Quick Answer
Quick Answer
SS 304 (EN 1.4301) is the most produced austenitic stainless steel grade, commonly called 18-8 for its nominal 18 % chromium and 8 % nickel content. It offers good corrosion resistance in atmospheric and mild chemical environments, excellent formability, and broad availability across ASTM A240, ASME SA-240, and EN 10088.
Overview
Grade 304 accounts for approximately 50 % of all stainless steel produced globally. Its combination of good corrosion resistance, excellent workability, weldability, and competitive cost makes it the default choice across industries — from kitchen equipment and architectural cladding to storage tanks and heat exchangers operating in non-chloride environments.
The European equivalent is 1.4301 per EN 10088. In ASME pressure vessel applications the material is designated SA-240 Type 304. The informal "18-8" label reflects the nominal composition but should not be used on MTCs or purchase orders, where the specific grade designation is required.
Chemical Composition — SS 304 / 1.4301
| Element | ASTM A240 Type 304 | EN 1.4301 |
|---|---|---|
| Carbon (C) | ≤ 0.08 | ≤ 0.07 |
| Manganese (Mn) | ≤ 2.00 | ≤ 2.00 |
| Silicon (Si) | ≤ 0.75 | ≤ 1.00 |
| Phosphorus (P) | ≤ 0.045 | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 | ≤ 0.015 |
| Chromium (Cr) | 18.0 – 20.0 | 17.5 – 19.5 |
| Nickel (Ni) | 8.0 – 10.5 | 8.0 – 10.5 |
| Nitrogen (N) | ≤ 0.10 | ≤ 0.11 |
Note the absence of molybdenum — the key compositional difference from 316/316L. The higher chromium range (18–20 %) in 304 vs 316 (16–18 %) partly compensates, but does not replicate the pitting resistance that molybdenum provides.
Mechanical Properties — SS 304 (Annealed Plate)
Minimum values per ASTM A240 for annealed flat-rolled product:
| Property | ASTM A240 Type 304 | EN 1.4301 (+A) |
|---|---|---|
| Ultimate Tensile Strength (UTS) | 515 MPa (75 ksi) | 500 – 700 MPa |
| 0.2 % Proof Strength (YS) | 205 MPa (30 ksi) | 210 MPa |
| Elongation in 50 mm | 40 % | 45 % |
| Hardness (max) | 217 HBW / 95 HRB | 215 HBW |
Physical Properties
| Property | Typical Value |
|---|---|
| Density | 7.93 g/cm³ |
| Thermal conductivity (20 °C) | 16.2 W/(m·K) |
| Thermal expansion (20–100 °C) | 17.2 × 10⁻⁶ /°C |
| Modulus of elasticity | 193 GPa |
| Magnetic permeability (annealed) | ≤ 1.02 |
Standards Coverage
| Standard | Product Form | Designation |
|---|---|---|
| ASTM A240 | Plate, sheet, strip | Type 304 |
| ASTM A276 | Bar and shapes | Type 304 |
| ASTM A312 | Seamless and welded pipe | TP304 |
| ASTM A182 | Forgings and fittings | F304 |
| ASME SA-240 | Pressure vessel plate | Type 304 |
| EN 10088-2 | Flat products | 1.4301 |
| EN 10088-3 | Long products | 1.4301 |
| JIS G4304 | Hot-rolled sheet | SUS304 |
Applications
Grade 304's versatility means it appears across nearly every industry:
- Food and beverage — brewing vessels, dairy pipework, food preparation equipment; easily cleaned and resistant to organic acids.
- Architectural and structural — handrails, facades, and roofing in inland or low-salinity environments.
- Kitchen equipment — sinks, countertops, catering equipment.
- Chemical storage — tanks for dilute acids, alkalis, and solvents where chloride concentration is low.
- Heat exchangers — shell-and-tube units handling non-chloride process streams.
- Cryogenic vessels — liquid nitrogen and oxygen storage (retains toughness at low temperature).
Avoid 304 where: chloride concentrations exceed a few hundred ppm, especially at elevated temperatures. Pitting and stress corrosion cracking become significant risks; 316, 316L, or duplex grades are more appropriate.
Corrosion Resistance
| Environment | 304 Performance | Recommendation |
|---|---|---|
| Fresh water / atmospheric | Excellent | Suitable |
| Dilute organic acids | Good | Suitable |
| Dilute sulfuric acid (cold) | Moderate | Check concentration limits |
| Seawater / marine spray | Poor (pitting risk) | Use 316L or duplex |
| Chloride solutions (hot) | Poor (SCC risk) | Use duplex |
| Oxidizing acids (nitric) | Excellent | Preferred grade |
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Why is 304 called 18-8 stainless steel?
The "18-8" label derives from the nominal composition: approximately 18 % chromium and 8 % nickel. While convenient, it is imprecise — actual ranges are 18–20 % Cr and 8–10.5 % Ni per ASTM A240. Some 18-8 references may also encompass 302 and 305, which have similar nominal compositions. Always use the specific grade designation (Type 304, 1.4301) in formal documents.
What is the maximum service temperature for SS 304?
SS 304 can be used continuously up to 870 °C (1600 °F) in non-sensitization-critical applications. For cyclic service in the 425–860 °C range in corrosive environments, use 304L to reduce sensitization risk. Above 870 °C, consider 309, 310, or other high-temperature grades.
Is SS 304 food-safe?
Yes. SS 304 meets the material requirements of food contact regulations including EU Regulation 10/2011, FDA requirements, and 3-A Sanitary Standards. Its smooth surface finish and passive chromium oxide layer make it resistant to bacterial adhesion. For pharmaceutical and biotech applications requiring stricter surface roughness (Ra ≤ 0.8 µm), 316L with low sulfur is often specified instead.
What is the difference between 304 and 304L on an MTC?
The only intentional difference is carbon content: 304 allows ≤ 0.08 % C while 304L is limited to ≤ 0.030 % C. Many mills produce dual-certified 304/304L material that meets both limits simultaneously. On an MTC, check the grade designation, the reported carbon value, and that it falls within the applicable limit for the grade ordered.