Martensite
Martensite is a form of steel constituent that is primarily ferromagnetic. It is an unstable body-centered-cubic (BCC) arrangement of atoms that usually forms from austenite when it is rapidly cooled. Martensite consists mainly of iron and carbon atoms and is usually found in the range of 0.4% to about 2.1% carbon. It is typically formed during quenching, a process that involves rapidly cooling a material after it has been heat treated.
Most steels contain both ferrite and martensite, with the proportions varying according to the steel quality. Notably, the hardness of martensite can be four times higher than that of ferrite. The hardening of steel is generally directly related to the proportion of martensite present in the steel. This makes it an important component in many steel materials across various industries, such as automotive, construction, aerospace, and energy.
Martensite can form in various ways, including austenitizing, quenching, and tempering. These processes are used to alter the microstructure of steel alloy, making it stronger and more durable for certain applications.
Ferrite
Ferrite is a type of steel constituent formed from austenite that usually contains less than 0.2% carbon. It is also known as alpha iron and is ferromagnetic. It is a body-centered-cubic (BCC) structure and is the most stable form of iron at normal temperatures. It has a room-temperature yield strength of about 210 MPa and an ultimate tensile strength of 400 MPa.
Ferrite helps to create an elastic material with higher ductility, and it is typically used as a strengthening element in steel alloys, as it reduces the carbon content. It is important in the aerospace industry because it helps to create steels with better fatigue resistance, and also in the marine industry, where its resistance to corrosion is important. Ferrite is also used in the construction industry, where its ductility is important for the purposes of forming and bending steel members without fracturing.
Austenite
Austenite is a form of steel constituent with a non-magnetic BCC structure. It is generally found in steel materials that contain between 0.8% and 1.2% carbon, though a higher carbon content is possible. There is also a significant amount of chromium in austenite, as well as other alloying elements.
Austenite is a relatively soft form of steel, and is usually not used for applications that require high hardness, as it does not harden after being heat treated. However, it is popular in industries such as automotive and food processing since it is relatively resistant to corrosion. It is also popular in the heat treatment of stainless steel, as it can help to create a more even and consistent microstructure.
Duplex Stainless Steel
Duplex stainless steel is a type of steel that is composed of both ferritic and austenitic components, typically at a roughly equal ratio. This type of steel is generally found in many different industries, such as power generation, oil and gas, and automotive.
Duplex stainless steel is highly resistant to both stress corrosion cracking and pitting corrosion, making it ideal for many different applications. Its strength and corrosion-resistance make it popular for many applications, such as oil and gas pipelines, structural components, and marine applications. It is also often used for heat exchangers, pressure vessels, and reaction vessels, where its corrosion-resistance is especially important.
Duplex stainless steel contains between 22% and 27% chromium, with a varying percentage of nickel, molybdenum, and nitrogen. The particular combination of these components can vary depending on the application, and the alloying elements can be adjusted to create different levels of corrosion-resistance, strength, and toughness. In general, duplex stainless steel is a strong and highly corrosion-resistant type of stainless steel.
