Continuous Cooling Transforming Diagram
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Transcript of Continuous Cooling Transforming Diagram
1 2 4 6 8 10 20 40 60 100 200 400 600 1000 1000 4000
Cooling time from A3(789 ) to 500 sec℃ ℃
900
800
700
600
500
400
300
200
100
0
Tem
pera
ture
℃
A3789℃
A1696℃
5
95
2
1218
88 80
515
3540
6045
78
855
1020
2
400 397 396 385 370 309 290 250 235
0.15C-0.33Si-1.03Mn-0.010P-0.014S-0.80Ni-0.28Cr-0.25Cu-0.44Mo
A
F
Zw
P
M
A: austeniteF: ferriteP: pearliteZw:bainiteM: martensite
Continuous Cooling Transforming Diagram (Fig.C1)
CCT diagram for 800MPa class high tensile steel (Fig.C2)
1 2 4 10 20 40 100 400 1000
Cooling time from A3(789 ) to 500 sec℃ ℃
900
800
700
600
500
400
300
200
100
0
Tem
pera
ture
℃
0.15C-0.33Si-1.03Mn-0.010P-0.014S-0.80Ni-0.28Cr-0.25Cu-0.44Mo
A
F
Zw
P
M
Cooling time from A3(789 ) to 500 sec℃ ℃
Perc
enta
ge o
fm
icro
stru
cture
%
Vic
kers
hard
ness
num
ber
Thermal distribution during welding (Fig.C3)D.Rosenthal : Mathematical Theory of Heat Distribution during welding and cutting, Welding J., 20(1941), 220s
Three dimensional
θ - θ0 = ・exp( X - X2+R2)Q v
4πλk X2+R2
θ - θ0 = eX ・ K0( X2+Y2 ) 4πλh
QTwo dimensional
Three dimensional Two dimensional
Q; heat input per unit time (cal/sec)v; welding speedλ; thermal conductivity
k = c; specific heat ρ; density
K0; Bessel function of the second kind of order sezo
cρλ
X = x , Y = y , R = y2+z2
2kv
2kv
2kv
Experimental equation for estimation of cooling rate at 300℃ proposed by Cottrell (Fig.C4)
1
CR
E + 1000 N=
54 T 1 + ( N + 0.5 )( )1000T
CR : cooling rate of HAZ at 300℃T = 300 - θ0
θ0 : initial temperature of base metal plate (℃)E : heat input (Joule/in)N : Thermal Severity Number of joint
Determination of TSN
TSN = 2
TSN = 5
TSN = 4
TSN = 3
Heat input E
Heat conduction N
Estimation of cooling time from 800 to 500℃ or 800 to 300℃proposed by Inagaki
WeldingMethod n
for CT800→500 for CR800→300
K h0 α θm K h0 α θm
SMAW 1.51.35 (butt)
14.6 6
600
2 (butt)14.6 4.5
400
0.675 (T type) 1.6 (T type)
CO2, CO2-O2
welding 1.7 0.345 13 3.50.4 (butt)
14 50.222 (T type)
Submerged ArcWelding
[h<32]2.5 - 0.05h 12 3 20 7
[h>32]0.9 950
730 (butt)365 (T type)
109.5
5 - 0.22h10
7.35 - 0.22h
10
3.65
5 - 0.22h
(butt)
(T type)
Constants
CT =800→500 or800→300
K ・ J n
(θm - θ 0 ) 2 1 + tan-1π2 h - h0
α
J; heat input (Joule/cm)
θ0; initial temperature = preheating temperature
Nomograms for estimation of cooling time (Fig.C5)
464442
3836343230
2826
24
22
20
18
40
16
14
12
10
8
464442403836343230
28
26
24
22
20
18
16
14
12
10
100908070
6050
40
30
25
20
15
10
8
6
4
2
3
1000800600500400300
200150
10080
605040
30
20
15
10
866
43
2
400
350
300
250
200
150
100
50
100
4
6
8
10
12
14
16
18
20
2224263034
for SMAW
Heat input (kJ/cm)
Plate thickness(mm)
PreheatingTemp. (℃)
CT800→500
(sec)forroom temp.
forpreheating
butt T type
Problem
1. Estimate the microstructure of HAZ of 800 MPa class high strength steel, when it is cooled for 40 seconds from A3 to 500 ℃. 2. Estimate the cooling time from 800℃ to 500℃ with the following welding conditions. welding conditions welding joint T type joint of a steel plate of 10mm thickness welding process shielded metal arc welding welding current 200 A arc voltage 24 V travel speed 4 mm/s
3. Estimate the microstructure and maximum hardness in HAZ of 800 MPa class high strength steel, when it is welded with the above welding conditions.
