Self-lubricating wear-resistant surfacing flux-cored wire and preparation method thereof

Abstract

The application discloses a self-lubricating wear-resistant surfacing flux-cored wire. The flux-cored wire comprises a flux core wrapped in a low-carbon steel strip, the flux core comprises graphite powder and ferrosilicon alloy powder, and the balance is iron powder; the adding amount of various powders should ensure that the weight percentage content of silicon element in the flux-cored wire is more than twice the content of carbon element; and the filling rate of the flux core of the flux-cored wire is 10%-35%. The graphite equivalent of the flux-cored wire is determined according to the graphitization theory of the alloy, so that the specific content of each element is determined; meanwhile, the silicon-carbon ratio principle is followed, that is, when the silicon-carbon atom number ratio is increased to 1:1, the weight ratio of silicon to carbon is more than 2:1, the graphitization and stabilization of silicon reach the peak value and are in a stable state. The self-lubricating wear-resistant surfacing flux-cored wire prepared by the application has excellent self-lubricating performance and wear resistance, and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of welding materials, and in particular relates to a self-lubricating wear-resistant surfacing flux-cored welding wire. The invention also relates to a preparation method of the welding wire and the surfacing alloy. Background Art

[0002] In the oil drilling industry, the joints of oil drill pipes will wear out after being used for a period of time, so a layer of wear-resistant alloy must be welded on the outer surface of the joint to protect the drill pipe. The earliest wear-resistant alloy materials used for welding on drill pipe joints were mainly tungsten-cobalt series hard alloys such as tungsten carbide. Although it protected the drill pipe, this wear-resistant alloy severely wore the casing like a grinding wheel. With the increase in deep wells and directional wells, the casing wear became more serious, so the use of tungsten carbide was later banned. Because tungsten carbide wear-resistant alloys severely wore the casing, people began to stop using wear-resistant surfacing materials. However, it was found that the wear degree of the casing by drill pipe joints without wear-resistant surfacing materials was as serious as that of tungsten carbide, especially when the drill pipe joints were worn eccentrically, the wear was more serious. Casing wear will greatly reduce the life of the oil well and even make the well scrapped. The loss is much more serious than drill pipe wear.

[0003] A series of new wear-resistant materials have been developed at home and abroad to replace tungsten carbide to extend the life of drill pipe joints, so as to achieve the purpose of preventing drill pipe wear and reducing casing wear; however, the casing wear problem still exists and needs further improvement.

