Stainless Steel 304
SThese stainless steels are widely used in the petrochemical and food industries due to their corrosion resistance, tensile strength and ability to accommodate higher temperatures. There is a trade-off between corrosion resistance and temperature characteristics according to the specific grade.
Grade 304 is an austenitic steel with excellent welding and forming characteristics. The key elements in 304 are Chromium and Nickel which give it excellent resistance to corrosion.
It has good resistance to corrosion, and has good weldability
The austenitic structure allows it to be deep drawn without intermediate annealing. It is also unnecessary to anneal it following welding thin sections.
It is widely used in the food industry, water, architectural, cryogenic and high-temperature applications. Widely used for good quality cutlery where it is described as 18/8 referring to the percentages of Chromium and Nickel.
The range of properties of 304 mean that it is used in many industries.
Its resistance to corrosion makes it suitable for use in the food industry, particularly dairy, wine and beer production or processing.
Its malleability makes it easily formed into sinks, troughs and other kitchen appliances and it can be spun easily making it suitable for the production of pots and pans.
A good choice for architectural applications being less expensive than 316. Its corrosion resistance makes it an excellent choice for internal panelling or other fittings and it is also suitable for use externally when away from the marine environment. It is however not as resistant to chloride corrosion as 316 and if there is salt spray in the atmosphere it is generally best to use 316.
The combination of corrosion resistance and formability make it a good choice for chemical containers - including those used for transportation.
It has good heat resistance and is therefore widely used in heat-exchangers. Where particularly high temperatures 304H should be considered
Corrosion Resistance
304 has good corrosion resistance in a wide range of atmospheric conditions and to many corrosive media. It is however subject to pitting corrosion in chloride environments particularly in warm conditions.
It is also subject to stress corrosion cracking above 60o. It is generally resistant to concentrations of about 200mg/litre of chlorides at 20o but this drops to about 150mg/litre at 60o.
It is generally resistant to concentrations of about 200mg/litre of chlorides at 20o but this drops to about 150mg/litre at 60o.
Heat Resistance
304 is not generally regarded as a grade to be selected when very high temperatures are expected but it may have certain benefits. It resists oxidisation in continuous use up to 925o and in intermittent use to 870o. However, using it in a temperature range between 425o and 860o can result in carbide precipitation and subsequently intergranular corrosion.
304L, with its lower carbon content, is less prone to carbide precipitation and can be used at these temperatures.
304H has greater strength at high temperatures and may be the steel of choice where both high-temperature resistance and corrosion resistance are required. Thes requirements are often found in flue gas chimneys where gasses may condense forming aggressive often acidic liquids.
n common with other austenitic stainless steels, 304 grade has strong work hardening characteristics. Clearly, in some cases, this can be an advantage, but generally, it is an issue to be considered carefully.
If it is likely to be an issue, discussion with the producer can be valuable as minor variations to the precise composition and process can have benefits.
Where heavy sections have to be welded, post-weld annealing may be necessary to restore corrosion resistance.
| Chemical Element | % Present |
|---|---|
| Carbon (C) | 0.07 |
| Chromium (Cr) | 17.50 - 19.50 |
| Manganese (Mn) | 2.00 |
| Silicon (Si) | 1.00 |
| Phosphorous (P) | 0.045 |
| Sulphur (S) | 0.15 |
| Nickel (Ni) | 8.00 - 10.50 |
| Nitrogen (N | 0.1 |
| Iron (Fe) | Balance |
| Physical | Value |
|---|---|
| Density | 8.03 g/cm³ |
| Melting Point | 1450 °C |
| Thermal Expansion | 17.2 x10^-6 /K |
| Modulus of Elasticity | 193 GPa |
| Thermal Conductivity | 16.2 W/m.K |
| Electrical Resistivity | 0.072 x10^-6 Ω .m |
| Mechanical | Value |
|---|---|
| Proof Stress | 230 Min MPa |
| Tensile Strength | 540 to 750 MPa |
| Elongation A50 mm | 45 Min % |
| Hardness Brinell | 215 Max HB |
304 stainless is also available as 304H and 304L.
It is common for 304 and 304L to be stocked in "Dual Certified" form, particularly in plate and pipe. These items have chemical and mechanical properties complying with both 304 and 304L specifications. Such dual certified product does not meet 304H specifications and may be unacceptable for high-temperature applications.
- Tube
- Pipe
- Fittings
- Flanges
- Special Sections
- Sheet
- Plate
- Flat Bar
- Round Bar
- Hollow Bar
- I Beam
- U Channel