Welding electrode with functional coating

Abstract

The disclosed technology generally relates to welding electrodes, and more particularly to consumable welding electrodes with functional coatings. In one aspect, a welding electrode includes a core wire having a base metal composition and two or more coatings covering at least a portion of the core wire. The two or more coatings comprise a conductive coating in addition to or different from copper (Cu), the conductive coating further comprising one or more conductive elements or compounds. The two or more coatings additionally include an additional functional coating, the additional functional coating includes one or more additional elements or compounds adapted to reduce the friction of the welding electrode, stabilize the arc formed by the welding electrode, alter the microstructure of the weld metal formed by the welding electrode, and / or alter the surface tension of the droplets formed by the welding electrode. In another aspect, a method of manufacturing a welding electrode includes providing a cored wire having a base metal composition and forming two or more coating layers.

Description

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63,374,940, entitled “WELDING ELECTRODE WITH FUNCTIONAL COATINGS,” filed on September 8, 2022, and is a continuation-in-part of U.S. Patent Application No. 17 / 930,993, entitled “WELDING ELECTRODE WITH FUNCTIONAL COATINGS,” filed on September 9, 2022, which claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 261,462, entitled “WELDING ELECTRODE WITH FUNCTIONAL COATINGS,” filed on September 21, 2021, the contents of which are incorporated herein by reference in their entirety. background Technical Field

[0003] The disclosed technology relates generally to welding electrodes, and more particularly to consumable welding electrodes having a functional coating on a core wire. Background Art

[0004] Various welding techniques utilize consumable welding electrodes that serve as a source of weld metal. For example, in metal arc welding, an arc is created when a voltage is applied between the consumable welding electrode (serving as one electrode that is advanced toward the workpiece) and the workpiece (serving as the other electrode). The arc melts the tip of the metal wire, thereby producing a droplet of molten metal electrode that is deposited onto the workpiece to form weld metal or a weld bead.

[0005] The technical and economic requirements for welding technology continue to grow in complexity, where the need for greater manufacturing flexibility and the need for higher mechanical properties coexist. In addition, optimization of one performance parameter of the weld metal may compromise another performance parameter. Some welding technologies aim to address these competing requirements by improving consumables (e.g., by improving the physical design and / or composition of the consumable electrode). The disclosed technology addresses the need for an improved consumable welding electrode with a functional coating. Summary of the invention

[0006] In a first aspect, a welding electrode comprises a core wire having a base metal composition and two or more coatings covering at least a portion of the core wire. The two or more coatings comprise a conductive coating that, in addition to or other than copper (Cu), comprises one or more conductive elements or compounds. The two or more coatings further comprise an additional functional coating. The additional functional coating comprises one or more additional elements or compounds adapted to reduce friction of the welding electrode, stabilize an arc formed by the welding electrode, change a microstructure of a weld metal formed by the welding electrode, and / or change a surface tension of a molten droplet formed by the welding electrode.

[0007] In a second aspect, a method of making a welding electrode includes providing a core wire having a base metal composition and forming two or more coating layers of the first aspect.

[0008] In a third aspect, a welding electrode comprises a solid core welding wire having a base metal composition based on iron (Fe) and a conductive coating formed on the solid core welding wire. The conductive coating comprises one or more conductive elements or compounds in addition to or other than copper (Cu). The welding electrode further comprises an additional functional coating formed on the conductive coating and comprising one or both of elemental antimony (Sb) and one or more Sb oxides.

[0009] In a fourth aspect, a welding electrode comprises a solid core wire having a base metal composition based on iron (Fe) and two or more coatings covering at least a portion of the core wire. The two or more coatings comprise a conductive coating formed on the solid core wire, the conductive coating comprising one or more conductive elements or compounds in addition to or other than copper (Cu). The two or more coatings further comprise an additional functional coating having a porous structure formed on the conductive coating and comprising antimony (Sb). BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 An arc welding system that may be used in conjunction with a consumable electrode according to embodiments disclosed herein is shown.

[0011] Figure 2 A welding process using a consumable electrode according to embodiments disclosed herein is shown.

[0012] Figure 3 A covered welding consumable electrode according to an embodiment is shown.

[0013] Figure 4A A covered welding consumable electrode including two or more coatings is shown according to an embodiment.

[0014] Figure 4B A coated welding consumable electrode including three or more coating layers is shown according to an embodiment.

[0015] Figure 5 A method of manufacturing a coated welding consumable electrode according to an embodiment is shown.

[0016] Fig. 6A The weld metal formed using a conventional consumable electrode is shown.

[0017] Figure 6B Weld metal formed using a consumable electrode with a functional coating according to an embodiment is shown. DETAILED DESCRIPTION

[0018] Some welding electrodes have two main components: a core wire or rod and a covering or coating. The core includes the base alloying elements of the weld metal. The coating may include various materials that provide various functions. For example, the coating may be used to provide, among other things: protection of the weld metal, stabilization of the arc, various physical properties of the alloying elements of the weld metal, slag for fluxing, reduction of gas pockets in the weld metal, increased conductivity or insulation, protection from the environment, lubrication of the feed, and aesthetics.

[0019] Some conventional solid welding wires are coated with a coating containing copper on the surface of the wire to enhance the electrical conductivity and corrosion resistance of the wire and welding nozzle, as well as to reduce friction with the feed hose or welding nozzle. However, during the welding process, some copper may undesirably melt into the weld. Copper contamination of the weld may cause "copper cracking" or reduce the mechanical properties of the weld joint, especially impact toughness and elongation at low temperatures. Copper also oxidizes into copper particles and escapes into the air, which is harmful to human health when inhaled. The production of copper-coated welding wire may also generate waste acid and environmental pollution. Therefore, there is a need for a coated welding wire that at least reduces or eliminates copper in the coating from the welding electrode while maintaining its functional benefits.

[0020] To address these and other needs, embodiments disclosed herein relate to a welding electrode comprising a core wire having a base metal composition and two or more coatings covering at least a portion of the core wire. The two or more coatings include a conductive coating that includes one or more conductive elements or compounds in addition to or other than copper (Cu). The two or more coatings further include an additional functional coating that includes one or more additional elements or compounds adapted to reduce the friction of the welding electrode (friction modifier), stabilize the arc formed by the welding electrode (arc stabilizer), change the microstructure of the weld metal formed by the welding electrode (microstructure modifier), and / or change the surface tension of the molten droplet formed by the welding electrode (molten weld metal surface tension modifier).

[0021] Arc welding process for welding with electrodes having functional coatings

[0022] Arc welding is one of several fusion processes used to join metals. Intense heat is applied to melt the metal at the joint between two parts and cause it to intermix, either directly or more usually with an intermediate molten filler metal.

[0023] An arc welding system 100 that may be used in conjunction with the embodiments disclosed herein is shown in FIG. Figure 1A power supply system 110, including an AC or DC power supply and a controller, is connected to the workpiece 102 to be welded via a work cable 114 and to an electrode holder 118 that makes electrical contact with the welding electrode 106 via a "hot" cable. When the energized circuit contacts the workpiece 102 with the electrode tip and retracts, but still in close contact, an arc is generated across the gap between the workpiece 102 and the welding electrode 106. The arc can be generated between the welding electrode 106, which can be a consumable electrode that acts as one electrode (e.g., an anode (+) in DC) and the workpiece 102, which acts as the other electrode (e.g., a cathode (-) in DC). After the arc is initiated, a plasma 108 is maintained, which contains neutral and ionized gas molecules and neutral and charged clusters or droplets of the material of the metal wire that has been vaporized by the arc. The welding electrode 106 is advanced toward the workpiece 102, and droplets of the metal wire are deposited onto the workpiece, forming a weld bead or weld metal. The arc can generate temperatures up to about 6500°F at the tip. This heat melts both the workpiece 102 and the welding electrode 106, thereby creating a pool of molten metal, sometimes referred to as a "crater." As the crater moves along the joint, it solidifies behind the electrode. Upon cooling and solidification, a metallurgical bond is created. Because the joint is a mixture of metals, the resulting weld can have mechanical properties, such as strength, comparable to or substantially the same as the metals of the parts of the workpiece 102. This is in stark contrast to non-fusion processes of joining (e.g., soldering, brazing, etc.), in which the mechanical and physical properties of the base material at the joint may not be comparable to those of the workpiece 102.

