POWER ENGINEERING 2A2 EXAM TEST PAPER
QUESTIONS AND ANSWERS SURE A+
✔✔Examples of BCC metals? - ✔✔Chromium, tungsten, molybdenum, vanadium, alpha
iron (solid state iron below 910 deg.C) and delta iron (iron above 1390 deg.C)
✔✔How many atoms make up a Close-packed hexagonal structure? - ✔✔17 atoms
total
✔✔Characteristics of CPH structured unit cells? - ✔✔Intermediate strength and
Intermediate ductility
✔✔Materials that possess CPH unit cell structures? - ✔✔Zinc, magnesium, cadmium,
titanium
✔✔When molten metal cools and solidifies, what action do unit cells take? - ✔✔- Unit
cells become packed together to form 3 dimensional crystals that occupy a space
lattice.
Further growth of these crystals form dendrites (evergreen tree looking crystals)
✔✔Properties of materials with small grain size? - ✔✔- High tensile strength
- Highly ductile
,✔✔Properties of materials with large grain size? - ✔✔- High creep/deformation
resistance under constant loading
- More prone to cracking
✔✔Shear strength of metals is primarily determined by the type of Unit Cell Structure
exhibited. True or False? - ✔✔True.
1) HIGH ATOM PACKED DENSITY FCC structures are very ductile (easy to elongate)
with a low shear strength - Ex.) Lead.
2) LOW ATOM PACKED DENSITY BCC structures have high hardness and a high
shear strength. Ex.) Iron
✔✔Opposite of metal hardness is...? - ✔✔- A hard metal is does not possess
TOUGHNESS.
- Hardness: resistance to deformation
✔✔What is Polymorphism and what does it have to do with metals? - ✔✔- The ability of
a metal to change its unit cell structure through varying temperature ranges.
- Most metals exhibit this property; most important for the study of iron.
✔✔What is the allotropy of Iron? - ✔✔- The change in atomic cell structure dependant
on temperature
- Various physical forms of metals can affect their: melting point, hardness, metal
solubility, and alloying chemistry.
✔✔Properties of pure Iron? - ✔✔- Relatively soft
- Ductile
- Low strength
- Possesses few of the noble properties commonly associated with steel
✔✔Percentage carbon content in Carbon Steels and Cast Iron? - ✔✔Carbon Steels:
Alloys containing 2% or less carbon
Cast Iron: 2% - 6% carbon
✔✔Three grades of Carbon Steel? - ✔✔Low carbon steel: .04% to .30% carbon (mild
steel)
Medium carbon steel: .31% to .60% carbon steel
High carbon steel: .61% to 1-1.50% carbon steel (tool steel)
✔✔Steel properties as carbon content increases? Decreases? - ✔✔1) Hardness and
brittleness increase as carbon content increases
2) Ductility, softness and weldability increase as carbon content decreases
✔✔Weldability is more difficult for higher content carbon steels and even more difficult
for cast-iron metals. True or False? - ✔✔True. The higher carbon content, the harder to
weld.
, ✔✔4 varying factors that determine Iron-Carbon Equilibrium? - ✔✔- The initial
concentration of carbon in the ferrite mixture
- Temperature
- Cooling rate
- Presence of other alloy metals
✔✔Describe Austenite. - ✔✔- Structural name of Iron in the FCC form; also referred to
as 'Gamma Iron'
- Contains dissolved carbon up to 2% concentration
- All quenching heat treatment procedures must begin from the gamma iron phase
- Non-magnetic allotrope of Iron that exists of the critical Eutectoid temperature of 727
deg.C
- This state exists at room temperature in some stainless steels
✔✔Describe Cementite. - ✔✔- The common name for Iron-Carbon in the form of
molecular iron carbide (Fe3C)
- High carbon content and very brittle - normally considered a ceramic in its pure form
✔✔What is the lowest melting point of any iron-carbon mixture according to the Iron-
Carbide Equilibrium diagram? - ✔✔- 1130 deg.C and at 4% carbon concentration;
austenite and cementite are formed simultaneously
✔✔Eutectic Reaction? - ✔✔- No pasty state phase; liquid alloy of iron-carbon changes
directly into solid state austenite and cementite
- Occurs with 4% carbon content and temperature of 1130 deg.C
✔✔Describe Ferrite. - ✔✔- Structural name for iron in the BCC form and occurs at
temperatures below 912 deg.C
- Maximum amount of carbon atoms that ferrite can contain is .025% at 723 deg.C
- Ferrite describes a structure - not a composition
- Above 771 deg.C = Paramagnetic, Below 771 deg.C = Ferromagnetic
✔✔Purpose of the Lower Critical Change Line on the Iron-Carbide Equilibrium diagram?