[0004] Patent document CN103170761B discloses a flux-cored wire for drill pipe wear-resistant hardfacing and its manufacturing method. The wire is composed of the following raw materials by mass: 8-9% chromium, 2-3% boron, 0.2-1% molybdenum, 1-2% nickel, 0.3-0.8% carbon, and the balance iron. The manufacturing process includes: passing chromium, boron, molybdenum, nickel, carbon, and iron powders through a 60-mesh sieve and thoroughly mixing; adding the raw materials to a wire sheath and sealing it; achieving a filling ratio of 27 wt%, and kneading the opening of the U-shaped wire sheath; and rolling a 15 mm wide, 0.4 mm thick cold-rolled steel strip into the U-shaped wire sheath, which is then reduced in diameter through a drawing die. Patent document CN101537548A discloses a flux-cored wire for surfacing. The composition and weight percentage of the flux core are as follows: Mo 1-3%, B 2-6%, Si 1-4%, Mn 1-4%, C 0.5-4%, Nb 3-7%, Cr 10-40%, Re 1-4%, with the balance being Fe. These developed wear-resistant surfacing materials prevent drill pipe wear and reduce casing wear to a certain extent, but none of them are self-lubricating. Patent CN200710018767.7 invents a self-lubricating wear-resistant surfacing material, which includes the following elements in weight percentage: carbon C 2.5-4.5%, silicon Si 1.8-4.9%, magnesium Mg 0.02-0.18%, rare earth 0.02-0.18%, and the balance is iron and inevitable impurities, among which sulfur S ≤ 0.1% and phosphorus P ≤ 0.4%. It also includes the following elements in weight percentage: manganese Mn 2.0% < 5.0%, chromium Cr 0-2.5%, nickel Ni 0-1.5%, molybdenum Mo 0-1.0%, vanadium V 0-0.6%, titanium Ti 0-0.5%, zirconium Zr 0-0.5% and niobium Nb 0-0.5%. This alloy's composition is similar to that of gray cast iron and ductile iron. However, because the weld pool cools much faster than cast iron after casting, solidification occurs very quickly, leaving insufficient time for carbon atoms to diffuse and form sufficient graphite. Years of practice have shown that the desired self-lubricating effect is not achieved. Furthermore, due to the high magnesium content, the alloy suffers from poor weldability, resulting in significant smoke and spatter. Patent CN202010535613.0 relates to a self-lubricating, wear-resistant flux-cored welding wire containing nickel-coated graphite and a welding method thereof. The self-lubricating, wear-resistant flux-cored welding wire comprises a flux core and a carbon steel strip surrounding the flux core. The flux core comprises the following components, by mass: 18-22% ferrochromium; 7-9% ferroboron; 3-5% ferrosilicon; 3-5% ferromanganese; 0.4-0.6% aluminum; 2-3% rare earth elements; 3-5% nickel-coated graphite; and the balance iron. The wear-resistant surfacing layer prepared by adopting the flux-cored welding wire containing nickel-coated graphite powder and using a double constant current source droplet-free arc hot wire GTAW surfacing method has a self-lubricating function.This flux-cored wire, containing nickel-coated graphite powder, has a diameter of 1.6mm and is welded using the dual constant current source droplet-free hot wire GTAW method. Some of the graphite does not melt at the electrode and transfers into the weld, resulting in a significant amount of graphite remaining in the wear-resistant hardfacing layer, providing self-lubrication. The remaining graphite melts into carbon atoms, which solid-dissolve into the alloy or form carbides, increasing the alloy's hardness. This patent utilizes the GTAW method but employs proprietary dual constant current source droplet-free hot wire technology, significantly increasing welding heat input and enabling the use of wires as large as 1.6mm in diameter. This welding machine is a proprietary experimental device developed by the inventors and is not a mature commercial device widely used in engineering applications. The patented wire can only be welded using the inventors' proprietary welding equipment, and only with a wire diameter of 1.6mm to achieve the patented effect. Commonly used welding methods in engineering applications are gas metal arc welding (MIG, GMAW) and gas tungsten arc welding (TIG, GTAW). If the patented welding wire is welded using a gas metal arc welding machine, the welding wire serving as the electrode melts, and part of the nickel-coated graphite in the welding wire flux core will melt at the electrode. The remaining graphite that has not melted will transition to the molten pool and continue to dissolve, with some remaining. The dissolved graphite will solid-dissolve into the alloy as carbon atoms or form carbides and cannot reform into graphite. The amount of graphite in the final alloy is too small to form a self-lubricating function. If the patented welding wire is welded using the argon tungsten arc welding (TIG, GTAW) method, due to the low heat input of the argon tungsten arc welding machine, even if hot wire technology such as resistance heating wire technology is used, the welding heat input is still low, so only welding wires with a diameter of less than 1.0 mm can be used. Small diameter welding wires cannot be filled with enough flux powder, resulting in too little nickel-coated graphite in the welding wire, and insufficient graphite cannot be transferred to the welded alloy, which is insufficient to achieve self-lubricating function. Practice has shown that if the patented flux-cored welding wire is welded using general welding equipment, there will be too little residual graphite in the prepared wear-resistant surfacing layer and it will have almost no self-lubricating function, making the application of this invention patent very difficult. Summary of the Invention

[0005] The purpose of the present invention is to provide a self-lubricating wear-resistant surfacing flux-cored welding wire, which achieves the purpose of simultaneously improving the wear resistance and self-lubricating performance of the welding wire.

[0006] Another object of the present invention is to provide a method for preparing a self-lubricating wear-resistant surfacing flux-cored welding wire.

[0007] The first technical solution adopted by the present invention is a self-lubricating wear-resistant surfacing flux-cored welding wire, which includes a flux core wrapped in an outer sheath, and the flux core includes graphite powder and ferrosilicon alloy powder, with the balance being iron powder; the amount of each powder added should ensure that the weight percentage content of silicon in the flux-cored welding wire reaches more than twice the weight percentage of carbon; the outer sheath of the flux-cored welding wire is a low-carbon steel strip; and the flux core filling rate of the flux-cored welding wire is 10% to 35%.

[0008] The present invention is also characterized in that:

[0009] One or more of nickel powder, aluminum powder, copper powder and cobalt powder can also be added to the flux core.

