Journal or
Materials
Proeesshag
Teehnelogy
ELSEVIER
Journ,il of .Materials Pr~lce,,,,iug -i'ccht~olo~ 68 11997~ 43 49
On crack susceptibility in the submerged arc welding of
medium-carbon steel plates
M.E. Khallaf
M.A. Ibrahim h, N.A. EI-Mahallawy h M.A. Taha u.,
" I lw El,'.vption lrms and .S'tCt'/ I I'o.r/~.+. th'/wtm. ('uiro. Et.'ff,t
h Dtpartmt'nl ~1 Design atul Producth,n En.eim,criog. Facultl. t , / E n g b w o l t t g . . Jitl-Sham ~ I itil o ~ i l i..41,tt.~t,la. ('~tir,. [?g.ipt
Rccci~etl g Seplember 1995
Abstract
The present paper describes cracking behaviour during the submerged art: x~cldingof medium carbon steel plates (11.45".,(~. It
discusses the results of tests made to examine the effect of welding variables (current. welding speed and wire feed rate}, plate
fabricatiop, conditions (rolling reduction ratio) and plate thickness o,1 cracking susccptibilily using trans-varestraint tests.
It is foun6 that the cracking susceptibility increases with an increase in the welding current, and decreases with an increase in
the welding sF~.ed or the electrode wire feed ,-ate. It also increases with increases in the plate rolling :'eduction ratio and ~vith
decreases in the plate thickness. These results have a practical signilicance t\~r industrial ticlds, especially where welded machine
spate parts are concerned. :(;, 1997 Elscvier Science S.A.
Kcj'u'ord.~: Submerged arc welding: Welding of mediom carbon ~,teel: Welding of steel plales: Crack suso.'ptibilit} in x~elding
I. Introduction
Engineers concerned with the design and manufacture of welded machine ;pare parts arc aware of the
existence of cracking problems in the welded joints. In
the submerged arc welding process, using higher deposition rates and greater heat input leads to welding
conditions that are more likely to lead to cracking.
Previous investigations have been concerned with the
nature and mechanisms of solidification cracking. During solidification of weld metal, grains begin to grow
from the fusion boundary towards the central region of
the weld pool. Many alloying elements, as well as
impurities, are rejected ahead of the growing crystals
and become concentrated in the last part of the liquid
to solidify. Their presence lowers the freezing temperature of this liquid. As solidification is taking place, the
weld and surrounding material progressively cool, thu~
giving rise to contraction strains across the weld [1].
The presence of residual low-melting-point liquid may
then lead to lowering of the ductility, so that the
* Corr~-sponding author. Fax:
mtaha@ASUNET.SHMS.eun.eg
+ 20
4152991: c-mail:
0924-0136!97!$17.00 ~t) 1997 ElsevierScience S.A. All rights reserved.
PII S0924-0136(96)02530-7
contra,:fion strains produce ,:racking [2]. In other
words, the ductility is low due to the residual liquid,
but. on the other hand. the amount of residual liquid is
insufficient to lill any voids produced by cracking. It is
c~ideut that this problem must depend on the weld
metal composition [3,4]. In the present work the effect
of welding variables, plate thickness and the plate forming reduction ratio (during fabrication) on the crack
susceptibility is presented and discussed.
2. Experimental work
2. I. Wehli:lg equipment
The automatic welding system used for the DC submerged arc welding ~wocess has a control unit by which
the welding variables (current, u'a~el speed and ~virc
feed rate) can be controlled automatically. The main
technical data of the welding equipment arc: wire dia m e t e r = 3--7 ram; travel speed = 0-120 m:h: welding
current = 0-1250 A; and maximum voltage = 44 V.
Copper coated steel electrodes of 3.2 mm diameter
were used throughout the experiments. The angle be-
44
M.E. Khallaf et aL / Journal of Materials Processing Technology 68 (1997) 43-49
tween the electrode and the test-piece is 40*; the overhanging length of the electrode beyond the nozzle is 25
nun and the distance between the electrode tip and the
test-piece is 3 ram, all of these values being kept constant.
