Forging materials

The main materials for forging are carbon steels and alloy steels of various compositions, followed by aluminum, magnesium, copper, titanium and their alloys. The original states of 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 starting 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 billet 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 large forging deformations.

Ingots are only used for large forgings. The ingot has a 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 porosity in order to obtain excellent metal structure 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 powder of the forging is close to the density of general die forgings, has good mechanical properties, and 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 common bars, which limits its application in production to a certain extent.

When static pressure is applied 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 the die forging with the required 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 by general die forging.

In addition to the common materials such as carbon steels and alloy steels of various compositions, followed by aluminum, magnesium, copper, titanium and their alloys, wrought iron-based superalloys, nickel-based superalloys and cobalt-based superalloys are also completed by forging or rolling. However, due to their relatively narrow plastic zones, the forging difficulty of these alloys is relatively greater. There are strict requirements for the heating temperature, starting forging temperature and final forging temperature of different materials.