Alternative Designations of AISI 304
| Standard | ISO | EN | DIN | AISI/SAE | UNS | JIS | GB (China) | BS | AFNOR |
| Designation | X5CrNi18-10 | 1.4301 | X5CrNi18-10 | 304 | S30400 | SUS304 | 0Cr18Ni9 (old) / 06Cr19Ni10 (new) | 304S15, 58E | Z6CN18.09 |
AISI 304 stainless steel (0Cr18Ni9/1.4301/SUS304) is an austenitic 18-8 series chromium-nickel alloy with excellent corrosion resistance in oxidizing environments and good formability/weldability. Its face-centered cubic structure remains non-magnetic when annealed but may become slightly magnetic after cold working. While suitable for food processing, architecture and medical applications, it has limited chloride resistance compared to 316 stainless steel. The material offers good mechanical properties (515 MPa tensile strength, 40% elongation) and can be used from cryogenic temperatures to 425°C long-term. Common issues like intergranular corrosion can be mitigated using low-carbon 304L or solution annealing. Available in various surface finishes (2B, BA, No.4), it’s the world’s most widely used stainless steel grade for general purposes.
Basic Classification and Crystal Structure of AISI 304
- Type: Austenitic stainless steel (part of the 18-8 series – 18% Cr, 8% Ni).
- Crystal Structure: Face-Centered Cubic (FCC) structure, providing excellent toughness and ductility from low to high temperatures.
- Microstructure: After solution annealing, the structure consists of a single austenitic phase and is non-magnetic (may become slightly magnetic after cold working).
Chemical Composition of AISI 304
| Element | Chromium (Cr) | Nickel (Ni) | Carbon (C) | Manganese (Mn) | Silicon (Si) | Phosphorus (P) | Sulfur (S) | Iron (Fe) |
| % Range (Weight) | 18.0–20.0 | 8.0–10.5 | ≤0.08 | ≤2.0 | ≤1.0 | ≤0.045 | ≤0.03 | Balance |
Mechanical Properties of AISI 304
| Property | Tensile Strength | Yield Strength (0.2%) | Elongation | Hardness (Brinell) | Hardness (Rockwell) |
| Value (Annealed Condition) | 515 MPa (min) | 205 MPa (min) | 40% (min) | 201 HB (max) | 92 HRB (max) |
Physical Properties of AISI 304
| Property | Density | Melting Point | Thermal Conductivity | Electrical Resistivity | Magnetic Permeability |
| Value | 8.0 g/cm³ | 1400–1450°C | 16.2 W/m·K (at 100°C) | 0.72 μΩ·m | ~1.02 (non-magnetic) |
Applications & Products
- Food Industry: Kitchen sinks, cutlery, brewing tanks.
- Architecture: Decorative panels, handrails, flanges, fasteners.
- Medical: Surgical instruments, hospital equipment.
- Chemical: Storage tanks, piping (for mild chemicals).
- Automotive: Exhaust systems, trim components.
- Household: Appliances (refrigerators, dishwashers).
Material Characteristics Overview of AISI 304
Corrosion Resistance:
- Excellent in oxidizing environments (e.g., atmosphere, freshwater, nitric acid).
- Good resistance to organic acids (e.g., acetic acid, lactic acid) and weak alkaline media.
- Limitation: Prone to pitting and stress corrosion cracking (SCC) in chloride (Cl⁻) environments (e.g., seawater, salt spray). In such cases, molybdenum-containing 316 stainless steel is recommended.
Workability:
- Cold Working: Can be formed by cold rolling, stamping, deep drawing, etc., but has a high work-hardening rate (intermediate annealing may be required).
- Hot Working: Hot forming temperature range is 900–1200°C. Avoid prolonged exposure to 425–860°C to prevent chromium carbide precipitation and intergranular corrosion.
- Weldability: Good weldability; conventional methods (TIG, MIG, arc welding) can be used. Post-weld heat treatment is not required, but heat input should be controlled to avoid intergranular corrosion.
Heat Treatment:
- Solution Annealing: Heat to 1010–1120°C followed by rapid cooling (water quenching) to dissolve chromium carbides and restore corrosion resistance.
- Stress Relief Annealing: Heat at 300–450°C to relieve cold-working stresses (does not affect corrosion resistance).
Surface Treatment and Cleaning
- Surface Finish: Common finishes include 2B (cold-rolled + annealed + pickled), BA (bright annealed), and No.4 (brushed), suitable for different decorative or functional requirements.
- Passivation: Enhances the density of the surface chromium oxide layer (Cr₂O₃) using nitric or citric acid, improving corrosion resistance.
- Cleaning Methods: Avoid chlorine-containing cleaners (e.g., bleach). Neutral detergents or alcohol wipes are recommended.
Environmental Adaptability
Low-Temperature Performance: Maintains toughness even at liquid nitrogen temperatures (-196°C), making it suitable for cryogenic equipment (e.g., liquid nitrogen tanks).
High-Temperature Performance:
- Short-term use limit: 870°C (oxidizing environment).
- Long-term use limit: 425°C (higher temperatures may lead to sensitization due to chromium carbide precipitation).
AISI 304 Comparison with Other Stainless Steels
| Property | 304 (0Cr18Ni9) | 316 (0Cr17Ni12Mo2) | 430 (1Cr17) |
| Primary Alloy | Cr-Ni | Cr-Ni-Mo | Cr (Ferritic) |
| Chloride Resistance | Moderate | Excellent (due to Mo) | Poor |
| Magnetism | Typically none (slight after cold work) | Typically none | Yes |
| Cost | Low | Higher | Lowest |
Common Issues and Solutions
Intergranular Corrosion: Chromium carbide (Cr₂₃C₆) precipitation at grain boundaries after welding or high-temperature exposure, leading to chromium-depleted zones.
- Solution: Use low-carbon versions (304L, C ≤ 0.03%) or perform solution annealing.
Pitting Corrosion: Localized perforation in chloride environments.
- Solution: Switch to 316 stainless steel or improve surface passivation.
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