Product Description
303 (1.4305) is a free-machining austenitic stainless steel specially formulated for applications requiring extensive machining operations. This grade is distinguished by its controlled sulfur addition (0.15-0.35%), which significantly enhances machinability by promoting chip breaking and reducing tool drag during cutting operations. As the most readily machinable of all austenitic stainless steels, 303 allows for high-speed machining with deep cuts and heavy feeds, making it ideal for precision components produced in high volume.
The chemical composition of 303 stainless steel includes approximately 17-19% chromium and 8-10% nickel, providing good corrosion resistance in mild environments, though somewhat lower than that of standard 304 stainless steel due to the sulfur addition. Despite this trade-off, 303 maintains excellent mechanical properties including good strength, ductility, and the non-magnetic characteristics typical of austenitic stainless steels in the annealed condition, though it may become slightly magnetic after cold working.
While the sulfur addition significantly improves machinability, it does result in reduced formability, weldability, and slightly lower toughness compared to standard austenitic grades. Nevertheless, 303 stainless steel remains an excellent choice for applications where component design involves extensive machining operations and exposure to mild corrosive environments.
FUSHUN METAL supplies premium 303 stainless steel in various bar forms, ensuring consistent machinability and reliable performance for high-precision components across aerospace, automotive, general engineering, and industrial applications where machining efficiency and moderate corrosion resistance are essential requirements.
Applications
303 (1.4305) stainless steel is specifically designed for applications requiring extensive machining while maintaining good corrosion resistance in mild environments. Its exceptional machinability makes it the preferred choice for components that involve complex turning, drilling, and thread cutting operations, particularly when produced in high volumes on automatic screw machines.
Primary applications for 303 stainless steel include:
- Fasteners and Fittings: Nuts, bolts, screws, and various fastener components that require precision threads and tight tolerances. The excellent machinability of 303 makes it ideal for the high-speed production of these components while maintaining good corrosion resistance for indoor and moderate outdoor environments.
- Aircraft Components: Aircraft fittings, bushings, retainers, and other precision-machined aerospace parts where the combination of good machinability, moderate strength, and acceptable corrosion resistance is advantageous. 303 allows for the efficient production of complex aerospace components with tight dimensional tolerances.
- Gears and Power Transmission Components: Precision gears, shafts, and other power transmission components that require extensive machining operations. The excellent chip breaking characteristics of 303 make it well-suited for gear cutting and similar operations.
- Bushings and Bearings: Sleeve bushings and bearing components for moderate load applications where corrosion resistance is required. The machinability of 303 allows for precise dimensional control and excellent surface finish necessary for these components.
- Electrical Components: Electrical switchgear components, connectors, and other electrical parts that require both good electrical conductivity and moderate corrosion resistance. The machinability of 303 allows for the efficient production of complex electrical components with precise dimensions.
- Automotive Parts: Various automotive components requiring good machinability and moderate corrosion resistance, including certain valve components, fittings, and specialized fasteners.
- Instrument Components: Precision parts for scientific and measuring instruments where dimensional accuracy and moderate corrosion resistance are required.
- General Engineering Components: Any precision-machined components requiring good dimensional control and surface finish in environments where the corrosion resistance of 303 is sufficient.
While 303 stainless steel offers excellent machinability and good corrosion resistance in mild environments, it is not recommended for applications involving welding, severe forming operations, or exposure to highly corrosive environments such as marine or high-chloride settings. For these applications, alternative grades with better formability, weldability, or corrosion resistance should be considered.
Standards
303 (1.4305) stainless steel conforms to numerous international standards and specifications, ensuring consistent quality and performance in demanding machining applications:
European Standards:
- EN 10088-3: Stainless steels – Part 3: Technical delivery conditions for semi-finished products, bars, rods, wire, sections and bright products of corrosion resisting steels for general purposes (1.4305)
- EN 10270-3: Steel wire for mechanical springs – Part 3: Stainless spring steel wire
American Standards:
- ASTM A582/A582M: Standard Specification for Free-Machining Stainless Steel Bars
- ASTM A895: Standard Specification for Free-Machining Stainless Steel Bar, Rod, and Wire for Screw Machine Parts
- ASTM A484/A484M: Standard Specification for General Requirements for Stainless Steel Bars, Billets, and Forgings
- SAE J405: Chemical Compositions of SAE Wrought Stainless Steels
British Standards:
- BS 303S31: Stainless Steel Bar for Machining
- BS EN 58M: Free-Cutting Stainless Steel
Japanese Standards:
- JIS G4303: Stainless Steel Bars (SUS 303)
These comprehensive standards ensure that 303 stainless steel from FUSHUN METAL meets the rigorous requirements for applications requiring exceptional machinability and consistent performance in precision-machined components across various industries.