[0024] At high temperatures, metals tend to react chemically with the elements in the air - oxygen and nitrogen. When the metal in the molten pool comes into contact with air, oxides and nitrides may form, which may adversely affect the strength and toughness of the welded joint. Therefore, some arc welding processes provide some means of covering the arc and the molten pool with protective protection of gas, vapor and / or slag. This is called arc shielding. This protection reduces or minimizes the contact of the molten metal with air. Protection can also improve the weld. An example is flux, which may include a deoxidizer for the welded metal.

[0025] In welding, the arc not only provides the heat required to melt the electrode and base metal, but must also, under certain conditions, provide a means of transporting the molten metal from the tip of the electrode to the workpiece. There are several mechanisms for metal transfer. Examples include surface tension transfer, in which a droplet of molten metal contacts a pool of molten metal and is drawn into the pool by surface tension, and the jet arc, in which a droplet of molten metal is ejected from the molten metal at the tip of the electrode by an electric pinch, which propels the droplet into the pool.

[0026] When the electrode 106 is a consumable electrode as disclosed herein, the tip melts under the heat of the arc, and the molten droplets separate and are transported to the workpiece 102 through the arc column. Arc welding in which the electrode according to the embodiments described herein is melted to become part of the weld is described as metal arc welding. This is in contrast to carbon or tungsten (TIG) welding, in which no molten droplets are forced through the gap and onto the workpiece. The filler metal is melted into the joint from a separate electrode or wire. More of the heat generated by the arc is transferred to the weld pool with the consumable electrode. This produces higher thermal efficiency and a narrower heat affected zone.

[0027] Arc welding can be performed with direct current (DC) or alternating current (AC) with the electrode being positive (DCEP) or negative (DCEN). The choice of current and polarity depends on the process, the type of electrode, the arc atmosphere, and the metals being welded.

[0028] In a process using a consumable electrode, the electrode or welding wire melts to provide additional metal that fills the gap, thereby forming a weld joint that joins two metal workpieces. Welding processes using consumable electrodes include shielded metal arc welding (SMAW), gas metal arc welding (GMAW) or metal inert gas (MIG) welding, flux cored arc welding (FCAW), metal cored arc welding (MCAW) and submerged arc welding (SAW), etc. Welding processes using consumable welding electrodes can be performed in direct current electrode positive (DCEP) mode, direct current electrode negative (DCEN) mode or alternating current (AC) mode. In DCEP mode, a direct current is used, and the welding wire is connected to the positive terminal of the power supply, and the (multiple) workpieces or (multiple) plates to be welded are connected to the negative terminal, and the opposite is true when welding in DCEN mode. In AC mode, the welding wire and (multiple) workpieces or (multiple) plates switch from positive connection to negative connection in a cycle according to the frequency. The terminal used as the positive electrode can be called the anode, and the terminal used as the negative electrode can be called the cathode. Hereinafter, various consumable electrode-based welding processes that may be performed with oxide-coated welding wires according to embodiments are described.

[0029] Figure 2A gas metal arc welding (GMAW) process 200, sometimes referred to as a metal inert gas (MIG) welding process, is shown, which can be used in conjunction with the embodiments disclosed herein. The GMAW process uses a continuous solid wire electrode 106 for filler metal and an externally supplied gas (typically from a high pressure cylinder) for shielding. The electrode 106 can be mild steel or stainless steel and can be coated with a thin coating layer according to various embodiments, which can include two or more coatings, including a conductive coating and an additional functional coating adapted to reduce friction of the welding electrode (friction modifier), stabilize the arc formed by the welding electrode (arc stabilizer), change the microstructure of the weld metal formed by the welding electrode (microstructure modifier), and / or change the surface tension of the molten droplet formed by the welding electrode (molten weld metal surface tension modifier). When the arc 108 strikes between the electrode 106 and the workpiece 102, both the electrode 106 and the surface of the workpiece 102 evaporate to form a metal ball that is transferred to the surface of the workpiece 102, thereby forming a weld pool 204 including the metal of the coated electrode 106 and the metal of the workpiece 102. The welding machine can be set to DC positive polarity. A shielding gas, typically carbon dioxide or a mixture of carbon dioxide and argon, protects the molten metal from the atmosphere. The shielding gas flows through the welding gun and cable assembly and flows out of the welding gun nozzle with the welding wire to protect and shield the molten weld pool. If the molten metal is exposed to the atmosphere, it can have a very high reactivity to oxygen, nitrogen and hydrogen from the atmosphere. According to various embodiments, a welding electrode configured for various welding processes (e.g., GMAW) described above includes a core wire having a base metal composition and two or more coatings covering at least a portion of the core wire. As described herein, the two or more coatings include a conductive coating, which, in addition to copper (Cu) or different from copper, also includes one or more conductive elements or compounds. The two or more coatings additionally include an additional functional coating. The additional functional coating includes one or more additional elements or compounds adapted to reduce the friction of the welding electrode, stabilize the arc formed by the welding electrode, change the microstructure of the weld metal formed by the welding electrode and / or change the surface tension of the molten droplet formed by the welding electrode.

[0030] Figure 3A welding consumable electrode 300 is shown according to various embodiments. The electrode 300 includes a core wire 304 and a coating 308. In some embodiments, the core wire 304 may include a suitable carbon steel, such as a low carbon steel for GMAW. However, in other embodiments, the core wire 304 includes another metal or metal alloy. For example, in some embodiments, the core wire 304 may include stainless steel. The coating 308 coats the core wire 304 to provide alloying elements, as well as various additional non-alloying functions, to the resulting weld metal, as described herein. The chemical elements and compounds of the core wire 304 and the coating 308 disclosed herein can be distinguished based on whether the constituent elements are incorporated as part of an alloy of the weld metal. Hereinafter, elements that are substantially incorporated into the resulting weld metal may be referred to as alloying elements, while elements that are substantially not incorporated into the resulting weld metal to perform other functions (such as slag or gas formation or arc stabilization) may be referred to as non-alloying elements.

[0031] Figure 4A and 4B 4 and 400B are respectively shown as consumable electrodes for coated welding according to some other embodiments. The electrodes 400A and 400B include a core wire 304 and a coating 308, and in addition to the electrodes 400A and 400B including multiple coatings, the electrodes 400A and 400B are connected to the core wire 304 and the coating 308. Figure 3 300A is configured in a similar manner as shown in . As an example, electrode 400A includes two coatings 308, including a first coating 308A and a second coating 308B. Electrode 400B includes multiple coatings 308, including a first coating 308A, a second coating 308B, and a third coating 308C. In addition, although not shown, the multiple coatings according to other embodiments may include n coatings, including first to nth coatings.

