What are the requirements for the materials used in forgings?

The materials used for forging parts are mainly carbon steels and alloy steels of various compositions, followed by aluminum, magnesium, copper, titanium, and their alloys. The original states of the materials include bar stock, ingots, metal powders, and liquid metals. The ratio of the cross-sectional area of a metal before deformation to that after deformation is called the forging ratio. The correct selection of forging ratio, reasonable heating temperature and holding time, reasonable initial forging temperature and final forging temperature, as well as reasonable deformation amount and deformation speed, are of great significance to improving product quality and reducing costs.

Generally, round or square bar stock is used as the blank for medium and small-sized forgings. The grain structure and mechanical properties of the bar stock are uniform and good, with accurate shape and size, and good surface quality, which is convenient for organizing batch production. As long as the heating temperature and deformation conditions are reasonably controlled, forgings with excellent performance can be forged without significant forging deformation.

Ingots are only used for large forgings. The ingot has an as-cast structure with large columnar crystals and a loose center. Therefore, it is necessary to undergo large plastic deformation to break the columnar crystals into fine grains and compact the loose ones to obtain excellent metallic microstructure and mechanical properties.

Powder metallurgy preforms that have been pressed and sintered can be forged into powder forgings in a hot state through die forging without flash. The density of the forging powder is close to that of general die forgings, featuring excellent mechanical properties and high precision, which can reduce subsequent cutting processes. 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 common rods, which limits its application in production to a certain extent.

By applying static pressure to the liquid metal poured into the die chamber, it solidifies, crystallizes, flows, undergoes plastic deformation, and takes shape under the action of pressure, and thus, a die forging with the desired shape and performance can be obtained. Liquid metal die forging is a forming method between die casting and die forging, and is particularly suitable for complex thin-walled parts that are difficult to form through general die forging.

In addition to the common materials such as carbon steel and alloy steel of various compositions, the forging materials also include aluminum, magnesium, copper, titanium, and their alloys. The wrought alloys of iron-based superalloys, nickel-based superalloys, and cobalt-based superalloys are also completed by forging or rolling. However, due to the relatively narrow plastic zone of these alloys, the forging difficulty is relatively high. The heating temperature, starting forging temperature, and final forging temperature of different materials all have strict requirements.