CWI Metallurgy and Weld Discontinuities 2 — Questions and Answers
Question 1: Which weld discontinuity is caused by the base metal melting away beneath the weld toe, creating a groove along the weld edge?
- Overlap
- Undercut (Correct answer)
- Incomplete fusion
- Cold lap
Correct answer: Undercut
Undercut is a groove melted into the base metal at the weld toe that remains unfilled by weld metal, reducing the effective cross-section.
Question 2: In welding metallurgy, what does the term 'HAZ' refer to?
- High Alloy Zone
- Heat-Affected Zone (Correct answer)
- Hardened Arc Zone
- Horizontal Arc Zone
Correct answer: Heat-Affected Zone
HAZ stands for Heat-Affected Zone, the region of base metal adjacent to the weld that has had its microstructure altered by welding heat without melting.
Question 3: Which type of crack forms along the centerline of a weld bead due to solidification shrinkage and low-melting-point segregates?
- Toe crack
- Underbead crack
- Centerline solidification crack (Correct answer)
- Lamellar tear
Correct answer: Centerline solidification crack
Centerline solidification cracks occur along the weld centerline as the last liquid to solidify contains low-melting-point impurities that cannot withstand shrinkage stresses.
Question 4: What is the primary cause of porosity in a weld?
- Excessive preheat temperature
- Gas entrapment during solidification (Correct answer)
- High interpass temperature
- Insufficient arc voltage
Correct answer: Gas entrapment during solidification
Porosity results from gas being trapped in solidifying weld metal, commonly caused by moisture, contamination, or inadequate shielding gas coverage.
Question 5: Which discontinuity occurs when weld metal flows over the base metal surface without fusing to it?
- Underfill
- Overlap (Correct answer)
- Concavity
- Burn-through
Correct answer: Overlap
Overlap (cold lap) occurs when molten weld metal flows over the base metal surface but fails to fuse with it, creating a sharp notch.
Question 6: In carbon steel, what phase transformation occurs when steel is rapidly cooled (quenched) from the austenite region?
- Ferrite formation
- Pearlite formation
- Martensite formation (Correct answer)
- Bainite formation
Correct answer: Martensite formation
Rapid quenching of austenite produces martensite, a hard and brittle body-centered tetragonal (BCT) crystal structure that forms without diffusion.
Question 7: A weld inspector finds a discontinuity classified as 'incomplete joint penetration' (IJP). What does this mean?
- The weld bead is too wide
- The weld metal did not fully penetrate to the root of the joint (Correct answer)
- The cap pass is missing
- The weld has excessive reinforcement
Correct answer: The weld metal did not fully penetrate to the root of the joint
Incomplete joint penetration means the weld metal failed to extend through the full thickness of the joint to the root, leaving an unfused area at the root.
CWI Metallurgy and Weld Discontinuities 2
Which weld discontinuity is caused by the base metal melting away beneath the weld toe, creating a groove along the weld edge?