304 vs 316 Stainless Steel: The Most Critical Difference

1. Differences in chemical composition
The main components of stainless steel are iron, chromium and nickel, among which chromium is the key factor that determines the corrosion resistance of stainless steel. 304 stainless steel contains 18% chromium and 8% nickel, so it is also called 18-8 stainless steel. 316 stainless steel improves its corrosion resistance by reducing the chromium content and increasing nickel and molybdenum (generally 2-3%), especially enhancing its resistance to chloride and acidic environments.

2. Comparison of corrosion resistance
Due to the addition of molybdenum to 316 stainless steel, it exhibits superior corrosion resistance in seawater or other chloride environments. Molybdenum can combine with chloride ions to reduce the corrosion of chloride ions on stainless steel, so 316 stainless steel is a better choice in marine environments or industrial environments containing a large amount of chloride ions.
In contrast, 304 stainless steel performs well in general atmospheric environments or mildly corrosive environments, but its corrosion resistance is not as good as 316 stainless steel in environments with high chloride content.

3. Physical and mechanical properties
In terms of physical properties, the density, melting point, etc. of 304 and 316 stainless steel are basically similar. However, in terms of mechanical properties, since 316 stainless steel contains more nickel and molybdenum, it generally exhibits better ductility and toughness. This makes 316 stainless steel more suitable for certain applications that require high strength and high toughness.

4. Temperature tolerance
Both 304 and 316 stainless steels maintain good strength and corrosion resistance in high temperature environments. However, when it comes to extremely low temperatures, 316 stainless steel generally has better low-temperature impact toughness due to its higher nickel content. This gives 316 stainless steel a more obvious advantage in applications that need to withstand extreme temperature changes, such as liquefied natural gas (LNG) storage tanks.

5. Processing and welding properties
From a processing and welding perspective, both 304 and 316 stainless steels have good plasticity and weldability. However, since 316 stainless steel contains more alloying elements, it may require more heat input during welding. In addition, during the heat treatment process after welding, 316 stainless steel also requires more delicate control to avoid sensitization (i.e., the precipitation of chromium carbides leads to a decrease in corrosion resistance).