The Nature and Morphology of

Fissures in Austenitic Stainless Steel

Weld Metals
Fissures occur primarily along grain boundaries in the
HAZ from the previous weld deposit, and fissuring is en-
hanced by multiple thermal cycling in the HAZ and is
more likely to occur in ferrite-free areas.

BY C. D. LUNDIN AND D. F. SPOND

ABSTRACT. As a result of the testing (i.e.. heat-affected zone) of the pre- correlation exists between the Fis-
program to develop the relationship viously deposited pass. sure Bend Test observations and
between ferrite and fissuring in Types 2. The fissuring tendency is en- those recorded from production
308, 308L, 316, 316L, 309, 318, 347 hanced by multiple thermal cycling in welds.
and 16-8-2 austenitic stainless steel the HAZ.
weld metals sponsored by the Stain- 3. The fissures are invariably more Introduction
less Steel Advisory Subcommittee of prone to form in ferrite-free areas. It is recognized that austenitic
the High Alloys Committee of the 4. The origin of the fissures is re- s t a i n l e s s steel w e l d m e t a l s a r e
Welding Research Council, numerous lated to a liquation mechanism. susceptible to fissuring in the fusion
well documented specimens were 5. The size distribution of fissures zone of single-run beads (Refs. 1-4),
available for study. These specimens determined by light metallography at in the HAZ (i.e. heat-affected zone) of
included those prepared by the 12 in- X200 reveals that the average fissure the base metal (Refs. 1, 5-12), and in
dustrial laboratories involved in the length in Type 308 stainless steel weld the HAZs of weld metal produced by
initial testing and the material depos- metal is 0.004 in. (0.1 mm). subsequent beads in multipass welds
ited in the extension of the original The thermal distribution in the HAZ (Refs. 5, 6, 13, 14, 15). The fissuring in
test scheme by the University of Ten- was determined for the actual weld- single-run welds is normally c o m -
nessee. Each weld metal was avail- ing conditions utilized in the test, and bated by reduction of weld metal re-
able at four ferrite levels so the effect the peak temperature range in which straint and by composition control to
of ferrite could be readily assessed. the fissures form is discussed. The in- assure residual ferrite in the room
Careful study of these specimens by fluence of weld bead sequence and t e m p e r a t u r e m i c r o s t r u c t u r e . The
light metallography, scanning elec- the effect of multiple thermal cycling' base metal HAZ phenomenon has
tron microscopy and energy disper- on fissuring tendency were evaluated been largely associated with the
sive x-ray techniques has revealed in- with both SMA deposits and GTA re- stabilized grades of stainless such as
formation as to the nature and mor- melting of previously deposited SMA Type 347 and in recent years has
phology of the fissures present at low weld metal. The multiple thermal cy- become a relatively minor problem
ferrite levels. cle effect can produce a several-fold due to improved residual elemental
In essence the study showed: increase in fissuring propensity and control in the melting and processing
1. The fissures occur p r i m a r i l y extend the fissuring t e n d e n c y to of the wrought materials.
along grain boundaries in the HAZ higher ferrite levels. Microfissuring in multipass welds in
The fissures formed in the weld austenitic stainless steels has become
metals studied do not propagate u n - of greater importance in recent years
C. D. LUNDIN is Section Manager — Weld- der room temperature, slow bend due to the increased utilization of
ing, Research & Development Division, conditions even when subjected to heavy section stainless weldments.
Babcock & Wilcox Co., Alliance, Ohio, and 20% plastic strain. The fissures mere- There is almost universal agreement
D. F. SPOND is with AFCO Steel. Little ly open and thus are more easily re- among investigators that the fissur-
Rock. Arkansas; both authors were with vealed at low magnifications. ing in multipass welds is restricted to
the Chemical and Metallurgical Engi- The data obtained in this investi- the weld metal HAZs produced by the
neering Dept., University of Tennessee, at
gation are c o m p a r e d to the observa- multiple weld passes needed to c o m -
the time the program described in this
paper was conducted. tions and studies by others (unpub- plete a heavy section weldment (Refs.
Paper presented at the AWS 57th An- lished) for service-fabricated, heavy 15. 18, 19, 20, 22-25). It has also been
nual Meeting held in St. Louis. Missouri, section weldments. It is more than established that composition control
during May 10-14, 1976. comforting to note that a one-to-one of the deposited weld metal, result-

356-s | N O V E M B E R 1976
 ing in a modest amount of ferrite in The cause of fissure formation has
the room temperature microstruc- been studied by several investigators
ture, will essentially eliminate the (Refs. 1, 3, 4, 6, 7, 10, 12, 14-18, 20,
microfissuring tendency. This level of 21, 26-31) in recent years. Three
ferrite was more firmly established by theories have been presented to ex-
Lundin, DeLong and Spond (Ref. 25) plain the mechanism of hot cracking
in a recent article documenting the in stainless steels:
ferrite-fissuring tendency of austen- 1. Solidification-segregation (Su-
itic stainless steel weld metals. per Solidus) Cracking. This mode
In some studies utilizing actual pro- of cracking occurs during the actual
duction weldments of Type 316 stain- deposition of individual weld beads
less steel, the investigators (Refs. 22, and is related to solute redistribution
23, 24) did not find any instance of upon s o l i d i f i c a t i o n . As indicated /
base metal HAZ cracking, nor did above, this mode does not appear to
they find any microfissures in the last be significant in austenitic stainless
or cover passes in the weld metal. All steel weld metals because it is not
of the fissures found were within the often observed with commercially uti-
bulk of the weld metal (buried) in the lized filler metals.
H A Z of s u b s e q u e n t l y d e p o s i t e d 2. HAZ Liquation Cracking. This
beads. Literally hundreds of micro- phenomenon is the basis for most hot Fig. 1 — Light micrograph of a fissure
fissures were observed and fissure cracking theories applied to austen- along a grain boundary near an interpass
densities of up to 70 fissures/in. 2 (11 itic stainless steel weld metals. It re- boundary (see arrow) in a polished and
fissures/cm 2 ) were recorded on pol- quires that liquation of low melting etched sample of Type 316L austenitic
ished and etched weld sections. Lun- segregates, partitioned to grain b o u n - stainless steel weld metal (0.5 FN), un-
din, DeLong and Spond (Ref. 25) also daries, occurs in a given temperature bent, transverse section. X100 (reduced
studied fissures in a variety of weld 30% on reproduction)
range (usually near the bulk solidus
metals in Fissure Bend Test spec- temperature) in concert with a strain
imens, and their observations con- of sufficient magnitude to rupture the
firm those reported for the produc- liquid films. ing passes. After the weld metal has
tion weld metals. 3. Ductility-dip Cracking. This type been thermal cycled by subsequent
of cracking results from a loss in duc- passes, it may be more susceptible to
Haddrill and Baker (Ref. 15) and
tility occurring over a given temper- fissuring. In addition, if the matrix is
Honeycombe and Gooch (Refs. 18,
ature range below the bulk solidus strengthened by a precipitation reac-
19, 20) utilized Types 310 and 316
(from 1650-1830 F for Type 310 ac- tion which is enhanced by subse-
stainless steel weld metals in their
cording to Haddrill and Baker (Ref. quent weld cycles, the fissuring ten-
work and f o u n d , as others had be-
15), and around 1560 F and again dency may be influenced in that the
fore (Ref. 14), that fully austenitic weld
around 2010 F for Type 347 accord- strains occurring during the subse-
metals are prone to microfissuring.
ing to T r u m a n and Kirkby (Ref. 20)). quent thermal cycles may be forced to
They confirm the observations in the
This loss in ductility is sufficient to occur in and about the degraded
m u l t i r u n welds (using pad s p e c -
produce cracking under the influ- microstructural region.
imens) that the fissuring is relegated
to the underlying HAZs and virtually ence of welding-induced strains. Alternately, it may be the accu-
never occurs in passes not subjected H a d d r i l l a n d B a k e r (Ref. 15), mulation of strains produced by sub-
to subsequent thermal cycles. Unfor- S h a c k l e t o n (Ref. 12) and Honey- sequent thermal cycles which is re-
tunately, the fissuring of austenitic combe and Gooch (Ref. 18) report sponsible for cracking. When the
stainless steel weld metals in multi- that both HAZ liquation and ductility- strain accumulation is sufficient, rup-
pass heavy section weldments has dip cracking may be operative in the ture or fissuring occurs. It is, how-
not been studied extensively to date weld metal at the same time. How- ever, most likely a number of factors
and much work remains to be done. ever, Honeycombe and Gooch be- operating together which are ulti-
Most investigators (Refs. 15, 17, 18, lieve that HAZ liquation is the d o m - mately responsible for the type of fis-
22-25) writing on the specific nature inant mechanism while Haddrill and suring observed in austenitic stain-
of the fissures, their location in the Baker maintain that d u c t i l i t y - d i p less steel weld metals. It is to be this
microstructure and the mechanism of cracking is more prevalent. end that the current research has a d -
the fissures agree that: Regardless of the specifics of the dressed the issue of fissuring in aus-
mechanism, it can be simply stated tenitic stainless steel weld metals.
1. Fissures invariably occur along
g r a i n b o u n d a r i e s r e g a r d l e s s of that:
whether they are located in the base 1. The material comprising a weld- Fissure M o r p h o l o g y in Austenitic
metal HAZ, weld metal HAZ or in weld ment exhibits a region (degraded Stainless Steel W e l d M e t a l s
beads minimally affected by subse- microstructure) which possesses a General
quent weld passes. limited capacity to tolerate strain
2. The fissures are most prone to within some critical range of t e m - As a result of the testing program to
form in the weld metal HAZs p r o - perature. develop the relationship between fer-
duced by subsequent weld passes. 2. The strain imposed upon the rite and fissuring in Types 308, 308L,
3. The fissures form at elevated weldment by the combined action of 316, 316L, 309, 318, 347, and 16-8-2
t e m p e r a t u r e s ( a b o v e 1600 F or t h e r m a l and restraint c o n d i t i o n s austenitic stainless steel weld metals,
871 C) and may result from more within this critical range of temper- numerous well documented spec-
than one basic (hot cracking) ature exceeds the strain tolerance of imens were available for study (Ref.
mechanism. the degraded microstructural region. 25). With the exception of 16-8-2,
4. Fissuring tendency decreases A degraded microstructural region each weld metal was available at four
when the weld metal contains ferrite in austenitic stainless steel weld metal ferrite levels (approximately OFN,
(room temperature microstructure); may be solidification segregation re- 2FN, 4FN, and 6FN) so that the influ-
and when fissures occur in ferrite- lated but may not be influential in ence of ferrite on fissure morphology
containing weld metals, they form in regard to fissuring until conditioned and location could be assessed. The
"ferrite free" areas. by the thermal cycles from succeed- 16-8-2 weld metal was deposited from

