The influence of forging process on the quality of forgings

The forging process is generally composed of the following processes: blanking, heating, forming, cooling after forging, pickling and post forging heat treatment. If forging process is improper, a series of forging defects may occur. The heating technology includes furnace temperature, heating temperature, heating speed, holding time and furnace gas composition. If the heating is unsuitable, such as too high heating temperature and too long heating time, it will cause carbon removal, overheating and over burning. For the billets with large section size, poor thermal conductivity and low plasticity, if the heating speed is too fast and the holding time is too short, the temperature distribution is often uneven, the thermal stress is caused, and the billet is cracked. The forging process includes deformation mode, deformation degree, deformation temperature, deformation speed, stress state, man's brother and lubrication condition. If the forming process is improper, it may cause coarse grain, uneven grain, all kinds of cracks and folding. Cold current, eddy current, cast microstructure residue and so on. During the cooling process after forging, if the process is not proper, it may cause cooling cracks, white spots, netted carbide and so on.

Cracking is a shallow tortoise crack on the surface of the forging. A surface (such as an unfilled convex part or a curved part) that is subjected to tensile stress in the forming of a forgings.

It is easy to produce this defect. The internal causes that cause the cracking may be multifaceted:

(1) the raw materials are too many melting elements such as Cu and Sn. (2) when heated for a long time, the surface of the steel is precipitated by copper, coarse grains, decarburization, or repeated heating. (3) the sulfur content of the fuel is too high, and sulphur infiltrate the surface of the steel.

Flying crack

Flash crack is the crack produced at the parting surface when forging and trimming. The reason for the flash crack may be: (1) in the die forging operation, the strong flow of metal causes the phenomenon of steel penetration. 2. The cutting temperature of magnesium alloy die forging is too low; the trimming temperature of copper alloy die forging is too high.

Mold surface crack

The parting surface crack is the crack produced along the parting surface of the forgings. There are many non-metallic inclusions in the raw material. When forging dies, the flow to the parting surface and the residual of the concentrated or residual pipes during the forging process are often followed by the surface cracks of the constant components.

Fold

Folding is formed by merging the surface metal that has been oxidized during metal deformation. It can be formed by two strands (or more) of metal convection; it can also be formed by the rapid and rapid flow of a metal with the flow of surface metals in the adjacent parts, both of which are formed by the combination of the bending and reflux of the deformed metal, and the partial deformation of the metal. The other part of the metal is formed. Folding with the shape of raw materials and blanks, the design of the mold, the arrangement of the forming process, the lubrication and the actual operation of the forging, not only reduces the bearing area of the parts, but also the stress concentration here often becomes a fatigue source.

Flow through flow

Flow through flow is a form of improper distribution of streamlines. In the cross flow region, the streamlines which are initially angled together form a cross flow, and may cause the difference in grain size between the inside and outside of the cross flow area. The cause of flow through flow is similar to that of folding, which is formed by two strands of metal or one piece of metal with another metal. However, the mechanical properties of the forgings are reduced by the flow part of the metal, especially when the difference of the grain between the two sides of the flow zone is very distinct.

The flow line distribution of forgings is not well distributed

The flow line distribution of forging is not smooth. It refers to the phenomenon of streamline disconnection, reflux, eddy current and so on.