303 Stainless Steel
An austenitic stainless steel with sulfur, for free machining
Typical values for the temper in the title
303 is essentially 304 with a deliberate sulfur addition (at least 0.15%). The sulfur forms manganese sulfide inclusions that break the chip and reduce friction, so it machines much faster than 304. It is the common stainless for automatic lathes.
The cost: the same inclusions lower corrosion resistance (mainly to pitting), hurt weldability (hot cracking), and reduce ductility somewhat. It suits machined parts in mild environments.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | 515–620 MPa | |
| Yield strength Rp0.2 | 205–310 MPa | |
| Elongation A | 40% | |
| Hardness | 160–190 HB | |
| Modulus of elasticity E | 193 GPa | |
| Density ρ | 7.93 g/cm³ | |
| Machinability | 85% | relative rating in the site database |
Chemical composition (wt %)
| Element | Range | Role |
|---|---|---|
| Cr chromium | 17.0–19.0 | the protective layer |
| Ni nickel | 8.0–10.0 | austenitic structure |
| S sulfur | min 0.15 | MnS inclusions that break the chip |
| P phosphorus | max 0.20 | helps machining |
| C carbon | max 0.15 | |
| Mn manganese | max 2.00 | forms the MnS inclusions |
| Si silicon | max 1.00 | |
| Fe iron | balance |
Ranges per ASTM A582 (free-machining bar).
Conditions and heat treatment
Like all austenitic stainless, 303 is not hardened by heat treatment. It is supplied mainly as annealed or drawn bar.
| Condition | Properties | When to choose it |
|---|---|---|
| Annealed | soft, most corrosion resistant | most uses |
| Cold drawn | higher strength and dimensional accuracy | bar for automatic lathes |
Applications
- Automatic lathe parts
- Shafts, pins and bushings
- Fittings and pipe connectors
- Food machinery parts (in mild environments)
- Bolts and nuts (A1 per ISO 3506)
Fabrication
Machining
This is the reason to choose it: short broken chips, high cutting speeds, and long tool life compared with 304.
Welding
Not recommended. Sulfur causes hot cracking in the weld. If unavoidable, use a ferrite-rich filler (for example ER312), with care.
Corrosion
Lower than 304, especially to pitting. Not suited to marine or chloride environments.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| 304 / 304L | 515–620 / 205–310 MPa | Good — ER308L | more resistant and weldable, but machines slower · material page |
| 316 / 316L | 485–620 / 170–310 MPa | Excellent — ER316L | for chloride environments · material page |
| 416 | 515–800 / 275–620 MPa | Poor | a martensitic free-machining stainless that can be hardened · material page |
Common mistakes
Welding 303
Sulfur causes weld cracking. For a welded part, choose 304L.
Using 303 in a marine environment
The inclusions are starting points for pits. For such an environment, 316.
Choosing 303 when there is little machining
If most of the cost is material rather than machining, 304 is better for corrosion.
Equivalents, standards and supply
| EN | 1.4305 |
|---|---|
| DIN | X8CrNiS18-9 |
| JIS | SUS303 |
| Standards | ASTM A582 / EN 10088-3 |
| Forms | rod · wire |
| Producers | Outokumpu · Carpenter · Sandvik · Valbruna |
Learn more
Values are typical and for comparison only. For design, rely on the standard and on the mill certificate. Sources: ASTM A240, ASTM A276 and EN 10088 (composition), producer data sheets, and the METAL HUB materials database.
Updated: October 31, 2026