Metallurgy Question:

Answer #1
The epsilon carbide is transition carbide of between Fe2C and Fe3C composition, with hexagonal close packing microstructure, which forms over a range of 250-400 ºC temperature during lower-bainite transformation. This transformation happens during tempering heat treatment of quenched steels, or during slow cooling in that temperature range.

It is fine dispersed carbide in a ferrite needle-like matrix. Lower bainite has lower tensile strength (about 5-10%), but usually same hardness as martensite structures, but with a higher toughness.

Answer #2
Carbide termed as Fe3C is the hardest microstructure in steel having carbon percentage of 6.67. There are two forms of carbides as per iron-iron carbide diagram of plane carbon one which is exist along with ferrite as alternate layers in pearlite and free carbide in steels having carbon % more than 0.8%. It is spreaded over the matrix of martensite in tool steels and high carbon steels.