POWER ENGINEERING 2A2 UPDATED FINAL EXAMS
QUESTIONS AND ANSWERS SURE A+
✔✔What type of weld is used when the strength of the joint is not crucial or complete
sealing of the joint is not necessary? - ✔✔Staggered intermittent fillet welds. In order to
successfully produce these welds, the welder must know the length of the individual
welds and the pitch. The pitch is the distance between the mid point of the adjacent
welds. In many cases the intermittent welds are not staggered, but directly across from
each other, with identical length and pitch.
✔✔What is a plug or slot weld? - ✔✔This involves joining two relatively flat pieces with a
series of small welds that are deposited into drilled plugs or machined slots into on
piece. The piece with the slots or plugs is usually relatively thin and the sides may be
perpendicular or bevelled.
✔✔What are the three types of metallurgy? - ✔✔-Exctractive
-Mechanical
-Physical
✔✔What is extractive metallurgy? What are the different types? - ✔✔The study of
extraction and purification of metal from their ores, which is conducted in several steps.
Each step increases the purity by removing unwanted impurities.
,Pyrometallurgy - melting the ore in a furnace to release the metal.
Hydrometallurgy - dissolving the metal from the ore and recovering it as a powder.
Electrometallurgy - dissolving the metal from the ore with the use of electricity, plate the
metal out of solution.
✔✔What is mechanical metallurgy? - ✔✔It is the study of the techniques and
mechanical forces that shape and make the finished forms of metal. This includes
studying the effects of stress, time and temperature.
✔✔What is physical metallurgy? - ✔✔It is the study of the structure of metals.
Properties of metals are intimately related to their structures. Careful modification of the
structure can produce more desirable and useful properties in a metal.
✔✔Define metals - ✔✔Metals are substances that good conductors of heat and
electricity. They are generally malleable and ductile. They occur naturally in ores in the
form of chemical compounds such as sulphides or oxides. With the exception of the
noble metals, such as platinum and gold, metallic materials tend to react chemically with
the environment and revert to compound forms (corrosion).
✔✔In most metals, what are the three basic arrangements can the atoms of a metal
take? - ✔✔-Face-centered cubic (FCC) - Fourteen atoms form the FCC unit cell. High
ductility, low shear and low tensile strength but good thermal and electrical conductivity.
Gold, aluminum, silver, lead, nickel, and gamma iron (between 910 and 1390 DegC)
-Body-centered cubic (BCC) - Nine atoms are contained in the BCC structure. High
strength, low ductility, and are very resistant to shear deformities. Chromium, tungsten,
molybdenum, vanadium, alpha iron (below 910 DegC), and delta iron (above 1390
DegC)
-Close packed hexagonal (CPH) - Seventeen atoms in the CPH unit cell structure.
Intermediate strength and ductility. Zinc, magnesium, cadmium, and titanium.
✔✔How does grain size effect the properties of metals? - ✔✔Smaller grain size
increases tensile strength and ductility, while larger grain size tends to resist creep and
deformation under constant loading but may be more prone to cracking. At the atomic
level, the shear strength of metals is determined primarily by the type of unit cell
structure exhibited.
✔✔What is polymorphism? - ✔✔It is defined as the ability of metal to change to a
different unit cell structure depending on its temperature. Most metals and alloys exhibit
this, including iron.
, ✔✔What is allotropy of iron? - ✔✔The change of the unit cell structure, dependent on
temperature, is known as the allotropy of iron. The metal can exist in different physical
forms that affect its melting point, hardness, metal solubility, and alloying chemistry.
✔✔What is the difference between carbon steel and cast iron? How many grades are
there? - ✔✔Carbon steels are alloys containing 2% or less carbon, where cast iron
contains from 2% to 6% carbon.
Carbon steel is divided into 3 grades
Low - Max carbon content 0.30%
Medium - Carbon content 0.30% to 0.60%
High - Carbon content 0.60% to 1.50%
✔✔Iron-carbon equilibrium in steel is determined by what? - ✔✔-Initial concentration of
carbon in the ferrite mixture
-Temperature
-Cooling rate
-Presence of other alloying metals
✔✔What is annealing? - ✔✔Annealing processes heat the steel to just above the
transition temperature required to produce austenite, hold it at that temperature to allow
uniform crystal restructuring, and then cool it very slowly to room temperature at a
maximum rate of 38 DegC/hour.
Annealing high carbon steels can induce brittleness by allowing larger grain formations
which reduces toughness and ductility. Heat soaking for too long a period encourages
grain enlargement in any annealing procedure and increases brittleness.
✔✔What is sub-critical annealing? - ✔✔Sub-critical annealing, or process annealing, is
a similar process to annealing, but the steel is heated to just below it austenite
transformation temperature. It is then cooled slowly to reduce internal stresses in the
metal.
✔✔Why would you normalize metal? - ✔✔Carbon steels containing less than 0.8%
carbon are normalized to:
- Relieve internal stresses from welding, machining, or forging
- Refine grain size and promote uniform composition to increase strength and
toughness
- Improve machinability
✔✔What is normalizing? - ✔✔Normalizing raises the temperature of the steel to approx
55 DegC above the upper transition temperature into the austenite region. The steel is
held at that temperature just long enough to ensure even heating throughout. It is
allowed to cool in still air at a rate not exceeding 100 DegC/hour. If a furnace is used,
QUESTIONS AND ANSWERS SURE A+
✔✔What type of weld is used when the strength of the joint is not crucial or complete
sealing of the joint is not necessary? - ✔✔Staggered intermittent fillet welds. In order to
successfully produce these welds, the welder must know the length of the individual
welds and the pitch. The pitch is the distance between the mid point of the adjacent
welds. In many cases the intermittent welds are not staggered, but directly across from
each other, with identical length and pitch.
