Lamellar Perlite
A two-phase microstructural constituent consisting of alternating ferrite and cementite lamellae, formed by the eutectoid transformation of supercooled austenite. This structure provides steel with a balanced combination of strength and toughness.
Pearlite is the typical structure that forms when steel cools normally – a fine lamellar mixture of ferrite and cementite. When welding, you don't want to set this specially; it comes by itself if the cooling is right. If you cool too fast, the structure becomes hard and crack-prone; if you cool too slowly, it becomes soft and coarse. For normal structural steel welding, it's enough to choose preheating and heat input so that cooling is in the middle range – then you get a clean, tough structure without surprises.