JIS SUS304 is Japan’s most widely used austenitic stainless steel, virtually identical to ASTM/AISI 304 and EN 1.4301. It offers excellent corrosion resistance, good formability, and is the go-to choice for food processing, chemical equipment, and architectural applications where moderate corrosion resistance is sufficient.
Quick Comparison Box
| Standard | Designation | Region | Match Type |
|---|---|---|---|
| JIS G4303 | SUS304 | Japan | — (Base) |
| ASTM A240 / AISI | Type 304 (UNS S30400) | USA | Exact Match |
| ISO 15510 | X5CrNi18-10 | International | Exact Match |
| DIN 17440 / EN 10088 | X5CrNi18-10 (1.4301) | Europe / Germany | Exact Match |
| GB/T 20878 | 06Cr19Ni10 | China | Exact Match |
| BS 970 | 304S31 | UK (legacy) | Nearest Equivalent |
Exact Match: Chemical composition and mechanical property limits are essentially identical; direct substitution is generally acceptable with engineering judgment.
Nearest Equivalent: Composition overlaps significantly but minor differences may exist; verify specifications before substitution in critical applications.
Chemical Composition
| Element | JIS SUS304 (JIS G4303) |
ASTM 304 (ASTM A240) |
EN 1.4301 (EN 10088-2) |
|---|---|---|---|
| C (Carbon) | ≤ 0.08% | ≤ 0.08% | ≤ 0.07% |
| Si (Silicon) | ≤ 1.00% | ≤ 0.75% | ≤ 1.00% |
| Mn (Manganese) | ≤ 2.00% | ≤ 2.00% | ≤ 2.00% |
| P (Phosphorus) | ≤ 0.045% | ≤ 0.045% | ≤ 0.045% |
| S (Sulfur) | ≤ 0.030% | ≤ 0.030% | ≤ 0.015% |
| Cr (Chromium) | 18.00–20.00% | 18.00–20.00% | 17.50–19.50% |
| Ni (Nickel) | 8.00–10.50% | 8.00–10.50% | 8.00–10.50% |
| N (Nitrogen) | ≤ 0.10% | ≤ 0.10% | ≤ 0.11% |
Sources: JIS G4303:2012, ASTM A240/A240M-22, EN 10088-2:2014
Mechanical Properties
| Property | JIS SUS304 (JIS G4303) |
ASTM 304 (ASTM A240) |
EN 1.4301 (EN 10088-2) |
Condition |
|---|---|---|---|---|
| Tensile Strength | ≥ 520 MPa (75.4 ksi) | ≥ 515 MPa (74.7 ksi) | 500–700 MPa (72.5–101.5 ksi) | Annealed |
| 0.2% Proof Stress (Yield) | ≥ 205 MPa (29.7 ksi) | ≥ 205 MPa (29.7 ksi) | ≥ 210 MPa (30.5 ksi) | Annealed |
| Elongation | ≥ 40% | ≥ 40% | ≥ 45% | Annealed |
| Hardness (HB) | ≤ 187 HB | ≤ 201 HB | ≤ 215 HB | Annealed |
| Hardness (HRC) | ≤ 90 HRB | ≤ 92 HRB | — | Annealed |
| Charpy Impact (V-notch) | ≥ 100 J (73.8 ft·lbf) | — | — | Room temp. |
Sources: JIS G4303:2012, ASTM A240/A240M-22, EN 10088-2:2014
SUS304 / AISI 304 work-hardens rapidly during cold forming. Tensile strength can reach 1,000–1,300 MPa (145–188 ksi) in heavily cold-worked conditions, with significant reduction in ductility. Plan for this in deep-drawing or tube-expanding operations.
