304 stainless steel is the most common stainless steel. The steel contains both chromium (between 15–20%) and nickel (between 2–10.5%) 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”.
It is specified by SAE International as part of its SAE steel grades. Outside of the US it is commonly known as A2 stainless steel, in accordance with ISO 3506 for fasteners. In the commercial cookware industry it is known as 18/8 stainless steel. In the unified numbering system it is UNS S30400. The Japanese equivalent grade of this material is SUS304. It is also specified in European norm 1.4301.
CHEMICAL COMPOSITION: (PER ASTM A240)
17.5 to 19.5
18.0 to 20.0
8.0 to 10.5
8.0 to 12.0
MECHANICAL PROPERTIES: (PER ASTM A240, A666)
Yield Strength 0.2% offset (KSI)
Tensile Strength (KSI)
% Elongation(2″ Gauge length)
304 ¼ Hard
304 ½ Hard
304L ¼ Hard
304L ½ Hard
They all possess the same nominal chromium and nickel contents and thus possess the same corrosion resistance, ease of fabrication and weldability.
The carbon content of 304H (UNS S30409) is restricted to 0.04-0.10%, which provides optimal high temperature strength.
The carbon content of 304L (UNS 30403) is restricted to a maximum of 0.03%, which prevents sensitization during welding. Sensitization is the formation of chromium carbides along grain boundaries when a stainless steel is exposed to temperatures in the range of ~900 °F (480 °C)–1,500 °F (820 °C). The subsequent formation of chromium carbide results in reduced corrosion resistance along the grain boundary leaving the stainless steel susceptible to unanticipated corrosion in an environment where 304 would be expected to be corrosion resistant. This grain boundary corrosive attack is known as intergranular corrosion.