Effect of M i n o r Elements on HotCracking Tendencies of Inconel 600
Minor-element
additions, incorporated
into welds by a
powder-metallurgy-insert
technique, have a significant
effect on hot-cracking
propensity as evaluated by a
subscale Varestraint Test
BY W. F. SAVAGE, E. F. NIPPES A N D G. M. G O O D W I N
ABSTRACT. An investigation was undertaken to determine the effect of six
minor elements, S, P, Si, M n , Ti and Al,
on the hot-cracking propensity of
Inconel, a solid-solution strengthened
nickel-base alloy.
In order to determine the effects of
these six elements, a new weldability
evaluation test, the "Tigamajig" test,
was developed. An outgrowth of the
"Varestraint" test, the Tigamajig test
combines the advantages of its predecessor w i t h a reduced specimen size
and ease of specimen preparation. A
technique was used w h i c h allowed
the preparation of a large number of
specimens of systematically varied
composition by the incorporation of
compacted-and-sintered powder inserts containing the desired minorelement additions.
boundaries and the subsequent formation of grain-boundary films.
Manganese and Si were both found
to reduce the detrimental effect of S,
at least in part as a result of an increase
in the solid-liquid interfacial energy.
However, a significant Si-Mn interaction effect indicated that these elements were not as effective at reducing the effect of S w h e n both were
present together.
Titanium and Al also both had beneficial effects on hot-cracking propensity. It was proposed that the effect of
Ti and Al, and in part the effect of M n
and Si, was caused by the excellent
deoxidizing capabilities of these four
elements.
A full factorial experiment was then
performed, utilizing all of the 64
possible combinations of the six intentionally added minor elements. The
entire testing program was duplicated
at two levels of augmented strain to
give an accurate estimate of error.
W i t h the aid of the method of Yates
and the analysis of variance, the significant effects of the six minor elements
were determined for three cracking
parameters: the total crack length, the
maximum crack length, and the average crack length.
Sulfur and P were found to be highly
detrimental to all three of the cracking
parameters. The effect of S and P was
attributed to a high degree of segregation, and subsequent reduction in the
effective solidus and liquidus, coupled
w i t h a decrease in the solid-liquid
interfacial energy, w h i c h permitted
wetting of the grain and subgrain
The hot-cracking susceptibility of an
alloy is dependent upon its elemental
composition, and upon the distribution of these elements within the
material. Thus, even if t w o heats of
material could be produced w i t h
precisely the same overall composition
(an impossibility in itself), these materials w o u l d not necessarily exhibit
similar hot-cracking tendencies because of variations in the solute distribution. This distribution is dependent
Introduction
W. F. SAVAGE is Professor of Metallurgical
Engineering and Director of Welding
Research, and E. F. NIPPES is Professor of
Metallurgical Engineering, Rensselaer Polytechnic Institute, Troy, N. Y. C. M. COODWIN, former Graduate Research Assistant
at RPI, is now with the Metals and Ceramics
Div., Oak Ridge National Laboratory, Oak
Ridge, Tenn.
upon the entire past history of the
material, from the time the alloy was
cast as an ingot, to the time that the
welding is actually performed.
Thus, it is futile to attempt to assign
a meaningful cracking-susceptibility
index to a particular alloy. However,
one may attempt to explain the heatto-heat variations for a given alloy, and
eventually conclusions may be drawn
as to how to control the cracking
susceptibility of that alloy.
The Varestraint test' was developed
at Rensselaer as a "universal" w e l d ability test. This test was designed to
permit independent control of the
welding input parameters used during
testing and the degree of restraint to
which the specimen is subjected. The
"degree of restraint" was simulated by
the application of a controlled augmented strain during welding. Thus, it
was possible to use welding input
variables which were similar to those
used in commercial processes, and yet
provide any desired level of restraint in
a laboratory-scale specimen.
Over the years, the Varestraint test
has proven capable of discerning heatto-heat variations in a large variety of
materials.'•- In fact, the Varestraint test
has been so successful, that it seemed
appropriate to employ a similar concept in a large-scale factorial experiment in order to study both the effects
of individual elements and the interaction effects of many elements at
once.
Obviously, a testing program of this
type naturally requires a large number
of samples with a considerable number of compositional variations. This
becomes a problem w i t h the original
Varestraint test because of the consid-
W E L D I N G RESEARCH S U P P L E M E N T I 245-s
erable expense required to produce a
large number of heats of material and
fabricate sufficient samples for Varestraint testing of each heat.
Therefore, a sub-scale test based on
the augmented-strain concept was
devised to utilize small, readily produced specimens whose composition
could be varied as desired.
This test was then used in a largescale, full-factorial experiment to determine the effect of minor elements
on the hot-cracking susceptibility of
Inconel 600.
Object
The objective of this experiment was
to investigate the basic mechanisms
involved in the phenomenon of w e l d metal hot-cracking in Inconel 600, and
to determine the effect of six minor
elements, normally present in this
alloy, (S, P, Si, M n , Ti, and Al) on these
mechanisms.
Materials and Apparatus
Preparation of the Basic Ternary Alloy
High-purity (99.9 + %) Fe, Cr, and Ni
powders were mixed in proportions
corresponding to the basic ternary
composition of Inconel and consolidated into 4 in. (102 mm) diam. rods,
each 24 in. (610 mm) long, by air
induction melting and casting in
graphite molds. These rods were then
welded together and vacuum consumable arc melted into 6 in. (152 mm)
molds.
To investigate the influence of the
six minor elements on hot-cracking
propensity, a full-factorial experimental design was chosen. 1 It was chosen
to investigate the effects of the six
elements at t w o levels of concentration in all possible combinations.
The high-level aim composition for
the six elements is given in Table 2.
Since it was impractical to produce the
64 alloys required by remelting the
basic ternary and preparing 64 "splitheats," a unique method, developed at
RPI, was used for producing the experimental alloys. 4
In this method, the composition of a
small volume within each plate of the
basic ternary alloy was modified by the
following technique:
imens, as indicated by dashed lines in
Fig. 1.
2. A series of three wide-weave GTA
welding passes (sinusoidal weave pattern w i t h Vi in. (12.7 mm) peak-to-peak
oscillation) were then made to melt
and mix the insert w i t h an appropriate
volume of the basic ternary alloy.
Thus, the resulting specimen contains
a remelted " p a d " of modified c o m p o sition with a reproducible pattern of
microsegregation typical of a weld
deposit made under controlled conditions. The solid lines in Fig. 1 represent
the typical appearance of a specimen
after the GTA remelting operation.
3. Atmospheric contamination was
minimized by performing the GTA
remelt operation in a high-purity Ar
atmosphere w i t h i n a dry-box. Contamination by refractory or mold
materials is impossible since the entire
remelted zone is contained w i t h i n the
basic ternary plate, w h i c h thus acts, in
effect, as a "crucible."