WELDING RESEARCH S U P P L E M E N T ! 357-s

 tion by fluorescent penetrant inspec- tained within the weld metal remote
tion and binocular microscopy. from a free surface. Thus it appears
From the well documented welds that fissures are present in as-de-
produced during the testing phase, a posited weld metal in much the same
number of metallographic and scan- form as in the bent weld pads.
ning electron microscopy (SEM) sam- L o c a t i o n s w h e r e two or m o r e
ples were removed from as-depos- HAZ's overlap in underlying beads
ited bent and unbent weld pads to througnout thick section, multipass
characterize the nature and mor- weldments are prime sites for fissure
phology of the fissures present. The format on. It will be shown later that
samples were chosen from weld weld metal at a location in a weld re-
specimens of low ferrite content (0-1 heated to a high temperature by two
FN) where a high incidence of fis- or m o r e s u b s e q u e n t l y d e p o s i t e d
suring was observed and from spec- beads (and thus lies in the over-
imens of higher ferrite content (2-3 lapping HAZ's of those beads), ex-
FN) where fissuring tendency was sig- p e r i e n c e s an i n c r e a s e d s u s c e p -
nificantly reduced. In addition, spec- tibility to fissuring.
imens exhibiting penetrant indica- The fissures discussed thus far
tions of unusual or unexpected nature occurred in weld metal of low ferrite
were thoroughly examined and doc- level (less than 1 FN in each case).
Fig. 2 — Light micrograph of a fissure umented.
along a grain boundary near an interpass Most austenitic weld metal types ex-
boundary (see arrow) in a polished and hibit a general fissuring tendency at
Fissure Appearance and Location this low a ferrite level. With in-
etched sample of Type 309 austenitic
stainless steel weld metal (0.4 FN), bent, In any discussion concerning creasing amounts of ferrite in the weld
transverse section. X100 (reduced 29% on planar sections through a discon- metal, the fissuring tendency quickly
reproduction) diminishes and is eventually elim-
tinuity-containing three-dimensional
solid, some knowledge of the vol- inated at a ferrite level which may vary
umetric configuration of the disconti- from 3 FN to 6 FN depending on the
nuity is necessary to gain a full appre- weld metal type. The nature and dis-
ciation for its appearance on a planar tribution of ferrite phase varies over
surface. For the case of fissures, they this same range. At low ferrite levels
s h o u l d be c o n s i d e r e d essentially the ferrite occurs as discrete par-
disc-shaped with a circular aspect ticles located at the cellular dendritic
Thus any cut through a fissure (except substructure boundaries with a d o m -
for that which lies in the plane of the inance for triple point intersections.
fissure and w o u l d be quite rare) As the nominal ferrite level is in-
would be displayed as a "line" on a creased, the ferrite tends to progres-
planar section regardless of the angle sively occupy more of the cell b o u n -
of cut. If the fissure has some thick- dary area until at about 4-7% (Ref. 33)
ness (separation), however, the more the network b e c o m e s c o n t i n u o u s
oblique cuts would yield more widely t h r o u g h o u t the cellular d e n d r i t i c
separated faces. structure.
Fig. 3 — Light micrograph of a fissure in a
ferrite-free area of Type 316 stainless steel All fissures examined in this inves- A high nominal ferrite content does
weld metal (avg. 2.5 FN), bent, longitudi- tigation, regardless of weld metal not e n s u r e u n i f o r m d i s t r i b u t i o n
nal, top view secion. X250 type, were located along weld metal throughout the weld metal. Gunia and
grain boundaries in the HAZ of a sub- Ratz (Ref. 34), for example, report that
sequently deposited bead. For exam- a weld metal having an average of
two commercial electrode lots of low ple, Fig. 1, a light micrograph showing 2.8% ferrite may actually vary in
ferrite level and could not be as- a fissure in a polished and etched, ferrite content from 0.3 to 8 . 1 % . This
sessed with regard to its cracking ten- transverse, unbent section of a Type type of variation in ferrite level was
dency over a ferrite range. The range 316L stainless steel weld pad (0.5 FN), observed and confirmed in many
of ferrite level for each weld metal was illustrates that the fissure occurs en- metallographic and SEM samples in
obtained by adjustment of the c o m - tirely within the weld metal and is lo- the present study and also has been
pounding in the electrode coatings. cated along a grain boundary. In addi- shown by others (Refs. 23, 33, 35,36).
The chemical analyses of the core tion, it is to be noted that the fissure is The result of ferrite variation with-
wires and of the d e p o s i t e d weld proximate to an interpass boundary in the microstructure is clearly illus-
metals were presented previously (see arrow) and is in the HAZ of the trated by a consideration of data pre-
(Ref. 25) and it is to be noted that the succeeding weld bead. sented in a previous article (Ref. 25)
trace elements (especially phospho- Figure 2, a light micrograph of a fis- and the micrographs shown in Fig-
rous and sulphur) are within the range sure revealed in a polished and etch- ures 3 and 4. Figure 3 is a light micro-
of commercial electrodes. ed, transverse, bent section of Type graph showing a fissure in a polished
The aforementioned testing utilized 309 stainless steel weld metal (0.4 and e t c h e d m e t a l l o g r a p h i c s p e c -
the Fissure Bend Test method (Refs. FN). also shows the grain boundary imen taken from a bent 316 weld pad
25, 32) which employs a multirun, mode of fissuring and the relation- (average 2.5 FN). This particular weld
double-layer, weld pad deposited by ship of the fissure to the interpass pad exnibited two penetrant indica-
the SMA process to evaluate fis- boundary (see arrow). Note that the tions wnich was considered unusual
suring in relatively undiluted weld fissure in the bent pad shown in Fig. 2 since the average ferrite level was
metal. In this testing scheme the pad is about the same width as the fissure higher than that d e t e r m i n e d to be
surfaces are prepared by milling, in the unbent pad shown in Fig. 1. The necessary to prevent fissuring in 316
grinding or polishing, and then are bending of the weld per se does not weld metal. One of the indications
bent in tension to a 120 deg included appear to influence the width of a was identified as a small area of lack
angle to expose fissures for detec- fissure as long as it is wholly con- of fusion between two weld beads

