SUS304 (JIS G4303) is Japan’s most widely used austenitic stainless steel — the direct Japanese equivalent of AISI 304 and EN 1.4301. The 18Cr-8Ni composition delivers broad corrosion resistance, excellent formability, and reliable weldability across food, chemical, architectural, and cryogenic applications. This guide covers international equivalents, full composition comparison, mechanical and physical properties, heat treatment limits, and the two specification mistakes that account for most SUS304 field failures.
- International Equivalent Grades
- Chemical Composition
- Mechanical Properties
- Physical Properties
- Heat Treatment Conditions
- Machinability
- Weldability
- Common Mistakes
- When to Choose SUS304
- FAQ
1. International Equivalent Grades
SUS304 is the JIS designation for the 18-8 austenitic stainless steel family. The grade has near-identical counterparts in every major international standard system.
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G4303 | SUS304 | Japan | Reference |
| ASTM A240 / A276 | AISI 304 / Type 304 | USA | ✅ Nearest Exact |
| EN 10088-1 | 1.4301 / X5CrNi18-10 | Europe | ✅ Nearest Exact |
| DIN | X5CrNi18-10 / 1.4301 | Germany | ✅ Nearest Exact |
| ISO 15510 | X5CrNi18-10 | International | ✅ Nearest Exact |
| GB/T 20878 | 06Cr19Ni10 | China | ✅ Nearest Exact |
Sources: JIS G4303:2021, ASTM A240/A240M-22, EN 10088-1:2014, GB/T 20878-2007
2. Chemical Composition
All three major variants (JIS SUS304, AISI 304, EN 1.4301) share the same 18Cr-8Ni core composition. Minor differences in C, Si, S, and N limits reflect the differing emphasis of each standard.
| Element | JIS SUS304 | AISI 304 | EN 1.4301 |
|---|---|---|---|
| C | ≤ 0.08% | ≤ 0.08% | ≤ 0.07% |
| Si | ≤ 1.00% | ≤ 0.75% | ≤ 1.00% |
| Mn | ≤ 2.00% | ≤ 2.00% | ≤ 2.00% |
| P | ≤ 0.045% | ≤ 0.045% | ≤ 0.045% |
| S | ≤ 0.030% | ≤ 0.030% | ≤ 0.015% |
| Ni | 8.00–10.50% | 8.00–10.50% | 8.00–10.50% |
| Cr | 18.00–20.00% | 18.00–20.00% | 17.50–19.50% |
| N | — | — | ≤ 0.10% |
Note on EN 1.4301 S limit: The EN standard specifies S ≤ 0.015% — half the JIS/ASTM limit of 0.030%. The lower sulfur reduces non-metallic inclusion content, providing marginally better corrosion resistance in weld heat-affected zones and cleaner surface finish in food-contact applications. For high-cleanliness specifications, EN 1.4301 plate may be preferred over JIS SUS304 even in Japan-domestic projects.
Sources: JIS G4303:2021 Table 1, ASTM A240/A240M-22 Table 1, EN 10088-1:2014 Table 2
3. Mechanical Properties
SUS304 cannot be hardened by heat treatment. All strength values below are for the annealed (solution-treated) condition. Cold working increases tensile strength significantly — cold-drawn bar can reach 860 MPa (125 ksi) or higher.
| Property | Metric | Imperial |
|---|---|---|
| Tensile strength (annealed) | ≥ 520 MPa | ≥ 75.4 ksi |
| Yield strength, 0.2% offset (annealed) | ≥ 205 MPa | ≥ 29.7 ksi |
| Elongation | ≥ 40% | ≥ 40% |
| Hardness (annealed) | ≤ 200 HB / ≤ HRB 92 | ≤ 200 HB |
| Tensile (cold-drawn bar, typical) | ~700–860 MPa | ~102–125 ksi |
Sources: JIS G4303:2021 Table 4, ASTM A276/A276M-17 Table 2
4. Physical Properties
| Property | Metric | Imperial |
|---|---|---|
| Density | 7.93 g/cm³ | 0.286 lb/in³ |
| Young’s modulus | 193 GPa | 28,000 ksi |
| Thermal conductivity (20°C / 68°F) | 16.2 W/(m·K) | 112 BTU·in/(hr·ft²·°F) |
| Thermal expansion (20–100°C / 68–212°F) | 17.2 × 10⁻⁶ /°C | 9.6 × 10⁻⁶ /°F |
| Specific heat (0–100°C / 32–212°F) | 500 J/(kg·K) | 0.119 BTU/(lb·°F) |
| Electrical resistivity | 0.73 μΩ·m | — |
| Magnetic (annealed) | Non-magnetic | Non-magnetic |
Magnetic behavior after cold work: Annealed SUS304 is non-magnetic (relative permeability ≈ 1.01). Cold working induces strain-martensite, raising permeability to approximately 1.05–2.0 depending on the degree of deformation. Heavily cold-drawn wire or deep-drawn cups will attract a magnet weakly. This is a normal physical response to cold work — not contamination or a wrong-material condition.
5. Heat Treatment Conditions
SUS304 is not heat-treatable for hardening. Two thermal processes are applicable:
| Process | Temperature | Cooling | Purpose |
|---|---|---|---|
| Solution annealing | 1010–1120°C (1850–2048°F) | Rapid water quench or fast air cool | Dissolve Cr carbides; restore full corrosion resistance |
| Stress relief | 400–430°C (752–806°F) | Air cool | Reduce residual stress in formed/welded parts |
Holding or slow-cooling SUS304 through the 425–860°C (797–1580°F) range precipitates chromium carbides at grain boundaries. The adjacent grain boundary zone is depleted of Cr, losing its passive film — a condition called sensitization. Sensitized material is highly susceptible to intergranular corrosion in acids and many process environments. For welded assemblies intended for corrosive service, specify SUS304L (C ≤ 0.03%) or perform a full post-weld solution anneal (1010–1120°C / 1850–2048°F, rapid quench).
