Forging Defects

1) Incomplete Penetration: Due to light and rapper hammer blowing the penetration of deformation during forging may be less. To minimize incomplete penetration forging of large cross-section are made in forging press.                                                               

2) Surface Cracking: It can occur as a result of excessive working of the surface too low temperature or as a result of hot shortness. A high sulphur concentration in the furnace atmosphere can produce hot shortness.

3) Cold Shut or Fold: When the two surface of metal fold against each other without welded completely a discontinuity is produced, it is called cold shut. A common cause of fold shut is too small and die radius and low temperature. It happened in close die forging common case of it is very small die radius.

4) Internal Crack: Internal crack can develop during upsetting of the cylinder or round as a result of circumferential tensile stress changes of internal cracking in less in case of close die forging. In open die forging using of concave dies during upsetting can minimize bulging and minimize the probability of cracking.

Extrusion Defects

1)Internal Pipe: Because of homogeneous of a billet, center of the billet moves faster than periphery. As a result of depth metal zone extend along the outer surface of billet. After 2/3rd of billet extruded, outer surface of billet moves towards the center. Since, the surface of billet after contain of oxidized layer (skin), this type of flow results in internal oxide stringers. This defect is known as internal pipe. Section of the extruded metal, it will appear as a ring. High friction between billet and container increase the probability of this defect.

2)Axial Hole: While extrusion is carried out to the point at which the length of the billet remaining in the container is about 1/4th its diameter, the rapid radial flow into the die results in the creation of an axial hole/funnel in the back end of extrusion. This region must be discarded. The length of this defect can be reduced by inclining the face of ram of an angle to the ram axis.


3)Fir Tree Cracking: When ram speed is too high for the extrusion , surface of the billet becomes badly rough. Repeat ting transverse cracking is called fir tree cracking.

 It is also called chevron cracking. It can decure at low extrusion ratio. High frictional resistance at the tool and billet interface produces a sound product while center burst occur while the friction is low


5)Surface Crack and Lamination: The lubricant film must be complete and continuous between the billet and container wall during extrusion. Gapes in the film will cause to initiate shear zones which can developed into surface cracks. Lamination of oxide can be created in the same way. 

DEFECTS OF ROLL PRODUCT

1) Long Edges: In rolling of steels if the rolls deflect in concave way the edges of the sheet will be elongated to a greater extent in longitudinal direction than the center which cause the metal sheet has long edges.

2) Edges Buckles:  If the edges are free to move relative to the center, the center portion at the sheet are stretched in tension and edges are compressed in rolling direction this results in an widely edge.

3) Zipper Breaks: Long edge may also result in short cracks in the center which is called zipper breaks.

4) Center Buckles: This problem may be minimized by making the role parallel to the axis. When the center of the sheet is more elongated more than the edge. The center portion is in compression and edge intention. Such a sheet usually content center buckles. Mild shape problem may be corrected by stretch rolling. Stretch leveling the sheet in a roller leveler.

5) Edge Cracking: During rolling elements across the width have some tendency to explain laterally.  This tendency is higher at the edge and lower at the center. In this carrier and in homogeneity occurs in homogeneity in stress distribution occurs along the thickness which need to edge cracking.

6) Center Cracking: Under savvier condition of low uniform stress distribution center speed may occur.

7) Alligatoring: In heavy reduction center tends to expands more than the surface with this type of deformation grates speed occurs to the center than the surface, So the surface are placed in tension and center is in compression. If there is any metallurgical witness along the center line of the slag fracture will occurs along the thickness, this is called alligatoring. Edge cracking is minimize by employing vertical edge roles.