1. An alloy insert, prepared by c o m pacting and sintering an appropriate
mixture
of
suitable
high-purity
powders was inserted in a premachined groove along the centerline
of the 6 X 6 in. (152 X 152 mm) spec-
After the inserts had been GTA
remelted into the base-metal plates,
the plates were mechanically straightened, sectioned, and drilled, to provide five test specimens with the
dimensions shown in Fig. 1.
in. (152 X 152 X 6.3 mm). The c o m position of this material is given in
Table 1.
Preparation of the Modified Alloy Pads
The resulting three ingots were then
hot extruded into sheet bar and rolled
into VA in. (6.35 mm) plate. This sheet
bar was initially hot rolled to 5/16 in.
(7.9 mm), followed by cold reduction
of 20% to final thickness.
The basic ternary material was
prepared at Oak Ridge National Laboratory and was delivered to Rensselaer
in the form of plates, each 6 X 6 X VA
Table 1-Composition of High-Purity
"Ternary" Base Material, wt-%
Fe
Cr
Ni
s
p
Si
Mn
11.6
15.2
72.8
0.004
0.001
0.06
0.064
Ti
Al
C
Cu
H,
N2
a,
0.02
0.03
0.003
0.014
0.0004
0.004
0.026
Table 2—High Level Aim Composition
After Remelting, %
s
p
Si
0.015
0.015
0.5
Mn
Ti
Al
246-s I A U G U S T 1977
1.0
0.5
0.5
Fig. 1-Schematic representation of Tigamajig sample preparation
B o t h t h e t o p a n d b o t t o m surfaces o f
each sample w e r e t h e n fly-cut to
assure c o n s t a n t c r o s s - s e c t i o n a n d t o
remove surface oxide. Sample t h i c k ness w a s m a i n t a i n e d in a n a r r o w
r a n g e , n o m i n a l l y 0.250 i n . (6.35 m m ) .
T h e 1 3 / 3 2 i n . (10.3 m m ) d i a m . h o l e s
w e r e d r i l l e d in s u c h a m a n n e r t h a t t h e
center of the w e l d deposit was located
equidistant between the hole centers.
Chemical Analyses
T h e results o f t h e c h e m i c a l analyses
o f t y p i c a l w e l d p a d s are g i v e n in T a b l e
3. A n asterisk (*) d e n o t e s t h e a i m
c o m p o s i t i o n of an e l e m e n t . N o t e , f o r
e x a m p l e , t h a t Insert 1 c o n t a i n s all six
f a c t o r s at t h e i r l o w e r l e v e l s , Insert 64
c o n t a i n s all six f a c t o r s at t h e i r h i g h e r
levels, a n d so o n . T h e s e c o m p o s i t i o n s
may be c o m p a r e d w i t h the desired
f u s i o n - z o n e c o m p o s i t i o n s g i v e n in
T a b l e 2.
The significance of the above analyses is best seen b y l o o k i n g at a t y p i c a l
distribution of compositions obtained.
Figure 2 is a h i s t o g r a m s h o w i n g t h e
f r e q u e n c y of o c c u r r e n c e of a particular
S c o n c e n t r a t i o n as a f u n c t i o n o f % S.
I d e a l l y , this d i s t r i b u t i o n w o u l d s h o w
o n e h a l f (32) o f t h e s a m p l e s at 0% S
a n d t h e o t h e r half at t h e d e s i r e d
n o m i n a l c o m p o s i t i o n , 0.015% S.
T h e a v e r a g e h i g h level o f S c o n centration was then f o u n d by taking
t h e average S c o n t e n t of those samples
to w h i c h S was intentionally added.
S i m i l a r l y , t h e average l o w e r level o f S
c o n t e n t is d e t e r m i n e d f r o m
those
samples to w h i c h S was n o t i n t e n t i o n ally a d d e d . T h e n u m b e r s u s e d in t h e s e
c a l c u l a t i o n s a r e i n d i c a t e d at t h e b o t t o m o f T a b l e 3. H i s t o g r a m s f o r o t h e r
m i n o r - e l e m e n t a d d i t i o n s have b e e n
p r e s e n t e d in a p r e v i o u s paper. 4
Description of the TIGAMAJIG* Test
In t h e d e v e l o p m e n t o f a s u b - s c a l e
Varestraint testing d e v i c e , an a t t e m p t
was m a d e to preserve t h e desirable
features of t h e original Varestraint
device. The major modifications incorp o r a t e d in t h e n e w test w e r e :
*A humorously applied nickname
adopted
for this version of the Varestraint test.
Table 3—Composition of Typical Inconel W e l d Pads, wt-%—Asterisk (*) Indicates Element
Intentionally Added
Insert
Fe
Cr
Ni
1
11
19
22
30
39
53
56
64
Avg. w i t h o u t
element
addition
Avg. w i t h
element
addition
9.6:
9.54
9.92
9.23
9.34
8.97
9.99
9.55
8.76
14.8
14.4
14.8
14.5
14.8
14.6
14.7
14.7
14.4
74.5
74.7
74.5
75.0
74.4
73.4
72.3
74.6
74.5
Al
Mn
Cu
0.00
0.001
0.0005
0.001
0.001
0.0008
0.010*
0.004*
0.004*
0.07
0.07
0.23*
0.07
0.15*
0.30*
0.08
0.23*
0.32*
0.056
0.054
0.050
0.060
0.060
1.200*
1.400*
0.050
1.400*
0.02 ' 0.03
0.31*
0.03
0.01
0.21*
0.35*
0.33*
0.23*
0.03
0.01
0.21*
0.01
0.27*
0.22*
0.03
0.37*
0.23*
0.003
0.003
9.95 14.6 73.7 0.004
0.0013
0.072
0.093
0.014
0.03
0.0028
0.012
9.95 14.6 73.7 0.016
0.0097
0.294
1.331
0.32
0.25
0.0028
0.012
0.005
0.020*
0.004
0.004
0.016*
0.004
0.022*
0.014*
0.013*
0.003
0.002
0.016
0.016
0.01
0.014
0.014
0.01
0.01
0.01
0.01
1. A r e d u c t i o n in t h e s p e c i m e n
size.
2. A w o r k a b l e m e t h o d o f i m p o s i n g
suddenly applied, reproducible, augm e n t e d strain d u r i n g t h e p r o d u c t i o n
of a G T A s p o t w e l d in t h e m o d i f i e d
composition
contained within
the
r e m e l t e d p a d d e s c r i b e d in t h e p r e vious section.
The
specimen
geometry
finally
a d o p t e d is s h o w n in Fig. 1. N o t e t h a t it
is o n l y 6 i n . (152 m m ) l o n g b y 1 i n . (25
m m ) w i d e w i t h a m a x i m u m thickness
o f VA i n . (6.35 m m ) . T e s t i n g o f t h i s t y p e
o f s p e c i m e n has b e e n
performed
s u c c e s s f u l l y o n sheet m a t e r i a l as t h i n
as 0.060 i n . (1.5 m m ) , b u t f o r t h i s
e x p e r i m e n t , all s a m p l e s w e r e n o m i n a l l y VA i n . (6.35 m m ) in t h i c k n e s s .
