ABSTRACT
Forging includes a wide range of compressive processes, which develop discrete products with dimensions de‰ned in three directions [1-7]. There can be a very wide range in sizes, in complexities, in rate and temperature, in feedstock shape and microstructure, in dimensional tolerances and product ‰ber, grain and subgrain structures; these are summarized in Table 16.1. Some forging processes, which involve progressive displacement of the workpiece, can produce long components like rolling or extrusion, but these may be of changing section unlike those two. The great variety of machines and die types will be described with the principal objective of discussing their in§uence on microstructure evolution. This includes the ‰ber structure which stems from the drawing out of minor phases, either impurity or intentional additions, as the grains elongate in response to die shape, friction, and chilling (Table 16.2) (Section 12.3.1); the exploitation of ‰brous structures was ‰rst developed in wrought iron in relation to retained slag [8,9]. The ‰ber pattern in rolling or extrusion provides an anisotropy, which is well de‰ned and is not easily manipulated; however, the in§uence on product properties can be exploited or minimized. In forging, the goal is to control the strain path so that the ‰bers roughly follow the outer shape with the objective of being normal to potential cracks arising from stress concentrations related to the shape. The ‰ber continuity and thickness depends upon the second-phase volume fraction and its initial distribution. An excessive quantity of second phase, notably if brittle (or low melting point), can cause failure in the forging process.
