CWI Metallurgy and Weld Discontinuities 4 — Questions and Answers
Question 1: A tungsten inclusion in a weld is most associated with which welding process?
- SMAW (Shielded Metal Arc Welding)
- SAW (Submerged Arc Welding)
- GTAW (Gas Tungsten Arc Welding) (Correct answer)
- FCAW (Flux-Cored Arc Welding)
Correct answer: GTAW (Gas Tungsten Arc Welding)
Tungsten inclusions occur in GTAW when the non-consumable tungsten electrode contacts the weld pool or is contaminated, depositing tungsten particles in the weld.
Question 2: Which of the following best describes 'liquation cracking'?
- Cracking caused by hydrogen in the HAZ
- Cracking in the partially melted zone due to segregation of low-melting-point constituents (Correct answer)
- Cracking at the weld root from incomplete fusion
- Cracking caused by rapid cooling after welding
Correct answer: Cracking in the partially melted zone due to segregation of low-melting-point constituents
Liquation cracking occurs in the partially melted zone (PMZ) or HAZ when low-melting-point grain boundary films form and cannot withstand solidification shrinkage stresses.
Question 3: When inspecting austenitic stainless steel welds, which defect is a primary concern related to sensitization?
- Hydrogen cracking
- Carbide precipitation at grain boundaries (Correct answer)
- Lamellar tearing
- Centerline hot cracking
Correct answer: Carbide precipitation at grain boundaries
Sensitization in austenitic stainless steel causes chromium carbides to precipitate at grain boundaries, depleting adjacent areas of chromium and reducing corrosion resistance.
Question 4: What does 'interpass temperature' refer to in a multi-pass weld?
- The temperature of the weld at the start of the root pass
- The maximum or minimum temperature of the weld before starting the next pass (Correct answer)
- The temperature of the base metal before welding begins
- The temperature at the midpoint of welding
Correct answer: The maximum or minimum temperature of the weld before starting the next pass
Interpass temperature is the temperature of the weld joint immediately before depositing the next pass in a multi-pass weld, with both maximum and minimum limits often specified.
Question 5: Which discontinuity involves incomplete bonding between weld passes or between weld metal and base metal, without a groove melted into the base metal?
- Undercut
- Lack of fusion (LOF) (Correct answer)
- Incomplete joint penetration
- Overlap
Correct answer: Lack of fusion (LOF)
Lack of fusion (LOF) is the absence of bonding between weld beads or between weld metal and base metal, caused by insufficient heat input or improper technique.
Question 6: In the iron-carbon phase diagram, at approximately what carbon content is the eutectic point (ledeburite) located?
- 0.77% carbon
- 2.11% carbon
- 4.30% carbon (Correct answer)
- 6.67% carbon
Correct answer: 4.30% carbon
The eutectic point in the iron-carbon system (ledeburite) occurs at approximately 4.30% carbon, where liquid iron solidifies directly into a mixture of austenite and cementite.
Question 7: Which factor most directly influences the width of the Heat-Affected Zone (HAZ) during welding?
- Electrode diameter
- Heat input (kJ/mm) (Correct answer)
- Shielding gas composition
- Electrode polarity
Correct answer: Heat input (kJ/mm)
Heat input directly controls the amount of thermal energy introduced per unit length of weld, which determines how much base metal is heated and therefore the HAZ width.
CWI Metallurgy and Weld Discontinuities 4
A tungsten inclusion in a weld is most associated with which welding process?