Note: Descriptions are shown in the official language in which they were submitted.
:~33~9392
BACKGROUND OF THE INVENTION
This invention relates to a welding process using an
eutectic alloy wire suitable for welding a superlow-temperature
steel such as 9% nickel steel.
9% nickel steel is a high tensile steel which may be
used at a superlow--Lemperature up to -196C. The tensile
strength o the 9~ nickel steel is defined to be on the order of
70.3 - 84.4 kg/mm according to the ASTM standard, A353 (NNT
material) and A553 (QT material~, and the yield point (0.2%
yield strength~ higher than 52.7 kg/mm2 and higher than 59.8
kg/mm2 according to A353 and A553. The ASTM standard also re-
quires that thQ impact value thereof be greater than 3.5 kg-m at
-196 C. A fuxther requirement of the ASTM standard, case 1308-5,
when a building construction is made by welding the 9% nickel
steel is that the tensile strength of a joint including a base
metal material be higher than 66.~ kg/mm2 and lower than that of
the base metal material per se in order to assure joint perform-
ances when annealing is not carried out as weld condition for the
removal of stress.
In recent years, howeyer, there have been strong
des;res for the development of joints of a tensile strength well
above the standard value as defined by the case 1308-5 and
welding Materials of a strength not less than that of the base
metal material for increasing stress at ti~e of design for weld-
ing. As is obvious from the AST~ standard, proper strengt~ and
low-temperature toughness of the ~% Ilickel steel is o~tainable
from heat treatment but in the case o~ a huge building con~truc-
t~on, for example, a storage tank such heat treatment is
substant~ally impossible after the building of the construction.
To this end the construction is made serviceable as weld
condition.
--1--
~ .~
~335~2
1 While it is most desirable to use a welding wire whose
composition is identical to that of the base material for welding
the 9% nickel steel, high nickel alloy wires as defined ~y the
AWSA standard, 5.11 ENiCrFe l - 3, etc. are very often actually
used for welding because there are difficulties in obtaining
stable low-temperature toughness of the 9% nickel steel wire.
While joints made through using the high nickel welding wire
exhibit excellent toughness at a temperature of -196C after
welding, they undergo very small tensile strength (particularly,
0.2~ yield strength) as compared to that of the base metal
material. No matter when the ~% nickel steel or a 70 kg/mm2
high tensile steel is used, the strength of the joints is low so
that stress should be low at the time of design for welding and
the overall construction welded be thick. The conventional
welding methoa failed to take full advantage of the strength
property of the ~% nickel steel and, in fact, suffered rrom two-
old economical expenditures, an increased thickness of the
construction welded and an increased amount of the expensive high
nickel alloy welding wire consumed. I~elding by the high nickel
alloy was further disadvantageous of undergoing hot cracks and
thermal fatlgue due to a difference between the coefficients
of thermal expansion and requiring laboursome welding procedures.
For those reasons the ~% nickel steel is severely
limited in application while showing excellent performances as a
superlow~temperature steel.
OBJEC~S OF ~HE XN~ENTION
W~th the foregoing in mind, it is an object of the
present invention to provide a welding process using a welding
wire having sta~le low-temperature toughness comparable with that
of the conventional high nickel alloy welding wire and streng-th
~2-
~399Z
1 comparable with that of 9% nickel stee] ensuring more stable
performances.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present in-
vention and for further objects and advantages thereof, reference
is now made to the following description ta~en in conjunction
with the accompanying drawings, in which:
Fig. 1 is a block diagram of an embodiment of the
present invention constructed for controlling arc length;
Fig. 2 is a circuit diagram of an example of an arc
voltage control method;
Fig. 3 is a circuit diagram of another example of the
arc voltage control method;
Fig. ~ is a graph showing the input versus output
characteristics of the example of Fig. 3;
Fig. 5 is a perspective view of a drive section;
Fig. 6 and 7 are perspective views of the concept of a
magnetic arc blow;
Fiq. 8 and 9 are schematic cross sectional views of a
weld zone;
Fig. 1~ and 11 show an e~bodiment of the present in-
; vention wherein Figs. 10 and 11 are side ~iews;
Fig~ 12 is a wave~orm diagram of pulsating current;
Figs. 13 and 14 are graphs showing the relationshipbetween the sum of the oxygen cont0nt and nitrogen content of a
wire and double oxygen content and double nitrogen content of a
base metal and the V notch absorption energy of a weld metal.
Fig. 15 is a plot of the impact resistance of a joint
against the boron content of the wire;
~L~33~92
Figs. 16 and 17 are graphs showing the relationship
between the oxygen content and nitrogen content of a wire and
the "V" notch absorption energy of a weld metal;
Fig. 1~ is a graph showing the relationship between the
cool period and the breaking strength of a final layer during
TIG welding;
Figs. 19 and 20 are photographs showing ~he joint
welded according to the present invention; and
Fig. 21 is a representation of groove shapes used with
the embodiment of the present invention.
Fig. 22(A), (B) and (C) shows various arc deflection
states when the DC voltage sources are connected as in
Fig. 1.
DETAILED DESCRIPTIO~ OF THE PREFERRED EMBODIMENTS
The present invention achieves the above discussed
objectives by providing a wire of which composition is as follows,
wherein ~ means ~ by weight: The welding wire according to the
major features of the present invention essentially includes
~ - 15% of nickel and 0.1 - 0.8% of manganese or essentially
includes, in addition to those ingredients, less than 0.15% of
silicon, less than 0.1~ of carbon, less than 0.1% of aluminum
and less than 0.1% of titanium. It further includes less than
0.0006~ of boron, less than 100 ppm of oxygen and less than 100
ppm of nitrogen. The following detailed description will first
set forth the wire and then a welding process using the wire.
Although the wire embodylng the present inYention is applicable
to the TIG welding method and the TIG plasm arc welding method,
they may be called simply as "the TIG welding method", "TIG
welding wire", etc. hereinafter.
1~33~9~
1 The TIG welding wire according to the present lnvention
is less expensive than any high nickel alloy welding wires and
free from the various problems with the high nickel alloy wires
as discussed above, thus providing joints which are excellent
in low-tempexature toughness, tensile strength, etc. This makes
it possible to reduce substantially the thickness of an overall
construction welded, ta]ce full advantage of the inherent proper-
ties of the 9% nickel steel and e~pand applications of -the 9%
nickel steel. ~lthough the foregoing has discussed the problems
in welding the 9% nickel steel, a typical example of superlow-
temperature steels, it is understood that the present invention
is applicable to not onl~ the ~% nickel steel but also lower-
grade nickel steels such as 5.5~ nickel steel and 3.5% nickel
steel.
~, Since as stated above the wire according to the present
invention is required to exhibit excellent low-temperature
toughness in welding the superlow-temperature steel such as the
9% nickel steel, the content of such a deoxidizer as Al, Ti, ~In
and Si is severely limited. In the case of welding materials
~ containing a very small amount of the deoxidizer, more than lQ0
~ ppm ox~gen in the weld metal leads to the possibility of such
.~ weLd defects as blow holes and has adverse effects on low-
temperature toughness. On the otr~er hand, oxides in fluxes are
generall~ reduced in the shielded arc weld;ng method and the
su~merged arc welding method and an active gas (CO2 or 2~
which ~s sllghtly mixed ~nto a shield gas for arc stabili~ation
is also reduced in the MIG welding method. In an~ case it is
difficult to limit the oxygen content of the weld metal below
100 ppm. However, since the TIG weldi,ng method uses neither
oxides as weldiny material nor active gas in the shield gas, it
-5~
~339g2
1 can provide a weld joint which is free of joint de~ects at a
superlow-temperature of -196C and excellent in low-tempera-ture
toughness and other mechanical stren~ths, by using the welding
wire and the base metal material which will be detailed with
respect to the compound thereof.
As described briefly above, the welding wire according
to the present invention includes ~ - 15~ nickel by weight and
0.1 - 0.8% manganese by weight, less than 0.15% silicon, less
than 0.1% carbon, less than 0.1~ aluminum, less than 0.1%
titanium, less than 0.0006% boron, less than 100 ppm oxygen and
less than 100 ppm nitrogen.
