U.S. patent application number 17/037806 was filed with the patent office on 2021-06-17 for tig welding flux for super duplex stainless steel.
The applicant listed for this patent is NATIONAL PINGTUNG UNIVERSITY OF SCIENCE & TECHNOLOGY. Invention is credited to Kuang-Hung TSENG.
Application Number | 20210178526 17/037806 |
Document ID | / |
Family ID | 1000005133318 |
Filed Date | 2021-06-17 |
United States Patent
Application |
20210178526 |
Kind Code |
A1 |
TSENG; Kuang-Hung |
June 17, 2021 |
TIG Welding Flux for Super Duplex Stainless Steel
Abstract
A tungsten inert gas (TIG) welding flux for super duplex
stainless steel (SDSS) is used to solve the problems of low weld
depth/width ratio, low corrosion resistance, and arc blow existing
in the conventional TIG welding flux for duplex stainless steel.
The TIG welding flux for SDSS includes 20-30 wt % of silicon
dioxide (SiO.sub.2), 20-25 wt % of titanium dioxide (TiO.sub.2),
15-20 wt % of vanadium dioxide (VO.sub.2), 10-15 wt % of molybdenum
trioxide (MoO.sub.3), 10-15 wt % of zirconium diboride
(ZrBr.sub.2), 5-10 wt % of aluminum nitride (AlN), 5-10 wt % of
manganese carbonate (MnCO.sub.3) and 5-10 wt % of nickel carbonate
(NiCO.sub.3).
Inventors: |
TSENG; Kuang-Hung; (Pingtung
County, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL PINGTUNG UNIVERSITY OF SCIENCE & TECHNOLOGY |
Pingtung County |
|
TW |
|
|
Family ID: |
1000005133318 |
Appl. No.: |
17/037806 |
Filed: |
September 30, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 35/362
20130101 |
International
Class: |
B23K 35/362 20060101
B23K035/362 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2019 |
TW |
108145532 |
Sep 24, 2020 |
TW |
109133135 |
Claims
1. A tungsten inert gas (TIG) welding flux for super duplex
stainless steel (SDSS), comprising: 20-30 wt % of silicon dioxide
(SiO.sub.2), 20-25 wt % of titanium dioxide (TiO.sub.2), 15-20 wt %
of vanadium dioxide (VO.sub.2), 10-15 wt % of molybdenum trioxide
(MoO.sub.3), 10-15 wt % of zirconium diboride (ZrBr.sub.2), 5-10 wt
% of aluminum nitride (AlN), 5-10 wt % of manganese carbonate
(MnCO.sub.3) and 5-10 wt % of nickel carbonate (NiCO.sub.3).
2. The TIG welding flux for SDSS as claimed in claim 1, wherein the
TIG welding flux for SDSS comprises 5-9 wt % of AlN, 5-7 wt % of
MnCO.sub.3 and 5-7 wt % of NiCO.sub.3.
3. The TIG welding flux for SDSS as claimed in claim 1, wherein the
TIG welding flux for SDSS comprises 9 wt % of AlN, 5 wt % of
MnCO.sub.3 and 5 wt % of NiCO.sub.3.
4. The TIG welding flux for SDSS as claimed in claim 1, wherein the
TIG welding flux for SDSS comprises 5 wt % of AlN, 6 wt % of
MnCO.sub.3 and 5 wt % of NiCO.sub.3.
5. The TIG welding flux for SDSS as claimed in claim 1, wherein the
TIG welding flux for SDSS comprises 5 wt % of AlN, 5 wt % of
MnCO.sub.3 and 5 wt % of NiCO.sub.3.
6. The TIG welding flux for SDSS as claimed in claim 1, wherein the
TIG welding flux for SDSS comprises 9 wt % of AlN, 5 wt % of
MnCO.sub.3 and 6 wt % of NiCO.sub.3.
7. The TIG welding flux for SDSS as claimed in claim 1, wherein the
TIG welding flux for SDSS comprises 6 wt % of AlN, 6 wt % of
MnCO.sub.3 and 5 wt % of NiCO.sub.3.
8. The TIG welding flux for SDSS as claimed in claim 1, further
comprising a volatile solvent.
9. The TIG welding flux for SDSS as claimed in claim 1, wherein the
volatile solvent comprises methanol, acetone or isopropanol.
