Common Forging Ingot Defects and How They Are Prevented
Pipe, segregation, cracks, inclusions and flakes in forging ingots: what causes them and how to reduce them.
Shrinkage pipe
As steel solidifies it shrinks, leaving a cavity at the top. A properly designed and insulated hot top keeps the cavity in the cropped head. Prevention: correct hot top size and pouring temperature.
Segregation in forging ingots
Alloying elements and carbon concentrate in the last steel to freeze, usually in the centre and top. Heavy ingots show more segregation. Prevention: controlled pouring speed and temperature, ingot shape, and enough forging reduction to homogenise the structure.
Forging ingot surface defects: surface and corner cracks
Thermal stresses can crack the surface or corners of the ingot, particularly in square sections of crack-sensitive alloys. Prevention: fluted shape, rounded corners, correct mould temperature and controlled stripping and cooling.
Non-metallic inclusions
Oxides and sulphides trapped in the steel reduce fatigue life. Prevention: ladle refining, vacuum degassing, clean refractories and bottom pouring.
Hydrogen flakes
Hydrogen causes internal flake cracks in heavy forgings. Prevention: vacuum degassing to a low hydrogen level, plus a slow, controlled cooling or hydrogen diffusion cycle after forging.
Related guides
Vacuum Degassed Forging Ingots: Why Vacuum Matters
How vacuum degassing removes hydrogen, oxygen and nitrogen from steel and why it matters for heavy forgings.
Hot Top Forging Ingots: Over Imposed vs Semi Inserted
What a hot top does, how over imposed and semi inserted hot tops differ, and how it affects ingot yield and soundness.
Forging Ingot Quality Checks: Chemistry, Gas, Ultrasonic Testing
The tests that matter for forging ingots: spectrometer analysis, oxygen-nitrogen-hydrogen, PMI and ultrasonic inspection.