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Why must alloy steels be heated more slowly than carbon steels during heat treatment?
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steel
Molten steel being poured into a ladle from an electric arc furnace, 1940s.
Alloy steels must be heated more slowly than carbon steels during heat treatment primarily because they possess lower heat conductivity.1
When steel is subjected to heat treatment, the rates of heating and cooling must be carefully managed based on the material's chemical composition, size, and shape. Because alloy steels conduct heat less efficiently than plain carbon steels, heating them too rapidly can lead to uneven temperature distribution within the workpiece. This thermal gradient creates internal stresses that can compromise the integrity of the metal. By heating these materials more slowly, engineers ensure a more uniform temperature throughout the piece, thereby minimizing the risk of damage from internal stress.1