Question

Using an iron-iron carbide (Fe-Fe3C) Phase Diagram, identify and discuss the different important phases found in this diagram and the development of microstructure in iron-carbon alloys.

Answer 1

In iron and iron- carbide phase diagram exhibit various types of phases developed depending on carbon content, heating cooling rate and temperature of transformation. The various phases include martensite, pearlite, bainite, austenite, ferrite. Austenite phase is found above eutectoid temperature 727 0C and it consists of a uniform mixture of carbon in iron at lower carbon region. In temperature time transformation curve

1. Fast cooling leads to formation of martensite.

2. Slow cooling near eutectic temperature form coarse pearlitic structure.

3. Slow cooling below 600 0C will leads to formation of fine perlitic structure.

4 Rapid cooling to 550 and then continuous cooling leads to formation of bainite in mucrostructure.

Austenite, ferrite and cementite microstructure consist of 0.8% , 0.025%, 6.67% respectively.

Martensite is needle like microstructure form by rapid cooling of iron. Pearlite is lameller structure of ferrite and cementite form by slow cooling of iron. Bainite is nonlemeller structure firm by continuous cooling if iron.