[0032] As described above, the weld metal may include the solidified metal of the workpiece and the metal of the consumable electrode. Because the amount of dilution or concentration of elements in the weld metal due to incorporation of the molten workpiece can vary significantly, unless otherwise indicated, the weight percentages of the various elements and compounds in the weld metal as disclosed herein refer to those of the undiluted weld metal that would be obtained if no dilution or concentration had occurred from the workpiece.

[0033] Still reference Figure 3 and 4A-4B, in some embodiments, the core wire 304 includes a carbon steel composition, for example, a low carbon steel composition. In some embodiments, the carbon steel composition according to various embodiments contains Fe and one or more of C, Cr, Ni, Mo, V, Cu, Mn and Si at a concentration greater than the impurity level. In some embodiments, the core wire 304 includes a low alloy steel composition, including an alloying element content of about 1.5% to 5% by weight. There may be additional elements that may be present at an impurity level. As described herein, the impurity level refers to the weight percentage of an element that is not intentionally introduced but still exists, which may generally be less than 0.05%. Impurities that are not intentionally added but still exist in the core wire 304 include S, P, Al, Cu, N, Cr, Ni, Mo, V, Nb and Ti. The balance of the weight of the core wire 304 may be Fe. In some embodiments, the core wire 304 is formed of a low carbon steel composition known in the art according to a numbering system developed by the American Welding Society (AWS). For example, in some embodiments, the core wire 304 is formed of AWS A5.18 mild steel, AWS A5.28 mild steel, AWS or D1.5 mild steel.

[0034] However, in other embodiments, the core welding wire 304 includes a composition different from the carbon steel composition. For example, in some embodiments, the core welding wire 304 includes a stainless steel composition. In these embodiments, the stainless steel composition according to various embodiments includes Fe, at least 11 wt.% Cr, and one or more of C and Ni at a concentration greater than the impurity level. In some embodiments, the core welding wire 304 includes at least 11 wt.% Cr, or includes between 8 wt.% and 30 wt.% Cr. In some embodiments, the core welding wire 304 is formed of a stainless steel alloy composition known in the art according to a three-digit system developed by the International Society of Automatic Machinery Engineers (SAE International) for classifying stainless steel grades (including 100, 200, 300, 400, 500, 600, 900 series, etc.). For example, in some embodiments, the core welding wire 304 is formed of 308 steel, 309 steel, 316 steel, or 410 steel.

[0035] Still refer to Figure 4A-4B The coating 308 includes a conductive coating and an additional functional coating, in addition to copper (Cu) or other than copper, the conductive coating also includes one or more conductive elements or compounds, and the additional functional coating includes one or more additional elements or compounds adapted to reduce friction of the welding electrode, stabilize the arc formed by the welding electrode, change the microstructure of the weld metal formed by the welding electrode, and / or change the surface tension of the molten droplet formed by the welding electrode. As described herein, the electrode 400A ( Figure 4A) of either the first and second coatings 308A, 308B or the electrode 400B ( Figure 4B ) Any of the first, second, and third coatings 308A, 308B, and 308C of the electrode 400A, 400B may be a conductive layer or an additional functional layer in any order. Therefore, although the conductive coating according to an embodiment may be referred to as the first coating 308A of the electrode 400A, 400B, which is the innermost coating of the plurality of coatings 308, it should be understood that the conductive coating may also be the second coating 308B of the electrode 400A, 400B, or the third coating 308C of the electrode 400B. Similarly, although the additional functional coating according to an embodiment may be referred to as the first coating 308A of the electrode 400A, 400B, which is the innermost coating of the plurality of coatings 308, it should be understood that the additional functional coating may also be the second coating 308B of the electrode 400A, 400B, or the third coating 308C of the electrode 400B.

[0036] Conductive coating

[0037] According to various embodiments, the first, second and third coatings 308A, 308B, 308C ( Figure 4A or 4B) is a conductive coating comprising one or more conductive elements or compounds selected from the group consisting of magnesium (Mg), aluminum (Al), zinc (Zn), tin (Sn), chromium (Cr), platinum (Pt), silver (Ag), graphite, graphene, graphene oxide and titanium (Ti).

[0038] According to various embodiments, the conductive coating is used to provide substantial conductivity to the electrodes 400A, 400B such that a substantial amount (e.g., >10%, >30%, >50%, >70%, >90%, or a value within a range defined by any of these values) of the current passing through the electrodes 400A and 400B during welding flows through the first coating 308 A. In some embodiments, the one or more conductive elements or compounds are present in an amount and form that causes the welding electrodes 400A, 400B to have a lower resistance relative to the core wire 304 without the conductive elements or compounds.

[0039] In some embodiments, the one or more conductive elements or compounds are present without Cu as part of the conductive coating or as part of any of the plurality of coatings 308. That is, in some embodiments, the one or more conductive elements or compounds may obviate the need to use Cu as part of the coating, e.g., to provide the necessary conductivity, and Cu may be omitted from the plurality of coatings 308. In some other embodiments, the one or more conductive elements or compounds are present as part of the conductive coating or as part of any of the plurality of coatings 308 in addition to Cu. That is, in some embodiments, the one or more conductive elements or compounds may supplement Cu as part of the same or a different coating, e.g., to provide the necessary conductivity.

[0040] The one or more conductive elements or compounds can greatly reduce or eliminate the need for copper as part of the coating in conventional coated electrode welding wires. Therefore, according to an embodiment, the one or more conductive elements or compounds can be present without Cu or in addition to Cu. When present in addition to Cu, the one or more conductive elements are present in an amount exceeding 50at%, 60at.%, 70at.%, 80at.%, 90at.%, or a value within a range defined by any of these values, of the combined sum of the one or more conductive elements or compounds and Cu. Therefore, the reduced Cu content can advantageously reduce the adverse effects of copper cracking in the weld.

[0041] When present, Cu is present in an amount exceeding 0.0005 wt.%, 0.0010 wt.%, 0.0020 wt.%, 0.0050 wt.%, 0.010 wt.%, 0.020 wt.%, 0.050 wt.%, 0.10 wt.%, 0.20 wt.%, 0.5 wt.%, or a value within a range bounded by any of these values, based on the weight of the welding wire.

[0042] Additional functional coating

[0043] According to various embodiments, the first, second and third coatings 308A, 308B, 308C ( Figure 4A or 4B) is an additional functional coating comprising one or more of a friction modifier, an arc stabilizer, a microstructure modifier layer, and a molten weld metal surface tension modifier, as described below.

[0044] During welding, the welding wire travels from a drum or reel, through a conduit, an inlet guide, a feed roller, into a welding gun, a liner, and out of a contact tip. As such, various frictional forces must be overcome to achieve uniform, efficient wire feeding. High levels of friction between the welding wire and the contact surfaces of the welding system may result in irregular wire feeding, vibration, burnback, and eventual birdnesting, which may greatly disrupt manufacturing. In order to reduce the friction between the welding wire and the various contact surfaces of the welding system, according to some embodiments, the additional functional coating includes a friction modifier. The friction modifier includes one or more additional elements or compounds adapted to reduce the friction of the welding electrodes 400A, 400B. According to various embodiments, the one or more additional elements or compounds adapted to reduce the friction of the welding electrodes are selected from the group consisting of graphite, metal sulfides, polytetrafluoroethylene, graphene, and graphene oxide. When the one or more additional elements or compounds include metal sulfides, the metal sulfide may include molybdenum disulfide (MoS2) or tungsten disulfide (WS2). Some metal sulfides such as MoS2 and WS2 advantageously have a layered structure that is particularly suitable as a lubricant. When present, the one or more additional elements or compounds adapted to reduce friction are present in an amount and form that causes the wire feed force for feeding the wire through the wire liner to be 30%, 40%, 50%, 60% or more lower, or a value within a range bounded by any of these values, relative to the wire feed force for feeding a core wire not adapted to reduce friction.

