TITLE:
Fused Alumina Basic Flux for Narrow Gap Submerged ARC Welding process.
FIELD OF INVENTION:
This invention relates to a method of preparing fused alumina basic welding flux for
narrow gap submerged arc welding.
BACKGROUND OF THE INVENTION
Thick plates vessels made up of carbon steel is widely used in parts of thermal,
nuclear power plants and in various chemical devices. The larger such parts and
devices, the thicker and stronger the carbon steel is required to be. Conventionally,
the thicker plates of carbon steel has been welded by "U" groove Submerged Arc
welding and semi-automatic welding. However, when thick carbon steel plate is
welded by "U" groove Submerged Arc welding and semi-automatic welding,
deposition efficiency decreases and welding defects such as slag inclusion and
blowholes easily occur.
Prior to the present invention of fused alumina basic flux, flux was imported for
welding of HP heaters for nuclear steam generators. There has also been a need for
introducing narrow gap sub arc welding in boiler drum in longitudinal and circular
seam welds, having plate thickness up to 175mm thickness. The narrow gap welding

technology reduces the weld volume to an extent of 60% comparing with
conventional "U" groove welding, when plate thickness is above 100mm.
US patent search has been made and a bonded flux for submerged arc welding
applicable in narrow grooves is found with patent numbers US4436562A and
CA1198657A1. The type of flux claimed is of bonded nature, bonded at room
temperature. This has different characteristics of processing compared with the
fused flux described in this claim.
Fused flux is homogeneous in its chemical structure and is non-hygroscopic. While
recycling due to its non-fragile nature the chemistry of flux mass is not altered.
Whereas the bonded flux is hygroscopic in nature and needs higher redrying
temperature. It is fragile in nature, and due to that segregation takes place and the
chemistry of flux is altered. Across the thickness of the weld metal there could be
change in weld metal chemistry.
The bonded flux narrated in the U.S patent US4436562A and Canada patent
CA1198657A1 teaches of an exotic constituent BaO which will increase the cost of
production. When both choices are available i.e. fused and agglomerated, fused will
be preferred by the shop because of uniform chemistry, non-hygroscopic and non-
fragile nature that enables repeated recycling without losses.

EP006660B1 is same as found in US patent (US4436562A) described above. There
are no other claims relevant to narrow gap sub merged arc welding.
In order to solve the foregoing and/or other problems, it is an objective of the present
invention to provide a fused alumina basic flux for submerged arc welding which has
excellent arc stability and slag detachability during submerged arc welding of plate
thickness up to 175mm thickness carbon steel with narrow grooves, prevents
welding defects such as poke marks and pits, and has excellent bead shape and can
give good mechanical properties viz, strength and impact. A typical "U" and narrow
groove joints are shown in figures 1&2.
OBJECTS OF THE INVENTION
It is an object of the present invention to propose a method of preparing the fused
alumina basic welding flux for welding in fabrication industries for thickness of
sections varying from 3.5mm to 300mm. Single "V" or double "V" groove joints are
used for up to 20mm. For over 20mm, U groove joints are used to save weld metal
deposited. For thickness (t) over 40mm narrow groove joints are preferred to save
large quantum of weld metal.
Another object of the present invention is to modify the fused flux to have good slag
detachability from the narrow grooves without much difficulties, a special flux with
good detachability needs to be designed for narrow groove submerged arc welding
which can give smooth side wall wash and good slag detachable

Still another object of the present invention is being aimed at, which gives chemical
homogeneity in each grains and non-hygroscopic in nature that helps in avoiding
weld porosity and remains stable (non fragile) while recycling.
BRIEF DESCRIPTION OF THE INVENTION:
According to this invention there is provided a method of preparing a fused alumina
basic welding flux comprising the step of:
mixing an effective amount of SiO2, Al2O3l CaO, MnO, MgO and TiO2 and optionally
CaF2;
subjecting the said mixture to the step of drying and arc melting in a furnace,
granulating the molten flux to a desired grain size of 0.2 mm to 1.5mm,
baking the said granulated in an oven at 400-450°C for about two hours,
cooling the flux and packing the same.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig.1, there is shown the typical "U" groove joint. The two metals to be joined
together, first metal piece 1 and second metal piece 4 are shown. A "U" groove is
shown between the first metal piece 1 and second metal piece 4 with thickness 't' 5.
Angle of "U"-groove 2 against vertical plane is 514 degree. Radius of "U" groove 3 is
13mm.

