Materials Flashcards
What are mechanical properties of a material?
Mechanical properties are:
- Ductility
- Hardness
- Hardenability
- Elasticity
- Toughness.
What are the three physical properties of a material?
Physical properties are:
- Density
- Thermal expansion
- Conductivity.
What are chemical properties of a material?
Chemical properties are:
- Oxidisation
- Corrosion
What is steel?
Steel is a ferrous metal which contains varying amounts of carbon (0.05% - 1.4%) as well as other alloying elements.
What is wrought iron and what are it’s properties?
- 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
Explain the microstructure of Steel.
Steel has three phases (ferrite, austenite and cementite). The amount of each and their distribution determines the properties of the steel.
Define a phase.
A phase is a chemically distinct, homogenous part of a material. Ferrite, cementite and austenite are the three phases seen in steel.
What is ferrite?
- A soft, ductile phase
- BCC (Body Centred Cubic)
What is cementite?
- A hard, brittle phase
- BCC (Body Centred Cubic)
- It is a compound and therefore has the chemical
formula Fe3C
What is pearlite?
- A mixture of ferrite and cementite
- Lamella (plate-like) structure
- Alternating thin plates of ferrite and cementite
What is Dead Mild Steel?
- 0.05 - 0.15% Carbon and Iron
- Very soft
- Used in wheel rims, 1800s
What is Mild Steel?
- 0.15 - 0.3% Carbon
- Used in brake nuts and bolts, 1920s
- Tough, malleable
What is High Carbon Steel?
- 0.6 - 0.9% Carbon
- Used in brake cable wire, 1950s
What is Medium Carbon Steel?
- 0.3 - 0.6% Carbon
- Used in brake springs, 1950s
What is Tool Steel?
- 0.9 - 1.4% Carbon
- Used in cutting tools, 1950s
Explain the microstructure of Cast Irons.
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.
Describe ferrite.
Ferrite a soft, ductile phase.
Describe cementite.
Cementite is a hard, brittle phase.
What is the percentage of Carbon found in Cast Iron?
2-5% (Steels have a lower Carbon content than Cast Irons)
Name some non-ferrous metals.
Any metals without iron:
- Brass
- Copper
- Titanium
- Bronze
What are some of the properties of Ceramics?
- Harder than metals
- Better insulators of electricity than metals
- Very high durability
- High temperature stability
Describe the forming process of Rolling.
Produces elongated grains (grainflow) in metals.
NEEDS MORE
What is the indication of the toughness of a material on a stress-strain diagram?
The ultimate tensile stress of the material (just before necking occurs)
Describe the mircostructure of grey cast iron.
Graphite flakes in a pearlite or ferrite matrix.
Describe the annealing process for 0.6% carbon steel.
Heat to red hot and then cool slowly.
What is Eutectoid Steel?
Steel with a composition of 0.83% carbon. Used in brake cable wire in the 1950s.
What is Hypo-eutectoid Steel?
Steel with LESS THAN 0.83% carbon.
- Ferrite and pearlite. The less carbon the more ferrite.
What is Hyper-eutectoid Steel?
Steel with MORE THAN 0.83% carbon
- Pearlite with a cementite network. The more carbon the greater the cementite
Describe the change in microstructure of steels as they go up in carbon content.
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
What is Steel?
A iron and carbon alloy that contains up to 2% carbon. If this carbon content is exceeded it becomes Cast Iron.
What are some of the properties of Cast Iron that make it a desirable engineering material?
- 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
Name the alloying elements of cast irons and their effects.
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
