Austenitic stainless steel is among the top varieties of stainless steel. It has a crystalline structure and is known for its high durability and non-magnetic properties. Due to these reasons, it finds applications in automotive trims, cookware, and even other industry-related equipment. If you want to learn more about austenitic stainless steel, its types, grades, and advantages, keep reading!
What is Austenitic Stainless Steel?
Typically, austenitic stainless steel has a face-centered cubic atom structure (austenite), which contributes to its toughness. This structure is due to the presence of nickel, manganese, and nitrogen as alloying elements.
It has high machinability, formability, and weldability, so you can use it to create complete geometric shapes. The best part is that it finds applications in various industries, contributing to its rapid market growth, which is going to hit a massive USD 88.81 Bn by 2030.
Brief History of Austenitic Stainless Steel
The history of austenitic stainless steel is quite rich. Some early observations began in the 1800s when metallurgists in England and France noted that the Fe-Cr alloy showed excellent corrosion resistance.
However, later on, in 1913, Harry Brearley, working in Sheffield, UK, accidentally discovered a steel alloy with 12.8% chromium. He saw that this new material was resistant to corrosion and rust and called it “Rustless Steel.”
Around 1912-14, German industrialist Friedrich Krupp and his research team also developed a chromium-modified steel. They named it “Versuchsschmelze 2 Austenit” or “V2A,” and the material possessed pretty much the same characteristics as the Rustless Steel developed by Brearley.
Manufacturing Process
Now that you are aware of the basic definition and history of austenitic stainless steel, here’s an overview of its manufacturing process:
- Firstly, raw materials like iron ore and other alloying elements, including chromium, nickel, molybdenum, etc., are placed inside an electric furnace.
- Next, reducing agents are added that bring contaminants and other oxides to the top in the form of slag, which is removed to refine the steel.
- The refined steel is then cast into molds of different shapes and undergoes hot and cold forming processes.
- Hot forming typically happens at temperatures that are higher than the austenitic stainless steel’s recrystallization temperature and is useful for making thick steel plates.
- On the other hand, cold forming occurs at room temperature and is better suited to produce sheets and wires.
- To ensure the final products maintain their accurate structure, the steel requires heat treatment or rolling followed by annealing. While some steel materials may require cold rolling to improve the overall surface finish.
- The cold rolled steel is submerged in an acid bath to get rid of all impurities. After that, the stainless steel sheets or coils are cut and welded into different shapes to get the final desired products.
Grades of Austenitic Stainless Steel
The austenitic stainless steel comes in a variety of grades due to variations or changes in their chemical composition. Here are some common ones:
Grade 316
Due to its incredible chloride corrosion resistance, Grade 316 stainless steel is also known as marine-grade. It’s generally used to develop products such as boat fittings, food processing equipment, and other marine hardware.
Grade 304
It’s one of the most widely used grades of austenitic stainless steel. It contains high nickel content, ranging from 8 to 10.5 percent by weight and around 18 percent chromium. That’s the reason it also goes by the name 18/8 and has high formability and weldability. Common applications of grade 304 include fittings, steel pipes, heat exchangers, and industrial equipment.
Grade 303
Grade 303 is the most machinable of all the other grades of austenitic stainless steel. It’s primarily due to the presence of sulfur (0.15% and 0.35%) in the steel composition, which also contributes to lower corrosion resistance and reduced toughness. However, it is not heat-treatable and has good oxidation resistance. You can use this type of stainless steel to create complex products like automatic screw machines, nuts, bolts, and gears.
Grade 321
Grade 321 is the standard 18/8 chromium-nickel alloy, but with the addition of titanium that stabilizes the material by eliminating its susceptibility to intergranular corrosion. There’s no chromium carbide precipitation from welding, which renders it suitable for manufacturing aircraft exhaust, spiral welded tubes, and furnace parts.
Grade 347
Another one on the list is grade 347 austenitic stainless steel that has Niobium to suppress the formation of chromium carbide precipitation. It’s non-magnetic in the annealed condition and is suitable for applications requiring intermittent heating in the 800°F – 1650°F (427°C – 899°C) range. You can utilize it to produce a branch pipe of an aero engine, a turbine compressor hot gas pipeline, and an exhaust manifold.
Composition Form of Stainless Steel
Austenitic stainless steel is actually a combination of different elements. To give you a better idea of what constitutes its structure, here’s a general overview of its chemical composition:
Elements | Percentage |
Chromium | 18-20% |
Nickel | 8-10.5% |
Manganese | 2% |
Carbon | 0.08% |
Phosphorus | 0.045% |
Silicone | 1.0% |
Sulfur | 0.030% |
Properties of Austenitic Stainless Steel
The main properties of austenitic stainless steel that make it a popular choice for different industrial and other applications are:
Corrosion Resistance
One of the most important properties of austenitic stainless steel is its incredible corrosion resistance. This stems from a thin, constantly self-repairing layer of chromium oxide that makes the surface of the material passive, so it resists corrosion, especially in oxidizing and reducing media. The best part of this layer is that if there’s a scratch or damage due to harsh chemical conditions, it spontaneously forms again, ensuring continuous protection.
Note: On top of preventing corrosion, this layer also makes the steel heat resistant as there’s no chance of oxidation and scaling at high temperatures.
Non-Magnetic Nature
Contrarily to other stainless steel types, almost all grades of austenitic stainless steel are non-magnetic in nature. It’s because of their face-centered cubic crystal structure, achieved by adding sufficient amounts of nickel, which prevents the alignment of the magnetic moments of iron atoms. The steel is then rendered non-magnetic, making it suitable for applications where you don’t want magnetic interference at all.
Ductility and Formability
Austenitic stainless steel is also highly ductile and formable; all hail its crystal structure. It has a high packing density, so when pressure is applied, or deformation occurs, the atoms slide over each other. This allows the steel to be bent and shaped in any way without worrying about fracturing and cracking, so you can create complex geometric designs.
Mechanical Properties of Austenitic Stainless Steel
Here’s an overview of the mechanical properties of the different grades of austenitic steel:
Austenitic Stainless Steel Grades | Tensile Strength (MPa) min. | Tensile Strength (ksi) | Elongation % (HB) max | Hardness (Brinell) HB max |
304 | 515 | 74 | 40 | 201 |
316 | 515 | 74 | 40 | 217 |
321 | 515 | 74 | 40 | 217 |
Applications of Austenitic Stainless Steel
The applications of austenitic stainless steel range from industrial applications to food and beverage processing equipment and medical instruments. Here are some:
- Surgical scalpels
- Implants
- Dental prostheses
- MRI scanners
- Roofing and cladding
- Bridge components
- Exhaust systems
- Oil and gas pipelines and tanks
- Fuel tank systems
- Turbine blades
- Conveyor belts
- Storage containers
- Brewing vats
- Sinks, saucepans, and other domestic items
Conclusion
Austenitic stainless steel is indeed a durable material that can be used to create a variety of high-quality industrial, automotive, and other products. If you need access to authentic austenitic stainless steel products, contact Jianglin. We have a network of certified stainless steel manufacturers who maintain excellent quality assurance. Whether you work in aerospace or deal with medical equipment, you are sure to find the solution for your needs!