N o t e f r o m Fig. 1 t h a t several s a m p l e s
w i t h t h e same c o m p o s i t i o n c o u l d be
m a c h i n e d f r o m e a c h 6 x 6 X VA i n .
(152 X 152 X 6.4 m m ) p l a t e . This p e r mitted replication of t w o different
testing conditions.
T h e a c t u a l t e s t i n g is a c c o m p l i s h e d
b y i n i t i a t i n g a s t a t i o n a r y G T A w e l d at
the center of the specimen. After
a l l o w i n g sufficient t i m e for the establishment of a p p r o x i m a t e l y steady-state
thermal conditions, the desired augm e n t e d s t r a i n is s u d d e n l y a p p l i e d , a n d
t h e arc c u r r e n t i n t e r r u p t e d . T h e s t r a i n
is a p p l i e d b y l o a d i n g t h e s a m p l e in
b e n d i n g as a f i x e d - e n d b e a m , a n d t h e
approximate longitudinal augmented
s t r a i n in t h e o u t e r f i b e r s c a n b e c a l c u lated f r o m t h e r e l a t i o n s h i p :
e St/2R
w h e r e t h e t a n g e n t i a l strain o n t h e t o p
surface o f t h e s p e c i m e n , e , is g i v e n as
a f u n c t i o n o f s p e c i m e n t h i c k n e s s , t,
a n d b e n d i n g r a d i u s , R.
Because o f t h e t h e r m a l c o n d i t i o n s
p r o d u c e d b y t h e l o n g - d u r a t i o n , stationary G T A w e l d , a n d t h e essentially
LOW AVG = 0.0 0 4
tn
UJ
a. 30
2
'
tn
O 20
rr
Lit
CD
HIGH AVG =0.016
|
2
-
i .0
n
•
y
k2 y 71,.,,
Ar AA.
/
0
Fig. 2—Distribution
J
7] [7-1
wA i
O.Ol
L"2 _ _ i _ -J22L.
'',
0.02
0.03
0.04
% SULFUR
of S concentrations
in Inconel
Tigamajig
samples
f* # 1 f
Fig. 3—Photograph ot a portion
majig test device
WELDING
of the Tiga-
R E S E A R C H S U P P L E M E N T I 247-s
transverse orientation of the solidification substructure which already exists
in the remelted pad w i t h respect to the
augmented strain, the test is extremely
sensitive to variations in cracking
susceptibility.
The Tigamajig test device is shown
in Fig. 3; it consists of four major
c o m p o n e n t s - a pneumatic air cylinder, a loading ram and die block
assembly, a sample holding fixture,
and a torch assembly.
The arc duration and current selected w i l l , of course, depend upon
the material under consideration and
the specimen thickness; it is desirable
to choose these variables such that
steady-state thermal conditions are
approached before loading occurs.
Under such conditions, the transverse
thermal gradients established are relatively gradual and the severity of
cracking is enhanced. In general, hot
cracking occurs over a relatively narrow range of temperatures in the
vicinity of the solidus, and a gradual
temperature gradient expands the region exposed to the cracking-temperature range at the time of application of
the augmented strain.
providing a single replication of the
entire experiment. To minimize the
effect of systematic errors, the actual
order of testing of each of the samples
within a set was selected from a table
of random numbers.'
Immediately prior to testing, each
sample was thoroughly degreased
w i t h acetone. Shielding gas was allowed to prepurge for at least 30 s
before the automated sequence was
initiated, and the delay time between
samples was maintained such that the
radius die blocks and other parts of the
Tigamajig device were not allowed to
overheat.
Each of the four sets of 64 samples
was tested as a unit, and the data were
read from each set before testing
began on the following set. To minimize the effect of surface oxidation
upon the measurement of cracking
parameters, the as-welded surface of
each of the specimens was cleaned
prior to its measurement with the
following pickling solution: 700 parts
H , 0 , 250 parts cone. (70%) H N O „ and
50~ parts cone. (52%) HF. The samples
were immersed in the solution at 130 F
(54 C) and swabbed for 1-3 min,
followed by a rinse in cold water.
Procedure
Tigamajig Testing Procedure
Data Accumulation
The sample-preparation procedure
w h i c h was discussed in the previous
section yielded five essentially identical test specimens of each of the 64
different nominal compositions. The
results of this work are based on Tigamajig testing of four of these sets of
samples, w i t h the remaining set of
samples being utilized to establish
suitable test conditions.
All Tigamajig testing was performed
under the standard conditions shown
in Table 4. Arc current and voltage
were continually monitored and maintained to within ± 5 % of the nominal
values reported.
Two nominal levels of augmented
strain—1 ?6 and 2%—were investigated
in the experiment, w i t h t w o samples
being tested at each strain level, thus
The cracking data were measured
from the specimen surface using a
stereo binocular microscope at a magnification of X40 and a filar eyepiece
w i t h 200 divisions, 0.5 mil (0.013 mm)
per division.
Throughout this investigation, the
only cracks considered were those
which actually touched the fusion
boundary between the Tigamajig weld
nugget and the weld pad. Referring to
the schematic representation of the
Tigamajig specimen shown in Fig. 1,
note that, to be included in the data, a
crack had to touch the circular fusion
boundary of the Tigamajig test nugget
in the center of the specimen. Thus,
crater cracks w i t h i n the Tigamajig
nugget were ignored, as were cracks in
remote regions of the weld pad which
formed during the GTA-remelting process used to prepare the specimens.
A photomacrograph of a typical
Tigamajig specimen, showing numerous hot cracks, is presented in Fig. 4 in
the polished-and-etched condition at
X9.5. The plane of polish of this
metallographic section is approximately 0.005 in. (0.13 mm) below the
original sheet surface. In Fig. 4, the
structure of the high-purity base metal
is evident at both sides of the wide
weave GTA bead. The oscillation
patterns in this wide-weave bead, and
the epitaxial growth from the base
metal can be readily identified. The
diameter of the GTA spot w e l d is
clearly delineated by a narrow region
of planar growth. Also evident is the
epitaxial growth of the spot w e l d from
the wide-weave bead.
In addition, the more rapid cooling
during solidification of the GTA spot
weld has resulted in a finer subgrain
structure than that of the wide-weave
bead. The discontinuity at the center
of the photomacrograph is a consequence of the shrinkage void which
occurred during the solidification of
the GTA spot.
The length of each of the fusionboundary cracks was recorded, so that
Table 4-Standard Conditions for
Tigamajig Testing of Inconel
Arc
Arc
Arc
Arc
current
time
voltage
length
Electrode
Shielding gas
Power supply
90 A dcsp
30 s
11 V
1/4 in. (6.4 mm) measured cold
1/8 in. (3.2 mm) EWTh,
ground to an incl. angle of 90 deg
25 cfh (18.9 liters/min.)
Ar prepurified grade
(99.998% min.)
