Questions and answers from 21 to 30 on Material Science and Engineering.
21. What is the common element between the brass and bronze metal alloys ?
22. What does the alloy designation FG 250 indicate?
FG 250 alloy designation indicate Grey cast iron with a tensile strength of 250 MPa.
23. Define Ceramic?
is a solid formed by the combination of metallic and non-metallic elements.
24. Give one example of metal classified as per structure as BCC, FCC, HCP and CCP.
Examples of BCC, FCC, HCP and CCP structures:
BCC (Body Centred Cubic) structure – molybdenum;
FCC (Face Centred Cubic) structure – Alumimum;
HCP (Hexagonal Close Packed) structure – Zinc;
CCP (Cubic Close Packing) structure – Copper.
25. What is the name of solid solution of carbon in alpha-iron and delta iron ?
Ferrite and Austenite respectively.
26. Explain the difference between pearlite and cementite ?
Pearlite is a eutectoid mixture of ferrite and cementite. Cementide is a chemical compound of iron and carbon.
27. Give one example each of the following proportion of materials – dimensional, physical, technological and mechanical.
Roughness, enthalpy, toughness and hardness respectively.
28. For which parts the Wahl factor and Lewis factor is used ?
Wahl factor and lewis factor is used for springs and gears respectively.
29. How oxygen gas can be removed from steel during melting? What are fully killed steels?
Oxygen gas can be removed from steel during melting by adding elements such as manganese, silicon or aluminium which, because of their high affinity for oxygen, react with it to form non-metallic oxides such as manganese oxide, silicon oxide and aluminium oxide. which rise into the slag. Steels in which have has most of their dissolved oxygen removed are called ‘fully killed steels’.
30. Hydrogen cannot be removed easily from molten steel. What harm hydrogen has on property of steel ?
Excessive hydrogen in molten steel results in the formation of small fissures often described as hairline cracks or flakes in the steel. Large forgings
an alloy steel are particularly sensitive to this phenomenon.