SUBMERGED ARC WELDING PROCESS FOR NICKEL CONTAINING STEEL

PROCEDE DE SOUDAGE A L'ARC IMMERGE POUR ACIER A TENEUR DE NICKEL

English Abstract

ABSTRACT OF THE DISCLOSURE
Submerged arc welding for nickel containing steel such
as steel containing 3.5 weight percent of nickel. The process
uses a bond type of flux of specific composition to suppress
the oxygen content in the weld metal. Further, the process
utilizes a cored welding wire including a core material of
specific composition. As the result, it is possible to obtain
a weld metal of high impact-resistance at low temperature such
as minus 100°C. The welding electrode is a cored wire consist-
ing of a mild steel and core material, the core material includ-
ing, on the basis of weight to the total weight of the welding
electrode, 5 to 25 percent of CaF2, 2.5 to 5.5 percent of nickel,
O to 0.5 percent of Mo, 0 to 0.5 percent of Ti. The flux is a
bond type flux having a composition of, by weight percent, 10
to 30 percent of SiO2, 8 to 20 percent of A12O3, 25 to 45 per-
cent of MgO, 10 to 30 percent of CaO, 7 to 20 percent of CaF2,
and at least one member selected from the group consisting of
metallic Si, Fe-Si, Fe-Si-Mn, the amount of Si in all cases
being 6 percent or less calculated in terms of metallic Si. The
flux has a basicity B higher than 1.5, the basicity being defined
on the basis of weight by the following equation:
<IMG> .

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:-
1. A submerged arc welding process for welding nickel con-
taining steel with a welding electrode in the presence of a flux,
said welding process being characterized in that;
A. said welding electrode is a cored wire consisting
of a mild steel and core material, the core material
including, on the basis of weight to the total weight
of the welding electrode, 5 to 25 percent of CaF2,
2.5 to 5.5 percent of nickel, 0 to 0.5 percent of
Mo, 0 to 0.5 percent of Ti, and
B. said flux is bond type flux having a composition
of, by weight percent, 10 to 30 percent of SiO2,
8 to 20 percent Al2O3, 25 to 45 percent of MgO, 10
to 30 percent of CaO, 7 to 20 percent of CaF2, and
at least one member selected from the group consist-
ing of metallic Si, Fe-Si, and Fe-Si-Mn, the amount
of Si in all cases being 0.6 percent or less calcu-
lated in terms of metallic Si, and having a basicity
B higher than 1.5, the basicity being defined on
the basis of weight by the following equation:
<IMG>
2. A submerged arc process as claimed in claim 1, wherein
said electrode consists of a mild steel hoop turned over to form
an elongated tube, and the core material is contained in the
space defined by the turned mild steel hoop.
3. A submerged arc welding process as claimed in claim 2,
wherein said mild steel hoop has a composition of, by weight
percent, less than 0.15 percent of C, less than 1.0 percent of
Mn and the balance consisting essentially of Fe except the inevit-
able amount of impurities.
14

4. A submerged arc welding process as claimed in claim 2,
wherein said core material consists essentially of CaF2, metal-
lic Ni, Fe-Mo, and Fe-Ti.
5. A submerged arc welding process as claimed in claim 1,
wherein said nickel containing steel contains about 3.5 per-
cent by weight of nickel.
6. A submerged arc welding process for welding steel con-
taining nickel comprising welding the steel with a welding elec-
trode in the presence of a bond-type flux,
(a) said welding electrode being a cored wire consisting
of a mild steel and a core material, the core material
containing, in percent by weight based on the total
weight of the welding electrode, from 5 to 25 percent
of CaF2, from 2.5 to 5.5 percent of Ni, from 0 to 0.5
percent of Mo, and from 0 to 0.5 percent of Ti; and
(b) said bond-type flux having a composition containing,
in percent by weight, from 10 to 30 percent of SiO2,
from 8 to 20 percent of Al2O3, from 25 to 45 percent
of MgO, from 10 to 30 percent of CaO, from 7 to 20
percent of CaF2, and at least one deoxidizing agent
selected from the group consisting of metallic Si,
Fe-Si, Fe-Si-Mn, metallic Mn, and Fe-Mn, the amount of
Si in all cases being 0.6 percent or less calculated
in terms of metallic Si, said flux having a basicity
(B) higher than 1.5, the basicity being defined, on a
weight basis, by the following equation;
<IMG>
thereby to produce a weld metal having a high impact-
resistant property at a temperature below minus 100°C,
and having a silicon content not exceeding 0.20%, a
carbon content not exceeding 0.08%, and an oxygen con-

