Common Defects That caused by Improper Forging Process
1. Large Grain: due to the beginning of forging temperature is too high and the degree of deformation is insufficient, or the end forging temperature is too high, or the degree of deformation fall into the critical deformation zone caused. The degree of deformation of aluminum alloy is too large, the formation of texture; high temperature alloy deformation temperature is too low, the formation of mixed deformation of the organization may also cause coarse grains.
Coarse grain forgings will reduce the ductility and toughness, fatigue performance decreased significantly. Uneven grain means some parts of the forging grains are particularly coarse, some parts are small. The main reason for the non-uniform grain deformation is uneven throughout the blank so that the degree of grain crushing varies, or the degree of deformation of the local area off the people critical deformation zone, or superalloys local hardening, or quenching local coarse grain. Heat-resistant steel and high-temperature alloys are particularly sensitive to grain unevenness. Uneven grain will make the lasting performance of forging, fatigue performance decreased significantly.
2. Cold Hard Phenomenon: deformation due to the low temperature or deformation speed too fast, and after forging cooling too fast, may cause recrystallization softening can not keep up with the deformation caused by strengthening (hardening), so that the internal part of the forging after forged still retain cold deformation organization. The presence of this organization increases the strength and hardness of the forging, but reduces the ductility and toughness. Several cold and hard phenomenon may cause forging crack.
3. Cracks: cracks are usually caused by the presence of large tensile stress, shear stress or additional tensile stress during forging. Cracks occur in the site is usually the largest blank stress, the thinnest part. If the blank surface and internal microcracks, or blank memory in tissue defects, or improper thermal processing temperature to reduce the plasticity of material, or deformation speed is too fast, the degree of deformation is too large, exceeding the material allows the plastic pointer, etc., in the withdrawal of thick, pull long, punching, reaming, bending and extrusion processes are likely to crack.
4. Map Cracking: Map cracking is a shallow tortoise-like crack on the surface of the forging. In the forging forming surface tensile stress (for example, not filled by the projecting portion or curved portion) is most likely to produce such defects.Internal causes of cracking may be many:
1) The Raw Material Co Cu, SN and other fusible elements too much.
2) High temperature for a long time heating, steel surface copper precipitation, coarse grain surface, decarbonization, or after repeated heating of the surface.
3) Fuel sulfur content is too high, sulfur seepage steel surface.
