SS303 is an austenitic stainless steel like 304 with added sulphur, which breaks the chips and makes it much easier to machine. It is popular for turned parts made in large numbers on CNC and sliding-head lathes. The price is slightly lower corrosion resistance and poor weldability.
Quick facts
- Type
- Free-machining austenitic stainless steel
- Key addition
- Sulphur, about 0.15% min
- Machinability
- The best of the common stainless steels
- Corrosion
- Lower than 304; avoid marine and acid service
- Weldability
- Poor; not recommended for welding
- Magnetic
- No (annealed)
Equivalent grades
| Standard | Grade |
|---|---|
| AISI / ASTM | 303 |
| EN | 1.4305 (X8CrNiS18-9) |
| UNS | S30300 |
| JIS | SUS303 |
Equivalents are close, not identical. Name the grade and standard on the drawing.
Typical chemical composition
| Element | % |
|---|---|
| Carbon (C) | 0.10–0.15 max |
| Chromium (Cr) | About 17–19 |
| Nickel (Ni) | About 8–10 |
| Sulphur (S) | 0.15 min (often 0.15–0.35) |
| Manganese (Mn) | Up to 2 |
Values are typical. The exact limits depend on the standard and supplier; ask for the mill test certificate when it matters.
SS303 or SS304?
| SS303 | SS304 | |
|---|---|---|
| Machining | Easy, short chips | Gummy, long stringy chips |
| Corrosion | Fair | Good |
| Welding | Not recommended | Excellent |
| Typical use | Turned parts in volume | Sheet, fabrication, tanks |
Typical uses
- Shafts, pins, bushes and spacers
- Nuts, bolts and fittings
- Valve and pump parts
- Instrument and electronic parts
Need parts made in SS303 stainless steel?
Post your requirement free. Workshops that take your kind of work see it and get in touch. You only talk to the ones that fit.
Get startedRelated
Related job work
Questions
- Why is SS303 easier to machine than SS304?
- The added sulphur forms small inclusions that break the chips, so tools cut freely and last longer. SS304 forms long tough chips and work-hardens.
- Can SS303 be welded?
- It is not recommended: the sulphur causes cracking in the weld. Choose SS304 or SS316 for welded parts.
- Is SS303 food grade?
- It is used in some food machinery parts, but SS304 or SS316 are preferred where the part touches food or cleaning chemicals, because of their better corrosion resistance.
The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 16 October 2026.