2.2. Test equipment
The principles of the trans-varestraint test equipment
of Farrer and Garland [5] have been used to design a
simplified test rig for this work. Fig. l(a) shows the
trans-varestraint test equipment used in the present
work and the applied forces, as well as the sample
dimensions and positioning.
In the test equipment, the specimen is mounted by
means of two clamping forces at its ends. The required
strain with a suitable deflection (1.5 mm) is exerted in
the middle of the specimen during the welding process,
4
r
2
-]-~\
3
~
P R
F7
5
6
L..
(a)
300 - -
[
Oetail o f
t= 12,16,20mm.
.groove
where the electrode tip is at point (A), as shown in Fig.
l(a). The deflection is kept constant (1.5 mm) during all
experiments.
2.3. Welding specbnens
Medium carbon steel, C 45, has been used for welding, its chemical analysis (wt%) being: C = 0.46, Si =
0.29, Mn = 0.6, P = 0.032 and S = 0.03. The electrode
used was of type ASW A5. 17-80 EMI2, which has the
following chemical analysis (wt%): C = 0.12, Si = 0.1
and Mn = 1.0.
The welding specimens have a rectangular shape with
different thicknesses (12, 16 and 20 ram). They were
fabricated by rolling to different reduction ratios (11.3,
8.5 and 6.8). Fig. l(b) shows the details of the welding
specimen. All of the test specimens were selected from
the rolled plates such that the direction of welding is
the same as the direction of rolling. This was considered in order to eliminate any possible effect of the
rolling direction on the mechanical properties, and
consequently on the cracking susceptibility.
In the present experiments, the current varied from
450 to 550 A, the travel speed (s) varied from 24 to 36
m/h, the wire feed rate (wfr) varied from 10 to 20 kg/h
and the voltage varied from 35 to 37 V. In order to
study each welding parameter individually, the other
parameters were kept constant.
To study the effect of plate thickness, specimens with
different thicknesses (t) of from 12 to 16 m m were
obtained by machining from a plate which was already
fabricated using a rolling reduction ratio of 6.8 with an
original thickness of 20 ram.
To study the effect of the rolling reduction ratio
(RR), plates of 20 and 16 mm thickness were reduced
to 12 mm thickness by employing reduction ratios of
6.8 and 8.5, respectively. Further to the above plates,
there was the original plate of 12 m m thickness, which
had been subjected to a reduction ratio of 11.3, together with another specimen of zero reduction ratio,
obtained by shaping the original as-cast slab to the
same thickness, 12 ram.
3. Results and discussion
welding direction
~un.in_~o~
,,,,
Ill
Fig. 1. Details of the experimental set-up. (a) Trans-variant strain
equipment: 1, clamping plate; 2, specimen; 3, flux; 4, torch; 5, present
travel distance; and 6, die block. (b) Test-piece: F i = holding forces;
F2 = exerted force; P = penetration; and R = plate resistance thickness.
The observed cracks are characterized by single route
cracks (without branching), as shown in Fig. 2(a),
microscopic observations revealing that the cracks are
inter-granuPar, as indicated in Fig. 2(b).
3.1. Effect of welding current on crack length
Fig. 3 indicates that, for all plate thicknesses used,
the crack length increases with an increase in the welding current. The curves obtained in Fig. 3 are almost
M.E. Khalh!/'et al..,rJotti'Hal OJ Materials Processing Techm,!o~,q. 6g (19971 43-49
45
Fig. 4. Effect of the welding current on the penetration ~lt: (~1) 45[) A"
(b) 5(1it A, and It) 550 A.
(a)
(b)
Fig. 2. Micrographs showing: (a) a single-route crack ( x 75): (b) an
inter-granular crack ( × 150).
parallel, except at the lowest current. In this latter case.
little penetration is obtained, which corresponds to a
great plate resistance thickness, the plate resistance
thickness being the unmelted part of the base metal
under the weld bead, Fig. 1. In contrast, in the case of
greater currents, greater penetration is obtained resulting in a weaker plate resistance thickness, as shown in
Fig. 4, these results being due to the direct effect of the
current on the heat input during the welding process.
