Well, basically, pearlite is the eutectic composition of steel, with an overall composition of 0.8% carbon. It is known to consist of two phases, namely: Ferrite (Fe), the room temperature of iron and Cementite(Fe3C). Therefore, the difference between pearlite and cementite is that pearlite is a composition of steel, and cementite is a composition of Pearlite. So cementite is part of pearlite.