tent not exceeding 400 ppm.
7. The process of claim 6 wherein the welding electrode
consists of a mild steel hoop turned over to form an elongated
tube, and the core material is contained in the space defined
by the turned mild steel hoop.
8. The process of claim 7 wherein the mild steel hoop
contains, in percent by weight, less than 0.15% of carbon, less
than 1.0% of manganese, with the remainder consisting essent-
ially of iron.
9. The process of claim 6 wherein the nickel, molybdenum,
and titanium are each present in the core material in its
metallic form or in the form of its ferrous alloy.
10. The process of claim 9 wherein the core material
consists essentially of CaF2, metallic Ni, Fe-Mo, and Fe-Ti.
11. The process of claim 6 wherein the steel contains
about 3.5% by weight of nickel.
16

Description

V309 ~ :
The present invention relates to a submerged arc -
welding process and more particularly to a submerged arc
welding process for nickel containing steel. More specifi-
cally, the present invention pertains to a submerged arc weld-
ing process for nickel containing steel which can provide a
weld metal having an improved toughness. The present invention
is particularly suitable for welding 3.5% nickel containing
steel but is not limited to such purpose.
Conventionally, 3.5% nickel containing steel has been -
utilized for constructing vessels which are used for storing
liquefied gas such as liquefied nitrogen, liquefied oxygen or
the like. Since such vessels are constructed from the steel
material by means of welding and subjected in use to an extreme
cold temperature, it is very important to provide an adequate
impact-resistant property at low temperature such as below
minus lOO~C even at the welded portion. From the viewpoint of
manufacture, it is of course desirable to perform the welding
operation automatically making use of a submerged arc welding
technique, however, since it has been difficult to ensure a
satisfactory impact-resistant property through a conventional
submerged arc welding, manually operated welding technique has
; been employed for the manufacture of such vessels so that
thermal input at the welding portion can be maintained as low
as possible to provide a weld metal of high toughness.
It has previously been proposed and actually been -~
' practiced, in order to obtain an increased tou~hness in the
`~I weld metal, to increase the amount of nickel content in the
'~ weld metal. However, experiences have shown that the increase
in the nickel content does not provide any improvement in the
; 30 toughness but there have rather been an adverse effect thereon
when the nickel content exceeds 3%. The reason of this tendency
is understood that the increased nickel content serves to pro-
- 1 ~
.

1080309
vide the weld metal of brittle structures such as bainite. Thus,
according to prior art, it has been very difficult to ensure an
impact-resistant property at low temperatures such as below
minus 100C.
The present invention has therefore an object to pro-
vide a submerged arc welding process which can provide a weld
metal of improved toughness.
Another object of the present invention is to provide
a novel submerged arc welding process for nickel containing
steel which uses flux and welding electrode of specific composi-
tion.
A further object of the present invention is to pro-
vide a submerged arc welding process which is particularly
suitable, although not limited, to the welding of 3.5% nickel . -
containing steel.
According to the present invention, the above and
other objects can be accomplished by a submerged arc welding
process for weldi.ng nickel containing steel with a welding
electrode in the presence of a flux, said welding process ::
being characterized in that:
A) said welding electrode is a cored wire consisting
of a mild steel and core material, the core
material including, on the basis of weight to the
total weight of the welding electrode, 5 to 25 :
percent of CaF2, 2.5 to 5.5 percent of nickel, 0
to 0.5 percent of Mo, 0 to 0.5 percent of Ti,
B) said flux is bond type flux having a composition
of, by weight percent, 10 to 30 percent of SiO2,
.
~: . . . . .

