304g vs 316g – what is the difference?

What is the difference between 304g and 316g? This is a question we often get asked, and in this article, we’ll cover what the differences are and which is best for your project.

Stainless steel is a loose term that covers an overall category of steel. Stainless steel is an iron-carbon alloy that contains a minimum of 10.5% chromium and a maximum of 1.2% carbon. 304 and 316 are the two primary grades of stainless steel used in balustrading. The word grade is often shortened to ‘g’, which is commonly confused for grams, which is undoubtedly the more common meaning of ‘g’.

Outwardly 304 stainless steel and 316 stainless steel look the same. Both are non-magnetic, austenitic and non-hardenable through heat treatment. Each stainless steel grade resists corrosion, is durable, and easily formed and fabricated. So what’s the difference?

What is the difference between 304g and 316g?

The exact difference between the two grades comes down to the chemical composition of the steel. Stainless steel is an alloy, and slightly altering the ‘ingredients’ can make a big difference to the properties of the metal. There are three main ‘types’ of stainless steel – austenitic, ferritic and martensitic. The structure of each type of stainless steel causes specific different properties.

Chromium, nickel and carbon are the three elements that impact the steel’s structure and composition the most. Carbon boosts the mechanical properties; chromium is highly corrosion resistant; and nickel improves toughness and strength by refining the grain size. Changes in the exact composition of stainless steel can also affect its traits. For instance, added molybdenum or nitrogen improves corrosion resistance, while added manganese acts as a stabiliser.

The table below shows the average chemical composition of 304g and 316g. As you can see, 304 and 316 grades are pretty similar in composition. However, the higher chromium content and presence of molybdenum in 316g increases its corrosion resistance.

3040. – 19.58.0 – 10.5
3160. – 13.02.0 – 2.5

Which grade is best for my project?

To determine which grade is best for your project, there are a couple of questions to answer first.

– Is your project indoors or outdoors?

– Is it in a harsh environment? (Think swimming pool, sauna etc.)

As a general rule, 304 grade stainless steel is an internal grade. It is most suited for indoor uses, such as internal staircases or mezzanines. 316 grade stainless steel is an exterior grade suitable for all outdoor projects, such as decking areas, patios and balconies.

One exception is an indoor pool and spa area; any stainless steel handrails or balustrading would need to be 316g to resist the chlorine and chemicals. We recommend that mirror-polished stainless steel is used in this instance. Click here for more information about brushed satin and mirror-polished finish.

Can I see the difference between 304g and 316g? 

Visually there is no difference between 304 and 316. 316g is better at withstanding the elements than 304g, and tea-staining may appear on 304g stainless steel outside with time. When newly installed, it is impossible to tell by looking at the balustrade which grade the stainless steel is. If 304g stainless steel is installed outdoors, this is only visible further down the line.  

What about fixings?

The majority of the fixings we use and supply are stainless steel. Both A2 and A4 are stainless steel fixings, with A2 the equivalent of 304g and A4 the equivalent of 316g. There is no visual difference between A2 and A4, as they are polished and finished with the same process.

How to keep your stainless balustrade looking perfect

Unfortunately, corrosion is a natural phenomenon. Very few elements are naturally found in their pure form because they react with their surroundings. Iron is no exception. 

The chromium in stainless steel reacts quickly with oxygen environments, much the same as iron. The difference, however, is that only a very fine layer of chromium will oxidise (often only a few molecules in thickness). Unlike flaky and unstable iron oxide, chromium oxide is highly durable and non-reactive. It adheres to stainless steel surfaces and won’t transfer or react further with other materials. It is also self-renewing – if removed or damaged, more chromium will react with oxygen to replenish the barrier. The higher the chromium content, the faster the barrier repairs itself. 

Although stainless steel is very hardy and easy to care for, it does require regular maintenance. The brown marks that can form on the surface look like rust but are actually ‘tea-staining’. This is just surface discolouration and doesn’t affect the metal underneath. Doing a thorough wash-down immediately after installation goes a long way towards keeping your balustrade perfect. This first installation clean removes any dirt and impurities from the surface of the stainless steel. 

Remember, it is stain-less steel, not stain-free steel.

To recap, the most significant difference between 304g and 316g is the level of chromium in the stainless steel. We recommend that 316g is always used in outdoor projects, with 304g used in internal projects.

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