30403 Stainless Steel: Low-Carbon 304 for Welded Corrosion Resistance

30403 is a designation that appears in Chinese material tables for the low-carbon version of 304; it corresponds to UNS S30403, the grade the world knows as 304L. This article explains the composition, the reason the carbon limit is so important, the mechanical trade-off, and where the grade is specified for welded service.

What the Designation 30403 Means

30403 maps directly to UNS S30403, commonly called 304L, where the L stands for low carbon. The same material is designated SUS304L in JIS G4304/G4305, X2CrNi18-9 (1.4307) in EN 10088, and 022Cr19Ni10 in the current Chinese GB/T 20878 system (formerly 00Cr19Ni10). It is produced in plate, sheet, strip, bar, pipe and tube, and appears in standards such as ASTM A240 (plate/sheet), ASTM A312 (pipe) and ASTM A269 (tube).

Chemical Composition per ASTM A240

Composition ranges per ASTM A240, wt%:

Element	304 / UNS S30400	30403 / 304L / UNS S30403
Carbon, max	0.08	0.030
Manganese, max	2.00	2.00
Phosphorus, max	0.045	0.045
Sulfur, max	0.030	0.030
Silicon, max	0.75	0.75
Chromium	18.00-20.00	18.00-20.00
Nickel	8.00-10.50	8.00-12.00
Nitrogen, max	0.10	0.10

Apart from the carbon limit and the slightly wider nickel range, the chemistry of 304L is the same as 304: about 18-20% chromium for corrosion resistance and 8-12% nickel for austenitic structure and toughness.

Mechanical Properties

Annealed minimums per ASTM A240:

Property	304	304L
Tensile strength, min	515 MPa	485 MPa
Yield strength (0.2% offset), min	205 MPa	170 MPa
Elongation in 50 mm, min	40%	40%

The lower strength of 304L is a direct consequence of the lower carbon, which removes solid-solution hardening. For design, the applicable code minimums should be checked, but the difference is small enough that 304L is the default specification for welded process equipment.

Why Low Carbon Protects Welded Joints

When ordinary 304 is heated in the range of about 425-815 °C - which happens in the heat-affected zone of a weld or during service at moderate temperature - carbon can combine with chromium at grain boundaries to form chromium carbides. The metal immediately adjacent to those carbides becomes chromium-depleted and can no longer form its protective oxide film, so it corrodes preferentially along the grain boundaries. This is intergranular corrosion, and it is the classic failure mode of welded 304 in corrosive media. Limiting carbon to 0.03% maximum leaves too little carbon to form a continuous network of grain-boundary carbides, so 304L resists sensitization in the as-welded condition without any post-weld heat treatment. This is why pipe and vessels in the chemical and food industries are almost always specified as 304L rather than 304.

Formability, Fabrication and Applications

304L is highly formable and suitable for bending, rolling and deep drawing, and it welds with all standard techniques using low-carbon or stabilized fillers such as 308L. It replaces 304 in welded structures where post-weld corrosion resistance is critical: welded tanks and silos, food-processing equipment, pharmaceutical vessels, water pipelines, pressure vessels and architectural stainless steel where welded joints must resist corrosion. For non-welded parts that need slightly higher strength, plain 304 remains the better value.

Frequently Asked Questions

Is 30403 the same as 304L?

Yes. 30403 is the Chinese shorthand for UNS S30403, which is 304L, the low-carbon grade with 0.03% carbon maximum. The same material is SUS304L (JIS), X2CrNi18-9 / 1.4307 (EN) and 022Cr19Ni10 (GB/T 20878).

What is the difference between 304 and 304L?

The carbon limit: 0.08% maximum for 304 versus 0.030% maximum for 304L. 304L also has slightly lower minimum strength (485 MPa versus 515 MPa tensile) but identical 40% elongation.

Why does low carbon matter for welding?

Low carbon prevents chromium-carbide precipitation at grain boundaries in the weld heat-affected zone, which would otherwise deplete chromium and cause intergranular corrosion in service. 304L is therefore used where welded joints must keep their corrosion resistance without post-weld heat treatment.

Can 304L be used in food-processing equipment?

Yes. 304L is a standard material for welded food-processing equipment, tanks and piping because its as-welded corrosion resistance survives the cleaning and sanitizing cycles used in food plants.

What is the tensile strength of 30403 stainless steel?

Per ASTM A240, the minimum tensile strength is 485 MPa with a 170 MPa minimum yield strength and 40% minimum elongation in the annealed condition.

Should I specify 304 or 304L for a pressure vessel?

For welded pressure vessels, 304L is generally specified so that the welded joints retain corrosion resistance without post-weld heat treatment; the small strength penalty is usually accepted. Consult the governing pressure-vessel code for the design stress values applicable to the chosen grade.