Overview
SS303 (AISI 303 Stainless Steel) is a free-machining austenitic stainless steel belonging to the 300 Series Stainless Steel Family. It is specifically designed for high-speed machining applications by adding sulfur to improve chip breaking and reduce tool wear.
SS303 offers excellent machinability, good corrosion resistance, and satisfactory mechanical properties, making it one of the most widely used stainless steels for CNC machining, automatic lathes, precision turned parts, shafts, fittings, valves, and fasteners.
Compared with SS304, SS303 provides significantly better machinability but slightly lower corrosion resistance and weldability.
Material Specification
| Property | Value |
|---|---|
| Material Designation | AISI 303 |
| Material Family | Austenitic Stainless Steel |
| UNS Number | S30300 |
| EN Grade | 1.4305 |
| Density | 7.93 g/cm³ |
| Magnetic Property | Non-Magnetic (Annealed), Slightly Magnetic After Machining |
| Standard Forms | Bar, Rod, Round Bar, Hex Bar, Flat Bar, Wire |
Chemical Composition
| Element | Content (%) |
|---|---|
| Iron (Fe) | Balance |
| Chromium (Cr) | 17.0–19.0 |
| Nickel (Ni) | 8.0–10.0 |
| Sulfur (S) | 0.15–0.35 |
| Carbon (C) | ≤0.15 |
| Manganese (Mn) | ≤2.00 |
| Silicon (Si) | ≤1.00 |
| Phosphorus (P) | ≤0.20 |
| Nitrogen (N) | ≤0.10 |
Mechanical Properties
Annealed Condition
| Property | Value |
|---|---|
| Tensile Strength | ≥515 MPa |
| Yield Strength | ≥205 MPa |
| Elongation | ≥30% |
| Hardness | ≤95 HRB |
| Elastic Modulus | 193 GPa |
Physical Properties
| Property | Value |
|---|---|
| Density | 7.93 g/cm³ |
| Melting Point | 1400–1455°C |
| Thermal Conductivity | 16.3 W/m·K |
| Electrical Resistivity | 0.72 μΩ·m |
| Thermal Expansion Coefficient | 17.3 × 10⁻⁶/K |
| Specific Heat Capacity | 500 J/kg·K |
Corrosion Resistance
| Environment | Performance |
|---|---|
| Indoor Environment | Excellent |
| Atmospheric Exposure | Good |
| Industrial Environment | Good |
| Humid Environment | Good |
| Marine Environment | Fair |
| Chloride Environment | Fair |
| Chemical Environment | Moderate |
The sulfur added to improve machinability slightly reduces corrosion resistance compared with SS304. For highly corrosive or marine environments, SS304 or SS316 is preferred.
International Equivalent Grades
| Standard | Equivalent Grade |
|---|---|
| ASTM / AISI (USA) | 303 |
| UNS | S30300 |
| EN (Europe) | 1.4305 |
| DIN (Germany) | X8CrNiS18-9 |
| JIS (Japan) | SUS303 |
| GB/T (China) | Y12Cr18Ni9 |
| ISO | X8CrNiS18-9 |
Available Forms
| Product Type | Availability |
|---|---|
| Round Bar | Yes |
| Hex Bar | Yes |
| Flat Bar | Yes |
| Precision Rod | Yes |
| Wire | Yes |
| Forging Stock | Yes |
| Machining Blank | Yes |
Typical Applications
CNC Machining Industry
- Precision Turned Parts
- CNC Milled Components
- Custom Machined Parts
- Instrument Components
Fastener Industry
- Screws
- Bolts
- Nuts
- Studs
- Threaded Components
Valve & Fluid Systems
- Valve Bodies
- Valve Stems
- Hydraulic Fittings
- Pneumatic Components
Electronics Industry
- Connectors
- Sensor Housings
- Electrical Components
Medical Equipment
- Surgical Instrument Components
- Diagnostic Equipment Parts
- Precision Mechanical Components
General Engineering
- Shafts
- Bushings
- Couplings
- Fittings
- Precision Assemblies
Manufacturing Characteristics
| Manufacturing Process | Rating |
|---|---|
| CNC Turning | Outstanding |
| CNC Milling | Excellent |
| Swiss Machining | Outstanding |
| Automatic Screw Machining | Outstanding |
| Drilling | Excellent |
| Tapping | Excellent |
| Threading | Excellent |
| Welding | Poor |
| Cold Forming | Fair |
| Polishing | Good |
Advantages
Outstanding Machinability
One of the easiest stainless steels to machine.