[0045] The conductivity of air is not sufficient to maintain a stable arc. Therefore, there is a need for a coating composition that will provide a stable plasma for current flow while reducing voltage fluctuations. At least in part to address this need, according to various embodiments, the additional functional coating includes an arc stabilizer. The arc stabilizer includes one or more additional elements or compounds adapted to stabilize the arc formed by the welding electrodes 400A, 400B. According to various embodiments, the one or more additional elements or compounds adapted to stabilize the arc are selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), cerium (Ce), barium (Ba) and radium (Ra). When present, the one or more additional elements or compounds adapted for stabilizing the arc are present in an amount and form such that one or both of the oxygen content and the nitrogen content of the weld metal formed by the welding wire are 30%, 40%, 50%, 60% or more, or a value within a range bounded by any of these values, lower relative to a weld metal formed by a core welding wire without the one or more additional elements or compounds adapted for stabilizing the arc. Advantageously, the reduction in the amount of oxygen and nitrogen absorbed in the weld results in a reduction in the formation of oxides and nitrides, which can act as crack initiation sites and reduce the impact toughness of the weld.

[0046] Various mechanical properties of the weld metal, including hardness and impact toughness, are largely determined by its microstructure, which in turn is determined in part by the chemical composition. In order to provide the desired microstructure from the steel-based composition of the cored wire, according to some embodiments, the additional functional coating includes a microstructure modifier. The microstructure modifier includes one or more additional elements or compounds adapted to change the microstructure of the weld metal formed by the welding electrodes 400A, 400B. According to various embodiments, the one or more additional elements or compounds adapted to change the microstructure are selected from the group consisting of titanium (Ti), zirconium (Zr), nickel (Ni), boron (B), molybdenum (Mo) and niobium (Nb). When present, the one or more additional elements or compounds adapted to change the microstructure of the weld metal are present in an amount and form that makes the impact toughness of the weld metal formed by the welding wire 30%, 40%, 50%, 60% or more higher relative to the weld metal formed by the cored wire without the one or more additional elements or compounds adapted to change the microstructure. When present, the one or more additional elements or compounds adapted to modify the microstructure of the weld metal are present in an amount and form such that the ductile-to-brittle transition temperature of the weld metal formed by the welding wire is at least 30%, 40%, 50%, 60% or more lower relative to the weld metal formed by a core welding wire not adapted to modify the microstructure of the one or more additional elements or compounds.

[0047] Various productivity parameters, such as the travel speed for forming the weld metal, can be determined in part by the surface tension of the molten droplet of the weld metal. In order to provide the desired molten weld metal surface tension, according to some embodiments, the additional functional coating includes a molten weld metal surface tension modifier. The molten weld metal surface tension modifier includes one or more additional elements or compounds adapted to change the surface tension of the molten droplet of the weld metal formed by the welding electrodes 400A, 400B. According to various embodiments, the one or more additional elements or compounds adapted to change the surface tension are selected from the group consisting of cadmium (Cd), mercury (Hg), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), sulfur (S), selenium (Se), tellurium (Te) and polonium (Po).

[0048] The one or more additional elements or compounds adapted to change the surface tension of the molten weld metal can change (e.g., reduce) the surface tension of a molten weld metal droplet so that the droplet separates from the electrode at a faster rate relative to a metal droplet formed by a reference electrode that is not adapted to change the surface tension of the molten weld metal. The size of the droplet can be related to the equilibrium contact angle of the droplet formed on the solidifying weld metal or workpiece, as defined by a relationship known as the Young-Dupré equation. If the solid-gas interface energy between the molten weld metal is given by γ SG The solid-liquid interface energy is represented by γ SL , and the liquid-gas interface energy (i.e., surface tension) is represented by γ LG The equilibrium contact angle θ is C From these quantities the following Young's equation is determined:

[0049] γ SG -γ SL -γ LG ×cosθ C =0

[0050] In other words, the contact angle is established by a balance of adhesion (the liquid that wants to maintain contact with the solid) and cohesion within the liquid (both internal cohesion and surface tension). An increase in adhesion between the liquid and the solid or a decrease in cohesion (surface tension) within the liquid will result in greater wettability and a smaller contact angle. Lower surface tensions may be advantageous for greater travel speeds because the molten weld metal reduces the droplet size and improves wettability of the workpiece or solidified weld metal. For example, the average droplet size formed by an electrode according to an embodiment may be reduced by 30%, 40%, 50%, 60%, or a value within a range defined by any of these values ​​for the addition of these elements. The surface tension of the droplet formed by the welding electrode is reduced by 10%, 20%, 30%, 40%, 50% or more relative to a reference droplet formed by a reference welding electrode that is identical to the welding electrode except for the presence of the surface tension modifying element under the same welding conditions. The average droplet size and surface tension can be reduced so that the travel speed for forming the weld metal using the welding electrode according to the embodiment can be 30%, 40%, 50%, 60% or more higher than the travel speed for forming the weld metal using the welding electrode without the one or more additional elements or compounds adapted to change the surface tension of the molten weld.

[0051] The inventors have discovered that the one or more additional elements or compounds adapted to modify the surface tension of the molten weld metal can synergistically and simultaneously reduce the amount of slag or residual oxide or silicate islands formed on the weld metal. Oxide islands can be difficult to remove and degrade the visual appearance of the weld metal. The relative ease of oxide or silicate island removal can be related to the equilibrium contact angle of the oxide or silicate islands formed on the weld metal, as defined by a relationship known as Young's equation. If the solid-gas interface energy is reduced from γ SG The solid-liquid interface energy is represented by γ SL , and the liquid-gas interface energy (i.e., surface tension) is represented by γ LG , then the equilibrium contact angle θc is also determined from these quantities by Young's equation defined above. That is, although the same equation applies, the interface of interest is that between the silicate islands and the underlying weld metal.

[0052] According to an embodiment, the one or more additional elements or compounds adapted to change the surface tension of the molten weld metal are present in an amount and form such that the volume of the silica islands formed on the weld metal formed by the weld wire is at least 30%, 40%, 50%, 60% or more lower relative to the volume of the silica islands formed on the weld metal formed by a core weld wire that does not have the one or more additional elements or compounds adapted to change the surface tension of the molten weld.

[0053] According to various embodiments, each of the one or more conductive elements or compounds and additional elements or compounds is present in an amount exceeding 0.0005wt.%, 0.0010wt.%, 0.0020wt.%, 0.0050wt.%, 0.010wt.%, 0.020wt.%, 0.050wt.%, 0.10wt.%, 0.20wt.%, 0.5wt.%, 1.0wt.%, 2.0wt.%, 5.0wt.%, or a value within a range defined by any of these values, based on the weight of the welding wire.

[0054] Thus, the welding wire comprises a core welding wire having an iron or steel based composition (e.g., a low carbon steel composition) including Fe and one or more of C, Mn, Si, Ni, Mo, Cr and V at a concentration greater than the impurity level, one or more conductive elements or compounds, and additional elements or compounds. The core welding wire herein refers to a solid welding wire having a substantially uniform composition.

[0055] refer to Figure 4B In some embodiments, two of the first, second and third coatings 308A, 308B and 308C are configured as conductive coatings. For example, the first and third coatings 308A and 308C may be the same or different conductive coatings, and may be interposed with the second coating 308B arranged as an additional functional coating.

[0056] Also refer to Figure 4B In some other embodiments, two of the first, second and third coatings 308A, 308B and 308C are configured as additional functional coatings. For example, the first and third coatings 308A and 308C may be the same or different additional functional coatings, and the second coating 308B arranged as a conductive coating may be inserted.

