Final answer:
Process annealing in steel reduces hardness and improves ductility by heating the steel below its critical point, holding it there, and allowing it to cool slowly. This improves workability and reduces internal stresses from prior processing, contributing to the steel's quality for industrial use.
Step-by-step explanation:
The purpose of process annealing in steel is to improve its ductility and reduce its hardness, making it more workable for subsequent industrial processes or applications. This heat treatment process involves heating the steel to a temperature below its critical point, maintaining that temperature for a period of time, and then cooling it slowly. This treatment allows the reduction of stresses that have been built up in the material during its previous processing.
Process annealing is particularly useful in the case of steel that has been work-hardened or distorted due to cold working. By heating the steel, the atomic structure is allowed to re-arrange into a more stable state, thus reducing stress and making the steel more ductile.
The mass production of steel during the industrial era, using processes like the Bessemer process and the Siemens-Martin process, was greatly enhanced by techniques such as process annealing. This was critical in manufacturing high-quality steel that could be used for constructing skyscrapers, expanding railroads, and other engineering feats of the Second Industrial Revolution.