10. The TIG welding flux for SDSS as claimed in claim 1, wherein
the TIG welding flux for SDSS has a plurality of powdered particles
each having a diameter of 50-90 .mu.m.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The application claims the benefit of Taiwan application
serial No.108145532, filed Dec. 12, 2019, as well as of Taiwan
application serial No.109133135, filed Sep. 24, 2020, the entire
contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention generally relates to a welding flux
and, more particularly, to a tungsten inert gas (TIG) welding flux
for super duplex stainless steel (SDSS).
2. Description of the Related Art
[0003] Duplex stainless steel (DSS) belonging to Fe--Cr--Ni alloy
has a two-phase structure consisting of austenite and ferrite, in
which both austenite and ferrite phase should be more than 30% and
less than 70%.
[0004] Due to the two-phase structure, DSS has advantages of both
ferrite and austenite stainless steels. That is, DSS has better
fracture toughness, better intergranular corrosion resistance, and
is easier to be welded than ferritic stainless steel. DSS has
properties the same as ferritic stainless steel such as small
coefficient of thermal expansion and high thermal conductivity.
Moreover, DSS has a two-fold yield strength compared to austenitic
stainless steel, a resistance to chloride-induced stress corrosion
cracking significantly higher than SUS 304 austenitic stainless
steel, and a pitting corrosion resistance, as well as a crevice
corrosion resistance, equal to SUS 316 austenitic stainless
steel.
[0005] Compared to standard DSS such as SAF 2205/UNS 532205, SDSS
such as SAF 2507/UNS 532750 has excellent pitting and crevice
corrosion resistances due to extremely low carbon content, high
molybdenum and nitrogen contents. As a specialized stainless steel
with excellent advantages such as good corrosion resistance, great
mechanical strength and easily manufactured, SDSS is widely applied
to high value-added metal products such as heat exchanger,
petrochemical equipment, oil and gas pipelines and seawater
desalination plant.
[0006] The welding quality of SDSS depends on the ferrite/austenite
phase ratio in the weld metal and the heat-affected zone (HAZ).
However, the fast cooling, after the welding process, causes
increased ferrite phase in the weld metal and the HAZ, reducing the
corrosion resistance of the weld metal and the HAZ. It can be seen
that the ferrite/austenite phase ratio in the weld metal and the
HAZ should be strictly controlled during the welding process for
SDSS. That is, the weld metal and the HAZ should have ferrite phase
less than 50%. Alternatively, the weld metal and the HAZ should
have austenite phase more than 50%.
[0007] Taiwan patent number I 633059 discloses a conventional
welding flux for DSS, which includes 25-35 wt % of silicon dioxide
(SiO.sub.2), 20-25 wt % of chromium oxide (Cr.sub.2O.sub.3), 10-20
wt % of molybdenum trioxide (MoO.sub.3), 10-15 wt % of nickel oxide
(NiO), 5-10 wt % of ferric oxide (Fe.sub.2O.sub.3), 5-10 wt % of
cobalt oxide (Co.sub.3O.sub.4), 5-10 wt % of manganese dioxide
(MnO.sub.2) and 3-5 wt % of copper oxide (CuO). When two DSS
workpieces, made of SAF 2205/UNS 532205 as an example, are joined
by the TIG welding process utilizing the conventional welding flux
for DSS, a weld formed between the two joined DSS workpieces has a
higher weld depth/width ratio (D/W ratio) and a better corrosion
resistance. However, if the conventional welding flux for DSS is
utilized to join two SDSS workpieces, such as the workpieces made
of SAF 2507/UNS 532750, by the TIG welding, a weld formed between
the two joined SDSS workpieces cannot has a higher weld D/W ratio
and a better corrosion resistance. Moreover, arc blow occurs during
the TIG welding for SDSS.
[0008] In light of this, it is necessary to provide a TIG welding
flux for SDSS.
SUMMARY OF THE INVENTION
[0009] It is therefore an objective of the present invention to
provide a TIG welding flux for SDSS, which is suitable to join two
SDSS workpieces.
[0010] "A" or "an" used in the elements and components recited in
the disclosure of the present invention is for convenient use and
provides generally meanings of the scope of the present invention.
"A" or "an" used in the present invention is interpreted as
comprising one or at least one, and the single concept also
includes plural conditions, otherwise obviously indicating other
meanings.
[0011] One embodiment of the present invention discloses the TIG
welding flux for SDSS includes 20-30 wt % of silicon dioxide
(SiO.sub.2), 20-25 wt % of titanium dioxide (TiO.sub.2), 15-20 wt %
of vanadium dioxide (VO.sub.2), 10-15 wt % of molybdenum trioxide
(MoO.sub.3), 10-15 wt % of zirconium diboride (ZrBr.sub.2), 5-10 wt
% of aluminum nitride (AlN), 5-10 wt % of manganese carbonate
(MnCO.sub.3) and 5-10 wt % of nickel carbonate (NiCO.sub.3).