[0010] The weight percentage contents of various powder materials in the flux core of the flux cored welding wire are as follows: graphite powder 10% to 15%, ferrosilicon alloy powder 35% to 85%, nickel powder 0% to 30%, aluminum powder 0% to 20%, copper powder 0% to 10%, cobalt powder 0% to 5%, and the balance is iron powder.

[0011] According to the required graphite volume percentage C in the self-lubricating wear-resistant cladding alloy G , according to formula C G (%) = 3(1-mn)C E , calculate the minimum graphite equivalent C required for the flux-cored wire E Then according to the formula k[C%+0.4Si%+0.1(Ni%+Al%+Cu%+Co%)]≥C E Determine the addition amount of various alloy elements and powder thereof in the flux core of the flux cored welding wire.

[0012] The calculation method of the volume percentage of graphite in self-lubricating wear-resistant cladding alloy is: C G (%) = 3(1-mn)C E , where m is the burnout rate of the alloy element in the welding arc, and m is 0.10 to 0.25; n is the dilution rate of the alloy element in the wear-resistant surfacing alloy, and n is 0.10 to 0.25; C E is the graphite equivalent of the flux-cored wire; C E =k[C%+0.4Si%+0.1(Ni%+Al%+Cu%+Co%)], wherein k is the flux core filling rate of the flux cored welding wire, and C%, Si%, Ni%, Al%, Cu% and Co% represent the contents of C, Si, Ni, Al, Cu and Co elements in the flux core, respectively.

[0013] Another technical solution adopted by the present invention is: a method for preparing the above-mentioned self-lubricating wear-resistant surfacing flux-cored welding wire, the specific steps are as follows:

[0014] Step 1: Weigh the following powders by mass percentage: graphite powder 10% to 15%, ferrosilicon alloy powder 35% to 85%, nickel powder 0% to 30%, aluminum powder 0% to 20%, copper powder 0% to 10%, cobalt powder 0% to 5%, and the balance iron powder;

[0015] Step 2: placing the graphite powder, ferrosilicon alloy powder, nickel powder, aluminum powder, copper powder, cobalt powder and iron powder weighed in step 1 in a vacuum heating furnace for drying; placing the dried powder in a powder mixer for mixing to obtain a mixed powder;

[0016] Step 3: Fill the mixed powder into the U-shaped groove of the low-carbon steel strip and make flux-cored welding wire after closed rolling.

[0017] The present invention is also characterized in that:

[0018] The addition amount of various powders should ensure that the weight percentage content of silicon element in the flux-cored welding wire reaches more than twice the weight percentage of carbon element; the flux core filling rate of the flux-cored welding wire is 10% to 35%.

[0019] A method for preparing a surfacing alloy using a flux-cored wire, wherein the flux-cored wire is surfacingly welded on a workpiece surface using tungsten inert gas arc welding or metal arc gas shielded welding to form a surfacing alloy;

[0020] Among them, when using metal arc welding, a mixture of carbon dioxide and argon is used as the shielding gas;

[0021] When using tungsten inert gas welding, argon is used as the shielding gas;

[0022] During the welding process, the alloy element burnout rate m is: 0.10≤m≤0.25; the alloy dilution rate n is: 0.10≤n≤0.25.

[0023] The beneficial effects of the present invention are as follows: To improve the wear resistance and self-lubrication properties of the hardfacing alloy, the present invention determines the graphite equivalent in the flux-cored welding wire based on the graphitization theory in the alloy, thereby determining the specific content of each element; at the same time, the silicon-carbon ratio principle is adhered to, that is, when the silicon-to-carbon atomic ratio is increased to 1:1, equivalent to increasing the weight percentage to 2:1, the graphitization and stabilization effect of silicon reaches a peak and remains in a stable state. The flux-cored welding wire prepared by the present invention has excellent self-lubrication and wear resistance, and the content of each component of the welding wire can be determined according to the actual performance requirements of the wear-resistant hardfacing alloy and the welding method. This is an unprecedented innovation in the field and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the phase diagram of iron-carbon alloy;

[0025] Figure 2 The relationship between the free enthalpy of each phase in the iron-carbon alloy melt and the temperature;

[0026] Figure 3(a) and Figure 3(b) show the microstructures of wear-resistant alloys prepared by tungsten inert gas arc welding;

[0027] Figure 4(a) and Figure 4(b) show the microstructures of the wear-resistant alloy prepared by metal arc welding. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] The self-lubricating, wear-resistant surfacing flux-cored welding wire of the present invention comprises a flux core wrapped in an outer sheath, wherein the flux core comprises graphite powder and ferrosilicon alloy powder, with the remainder being iron powder; the addition amount of various powders should ensure that the weight percentage content of silicon element in the flux-cored welding wire reaches more than twice the weight percentage content of carbon element; the outer sheath of the flux-cored welding wire is a low-carbon steel strip; and the flux core filling rate of the flux-cored welding wire is 10% to 35%.