Nickel is essential in ensuring low-temperature tough-
ness as in the case of the high nickel steels used with the wire
of the present invention. Less than 8% of nickel results in
failure to afford sufficient low-temperature toughness to the
joints. More than 15% of nic]el, on the other hand, makes the
mechanical strength. of the joints too high and brings forth a
remarka~le reduction in duct;`lity ~ith.the results that an
unsta~le residual austinite i.s developed and then transformed
into the martensitic structure at a s.uperlow~temperature to
thereby decrease low-temperature toughness. Wh~.le ~qn is very
effective in lmproving weldahili.ty and as a deoxidizer and a
sulfur captor, a less than 0.1% amount of ~n impai.rs greatly
welda~ility and tends to develop blow holes, etc. in the joints
due to lack of deoxidization. Accordi.ngly, in this case the
effects of ~In i5 not expected. For ~n in excess of ~.8~ there
is the trend to develop an unstable residual austinite and
deterioxate low~temperature tou~hness to a great e.xtent.
The silicon content should ~e smaller than 0O15~ since
si.l~con ~mproves weldability and serves as a deoxidizer but on
~33~92
1 the other hand lowers low-temperature toughness and increases
remarkably susceptibility to hot cracks. While only a small
amount of carbon is enough to enhance tensile strength, the
content should be less than 0.1~ not to decline low-temperature
toughness. Aluminum and titanium are both required to be added
at less than 0.1% since both are effective as a deoxidizer and
in preventing the occurrence of blow holes, etc. but the former
impairs significantly crack resilience and the latter accompanies
a substantial decline of low-temperature toughness due to
precipitation hardening of titanium carbite~
The results of the inventors' experiments indicate that
boron is very detrimental in ensuring excellent low-temperature
toughness at a superlow-temperature when the welding wire of the
above defined compound is used. If the boron content exceeds
O.QOQ6%, then the wire is more susceptible to hot cracks, easier
to harden and more tough at low-temperatures. For the purpose of
the present invention it is most preferable that the boron
content be zero and as a practical matter, the boron should be
at least less than O.OOQ6%. It îs well known that boron is
~0 mixed as an impurit~ into iron system materials such as electro-
lytic iron, one of the chief ingredients of the wire and its
content may sometimes exceed Q.02% with the electrolytic iron
containing the least amount of impurities. In the case where a
su~stantial amount of ~oron is mixed the material, the vacuum
degassing solution method would ~e unsuccessful in removing the
boron. Pursuant to the teachings of the present invention, the
boron content of the starting mater~al should be severly
goYerned and the starting material ~e selected such that the
boron content of the welding wire does not exceed O.OOQ6%,
preferabl~ 0.0004%. It was not until the inventors' findings
~33992
1 that such adverse effects of boron were unveiled. ~ven the
ingredients other than boron are within the above defined ranges,
it is by no means easy to achieve the objects of the present
in~ention so long as the boron content fails to meet the require-
ment.
Since oxygen causes oxides to be deposited on a grain
boundary or the like, it is necessary to control the oxygen
content of the welding wire such that oxygen amounts to less than
` 100 ppm within the weld metal, while it is therefore recommended
to keep the oxygen content of the welding wire below 100 ppm.
Since the oxygen in the weld metal is correlated with not only
the oxygen in the welding wire but also the counterpart in the
base metal, the oxygen content of the base metal should be as
small as possible for the purpose of the present invention. The
results of the inventors-' experiments also indicate that the
oxg~en content of the base metal should be less than 100 ppm and
a total of the oxygen content of the wire and the double oxgyen
content of the base metal ~e less than 200 ppm in order to attain
the objects of the present invention. Why the oxygen content of
the base metal should be less than lOQ ppm is due to the fact that
the oxg~en in the base metal is hardly affected by the deoxidiz-
ing activitv of the deoxidizer contained within the welding wire
and dif~icult to remove in the progress of the welding process.
Finall~, nitrogen has the propertie~ o~ precipîtating
nitrides ~n the weld metal and deteriorating significantly low-
temperature toughness. It leads to that the nitrogen content of
t~e welding wire should ~e smaller than lQ0 ppm. Since the
nitrogen in the weld metal has a correlation with both the
nitrogen in the welding wire and in the ~ase metal, the nitrogen
content should be as small as possible for the purpose of the
-8~
1~3399;2
1 present invention. The inventors' experiments proved that the
nitrogen content of the base metal should not exceed 100 ppm nor
the sum of the nitrogen content of the wire and the double
nitrogen content o~ the base metal exceed 200 ppm in order to
attain the objects of the present invention~
Figs. 13, 14, 16, 17 are ~raphs showing that the "V"
notch absorption energy falls below 80J at -196C in the presence
of more than 100 ppm oxygen and more than 100 ppm nitrogen and
the oxygen and nitrogen contents are needed to be smaller than
10~ ppm and when the sum o each gas content of the wire and
double each gas content of the base metal is more than 200 ppm.
Since as noted above the welding wire according to the
present invention is allowed to contain only extremely small
amounts of o~ygen and nitrogen along with a very small amount of
the deoxidizer, it is most desirable to apply the vacuum degass-
ing solution ~ethod to prevent the mixture of oxygen and
nitrogen. It is evident from the foregoing that the present
invention is aimed at using superlow~temperature steels as the
base metal material and the most significant advantages of the
present invention are assured when low-temperature steels
containing nickel in the range of 3.5 - q.5%, for example, 9%
nickel steel, 5.5% nickel steel and 3.5~ nickel steel, are used
as the base metal material,
Supposing that the TIG welding method is carried out,
the present invention makes it pos-sible to provide joints bearing
tensile strength and lo~--temperature thoughness comparable with
those of lo~-temperature steels such as 9% nickel steel be
defining the compound of the welding wire and more particularly
the ceiling contents of boron, oxygen and nitrogen. The welding
w;re accord~ng to the present invention has substantially the
~9~
~133'~92
1 same compound as the base metal material and thus provides the
joints which are free from the problems such as thermal fatigue
aue to differences bet~een coefficients of thermal expansion and
hot cracks and exhibit very high mechanical strengths. It is
accompanied by providing an economical construction welded which
i5 designed with permissible lowest stresses with taking
advantage of the properties of the low-temperature steels.
The foregoing has set forth in detail the compound of
the welding wire, the oxygen and nitrogen contents of the base
metal material which are defined to make sure the performances
of the welding wires, and the critical values thereof in taking
the oxygen and nitrogen contents of the wire into consideration.
If those requirements are fulfilled, then joints which are
excellent in both low-temperature toughness and tensile strength
are available anywhere in a weld metal zone, a bond zone and a
heat-affected zone (~IAZ2 through the TIG welding method or the
TIG plasm arc welding method. A welding process according to
the present invention will now be described together with its
welding conditions.
Shield gas is of great importance in carrying out the
TIG welding method or the TIG plasm welding method. A pure inert
gas such as pure Ar or pure He is employed in the welding process
of the present invention as is in the con~entional procedure.
Since the oxygen and nitrogen contents of the wire and the base
metal material are limited as discussed a~ove according to the
present inYention, the advantages of the use of the pure inert
gas are enjoyable to the greatest extent. Since the welding
process according to the present invention belongs to the TIG
welding method or the TIG plasm welding method, the wire embody~
ing the present invention may be defined in terms of a filler
~10--
3992
1 material throughout the following descrip-tion and the append~d
claims.
Automatic adjust~ent for the length of an arc developed
between a nonconsumable electrode and the base metal material
will be set forth as a first condition for the TIG welding method.
In order to gain a homogeneous welding result, the
automatic arc ~elding method of the nonconsumable electrode type
is needed to maintain a constant arc length at all times
irrespective of torch electrode moving method and groove shape
and hold in a homogeneous liqui~ pha~e the welding material being
supplîed automatically. Since, when the nonconsumable electrode
type automat;c arc welding method is to be conducted in every
positi,on, it is desira~le to ~eave the torch in such a manner as
to make even the surface of beads and minimize internal defects,
failure to control the arc length.accurately would result in
concave-convex configurations in the grooves or in underla~ing
weld ~eads ;n the casa of multi-layer welding and misalignment
between the weaving movement and th.e grooYeS. Consequently, the
arc length. i5 varied and, ~hen the arc becomes too short, the
nonco~sumable electrode may be short-circuited with the base
metal w;th.the resulting accidents $uch as the destruction of
theelectrode and the mixture o~ th~ electrode material into the
weld metal. Moreover, variations in the arc length, that is,
variations in the current densit~ o~ an arc column and in the
area occupied ~y the arc column w~.thin a molten pool lead to not
onl~ lack of penetrat;on but als.o an uneven bead configuration
due to failure to gain a homogeneous. molten pool.
While the filler material i~ automatically conveyed
in the nonconsum,able electrode type automatic arc welding method,
a sligh.t variation in the arc length causes a variation in the
~33~9~:
1 melting speed of the filler wire. Under the circumstance the
~eads ~ecome uneven and the molten pool is not held at a constant
temperature, resulting in insuffi.cien~ or uneven penetration of
the filler wire into the molten pool or premature penetration.
