304 vs 304L: Composition, Heat Treatment, Properties and Applications

Standards and Designations

304 (UNS S30400) and 304L (UNS S30403) are austenitic stainless steels specified for plate, sheet and strip under ASTM A240/ASME SA240, for bar under ASTM A276/A276M, and across the EN 10088 series. The JIS designations are SUS304 and SUS304L, and the GB/T 3280 designations are 06Cr19Ni10 and 022Cr19Ni10. Both grades are corrosion-resistant alloys and are not carbon steels, tool steels or high-strength low-alloy steels.

Chemical Composition

The specification ranges below follow the limits of ASTM A240/A276, EN 10088 and JIS G4303/G4304.

Element (wt %)	304 (S30400)	304L (S30403)
Carbon, max	0.08	0.03
Manganese, max	2.0	2.0
Silicon, max	1.0	1.0
Phosphorus, max	0.045	0.045
Sulfur, max	0.03	0.03
Chromium	18.0-20.0	18.0-20.0
Nickel	8.0-10.5	8.0-12.0
Molybdenum, max	0.10	0.10
Nitrogen, max	0.10	0.10

Mechanical Properties

Minimum values for annealed plate per ASTM A240/A240M.

Property	304	304L
Tensile strength, min (MPa)	515	485
0.2% yield strength, min (MPa)	205	170
Elongation in 50 mm, min (%)	40	40
Impact toughness at room temperature	High, ductile	High, ductile

Both grades strain harden during cold working. The lower minimum strength of 304L reflects the softer effect of the reduced carbon content, while ductility and toughness remain equivalent.

Heat Treatment and Sensitization

Both grades are supplied in the solution-annealed condition, typically heated to about 1010-1120°C (1850-2050°F) and rapidly cooled. During welding or service in the 425-815°C (800-1500°F) range, carbon can precipitate at grain boundaries as chromium carbides, depleting the adjacent matrix of chromium and creating susceptibility to intergranular corrosion; this is known as sensitization. The 0.03% maximum carbon of 304L suppresses this reaction, so 304L is preferred for heavy welded sections, large weld volumes and components that cannot be solution annealed after fabrication. 304 remains suitable where weld volumes are small or where post-weld annealing is performed.

Applications and Selection

304 is used for kitchen equipment, food processing and beverage plants, architectural trim, decorative panels, fasteners, springs and consumer goods. 304L is used for heavy welded vessels and piping in chemical plants, welded storage tanks, sewage and wastewater piping, pharmaceutical and biotech welded systems, and pressure vessels with large weld volumes. 304 is typically the most common grade and is often marginally less expensive; 304L may carry a small premium for tighter carbon control, but this is usually small compared with the cost of eliminating post-weld heat treatment. Selection should weigh corrosion, welding volume, strength requirements and total fabrication cost.

Frequently Asked Questions

What is the main difference between 304 and 304L? Carbon content: 304L limits carbon to 0.03% max versus 0.08% max for 304, reducing sensitization risk during welding.

Why is 304L called low carbon? Its carbon limit of 0.03% max is roughly one-third of the 304 limit, which limits chromium carbide precipitation.

Is 304L weaker than 304? Minimum tensile strength is lower (485 MPa versus 515 MPa) and minimum yield is lower (170 MPa versus 205 MPa), while elongation and toughness are equivalent.

Can 304 be used instead of 304L? For small weld volumes and where post-weld annealing is possible, yes; for heavy weldments, 304L is the safer choice.

Are 304 and 304L magnetic? In the fully annealed condition they are essentially non-magnetic; cold working can induce some magnetic response.

Which standard applies to 304/304L plate? ASTM A240/A240M for pressure vessel plate, sheet and strip; EN 10088, JIS G4303/G4304 and GB/T 3280 are equivalent regional standards.

Frequently Asked Questions

Q1. What designations cover 304 and 304L?
304 (UNS S30400) and 304L (UNS S30403) are specified for plate, sheet and strip under ASTM A240/ASME SA240 and for bar under ASTM A276/A276M, with EN 10088, JIS SUS304/SUS304L and GB/T 3280 designations 06Cr19Ni10 and 022Cr19Ni10 as regional equivalents.

Q2. What is the difference in chemical composition?
Carbon is the only significant difference: 0.08 max for 304 versus 0.03 max for 304L, while manganese 2.0, silicon 1.0, phosphorus 0.045, sulfur 0.03, chromium 18.0-20.0, molybdenum 0.10 max and nitrogen 0.10 max are common to both; nickel is 8.0-10.5 for 304 and 8.0-12.0 for 304L.

Q3. What is sensitization and when does it occur?
During welding or service in the 425-815 C (800-1500 F) range, carbon can precipitate at grain boundaries as chromium carbides, depleting the adjacent matrix of chromium and creating susceptibility to intergranular corrosion; the 0.03 percent carbon limit of 304L suppresses this reaction.

Q4. Where is 304L preferred over 304?
304L is preferred for heavy welded vessels and piping in chemical plants, welded storage tanks, sewage and wastewater piping, pharmaceutical and biotech welded systems, and pressure vessels with large weld volumes that cannot be solution annealed after fabrication.

Q5. What annealing temperature is used for both grades?
Both are supplied in the solution-annealed condition, typically heated to about 1010-1120 C (1850-2050 F) and rapidly cooled; 304 remains suitable where weld volumes are small or where post-weld annealing is performed.