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How do hot rolling and hot forging improve cast metal shapes?

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Diagram of a zinc-lead blast furnace system showing ore and coke entering through charge hoppers, with labeled furnace, air preheater, blower, taphole for slag and lead bullion, and a connected lead-splash condenser using rotors to separate and cool lead and zinc, with pathways for molten metals and off-gas. — metallurgy A zinc-lead blast furnace and lead-splash condenser. This technology is utilized mainly for producing zinc while managing both lead and zinc from raw materials, a technique that was highly influential in 20th-century smelting.

Hot rolling and hot forging are essential metalworking processes that significantly enhance the mechanical properties of cast metal shapes. By performing these operations above the metal's recrystallization temperature, the material can undergo extensive compressive plastic strain without reaching the limits that typically cause cracking in cold-worked parts.12

These processes improve cast metal shapes by eliminating much of the porosity, segregation, and directionality often found in raw castings. As the metal is worked, the internal grain structure is refined and reorganized. During forging, for example, the grains become elongated in the direction of flow, which substantially increases the toughness of the metal in that direction.1

By carefully controlling the flow lines during these operations, engineers can ensure that the finished product is oriented to withstand maximum stress when in service. The resulting "wrought" product exhibits superior ductility and structural integrity compared to the original unworked casting.1