In the latter case, molten globules fail to move into the molten
pool in the normal way in vertical position, overhead position,
etc. Particularly, in the case where the nonconsumable electrode
type automatic arc welding method is conducted with high alloy
steels such as low-temperature steels and stainless steels and
non~errous metals, the above discussed pro~lems are more severe
because the shape o~ the molten pool is easily variable upon
even a slight variation in the arc length in conjunction with
the melting point of the ~eld metal and the melting speed of the
filler material,
Therefore, in the case of the nonconsumable electrode
type automatic arc welding method and particularly overall
position weaving ~elding and welding with high. alloy steels and
nonferrous metals, it is necessary to keep the arc length at the
optimum value. very accurately and a measure to control the arc
lengt~ ~s necessary and indispensable.
In the past, an attempt to keep substantiall~ constant
the arc length. ln the nonconsuma~le electrode type automatic
arc weIding method was made by sensing and amplifying the arc
voltage and moving ~orward and ~ackward the electrode. The
attempt was intended to obvlate motor hunting b~ giving the
linear relationship between a motor supply voltage enabling the
weld electrode and the arc voltage a specific arc voltage range
where the motor is not responsible.
~ithin the specific arc voltage range or a blind zone
where the motor is not responsible, the motor comes to a stop in
12-
~L33~92
1 different positions between when the arc voltage returns to a
stable point in the decreasing process and when in the increasing
process. The stable point is dependent on the amplitude of the
varying arc voltage and the movement range of the motor is also
dependent on the applied voltage thereto, thus presenting
difficulties in stopping the motor in a desired fixed position.
If it is unknown ~Jhere the stable operating point is located
within the blind zone, t~en d;fficulties are experienced in
adjusting the arc voltage and response relevant ~o variations in
the arc voltage declines by the voltage range of the ~lind zone.
In view of the foregoing, the conventional way of
controlling the arc length in the nonconsumable electrode type
automatic arc welding method is particularly unsatisfactory for
the various welding processes which require accurate arc lengths
to achieve uniform fusion of the wire being automatically fed and
high ~ualit~ weld zones, for instance, fine welding with high
allo~ steels and nonferrous metals, weaving welding and overall
position welding.
The same applicant as this application has studies on
those practical problems, devised improved welding machines and
applied for patents therefore. Throughout th.e specification
there are disclosed two representative ways. of controlling
automaticall~ the arc length.as follows, whether the TIG welding
method or the TIG plasm ~elding meth.od:
(~ Through the use of an integrator element~ a dif~
rerential voltage bet~een a detected arc voltage and a preset
reference Yoltage is proportionally integrated or multiplied and
the resulting signal is us.ed to energize an electrode drive
motor, thus controlling automatically-precisel~ the arc length
between th2 noncomsua~le electrode and the weld metal; and
-13-
~33~9Z
1 (B) As an alternative, there is provided an arc vol-
tage detector including an integrator element, a re~erence
voltage setting section, an arc voltage control including an
integrator or a multiplier, a motor control including an operator
and a polarity decision element, and a drive section for moving
the nonconsumable electrode by the motor. The difference between
an output voltage of the arc voltage detector and the counterpart
of the reference voltage setting section is stabilized tnrough
the arc voltage control, controlling appropriately the arc length
between the nonconsumable electrode and the weld metal.
A specific embodiment of the present invention will be
set forth by reference to the accompanying drawings. The
illustrative embodiment of the present invention (Fig. 1~
comprises an arc voltage detector 1 including an integrator
element 11, a reference voltage setting section 2, an arc voltage
control 3 for comparing an arc voltage and a reference voltage
or calculation, a motor drive control a and a drive section 5
for moving forward and ~ackward a nonconsumable electrode 43
according to the arc length by the action of a motor.
The arc voltage C-Ea) is sensed by the arc voltage
detector 1 and stabilized by the integrator element 11 hav;ng a
time constant greater than its hîgh frequency component and the
response rate of the motor. The integrator element may be
i~plemented ~ith.an CR integrator or integration operational
amplifier of an appropriate gain in relation to an input thereto.
The reference voltage setti.ng section 2 divides a DC
constant voltage C~E~ through a variable resistor, a desira~le
arc voltage or a desirable arc length ~eing determ;ned by the
positi.on of an arm of th.e varia~le resi.stor.
The arc voltage control 3 is adapted to linearly
-14~
1~33992
1 integrate and amplify the differential voltage (hereinafter
referxed to as "error voltage") between the output voltage of
the arc voltage detector 1 and the output voltage of the re-
ference voltage setting section 2, whi.ch con~rol 3 includes a
linear integration amplifier consi.sting of a resistor 12, an
operational amplifier 13, a capacitor 14 and a gain adjusting
variable resistor 15, but the last two elements in its feedback
circuit. See Fig. 2
The linear integration amplifier achieves the integrat-
ing and amplifying operation according to the error voltage andthen provides the next-stage motor drive control 4 with a signal
for regain;ng the desirable or appropriate arc length in response
to only a small variation of the error voltage, thus making sure
that welding i5 effected at the optimum value of the arc voltage.
As des:cribed above, the electrode drive motor 2a is
~raked not to operate in the vicinity of its optimum operating
point with.an overload o~ work through the utilization of the
inte~rator element 11 and the arc vcltage control 3. The
problem with.hunting is thus altogether avoided.
~ As indicated i.n Fig. 3, a pair of multipliers 21 and
22 within th.è arc voltage control 3 may bear the "n"th. (n=2, 3,
4...l power correlation bet~een th.e input and output thereof.
The control 3 includes the two se~ially connected
multi.plier~ 21 and 22 and a coefficient potentionmeter 26 next
to one of th.e ~ultipliers 22, the potentionmeter 26 comprising a
resistor 23 t a operational amplifier 24 and a varia~le resistor
25.
Through. the control 3 the error voltage (input2 and
the arc length.control si~nal Coutputl applied to the next-stage
motor dri.ve control are correlated as depicted by the cubic
curve in Fi~ 4.
~L~33~
1 In this manner, the higher the error voltage the greater
the output signal applied to the next-stage motor drive control
4. As a result, welding i5 carried out in the vicinity of the
optimum arc length more quickly. The braking torque increases
as the optimum arc length is approached. ~ventually the arc
length rests on the optimum value. Since no excessive output
signal i5 applied to the motor drive control 4 when the error
volta~e i5 lo~, the electrode drive motor 20 becomes operative
~ithout hunting in the event that the time-related linear inte-
gration met~od is not relied upon.
The motor drive control 4 amplifies the output signal
from the arc voltage control 3 and keeps the electrode drive
motor from being overloaded. The electrode drive motor is
reversi~le according to the polarity of the output signal. The
control 4 comprises an operator 28 and a next-stage polarity
decision element 3Q.
The operator 28 includes an operational amplifier 31,
a feedback element 32 and a tachogenerator 32 for generating an
output voltage în proportion to the number of revolutions of the
electrode drive motor 20, the output of the tachogenerator being
ne~ativly ~ed back via the feedback element 32 to the input of
the operational amplifier 31. The feedback element 32 is to
reduce variations in the output of the motor 2Q caused by a
varyin~ load on the eIectrode driye motor 20.
The polarity decision element 30 includes an npn
transistor Trl and a pnp transistor Tr2, base terminals of the
transistors Trl and Tr2 being connected to an output terminal
of thQ operational amplifier 31, a collector terminal of the
transistor Trl bein~ connected to a terminal b of the electrode
driye motor 20 via a power source 34 and the equivalent of the
~16-
~L~L33992
1 transistor Tr2 being also connected to the terminal b via a
different power source 35. Emitter terminals of both the tran-
sistors Trl and Tr2 are connected to a grounded terminal a of
the electrode dri~e motor 20. ~hen a positive signal is applied
to the polarity decision element 30, the transistor Trl is
conducting so that the electrode drive motor 20 rotates in a
positive direction upon current flowing from the terminal a into
the texminal b of the electrode drive motor 20. Contrarily, iL
a negative signal is applied to the polarity decision element 30,
then the other transistor Tr2 is conducting so that current flows
rom the terminal b into the terminal a of the motor 20 to revert
the revolu~ion direction of the motor 20. The drive section 5
includes an electrode section 40 and an electrode driving
assembly 41, cf. Fig. 5. The electrode section 40 contains the
nonconsuma~le electrode 43 and an insulator 44 supporting the
electrode 43, the nonconsumable being connected to a weld cable
45 via a lead conductor extending wi.th;n the insulator. The
electrode driving assembly 41 comprises electrode support arms
46, a guide lever 47 for quidin~ the arms 46, a screw 48 for
thrusting ~orward and backward the arms 46 and a frame 4~
support~ng the guide lever 47 and th.e screw 48. The electrode
supporting arms 46 has three arms 7 the first supports the
electrode section 4Q and supports a welding guide chip 5Q at an
appropr;ate angle with respect to the nonconsumable electrode
43; the second having a sli.de slot of an appropriate dimension
wherein a ~u~de ~ar 47 is slida~le; and the third and last carry-
ing a male.screw in mesh.with the screw 4~. The scre~ 48 is
coupled with a rotation shaft of the electrode driver motor 20..
