Forge welding is the core technique involved in creating Damascus steels. It is a solid-phase bonding technique that uses heat and pressure to make the weld. To make Damascus steels the current method is to stack alternating pieces of steel, each with a contrasting composition, heat the billet in a fire and at the proper temperature apply pressure to make the weld. (Don Fogg Custom knives )

One of the most common mistakes with forge welding is to hammer too hard which instead of imparting the energy required for the electrons to jump the boundaries, it shears the bonds already produced. (Article Alley)

A good forge weld is achieved by applying sufficient pressure when the material is in the correct temperature range. The amount of pressure that can be applied depends on the yield characteristics of the material, which are affected by temperature. (thefabricator)