CWB Welding Inspector Level 3 Exam
—Questions and Answers With Rationales | L a t e s t U p d a t e
Q1. Pure iron transforms from BCC (alpha/ferrite) to FCC
(gamma/austenite) as it is heated through which approximate
temperature?
A. 723 C (1333 F)
B. 912 C (1674 F)
C. 1148 C (2098 F)
D. 1538 C (2800 F)
Answer: B
Rationale: Iron undergoes an allotropic transformation from BCC alpha-iron to
FCC gamma-iron (austenite) at approximately 912 C (A3 point for pure iron).
The 723 C value is the eutectoid temperature (A1) on the Fe-Fe3C diagram,
1148 C is the eutectic temperature, and 1538 C is the melting point of pure
iron.
Q2. On the iron-carbon equilibrium diagram, the eutectoid reaction
produces which microconstituent upon slow cooling of a 0.8% carbon
steel through 723 C?
A. Martensite
B. Pearlite
C. Bainite
D. Cementite only
Answer: B
, Rationale: The eutectoid reaction, austenite to ferrite plus cementite, occurs at
0.8% carbon and 723 C under slow (equilibrium) cooling, producing the
lamellar microconstituent pearlite. Martensite and bainite are non-equilibrium
products of faster cooling rates, and cementite alone would only form as a
separate phase, not the eutectoid product.
Q3. A steel containing less than 0.8% carbon is classified metallurgically
as:
A. Eutectoid steel
B. Hypereutectoid steel
C. Hypoeutectoid steel
D. Ledeburitic steel
Answer: C
Rationale: Steels with carbon content below the eutectoid composition of 0.8%
are termed hypoeutectoid; their microstructure on slow cooling consists of
proeutectoid ferrite plus pearlite. Hypereutectoid steels contain more than
0.8% carbon and form proeutectoid cementite plus pearlite. Ledeburite refers
to the cast iron eutectic constituent.
Q4. Which crystal structure is characteristic of austenite (gamma-iron)?
A. Body-centred cubic (BCC)
B. Face-centred cubic (FCC)
C. Hexagonal close-packed (HCP)
D. Tetragonal
Answer: B
Rationale: Austenite is the face-centred cubic form of iron, stable at elevated
temperature in plain carbon steels, and it can dissolve substantially more
carbon interstitially (up to about 2.1%) than the BCC ferrite phase because the
FCC octahedral interstitial sites are larger. BCC describes ferrite and
delta-iron, while body-centred tetragonal describes martensite.
Q5. Which heat treatment involves heating steel above the upper critical
temperature followed by slow furnace cooling to produce a soft,
equilibrium microstructure?
—Questions and Answers With Rationales | L a t e s t U p d a t e
Q1. Pure iron transforms from BCC (alpha/ferrite) to FCC
(gamma/austenite) as it is heated through which approximate
temperature?
A. 723 C (1333 F)
B. 912 C (1674 F)
C. 1148 C (2098 F)
D. 1538 C (2800 F)
Answer: B
Rationale: Iron undergoes an allotropic transformation from BCC alpha-iron to
FCC gamma-iron (austenite) at approximately 912 C (A3 point for pure iron).
The 723 C value is the eutectoid temperature (A1) on the Fe-Fe3C diagram,
1148 C is the eutectic temperature, and 1538 C is the melting point of pure
iron.
Q2. On the iron-carbon equilibrium diagram, the eutectoid reaction
produces which microconstituent upon slow cooling of a 0.8% carbon
steel through 723 C?
A. Martensite
B. Pearlite
C. Bainite
D. Cementite only
Answer: B
, Rationale: The eutectoid reaction, austenite to ferrite plus cementite, occurs at
0.8% carbon and 723 C under slow (equilibrium) cooling, producing the
lamellar microconstituent pearlite. Martensite and bainite are non-equilibrium
products of faster cooling rates, and cementite alone would only form as a
separate phase, not the eutectoid product.
Q3. A steel containing less than 0.8% carbon is classified metallurgically
as:
A. Eutectoid steel
B. Hypereutectoid steel
C. Hypoeutectoid steel
D. Ledeburitic steel
Answer: C
Rationale: Steels with carbon content below the eutectoid composition of 0.8%
are termed hypoeutectoid; their microstructure on slow cooling consists of
proeutectoid ferrite plus pearlite. Hypereutectoid steels contain more than
0.8% carbon and form proeutectoid cementite plus pearlite. Ledeburite refers
to the cast iron eutectic constituent.
Q4. Which crystal structure is characteristic of austenite (gamma-iron)?
A. Body-centred cubic (BCC)
B. Face-centred cubic (FCC)
C. Hexagonal close-packed (HCP)
D. Tetragonal
Answer: B
Rationale: Austenite is the face-centred cubic form of iron, stable at elevated
temperature in plain carbon steels, and it can dissolve substantially more
carbon interstitially (up to about 2.1%) than the BCC ferrite phase because the
FCC octahedral interstitial sites are larger. BCC describes ferrite and
delta-iron, while body-centred tetragonal describes martensite.
Q5. Which heat treatment involves heating steel above the upper critical
temperature followed by slow furnace cooling to produce a soft,
equilibrium microstructure?