4. Determine the preheating temperature to reduce the maximum hardness of HAZ to 300 VHN for the same steel.
1. Estimate the microstructure of HAZ of 800 MPa class high strength steel, when it is cooled for 40 seconds from A3 to 500 ℃.
1 2 4 6 8 10 20 40 60 100 200 400 600 1000 1000 4000
Cooling time from A3(789 ) to 500 sec℃ ℃
900
800
700
600
500
400
300
200
100
0
Tem
pera
ture
℃
A3789℃
A1696℃
5
95
2
1218
88 80
515
3540
6045
78
855
1020
2
400 397 396 385 370 309 290 250 235
0.15C-0.33Si-1.03Mn-0.010P-0.014S-0.80Ni-0.28Cr-0.25Cu-0.44Mo
A
F
Zw
P
M
A: austeniteF: ferriteP: pearliteZw:bainiteM: martensite
CCT Diagram for 800MPa class high strength steel
Answer 1 (Fig.C6)
Answer15% ferrite-40% bainite-45% martensute
Nomogramsfor
Estimationof
cooling timefor SMAW
464442
3836343230
2826
24
22
20
18
40
16
14
12
10
8
464442403836343230
28
26
24
22
20
18
16
14
12
10
100908070
6050
40
30
25
20
15
10
8
6
4
2
3
1000800600500400300
200150
10080
605040
30
20
15
10
866
43
2
400
350
300
250
200
150
100
50
100
4
6
8
10
12
14
16
18
20
2224263034
Heat input (kJ/cm)
Plate thickness(mm)
PreheatingTemp. (℃)
CT800→500
(sec)forroom temp.
forpreheating
butt T type
Answer 2 (Fig.C7)
2. Estimate the cooling time from 800℃ to 500℃ with the following welding conditions.
T type joint of a steel plate of 10mm thickness, SMAW, 200 A, 24 V, 4 mm/s
Heat input (J/cm)
= ・ 60E(V)・ I(A)v(cm/min)
=12000(J/cm)
Answer 6 seconds
1 2 4 6 8 10 20 40 60 100 200 400 600 1000 1000 4000
Cooling time from A3(789 ) to 500 sec℃ ℃
900
800
700
600
500
400
300
200
100
0
Tem
pera
ture
℃
A3789℃
A1696℃
5
95
2
1218
88 80
515
3540
6045
78
855
1020
2
400 397 396 385 370 309 290 250 235
0.15C-0.33Si-1.03Mn-0.010P-0.014S-0.80Ni-0.28Cr-0.25Cu-0.44Mo
A
F
Zw
P
M
A: austeniteF: ferriteP: pearliteZw:bainiteM: martensite
Answermicrostructure about 8% bainite- 92% martensute
maximum hardness about 390 VHN
Answer 3 (Fig.C8)
3. Estimate the microstructure and maximum hardness in HAZ of 800 MPa class high
strength steel, when it is welded with the above welding conditions.
CCT Diagram for 800MPa class high strength steel
Answer 4 (Fig.C9)4. Determine the preheating temperature to reduce the maximum hardness of HAZ to 300 VHN for the same steel.