358-s | N O V E M B E R 1976
which was not removed during pad ."'
surface preparation. The second indi-
cation proved to be the fissure shown
in Figure 3. The ferrite in this figure is
the dark constituent appearing p r e -
dominantly along the cellular b o u n -
daries on the left and right sides of
the micrograph. It is to be noted that
the ferrite content in the immediate
vicinity of the fissure is significantly
lower than that in the surrounding --- ft
areas.
it
i\'
The o c c u r r e n c e of fissures in
ferrite-free areas was also observed
in 308L weld metal. It had been
previously determined that a ferrite
V
level of approximately 3 FN in 308L
weld metal is sufficient to prevent „.,
fissuring. However, in one bent weld Fig. 4 — Light micrograph of a fissure in a
specimen of 308L with a ferrite level ferrite-free area in a polished and etched
of approximately 4 FN, six closely - '
grouped fissures were f o u n d . These
sample of Type 308L stainless steel weld
metal (4.0 FN), bent, longitudinal, top view a
fissures were approximately 0.010 to section. X150
0.020 in. in length- and were all lo-
cated within 0.20 in. of each other preparation and they were detect-
near an interpass boundary. The fer- able by fluorescent penetrant test-
rite level of this general area was ing. Tears such as these occurred in
recorded to be 4.0 FN when mea- areas of high ferrite content and they
sured with a Magne Gage. Metal- did not appear in areas almost wholly
lographic evaluation of a polished austenitic. The observation of these
and etched sample taken to include grinding tears in high ferrite areas is
these six fissures revealed that they in contrast to the occurrence of fis-
were located in an essentially ferrite- sures w h i c h generally a p p e a r in
free area. One of these six fissures ferrite-free areas.
discussed above is shown in the light Another penetrant indication
micrograph in Figure 4. From this originally identified as a fissure was a
figure it is clear that the fissure is in discontinuity found in a bent 316L
an area devoid of ferrite, but high weld pad at a ferrite level of 5.6 FN.
concentrations of ferrite exist in close This discontinuity is shown in a SEM
proximity to the fissure. micrograph of the pad surface in
The evidence uncovered in this in- Figure 6a and outwardly appears to
v e s t i g a t i o n , as illustrated a b o v e , be a true fissure. However, because it
shows that fissures can occur in had been determined that a ferrite
nominally " h i g h " ferrite-containing level of 1.5 FN was sufficient to pre-
weld metals, but these fissures are vent fissuring in 316L weld metal, an
confined to the randomly occurring explanation for the occurrence of this
ferrite-free regions. "fissure" at a ferrite level 5.6 FN was
in order. Thus a metallographic s a m -
Fig. 5 — Light micrograph of grinding
ple containing the "fissure" was re- tears in a polished and etched sample of
Other Discontinuities Detected moved from the pad and polished Type 308L stainless steel weld metal (2.5
During the course of the investiga- and etched in order to determine its FN), bent, longitudinal, top view section,
tion to determine the ferrite-fissuring true nature. Figure 6b, a SEM micro- (a) — X250; (b) — X500
relationship in austenitic stainless graph obtained from the polished and
steel weld metals (Ref. 25), several etched sample, clearly shows that the was performed on various areas (see
penetrant indications were found that discontinuity is, in actuality, a crack in Figure 6b, areas A, B, and C) by utiliz-
resulted from discontinuities other an inclusion within the weld metal. ing the energy dispersive x-ray mode
than fissures. These indications were Note that the distribution of ferrite in of the SEM. The elemental distribu-
originally considered to be fissures, the cell boundaries of the weld metal tion was determined in the three
but m e t a l l o g r a p h i c and s c a n n i n g surrounding the inclusion is virtually regions s h o w n . Iron, nickel and
electron microscopy examination continuous at this ferrite level of 5.6 c h r o m i u m were found in region A and
later revealed the true nature of the FN. The crack extends across the the analysis of region B yielded iron,
discontinuities. inclusion but does not extend into the nickel, and c h r o m i u m with a small
surrounding weld metal. Thus the dis- indication of sulphur. The elements in
One type of indication is illustrated
continuity is not related to fissuring of the center region C were iron and sul-
in Figs. 5a and 5b, which are light
t h e w e l d m e t a l in any m a n n e r . phur only. Thus the inclusion was
micrographs of the surface of a pol-
Apparently, the crack formed as a re- determined to be of a duplex nature
ished and etched, bent sample of
sult of differential contraction rates with the crack occurring in the center
308L weld metal (2.5 FN). These
during solidification or because the core of FeS.
figures show, at 250X and 500X re-
inclusion was unable to deform with
spectively, tears along cellular inter- While the occurrence of the discon-
the s u r r o u n d i n g m a t e r i a l d u r i n g
sections where austenite and ferrite tinuities discussed above has been
bending. Due to the unusual appear-
exist. The tears were caused by sur- observed only in isolated cases, the
ance of the inclusion, microanalysis
face g r i n d i n g d u r i n g weld pad documentation of their true nature

WELDING RESEARCH S U P P L E M E N T ! 359-s

has proven beneficial because it has 3. W h e t h e r f i s s u r e s e x t e n d in as the bend angle increased or alter-
been shown that "fissure-like" indica- length during bending. nately as the extent of straining inten-
tions at high ferrite levels in austen- To accomplish this task, several sified. To document the p h e n o m -
itic stainless steel weld metals may be Fissure Bend Test pads of Types 308, enon occurring as bending strain was
unrelated to the fissuring behavior of 316 and 16-8-2 weld metal (all of low increased, photomicrography at X200
the weld metal per se. Thus it is not ferrite level) were deposited, ground was carefully and painstakingly per-
always equitable to disparage the and metallographically polished; and formed to unequivocally document
soundness of the weld metal with- then the pads were examined for fis- the change in fissure appearance. It is
out sufficient investigation and doc- sures. The surfaces were then etched to be noted that it was extremely diffi-
umentation of the occurrence. and reexamined. The pads were next cult to predetermine the location of
subjected to bending in incremental fissures in unbent samples even when
Fissure Behavior During Bend Testing steps and were thoroughly examined the microstructure was studied at
The examination of unbent, sur- after each bending operation. During X500 magnification.
face prepared Fissure Bend Test each examination, particular atten- The effect of bending strain on the
pads (whether they be milled, ground tion was paid to the interpass b o u n - appearance of a fissure in 316 weld
or metallographically polished and dary region where fissures were ex- metal (0.4 FN) is illustrated in Figures
etched) rarely reveals any fissures for pected to be found. Examination of 7a-7d. Figure 7a is a light micrograph
most austenitic weld metals. Types these test specimens at X100 to X200 showing the fissure in the weld metal
347 and 318 stainless steel weld revealed only two fissures in the un- subjected to 0.4% bending strain. The
metals studied here are notable ex- bent pads, one being in a Type 308 fissure, 0.010 in. in length, is located
ceptions as these metals exhibited a specimen and the other in a Type 316 along a grain boundary and its ends
significant number of fissures on sur- s p e c i m e n . It was s o m e w h a t sur- appear well defined. Only a small
face g r o u n d , unbent pads of low fer- prising that so few fissures were number of slip bands are evident on
rite level. To enhance fissure detec- found even though the pads were pol- the weld metal surface. Figure 7 is a
tion, the test specimen is bent so that ished, etched and examined at X200. light micrograph showing the same
the pad surface is subjected to a ten- When each pad was bent to cause a fissure after the weld metal has been
sile strain. small but p e r c e p t i b l e d e g r e e of s u b j e c t e d to 1 % plastic b e n d i n g
In general, for all weld metal types plastic flow ( ^ 0 . 4 % strain, ~ 1 deg strain. The extent of strain at the ends
at low ferrite content, the bending bend angle), each was carefully and of the fissure is evident from the slip
operation exposes fissures intersect- thoroughly examined and some fis- band concentration. By c o m p a r i s o n
ing or proximate to the pad surface. sures were found in the Types 308 of Figures 7a and 7b, it appears that
The number of fissures detected is and 316 stainless steel weld metal. the fissure increased slightly in length
dependent on many factors including: However, for the 16-8-2 weld metal at one end (see small arrow in Figure
the weld metal type, the bending pads about 2% plastic strain ( » 4 deg 7b). However, this small portion of the
strain, the method of surface prep- bend angle) was necessary to initially fissure lies approximately parallel to
aration, the type of microscope uti- discover any fissures on the pad sur- the direction of bending (see large
lized, and the magnification at which face. arrows), and thus the 0.4% plastic
the pads are examined for fissures Upon further study it became ap- bending strain as shown in Figure 7a
(Ref. 32). However, since fissure de- parent that the orientation of a fis- may have been insufficient to expose
tection was facilitated by bending, the sure with regard to the longitudinal this segment of the fissure. Figure 7c
question of whether the bending op- strain applied was the primary condi- is a light micrograph showing the fis-
eration produced fissures, caused tion determining the extent of fissure sure after the weld pad was subjected
fissures to propagate or elongate, or interface separation. The degree of to 2% plastic strain. The concentra-
merely opened the fissures laterally plastic flow on a microscale as in- tion of strain at both ends of the fis-
for detection had to be answered. fluenced by the orientation of the sure is severe, but it is obvious that
Thus a testing program was initiated grains surrounding the fissure loca- the fissure has not propagated. The
to determine: tion also affects the extent of fissure fissure has widened and it is to be
1. Whether the bending operation interface separation. For each weld noted that the direction of shift of the
produces fissures. pad examined, the number of fis- fissure walls is in the direction of the
2. The extent of bending strain sures was counted at different de- applied bending strain (see arrows).
necessary to expose fissures for de- grees of bending, and it was deter- Figure 7d is a SEM micrograph of
tection. mined that more fissures were found the fissure, taken at a slightly re-
duced magnification and at a high d e -
gree of tilt, after the weld metal was
subjected to about 20% plastic b e n d -
ing strain. The fissure has opened but
clearly has not increased in length
even with this extensive amount of
bending strain.

