cold working under high pressure. But pure chrome steel and low alloy steel are strong magnetic steel.
Two, nitric acid point test stainless steel tube is a remarkable characteristic of concentrated nitric acid and dilute nitric acid has inherent corrosion resistance. This property allows it to be easily distinguished from most other metals or alloys. But high carbon 420 and 440 steel in the nitric acid point test is slightly corroded, non-ferrous metals encounter concentrated nitric acid will be corroded immediately. Dilute nitric acid has strong corrosive effect on carbon steel.
Copper sulfate point test Copper sulfate point test is the easiest way to quickly distinguish between ordinary carbon steel and all types of stainless steel. The concentration of copper sulfate solution used is 5~10%. Before the spot test, the test area should be thoroughly cleaned of grease or various impurities, and a small area should be polished with a soft cloth, and then copper sulfate solution should be dripped into the cleaned area with a drop bottle. Ordinary carbon steel or iron forms a coating of copper in a matter of seconds, while stainless steel’s surface does not produce copper deposits or show the color of copper.
Four, sulfuric acid test sulfuric acid immersion stainless steel tube test can distinguish 302 and 304 from 316 and 317. The cut edge of the sample should be finely ground, and then cleaned and passivated for half an hour in nitric acid (specific gravity 1.42) with a volume concentration of 20~30% and a temperature of 60~66℃. The sulfuric acid test solution has a volume concentration of 10% and is heated to 71℃. When the steel 302 and 304 is immersed in this hot solution, it is rapidly corroded and produces a large number of bubbles, and the sample turns black in a few minutes. The samples of 316 and 317 steels are not corroded or react very slowly (no bubbles are produced), and the samples do not change color within 10 to 15 minutes. The test can be more accurate if a similar comparison is made by simultaneously testing samples of known composition.