What is the difference between 304 and 304L?

Carbon: 0.07% maximum for 304, 0.030% for 304L. Low carbon prevents chromium carbide precipitation at grain boundaries as a weld cools. On welded piping, 304L is the one to specify.

It develops superficial rust staining in the presence of iron particles or polluted atmosphere — that is contamination, not corrosion of the grade. In chlorinated media, however, it genuinely pits, and the pit goes through the wall.

Why is its cost index 100?

It is the catalogue's baseline. A 316L at 130 costs 30% more, a 2507 at 260 costs 2.6 times more. The index is relative and indicative; it does not replace a quotation.

GRADE PROFILE

304L stainless steel — 1.4307 / X2CrNi18-9

304L is the default stainless: 18% chromium, 9% nickel, no molybdenum. It covers the majority of industrial uses away from chlorides, and it is the benchmark every other grade should be compared against before it is ordered.

Austenitic
PREN 18–20
Cost index 100
Welded · Seamless · Heat exchanger
Ø 6 to 610 mm

When to choose it

Anywhere there are no chlorides. General process piping, non-chlorinated food processing, structures and supports, fresh water networks. This is by far the most common case, and the reflex of stepping up to 316L "to be safe" is a 30% premium for identical service.

The L suffix matters on welded assemblies: at 0.030% carbon the grade does not sensitise as a weld cools, which avoids post-assembly heat treatment on site.

When not to choose it

As soon as chlorides exceed roughly 200 ppm. The passive film breaks down locally and pitting starts. That is the threshold separating 304L from 316L, and it is crossed more easily than people expect: chlorinated cleaning water, a marine atmosphere, damp insulation are all enough.

In seawater, without reservation: that is the domain of duplex, super austenitics or copper-nickel.

In reducing acids, where chromium alone does not protect.

Composition

Chemical composition (% by mass)
Element	%
C	≤ 0.03
Cr	17.5–19.5
Ni	8–10.5
Mo	≤ 0
Mn	≤ 2
Si	≤ 1
P	≤ 0.045
S	≤ 0.015
N	≤ 0.11

Mechanical properties

We only publish mechanical properties tied to a specific standard and product form — welded tube, seamless tube and bar do not share the same values, and the gap routinely exceeds 30%. The figures that apply to your specification appear on the material certificate; ask us at enquiry stage.

Designations and standards

Equivalent normative designations
Reference	Designation
EN (numeric)	1.4307
EN (symbolic)	X2CrNi18-9
ASTM / AISI	304L
UNS	S30403
JIS	SUS304L
AFNOR	—

Tube product standards :

EN 10216-5
EN 10217-7
ASTM A312
ASTM A269

Availability

Welded, seamless and heat exchanger tube, Ø 6 to 610 mm, plus fittings, flanges and bar. Partner stock or mill depending on the size and quantity: no restriction in principle. EN 10204 3.1 material certificates supplied with the goods.

Related grades

316L (1.4404) — the same alloy with 2 to 2.5% molybdenum, as soon as chlorides are present.
321 (1.4541) — titanium stabilisation for hot service.
444 (S44400) — the nickel-free ferritic route, at higher PREN.

My grade isn't listed → · PREN calculator → · Compare grades →

Frequently asked questions

What is the difference between 304 and 304L?: Carbon: 0.07% maximum for 304, 0.030% for 304L. Low carbon prevents chromium carbide precipitation at grain boundaries as a weld cools. On welded piping, 304L is the one to specify.
Does 304L rust?: It develops superficial rust staining in the presence of iron particles or polluted atmosphere — that is contamination, not corrosion of the grade. In chlorinated media, however, it genuinely pits, and the pit goes through the wall.
Why is its cost index 100?: It is the catalogue's baseline. A 316L at 130 costs 30% more, a 2507 at 260 costs 2.6 times more. The index is relative and indicative; it does not replace a quotation.