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13.

Recrystallization temperature is one

A.	at which crystals first start forming from molten metal when it is cooled	B.	at which new spherical crystals first begin to form from the old deformed one when a strained metal is heated
C.	at which change of allotropic form takes place	D.	at which crystals grow bigger in size

14.

Points of arrest for iron correspond to

A.	stages at which allotropic forms change	B.	stages at which further heating does not increase temperature for some time
C.	stages at which properties do not change with increase in temperature	D.	there is nothing like points of arrest

15.

A material is known as allotropic or polymorphic if it

A.	has a fixed structure under all conditions	B.	exists in several crystal forms at different temperatures
C.	responds to heat treatment	D.	has its atoms distributed in a random pattern

16.

Super conduction by metals is observed in the temperature range of

A.	below 10°K	B.	above 100°K
C.	around 0°C	D.	around 100°C

17.

Which of the following constituents of steels is softest and least strong

A.	austenite	B.	pearlite
C.	ferrite	D.	cementlte

18.

Which of the following represents the allotropic forms of iron

A.	alpha iron, beta iron and gamma iron	B.	alpha iron and beta iron
C.	body centered cubic a-iron and face centered cubic a-iron	D.	alpha iron, gamma from and delta iron

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