6. Machinability
SUS304 machines at approximately 45–50% of the AISI 1212 baseline. The primary challenge is work hardening — not initial hardness. SUS304 work-hardens rapidly during cutting; a tool that dwells or rubs without cutting generates heat and a hardened surface that accelerates wear.
Recommended Machining Parameters
| Parameter | Recommendation |
|---|---|
| Cutting speed | 60–90 m/min (200–300 ft/min) with coated carbide |
| Insert coating | PVD TiAlN preferred over CVD TiN |
| Feed rate | Higher feed rates reduce rubbing and work hardening |
| Cutting fluid | Sulfurized or sulfochlorinated oil |
| Tool geometry | Sharp edges; positive rake angle; avoid worn tools |
7. Weldability
SUS304 has excellent weldability. For thin sheet (t ≤ 3 mm / 0.12 in), autogenous GTAW (TIG) without filler metal produces clean, low-distortion welds. For thicker sections requiring filler, use ER308 or ER308L (AWS A5.9).
Filler Metal Selection
| Application | Recommended Filler | Notes |
|---|---|---|
| General welding, non-corrosive service | ER308 | Matching composition |
| Welded assemblies in corrosive service | ER308L | Low C prevents HAZ sensitization |
| Autogenous (sheet, no filler) | — | Full penetration GTAW; purge root side |
Preheat is not required. Interpass temperature should be kept below 150°C (302°F) to minimize HAZ sensitization risk in multi-pass welds.
Sources: AWS A5.9/A5.9M, JIS Z3321
8. Common Mistakes
SUS304’s passive film breaks down above approximately 200 ppm Cl⁻ at ambient temperature. In marine environments, coastal locations, swimming pools, or chemical processes with chloride content above this threshold, SUS304 suffers pitting and crevice corrosion — often without visible warning until perforation occurs. The correct material for chloride service is SUS316 or SUS316L, which contains 2.00–3.00% Mo. The Mo addition dramatically improves pitting resistance: PREN (Pitting Resistance Equivalent Number) for SUS316 is approximately 24, versus 18 for SUS304. For highly aggressive chloride environments (seawater, concentrated process streams), duplex 2205 (PREN ≈ 34) should be evaluated.
The standard SUS304 C limit (≤ 0.08%) is sufficient for thin-section welds that cool rapidly through the sensitization zone. For thick sections (t > 6 mm / 0.24 in) with slow weld cooling, the HAZ dwells in the 425–860°C (797–1580°F) sensitization range long enough to precipitate Cr carbides. In subsequent corrosive service, the depleted grain boundary zones corrode preferentially (intergranular corrosion), causing premature failure that looks superficially like a general corrosion attack. The solution is simple: specify SUS304L (C ≤ 0.03%) for all welded assemblies intended for corrosive service. SUS304L is available in the same product forms as SUS304 at minimal price premium.
9. When to Choose SUS304
- ✅ Food and beverage equipment — tanks, conveyors, fittings, dairy processing
- ✅ Kitchen equipment, sinks, countertops, and architectural trim
- ✅ Chemical processing in low-chloride environments (Cl⁻ < 200 ppm)
- ✅ Pharmaceutical and cleanroom components requiring smooth, cleanable surfaces
- ✅ Fasteners, springs, and structural parts where mild corrosion resistance is needed
- ✅ Cryogenic vessels and equipment — austenite retains full toughness to −196°C (−321°F)
- ❌ Marine, coastal, or splash-zone environments — specify SUS316 or duplex 2205
- ❌ High-chloride process streams (Cl⁻ > 200 ppm) — specify SUS316L or SUS317LMN
- ❌ Sustained high-temperature service above 870°C (1598°F) — sensitization and scaling risk
- ❌ Through-hardened or wear-resistant applications — use martensitic stainless (SUS410, SUS440C) or tool steel
10. FAQ
What is the difference between SUS304 and SUS304L?
Carbon content only. SUS304: C ≤ 0.08%. SUS304L: C ≤ 0.03%. The lower C in 304L prevents chromium carbide precipitation (sensitization) in the heat-affected zone during welding and during stress relief heat treatment in the sensitization range. For unwelded wrought parts in non-corrosive service, 304 and 304L are mechanically interchangeable and may be stocked together as “304/304L dual-certified” material. For welded assemblies in corrosive environments, 304L is the technically correct specification.
Is SUS304 magnetic?
Annealed SUS304 is non-magnetic (relative permeability ≈ 1.01). Cold working induces strain-martensite, increasing magnetic permeability to approximately 1.05–2.0 depending on the amount of deformation. Heavily cold-drawn SUS304 wire or springs will attract a magnet weakly. This is a normal physical consequence of cold work and does not indicate contamination, wrong material, or degraded corrosion resistance from the cold working alone.
What is the maximum service temperature for SUS304?
Continuous service is acceptable to 870°C (1598°F) with tolerable oxidation. Intermittent service can reach 925°C (1697°F). Above 870°C (1598°F) in continuous operation, carbide precipitation during cooling reduces aqueous corrosion resistance. For sustained high-temperature service above 870°C, specify SUS310S (25Cr-20Ni) or an appropriate heat-resistant alloy. Note that SUS304’s elevated-temperature mechanical allowables drop sharply above 500°C (932°F) — consult the applicable design code (ASME Section VIII, JIS B 8265) for temperature-derated allowable stresses.
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