[0057] Reference Figure 3 and Figure 4A-4BAccording to various embodiments, the core wire 304 may have a diameter of 1 / 16 inch (1.6 mm), 3 / 32 inch (2.5 mm), 1 / 8 inch (3.2 mm), 5 / 32 inch (4.0 mm), 3 / 16 inch (5.0 mm), or a diameter within a range defined by any of these values, such as 3.2 mm. The core wire 304 may have a length of 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, 500 mm, or a length within a range defined by any of these values. The coating 308 may have a thickness of 1-1.5 mm, 1.5-2.0 mm, 2.0-2.5 mm, 2.5-3.0 mm, or a thickness within a range defined by any of these values, such as 1.2 mm. By way of example only, an electrode having a core wire diameter of 3.2 mm and a coating thickness of 1.2 mm may have an overall diameter of 5.6 mm; and an electrode having a core wire diameter of 4.0 mm and a coating thickness of 1.35 mm may have an overall diameter of 6.7 mm. According to various embodiments, the coating 308 may have a weight percentage based on the total weight of the electrode 300 of 10%-15%, 15%-20%, 20%-25%, 25%-30%, 30%-35%, 35%-40%, or a value within a range defined by any of these values.

[0058] In a specific embodiment, the additional functional coating 308B is formed on the conductive coating 308A. When the additional functional coating 308B includes a molten weld metal surface tension modifier, it includes one or both of elemental antimony (Sb) and one or more Sb oxides. The one or more Sb oxides may be in the form of antimony tetroxide (Sb2O4), antimony trioxide (Sb2O3), antimony pentoxide (Sb2O5), antimony trioxide (Sb6O5), antimony trioxide (Sb6O5), and antimony trioxide (Sb6O5). 13 ) and yellow antimony fluoride (Sb3O6(OH)) in the form of one or more. Substoichiometric oxides of these oxides are also possible.

[0059] The inventors have discovered that forming the additional functional coating 308B comprising Sb by electrochemical deposition techniques is particularly advantageous for various reasons described herein. The electrode structures described herein comprising a solid core wire coated with two or more functional coatings are particularly advantageous for electrodeposition because the underlying solid core wire 304 or conductive coating 308A can act as an effective electrode for the associated electrochemical reaction. This is in contrast to electrodes where the core may be discontinuous or not sufficiently conductive, such as when the core is formed from a powder (e.g., in a metal core electrode).

[0060] The inventors have further found that forming an additional functional coating 308B including Sb by electrochemical deposition can be particularly advantageous because it can provide a high degree of control over composition at both macroscopic and microscopic levels. In particular, electrodeposition allows the formation of one or both of elemental antimony (Sb) and one or more Sb oxides. In a specific example, as an example, an additional functional coating of particles including Sb and one or more Sb oxides can be deposited by constant current reduction of antimony tartrate. Using such electrodeposition techniques, a composite film including one or both of elemental antimony (Sb) and / or one or more Sb oxides can be formed. The relative amount of Sb and / or Sb oxide can be controlled so that the total composition of the resulting Sb / Sb oxide mixture can have a Sb:O ratio of 0.1, 0.2, 0.5, 1, 2, 5, 10 or a value within the range defined by any one of these values.

[0061] In some embodiments, the resulting film may be a uniform mixture of elemental Sb and Sb oxide. In some other embodiments, the resulting additional functional coating 308B may include islands, domains, grains or particles, which may include any one or more of elemental Sb and / or Sb oxide. As an example, the relative amounts of elemental Sb and Sb oxide, for example, the relative amounts of elemental Sb particles and Sb oxide particles, may be controlled by controlling the local pH at the electrode / electrolyte interface. An intermediate product of a welding electrode having a solid core wire coated with a conductive coating (e.g., a Cu coating) may serve as an electrode in these electrochemical reactions. Without being bound by any theory, although Sb is thermodynamically stable at low pH, it is beneficial to the formation of Sb2O3 at higher pH values. Therefore, by controlling the pH at the electrode / electrolyte interface, the additional functional coating may have a controlled amount of Sb particles and one or more Sb oxide particles. In addition, depending on the initial pH of the pH at the electrode / electrolyte interface, the additional functional coating 308B may be controlled to have an initial nucleation layer that is primarily or more enriched in one or the other of elemental Sb and Sb oxide. Using these and other methods, the weight ratio of elemental Sb particles to Sb oxide particles can be controlled to be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or a value within a range bounded by any of these values.

[0062] The inventors have further discovered that forming the additional functional coating 308B including Sb by electrochemical deposition can be particularly advantageous, which provides control over the morphology of the additional functional coating. In particular, the inventors have discovered that forming the coating with submicron particles can be advantageous, which can provide a high degree of control over the morphology of the resulting coating at both the macroscopic and microscopic levels. By controlling the surface conditions of the underlying conductive coating, for example, a Cu coating formed on a solid core welding wire, the nucleation density can be controlled in the electrochemical deposition of elemental Sb and Sb oxides. For example, by providing a rougher underlying surface, a higher density of nuclei can be obtained, resulting in a smaller average size of islands, domains, grains, or particles. The average size of the islands, domains, grains, or particles can be less than 1000nm, 800nm, 600nm, 400nm, 200nm, 100nm, 50nm, 20nm, 10nm, or a value within a range defined by any of these values.

[0063] The islands, domains, grains or particles may have a controlled shape and average size and size distribution, so that the resulting additional functional coating 308B has a controlled porosity. Controlled porosity may be advantageous for a variety of reasons, including physical appearance, improved adhesion to overlying coatings, and controlled exposure of underlying materials. For example, the porosity (defined as the ratio of the void volume to the total volume of the coating) may be controlled to be 0.1, 0.2, 0.3, 0.4, 0.5, or a value within a range defined by any of these values.

[0064] Additionally, in some embodiments, the additional functional coating 308B may be discontinuous, flaky, or otherwise formed to partially cover the underlying solid core wire 304 or conductive coating 308A. Partial coverage may be beneficial in certain circumstances, for example, to optimize the surface friction and travel speed of the wire. For example, when the underlying conductive coating 308A, such as a Cu coating, has a substantially lower friction, it may be desirable to partially expose the conductive coating 308A. The surface coverage (defined as the ratio of the surface area of ​​the underlying material (e.g., conductive coating 308A) covered by the additional functional coating 308B to the total surface area of ​​the underlying material) may be controlled to be 0.1, 0.2, 0.3, 0.4, 0.5, or a value within a range defined by any of these values.

[0065] The inventors have discovered that in order to improve the surface tension reducing effect of Sb while reducing the likelihood that Sb has a deleterious effect on the mechanical properties of the resulting weld metal, it may be advantageous to configure the welding wire so that a controlled amount of Sb becomes part of the weld metal. According to an embodiment, the amount of Sb in the welding electrode that is alloyed with the weld metal may be less than 60%, 50%, 40%, 30%, 20% of the total amount of Sb present in the welding wire, such as 25%-60% of the total amount of Sb present in the welding wire. The relatively small amount of Sb incorporated into the weld metal may be attributed to the various features of the additional functional coating 308B described above, including the presence of both elemental Sb and Sb oxides, which may be achieved by electrochemical deposition. For example, by controlling the ratio of elemental Sb to Sb oxides, different amounts of Sb may be volatilized. Table 1 below shows the experimental atomic % of Sb in the experimentally produced welding wire and the detected atomic % of Sb in the resulting weld metal. As shown, 0.009%-0.024% Sb in the welding wire results in 0.004%-0.010% Sb in the resulting weld metal.

