Stainless steel is primarily alloyed with Chromium, crucial for its corrosion resistance. When Chromium responds with oxygen, it forms a protective layer on the steel’s surface, safeguarding it from environmental damage. Stainless steels include at least 10.5% Chromium, and there are through 150 grades of stainless steel categorized into five types based on their internal structure at room temperature: Austenitic, Ferritic, Martensitic, Duplex, and Precipitation Hardened. Austenitic grades account for approximately 70% of stainless steel consumption. Austenitic stainless steels feature a Body-Centered Cubic (BCC) structure and are non-magnetic. While they cannot be hardened through heat treatment, they can be work-hardened. AISI 304 is a prominent grade within the Austenitic category, known for its versatility and widespread use across various industries due to its excellent properties.
Composition
AISI 304 Stainless Steel round bar , usually referred to as 18/8 Stainless Steel, derives its name from its composition—18% Chromium and 8% Nickel. This alloy’s distinctive characteristics are influenced by these elements. Below is a table showing variations of the 304 grade with notable chemical composition differences.
Properties of 304/304L
Chemical Properties (as per Standard EN 10088-3:2014)
| Composition | 304/1.4301 | 304L/1.4307 |
| Carbon (%) | Max. 0.07 | Max. 0.03 |
| Silicon (%) | Max. 1 | Max. 1 |
| Manganese (%) | Max. 2 | Max. 2 |
| Phosphorous (%) | Max. 0.045 | Max. 0.045 |
| Sulphur (%) | Max. 0.030 | Max. 0.030 |
| Chromium (%) | 17.5-19.5 | 17.5-19.5 |
| Nickel (%) | 8.0-10.5 | 8.0-10.5 |
| Nitrogen (%) | Max 0.11 | Max 0.11 |
Mechanical Properties (as per Standard EN 10088-3:2014)
| Grade | Hardness (HBW) max. | (0.2%) Proof strength (MPa) min | Tensile strength (MPa) min. | Elongation after fracture (long. min.) | Impact energy (J) min. |
| 304/1.4301 | 215 | 190 | 500-700 | 45 | 100 |
| 304L/1.4307 | 215 | 175 | 500-700 | 45 | 100 |
Characteristics
Strengths:
- Excellent Formability: AISI 304 stainless steel can be easily drawn and shaped without intermediate heat-softening processes.
- Cryogenic Toughness: It maintains good toughness even at cryogenic temperatures.
- Corrosion Resistance: Post-weld annealing is usually unnecessary to restore corrosion resistance, making it versatile for various applications. The low-carbon variant, 304L, helps minimize carbide precipitation.
- Acid Resistance: It offers strong resistance to many oxidizing acids and is simple to clean and sterilize.
Weaknesses:
- Machinability: AISI 304 is harder to machine compared to carbon steels. Effective machining requires slower speeds, high feed rates, and cutting fluids.
- Stress Corrosion Cracking: The grade is prone to stress corrosion cracking and exhibits lower resistance in chloride and saline environments. Chloride ions can cause localized pitting corrosion, which can compromise the material’s structural integrity.
Applications:
- Kitchen sinks and consumer durables
- Chemical containers, including those for transportation
- Food processing equipment, such as for brewing beer, processing milk, and making wine
- Manufacturing of fasteners and flanges
- Architectural uses, including roofing, cladding, doors, and windows
- Automotive and aerospace components
- Heat exchangers
Other Trade names of AISI 304 & 304L
| AISI | UNS | Europe (EN) | Japanese (JIS) |
| 304 | S30400 | 1.4301/ DIN X5CrNi 18-10 | JIS SUS304 |
| 304L | S30403 | 1.4307/ DIN X2CrNi18-9 | JIS SUS304L |
