What are the differences between 304 and 316 stainless steel?

Understanding the components of stainless steel

Although stainless steel is less easily stained than other iron-based materials, over time it can still get marked by fingertips and grease and can develop discolouration and rust. This is referred to as ‘tea coloured’ staining. This can be visually unappealing but will not generally affect the performance of the stainless steel.

What gives stainless steel its added durability is its resilience? Stainless steel can withstand prolonged atmospheric exposure and use before showing signs of wear, unlike other steels.

All steels have the same basic iron and carbon composition, but stainless steel also contains a healthy dose of chromium—the alloy that gives stainless steel its famous corrosion resistance.

What is grade 304 stainless steel?

Grade 304 stainless steel is the most common austenitic stainless steel. It is commonly known as ‘kitchen grade’ and is sometimes marked or stamped with 18/10 or 18/8 grade. 304 grade stainless steel contains between 16 and 24% chromium and up to 35% nickel, as well as small amounts of carbon and manganese. The remainder of the chemical composition is primarily iron.

The most common form of 304 stainless steel is 18-8 or 18/8 stainless steel, which contains 18% chromium and 8% nickel.

The high amounts of chromium and nickel give 304 stainless steel excellent corrosion resistance. Grade 304 stainless steel is commonly used in the following applications:

• Refrigerators and dishwashers
• Commercial food processing equipment
• Fasteners
• Piping
• Heat exchangers
• Structures in environments that would corrode standard carbon steels

For more aggressive environments, 304 grade stainless steel will struggle to maintain its performance and you’ll need to look at the next step up to what is the second most common grade of stainless steel.

What is grade 316 stainless steel?

Grade 316 stainless steel is commonly called a marine grade stainless steel. It has higher amounts of nickel and chromium and the addition of molybdenum to improve its corrosion resistant properties. Grade 316 stainless steel also contains silicon, manganese and carbon, with the majority of the composition being iron.

Grade 316 stainless steel is often considered one of the most suitable choices when selecting austenitic stainless steel for marine applications. This makes grade 316 stainless steel particularly desirable for applications where exposure to salt may be an issue.

Grade 316 stainless steel is more optimal in environments that include a high amount of corrosive elements, the material will be placed underwater, or in applications that require greater strength and hardness.

The major difference between 304 and 316 stainless steel

The major difference between 304 and 316 stainless steel is the chemical composition, with grade 316 containing molybdenum while grade 304 does not include molybdenum.

The molybdenum content results in grade 316 possessing increased corrosion resistance.

However, the molybdenum content in grade 316 stainless steel can have adverse effects on formability and machinability, and then there are also cost impacts, as grade 316 stainless steel is generally more expensive than grade 304.

Which is better: grade 304 or 316?

Both 304 and 316 stainless steel use nickel to maintain an austenitic composition at lower temperatures.

Austenitic steels ensure a versatile balance of strength, workability and corrosion resistance, making them ideal for outdoor architectural features, surgical instrumentation and food processing equipment.

However, a large volume of 316 stainless steel can be found in products related to the food and beverage industries. Grade 316 stainless steel is commonly found in commercial kitchens and food processing plants.

Due to its higher resistance to chlorides, 316 is a standard in the marine industry for boats, ships and marinas requiring extended performance from their metal fixtures.