[0066] Table 1

[0067]

[0068]

[0069] Method for making coated electrodes

[0070] Figure 5 5 shows a method 500 for forming two or more coatings on a cored welding wire according to an embodiment. The method 500 includes providing 510 a cored welding wire 304 ( Figure 4A , 4B ) and conditioning 520 the surface of the core wire to prepare for forming two or more coatings. The method 500 includes forming 530 a first coating 308A ( Figure 4A , 4B ), the first coating layer comprising one of a conductive coating layer (comprising one or more conductive elements or compounds other than copper (Cu) or other than copper) and an additional functional coating layer. After forming 530 the first coating layer 308A, the method 500 proceeds to post conditioning 540 the surface of the first coating layer 308A. The method 500 further comprises forming 550 a second coating layer 308B ( Figure 4A , 4B After forming 550 the second coating 308B, the method 500 proceeds to post conditioning 560 the surface of the second coating 308B.

[0071] In some embodiments, method 500 is optionally performed to form 540 a third coating 308C ( Figure 4B). In some embodiments, the third coating 308C may be a second conductive coating including one or more conductive elements or compounds other than copper (Cu) or other than copper. In some other embodiments, the third coating 308C may be a second additional functional coating different from the first functional coating.

[0072] As described above, the electrode 400A ( Figure 4A ) of either the first and second coatings 308A, 308B or the electrode 400B ( Figure 4B )'s first, second and third coatings 308A, 308B and 308C may be arranged as a conductive coating or an additional functional coating in any order.

[0073] The method 500 may be performed in a production line comprising a loading station for providing 510 a cored welding wire, a surface adjustment station for adjusting 520 the cored welding wire, a drawing station, a first coating station for forming 530 a first coating, a first post-adjustment station for post-adjusting 540 a surface of the first coating, a second coating station for forming 550 a second coating, a second post-adjustment station for post-adjusting 560 a surface of the second coating, a third coating station for forming 570 a third coating, and a third post-adjustment station for post-adjusting 580 a surface of the third coating.

[0074] Providing 510 a cored welding wire includes providing a cored welding wire 304 ( Figure 3 , 4A -4B). Conditioning 520 the surface of the cored welding wire includes cleaning the surface of the cored welding wire at a cleaning station. In an exemplary embodiment, the cleaning station uses a cleaning agent and / or a coating agent to clean the outer surface of the material.

[0075] After cleaning, the material moves to a drawing station. The drawing station includes at least one die. In an exemplary embodiment, the drawing station includes a series of dies, each of which has a successively smaller opening than the previous die. A lubricant (e.g., a powder lubricant) may be added to the dies to facilitate the passage of the cored wire through the dies and reduce wear on the dies. As the cored wire passes through the drawing station, the diameter of the material may be gradually reduced to a desired size by plastic deformation. In some embodiments, the drawing process uses a drawing soap, which may be a stearate, such as calcium stearate, sodium stearate, and the like. These soaps aid in the drawing process. After the drawing step, the cored wire may be further passed through an acid tank to further clean the introduced cored wire and to prepare for forming one or more coatings thereon. After cleaning, the desired Ca range on the wire will allow the wire to be further used for coating. The Ca content may vary from 0.0005wt% to 1wt% of the wire to form an optimized surface for further coating.

[0076] After conditioning 520 the surface of the core wire, method 500 proceeds to forming 530 the first coating 308A ( Figure 4A , 4B ), the first coating comprising one of a conductive coating (including one or more conductive elements or compounds other than copper (Cu) or other than copper) and an additional functional coating (e.g., the Sb-containing coating described herein).

[0077] In various embodiments, forming 530 the first coating includes, for example, wet coating in a welding wire plating tank including a desired coating formulation. The wet coating process can be performed via a chemical / electrochemical or mechanical / physical method. The chemical method can be a displacement reaction, a sol-gel thin film method, electroplating or chemical plating, etc. In a mechanical / physical method, a binder is used to adhere the coating to the welding wire surface.

[0078] After forming 530 the first coating 308A, the method 500 proceeds to post conditioning 540 the surface of the first coating 308A. In some examples, post conditioning 540 includes curing using, for example, inline heating. Inline heating is achieved by conduction, convection, radiation, or Joule heating, etc. The heating can be electrical / resistive heating, induction heating, heating by flame or hot air, laser heating, plasma heating, etc.

[0079] The method 500 further includes forming 550 a second coating 308B ( Figure 4A , 4B ). In various embodiments, forming 550 the second coating includes, for example, wet coating in a welding wire plating tank including a desired coating formulation. The wet coating process can be performed via chemical / electrochemical or mechanical / physical methods. The chemical method can be a displacement reaction, a sol-gel thin film method, electroplating or chemical plating, etc. In the mechanical / physical method, a binder is used to adhere the coating to the welding wire surface.

[0080] When present, method 500 includes forming additional coating(s) 308C ( Figure 4B ), the process may be similar to forming 530, 550 the first and / or second coatings 308A, 308B.

[0081] It should be understood that in some embodiments, one or both of the conductive coating and the additional functional coating contain a plurality of pores, wherein the pores are at least partially filled with a material different from the conductive coating and the additional functional coating having the pores. When present, having a porous structure can be beneficial to improve adhesion between different layers.

[0082] After forming 550 the second coating 308B, the method 500 proceeds to post-conditioning 560 the surface of the second coating 308B. In some embodiments, post-conditioning 560 includes passing through a finishing / polishing die. When the final coating comprises a metal coating such as a Cu coating, the polishing die smoothes the surface of the wire, removes excess copper, and makes the wire look uniform and shiny, among other effects. The die may be a polycrystalline diamond die or a tungsten carbide die.

[0083] Fig. 6A The weld metal formed using a conventional consumable electrode is shown. Figure 6B Weld metal formed using a consumable electrode with a functional coating according to an embodiment is shown. Fig. 6A and 6B The two consumable electrodes used to form the weld metal have the same composition except for the functional coatings. In particular, Figure 6B The weld metal shown in is formed using an electrode having a conductive coating including one or more conductive elements including copper (Cu) and an additional functional coating formed on the conductive coating and including elemental antimony (Sb) and one or more Sb oxides. Figure 4A As described, the weld metal formed using the consumable electrode according to the embodiment has a significantly reduced amount of silicate islands due to the increased contact angle between the silicate islands and the weld metal.

[0084] Further exemplary embodiments:

[0085] 1. A welding electrode, comprising:

[0086] a core welding wire having a base metal composition; and

[0087] Two or more coatings covering at least a portion of the core wire, wherein the two or more coatings comprise:

[0088] a conductive coating, in addition to or other than copper (Cu), the conductive coating comprising one or more conductive elements or compounds, and

[0089] An additional functional coating, which includes one or more additional elements or compounds adapted to reduce the friction of the welding electrode, stabilize the arc formed by the welding electrode, change the microstructure of the weld metal formed by the welding electrode and / or change the surface tension of the molten droplet formed by the welding electrode.

[0090] 2. The welding electrode of embodiment 1, wherein the one or more conductive elements or compounds are selected from the group consisting of magnesium (Mg), aluminum (Al), zinc (Zn), tin (Sn), chromium (Cr), platinum (Pt), silver (Ag), graphite, graphene, graphene oxide and titanium (Ti).

[0091] 3. The welding electrode of embodiment 1 or 2, wherein the one or more conductive elements or compounds are present in the absence of Cu.