1 2 4 6 8 10 20 40 60 100 200 400 600 1000 1000 4000
Cooling time from A3(789 ) to 500 sec℃ ℃
900
800
700
600
500
400
300
200
100
0
Tem
pera
ture
℃
A3789℃
A1696℃
5
95
2
1218
88 80
515
3540
6045
78
855
1020
2
400 397 396 385 370 309 290 250 235
0.15C-0.33Si-1.03Mn-0.010P-0.014S-0.80Ni-0.28Cr-0.25Cu-0.44Mo
A
F
Zw
P
M
A: austeniteF: ferriteP: pearliteZw:bainiteM: martensite
Answer 3maximum hardness about 390 VHN
CCT Diagram for 800MPa class high strength steel
prolong the cooling time
by using preheating
reduce the maximum
hardness
cooling timeof 40 seconds
(to be continued)
Nomograms for Estimation of cooling time for SMAW
464442
3836343230
2826
24
22
20
18
40
16
14
12
10
8
464442403836343230
28
26
24
22
20
18
16
14
12
10
100908070
6050
40
30
25
20
15
10
8
6
4
2
3
1000800600500400300
200150
10080
605040
30
20
15
10
866
43
2
400
350
300
250
200
150
100
50
100
4
6
8
10
12
14
16
18
20
2224263034
Heat input (kJ/cm)
Plate thickness(mm)
PreheatingTemp. (℃)
CT800→500
(sec)forroom temp.
forpreheating
butt T type
Heat input (J/cm)
= ・ 60E(V)・ I(A)v(cm/min)
=12000(J/cm)
Answer 3 about 6 seconds without preheating
Answer 4 (continued) (Fig.C10)
Required cooling time 40 seconds
Answer 4 about 380℃
Microstructures and cracking phenomena
Solidification structure
Transformation structureWeld metal
Heat affected zone Transformation structure
Hot cracking
Toughness of weld metalCold cracking
Toughness of HAZ or weld bond
Cold cracking
Weld
Microsegregation of solute + stress
Diffusible hydrogen + stress
-60
-40
-20
0
20
40
60
0
10
20
0 10 20 30 40 50
Abso
rbed
ene
rgy
kg-m
/cm
2
Tra
nsi
tion t
em
pera
ture
℃
Cooling rate at540℃ deg/sec
Base metal plate
Trs
Tr15
energy
High tensile steel (QT)0.16C-0.4Si-1.2Mn
Base metal
Cooling rate23℃/sec50℃/sec
Testing temperature ℃
Abso
rbed
ene
rgy
kg-
m/c
m2
0
4
8
12
16
20
0-60 -40 -20 20 40 60 80 1000
50
100
Perc
en
tage o
f bri
ttle
fra
cture
Su
rface
%
Mild steel (Peak temp.1350℃)0.15C-0.08Si-0.95Mn
Effect of cooling rate on toughness of low carbon steels (Fig.C11)
Calculated Tr15 ℃
Measu
red T
r 15℃
Q-tempering (Fig.C12)
Tr15(℃) = 400Ceq - m + - 5045
β
2
Ceq = C + - + +Mn40
Ni25
Cr20
Mo8
(C<0.18%)
m; amount of martensite (%)β; amount of bainite (%)
Effect of carbon content on the Ms temperature (Fig.C13)
Tem
pera
ture
Tem
pera
ture
Cooling time Cooling time
CCT diagrams for some steels with various carbon content
0.13%C 0.44%C
0.76%C 1.03%C
Carbon content of welded steels is less than 0.2%.
Temperature limit for martensite decomposition
Microstructure and cold cracking sensitivity
The factors affecting cold cracking sensitivity
1. Hydrogen i) Type of electrode and welding procedure ii) Welding conditions(diffusion time for hydrogen) iii) Post weld heat treatment ; PWHT
2. Restraint stress (residual stress) i) Joint configuration (position of joint in welded structure) (mainly) plate thickness ii) Welding conditions
3. Hardened microstructure (martensite) or hardness i) Chemical compositions (hardenability of steel)→CCT diagram, Ceq
ii) Cooling rate (cooling time from A3 to a defined temperature) a. heat input→energy used for heating b. cooling ability plate thickness joint configuration pre-heating →difference in temperature between weld and base metal
Microstructure and cold cracking sensitivity (Fig.C14)
Prediction ofoccurrence ofcold cracking
HydrogenRestraint stress
Microstructure
The harder structure is, the more sensitive is.
