IRON C EQM DIAGRAM.ppt (Size: 3.96 MB / Downloads: 345)
WHAT IS IT..?
It is a graphical plot between the different temperatures, Carbon content and phases of iron.
It is known as equilibrium diagram because the state of the system remains constant over a period of time
To produce the diagram or the graphical plot a series of cooling and heating curves of Iron with varying Carbon content was obtained.
Then the critical points of the cooling and heating curve were plotted on a temperature vs C content plot and thus the Iron carbon Equilibrium diagram was obtained
WHY STUDY IRON CARBON EQM. DIAGRAM..?
Iron is of great importance when mixed with certain other metals and with carbon to form steels.
There are many types of steels, all with different properties, and an understanding of the properties of the allotropes of iron is key to the manufacture of good quality steels.
Iron carbon equilibrium diagram provides a basis for carrying out heat treatment of steels in order to impart certain desirable properties to the steel
Provides a basis for specifying the thermal operating range for different structures in actual working conditions
It is the single most important topic in MATERIAL SCIENCE, forming base for understanding many key concepts
The layers of alternating phases in pearlite are formed for the same reason as layered structure of eutectic structures: redistribution C atoms between Ferrite (0.022 wt%) and
Cementite (6.7 wt%) by atomic diffusion.
Mechanically, pearlite has properties intermediate to soft, ductile ferrite and hard, brittle cementite.
Different phases of IRON
The solid solution of carbon in iron. At 0% C this is pure iron. BCC crystal structure.
The maximum solubility of carbon in iron is 0,02% at 723oC. At 0 oC temperature the solubility falls to 0,008%. The carbon atoms are located in the crystal interstices.
The solid solution of carbon in γ iron is called austenite . This has a FCC crystal structure with a high solubility for carbon compared with α ferrite. The solubility reaches a maximum of 2,08% at 1148oC . The solubility decreases to 0,8% at 723 oC The carbon atoms are dissolved interstitially. The difference in solubility between the austenite and α Ferrite is the basis for the hardening of steels