Question

A compound of iron and carbon, called iron carbide, is also known as: 
1. martensite 
2. bainite 
3. ferrite
4. cementite

Answer 1

Correct Answer - Option 4 : cementite

Explanation:

• Cast irons typically contain 2 - 4 wt % of carbon with a high silicon concentration and a greater concentration of impurities than steel.
• Carbon in cast iron can be present in two forms:
  • Free carbon or graphite form
  • Chemically combined form
• Carbon is present in the form of graphite in grey cast iron and in the form of combined cementite in white cast iron.
• A high cooling rate and a low carbon equivalent favor the formation of white cast iron whereas a low cooling rate or a high carbon equivalent promotes grey cast iron.
• The higher the percentage of carbon more will be cementite and the harder will be the iron.​

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​Ferrite:

• ​Ferrite, a ceramic-like material with magnetic properties that is useful in many types of electronic devices.
• Ferrites are hard, brittle, iron-containing, and generally grey or black and are polycrystalline i.e., made up of a large number of small crystals
• They are composed of iron oxide and one or more other metals in chemical combination.
• A ferrite is formed by the reaction of ferric oxide (Fe2O3, iron oxide, or rust) with any of a number of other metals, including magnesium, aluminum, barium, manganese, copper, nickel, cobalt, or even iron itself.

Cementite:

• Cementite (or iron carbide) is an interstitial compound of iron and carbon, with the formula Fe3C.
• By weight, it is 6.67% carbon and 93.3% iron.
• It has an orthorhombic crystal structure.
• It is a hard, brittle material, normally classified as a ceramic in its pure form, and is a frequently found and important constituent in ferrous metallurgy.

Pearlite:

• It is formed by the decomposition of austenite at 723°C.
• The decomposition of austenite leads to the formation of a eutectoid mixture of 87% ferrite and 13% cementite called pearlite.
• The pearlite constituent consists of alternate lamellae of ferrite and cementite and contains 0.8% carbon.