What is the difference between hot and cold working?

Answer 1

The names say it all...

Cold working is done cold, i.e. part at room temperature. It essentially pushed into something to deform it. This yields the part, technically increasing its yield for further use, but it will decrease the stress required to go from its new yield to its max tensile. Be advised, for very thick parts, like bars above 2", only the outer portions will cold work, the core will keep the same properties as un-worked metal.

Hot working heats the part up above its recrystallization temperature so along with deformation, the part recrystallizes, thereby not cold working it. Hot working does not give a yield strength increase like cold working does.

Answer 2

Hot working is done at high temperatures, making the metal more malleable and easier to deform, while cold working is done at room temperature or slightly above, resulting in increased strength and hardness of the metal. Hot working requires specialized equipment and precautions for safety due to the high temperatures involved, while cold working can often be done using simpler tools and machinery.