Stainless steel 303 vs 304: which one should you machine?

By the team at A.T. Industrial Part · Updated 2026-09-24

In short

303 (SUS303) is essentially 304 with added sulphur, which makes it much easier to machine: chips break cleanly, cutting is faster and tools last longer. The trade-off is lower corrosion resistance and poor weldability. 304 (SUS304) resists corrosion better and welds well, but it is harder to machine. Pick 303 for heavily machined parts in non-corrosive service; pick 304 for parts that meet water, food or chemicals, or that need welding.

What 303 and 304 have in common

Both are austenitic stainless steels with roughly 18% chromium and 8–10% nickel, the classic "18/8" stainless. Both are essentially non-magnetic when annealed, and neither can be hardened by heat treatment.

Where they differ

The key difference is that 303 contains added sulphur (about 0.15% minimum). Sulphur makes the chips break into short pieces instead of long strings that wrap around the tool, so 303 cuts faster and gives a more consistent finish. The same sulphur lowers corrosion resistance and makes welding unreliable.

	303 stainless	304 stainless
Machinability	Very good, chips break easily	Harder: gummy, stringy chips and work hardening
Corrosion resistance	Fair, lower than 304	Good
Welding	Not recommended	Welds well
Bending / cold forming	Poor	Good
Typical parts	Shafts, pins, bushings, screws, fittings, heavily machined parts	Food equipment, parts in contact with water or chemicals, welded assemblies

Which grade should you choose?

Choose 303 for parts with lots of machining, threads or steps, larger batches, indoor or dry service, and no welding. Machining cost is usually lower.
Choose 304 when the part meets water, humidity, food or chemicals, is used outdoors, or will be welded.
For sea water or chloride exposure, consider 316, which adds molybdenum for better pitting resistance.

If you are unsure, tell your machine shop where the part will be used, what it will touch and whether it will be welded. They can suggest the grade that balances performance and cost.

Stainless turning at A.T. Industrial Part

We machine both 303 and 304 stainless, as well as SS400 steel, hardened steel, aluminium 6061-T6/6063, brass, copper, POM and nylon. See examples such as stainless steel handles and other parts.

Need parts turned to your drawing?

A.T. Industrial Part has been turning parts to drawing in Bang Phli, Samut Prakan for 31 years. Send us your drawing for a quote.

Call sales +66 61 419 1518 LINE: atinpart Request a quote