Engineering 45
Metal Phase
Transforms (2)
Bruce Mayer, PE
Registered Electrical & Mechanical Engineer
BMayer@ChabotCollege.edu
Engineering-45: Materials of Engineering
1
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Learning Goals.1 – Phase Xforms
 Transforming one phase into another is
a Function of Time:
Fe
g
(Austenite)
C
FCC
Fe C
3
Eutectoid
transformation (cementite)
+
a
(ferrite)
(BCC)
 Understand How time & TEMPERATURE
(t & T) Affect the Transformation Rate
 Learn how to Adjust the Transformation
RATE to Engineer NONequilibrium
Structures
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Learning Goals.1 – PhaseX2
 Transforming one phase into another is
a Function of Time:
Fe
g
(Austenite)
C
FCC
Fe C
3
Eutectoid
transformation (cementite)
+
a
(ferrite)
(BCC)
 Understand the Desirable mechanical
properties of NONequilibrium-phase
structures
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Recall T-T-T Diagram
Iron-Carbon
 Adds time to Phase
Diagram
Engineering-45: Materials of Engineering
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4340 → 0.4C, 0.8Cr,
0.7Mn, 0.3Mo, 1.8Ni,0.2Si
 Cr, Ni, Mo, Si, Mn retard
g  a + Fe3C Xform
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
T-T-T Diagram Usage

Consider the Fe-C Eutectoid
IsoThermal Transformation diagram

Use the Diagram to
Find Steel-Morphology
Based on
Heat Treatments:
Case
I
II
III
Rapid Hold Rapid Hold Rapid
Cool To Time Cool To Time Cool To
350 °C
250 °C
650 °C
10 000s
100s
20s
Engineering-45: Materials of Engineering
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Troom
Troom
400 °C
1 000s
Troom
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Case-I: Cool & Hold @ 350C
 Tstart = 760 °C
1. Quench To Point-A
 C0 = 0.77 wt-%C
800
Austenite (stable)
T(°C)
A
600
A
400
1
S
200 M + A
M+A
M+A
10
10-1
100%B
0%
50%
90%
103
100% Bainite
10 5 time (s)
Engineering-45: Materials of Engineering
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•
2
100%A
100% SuperCooled
Austenite
2. Hold at 350C for
2.8hrs
P
B
•
Enter, Pass Thru,
and Exit A→B
Xform-Band to
arrive at 100%
Bainite
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Case-I: Cool & Hold @ 350C
 Tstart = 760 °C
3. Quench To Room
Temperature to
 C0 = 0.77 wt-%C
800
T(°C)
A
600
A
P
S
B
400
100%B
100%A
200 M + A
M+A
M+A
10
10-1

0%
50%
90%
Since Bainite is
STABLE at 350C
and Troom, No
Additional Xform
Occurs
Final State =
100% Bainite
3 100% Bainite
103
Engineering-45: Materials of Engineering
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•
Austenite (stable)
10 5 time
(s)
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Case-II: Cool & Hold @ 250C
 Tstart = 760 °C
1. Quench To Point-A
•
 C0 = 0.77 wt-%C
800
Austenite (stable)
T(°C)
A
S
A
400
1
100%A
B
2
200
M+A
M+A
M+A
10
10 -1
0%
50%
90%
M + trace of A
10 3
10 5 time (s)
Engineering-45: Materials of Engineering
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2. Hold at 250C for
1.7 minutes
P
600
100% SuperCooled
Austenite
•
Do NOT Reach the
Xform Band
•
Still have 100%
SuperCooled
Austenite
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Case-II: Cool & Hold @ 250C
 Tstart = 760 °C
 C0 = 0.77 wt-%C
800
•
Austenite (stable)
T(°C)
A
600
A
P
S
B

