1. Large grain
The large grain size of the forged blank is usually caused by the excessive initial forging temperature and insufficient deformation degree, or the final forging temperature is too high, or the degree of deformation falls into the critical deformation zone. The deformation degree of aluminum alloy is too large to form texture; the deformation temperature of high-temperature alloy is too low, and coarse grains may be caused when mixed deformation structure is formed. The coarse grain will reduce the plasticity and toughness of the forging, and the fatigue performance will be significantly reduced.
2. Uneven grain
Grain inhomogeneity means that the grains of some parts of the forging are particularly coarse, and some parts are small. The main reason for the grain inhomogeneity is that the deformation of the billet is uneven, the degree of grain breakage is different, or the degree of deformation of the local area falls into the critical deformation zone, or the local processing hardening of the superalloy, or the local grain during quenching heating. Coarse. Heat resistant steels and superalloys are particularly sensitive to grain irregularities. The uneven grain size will significantly reduce the long-term performance and fatigue performance of the forging.
3. Cold phenomenon
When the deformation is too low or the deformation speed is too fast, and the cooling after forging is too fast, the softening caused by recrystallization can not keep up with the strengthening (hardening) caused by the deformation, so that the inside of the forged part after hot forging still retains cold deformation. organization. The presence of such a structure increases the strength and stiffness of the forging but reduces plasticity and toughness. Severe chills can cause cracking.
Cracks are usually caused by large tensile stresses, shear stresses or additional tensile stresses during forging. The location where the crack occurs is usually at a portion where the billet has a large stress and a small thickness. If there are micro-cracks on the surface and inside of the blank, or there are tissue defects in the blank, or if the hot working temperature is improper, the plasticity of the material is lowered, or the deformation speed is too fast, the deformation degree is too large, and the plastic pointer is allowed to exceed the allowable material. Cracks may occur in processes such as lengthening, punching, reaming, bending, and extrusion.
The crack is a shallow turtle crack on the surface of the forging. A surface that is subjected to tensile stress in the forming of the forging (for example, an unfilled convex portion or a bent portion) is liable to cause such a defect. The internal cause of cracking may be multi-faceted: 1 the raw material is too much fusible elements such as Cu and Sn. 2 When the high temperature is heated for a long time, the surface of the steel material has copper precipitated, the surface crystal grains are coarse, decarburized, or the surface is heated several times. 3 The sulfur content of the fuel is too high, and there is sulfur on the surface of the steel.