FIELD OF THE INVENTION:
This invention relates to a coating formulation for a SMAW welding electrode.
This invention further relates to a coating formulation for a SMAW welding electrode to weld armour steels used in defence sector especially of high strength low alloy type, with manganese and other alloying elements.
BACKGROUND OF THE INVENTION:
Shielded metal arc welding process plays an important role in the welding of many thick walled steels in defence sectors. In modern times the defence sector is making use of steels of higher strength. Therefore, there has been a demand from the user industry for SMAW electrode with better operator appeal and good RT toughness. AWS FSA-5.5 standard specifies the chemical requirement of the weld metal deposited by this electrode. TherefNo such electrode coating is formulated which produce high toughness weld metals while having high carbon could content of 0.3 weight percentage without heat treatment.
OBJECTS OF THE INVENTION:
It is therefore an object of this invention to propose a coating formulation for a SMAW welding electrode.
It is a further object of this invention to propose a coating formulation for a SMAW welding electrode, which can deposit upper bainite microstructure having toughness more than 15 Joules at -510 C.
Another object of this invention is to propose a coating formulation for a SMAW welding electrode, which can produce weld metals having strength levels meeting SFA-5.5 requirement for 12018G electrode type. i.e. 800 MPa (UTS).
A further object of this invention is to propose a coating formulation for a SMAW welding electrode which produces high toughness weld metals while having high carbon could content of 0.3 weight percentage without heat treatment.
Yet another object of this invention is to propose a coating formulation for a SMAW welding electrode which is simple and cost effective.

These and other objects and advantages of the invention will be apparent from the ensuing description.
SUMMARY OF THIS INVENTION:
This invention relates to a coating formulation for a SMAW welding electrode, in particular, a coating formulation for a SMAW welding electrode to weld armour steels used in defence sector especially of high strength low alloy type, with manganese and other alloying elements. The electrode coating is designed and formulated in such a way that it produces upper bainite in the microstructure in the weld metal deposited by it, produces tougher weld material when tested and produces weld metal having strength levels meeting SFA 5.5 requirement for Electrode 12018G.
DETAILED DESCRIPTION OF THE INVENTION:
In accordance with this invention is provided a coating formulation for a SMAW welding electrode, in particular, a coating formulation for a SMAW welding electrode to weld armour steels used in defence sector especially of high strength low alloy type, with manganese and other alloying elements.
In accordance with this invention is further provided a process for the preparation of a coating formulation for a SMAW welding electrode.
The chemistry of the armour steel plate is obtained by spectroscopy. The basic composition is shown in Table 1 below:

The electrode coating is designed and formulated to produce the above chemistry in the weld metal. Hence proper coating ingredients are selected and mixed homogeneously in a dry mixer for sufficient time and are used to make coating over the carbon steel core wire of diameter 4 mm and length 450 mm.

Chemistry of the core wire is mentioned in Table 2 below, which is used for stick electrode.

The coated electrodes are made by extrusion process which consists of the steps of wet mixing, cake making, extruding and conveying. The final electrodes are used for welding of the armour steel (parent plate).
The electrode coating is made by choosing ingredients having different functions and different properties.
The coating According to the invention comprises
Gas formers 20%
Extrusion aids 10%
Slag formers 20%
Alloying elements 5% and
Extrusion aids.
The alloying compounds used in the coating according to the invention are as follows:
Ferro alloys including ferromanganese powders (high carbon, low carbon, and extra low carbon), ferrochrome, ferrosilicon, ferrotitanium, ferrosilicomanganese are also used as welding fluxes and electrode raw materials.
Other raw materials also include large amounts of acid grade fluorspar, metal powders including iron powder, copper powder, nickel powder, chromium powder, manganese powder, different grades of graphite and titanium dioxide.
The gas formers are gas forming components which are organic matters which form gas layer, thus isolating the welding zone from the ambient air. The gas forming compounds are selected from materials such as starch, wood pulp, cellulose, wood flour, limestone etc.

The slag forming components are china clay, feldspar, manganese and titanium ores etc. These components produce slag which by covering the molten metal prevents it from coming into contact with the ambient air, and also ensures gradual cooling of molten metal. The merging of welding metal with basic metal in this case, is considerably smooth. The slag forming components may be for example, rutile titania, asbestos, alumina, silica flour, iron oxide, fluorspar etc.
Extrusion aids/agents are those compounds which help in easy
extruding/slipping of coating during manufacture of electrodes. The extrusion aids are for example., clays such as bentonite, china clay, glycerine, talc, mica, sodium alginate, gums etc.
The binders are selected from rutile, ilmenite potassium silicate, sodium silicates and minerals like quartz, calcite, mica.
The coating with above ingredients are used to make covering over carbon steel core wire. The carbon steel core wire used here is 4.00 mm in diameter and 450 mm in length.
In accordance with an embodiment of the invention the following metals/compounds are used in the proportions provided hereinbelow, for making the coating:
Gas forming agents
Calcium carbonate: 16 to 31 %
Slag forming agents
Flourspar: 15 to 30 % Titanium dioxide: 0 to 5 % Potassium titanate: 0 to 5 % Feldspar: 0 to 5 %
Alloying elements
Iron powder: 20 to 42 % Ferrosilicon : 5 to 10 % Ferromanganese : 3 to 7 % Ferrochromium: 2 to 5 % Ferrotitanium: 0 to 4 %