The filler ~i.re 51 trayels withi.n the Eiller wire guide chip 50.
~ weaying mechani.sm S5 îs coupled with the Erame 49 to weave the
--11~
~3399%
1 nonconsumable electrode 43 to the left or right via the frame 49
In this manner, the drive section 5 travels along a weld line
with a suitable traveling device.
As stated above, the arc voltage is sensed by the
integrator element having the time constant greater than the high
frequency components thereof and the response rate of the motor
and the diferential voltage between the output of the integrator
element and the preset reference voltage is applied to the
linear inte~rator or the multiplier and derived therefrom as the
motor drive signal so that the electrode drive motor operates
without hunting in such a manner as to settle the arc length.at
the optimum point Accordingly, the arc length can ~e preset as
desired and settled quickly at th.e preset value in the noncon-
sumable electrode type automatic arc weldin~ method irrespective
of an uneven ~eld zone and the configuration of the grooves.
Thi~ protects the electrode material, gains a homogeneous fusion
of the filler wire, guarantees high quality of the weld zone and
makes possi~le oYerall position weldi.ng or precise nonconsumable
electrode type automatic arc ~eldi.ng with high.alloy steels,
nonferrous metals, etc.
The ab.ove described method enables automatic control
of the arc length. The following description will set forth.
deyices for preventing any magnetic blo~ when the DC TIG welding
method i5 carried out at a high.speedr These devices are un-
suitable for the TIG plasm ~eIding method and applicable only to
the TIG welding method in a narro~ sense.
The TIG weldin~ methbd is di.sadvantageous as follows:
. (.lL The TIG welding method is mainly intended to fuse
the weId metal into the base metal due to heat conduction. The
TIG arc itseIf develops- a~out the molten pool (hi~h temperature
~18-
~3L33~9;~
1 portion) without difficulties. If the melting speed is too high,
insufficient preheating will cause inferior association (wetness)
of the weld metal with the base metal and imperfect fusion of
the desposited metal into the base metal.
(2) When the TIG welding method is effected with a
DC voltage source, the TIG arc is very sensitive to variations in
the surrounding magnetic filed caused by magnetization and
varied shape of material to be welded and the weld disable state
is brought owing to a magnetic blow. By way of example, Figs. 6
and 7 show in a perspective view the concept of magnetic blow
states wherein Fig. 6 is an example of the magnetic blow due to
magnetization of steel sheets 61 and 61', ~he base metal material
and Fig. 7 is an example of the magnetic blow due to variations
in the shape of the steel sheets 61 and 61'. A tungsten
electrode 62 (hereinafter referred to as "electrode") extends
within grooves in the steel sheets 61 and 61' and the steel
sheets 61 and 61' are respectively magnetized with the "N" and
"S`' poles, developing a magnetic field within the grooves.
When, for example, a DC constant voltage source is interposed
between the electrode 62 and the steel sheets 61 and 61', current
flows in a direction normal to the magnetic field. In the case
that the current has a positive polarity, an electromagnetic
force is developed in the arrow direction f pursuant to the
Fleming's left hand law to deflect an arc column 63, a fle~ible
conductor, as depicted in the drawings. In Fig. 7 the steel
sheets 61 and 61' are not magnetized and the electrode 62 is
located near the edges of the steel sheets 61 and 61'~ In this
case the eIectromagnetic force is primarily oriented toward the
steel sheets 61 and 61' to deflect the arc column 63 in the
arrow direction f. Through Figs. 6 and 7 depict the few examples
of the magnetic blows. Figs~ 8 and 9 illustrate actual
--19--
1~339~Z
1 situations in a weld spot wherein Fig. 8 is a cross sectional
view showing upward oriented vertical position welding ~W: the
welding direction) and Fig. 9 shows lefthand Elat position
~elding. In any case the arc column 63 is deflected toward the
side where the amount of the steel material is large (that is,
opposite to the welding advance direct;on~. Under these circum-
stances the steel on which welding is about to be performed is
hardl~ affected by the arc. As discussed above, preheating and
melting are imperfect and inferior fusion occurs between the
groove face of the ~ase metal ma~erial and the deposited metal.
The arc is developed on previousl~ ~ormed beads 64 as shown in
Figs. 8 and ~ so that the beads 64 are locally fused and become
uneven in shape. With the upward oriented vertical position or
the overhead position as depicted in Fig, 8, the weld metal may
burn through due to overheating of the beads 6~, thus disabling
the next succeeding weldiny procedures.
~ ith the foregoing in mind, the inventors have studies
on high`speed weldiny conditions free of the above discussed
problems and concluded that it i5 desirable to deflect the arc
in the welding advance direction in an attempt to make good use
of the magnetic blo~ phenomena. The inventorsl attempt is
summarized as follows:
In the DC TIG welding method;
(1~ DC voltage sources are connected between the non-
consumable eIectrode and the base metal material and between the
filler and the base metal ~aterial, respectively;
C2 L flows of current therebetween are
(al same when the ~elding material is ahead of
the electrode along the welding advance
direction; and
-2Q-
~339~32
1 (b) opposite when the welding makerial is behind
the electrode along the welding advance
direction; and
(3) the arc is directed toward the welding advance
direction.
A few embodiments for meeting all the above require-
ments will be described by reference to the drawings.
Referring to Fig. 10 showing a side view of a first
embodiment, the filler wire 66 is located ahead of a shield gas
1 n cap 65 along the welding advance direction and supplied in the
arrow direction Y. As soon as the tip of the filler wire is
immersed in the molten pool, it enters into the arc 63 being
deflected. Fig. lO is depicted with a straight polarity wherein
the base metal 61 serves as an anode and the electrode 62 as a
cathode. Conduction current flows through the base metal 61 with
the same polarity as the electrode 62 (the base metal 61: an
anode and the filler wire 66: a cathode). If the flows of
current through the electrode 62 and the welding material 66 are
identical to each other in this manner, there are developed two
magnetic fields which are attractive to each other so that the
flexible arc column 63 is deflected toward the filler wire 66 and
hence the welding advance direction as viewed from Fig. 10. The
intensity of the magnetic field developing around the filler wire
66 and the degree of the deflection of the arc column are made
variable by varying the amplitude of the conduction current into
the filler wire 66.
Figure 22 (A), (B) and (C) shows various arc de-
flection states when the DC voltage sources are connected as in
Fig. 1. The tungsten electrode is conducting with 250A and 15
3~ and the filler wire is conducting with OV (A), lOOA and 4V (B)
-21-
1~33~2
1 and 16~A and 6V (C), separately. When the conduction current into
the filler is zero (the normal condition of the TIG arc welding
method), the arc is not deflected. In this case, the greater the
amplitude of the conduction current into the filler wire, the
greater the deflection angle of the arc.
Fig. 11 shows another embodiment wherein the filler
wire 66' is supplied from behind with respect to the welding
advance direction and the filler wire 66' is supplied with con-
duction current with the filler wire 66' as an anode and the base
metal 61 as a cathode, although the electrode 62 is of a positive
polarity as is the case in Fig. 10. Therefore, the direction of
current into the filler wire 66' is opposite to that of current
through the electrode 62 so that the two resulting magnetic fields
repel each other to steer the arc column 63 away from the filler
wire and thus toward the welding advance direction.
The closer the supply position of the filler wire is
placed w;.th respect to the nonconsumable electrode, the more the
influence of the magnetic fields comes into effect. The above
advantages may be expected with a very small amount of the con-
duction current.
The welding process according to the present inventionas described above is advantageous as follows:
(1) the TIG arc can be directed ahead of the weld line;
(2) the directing force is easily adjustable by vary-
ing the amplitude of the conduction current into the -filler wire;
(3) the region in front of the weld line is properly
heated and comes to the molten state or nearly the molten state,
thus completing the fusion of the filler wire;
(4) overheating of the deposited metal is avoided
without damaging the appearance of the beads or burning through
-22-
~33g92
1 the deposited me-tal in overhead position welding or upward
oriented vertical position we]ding; and
(5) the temperature gradient in the weld zone increases
gradually from before the arc to the arc point and decreases
gradually rom a fused metal region to a solidified metal region,
thus enabling high speed welding without humping the beads.