[0030] One or more of nickel powder, aluminum powder, copper powder and cobalt powder can also be added to the flux core.

[0031] The weight percentage contents of various powder materials in the flux core of the flux cored welding wire are as follows: graphite powder 10% to 15%, ferrosilicon alloy powder 35% to 85%, nickel powder 0% to 30%, aluminum powder 0% to 20%, copper powder 0% to 10%, cobalt powder 0% to 5%, and the balance is iron powder.

[0032] The volume percentage of graphite powder in the cladding alloy is calculated as C G (%) = 3(1-mn)C E , where m is the burnout rate of the alloy element in the welding arc, and m is 0.10 to 0.25; n is the dilution rate of the alloy element in the wear-resistant surfacing alloy, and n is 0.10 to 0.25; C E is the graphite equivalent of the flux-cored welding wire, and the graphite equivalent is calculated as C E =k[C%+0.4Si%+0.1(Ni%+Al%+Cu%+Co%)], wherein k is the flux core filling rate of the flux cored welding wire, and C%, Si%, Ni%, Al%, Cu% and Co% represent the contents of C, Si, Ni, Al, Cu and Co elements in the flux core, respectively.

[0033] According to the required graphite volume percentage C in the self-lubricating wear-resistant cladding alloy G , according to formula C G (%) = 3(1-mn)C E , calculate the minimum graphite equivalent C required for the flux-cored wire E Then according to the formula k[C%+0.4Si%+0.1(Ni%+Al%+Cu%+Co%)]≥C E Determine the addition amount of various alloy elements and powder thereof in the flux core of the flux cored welding wire.

[0034] The theoretical basis for the design of the components and contents of the self-lubricating wear-resistant surfacing flux-cored welding wire of the present invention is as follows:

[0035] Figure 1 The iron-carbon alloy dual state diagram shown in the figure shows that the solidification and crystallization process of iron-carbon alloy can be described according to the iron-graphite system ( Figure 1 The iron-carburizing system ( Figure 1However, graphite is a stable phase, while cementite is a metastable phase. Therefore, the iron-graphite phase diagram is a stable phase diagram of the iron-carbon alloy, and the iron-cementite phase diagram is a metastable phase diagram of the iron-carbon alloy. Moreover, the crystallization temperature of graphite is higher than that of cementite. Therefore, during the solidification and crystallization process of the iron-carbon alloy, carbon is more inclined to precipitate or exist in the graphite phase. This is the theoretical basis of gray iron casting and also one of the theoretical bases of the present invention.