[0012] Accordingly, when two SDSS workpieces are joined by the TIG
welding process utilizing the TIG welding flux for SDSS, with
specific weight percentages of SiO.sub.2, TiO.sub.2, VO.sub.2,
MoO.sub.3, ZrBr.sub.2, AlN, MnCO.sub.3 and NiCO.sub.3, according to
the present invention, a weld between the two joined SDSS
workpieces has a higher weld D/W ratio and a better corrosion
resistance. Moreover, no arc blow occurs during the TIG
welding.
[0013] In preferred form shown, the TIG welding flux for SDSS
includes 5-9 wt % of AlN, 5-7 wt % of MnCO.sub.3 and 5-7 wt % of
NiCO.sub.3. With such performance, the weld between the two jointed
SDSS workpieces has a higher weld D/W ratio and a better corrosion
resistance. Moreover, no arc blow occurs during the TIG
welding.
[0014] In preferred form shown, the TIG welding flux for SDSS
includes 9 wt % of AlN, 5 wt % of MnCO.sub.3 and 5 wt % of
NiCO.sub.3. With such performance, the weld between the two jointed
SDSS workpieces has a higher weld D/W ratio and a better corrosion
resistance. Moreover, no arc blow occurs during the TIG
welding.
[0015] In preferred form shown, the TIG welding flux for SDSS
includes 5 wt % of AlN, 6 wt % of MnCO.sub.3 and 5 wt % of
NiCO.sub.3. With such performance, the weld between the two jointed
SDSS workpieces has a higher weld D/W ratio and a better corrosion
resistance. Moreover, no arc blow occurs during the TIG
welding.
[0016] In preferred form shown, the TIG welding flux for SDSS
includes 5 wt % of AlN, 5 wt % of MnCO.sub.3 and 5 wt % of
NiCO.sub.3. With such performance, the weld between the two jointed
SDSS workpieces has a higher weld D/W ratio and a better corrosion
resistance. Moreover, no arc blow occurs during the TIG
welding.
[0017] In preferred form shown, the TIG welding flux for SDSS
includes 9 wt % of AlN, 5 wt % of MnCO.sub.3 and 6 wt % of
NiCO.sub.3. With such performance, the weld between the two jointed
SDSS workpieces has a higher weld D/W ratio and a better corrosion
resistance. Moreover, no arc blow occurs during the TIG
welding.
[0018] In preferred form shown, the TIG welding flux for SDSS
includes 6 wt % of AlN, 6 wt % of MnCO.sub.3 and 5 wt % of
NiCO.sub.3. With such performance, the weld between the two jointed
SDSS workpieces has a higher weld D/W ratio and a better corrosion
resistance. Moreover, no arc blow occurs during the TIG
welding.
[0019] In preferred form shown, the TIG welding flux for SDSS
further includes a volatile solvent. With such performance, a
plurality of powdered particles including SiO.sub.2, TiO.sub.2,
VO.sub.2, MoO.sub.3, ZrBr.sub.2, AlN, MnCO.sub.3 and NiCO.sub.3 can
be dispersed in the volatile solvent to form a paste-like slurry,
thus can be easily spread on surface of the two SDSS
workpieces.
[0020] In preferred form shown, the volatile solvent can include
methanol, acetone or isopropanol. With such performance, after
being spread on surface of the two SDSS workpieces, the volatile
solvent of the TIG welding flux for SDSS can evaporate quickly,
thus shorten the waiting time of welder.
[0021] In preferred form shown, the TIG welding flux for SDSS has a
plurality of powdered particles each having a diameter of 50-90
.mu.m. With such performance, the plurality of powdered particles
can form a homogeneous mixture with great uniformity. As such, the
TIG welding flux for SDSS can be easily spread on surface of the
two SDSS workpieces. Also, the welding flux for SDSS can be easily
melted by a heat source, and the weld depth can therefore be
increased. In addition, the residual slag easily forms when the TIG
welding process is carried out with the TIG welding flux for SDSS
having the plurality of powdered particles with the diameter larger
than 90 .mu.m, while the more TIG welding flux for SDSS is needed
when the TIG welding process is carried out with the TIG welding
flux for SDSS having the plurality of powdered particles with the
diameter smaller than 50 .mu.m, increasing manufacturing costs.
