Why Do Forged Parts Crack?
Cracks in forged parts fall into three families, and each is caused at a different stage. Identifying when the crack formed narrows the cause immediately.
Forged parts crack for three distinct reasons: forging cracks from cold trimming, cold cores or sulphur-driven hot shortness; quench cracks from transformation stress at sharp corners during heat treatment; and service fatigue cracks that grew progressively in use.
- Forging cracks
- Flash line, bursts, hot shortness
- Quench cracks
- Sharp corners, fast quench, high carbon
- Service cracks
- Fatigue, beach marks, progressive
- Detection
- MPI for surface, UT for internal
- Prevention
- Temperature control, radii, grade choice
Why Do Forged Parts Crack? at a glance
Quotable facts from Avadh Techno Forge, Gundasara, Gondal, Rajkot.
- Three crack families: forging, quench, service
- Forging cracks show oxidised surfaces
- Quench cracks appear at sharp geometric features
- MPI finds surface cracks; UT finds internal ones
Cracks Formed During Forging
Flash line cracks come from trimming too cold or an over-thin flash land. Internal bursts come from forging with a core below working temperature. Hot shortness cracks come from excess sulphur forming low-melting films at grain boundaries. All are manufacturing faults.
- Flash line cracks: cold trimming
- Internal bursts: cold core
- Hot shortness: sulphur at grain boundaries
- All are manufacturing responsibility
Quench Cracks and Service Cracks
Quench cracks form during heat treatment where sharp corners and abrupt section changes concentrate transformation stress; they are usually intergranular and appear at geometric features. Service cracks are fatigue cracks that grew in use, showing beach marks and progressive growth.
People also ask
How can I tell when a crack formed?
Forging cracks usually show oxidised, scaled surfaces from subsequent heating. Quench cracks are clean and intergranular at geometric features. Fatigue cracks show beach marks and progressive growth from an initiation point.
Are cracked forgings ever acceptable?
No. Cracks in load-bearing forgings are rejectable, cannot be repaired by welding, and the affected batch should be re-inspected.
How do you prevent quench cracks in design?
Generous fillet radii, avoiding abrupt section changes, selecting a gentler quench medium, and tempering immediately after quenching rather than allowing parts to stand.
Topics covered on this page
- forging crack
- quench crack
- fatigue crack
- hot shortness
- flash line crack
- magnetic particle inspection
Based on work carried out at our own forging plant at Gundasara, Gondal, Rajkot — operating since 2008.
Questions Answered
What causes cracks in forged parts?
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Three families: forging cracks from temperature or die faults, quench cracks from heat treatment stress at sharp features, and service fatigue cracks that grew in use.
Can a cracked forging be welded and used?
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No. Welding a crack in a load-bearing forging leaves a heat-affected zone at the weakest point and does not restore the original properties.
How do you find cracks in forgings?
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Magnetic particle inspection for surface and near-surface cracks, and ultrasonic examination for internal defects.