304 vs 316 stainless steel: composition, strength, corrosion resistance and when to use each

How 304 (1.4301) and 316 (1.4401/1.4404) stainless steel differ in composition, PREN, strength and chloride resistance, what the L grades and A2/A4 fasteners mean, and which grade to choose.

Updated October 17, 2026

304 and 316 are the two most used stainless steels. Both are austenitic chromium-nickel grades that weld and form well; the difference is about 2% molybdenum in 316, which makes it far more resistant to chlorides from seawater, de-icing salt and many chemicals. This guide compares composition, strength and corrosion resistance and shows when the extra cost of 316 is worth it.

Grade names in each system

Chemical composition

The molybdenum in 316 is the whole story: it strengthens the passive layer against attack by chloride ions. A common way to compare grades is the pitting resistance equivalent, PREN = %Cr + 3.3 × %Mo + 16 × %N: about 19 for a typical 304 and about 24 for a typical 316. A higher PREN means better resistance to pitting and crevice corrosion.

Strength and physical properties

• Strength is practically the same, so switching between 304 and 316 rarely changes a design.
• Density: about 7.9 kg/dm³ for 304 and 8.0 kg/dm³ for 316, so weights per metre are almost identical.
• Both are non-magnetic when annealed and can become slightly magnetic after cold working, such as bending or cold drawing.

Corrosion resistance: where 316 makes a difference

• 304 — indoor use, food and kitchen equipment, architectural parts in urban and rural air, water at normal temperatures with low chloride content.
• 316 — coastal and marine atmospheres, splash zones, road structures exposed to de-icing salt, swimming pool surroundings, salty foods and brines, chemical and pharmaceutical plants.
• Neither grade is suitable for every chloride environment: warm, stagnant seawater or concentrated acids can attack 316 too. In those cases a duplex or higher-alloyed grade is needed, and a corrosion specialist should be consulted.

304L and 316L: when to use the low-carbon grades

The L grades limit carbon to 0.030%. During welding, ordinary carbon levels can form chromium carbides at grain boundaries next to the weld (sensitisation), which leaves those zones open to intergranular corrosion. Low carbon prevents this, so 304L and 316L are preferred for welded parts, especially thicker sections. Their strength is slightly lower, and many mills certify products as dual grade, such as 316/316L, meeting both sets of limits.

A2 and A4 stainless fasteners

In ISO 3506 stainless fasteners, A2 corresponds to 304 and A4 to 316. The number after the dash is the strength class: A2-70 and A4-70 have a minimum tensile strength of 700 MPa. Use A4 fasteners on 316 structures and in marine or salted environments, so the bolts are not the weak point.

How to choose

• Indoors, dry or mildly exposed outdoors: 304 is the economical choice.
• Within a few kilometres of the sea, in contact with salt, chlorinated water or chemicals: 316.
• Welded assemblies: the L version (304L or 316L).
• Machined parts in large numbers: free-machining 303 cuts much faster, at the cost of lower corrosion resistance and weldability.
• 316 costs noticeably more than 304, because of the molybdenum and higher nickel content. Use it where the environment needs it, not by default.

Stainless steel we supply

• 304 — round bar, welded round tube, square tube, sheet, flanges, butt-weld fittings and A2 fasteners.
• 316L — round bar, flat bar, welded round tube and square tube.
• 316 / A4 — hex bolts, nuts, washers and slip-on flanges.
• 303 — free-machining round bar.

Frequently asked questions

Send your list with grade, size and quantity in a quote request. Mill certificates to EN 10204 3.1 are available on request.