What are the differences between 304 grade and 316 marine grade stainless steel?

Stainless steel is a metal alloy. It’s commonly used in everyday consumer products, from cutlery to kitchen appliances, wheel covers, hose clamps and car parts. 304 grade stainless steel comprises iron, nickel, titanium, aluminium, copper, nitrogen, phosphorus, selenium and chromium.

The crucial ingredient here is chromium, which makes up about 10.5 per cent of all steel. When metals such as iron react with water, they oxidise – leading to localised areas of rust known as ‘pitting’.

How chromium works

Thanks to the chromium content in stainless steel, this rusting process slows down. Just like iron, chromium reacts with oxygen when exposed to water. However, there is far less oxidisation than with iron alone, and the reactive process produces a thin protective layer on top of the steel.

This serves as a barrier against further oxidisation and corrosion, making it ideal for everyday uses such as running cutlery through the dishwasher.

With its durable properties, stainless steel is the material of choice for everyday applications. It’s also cheap to fabricate and easy to clean.

Where it is lacking is in the strength of its anti-corrosive properties. While it can handle non-severe environments, it’s not the best choice for chlorides (such as saltwater) or chemical conditions. This is where marine grade steel comes in.

316 marine grade stainless steel has all the benefits of stainless steel, with one extra. In addition to all the elements that make up stainless steel, marine grade steel contains molybdenum.

This can be found in some stainless steels but in far lower concentrations. In marine grade steel, it makes up around 2 to 3 per cent.

How molybdenum works

Molybdenum is a hard metallic element used to toughen marine grade steel and make it more resistant to submersion in water. It’s also better at tackling chlorides, bromides, iodides and fatty acids.

In simple terms, this means it’s perfect for use in saltwater, but it’s also ideal for chemical applications.

It can handle high temperatures and offers a more sterile alternative to stainless steel. The molybdenum content makes it less reactive, which means there is less chance of excessive metallic contamination. This is why 316 marine grade stainless steel is such a popular choice in surgical instruments and pharmaceutical products.

There are two key differences between 304 grade stainless steel and 316 marine grade stainless steel: corrosion protection and cost. Naturally, this impacts their applications and cost-effectiveness.

For higher-cost applications, such as medical equipment and chemical processing, marine grade steel is worth the extra investment. It will provide long-term protection against the elements and keep users safe.

Meanwhile, mass-produced items or products that don’t need exposure to harsh environments may benefit from 304 grade stainless steel. It is cheaper to produce and easy to use in everyday scenarios.

How you can make both last longer

Of course, both 304 grade stainless steel and 316 marine grade stainless steel will last longer if they’re properly maintained. Regular cleaning, lower concentrations of salt and lower exposure time or temperature will ensure they last.