That is, with the plurality of powdered particles with the diameter
of 50-90 .mu.m, the TIG welding flux for SDSS can not only prevent
from residual slag formation but also reduce the manufacturing
costs.
[0022] As a result, when two SDSS workpieces are joined by the TIG
welding process utilizing the TIG welding flux for SDSS, with
specific weight percentages of SiO.sub.2, TiO.sub.2, VO.sub.2,
MoO.sub.3, ZrBr.sub.2, AlN, MnCO.sub.3 and NiCO.sub.3, according to
the present invention, a weld between the two joined SDSS
workpieces has a weld D/W ratio more than or equal to 0.8. Thus, a
relative smaller HAZ can be obtained, reducing the risk of problems
such as thermal deformation and residual stress of the weldment.
The weld metal has a higher austenite phase content than a ferrite
phase content, improving the corrosion resistance of the weld.
Moreover, no arc blow occurs during the TIG welding.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The present invention will become more fully understood from
the detailed description given hereinafter and the accompanying
drawings which are given by way of illustration only, and thus are
not limitative of the present invention, and wherein:
[0024] FIG. 1 depicts a cross-sectional view of a weld of group
B08, which is formed between joined two SDSS workpieces by the TIG
welding process utilizing the TIG welding flux of group A08.
[0025] FIG. 2 depicts a cross-sectional view of a weld of group
B12, which is formed between joined two SDSS workpieces by the TIG
welding process utilizing the TIG welding flux of group A12.
[0026] FIG. 3 depicts a cross-sectional view of a weld of group
B17, which is formed between joined two SDSS workpieces by the TIG
welding process without the TIG welding flux.
DETAILED DESCRIPTION OF THE INVENTION
[0027] A TIG welding flux for SDSS according to a specific
embodiment of the present invention can include 20-30 wt % of
SiO.sub.2 (silicon dioxide), 20-25 wt % of TiO.sub.2 (titanium
dioxide), 15-20 wt % of VO.sub.2 (vanadium dioxide), 10-15 wt % of
MoO.sub.3 (molybdenum trioxide), 10-15 wt % of ZrBr.sub.2
(zirconium diboride), 5-10 wt % of AlN (aluminum nitride), 5-10 wt
% of MnCO.sub.3 (manganese carbonate) and 5-10 wt % of NiCO.sub.3
(nickel carbonate). In another specific embodiment, the TIG welding
flux for SDSS includes 9 wt % of AlN, 5 wt % of MnCO.sub.3 and 5 wt
% of NiCO.sub.3.
[0028] In another specific embodiment, the TIG welding flux for
SDSS includes 5 wt % of AlN, 6 wt % of MnCO.sub.3 and 5 wt % of
NiCO.sub.3. In another specific embodiment, the TIG welding flux
for SDSS includes 5 wt % of AlN, 5 wt % of MnCO.sub.3 and 5 wt % of
NiCO.sub.3. In another specific embodiment, the TIG welding flux
for SDSS includes 9 wt % of AlN, 5 wt % of MnCO.sub.3 and 6 wt % of
NiCO.sub.3. In another specific embodiment, the TIG welding flux
for SDSS includes 6 wt % of AlN, 6 wt % of MnCO.sub.3 and 5 wt % of
NiCO.sub.3. In another specific embodiment, the TIG welding flux
for SDSS includes 5 wt % of AlN, 10 wt % of MnCO.sub.3 and 5 wt %
of NiCO.sub.3.
[0029] Accordingly, when two SDSS workpieces are joined by the
[0030] TIG welding process utilizing the TIG welding flux for SDSS,
with specific weight percentages of SiO.sub.2, TiO.sub.2, VO.sub.2,
MoO.sub.3, ZrBr.sub.2, AlN, MnCO.sub.3 and NiCO.sub.3, according to
the present invention, a weld between the two joined SDSS
workpieces has a weld D/W ratio more than or equal to 0.8. Thus, a
relative smaller HAZ can be obtained, reducing the risk of problems
such as thermal deformation and residual stress of the weldment.
The weld metal has a higher austenite phase content than a ferrite
phase content, improving the corrosion resistance of the weld.
Moreover, no arc blow occurs during the TIG welding.
[0031] In a specific embodiment, the TIG welding flux for SDSS
according to the present invention can further include a volatile
solvent. In another specific embodiment, the volatile solvent can
include, but not limited to, methanol, acetone or isopropanol.
