Central discontinuity - Forging defects

Central discontinuity - Forging defects

Figure 1: Section through a heat-resistant alloy forging showing a central discontinuity that resulted from insufficient homogenization during conversion. Step machining was used to reveal the location of the rupture; original diameter is at right.

Defect name: Central discontinuity
Record No.: 3312
Type of defect (Internal/Surface): Internal
Defect classification: Forging defects
Steel name: Steel
Steel composition in weight %: No data.
Note: Internal bursts may also occur where the material is weak. For example, with ingot imperfections (such as pipe, porosity, segregation, or inclusions), tensile stresses can be sufficiently high to tear the material apart internally, particularly if the forging temperature is too high. Similarly, if the metal contains low-melting phases resulting from segregation, these phases may rupture during forging. Ingot pipe, unhealed center conditions, or voids associated with melt-related discontinuities may also induce center bursts if reduction rates are too severe or temperatures are incorrect during working. The conversion practice to bar or billet must impart sufficient homogenization or healing to produce a product with sound center conditions. An example of an unsound condition that did not heal is shown in Fig. 1.
Reference: Not shown in this demonstration version.