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WELDING RESEARCHSUPPLEMENT TO THE WELDING JOURNAL, JUNE, 1983

S p o n s o r e d b y t h e A m e r i c a n W e l d i n g S o c i e ty a n d t h e W e l d i n g R e s e a rc h C o u n c i l

(

Determination of Necessary PreheatingTemperature in Steel Welding

Findings include a new carbon equivalent to assess thesusceptibility of steel to cold cracking mo re satisfactorily

BY N. YURIOKA, H. SUZUKI, S. OHSHITA AND S. SAITO

ABSTRACT. Various tests used whendetermining cri t ical preheat ing temperatures to avoid cold cracking were examined. These included the Stout slot weld,H-slit type, V-groove res t raint , and y-groove restraint tests. Both conventionaland newly developed types of s teel having carbon contents ranging between0.02 and 0.26% were used.

Examination of the cracking testsresulted in the proposing of a new carbon equivalent that more satisfactorilyassesses the susceptibility of steel to coldcracking than do CE(IIW) and P cm . It isexpressed as:

CE: {i Mn Cu Ni+ + +

24 6 15 20' C + A(C)

Cr + M o + Nb + V+ + 5B}

{20he re A(C) = 0.75 + 0.25 tanh(C - 0.12)}.

As a param eter describing the pro babili ty of the occurrence of cold cracking

in steel weld ing, a cracking index (Cl) wasproposed. It is expressed as:

Cl = CE + 0.15 JJog H]is + 0.30og(0.017 KtOw)

According to the procedure proposedin this study, the necessary preheatingtemperatures to avoid cold cracking aredetermined by satisfying the followingcriterion:

N. YURIOKA, S. OHSHITA and S. SAITO arewith the Products R D La boratories, and H.

SUZU KI is with the Head Office, Nippon SteelCorporation, Japan.

Paper presented at the 63rd AWS AnnualMeeting, held In Kansas City, Missouri, duringApril 25-30, 1982.

tlOO 2 : (t-ioo)cr

w h e r e tioo is the cool ing t ime to 100C(212F); this is influenced, not only by thepreheat ing temperature employed, butalso by welding heat input, plate thickness and preheating method. Critical t ime(tioo)cr is given as:

(t .oo)cr = exp (67.6 C l3 -182.0 C l 2 + 163.8 Cl - 41.0)

In t roduc t ion

Methods to determine the necessarypreheat ing temperature for the prevention of cold cracking in steel weldinginclude the 1974 British Standard 5135(Ref. 1) and a procedure described inJapan Steel Structure Cons truction(JSSC - Ref. 2). How eve r, th ere is a c o nsiderable difference between the necessary preheating temperatures determined by the two procedures .

British Standard 5135 uses the IIWcarbon equivalent as a parameter fordetermining the preheat ing temperature,wh ile the JSSC pr oce du re uses Ito's car

bon equivalent , P cm (Ref. 3). The IIWcarbon equivalent satisfactorily evaluatesthe cold cracking susceptibili ty of o rd inary carbon or carbon-manganese steels;however, the low-carbon low-al loysteels, such as the recently developedpipeline steels, are more accuratelyassessed by P cm . This has been a probl em, especially in deciding the allowablevalue for the chemical composition ofpearlite-reduced pipeline steels or low-carbon low-alloy structural steels.

Exper imenta l Procedure

Weld Cracking Tests

Stout, et al. (Ref. 4) proposed a slot-weld cracking test in which the weldabili ty of pipeline steel, in the case of weld ing

with high-hydrogen types of celluloseelectrodes, can easily be evaluated. Figure 1 show s the dimensions of the standard test piece used.

It was noticed that fluctuations in widthof the root opening of this test piecegreatly influenced experimental results(Ref. 5). Therefore, slots with a 2.4 mm(0.09 in.) opening were machined on theflat plates. The accuracy of the machinedopenings was within 0.1 mm (0.004 in.).The weld metal was deposited on the slotusing flat position weld ing w ith a 4 m m(0.16 in.) diameter electrode cellulosic-type A WS E7010 in a cold cham berwhere the ambient temperature was heldat 10C (50F). The welding voltage,current and torch speed were approximately 28V, 160A, and 5 mm/s (11.8ipm), respectively.

In order to investigate cold cracking inthe case of low-hydrogen welding, thepresent study used the results of H-slittests (Ref. 6, 7), V-groove tests and y-groove tests (Ref. 8). Figure 2 shows theshape of the H-slit test piece in which therestraint intensity is varie d wi th a change

in the slit length B s. The restra int inte nsityR F (kgf/mm mm ) is a force per unitweld length necessary to reduce a rootopening by unit length. Table 1 shows R Ffor each test piece used in the presentstudy. The meaning of rf and Rp isexplained in the Appendix under thehead ing, Restra int Stress Ac ting onWe l d .

