Pearlitic matrix
A pearlitic matrix is a finely layered composite of ferrite and cementite that, acting as the base structure in cast iron materials or unalloyed steels, provides higher hardness and wear resistance than pure ferrite. It forms through diffusion-controlled transformation of austenite at intermediate cooling rates.
Perlite forms when austenite cools slowly enough after welding and transforms into ferrite and cementite. That gives a tough and wear-resistant structure. If you cool too fast, you get martensite or intermediate structures, which are hard but brittle. Cooling too slowly makes the structure coarse and soft. When welding, you have to keep an eye on the cooling, for example by preheating or post-heating, so that a clean perlite structure forms and no cracks appear.