Material Designation and Chemical Composition
303 stainless steel is known by various designations in different standards and specification systems:
| Standard System | Designation |
|---|---|
| UNS | S30300 |
| AISI/SAE | 303 |
| EN/DIN | 1.4305 |
| EN Designation | X8CrNiS18-9 |
| BS | 303S31 |
| BS EN | 58M |
| Swedish SS | 2346 |
| Japanese JIS | SUS 303 |
The chemical composition of 303 stainless steel is carefully controlled to provide optimal machinability while maintaining good corrosion resistance:
| Element | Minimum (%) | Maximum (%) |
|---|---|---|
| Carbon (C) | – | 0.10 |
| Chromium (Cr) | 17.0 | 19.0 |
| Nickel (Ni) | 8.0 | 10.0 |
| Sulfur (S) | 0.15 | 0.35 |
| Manganese (Mn) | – | 2.0 |
| Silicon (Si) | – | 1.0 |
| Phosphorus (P) | – | 0.20 |
| Copper (Cu) | – | 1.0 |
| Nitrogen (N) | – | 0.10 |
| Iron (Fe) | Balance | – |
The defining characteristic of 303 stainless steel is its sulfur content (0.15-0.35%), which significantly enhances machinability by facilitating chip breaking during machining operations. While this sulfur addition reduces corrosion resistance somewhat compared to standard 304 stainless steel, it provides the exceptional machinability that makes 303 the preferred choice for applications requiring extensive machining operations.
Physical and Mechanical Properties
303 (1.4305) stainless steel offers a good combination of mechanical properties and machinability, making it ideal for precision-machined components in various applications.
Physical Properties
| Property | Value |
|---|---|
| Density | 8.03 g/cm³ (0.285 lb/in³) |
| Melting Point | 1455°C (2650°F) |
| Modulus of Elasticity | 193 GPa (28 × 10⁶ psi) |
| Electrical Resistivity at 20°C | 0.072 × 10⁻⁶ Ω·m (72 microhm-cm) |
| Thermal Conductivity at 100°C | 16.3 W/m·K (112 BTU·in/hr·ft²·°F) |
| Coefficient of Thermal Expansion (20-100°C) | 17.3 × 10⁻⁶ /K (9.6 × 10⁻⁶ /°F) |
| Specific Heat Capacity at 0-100°C | 500 J/kg·K (0.12 BTU/lb·°F) |
Mechanical Properties
The mechanical properties of 303 stainless steel in the annealed condition:
| Property | Value |
|---|---|
| Tensile Strength | 500-700 MPa (72.5-101.5 ksi) |
| 0.2% Yield Strength (min) | 190 MPa (27.5 ksi) |
| Elongation in 50mm (min) | 35% |
| Hardness (max) | 262 HB |
| Compressive Strength | 190 MPa (27.5 ksi) |
Note: ASTM A582 primarily specifies hardness requirements for 303 stainless steel, with tensile properties provided for reference only. Drawn bars, generally up to 25.4mm diameter, will have higher strength values. Proof (yield) stress values in particular will be significantly higher, and the percentage elongation lower, for cold-worked material.
Heat Treatment
303 stainless steel cannot be hardened by heat treatment. The following heat treatment operations may be performed:
- Solution Annealing: Heat to 1010-1120°C (1850-2050°F) followed by rapid cooling (water quenching for thick sections, air cooling for thin sections) to restore ductility and corrosion resistance.
- Hot Working: Uniform heating to 1149-1260°C (2100-2300°F) followed by rapid cooling to ensure maximum corrosion resistance. Hot working operations should be carefully controlled due to the limited hot workability of 303 stainless steel.
It’s important to note that 303 stainless steel is sensitive to carbide precipitation when continuously exposed to temperatures in the range of 425-860°C (800-1580°F). This can reduce corrosion resistance, particularly resistance to intergranular corrosion. Therefore, prolonged exposure to this temperature range should be avoided to maintain optimal corrosion properties.
Available Dimensions
FUSHUN METAL supplies 303 (1.4305) stainless steel in various bar forms to meet the requirements of precision machining applications. Due to its free-machining characteristics, 303 is primarily available as bar products rather than sheet, plate, or tube forms.
