How can a press shape steel without melting it?

A forged metal part is shaped by compressive forces while the metal remains solid. A press or hammer pushes the workpiece between tools, causing permanent deformation. Hot forging often makes the metal easier to shape, but the glowing workpiece is not a liquid being poured into a mold.

Metals contain many tiny crystalline regions called grains. Within their structures, defects called dislocations allow layers of atoms to change position without every bond across a whole plane breaking simultaneously. When the applied stress is sufficient, these changes produce plastic deformation: the metal does not completely return to its earlier shape after the load is removed. Heating can make deformation easier by increasing atomic mobility and changing how the internal structure responds.

In closed-die forging, shaped tool surfaces guide the material into a cavity. As a thick section becomes thinner, material must move elsewhere because its volume changes very little under ordinary forming conditions. The drawing shows a short, thick billet spreading into a wider shape. Extra material may flow into a thin seam called flash, which is trimmed later. Tool design must allow the cavity to fill without trapping serious defects.

Deformation changes the arrangement and orientation of grains and inclusions. The resulting flow pattern can be useful when aligned with the loads a finished part will carry. Temperature, deformation and later heat treatment all affect the final structure. Forging does not automatically make every part stronger in every direction, and a poorly controlled process can still create cracks or folds.

After forging, a part may need trimming, machining, heat treatment and inspection. A connecting rod, wrench or turbine component is therefore often the result of several linked processes. Forging establishes an efficient overall shape and internal structure; machining can then provide precise holes and mating surfaces. The remarkable point is that solid metal can flow permanently under sufficient force. It retains its identity as a solid while its internal structure permits a new external form.