Are you looking to use stainless steel in your next construction project but don’t know which of the two popular varieties is right for you? We feel your confusion. Austenitic and ferritic stainless steel are both great options, depending on their intended uses. Let us help guide you through all the differences between these two families of stainless steels so that you can make an informed decision about which one is best for your application. Read this blog post to learn more about the distinctive characteristics of austenitic and ferritic stainless steels as well as when each one should be used. You’ll soon see that arming yourself with knowledge about both types will lead to a successful building project!
What is Austenitic Stainless Steel?
Austenitic stainless steel is a type of stainless steel alloy which consists mainly of chromium, nickel, and manganese. It is an austenitic material that offers excellent corrosion resistance and strength at high temperatures while remaining ductile and workable. Its formability allows it to be used in applications where bent or curved structures may be needed. Typical uses include kitchenware, food equipment, medical devices, heat exchangers, boilers/tanks/piping components, architectural facades and automotive trim.
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What is Ferritic Stainless Steel?
Ferritic stainless steel is an alloy of iron containing high levels of chromium, with low carbon content. It has good corrosion resistance and magnetic properties, making it a popular choice in many industrial applications.
Difference Between Ferritic and Austenitic Stainless Steel
The different types of microstructure allow for the classification of stainless steel. The two most popular stainless steel classes are ferritic and austenitic stainless steel. The internal arrangement of the crystal is the microstructure of these alloys. The crystal arrangement is what gives the alloy its mechanical and chemical properties. Ferritic stainless steel has a microstructure made up of ferrite crystals. Ferrite crystals are a type of iron that contains trace amounts of carbon, up to 0.025%. Ferrite crystals only absorb a small amount of carbon. Because of its body-centered cubic crystal structure, this is the case.
The arrangement includes one iron atom in each corner, as well as one in the center. This central ferrous atom is responsible for the magnetic properties of the ferritic class of stainless steel. Austenitic stainless steel, on the other hand, is a gamma-phase iron, which is an allotrope of iron. The alpha iron undergoes a phase transition at elevated temperatures ranging from 1,674 to 2,541 °F. As a result, alpha iron, which was a body-centered cubic or BCC structure, is converted to gamma iron’s face-centered cubic or FCC configuration. The altered configuration of a gamma iron is known as austenite.
Microstructures of ferrite and austenite
Ferritic steels have a cubic crystal structure that is centered on the body. This means that there is one ferrous atom in each of the eight corners and one atom in the center. Each of the eight corners is also the corner of another cube in this configuration. As a result, the corner ferrous or iron atoms will be distributed equally among the eight unit cells. Austenite, on the other hand, has atoms at the corners of its face-centered cubic crystal structure. The atoms are present at the center of the faces of its cellular unit, as the name implies. Atoms in an FCC, or face-centered cubic arrangement, are tightly packed together. As a result, the atoms in the microstructure will occupy approximately 74% of its volume. Because they are packed so tightly, this type of structure is also known as cubic closest packing or CCP.
Solubility of carbon in ferrite and austenite
In comparison to austenite, ferrite has a low carbon solubility. Because it is a solid solution of carbon and iron with a percentage of about 0.025%, the carbon solubility in ferrous is 0.02%. The interatomic spaces are small because pure iron is already a structure at room temperature. As a result, sphere-shaped carbon atoms are unable to accommodate ferrous atoms. This is why carbon has low solubility in ferrite.
Furthermore, the carbon atom is too small to act as a substitute while also being too large for an interstitial solid solution. Carbon solubility in iron in an austenite region, on the other hand, is approximately 2.11%, which is significantly higher than in ferrite regions. This is due to the fcc structure of austenite. Because of this structure, austenite has a larger interatomic spacing than ferrite. The larger spacing allows austenite to easily accommodate carbon atoms in their spaces.
The density of ferrite and austenite steel
BCC is heavier than FCC, implying that Ferrite has a higher density than austenite. FCC is lighter because their symmetry or arrangement provides closely packed planes in various directions. As a result, a face-centered cubic or FCC crystal structure will be more ductile. As a result, the chances of austenite deformation before breaking are higher under load, especially when compared to a body-centered cubic structure. The lattice in a body-centered cubic, while cubic, is not as tightly packed as the FCC type. As a result, BCC and ferrite are strong metals.
Hardness of ferrite and austenite
Ferrite is known to be more difficult to work with than austenite. Typically, elements like chromium, molybdenum, silicon, and niobium promote ferrite. Most ferritic steels have chromium content in the 13.5% range, which means they can undergo successive transformations from alpha to gamma and back to alpha during ferrite formation. In addition to being magnetic, ferrite crystals are known to be harder and brittle than austenite crystals, which are soft and ductile.ferritic
