Claims:We claim:
1. A welding consumable for joining high strength structural steels, the welding consumable comprising (in weight %):
Carbon (C) 0.07-0.12, Manganese (Mn) 1.60-2.10, Silicon (Si) 0.50-0.80 Phosphorus (P) 0.016-0.025, Sulphur (S) 0.005-0.025, Nickel (Ni) 0.006-0.15, Molybdenum (Mo) 0.40-0.60, Copper (Cu) 0.011-0.50;
Ultimate tensile strength of an all weld is 600-800 MPa and
Microstructure of elongated Ferrite and elongated Carbide or elongated Ferrite and elongated Martensite.
2. The welding consumable as claimed in claim 1, wherein the martensite is 2-5% by volume.
3. The welding consumable as claimed in claim 1, wherein the diameter is 1.2 + 0.05mm.
4. The welding consumable as claimed in claim 1, wherein the Yield strength of the all weld is 540 MPa-568MPa.
5. The welding consumable as claimed in claim 1, wherein the Elongation of the all weld is 17% -22%.
6. The welding consumable as claimed in claim 1, wherein the impact of all weld @ -300C (J) is 27-121.
7. The welding consumable as claimed in claim 1, wherein the welding consumable is copper coated.
8. A method of making welding consumable for joining high strength structural steels, the method comprising:
dry drawing a wire rod from a first diameter to a second diameter, the wire rod comprising (in weight %) of Carbon (C) 0.07-0.12, Manganese (Mn) 1.60-2.10, Silicon (Si) 0.50-0.80 Phosphorus (P) 0.016-0.025 max, sulphur (S) 0.005-0.025, nickel (Ni) 0.006-0.15, molybdenum (Mo) 0.40-0.60, copper (Cu) 0.011-0.50;
annealing the wire rod at temperature 550-750 deg. C for 2 hrs-6 hrs at second wire diameter; and
wet drawing the wire rod, from second diameter to third diameter.
9. The method as claimed in claim 8, wherein the first diameter is 5.5mm (+0.12 mm, -0.03 mm).
10. The method as claimed in claim 8, wherein the second diameter is 2.13 + 0.05 mm.
11. The method as claimed in claim 8, wherein the third diameter is 1.2 + 0.05 mm.
12. The method as claimed in claim 8, wherein the hot rolled wire rod is mechanically descaled before dry drawing.
13. The method as claimed in claim 8, wherein the hot rolled wire rod is mechanically descaled after wet drawing to remove oxide scales.
14. The method as claimed in claim 8, wherein the wire rod is hot rolled.
, Description:TECHNICAL FIELD

Present disclosure relates in general to a field of welding. More particularly, but not exclusively, the present disclosure relates to welding consumable used in Gas metal arc welding (GMAW) of high strength structural steels.

BACKGROUND OF THE DISCLOSURE

Increasing focus on the use of high tensile steels and requirement of superior mechanical performance in terms of all weld tensile properties. The such tensile properties are ultimate tensile strength, yield strength, Elongation, and impact strength. These properties have led to increase in use of high tensile Gas metal arc welding consumables in various industries e.g. Railways, L&E etc.

At present AWS ER90S-G grade welding consumable (Min. UTS 620 MPa) is widely used in addition to most commonly used AWS ER70S-6 (Min. UTS 480 MPa).

Producing such welding consumables is a big challenge as drawing of high tensile wire rod is difficult considering high tensile properties with inherent microstructure containing hard phases of martensite. Precisely during wet drawing from 2.13±0.05 mm to 1.2±0.05 mm dia. wire breakeages are encountered as tensile strength shoots up during intermediate dry drawing operation. In the dry drawing operation wire diameter is reduced from 5.5 mm to 2.13 mm.

