Type 304 and 304L Stainless Steel

Stainless steel takes its name from its ability to resist rusting thanks to the interaction between its alloying components and the environment to which they're exposed. Numerous types of stainless steel serve a variety of purposes and many overlap. All stainless steels are comprised of at least 10% chromium. But not all stainless steels are the same.

Stainless Steel Grading

Each type of stainless steel is graded, usually in a series. These series classify the different types of stainless from 200 to 600, with many categories in between. Each comes with distinct properties and falls into families including:

• austenitic: non-magnetic
• ferritic: magnetic
• duplex
• martensitic and precipitation hardening: high strength and good resistance to corrosion 

Here, we explain the difference between two common types found on the market — 304 and 304L. 

Type 304 Stainless Steel 

Type 304 is the most widely used austenitic stainless steel. It is also known as "18/8" stainless steel because of its composition, which includes 18% chromium and 8% nickel. Type 304 stainless steel has good forming and welding properties as well as strong corrosion resistance and strength.

This kind of stainless steel also has good drawability. It can be formed into a variety of shapes and, in contrast to type 302 stainless, can be used without annealing, the heat treatment that softens metals. Common uses for type 304 stainless steel are found in the food industry. It's ideal for brewing, milk processing, and wine-making. It's also suitable for pipelines, yeast pans, fermentation vats, and storage tanks.​

Type 304 grade stainless steel is also found in sinks, tabletops, coffee pots, refrigerators, stoves, utensils, and other cooking appliances. It can withstand corrosion that can be caused by various chemicals found in fruits, meat, and milk. Other areas of use include architecture, chemical containers, heat exchangers, mining equipment, as well as marine nuts, bolts, and screws. Type 304 is also used in mining and water filtration systems and in the dyeing industry. 

Type 304L Stainless Steel 

Type 304L stainless steel is an extra-low carbon version of the 304 steel alloy. The lower carbon content in 304L minimizes deleterious or harmful carbide precipitation as a result of welding. 304L can, therefore, be used "as welded" in severe corrosion environments, and it eliminates the need for annealing.

This grade has slightly lower mechanical properties than the standard 304 grade, but is still widely used thanks to its versatility. Like Type 304 stainless steel, it's commonly used in beer-brewing and wine-making, but also for purposes beyond the food industry such as in chemical containers, mining, and construction. It is ideal for use in metal parts such as nuts and bolts that are exposed to salt water. 

304 Stainless Physical Properties:

• Density: 8.03g/cm³
• Electrical resistivity: 72 microhm-cm (20C)
• Specific Heat: 500 J/kg °K (0-100°C)
• Thermal conductivity: 16.3 W/m-k (100°C)
• Modulus of Elasticity (MPa): 193 x 10³ in tension
• Melting Range: 2550-2650°F (1399-1454°C)

Type 304 and 304L Stainless Steel Composition:

Element	Type 304 (%)	Type 304L (%)
Carbon	0.08 max.	0.03 max.
Manganese	2.00 max.	2.00 max.
Phosphorus	0.045 max.	0.045 max.
Sulfur	0.03 max.	0.03 max.
Silicon	0.75 max.	0.75 max.
Chromium	18.00-20.00	18.00-20.00
Nickel	8.00-10.50	8.00-12.00
Nitrogen	0.10 max.	0.10 max.
Iron	Balance	Balance

Source: AK Steel Product Data Sheet. 304/304L Stainless Steel