In each type of cracking test , testpieces were preheated to the varioustemperatures up to 200C (392F) untilcrack initiation was completely stopped.The Stout test pieces were preheated inthe furnace, while other test pieces werelocally preheated by electrical strip heaters in the manner shown in Fig. 2. In thecase of multipass welding, the interpasstemperatures were kept almost the same

WELDING RESEARCH SUPPLEMENT 1 147-s


2/7

EEoin

2.4mm through-th ickness slit

weld

~25~m m

9 0 -m m

2 5 -mm

EE

a-CN

Tw

J_

200mm- H t ht h i ckness

Fig. 1 - Shape of Stout slot-weld test piece

Fig. 2 right) Shape of H-slit restraint cracking test piece

2b : wid th of preheating zone

Dimension

B s

wR

L s

L c

C

Type I

0

4 0 0

4 0 0

100

200

0

(mm)

Type I I5 0 -

1600

4 0 0

4 0 0

7 5

150

5 0

-45'.y

1f

h/2

*~

/ i/

f2mm

AA' Section

as the preheating temperatures.Each test piece was transversely cut

into five sections after more than 72hours (h) had passed since com pletio n ofthe welding. Macrographic observat ionof nital-etched weld sections led to thedetermination of the crit ical preheatingtemperatures T 0 * a t which the occurrence of cold cracks was prevented.Figure 3 shows an example of a weldwith a root crack in the Stout test .

MaterialsThe Stout slot weld tests were carried

out with various types of steels employedfor ordinary structures, pressure vessels,boilers, and pipelines. Their tensilestrengths ranged between 40 and 85k g f / m m2 (57 and 121 ksi), and theirchemical compositions are shown inTable 2. In the Stout test, one type ofelectrode, i .e. , AWS E7010, was usedirrespective of the strength level of thetested steel. The hydrogen content in thedeposited weld metal using this electrodewas 35 ml/100g by JIS glycerin displace

ment method. This value, HjIS, can beconver t ed to Hiw by the mercury displacement method as (Ref. 9):

H|,w= 1.30 H,|S + 0.61 (1)

Table 3 shows the chemical compositions of steels used in the H-slit crackingtests, the V-groove tes ts and the y-groove restraint tests. These steels werefor structural or pressure vessel usagewith greater thicknesses up to 100 mm(3.9 in.). Tests, other than the Stout test,employed elect rodes whose s t rengthcorresponded to those of the steelstested. Table 4 shows nominal yieldstrengths and hydrogen contents of thewelding materials used; welding condi

tions for the cracking tests are alsodescribed in Table 4.

Results and Discussion

Critical Preheating TemperatureMeasured in Tests

Critical preheating temperature T 0 * inthe Stout tests is shown in Table 2. Theresults of the H-slit, V-groove and y-groove restraint tests are summarized inTable 5. K t in Table 5 is the stress concentration factor at the notch where a crackis initiated, and its value is given in theAppendix under the heading, RestraintStress Acting on W e ld . The mean stressacting on the weld metal is given as afunct ion of

2-D restraintcoefficient, rf Plate thickness

k g f / m m2 mm

69.069.069.069.020.0

5.9

h , mm

385075

1005050

Restraint intensity R F.k g f / m m m m

2765337442654784

998290

Fig. 3-Root crack in Stout's slot test

20 (Ty)

(2)

( a) C on v e rs io n fa c to r s : pou nd fo rc e / in .3 = 375.7 X k g f / m m2 - m m; in . = 25.4 X mm ; ks i = 1.422 X kg f/m m mm.

The crit ical preheating temperatureswere obtained separately for single-passroot cracking (Fig. 4), multipass rootcracking (Fig. 5) and multipass toe cracking (Fig. 6) for each steel tested. Toecracks were not observed in the specimens of SM41B, SM53B, HW45, andHW70 s teel . T Q * for multi-pass root

cracking was found to be less than thatfor single-pass root cracking by over50C (122F). Table 5 also lists t 100 , wh ichis the duration of the cooling time to100C (212F) af ter welding and corresponds to T 0 * measured in the tests.

The weldment eventually cools to theambient temperature whether i t is preheated or not. Some hydrogen escapesfrom the weld metal surface during thecool ing period after welding. However,hydrogen escape becomes more andmore inactive with a decrease in thetemperature of the weld metal and i tbecomes negligibly small at temperaturesless than 100C (212F).

