Forging is a metal forming process shapes heated metal by applying force. It also refines the grain structure of the metal in the direction it is forged, making it stronger in that direction. Relative to cold forming, it can be used on thicker sections, since they are softened by the heat, and greater elongation and bending without cracking is possible. Relative to casting, it uses a lower temperature. For some materials melting requires too high a temperature to be practical, and burns out alloying elements or even the base metal, if not done in a vacuum or protective gas.
Forging is an ancient technology, and can be done with as little as a hammer, anvil, and some means to heat the metal. Modern versions use mechanical hammers, presses, and shaped dies to work the metal faster and more accurately than by hand. Post-processing of the metal is commonly needed after forging. This can include machining to final shape, and heat treating.
With Modern Alloys , Heat Treating , and Post Processing methods, the differences are less stark, HOWEVER there still are some differences between, and debate on Forged vs Cast Metal Parts