SUS304 Stainless Steel: All-Purpose Industrial Alloy

SUS304 is the Japanese Industrial Standard designation for the austenitic stainless steel known internationally as Type 304. It is the most widely used stainless steel in the world because it combines good corrosion resistance, excellent formability and weldability with moderate cost. In JIS terminology, SUS is the prefix for stainless steel products covered by standards such as JIS G4303 (bars), JIS G4304 (hot-rolled plates) and JIS G4305 (cold-rolled sheets and strips). The same material is designated UNS S30400 in the United States, 1.4301 in the European EN 10088 system, and 06Cr19Ni10 in the Chinese GB/T 20878 system.

Chemical Composition of SUS304

The composition limits below follow JIS G4304 for SUS304 and match the Type 304 limits of ASTM A240 (plate, sheet and strip):

Element	SUS304 (wt%)
Carbon (C)	0.08 max
Silicon (Si)	1.00 max
Manganese (Mn)	2.00 max
Phosphorus (P)	0.045 max
Sulfur (S)	0.030 max
Chromium (Cr)	18.00-20.00
Nickel (Ni)	8.00-10.50
Iron (Fe)	Balance

Chromium above 18% is responsible for the self-healing passive oxide film that gives stainless steel its corrosion resistance, while nickel in the 8-10.5% range stabilizes the austenitic structure, providing toughness, formability and non-magnetic behavior in the annealed condition.

Mechanical Properties of Annealed SUS304

For hot-rolled plate to JIS G4304, SUS304 is specified with a minimum tensile strength of 520 MPa, a minimum 0.2% proof stress of 205 MPa, and a minimum elongation of 40% for plate in the 3-6 mm thickness range. ASTM A240 for Type 304 specifies a minimum tensile strength of 515 MPa, a minimum yield strength of 205 MPa, minimum elongation of 40%, and a maximum hardness of 201 HBW. The density of the alloy is approximately 7.93 g/cm3, and its modulus of elasticity is about 193 GPa.

Corrosion Resistance and Heat Resistance

SUS304 resists corrosion in fresh water, dry air, food acids, most organic chemicals and mildly aggressive industrial atmospheres at room temperature. It is not resistant to chlorides: saltwater, marine splash and chloride-containing cleaning agents can cause pitting and stress-corrosion cracking, and for such environments a molybdenum-bearing grade such as 316 is preferred. In continuous service, 304 resists oxidation up to about 870°C, with short intermittent exposure possible up to about 925°C. Above these temperatures the oxide film becomes unstable and scaling accelerates, so heat-resistant grades such as 309S or 310S should be selected for furnace parts.

Typical Industrial Applications

Because of its balanced properties, SUS304 appears across almost every industry: food processing equipment such as tanks, conveyors, tableware and brewing vessels; architectural panels, handrails and cladding; indoor water-supply piping; chemical storage vessels for dilute media; medical device housings and surgical instruments; automotive trim; and general machinery components in low-corrosion environments. It is available as plate, sheet, strip, bar, wire, pipe and tube, which further explains its status as the default all-purpose industrial alloy.

FAQ

Q1: Is SUS304 the same as 304 and 1.4301?
A1: Yes. SUS304 is the JIS designation, 304 is the common name used in ASTM/AISI practice, UNS S30400 is the unified numbering system code, and 1.4301 is the EN 10088 designation for the same alloy.

Q2: Can SUS304 be used in coastal environments?
A2: Not recommended for long unprotected outdoor service. Chloride aerosols cause pitting, especially at welds. For coastal use, 316 or a duplex grade should be specified; 304 may be acceptable indoors with regular cleaning.

Q3: Why is annealed SUS304 only weakly magnetic?
A3: The austenitic structure is essentially non-magnetic. Cold working such as bending or deep drawing transforms some austenite to martensite, which is magnetic; annealing at 1050-1100°C followed by rapid cooling restores the non-magnetic austenitic condition.

Q4: What filler metal is used for welding SUS304?
A4: ER308L filler wire or E308L electrodes are standard because their composition matches the base metal while the low carbon content protects the weld from sensitization and intergranular corrosion.

Q5: How can SUS304 be distinguished from carbon steel?
A5: Typical checks: the bright surface and slow reaction to a stainless steel identification solution, weak magnetism in the annealed condition compared with strongly magnetic carbon steel, and slightly higher density (7.93 versus about 7.85 g/cm3). A spark test also differs, but chemical analysis remains the definitive verification.