**Martensite:**
Martensite is a type of microstructure that forms in certain steels when they are rapidly cooled from a high temperature. It is characterized by a needle-like or plate-like structure and is extremely hard and brittle. Martensite is formed due to a diffusionless transformation, meaning that it occurs without the movement of atoms.

**Super Saturated Solution:**
A super saturated solution is a solution that contains more solute than it should be able to hold at a given temperature. In other words, it is a solution that is unstable and contains an excess amount of solute.

**Martensite as a Super Saturated Solution of Carbon:**
In the case of martensite, it is considered a super saturated solution of carbon in iron. This means that the martensite structure contains more carbon atoms than can normally be accommodated in the iron lattice.

**Explanation:**
When steel is heated to high temperatures, the carbon atoms dissolve into the iron lattice, forming a solid solution. This is known as austenite, which has a face-centered cubic (FCC) crystal structure. When the steel is rapidly cooled, the carbon atoms are trapped in the iron lattice, leading to a supersaturated solution.

The rapid cooling process prevents the carbon atoms from diffusing out of the lattice and forming cementite, which is a compound of iron and carbon with a distinct crystal structure. As a result, the excess carbon remains trapped in the iron lattice, resulting in a super saturated solution known as martensite.

**Significance of Martensite:**
Martensite is significant because it imparts hardness and strength to steels. It is harder and stronger than the original austenite structure. However, it is also extremely brittle, which can limit its applications. Therefore, it is often desirable to temper martensite to reduce its brittleness and improve its toughness.

**Conclusion:**
In conclusion, martensite is a super saturated solution of carbon in iron. It forms when steel is rapidly cooled, trapping excess carbon atoms in the iron lattice. Martensite is known for its hardness and strength but is also brittle. It is an important microstructure in the field of metallurgy, especially in the development of high-strength steels.