Three simple methods for identifying different types of stainless steel

When the specific steel grade (number) is unknown, we can determine whether it is stainless steel and which type of stainless steel it belongs to by using simple tools and relying on our senses, based on the inherent physical and chemical properties of the goods (including raw materials, scraps, waste materials, etc.). 

It should be noted that sensory identification cannot distinguish specific steel grades. It can only basically differentiate among the three major categories: chromium stainless steel, chromium-nickel stainless steel (SUS303, 304), and chromium-manganese-nitrogen stainless steel (200 series). The identification methods are as follows: 

1. Identification of color 

The surface of stainless steel that has undergone acid washing appears silver-white and smooth: the chrome-nickel stainless steel has a silver-white color resembling jade; the chrome stainless steel is white with a slightly grayish luster; the chrome-manganese-nitrogen stainless steel has a color similar to that of the chrome-nickel stainless steel but slightly lighter. The surface color of stainless steel that has not undergone acid washing: the chrome-nickel steel is brownish white, the chrome steel is brownish black, and the chrome-manganese-nitrogen is black (these colors refer to the darker oxidized colors). The surface of cold-rolled chrome-nickel stainless steel that has not been annealed is silver-white with a reflective luster. 

2. Use copper sulfate for identification 

The method is to remove the oxide layer on the steel, add a drop of water, and then rub it with copper sulfate. If there is no color change after the rubbing, it is generally stainless steel; if it turns purplish red, it is high manganese steel (without magnetism); if it has magnetism, it is usually ordinary steel or low alloy steel. 

3. Use a magnet for identification 

Magnetic stones can basically distinguish between two types of stainless steel. Because chromium stainless steel can be attracted by magnetic stones in any state; chromium-nickel stainless steel is generally non-magnetic in the annealed state, and after cold processing, some may become magnetic. However, high manganese steel with a high manganese content is non-magnetic; the magnetic properties of chromium-nickel-nitrogen stainless steel are more complex: some are non-magnetic, some are magnetic, and some have no magnetic property on the longitudinal surface but have magnetic property on the cross-sectional surface. 

Therefore, although magnets can basically distinguish between chromium stainless steel and chromium-nickel stainless steel, they cannot accurately distinguish some special types of steel, let alone specific steel grades.