` ~080309
8 to 20 percent of A1203, 25 to 45 percent of MgO,
10 to 30 percent of CaO, 7 to 20 percent of CaF2,
and at least one me~ber selected from the group con-
sisting of metallic Si, Fe-Si, Fe-Si-Mn, the amount of
. Si in all cases being 0.6 percent or less calculated
- in terms of metallic Si, and having a basicity B higher
. than 1.5, the basicity being defined on the basis of
weight by the following equation: ~:
B CaO + MaO
SiO2 + Ai2o3
Through extensive investigations in obtaining an
improved toughness through a submerged arc welding of steel
material of high nickel content, the inventors have found that ::
: the Si and C contents in the weld metal have an important effect
on the property. More specifically, in case of a weld metal
having nickel content exceeding 2 percent, a decrease in silicon
content and also a decrease in carbon content are effective to
provide a high toughness at low temperatures~ Particularly,
with a weld metal having a silicon content not exceeding 0.20
percent and a carbon content not exceeding 0.08 percent, it has
been ensured that a high impact-resistant property can be
attained even at an extremely low temperature around minus
100C. The reasons for such an improvement in toughness through
the decreased carbon and silicon contents of weld metal have not
been fully clarified but it i9 understood that the reducing in
the carbon and silicon amounts is effective to suppress the
., ~trength of the weld metal including a relatively high per-
centage of nickel.
However, in welding processes utilizing a melt type
flux, it is very difficult to maintain the silicon content of
the weld metal lower than 0.20 percent because the flux
normally contains a large amount of SiO2 and the basicity of
the flux cannot be as high as desirable, whereby there will be
. -
,. ~ , : :

~0803V9
a tendency that the SiO2 content will be reduced in the slagwhich will be formed during the welding process, and the silicon
content in the weld metal will correspondingly be increased.
Thus, it is impractical to use such melt type flux for the pur-
pose of the present invention and it is therefore essential for
the present invention to utilize a bond type flux having a high
basicity and less SiO2 content.
The use of such bond type flux of high basicity may
also be effective to decrease the oxygen content in the weld
metal but there still exists surplus oxygen so that it is
required to add deoxidizing agents such as silicon, metallic
silicon, Fe-Si, Fe-Si-Mn, metallic manganese and Fe-Mn. The
amount of such de-oxidizing agents is very important because,
when the agents are added excessively, they will cause an
increase in the silicon content but if the amount is insuffi-
cient there will be produced welding defects such as blow-
holes and there will also be a decrease in the toughness due
to insufficient de-oxidization. Thus, in order to decrease
the silicon content in the weld metal and to achieve an adequate
de-oxidization, it is necessary to utilize a bond type flux
having a low silicon content and a high basicity and, at the
same time, to decrease the oxygen content in the pool of the
molten metal produced during welding operation.
.~ According to the present invention, a welding elec-
trode of cored wire is employed because it provides a stable
welding arc with a relatively large input. The welding elec-
trode may be manufactured by turning over a mild steel hoop to ~ -
form an elongated wire or tube and then incorporating the above-
mentioned core material in the space defined in the tube. The
hoop is preferably of a composition by weight of less than 0.15
percent of carbon, less than 1.0 percent of manganese and the
balance of iron because of its workability. ~ -
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.. - . . . . . .. .

~08U309
It has been found that CaF2 is very effective to de-
crease the oxygen content in the welding pool of the molten
metal. The inventors found that the oxygen content in the
molten metal could substantially be decreased in a submerged
arc welding through a use of a bond type flux of high basicity
in combination with a welding electrode of cored wire including
CaF2. The weld metal thus produced has been found substantially
free from any defects such as blow-holes.
It is understood that CaF2 in the core material of the
welding electrode is subjected to a high temperature of the
welding arc and vaporized and decomposed as soon as the electrode
is molten, to produce a large amount of fluoric gas which serves
to shield the arc space and the surface of the molten metal so
as to prevent air or other gaseous impurities from reaching the
molten metal. Thus, CaF2 is effective to decrease the amounts
of oxygen and other impurities in the molten metal.
Thus, it has been ensured that through a submerged arc
welding utilizin~ a bond type flux of high basiclty and a weld-
ing electrode of cored wire containing CaF2, it is possible to
produce a welded metal of low carbon and low silicon contents
without causing any defects such as blow holes. Further, it has
' also been ensured that the silicon content in the weld metal can
be maintained below 0.20% and the oxygen content below 400 ppm.
, The inventors have further made investigations on the
influence of Ni, Mo and/or Ti contents in the welding electrode
on the weldability, the strength and the impact-resistant pro-
perty at minus 100C. As the result, the inventors have found
that adequate impact-resistant property at minus 100C cannot
be stably provided unless the Ni content in the cored wire is ;~
maintained above 2.5%. On the other hand, it has also been found
that excessive nickel content has a tendency of producing bainite
structure even where the silicon content in the weld metal is
.