The residual hydrogen in welds c o ntributes to the initiation of cold crackingwhen it cools below 100C (212F) in an

148-s I JUNE 198 3


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Fig. 4 Single-pass root crack in H-slit test

ordinary structural steel w e l d , l t followsthat the tioo is significant in selectingpreheat ing temperatures .

Preheating increases the cooling timeto 100C (212F) and thus is effective inpreventing the initiation of cold cracking.However, the durat ion of the cool ingtime to 100C (212F) i s determ ined, n otonly by the preheat ing temperature, butalso by the plate thickness, the particularpreheat ing method used and other factors. These relations are shown in Figs. 11and 12 in the Appendix. Consequently, i tis advisable to consider the critical coolingt ime to 100C (212F) rather than relysolely on the preheating temperaturewhen desiring to avoid cold cracking insteel welding (Ref. 2).

= Carbon Equivalent to Assess Co ld Cracking

Many carbon equivalents have beenproposed as parameters indicating asteel's susceptibility to cold cracking atthe heat-affected zone. They can bedivided into two groups wherein CE(IIW)

is of the first group, and Ito's carbonequivalent, P cm (Ref. 3), belongs to thesecond. They are expressed as:

M n Cu + NiCE(IIW) = C + +v ' 6 15

Cr + Mo + V+ : (3)

Si Mn Cu NiP cm = C-F + + + 30 20 20 60

Cr M o V+ + 5B 4

20 15 10

P cm has been shown to be reliable forevaluating the cold cracking tendency inlow -ca rbo n low-allo y steel (Ref. 11). Onthe other hand, CE(IIW) is reported to bea more appropriate parameter than P cmfor evaluating the cold cracking susceptibili ty of steels whose carbon content ismore than 0.16% (Ref. 7). Therefore, i t isnot possible for one simple carbon equivalent formula to describe, overall , thecold cracking tendency of steels if their

Table 2-

Symbol

ABCDEFCHIIKLMNOPQRST

-Chemical Composit ions (%)

Steel

JIS SM53JIS SM53BJIS SM50CBS4360 50DASTM A516 Cr. 70A S T M A 5 3 7 C1.2A S T M A 6 3 3 CASTM A299JIS SB49WES HW45W E S H W 4 5W E S H W 7 0W E S H W 7 0JIS STK41API X60API X65API X65API X70API X70API X80

Thickness,m m

2020202020202020202020202012.7201420162020

and Critical

C

.160

.159

.149

.173

.231

.142

.099

.254

.240

.141

.065

.130

.112

.230

.091

.240

.049

.021

.020

.018

Si

.40

.37

.25

.45

.27

.41

.35

.27

.29

.30

.28

.29

.24

.04

.29

.35

.29

.14

.13

.16

Preheating Temperatures of Steels

M n

1.411.401.331.481.191.441.461.37

.871.331.38

.88

.87.68

1.321.391.561.591.892.01

P

.020

.018

.019

.0210.19.025.013.016.019.020.013.010.019.014.017.015.017.018.020.019

S

.008

.012

.005

.006

.007

.003

.004

.005

.005

.006

.003

.005

.006

.012

.003

.012

.005

.003

.002

.003

Cu

.01

.01

.01-.02-

.15

. 14-

.01

.03

.22

.23

.01

.01

.01

Ni

.01

.02

.01

.01

.03

.20

.17If,

.13-

.81

.02

.01

.01

.0 1

.27

.32

Cr

.01

.01

.01

.01

.03

.02

.02

.15

.12

.01

.2 1

.54

.85

.02

.01

.02

.01

in Stout Slot W eld Tests *

M o

-------

.14-

.21

.47

.33

.09-

.25

.30

V

.059

.026-

.056

.036

.016

.040--

.055

.038

.044

.046--

.068

-

Nb

.038-

.026

.046-

.039--

.040-

.049

.041

.048

.052

Ti

-----

.007

.017

.016

.018

B

----

.0005

.0002

.0006

.0002

.0003

.0002

.0015

.0018

.0005---

.0002

.0010

.0010

.0010

CE(IIW)

.410

.401

.374

.434

.446

.403

.376

.560

.418

.376

.389

.556

.519

.349

.331

.477

.393

.286

.335

.434

cm

.251

.245

.225

.268

.309

.236

.202

.358

.301

.224

.181

.280

.247

.267

.176

.323

.166

.110

.124

.154

CE eq (5)

.411

.395

.361

.446

.458

.377

.294

.569

.428

.352

.254

.477

.410

.350

.253

.491

.240

.166

.191

.239

To,*C

757550

10015012575

20010075


4/7

Table 4Welding

Electrode

AWS E7010AWS E7010JIS D4301JIS D4316JIS D5016JIS D5816JIS D5816JIS D8016

Materials and Conditions for Restraint Cracking Tests (a)

