phase degine

8/14/2019 phase degine

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Chapter 9 - 1

ISSUES TO ADDRESS... When we combine iron and carbon what kinds of steels do we get?

In particular, if we specify the composition, what kinds ofmicrostructures are created & how do they control the properties

Steel is the most important structural material created by humans

so what is the terminology of the Fe-Fe3C diagram & microstructures

Chapter 9: Phase Diagrams III:

The Fe Fe3C Phase Diagram

Class 14 Chapter 9: Phase Diagrams Fe-Fe3C- Topic #5.3

What are these microstructures, how are they created, what are

their properties, and what applications are they used for?


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Chapter 9 -

Fe Fe3C Phase Diagram

Concept Map


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Chapter 9 -

Fe Fe3C Phase Diagram Cast Irons & Steels


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Chapter 9 -

The Fe Fe3C Phase Diagram - Steels

Year 1781

Lower Tm;

higher %C

Year 1891

Higher Tm;

lower %C

Cast Irons

Steels


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Chapter 9 -

The Worlds First First Cast Iron Bridge, 1-1-1781

Ironbridge, Shropshire, England


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Chapter 9 -

Monadnock Building, 1891-1893 Chicago

The First Steel Skyscraper, AT Least of It Was


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Chapter 9 -

Where is Pearlite & Where Does It Come From?


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Chapter 9 -

Steel Microstructures The Big Picture


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Chapter 9 - 9

Iron-Carbon (Fe-C) Phase Diagram and Steel Microstructures

2 importantpoints

- Eutectoid (B):

+Fe3C

- Eutectic (A):

L +Fe3C

Adapted from Fig. 9.24,

Callister & Rethwisch 8e.

Fe3

C

(cem

entite)

1600

1400

1200

1000

800

600

4000 1 2 3 4 5 6 6.7

L

(austenite)

+L

+Fe3C

+Fe3C

+

(Fe) C, wt% C

1148C

T(C)

727C = Teutectoid

4.30

Result: Pearlite =alternating layers of

and Fe3C phases

120 m

(Adapted from Fig. 9.27,

Callister & Rethwisch 8e.)

0.76

B

AL+Fe3C

Fe3C (cementite-hard)

(ferrite-soft)


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Chapter 9 -

General Properties:

Ferrite - BCC Fe 0.2wt% C max. Fairly Soft.Austenite - FCC Fe can have more C. Ductile.Cementite Fe3C - Hard ceramic.

Terminology: YY XXX steel

First two or three numbers give steel alloy type

10xx is plain carbon steel (no alloy elements)

43xx is low alloy steel (.5-1% Ni, Cr, Mo)

Second 2 or 3 numbers give %C content x 100

YY80 has 0.80 wt% C

YY100 has 1.0 wt.% C

Steel Terminology & Phase Properties

727 C


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Chapter 9 -

Eutectoid Steel Microstructure


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Chapter 9 -

Hypoetutectoid Steel Microstructure Proeutectoid Ferrite + Pearlite


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Chapter 9 -

Hyperetutectoid Steel Microstructure Proeutectoid Carbide + Pearlite


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Chapter 9 -

.

..

Effect of C on Microstructure & Properties


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Chapter 9 -

1060 (0.60wt% C) Hypoeutectoid Steel Microstructure: Te +1oC

proeutectoid ferritepearlite

100 mHypoeutectoid

steel


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Chapter 9 -

1060 (0.60wt% C) Hypoeutectoid Steel Microstructure: Te -1oC

proeutectoid ferritepearlite

100 mHypoeutectoid

steel


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Chapter 9 - 17

Hypereutectoid Steel

Fe3

C

(cementite)

1600

1400

1200

1000

800

600

4000 1 2 3 4 5 6 6.7

L

(austenite)

+L

+Fe3C

+Fe3C

L+Fe3C

(Fe) C, wt%C

1148C

T(C)

Adapted from Figs. 9.24

and 9.32,Callister &

Rethwisch 8e. (Fig. 9.24

adapted from Binary AlloyPhase Diagrams, 2nd

ed., Vol. 1, T.B.

Massalski (Ed.-in-Chief),

ASM International,

Materials Park, OH,

1990.)

(Fe-C

System)

0.76 C0

Fe3C

Adapted from Fig. 9.33, Callister & Rethwisch 8e.

proeutectoid Fe3C

60mHypereutectoidsteel

pearlite

pearlite


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Chapter 9 -

Activity Identify and Describe Microstructural Components in

Steels that are Hypoeutectoid, Eutectoid, & Hypereutectoid

For each micrograph

identify each microstructural

component by:

1) Labeling each one,

2) Describing each one, &

3) Stating how each got there

Describe components & how they got there

Print labels and draw arrows

Describe components & how they got there Describe components & how they got there

Print labels and draw arrowsPrint labels and draw arrows


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Chapter 9 -

Activity Drawing Steel Microstructures

Teutectoid + 1 C

Teutectoid - 1 C

727C

0.76

Describe how the microstructure developed

Teutectoid + 1 C Teutectoid + 1 C

Teutectoid - 1 C

Teutectoid - 1 C


Describe how the microstructure developedDescribe how the microstructure developed



1020 steel

727C

1076 steel 10120 steel


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Chapter 9 - 20

The phase diagram of steel helps explain microstructure & properties:

-- number and types of phases present,

-- composition of each phase,

-- weight fraction of each phase

Given the temperature and composition of the system.

The microstructures and associated properties of steel depend on

-- its composition, and

-- the manner in which it was cooled.

For steel the most important phase transformation is the eutectoid

Summary

Steels with %C less thatn, equal to, and greater than the euectoidcomposition are call hypoeutectoid, eutectoid, & hypereutectoid

The microstructure of hypoeutectid steels contain proeutecoid ferrite &

the microstructure of hypereuteoid steels contain proeutectoid carbide &

the microstructure of eutectoid steel contains pearlite


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Chapter 9 -

Homework #14 Fe Fe3C Phase Diagram Phases and Microstructures

1. For a 0.30 wt% C steel (1030) at 728C and then at 726C, identify the phases present, the chemical composition of each

phase, the fraction of each phase, and draw the microstructure and label the components of the microstructure.

2. For a 1.20 wt% C steel (10120) at 728C and then at 726C, identify the phases present, the chemical composition of each

phase, the fraction of each phase, and draw the microstructure and identify the components of the microstructure

3. The microstructure of the reinforcing rod of Frank Lloyds Fallingwater house in Pennsylvania was studied and is shown

at the right. Specify the microstructural components present and the wt% C in the steel.

4. The properties of steels are controlled by the carbon content, the alloy content, and the thermal treatment. When a steel

is cooled faster from the gamma (austenite region) below the eutectoid temperature,the lamellar, alternating platelets of

ferrite and carbide in pearlite get thinner and are more closely spaced. Why do you think that this is so? What do youthink will happen to the strength and ductility of the steel which has been cooled faster and why do you think that is so?


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Chapter 9 -

Points of Reflection on Todays Class

Please briefly describe your insights on the following points from todays class.

Point of Interest: Describe what you found most interesting in todays class.How Interesting? (circle) Little Bit 1 2 3 4 5 Very Much

Muddiest Point: Describe what was confusing or needed more detail.How Muddy? (circle) Little Bit 1 2 3 4 5 Very Much

Learning Point: Describe what you learned about how you learn?

Letter + 4 digit number ______________ F M

Class Topic: _______________________Date: ________________

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