` 10~1~J3(~
very low, resulting in an unstable impace-resistant property at
low temperatures. It is of course true that, even in this in-
stance, the decrease in the toughness is not as significant as
in the case where the weld metal contains more than 0~2 percent
of silicon, however, in view of an expensive cost of nickel and
in view of the fact that an excessive nickel content may be a
cause of cracks at a high temperature, it is recommendable to
maintain the nickel content in the welding electrode between 2.5
and 5.5 percent.
Molybdenum may be incorporated into the welding elec-
trode in order to secure the strength of the welded part because -
there is a tendency that the strength of the welded part is
relatively low with low carbon and silicon contents. However,
the Mo content should be limited lower than 0.5 percent because
an increased Mo content has a tendency of producing a weld metal
of bainite structure resulting in a remarkable decrease in the
impact-resistant property at low temperatures.
Titaniummay be also incorporated to the welding elec-
trode as a de-oxidizing agent and further serves to make the
weld metal of fine crystals and fine structures which are
effective to improve the toughness of the weld metal. Although
thetitanium is thus effective to improve the toughness of the
weld metal, the content must be maintained lower than 0.5 per-
cent because the titanium content exceeding this value has a ;~
tendency of increasing the silicon content in the weld metal
and of producing a bainite structure resulting in a decrease in
the impact-resistant property at low temperatures.
With respect to the flux, the basicity is of impor-
tance because, under the basicity less than 1.5, the SiO2 in ;"
the flux will be increased and the Si content in the weld metalis correspondingly increased. Further, with the basicity less
than 1.5, there is also a tendency that the oxygen content in
' :
- 6 -

108030~
the weld metal is increased and blow holes are produced. ;~
The SiO2 has an influence on the melting point of the
flux and where the SiO2 content is less than 10 percent there
will be an increase in the melting point of the flux so that
adverse effects will be seen in the performance of the welding
operation and also in the appearance of the welded beads. With
the SiO2 content exceeding 30 percent, the SiO2 will be chemi-
cally reduced and there will be an increase in the Si content
in the weld metal resulting in a poor toughness of the weld
metal.
The A1203 has an influence on the appearance of the
welded beads and an acceptable range is between 8 and 20 per-
cent. With the MgO content less than 25 percent, it will be
difficult to maintain the basicity at a desirable level but
where the content is greater than 45 percent the melting point
of the flux will be increased to an unacceptable level. The
CaO content should be greater than 10 percent in order to main-
tain the basicity within the desired range but it will have an
adverse effect on the workability if it is increased beyond 30
percent.
The CaF2 content should be greater than 7 percent in
order to provide a satisfactory appearance on the welded beads.
However, excessive addition of CaF2 causes an unstable welding
arc so that the content should be lower than 20 percent. In
order to maintain the silicon content in the weld metal below
0.20 percent, it is required to maintain the silicon content of
metallic Si, Fe-Si and Fe-Si-Mn in the flux to lower than 0.6
percent. Otherwise, there will be an adverse effect on the
toughness at low temperatures due to an increase in the silicon
content in the weld metal. As mentioned above, silicon contain-
ing de-oxidizing agent may be metallic Si, Fe-Si, Fe-Mn-Si. It
is of course possible to use a material other than silicon as -
~.
-- 7 --
: - :
. - . - .: . .