[0036] The above principle can be explained by thermodynamics. Figure 2 is the free enthalpy G of the molten iron L containing dissolved carbon atoms, the two-phase mixture of molten iron L and cementite Fe3C4, and the two-phase mixture of molten iron L and graphite g. L+C , G L+Fe3C4 , G L+g The trend graph of temperature T shows that as the temperature decreases, the free enthalpy of each substance increases, but the rate of increase is different. Therefore, when the temperature drops to T g , that is Figure 1 The dotted line in the middle is the free enthalpy G of the molten iron and graphite phases. L+g Lower than the free enthalpy G of molten iron L+C , graphite becomes more stable, and part of the carbon element will crystallize and precipitate in the form of more stable graphite. When the temperature is reduced to T Fe3C4 , that is Figure 1 The solid line in the figure shows that the free enthalpy of the mixture of molten iron and cementite is G L+Fe3C4 It is also lower than molten iron, but the free enthalpy of the mixture of molten iron and graphite is G L+g Lower, so graphite is more stable, carbon tends to exist in the form of graphite. Obviously, any reduction in free enthalpy G L+g , or increase the free enthalpy G L+Fe3C4 Factors promote the graphitization of molten iron. This is the thermodynamic basis of gray cast iron manufacturing and the thermodynamic theoretical basis of this invention. Graphitization technology is the basis of gray cast iron manufacturing. Most gray cast iron is a hypoeutectic alloy close to the eutectic composition. During the smelting process, all alloying elements including carbon are dissolved into the molten iron. When the temperature is lowered to Figure 1At the eutectic reaction temperature of 1154°C, carbon atoms in the molten iron precipitate and crystallize into flake graphite, a process known as graphitization. Unlike gray cast iron, the present invention relies on the synergistic effect of graphite stabilization and graphitization. Graphite is pre-added to the welding wire. During the overlay welding process, some of the graphite escapes arc melting and transfers into the molten pool. Graphite has a very high melting point (approximately 3700°C), far exceeding that of molten iron. Furthermore, the welding wire contains numerous elements that enhance graphite stability. This unmelted graphite dissolves less readily in the molten iron, resulting in a large number of fine graphite particles in the overlay weld pool. Compared to drill pipe joints, which are tens of millimeters thick, the overlay weld pool on their surface is only a few millimeters thick and very small. The heavy weight of the drill pipe joint significantly accelerates the cooling of the molten pool. Some of the graphite that enters the molten pool does not dissolve quickly enough and remains in the wear-resistant alloy weld bead until the pool solidifies. However, this residual graphite is minimal and insufficient to provide sufficient self-lubricating properties for the wear-resistant alloy. Another portion of the graphite melted by the arc or in the molten pool decomposes into carbon atoms and dissolves into the pool. Because many fine graphite particles already remain in the weld pool, and because many elements promoting graphitization are added to the welding wire, these dissolved carbon atoms continue to crystallize with the residual graphite as the pool temperature decreases. The graphite particles continue to grow until the pool solidifies, resulting in a sufficient volume of graphite in the weld pool to exhibit a significant self-lubricating effect. Therefore, the technical basis of the present invention, unlike the graphitization of gray cast iron, is the synergistic effect of graphite stabilization and graphitization. Any factors that enhance graphite stabilization and promote graphitization are beneficial to the weld overlay manufacturing of the self-lubricating wear-resistant weld overlay alloy.

[0037] The roles and functions of the main components in this flux-cored welding wire are as follows:

[0038] Carbon is the only element that constitutes graphite. It is also the element that most significantly promotes the graphitization of cast iron and enhances graphite stability. Therefore, graphite is the primary additive in flux-cored welding wire. During the overlay welding process, some graphite that is not melted by the arc passes into the molten pool, where it does not have time to dissolve and remains, forming the core where the graphite continues to grow. Another portion of graphite dissolves into the molten pool, increasing the pool's carbon content and further enhancing the stability of the residual graphite. During the solidification process of the molten pool, the dissolved carbon atoms continue to crystallize on the residual graphite, growing into a sufficiently large volume of graphite. Therefore, a sufficient amount of graphite must be added to the flux-cored overlay welding wire. However, excessive graphite can affect welding processability, increase spatter, and increase smoke. Therefore, the amount of graphite added should be limited. Other elements that enhance graphite stability and promote graphitization must be added to further reduce graphite dissolution in the molten pool and promote the crystallization and growth of dissolved carbon atoms on the graphite.

[0039] Silicon, nickel, aluminum, copper, and cobalt are also elements that promote graphitization of cast iron or enhance the stability of graphite. The chemical mechanism by which these elements promote graphitization is not yet clear and still needs to be studied. These elements have one thing in common: silicon, nickel, aluminum, copper, and cobalt cannot form carbides in steel.

