Steel is an alloy from iron and carbon, with a carbon content of 2.1% maximum possible. Stainless steel is a type of steel that is resistant to corrosion with the addition of alloying elements. Stainless steel is part of a family of about 200 alloys of steel that has high heat and corrosion resistance. The carbon percentage of stainless steel can range from 0.03% to 1.2%. A wide number of industries use different grades of stainless steel in manufacturing products. Therefore, its demand is increasing at 5% each year. Stainless steel is also 100% recyclable and made from scrap. This makes it an eco-friendly material. Industries that use stainless steel are:
- Food and catering
- Medical equipment
- Home appliances
- Chemicals and pharmaceuticals
- Offshore and shipbuilding
- Automotive manufacturing
- Energy and industry
- Architecture and construction
Properties of Stainless Steel
- Stainless steel exhibits high strength and low elongation or low strength and high elongation properties.
- Stainless steel works better at high temperatures due to better resistance properties.
- Stainless steel material has the highest tensile strength.
- The cryogenic properties of stainless steel are high, making it suitable for modern technologies.
- Stainless steel material is highly ductile.
- The electrical conductivity of stainless steel is extremely low.
- Stainless steel material has high oxidation resistance due to the presence of chromium metal present in it.
- This material is biologically inert, making it best for kitchen appliances and cutlery making.
- This material is resistant to acids, bases, and other organic compounds.
- Stainless steel material is recyclable, easy to work with and can be cleaned easily.
Types of Stainless Steel
There are four principal types of stainless steel. These are:
● Ferritic Stainless Steel
- The ferritic phase of alloy stabilizes by the addition of chromium (>17%).
- This makes the material highly corrosion resistant but not exceptionally strong.
- Heat treatments cannot help in the hardening of the material.
- Cold treatments can be done to increase the hardness of a material.
- Ferritic is an inexpensive grade of stainless steel and therefore is used for kitchen equipment and ornamental applications.
● Martensitic Stainless Steel
- An addition of chromium-iron alloy up to 2% increases its hardenability.
- The hardened martensitic can be sufficiently hardened to produce rust-resistant cutlery, surgical instruments, ball valves, and seats.
- The martensitic stainless steel is magnetic and has a carbon content that makes it difficult to weld.
● Austenitic Steel
- Austenitic steel is produced by adding 8-20 % nickel to chromium-iron alloy.
- It is a face-centered cubic structure that offers corrosion resistance and a soft magnetic field.
- These steels have relatively low carbon content which means they are weldable.
- These steels are used in applications where corrosion resistance is needed.
● Duplex Steel
- Duplex steel is a combination of both ferritic and austenitic phases.
- The strength of these steels is twice the strength of austenitic varieties.
- Duplex steel offers good corrosion resistance and weldability.
- These steels are used for special applications where strength is the main concern such as in pressure vessels.
The best and most economical type of stainless steel is austenitic. These steels are widely used in the cutlery industry because of their corrosion resistance and welding properties.
Different Grades of Stainless Steel
There are many different types of grades of stainless steel, and each belongs to one of the principal types of steel. Each one has different properties and is used in different industries.
Grade 304 Stainless Steel
- SS304 is commonly known as 18-8 stainless steel.
- It contains 18-20% Cr and 8-10.5% nickel in it.
- SS304 is non-magnetic under annealing conditions but can be made weakly magnetic by cold treatments.
- It cannot be hardened by heat treatments, but can be hardened by cold treatments.
- It has excellent corrosion resistance to mild atmosphere and freshwater, but halides can make them corrode easily.
- 18-8 stainless steel does not require preheating for welding purposes and has excellent welding properties.
- It is the most widely used austenitic steel in industries such as food, electronics, medical equipment, hardware tools, water treatment plants, and the petrochemical industry.
Grade 310 Stainless Steel
- SS310 is commonly known as 18-10 stainless steel.
- It is a high chromium-nickel austenitic steel that also has high carbon content.
- This grade shows high oxidation, creep, and heat resistance.
- SS310 is widely used in the petrochemical industry in carburizing conditions.
- It is commonly used in cryogenic applications because of its stiffness and lower magnetic permeability.
- It cannot be toughened by heat processing but with cold processes.
- This grade is easily weldable and can be found in different forms such as mesh, wires, strips, foil, plate, and sheets.
- 18-10stainless steel is used in industries for heat and chemical processes.
Grade 430 Stainless Steel
- SS430 is commonly referred to as 18-0 stainless steel.
- It contains 18% of chromium and the amount of nickel is negligible in it.
- It is less costly than that of 300 series because of the absence of nickel elements.
- It is a low-carbon and non-hardenable steel.
- It cannot be hardened by heat processes but cold forging methods can be applied to it.
- This grade can be welded but to a very limited level therefore, it should not be used for load-bearing applications.
- This grade has high oxidation and temperature resistance and can withstand many chemicals.
- The 18-0 grade is not suitable for low temperatures because they turn brittle when cooled down from elevated temperatures.
- It has a high elastic modulus meaning that it cannot bend and is stiff and stronger than other series.
- It is widely used in manufacturing dishwasher linings, automotive trim, formed parts, industrial roofing, wall cladding, utensils, mining equipment, and heat-resisting applications.
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