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Should I use 303 or 304 stainless steel?
Use 303 for turned and machined parts that are not welded or cold formed: added sulfur lifts its machinability rating to about 78% versus 45% for 304, so parts cut roughly 70% faster. Use 304 when parts are welded, bent, drawn, or exposed to chlorides and acids, where 303's sulfide inclusions reduce corrosion resistance and cause weld cracking.
Stainless steel 303
Stainless steel 304
By the numbers
Priced on the same representative part: turned shaft, screw machining, 10,000 pcs.
Tensile strengthMPa
303 SS
620
304 SS
505
Yield strengthMPa
303 SS
240
304 SS
215
Densityg/cm³
303 SS
8
304 SS
8
Elongation%
303 SS
50
304 SS
70
Raw material cost$/kg
303 SS
6.5
304 SS
6
Which should you pick?
Pick 303 SS when
- The part is turned on a screw machine, Swiss or CNC lathe
- It is never welded, crimped, flared or bent
- Service is indoors or in fresh water
- Machine time is the largest share of part cost
Pick 304 SS when
- The part is welded; specify 304L for welded sections
- It is sheet metal, deep drawn, headed or crimped
- It sees food acids, cleaning chemicals or wash-down
- You need sheet, tube, wire or pipe as well as bar
Key differences
| 303 SS | 304 SS | |
|---|---|---|
| Chip form | Short, broken chips; suits unattended runs | Stringy chips; work-hardens under dull tools |
| Weldability | Not recommended; welds hot-crack | Excellent; 304L for welded parts |
| Cold forming | Poor for heading, crimping and tight bends | Deep draws and bends well when annealed |
| Corrosion | Good indoors and in fresh water; weaker in chlorides and acids | Better across the board; still pits in chlorides |
| Passivation | Needs a process validated for free-machining grades to avoid flash attack | Standard nitric or citric passivation per ASTM A967 |
| Stock forms | Mostly bar | Sheet, plate, bar, tube, wire and pipe |
Questions
Is 303 or 304 stainless stronger?
They are close. Annealed yield is about 35 ksi (240 MPa) for 303 and 31 ksi (215 MPa) for 304, and neither hardens by heat treatment. Choose on machining, welding and corrosion, not strength.
Can I substitute 303 for 304?
Only when the part is not welded, cold formed or exposed to chlorides, and the drawing allows it. Many drawings call out 304 for corrosion reasons, so get the substitution approved in writing before production.
Are 303 and 304 stainless magnetic?
Neither is magnetic when annealed. Cold work such as machining, bending or drawing can make both slightly magnetic, which is normal and not a sign of the wrong grade.
Can 303 stainless be welded?
It is not recommended. The sulfur that makes 303 machine well causes hot cracking in the weld. If the part must be welded, switch to 304 or 304L and accept slower machining.
Try both on your part.
The builder prices the same geometry in every suitable process and material, with DFM for each.