[0040] Since the atomic bonding force between silicon and iron is greater than that between carbon and iron, when silicon dissolves in molten iron, it weakens the bonding force between carbon atoms and iron atoms, so silicon increases the free enthalpy G L+Fe3C4 , which also reduces the free enthalpy G L+gTherefore, silicon increases the temperature of the dotted line in the iron-carbon phase diagram, which means it reduces the solubility of carbon in molten iron or solid solution, and reduces the carbon content of the iron-carbon eutectic phase. Therefore, thermodynamically, silicon strongly promotes graphitization and increases graphite stability. Therefore, silicon is an indispensable and most important alloying element in the flux core of the flux-cored welding wire. Experiments in the present invention have found that silicon's enhanced graphite stability and promotion of graphitization are related to the ratio of silicon and carbon atoms. When the silicon-carbon atomic ratio is less than 1 to 10, silicon has almost no effect on graphite stabilization and graphitization. As the silicon-carbon atomic ratio increases, the amount of graphite in the hardfacing wear-resistant alloy gradually increases under the same graphite addition amount in the welding wire, indicating that graphite stability gradually increases and graphitization accelerates. When the silicon-carbon atomic ratio increases to above 1 to 6, the amount of graphite in the hardfacing wear-resistant alloy significantly increases under the same graphite addition amount, and silicon's graphitization and stabilization effects are obvious. When the silicon-carbon atomic ratio increases to above 1 to 2, the graphitization and stabilization effects of silicon are accelerated. When the silicon-carbon atomic ratio reaches 1:1, the graphite content in the hardfacing wear-resistant alloy is the highest, given the same graphite addition level. This indicates that silicon's graphitization and stabilization effects reach their peak. Thereafter, as the silicon-carbon atomic ratio continues to increase, the graphitization and stabilization effects gradually stabilize and no longer increase. Therefore, sufficient silicon must be added to the flux-cored welding wire of the present invention to increase the silicon-carbon atomic ratio to above 1:1, equivalent to a silicon-carbon weight ratio of at least 2:1. Therefore, the amounts of various powders added to the core of the flux-cored welding wire of the present invention should ensure that the weight percentage of silicon in the flux-cored welding wire is at least twice that of carbon. Clearly, the flux-cored welding wire of the present invention contains significantly more silicon than ordinary gray cast iron. Silicon increases the alloy's strength and hardness, but also its brittleness. Therefore, such a high silicon content is unsuitable in ordinary gray cast iron. However, the self-lubricating hardfacing alloy of the present invention is primarily subjected to compressive stress and friction during operation, with wear resistance and friction reduction as its primary performance indicators. Therefore, the alloy's greater brittleness does not affect its service performance. Furthermore, because silicon significantly increases the alloy's phase transition temperature, A1, a higher silicon content significantly improves the heat resistance of hardfacing alloys. For example, friction between a wear-resistant alloy and a component generates significant heat, raising the surface temperature to high levels, even reaching over 800°C in a short period of time. Therefore, a higher silicon content in wear-resistant alloys can also improve heat resistance. However, excessive silicon can also form excessive inclusions in the weld, creating pores. Therefore, silicon should be added in moderation. Other elements that promote graphitization and stability can also be added.

[0041] Nickel, cobalt and iron are all group VIII elements, and their crystals are all face-centered cubic structures. The valence electron layer structure of iron, cobalt and nickel atoms is 3d 6 4s 2 , 3d 7 4s 2 , 3d 8 4s 2, the outermost layer has two 4s electrons, but the number of 3d electrons in the second outer layer is different, which are 6, 7, and 8 respectively. The atomic weights are 55.8, 58.9, and 58.7 respectively. The atomic radius of iron, cobalt, and nickel are 117, 116, and 115pm respectively. The melting points are 1538℃, 1495℃, and 1455℃ respectively. The physical and chemical properties of iron, cobalt, and nickel are very similar, so cobalt and nickel atoms can completely dissolve in the γ-Fe solid solution, replacing the iron atoms on the crystal lattice. They can also dissolve into the cementite Fe3C4 and replace the iron atoms. Since cobalt and nickel atoms cannot combine with carbon atoms to form carbides, they decompose the cementite Fe3C4, releasing carbon atoms to form graphite. In terms of thermodynamics, nickel and cobalt increase the free enthalpy G L+Fe3C4 , thermodynamically promoting the graphitization of cast iron. Nickel and cobalt simultaneously increase the alloy's crystallization temperature and narrow the crystallization temperature range, thereby reducing the molten pool solidification time, reducing graphite dissolution, and improving graphite stability. Nickel and cobalt also enhance the alloy's toughness and reduce the alloy's brittleness caused by silicon. Nickel and cobalt also improve the weldability of the wire. Therefore, nickel can be used as the primary alloying element in flux-cored wire. However, cobalt is relatively expensive and can be added selectively in small amounts.

[0042] Aluminum also has a strong effect on promoting graphitization. The oxide structure of aluminum is similar to that of graphite, and it can become the core of graphite crystallization. The aluminum atoms dissolved in ferrite occupy the original carbon atom positions, reducing the solubility of carbon atoms in ferrite and promoting the stability of graphite. At the same time, since aluminum increases the eutectic transition temperature, that is, it increases the solidification temperature of cast iron and reduces the solidification time of cast iron, it reduces the dissolution of graphite in the welding pool, further promoting the stability of graphite. However, too much aluminum will also form too many inclusions in the wear-resistant alloy and produce pores. Copper is a non-carbide element, so it also has a strong effect on promoting graphitization, but too much copper will form a low-melting-point copper solid solution phase at the grain boundaries of the wear-resistant alloy, increasing the brittleness of the alloy. Therefore, aluminum and copper can be used as selective alloying elements of the flux-cored welding wire and added in appropriate amounts.