3-phase rectifier
248-s I A U G U S T 1977
Fig. 4—Example of hot cracking in a specimen tested in the Tigamajig device, polished-andetched, X9.5
Table 5—Total Crack Length (TCL), M a x i m u m Crack Length (MCL), and Average Crack Length (ACL) for Inconel Tigamajig Specimens
( 1 % Augmented Strain)
lsert
1
2
3
4
5
6
7
8
9
10
II
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Alloy
additions
S
P
Si
Mn
Ti
Al
S-P
S-Si
S-Mn
S-Ti
S-AI
P-Si
P-Mn
P-Ti
P-AI
Si-Mn
Si-Ti
Si-AI
Mn-Ti
Mn-AI
Ti-AI
S-P-Si
S-P-Mn
S-P-Ti
S-P-AI
S-Si-Mn
S-Mn-Ti
S-Ti-AI
S-Si-Ti
S-Si-AI
S-Mn-AI
Avg. TCL,
mils
Avg. MCL,
mils
Avg. ACL,
mils
301
872
524
432
330
206
304
951
636
360
735
757
466
294
319
524
234
240
332
155
104
196
640
600
1069
962
316
336
468
555
524
316
16
194
32
22
20
10
18
227
32
22
105
93
22
18
17
20
24
26
24
14
14
16
174
65
196
153
24
22
48
108
27
20
10
41
12
10
8
6
8
40
12
10
19
24
10
8
10
10
10
8
10
8
8
8
20
15
35
29
11
9
14
18
11
8
for each sample, the f o l l o w i n g p a r a m eters w e r e o b t a i n e d :
1. T o t a l C r a c k L e n g t h
(TCL)-The
s u m of t h e l e n g t h s of all c r a c k s
m e a s u r e d in a s p e c i m e n .
2. M a x i m u m C r a c k L e n g t h ( M C L ) —
T h e l e n g t h o f t h e s i n g l e largest c r a c k
observed for a particular specimen.
Results
T h e e f f e c t s w h i c h w i l l be d i s c u s s e d
w e r e d e t e r m i n e d b y a p p l i c a t i o n of t h e
m e t h o d o f Yates, a n d t h e s i g n i f i c a n c e
of t h e s e e f f e c t s w a s e s t i m a t e d b y t h e
analysis of v a r i a n c e . ' ' " O n l y t h o s e
e f f e c t s d e t e r m i n e d t o b e s i g n i f i c a n t at
t h e a = 0 . 1 % l e v e l are c o n s i d e r e d i n
t h e d i s c u s s i o n of c r a c k i n g p a r a m e t e r s .
This h i g h level o f s i g n i f i c a n c e w a s
o b t a i n e d since the entire experiment
w a s r e p l i c a t e d , p r o v i d i n g an e s t i m a t e
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
Alloy
additions
P-Si-Mn
Si-Mn-Ti
P-Mn-Ti
P-Si-Ti
P-Mn-AI
P-Si-AI
Si-Mn-AI
P-Ti-AI
Si-Ti-AI
Mn-Ti-Al
Si-Mn-Ti-AI
P-Mn-Ti-AI
P-Si-Ti-Al
P-Si-Mn-AI
P-Si-Mn-Ti
S-Mn-Ti-AI
S-Si-Ti-Al
S-Si-Mn-AI
S-Si-Mn-Ti
S-P-Ti-AI
S-P-Mn-AI
S-P-Mn-Ti
S-P-Si-AI
S-P-Si-Ti
S-P-Si-Mn
P-Si-Mn-Ti-AI
S-Si-Mn-Ti-AI
S-P-Mn-Ti-AI
S-P-Si-Ti-AI
S-P-Si-Mn-AI
S-P-Si-Mn-Ti
S-P-Si-Mn-Ti-AI
Avg. TCL,
mils
Avg. MCL,
mils
Avg. ACL
mils
362
194
174
217
329
433
242
286
202
149
184
246
192
304
274
306
392
247
344
724
429
450
912
840
446
214
216
402
506
456
383
338
35
20
18
26
22
28
26
17
22
16
28
20
21
34
24
21
24
29
18
84
30
26
117
94
26
21
20
22
53
26
22
24
12
10
10
11
9
12
12
8
10
9
10
9
10
16
9
10
12
12
8
20
12
12
21
16
10
12
9
10
13
10
10
11
Table 6—Summary of Results—Total Crack Length (a = 0.1%)
Treatment
combination
1%
strain
3. A v e r a g e C r a c k L e n g t h ( A C L ) - T h e
l e n g t h o f t h e average c r a c k in a p a r t i c ular s p e c i m e n , f o u n d b y d i v i d i n g t h e
TCL by t h e t o t a l n u m b e r o f cracks.
To m i n i m i z e the effects of h u m a n
error, t w o o b s e r v e r s m e a s u r e d a n d
recorded the cracking data i n d e p e n d e n t l y f o r e a c h set o f d u p l i c a t e s p e c imens. The average data o b t a i n e d for
t h e 1 % a u g m e n t e d strain are p r e s e n t e d
as T a b l e 5 f o r all 64 test c o m p o s i tions.
Inse
2%
strain
Effect
S
P
S-Si
Ti
S-Mn
Mn
Mean
26.5
12.6
-7.0
-10.9
S
P
S-Si-Mn
Si
Ti
S-Si
S-Mn
Mn
Mean
29.8
14.2
11.2
-13.6
-14.1
-15.2
-16.4
-20.1
-13.1
-21.6
o f e r r o r b a s e d o n 64 s e p a r a t e c o m p a r i sons f o r e a c h p a r a m e t e r .
Total Crack Length
A s u m m a r y of the significant effects
o b t a i n e d f o r t o t a l c r a c k l e n g t h at t h e
t w o s t r a i n levels is s h o w n i n T a b l e 6.
Note immediately the f o l l o w i n g gene r a l i t i e s : t h e t o t a l crack l e n g t h at 2%
a u g m e n t e d s t r a i n s h o w s a 50% i n crease o v e r t h e v a l u e at 1 % s t r a i n . T h i s
indicates that a l t h o u g h the total crack
WELDING
Best value,
mils
745
405
675
170
398
194
412
1167
583
514
569
300
767
690
516
636
l e n g t h vs. % a u g m e n t e d s t r a i n c u r v e is
f l a t t e n i n g o u t , 2% s t r a i n is still b e l o w
"saturation
level" for
total
crack
l e n g t h . This is also a t t e s t e d b y t h e fact
t h a t t h e r e are m o r e s i g n i f i c a n t e f f e c t s
at 2% t h a n at 1 % a u g m e n t e d s t r a i n , i.e.,
it w a s a d v a n t a g e o u s t o test at t h e
h i g h e r strain l e v e l as far as t h e t o t a l c r a c k - l e n g t h p a r a m e t e r is c o n c e r n e d .