OBJECTS

An object of the invention is to make a welding consumable for joining high strength structural steels with high physical properties.
Another object of the invention is to make the weld consumable with appropriate phases so that the wet drawing is convenient.
Another object of the invention is to design a process to make the welding consumable for joining high strength structural steel process in which breakages of wire rod is controllable.
STATEMENT OF DISCLOSURE
The present invention provides a welding consumable for joining high strength structural steels. The welding consumable comprising (in weight %):
Carbon (C) 0.07-0.12, Manganese (Mn) 1.60-2.10, Silicon (Si) 0.50-0.80 Phosphorus (P) 0.016-0.025, Sulphur (S) 0.005-0.025, Nickel (Ni) 0.006-0.15, Molybdenum (Mo) 0.40-0.60, Copper (Cu) 0.011-0.50;
Ultimate tensile strength of an all weld is 600-800 MPa and
Microstructure of elongated Ferrite and elongated Carbide or elongated Ferrite and elongated Martensite.
In an embodiment, the martensite is 2-5% by volume.
In another embodiment, the diameter is 1.2 + 0.05mm.
In another embodiment Yield strength of the all weld is 540 MPa-568MPa.
In yet another embodiment the Elongation of the all weld is 17% -22%.
In yet another embodiment the impact of all weld @ -300C (J) is 27-121.
In yet another embodiment the welding consumable is copper coated.
In another embodiment the present invention describes a method of making welding consumable for joining high strength structural steels, the method comprising:
dry drawing a wire rod from a first diameter to a second diameter, the wire rod comprising (in weight %) of Carbon (C) 0.07-0.12, Manganese (Mn) 1.60-2.10, Silicon (Si) 0.50-0.80 Phosphorus (P) 0.016-0.025 max, sulphur (S) 0.005-0.025, nickel (Ni) 0.006-0.15, molybdenum (Mo) 0.40-0.60, copper (Cu) 0.011-0.50;
annealing the wire rod at temperature 550-750 deg. C for 2 hrs-6 hrs at second wire diameter; and
wet drawing the wire rod, from second diameter to third diameter.
The microstructure of Ferrite and Carbide or Ferrite and Martensite is formed after annealing. The said microstructure are relatively softer phases and thereby they help in easy drawability of the wire rods during wet drawing.
In an embodiment, the first diameter is 5.5mm (+0.12 mm, -0.03 mm).
In another embodiment the second diameter is 2.13 + 0.05 mm.
In another embodiment the third diameter is 1.2 + 0.05 mm.
In another embodiment the hot rolled wire rod is mechanically descaled before dry drawing.
In another embodiment the hot rolled wire rod is mechanically descaled after wet drawing to remove oxide scales.
In another embodiment the wire rod is hot rolled.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The novel features and characteristics of the disclosure are set forth in the appended description. The disclosure itself, however, as well as a preferred mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:
FIG. 1 illustrates a flow diagram of a method for making the welding consumable in accordance with an embodiment of the invention.
FIGs. 2a-2f illustrates microstructures of a wire rod post annealing at various temperature and residence time in accordance with an embodiment of the invention.
FIG. 3 illustrates mechanical property comparison of the all weld consumable in accordance with an embodiment of the invention and mechanical properties of benchmarked weld consumable.
FIGs. 4a & 4b illustrates tensile strength and hardness variation before and after annealing on the welding consumable in accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
In accordance with an embodiment of the invention, a method (100) for making a welding consumable for joining high tensile structural steels is described. The method (100) is being shown in FIG. 1. The method (100) comprises step (101) for dry drawing a wire rod from a first dia. to a second dia. In dry drawing, the wire rod is passed through several dies arranged in a series to reduce the diameter. The wire rod is passed through container comprising lubricant. The wire rod is descaled before dry drawing to make it free from scales.
The wire rod in an embodiment is hot rolled.
The lubricant in such container may be Sodium stearate or calcium stearate for smooth manoeuvring.
The composition of the wire rod is Carbon (C) 0.07-0.12, Manganese (Mn) 1.60-2.10, Silicon (Si) 0.50-0.80 Phosphorus (P) 0.016-0.025, Sulphur (S) 0.005-0.025, Nickel (Ni) 0.006-0.15, Molybdenum (Mo) 0.40-0.60, Copper (Cu) 0.011-0.50 (all in wt%).
During dry drawing, the first diameter is 5.5mm (+0.12, -0.03) and second diameter is 2.13 + 0.05 mm.
Post dry drawing, the wire rod is annealed at temperature 550-750 deg. C for 2 hrs-6 hrs. at second wire diameter (step 102). The annealing is performed at a furnace capable of maintaining such temperature as mentioned. The annealing is performed by maintaining the requisite temperature and feeding the furnace with the wire rod. Alternatively, the annealing can be performed by first feeding the wire rod and raising the temperature subsequently. During the annealing industrial Argon (100% volume) is purged to provide inert atmosphere to restrict any oxidation.
At step (103) wet drawing of the wire rod from second diameter to a third diameter is performed. In the wet drawing operation, wire rod is completely immersed in lubrication tanks and wire diameter is reduced further to achieve the desired size. The lubricant in such container may be Sodium stearate or calcium stearate smooth manoeuvring.
In an embodiment of the invention, the second diameter is 2.13 + 0.05 mm. and the third diameter is 1.2 + 0.05 mm. Post wet drying the obtained is the weld consumable with 1.2 + 0.05 mm.
The weld consumable is mechanically descaled to remove oxide scales. The weld consumable can be further coated with copper depending upon the requirement.
The all weld UTS of the welding consumable obtained is 600-800 MPa.
It is to be appreciated that the all weld is obtained by depositing the weld consumable over to calculate mechanical properties. The welding is performed under influence of shielding gas of Ar + CO2 mixture (82% Ar+ 18% CO2).

