Put a piece of metal into a fire and things start to change. Steel is made up of carbon and iron atoms. The atoms are in a frozen state. As the metal begins to warm the atoms start to wiggle and bump into each other. The atoms' ability to change when heated gives steel its versatility. The atoms can change to make the steel harder so we can make tooling and softer so we can push it around with the tooling. The reaction of the atoms to heat also allows us to forge weld. Forge welding is the practice of blending metal forms together by forcing an atomic bond between the pieces. It is an ancient technique that has allowed us the versatility to make an incredible number of things out of steel. Forge welding takes place when you heat the steel above a certain temperature and then apply pressure. I apply this pressure with a hammer or a flypress.
I find it fascinating that we, humans, can observe some small process and then put all of our intention and drive into developing that process into something that has such a huge effect on the entire ecosystem. Forge welding is one of these things. Some person, more then 3000 years ago, dug a pit, built a fire and added some rock fragments. The iron ore in the rock when heated turned into metallic iron and was folded and forge welded over and over again to make it more usable. Forge welding was the only way to weld two pieces of steel together for thousands of years. The invention during the industrial revolution of gas and electric welding has almost ended the common use of manual forge welding but automated forge welding is still common in manufacturing.