H o w e v e r , it is p o s t u l a t e d o n t h e basis
o f past e x p e r i e n c e t h a t a f u r t h e r
increase in s t r a i n m i g h t c a u s e t h e t o t a l
RESEARCH S U P P L E M E N T I 249-s
crack l e n g t h t o a p p r o a c h a s a t u r a t i o n
v a l u e . If t h i s w e r e t h e case, f u r t h e r
increase in a u g m e n t e d s t r a i n w o u l d
n o t be l i k e l y t o p r o v i d e a n y m o r e
i n f o r m a t i o n a n d m i g h t , in f a c t , fail t o
s h o w s o m e of t h e e f f e c t s f o u n d s i g n i f i c a n t at t h e l o w e r a u g m e n t e d strain
levels.
c o m b i n a t i o n as w h e n t h e y are p r e s e n t
separately.
5. P is d e t r i m e n t a l , e s p e c i a l l y in t h e
presence of other i n t e n t i o n a l " i m p u r i ty" additions.
6. Si a n d Ti are b o t h b e n e f i c i a l f o r
r e d u c i n g the total crack length.
To summarize the significant effects
o n t o t a l c r a c k l e n g t h at b o t h levels o f
a u g m e n t e d strain:
M a x i m u m Crack Length
1. S has a s t r o n g d e t r i m e n t a l effect.
2. T h e d e t r i m e n t a l e f f e c t of S is
m i n i m i z e d by t h e a d d i t i o n of M n .
3. Si is also b e n e f i c i a l in m i n i m i z i n g
t h e d e t r i m e n t a l e f f e c t o f S.
4. Si a n d M n d o n o t w o r k as w e l l in
The effects w h i c h w e r e d e t e r m i n e d
t o be s i g n i f i c a n t o n t h e basis o f t h e
m a x i m u m c r a c k l e n g t h are s u m m a r i z e d in T a b l e 7.
Before considering the data, s o m e
g e n e r a l c o m m e n t s s h o u l d be m a d e
a b o u t b o t h levels o f a u g m e n t e d s t r a i n :
t h e r e are 16 e f f e c t s f o u n d t o b e s i g n i f -
Table 7—Summary of Results—Maximum Crack Length (a = 0.1%)
Treatment
combination
1%
strain
2%
strain
S
P
S-Mn-Al
S-P
Si-Mn
S-Si-Mn
Si
P-Mn
S-P-Mn
Ti
Mn-AI
Al
S-AI
S-Si
Mn
S-Mn
Mean
S
S-Si-Mn
Si-Mn
Si
S-Si
Mn
S-Mn
Mean
Effect
45.4
18.4
15.0
14.7
14.2
12.8
-12.3
-12.6
-12.8
-13.5
-15.8
-17.6
-17.9
-19.4
-40.5
-41.6
46
30
30
-24
-31
-39
-44
Best value,
mils
132
11
13
191
46
45
13
42
57
0
8
39
98
74
38
49
44
171
33
32
27
56
25
28
49
Table 8—Summary of Results—Average Crack Length (a = 0.1%)
Treatment
combination
1%
strain
2%
strain
250-s I AUGUST 1977
Effect
Best value,
mils
S
Si-Mn
S-Si-Mn
P
Si
Ti
S-Si
Mn
S-Mn
Mean
3.13
1.69
1.28
1.22
-1.16
-1.22
-2.13
-2.69
-2.91
27.9
11.4
10.1
11.4
10.1
6.6
15.4
8.6
10.8
13.0
S
Si-Mn
S-Si-Mn
S-Si
Mn
S-Mn
Mean
3.1
2.4
2.2
-2.8
-3.0
-3.8
32.3
15.7
13.1
17.5
9.7
9.5
15.0
icant at t h e a = 0 . 1 % level f o r 1 %
s t r a i n , w h i l e t h e r e are o n l y 7 e f f e c t s
s i g n i f i c a n t at t h e 0 . 1 % l e v e l w i t h 2%
strain. N o t e t h a t d o u b l i n g t h e s t r a i n
o n l y c a u s e d an i n c r e a s e in t h e m e a n
m a x i m u m c r a c k l e n g t h f r o m 44 m i l s t o
49 m i l s . T h i s b e h a v i o r a p p e a r s t o i n d i cate t h a t a b o v e a c e r t a i n strain level
t h e m a x i m u m c r a c k l e n g t h is m o r e
dependent on the thermal gradients
w h i c h exist in t h e T i g a m a j i g s p e c i m e n
than o n t h e level of a u g m e n t e d strain.
Thus, the
maximum
crack
length
p r o v e d t o b e an e x t r e m e l y s e n s i t i v e
i n d i c a t o r o f c r a c k i n g t e n d e n c i e s at t h e
1 % a u g m e n t e d s t r a i n l e v e l , b u t less
e f f e c t i v e at t h e 2% s t r a i n l e v e l .
To s u m m a r i z e t h e effects o n m a x i m u m crack l e n g t h :
1. S has a d e t r i m e n t a l e f f e c t o n t h e
m a x i m u m crack length.
2. T h e e f f e c t is r e d u c e d b y t h e a d d i t i o n o f e i t h e r M n or Si, w i t h M n b e i n g
more effective.
3. T h e b e n e f i c i a l e f f e c t o f e i t h e r M n
or Si is r e d u c e d w h e n b o t h e l e m e n t s
are p r e s e n t t o g e t h e r .
4. P has a d e t r i m e n t a l e f f e c t , e s p e c i a l l y in t h e p r e s e n c e o f S.
5. M n h e l p s t o r e d u c e t h e e f f e c t
of P.
6. Ti a n d
Al
both
reduce
the
maximum
crack l e n g t h , t h e
latter
t h r o u g h an i n t e r a c t i o n w i t h S.
Average Crack Length
T h e s i g n i f i c a n t e f f e c t s o n t h e average c r a c k l e n g t h are s u m m a r i z e d in
T a b l e 8. N o t e t h a t , as w a s t h e case f o r
the m a x i m u m - c r a c k - l e n g t h considerat i o n , m o r e s i g n i f i c a n t e f f e c t s are f o u n d
at t h e 1 % t h a n at t h e 2% a u g m e n t e d
strain l e v e l .
T h e six e f f e c t s s i g n i f i c a n t at t h e
a = 0 . 1 % l e v e l f o r 2% s t r a i n are t h e
s a m e as t h e first six s i g n i f i c a n t e f f e c t s
at 1 % s t r a i n ; t h u s it a p p e a r s t h a t t h e
a d d i t i o n a l strain c l o u d s t h e issue,
decreasing the significance of s o m e
effects w h i c h a p p e a r e d at t h e l o w e r
a u g m e n t e d strain l e v e l . N o t e t h a t t h e
mean v a l u e of t h e average crack l e n g t h
o n l y increases f r o m 13 t o 15 m i l s w h e n
t h e strain level is i n c r e a s e d f r o m 1 %
t o 2%.
To s u m m a r i z e the effects o n t h e
average c r a c k l e n g t h :
1. S has t h e s t r o n g e s t d e t r i m e n t a l
effect.