[0092] 4. The welding electrode of any one of embodiments 1 or 2, wherein, excluding Cu, the one or more conductive elements or compounds are present in an amount exceeding 90 atomic % of the combined sum of the one or more conductive elements or compounds and Cu.

[0093] 5. A welding electrode as described in any of embodiments 1-4, wherein the one or more conductive elements or compounds are present in a certain amount and form, which makes the welding electrode have a lower resistance than a core wire without the conductive elements or compounds.

[0094] 6. A welding electrode as described in any one of embodiments 1-5, wherein the additional functional coating includes one or more additional elements or compounds adapted to reduce the friction of the welding electrode, and the one or more additional elements or compounds are selected from the group consisting of graphite, metal sulfides, polytetrafluoroethylene, graphene and graphene oxide.

[0095] 7. The welding electrode as described in embodiment 6, wherein the metal sulfide is molybdenum disulfide (MoS2) or tungsten disulfide (WS2).

[0096] 8. A welding electrode as described in any of Examples 1-7, wherein the one or more additional elements or compounds adapted for reducing friction are present in an amount and form such that a wire feed force for feeding the welding wire through a wire liner is 50% or more lower than a wire feed force for feeding a core wire that is not adapted for reducing friction.

[0097] 9. A welding electrode as described in any one of embodiments 1-8, wherein the additional functional coating includes one or more additional elements or compounds adapted to stabilize the arc formed by the welding electrode, and the one or more additional elements or compounds are selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), cerium (Ce), barium (Ba) and radium (Ra).

[0098] 10. A welding electrode as described in any of Examples 1-9, wherein the one or more additional elements or compounds adapted for stabilizing the arc are present in an amount and form such that one or both of the oxygen content and the nitrogen content of the weld metal formed by the welding wire are 50% or more lower than the weld metal formed by a core welding wire not adapted for stabilizing the arc.

[0099] 11. A welding electrode as described in any of Examples 1-10, wherein the additional functional coating includes one or more elements or compounds adapted to change the microstructure of a weld metal formed by the welding electrode, and the one or more elements or compounds are selected from the group consisting of titanium (Ti), zirconium (Zr), nickel (Ni), boron (B), molybdenum (Mo) and niobium (Nb).

[0100] 12. A welding electrode as described in any of Examples 1-11, wherein the one or more additional elements or compounds adapted to modify the microstructure are present in an amount and form such that the impact toughness of the weld metal formed by the welding wire is 50% or more higher than that of the weld metal formed by a core welding wire that is not adapted to modify the microstructure.

[0101] 13. A welding electrode as described in any of Examples 1-12, wherein the one or more additional elements or compounds adapted to modify the microstructure are present in an amount and form such that the ductile-brittle transition temperature of the weld metal formed by the welding wire is at least 50°C lower than that of the weld metal formed by the core welding wire without the one or more additional elements or compounds adapted to modify the microstructure.

[0102] 14. A welding electrode as described in any one of embodiments 1-13, wherein the additional functional coating includes the one or more elements or compounds adapted to change the surface tension of the molten droplet, and the one or more elements or compounds are selected from the group consisting of cadmium (Cd), mercury (Hg), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), sulfur (S), selenium (Se), tellurium (Te) and polonium (Po).

[0103] 15. A welding electrode as described in any of Examples 1-14, wherein the one or more additional elements or compounds adapted for changing the surface tension of the molten weld are present in an amount and form such that the welding electrode is configured to form a weld metal at a travel speed that is 30% or more higher than a travel speed for forming a weld metal without the one or more additional elements or compounds adapted for changing the surface tension of the molten weld.

[0104] 16. A welding electrode according to any one of embodiments 1-15, wherein the one or more additional elements or compounds adapted to change the surface tension of the molten weld are present in a certain amount and form, which amount and form make the volume of the silica islands formed on the weld metal formed by the welding wire at least 50% lower than the volume of the silica islands formed on the weld metal formed by the core welding wire without the one or more additional elements or compounds adapted to change the surface tension of the molten weld.

[0105] 17. A welding electrode according to any one of embodiments 1-16, wherein one or both of the conductive coating and the additional functional coating comprises a plurality of pores, wherein the pores are at least partially filled with a material different from the conductive coating and the additional functional coating having the pores.

[0106] 18. A welding electrode as described in any of Examples 1-17, wherein one or both of the conductive coating and the additional functional coating are porous or mixed so that the conductive element and the additional functional material at least partially wet each other in a direction orthogonal to the surface of the core wire.

[0107] 19. The welding electrode of any one of embodiments 1-18, wherein the conductive coating and the additional functional coating form a continuous layer with a clearly detectable boundary therebetween.

[0108] 20. A welding electrode as described in any of Examples 1-19, wherein at least some of the one or more additional elements or compounds adapted for reducing the friction of the welding electrode, stabilizing the arc formed by the welding electrode, changing the microstructure of the weld metal formed by the welding electrode, and changing the surface tension of the molten droplet formed by the welding electrode are arranged in different coatings among the two or more coatings.

[0109] 21. The welding electrode of any of embodiments 1-20, wherein each of the one or more conductive elements or compounds and the one or more additional elements or compounds is present in an amount of 0.0005-5 wt % based on the weight of the welding wire.

[0110] 22. The welding electrode of any one of embodiments 1-21, further comprising calcium (Ca) located at an interface region between the core wire and the two or more coating layers.

[0111] 23. The welding electrode of any one of embodiments 1-22, further comprising calcium (Ca) located at the interface region between the core wire and the two or more coating layers, the amount of calcium being 0.0005-1 wt % of the weight of the welding wire.

[0112] 24. The welding electrode of any one of embodiments 1-23, wherein the two or more coatings further comprise a second conductive coating that includes one or more conductive elements or compounds in addition to or other than copper (Cu).

[0113] 25. The welding electrode of embodiment 24, wherein the additional functional coating is interposed between the conductive coating and the second conductive coating.

[0114] 26. A welding electrode as described in any of Examples 1-24, wherein the two or more coatings further include a second additional functional coating, which includes one or more additional elements or compounds adapted to reduce the friction of the welding electrode, stabilize the arc formed by the welding electrode, change the microstructure of the weld metal formed by the welding electrode, and / or change the surface tension of the molten droplet formed by the welding electrode.

[0115] 27. The welding electrode of embodiment 26, wherein the conductive coating is interposed between the additional functional coating and the second additional functional coating.

[0116] 28. A method of manufacturing a welding electrode as described in any one of embodiments 1-23, the method comprising:

[0117] providing a core welding wire having a base metal composition; and

[0118] Two or more coatings are formed, including forming a conductive coating and forming an additional functional coating.

[0119] 29. The method of embodiment 28, wherein one or both of forming the conductive coating and forming the additional functional coating is performed by a chemical or electrochemical reaction.

[0120] 30. The method of embodiment 28 or 29, wherein one or both of forming the conductive coating and forming the additional functional coating is performed using a dip coating process.

[0121] 31. The method of any one of embodiments 28-30, wherein one or both of forming the conductive coating and forming the additional functional coating is performed using one or more of a replacement reaction, a sol-gel thin film process, electroplating, and electroless plating.

[0122] 32. The method of embodiment 28, wherein one or both of forming the conductive coating and forming the additional functional coating is performed using a physical or mechanical deposition process.

[0123] 33. The method of any one of embodiments 28-32, wherein one or both of forming the conductive coating and forming the additional functional coating are performed sequentially in different process stations.

[0124] 34. The method of any one of embodiments 28-23, wherein one or both of forming the conductive coating and forming the additional functional coating are performed simultaneously in the same process station.

[0125] 35. The method of any one of embodiments 28-34, further comprising conditioning the outer surface of the core wire with a compound comprising calcium (Ca) prior to forming the two or more coating layers.

