Test: Equilibrium Diagrams & Phase Changes - 1 - Mechanical Engineering MCQ

Modified form of phase rule, F = C - P + 1
The minimum number of components correspond . - to minimum degrees of freedom, which is zero
∴ 0 = C - 4 + 1 or C = 3

Let fulcrum is at 0.5% carbon to apply lever rule. % Proeutectoid ferrite

% Pearlite = 100 - 37.5 = 62.5%

Bainite: When austenite is cooled rapidly past the nose of C-curve and kept isothermally in a constant temperature bath, it transforms to a nonlamellar product known as bainite. It is an extremely fine mixture of ferrite and carbide. Bainite is present in two forms: the feathery bainite obtained in the upper part of temperature range and needie-like or accicular bainite produced by lower reaction temperature.

Pearlite phase in steel is made up of alternate layers of ferrite and cementite.

0.2% C Martensite →50 RC
0.4% C Martensite →58 RC
0.8% C Martensite→ 65 RC

Increasing the carbon content in steel alloys causes the material to become harder. This is because the carbon sits in the interstitial sites of the lattice structure and hinders the movement of dislocation lines. It also increases the strength of the material but it decreases the ductility, carbide is hard phase,

A eutectic reaction occurs at 1146°C

On cooling through the eutectic temperature, the lowest melting liquid of the system decomposes to solid phases, austenite and cementite. This eutectic mixture is knonw as ledeburite.