The preceding micrographs are

typical of all weld metals tested with
regard to the appearance of fissures
and the manner in which they open
with increasing amounts of bending
strain. In only two instances were fis-
sures observed to propagate or inter-
connect during bending. This oc-
curred only when two fissures were
very closely aligned axially (and thus
Fig. 6 — S E M micrographs ota discontinuity In a Type 316L stainless steel weld metal pad
most likely situated along a mutually
(5.6 FN), bent, longitudinal, top view section. Left (a) — discontinuity on as-ground pad sur-
face; right (b) — discontinuity on polished and etched surface. X500 (reduced 39% on
shared grain boundary). In both i n -
reproduction) stances the amount of weld metal

360-s | NOVEMBER 1976

separating the fissures was small in
comparison to the size of the fissures,
and the fissures may very well have
been interconnected before bending
along the grain boundary in the weld
metal beneath the plane of e x a m -
ination.
In order to determine if the orienta-
tion of the weld beads with regard to
the direction of applied strain (longi-
tudinal) in the Fissure Bend Test
scheme would alter the location of the
fissures or change the extent of fis-
suring, a study where the beads were
deposited transverse to the longi-
tudinal axis of the test specimen was
undertaken. This transverse bead se-
quence yielded the same area for
evaluation and about the same length
of interpass boundary. There was no
difference in location, size or dis-
tribution of fissures, and the number
of fissures was of the same order as
that found in the longitudinal weld
beads.
Before leaving the subject of the in-
fluence of strain on fissuring, several
salient points should be made. As
indicated in the introduction, strain in-
variably plays a part in the fissuring
m e c h a n i s m . Naturally the strains
experienced by actual weldments oc-
cur over a range of temperatures and
are altered as each bead is depos-
ited in a multipass weld.
The level of strain experienced dur-
ing welding has been the subject of
continued research but is fraught with
the necessity to deal with high tem- Fig. 7 — Micrographs of a fissure in a polished and etched Type 316 stainless weld metal
pad (0.4 FN) as a function of bending strain, longitudinal, top view section, a — Light micro-
peratures and their attendant prob- graph, 0.4% plastic strain; X200. b — Light micrograph. 1% plastic strain; X200. c — Light
lems in the realm of measurement. micrograph, 2% plastic strain; X200. d — SEM micrograph, 20% plastic strain; X180 (All
However, several investigators have micrographs reduced 21% on reproduction)
documented the extent of surface
strains both transverse and longitud-
inal to the weld bead. Williams et al Table 1 — Average Number of Fissures and Average Fissure Size (Based on Disc
(Ref. 37) report that the transverse Assumption) for Type 308 and 316 Stainless Steel Weld Metal as a Function of Pad
strains are approximately twice as Surface Preparation Technique (Measured on Bent Sample)
large as the longitudinal strains in
austenitic stainless steel welds. For a 308(0. 4 F N ) 316 (0.4 FN)
single weld bead d e p o s i t e d in a
groove in thick plate, surface strains Surface Preparation Ave. No Ave. Size, In. Ave. No. Ave. Size, In.
of approximately 4% are obtained in 6 0.016 8 0.013
Milled
the t r a n s v e r s e d i r e c t i o n . T h e s e Surface G r o u n d 44 0.008 17 0.009
authors also state that the strains be- Metallographically
neath the surface are much higher but Polished 151 0.004 102 0.005
naturally defy direct measurement.
Zhitnikov and Zemzin (Ref. 38)
report very similar results for austen- Brooks and Spruiell (Ref. 40) report Consider now the pad type spec-
itic stainless steel, confirming that the that from dislocation densities pres- imens utilized for bend testing (Ref.
strains adjacent to a weld bead are 3- ent in 21/2 in. (63.5 m m ) thick Type 25). These "deposited on the sur-
4 % as a m i n i m u m . They further state 308 stainless steel weldments, the face" beads would naturally be less
that the strains between two closely accumulated strain may be as high as severely strained than those beads
spaced beads may be twice as high as 20%. One can easily visualize high deposited in a groove in a heavy sec-
those occurring along side a single strains in thick section weldments tion weldment. In fact these test pads
weld bead. Shron (Ref. 39) discussed after once observing the extent of dis- should represent the minimum re-
the triaxiality of strain in thick weld- tortion evident if proper weld re- straint. The additional strain applied
ments and relates the strain accu- straint is not utilized during welding. during bend testing may be equated
mulation in any one zone to the prop- Suffice it to say that strains of 4 % and to the additional strains occurring in
erties of that zone. greater always occur during welding thick section weldments (where fis-
The extent of strain through the of stainless steels and that the sub- sures are o b s e r v e d ) . However, it
thickness of a heavy section, multi- surface strains are much higher and should be recognized that all the
pass weld is not well known but may reach 20%. additional strain in bend testing is

WELDING RESEARCH S U P P L E M E N T ! 361-s

applied at room temperature whereas of certain elemental species. This region at the time separation of the
in a weldment the strains accumulate examination technique and an indi- material occurred causing a fissure.
over a range of temperatures (any cation of the useful information which The general shape of the cellular d e n -
testing scheme suffers from some can be obtained has been described drites can be discerned (extending
deficiencies). Nevertheless, the by Lundin (Refs. 17, 31) and Honey- upwards in these micrographs). The
fissures observed in the bend spec- combe and Gooch (Refs. 18, 19, 41). protuberances extending upward
imens occur at the precise location Honeycombe and Gooch (Ref. 18) from the surface result from the li-
and have the same appearance as claim to have documented three dif- quid metal necks that developed dur-
those occurring in thick section weld- ferent f r a c t u r e m o r p h o l o g i e s for ing separation with the liquid film pre-
ments (Refs. 22, 23, 24). An almost Types 310 and 316 stainless steel: sent. The necked regions s u b s e -
unbelievable one-to-one correlation 1. A morphology which exhibited quently ruptured as the fissures
exists. generally smooth features. opened. The features present on the
These observations strongly 2. A morphology which showed surface defy explanation except for a
suggest that the same phenomena dendritic films. liquid film hypothesis. Thus the
are occurring during pad production 3. A morphology which showed a fissures exposed during fissure bend
as occur in the heavy section weld- relatively featureless surface with testing originated at an elevated t e m -
ments, save for a lesser total amount many small particles on the surface. perature and were not created during
of strain accumulating in the pad. Ludin (Refs. 17, 31) has observed bending.
Thus, it appears that the fissures are morphology 1 in nickel, Type 310 The fissure surface shown in Fig. 9
present but tightly closed until the stainless steel, X-750, TZM, molyb- at X4500 is typical of only a small
strain is applied during bend testing. denum and Inconel 600, and he has number of fissures, and it appears to
Then and only then do they open suf- observed morphology 3 in Inconel be slightly different from those sur-
ficiently for detection. 600. Honeycombe and Gooch report faces typified by Figs. 8a and 8b.
that form 1 predominates and that Although it has relatively smooth fea-
If fissures in austenitic stainless
forms 2 and 3 were less prevalent. tures c h a r a c t e r i s t i c of the p r i o r
steels are to be assessed as impor-
This is in line with the observations of presence of liquid film, its features
tant in regard to mechanical p r o p -
Lundin and the studies in this case for are somewhat finer. It is not c o n -
erties, the "openness" of the fissures
all the weld metals investigated. sidered to be associated with distinct-
will not be an influential parameter.
The size, shape, location and notch In both morphologies 1 and 2, a li- ly different mechanisms of fissure for-
acuity are the truly important aspects. quid film plays a role in the cracking mation.
Thus whether a fissure is "tight" or mechanism. In morphology 1 a single The fissure surfaces were ana-
" o p e n " should not be important, and film generally covers the entire sur- lyzed using the energy dispersive
an incipient (unopened) fissure will be face, while in morphology 2 the film X-ray mode of operation in the scan-
as important (if important at all) as may result f r o m two different l i - ning electron microscope. As was an-
one which is open and observable. In quated phases. In all of the observa- ticipated and attested to by Honey-
light of the influence of a fissure on tions in this study, only one film type combe and Gooch (Ref. 18), only the
the mechanical properties of aus- was noted. major alloying elements, iron, nickel
tenitic stainless steel, it should be The three SEM fractographs shown and c h r o m i u m , and where appro-
noted again that the fissures did not in Figs. 8a, 8b and 9 characterize the priate molybdenum and columbium,
propagate during bend testing and, in observations in this instance. Fig- were revealed. The SEM does not
fact, the ends of the fissures actually ures 8a and 8b show the p r e d o m - have the capability of detecting, even
become blunted during deformation. inant morphology at approximately qualitatively, small amounts of trace
X1000 and X2000 respectively. The elements on fracture surfaces, and it
pad surface can be seen in the upper fluoresces the material to a consid-
Fissure Surface Morphology and
Energy Dispersive Analysis and lower portions of Fig. 8a with the erable depth thus precluding elemen-
fissure surface extending across the tal characterization of the remnants of
To gain insight into the mechanism central portion. The central portion the liquid film alone. Auger electron
of fissure f o r m a t i o n in austenitic only is shown in Fig. 8b. Note that the spectroscopy is perhaps an alterna-
stainless steels, the surfaces of the surface has a smooth appearance t i v e a p p r o a c h to t h e p r o b l e m
fissures in many weld metal types with a number of small holes and also although it is difficult to apply.
were examined utilizing the scanning protuberances extending upward In summation, it is clear that a li-
electron m i c r o s o p e . In a d d i t i o n , from the surface. quid film plays a dominant role in the
energy dispersive X-ray analysis was All of these features suggest, as fissure formation observed in all of
performed on the fissure surfaces in has been shown by others (Refs. 17, the s t a i n l e s s steel w e l d m e t a l s
an attempt to document segregation 18, 31), that a liquid film existed in this s t u d i e d . However, the elemental

