Steel forging comes from the ancient craft of shaping lumps of iron into the desired form by using heat and pressure. Today, the forging process is carried out with hi-tech, modern machinery.
Forged steel is incredibly strong and reliable.
Steel is normally hot forged. Starting with tons of scrap iron, giant furnaces reaching up to 3,000 degrees melt down the metal. Other metals or non-metallic elements such as nickel, chromium, carbon, manganese, and so on may also be added. The amounts of these other elements determine the grade and type of steel.
For example, in making carbon steel which the American Iron and Steel Institute has called “the world’s most useful structural material”, carbon and small traces of other elements are added.
The chemical composition of the steel must be carefully controlled and tested to ensure strength and superiority. Fluoride is added to bind the elements together while aluminum and lime are added to work against oxidation. Then once the steel is molten, it can be shaped into blocks or rounds and cooled to a solid form.
Although the steel has been softened, it still requires a lot of pressure or force to shape it. Drop forging involves the use of heavy duty machinery to replicate and repeat the motion of dropping a heavy hammer-like part onto the metal to gradually beat it into the shape wanted.
In closed die forging, predetermined molds, or dies, are used. The hammer is one die and the receiving surface is the other die. The metal is then pounded between these two dies until the desired shape is achieved.
Although closed die forging can produce parts of over 50,000 pounds, it is commonly used to make smaller parts that require strength and durability.
In open die forging, the metal isn’t pressed or hammered to fit inside the walls of the dies. Instead, the final shape is created through the controlled and precise use of motion and force. When mechanical anvils are dropped and pressed, they slowly cause the metal to change shape.
This method is particularly useful for fabricating very large parts.
In roll forging, the steel is formed into a round and then a hole punched through its center. The hot round of metal is then rolled, pressed, and/or hammered repeatedly into a thinner, flatter ring by carefully monitored, sophisticated machinery.
This technique is preferred in the making of engine parts which are able to withstand high pressure and torque.
During the forging process, the crystals that make up the metal have been repeatedly pressed, warped, and destabilized. The metal is reheated to create new smaller and stronger crystals.
Then, it is soaked in a water and chemical bath. This final heat treatment strengthens and stabilizes the steel. How long it takes depends on the grade of steel desired.
Today, sophisticated machinery, methodology, and scientific calculations are all used in the process of forging steel. Notably, engineers and manufactures choose steel to build infrastructure and transportation systems as well as machinery and buildings. So we can expect this ancient craft to continue to modernize itself.