- ✔✔- The temperature at which an iron alloy of ANY carbon composition returns to a
BCC unit cell structure. The diagram indicates this temperature at 723 deg.C
✔✔What is Pearlite in relation the Iron-Carbide Equilibrium diagram? - ✔✔- Layered
Structure (microscopically) of Ferrite and Cementite
- Appears dark grained in colour and forms in iron-carbon alloys BELOW the lower
critical change line (723 deg.C)
- Occurs in steels and cast irons
- Forms from slow cooling from 723 deg.C and occurs as a Eutectoid reaction
QUESTIONS AND ANSWERS SURE A+
✔✔Examples of BCC metals? - ✔✔Chromium, tungsten, molybdenum, vanadium, alpha
iron (solid state iron below 910 deg.C) and delta iron (iron above 1390 deg.C)
✔✔How many atoms make up a Close-packed hexagonal structure? - ✔✔17 atoms
total
✔✔Characteristics of CPH structured unit cells? - ✔✔Intermediate strength and
Intermediate ductility
✔✔Materials that possess CPH unit cell structures? - ✔✔Zinc, magnesium, cadmium,
titanium
✔✔When molten metal cools and solidifies, what action do unit cells take? - ✔✔- Unit
cells become packed together to form 3 dimensional crystals that occupy a space
lattice.
Further growth of these crystals form dendrites (evergreen tree looking crystals)
✔✔Properties of materials with small grain size? - ✔✔- High tensile strength
- Highly ductile
,✔✔Properties of materials with large grain size? - ✔✔- High creep/deformation
resistance under constant loading
- More prone to cracking
✔✔Shear strength of metals is primarily determined by the type of Unit Cell Structure
exhibited. True or False? - ✔✔True.
1) HIGH ATOM PACKED DENSITY FCC structures are very ductile (easy to elongate)
with a low shear strength - Ex.) Lead.
2) LOW ATOM PACKED DENSITY BCC structures have high hardness and a high
shear strength. Ex.) Iron
✔✔Opposite of metal hardness is...? - ✔✔- A hard metal is does not possess
TOUGHNESS.
- Hardness: resistance to deformation
✔✔What is Polymorphism and what does it have to do with metals? - ✔✔- The ability of
a metal to change its unit cell structure through varying temperature ranges.
- Most metals exhibit this property; most important for the study of iron.
✔✔What is the allotropy of Iron? - ✔✔- The change in atomic cell structure dependant
on temperature
- Various physical forms of metals can affect their: melting point, hardness, metal
solubility, and alloying chemistry.
✔✔Properties of pure Iron? - ✔✔- Relatively soft
- Ductile
- Low strength
- Possesses few of the noble properties commonly associated with steel
✔✔Percentage carbon content in Carbon Steels and Cast Iron? - ✔✔Carbon Steels:
Alloys containing 2% or less carbon
Cast Iron: 2% - 6% carbon
✔✔Three grades of Carbon Steel? - ✔✔Low carbon steel: .04% to .30% carbon (mild
steel)
Medium carbon steel: .31% to .60% carbon steel
High carbon steel: .61% to 1-1.50% carbon steel (tool steel)
✔✔Steel properties as carbon content increases? Decreases? - ✔✔1) Hardness and
brittleness increase as carbon content increases
2) Ductility, softness and weldability increase as carbon content decreases
✔✔Weldability is more difficult for higher content carbon steels and even more difficult
for cast-iron metals. True or False? - ✔✔True. The higher carbon content, the harder to
weld.
, ✔✔4 varying factors that determine Iron-Carbon Equilibrium? - ✔✔- The initial
concentration of carbon in the ferrite mixture
- Temperature
- Cooling rate
- Presence of other alloy metals
✔✔Describe Austenite. - ✔✔- Structural name of Iron in the FCC form; also referred to
as 'Gamma Iron'
- Contains dissolved carbon up to 2% concentration
- All quenching heat treatment procedures must begin from the gamma iron phase
- Non-magnetic allotrope of Iron that exists of the critical Eutectoid temperature of 727
deg.C
- This state exists at room temperature in some stainless steels
✔✔Describe Cementite. - ✔✔- The common name for Iron-Carbon in the form of
molecular iron carbide (Fe3C)
- High carbon content and very brittle - normally considered a ceramic in its pure form
✔✔What is the lowest melting point of any iron-carbon mixture according to the Iron-
Carbide Equilibrium diagram? - ✔✔- 1130 deg.C and at 4% carbon concentration;
austenite and cementite are formed simultaneously
✔✔Eutectic Reaction? - ✔✔- No pasty state phase; liquid alloy of iron-carbon changes
directly into solid state austenite and cementite
- Occurs with 4% carbon content and temperature of 1130 deg.C
✔✔Describe Ferrite. - ✔✔- Structural name for iron in the BCC form and occurs at
temperatures below 912 deg.C
- Maximum amount of carbon atoms that ferrite can contain is .025% at 723 deg.C
- Ferrite describes a structure - not a composition
- Above 771 deg.C = Paramagnetic, Below 771 deg.C = Ferromagnetic
✔✔Purpose of the Lower Critical Change Line on the Iron-Carbide Equilibrium diagram?
- ✔✔- The temperature at which an iron alloy of ANY carbon composition returns to a
BCC unit cell structure. The diagram indicates this temperature at 723 deg.C
✔✔What is Pearlite in relation the Iron-Carbide Equilibrium diagram? - ✔✔- Layered
Structure (microscopically) of Ferrite and Cementite
- Appears dark grained in colour and forms in iron-carbon alloys BELOW the lower
critical change line (723 deg.C)
- Occurs in steels and cast irons
- Forms from slow cooling from 723 deg.C and occurs as a Eutectoid reaction
