FIELD OF THE INVENTION
This invention relates to a composition of basic low hydrogen iron powder-type
coating depositing high strength bainitic weld metal with a higher deposition
rate. The invention further relates to a high deposition-rate low hydrogen type
shielded metal arc welding electrode depositing high strength bainitic weld
metal.
BACKGROUND OF THE INVENTION
In recent years, there has been a resurgence in research and development in
alloy design and in an attempt to bring down component weight, use of high
steels with strength to weight ratio approaching that of aluminum and titanium
has been gaining momentum. Bainitic steels with excellent strength (approaching
1000 mPa and adequate CharpyV-Notch toughness at subzero temperatures)
have been developed abroad. These steels find use in military equipment and
naval equipment like tanks and war ships. The chief advantage of these steels is
the elimination of preheating during welding unlike quenched and tempered
steels like HY 80, HY 100.
During welding, it becomes imperative to protect the weld metal from
atmospheric contamination. All welding processes rely on either gas shielding or
slag shielding (produced from a welding flux) or a combination thereof to
accomplish this. Thus the SMAW (shielded metal arc welding) process uses

fluxes as a coating. In SAW (submerged arc welding) the welding arc is buried
under a blanket of flux which on melting protect the weld metal and is finally
discarded as a slag. The TIG process uses inert gas shielding.
But due to inherent problems like the need to clean out solidified slag (molten
and cooled flux) and electrode change time, SMAW process has only low
deposition rate per hour. TIG process also suffers from low productivity . Only
GMAW AND SAW processes are amenable for mechanization and automation. IN
terms of deposited metal weight per hour of arc time SMAW is at the lower end
with typical values like 1.5 kg/hr as compared to 2.5-4.5 kg/hr from GMAW and
5-8 kg/hr for SAW.
According to the prior art, the coating thickness to core wire diameter and the
iron powder content in basic coated low hydrogen electrodes is in the levels of
D/d ratio of 1.7 and 30% respectively.
It is known that all types of coated SMAW electrodes contain slag formers, gas
formers, de-oxidizers, de-nitriders, alloying elements and other materials like
mineral silicates and iron powder. Basic coated low hydrogen electrodes
conforming to the American Welding Society standard AWS 5.1 E7018-1 and low
alloy high strength steels for example, E 9018M and E11018 M typically have
about 30 weight % iron powder in the electrode coating and the balance may
comprise materials like limestone and fluorspar and titania and other materials.

OBJECTS OF THE INVENTION
It is therefore, an object of the invention to propose a composition of basic low
hydrogen iron powder-type coating depositing high strength bainitic weld metal
with a higher deposition rate.
Another object of the invention is to propose a high deposition-rate low
hydrogen type shielded metal arc welding electrode depositing high strength
bainitic weld metal.
A further object of the invention is to propose a process for producing a high
deposition-rate low hydrogen type shielded metal arc welding electrode
depositing high strength bainitic weld metal.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides in a first aspect a composition of
basic low hydrogen iron powder-type coating deposition high strength bainitic
weld metal with a higher deposition rate consisting of :


In a second aspect of the invention there is provided a high deposition-rate low
hydrogen type-shielded metal arc welding electrode depositing high strength
bainitic weld metal.
The invention further provides a process for producing a high deposition-rate low
hydrogen type-shielded metal arc welding electrode depositing high strength
bainitic weld metal, comprising the steps of providing a basic low hydrogen iron
powder type coating as claimed in claim 1; mixing the powder composition with
a mixture of potassium and sodium silicates acting as a binder and forming
cakes; extruding the cakes into a core wire in an hydraulic extruder; and air
drying the core wire for about a day and subsequently over dried upto 450°C.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
It is known that all types of coated SMAW electrodes contain slag formers, gas
formers, de-oxidizers, de-nitriders, alloying elements and other materials like
mineral silicates and iron powder. Basic coated low hydrogen electrodes
conforming to the American Welding Society standard AWS 5.1 E7018-1 and low
alloy high strength steels for example, E 9018M and E11018 M typically have
about 30 weight % iron powder in the electrode coating and the balance may
comprise materials like limestone and fluorspar and titania and other materials.

