Why use a forging? Experts agree that a forged shaft, of identical material, will be stronger than a cast or machined shaft (billet). The reason is that the grain of the material is aligned with the shape of the shaft with a forging. On a machined shaft, unidirectional grain flow has been cut when changing contour, exposing grain ends. This renders the material more liable to fatigue and more sensitive to stress corrosion cracking. Want to learn more about forgings? Hit your favorite search engine and type in forged versus billet. You'll find many articles describing why forgings are the best choice for formed shafts (especially gear shafts). SAE and the Forging Industry Association all have peer reviewed engineering research papers comparing the two processes.