Fig. 9 — SEM micrograph of secondary

Fig. 8 — SEM micrograph showing the predominant type of fissure surface morphology. fissure surface morphology. X4500 (re-
Left (a) — XT000; right (b) — X2000 (reduced 44% on reproduction) duced 46% on reproduction)

362-S I N O V E M B E R 1976
 CO M
L L U)

"0 0005 0010 0015 0020 0025 0 0005 0010 0015 0020 0025 0 0005 0 010 0 015 0 020 0025
FISSURE LENGTHS (INCHES) FISSURE LENGTHS (INCHES) FISSURE LENGTHS (INCHES)

Fig. 10 — Fissure size distribution for Type Fig. 11 — Fissure size distribution for Type Fig. 12— Fissure size distribution for Type
308 stainless steel weld metal (0.4 FN), 308 stainless steel weld metal (0.4 FN), 308 stainless steel weld metal (0.4 FN),
milled surface, bend pad — 11 fissures ground surface, bent pad — 87 fissures polished and etched surface, bent pad —
measured measured 302 fissures measured

species responsible for, or associ- and finished by metallographically

ated with, these films has not been polishing the surface. Table 2 — Influence of Thermal Cycling
on Fissure Occurrence
revealed. The fissure size distribution for the
11 fissures in two bent pads of Type
Fissure Sizes 308 stainless steel weld metal (0.4 Area Linear
fissure fissure
FN), surface prepared by the " m i l l -
The size of fissures present in density density
i n g " technique and examined at X40-
austenitic stainless steel weld metals no. / i n . 2 no./in.
X50, is shown in Fig. 10. Note that
is of prime importance when consid- most of the fissures detected were ap- Single HAZ cycle 8-17 2-4
ering their influence on the mechan- proximately 0.010 to 0.012 in. (0.25 to Double HAZ cycle 95-120 19-24
ical properties of weldments. This 0.30 mm) long and that no fissure
area of interest was discussed briefly smaller than about 0.008 in. (0.20
in a previous article (Ref. 25) de- mm) in length was detected. It is ap-
scribing the early results in the over- parent that if fissures smaller than length) than those observed on the
all study. It was also determined (Ref. 0.008 in. (0.20 mm) are present, the milled pads could be detected. It
32) that the sizes of fissures revealed surface roughness from milling pre- should be noted that the majority of
on the surfaces of the weld pad spec- vented their detection. Also because the additional fissures detected are in
imens was a direct function of the sur- of the high degree of surface rough- the smaller size range (less than
face preparation technique and of the ness, examination of these pads at a 0.010 in. or 0.25 mm in length). Utiliz-
type of microscope and magnifica- magnification higher than X40-X50 ing the data from the g r o u n d pads,
tion used in the assessment. was not possible optically nor prac- the average fissure length is calcu-
The fissure size-preparation data tical in the SEM. lated to be 0.008 in. (0.20 mm).
are shown for Type 308 in Figs. 10-12. Fissures are considered to be pre- Figure 12 presents the fissure size
These figures will be useful in gain- sent in the weld metal in approx- distribution for two bent pads of Type
ing an appreciation for the size dis- imately the shape of a disc, and thus 308 stainless steel weld metal (0.4 FN)
t r i b u t i o n of the f i s s u r e s and for the extent of a fissure exposed by sur- surface finished by metallographic
illustrating how the " a p p a r e n t " aver- face preparation can vary from the full polishing and etching and examined
age fissure size varies with the ulti- diameter of the disc to a very short at X100-X200. Type 302 stainless
mate resolution possible f r o m the segment of it. When a disc assump- steel fissures were detected in the two
preparation and measurement tech- tion is utilized, the average length of pads and it is to be noted that the ma-
niques. In these figures the percent- the fissures in the weld metal can be jority of them were less than 0.005 in.
age of the total number of fissures calculated from lengths of the fis- (0.13 mm) in length. The calculated
observed within each 0.0025 in. (0.06 sures measured on the pad surface average length of the Type 302 fis-
mm) size increment is shown. (Note (Ref. 42). The average length of the sures found in the metallographically
that the total number of fissures o b - fissures in the Type 308 stainless steel polished and etched 308 weld pads
s e r v e d v a r i e s for e a c h s u r f a c e weld metal detected on the milled sur- was 0.004 in. (0.10 mm).
preparation technique.) Three dif- face (Fig. 10) was calculated to be Quite obviously the smooth and
ferent s u r f a c e p r e p a r a t i o n t e c h - 0.016 in. (0.41 mm). well defined nature of the metallo-
niques were evaluated:
Figure 11 shows the fissure size graphically polished and etched pads,
1. "Milled"-milling the surface and distribution for the 87 fissures detect- in conjunction with the high magnifi-
finishing with a 0.002 in. (0.05 mm) ed in two bent pads of Types 308 cation at which they could be exam-
milling cut. stainless steel weld metal (0.4 FN) ined, permitted the detection of a
2. " S u r f a c e g r o u n d " - m i l l i n g the finished by the "surface g r o u n d " tech- large number of very small fissures.
pad surface followed by grinding with nique and e x a m i n e d at X40-X50. The number of larger fissures (greater
eight passes of 0.001 in. (0.025 mm) Clearly the surface ground pad prep- than 0.010 in. or 0.25 mm In length)
and finishing with four passes of aration technique reveals significant- f o u n d in t h e m e t a l l o g r a p h i c a l l y
0.0005 in. (0.013 mm). ly more fissures (Ref. 87) than does polished pads compares favorably
3. "Metallographically polished"- milling (Ref. 11). Moreover, because with the number (which are greater
milling followed by grinding with eight the grinding technique causes less than 0.010 in. or 0.25 mm) found in
passes of 0.001 in. (0.025 mm) and surface distortion, fissures smaller (as the surface ground pads. In general,
four passes of 0.0005 in. (0.013 mm) small as 0.002 in. or 0.05 mm in the larger fissures on the weld pad

WELDING RESEARCH S U P P L E M E N T I 363-s

 X 1/4" approx.

