Discontinuities/Defects (4,5,6,7,9)

Question 1

Discontinuity

Answer 1

An interruption in the normal physical structure or configuration of an article.
- Defect

Question 2

Inherited Discontinuities

Answer 2

Discontinuities that result from the Molding Process.

- Inclusions, Shrinkage, Porosity, Segregation Cold-Shuts, Cold-Shots, Hot + Cold Cracking, Misruns, Core Shifts

Question 3

Pipe

Answer 3

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

Question 4

Shrinkage

Answer 4

Occurs when metal solidifies at different rates throughout the Ingot. Occurs from an insufficient amount of product.

Question 5

Blowholes + Porosity

Answer 5

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.

Question 6

Inclusions

Answer 6

Non-Metallic materials within a low-melting point, usually oxides or sulphides.

• Irregular in shape
• Brittle
• Promote cracks from stress
• Often seen as “seams”

Question 7

Segregation

Answer 7

Irregular distribution of alloying elements and impurities.

- Impacts corrosion resistance, Mechanical Properties, fatigue resistance

Question 8

Hot Crack

Answer 8

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

Question 9

Cold Crack

Answer 9

Mechanical Cracks. From rough handling, thermal shock, bad Heat-Treatment.

Question 10

Misrun

Answer 10

When the Casting or Mold is not sufficiently filled.

Question 11

Coreshift

Answer 11

When the Core piece shifts and the centre is not correctly Casted.

Question 12

Cold Shots

Answer 12

Specs of metal that solidify before the majority of molten metal.
- May chip off

Question 13

Cold Shuts

Answer 13

Molten metal that solidifies before fully filling the mold

Question 14

Hot Shots

Answer 14

Highest temperature areas that are most likely to have Defects occur.
- Located where the Gates connect to the Casting, and Riser

Question 15

Laminations

Answer 15

Caused by Pipe, Porosity and Blowholes, and Inclusions that are rolled out from the Rolling Process.
- Parallel to the materials work surface

Question 16

Forging Laps

Answer 16

Caused by faulty or mismatched Dies, oversized Blanks or metal forced between the mating surfaces of the dies.

Question 17

Rolling Laps

Answer 17

Caused by excessive material squeezed out during a Rolling pass caused by an overfill, fin, or section of “peened” or “smeared” material.

Question 18

Stringers

Answer 18

Caused by Non-Metallic Inclusions thinned and lengthened by Working and/or Rolling.

Question 19

Seams

Answer 19

Caused by Cracks or Blowholes stretched out/lengthened by Rolling.

Question 20

Cupping

Answer 20

Caused by Segregation from the inherent process located in the centre of the bar.

• Series of internal ruptures from excessive working
• Chevron shape

Question 21

Forging Bursts

Answer 21

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

Question 22

Hydrogen Flakes

Answer 22

Caused by stresses produced by localized Metallurgical transformations. Decreased solubility of hydrogen during rapid cooling during Hot-Working.

Question 23

Machining Tears

Answer 23

Jagged Cracks caused by high thermal stresses, dull cutting tools, or too large a cut in one pass.

Question 24

Flash Line Tears

Answer 24

Excess material squeezed out of Dies during Forging operations (The Flash). From the material moved from the cutting action to smooth edges.

Question 25

Grinding Cracks

Answer 25

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.

Question 26

Pickling Cracks

Answer 26

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.

Question 27

Plating Cracks

Answer 27

Caused by the diffusion of hydrogen during Plating operations.
- Results in high-internal stresses that can propagate