Objective 02: Iron-Carbon Equilibrium Diagram Flashcards Preview

2A2-4: Metallurgy > Objective 02: Iron-Carbon Equilibrium Diagram > Flashcards

Flashcards in Objective 02: Iron-Carbon Equilibrium Diagram Deck (27)
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1

What are the properties of pure iron?

Relatively soft, ductile element with low strength

2

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

3

Carbon Steel

Steel alloy containing 2% or less carbon

4

Cast Iron

Steel alloy containing 2% - 6% carbon

5

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)

6

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

7

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

8

What factors determine the iron-carbon equilibrium in steel?

1. Initial concentration of carbon in the ferrite mixture
2. Temperature
3. Cooling rate
4. Presence of other alloying metals

9

What does the area below the Solidus Line represent in an Iron-Carbon Equilibrium Diagram?

Solid state phase

10

What does the area above the Liquidus Line represent in an Iron-Carbon Equilibrium Diagram?

Molten state phase

11

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

12

Austenite

Structural name of iron in a unit cell of FCC form that can contain dissolved carbon, up to 2%, i.e. gamma iron

13

What phase must all quenching heat treatment procedures begin with?

Austenite

14

Cementite

Iron-Carbon in the form of molecular iron carbide (Fe3C)

15

Eutectic Reaction Point

The point at which liquid alloy changes directly into solid austenite and cementite without going through a pasty state phase

16

When is the only point that a Eutectic Reaction takes place?

An alloy composition of 4.0% carbon and a temperature of 1130ºC

17

Ferrite

Structural name for iron in the BCC form that can contain a max of 0.025% of carbon at 723ºC

18

Lower Critical Change Line

Temperature at which an iron alloy of any carbon composition returns to BCC, i.e. 723ºC

19

Pearlite

Dark-grained, layered structure of ferrite and cementite that forms in iron-carbon alloys below the lower critical change line.

20

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

21

Hypoeutectoid Steels

Low and Medium Carbon Steels (below 0.8% carbon) that contains ferrite and pearlite

22

At room temperature, what are always the components of Hypoeutecoid Steels and the properties they bestow?

1. Ferrite - toughness and ductility
2. Pearlite - hardness

23

Eutecoid Steel

Steel having 0.8% carbon that is 100% pearlite

24

What is an application of Eutecoid Steel?

Railway rails

25

Hypereutectoid Steel

Steel having above 0.8% carbon and at 723ºC consists of a mixture of cementite and pearlite

26

What are the properties of Hypereutectoid Steel?

1. Hardness
2. High Tensile Strength

27

What are some applications of Hypereutectoid Steel?

Tools such as axes and chisels