The microstructure of the welding consumable is Ferrite & Carbide when annealed at 550-650 0C as shown in FIGs 2d-2f. Also, when the annealing temperature is 650-750 0C, the microstructure is Ferrite & Martensite as shown in FIGs 2a-2c. The martensite is 2-5% in volume.
Post wet drawing the microstructures of welding consumable transforms into elongation. The ferrite and carbide microstructure transforms into elongated ferrite and elongated carbide and ferrite and martensite microstructure transforms into elongated ferrite and elongated martensite.
Conventionally in the wire rods, hard phases such as martensite used to get generated that makes the wire rod less ductile and breakages happened during wet drawing. The annealing done at step 102 tends to remove the hard phases. In other words, hard phases are being replaced with softer phase or reduce such phase as minimal as possible.

The all-weld properties of the welding consumable are the following
Yield strength is 540-568 Mpa.
Elongation is 17-22%
Impact @ -300C (J) is 27-121.
The obtained welding consumable can be efficiently used in wagons of the Railways. Also the usability of the welding consumable can be found in high tensile structural steels, Pressure vessel forging and valves (High temperature).
EXPERIMENTAL ANALYSIS:
Two wire rods WR1 & WR2 are taken with following composition (in weight %):
Carbon (C) 0.08, Manganese (Mn)- 1.71, Silicon (Si)- 0.53, Phosphorus (P)- 0.016, Sulphur (S)- 0.005, Nickel (Ni)- 0.006, Molybdenum (Mo)- 0.41, Copper (Cu)-0.011. Both WR1 and WR2 are descaled then dry drawn from 5.5 mm (+0.12, -0.03) mm to 2.13 + 0.05 mm.
Post dry drawing, the samples of WR1 is annealed at 550 deg at 2 hrs, 600 deg at 2 hrs and 650 deg at 2 hrs. Samples of WR2 is annealed at 700 deg at 2 hrs, 750 deg at 2 hrs and 750 deg at 6 hrs. Post annealing, both WR1 and WR2 are wet drawn from 2.13 + 0.05 mm to 1.2 + 0.05 mm. The annealed wire is descaled again and copper coated.
The SEM of microstructure obtained for WR2 is shown in FIGs. 2a – 2c. It could be witnessed from figures that the microstructres are Ferrite and Martensite. The martensite is 2-5% by volume.
The SEM of microstructure obtained for WR1 is shown in FIGs. 2d – 2f. It could be witnessed from figures the microstructres are Ferrite and carbide.
The microstructures of ferrite + martensite and ferrite + carbide are relatively softer phases and thereby they help in easy drawability of the wire rods as opposed to the harder phases obtained conventionally.
Ultimate tensile strength of all weld for WR1 & WR2 obtained is 644 MPa, Yield strength for WR1 & WR2 is 569 MPa, total elongation for WR1 and WR2 is 27 and the impact at -30 0C (J) is 121.
Qualification of performance tests done are in accordance with AWS/IS/RDSO & others specifications.
Shown in FIG. 3 is the mechanical properties comparison of the all weld consumable WR1 and WR2 and benchmarked weld consumable (AWS, Wire-A, Wire-E, Wire-J and AWS A5 28). As one can witness WR1 and WR2 has qualified all weld tensile properties as per AWS requirement and properties are in line with other benchmarked products available in the market. WR1 and WR2 wire exhibited YS, UTS, Elongation and impact strength of 569 MPa, 644 MPa, 22% and 121 J (at -30 deg. C) respectively.
Tensile strength and hardness variation before and after annealing can be seen in FIGs 4a & 4b. Here HT refers to Heat Treatment (or Annealing for instant case) and no. of hrs. In both the figures it can be clearly witnessed that UTS and Hardness are being lowered which signifies that the wire drawability improves.
Equivalents

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be understood by those within the art that, in general, terms used herein, are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding the description may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated in the description.