What are the advantages and disadvantages of hot forging in comparison to cold forging ?
Answer:
The strength and stiffness (resistance to deformation) of steel reduces with temperatures over 200 Celsius. So forging when hot requires less force. As the temperature gets to about 900 C the steel is "plastic"and can easily be deformed. Also with cold forging as you are basically beating something into shape you end up with residual stresses which can decrease the strength of the part and make it more prone to buckling if loaded in particular ways. This residual stress can be relieved by heating the part, but this may cause buckling.
An obvious disadvantage of heating the steel is that you have to heat it up, work on it when it is hot and cool it down again. Rapid cooling, e.g. quenching by dropping it in water or oil changes the crystalline structure of the steel at the surface and can cause microscopic cracking.
In structural steel hot formed sections are preferable for elements laoded in bending and compression as they are less proney to buckling without residual stesses. The way steel is forged affects the strength and brittleness but I can't remember which way it goes but generally higher strength steels are more brittle.
in cold forging, the product needs to be heat treated to releave the work hardening. in hot forging it is not so
cold forging will need more energy to deform the metal than the hot forging
the end product from hot forging is more exact and presise but the one from cold forging is more stronger.
In cold forging you deform the crystal stucture of the metal. This makes it more malleable, but subject to work harding fractures.
Hot forging does not deform the structure because it reforms when cool. It is, however automatically case hardened which makes it less malleable, but of higher tensile strength.
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