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


900

800

700

600

500

400

300

200

100

0

Tem

pera

ture

℃


A

F

Zw

P

M


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


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


A

F

Zw

P

M


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)


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


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


A

F

Zw

P

M


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.


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


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


A

F

Zw

P

M


Answer 3maximum hardness about 390 VHN


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)


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

continuous cooling transforming diagram

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