304 Stainless Steel

What Is 304 Stainless Steel?

304 is the most common austenitic stainless steel in the world. Its nominal composition of 18 percent chromium and 8 percent nickel gives it a fully austenitic, essentially non-magnetic structure with a good combination of corrosion resistance, ductility, toughness and weldability. The grade is designated UNS S30400 in ASTM A240/A240M, 1.4301 (steel name X5CrNi18-10) in EN 10088, and SUS304 in JIS G4304/G4305. Family variants cover specific needs: 304L (UNS S30403, EN 1.4307) limits carbon to 0.030 percent for heavy welded structures, and 304H (UNS S30409) holds carbon between 0.04 and 0.10 percent for high-temperature strength. Dual-certified plates and pipes are commonly supplied to both 304 and 304L limits so that fabricators can weld without losing the low-carbon benefit.

Chemical Composition

Limiting composition of the three common variants per ASTM A240/A240M.

Element (%)	304 (S30400)	304L (S30403)	304H (S30409)
C	≤0.08	≤0.030	0.04-0.10
Mn	≤2.00	≤2.00	≤2.00
Si	≤0.75	≤0.75	≤0.75
P	≤0.045	≤0.045	≤0.045
S	≤0.030	≤0.030	≤0.030
Cr	18.0-20.0	18.0-20.0	18.0-20.0
Ni	8.0-10.5	8.0-12.0	8.0-10.5
N	≤0.10	≤0.10	-

Mechanical Properties

Minimum room-temperature properties of annealed plate, sheet and strip per ASTM A240/A240M.

Property	304	304L	304H
Tensile strength	≥515 MPa	≥485 MPa	≥515 MPa
Yield strength (0.2%)	≥205 MPa	≥170 MPa	≥205 MPa
Elongation	≥40%	≥40%	≥40%
Hardness	≤201 HBW / ≤92 HRB	≤201 HBW / ≤92 HRB	≤201 HBW / ≤92 HRB

Corrosion Resistance

304 resists atmospheric corrosion, fresh and potable water, foodstuffs, organic acids and many dilute inorganic chemicals, which is why it dominates food processing, beverage, brewery, dairy and architectural applications. Its calculated pitting resistance equivalent (PREN) is about 19, so it is only marginally resistant to chlorides: in seawater, splash zones, swimming-pool atmospheres or de-icing salt exposure it can pit, and above roughly 60 C it is susceptible to chloride stress corrosion cracking. For such service, molybdenum-bearing 316 or higher-alloyed grades should be specified. In welded heavy sections, 304L or stabilised grades avoid the chromium carbide precipitation that occurs in the 450-850 C sensitisation range.

Heat Treatment and Fabrication

304 is supplied in the solution-annealed condition, typically heated to 1010-1120 C and rapidly cooled in water or air. It cannot be hardened by heat treatment; cold working is the only way to raise strength, at the cost of ductility and slight magnetism. The grade is outstanding for forming: it deep draws, bends, rolls and spins readily, and it welds by all common processes without preheat. For food-contact and architectural use, pickling and passivation restore the chromium-rich passive film after welding and grinding.

Typical Applications

Applications include kitchen sinks and catering equipment, food processing and storage tanks, brewery and dairy vessels, pharmaceutical equipment, chemical storage tanks for dilute media, heat exchanger tubing, architectural panels and handrails, cryogenic vessels (down to -196 C), and domestic appliance parts.

Frequently Asked Questions

Q: What does 18/8 stainless steel mean?

A: It refers to the nominal composition of 304: about 18 percent chromium and 8 percent nickel. The term is commonly used as a synonym for 304 in tableware and kitchenware.

Q: What is the difference between 304 and 304L?

A: 304L limits carbon to 0.030 percent maximum. The low carbon content prevents chromium carbide precipitation in the heat-affected zone during welding, so 304L is specified for heavy welded sections that cannot be annealed after welding.

Q: Is 304 stainless steel magnetic?

A: In the annealed condition 304 is essentially non-magnetic. Cold working such as bending or drawing can form strain-induced martensite, which makes the material slightly magnetic.

Q: Can 304 be hardened by heat treatment?

A: No. Like all austenitic grades, 304 can only be strengthened by cold working, not by heat treatment.

Q: Is 304 suitable for seawater service?

A: Not for continuous immersion. 304 has low resistance to chloride pitting and stress corrosion cracking in seawater; molybdenum-bearing 316 or duplex grades are the standard choices for marine duty.

Q: What temperature can 304 withstand?

A: For oxidation resistance in air, 304 is rated for continuous service to about 800 C and intermittent service to about 870 C. For load-bearing high-temperature design, use it within the allowable stresses of the applicable code, or select 304H, 321 or 310S for higher strength.

Frequently Asked Questions

Q1. Which designations cover grade 304 stainless steel?
304 is designated UNS S30400 in ASTM A240/A240M, 1.4301 with steel name X5CrNi18-10 in EN 10088, and SUS304 in JIS G4304/G4305; the low-carbon variant 304L is UNS S30403 or EN 1.4307, and the high-carbon variant 304H is UNS S30409.

Q2. What are the composition limits of 304?
Per ASTM A240/A240M, carbon is 0.08 max, chromium 18.0-20.0, nickel 8.0-10.5, manganese 2.00 max, silicon 0.75 max, phosphorus 0.045 max, sulfur 0.030 max and nitrogen 0.10 max; 304L restricts carbon to 0.030 max and 304H holds carbon between 0.04 and 0.10 percent.

Q3. What are the minimum mechanical properties of annealed 304?
Minimum tensile strength is 515 MPa, 0.2 percent yield strength is 205 MPa, elongation is 40 percent and hardness is 201 HBW or 92 HRB maximum; 304L shows the same elongation but lower minimums of 485 MPa tensile and 170 MPa yield.

Q4. Why is 304 only marginally resistant to chlorides?
Its calculated pitting resistance equivalent (PREN) is about 19, so in seawater, splash zones, swimming-pool atmospheres or de-icing salt exposure it can pit, and above roughly 60 C it is susceptible to chloride stress corrosion cracking; molybdenum-bearing 316 or higher-alloyed grades should be specified for such service.

Q5. What heat treatment and service limits apply to 304?
304 is supplied solution-annealed at 1010-1120 C with rapid cooling, cannot be hardened by heat treatment, and in welded heavy sections the 450-850 C sensitisation range must be avoided, which is why 304L or stabilised grades are used there; for oxidation resistance in air it is rated to about 800 C continuous and 870 C intermittent service.