Nickel: 0 to 5% Chromium: 0 to 4%
Binders
Sodium silicate : 0 to 5 % Potassium silicate : 5 to 10 %
Extrusion aids
China clay: 2 to 3%
Mica: 0 to 5 %
Sodium alginate: 3 to 10%
The process involves the steps of weighing the gas forming agents, slag forming agents, alloying elements and extrusion aids and mixing the same to form a flux powder,
wet mixing the flux powder with binders and subjecting the mixture to pressure of 40 to 50 bar to form a cake extrusion for final electrode covering, followed by extrusion of the cake over a core wire to form the electrode and storing the final extruded electrode for drying in closed atmosphere maintained at temperature of 20 to 50°C.
The main parameters and conditions to be taken care of during weighing the fluxes, powders and compounds for electrode manufacturing are maintenance of temperature (20 to 50°C) and humidity (35 to 45%) of the laboratory/room.
During welding of the armour steel plate with the developed electrodes, preheating is done between the temperature range of 2500 C to 3000 C, while maintaining an inter pass temperature of 3000C.
During welding 8 layers of weld were made with 2 beads in each layer. The welding was done with weaving method of bead laying technique.
The testing of the weld metal is done without any PWHT.
The parent plate is edge prepared as per welding electrode qualification code SFA5.5. Then the weld metal is tested for its chemistry and mechanical properties. The chemistry, mechanical strength and toughness is reported below.
The chemical composition obtained in the weld in plate weldment.

WE CLAIM:
1. A coating formulation for a SMAW welding electrode for producing weld
metal with following chemical composition:

said weld metal having strength levels

2. A preheat temperature range of (2500 C-3000 C) and inter pass temperature of 3000C during welding will assure the above mechanical properties.
3. The coating formulation for a SMAW welding electrode as claimed in Claim 1, prepared from alloying elements, gas forming agents, slag forming agents, binders and extrusion aids.
4. The coating formulation for a SMAW welding electrode as claimed in Claim 2, wherein said alloying compounds are selected from ferro alloys including ferromanganese powders (high carbon, low carbon, extra low carbon), ferrochrome, ferrosilicon, ferrotitanium, ferrosilicomanganese, acid grade fluorspar, metal powders including iron powder, copper powder, nickel powder, chromium powder, manganese powder, different grades of graphite and titanium dioxide.
5. The coating formulation for a SMAW welding electrode as claimed in Claim 2, wherein said slag forming components are selected fromchina clay, feldspar, manganese and titanium ores such as rutile titania, asbestos, alumina, silica flour, iron oxide, fluorspar etc.

6. The coating formulation for a SMAW welding electrode as claimed in Claim 2, wherein said gas formers are selected from materials such as starch, wood pulp, cellulose, wood flour, limestone etc.
7. The coating formulation for a SMAW welding electrode as claimed in Claim 1, wherein said extrusion aids/agents are those compounds which help in easy extruding/slipping of coating during manufacture of electrodes. The extrusion aids are for example., clays such as bentonite, china clay, glycerine, talc, mica, sodium alginate, gums etc.
8. The coating formulation for a SMAW welding electrode as claimed in Claim 1, wherein said binders are selected from rutile, ilmenite potassium silicate, sodium silicate and minerals like quartz, calcite, mica.
9. The coating formulation for a SMAW welding electrode as claimed in Claim 1, wherein said core wire is a carbon steel core wire.
10. The coating formulation for a SMAW welding electrode as claimed in
Claim 2, prepared from the the following:
Gas forming agents
Calcium carbonate: 16 to 31 %
Slag forming agents
Flourspar: 15 to 30 % Titanium dioxide: 0 to 5 % Potassium titanate: 0 to 5 % Feldspar: 0 to 5 %
Alloying elements
Iron powder: 20 to 42 % Ferrosilicon : 5 to 10 % Ferromanganese : 3 to 7 % Ferrochromium: 2 to 5 % Ferrotitanium: 0 to 4 % Nickel: 0 to 5% Chromium: 0 to 4%
Binders

Sodium silicate : 0 to 5 % Potassium silicate : 5 to 10 %
Extrusion aids
China clay: 2 to 3%
Mica: 0 to 5 %
Sodium alginate: 3 to 10%.
11. A process for the preparation of a SMAW welding electrode with the coating formulation as claimed in Claims 1 & 2, comprising the steps of weighing the gas forming agents, slag forming agents, alloying elements and extrusion aids and mixing the same to form a flux powder, wet mixing the flux powder with binders and subjecting the mixture to pressure of 40 to 50 bar to form a cake for extrusion for final electrode covering, followed by extrusion of the cake over a core wire to form the electrode and storing the final extruded electrode for drying in closed atmosphere at temperature of 20 to 50°C.
12. The process as claimed in claim 10, wherein during weighing the fluxes, powders a temperature of 20 to 50°C and humidity of 35 to 45% is maintained.
13. A SMAW welding electrode produced by the process as claimed in claim 10, for producing weld metal with the following chemical composition

said weld metal having strength levels

and having toughness value of 19 joules at -51 oC

14. A process for welding armour steel plate with the SMAW welding electrode
as claimed in claim 12, wherein welding is done with weaving method of bead
laying technique and preheating is done between the temperature range of 2500