The most widely used types of stainless steel are graded as 304 and 316. The grading system used to classify these two steel grades comes from a numbering system started by the American Iron and Steel Institute (AISI), one of the oldest trade unions that dates back to 1855. These classifications indicate their compositions, with most stainless steels rated in the 200s and 300s considered austenitic. The austenitization process involves heating the iron, iron alloy, or steel to a point where it changes its crystalline structure from ferrite to austenite. Though difficult to distinguish between the two with the naked eye, the distinctive properties between 304 vs 316 stainless steel make each better for certain applications.
About 304 Stainless Steel
The most commonly used of the austenitic stainless steel, the 304 grade is made up of 8-10.5 percent of nickel and 18-20 percent of chromium. Alloys also include other elements – including carbon, manganese and silicon – with the rest of the composition being primarily iron. With the high nickel and chromium content, the 304 grade of stainless steel offers excellent protection against corrosion.
Common applications for 304 stainless steel include:
- Automotive moldings and trim
- Commercial equipment used for processing food
- Electrical enclosures
- Fasteners and finishing hardware like nuts, bolts, screws, plates and handles
- Harsh environments where carbon steel readily corrodes
- Heat exchangers
- Interior architecture and decorative hardware, such as panels and sculptures
- Piping
- Pots, pans and other kitchen utensils and implements
- Residential kitchen appliances
- Residential sinks and their components
- Storage tanks
- Tubing for equipment
- Wheel covers
One notable difference between 304 and 316 stainless steel is their levels of nickel and chromium. The former grade usually has a higher chromium content while the latter generally contains more nickel.
About 316 Stainless Steel
The 316 grade is also mostly comprised of iron, and similarly contains high amounts of nickel and chromium – at 10-14 percent and 16-18 percent respectively – as well as smaller amounts of carbon, manganese, molybdenum and silicon. For this reason, the 316 grade of stainless steel tends to be the preferred choice for use in marine environments.
Common applications for 316 stainless steel include:
- Cisterns and piping used in chemical applications
- Commercial kitchens and appliances
- Containers used to hold pressurized gasses or liquids
- Equipment for chemical storage and processing
- Equipment used for industrial and chemical transportation
- Marine components
- Marine settings
- Medical devices and equipment not requiring surgical steel
- Outdoor electrical enclosures
- Outdoor furnishing
- Pharmaceutical manufacturing
- Refinery infrastructure
- Seafood production and other food processing in saline environments
- Stainless steel floats
The main difference between 304 vs. 316 stainless steel involves the 316 grade’s much higher levels of molybdenum, which are typically 2-3 percent by weight and provide better corrosion resistance.
Molybdenum & Stainless Steel
The name for the chemical element molybdenum evolved from the ancient Greek word for lead, as it was often confused with lead ores. It is not found alone as metal but occurs as an oxide in various minerals. Silvery-gray in appearance, it has one of the highest melting points of any element. Because of this property, it provides incredible strength and stability to steel alloys, which is why its most common use involves steel production. All of the 300-series grades of stainless steel contain some molybdenum, with certain grades that are highly resistant to corrosion containing up to 7 percent molybdenum. However, these higher grades are only necessary for use in extreme environments where metals are exposed to extremely high chloride levels.
Comparison Between 304 vs 316 Stainless Steel
When looking at these two steel grades, both look similar in appearance and have comparable chemical compositions. Both resist rusting and corrosion well, while also offering added durability. When comparing 304 vs. 316 stainless steel, the latter’s higher cost can be attributed to its better corrosion resistance. Because of this price differential and the limited environments in which 316 steel is advantageous, the 304 grade is the most widely used austenitic stainless steel.
Because of its better corrosion resistance, the stainless 316 grade costs more. For applications that expose an alloy to chlorinated solutions and chlorides, including seawater, using this higher grade is especially recommended. It can add years to the life of components or equipment exposed to harsh and corrosive conditions, particularly if it involves exposure to salts. Yet for most applications, the 304 grade will work perfectly well. In summation, when looking at 304 vs. 316 stainless steel, for applications that require superior resistance to corrosion or water, use 316 stainless. For other applications, 304 stainless will work just fine.
To sum it up, 316 steel is worth the expense if you need superior corrosion resistance and your application contains water. If not, 304 steel will serve your needs just fine.