Btw, the term 'cold forging' is also commonly used to indicate forging close to but not quite cherry red, which is of course differente from room temperature..
Additionally, and very important: the deformation of a piece of yellow or orange steel acts as a 'crumple zone' to dampen the impact energy.
If you hit cold steel, there is very little deformation, meaning that all that energy will bounce right back into your arm.
By hitting cold steel hard for the purpose of forging it, you will damage your anvil, you will damage your hammer, and you will most certainly damage your elbow.