The 303 vs 304 vs 316 decision is the most common stainless steel question on machined parts. All three are austenitic, non-magnetic in the annealed condition, and cannot be hardened by heat treatment. The differences are in machinability, corrosion resistance and weldability. 303 machines fastest because of added sulfur, 304 is the general-purpose grade, and 316 adds molybdenum for better resistance to chlorides and many chemicals.
303 vs 304 vs 316: Comparison Table
Values are typical. Machinability is relative to free-machining steel 1212 at 100 percent. Cost is a relative per-part index including material, where one 303 part at quantity 1 equals 100.
| Factor | 303 | 304 / 304L | 316 / 316L |
|---|---|---|---|
| Relative cost, qty 1 | 100 | 105 to 115 | 115 to 130 |
| Relative cost, qty 10 | 40 | 45 to 52 | 50 to 60 |
| Relative cost, qty 100 | 18 | 22 to 26 | 26 to 32 |
| Relative cost, qty 1,000 | 10 | 13 to 16 | 16 to 20 |
| Machinability rating | About 75 to 80 percent | About 40 to 45 percent | About 35 to 40 percent |
| Typical machined tolerance | ±0.0005 to ±0.002 in | ±0.001 to ±0.003 in | ±0.001 to ±0.003 in |
| Surface finish | Ra 32 to 63 µin readily | Ra 32 to 63 µin with care | Ra 32 to 63 µin with care |
| Corrosion resistance | Moderate; sulfide inclusions can pit | Good in most atmospheres and fresh water | Very good, including chlorides and many chemicals |
| Weldability | Poor | Good | Good |
| Tensile strength (annealed) | About 90 ksi | About 75 to 90 ksi | About 75 to 90 ksi |
| Typical use case | Fittings, fasteners, shafts, bushings in mild service | Food equipment, general hardware, enclosures | Marine, chemical, pharmaceutical, medical, coastal |
When 303 Wins
- High-volume turned parts. Sulfur breaks chips cleanly, which makes 303 well suited to Swiss and bar-fed lathe work.
- Parts that will not be welded. Fittings, bushings, pins and shafts in dry or mild environments.
- Cost-driven stainless parts. Faster cycle times lower cost per part.
When 304 Wins
- General corrosion resistance. Indoor, food contact and fresh water service.
- Welded components. 304L, the low-carbon version, reduces sensitization in welded zones.
- Balance of cost and performance. The default stainless for many industrial parts.
When 316 Wins
- Chlorides and salt. Marine hardware, coastal installations and parts exposed to de-icing salts.
- Chemical and process equipment. Molybdenum improves resistance to pitting and crevice corrosion.
- Medical and pharmaceutical. 316L is common for components that are passivated or electropolished.
Common Mistakes
- Specifying 303 for a welded part or a chloride environment. It is a machining grade, not a corrosion grade.
- Specifying 316 by default when 304 is adequate, which adds cost and machining time.
- Skipping passivation. Machining leaves free iron on the surface, and passivation per ASTM A967 or AMS 2700 restores the passive layer.
- Expecting to harden these grades by heat treatment. For hardenable stainless, look at 400-series or precipitation hardening grades such as 17-4 PH.
Machining Notes
304 and 316 work harden quickly, so sharp tools, steady feed and avoiding rubbing cuts matter. 303 is more forgiving. For tight bores and threads in 304 and 316, finishing passes should take a meaningful chip rather than skim a work-hardened surface.
How This Applies at Wexmar
Wexmar machines 300-series, 400-series and PH stainless, along with Nitronic 50, on our lathes, horizontal machining centers and Maier Swiss-type machines. Material certs and heat-lot traceability are available, and DFARS-compliant specialty metals sourcing is available where required. Passivation is performed by qualified outside processors that we manage. See materials, Swiss machining, and the guide on passivation vs electropolish.
Getting a Quote
Note the grade, condition and any finish on the drawing. You can upload a drawing for an instant estimate, with a human estimator confirming every quote, or call (315) 400-2654.