Although the present invention overcomes the major pro-
blems inherent to the TIG welding method, the inventors' effort
has further been devoted to make sure the advantages of the
present invention. In other words, improvements have been deemed
necessary to enhance facility in fusing the weld metal into the
base metal in welding with various welding positions and various
stee]s and eliminate possible blow holes in high speed welding.
Since the welding process is not the so-called hot wire method
per se and the welding material is not heated, if the tip of the
filler is moved away from the fused poo~ for any reason, then the
filler wire will be thereafter conveyed onto the solidified beads
to discontinue further welding procedures.
One powerful approach to solve the above probIem is to
weave the arc, but is still disadvantageous as follows:
(1) in the case of a mechanical method wherein a
weaver is installed about a welding hèad, the overall construc-
tion is massive and bulky and difficult to carry and apply
within a narrow space due to installation of the weaver, a motor,
a slide base, etc.
(2) the above mechanical method generally needs a
proper relative distance between the arc point and the tip of
the filler wire. The welding torch and a filler wire guide are
therefore mounted integrally on the slide base within the weaver
but the relative distance therebetween varies unavoidably due
-23~
~33992
1 to vibrations in the weaving operation. In some cases it becomes
impossible for the filler wire to enter into the molten pool in
a proper position.
(3~ for another approach to develop a magnetic field
through an electromagnet, it is required that the electromagnet
be located as close to the arc point as possible. In the case of
welding with thick sheet steels, the end of the electromagnet
should be exposed into the grooves and exhibit an extreme high
heat resistance since magnetic force may be centered on a steel
of a good magnetic permeability. Satisfaction to these
requisites is possible to a limited extent and the overall
construction is large sized as set forth in the paragraph (1)
even when a water coolins scheme is used at the same time.
In view of the foregoing, investigations have been
conducted into the inherent characteristics of the TIG arc in the
search fora new weaving method. The results of the investigation
indicate that the pinch effect is little since the nonconsumable
eIectrode used with the TIG welding method is generally thick
(say, 4mm~) to reduce eIectrode consumption toa minimum and
~0 current density is lower than that in the MIG welding method
(generally, approximately lmm~). In addition, since the rigidity
of the arc is small in comparison with that of the MIG welding
method (for example, an inert gas and a metal plasm), the TIG
arc has great flexibility not comparable with that of the r~IG arc.
To take advantage of these inherent characteristics of the TIG
arc, the magnetic fields used in the above disclosed welding
process are varied in a fixed or variable rhythm by pulsating the
condùction current into the filler wire, steering the TIG arc
from a position a little ahead along the welding advance direc-
tion to a position beneath the nonconsumable electrode and vice
; -24-
,.
~IL33~Z
1 versa. In this instance it is only necessary to pulsa~e the
conduction current into the filler wire so that weaving welding
needs no large sized and complex peripheral devices about the
torch and is applicable to a narrow space. A similar technique
for the MIG welding method is disclosed in Japanese Patent
Publication 45/39931, for example. This technique employs a
current carrying wire conductor other than a consumable electrode,
feeds the conductor from behind the consumable electrode and
decides flows of current through the consumable electrode and the
conductor for deflecting forward the MIG arc along the welding
advance direction. ~s noted earlier, the MIG arc is much less
flexible than the TIG arc and thus more difficult to deflect
forward, as a matter of prac~ice. However, some difficulties
are supposed in weaving the arc by the application of the
pulsating current. The MIG welding method requires a consider~
able amount of the conduction current into the filler wire
because of its high rigidity of the arc if it is desired to
deflect the arc by conducting current into a portion of the filler
wire being fed near the arc. Under such high current condition
it is necessary to increase the feed speed of the filler wire
or decrease the current density through the use of a filler wire
thick in diameter; otherwise the filler wire becomes fused or an
arc develops about the filler wire until the filler wire reaches
the fusion pool. Whereas the MIG welding method suffers from
the occurrence of the arc but is never unable to go on the
welding operation, the nonconsumable electrode is contaminated
with metal vapor to an extent to disable substantially the weld-
ing operation. Therefore, measures to increase the feed speed
of the filler wire and use the filler wire of a great dimension
are still available but an increase in the amount of the weld
-25-
~39~Z
1 metal leads necessarily to insufficient melting with the MIG
welding method. The above described measures are difficult to
adopt with the MIG welding method since the main arc penetrates
deeply. In this way, with the MIG welding method it is greatly
difficult to deflect the arc and in the case of the TIG welding
method various conditions are carefully considered.
Although the -Figures 22 are depicted with 250A of
the conduction c~rrent into the nonconsumable electrode, it is
generally desirable that the current amplitude be 500A ox less
since an excessive amount of current causes an increase in the
current density and the rigidity of the arc to thereby mate the
deflection and weaving impossible. The electrode is convention-
ally supplied with constant current and, if desirable, is
energized to develop a pulsive arc. The characteristics of the
TIG arc per se are not intended to limit the scope of the present
invention.
As is in the conventional combined MIG and TIG welding
method or plasm MIG welding method, the conduction current into
the ~iller wire should be low enough to avoid the operating
~0 situation where an arc develops from the filler wire and an
operating state like a hot wire. Preferably, the conduction
current is 200A or less and a voltage at a porjection of the
welding wire is lower than the TIG arc voltage; otherwise the
magnetic field is too intense and the TIG arc is blown off or
blown out. In order that the operating state like the hot wire
is avoided and the weIding wire is certainly short-circuited with
and brought into contact with the fusion pool, a higher wire
feed speed is required. Furthermore, the problem with excessive
deposited metal should be avoided.
As discussed above, the present welding process makes
-26-
~L3~31t92
1 the weaving action by supplying the pulsating current to the
filler wire as shown in Fig. 12. Fig. 12 depicts waveforms of
the pulsating current on the left side (A)-(E) and the arc
deflecting states on the right side (A)-(D). In the examples
(A)-(C) the conducting period alternates with the non-conducting
period and particularly in the e~ample (C) -the nonconducting
period is zero. In the examples (D) and (E) the filler wire is
always supplied with the welding current and high current (Ah)
alternates with low current (Al) to form the pulsating current.
(Th) represents the time period where the high current flows and
(Tl) the time period where the low current flows. It is under-
stood that the deflection state of the arc column in each step
is dependent on the amplitude of current. The example (E)
indicates that current varies slightly for both the conducting
period and the non-conducting period and the present invention is
also applicable to this example. The weaving width (weaving
angle) and the weaving cycle are freely selectable by a proper
selection of the various values (Ah), (Al), (Th) and (Tl) and the
weaYing progress and the behavior at both ends of the weaving
~0 amplitude are freely adjustable by varying the amplitude of the
current. For example, when butt welding is carried out with the
circumference of a pipe in a sequential fashion in vertical ~
horizontal ~ flat positions, the direction of gravity varies
with respect to the molten pool so that the most desirable weav-
ing pattern may be selected from time to time. This is one of
the major advantages of the present invention.
` If unusual situations such as a variation in the groove
root gap and an error in the root face are met along the weld
line in the conventional one side backing welding method, then
the amplitude of the TIG arc current is varied and the arc
. -27-
~33~Z
1 temperature and shape and the si~e of the molten pool are also
varied. ~'o this end it is required to var~ the melting rate of
the filler wire and bring the TIG arc current into synchronism
with the feeding rate of the filler wire. Such adjustment is
rather laboursome but the welding process according to the present
`invention can cope with such unusual situations by merely varying
the amplitude of the welding current into the filler wire,
several measures are listed below:
(1) for example, when welding goes on in the pattern
shown in Fig. 12 (A) and the root face becomes thicker, the back
bead at that zone is difficult to go out as it is. If the
amplitude of the high current (Ah) is increased for this reason,
then the forward direction angle of the arc rolumn increases and
the arc acts directly on a groove root in a forehand non-deposited
metal zone. As a result/ the melting of the root becomes
suf~icient and the back bead is completely formed;
(2) in conjunction with the above measure, if the con-
duction pexiod of the filler wire is extended, the forward
direction period of the arc also becomes longer enough to gain
sufficient penetration;
(3) the above measures (lJ and (2) are combined;
(4) the pattern is modified as viewed from Figs. 12 (D)
and 1~ (E) and if necessary the current ~Ah) is increased;
(S) the measures (2) and (4) are used together;
(6) the measures (4) and (5) are used together; and
(7) several other measures are available through fine
adjustment of those factors.
The welding process according to the present invention
is successful in obtaining a subtle weaving pattern by applying
the pulsating current in the case that welding is effected with
-28-
~.339gz
1 the DC straight polarity and the filler wire is fed from ~ehind
the nonconsumable electrode. It is only necessary to make
identical the directions of the conducting currents in the case
that the filler wire is fed from ahead of the nonconsumable
electrode. Moreover, in the case of reverse polarity welding
the directions of the conduction currents may be opposite to
those of straight polarity welding. The present welding process
is also applicable when the filler wire is fed before and after
- the nonconsumable electrode.
Satisfactory results are given in low-temperature
toughness, tensile strength, etc. as long as the above require-
ments are fulfilled. One way to evaluate the mechanical
strength of the resulting weld joints is to use small sized
specimens such as the charpy test. As long as such evaluation
method is traced, there is no problem with the low-temperature
characteristics of the joints made according to the requirements
at all. However, a few problems still remain with the joints in
the` event that they are evaluated through the COD test which has
proved itself an appropriate method for evaluating the brittle
~O breakdown characteristics of building constructions welded. The
inventors have revealed through extensive studies that such
problems are attributable to the heat history of the final layer
when multi-layer welding is carried out through the TIG welding
method or the TIG plasm weldiny method. It has been concluded
that the final layer is also to be given sufficient heat history.
This is achieved by, following multi-layer weIding, cooling the
weld bead surface of the final layer below 150C and re-melting
the final alyer with the arc generated from the noncomsumable
eLectrode while the final bead surface is shielded with an inert
gas. Further details thereof will be set forth beIow.
-29-
1 The results of the inventors' experiments indicate that,
when multi-layer welding is carried out on such a superlow-
temperature steel as 9% nickel steel through the use of the
welding wire including 8 - 15% of Ni, a central portion of the
groove, that is, lower layers are influenced by the effects of
heat treatment due to heat cycle during welding of upper layers,
the effects of such heat treatment being effective in enhancing
the low-temperature toughness of the lower layers. However, the
final layer does not enjoy the benefit of such heat treatment and,
as a result, the low-temperature toughness of the overall weld
metal is decreased remarkably. This tendency is significant when
the effects of heat treatment are extremely great as is in
eutectic alloy welding with Ni containing ferrite steels such as
9~ nickel steel (grains become greater without difficulties
because of Ni contained therein). If the bead surface of the
eutectic alloy weld zone of the Ni containing steel is molten
again with the nonconsumable electrode, then residual stress is
remarkably reduced from the final layer and the low-temperature
toughness of the overall weld metal is greatly improved.
A distinguished feature of the welding process of the
present`invention, an increase in low-temperature toughness can
be evaluated by the COD test which has proved ~o be more
appropriate than the conventional Charpy test for evaluation of
toughness-at low-temperatures or fracture toughness.
Although the welding process of the present invention
using a Ni containing steeI as the base metal will be set forth
below, it is obvious that the present invention is also applicable
to weld other low-temperature steels.
According to the present weIding process, a joint of a
superlow-temperature steel containing Ni is multi-layer welded
~30-
~L~3.~
1 through the utilization of an eutectic alloy steel material
containiny 8 - 15% Ni by wei~ht and subsequently subjected to re-
fusion treatement.
The re-fusion treatment is intended to remove residual
welding stress from the final finishing layer in the multi-layer
weld zone and give the weld metal low-temperature toughness
through the treatment thereof. This treatment is accomplished by
the arc heat from the nonconsumable electrode. The depth of
penetration during the re-fusion treatment shculd be equal to or
less than the depth of the final finishing layer. Otherwise,
excessive penetration reduces the effects of the re-fusion
treatment. As stated hereinbefore, the object of the re-fusion
treatment is to eliminate the residual welding stress on the
final finishing layer and increase low-temperature toughness.
For the purpose of the re fusion treatment is is desirable that
the depth of penetration during the re-fusion treatment be equal
to or less than the depth of the final finishing layer. In the
event that penetration is deeper than the final finishing layer
during the re-fusion treatment, the re-fused beads become
larger than the previous to suppress the effects of the re-fusion
treatement~ The re-fused zone is preferably more than half as
wide as the final finishing layer in order to allow the whole
of the joint to enjoy the desirable effects of the heat treatment.
In the case that there-fused zone is more than 1.3 times as wide
as the final finishing layer, heat input becomes excessive
and excessive influence of the heat occurs on the base metal.
In carrying out the re-fusion treatment the bead surface of
the multi-layer weld zone should be air~ or water-cooled below
150C. In the event that the re-fusion treatment is carried
out with a bead surface temperature over 150C, the cooling
-31-
~l339g;i~
1 rate decreased in the re-fused zone so that grains on the bead
surface becomes coarse with a resulting reduction in low-tempera-
ture toughness. If the bead surface is cooled below 150C once
after the completion of welding, then it is allowed to be coded
through heat release for a relatively brief period of time after
the re-fusion treatment so that the bead surface shows a fine
crystalline structure with an excellent low-temperature toughnessO
The reason why the cooling rate should not decrease after the
re-fusion treatment is evident from analysis of Fig. 18. The
beads are cooled gradually through heat release subsequent to
the re-fusion treatment. In particular, when the length of time
; where the beads are cooled from 800C ~o 500C extends over 100
seconds, the COD value (the fracture toughness of the most
brittle portion at -162C~ becomes lower than 0.1. It is there-
fore p~eferable that the beads be cooled from 800C to 500C
for a period of time of about 50 seconds. In other words, an
excessive amount of weIding heat input during the re-fusion
~ treatment expands the heat affected zone, prolongs the cooling
3 period and renders the crystal grains coarse, thereby preventing
low-temperature toughness from increasing. While the re-fusion
treatment goes on under the conditions that the nonconsumable
eIectrode is made up of tungsten and the re-fused zone is
' shieIded with an inert gas such as argon and helium, the amount
of the shield gas supplied is preferably within the range of 10 -
100 ~/min. A supply amount less than 10~ /min leads to various
troubles due to lack of shield and on the other hand an amount
in excess of 100~/min causes a flow of the shield gas to be
disturbed and involved into the re-fused zone, resulting in the
occurrence of joint d~fects such as bits.
A well known technique similar to the welding pro~ess
~.
-32-
~L~33~9~
1 Of the present invention is disclosed in Japanese Patent Laid-
open specifications ~9.55538 and 49/66548. The former teaches
'1an attempt to prevent brittle fracture after welding by reheating
both the heat-affected zone and bond zone with the heat radiated
from the TIG arc" and is considered to be similar to the welding
method in that post-treatment is carried out by the TIG arc heat
after welding. However, both are totally different from each
other in the following aspects:
(1) Whereas the object of the technique disclosed in
laid-open publication 49/55538 is achieved by re-heating the
heat-affected zone and bond zone, the welding process according
to the present invention re-fuses the final finishing portion of
the weId metal itself. The distinction results from that the
welding process according to the present invention is to enhance
the low-temperature toughness of the weld metal zone itself.
In other words, according to the present invention using a super-
low_temperature steel as the base metal, it is necessary to
increase`the low-temperature toughness of the weld metal in order
to gain joint performances comparable to the base metal. The
heat treatment on only the heat affected zone and the bond zone
as disclosed in publication 49/55538 is, however, not instru-
mental in achieving such object.
(2) The technique disclosed in publication 49/55538
achieves its major objects by mereIy re-heating without bringing
the weId metal into the molten state, while the re-fusion
treatment on the final finishing layer of the weld metal is
essential for the welding process of the present invention. The
second distinction is due to the background that present invention
is applied to the welding of superlow-temperature steels and
also the inventors' findings that the object of the present
-33-
~33~9Z
1 invention is impossible to achieve unless the re-fusion treatment
is effected when a Ni containing steel is employed as the base
metal material and the weld metal. In addition, publication 49/
55538 suggests nothing about the concept of the present invention
that the weld beads should be kept at a less than 150C tempera-
ture in the progress of the re-fusion treatment. ~his fact
reflects essential differences in object and technical solution
between the present invention and the disclosure of publication
49/55538.
On the contrary, laid-open publication 49/665~8
suggests "an attempt to make smooth the bead surface by re-fusing
the same with a TIG welding torch after MIG welding". It also
sets forth that the technique disclosed herein prevents in-
sufficient solution of the weld metal zone and joint deficits
such as blow holes and undercuts and enhance joint strengths.
There is further a suggestion that such attempt is applicable
to the welding of a Ni containing steel. The only object that
the attempt achieves is to make smooth the bead surface and there
is no relevanc~ to technique for enhancing the low-temperature
toughness of the weId metal æone.
The primary object of the present invention, on the
other hand, is to enhance the low-temperature toughness of the
final finishing layer in the weId metal zone. The present
invention achieves its primary object by limiting the surfacial
temperature of the weld beads below 150 C and carrying out the
re-fusing treatment. A variety of desirable conditions for the
re-fusing treatment are also defined by the present invention,
There is no disclosure about those criteria in publication
49/~6548.
Eventually, the welding process of the present
-3~-
~33~2
1 invention has the following advantages throuyh the re-fusion
treatment of the final finishing layer of the weld metal subsequ-
ent toeutectic alloy welding. A significant feature of the
present invention resides in extended applications of superlow-
temperature steels.
(1) The resulting joint and the base metal material
exhibit substantially the same low-temperature toughness, thus
enhancing the low-temperature toughness of the overall construc-
tion welded;
(2) The welding wire is economical because of no need
to use a high Ni steel;
, (3) Both the joint and the base metal material are
substantially the same in chemical composition and coefficient of
thermal expansion, thus unifying mechanical strengths of the
whole construction such as 0.2% strength and hot crack resistance
without thermal fatigue due to varying temperature;
(4) As a consequence, the whole construction is
relatively thin and light in weight;
(5) It is only necessary to re-fuse the bead surface
~ so that the welding procedures are simple and less expensive;
(6) The effects of the re-fusion treatment are surely
attainable by merely keeping the surface temperature below 150C
during the re-fusion treatment.
Although specific examples of the present in~ention
will be described in detail, it is not intended to limit the
present invention thereto. It is to be understood in view of the
whole disclosure that many changes and modifications may be made
and are intended to be included within the scope of the present
invention.
35-
:~33~9~
1 Example 1
Base metals whose composition are shown in Table 1 were
prepared and provided with 60 de~rees grooves through gas cutt,ing.
A~ter the removal of scales ~rom the grooves with a grinder, the
TIG welding was carried out ~nder the conditions of Table 3
through the utilization of welding wires of which the composition
is enumerated in Table 2. Welding was conducted in such a
manner that the front side was first welded and, subsequent to
arc air gouginy on the groove root, the xear side was welded. An
automatic TIG welding machine with an automatic arc control
scheme was employed.
Table 1
9% nickel steel (sheet thickness 200mm)
, . . ...................... ~
Symbol C . Si _ S Ni O N
A 0.06 0.42 0.21 0.012 0.004 9.2 20 ppm 25 ppm
B 0.06 0.34 0.31 0.006 0.004 8.9 115 ppm 130 ppm
C 0.04 0.31 0.25 0.005 0.006 9.0 100 ppm 110 ppm
Table 2
~O Symbol a _ _ . __, d e
. - 1- --
C 0.08 0.02 0~06 0.07 0.03
Mn 0.45 0.64 0.24 0.72 0.42
Si 0.12 0.03 0.13 0.05 0.06
P 0.010 0.009 0.006 0.010 0.004
S 0.008 0.006 0.004 0.008 0.003
Ni 10.4 12.8 13.4 9.8 11.0
Al 0.04 0.06 0.01 0.01 0.01
Ti 0.01 0.02 0.008 0.01 0.01
B 0.0002 0.0003 0.0008 0.001 0.0002
O 70 ppm 60 ppm 140 ppm 220 ppm 75 ppm
60 ppm 80 ppm 250 ppm 150 ppm 60 ppm
Example Example Comparison Comparison Example
. _ Examp1e Example __
-36-
~3~99~
1 Table 3 (Welding conditions)
Welding position Vertical lIorizontal
Current (DC.SP) 250A 350A
Voltage 12V 14V
! Welding rate 5.5 cm/min 15.0 cm/min
Weldi.ng heat input 32.7 KJ/cm 19.6 KJ/cm
Shield gas argon argon
Bath temperature Max. 150 C ~ax. 150 C
difference
Weldability was satisfactory in welding in both verti-
I cal and horizontal positions.
After welding all the examples were subject to tension
test (JIS-Z-3112. A2; measured at room temperature), impact test
(JIS-Z-3112, 4; measured at -196C) and side bend test (JIS-3122),
the results thereof being listed in Table 4.
~33g9~
_ _
o
~ a) ~ Oo o ~ ~D ~D ~ O M
O 11~ 07 ~1
~C
.~
~ ~ ~ O ~ O
CO ~ ~ 1` CO ~ O ~ Z
a).~
, . ____ _
~ U~
1~ ~ n o u~ O ~ O
~ ~ O ~ Z
~C.) P~
_.. _ ... _ .
' O
N ~ ~ U~
rl r~ o ~ co ~ o O u~ Q)
Q F~ h ~ D ~ O ~1 :>-
~0~ ~
__
.~ . oo ~
~ h ~ u) o l_ ~ ~ ~o ~ ~ O
- a) In C) m ~ O ~ z
. ~1 ~
0 . ~ .
E~
N ~)
~r ~ 1 u7 o ~ ~ ~ ~ ~ u~ O
o~l CO O 1~ O ~ Z
I ~ ~
2 0 __ . ___ ___ __ ____._ _ __ ___ _ _ . ~ _
~ Q ~ o oo ci~
~ o
a) ~ o
_ . _
u~ O
m h~l o o co co ~ o ~ Z;
~g ~ o
----- - -
l ~ ~
~1 ~ o\O . ~ <U ~ U~
q Q)
~ o u~ ~ ~ ~
O ~ o o u~ a:\ ~ O ,~
~ --~ -----------
aJ
S~
~1 ~ O ~ rl
3 (~ a) ~ ~
. ~ rl ~ ~ ~ h ~ rd O
3 0 O ~ ~ ~ rl
~z: ~ J to o ~ to ~ ~ ~
~ a) o ~ ~ a) ~:
~o ~ o~
ol ,~ O ~ ~ ~ ~ ~ 0
O (d O rl X ~ rl O O ~ ~) E3 ~ rl I r~ ~ ~
~: al 3 -IJ O 3 ~ O E-l U~ U~ H U~ U~ ~ ~) 1:1~ H
_____ _ _ _ _ _ _, . . - -I
-38~
~3399Z
1 The results of Table 4 can be analyzed as follows:
Nos. 1, 3, 6 and 9: examples within the requirements
of the present invention were excellent not only in mechanical
strengths such as tensile strength and impact strength but also
in the results of X-ray radiation examination.
No. 2: This example (comparison example) contained
considerable amounts of the oxygen and nitrogen in the weld metal
wherein both the oxygen and nitrogen content thereof are in
excess of 100 ppm. The impact strength (low-temperature tough-
ness) thereof was very poor and the side bend strength and the
X-ray radiation results were also poor.
No. 4: the boron content of the welding wire (com~
parison example) exceeded 0.0006~ with a relativeIy very low
fracture strength. The nitrogen content of the wire was also too
much.
No. 5: the boron content of the welding wire was too
much'and the oxygen and nitrogen contents of the weld metal were
both in excess of 100 ppm (comparison example) with unsatisfac-
tory results in fracture strength,` stretch'and side bend
~0 strength along with poor outcomes of ~-ray radiation.
No. 7: while the oxygen contents of the filler wire
and the base metal met the requirements of the present invention,
the'sum of the oxygen content t70 ppm) of th~ welding wire and
the double oxygen content (100 x 2 = 200 ppm) of the base metal
was-in excess of 270 ppm (i.e., 70 ~ 200 - 270 ppm).
Unsatisfactory res'ults were given in fracture strength, side
bend strength'and X-ray examination.
No. 8: this example (comparison example) contained
the oxygen content of the filler wire in excess of 200 ppm and
3~ the boron content thereof in excess of 0.0006~ by weight. The
-39-
!
~33~9'~
fracture strength, the side bend strength and outcomes of X~ray
' radiation examination were unsatisfactory.
Subsequently, the impact strength of the resulting
weld joint was measured at ~196C when the 9% nickel steel as
denoted by the symbol A in Table 1 was used as the base metal
material and the boron content of the welding wire was varied.
Fig. 15 is the results of such measurement indicating that the
impact strength of the weld joint greatly decreased with the
boron content in excess of 0.0006%. The welding wire exhibited
a very high impact strength when the boron content was 0.0006%
or less particularly less than 0.0004~.
The following will discuss various exemplary welding
$ conditions as required by the present invention. Unless provided
otherwise, a wire used comprised the wire "a" of Table 2 in
~ Example 1 and a base metal material used the Ni steel "A" of
; Table 1.
