The main materials used for forging are carbon steel and alloy steel of various compositions, followed by aluminum, magnesium, copper, titanium, and their alloys. The original states of the materials include bars, ingots, metal powders, and liquid metals. The ratio of the cross-sectional area of the metal before deformation to the cross-sectional area after deformation is called the forging ratio. Correctly selecting the forging ratio, reasonable heating temperature and holding time, reasonable initial and final forging temperatures, and reasonable deformation amount and speed are very important for improving product quality and reducing costs.
　　Generally, small and medium-sized forgings use round or square bars as blanks. The grain structure and mechanical properties of the bars are uniform and good, the shape and size are accurate, the surface quality is good, and it is easy to organize mass production. As long as the heating temperature and deformation conditions are reasonably controlled, excellent forgings can be forged without large forging deformation.
　　Ingots are only used for large forgings. Ingots have a cast structure with large columnar crystals and a loose center. Therefore, large plastic deformation must be used to break up the columnar crystals into fine grains and compact the looseness in order to obtain excellent metal structure and mechanical properties.
　　Powder metallurgy preforms formed by pressing and sintering can be made into powder forgings by hot forging without flash. The powder of the forgings is close to the density of general die forgings, has good mechanical properties, and has high precision, which can reduce subsequent cutting processing. The internal structure of powder forgings is uniform, without segregation, and can be used to manufacture small gears and other workpieces. However, the price of powder is much higher than that of general bar materials, and its application in production is limited.
　　Applying static pressure to liquid metal poured into a die cavity, allowing it to solidify, crystallize, flow, plastically deform, and shape under pressure, can obtain die forgings with the desired shape and properties. Liquid metal die forging is a forming method between die casting and die forging, especially suitable for complex thin-walled parts that are difficult to form by general die forging.
　　In addition to the usual materials used for forging, such as carbon steel and alloy steel of various compositions, followed by aluminum, magnesium, copper, titanium, and their alloys, iron-based superalloys, nickel-based superalloys, and cobalt-based superalloys are also formed by forging or rolling. However, due to the relatively narrow plastic region of these alloys, the forging difficulty is relatively large, and the heating temperature, initial forging temperature, and final forging temperature of different materials have strict requirements.