The SAE/ANSI 304 (AISI 304) is the most commonly available and used type of stainless steel. It is also referred to as 18/8 stainless steel, A2 stainless steel (as per the ISO 3506), or 304S15 (as per the British Standard). This is an austenitic chromium-nickel alloy which practically means that it has a very high corrosion resistance. It is also nonmagnetic and can’t be hardened through heat treatment. As AISI 304 can withstand extremely corrosive environments and can be shaped, machined and welded relatively easy, it is very popular for a wide range of applications:
- Food-handling products
- Automotive parts like exhausts
- Building exteriors
- Vaporizer coils
- Industrial components such as screws, nuts and bolts
- Springs for bottling facilities
- Kitchen sinks
- Cooking pans
- Tubing
- Brewery parts
- Power generation components
- Chemical processing units
- Medical equipment
There are also additional reasons why 304 is used in the aforementioned sectors. These include the aesthetically pleasing appearance, easiness in cleaning, relatively high-strength to weight ratio and high availability in many different forms.
Achilles heel of SS 304/AISI 304
The Achilles heel of SS AISI 304 is chloride environments and high temperatures (above 60 degrees Celsius). These environments can cause corrosion cracking and general damage to the protective layers of the steel. However, because chloride is usually only found in controlled environments and relatively low concentrations, SS 304 remains suitable for a very wide range of applications. It will be no surprise to learn that it is the most popular stainless steel available today along with the superior grade, SS AISI 316. Indicatively, SS 304 can withstand temperatures to up to 925 degrees Celsius while maintaining enough strength and the same corrosion resistance properties.
Fabricating SS 304/AISI 304
Fabricating stainless steel 304 requires care and precision. The concentration of the various components that make up SS 304 must be kept at a certain and precise level. As a consequence even the tools that will be used for the fabrication of the SS AISI 304 must be thoroughly cleaned beforehand. If the fabrication is done with the cold working method, there needs to be an annealing stage before the completion. This ensures that the risk of tears and cracks is minimized. When fabrication is achieved using the hot method, the forging must be done at a temperature of up to 1260 degrees Celsius. Then immediately cooled in a solution for the retention of the corrosion resistance properties, ductility and toughness.
Physical Properties and Datasheet for AISI 304
Approximate Average Composition
| Iron (Fe) | 70.5% |
| Chromium (Cr) | 18.7% |
| Nickel (Ni) | 9.2% |
| Manganese (Mn) | 1% |
| Silicon (Si) | 0.5% |
| Nitrogen (N) | 0.05% |
| Carbon (C) | 0.04% |
| Phosphorus (P) | 0.023% |
| Sulfur (S) | 0.015% |
Physical Properties of AISI 304
| Material Density | 7900 kg/m3 |
| Elastic Modulus | 193 GPascal |
| Mean Thermal Expansion Coefficient | 17.8 μm/m/oC |
| Mean Thermal Conductivity | 18.9 W/m*K |
| Specific Heat Capacity | 500 J/kg*K |
| Electrical Resistivity | 720 (nΩ*m) |
| Melting Onset | 1400Â oC / 2550Â oF |
| Â Melting Completion | 1450Â oC / 2640Â oF |
| Â Embodied Energy | 43 MJ/kg |
| Calomel Potential | -80 mV |
Mechanical Properties of AISI 304
| Tensile Strength | 515 Mpa |
| Yield Strength | 205 Mpa |
| Elongation | 40% (50 mm) |
| Rockwell Hardness | 92 |
| Brinell Hardness | 201 |