The present inventors recognized that coating thickness may be increased for
example, from 6.8 mm for a 4.0 mm core wire to 8.0 mm and higher, and the
iron powder content can be simultaneously increased from 30 % to upto a value
of 60%. However value is limited by the fact that the usability of the electrode
may be limited to down-hand or flat welding position . but without any
compromise on mechanical properties for example, tensile and yield strength,
elongation and subzero notch toughness upto -51*C.
It is well known that steel exhibits various microstructures depending upon
composition and cooling rate. These microstructures in turn "determine" the
strength and toughness of steel. Ordinary bainite consists of a mixture of plates
of ferrite and cementite particles. The cementite usually precipitates from carbon
enriched austenite but silicon additions can suppress this reaction. The austenite
then becomes stabilized by the carbon and the resulting microstructure can be
tough and strong. This is exploited in the present invention.
Accordingly, the invention provides a formulation for basic coated low hydrogen
iron powder type electrode for use in welding of high strength steels and/or
welding of thick walled pressure vessels. This novel formulation has a coating
(D) to core wire dia (d) ratio D/d more than 1.7 and upto 60% iron powder in
the coating, the balance materials in the coating comprising slag formers, gas
formers, de-oxidisers, de-nitriders,, alloying and microalloying elements.
The following table illustrates the technical effect of the present invention, when
implemented on a plate of nominal thickness 100 mm groove Single V included
angle 60 degrees.


The project savings in arc time will be even more for higher diameter electrodes
for example 5 mm. For experimental purpose, a development batch was
extruded with the following coating on a 5 mm mild steel core wire. The coating
thicknes is 10.1 mm (D/d = 2.0 or higher)



This was mixed with mixture of potassium and sodium silicates as a binder,
made into a cake and extruded into the core wire in an hydraulic extruder.
It was then air dried for a day and then subsequently oven dried upto 450*C.
When tested as per the provisions of AWS 5.1 specification, excellent results
were obtained, as tabulated below: Chemical analysis of all weld metal.


After the plate was tested and accepted by radiographic testing and after SR
treatment at 620± 10deg C for 300 minutes, mechanical properties were tested
and reported as follows:


WE CLAIM :
1. A composition of basic low hydrogen iron powder-type coating depositing
high strength bainitic weld metal with a higher deposition rate consisting
of: .

SL MATERIAL WT% RANGE PREFERRED
RANGE
1 CALCITE POWDER 7.5-15 12.5
2 FLOURSPAR 7.5-12.5 10.0
3 RUTILE/TITANIA 2.5-7.5 7.5
4 IRON POWDER 100 MESH 45-60 50.0
5 IRON POWDER 60MESH 2.5-7.5 5.0
6 FEEROSILICON 25% 2.5-7.5 . 6.0
7 FEEROMANGANESE/ELECTROLYTIC
MANGANESE 3.5-6.5 .5.0
8 TOTAL OF BALANCING ALLOY
POWDERS(CHROMIUM
MOLYBDENUM &
NICKEL,VANADIUM & GRAPHITE 1-2 2.5
9 SLAG FORMERS, GAS
FORMERS,EXTRUSION AIDS 0.5-1.5 1.5
TOTAL 100

2. A high deposition-rate low hydrogen type shielded metal arc welding
electrode depositing high strength bainitic weld metal having coating
thickness (D/d) more or equal to 2 and containing major quantity of iron
powder in the electrode, substantially of the basic coated low hydrogen
type with UTS in excess of 690 mPa, tensile strength after SR of 300 min
at 625 deg Celcius exhibiting acceptable CVN energy value in a range of 9
to 18 when tested at minus 45 deg Celcius.
3. A process for producing a high deposition-rate low hydrogen type
shielded metal arc welding electrode depositing high strength bainitic weld
metal comprising the steps of:
providing a basic low hydrogen iron powder type coating as claimed in
claim 1;
mixing the powder composition with a mixture of potassium and sodium
silicates acting as a binder and forming cakes;
extruding the cakes into a core wire in an hydraulic extruder; and
air drying the core wire for about a day and subsequently over-dried upto
450°C.

ABSTRACT

The invention relates to A composition of basic low hydrogen iron powder-type
coating depositing high strength bainitic weld metal with a higher deposition rate
consisting of:

SL MATERIAL WT% RANGE PREFERRED
RANGE
1 CALCITE POWDER 7.5-15 12.5
2 FLOURSPAR 7.5-12.5 10.0
3 RUTILE/TITANIA 2.5-7.5 7.5
4 IRON POWDER 100 MESH 45-60 50.0
5 IRON POWDER 60MESH 2.5-7.5 5.0
6 FEEROSILICON 25% 2.5-7.5 6.0
7 FEEROMANGANESE/ELECTROLYTIC
MANGANESE 3.5-6.5 5.0
8 TOTAL OF BALANCING ALLOY
POWDERS(CHROMIUM
MOLYBDENUM &
NICKEL,VANADIUM & GRAPHITE 1-2 2.5
9 SLAG FORMERS, GAS
FORMERS,EXTRUSION AIDS 0.5-1.5 1.5
TOTAL 100