Round Bar
| Diameter | Length | Condition |
|---|---|---|
| 3 mm – 300 mm (0.118″ – 12″) | Up to 6,000 mm (236″) | Annealed, Centerless Ground, Polished |
Hexagonal Bar
| Across Flats | Length | Condition |
|---|---|---|
| 4 mm – 100 mm (0.157″ – 4″) | Up to 6,000 mm (236″) | Annealed |
Square Bar
| Dimension | Length | Condition |
|---|---|---|
| 4 mm – 100 mm (0.157″ – 4″) | Up to 6,000 mm (236″) | Annealed |
Flat Bar
| Thickness | Width | Length |
|---|---|---|
| 4 mm – 50 mm (0.157″ – 2″) | 10 mm – 150 mm (0.394″ – 6″) | Up to 6,000 mm (236″) |
Wire
| Diameter | Condition |
|---|---|
| 0.5 mm – 20 mm (0.020″ – 0.787″) | Annealed, Drawn |
Custom dimensions, tolerances, and surface finishes are available upon request to meet specific application requirements. FUSHUN METAL can provide 303 stainless steel in precision-ground and polished conditions for applications requiring tight dimensional tolerances and superior surface finish.
Note: While 303 stainless steel is theoretically available in other product forms such as plate and sheet, it is rarely supplied in these forms due to its limited formability and the specific applications for which it is designed. 303 is primarily used in applications requiring extensive machining, for which bar products are most appropriate.
Fabrication and Machining Properties
303 (1.4305) stainless steel is specifically designed for optimal machinability, but this comes with certain limitations in other fabrication processes. Understanding these characteristics is essential for successful manufacturing with this material.
Machining
The exceptional machinability of 303 stainless steel is its defining characteristic and primary advantage:
- 303 provides superior chip formation and breaking during machining operations due to its sulfur content.
- It allows for higher cutting speeds, deeper cuts, and heavier feeds compared to standard austenitic stainless steels.
- Tool life is significantly extended when machining 303 compared to other austenitic grades.
- For optimal machining performance, the following practices are recommended:
- Keep cutting edges sharp to prevent excessive work hardening.
- Use cuts that are light but deep enough to prevent work hardening by riding on the surface of the material.
- Employ chip breakers to ensure swarf remains clear of the workpiece.
- Use ample coolants and lubricants to manage heat at the cutting edges, as the low thermal conductivity of austenitic alloys concentrates heat in these areas.
Formability
The formability of 303 stainless steel is limited compared to standard austenitic grades:
- 303 is not readily cold workable due to its sulfur content.
- Some cold forming is possible, but sharp bending should not be attempted as it may lead to cracking.
- For applications requiring significant forming operations, alternative grades with better formability should be considered.
Welding
The weldability of 303 stainless steel is poor due to its high sulfur content:
- Welding is generally not recommended for 303 stainless steel.
- If welding is unavoidable, the recommended filler materials are grades 308L and 309 stainless steels.
- For maximum corrosion resistance, welds should be annealed after welding.
- Even with proper procedures, welded joints in 303 will have reduced mechanical properties and corrosion resistance.
- For applications requiring welding, alternative grades with better weldability should be considered.
Hot Working
Hot working of 303 stainless steel requires careful control due to its limited hot workability:
- Hot working operations such as forging should be performed after uniform heating to 1149-1260°C (2100-2300°F).
- After hot working, components should be rapidly cooled to ensure maximum corrosion resistance.
- The presence of sulfur in 303 reduces its hot workability compared to standard austenitic grades.
Surface Finish
303 stainless steel can be finished to a high standard:
- It can be polished to achieve good surface finishes, though the presence of sulfide inclusions may result in some visible stringers.
- For optimal corrosion resistance, it is recommended that 303 stainless steel be chemically treated to remove sulfides from the final surfaces.
- The surface finish significantly affects corrosion resistance, with polished surfaces exhibiting better corrosion resistance than rough surfaces.
Understanding these fabrication characteristics is essential for successful manufacturing with 303 stainless steel. When designing components from this material, it’s important to leverage its exceptional machinability while being mindful of its limitations in forming, welding, and other fabrication processes.
Corrosion Resistance and Service Limitations
While 303 (1.4305) stainless steel offers good machinability and reasonable corrosion resistance, it’s important to understand its performance characteristics and limitations in various environments to ensure appropriate material selection for specific applications.
Corrosion Resistance
- General Corrosion: 303 provides good resistance to atmospheric corrosion and mild corrosive environments. However, its corrosion resistance is lower than that of standard 304 stainless steel due to the presence of sulfur inclusions, which act as initiation sites for corrosion.
- Pitting and Crevice Corrosion: The sulfur additions in 303 significantly reduce its resistance to pitting and crevice corrosion, particularly in chloride-containing environments. In environments containing chlorides at temperatures above 60°C, 303 is susceptible to localized corrosion.
