The big pressure cold processing will have mild magnetic; pure chrome steel and low alloy steel is strong magnetic steel. Magnetic test is the simplest way to distinguish between annealed austenitic stainless steel and ferritic stainless steel. Austenitic stainless steel is non-magnetic steel.
Two, the point of nitric acid test, non-ferrous metals encounter concentrated nitric acid will be immediately corroded. Dilute nitric acid has a strong corrosive effect on carbon steel. One of the remarkable characteristics of stainless steel tubes is inherent corrosion resistance to concentrated nitric acid and dilute nitric acid. This property allows it to be easily distinguished from most other metals or alloys. However, high carbon type 420 and 440 steels were slightly corroded when they were subjected to nitrate point test.
Three, copper sulfate point test, copper sulfate point test is the fastest way to distinguish between ordinary carbon steel and all types of stainless steel the easiest way. The concentration of copper sulfate solution used is 5~10%. The test area of stainless steel pipe should completely remove grease or various impurities, before point test. Polish a small area and soft cloth, then dropping to clean up after the regional infusion of copper sulfate solution. Ordinary carbon steel or iron will form a layer of surface copper in seconds, while stainless steel does not produce copper precipitation or show the color of copper.
Four, sulfuric acid test, and then in the volume concentration of 20~30% temperature of 60~66 degrees of nitric acid (specific gravity of 1.42 cleaning and passivation for half an hour). Sulfuric acid immersion stainless steel tube test can distinguish between 302 and 304 and 316 and 317. The cutting edges of the sample should be finely ground. It is rapidly corroded and produces a large number of bubbles. The volume concentration of sulfuric acid test solution is 10%, heated to 71 degrees centigrade, when.302 and 304 steel are immersed in this thermal solution. The sample is black in a few minutes; the specimens of 316 and 317 steel are not corroded or react slowly (without bubbles), and the sample does not change in 10~15 minutes. The test can be made more accurate if the simultaneous tests are carried out on the samples with known components for approximate comparison.