Stainless steel 304, 303, 304L or 316? Check the differences

Steel grades: 304, 303, 304L and 316 are corrosion-resistant steels with an austenitic structure. They are well-known and widely used in households (including sinks, kitchen appliances), construction, and the food and pharmaceutical industries. The chromium-nickel stainless steels in question are characterized by very good formability and high mechanical properties. They are very often used in environments of steam, moisture and continuous contact with water. They exhibit good mechanical properties such as strength, hardness and ductility. Austenitic stainless steels are suitable for applications that require corrosion resistance and maintenance of high metal surface hygiene.

In addition, grade 304L is a low-carbon steel, making it amenable to welding. It is used especially in the food, automotive and construction industries.

Although they belong to the group of corrosion-resistant steels they show some differences.

The difference between the 304, 303, 304L and 316 grades

The main differences between the described grades of stainless steels:

• chemical composition
• corrosion resistance in aggressive environments
• mechanical properties
• costs.

Steel 304 and 304L differ primarily in their carbon content. 304 steel contains 0.07% C and exhibits a higher yield strength of about 190MPa than 304L steel, which contains 0.03% C and has a yield strength value of 175 MPa. This difference is important in structural design. Other properties including impact strength, weldability ductility for both grades are very similar. In terms of corrosion resistance, the grade with a lower carbon concentration, i.e. 304L, shows greater resistance to intergranular corrosion in welded structures, where carbide precipitation can occur in the heat affected zone, causing intergranular corrosion.

Steel grade 303 is classified as an automatic stainless steel with an increased concentration of sulfur (0.15% - 0.35%) and carbon (0.10%). The increased concentration of carbon compared to 304 steel is the reason for the lack of resistance to intergranular corrosion. The chemical composition of 303 steel has a beneficial effect on machining, i.e. it improves chip breakability due to the sulfides emitted during the process.

The chemical composition of 304 and 316 steel differs, 304 steel contains 18-20% chromium and 8-10.5% nickel, plus manganese and silicon addition, while 316 grade contains 17-19% chromium, 13-15% nickel, manganese and silicon addition, plus 2% molybdenum. Due to its different chemical composition, 316 steel has higher corrosion resistance, especially in acidic environments. The addition of molybdenum (Mo) in stainless steel improves resistance to chlorides. This grade of steel effectively protects against corrosion caused by sulfuric, hydrochloric, acetic, formic and tartaric acids, as well as acidic sulfates and alkaline chlorides. It retains its properties when in contact with seawater , hence it is commonly referred to as "sea" steel.

Due to its different chemical composition and consequently better corrosion resistance and higher mechanical properties, steel grade 316 is more expensive. If the parts made of it are not exposed to an aggressive environment, its use is unreasonable and can be replaced by 304, 303 or 304L steel grade.

Chemical composition of 304, 303, 304L and 316 steel grades

Can they be used interchangeably?

These steels can be used interchangeably, but only for elements exposed to water, but then you should pay attention to the price and choose the cheaper grade, which is 304, 303 or 304L steel. If the components will be used in an aggressive environment, then definitely choose the 316 grade. If the conditions in which the components will work require greater strength - you should also choose the 316 grade. The advantage of 304 and 303 steel is greater formability and susceptibility to machining.