Defects

Question 1

What causes blowholes and porosity in castings?

Answer 1

Trapped gas during solidification due to poor venting, moisture in mold, or turbulence.

Question 2

What is a cold shut and why does it occur?

Answer 2

A lack of fusion where two streams of molten metal meet but do not bond, caused by low pouring temperature or interrupted flow.

Question 3

Define hot tears and their cause.

Answer 3

Cracks formed during cooling due to uneven contraction and high thermal stresses.

Question 4

What are nonmetallic inclusions?

Answer 4

Foreign materials like slag or oxides trapped in the metal, often due to improper refining or dirty molds.

Question 5

What is microshrinkage and how is it detected?

Answer 5

Small voids from insufficient feeding during solidification; detected by radiography.

Question 6

How do shrinkage cracks form?

Answer 6

Uneven cooling and contraction during solidification.

Question 7

What are bursts in forging?

Answer 7

Internal ruptures caused by excessive working at low temperature.

Question 8

Explain cupping in rolling.

Answer 8

End splitting during rolling due to uneven deformation.

Question 9

What are forging laps?

Answer 9

Overlapping metal folds caused by improper die design.

Question 10

What is hydrogen flake?

Answer 10

Internal cracks from hydrogen embrittlement during cooling.

Question 11

What are laminations and how do they occur?

Answer 11

Layers of metal separated due to rolling defects or inclusions.

Question 12

What are seams in rolled products?

Answer 12

Surface cracks from rolled-in defects or poor billet preparation.

Question 13

What is an arc strike?

Answer 13

Localized overheating causing hard spots or cracks.

Question 14

What causes HAZ cracking?

Answer 14

Thermal stresses in the heat-affected zone adjacent to the weld.

Question 15

What is lack of penetration in welding?

Answer 15

Incomplete fusion at the root of the weld.

Question 16

What are welding inclusions?

Answer 16

Slag or flux trapped in weld metal.

Question 17

What causes grinding cracks?

Answer 17

Excessive heat during grinding.

Question 18

What are heat-treat cracks?

Answer 18

Cracks from uneven heating or quenching.

Question 19

What are machining tears?

Answer 19

Surface tearing due to improper cutting speed or tool geometry.

Question 20

Which NDT method is best for detecting internal voids like porosity?

Answer 20

Radiographic Testing (RT).

Question 21

Which method detects surface-breaking cracks?

Answer 21

Liquid Penetrant Testing (PT).

Question 22

What is Pipe in Casting?

Answer 22

Definition: Pipe is a shrinkage cavity that forms in the upper central region of an ingot or casting as the metal solidifies and contracts.
Appearance: It looks like a funnel-shaped void or cavity extending downward from the top surface.
Cause: When molten metal cools, it contracts. If there is insufficient feed metal to compensate for this shrinkage, a cavity forms. This usually happens because the top of the casting solidifies last and cannot draw enough molten metal from the riser or feeder.

Question 23

Answer 23

Cold Shut

Question 24

Primary or secondary processing discontinuities?

• Grinding cracks
• Heat-treat cracks
• Machining tears

Answer 24

Secondary processing

Question 25

Primary or secondary processing discontinuities? * Arc strikes * Heat-affected zone cracking inclusions (welding) * Lack of penetration * Surface shrinkage cracks

Answer 25

Primary processing (welding)

Question 26

Primary or secondary processing discontinuities? * Bursts * Cupping * Flash line racks/tears * Forging laps * Hydrogen flake * Inclusions (stringers) * Laminations * Seams * Seams (rolled threads)

Answer 26

Primary processing

Question 27

Inherent or processing discontinuities? * Blowholes and porosity * Cold shuts * Hot tears * Nonmetallic inclusions * Shrinkage (microshrinkage) * Shrinkage cracks

Answer 27

Inherent