How do cast irons differ from steels in terms of carbon content?
Composition from 0.008% to 2% carbon represent steel and those above 2% carbon
represent cast iron.
Distinguish between hypoeutectic and hypereutectic cast irons.
Cast irons that contain less than 4.3% C are termed as hypoeutectic whereas cast irons
that contains more than 4.3% C termed as hypereutectic.
What do you mean by substitutional solid solution? Briefly explain the rules
governing the formation of substitutional solid solution.
When the solute atoms (impurities) substitute for parent solvent atoms in a crystal lattice
they are called substitutional atoms and the mixture of the two elements is called a
substitutional solid solution.
Hume Rothery’s rules govern the formation of substitutional solid solution.
1. Size factor 2.Crystal structure 3.Valence 4.Electronegativity
Why carbon solubility is more in an austenite?
Austenite is a primary solid solution based on γ iron having FCC structure.
Carbon solubility is more in austenite, because austenite is an interstitial solid structure of
carbon in iron.
What is substitutional solid solution? Give two examples.
When the solute atoms (impurities) substitute for parent solvent atoms in a crystal lattice,
they are called substitutional atoms, and the mixture of the two elements is called a
substitutional solid solution. E.g. Cu-Ni system, Cu-Zn system and Au-Cu system.
Distinguish between hypo-eutectoid steels and hyper-eutectoid steels.[May/Jun 2007]
Hypoeutectoid steels: Steels having less than 0.8% C are known as hypoeutectoid
Hypereutectoid steels: Steels having more than 0.8% C are known as hypereutectoid
State the conditions under which two metallic elements will exhibit solid solubility.
To exhibit unlimited solid solubility, the solute and solvent elements should obey the
general rules of Hume’s Rothery : 1.Size factor 2.Crystal structure 3.Valence
Define polymorphism and Allotropy.
Polymorphism is a physical phenomenon where a material may have more than
one crystal structure. A material that shows polymorphism exists in more than one type of
space lattice in the solid state. If the change in structure is reversible, then the polymorphic
change is known as allotropy. The best known example for allotropy is iron.
Name the various micro structures of Fe-Fe3C phase diagram.
Various micro structures of Iron carbon equilibrium diagram are Ferrite, Austenite,
Pearlite, Cementite, Ledeburite, Martensite, Troostite, Sorbite and Bainite.