Stainless 304 vs 316

Both corrosion resistant.
316 handles seawater.
304 handles everything else.

Stainless 304 and 316 look identical but behave differently. 316 has 2–3% molybdenum that provides dramatically better chloride-corrosion resistance. That molybdenum also costs 15–25% more. Here's when the premium is worth it.

Get a Quote DFM guide

01 · At a glance

Side-by-side summary.

Option A

Stainless 304

General-purpose austenitic stainless. Excellent corrosion resistance in most environments, weldable, formable, widely available. The default stainless for indoor, food, and mild-environment applications.

Option B

Stainless 316L

Marine-grade stainless with molybdenum addition. Superior chloride-corrosion resistance, standard for seawater, chemical processing, medical implants. 15–25% more expensive than 304.

02 · Detailed comparison

Feature-by-feature breakdown.

Attribute	304	316L
Composition	18% Cr, 8% Ni	16% Cr, 10% Ni, 2–3% Mo
Yield strength	207 MPa	172 MPa
Density	8.00 g/cc	8.00 g/cc
Corrosion (general)	Excellent	Excellent
Corrosion (chloride)	Susceptible to pitting	Highly resistant
Saltwater service	Not recommended	Suitable
Food grade	Yes (FDA 21 CFR 177)	Yes
Medical implantable	No	Yes (ASTM F138)
Pharma sanitary	Good	Better (most common choice)
Weldability	Excellent	Excellent
Machinability	Moderate (work hardens)	Similar to 304
Magnetic	Non-magnetic (unless heavily cold-worked)	Non-magnetic
Cost	$	$$
Availability	Very common	Common (specify "L" for weldable)

03 · Decision guide

When to choose each.

Choose Stainless 304 when:

Indoor applications without chloride exposure
Food processing equipment (non-marine)
Architectural hardware (non-coastal)
Commercial kitchen, dairy, beverage
Decorative hardware with minimal corrosion exposure
Cost-sensitive applications where 316 premium isn't justified

Choose Stainless 316L when:

Marine hardware, saltwater exposure
Chemical processing, especially chlorides
Pharmaceutical and biotech (specify electropolished)
Medical implantable devices (ASTM F138)
Coastal outdoor applications
Food processing with saline solutions (brine, seawater-adjacent)

FAQ

Common questions.

316: standard molybdenum-bearing stainless, carbon content up to 0.08%. 316L: "Low carbon" variant, carbon content limited to 0.03%. The lower carbon prevents chromium carbide precipitation at grain boundaries during welding — critical for welded assemblies. For welded 316 applications, always specify 316L. For non-welded parts, either 316 or 316L works. Most mill stock is 316L now — the small premium over 316 is worth the versatility.

Significantly — measured in orders of magnitude. ASTM B117 salt spray testing: 304 starts pitting after 100–500 hours; 316L typically passes 1000+ hours without pitting. In actual saltwater service: 304 may pit or tea-stain in weeks to months; 316L lasts 10+ years. The molybdenum addition specifically stabilizes the passive layer against chloride attack.

316L material is typically 15–25% more expensive than 304 per kg. For finished CNC parts, the total cost difference is usually 10–20% since machining cost is similar. For a $50 machined part, 316L version costs $55–60. Over 1000-part production: 304 saves $5,000–10,000. When marine or chemical service actually requires 316L, the savings from specifying 304 disappear in warranty/replacement costs.

Yes, in non-coastal, low-chloride environments. 304 handles outdoor rain and humidity fine for 10–20 years. Problem arises near oceans (salt spray), on roads treated with salt (winter de-icing), in industrial pollution areas, or in chlorinated pools. For coastal or road-salt exposure, 316L is worth the premium. For inland, suburban, non-industrial outdoor use, 304 is adequate.

304 is austenitic (FCC crystal structure — non-magnetic) in annealed condition. Heavy cold working (bending, deep drawing) can partially transform to martensite (BCT structure — magnetic). Slight magnetism in 304 sheet that's been bent is normal and doesn't indicate 430 (which is ferritic and fully magnetic). For non-magnetic applications (MRI compatibility, sensor housings), specify "annealed" or use 316 (more stable austenitic due to higher nickel).

Both benefit from passivation per ASTM A967. Passivation removes free iron from the surface (contamination from machining tools), allowing full chromium oxide passive layer to form. Nitric acid passivation standard. For medical or food-contact parts, passivation is typically required. We include ASTM A967 passivation at no additional cost on most stainless orders.