✔✔What is a plug or slot weld? - ✔✔This involves joining two relatively flat pieces with a
series of small welds that are deposited into drilled plugs or machined slots into on
piece. The piece with the slots or plugs is usually relatively thin and the sides may be
perpendicular or bevelled.
✔✔What are the three types of metallurgy? - ✔✔-Exctractive
-Mechanical
-Physical
✔✔What is extractive metallurgy? What are the different types? - ✔✔The study of
extraction and purification of metal from their ores, which is conducted in several steps.
Each step increases the purity by removing unwanted impurities.
,Pyrometallurgy - melting the ore in a furnace to release the metal.
Hydrometallurgy - dissolving the metal from the ore and recovering it as a powder.
Electrometallurgy - dissolving the metal from the ore with the use of electricity, plate the
metal out of solution.
✔✔What is mechanical metallurgy? - ✔✔It is the study of the techniques and
mechanical forces that shape and make the finished forms of metal. This includes
studying the effects of stress, time and temperature.
✔✔What is physical metallurgy? - ✔✔It is the study of the structure of metals.
Properties of metals are intimately related to their structures. Careful modification of the
structure can produce more desirable and useful properties in a metal.
✔✔Define metals - ✔✔Metals are substances that good conductors of heat and
electricity. They are generally malleable and ductile. They occur naturally in ores in the
form of chemical compounds such as sulphides or oxides. With the exception of the
noble metals, such as platinum and gold, metallic materials tend to react chemically with
the environment and revert to compound forms (corrosion).
✔✔In most metals, what are the three basic arrangements can the atoms of a metal
take? - ✔✔-Face-centered cubic (FCC) - Fourteen atoms form the FCC unit cell. High
ductility, low shear and low tensile strength but good thermal and electrical conductivity.
Gold, aluminum, silver, lead, nickel, and gamma iron (between 910 and 1390 DegC)
-Body-centered cubic (BCC) - Nine atoms are contained in the BCC structure. High
strength, low ductility, and are very resistant to shear deformities. Chromium, tungsten,
molybdenum, vanadium, alpha iron (below 910 DegC), and delta iron (above 1390
DegC)
-Close packed hexagonal (CPH) - Seventeen atoms in the CPH unit cell structure.
Intermediate strength and ductility. Zinc, magnesium, cadmium, and titanium.
✔✔How does grain size effect the properties of metals? - ✔✔Smaller grain size
increases tensile strength and ductility, while larger grain size tends to resist creep and
deformation under constant loading but may be more prone to cracking. At the atomic
level, the shear strength of metals is determined primarily by the type of unit cell
structure exhibited.
✔✔What is polymorphism? - ✔✔It is defined as the ability of metal to change to a
different unit cell structure depending on its temperature. Most metals and alloys exhibit
this, including iron.
, ✔✔What is allotropy of iron? - ✔✔The change of the unit cell structure, dependent on
temperature, is known as the allotropy of iron. The metal can exist in different physical
forms that affect its melting point, hardness, metal solubility, and alloying chemistry.
✔✔What is the difference between carbon steel and cast iron? How many grades are
there? - ✔✔Carbon steels are alloys containing 2% or less carbon, where cast iron
contains from 2% to 6% carbon.
Carbon steel is divided into 3 grades
Low - Max carbon content 0.30%
Medium - Carbon content 0.30% to 0.60%
High - Carbon content 0.60% to 1.50%
✔✔Iron-carbon equilibrium in steel is determined by what? - ✔✔-Initial concentration of
carbon in the ferrite mixture
-Temperature
-Cooling rate
-Presence of other alloying metals
✔✔What is annealing? - ✔✔Annealing processes heat the steel to just above the
transition temperature required to produce austenite, hold it at that temperature to allow
uniform crystal restructuring, and then cool it very slowly to room temperature at a
maximum rate of 38 DegC/hour.
Annealing high carbon steels can induce brittleness by allowing larger grain formations
which reduces toughness and ductility. Heat soaking for too long a period encourages
grain enlargement in any annealing procedure and increases brittleness.
✔✔What is sub-critical annealing? - ✔✔Sub-critical annealing, or process annealing, is
a similar process to annealing, but the steel is heated to just below it austenite
transformation temperature. It is then cooled slowly to reduce internal stresses in the
metal.
✔✔Why would you normalize metal? - ✔✔Carbon steels containing less than 0.8%
carbon are normalized to:
- Relieve internal stresses from welding, machining, or forging
- Refine grain size and promote uniform composition to increase strength and
toughness
- Improve machinability
✔✔What is normalizing? - ✔✔Normalizing raises the temperature of the steel to approx
55 DegC above the upper transition temperature into the austenite region. The steel is
held at that temperature just long enough to ensure even heating throughout. It is
allowed to cool in still air at a rate not exceeding 100 DegC/hour. If a furnace is used,
