304 vs 316 Stainless Steel – What’s the Difference?

304 vs 316

One of the most common questions about stainless steel revolves around two alloys, 304 vs 316. What do these numbers mean, and what are they good for? In the most basic answer, 316 is “marine grade” while 304 is not. But it’s more complicated than that and requires some further explanation about the metal. Stainless steel provides superior corrosion resistance, strength, and versatile surface appearance. Iron provides strength, and chromium provides the corrosion resistance. These properties, as well as the versatility of its surface to be polished or left matte, make it popular for both industrial as well as domestic uses.

How does rust work?

Rust is created when iron molecules combine with oxygen in the presence of water. The result is a red flaky oxide that deteriorates easily, exposing more material to further corrosion. Iron and standard carbon steels are highly susceptible to this type of corrosion.

Stainless steel has the ability to form a protective surface that prevents such corrosion. How does this happen? The chromium in stainless steel reacts with oxygen, like iron. The difference is that only a very fine layer of chromium will oxidize. This layer is often only a few molecules in thickness. This barrier is highly durable and non-reactive. It also adheres to the rest of the stainless steel and won’t break off or react further with other materials. It will also replenish if damaged or removed. Once oxidized, also called passivized, stainless steel typically rusts at a rate of less than 0.002″ in a given year.

Corrosion Resistance of 304 vs 316

As the amount of chromium and molybdenum (among other elements) varies, so do the corrosion resistance. Today we’ll be focusing on 304 vs 316, which are the two most popular grades. There are a lot of other different alloys in stainless, but we’ll talk about those another time. One big difference between 304 and 316 is the presence of molybdenum in the latter’s makeup, which gives it the extra corrosion resistance that befits the name “marine grade stainless”.

Corrosion is a natural part of exposure to the wind, water and environment. Pure elements such as iron inherently react with the surrounding environment. This is especially true when alkaline or salt water is present. Because of this, very few elements can be found naturally in their pure form. They naturally mix with other elements or change due to exposure. These sort of mixtures – alloys – have synergistic properties that retain the special characteristics from each of the elements.

When kept in best condition, stainless steel offers clean and bright surfaces ideal for many building and landscape designs.

304 vs 316

304 Stainless Steel Diagonal backsplash

304 Stainless Steel

Also known as A2 stainless, 304 is the most common of the stainless steel family. It contains roughly 16-25% chromium and up to 36% nickel by composition. It also has small amounts of carbon and manganese. The most common form of 304 stainless is 18-8, or 18/8 stainless steel which contains 18% chromium and 8% nickel.

An austenite steel, 304 is non-magnetic and exhibits poor thermal and electrical conductivity. It boasts excellent malleability and can be formed into many shapes. But it also has less corrosion resistance than other stainless steels. Due to this, 304 is often seen in household and industrial applications like machinery parts and screws. Despite this, 304 offers a good balance of strength, corrosion resistance, and workability that last when properly maintained.

316 Stainless Steel

Also known as marine grade or A4 stainless, 316 is well-known for its increased resistance to corrosion. Particularly, it has superb abilities in salt-water and marine applications. 316 comes with similar physical properties and uses as 304. The big difference is the incorporation of molybdenum, generally ranging from 2-3% by composition.  Some specialty 300-series stainless steels can contain up to 7-8% molybdenum.

316 stainless steel is widely used in chemical process and high-salinity environments. For these reasons it is also often used to manufacture surgical equipment.

Choosing 304 vs 316

If you’re planning on using stainless steel in salt water environments, 316 is the proper alloy. Similarly, if your project is exposed to corrosive chemicals, 316 is preferable. If you’re looking for a durable alloy but superior corrosion resistance isn’t necessary, 304 stainless can work perfectly. Lastly, if your wallet is the biggest factor, 304 is less expensive.

We also have a Guide to Stainless Steel which has hard numbers if you want to see those.

We hope this helps you decide which material is right for you!

Would you like to know more?

Looking to weld your Stainless? Whether your project uses 304 vs 316, or a different grade, check out our tips for welding the different types of stainless steel.

304 vs 316