Stainless Steel 303

Stainless Steel 303 is a free-machining austenitic stainless steel specifically designed to overcome the machining challenges associated with standard austenitic grades like 304. The addition of selenium and/or sulfur (0.15–0.35%) forms manganese sulfite inclusions that act as internal chip breakers, dramatically reducing tool forces, improving surface finish, and extending tool life. These inclusions make 303 the easiest-to-machine austenitic stainless steel, with machining speeds up to 30–40% faster than 304. However, the improved machinability comes at a cost: reduced corrosion resistance compared to 304 and significantly compromised weldability. 303 is the preferred choice for precision-machined components such as shafts, gears, and fittings where excellent machinability is the primary selection criterion and moderate corrosion resistance is acceptable.

Mechanical Properties

• Density: 8.00 g/cm³
• Tensile Strength: 620 MPa
• Yield Strength: 240 MPa
• Elongation at Break: 35%
• Reduction of Area: 50%
• Hardness: HRB 78-90
• Modulus of Elasticity: 193 GPa
• Thermal Conductivity: 16.2 W/m·K
• Melting Point: 1398 – 1454°C
• Coefficient of Thermal Expansion: 17.3 × 10⁻⁶ /°C

Advantages

✔ Best machinability among austenitic stainless steels — machined up to 30–40% faster than 304 with significantly lower tool wear

✔ Excellent chip control — MnS inclusions act as built-in chip breakers, preventing long stringy chips

✔ Superior surface finish achievable — machined surfaces can reach Ra 0.8–1.6 μm without secondary operations

✔ Good corrosion resistance in mild environments — adequate for indoor, atmospheric, and light chemical exposure

✔ Good strength and ductility — tensile and yield strength higher than 304

Machining & Manufacturing

Common Applications