As a materials science expert, I am well-versed in the nuances of various alloys, including the differences between 304 and 316 stainless steel. Let's delve into the specifics.

Stainless Steel Basics
Stainless steel is an alloy primarily composed of iron, chromium, and nickel. The chromium content provides the steel with its characteristic corrosion resistance, while nickel enhances the alloy's strength and formability. Both 304 and 316 stainless steels are austenitic, which means they have a face-centered cubic crystal structure, offering excellent toughness and weldability.

Chemical Composition Differences
The fundamental difference between 304 and 316 stainless steel lies in their chemical composition. As you mentioned, 304 stainless steel typically contains 18% chromium and 8% nickel. This composition provides good corrosion resistance and is widely used in various applications due to its balance of properties and cost-effectiveness.

On the other hand, 316 stainless steel has a slightly different composition, with 16% chromium, 10% nickel, and the critical addition of 2% molybdenum. This molybdenum addition is what sets 316 apart from 304, providing enhanced pitting and crevice corrosion resistance, particularly in environments where chlorides are present, such as in marine environments or in applications involving de-icing salts.

Corrosion Resistance
The superior corrosion resistance of 316 stainless steel is due to the presence of molybdenum, which forms a passive oxide film on the surface of the steel. This film is highly resistant to the penetration of corrosive agents, making 316 more suitable for use in corrosive environments than 304. The molybdenum also helps to prevent stress corrosion cracking, which can be a problem in certain high-stress applications.

Mechanical Properties
Both grades have similar mechanical properties, but 316 may exhibit slightly higher strength due to the alloying elements. However, the difference is generally not significant enough to impact the choice between the two for most applications.

Cost and Availability
304 stainless steel is generally more cost-effective and widely available compared to 316. The additional molybdenum in 316 makes it more expensive, but the cost is justified in applications where the superior corrosion resistance is required.

Applications
304 stainless steel is commonly used in household appliances, food processing equipment, and architectural applications where corrosion resistance is needed but the environment is not highly corrosive. 316 stainless steel, with its enhanced corrosion resistance, is often chosen for marine applications, chemical processing, paper manufacturing, and medical devices where exposure to chlorides and other corrosive substances is a concern.

Weldability and Formability
Both 304 and 316 stainless steels are weldable and formable, but 316 may require a slightly lower interpass temperature during welding to avoid sensitization, which can lead to intergranular corrosion.

Summary
In summary, while both 304 and 316 stainless steels are austenitic and share many properties, the key difference is the addition of molybdenum in 316, which provides superior corrosion resistance in chloride-containing environments. The choice between the two grades should be based on the specific requirements of the application, considering factors such as corrosion resistance, mechanical properties, cost, and availability.

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What's the difference between 304 and 316 stainless steel? The simple answer is 304 contains 18% chromium and 8% nickel while 316 contains 16% chromium, 10% nickel and 2% molybdenum. The molybdenum is added to help resist corrosion to chlorides (like sea water and de-icing salts).Sep 27, 2012read more >>