[0043] The principle of the present invention is to pre-add graphite to the flux-cored welding wire. During the cladding process, due to the high melting point of graphite, a portion of the graphite is not melted by the arc and transfers to the molten pool. Because the molten pool contains a large amount of graphite-stabilizing elements, a portion of this graphite remains stable until the molten pool solidifies. The remaining carbon atoms dissolved in the molten pool will also recrystallize with the residual graphite as the temperature decreases, and the graphite continues to grow to a sufficient volume. Graphite Volume Percentage C G (%) is the main technical index of the self-lubricating wear-resistant surfacing alloy. Practice has shown that the volume percentage of graphite C G (%) and the burnout rate m of alloy elements in flux-cored wire in the cladding arc, the dilution rate n of alloy elements in wear-resistant cladding alloy, and the graphite equivalent C of flux-cored wire. EThe estimation method is C G (%) = 0.7 (density of hardfacing alloy / density of graphite) (1-mn) C E =3(1-mn)C E Only about 70% of carbon atoms can exist in the form of graphite, and the density of wear-resistant surfacing alloy is about 8g / cm 3 , the density of graphite is about 2g / cm 3 .

[0044] Some graphite will oxidize in the overlay arc, releasing carbon monoxide. The oxidation loss rate (m) depends on the properties of the overlay gas and the heat input. The more oxidizing the gas, the greater the graphite loss. Carbon dioxide (CO2) is a commonly used oxidizing atmosphere, causing significant oxidation of graphite and other alloying elements, with a loss rate of up to 25%. Inert shielding gases such as argon and nitrogen significantly reduce graphite oxidation, reducing the loss rate to below 10%. The loss rate of a mixed CO2 / argon shielding gas falls between these values. Therefore, the alloying element loss rate (m) can be between 10% and 25%.

[0045] When flux-cored wire is applied to a mechanical part, the surface also melts, fusing the wire and the surface material. This dilutes the concentration of alloying elements in the hardfacing alloy. Therefore, the dilution rate (n) of alloying elements in the hardfacing alloy is related to the heat input. Metal arc welding (MIG) has a higher heat input, and the dilution rate (n) can reach 25%. Tungsten inert gas arc welding (TIG) has a lower heat input, and the dilution rate (n) can be as low as 10%.

[0046] Carbon equivalent is an important design index of gray cast iron. In contrast to this index, the present invention proposes the concept of graphite equivalent and uses graphite equivalent C E As the design index of the flux-cored welding wire, the calculation method is C E =[C% + 0.4Si% + 0.1(Ni% + Al% + Cu% + Co%)], where k is the core filling rate (%) of the flux-cored welding wire, and C% is the graphite content in the core. Si% represents the silicon content in the core. Silicon is typically added in the form of ferrosilicon alloy powder, so the silicon content is calculated from the amount of ferrosilicon alloy powder added and the silicon content in the alloy powder. Ni%, Al%, Cu%, and Co% represent the nickel, aluminum, copper, and cobalt powder contents in the core, respectively. Alloying elements such as Ni, Al, Cu, and Co are typically added in the form of pure alloy powders. The present invention has discovered that when the silicon-to-carbon atomic ratio is increased to greater than 1:1, equivalent to a silicon-to-carbon weight ratio of greater than 2:1, the graphite content in the hardfacing alloy is maximized at the same graphite addition level. The silicon atom's effect on graphite stability and graphitization can be as high as 40% of that of a carbon atom. Nickel, aluminum, copper, and cobalt, among others, contribute to graphite stability and graphitization as much as 10% of that of a carbon atom.

[0047] The preparation method of the self-lubricating wear-resistant surfacing flux-cored welding wire comprises the following specific steps:

[0048] Step 1: Weigh the following powders by mass percentage: graphite powder 10% to 15%, ferrosilicon alloy powder 35% to 85%, nickel powder 0% to 30%, aluminum powder 0% to 20%, copper powder 0% to 10%, cobalt powder 0% to 5%, and the balance iron powder;

[0049] Step 2: placing the graphite powder, ferrosilicon alloy powder, nickel powder, aluminum powder, copper powder, cobalt powder and iron powder weighed in step 1 in a vacuum heating furnace for drying; placing the dried powder in a powder mixer for mixing to obtain a mixed powder;

[0050] Step 3: Fill the mixed powder into the U-shaped groove of the low-carbon steel strip, and make the flux-cored welding wire after closed rolling. The flux-cored welding wire has a core filling rate of 10% to 35%.