1/2" Uf"tf/8*-l T 1/2' I—1"± 1/8—J

Fig. 13 — Weld pads* cross-section showing bead sequence. Left (a) — recommended bead sequence; right (b) — alternate bead
sequence resulting in two high peak temperature HAZ thermal cycles in bead 2

surface can be detected by any of the weldments were about the same, temperature HAZ excursions. This
three methods of surface prepara- = 0.5 FN). The larger sizes in heavy was the only bead so influenced in the
tion while most of the smaller fis- section production weldments may be upper layers with the remainder ex-
sures can be found only on metallo- due to the fact that the strains accu- periencing only one high temper-
graphically polished pad surfaces. mulate at higher temperatures than in ature HAZ excursion as described
The size distributions of fissures the room temperature bent pads and above.
measured in the 316 weld metal pads the degree of restraint may even i m - For tne specimens with the altered
finished by three different surface pose higher total strains. bead sequence, it became apparent
preparation methods can be c o m - that the majority of the fissures found
pared to 308 by inspection of Table 1.
The Influence of Thermal Cycling were occurring in bead 2 (in the d o u -
It is to be noted that for both weld on Fissure Occurrence ble HAZ produced by beads 3 and 8).
metal types (308 and 316), a similar- In previous discussion it was e m - The fissure count for the low ferrite
ity is evident in the size distribution phasized that fissures occur only in pads (0.4 FN for 308 and 316, and 1.5
when comparing corresponding sur- the weld metal HAZs of subsequent FN for 16-8-2) was treated so as to
face preparation techniques. weld passes. This was invariably true recognize this occurrence by c o m -
16-8-2 weld metal was also eval- for the Fissure Bend Test pad studies puting the areal fissure density and
uated using metallographically (Refs. 25, 32) and those fissures the density along each interpass
polished and etched pads. However studied by others (Refs. 22, 23, 24) in boundary (a linear density) for the
only three fissures were detected, and production weldments. single and double HAZ instances.
thus the data were not amenable to In the original fissure bend testing The areal density in the double HAZ
either graphic presentation or the cal- scheme, the top layer weld beads region revealed approximately 95-120
culation of an average fissure size. were deposited in sequence from one fissures per square in., whereas for
The fissures found in the 16-8-2 mate- side of the pad to the other. This bead the single HAZ region the density was
rial were 0.0015 to 0.0020 in. (0.04 to sequence is shown in Fig. 13a where only 8-17 fissures per square in. The
0.05 mm) long and fall in the smallest beads 7-12 constitute the top layer linear density (along the interpass
size range of the Types 308 and 316 and were deposited from left to rigrv: boundary) was 19-24 fissures per in.
stainless steel weld metal. in the order shown. Thus bead 7 of interoass for the double HAZ oc-
receives the high temperature ther- currence while it was 2-4 fissures per
By referring to Table 1, the above
mal cycle effects from bead 8, and in. of interpass for the single HAZ.
presentation may be summarized by
bead 8 is subjected to the same ther- These data encompass both Types
noting that the apparent fissure size
mal cycles by bead 9, and so on with 308 and 316 weld metal with no clear
decreases as the surface preparation
bead 12 being the only deposited up- distinction between the two. The 16-8-
technique improves and the obser-
per layer bead not to be subsequent- 2 fissured an insignificant amount
vation magnification and the resolu-
ly thermal cycled. Fissures were never with only three fissures being found
tion increase. The true average fis-
found in bead 12 but only in the HAZ on two pads (8 sq. in., 40 in. of inter-
sure size (disc assumption) is c o n -
regions of beads 7-11, thus under- pass). However, it is to be noted that
sidered to be that determined from
scoring the weld metal HAZ fissuring the three fissures found were in the
the polished pad data since it in-
phenomenon. double HAZ region.
cludes a statistically significant
In follow-on investigations eval- From this treatment (see Table 2) it
number and accounts for even the
uating the Fissure Bend Test vari- was clear that the double HAZ occur-
small fissures present. This yields an
ables (Ref. 32) an altered weld pac rence is a significant factor in the
average fissure size of approximately
bead sequence was fortuitously uti- fissuring tendency of 308, 316, and
0.004-0.005 in. (0.10 to 0.13 mm) for
lized for the Types 316, 308 and 16-8- 16-8-2 weld metals at low ferrite
Types 308 and 316 weld metal.
2 stainless steel pads to be evaluatec levels. When the ferrite level for 316
When comparing the average size
with metallographic preparation of was increased to 3.2 FN, fissures
for Type 316 stainless steel weld
the pad surface. This altered bead se- again occurred but only in the double
metal with those obtained from pro-
quence is shown in Fig. 13b. Notice HAZ region. For this pad there was a
duction fabricated heavy section Type
that bead 1 in the lower layer and linear density of 3 fissures per in. of
316 weldments, a significant differ-
bead 2. which forms a portion of the interpass ( c o m p a r e d to a p p r o x -
ence is n o t e d . The average size
upper layer, were deposited before imately 20 fissures per in. at 0.4 FN) in
reported for actual weldments is ap-
any other beads. Bead 3 caused beac the double HAZ region. However, for
proximately 0.014 in. (0.36 mm) (Ref.
2 to experience a high temperature a Type 308 pad, at a nominal ferrite
22). (The ferrite levels for the tests
excursion and later bead 8 subjectec level of 2.5 FN, no fissures were found
reported here and the production
bead 2 to a high temperature therma even in the interpass region of the
history. Thus, bead 2 in the upper bead subjected to the double HAZ
"Weld pad must be within these limits to thermal cycle. Additional testing has
minimize variation in total pad surface layer and in the final plane of exam-
ination was subjected twice to high supported the fact that Type 316 weld
area and variation in pad height.

364-s I N O V E M B E R 1976
 WELD PAD a J 0.050"|-C-
PREPARED SURFACE-^
^FISSURE

%3/7%>&* 8
/ 2
/ FUSION LINE

<^ ^v. ^ 1 _ V ^
• ^ ^ 1 ^ — \ x^-
X
BASE PLATE

b
p/jf. 74 _ Portion of weld pad cross-section showing overlapping HAZ and its intersection with the prepared pad surface. Left (a) •
light micrograph; right (b) — sketch. X12 (reduced 24% on reproduction)

metal at ferrite levels of 3.0 FN to 3.2 jected to only a single HAZ experi- range for austenitic stainless steels
FN displays a low fissuring tendency ence. Only when a weld bead under- was determined by Honeycombe and
in double HAZ regions, but that 308 went double or triple HAZ expe- Gooch (Ref. 18), Shackleton (Ref. 12)
weld metal at ferrite levels of 2.5 FN to riences did any fissures appear upon and Senda et al (Ref. 2), using the
3.1 FN is insensitive to this occur- bend testing, thus confirming the Varestraint-thermocouple technique
rence. Thus double HAZ overlapping results of the directly deposited SMA developed by Savage and Lundin
will be influencial in the determina- weld bead studies. (Ref. 44, 45). Shorshorov and Soko-
tion of the m i n i m u m ferrite level to Measurement of fissure locations lov (Ref. 46) utilized an implanted
prevent fissuring. from both the GTA and SMA pads thermocouple technique and Had-
To more clearly define the effect were utilized to determine the exact drill and Baker (Ref. 15) utilized a hot
double HAZ thermal cycling has on region of the HAZ in which fissures ductility apparatus for their determi-
fissuring tendency, a series of experi- occurred. These measurements for nations of the cracking range.
ments was conducted utilizing a GTA SMA beads showed that fissures were Those investigators utilizing the
remelt of surface ground SMA de- found in a region from the fusion line Varestraint technique record the hot
posited pads. Both Types 316 and to approximately 0.050 in. (1.3 mm) cracking temperature range as ex-
308 stainless steel (0.6 FN) were uti- from the fusion line. The fissures tending from the bulk solidus to about
lized in the study. The GTA process never crossed the interpass b o u n - 2300 F (1260 C) for a variety of
was selected to remelt the SMA pads, dary and rarely extended to the inter- austenitic stainless steel weld metals
because it produces a smooth flat pass boundary. The majority of the (GTA remelted). These data should
bead with a well defined fusion line fissures were found in a band 0.010 to be treated with caution especially at
and is a quiescent process with m i n - 0.030 in. (0.25 to 0.76 mm) from the the high end of the range because
imal weld pool perturbation.Thus, it is fusion line. Lundin (Ref. 47), utilizing high speed
easy to document the location of any With the precise fissure location in motion pictures showing Varestraint
fissure with regard to the weld fusion •he HAZ thus defined, it was now pos- crack formation, has found that
line. s i b l e to d e t e r m i n e t h e c r a c k i n g cracking initiates a short distance
The entire SMA pad surface was temperature range by measuring the behind the instantaneous position of
remelted by a series of overlapping thermal distribution in the HAZ. This the s o l i d - l i q u i d interface and t h e
GTA beads. Where double and triple was accomplished for both the SMA cracks often propagate to the solid-
HAZ experiences were desired, a and GTA weld beads utilizing the ther- liquid interface. (Cracks which prop-
given bead was refused two or three mocouple implantation technique agate to the solid-liquid interface will
times thus producing double or triple (Ref. 43). The welding conditions ex- always be coated with a liquid film.)
HAZ experiences in the preceding actly duplicated the SMA (16 k J / i n . or Haddrill and Baker report a cracking
bead. Care was exercised to control 6.3 X 105 J / m ) conditions. From these temperature range of from 1650 to
preheat and interpass temperatures thermal measurements it was deter- 1830 F (899 to 999 C) and Shor-
in all cases to precisely maintain f u - mined that a point 0.050 in. (1.3 mm) shorov and Sokolov report a range of
sion line location. The energy input from the fusion line reached a peak 1740 F (949 C) to the bulk solidus.
was varied f r o m 6-60 k J / i n . (2.4 X 10 5 t e m p e r a t u r e of a p p r o x i m a t e l y The overall t e m p e r a t u r e range
to 23.6 x 105 J/m) for individual weld 1630 F, a point 0.030 (0.76 mm) d e t e r m i n e d in this study (1630-
pad studies, thus incorporating reached a peak of 1950 F and a point 2630 F or 888-1443 C) fits well with
energy input as a variable. It is to be 0.010 (0.25 mm) from the fusion line those of others. However, this study
noted that the Ferrite Number was reached 2400 F (1316 C). Thus the has shown that the majority of the fis-
altered by the energy input variation. overall HAZ temperature range in sures form at a temperature signif-
At low energy input, the Ferrite which the fissures were found ex- icantly below the bulk solidus in a
Number was 0.5 FN and with 60 k J / i n . tended from the bulk solidus range of 1950-2400 F (1066-1316 C).
(23.6 x 105 J / m ) the Ferrite Number (%2650 F or 1454 C) to 1630 F By combining the information or
was 1.4 FN. (888 C) while the majority of the observations as to the bead se-
Regardless of the energy input for fissures fell in a range experiencing quence in multipass welds and the
the GTA remelt studies, no fissures peak temperatures of 2400-1950 F data on the location of fissures and
were found upon bend testing along (1316-1066 C). the temperature range over which
interpass boundaries which were sub- The hot c r a c k i n g t e m p e r a t u r e they are most prone to occur, one can

