303 and 304 stainless steel have similar properties, but their composition and properties are different.

In terms of composition:

303 stainless steel contains sulfur, which can improve its machinability but also affect its corrosion resistance. It contains 17-19% chromium, 8-10% nickel, and up to 0.15% sulfur.

304 stainless steel does not contain sulfur, but has a carbon content higher than 303. Contains 18-20% chromium and 8-10.5% nickel.

Features:

Machinability: 303 stainless steel has excellent machinability due to its sulfur content, making it a popular choice for parts that require extensive machining. In contrast, 304 stainless steel is more difficult to process, but it provides better comprehensive mechanical properties.

Corrosion resistance: The overall corrosion resistance of 304 stainless steel is better than that of 303. 304 stainless steel is sulfur free, making it more resistant to corrosion and pitting in corrosive environments such as seawater and chloride environments.

Strength: 304 stainless steel has higher tensile strength and yield strength than 303.

In summary, although 303 and 304 stainless steel have similar performance, 304 stainless steel has better overall corrosion resistance and mechanical properties, but the processing difficulty is higher. 303 stainless steel is a good choice for parts that require extensive machining but are not as corrosion-resistant as 304. The selection of materials ultimately depends on specific application requirements and factors such as machinability, corrosion resistance, and mechanical properties.