The amount of heat put into the weld joint has many
effects, one of the most important of which is the
50
40
nilulion ratio %
Cr~.k k.lUa ( u )
80 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
S-24m/b
w . f . r : 16kK/l~
10
0
___~;
_._..~--- ~ -
"-,. . . . . . . . . .
. _ / ~ --4"-~
/- -~
30
20
change in the dilution rati(,~ i.e. the ratio of the crosssectional area of the molten base metal in the weld bead
to the total cross-sectional area of the weld bead. which
in turn affects the chemical composition of the weld
bead, the latter having a major role in changing the
cracking susceptibility [1,4,6-9].
This means that an increase in the heat input (which
is caused by an increase in the current) leads to an
increase in the dilution ratio, i.e. a greater part of the
base metal is molten and added to the weld bead.
Therefore. by increasing the current the share of the
base metal in the chemical composition is increased
relative to the wire.
Fig. 5 shows that, under the present experimental
conditions, the dilution ratio increases with current
from about 50 to 75%. As a result of the increase in
dilution ratio, the carbon content in the weld metal
increases, Fig. 6(a), and the crack length consequently
increases, Fig. 6(b). The carbon content was also calculated and the results are super-imposed on Fig. 6(a),
indicating that the calculated values arc very close to
the measured values.
As the carbon content increases, the solidification
temperature range, which is :'ritical for the occurrence
of hot cracking [6], increases [I,8.10]. Fig. 7 shows that
as the carbon content measured in the weld metal
increases, the crack length increases. This is in agreement with the relationship between the dilution ratio
and the crack length, shown in Fig. 6(b). This figure
shows that any increase in the dilution ratio is accompanied by an increase in the crack length.
For a welding current starting from 450 A up to 550
A, micro examinations reveal that, as the current increases, the grain orientation becomes steeper, as shown
.
.
.
.
~-.~_ ........
~5_-~.. ~
72.?". . . .
-
40
~ /
450
475
R.R
..--~f
SOl)
Curr~t
20
+
llJ' &|2 m.m
8.6 & 16 m.m
o
6 . 8 & 2 0 m.m
525
550
(amp)
Fig. 3. Effect o f the current on the crack length for different plate
thicknesses and different reduction ratios.
0
.
450
&t
m.m.
o I1.3 &12 m.m.
+ 8.5 & 16 m.m.
$-24m/h
w.Lr.=iQkl~lh
.
.
.
* 6.8
475
.S00
525
&
20 m . m .
550
Cur~nl (Imp)
Fig. 5. Effect o f the current on the dilution ratio for different
different plate thicknesses and rcdvetion ratios.
46
M.E. KhaUaf et al./ Journal of Materials Processing Technology 68 (1997) 43-49
'trice hi weld
0.4
metJl ("k)
w.f.r=lOkglb
o Actual
0.3
61
64
71
(a)
76
74
mlu~on (%)
SO Crick length (m.m.)
.
f
f
40
jJ
30
F i g . 8. Micrograph showing the grain orientation observed at 5 5 0 A .
J
for a high depth/width ratio of lhe weld bead ( x i 50).
R.R-6.8
S=24 m/b
w.f.r.=lO kglk
t=12 m.m.
20
56
58
60
(b)
62
66
aU.aon (%)
F i g . 6. E f f e c t o f the dilution ratio on: (a) the carbon content in the
welding metal; and (b) the crack length.
in Fig. 8. Such steeper orientation is found to promote
solidification cracking, similar to that found in a previous investigation [! l].
3.2. Effect of the welding travel speed
Crzek length (re.m)
R.R~ 6.8
S=24 mlh
tO
~
+ t-12 m.m
o t=16m.m
* l= 20 m.m
1=550 A
w.f.r - 1 0 kg/h
0
24
2"1
J.l
,t0
(a)
36
Third sped (m/b)
~enetration (re.m)
12
IO
,*----~.~...