Example 2
A bead-on-plate was formed with the conditions of Table
5. An excellent appearance was obtained with a high speed of
~0 60 cpm according to the present invention, whereas the conven-
tional way resulted in a humping bead at a low speed of 40 cpm.
-40-
~3399Z
~ Table 5
.__ ___
Conventional way Present invention
. ._ . . __
Welding current 300A (DCSP) Same
Welding voltage 12V Same
Welding rate 40cm/min60 cm/min
Filler wire 1.2 mm~ Same
~ire feed direction behind in rela- Same
tion with welding
advance direction
Wire conduction Non-conductionConduction (60A):
Opposite polarity
Shield gas Pure Ar25~/minSame
Tungsten 3.2 mm~ Same
Base metal 12 mmt Same
.
Example 3
Upward vertical position welding was effected with the
conditions of Table 6. Fig. 19 shows a bead cross sectional
macroscopic structure at an end portion of a welded sheet accord-
ing to the conventional way, while Fig. 20 shows the counterpart
according to the present invention. The conventional way made a
significant convex bead configuration, whereas an excellent
bead configuration was provided by the present invention.
-41-
~3~92
1 Table 6
. .~ _ . .
Welding conditions Conventional way Present invention
. . _ _ _ _ . __ .
Welding current 28OA (DCSP) Same
Welding voltage llV Same
Welding rate 4 cm/min 7 cm/min
Filler wire 1.2 mm~ Same
Wire feed direction behind in rela- Same
tion with weld-
ing advance
direction
Wire conduction Non-conduction Conduction (60A):
Opposite polarity
Shield gas Pure Ar. 25~/min Same
Tungsten 3.2 mm~ Same
Base metal 25 mmt "V" groove Same
Example 4
Welding was carried out in all welding positions on a
tube hàving a groove shape as shown in Fig. 21 under the con-
ditions of Tables 7 and 8. While-the conventional ~ay provided
a convex shàped bead in a flat position and a concave shaped
in a vertical position, the present invention made a hbmogeneous
and clean bead in all positionsO
-42-
339~Z
.
1 Table 7
_-- ~
Welding conditions. . Conventional way .. Present invention
Welding current 20OA (DCSP) Same
; Welding voltage llV Same
Welding rate 7 cm/min Same
Filler wire 1.2 mm~ Same
Wire feed direction behind in rela- Same
tion with weld-
ing advance
direction
10 Wire.conduction Non-conduction Conduction (Table 8)
Shield gas Pure Ar 30~/min Same
Base metal 50 mmt "U" groove Same
,: . : . , . - -
. _ _
Table 8
Tube position Time
.
1:30 Conduction period in one cycle 0.4 sec
_
. 4:30 Non-conduction period in one cycle` 0.6 sec
4:30 Conduction period in one cycle 0.. 6 sec
S
7:30 Non-conduction pe.iod in one:c.ycle.. . Ø4.. sec
.
207:30 Conduction period in one cycle . . .. 00.4 sec
S
10:30 Non-conduction period in one cycle .. Ø6.. sec
_ . _ __
10:30 .Conduction period in one cycle .-
S _ Non-conduction
1:30 Non-conduction period in one cycle
Example 5
Horizontal direction welding was carried out under the
conditions of Table 9. While tubes made by the conventional way
were located in JI5-lst class, 2nd grade (blow holes) from the
i
-43-
::
~3399Z
t outcomes of X-ray transmittance test, the tubes according to the
present invention were free of any deficits (the groove shape
and the procedures of forming deposited metal are viewed from
Fig. 20).
Table 9
Welding conditions Conventional way Present invention
_ . .
Welding current 350A (DCSP~Same
Welding voltage 12V Same
Welding rate 13 cm/min21 cm/min
~elding wire 1.6 mm~ Same
Wire feed direction behind in relat- Same
tion with weld-
ing advance
. direction
Wire conduction Non-conductionPeriodic conduction
Shield gas Pure Ar 50~/min Same
Deposition proce- Straight beadStraight + arc
dure weaving
Base metal 25 mmt Same
ExampLe 7
A commerical available 9% Ni Steel of 20 mm thick was
provided with a 60 "V" shaped groove and the front surface side
of the groove was multi-layer welded. Subsequently, arc air
gouging was effected on the groove root and the rear surface side
of the groove was welded. The chemical compositions of the 9%
-44-
~L~33~92
1 nickel steel used (base metal material) and the ~lelding wire used
are illust~ated in Table 11 and the welding conditions in Table
12.
Table 11
_ C Mn Si S Ni Ti Co B O N
Filler ~ _ _ (ppm) (ppm)
wixe _ _ _ _ __ _ _ _ ___
A 0.03 0.55 0.25 0.008 0.005 9.5 _ 2.4 0.0004 75 60
Base 0.04 0.68 0.05 0.004 0.004 12.3 0.03 3.5 0.0005 80 50
10Metal 0.06 0.38 0.25 0.007 0.008 9.5 _ _ _ 30 50
(Unit: % by weight)
Table 12
Welding Welding Shield
method position Current Voltage Date gas Polarity
_
Automatic Vertical 300A lOV 70cm/min Ar DC-SP
_ 25~/min _ _
After the bead surface had been cooled below 100C upon
the completion of welding, it was subjected to re-fusion treat-
ment through the utilization of the TIG arc. The conditions forthe re-fusion treatment are listed in Table 13, wherein the
cooling rate is the length of time where temperature falls from
800C to 500C.
Table 13
Condi- ¦ Cooling _ Width of re- Depth of re-
'tion rate Shield gas fusion zone fusion zone
: .. , ,_
a 50 sec Ar. 25Q/min 1/2 W 1/2 t
b 120 sec Ar. 30 1.0 W 1/2 t
c70 sec Ar. 30 " 2/3 W 1/2 t
d40 sec Ar. 30 " 1.3 W 1/3 t
::: .::;: : .. .. __~
-45-
~33~2
1 Table 13 continued
W: the width of the final
finishiny bead
t- the depth of the final
finishing bead
The resulting weld joints were subjected to impact
test (JIS-Z-3112; with a 4th Charpy test specimen and at -196C)
and three-point bend COD test (BS standard DD-l9; with fatigue
notch added and at -196C), the results thereof being
indicated in Table 14.
: Table 14
Weld- . . . COD .
ing Welding Re-fusion vE-196 value
wire method conditions (kg.m) (mm) Remarks
_ . ,
B TIG a 13.0 0.25 Exam~le
B .. b 12.5 0.05 CoOnmpari-
B .. c 15.0 0.25 Exxammple
B .. d 18.0 0.30 Example
B .. Non re-fusion9.0 0.08 CsOnmpari-
: ~ ~ _ ~
Blank (base
metal~ 12.0 0.23 .
Analysis of the results of Table 14 reveals that,
through the outcomes of the Charpy test are not necessarily in
agreement with the COD evaluation values, the low-temperature
toughness of the joint subject to the re-fusion treatment
-~6-
~33~
1 according to the present invention was comparable with that of
the base metal (examples X-Z) and relatively very high unlike
comparison example Z (non re-fusion treatment). Comparison
example X was made when the cooling rate was slow after the re-
fusion treatment (Table 13). In this case the COD values indica-
tive of low-temperature toughness were very low no matter how
excel]ent the Charpy test results were. Comparison Y was made
when-a steel containing a large amount of Ni (the Ni content:
17.4%, Table 11) was emplo~ed as the welding wire and could not
be expected to have the advantages of the present invention.
Example 8
After welding had been carried out with the same base
metal, the same filler wire A, the same groove formation method
and the same TIG welding conditions as Example 7, the re-fusion
treatment was effected with varying the bead surface temperature
(heat input: 45 KJ/cm, shield gas: Ar. 30~/min, width of
re-fusion zone: 2/3W, and depth of re~fusion: 1/2t). The
results of the Charpy test and the COD test on the resulting
joints are depicted in Table 15.
Table 15
Bead surface temp. vE-196 COD value Remarks
(C) (k~/m) (mm)
.. . _
100 15.0 0.25 Example Y
150 14.3 0.22 Example O
300 13.8 0.04 Comparison
Example O
450 4.7 0.02 Comparison
Example P
It is obvious from Table 15 that the bead surface
temperature during the re-fusion treatment had great influences
on low-temperature toughness. In other words, the present
~47-
9~ '
1 invention remained in effect when the temperature was 150C or
less but a considerable reduction in low-temperature was
experienced when the temperature exceeded 150C ~comparision
examples O and P).
-48-