108V309
the de-oxidi~ing agent. For example, manganese may be used for
the purpose. Thus, the flux of the present invention may con-
tain de-oxidizing agent in an amount of less than 0.6% calculated
in terms of silicon.
Regarding the cored wire, it has been found that the ~ -
CaF2 content should be greater than 5 percent to the total
weight of the wire. Otherwise, blow-holes are apt to be pro-
duced in the weld metal and there will be a decrease in the
toughness. With the CaF2 content greater than 5 percent, there
is a remarkable decrease in the oxygen content in the molten
metal so that blow holes are prevented and the toughness is
improved. However, the CaF2 content should not exceed 25 per-
cent because an excessive CaF2 content makes the welding arc
unstable and causes apoor workability.
In order to ensure an adequate impact-resistant pro-
perty at minus 100C, it is necessary to maintain the nickel
content in the core wire in an amount of higher than 2.5 per-
cent, however, where the content increases beyond 5.5 percent,
it may cause cracks under high tempera-ture.
Molybdenum may be incorporated to the cored wire for
obtaining an increased strength of the weld metal but the con-
tent shall not exceed 0.5 percent because it may have an adverse
effect on the impact-resistant property at low temperatures
where the Mo content is above this value.
Titanium may be also incorporated to the cored wire
because it is effective to produce fine crystalline structures
which serve to provide an improved impact-resistant property
under low temperature. However, the titanium may be omitted
because it is possible to obtain a satisfactory impact-resistant
property around minus 100C. Where the Ti content is greater
than 0.5 percent, there will be a decrease in the toughness due
to an increase in the silicon content in the weld metal.

~0~30309
Nickel, molybdenum and titanium in the core material
may be incorporated in the welding electrode in the form of
ferrous alloy thereof, for example Fe-Ni, Fe-Mo and Fe-Ti.
Fe-Ni, Fe-Mo or Fe-Ti may be incorporated to the electrode in
the above mentioned amount calculated in term of nickel, molyb-
denum or titanium. It is of course that nickel, molybdenum or
titanium may be added to the electrode in the form of elementary
metal.
It has been found that, when a submerged arc welding
using the aforementioned flux and welding electrode of cored wire
is applied to 3.5% Ni containing steel, it is possible to pro-
duce a weld metal having an excellent toughness at low tempera-
tures. It should be noted, however, that the submerged arc
welding process in accordance with the present invention can also
be applied to other types of nickel containing steel such as
3.5% Ni containing steel. Further, it should also be noted
that the welding conditions may suitably be selected in prac-
tice.
The present invention will now be described by way of
examples.
Examples:
Butt welding operations were performed in specimens
of 3.5% Ni containing steel (ASTMA 203D) of 25 mm thick with a
welding current of 600 A under 40 V and a welding speed of
40 cm/min. to form multiple layers of weld metal. The operations
were performed in accordance with conventional process as well
as in accordance with the present invention. In the welding
operations, metal sheets were shaped to have edges sloped by
an angle of 20 degrees, and a pair of such sheets were placed
at a minimum distance of 10 mm.
The welded specimens were subjected to tests for weld-
ing defects. The specimens were then formed with V-shaped notches
_ g _

1~80309
and subjected to Charpy impact test at minus 100C. The
results are shown in the following table.
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: Example of the Invention
o .
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-- 12 --
, . . , . - . .~ . , :: .

10~0309
In the above table, the wire composition designates
the constituents of core material in weight percentages with
respect to the wire as a whole. Mild steel in the Table had a
composition by weight, of 0.06 percent of carbon, 0.50 percent
of manganese and the balance of iron. In the table, it will be
noted that the specimen A shows unsatisfactory toughness because
the welding employed a melt type flux with a low basicity. The
specimen B shows blow holes due to insufficient deoxydization
because the flux does not contain silicon. The specimen C does
not have a satisfactory toughness because the process employed for
for the specimen uses a welding electrode of solid wire which
did not provide adequate amount of oxygen~ The specimen D shows
unqatisfactory toughness due to insufficient nickel content.
The specimen E has blow holes due to insufficient deoxydization
because the flux used for the specimen had lower basicity.
The specimens J through N which have been welded in
accordance with the present invention show satisfactory impact
resistance under low temperature. In the specimen L, the flux
did not contain Si but deoxydization was effected due to the
existence of Ti.
The specimen F had blow holes which have produced due
to insufficient content of CaF2 in the welding wire. The speci-
men G had been welded with a welding wire containing excessive
amount of nickel. As the result, the weld metal did not possess
a satisfactory toughness. ~he ~pecimen H had been welded with
the welding wire containing excessive titanium and as the result
the weld metal had insufficient toughness. The specimen I had
unacceptable appearance of welded beads due to excessive amount
of CaF2 in the welding wire.
The invention has thus been shown and described with
reference to examples but it should be noted that modifications
may be made without departing from the scope of the appended
claims.
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.: