Question

The metastable aggregate consisting of supersaturated ferrite in which carbon has been finely precipitated in the form of carbides, is

1. bainite
2. ferrite
3. martensite 
4. cementite

Answer 1

Correct Answer - Option 1 : bainite

Explanation:

Bainite:

• Very fine microstructure of ferrite and carbides (Fe₃C)
• Properties are like ferrite but different structure.
• Stronger and more ductile than particle at same hardness level.

Martensite:

• Hardest, brittle and least ductile constituent of steel.
• Needle like structure.
• Solid solution of non carbide in α - iron.
• It has a body - central tetragonal structure.

​Ferrite:

• There are two forms of ferrite i.e., α - ferrite and δ - ferrite
• α - ferrite, is a solid solution of body-centered cubic iron.
• It has a maximum solid solubility of 0.022% C at a temperature of 727 °C.
• δ - ferrite is another form that is stable only at very high temperature and is of no practical significance in engineering.
• Ferrite is relatively soft and ductile 

​Cementite:

• Cementite, which is 100% iron carbide (Fe₃C), having a carbon content of 6.67%.
• It is also called carbide.
• It is a very hard and brittle intermetallic compound and has a significant influence on the properties of steel.