[0032] In a specific embodiment, the TIG welding flux for SDSS
according to the present invention can have a plurality of powdered
particles each having a diameter of 50-90 .mu.m.
[0033] In a specific embodiment, the TIG welding flux for SDSS
according to the present invention can be applied to join two
workpieces made of SDSS including, but not limited to, UNS 532750
and UNS 532760.
[0034] To validate whether a weld between the two joined SDSS
workpieces has a higher weld D/W ratio and a better corrosion
resistance, as well as whether arc blow occurs during the TIG
welding, when two SDSS workpieces are joined by the TIG welding
process utilizing the TIG welding flux for SDSS according to the
present invention, the following trials are carried out.
[0035] Trial (A).
[0036] Powdered particles of SiO.sub.2, TiO.sub.2, VO.sub.2,
MoO.sub.3, ZrBr.sub.2, AlN, MnCO.sub.3 and NiCO.sub.3 are mixed
according to TABLE 1. The TIG welding fluxes of groups A1-A15 are
prepared by forming paste-like slurries by dispersing the mixtures
in acetone.
TABLE-US-00001 TABLE 1 SiO.sub.2 TiO.sub.2 VO.sub.2 MoO.sub.3
ZrBr.sub.2 AlN MnCO.sub.3 NiCO.sub.3 Groups (wt %) (wt %) (wt %)
(wt %) (wt %) (wt %) (wt %) (wt %) A01 20 20 15 11 11 10 7 6 A02 20
25 15 10 15 5 5 5 A03 20 22 16 15 10 6 6 5 A04 21 21 18 10 10 9 5 6
A05 23 20 20 10 10 5 5 7 A06 25 20 15 10 10 5 10 5 A07 25 20 15 10
10 5 5 10 A08 26 20 15 10 10 9 5 5 A09 28 20 15 10 10 5 6 5 A10 30
20 15 10 10 5 5 5 A11 20 25 20 15 10 0 5 5 Al2 25 23 15 10 15 2 0
10 A13 25 22 15 10 15 3 10 0 A14 28 21 15 10 15 7 2 2 A15 30 20 15
11 11 4 5 4
[0037] Moreover, powdered particles of SiO.sub.2, Cr.sub.2O.sub.3,
MoO.sub.3, NiO, Fe.sub.2P.sub.3. Co.sub.3O.sub.4, MnO.sub.2 and CuO
are mixed according to TABLE 2. The conventional TIG welding flux
of group A16 is prepared by forming paste-like slurries by
dispersing the mixtures in acetone.
TABLE-US-00002 TABLE 2 SiO.sub.2 Cr.sub.2O.sub.3 MoO.sub.3 NiO
Fe.sub.2O.sub.3 Co.sub.3O.sub.4 MnO.sub.2 CuO Group (wt %) (wt %)
(wt %) (wt %) (wt %) (wt %) (wt %) (wt %) A16 30 23 12 10 7 10 5
3
[0038] Trial (B).
[0039] In this trial, UNS 532750 plates with thickness being 6.0 mm
are used as the SDSS workpieces. After removing contaminants
attached on surface of the SDSS workpieces using a 400-grit silicon
carbide sandpaper. The SDSS workpieces are swiped by acetone wipes.
Then, the paste-like slurries formed by TIG welding fluxes for SDSS
of groups A01-A16 are spread on surface of the two SDSS workpieces.
The TIG welding process is carried out after acetone is completely
evaporated to obtain the welded assembly (the joined two
workpieces) of groups B1-B16, as shown in TABLE 3. In addition, a
welded assembly of group B17 is obtained by the TIG welding without
the TIG welding flux of groups A01-16.
TABLE-US-00003 TABLE 3 Group TIG welding flux used during the TIG
welding B01 Group A01 (the TIG welding flux for SDSS according to
the present invention) B02 Group A02 (the TIG welding flux for SDSS
according to the present invention) B03 Group A03 (the TIG welding
flux for SDSS according to the present invention) B04 Group A04
(the TIG welding flux for SDSS according to the present invention)
B05 Group A05 (the TIG welding flux for SDSS according to the
present invention) B06 Group A06 (the TIG welding flux for SDSS
according to the present invention) B07 Group A07 (the TIG welding
flux for SDSS according to the present invention) B08 Group A08
(the TIG welding flux for SDSS according to the present invention)
B09 Group A09 (the TIG welding flux for SDSS according to the
present invention) B10 Group A10 (the TIG welding flux for SDSS
according to the present invention) B11 Group A11 (the TIG welding
flux without MN) B12 Group A12 (the TIG welding flux without
MnCO.sub.3) B13 Group A13 (the TIG welding flux without NiCO.sub.3)
Group A14 (the TIG welding flux with 2% of MnCO.sub.3 B14 and 2% of
NiCO.sub.3) B15 Group A15 (the TIG welding flux with 4% of
NiCO.sub.3) B16 Group A16 (the conventional TIG welding flux) B17
No
[0040] During the TIG welding for obtaining the joined two SDSS
workpieces of groups B01-B17, the occurrences of arc blow are
recorded. After the TIG welding, cross sections of the joined two
SDSS workpieces of groups B01-B17 are obtained. The weld depth "D"
and the bead width "W" of the resultant weld between the jointed
two SDSS workpieces of groups B01-B17 are recorded. NM stands for
not measured. The weld D/W ratio of groups B01-B17 is calculated.
