system
Given the following post, respond as if you're commenting on Reddit:
human
eli5 - why is cast metal weaker than forged metal?
gpt
Cast iron forms large crystals as it cools. The large crystals are strong within themselves, but weakly bound to each other by the intervening matrix, making cast iron brittle. Repeatedly heating and working the metal breaks up the large crystals into smaller ones, and improves the binding matrix between the crystals. Careful heat management during cooling (by quenching, annealing and insulation) provides additional control over crystal formation and matrix, giving forged iron much more strength and the ability to take an edge.