Question

a)(10%) What is the distinction between hypoeutectoid and hypereutectoid steels? b)(10%) For a 99.65 wt% Fe – 0.35 wt% C alloy at a temperature just below the eutectoid, determine the following: i.The fractions of total ferrite and cementite phases. ii.The fractions of the proeutectoid ferrite and pearlite. Sketch the microstructure. iii.The fraction of eutectoid ferrite.

Answer 1

a)

The difference between hypoeutectoid steels and hypereutectoid steels is the difference in carbon content.

For hypoeutectoid steels, the carbon content is less than 0.77%

For hypereutectoid steels, the carbon content is greater than 0.77%

b)

From Iron-Iron Carbide diagram as shown below

(i)

Fraction of total ferrite

=   

Fraction of total cementite

=

(ii)

Fraction of Proeutectoid ferrite

=   

Fraction of pearlite

=   

(iii)

Fraction of eutectoid Ferrite