1. raw material defects
If there are residual shrinkage holes, bubbles, loose and inclusions in
ingot or steel, cracking may occur. The high strength inspection
characteristics of forging cracks caused by metallurgical reasons are
often accompanied by a large number of inclusions of oxides, sulphides
and silicates. The raw materials of high carbon and high alloy steel are
easy to have serious second phase segregation of carbides. If the
forging is not broken and distributed evenly, the mechanical properties
of the forgings will be reduced, and the cracking or distortion of the
forgings may be caused by heat treatment. Scratching, scarring, folding
and cracking will result in defects on the surface of the raw material.
Therefore, raw materials must be inspected in die forging.
2. heating specification
When forging large mould forgings and alloy steel forgings, if the
heating speed is too fast and the temperature difference between the
inner and outer layers is large, the central part of the crack will be
caused by the temperature stress and the tissue stress.