Cementite is in the lamellar form in the __________ phase of steel.

ANS:C - pearlitic

Pearlite is a microstructure that forms in steels when they are cooled slowly from elevated temperatures. It consists of alternating layers of two phases: ferrite and cementite.

1. Ferrite: Ferrite is a solid solution of carbon in iron (α-iron). It has a body-centered cubic (BCC) crystal structure and is relatively soft and ductile. Ferrite is the more ductile component of pearlite.
2. Cementite: Cementite (Fe3C) is an intermetallic compound of iron and carbon. It has a very hard and brittle nature. Cementite is the more brittle component of pearlite.

In the pearlitic microstructure, these two phases (ferrite and cementite) are arranged in alternating layers, resembling a lamellar structure. The layers can be very fine, and under a microscope, pearlite appears as a series of parallel bands or layers. The formation of pearlite occurs during the cooling of austenite (the high-temperature phase of steel) through a eutectoid reaction. As the steel cools, carbon atoms diffuse to form cementite, while the remaining iron forms ferrite. This process occurs simultaneously and leads to the formation of the lamellar pearlite structure. Pearlite is a common microstructure found in many types of steels, especially in medium to low carbon steels. It provides a balance of strength and ductility to the steel, making it suitable for various engineering applications.