Diameter,m m

3.24.05.05.05.04.05.05.0

Nominalyield strength,

k g f / m m2

5050404050606080

Hjism l /1 0 0 g

31.835.032.8

3.73.4

0.4 ~ 5.00.4 ~ 5.7

2.0

Current,A

130160220230230170230230

Voltage,V

2530282525252525

Speed,m m / m i n

290300123115115150115115

Heat input,J /m m

672960

300030003000170030003000

Crackingtest

V-groove tes tStout testH-slit testH-slit testH-slit testy-groove testH-slit testH-slit test

(a) Con vers ions : in. = 25.4 X mm ; ksi = 1.422 X k g f / m m2

carbon contents range widely.It is wit h this point of vie w in mind that

the authors propose the fol lowing carbon equivalent , which has an accommodation facto r A(C) as a function of thecarbon content :

CE = C + A(C)24

Mn Cu4-

6 15Ni Cr 4- M o + N b I V 5B20 5 } (5)

wh ere A(C) = 0.75 4- 0.25 tanh{20(C - 0.12)}. (6)

A(C) increases with an increase incarbon content. It approaches 0.5 as thecarbon content decreases below 0.08%and 1.0 as it increases above 0.18%. Therelationship between this carbon equivalent and CE(IIW) is sho wn in the A ppen dixunder N ew Carbo n Equivalent.

Experimental results from the Stout

cracking tests were used to compare thethree types of carbon equivalents forvalidity in assessing the cold crackingtendency of steels. The relation of T 0 * tothe three carbon equivalents was plottedin Fig. 7. It is seen that the carbonequivalent expressed in equation (5) had

the highest l inear correlation coefficient(r = 91.1%); therefore, i t is the most reliable of the three carbon equivalents,provided that the carbon content of thesteels to be compared ranges widely.

Index to Describe Cracking Probability

Ito, ef al . p roposed P w (Ref. 3) andSuzuki recently proposed P H (Ref. 11) asparameters to describe the likelihood ofcold cracking. The parameters involvechemical composi t ion, hydrogen contentand acting stress, which are three majorcauses of cold cracking in welds.

Table 5Results of Restraint Cracking

Steel

SM41BSM41BSM53BSM53BSM53BSM53BH W 4 5H W 4 5H W 4 5H W 4 5H W 4 5H W 4 5H W 4 5H W 4 5H W 7 0H W 7 0H W 7 0H W 7 0PMS25PMS25PMS25PMS35PMS35PMS35SM41BSM41BSM41BA516 Gr.70A516 Gr.70A516 Gr.70SB49MSB49MSB49MSB56MSB56MSB56M

h,m m

383850505050505050383838323250505050757575757575

100100100100100100100100100100100100

CE eq (5)

.294

.2944 3 0.430.430.430.356.356.356.358.358.358329329.390.390.390.390.467.4674 6 7.516.516.516.268.268.268.425.425.425.465.465.465.562.562.562

HJIS,

m l /100g

3.732.8

3.43.43.43.40.41.35.7.042.25.03.2

31.82.02.02.02.03.43.43.42.02.02.03.43.43.43.43.43.43.43.43.41.91.91.9

Tests and Estimated Critical

Oy,

kgf/mrri2

404050505050606060606060605080808080505050606060404040505050505050606060

Kt,(groove)

8 ( f )8 )8 ( f )8 ( f )8 ( f )8 ( f )8 ( f )8 ( f )8 ( f )4(y)4(y)4(y)1.5(V)1.5(V)8 ( f )8 ( f )8 ( f )8 ( f )8 ( f )8 ( f )1.5(toe)8 ( f )8 ( f )1.5(toe)8 ( f )8 ( f )1.5(toe)

8 ( f )8 ( f )1.5(toe)

8 ( f )8 ( f )1.5(toe)

8 ( f )8 ( f )1.5(toe)

RF,kgf/m m2

27652765

2903374337433743374337433742765276527651500150033743374998290

426542654265426542654265478447844784478447844784478447844784478447844784

Preheating Temperat

kgf/m m2

44.944.914.555.955.955.965.465.465.463.963.963.960.858.284.484.449.914.558.158.158.167.767.767.750.050.050.059.559.559.559.559.559.569.069.069.0

Cl

.615

.757

.598

.774-

.774

.581

.658

.754

.490

.601

.654

.462

.611

.753-

.685

.523

.816

.598

.850-

.632

.597-

.379

.777-

.559

.817-

.599

.895

.677

2b(mm)

100100100100100200100100100100100100200200100100100100200200200200200200200200200200200200200200200200200200

jres

Ej,(k j /mm)

3.03.03.03.03.03.03.03.03.01.71.71.71.01.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.03.0

Crack< a>

S.R.S.R.S.R.S.R.M.R.S.R.S.R.S.R.S.R.S.R.S.R.S.R.S.R.S.R.S.R.M.R.S.R.S.R.S.R.M.R.M.T.S.R.M.R.M.T.S.R.M.R.M.T.S.R.M.R.M.T.S.R.M.R.M.T.S.R.M.R.M.T.