,
- -
~----_.__._..__
---.
S:
6
4
+
*
R.R-6.8
1-550 A
2
24
t=lZm.m
t-16m.m
o l~2Om.m
,m..(.r~10kg/b
0
0.305
0.311
Carbon In wdd um,,tad(%)
0.1
w . L r - I O kg/h
t--20 mn.m.
~-
0.321
0,3.51
Fig. 7. E f f e c t o f the carbon content in the weld metal on the crack
length.
R.R.-6.8
I0
27
30
Travel speed (m/b)
,t6
33
C,arl~n in weld metal (%)
0.2
15
0.29
20
,/
20
0
l
0.3
25
S
Crm~k lemgth (re.m)
..10
O.4
j~J
30
SO
40
Fig. 9(a) describes the effect of welding travel speed
on the crack length, from which figure it is noted that,
as the travel speed increases, the crack length decreases.
The results obtained can be attributed to the decrease
in the heat input, which is related directly to the
decrease in the travel speed. As the heat input decreases, both the penetration and the dilution ratio
decrease, the carbon content in the weld metal as well
as the depth/width catio of the bead also decreasing.
Fig. 9b and c represent the effect of the welding
travel speed on the penetration and the carbon content
in the weld metal depth/width respectively. The results
of Fig. 9a-c are mutually supportive, as it is indicated
that the crack length increases as the penetration ratio
or the carbon content in the weld metal increases.
35
Microscopic observations indicate that the microstrtlcture of the weld metal obtained at the lowest
speed (2.4 m/h) consists of coarse columnar grains, as
shown in Fig. 10(a). According to the strain theory for
cracking susceptibility, such a structure is more susceptible to hot cracking [12,13]. At the highest travel speed,
* t-12m.m
o t-16m.m
+ t=20m.m
R.R-6.8
i-550A
w.f.r=10ks/h
0
(C)
24
27
JO
33
36
Trlvel speed {m/h)
F i g . 9, E f f e c t o f the welding travel speed on: (a) the crack length; (t
the penetration; and (c) the carbon content in the weld metal.
M.E. KhallaJet al. . d o u r m d o/" Mtttcrittls Prot c~il~.: '
;g
(a)
t'~.~' ~1997) 43
""
,v
dilution ratio decreases with a decrease in the wire feed
rate, as illustrated in Fig. I I(b), this greatly affecting
the resulting chemical composition of the weld me~.al.
The wire used is characterised by depletion in the
carbon content combined with enrichment in the Mn
content. As the decrease in the dilution ratio means an
increase m the wire content in the bead, then the bead
composition will also be characterised by depletion in
carbon and enrichment in manganese. This is supported
by chemical analysis of the welded beads, Fig. I llc)
indicating that increasing the wire feed rate results in
increased %C and decreased %Mn in the weld metal.
Previous investigations [4,6,10] have reported that the
Mn content in the welded bead tends to decrease its
cracking susceptibility.
Another effect of wire feed rate, which is thought to
play a considerable role in decreasing the cracking
susceptibility, is the change in the bead dimensions and
microstructure, which arc associated with the change in
the wire feed rate. It is observed from the macroscopic
observations of the welded beads that the greater the
wire feed rate, the wider is the weld bead, whilst the
weld depth remains constant, Fig. 12. This interpretaCrack I~gth (mm)
35
(tO
Fig. 10. M i c r o g r a p h s ( x 150) s h o w i n g the effect o f the w e l d i n g t r a v e l
s p e e d o n the w e l d m e t a l g r a i n size using c u r r e n t = 550 A. w i r e feed
r a t e = I0 k g / h , a n d S = 7.4 m ; h (a), S = 36 m ' h (b).
.......................................
30
..........
25
-LC - - ~
-
....
22Z - ~
--
-~-- _
- .....
....
,,>_. _
-~
_
--
_
-
-0 ....
-Oe-_
- " .- ......
q
15
R.R =6,8
5
0
I
----5,5 O A
S
= 36m/b
10
125
15
(a)
70
Wire
175
20
feed rate (1¢~)
Dilution ratio (%)
rio
- - "
.t
50
--,
.
