304 vs 316

304 vs 316

What do these numbers mean, and what are they good for?

In the most basic answer, 316 is “marine grade” stainless steel while 304 is not. But it’s more complicated than that and requires some further explanation about the metal.

Corrosion Resistance of 304 vs 316

As the amount of chromium and molybdenum (among other elements) varies, so do the corrosion resistance. One big difference between 304 and 316 is the presence of molybdenum in 316’s makeup. This is what gives it the extra corrosion resistance that befits the name “marine grade.”

You should use 304 when…

-Cost is more important than corrosion resistance

-You are not in marine environments

-The part is not exposed to corrosive chemicals

You should use 316 when…

-The part is in a marine environment

-The part is exposed to corrosive chemicals

304 vs 316

More info about 304

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, which contains 18% chromium and 8% nickel.

304 is non-magnetic and exhibits poor thermal and electrical conductivity. It boasts excellent malleability and can be formed into many shapes.

Due to having lower corrosion resistance and cost than 316, 304 is often seen in household and industrial applications like sinks, refrigerators, and other machinery parts.

304 offers a good balance of strength, corrosion resistance, and workability.

More info about 316

Also known as A4 stainless, 316’s defining attribute is stellar corrosion resistance. Like we said earlier, it has superb abilities in salt-water and marine applications.

The physical properties of 316 are similar to 304, though 316 is also a bit stronger. The big difference is the incorporation of molybdenum, generally ranging from 2-3% by composition.

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.

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. However, technically calling it “stainless” isn’t quite correct. It will still stain, just at a dramatically slower rate than standard steels.

This is possible because 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.

Would you like to know more?

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!

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.