Consider the pearlier formed by isothermal transformation of

Consider the pearlier formed by isothermal transformation of Austinite in a steel containing 0.50% C at 727 degree C. What is the composition of this partite? Calculate the ratio of the thicknesses of the alpha and Fe_3C lamellae. Assume equal densities of the two phases. What fraction of the microstructure transforms to partite?

Solution

Pearlite is a product of the eutectoid reaction in iron carbon diagram,

Eutecoid Reaction

Austentic (0.8% C) ---- Temperature (727C) --- Ferrite (0.025%) + Cementite(6.67%) (General Calculations)

Its is microstructure is laminar. it contains alternate laminas of Ferrite & cementite.

1) Composition of Pearlite

- 0.5 % Carbon (Austenite) - Ferrite (0.025%C) + Cementite(6.67%C)

Chemical formula for Fe₃C contating 6.67% iron and having orthorhomic crystal structure. it is brittle and hard, it is hardest phase found in the alloy of iron with carbon

C - Carbon

Fe - Iron

% of Ferrite = 6.67-.05/6.67

= 92%

Rest 8% is cementite

Ratio of the width of the two = 8/92 = 1:11.5