Which Phase has complex orthorhomic crystal structure?

Q.  Which of the following phases has a complex orthorhomic crystal structure?
- Published on 11 Sep 15

a. δ-ferrite
b. α-ferrite
c. Austenite
d. Cementite

ANSWER: Cementite


  • Sravanthi   -Posted on 21 Nov 15

    - It has complex orthorhomic crystal structure which contains 12 iron atoms and 4 carbon atoms in each unit cell. Cementite is also called as iron carbide.

    - It is a hard and brittle phase which influences properties of steels and cast irons.

    - It is an inter-metallic compound of iron (93.3%) and carbon (6.67%).

    - In carbon steel, cementite forms from austenite when cooled and during tempering it forms from martensite.

    - Orthorhombic crystal structures are formed when cubic lattice is stretched along its orthogonal pairs. They have rectangular prism with a rectangular base and height which are distinct from each other and intersect at 90°.

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