Chemical identification methods for stainless steel bars

Nowadays, many industrial products are made using stainless steel material. In order to identify the authenticity of stainless steel material, certain measures and methods can be taken. However, many people do not know what methods can be used for identification. The following are four chemical identification methods for stainless steel bars.

1. Magnetic testing method - The magnetic testing method is the simplest and most common method to distinguish austenitic stainless steel from ferritic stainless steel. Austenitic stainless steel is a non-magnetic steel, but after cold working under high pressure, it will have mild magnetism; Pure chromium steel and low alloy steel are both strong magnetic steels.

2. Nitric acid point test method - A significant feature of stainless steel is its inherent corrosion resistance to concentrated and dilute nitric acid, which makes it easy to distinguish from most other metals or alloys. However, high carbon steel 420 and 440 are slightly corroded during nitric acid point testing, and non-ferrous metals are immediately corroded when they encounter concentrated nitric acid, while dilute nitric acid has strong corrosiveness to carbon steel.

3. Copper sulfate spot test method - Copper sulfate spot test is the simplest method to quickly distinguish between ordinary carbon steel and all types of stainless steel. The concentration of copper sulfate solution used is 5% -10%. Before conducting the spot test, the test area should be thoroughly cleaned of oil or other impurities, and a small area should be polished with a polishing machine or soft cloth. Then, the test solution should be dropped onto the polishing area. Ordinary carbon steel or iron will form a layer of surface metallic copper within a few seconds, And the surface of stainless steel does not produce copper precipitation or display the color of copper.

4. Sulfuric acid test method - sulfuric acid immersion in stainless steel can distinguish 302 and 304 from 316 and 317. The cut edges of the sample need to be finely ground, and then cleaned and passivated in sulfuric acid with a volume concentration of 20%~30% and a temperature of 60-66 ℃ for half an hour. The sulfuric acid solution has a volume concentration of 10%, and when heated to 71 ℃, 302 and 304 are immersed in the solution. The steel is rapidly corroded and produces a large number of bubbles, and the sample turns black within a few minutes; The samples of 316 and 317 steel are not corroded or corrode slowly (without producing bubbles), and the test does not change color within 10-15 minutes. If samples with known components are tested simultaneously for approximate comparison, it can make the test more accurate.

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