Fig.2 shows the narrow groove joint by joining three metal pieces 7, 9 & 8. The Width
of narrow gap 6 is 18mm.
Fig. 3 shows the narrow gap submerged arc welding flux sample 10.
Fig. 4 shows a completed weld sample. The weld 11 requires substantially less weld
material than required by the method of the prior art. Two passes per layer technique
has been employed and the completed weld joints are shown. Thickness 12 of plate
is 125mm.
DETAILED DESCRIPTION OF THE PRESENT INVENTION:
In this invention, a fused flux which can give the above mentioned requirements in
narrow groove welding is designed which can function in groove width not less than
18mm. Two welding passes per layer technique is envisaged to give smooth side
wall wash & for building up layers to smoothly complete the joints without any under
cuts into the base metal.
A special alumina basic flux with good detachability has been prepared for narrow
groove submerged arc welding which can give smooth side wall wash and good slag
detachability. Conventional submerged arc welding flux, fused or agglomerated will
not function in narrow grooves due to slag removal difficuftMN. In this invention, a

fused flux which can give the above mentioned requirements in narrow groove
welding is designed which can function in groove width not less than 18mm. Two
welding passes per layer technique is envisaged to give smooth side wall wash & for
building up layers to smoothly complete the joints without any under cuts into the
base metal. This will minimise the use of large quantum of weld metal for joining
thick plates used for fabricating high pressure vessels and drums.
The present invention discloses a method for reducing of large quantum of weld
metal for joining thick plates used for fabricating high pressure vessels and drums,
with reasonably good tensile strength and Impact properties.
In the present invention, the chemical composition, and the flux-particle distribution
of the fused flux for submerged arc welding are controlled. Therefore, it is possible to
provide a fused flux for submerged arc welding which has excellent arc stability and
slag detachability during welding, prevents welding defects such as poke marks and
pits, and has excellent bead shape.
The components of a fused flux for submerged arc welding according to the
invention, is applied to carbon stainless steel welding thickness of sections varying
from 3.5mm to 300mm. Single "V" or double "V" groove joints are used for up to
20mm., and reasons for limiting the amounts of the components will be described.

[1]SiO2.: 12.0-20.0wt%
SiO2 is an acidic component and serves to adjust the viscosity and melting point of
molten slag, thereby enhancing bead shape and slag detachability.
When the amount of SiC>2 in the entire flux is less than 12.0wt%, viscosity is so
insufficient that bead width becomes non-uniform. Further, a spreading property is
reduced so that convex beads are formed, that is, welding beads are not uniform.
Furthermore, slag detachability is reduced and welding defects easily occur. When
the amount of SiO2 exceeds 20.0wt%, the basicity of molten slag is reduced so that
oxygen within deposited metal increases. Then, toughness is degraded and viscosity
becomes so excessive that non-uniform beads are formed and slag detachability is
degraded.
The SiO2- supply source, quartz (SiO2), quartz sand (SiO2), wollastonite (CaSiO4)
and the like can be added in the form of an oxide or oxide complex.
[2]AI203: 30-35.0wt%
Al2O3 is a neutral component and serves to enhance slag fluidity so as to stabilize
slag shape. Further, since Al2O3 has a strong affinity for oxygen, it enhances welding
performance without increasing the amount of oxygen in the welded metal. In
addition, Al2O3 adjusts the viscosity and melting point of molten slag such that bead
shape is enhanced. When welding is performed, Al2O3 enhances arc concentration
and stability, thereby improving welding performance.

When the amount of Al2O3 in the entire flux is less than 30.0 wt(%), the viscosity and
melting point are reduced so that bead widths and grains become non-uniform.
Further, welding defects such as undercut and the like may occur. When the amount
of AI2O3 exceeds 35.0 wt(%), the melting point of molten slag increases, and fluidity
is reduced so that arc stability is degraded. Further, the viscosity of molten slag
increases, and a bead spreading property is so insufficient that convex beads are
formed, that is, bead shape is degraded. In addition, welding defects such as slag
inclusion and the like occur.
The AI2O3 supply source, bauxite AI2O3-H2O, aluminum oxide (Al2O3) and the like
can be used,
[3]CaO: 15-20.0wt%
CaO is a basic component and serves to adjust basicity and viscosity and to reduce
the amount of oxygen in welded metal, thereby enhancing the toughness of a welded
metal portion. However, CaO increases the melting point of molten slag such that
slag inclusion is caused. Therefore, it is necessary to limit the amount of CaO.