Excellent Surface Finish
Produces high-quality machined surfaces.
High Production Efficiency
Suitable for automated machining and mass production.
Good Corrosion Resistance
Adequate for most industrial environments.
Dimensional Stability
Ideal for precision engineering applications.
Reduced Tool Wear
Improves tool life during machining operations.
Limitations
Lower Corrosion Resistance Than SS304
Sulfur additions reduce corrosion performance.
Poor Weldability
Not recommended for welded structures.
Lower Formability
Less suitable for deep drawing and severe cold forming.
Not Suitable for Marine Environments
SS316 performs better in saltwater applications.
Comparison with Other Stainless Steels
| Property | SS303 | SS304 | SS316 | SS302 | SS416 |
|---|---|---|---|---|---|
| Machinability | Outstanding | Good | Good | Good | Excellent |
| Corrosion Resistance | Good | Excellent | Outstanding | Excellent | Moderate |
| Weldability | Poor | Excellent | Excellent | Good | Poor |
| Formability | Fair | Excellent | Excellent | Excellent | Poor |
| CNC Machining | Excellent | Good | Good | Good | Excellent |
| Cost | Medium | Medium | High | Medium | Medium |
Comparison with Common Engineering Metals
| Material | Density (g/cm³) | Machinability | Corrosion Resistance | Strength |
|---|---|---|---|---|
| SS303 | 7.93 | Outstanding | Good | Medium |
| SS304 | 8.00 | Good | Excellent | Medium |
| Aluminum 6061 | 2.70 | Excellent | Good | Medium |
| Brass C360 | 8.47 | Outstanding | Good | Medium |
| Carbon Steel 12L14 | 7.85 | Outstanding | Poor | Medium |
| Titanium Grade 5 | 4.43 | Fair | Excellent | Very High |
Available Surface Finishes
Mill Finishes
- Turned Finish
- Ground Finish
- Bright Drawn Finish
- Cold Finished Surface
Decorative Finishes
- Mirror Polish
- Satin Finish
- Brushed Finish
- Hairline Finish
Functional Finishes
- Passivation
- Electropolishing
- Chemical Cleaning
- Laser Marking
Frequently Asked Questions (FAQ)
What is SS303 stainless steel?
SS303 is a free-machining austenitic stainless steel specifically designed for CNC machining and automatic screw machine production.
What is SS303 used for?
Typical applications include:
- Precision Machined Parts
- Fasteners
- Valve Components
- Shafts
- Bushings
- Fittings
Is SS303 better than SS304 for CNC machining?
Yes.
| Property | SS303 | SS304 |
|---|---|---|
| Machinability | Outstanding | Good |
| Tool Life | Longer | Shorter |
| Production Speed | Faster | Slower |
SS303 is generally the preferred stainless steel for high-volume machining.
What is the difference between SS303 and SS304?
| Property | SS303 | SS304 |
|---|---|---|
| Machinability | Better | Lower |
| Corrosion Resistance | Lower | Higher |
| Weldability | Poor | Excellent |
| Sulfur Content | Higher | Low |
Is SS303 magnetic?
In the annealed condition, SS303 is generally non-magnetic. Cold working and machining may induce slight magnetism.
Can SS303 be welded?
Welding is generally not recommended because sulfur additions can cause hot cracking and reduce weld quality.
Does SS303 rust?
SS303 has good corrosion resistance but is less corrosion-resistant than SS304 and SS316.
Is SS303 suitable for food-grade applications?
For general food-contact components, yes. However, SS304 is more commonly specified for food processing equipment.
Why is SS303 commonly used for CNC machining?
Because it combines:
- Excellent Chip Breaking
- Reduced Tool Wear
- High Machining Speed
- Good Surface Finish
making it one of the most efficient stainless steels for machining.
Does GCNOV provide custom manufacturing services for SS303?
Yes. GCNOV provides:
- CNC Turning
- CNC Milling
- Swiss Machining
- Precision Machining
- Thread Rolling
- Surface Finishing
- Electropolishing
- Passivation
- Prototype Development
- Low-Volume Production
- Mass Production