CWB Welding Inspector Level 3 Exam 200
Multiple Choice Questions with Bold Italic
Answers and Explanations
DOMAIN 1: WELDING METALLURGY – FERROUS MATERIALS
1. The maximum solubility of carbon in α-iron (ferrite) is:
A) 2.0%
B) 0.002%
C) 0.02%
D) 0.8%
Ferrite (α-iron) has a body-centered cubic (BCC) structure with very limited interstitial sites for carbon
atoms, resulting in a maximum carbon solubility of only 0.02% at the eutectoid temperature .
2. Multiplication and subsequent congestion of moving dislocations causes:
A) Elastic extension
B) Work or strain hardening
C) A drop in the yield stress
D) Increased ductility
As dislocations multiply and become congested during plastic deformation, they impede each other's
movement, requiring increasing stress for continued deformation—this is the fundamental mechanism of
work or strain hardening .
3. Which of the following elements are most likely to form interstitial solid solutions with iron?
A) Copper
B) Nickel
C) Carbon
D) Chromium
Carbon atoms are small enough to fit into the interstitial spaces of the iron lattice, forming interstitial
solid solutions. Copper and nickel form substitutional solid solutions because their atomic sizes are
similar to iron .
4. If FCC iron has a denser structure than BCC iron, why does it have a higher solubility for carbon?
,A) The FCC lattice has more space between atoms
B) The preferred site for carbon in BCC iron is smaller than that in FCC iron
C) Carbon atoms repel BCC iron atoms
D) BCC iron has a lower melting point
Although FCC iron is denser, the interstitial sites (octahedral holes) in FCC are actually larger than those
in BCC, allowing greater carbon solubility in austenite (FCC) compared to ferrite (BCC) .
5. The hardness of martensite depends mainly on the:
A) Alloy content
B) Rate of cooling
C) Carbon content
D) Size of the part
The hardness of martensite is primarily determined by the carbon content. Higher carbon content causes
greater tetragonal distortion of the body-centered tetragonal (BCT) lattice, resulting in higher hardness.
Alloying elements contribute to hardenability (depth of hardening) but have a lesser effect on the
maximum attainable hardness .
6. Can bainite normally be produced in continuous cooling of a plain carbon steel?
A) Yes
B) No
C) Only with very rapid cooling
D) Only with very slow cooling
Bainite typically requires isothermal transformation (holding at a constant temperature between the
pearlite and martensite start temperatures). Continuous cooling of plain carbon steel generally produces
a mixture of pearlite and martensite, not pure bainite .
7. What is the carbon content of a slowly cooled 0.2% carbon steel after applying the lever rule to the
iron-carbon phase diagram?
A) About 50% pearlite and 50% ferrite
B) About 25% pearlite and 75% ferrite
C) About 75% pearlite and 25% ferrite
D) 100% ferrite
The tie line begins at 0.0%C (α ferrite) and ends at 0.8%C (pearlite). The fulcrum for the lever rule is at
0.2%C: % pearlite = (0.2 - 0.0)/(0.8 - 0.0) × 100% = 25%; % ferrite = 75% .
8. True or False: Recrystallization always involves the formation of a new phase.
,A) True
B) False
Recrystallization involves the formation of new, strain-free grains from a cold-worked structure, but
these grains have the same crystal structure and composition as the original material—no new phase is
formed .
9. To get recovery and recrystallization, the metal must have been previously:
A) Quenched
B) Heated
C) Cold worked
D) Annealed
Recovery and recrystallization occur in metals that have been plastically deformed (cold worked). The
stored energy from cold working provides the driving force for these processes .
10. Why is the temperature range 150°C-400°C usually avoided when forming steels?
A) The steel becomes too soft
B) Because of "blue brittleness", i.e., lower ductility due to dynamic strain aging
C) The steel melts at these temperatures
D) Oxidation rates are highest
This temperature range produces "blue brittleness," a condition of lower ductility due to dynamic strain
aging. Interstitial atoms (carbon and nitrogen) diffuse to dislocations and pin them, causing reduced
ductility and increased strength .
