AISI 303 Austenitic Stainless Steel: Free-Machining Grade
ASTM A582/A895 · Published: 2026-06-01 · Updated: 2026-06-02
AISI 303 is the free-machining version of 304, with 0.15-0.35% sulfur added to break chips and lubricate the cutting tool—improving machinability by approximately 40% over 304. However, the sulfur addition significantly degrades corrosion...
AISI 303 is the free-machining version of 304, with 0.15-0.35% sulfur added to break chips and lubricate the cutting tool—improving machinability by approximately 40% over 304. However, the sulfur addition significantly degrades corrosion resistance (especially pitting resistance), formability, and weldability—303 is not recommended for welding due to hot cracking from low-melting-point sulfide phases at grain boundaries. Used for nuts, bolts, bushings, fittings, and shafts produced in high volumes on automatic screw machines where machinability is the primary cost driver. For applications requiring both machinability and weldability, consider 304L with optimized machining parameters instead.
Quick Facts
| Category | Stainless Steel |
| Standard | ASTM A582/A895 |
| Density | 8.00 g/cm³ |
| Yield Strength | 240 MPa (35 ksi) |
| Tensile Strength | 585 MPa (85 ksi) |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| EN 1.4305 | Compare |
| X8CrNiS18-9 | Compare |
| SUS303 | Compare |
| Y1Cr18Ni9 | Compare |
Related Materials
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Frequently Asked Questions
Why can't 303 be welded?
The sulfur added for machinability forms low-melting-point manganese sulfide stringers at grain boundaries. During welding, these sulfides melt and cause hot cracking (solidification cracking) in the weld metal and HAZ. For applications requiring welding, use 304/304L and accept the reduced machinability. There is no free-machining austenitic stainless steel with acceptable weldability.
References & International Standards
- ASTM International. Standard Specifications for Steel & Metal Alloys. astm.org
- International Organization for Standardization (ISO). Metallic Materials — Cross-Reference Database. iso.org
- American Iron and Steel Institute (AISI). Steel Grade Designations & Equivalents. steel.org
- European Committee for Standardization (CEN). EN Steel Standards & Numbering System. cencenelec.eu