Flashcards in Objective 02: Iron-Carbon Equilibrium Diagram Deck (27)
What are the properties of pure iron?
Relatively soft, ductile element with low strength
What is the major aim of the Science of Steelmaking?
To attempt to understand and control the phase changes of iron, in the presence of carbon and other alloying metals, in order to make high-strength steels for industry
Steel alloy containing 2% or less carbon
Steel alloy containing 2% - 6% carbon
What are the 3 grades of Carbon Steel?
1. Low (0.30% C max)
2. Medium (0.30 - 0.60% C max)
3. High (0.60 - 1.00% C max)
What are the factors that affect the physical properties of Carbon Steel?
1. The form that Carbon assumes in the iron matrix, i.e. single atoms, graphite flakes, spheres, or molecular combinations, e.g. cementite
2. The carbon atom's final resting place, i.e. inside the unit cell structures or in the exterior intra-granular spaces
3. The Carbon concentration
How does the amount of carbon affect steel?
1. As carbon content increases, hardness and brittleness increase
2. As carbon content decreases, softness, ductility and weldability increase
What factors determine the iron-carbon equilibrium in steel?
1. Initial concentration of carbon in the ferrite mixture
3. Cooling rate
4. Presence of other alloying metals
What does the area below the Solidus Line represent in an Iron-Carbon Equilibrium Diagram?
Solid state phase
What does the area above the Liquidus Line represent in an Iron-Carbon Equilibrium Diagram?
Molten state phase
What does the area between the Solidus and Liquidus lines represent in an Iron-Carbon Equilibrium Diagram?
Pasty state phasese where the mixtures exist in a solid-liquid state at the corresponding temperature
Structural name of iron in a unit cell of FCC form that can contain dissolved carbon, up to 2%, i.e. gamma iron
What phase must all quenching heat treatment procedures begin with?
Iron-Carbon in the form of molecular iron carbide (Fe3C)
Eutectic Reaction Point
The point at which liquid alloy changes directly into solid austenite and cementite without going through a pasty state phase
When is the only point that a Eutectic Reaction takes place?
An alloy composition of 4.0% carbon and a temperature of 1130ºC
Structural name for iron in the BCC form that can contain a max of 0.025% of carbon at 723ºC
Lower Critical Change Line
Temperature at which an iron alloy of any carbon composition returns to BCC, i.e. 723ºC
Dark-grained, layered structure of ferrite and cementite that forms in iron-carbon alloys below the lower critical change line.
Peritectic Reaction Point
The point where liquid delta iron in BCC form changes directly into solid austenite without going through a pasty state phase, at 1492ºC
Low and Medium Carbon Steels (below 0.8% carbon) that contains ferrite and pearlite
At room temperature, what are always the components of Hypoeutecoid Steels and the properties they bestow?
1. Ferrite - toughness and ductility
2. Pearlite - hardness
Steel having 0.8% carbon that is 100% pearlite
What is an application of Eutecoid Steel?
Steel having above 0.8% carbon and at 723ºC consists of a mixture of cementite and pearlite
What are the properties of Hypereutectoid Steel?
2. High Tensile Strength