O b se rv edTo*(C)

5012575

>200100175

50125200


5/7

Fig. 5 Multipass root crack in H-slit test

In this study, a cracking index, basedon the same concept as P w o r P H, wasint roduced using the new carbon e quivalent (CE) from equation (5) as:

CI = CE4-0.15 xog HJIS + 0.30xog(0.017 K,


6/7

Groove type

y (root)

Double-Vee (root)

Y (root)

Single-bevel (root)

V (root)

y. x. Y. V. U (t oe)

T~ r

w

~ ^

K,

4

3.5

4 - 5

6 - 8

1.5

1.5

Fig. 9 Stress concentration factors at root

and toe weld positions

higher than the preheating temperatures.

4 . If root cracks are to be remov ed bybackgouging, the preheating temperature for toe cracking (K t = 1.5) may beemployed.

Conclusions

1. The CE fr om equ at ion (5) is a moreappropriate parameter than CE(IIW) or

P cm for assessing the susceptibility of steelto cold cracking.

6

E

| 5

4

3

2

1

FU=71-r.(arctan(0.017h)-(h 400 ?\

FEM Analysis for r. 69

^ r ^~

Very severe restraint .s^^ ____-

/ S^ -^---' Ordinary restraint

r- = 70kgf mm 2-mm

r, = 60

r.=50

r f=40

ss ^ ^ r =30

/ / / / ^ ^ r = 2 0

/JFJ/\S'^ r f io

5 100Plate Thickness. h(mm)

150 200

Fig. 10 Relation of restraint intensity to plate thickness

2. The cracking index, C l, given byequation (7) satisfactorily describes thelikelihood of cold cracking of steel undervarying chemical compositions, weldingmaterial hydrogen content, and jointrestraint intensity.

3. The necessary preheating temperature can be determined by satisfying thecondition that t 10 o > (tioo)cr- The criticalcooling time (tioo)cr is given as a functionof Cl by equation (8).

Appendix

Restraint Stress Acting on Weld

The occurrence of cracking is greatlyinfluenced by the severity of the notchwhere a crack is initiated. Figure 9 showsthe stress concentration factors at weldroots and toes with various types of weldgrooves (Ref. 11).

Watanabe, ef al. (Ref. 12) calcula tedthe two-dimensional restraint coefficient,rf, for an H-slit test specimen as:

r f = E/{B s + (L c /2L s )B s + B s '} (A1)

where E is Young's modulus; B 5, Lc and Ls

10000

5

2 1000 -

o

50 100 150 200* Preheating Temperatu re, T 0 (C)

25

Fig. II Relation between cooling time to 100C and preheatingtemperature Ej = 7,700 //mm)

10000

5

Qc

DC

O

1

500

100

5

-

-

-

: /

-

3,000J/mmh = 100mm

h=75mm 'h = 5 0mm

h = 38mm r L - ^ - -h = 25mm ^-^y-^A^rA

h = 20 m rn / < ^ 5 $ S 2 - 7 - ^

| - t ^ 2 K - h=?nmm

/ \JC / / // / / / h = 20mm

/ / / / h = 25mm

/ / * / h = 38mm

/ A. h = 50mm

/ h=75mm

h = 100mm

= 100mm

2b = 2 00m m

2b = 1 0 0 m m |

50 100 150 200* Preheating Temperatu re, ToCCJ

25

Fig. 12 Relation between cooling time to 100C and preheatingtemperature Ej = 3,000 J/mm)

152-s|JUNE 1983


7/7

1.0

.0.9

O i

0 7

0.5

^V

\ \ \ N\ \ \ v\ \ \ ^

> \ \ \ . / % * ,

\ \ \ A

\ A\A v * A ( C l - ^ / \ V CF ,C/ \ Ay^.b)

/ \^ y ^ ~~~.fv s. c e.fp.5.i

= 0 . 5 0 -

^0.45

= 0.40-

^0.35 -

=0 .3

0.6

UJ

LLl

o

0.5

Q .

CD

OO

5czUJo

3S

+5

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