304 Stainless Steel – Properties, Application
304 stainless steel is the most common form of stainless steel used around the world, largely due to its excellent corrosion resistance and value. It contains between 16 and 24 percent chromium and up to 35 percent nickel, as well as small amounts of carbon and manganese.
The most common form of 304 stainless steel is 18-8, or 18/8, stainless steel, which contains 18 percent chromium and 8 percent nickel.
304 can withstand corrosion from most oxidizing acids. That durability makes 304 easy to sanitize, and therefore ideal for kitchen and food applications. It is also common in buildings, décor, and site furnishings.
304 stainless steel does have one weakness: it is susceptible to corrosion from chloride solutions, or from saline environments like the coast. Chloride ions can create localized areas of corrosion, called “pitting,” which can spread beneath protective chromium barriers to compromise internal structures. Solutions with as little as 25 ppm of sodium chloride can begin to have a corrosive effect.
304 Stainless Steel Properties
- 304 stainless steel is non-magnetic and exhibits high resistance to corrosion and oxidation against atmospheric, chemical, petroleum, textile, and food industry sources.
- It has good drawability – the combination of low yield strength and high elongation permits fabrication into complex shapes. (Care should be taken to fully anneal them immediately after forming.)
- This austenitic kind of steel is easily weldable. (During welding, there is a likelihood of chromium carbide formation, which might compromise resistance to corrosion. To overcome this, welding needs to be followed by full annealing, which dissolves chromium carbide. Additionally, the austenitic structure is prone to cracking during welding – this is countered by adding a small amount of ferrite while resolidifying.)
- It has high strength and toughness, even at very low temperatures (cryogenic).
- It has a smooth surface, which is easy to clean.
The most common of austenitic grades, containing approximately 18% chromium and 8% nickel. It is used for chemical processing equipment, for food, dairy, and beverage industries, for heat exchangers, and for the milder chemicals.
Type 304L Stainless Steel
Type 304L stainless steel is an extra-low carbon version of the 304 steel alloy. The lower carbon content in 304L minimizes deleterious carbide precipitation as a result of welding. 304L can, therefore, be used “as welded” in severe corrosion environments and it eliminates the need for annealing.
This grade has slightly lower mechanical properties than the standard 304 grade, but it’s nonetheless widely used thanks to its versatility. Like Type 304 stainless steel, it’s commonly used in beer-brewing and wine-making, but also for purposes beyond the food industry such as in chemical containers, mining, and construction. It’s ideal for use in metal parts such as nuts and bolts that will be exposed to salt water.
- Vickers hardness = 129
- Melting Point = 1400 – 1455 degree C
- Modulus of Elasticity = 193 – 200 GPa
- Tensile Strength = 505 MPa
- Poisson’s Ratio = 0.29
- Density = 8 g/cc
- Magnetic Permeability = 1.008
- Electrical Resistivity = 7.2 e-005 ohm-cm
Applications and uses
- Chemical industry – Large storage tanks and containers for liquids and solids
- Food industry – food processing equipment like milking machines, storage tanks, hauling tanks, piping, valves, milk trucks etc. Also used in breweries, wine-making and the fruit juice industry.
- Domestic uses – 304 stainless steel can resist the corrosive action of acids found in fruits, milk, meat and vegetables, and is fairly resistant to abrasion. Therefore, it is widely used in sinks, tabletops, stoves, refrigerators, cutlery, utensils and various other appliances.
- Architectural uses – paneling, molding, railings, décor.
- Industrial applications – tools, bolts, nuts, screws etc.
- Automotive and aerospace industries – fuel tanks, various structural components.
- Hospitals – surgical equipment.
- Commercial – sanitary fittings, pipes.
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