11. Which of the following is a condition for an alloy to show precipitation hardening?
A) There must be a eutectoid system
B) The solubility of one component must rise with increasing temperature
C) There must be complete solid solubility
D) The alloy must be single-phase at all temperatures
For precipitation hardening, the solubility of the strengthening component must decrease with
decreasing temperature, allowing fine precipitates to form during aging. This creates obstacles to
dislocation movement .
12. How does yield strength vary with grain size?
A) Directly proportional to grain size
B) Inversely as the square root of the grain size
, C) Independent of grain size
D) Exponentially with grain size
According to the Hall-Petch relationship, yield strength is inversely proportional to the square root of
grain size. Finer grains provide more grain boundary area, which impedes dislocation motion .
13. Which of the following factors increases the degree of constitutional supercooling?
A) Very slow solidification rate
B) An alloy with a very narrow solidification range
C) An alloy with a wide solidification range
D) Pure metal
A wide solidification range means the liquid and solid compositions differ significantly. This creates a
larger solute-rich zone ahead of the solidification front, promoting constitutional supercooling and
dendritic growth .
14. Hot cracking during welding is more likely in:
A) Pure metals
B) Alloys with a wide solidification range
C) Alloys with a very high alloy content
D) Metals with low thermal expansion
Alloys with a wide solidification range have a large mushy zone where liquid and solid coexist. This
makes them more susceptible to hot cracking as the liquid films between dendrites cannot be fed during
solidification contraction .
15. Which of the following alloys would you expect to give the highest risk of hot cracking?
A) Al-0.1%Cu
B) Al-3%Cu
C) Al-8%Cu
D) Pure aluminum
Al-3%Cu is at the peak of the hot cracking susceptibility curve for aluminum-copper alloys. This
intermediate composition produces maximum cracking sensitivity during solidification .
16. If centerline solidification cracking is occurring in welding a structural steel, what is a likely cause?
A) Electrical extension too long
B) Arc voltage too high
Multiple Choice Questions with Bold Italic
Answers and Explanations
DOMAIN 1: WELDING METALLURGY – FERROUS MATERIALS
1. The maximum solubility of carbon in α-iron (ferrite) is:
A) 2.0%
B) 0.002%
C) 0.02%
D) 0.8%
Ferrite (α-iron) has a body-centered cubic (BCC) structure with very limited interstitial sites for carbon
atoms, resulting in a maximum carbon solubility of only 0.02% at the eutectoid temperature .
2. Multiplication and subsequent congestion of moving dislocations causes:
A) Elastic extension
B) Work or strain hardening
C) A drop in the yield stress
D) Increased ductility
As dislocations multiply and become congested during plastic deformation, they impede each other's
movement, requiring increasing stress for continued deformation—this is the fundamental mechanism of
work or strain hardening .
3. Which of the following elements are most likely to form interstitial solid solutions with iron?
A) Copper
B) Nickel
C) Carbon
D) Chromium
Carbon atoms are small enough to fit into the interstitial spaces of the iron lattice, forming interstitial
solid solutions. Copper and nickel form substitutional solid solutions because their atomic sizes are
similar to iron .
4. If FCC iron has a denser structure than BCC iron, why does it have a higher solubility for carbon?
,A) The FCC lattice has more space between atoms
B) The preferred site for carbon in BCC iron is smaller than that in FCC iron
C) Carbon atoms repel BCC iron atoms
D) BCC iron has a lower melting point
Although FCC iron is denser, the interstitial sites (octahedral holes) in FCC are actually larger than those
in BCC, allowing greater carbon solubility in austenite (FCC) compared to ferrite (BCC) .
5. The hardness of martensite depends mainly on the:
A) Alloy content
B) Rate of cooling
C) Carbon content
D) Size of the part
The hardness of martensite is primarily determined by the carbon content. Higher carbon content causes
greater tetragonal distortion of the body-centered tetragonal (BCT) lattice, resulting in higher hardness.