Physical Properties
| Property | Value | Condition |
|---|---|---|
| Density | 7.93 g/cm³ (0.286 lb/in³) | — |
| Melting Range | 1,399–1,454°C (2,550–2,650°F) | — |
| Thermal Conductivity | 16.2 W/(m·K) at 100°C (212°F) | Annealed |
| Specific Heat Capacity | 500 J/(kg·K) | 0–100°C (32–212°F) |
| Coefficient of Thermal Expansion | 17.2 × 10⁻⁶ /°C (9.6 × 10⁻⁶ /°F) | 0–300°C (32–572°F) |
| Electrical Resistivity | 72 × 10⁻⁸ Ω·m | 20°C (68°F) |
| Modulus of Elasticity | 193 GPa (28,000 ksi) | — |
| Magnetic Permeability | ≤ 1.02 (non-magnetic in annealed state) | Annealed |
Annealed SUS304 is essentially non-magnetic. However, cold working (drawing, bending, forming) can induce martensite transformation, making the material slightly magnetic. If magnetic permeability is critical (e.g., MRI equipment, sensitive electronics), specify SUS316 or verify permeability after forming.
Heat Treatment Conditions
| Treatment | Temperature | Cooling Method | Purpose |
|---|---|---|---|
| Solution Annealing | 1,010–1,120°C (1,850–2,050°F) | Water quench or rapid air cool | Dissolve carbides, restore corrosion resistance, relieve stress |
| Stress Relief | 870–900°C (1,600–1,650°F) | Rapid quench (avoid sensitization range) | Reduce residual stress post-welding or cold work |
| Sensitization Range (AVOID) | 425–860°C (800–1,580°F) | — | Carbide precipitation → intergranular corrosion risk |
SUS304 is susceptible to sensitization when held in the 425–860°C (800–1,580°F) range. Chromium carbides precipitate at grain boundaries, depleting adjacent areas of chromium and creating intergranular corrosion susceptibility. For applications requiring extended time in this range (e.g., heavy welding on thick sections), consider SUS304L (low-carbon variant) or SUS321 (titanium-stabilized).
SUS304 cannot be hardened by heat treatment (it is austenitic and non-hardenable by quenching). Strength increases are achieved only through cold working. This is a fundamental difference from carbon and alloy steels like S45C or SCM440.
Practical Advice
Machinability
SUS304 has a machinability rating of approximately 45–50% relative to free-machining carbon steel (AISI 1212 = 100%). Key considerations:
- Work hardening: SUS304 work-hardens rapidly. Use sharp tooling and maintain consistent chip load — “rubbing” without cutting generates heat and accelerates tool wear dramatically.
- Chip control: Stringy, tough chips are typical. Use chip-breaking geometry and adequate coolant flow.
- Tool recommendation: Carbide tooling (coated with TiAlN or TiCN) at moderate cutting speeds. Avoid high-speed steel for production work.
- Cutting speed: Turning: 60–100 m/min (197–328 ft/min) with carbide. Drilling: 20–40 m/min (66–131 ft/min).
- For improved machinability: SUS303 (free-machining grade with added sulfur) offers significantly better machinability at the cost of slightly reduced corrosion resistance and weldability.
Welding Tips
- Weldability: SUS304 is generally weldable by all common processes (TIG, MIG, resistance, plasma).
- Filler metal: Use ER308L (low-carbon) for TIG/MIG welding to minimize carbide precipitation. AWS ER308 is also acceptable for non-critical applications.
- Preheat: Not required for most applications.
- Post-weld treatment: Post-weld annealing (solution treatment) is recommended for corrosion-critical applications on thick sections. For thin sections or where annealing is impractical, SUS304L filler (ER308L) significantly reduces sensitization risk.
- Heat input control: Minimize heat input and inter-pass temperature (keep below 150°C / 302°F) to reduce the HAZ sensitization risk.
Common Mistakes
SUS304 lacks molybdenum and has significantly lower pitting resistance (PREN ≈ 18–20 vs. 24–27 for SUS316). In seawater, de-icing salt environments, or concentrated chloride solutions, SUS304 will pit and eventually suffer crevice corrosion. Always specify SUS316 or SUS316L for marine, coastal, or chemical processing applications involving chlorides.
