Materials

Question 1

What are mechanical properties of a material?

Answer 1

Mechanical properties are:

• Ductility
• Hardness
• Hardenability
• Elasticity
• Toughness.

Question 2

What are the three physical properties of a material?

Answer 2

Physical properties are:

• Density
• Thermal expansion
• Conductivity.

Question 3

What are chemical properties of a material?

Answer 3

Chemical properties are:

• Oxidisation
• Corrosion

Question 4

What is steel?

Answer 4

Steel is a ferrous metal which contains varying amounts of carbon (0.05% - 1.4%) as well as other alloying elements.

Question 5

What is wrought iron and what are it’s properties?

Answer 5

• Structure is iron with slag inclusions
• Easily formed
• Used for the rims of wheels and brake shoes, and so its use ended with the end of the external shoe brake

Question 6

Explain the microstructure of Steel.

Answer 6

Steel has three phases (ferrite, austenite and cementite). The amount of each and their distribution determines the properties of the steel.

Question 7

Define a phase.

Answer 7

A phase is a chemically distinct, homogenous part of a material. Ferrite, cementite and austenite are the three phases seen in steel.

Question 8

What is ferrite?

Answer 8

• A soft, ductile phase

- BCC (Body Centred Cubic)

Question 9

What is cementite?

Answer 9

• A hard, brittle phase
• BCC (Body Centred Cubic)
• It is a compound and therefore has the chemical
  formula Fe3C

Question 10

What is pearlite?

Answer 10

• A mixture of ferrite and cementite
• Lamella (plate-like) structure
• Alternating thin plates of ferrite and cementite

Question 11

What is Dead Mild Steel?

Answer 11

• 0.05 - 0.15% Carbon and Iron
• Very soft
• Used in wheel rims, 1800s

Question 12

What is Mild Steel?

Answer 12

• 0.15 - 0.3% Carbon
• Used in brake nuts and bolts, 1920s
• Tough, malleable

Question 13

What is High Carbon Steel?

Answer 13

• 0.6 - 0.9% Carbon

- Used in brake cable wire, 1950s

Question 14

What is Medium Carbon Steel?

Answer 14

• 0.3 - 0.6% Carbon

- Used in brake springs, 1950s

Question 15

What is Tool Steel?

Answer 15

• 0.9 - 1.4% Carbon

- Used in cutting tools, 1950s

Question 16

Explain the microstructure of Cast Irons.

Answer 16

Cast Irons have three phases (ferrite, cementite and pearlite). The shape of graphite helps determine the properties of the cast iron, along with the distribution and amount of each phase.

Question 17

Describe ferrite.

Answer 17

Ferrite a soft, ductile phase.

Question 18

Describe cementite.

Answer 18

Cementite is a hard, brittle phase.

Question 19

What is the percentage of Carbon found in Cast Iron?

Answer 19

2-5% (Steels have a lower Carbon content than Cast Irons)

Question 20

Name some non-ferrous metals.

Answer 20

Any metals without iron:

• Brass
• Copper
• Titanium
• Bronze

Question 21

What are some of the properties of Ceramics?

Answer 21

• Harder than metals
• Better insulators of electricity than metals
• Very high durability
• High temperature stability

Question 22

Describe the forming process of Rolling.

Answer 22

Produces elongated grains (grainflow) in metals.

NEEDS MORE

Question 23

What is the indication of the toughness of a material on a stress-strain diagram?

Answer 23

The ultimate tensile stress of the material (just before necking occurs)

Question 24

Describe the mircostructure of grey cast iron.

Answer 24

Graphite flakes in a pearlite or ferrite matrix.

Question 25

Describe the annealing process for 0.6% carbon steel.

Answer 25

Heat to red hot and then cool slowly.

Question 26

What is Eutectoid Steel?

Answer 26

Steel with a composition of 0.83% carbon. Used in brake cable wire in the 1950s.

Question 27

What is Hypo-eutectoid Steel?

Answer 27

Steel with LESS THAN 0.83% carbon.

- Ferrite and pearlite. The less carbon the more ferrite.

Question 28

What is Hyper-eutectoid Steel?

Answer 28

Steel with MORE THAN 0.83% carbon

- Pearlite with a cementite network. The more carbon the greater the cementite

Question 29

Describe the change in microstructure of steels as they go up in carbon content.

Answer 29

As carbon content increases, the amount of ferrite reduces, and pearlite increases. At 0.83% (Eutectoid) the microstructure is entirely pearlite. Past this point a network of cementite forms in the pearlite.

Ferrite ➡️ Pearlite ➡️ Cementite

Question 30

What is Steel?

Answer 30

A iron and carbon alloy that contains up to 2% carbon. If this carbon content is exceeded it becomes Cast Iron.

Question 31

What are some of the properties of Cast Iron that make it a desirable engineering material?

Answer 31

• It’s a relatively CHEAP material
• Good COMPRESSIVE STRENGTH and RIGIDITY
• Easily MACHINED if correct composition is used
• Good FLUIDITY WHEN MOLTEN means it flows well in castings

Question 32

Name the alloying elements of cast irons and their effects.

Answer 32

Carbon (3-4%)
• Carbon is usually present as cementite, which makes
the cast iron hard and brittle
• If cementite is prevented from forming, or decomposed,
then the material becomes more useful with good
machinability, tensile strength and toughness

Silicon (1-3%)
• Silicon makes cementite unstable and break down into
its components - iron and carbon
• The carbon forms as free graphite which reduces
strength and toughness, but facilitates machining and
vibration-absorbing characteristics

Manganese (0.5-1%)
• Toughens and strengthens the iron
• Combines with unwanted Sulphur to form slag. The rest
dissolves in ferrite

Sulphur (Up to 0.1%)
• Stabilises cementite
• Causes brittleness due to the formation of iron sulphide

Phosphorus (Up to 0.1%)
• Improves fluidity
• Causes brittleness