WELDING RESEARCH S U P P L E M E N T ] 365-s

 better analyze the nature of fissuring strength of the matrix may cause Acknowledgments
in austenitic stainless steels. In regard strain accumulation in the degraded
to the Fissure Bend Test specimens in grain boundary microstructural re- The authors acknowledge the sponsor-
which the double HAZ cycling occurs, gion thus leading to rupture. ship of the Welding Research Council,
the influence of bead sequence can 3. S t r a i n - i n d u c e d precipitation which provided a grant for the financial
be clearly discerned by reference to support through the auspices of the High
leading to a strengthened matrix and
Alloys Committee and the Stainless Steel
Fig. 14. the s u b s e q u e n t a c c u m u l a t i o n of Advisory Subcommittee. The program was
The p h o t o m a c r o g r a p h in Fig. 14a strain in the degraded microstruc- conducted at the University of Tennessee
was obtained from a transverse sec- tural region. and formed the basis of the Masters
tion of an unbent 316 (0.4 FN) weld 4. The s i m p l e a c c u m u l a t i o n of Thesis for Mr. D. F. Spond. Without the
pad in which bead 2 experienced a thermal and restraint strains over a dedicated help of Mr. Ray Bellamy, who
double HAZ cycle from beads 3 and 8 painstakingly prepared the specimens,
range of temperatures produced by
(see Fig. 13b and associated dis- this program could not have been com-
continued thermal cycling causing the pleted. Mr. Michael Hunter contributed
cussion). The passes are numbered strain tolerance of the grain b o u n -
on the macrograph and the interpass significantly on the SEM characterization
dary microstructural region to be ex- and micraanalysis of the discontinuities.
boundaries can be clearly seen. The ceeded.
sketch in Fig. 14b (at the same scale Each of the elements above may
as the macrograph) show the weld play a role in the composite mechan- References
bead fusion lines and the 1630 F ism. Since the fissure morphology
(888 C) peak temperature isotherms shows that liquation is virtually always 1. King, B. L., "Weld Metal and Heat
produced during the deposition of Affected Zone Hot Cracking in Wrought
associated with the occurrence of fis-
beads 3 and 8. Note that the cross- Austenitic Stainless Steels," BWRA Re-
sures, it must be a dominant factor. port C 139/A/2/65, Feb. 1966.
hatched region represents that area However, enhanced partitioning or
over which double HAZ (greater than 2. Senda, T., et al., "Fundamental
segregation during the thermal cycles Investigations on Solidification Crack
1630 F) t h e r m a l cycling has oc- experienced after initial deposition Susceptibility for Weld Metal with Trans-
c u r r e d . In this particular case a should not be overlooked as contrib- Varestramt Test," Welding Research
fissure exists in the center of the d o u - utory to the liquation. Abroad, Vol. 18 (6), 1972.
ble HAZ region (it is difficult to see, 3. Masumoto, I., Tamaki, K. and Kat-
however, at the magnification of the suna, M , "Hot Cracking of Austenitic
macrograph). Conclusions Stainless Steel Weld Metal," Journal of
When the weld pad plane of exam- 1. The fissures observed in this Japanese Welding Society, Vol. 41 (11),
ination passes through the double 1972, Brutcher Trans. No. 8965.
study correlate with those found in
HAZ region, fissures may be found on 4. Arata, Y., et al., "Varestraint Test for
production weldments with regard to Solidification Crack Susceptibility in Weld
the pad surface. However, when the location (along grain boundaries in Metal of Austenitic Stainless Steels,"
weld pad plane of examination does f e r r i t e - f r e e areas in HAZs), and Trans. Japan Welding Research Institute,
not pass through the double HAZ appearance. The size is somewhat Vol. 3 (1), 1974.
region, the chance of finding fissures smaller, however. 5. Poole, L. K., "The Incidence of
along the interpass exposed on the 2. Fissures do not propagate with Cracking in Weld Type 347 Steels," Weld-
weld pad plane of examination is applied strain (up to 20% plastic ing Journal, 32 (8), Aug. 1953, Res. Suppl.,
reduced. strain), but rather the fissure tips 403-s to 412-s.
6. Puzak, P. P., Apblett, W. R., and
become blunted as the bending strain
Pellini, W. S., "Hot Cracking of Stainless
increases. Steel Weldments," Welding Journal, 35 (1),
Factors Contributing to t h e 3. The overall fissuring temper- Jan. 1956, Res. Suppl., 9-s to 17-s.
Multiple H A Z T h e r m a l C y c l e ature range was defined as extend- 7. Puzak, P. P., and Rischall, H.,
Phenomenon ing from the bulk solidus temper- "Further Studies on Stainless Steel Hot
ature to 1630 F (888 C) with the m a - Cracking," Welding Journal, 36 (2), Feb.
The effect of multiple weld metal jority of the fissures forming in the 1957, Res. Suppl., 57-s to 61-s.
HAZ thermal cycles on the fissuring 2400 to 1950 F (1316 to 1066 C) 8. Fairchild, F. P., "Eight Years of Expe-
propensity of austenitic stainless steel range. rience with Austenitic Steel Piping Mate-
weld metal is unmistakable in light of rials at Elevated Steam Conditions," Trans,
4. Multiple HAZ thermal cycling
of ASME, Vol. 79 (8), 1957.
the foregoing discussions. This phe- plays a dominant role in fissuring of 9. Curran, R. M., and Rankin, A. W.,
nomenon appears to be the most in- multipass austenitic stainless weld- "Austenitic Steels in High Temperature
fluential element in the gamut of ments. Steam Piping," Trans, of ASME, Vol. 79
fissuring influences in austenitic 5. The factors which lead to an e n - (8), 1957.
stainless steels. hanced fissuring propensity when 10. Younger, R. IM., and Baker, R. G.,
Since the occurrence of a single multiple weld HAZ thermal cycles are "Heat Affected Zone Cracking in Welded
weld metal HAZ experience does not i m p o s e d on previously d e p o s i t e d High-Terr perature Austenitic Steels,"
produce myriads of fissures upon the weld passes are: Journal of Iron and Steel Institute, Vol. 196
(10), 1960.
application of strain, it is clear that the (a) The a c c u m u l a t i o n of strain
11. Christoffel, R. J., "Cracking in Type
strain tolerance of the grain b o u n - attendant upon multiple ther- 347 Heat Affected Zone During Stress Re-
dary microstructural region is signif- mal cycling. laxation," Welding Journal, 41 (6), June
icantly reduced by multiple thermal (b) Degradation of the strain toler- 1962, Res. Suppl., 251-s to 256-s.
cycling. This degradation of grain ance of the metallurgical struc- 12. Shackleton, D. N., "High Temper-
boundary ductility can be due to: ture in and about a grain b o u n - ature Cracking Mechanism in the Heat
1. Enhanced segregation due to dary by continued segregate Affected Zone of 25 Cr:20 Ni Stainless
c o n t i n u e d partitioning of h a r m f u l p a r t i t i o n i n g or p r e c i p i t a t i o n Steel Welds," BWRA Report M/47/69, Oct.
reactions. 1969.
trace elements to the grain boun-
13. Rollason, E. C, and Bystram, M. C ,
daries followed by liquation and r u p - (c) Liquation of the segregated
"Hot Cracking of Austenitic Welds with
ture under strain. grain boundary regions pro- Special Reference to 18/3/1 Cr-Ni-Nb
2. Strengthening of the matrix by duced upon solidification Alloy," Journal of Iron and Steel Institute,
thermally-induced precipitate reac- and/or those boundaries with Vol. 169 (12), 1951.
tions, as is the case for some duc- enhanced segregation pro- 14. Cordea, J. N., Evans, R. M., and
tility-dip incidences. The increased duced during thermal cycling. Martin, D. C , "Investigation to Determine

