Before we dive into the differences between the Stainless Steel Grades 304 and 316, we best cover what stainless steel is to make sure we’re all on the same level.
Stainless steel is a name given to a group of strong and durable steel alloys that contain more than 10.5% chromium (Cr). Chromium has a high affinity for oxygen – meaning it combines well with oxygen – and forms a stable oxide film on the surface of stainless steel. The film layer on the surface of stainless steel provides the material with its corrosion resistance properties.
This film is called the “passive oxide layer”, which forms instantaneously in ordinary atmospheres. It is self-healing and rebuilds when it has been removed, allowing stainless steel to maintain corrosion resistant after being sawed, perforated or notched.
The most common form of stainless steel is the austenitic Grade 304. Austenitic grades are ones that have nickel (Ni) added to the stainless steel to change the crystal structure from ferrite to austenite. Grade 304 is an example of the basic composition of austenitic stainless steel, as it is 18% chromium and 8% nickel.
The low maintenance cost, durability and favourable welding properties makes Grade 304 the most commonly used type of stainless steel. It’s typical applications include heat exchangers, brewery pipelines, food handling and processing equipment and chemical containers.
Commonly known as Marine Grade, Grade 316 is the second-most popular type of stainless steel and is another austenitic steel. It mechanical and physical properties are almost identical to that of Grade 304. The main difference comes in its molecular composition; Grade 316 structure consists of 2-3% of molybdenum (Mo), which improves the material’s corrosion resistance beyond that of Grade 304, particularly against chlorides and other industry-based solvents.
The superior corrosion resistance and its non-reactive qualities make Grade 316 a safe and reliable material for high-saline environments and industrial applications. This type of stainless steel was named Marine Grade from being the most common used grade of stainless steel in coastal and marine environments, where there are high levels of salt (sodium chloride) which would normally compromise less-resistant types of steel.
Grade 316 is a non-reactive compound; making it a suitable component in surgical instruments and environments where sanitation is paramount.
While both Grades 304 and 316 benefit from corrosion resistant properties – thanks to their passive oxide layers. Grade 316 boasts a comparatively-better resilience, making it the preferred option for applications where harsh conditions are expected and excellent corrosion resistance is required.
This superior corrosion resistance comes at a price. Grade 316 is more expensive, making it less suitable when price is a project concern. Conversely, Grade 316’s molybdenum content can have adverse effects on its formability – making Grade 304 the favoured option when it comes to fabrication purposes.
Grade 304 and Grade 316 are both strong and reliable materials. Both are available in a variety of finishes, from standard mill finish to decorative super mirror polished. Whether you use one grade over the other should be made on a case-by-case basis and after seeking expert advice.
At UKF Group, we supply stainless steel in a range of grades and are happy to support our customers through every stage of their projects.
To get started, call us on 01527 578686.