Alloying elements contribute to hardenability (depth of hardening) but have a lesser effect on the
maximum attainable hardness .
6. Can bainite normally be produced in continuous cooling of a plain carbon steel?
A) Yes
B) No
C) Only with very rapid cooling
D) Only with very slow cooling
Bainite typically requires isothermal transformation (holding at a constant temperature between the
pearlite and martensite start temperatures). Continuous cooling of plain carbon steel generally produces
a mixture of pearlite and martensite, not pure bainite .
7. What is the carbon content of a slowly cooled 0.2% carbon steel after applying the lever rule to the
iron-carbon phase diagram?
A) About 50% pearlite and 50% ferrite
B) About 25% pearlite and 75% ferrite
C) About 75% pearlite and 25% ferrite
D) 100% ferrite
The tie line begins at 0.0%C (α ferrite) and ends at 0.8%C (pearlite). The fulcrum for the lever rule is at
0.2%C: % pearlite = (0.2 - 0.0)/(0.8 - 0.0) × 100% = 25%; % ferrite = 75% .
8. True or False: Recrystallization always involves the formation of a new phase.
,A) True
B) False
Recrystallization involves the formation of new, strain-free grains from a cold-worked structure, but
these grains have the same crystal structure and composition as the original material—no new phase is
formed .
9. To get recovery and recrystallization, the metal must have been previously:
A) Quenched
B) Heated
C) Cold worked
D) Annealed
Recovery and recrystallization occur in metals that have been plastically deformed (cold worked). The
stored energy from cold working provides the driving force for these processes .
10. Why is the temperature range 150°C-400°C usually avoided when forming steels?
A) The steel becomes too soft
B) Because of "blue brittleness", i.e., lower ductility due to dynamic strain aging
C) The steel melts at these temperatures
D) Oxidation rates are highest
This temperature range produces "blue brittleness," a condition of lower ductility due to dynamic strain
aging. Interstitial atoms (carbon and nitrogen) diffuse to dislocations and pin them, causing reduced
ductility and increased strength .
11. Which of the following is a condition for an alloy to show precipitation hardening?
A) There must be a eutectoid system
B) The solubility of one component must rise with increasing temperature
C) There must be complete solid solubility
D) The alloy must be single-phase at all temperatures
For precipitation hardening, the solubility of the strengthening component must decrease with
decreasing temperature, allowing fine precipitates to form during aging. This creates obstacles to
dislocation movement .
12. How does yield strength vary with grain size?
A) Directly proportional to grain size
B) Inversely as the square root of the grain size
, C) Independent of grain size
D) Exponentially with grain size
According to the Hall-Petch relationship, yield strength is inversely proportional to the square root of
grain size. Finer grains provide more grain boundary area, which impedes dislocation motion .
13. Which of the following factors increases the degree of constitutional supercooling?
A) Very slow solidification rate
B) An alloy with a very narrow solidification range
C) An alloy with a wide solidification range
D) Pure metal
A wide solidification range means the liquid and solid compositions differ significantly. This creates a
larger solute-rich zone ahead of the solidification front, promoting constitutional supercooling and
dendritic growth .
14. Hot cracking during welding is more likely in:
A) Pure metals
B) Alloys with a wide solidification range
C) Alloys with a very high alloy content
D) Metals with low thermal expansion
Alloys with a wide solidification range have a large mushy zone where liquid and solid coexist. This
makes them more susceptible to hot cracking as the liquid films between dendrites cannot be fed during
solidification contraction .
15. Which of the following alloys would you expect to give the highest risk of hot cracking?
A) Al-0.1%Cu
B) Al-3%Cu
C) Al-8%Cu
D) Pure aluminum
Al-3%Cu is at the peak of the hot cracking susceptibility curve for aluminum-copper alloys. This
intermediate composition produces maximum cracking sensitivity during solidification .
16. If centerline solidification cracking is occurring in welding a structural steel, what is a likely cause?
A) Electrical extension too long
B) Arc voltage too high