[0126] Unless the context clearly requires otherwise, throughout the specification and claims, the words "comprise", "comprising", "include", "including", etc. should be interpreted in an inclusive sense, rather than an exclusive or exhaustive sense; that is, in the sense of "including but not limited to". As generally used herein, the word "coupled" refers to two or more elements that can be directly connected or connected through one or more intermediate elements. Similarly, as generally used herein, the word "connected" refers to two or more elements that can be directly connected or connected through one or more intermediate elements. In addition, when used in this application, the words "herein", "above", "below" and words of similar meaning shall refer to the application as a whole rather than to any particular part of the application. Where the context permits, words used in the singular or plural in the above specific embodiments may also include the plural or singular, respectively. The word "or" refers to a list of two or more items, and the word covers all the following interpretations of the word: any item in the list, all items in the list, and any combination of items in the list.

[0127] Furthermore, unless specifically stated otherwise or otherwise understood within the context of use, conditional language used herein (such as, among others, "can," "could," "might," "may," "eg," "for example," "such as," etc.) is generally intended to convey that certain embodiments include certain features, elements, and / or steps while other embodiments do not. Thus, such conditional language is generally not intended to imply that such features, elements, and / or statements are in any way required for one or more embodiments, or whether such features, elements, and / or statements are included in any particular embodiment or are to be performed in any particular embodiment.

[0128] Although certain embodiments have been described, these embodiments are presented only by way of example and are not intended to limit the scope of this disclosure. In fact, the novel devices, methods, and systems described herein can be implemented in various other forms; in addition, without departing from the spirit of this disclosure, various omissions, substitutions, and changes can be made to the form of the methods and systems described herein. For example, although the frames are presented in a given arrangement, alternative embodiments can perform similar functions with different components and / or circuit topologies, and some frames can be deleted, moved, added, subdivided, combined, and / or modified. Each of these frames can be implemented in various different ways. Any suitable combination of the elements and functions of the above-mentioned different embodiments can be combined to provide additional embodiments. The various features and processes described above can be implemented independently of each other, or can be combined in various ways. All possible combinations and sub-combinations of the features of this disclosure are intended to fall within the scope of this disclosure.

Claims

1. A welding electrode, comprising: A solid core welding wire having a base metal composition based on iron (Fe); a conductive coating formed on the solid core wire and including one or more conductive elements or compounds in addition to or other than copper (Cu), and An additional functional coating is formed on the conductive coating, wherein the additional functional coating includes one or more additional elements or compounds selected from the group consisting of graphite, metal sulfide, polytetrafluoroethylene, graphene, and graphene oxide.

2. The welding electrode according to claim 1, wherein: The one or more additional elements or compounds comprise metal sulfides.

3. The welding electrode according to claim 2, wherein: The metal sulfide includes molybdenum disulfide (MoS2) or tungsten disulfide (WS2).

4. The welding electrode according to claim 2, wherein: The metal sulfide has a layered structure.

5. The welding electrode according to claim 1, wherein: The one or more additional elements or compounds are adapted to reduce friction between the welding electrode and a welding wire lining.

6. The welding electrode according to claim 4, wherein: The one or more additional elements or compounds are compounds adapted for reducing friction and are present in an amount and form such that a wire feed force for feeding the welding electrode through a wire liner is 50% or more lower relative to a wire feed force for feeding a reference welding electrode that is identical to the welding electrode except for the presence of the additional functional coating.

7. The welding electrode according to claim 1, wherein: The one or more conductive elements or compounds are selected from the group consisting of magnesium (Mg), aluminum (Al), zinc (Zn), tin (Sn), chromium (Cr), platinum (Pt), silver (Ag), graphite, graphene, graphene oxide and titanium (Ti).

8. The welding electrode according to claim 7, wherein: The one or more conductive elements or compounds are present in the conductive coating in the absence of Cu.

9. The welding electrode according to claim 7, wherein: The one or more conductive elements or compounds, other than Cu, are present in an amount exceeding 90 atomic % of the combined total of the one or more conductive elements or compounds and Cu.

10. The welding electrode according to claim 1, wherein: The Fe-based base metal composition includes a stainless steel composition.

11. A welding electrode, comprising: A solid core welding wire having a base metal composition based on iron (Fe); and two or more coating layers covering at least a portion of the solid core welding wire, wherein the two or more coating layers comprise: a conductive coating formed on the solid core welding wire, comprising one or more conductive elements or compounds in addition to or other than copper (Cu), and An additional functional coating, the additional functional coating comprising one or more additional elements or compounds selected from the group consisting of: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), cerium (Ce), barium (Ba) and radium (Ra).

12. The welding electrode according to claim 11, wherein: The one or more additional elements or compounds are adapted for stabilizing the arc formed by the welding electrode.

13. The welding electrode according to claim 12, wherein: The one or more additional elements or compounds are present in an amount and form such that one or both of the oxygen content and the nitrogen content of the weld metal formed by the welding electrode is 50% or more lower than one or both of the oxygen content and the nitrogen content of a reference weld metal formed by a reference welding electrode that is identical to the welding electrode except for the presence of the additional functional coating.

14. The welding electrode according to claim 11, wherein: The Fe-based base metal composition includes a stainless steel composition.

15. The welding electrode according to claim 11, wherein: The one or more conductive elements or compounds are selected from the group consisting of magnesium (Mg), aluminum (Al), zinc (Zn), tin (Sn), chromium (Cr), platinum (Pt), silver (Ag), graphite, graphene, graphene oxide and titanium (Ti).

16. A welding electrode comprising: A solid core welding wire having a base metal composition based on iron (Fe); a conductive coating formed on the solid core wire and including one or more conductive elements or compounds in addition to or other than copper (Cu), and An additional functional coating is formed on the conductive coating, wherein the additional functional coating includes one or more additional elements or compounds selected from the group consisting of: titanium (Ti), zirconium (Zr), nickel (Ni), boron (B), molybdenum (Mo) and niobium (Nb).

17. The welding electrode according to claim 16, wherein: The one or more additional elements or compounds include Mo.

18. The welding electrode according to claim 16, wherein: The one or more additional elements or compounds are adapted to change the microstructure of the weld metal formed by the welding electrode so that the impact toughness of the weld metal is higher than the impact toughness of a weld metal formed by a reference welding electrode that is identical to the welding electrode except for the presence of the additional functional coating.

19. The welding electrode according to claim 18, wherein: The one or more additional elements or compounds are present in an amount and form that results in an impact toughness of the weld metal that is 50% or more higher relative to the weld metal formed by the reference welding electrode.

20. The welding electrode according to claim 16, wherein: The one or more additional elements or compounds are adapted to modify the microstructure of the weld metal such that the ductile-to-brittle transition temperature of the weld metal is lower than the ductile-to-brittle transition temperature of a weld metal formed by a reference welding electrode that is identical to the welding electrode except for the presence of the additional functional coating.

21. The welding electrode according to claim 20, wherein: The one or more additional elements or compounds are present in an amount and form such that the ductile-to-brittle transition temperature of the weld metal is at least 50° C. lower than the weld metal formed by the reference welding electrode.

22. The welding electrode according to claim 16, wherein: The one or more conductive elements or compounds are selected from the group consisting of magnesium (Mg), aluminum (Al), zinc (Zn), tin (Sn), chromium (Cr), platinum (Pt), silver (Ag), graphite, graphene, graphene oxide and titanium (Ti).

23. The welding electrode according to claim 16, wherein: The Fe-based base metal composition includes a stainless steel composition.

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