366-s I N O V E M B E R 1976
Causes of Fissuring in Stainless Steel and Duke Power Company," Report No. 1057, by IIW C o m m i s s i o n 2 in 1963-1973.
Nickel-Base Alloy Weld Metals," Tech- Dec. 23, 1972. 36. Goodwin, G., Cole, N., and Slaugh-
nical Documentary Report No. ASD-TDR- 25. Lundin, C. D., DeLong, W. T., and ter, G., "A Study of Ferrite Morphology in
62-317, Battelle Memorial Institute, June Spond, D. F., "Ferrite-Fissuring Relation- Austenitic Stainless Steel Weldments,"
1962. ship in Austenitic Stainless Steel Weld Welding Journal, 51 (9), Sept. 1972, Res.
15. Haddrill, D. M., and Baker, R. G., Metals," Welding Journal, 54 (8), Aug. Suppl., 425-s to 429-s.
" M i c r o c r a c k i n g in Austenitic W e l d Metal," 1975, Res. Suppl., 241-s to 246-s. 37. Williams, N. T., et al., "Stresses and
Brit. Welding Journal, Vol. 13 (1), 1966. 26. T r u m a n , R. J., and Kirkby, H. W., Strains in Thick Austenitic Steel Plates
16. Fredriks, H., and van der Toorn, L. " S o m e Ductility Aspects of 18-12-1 Nb During Welding," Proceedings of the
J., "Hot Cracking in Austenitic Stainless Steel," Journal of Iron and Steel Institute, Second Commonwealth Welding Confer-
Steel Weld Deposits," Brit. Welding Jour- Vol. 196 (10), 1960. ence, The Welding Institute, London,
nal, Vol. 15 (4), 1968. 27. Borland, J. C , and Younger, R. N., England, 1965.
17. Lundin, C. D., "Welding Defects, "Some Aspects of Cracking in Welded Cr- 38. Zhitnikov, N. P., and Zemzin, V. N.,
Their Origin and Effect," II Interamerican Ni Austenitic Steels," Brit. Welding Jour- "Brittle Failure Tendency of C h r o m i u m -
C o n f e r e n c e on Materials T e c h n o l o g y , nal, Vol. 7 (1), 1960. Nickel Steel Welds," Svar. Proiz, No. 10,
Mexico City, Mexico, A u g . 1970. 28. Borland, J. C , "Generalized Theory 1970.
18. Honeycombe, J., and Gooch, T. G., of Super-Solidus Cracking in Welds (and 39. S h r o n , R. Z., " I n f l u e n c e of the
"Microcracking in Fully Austenitic Stain- Castings)," Brit. Welding Journal, V o l . 7 M e c h a n i c a l H e t e r o g e n e i t y of W e l d e d
less Steel Weld Metal," Metal Construc- (8), 1960. Joints in Austenitic Steels on Their Sus-
tion and Brit. Welding Journal, Vol. 2 (9), 29. Irvine, K. J., Murray, J. D., and ceptibility to Local Failure," Sirar. Proiz,
1970. Pickering, F. B., "The Effect of Heat-Treat- No. 4, 1965.
19. Honeycombe, J., and Gooch, T. G., ment and Microstructure on the High 40. Brooks, C. R. and Spruiell, J. E.,
"Effect of Manganese on Cracking and Temperature Ductility of 18 Cr-12 Ni-1 Nb University of Tennessee, Private C o m m u -
Corrosion Behavior of Fully Austenitic Steels," Journal of Iron and Steel Institute, nications, Aug. 1974.
Stainless Steel Weld Metals," Metal Con- Vol. 196 (10), 1960. 4 1 . Honeycombe, J., and Gooch, T. G.,
struction and Brit. Welding Journal, Vol. 4 30. Hemsworth, B., ef al., "Classifica- "Effect of Microcracks on Mechanical
(12), 1972. tion and Definition of High Temperature Properties of Austenitic Stainless-Steel
20. Honeycombe, J., and Gooch, T. G., Welding Cracks in Alloys," Metal Con- Weld Metals," Metal Construction and Brit.
" M i c r o c r a c k i n g in Fully Austenitic Stain- struction and Brit. Welding Journal, Vol. 1 Welding Journal, Vol. 5 (4), 1973.
less Steel Weld Metal," Metal Construc- (2), 1969. 42. DeHoff, R. T., and Rhines, F. N.,
tion and Brit. Welding Journal, Vol. 7 (3), 3 1 . Lundin, C. D., and Bennett, R. K., Quantitative Microscopy, McGraw-Hill,
1975. "Scanning Electron Microscopy of Frac- New York, 1968.
2 1 . T a m u r a , H., and W a t a n a b e , T., tures in Welded Structures," IMS Pro- 43. Lundin, C. D., ef al., Unpublished
" M e c h a n i s m of Liquidation Cracking in ceedings, 1971. research at University of Tennessee, May
Weld Heat Affected Zone of Austenitic 32. Lundin, C. D., DeLong, W. T., and 1975.
Stainless Steels," Welding Research S p o n d , D. F., "The Fissure Bend Test," 44. Savage, W. F., and Lundin, C. D.,
Abroad, Vol. 20 (6), 1974. submitted to Welding Journal tor publica- "The Varestraint Test," Welding Journal,
22. Burghard, H. C , et al., " A n Inves- tion. 44 (10), Oct. 1965, Res. Suppl., 443-s to
tigation of the Properties of Type 316 33. DeLong, W. T., "Ferrite in Austen- 442-s.
Stainless Steel Weldments Containing itic Stainless Steel Weld Metal," Welding 45. Savage, W. F., and Lundin, C. D.,
Austenitic Microfissures," SWRI Topical Journal, 53 (7), July 1974, Res. Suppl., "Application of the Varestraint Technique
Report No. 1, Project 17-3078, Aug. 15, 273-s to 286-s. to the Study of Weldability," Welding Jour-
1971. 34. Gunia, R., and Ratz, G., "The Mea- nal, 45 (11), Nov. 1966, Res. Suppl., 497-s
23. Buchhoit, R. D., et al., "Laboratory surement of Delta Ferrite in Austenitic to 503-s.
Studies of Type 316 Stainless Steel Weld Stainless Steels," WRC Bulletin No. 132, 46. Shorshorov, N. K., and Sokolov,
Metal from Maine Yankee Reactor Coolant A u g . 1968. Y. V., "The T e m p e r a t u r e Range in W h i c h
System," Battelle Final Report, Sept. 17, 35. Stalmasek, E., "Measurement of Hot Cracks Develop W h e n Single Phase
1971. Ferrite Content in Austenitic Stainless Nickel Alloys are Fusion W e l d e d , " Avtom.
24. Thielsch, H., "Examination of Type Steel Weld Metal Yielding Internationally Svarka, Vol. 16 (4), 1963.
316 Stainless Steel W e l d Deposit for Compatible Results," International Insti- 47~ L u n d i n , C. D., U n p u b l i s h e d r e -
Microfissuring and Delta Ferrite Contents tute of Welding — Commission No. 2, "Arc search at Rensselaer Polytechnic Insti-
for the Oconee Nuclear Power Station, W e l d i n g , " S u m m a r y Report of Work Done tute, 1968.

WRC Bulletin No. 219

"Experimental Investigation of Limit Loads of Nozzles in Cylindrical Vessels"
by Fernand Ellyin
Experimental results of elastic-plastic behavior and plastic limit loads (yield point loads)
of five tee-shaped cylinder-cylinder intersections and a plain pipe are reported herein. The
intersecting models were machined from a single hot-rolled steel plate. The nozzle-vessel
attachments (or branch-pipe tee connections) were subjected to one of the loading modes:
internal pressure, in-plane or out-of-plane couples applied to the nozzle extremity. The out-
of-plane couple loading is found to be the critical case.

Publication of this report was sponsored by the Pressure Vessel Research Committee of
the Welding Research Council.
The price of WRC Bulletin 219 is $6.00 per copy. Orders should be sent with payment to
the Welding Research Council, United Engineering Center, 345 East 47th St., New York, N.Y.
10017.

WELDING RESEARCH S U P P L E M E N T ! 367-s