2. T h e d e t r i m e n t a l e f f e c t o f S is
r e d u c e d m o s t e f f i c i e n t l y by t h e p r e s e n c e of M n .
3. Si is also e f f e c t i v e at r e d u c i n g t h e
d e t r i m e n t a l e f f e c t o f S.
4. As w a s seen f o r t h e case o f t o t a l
crack length and m a x i m u m
crack
l e n g t h , Si a n d M n h a v e an a d v e r s e
s y n e r g i s t i c e f f e c t , a n d t h u s are less
e f f e c t i v e in c o m b i n a t i o n t h a n w h e n
e a c h e l e m e n t is p r e s e n t s e p a r a t e l y .
5. P is seen to have a detrimental
effect.
6. Ti has a beneficial effect, as was
also seen for both of the other
cracking parameters.
Discussion of Results
In general, it is seen that all three of
the cracking parameters considered
are significant indicators of cracking
propensity. For this alloy, the maximum crack length at 1% augmented
strain appears to be the most sensitive
indicator of cracking
tendencies,
showing at least twice as many effects
significant at the a = 0.1% level as
either of the other parameters. Note,
however, that coupled w i t h this high
sensitivity is a high degree of scatter,
so that it w o u l d be extremely risky to
base conclusions upon only a few
measurements of the maximum crack
length. In general, if only a few specimens are available, more valid conclusions may be formed from measurements of the total crack length and/or
average crack length.
It should be noted that the maximum crack length is highly sensitive to
the temperature gradient present at
the instant of straining. In fact, it
appears that the maximum crack
length exhibits a saturation value
directly related to the distance from
the weld pool to a point where the
temperature falls below the effective
solidus of the segregated boundary
experiencing cracking. Once sufficient
augmented strain is imposed to propagate a crack to this point, a further
increase in strain has little effect on
maximum crack length. Therefore, in
all cases, care must be taken to ensure
that the testing is performed below
this saturation strain level for the
material under investigation.
Note also that the saturation strain
may have a different value for each of
the cracking parameters considered.
For example, in this experiment, there
was a greater number of significant
effects on the total crack length at the
2% than at the 1 % augmented strain
level, while the opposite was true for
both the maximum crack length and
the average crack length.
For all three of the cracking parameters considered, S had by far the
strongest detrimental effect. Some of
the reasons for this strong effect of S
may be deduced from the Ni-S binary
phase diagram. The addition of S to Ni
causes a drastic reduction in both the
liquidus and solidus temperatures.
Furthermore, the average distribution
coefficient*, kave., is approximately
*The distribution coefficient, k, is defined
as k = Q/C,., where Q is the composition
of a solid in equilibrium with a liquid of
composition C,..
0.0005. Thus, -during solidification,
even a weld w i t h an extremely low
nominal S content may develop segregated areas which are high in S and
therefore have a correspondingly low
melting point. Such regions are particularly prone to cracking w h e n subjected to either a thermally induced or
an augmented strain at temperatures
near or above their effective solidus
temperature.
A typical hot crack in a sample
containing S as an intentional addition
is shown in Fig. 5. This photomicrograph was taken of the etched surface
utilizing Normarski phase contrast.
The fusion boundary between the
Tigamajig nugget on the left and the
weld pad on the right is readily
evident. Also note that there are
second-phase particles, probably oxides, in both the GTA spot fusion zone
and the weld pad. The inclusions tend
to be located along grain and subgrain
boundaries produced during solidification in both instances. Thus, the
slow cooling w h i c h caused the coarser
substructure in the weld pad is probably the explanation for the larger
inclusions apparent in this region as
well.
The portion of the hot crack w i t h i n
the GTA spot weld in Fig. 5 proceeds
along grain and subgrain boundaries,
as did all such cracks observed in this
investigation. It is in these last regions
to solidify that one w o u l d expect to
find segregated those elements such as
S which have a distribution coeffi-
cient, k, less than unity. Therefore, this
work confirms the classical theory that
S causes hot cracking by lowering the
liquidus and solidus temperatures of
the regions in which segregation
occurs.
The detrimental effect of P on
cracking might also be anticipated
from inspection of the Ni-P binary
diagram, w h i c h contains a eutectic
system with an average distribution
coefficient, kavK., considerably less
than unity. Thus, the effect of P is
somewhat similar to that of S. It is
interesting to note there is a beneficial
P-Mn interaction effect on the maximum crack length at 1% augmented
strain, indicating that M n is beneficial
in minimizing the effect of P as well as
that of S.
Note that there is also a detrimental
S-P interaction effect. It is probable
that the Ni-S-P ternary diagram, if it
were available, would show even more
drastic reductions in liquidus and
solidus temperatures and smaller distribution coefficients than either binary system, indicating that greater
degrees of segregation w o u l d occur
when S and P are present together.
It is proposed, however, that S and P
have an additional effect which promotes the formation of hot cracks.
Figure 6 shows the etched view,
utilizing Normanski phase contrast, of
a crack in the specimen containing
additions of S, P, and Ti. Both the
location and morphology of this particular crack are unique and deserve
Fig. 5—Typical Hot Crack in specimen containing S (Wazau's Etch), Normarski phase contrast,
X 700 (reduced 49% on reproduction)
Fig. 6—Crack at weld pad fusion line in specimen containing S, P, and Ti (Wazau's Etch),
Normarski phase contrast, XlOO (reduced 50% on reproduction)
W E L D I N G RESEARCH S U P P L E M E N T I 251-s
special c o n s i d e r a t i o n .
N o t e at t h e e x t r e m e r i g h t t h e f u s i o n
b o u n d a r y b e t w e e n the w e l d pad a n d
t h e base m a t e r i a l . T h e r e g i o n to t h e
l e f t o f t h i s l i n e i n Fig. 6 is t h e " p u r e "
w r o u g h t t e r n a r y base m a t e r i a l , w h i l e
t h e area t o t h e r i g h t o f this l i n e
c o n t a i n s i n t e n t i o n a l a d d i t i o n s of S, P,
a n d Ti. As s h o w n in Fig. 6, t h e h o t
c r a c k has p r o g r e s s e d a p p r o x i m a t e l y
0.085 i n . (2.16 m m ) (8.5 i n . (216 m m ) at
X100) into the pure ternary material
a l o n g a n e t w o r k of g r a i n b o u n d a r i e s .
This particular t r e a t m e n t c o m b i n a t i o n ,
S-P-Ti, h a d n e a r l y t h e h i g h e s t p o s s i b l e
best v a l u e f o r c r a c k i n g t e n d e n c i e s a n d
w a s t h e o n l y o n e o f 64 t r e a t m e n t
c o m b i n a t i o n s w h i c h r e s u l t e d in c r a c k i n g in this r e g i o n o f t h e s p e c i m e n s
d u r i n g t h e G T A - r e m e l t i n g passes.
