Various stainless steel round steel types, characteristics list
Austenitic stainless steel and ferritic stainless steel can be easily distinguished using a magnetic test. Austenitic stainless steel is known for its excellent corrosion resistance, good cold workability, toughness, and ductility, as well as strong weldability. It is typically non-magnetic in its natural state. However, after significant cold working, it may develop slight magnetism. On the other hand, ferritic and martensitic stainless steels are usually magnetic. This makes the magnetic test one of the simplest and most effective methods to differentiate between austenitic and other types of stainless steel.
The corrosion resistance of stainless steel tubes is a key feature that sets them apart from other metals and alloys. A quick and reliable method to identify this property is the nitric acid spot test. When applied to stainless steel, the surface should remain largely unaffected or only slightly etched. However, certain grades like high-carbon 420 and 440 stainless steels may not show significant reaction. In contrast, concentrated nitric acid can severely corrode non-ferrous metals, while even dilute nitric acid can rapidly corrode carbon steel, making it easy to distinguish.
To identify whether a material is ordinary carbon steel or stainless steel, the copper sulfate spot test is commonly used. The process involves cleaning the test area thoroughly to remove oils and impurities, then polishing a small section with a soft cloth. After applying copper sulfate solution, if the surface shows no copper deposition or a copper color, it is likely stainless steel. If a layer of metallic copper appears, it indicates the presence of carbon steel or iron.
Another useful method involves sulfuric acid to differentiate between various stainless steel grades, such as 302 vs. 304, and 316 vs. 317. Prepare a nitric acid solution with a volume concentration of 20–30% and heat it to 60–66°C. Grind the sample finely, clean it in the nitric acid, and allow it to passivate for about an hour. Then, immerse the samples in a 10% sulfuric acid solution heated to 71°C. The 302 and 304 grades will react quickly, producing many bubbles and turning black, while 316 and 317 will either remain unreacted or react very slowly. This test helps in identifying the type of stainless steel accurately.
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