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May 29, 2018
SAE 304 stainless steel also known as A2 stainless steel (not the same as A2 tool steel) or commercially as 18/10 or 18/8 stainless steel, European norm 1.4301, is the most common stainless steel. The steel contains both chromium (between 18–20%) and nickel (between 8–10.5%) metals as the main non-iron constituents. It is an austenitic stainless steel. It is less electrically and thermally conductive than carbon steel and is essentially non-magnetic. It has a higher corrosion resistance than regular steel and is widely used because of the ease in which it is formed into various shapes.
The composition was developed by W. H. Hatfield at Firth-Vickers in 1924 and was marketed under the trade name “Staybrite 18/8”. The Japanese equivalent grade of this material is SUS304.
304 stainless steel has excellent resistance to a wide range of atmospheric environments and many corrosive media. It is subject to pitting and crevice corrosion in warm chloride environments and to stress corrosion cracking above about 60 °C. It is considered resistant to potable water with up to about 200 mg/L chlorides at ambient temperatures, reducing to about 150 mg/L at 60 °C.
304 stainless steel is also very sensitive at room temperature to the thiosulfate anions released by the oxidation of pyrite (as encountered in acid mine drainage) and can undergo severe pitting corrosion problems when in close contact with pyrite- or sulfide-rich clay materials exposed to oxidation.
For more severe corrosion conditions, when 304 stainless steel is too sensitive to pitting or stress corrosion cracking, the 316 stainless steel is the second grade of stainless steel the more commonly used.
304 stainless steel is used for a variety of household and industrial applications such as screws, machinery parts, car headers, and food-handling equipment. 304 stainless steel is also used in the architectural field for exterior accents such as water and fire features. It is also a common coil material for rebuildable vaporizers.
Difference between 304, 304H and 304L
According to the content of chromium and nickel, they are all 304 stainless steel, the composition is containing 18% chromium (Cr), 8% nickel (Ni), but the main difference is the percentage of carbon between them, 304L is ultra-low carbon stainless steel, the carbon content is down to 0.03% or less, the carbon content of 304H should not be less than 0.04%, 304 stainless steel carbon content is in the middle.The application is different, the property is different correspondingly, 304L stainless steel seamless tubes have lower tensile strengh (≥485 MPa) and yield strength (≥175 MPa) than 304 and 304H.