A m e c h a n i s m by w h i c h s u c h a c r a c k
c o u l d f o r m m a y be s u m m a r i z e d as
f o l l o w s : t h e p r o g r e s s of t h e G T A
p r o d u c i n g t h e w e a v e b e a d results in
h i g h l y s e g r e g a t e d g r a i n b o u n d a r i e s in
t h e w e l d p a d w h i c h , as s h o w n b y
p r e v i o u s w o r k at R P I , ' 8 m u s t be c o n t i g u o u s w i t h t h e b o u n d a r i e s in t h e
base m e t a l f r o m w h i c h t h e g r o w t h w a s
e p i t a x i a l l y n u c l e a t e d . If c e r t a i n e n e r g y
c o n d i t i o n s are s a t i s f i e d , t h e s e g r e g a t e d
l i q u i d , r i c h in S a n d P, w i l l w e t t h e
boundaries, forming a liquid film.
The energy c o n d i t i o n s w h i c h must
b e satisfied are s h o w n in Fig 7; in o r d e r
for l i q u i d to w e t the grain b o u n d a r y
(i.e., f o r 0 = 0 ) , t h e g r a i n - b o u n d a r y
e n e r g y , a s s , m u s t be g r e a t e r t h a n t w i c e
the
liquid-solid
interfacial
energy,
a S L —that is, t h e ratio a^./a^
must be
less t h a n or e q u a l t o o n e - h a l f . B o r l a n d "
suggests t h a t l o w v a l u e s of this r a t i o
are e x t r e m e l y h a r m f u l , s i n c e n e a r l y
c o n t i n u o u s f i l m s are f o r m e d a l o n g t h e
b o u n d a r i e s . Ratios h i g h e r t h a n 0.5 are
beneficial, Borland points o u t , because
GRAIN
s h o w e d t h i s d i s t i n c t i v e flat p u d d l e
surface
represented
the
following
e i g h t t r e a t m e n t c o m b i n a t i o n s : S, S-P,
S-Al, S-Ti, S - A I - T i , S-P-Ti, S-P-AI, a n d
S-P-Ti-AI.
N o t e t h a t t h i s g r o u p r e p r e s e n t s all o f
the possible treatment c o m b i n a t i o n s
w h i c h c o n t a i n S, a n d yet at t h e s a m e
t i m e d o n o t c o n t a i n e i t h e r M n or Si.
O n e of the consequences of such a
p u d d l e c o n t o u r is seen f r o m
the
e n e r g y c o n s i d e r a t i o n s s h o w n in Fig. 8.
N o t e t h a t , as t h e p u d d l e
surface
c o n t o u r b e c o m e s f l a t t e r (i.e., as t h e
angle Q approaches 0 deg, the angle a
a p p r o a c h e s 180 d e g ) , t h e m a x i m u m
value w h i c h the liquid-solid interfacial
energy, aLS, may have u n d e r e q u i l i b r i u m c o n d i t i o n s m u s t be d e c r e a s e d ,
s i n c e at e q u i l i b r i u m , b y t h e l a w o f
sines:
t h e l i q u i d is t h e n r e s t r i c t e d to g r a i n
edges a n d c o r n e r s .
It is o b v i o u s t h a t t h e r a t i o a S I . / a s s
m u s t h a v e b e e n less t h a n 0.5 in t h i s
case b e c a u s e l i q u i d r i c h i n S a n d P has
penetrated along the grain boundaries
in t h e u n m e l t e d base m e t a l . T h i s p e n e tration process was u n d o u b t e d l y a i d e d
b y t h e l o n g i t u d i n a l s h r i n k a g e stresses
w h i c h w o u l d be transverse to t h e grain
boundaries being penetrated.
W i t h e a c h successive pass o f t h e arc,
t h e s i t u a t i o n is w o r s e n e d as t h e o n e
b a c k - f i l l e d c r a c k p r o v i d e s l o c a l stress
relief for s u r r o u n d i n g grain b o u n d a r i e s
a n d g r o w s p r o g r e s s i v e l y larger as t h e
plate attains higher a n d higher t e m p e r a t u r e s . T h e S- a n d P-rich l i q u i d t h u s
proceeds farther each t i m e before
e n c o u n t e r i n g t h e effective solidus isotherm.
A c c o r d i n g to this reasoning, any
e l e m e n t s , s u c h as P a n d S, w h i c h l o w e r
t h e s u r f a c e free e n e r g y o f a l i q u i d solid interface t e n d to increase the
hot-cracking propensity and become
t h e m o r e d e t r i m e n t a l if t h e i r d i s t r i b u t i o n c o e f f i c i e n t is s m a l l as w e l l .
O n e further observation should be
m e n t i o n e d s i n c e it s u p p o r t s t h e p r o posed m e c h a n i s m of f o r m a t i o n of the
crack s h o w n in Fig. 6. It w a s n o t e d
d u r i n g t h e process o f T i g a m a j i g testi n g , t h a t t h e r e w a s a w i d e v a r i a t i o n in
the surface c o n t o u r of t h e GTA spot
f u s i o n z o n e . In m o s t o f t h e s p e c i m e n s ,
the center of the t o p surface of the
fusion zone was depressed, and the
material displaced f r o m this center
region was " m o u n d e d " up a r o u n d the
e d g e o f t h e c i r c u l a r G T A s p o t w e l d , as
i n d i c a t e d in Fig. 8B.
Eight of t h e specimens, h o w e v e r ,
s h o w e d a r e l a t i v e l y flat p u d d l e s u r f a c e
c o n t o u r , as i n d i c a t e d s c h e m a t i c a l l y in
Fig. 8A. T h e e i g h t s p e c i m e n s w h i c h
ar.s
a,. v
aSv
sin a
sin /?
sin Y
w h e r e a L S , a,, v a n d a s v are t h e s u r f a c e
free
energies
of
the
liquid-solid,
liquid-vapor, and solid-vapor
interfaces, r e s p e c t i v e l y , a n d a, ji, a n d y ate
t h e angles as s h o w n in Fig. 8.
The fact that o n l y specimens c o n t a i n i n g S in t h e a b s e n c e o f b o t h M n
a n d Si e x h i b i t e d flat p u d d l e c o n t o u r s
provides qualitative support for the
argument that S lowers the liquid-solid
interfacial energy. Furthermore, o n t h e
basis o f t h e c h a n g e in s u r f a c e c o n t o u r
in t h e p r e s e n c e o f e i t h e r M n or Si, it
appears h i g h l y likely that b o t h these
e l e m e n t s are c a p a b l e o f i n c r e a s i n g t h e
surface free energy of t h e s o l i d - l i q u i d
interface, thereby m i n i m i z i n g b o u n d ary p e n e t r a t i o n a n d s u b s e q u e n t c r a c k ing. T h i s a r g u m e n t is e q u a l l y v a l i d in
explaining t h e effect of these e l e m e n t s
on cracking occurring within the highly s e g r e g a t e d s t r u c t u r e in t h e r e m e l t e d
A
'sv
a
GRAIN
BOUNDARY
ss
LIQUID
GRAIN
<ASL
^ss
Fig. 7—Schematic representation
grain-boundary
wetting
Fig. 8 (right)-Schematic
252-s I A U G U S T
1977
B
<
~
2
ot energy conditions
view of Tigamajig
required
fusion-zone
for
surface
contour
_.