When the amount of CaO is less than 15.0wt%, its effect is insignificant. When the
amount of CaO exceeds 20.0wt%, the melting point and viscosity of molten slag
increase so that bead shape and slag detachability are degraded and welding
defects such as poke marks occur.
The CaO supply source, wollastonite (CaSiO4), dolomite (MgC03 -CaC03), anorthite
(CaO-Al2O3 -SiO2) and the like can be used.
[4]CaF2: 7.0-15.0wt%
CaF2 is a basic component and serves to reduce the melting point and viscosity of
molten slag such that slag fluidity is enhanced and bead shape is improved. Further,
when welding is performed, CaF2 reacts with oxygen to generate fluorine gas such
that partial vapour pressure is reduced. Thus, it helps to reduce oxygen and
hydrogen and enhance the toughness of welded metal.
When the amount of CaF2 is less than 7.0wt%, its effect is so insignificant that bead
shape and toughness of welded metal are not excellent. When the amount of CaF2
exceeds 15.0wt%, arc becomes so unstable that bead shape and slag detachability
are degraded. Further, the generated gas has a bad smell, and welding defects such
as poke marks, undercut and the like occur.

The CaF2 supply source, fluorspar (CaF2) or the like can be used.
[5]MnO: 5.0-10.0wt%
MnO is an effective component for improving bead shape. In particular, during high
speed welding, MnO serves to improve bead shape and prevent welding defects
such as undercut and the like. When the amount of MnO is less than 5.0wt%, its
effect is insignificant. When the amount of MnO exceeds 10.0wt%, MnO reaction in a
molten weld pool becomes so severe that bead shape and slag detachability are
considerably degraded.
The MnO supply source, Ferro-manganese, manganese oxide (MnO) and the like
can be used.
[6] MgO: 15.0-20.0wt%
MgO is a basic component and serves to increase the basicity of molten slag and
reduce the amount of oxygen within welded metal, which enhances the toughness of
welded metal. Further, when welding is performed, MgO stabilizes arc and improves
slag detachability and bead shape. However, since MgO increases the melting point
of molten slag such that slag inclusion may be caused, there is a limit to the amount
of MgO that can be added.

When the amount of MgO is less than 15.0wt%, its effect is insignificant, and slag
adheres to the surface of welding beads such that the slag detachability is degraded.
When the amount of MgO exceeds 20.0wt%, arc becomes unstable, and convex
beads are formed, thereby degrading bead shape. Further, the melting point of slag
excessively increases so that slag detachability is degraded, and welding defects
such as poke marks and the like occur.
The MgO supply source, magnesite (MgCOs), magnesia clinker (MgO), dolomite
(MgC03 - CaCOs) and the like can be used.
[7]TiO2: 7.0-15.0wt%
TIO2 Rutile is the most common natural form of TiO2 and is a chemically neutral
oxide. It is effective in reducing the viscosity, especially when aluminum oxide or
silica is to be replaced and is added for bead appearance. It promotes the formation
of acicular ferrite and refines the grains that results in increase of ductility and
toughness of the weld metal. Rutile is employed to provide for good slag removal
after the weld has solidified and to reduce the oxygen content of the weld metal
The TiO2- supply source, Rutile (TiO2).
In the present invention, not only is the composition of flux controlled, but a relational
expression for expressing a viscosity rate is set. When the viscosity rate is properly
controlled within the following numerical range, welding performance is improved:

[8]Viscosity
The viscosity during submerged arc welding considerably affect arc stability, bead
shape, and welding defects. The present inventor has recognized that, among the
components of the flux, CaO, Al2O3, and MgO increase the melting point of slag and
the viscosity of mixed slag, but SJ02 and CaF2 reduce the melting point of slag and
the viscosity of mixed slag.
When the viscosity of slag is excessively high, the fluidity of slag is reduced during
welding such that arc becomes unstable and bead spreading properties become
insufficient. Accordingly, bead shape is degraded. Further, slag inclusion is
frequently caused so that welding defects occur. On the contrary, when the viscosity
of slag is excessively low, bead width becomes non-uniform so that bead shape is
degraded. Further, slag detachabflity is reduced and welding defects occur.
[9]Determination of the contents of the fused flux:
The chemical constituents of the fused Alumina basic flux for submerged arc welding
according to the invention can be determined quantitatively using Inductively
Coupled Plasma Atomic Emission Spectrometry (ICP-AES), X-ray Fluorescence
Spectrometry (XRF).

