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The Effects of Heat Input and WeldProcess on Hot Cracking in
Stainless Steel
The Sigmajig test was used to quantify the hot-crackingresponse
of Type 316 stainless steel welded with the
GTA W EBW and LBW processes
BY G . M . G O O D W I N
ABSTRACT. The Sigmajig cracking response of a single heat of
0.010-in.-thick(0.25-mm) Type 316 stainless steel wasdetermin ed as
a funct ion of we lding p rocess and parameter variations within
aprocess. It was found that changes inwelding parameters resulted
in changesin cracking response, even when grossenergy input was
maintained constant.Higher travel speeds and elongated we ldpool
shapes increased the crackingresponse, as did increased heat
input.Cracking responses for all three weldingprocesses, gas
tungsten arc (CTA), electron beam (EB), and pulsed solid-statelaser
beam (LB), were found to follow acommon relat ionship with net heat
input .Both EB and LB we lds sh ow ed highercracking resistance
than GTA welds.
In t roduc t ion
The initial application of the Sigmajigtest (Ref. 1) used a
standard set of w e l ding parameters with the CTA process
toevaluate the dependence of crackingsensitivity on heat-to-heat
compositional
K E Y W O R D S
Sigmajig Test316 Stainless SteelHot Cracking ResponseHeat
InputElectron Beam WeldingPulsed Laser WeldingGTA Weld ingCracking
ResistanceThreshold StressArgon Shielding
G M. GOODWIN is a mem ber of the Metalsand Ceramics Division,
Oak Ridge NationalLaboratory, Oak Ridge, Tenn.
Paper presented at the 68th A nnual AWSMeeting, held March
22-27, 1987. in C hicago,III.
effects in stainless steels. In this work, aspecific, relatively
crack-sensitive heat ofType 316 stainless steel was used tostudy
the effect of heat input variationson cracking sensitivity using
three welding processes: gas tungsten arc, electronbeam, and pulsed
solid-state laser.
There are numerous examples in theliterature documenting the
effects of heatinput on hot cracking. Typically, anincrease in heat
input increases crackingsensitivity, but often, there are also
complicating factors to be considered, including changes in
solidification mode (Refs.2-4) or compositional effects (Refs.
5-7).Solidif icat ion growth morphology hasalso been shown to be an
importantfactor (Refs. 8, 9). Few studies haveattempted to isolate
the effect of individual parameters (Ref. 10), and fewer yet
have addressed process-to-process variations (Ref. 11). In this
study, w e hav eintentionally selected a single crack-sensitive
heat of material known to solidify asprimary austenite for the
processes andparameters investigated. The variations inresponse are
thus attributable as nearly aspossible to changes in stress at the
trailingedge of the weld pool , which are determined by heat input,
heat flow, thermalgradients , and weld pool geometry.
Experimental Conditions
A single heat of 0.010-in.-thick (0.25-mm) Type 316 stainless
steel was usedthrougho ut the experiment . Its com position is
given in Table 1. Previous w or k(Ref. 1) established a threshold
crackingstress 1 o f 18 ksi (124 MPa), as comparedwith other
commercial heats rangingfrom 15 to 53 ksi (103 to 365 MPa). It hasa
reasonably high P 4- S content (0.042wt- ), a Cr-N i ratio of 1.47
(Ref. 12), apredicted ferrite number (FN) of 0 (Ref.13), and, as
typified in Fig. 1, invariablysolidifies as primary austenite with
a smallamount of residual eutectic ferrite.
Gas tungsten arc welds were produced under argon w ith a
constant arclength of 0.035 in. (0.88 mm). UsingDCEN and a 1/16-in.
(1.6 mm) diameter
thoriated tungsten electrode with a 45-deg included angle and a
0.010-in. t runcat ion, arc current and travel speed
weresystematically varied above and belowthe standard conditions of
20 A and 35ipm (14.8 mm/s) (Ref. 1). Five specimenswere run at each
combinat ion of param-
1 Threshold cracking stress, a m in, is defined inRef. 1 as the
ap plied stress above whichcracking first occurs.
I .aa
y : ~~y^
Fig. 1 Typicalmicrostructure of gastungsten arc w eld inType 316
stainlesssteel. Heat 828013.Solidification mode isprimary austenite
witha small amoun t ofeutectic ferrite.Murakam i s e tch
88-S | APRIL 1988
