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What is Cementite?

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Author : trunnano
Update time : 2022-07-21 11:35:20
Cementite or iron carbide is a compound of iron and carbon, or more accurately, an intermediate transition metal carbide with the molecular formula Fe3C. By weight, it is 6.67% carbon and 93.3% iron.
It is a gray-white crystalline powder with a relative density of 7.694. Insoluble in cold, hot water and dilute acid, soluble in hot concentrated hydrochloric acid to produce mixtures of hydrogen, methane, ethane, ethylene and other more complex hydrocarbons and free carbon. Does not react with dry air. Oxidize in moist air to form iron oxide and carbon. It has orthorhombic crystal structure. It is a hard and fragile material, which is usually classified as ceramic in its pure form, and is a common and important component in black metallurgy.
 
What is Fe3C called?
Fe3C (iron carbide) is also called cementite.
 
How is cementite formed?
Primary cementite:
In the process of equilibrium crystallization of iron-carbon alloy, the cementite precipitated when the liquid alloy of hypereutectic alloy (hypereutectic white cast iron) is cooled below the liquidus is called primary cementite.
 
Eutectic cementite:
In the ledeburite structure, the point strip cementite is uniformly distributed on the austenite matrix, and this cementite is called eutectic cementite.
 
Pre-eutectoid phase and cementite:
For alloys with hypoeutectoid and hypereutectoid composition, with the decrease of temperature, a phase forming the product of eutectoid transformation is always precipitated with the decrease of temperature, and the first precipitated phase is called proeutectoid phase, such as proeutectoid ferrite in hypoeutectoid steel and proeutectoid cementite in hypereutectoid steel. Due to the different forming conditions, the morphology of proeutectoid phase can be divided into three types: block, reticulate and Widmanstatten structure.
 
Eutectoid cementite:
The cementite in pearlite is called eutectoid cementite.
 
Secondary cementite:
In the process of equilibrium crystallization of iron-carbon alloy, when the alloys with more than eutectoid composition (hypereutectoid steel, hypoeutectic white cast iron, eutectic white cast iron, hypereutectic white cast iron) are slowly cooled to a certain extent, the carbon content in austenite reaches saturation, and the cementite will precipitate along the austenite grain boundary with a network distribution in microstructure. This cementite precipitated from austenite is called secondary cementite.
 
Tertiary cementite:
When the equilibrium cooling of industrial pure iron is below the solid solution line of carbon in iron (Fe-C equilibrium diagram PQ line), the solubility of carbon in ferrite reaches saturation, and the temperature decreases again, and the tertiary cementite will precipitate from ferrite. The tertiary cementite precipitates from the ferrite grain boundary and generally distributes intermittently along the ferrite grain boundary because of its small quantity.
 
Free cementite:
It refers to those that exist as an independent phase outside the mechanical mixture (structure) such as pearlite (eutectoid structure) or ledeburite (eutectic structure), such as pre-eutectoid cementite, primary cementite and so on.
 
Iron Carbide Fe3C Powder Price
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Iron Carbide Fe3C Powder Supplier
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