Moreover, the ferrite phase content of the weld metal between the
joined two SDSS workpieces of groups B01-B17 is also measured, and
the ferrite/austenite phase ratio is calculated. All results are
shown in TABLE 4.
TABLE-US-00004 TABLE 4 Ferrite/ Weld depth Bead width Weld D/W
austenite Arc blow Groups (mm) (mm) ratio phase ratio occurs B01
5.7 7.1 0.80 38%/62% No B02 5.8 6.9 0.84 47%/53% No B03 6.0 6.8
0.88 41%/59% No B04 6.2 7.0 0.89 40%/60% No B05 6.1 7.1 0.86
46%/54% No B06 5.9 6.8 0.87 45%/55% No B07 5.8 7.0 0.83 44%/56% No
B08 7.1 7.3 0.97 40%/60% No B09 6.8 7.4 0.92 47%/53% No B10 6.9 7.6
0.91 46%/54% No B11 NM NM NM 58%/42% Yes B12 4.1 9.6 0.43 56%/44%
Yes B13 NM NM NM 55%/45% Yes B14 NM NM NM 53%/47% Yes B15 NM NM NM
54%/46% Yes B16 NM NM NM 60%/40% Yes B17 2.8 10.7 0.26 64%/36%
No
[0041] FIGS. 1-3 show the cross sections of the joined two SDSS
workpieces of groups B08, B12 and B17, respectively. The weld
between the jointed two SDSS workpieces of group B08 completely
penetrates the SDSS workpiece, while the weld between the two
jointed SDSS workpieces of groups B12 and B17 cannot completely
penetrate the SDSS workpiece. Moreover, referring to TABLE 3 and
FIGS. 1-3, compared to the welds between the jointed two SDSS
workpieces of groups B12 and B17, the welded joint of groups
B01-B10 has an increased weld depth and a reduced bead width. The
weld D/W ratio of the resultant weld of groups B01-B10 is more than
or equal to 0.8, and even up to 0.97. Thus, relative smaller HAZ
can be obtained, reducing the risk of problems such as thermal
deformation and residual stress of the weldment.
[0042] Moreover, referring to TABLE 3, compared to the welds
between the jointed two SDSS workpieces of groups B11-B17, the
welds between the jointed two SDSS workpieces of groups B01-B10
have a lower ferrite phase content, which is lower than 50%. That
is, the welds between the jointed two SDSS workpieces of groups
B01-B10 have an austenite phase content higher than the ferrite
phase content, indicating the weld between the jointed two SDSS
workpieces of groups B01-B10 have good corrosion resistance. In
addition, no arc blow occurs during the TIG welding for forming the
joined two SDSS workpieces of groups B01-B10.
[0043] Accordingly, when two SDSS workpieces are joined by the TIG
welding process utilizing the TIG welding flux for SDSS, with
specific weight percentages of SiO.sub.2, TiO.sub.2, VO.sub.2,
MoO.sub.3, ZrBr.sub.2, AlN, MnCO.sub.3 and NiCO.sub.3, according to
the present invention, the weld between the two joined SDSS
workpieces has a weld D/W ratio more than or equal to 0.8. Thus, a
relative smaller HAZ can be obtained, reducing the risk of problems
such as thermal deformation and residual stress of the weldment.
The weld metal has a higher austenite phase content than a ferrite
phase content, improving the corrosion resistance of the weld.
Moreover, no arc blow occurs during the TIG welding.
[0044] Although the invention has been described in detail with
reference to its presently preferable embodiment, it will be
understood by one of ordinary skill in the art that various
modifications can be made without departing from the spirit and the
scope of the invention, as set forth in the appended claims.
* * * * *