ASTM A240 permits Si up to 0.75%, while JIS G4303 allows up to 1.00%. In most applications this is irrelevant, but for castings or high-temperature oxidation-resistant applications, the slightly higher Si in JIS material can matter. Verify with your supplier when exact match is essential.
Cold-worked SUS304 (bent, drawn, formed tube) can become detectably magnetic due to strain-induced martensite. Magnetic permeability can reach 1.05–1.10 or higher in heavily deformed areas. If non-magnetic properties are a functional requirement, specify SUS316 or test the final component.
Using the wrong filler (e.g., carbon steel ER70S-6) on SUS304 produces a weld that corrodes rapidly and has poor mechanical compatibility. Always verify filler metal type before welding stainless steel.
When to Choose SUS304
- General-purpose stainless applications: food processing equipment, kitchen sinks, cookware, dairy equipment
- Architectural and decorative: handrails, cladding, signage (urban/inland environments only)
- Chemical equipment: mild acids, organic chemicals, non-chloride environments
- Cryogenic applications: austenitic structure maintains toughness at very low temperatures
- When formability is critical: excellent deep-drawing and forming properties
Choose SUS316/316L instead when: chloride exposure is significant, higher-temperature strength is needed, or better pitting resistance is required.
Choose SUS304L instead when: heavy welding is involved on thick sections and post-weld annealing is not feasible.
FAQ
Yes, for the vast majority of practical purposes. JIS G4303 SUS304 and ASTM A240 Type 304 have nearly identical chemical composition limits (18–20% Cr, 8–10.5% Ni, C ≤ 0.08%). The UNS number is S30400. Minor differences exist in Si upper limit (JIS: 1.00%, ASTM: 0.75%) but do not affect performance in standard applications. They are considered interchangeable on most international engineering specifications.
SUS304L is a low-carbon variant with C ≤ 0.03% (vs. ≤ 0.08% for standard SUS304). The lower carbon content dramatically reduces the risk of sensitization during welding and high-temperature exposure. The trade-off is slightly lower tensile and yield strength at room temperature. SUS304L is preferred for welded fabrications where post-weld heat treatment is not performed. ASTM equivalent: Type 304L (UNS S30403).
Not recommended without precautions. SUS304 is susceptible to pitting and crevice corrosion in chloride-containing environments, including coastal air within approximately 500 m (1,640 ft) of the sea. For marine or coastal outdoor applications, specify SUS316 or SUS316L, which contains 2–3% molybdenum for significantly improved pitting resistance. If SUS304 must be used, ensure the surface is regularly cleaned and maintained free of deposits.
Yes. EN 1.4301 (material number) corresponds to the grade designation X5CrNi18-10 under EN 10088-2 and is the direct European equivalent of JIS SUS304 and ASTM 304. The chemical composition limits are essentially the same (note EN specifies S ≤ 0.015%, slightly tighter than JIS/ASTM at 0.030%). These grades are treated as equivalents in international supply chains.
SUS304 can be used continuously up to approximately 870°C (1,600°F) in intermittent service and up to 925°C (1,700°F) in continuous service for oxidation resistance. However, if the component will be in the sensitization range (425–860°C / 800–1,580°F) for extended periods, consider SUS321 (Ti-stabilized) or SUS347 (Nb-stabilized) to prevent intergranular corrosion. Above 870°C, carbide precipitation and grain growth become design considerations.
- SUS304 = ASTM 304 = EN 1.4301 = DIN X5CrNi18-10: all exact matches for most engineering purposes
- 18–20% Cr + 8–10.5% Ni austenitic structure provides excellent corrosion resistance, formability, and weldability
- Cannot be hardened by heat treatment; only cold working increases strength
- Sensitization risk at 425–860°C: use SUS304L or stabilized grades for weld-heavy fabrication
- Not suitable for chloride-rich environments; upgrade to SUS316/316L for marine or chemical service
- Machinability approx. 45–50% of carbon free-machining steel; use sharp carbide tooling and avoid rubbing cuts
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