Why iron carbon is equilibrium diagram?
The iron-carbon diagram. It should first be pointed out that the normal equilibrium diagram really represents the metastable equilibrium between iron and iron carbide (cementite). Cementite is metastable, and the true equilibrium should be between iron and graphite.
What is iron equilibrium diagram?
The Iron carbon equilibrium diagram (also called the iron carbon phase diagram) is a graphic representation of the respective microstructure states of the alloy iron – carbon (Fe-C) depending on temperature and carbon content.
Which is the equilibrium phase in iron carbon system?
For steels, the stable equilibrium phases include: Ferrite. Ferrite or α-ferrite is a body-centered cubic structure phase of iron which exists below temperatures of 912°C for low concentrations of carbon in iron.
What is the carbon equilibrium diagram?
The Fe – C diagram (also called the iron – carbon phase or equilibrium diagram) is a graphic representation of the respective microstructure states of the alloy iron – carbon (Fe-C) depending on temperature and carbon content. To explain this diagram, an introduction about metal structures and pure iron must be done.
What is the use of TTT diagram?
This diagram shows the time, at a particular temperature, to start to transform and finish transforming to a transformation product such as ferrite, pearlite or bainite. This diagram can be thought of as a map which plots the transformations of austenite as a function of constant temperature and time.
Why is iron-carbon equilibrium diagram not a true equilibrium diagram?
Iron-Cementite diagram is not a true equilibrium diagram, since equilibrium means no change of phase with time, however long it may be. Graphite is more stable form of carbon. Cementite is a metastable phase, which decomposes to graphite if given long periods of time.
Why is iron carbon equilibrium diagram not a true equilibrium diagram?
What are the invariant reactions in iron carbon equilibrium diagram?
The invariant eutectoid reaction in Fe-Fe3C diagram is given by equation: i.e. during cooling, austenite of 0.77%C at constant eutectoid temperature, 727°C undergoes eutectoid transformation to form a mixture of ferrite (e = 0.02%) and cementite i.e. there are alternate lamellae of ferrite and cementite.
What is upper critical temperature on the iron carbon equilibrium diagram?
Thus, it is the temperature corresponding to gamma + alpha / gamma phase boundary for hypo-eutectoid steel and is a function of carbon content of the steel, as it decreases from 910 deg C at 0 % C to 727 deg C at 0.76 % C. It is also called the upper critical temperature of hypo-eutectoid steels.
What is the importance of TTT diagram in heat treatment process?
The time and the temperature of holding is given by the TTT curve of the steel. As the isothermal annealing is normally done to soften the steel, the temperature of isothermal holding is very close to but below A1 (by 30- 100°C).
What is TTT diagram in material engineering?
Isothermal transformation diagrams (also known as time-temperature-transformation (TTT) diagrams) are plots of temperature versus time (usually on a logarithmic scale).
What are the limitations on the use of iron carbon equilibrium diagram?
10.9 Two limitations of the iron-iron carbide phase diagram are: 1) The nonequilibrium martensite phase does not appear on the diagram; and 2) The diagram provides no indication as to the time-temperature relationships for the formation of pearlite, bainite, and spheroidite, all of which are composed of the equilibrium …
What is Curie temperature on iron carbon equilibrium diagram?
The A2, point is the Curie point when iron changes from the ferro- to the paramagnetic condition. This temperature is 769°C for pure iron, but no change in crystal structure is involved.
What reactions are involved in iron carbon diagram?
Which is the maximum hardness in an iron carbon diagram?
Cementite or iron carbide, is very hard, brittle intermetallic compound of iron & carbon, as Fe3C, contains 6.67 % C. It is the hardest structure that appears on the diagram, exact melting point unknown.
What are the limitations of iron-carbon phase diagram?
How does iron-carbon diagram work?
The iron-carbon phase diagram is widely used to understand the different phases of steel and cast iron. Both steel and cast iron are a mix of iron and carbon. Also, both alloys contain a small amount of trace elements.