Engineering Alloys Flashcards
What is a ferrous alloy
An alloy with iron in it (at least 50%)
What elements are required to make a steel
Iron and carbon
(1% carbon maximum)
Why are ferrous alloys used
- Relatively cheap
- Iron is abundant
- Extremely versatile
On the tree what comes after ferrous alloys
Steels and cast irons
Name the different sections of the iron-iron carbide diagram
Check answer
What is the symbol for ferrite
Alpha
What does alpha represent
Ferrite
Where on the graph does it switch from steels to cast irons
2.14 composition
Formula for cementite
Fe3c
What is Fe3C
Cementite
What is the symbol for austenite
Gamma
What does gamma represent
Austenite
Symbol for the other ferrite
Delta
What does delta represent
The other ferrite
What is the structure of alpha ferrite
BCC body centred cubic
What is the structure of gamma austenite
FCC face centred cubic
What is the structure of delta ferrite
BBC
Where is the maximum solubility of carbon into alpha ferrite on the diagram
0.022
What is the eutectoid reaction in steels
Austenite <-> alpha ferrite + Fe3C
What effect does increment of C have in steel have on its strength hardness toughness and ductility
As the amount of carbon increases, strength and hardness also increase while toughness and ductility decrease
What is a maraging steel
Martensitic + aging
Low carbon but ultra high strength due to Ni (usually) forming precipitates
Used for engine components such as crank shafts and gears
What is pearlite?
Alpha ferrite + Fe3C
What is Eutectic
L <~> gamma + Fe3C
What is eutectoid
Gamma <~> alpha ferrite + Fe3C (pearlite)
What are eutectoid steels
Has exactly the amount of carbon as at the eutectoid point
Draw a graph cooling from austenite (gamma)
Draw ya bitch
Draw pearlite
U got this
What are hypoeutectoid steels
Carbon content is lower than the eutectoid point
What are hypereutectoid steels
Carbon content above the eutectoid point
What are plan carbon steels divided into
Low carbon <0.25 wt. % C
Medium carbon 0.25 - 0.6 wt. % C
High carbon > 0.6 wt. % C
As strength is increased ductility decreases
Features of solid phases of phase diagram
Ferrite - bbc structure, relatively soft
Fe3C - very hard but brittle
Austenite - fcc structure, non-magnetic
What is the influence of alloying elements on the eutectoid temp
Some shift temp up - stability of austenite decreases
Some shift temp down - stability of austenite increases
How are low carbon steels strengthened
Cold working
Why are low carbon steels unresponsive to heat treatments?
Due to the carbon content being less than 0.25wt.%
What are the microstructures of low carbon steels (made out of)
Ferrite and very little pearlite
The properties of low carbon steels
- soft and weak
- high ductility and toughness
What are low c steels used for?
Sheet forming
Car body parts
What are high strength low alloy steels (HSLA)?
A group of low c steels
Contain other alloying elements such as Cu, Ni, V, Mo in concentrations as high as 10 wt.%
Strength of HSLA’s
Higher strengths than plain c steels
Strengthened by heat treatment
Properties of HSLA’s (not strength)
Ductile
Formable
Machinable
What are HSLA’s used for?
Structural components of bridges, towers
Pressure vessels
How to improve the mechanical properties of medium c steels?
Heat treatment
Additions of Cr, Ni, Mo increase the response of heat treatments
Applications of medium c steels
Railway wheels and tracks
Gears
Crankshafts
Properties of 0.3 wt.% c steels (medium)
-Stronger than low carbon steels
- Used for structural applications such as steel plate for ships
High ductility but can fail in a brittle manner
Properties of 0.4 wt.% carbon steels (medium)
- medium carbon content (50% pearlite)
- medium strength and can be hardened by quenching and tempering
- used for shafts, gears, and other machine components
Properties of high carbon steels?
Hardest, strongest and lest ductile of plain c steels
How are high c steels made stronger
Heat treatment (almost always done)
What r high c steels used for?
Capability to hold a sharp edge
Superior tensile strength
What are tool and die steels
High carbon steel alloys usually containing Cr, V, W and Mo
Forms very wear resistant carbide compounds
0.6 wt.% c steels
High hardness but low toughness
Used for knives chisels
Can be hardened by quenching and tempering
What is weldability
The ease of welding without development of weld defects such as thermal cracks
Regions close to the weld normally experience microstructural and properties alterations
Related to hardenability
Hardenability
The depth to which a specific ferrous alloy may be hardened by the formation of martensite upon quenching
How does alloying and carbon content affect hardenability
Alloying normally improves hardenability
Lower the carbon content the poorer the hardenability
Machinability
Determined by different aspects related to the cutting performance among which, tool life, cutting speed, power consumption, quantity of surface finish
Tool steels
High C steels with the addition of carbide forming elements
Commonly used for manufacturing tools used in cutting, forming and shaping operations
Must be resistant to softening at high temps
Resistant to wear
Toughness to absorb shock loading
What are the 3 main categories of stainless steels
Martensitic
Ferritic
Austenitic