400
100%A
200
M+A
M+A
M+A 3
10
10 -1
0%
50%
90%
M + trace of A
10 3
10 5 time (s)
Engineering-45: Materials of Engineering
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3. Quench To Room
Temperature to
Enter, Pass Thru,
and Exit the
Martensite
Formation Band
Final State =
Almost 100%
Martensite
•
Small Amount of
Austentite is
“Frozen” in place
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Case-III: Cool 650C→400C→20C
 Tstart = 760 °C
1. Quench To 650C
•
 C0 = 0.77 wt-%C
800
T(°C)
Austenite (stable)
A
100%A
600
1
A
400
50%P, 50%A
200 M + A
M+A
M+A
10
10-1
50%P, 50%A
P
S
B
•
50%P, 50%B
0%
50%
90%
Engineering-45: Materials of Engineering
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2. Hold at 650C for
20s
2
103
100% SuperCooled
Austenite
105 time
(s)
Enter the A→P
Xform Band and
Reach 50% Pearlite
Condition
– Still have 50%
SuperCooled
Austenite
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Case-III: Cool 650C→400C→20C
 Tstart = 760 °C
 C0 = 0.77 wt-%C
800
T(°C)
A
600
A
400
50%P, 50%A
200 M + A
M+A
M+A
10
10-1
50%P, 50%A
P
S
B
50%P, 50%B
•
0%
50%
90%
103
Engineering-45: Materials of Engineering
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•
Austenite (stable)
100%A
3
3. Quench
650C → 400C
105 time
(s)
50% PEARLITE is
Thermodynamically
Stable at this This
Temperature, and so it
DOES NOT CHANGE
To The 50%
SuperCooled Austenite
it Looks like a
DIRECT Quench
to the 400C Point
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Case-III: Cool 650C→400C→20C

 Tstart = 760 °C
Summary at This Point
 C0 = 0.77 wt-%C
800
T(°C)
Austenite (stable)
A
100%A
600
A
400
50%P, 50%A
200 M + A
M+A
M+A
10
10-1
•
50% Pearlite is Stable
Thermodyamically
•
50% Austenite
SuperCooled to 400C at
Essentially ZERO Time
50%P, 50%A
P
S
B 4
50%P, 50%B
4. Hold at 400C for 1.7hr
•
0%
50%
90%
103
105 time
(s)
For the 50% Austenite
– Enter, Pass Thru, and Exit
A→B Xform Band to arrive
at 100% Bainite
 i.e., ALL the Austenite
Transforms to Bainite
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Case-III: Cool 650C→400C→20C
 Tstart = 760 °C
5. Quench
400C → Troom
 C0 = 0.77 wt-%C
800
T(°C)
Austenite (stable)
A
100%A
600
A
50%P, 50%A
P
S
B
50%P, 50%A
200 M + A
M+A
M+A
10
10-1
•
3
Engineering-45: Materials of Engineering
105 time
Arrive at the FINAL
Condition of
– 50% Pearlite
– 50% Bainite
0%
50%
90%
510
MAINTAINS the
Transformations:
– Austenite → Pearlite
– Austenite → Bainite
50%P, 50%B
400
13
•
(s)
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Practical Considerations
 It is VERY Difficult to
Rapidly Cool a 1-ton
Slab of Steel From g
Temperatures (750C
 1400F) to Bainite
Temp+HoldTime
(400C, 1hr)
 Almost all cooling is
CONTINUOUS:
• 750C → Troom
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Practical Considerations cont.1.
 Thus in C-Steel
PRODUCTION, NO
Bainite Forms EVER
 Although QuenchTo-IntermediateTemp HeatTreatments are
Impractical; The
CONTINOUScooling RATE can
be Controlled
Engineering-45: Materials of Engineering
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NO Martensite
NO Pearlite
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Practical Considerations cont.2
 Quenches
• Water → Fastest
– 100% Martensite
• Hot Oil → Higher
quench Temp,
~200C
– Terminate in
Martensite Band with
Residual Austenite
 Prevents Cracking
 Xforms to ~100%
Martensite When
Cooled to Troom
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Practical Considerations cont.4
 Controlled
Cooling Rates
• Air Cooled → High
Cooling Rate
• Furnace cooled →
Low Cooling Rate
– Used to AVOID
Martensite Formation
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Summary T-T-T Diagram
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Tempered MartenSite
 As Quenched,
Martensite is Hard &
Strong, but
Impractically BRITTLE
 The Ductility Can be
Improved by
TEMPERING
(heating) at a
SubEutectiod Temp
Temp
Martensite (100% BCT ) Med