CCT diagram
Estimation of cooling rate or time
Welding conditions
Chemical compositions
Carbon equivalent
Effect of cooling rate
Effect of chemial bompositions
Methods proposed by 1. Bastien 2. Beckert 3. Yurioka
Kihara and Suzuki (IIW Doc.IX-288-61, 1961)
Ceq = C + + + + +
→ Hvmax = 666 Ceq + 40 (WES)
Estimation of maximum hardness in HAZ (Fig.C15)
Studies in 1940 ~ 1969Investigations of the effects of the chemical compositions on the maximum hardness→Experimental data are summarized as carbon equivalent; Ceq. (Welding conditions are constant.)
Dearden and O’Neill (Trans. Inst. Weld. 3-4(1940), 203)
Ceq = C + + + + + + → Hvmax = 1200 Ceq - 200 (IIW)%Mn
6%Ni15
%Cr5
%Mo4
%V14
%Cu13
%Mn6
%Si24
%Ni
40%Cr
5%Mo
4
Maxim
um
Vic
kers
hard
ness
num
ber
Ceq proposed by Kihara and Suzuki
Estimation of maximum hardness in HAZ (continued)
Studies in 1970 ~ 1979Investigations of the effects of welding conditions on the maximum hardness
Bastien (Metal Constr. & British Weld. J., 49-1(1970),9)Beckert (Schweiss Technik, 23-8(1973),234)
Hv = Hv (HM ,HB,τ)
HM = HM(%C) ; hardness of 100% martensite HB = HB(%C,%Si,%Mn,%Cu,%Ni,%Mo) ; hardness of 100% bainite τ; cooling time from 800 to 500℃, which is determined by the welding conditions
Studies in 1980 ~Improving the accuracy of the hardness estimation
Method for maximum hardness estimation proposed by Yurioka (Fig.C16)
AWRI Symposium “Pipeline welding in the 80’s” March 1981 → modified in 1987
Hv = - arctan(X) HM + HB
2
HM - HB
2.2 X(in rad) = 4 - 2, τ;cooling time between 800 to 500℃τB
τMlog
ττM
log
HM = 884%C(1 - 0.3(%C)2) + 294
HB = 145 + 130 tanh(2.65 CeqII - 0.69)
τM = exp(10.6 CeqI - 4.8)
τB = exp(6.2 CeqIII + 0.74)
CeqI = Cp + + + + + + (1 - 0.16 %Cr) + ΔH%Si24
%Mn6
%Cu
15%Ni12
%Mo4
%Cr8
Cp = %C (%C≦0.3%) %C + 0.25 (%C > 0.3%) ΔH = 0 (B≦1ppm)
0.03fn (B = 2ppm) 0.06fn (B = 3ppm) 0.09fn (B≧4ppm)
fn =0.02 - %N
0.02
CeqII = %C + + + + + + + +%Si24
%Mn
5
%Cu10
%Cr5
%Mo2.5
%Ni18
%V5
%Nb3
CeqIII = Cp + + + + +%Mn3.6
%Cu20
%Ni
9%Cr
5%Mo
4
-4 -2 0 2 4-2
-1
0
1
24
-arc
tan
X
X
2.2
arctan X
-arctan X
-2 -1 0 1 2
hard
ness
HM+HB
2HM - HB
X parameter
τ τ= M τ τ= B
Fig.C17
0 0.2 0.4 0.6 0.8 10
200
400
600
800
1000
HM
Effect of carbon on HM (Fig.C18)
Carbon content mass%
HM=884%C+294
-2 -1 0 1 2 3 40
100
200
300
HB
CeqII
=0.260.692.65
145
CeqII = %C + + + + + + + +%Si24
%Mn
5
%Cu10
%Cr5
%Mo2.5
%Ni18
%V5
%Nb3
Change in HB with CeqII (Fig.C19)
0 0.5 110-2
10-1
100
101
102
103
τB
τM
CeqI, CeqIII
τ Bτ M
τM, τB (Fig.C20)
Estimation of maximum hardness by the Yurioka’s method (Fig.C21)
Cooling time between 800 and 500℃ sec
HAZ
har
dnes
s H
v