Discontinuities/Defects (4,5,6,7,9) Flashcards
Discontinuity
An interruption in the normal physical structure or configuration of an article.
- Defect
Inherited Discontinuities
Discontinuities that result from the Molding Process.
- Inclusions, Shrinkage, Porosity, Segregation Cold-Shuts, Cold-Shots, Hot + Cold Cracking, Misruns, Core Shifts
Pipe
As the Ingot solidifies the metal contracts, if there is not enough product towards the centre of the Casting, Pipe will occur.
- Elongated sub-surface discontinuity
- If rolled the Pipe becomes a Lamination
Shrinkage
Occurs when metal solidifies at different rates throughout the Ingot. Occurs from an insufficient amount of product.
Blowholes + Porosity
Gas-cavities. When the solubility of gases in a liquid decreases rapidly during solidification.
- Often at the top end of the Ingot because gas was trapped between the growing columnar Dendrites.
Inclusions
Non-Metallic materials within a low-melting point, usually oxides or sulphides.
- Irregular in shape
- Brittle
- Promote cracks from stress
- Often seen as “seams”
Segregation
Irregular distribution of alloying elements and impurities.
- Impacts corrosion resistance, Mechanical Properties, fatigue resistance
Hot Crack
Cracks from the internal residual stresses that initiate after solidification
- Inclusions and Segregation increase the chance
- Alloys with different Crystallization temperatures increase the chance
- Impurities and high-heat increase the chance
Cold Crack
Mechanical Cracks. From rough handling, thermal shock, bad Heat-Treatment.
Misrun
When the Casting or Mold is not sufficiently filled.
Coreshift
When the Core piece shifts and the centre is not correctly Casted.
Cold Shots
Specs of metal that solidify before the majority of molten metal.
- May chip off
Cold Shuts
Molten metal that solidifies before fully filling the mold
Hot Shots
Highest temperature areas that are most likely to have Defects occur.
- Located where the Gates connect to the Casting, and Riser
Laminations
Caused by Pipe, Porosity and Blowholes, and Inclusions that are rolled out from the Rolling Process.
- Parallel to the materials work surface
Forging Laps
Caused by faulty or mismatched Dies, oversized Blanks or metal forced between the mating surfaces of the dies.
Rolling Laps
Caused by excessive material squeezed out during a Rolling pass caused by an overfill, fin, or section of “peened” or “smeared” material.
Stringers
Caused by Non-Metallic Inclusions thinned and lengthened by Working and/or Rolling.
Seams
Caused by Cracks or Blowholes stretched out/lengthened by Rolling.
Cupping
Caused by Segregation from the inherent process located in the centre of the bar.
- Series of internal ruptures from excessive working
- Chevron shape
Forging Bursts
Caused by excessive heat or cold and prior Discontinuities or too fast of a reduction, that appears as Bursts or cavities.
- Can be external or internal
Hydrogen Flakes
Caused by stresses produced by localized Metallurgical transformations. Decreased solubility of hydrogen during rapid cooling during Hot-Working.
Machining Tears
Jagged Cracks caused by high thermal stresses, dull cutting tools, or too large a cut in one pass.
Flash Line Tears
Excess material squeezed out of Dies during Forging operations (The Flash). From the material moved from the cutting action to smooth edges.
Grinding Cracks
Shallow cracks at right angles from the direction of grinding caused by overheating under the grinding wheel, lack of coolant, removal of to much material in one pass, residual stresses from other treatment processes.
Pickling Cracks
Result of diffusion of hydrogen generated during the Pickling operation.
- Create high internal stresses that can lead to propagation
- Common in materials that have residual stress from hardening or cold working operations.
Plating Cracks
Caused by the diffusion of hydrogen during Plating operations.
- Results in high-internal stresses that can propagate
