What is Austenitic Stainless Steel?
Stainless steel, including austenitic stainless steel, is popular for its strength, durability, and corrosion resistance. It's aesthetically pleasing, easy to produce, clean, and maintain, and environmentally friendly, making it a top choice for components for architecture, automobiles, and many other products.
However, there's more than one kind. Stainless steel is actually a broad term used to refer to iron based alloys which contain chromium; there are more than 100 grades of stainless steel. These are differentiated by the percentage of chromium, nickel, molybdenum, and other alloying elements. Each grade is used for specific purposes and comes with its own advantages and disadvantages.
The grades are grouped within five main categories: austenitic, ferritic, martensitic, duplex, and precipitation-hardened (PH). Let's take a closer look at austenitic stainless steel and how it compares to some of the others.
Austenitic Stainless Steel
The term austenite is used to describe a face-centered cubic (FCC) iron or steel alloys that have this type of structure. It was named after Sir William Chandler Roberts-Austen, an Englishman known for his studies of the physical properties of metals.
This is the most commonly used type of stainless steel, and with good reason. With its exceptional resistance to heat and corrosion, it's used extensively in many industries including medical, automotive, aerospace, and industrial applications. This category is known for unsurpassed strength and formability and that it can not be hardened by heat treatment.
Medical Applications
Typical medical applications of austenitic stainless steel that give you a general idea of its use include surgical anvils, hypodermic needles, needle caps or guards, and drawn staple gun components.
Automotive Applications
When discussing automotive manufacturing applications of austenitic stainless steel, commonly you will find it is used often in fuel rails, orifices, and deep drawn automotive parts. Manufacturers in automotive often look to austenitic grades for its formability and versatility.
Industrial & Consumer Applications
Industrial and consumer applications of cold-worked austenitic stainless steel strip material include razor blade components, power generation parts, springs, and cutters.
Aerospace Applications
There are several aerospace applications for austenitic stainless steel strip that require precision cold processing for military and helicopter applications, jet engine components, and landing gears.
All steels contain carbon, but they can be differentiated by whether they are low carbon or high carbon. The difference between "carbon steel" and stainless steel is in the alloy content: stainless steels have at least 10.5 percent chromium, while carbon steels must have less than that in order to earn the carbon steel classification. Still, carbon levels vary within the stainless steel families and even within the various austenitic stainless steels, as well. Straight grades of stainless steel wire or stainless steel strip & foil — or what would be considered high carbon within this category, must max out at 0.08 percent carbon, while low carbon grades contain no more than 0.03 percent carbon. Lower carbon stainless steel grades have significantly improved welding capabilities, often referred to as weldability. When considering certain alloys such as 304 Stainless Steel or it's 304L counterpart, you would choose 304L stainless steel if your manufacturing requirements called for welding the metal.
What Makes a Stainless Steel Austenitic?
When nickel or nitrogen is added to steel, it becomes "austenite" by nature. The chemical composition determines the specific grade of stainless steel, while the austenite crystalline structure in the material is a key characteristic. In the annealed condition it is important to note that Austenitic stainless steel is often characterized as non-magnetic, however cold rolling austenitic steel, or reducing its thickness and increasing its hardness, introduces a certain amount of magnetism to the material. It’s known for its formability, making it excellent for fabrication, and its resistance to corrosion.
Chemical Composition: Austenitic stainless steel contains at least 10.5 percent and 8 to 12 percent nickel, as well as nitrogen, carbon, and many other elements in solution. Chromium is what gives the steel it’s the high corrosion resistance, while nitrogen is a stiffening agent.
Austenite Crystalline Structure: A stainless steel that presents an austenite crystalline structure in addition to the face-centered-cubic lattice structure is present throughout both hot and cold temperatures. Nickel, Magnesium, and Nitrogen are stabilizing elements for the austenite structure.
What Are the Characteristics of an Austenitic Stainless Steel?
Austenitic stainless steel has many positive characteristics driving demand; this category makes up approximately three-quarters of the global stainless steel market, which was valued at $93.69 billion in 2018 and is expected to show a CAGR of 5.2 percent by 2025. Austenitic stainless steel is
Strength at Temperature: Austenitic stainless steel can withstand extreme temperatures degrees, depending upon the grade up to approximately 1900F. Some grades start to see some deforming, softening, or loss of strength at 800 degrees Fahrenheit.
Cold Workability: Austenitic Stainless Steels cannot be hardened via heat treatment. Only cold working or reduction can increase the strength of austenitics. Cold working refers to shaping a metal without heating it, which can be done with austenitic stainless steel.. Austenitic stainless steels can be annealed before rapidly cooling or “quenching” the metal to bring it back to its original state. Cold rolled stainless steel comes with several advantages: improved surface finish which is beneficial because a steel with an improved surface finish will have a higher hardness which resists crack propagation, and improved strength.
Low Thermal Conductivity: Heat transfers slowly through austenitic stainless steel. Ferritic stainless steel, on the other hand, has higher thermal conductivity.
Formability: Austenitic stainless steel is highly formable, making it especially versatile for a wide variety of applications.
Cold working austenitic stainless steel increases its strength and decreases its ductility. Of course, different stainless steels have advantages in different applications, as well. Austenitic stainless steel is more susceptible to stress corrosion cracking than ferritics.
Austenitic stainless steel is usually not magnetic, while ferritic stainless steel usually is magnetic. You may have wondered why some refrigerators are magnetic while others are not: it's because they're made of different stainless steels.
We say these are each "usually" the way they are because there are exceptions. Certain processes or temperatures can cause the crystal structure to rearrange, giving the material magnetic properties.
Applications for Austenitic Stainless Steel
With so many purposes for austenitic stainless steel, it's no wonder it accounts for such a large portion of the overall global market share. These stainless steels are divided into two series—the 200 series and the 300 series.
The 300 series is nickel-based and includes standard austenitic stainless steel, which is grade 304 stainless steel — the most commonly used one. It usually contains 18 percent chromium and eight percent nickel, which the minimum amount of nickel required to turn ferritic stainless steel into austenitic when that much chromium is present. The 200 series is low in nickel and high in nitrogen, or manganese making it a less expensive alternative to the 300 series. Here are some of the applications for austenitic stainless steel by series:
300 Series
- Aerospace Tubing
- Storage Containers
- Tanks
- Food and Beverage Equipment
- Pharmaceutical Equipment
- Mining and Chemical Equipment
- Cutlery
- Sinks
- Components for Catalytic Converters
- Furnaces
- Afterburners
- Compensators
200 Series
- Home Water Tanks
- Washing Machines
- Dishwashers
- Cookware and Cutlery
- Automobile Parts
- Indoor Architecture
We have 33 austenitic stainless steel grades and options available in strip and/or wire to meet a wide variety of purposes. Due to our wide selection of alloys, and engineering team on site, we our able to work with you to develop your project from trials to production.
Ulbrich has teams that can determine which grade of austenitic is most appropriate for your project, and depending on your unique specifications and manufacturing requirements, which form factor will work best. Our metallurgy and tooling teams in both strip and wire are industry experts, and our precision cold rolling capabilities are unmatched in the industry. We also have great relationships with our melt mill partners, which makes meeting unique and challenging requirements much easier.
Trial orders for prototypes are common for customers interested in sampling materials for their specific application are also common. Feel free to reach out to one of our metallurgical experts for more information. No matter your project, we can help you determine whether you need austenitic, ferritic, martensitic, duplex, or PH stainless steel, and which grade would be best for you.