- Intergranular Corrosion: Like other austenitic stainless steels, 303 can be susceptible to intergranular corrosion if exposed to temperatures in the range of 425-860°C (800-1580°F) for extended periods, which can lead to carbide precipitation at grain boundaries.
- Stress Corrosion Cracking: 303 is subject to stress corrosion cracking in chloride-containing environments above approximately 50°C, similar to other common austenitic stainless steels.
- Marine Environments: 303 stainless steel is not suitable for use in marine environments due to its reduced resistance to chloride-induced corrosion.
Heat Resistance
- Oxidation Resistance: 303 stainless steel has good resistance to oxidation when intermittently exposed to temperatures up to 760°C (1400°F) and in continuous service up to 870°C (1600°F).
- Sensitization Range: Continuous use in the temperature range of 425-860°C (800-1580°F) is not recommended as 303 is sensitive to carbide precipitation in this range, which can reduce its corrosion resistance.
Service Limitations
- Environmental Restrictions: 303 is not recommended for use in:
- Marine or coastal environments
- Applications with exposure to high concentrations of chlorides
- Environments involving strong acids or aggressive chemicals
- Applications requiring welding or severe forming operations
- Temperature Limitations:
- Not recommended for continuous service in the 425-860°C (800-1580°F) range due to sensitization concerns
- For high-temperature applications, care should be taken to avoid prolonged exposure to temperatures that could cause carbide precipitation
- Mechanical Limitations:
- Limited formability restricts complex forming operations
- Poor weldability limits joining options
- Not suitable for applications requiring high hardness or wear resistance
Application Recommendations
For optimal performance of 303 stainless steel:
- Utilize in applications that fully leverage its exceptional machinability
- Limit use to mild corrosive environments
- Avoid applications requiring welding when possible
- Consider chemical treatment of finished surfaces to remove sulfides and enhance corrosion resistance
- For improved surface corrosion resistance, specify polished or smooth surface finishes
- Avoid applications involving chloride exposure at elevated temperatures
Understanding these characteristics and limitations is essential for successful application of 303 stainless steel. When properly applied in suitable environments, 303 provides an excellent combination of machinability and adequate corrosion resistance for many precision-machined components.
Why Choose FUSHUN METAL for 303 Stainless Steel
When selecting a supplier for premium 303 (1.4305) free-machining stainless steel, FUSHUN METAL stands as your preferred partner for several compelling reasons:
Superior Machining Performance
At FUSHUN METAL, we understand that the primary reason for selecting 303 stainless steel is its exceptional machinability. Our metallurgical experts carefully control the sulfur content and distribution to ensure optimal chip formation and breaking during machining operations. This attention to detail results in consistent, reliable machining performance that reduces tool wear, increases productivity, and ensures high-quality surface finishes on your precision-machined components.
Consistent Mechanical Properties
We implement rigorous quality control processes throughout our production chain to ensure consistent mechanical properties in our 303 stainless steel products. Our comprehensive testing includes chemical composition analysis, mechanical property verification, and microstructure examination to guarantee that every batch meets or exceeds international standards. This consistency allows you to confidently design and manufacture components with predictable performance characteristics.
Dimensional Precision and Surface Quality
FUSHUN METAL offers 303 stainless steel bar products with precise dimensional tolerances and superior surface quality. Our centerless grinding and polishing capabilities ensure that our bar products meet the most demanding dimensional requirements for precision machining applications. This attention to dimensional accuracy and surface finish quality helps you minimize machining allowances and achieve excellent results in your final components.
Technical Support and Material Selection
Our team of metallurgical experts provides comprehensive technical support to help you optimize the use of 303 stainless steel in your applications. We can assist with material selection, machining parameter recommendations, and corrosion resistance guidance to ensure you achieve the best results with our products. This expertise ensures that you can fully leverage the exceptional machinability of 303 stainless steel while understanding its limitations in specific applications.
Custom Solutions and Specialized Processing
We understand that standard products don’t always meet specialized requirements. FUSHUN METAL offers custom processing services including precision cutting, specialized surface treatments to enhance corrosion resistance, and non-standard dimensions to meet your exact specifications. Our ability to provide tailored solutions helps you optimize your manufacturing processes and reduce overall costs.
For your next project requiring the exceptional machinability and reliable performance of 303 stainless steel, we invite you to contact our technical team to discuss your specific requirements. Our experts are ready to help you select the optimal material specifications and provide the premium quality products you need to achieve efficient machining operations and reliable component performance in your demanding applications.