[10] Reasons for limiting particle diameters of the fused flux for submerged arc
welding will be described in detail below.
[11] If the fused flux in which the respective flux components having the above-
described compositional ratios are mixed does not have proper flux-particle
distribution, arc stability and bead shape are degraded, and welding defects such as
pits, poke marks and the like easily occur. Therefore, the flux according to the
invention is composed of less than 5wt% flux particles with a diameter of more than
1.00mm, 20.0-50.0wt% flux particles with a diameter of 0.50 to less than 1.00mm,
40.0-75.0wt% flux particles with a diameter of 0.20 to less than 0.50mm, and less
than 5wt% flux particles with a diameter of less than 0.20mm, with respect to the
overall weight thereof.
[12] The diameters of the flux particles of the sintered flux for submerged arc welding
can be measured on the basis of the Standard Test Method for Sieve Analysis of
Metal Powders (ASTM B214). Mode for the Invention
The ingredients (minerals) are weighed, premixed in dry mixer and melted in an arc
melting furnace. The molten flux is granulated in water, the resultant mass is air
dried, crushed and sieved to get required grain size of 0.2mm -1.5mm. Then the
sieved flux is baked in electrical oven at 400-450°C for two hours to completely
remove moisture. The flux is cooled and packed in HDPE bags. Then the flux is used
for welding combined with different grades of welding wires required as per design.

Welding parameters
1. This flux is designed for use with moderate welding currents varying from 450 to
550 amperes using wires of 3.15 to 4.00mm.
2. Welding voltage range will be 28 to 32V and speed shall be minimum
0.4m/minute.
3. Higher current, high voltage and lower welding speed will result in wider weld
bead and wider slag that will cause difficulty in slag removal.
Examples
Hereinafter, the effects of Examples of the fused alumina basic flux for submerged
arc welding according to the invention will be described in detail and compared with
Comparative Examples that deviate from the ranges of the invention.
It can be seen from the table 2 that there is slight oxidation of manganese &
molybdenum and there is silicon pick up from the flux due to the presence of
considerable amount of silica in the flux & slag. The carbon recovery from the wire is
fairly good that gives required weld metal strength of minimum 520MPa comparing
with base metal. The fairly good carbon recovery is due to the basic nature of the
flux. If it were acidic the carbon recovery could be as low as 0.02% causing lowering
of weld metal tensile strength.
The transverse tensile strength is well above the minimum requirement of 520MPa.

The impact strength of weld metal at -20°C is very good at level more than 100
Joules. The TY107 brand of this flux has been approved by Nuclear Power
Corporation of India (NPCIL).
From table-4, the required tensile strength is met, so also the charpy "V"-notch
impact toughness at -29°C
After the brand approval tests, welding trails were conducted at the user end viz
BHEL Bhopal on test plates. With the successful completion of weld test plates, the
flux has been used in the welding of 'HP' heaters of steam generator having narrow
groove weld joints.
TABLE 1: Welding & post weld heat treatment condition.

WE CLAIM:
1. A method of preparing a fused alumina basic welding flux comprising the step of:
mixing an effective amount of SiO2, Al2O3, CaO, MnO, MgO and TiO2 and optionally
CaF2;
subjecting the said mixture to the step of drying and arc melting in a furnace,
granulating the molten flux to a desired grain size of 0.2 mm to 1.5mm,
baking the said granulated in an oven at 400-450°C for about two hours,
cooling the flux and packing the same.
2. The method as claimed in claim 1, wherein the amount of each of the components
in the flux is as follows:
12-20 wt% of SiO2
30-35 wt% of Al2O3
15-20 wt% of CaO
5 to 10 wt% of MnO
15 to 20 wt% of MgO
7 to15 wt% of TiO2
and optionally 7 to 15 wt% of CaF2

3. The method as claimed in claim 1, wherein the basicity index of the composition is
1.2 which gives good weld metal strength and impact toughness

4. The method as claimed in claim 1, wherein titanium oxide helps in smoothening
weld beads and also enhances slag detachability. CaO, MgO, MnO and CaF2 are
contributing to increase the basicity of flux & slag and the also reduce the O2
pickup.
5. The method as claimed in claim 1, wherein SiO2 and TiO2 tend to increase the
acidity of the flux which enables slag removal and also causes pickup of O2 in
weld metal.