.
__._...,~_.
.
.
.
.
.
....
.
40
i
[
30
R.R=6.$
l_-~r~0A
S=~mTn
20
!0
* t=12m.m /
o t=16m.m
+
t=-2Om.m
]
0
10
12.5
15
(13)
I
3.3. Effect of the wire feed rate
~
20
10
the microstructure of the weld metal consists of fine
columnar grains, Fig. 10{b), due to a decrease in the
heat input, this type of structure being less susceptible
to cracking.
Comparing the results given in Fig. 9(a) for the effect
of the welding travel speed, with those given in Fig. 3
for the effect of the welding current, indicates that the
crack length is more sensitive to variations in the
current than it is to variations in the speed. From this
it can be deduced that control of the crack length by
changing the welding current is more effective than by
changing the travel speed. Such a conclusion is of
practical importance.
--~ . . . . . . . . . . .
---~_3. . . . .
17.5
20
Wire feed rate (kg/h)
C&Mn
in weld metal
Ma
~ -M ~
0.8
-
(%)
....... , _ i
-
0.6
One of the factors that has an effect on the composition of the weld metal and therefore on the cracking
susceptibility, is the wire feed rate. as the wire composition is different from that of the base metal.
Fig. 11(a) shows the effect of wire feed rate on crack
length: as the wire feed rate increases the crack length
decreases. This can be attributed to the effect of the
wire feed rate on the bead dilution and dimensions. The
0.4
c%
O.2
--~-~--I,,..o
(c)
10
~--~-- . . . . . -'~......
t=2Om.m
*
0
~
t-16m.m
12,5
15
17.5
20
Wi~. feed rat~, ( l ~ J i a )
Fig. I I. Effect o f t h e w i r e feed rate on: (a) the c r a c k length: Ib) the
d i l u t i o n ratio: a n d (c) t h e C a n d M n c o n t e n t s in t h e weld metal.
48
M.E. Khallaf et al./ Journal of Materials Process#;g Technology 68 (1997) 43-49
Creek leog~ (re,m)
• R.R-I 1.3
+ R.H-8.6
40
R.R=6.8
50
30
R.R=AI casted
Fig. 12. Effect of the wire feed rate on the weld bead shape: (a) I0
kg/h; (b) 15 kg/h; and (c) 20 kg/h.
3.4. Effect of the plate thickness
The effect of plate thickness on crack susceptibility
was tested using different welding currents, keeping the
reduction ratio constant at 6.8. The results of crack
length versus the welding current are plotted in Fig. 13
for three different thicknesses: 12, 16 and 20 mm. The
figure indicates that a greater crack length is obtained
with decreasing plate thickness: the thinner the plate,
the more sensitive the weld bead is to cracking• The
plate thickness represents, then, a resisting distance to
cracking.
Previous studies about the relation between the weld
metal cooling rate and the plate thickness by Kihara et
al. [14] indicate that, for the same heat input, increasing
the plate thickness leads to an increase in the cooling
r~,'- of the weld metal. Thin plate is associated with a
lower weld metal cooling rate during solidification. The
strain theory of solidification cracking [12,13] indicates
that the cracking susceptibility increases with increase
in the solidification time, which is in agreement with the
shrinkage-brittleness theory [13]. Therefore, the hot
cracking is more probable in thin plates, as found in the
present work.
....
475
~ - ~
. ~ " ~~
..rS ' ' ~ / I / ~ / -
w't'r~lOklg TM
~
450
tion agrees with the analysis reported by Blodgett [11],
who reported that the weld bead width/depth ratio can
significantly affect solidification cracking, deep and narrow beads being more susceptible to weld centerline
cracking.
~ - ~ -
500
Curreut (Amp)
525
550
Fig. 14. Effect o f the welding current on the crack length for different
reduction ratios.
3.5. Effect of the plate rolling reduction ratio
It has been reported in the literature that crack
susceptibility in welding is greatly influenced by the
mechanical properties of the plate [2]. As these properties are determined by the amount of reduction in the
plate thickness during its forming process, studying the
direct effect of the reduction ratio on cracking susceptibility, will therefore be of l:ractical significance. For
such purposes, a special group of specimens was prepared with the same thickness (12 mm) but where the
reduction ratio was different: zero (as-cast), 4.25, 6.8,
8.5 and 11.3.
The results obtained applying different welding currents are presented in Fig. 14, from which figure ;,t is
noted that, as the reduction ratio increases, the crack
length increases. This is explained by the variation in
ultimate tensile strength, as discussed previously by
Garland [2]. in his work, Garland investigated the
influence of the ultimate tensile strength on the crack
length during the submerged arc welding process, using
a heat-treatment process (quenching and tempering) to
raise the ultimate tensile strength of mild steel. His
results revealed that the greater the tensile strength of
the base metal is, the more likely solidification cracking
is to occur.
4. Conclusions
SO Chick ksgtb (me)
40
R.R-6.$
S-24mth
w.f.r-lO kllh
2O
10
0
450
475
500
Curv~ut (Amp)
$25
SSO
Fig. 13. Effectof the weldingcurrent on the crack length for different
thicknesseshaving the same reduction ratio.
Crack susceptibility in the welding of medium carbon
steel plates by submerged arc welding is found to be
affected by welding conditions, plate thickness and
plate fabrication conditions, as follows.
1. The crack susceptibility decreases with decreasing
welding current and with increasing welding travel
speed or wire feed rate, the behaviour being related
to variations in the heat input, the dilution ratio, the
penetration and the carbon content.
2. Thin plates are more susceptible to hot cracking
than are thicker plates•
M.E. Khallaj' et al. ,r'JOlll'~l~il O~ Materiuls Prm'es.~ing Technology 68 (i997) 4 3 - 4 9
3. Plates that have been fabricated using greater forming reduction ratios are more susceptible to hot
cracking due to their greater ultimate ~,ensile
strength.
Acknowledgements
The authors wish to thank Dr. Eng. Ali Helmi,
chairman of the Egyptian Iron and Steel works, Helwan, for his valuable support throughout this work.
References
[I] N. Bailey and S. Jones. WHdi..zg R,'~. Sup., {Aug. 1978) 217- 231.
[2] B. Hems Worth, T. Boniszew.ki and N. Eaton, Me,. Con.strm't.
Br. Weld. J., (Feb. 19691 5 17.
49
[3] R.G. Baker and R P. Newman, ,1.let. Con~tru,'t. Br. WehZ. J..
(Feb. 1969) I--4.
[4] J.G. Garland, WeM. Re.s. lilt.. (Jan 19791 59 82.
[5] J.C.M. Farrar and J.G. Garlal~d, DerehJpmenl m "/'ran.~ar¢,.~traint Test ./or asse,~sing Solidi[i~ation Crack Su.sc~7~tthility ql
It'eh/ Metals. Weldinfg hist. Members Report M 7771. 1973.
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High Strength Steels, BOth Anniversary Series, Vol. I, Soc. of
Naval Architects of Japan. Tokyo, 1975.
[8] A.Yu. Sterenbogen and P.F. Petropv, Aurora. Weld., 32 {July
1979) 34-37.
[9] M.L.E. Davis and N. Bailey, The Wehling tn.~t. C'ot~i Wchl Pool
Chemistry and Metallurgy, 1979.
[101 J.G. Garland and N. Bailey, WeM. Res. int., 9 (Jan. 1979)
85- ! 05.
[I 1] O.W. Blodgett, Weld. hmor. Q., 2 {3) (1985) 4.
[12] A. Arne, Weld. Res.. {Sept. 1952) 58 66.
[131 J.C. Borland, Br. Wehl. J., (Aug.. 1960) 508 512.
[14] H. Kihara, H. Suzuki and H. Tamura, 60th Amlirersary Seric.~,
Vol. I, Society of Naval Architects of Japan, Tokyo. 1957.