In rolling, which condition defines cold rolling?

• A. Cold rolling occurs when the temperature is below its lower critical temperature and produces a shiny, smooth surface
• B. Cold rolling occurs at high temperature with scale
• C. Hot rolling is below lower critical temperature
• D. Warm rolling requires cryogenic cooling

Answer: (A)

Cold rolling is done below the recrystallization temperature of the metal, typically below its lower critical temperature, so the metal does not recrystallize during deformation. This keeps the material work-hardened, which increases strength, and it produces a shiny, smooth surface after processing as the surface is compressed and refined without the grain changing through recrystallization. That exact combination—lower than the lower critical temperature and a shiny, smooth surface—is what defines cold rolling.

The other descriptions don’t fit: rolling at high temperature with scale describes hot rolling, which occurs above recrystallization and leaves oxide scale and a rougher surface. Saying hot rolling is below the lower critical temperature contradicts that. Warm rolling is a middle-temperature process and isn’t tied to cryogenic cooling, so it doesn’t define cold rolling.