___ S r
/
V
JI
'
weld pad during Tigamajig t e s t i n g Figs. 5 and 6.
In the case of Fe-base alloys, Kiessling and Westman"' report that the
tendency for MnS to penetrate grain
boundaries increases w i t h decreasing
M n S / O , ratio. This implies that O
lowers the surface free energy of MnS,
and, presumably, of S-rich liquids in
general.
The oxygen content of the weld
pads analyzed ranged from 0.0097 to
0.028 wt%, presumably as a consequence of the surface oxides present
on the powders used in producing the
air-melted base metal and those used
in producing the inserts. Thus, if a
similar S-O interaction occurs for
Inconel, the beneficial effects of M n ,
Si, Ti, and Al could also be in part a
result of their strong deoxidizing capability. Unfortunately, no data are available currently on the amount of
dissolved and combined O present in
the weld pads, so the hypothesis
cannot be verified at this time.
The Si-Mn and S-Si-Mn interactions
are more difficult to explain, unless the
simultaneous presence of Si and M n
results in a lower solid-liquid surfacefree energy than is present w i t h M n
alone. If the effect of a Si-Mn interaction lowering the surface free energy
were to counteract part of the beneficial effects of Si on the dissolved O
and of M n when alone on the liquidsolid surface free energy, the observed
effects could be rationalized.
Conclusion
The following conclusions were
drawn during the evaluation of the
effect of six minor alloying elements,
normally present in Inconel 600, on the
hot-cracking propensity of the alloy.
Method of Testing
1. The Tigamajig test was found to
be a useful test for determining the
susceptibility of Inconel to hot cracking, combining the virtues of the
previously developed Varestraint test
w i t h a reduced specimen size and
greater ease of specimen preparation.
2. It was found that the composition of Tigamajig samples could be
altered and controlled w i t h i n reasonable limits by the introduction of
powder inserts containing the desired
additions and using a series of wideweave GTA passes to melt and mix the
additions w i t h the base metal.
3. The weave-bead technique used
to incorporate the powder inserts
produced a reproducible solidification
substructure w h i c h was particularly
sensitive to hot cracking due to the
orientation of substructure boundaries
w i t h respect to the strains imposed on
the Tigamajig specimen.
Choice of Cracking Parameters
1. The maximum crack length was
seen to be the most sensitive indicator
of cracking propensity at 1 % augmented strain w i t h the accompanying
disadvantage
that this
parameter
shows a high degree of experimental
scatter. When a large number of specimens are available, the maximum
crack length w i l l reveal more significant effects, but if few samples are
available, the total crack length or the
average crack length will give a more
reliable estimate of cracking sensitivity.
2. W i t h regard to the strain levels, it
was found that information concerning the effects on maximum crack
length and average crack length is lost
if testing is performed above the 1 %
augmented strain level, whereas increasing the augmented strain above
this level produces little new information about the total crack length.
Effect of Added Elements on the Cracking
Parameters for Inconel
1. S was found to have a highly
detrimental effect when the avg.
concentration was increased from
0.004 to 0.016 wt%. The adverse effect
of S was attributed to segregation of
this element and the subsequent
reduction in effective solidus and
liquidus, coupled with a lowering of
the liquid-solid interfacial energy,
causing the formation of thin films of
S-rich liquid at the grain and subgrain
boundaries.
2. P was found to have a detrimental effect similar to, but not as
severe as, that of S when the avg.
concentration of P was raised from
0.001 to 0.010%. A S-P interaction
increased the detrimental effect of the
t w o elements w h e n both were present
in combinations.
3. M n and Si both had beneficial
effects on the cracking parameters,
resulting at least in part from an
increase in the liquid-solid interfacial
energy by the addition of these
elements in the range 0.09-1.33% and
0.07-0.29%, respectively. The increase
in liquid-solid interfacial energy minimizes the formation of liquid grainboundary films, thus reducing hotcracking propensity. M n and Si had a
detrimental interaction w h i c h limited
the effectiveness of these t w o elements in reducing the effect of S,
when both M n and Si were present
simultaneously.
4. Ti and Al also had beneficial
effects on the cracking parameters
investigated when Ti was increased
from 0.01 to 0.32% and when Al was
increased from 0.03 to 0.25%. The
beneficial effect of Ti, Al, M n , and Si
was postulated to result from (in addition to the mechanism discussed
above for M n and Si) the excellent
deoxidizing influence of these four
elements. Since O has been observed
to lower surface free energy of
sulfides, it was suggested that these
elements could increase the surface
free energy by the reduction of
dissolved O, thereby decreasing cracking tendencies.
Acknowledgment
The authors wish to acknowledge
financial support provided by a NASA
Traineeship during the early phase of
the program.
The authors w o u l d like to acknowledge the support of the Oak Ridge
National Laboratories.
References
1. Savage, W. F., and Lundin, C. D., "The
Varestraint Test," Welding lournal, 44
(10), Oct. 1965, Research Suppl., pp. 433-s to
442-s.
2. Savage, W. F., and Lundin, C. D., "Application of the Varestraint Technique to
the Study of Weldability," Welding lournal,
45 (11), Nov. 1966, Research Suppl., pp. 497s to 503-s.
3. Davies, O. L., The Design and Analysis
of Industrial Experiments, Hafner Publishing Company, New York, N. Y. (1960).
4. Savage, W. F., Nippes, E. F., and Goodwin, G. M., "Effect of Minor Elements on
Fusion-Zone Dimensions of Inconel 600,"
Welding lournal, to be published.
5. Cochran, W. G., and Cox, G. M., Experimental Designs, John Wiley & Sons, Inc.,
New York, N. Y. (1957).
6. Bowker, A. H., and Lieberman, G. J.,
Engineering Statistics, Prentice-Hall, Inc.,
Englewood Cliffs, N. J. (1959).
7. Savage, W. F., and Aronson, A. H.,
"Preferred Orientation in the Weld Fusion
Zone," Welding lournal, 45 (2), Feb. 1966,
Research Suppl., pp. 85-s to 89-s.
8. Savage, W. F., Lundin, C. D., and
Chase, T. F., "Solidification Mechanics of
Fusion Welds in Face-Centered Cubic
Metals," Welding lournal, 47 (11), Nov.
1968, Research Suppl., pp. 522-s to 526-s.
9. Borland, J. C, "Suggested Explanation
of Hot Cracking in Mild and Low Alloy Steel
Welds," B.W.R.A. Report, Welding Research Abroad, VIII, 2, Feb. 1962.
10. Kiessling, R., and Westman, C, "Sulfide Inclusions and Synthetic Sulfides of the
(Mn, Mo)S-Type," lournal of the Iron and
Steel Institute, 204 (4), 377-379, 1966.
W E L D I N G RESEARCH S U P P L E M E N T I 253-s