 a  Fe3C
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Martensite Tempering
 Reduces Brittleness Of Martensite
 Reduces internal stress caused by quenching
TS(MPa)
YS(MPa)
1800
1400
TS
YS
%AR
1200
1000
60
50
40
30
%AR
800
200
9 mm
1600
400
600
Tempering T (°C)
Fe3C particles
• Produces Extremely Small
Fe3C particles Surrounded by a Matrix
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
a
Mechanical Prop: Fe-C System (1)
 Affect of Carbon Content
TS(MPa)
1100
YS(MPa)
Co<0.77wt%C
Hypoeutectoid
Hypo
Hyper
Co>0.77wt%C
Hypereutectoid
Hypo
%EL
Hyper
80
100
900
hardness
700
40
50
500
0
0.5
1
wt%C
0
0
0.5
• As C↑: u↑, y↑, %EL↓ Toughness ↓
Engineering-45: Materials of Engineering
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0.77
0
0.77
300
1
Impact energy (Izod, ft-lb)
Pearlite (med)
ferrite (soft)
Pearlite (med)
Cementite
(hard)
wt%C
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Mechanical Prop: Fe-C System (2)
 Fine vs Coarse Pearlite vs Spheroidite
Hypo
Hyper
90
Hypo
Hyper
240
fine
pearlite
coarse
pearlite
spheroidite
160
80
0
0.5
1
wt%C
Ductility (%AR)
Brinell hardness
320
spheroidite
60
coarse
pearlite
fine
pearlite
30
0
0
1
0.5
wt%C
• Hardness: Fine > Coarse > Spheroidite
• Ductility: Spheroidite >> Coarse > Fine
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Mechanical Prop: Fe-C System (3)
 Fine Pearlite vs
Martensite
Brinell hardness
• Hardness: Martensite
>>Fine Pearlite
Hypo
600
0
0
23
martensite
400
200
Engineering-45: Materials of Engineering
Hyper
fine pearlite
0.5
wt%C
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
1
Processing Flow Chart
Austenite (g)
slow
cool
Pearlite
Moderate Cool
Bainite
Martensite
T Martensite
bainite
fine pearlite
coarse pearlite
spheroidite
Martensite
(BCT phase
diffusionless
transformation)
reheat
Ductility
Strength
(a + Fe3C layers + a (a + Fe3C plates/needles)
proeutectoid phase)
rapid
quench
Tempered
Martensite
(a + very fine
Fe 3C particles)
General Trends
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
PowerPoint Example
 Work Prob 10.22

For 1.13 wt%C in
Fe-C system find
a) Transform Path for
6.2% ProEutectoid
(BEFORE
Euctectoid)
• This is a
Cementite &
HYPEReutectoid
93.8% Pearlite
phase transformation
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
(a) 93.8% Pearlite
 Use PHASE Diagram for Fractions
880C
1.13-0.76
•
6.7 – 1.13
By Lever Rule,
The Before
727C Cementite
1.13  0.76
WFe3C ' 
6.7  0.76
0.37
WFe3C ' 
5.94
WFe3C '  6.23%
1.13
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
(a) 93.8% Pearlite
 Turn ALL the 93.8% ProE Austenite into Pearlite
Form 6.2% ProE C
Remaining A
goes to Pearlite
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
(b) 50%-50% Pearlite-Bainite
•
Freeze-in 50%
Pearlite; Rest=A
Convert all of
Remaining-A
into Bainite
– Cannot Let ANY
Cementite, C, Form
•
•
Engineering-45: Materials of Engineering
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Must Start above
880C to Prevent
ProE Cementite
Freeze in 50% P,
with 50% still as
Austenite
Convert 100% of
Remaining A to
Bainite
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
(c) 100% Martensite
Must Miss “Nose”
•
•
Engineering-45: Materials of Engineering
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Must Start
above 880C to
Prevent ProE
Cementite
Must Avoid
ALL OTHER
Phases
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
(c) 100% Tempered Martensite
•
•
Start with 100%
Martensite
Heat Below
Eutectoid to
Convert BCT-M to
α + cementite
– B-Field implies
stable α & cementite
•
Engineering-45: Materials of Engineering
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Choose about
400C
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt
Austenizing Temp 1.13C
880 ºC
Compare to
Phase diagram
TTT Diagram for
1.13 wt-% C
Engineering-45: Materials of Engineering
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-45_Lec-24_Metal_Phase-Xforms-2.ppt