[0051] The amount of each powder added should ensure that the weight percentage of silicon in the flux-cored wire is more than twice the carbon content; the volume percentage of graphite powder is calculated as C G (%) = 3(1-mn)C E , where m is the burnout rate of the alloy element in the welding arc, and m is 0.10 to 0.25; n is the dilution rate of the alloy element in the wear-resistant surfacing alloy, and n is 0.10 to 0.25; C E is the graphite equivalent of the flux-cored welding wire, and the graphite equivalent is calculated as C E =k[C%+0.4Si%+0.1(Ni%+Al%+Cu%+Co%)], wherein k is the flux core filling rate of the flux cored welding wire, and C%, Si%, Ni%, Al%, Cu% and Co% represent the contents of C, Si, Ni, Al, Cu and Co elements in the flux core, respectively.

[0052] According to the required graphite volume percentage C in the self-lubricating wear-resistant cladding alloy G , according to formula C G (%) = 3(1-mn)C E , calculate the minimum graphite equivalent C required for the flux-cored wire E Then according to the formula k[C%+0.4Si%+0.1(Ni%+Al%+Cu%+Co%)]≥C E Determine the addition amount of various alloy elements and powder thereof in the flux core of the flux cored welding wire.

[0053] The method for preparing a cladding alloy using the flux-cored welding wire of the present invention is as follows:

[0054] The flux-cored welding wire is welded on the surface of the workpiece by tungsten inert gas welding or metal arc welding to form a cladding alloy; wherein, when metal arc welding is adopted, a mixture of carbon dioxide and argon is used as the shielding gas;

[0055] When using tungsten inert gas welding, argon is used as the shielding gas;

[0056] During the welding process, the alloy element burnout rate m is: 0.10≤m≤0.25; the alloy dilution rate n is: 0.10≤n≤0.25.

[0057] Tungsten Inert Gas Arc Welding (GTAW or TIG) utilizes a positive direct current connection method, with the positive electrode connected to the workpiece drill pipe joint and the negative electrode connected to the welding machine's tungsten electrode. During the overlay welding process, an arc is generated between the positive and negative electrodes, melting the surface of the workpiece drill pipe joint, which serves as the positive electrode. The welding wire can then be inserted into the molten pool, where it melts and dissolves into the molten pool. While argon gas provides shielding, this reduces the burnout rate of graphite and other alloying elements in the wire, achieving a minimum alloying element burnout rate (m) of 10%. Tungsten Inert Gas Arc Welding (GTAW) offers low heat input, a low molten pool temperature, and minimal base metal melting, resulting in a low alloying element dilution rate (n) of as little as 10%.

[0058] Gas metal arc welding (GMAW, MIG, MAG) uses reverse direct current (DC) connection, with the positive electrode connected to the welding tip and wire, and the negative electrode connected to the workpiece drill pipe joint. During the cladding process, an arc is generated between the positive and negative electrodes, melting the positive electrode wire and projecting it onto the drill tool surface. This cladding technique has a high heat input, as the arc directly heats the wire, resulting in significant graphite burn-off. Using highly oxidizing carbon dioxide as the shielding gas, the alloying element burn-off rate (m) can reach 25%. Using inert argon reduces this to 15%, and using a mixture of carbon dioxide and argon, the alloying element burn-off rate (m) ranges from 15% to 25%. The high heat input and high weld pool temperature associated with gas metal arc welding (GMAW, MIG, MAG) lead to a maximum alloying element dilution rate (n) of 25%.

[0059] Gas tungsten arc welding (GTAW or TIG) and gas metal arc welding (GMAW, MIG, MAG) each have their advantages and disadvantages. Due to its low heat input, GTAW produces a higher percentage of residual graphite in the weld pool. However, this same low heat input also leads to smaller wire diameters, less flux, and less alloy powder, resulting in less graphite in the final weld pool. This also results in lower weld efficiency and thin, sometimes unsatisfactory, wear-resistant hardfacing alloys. While gas metal arc welding produces a lower percentage of residual graphite in the weld pool due to its high heat input, the subsequent extended cooling time allows dissolved graphite more time to recrystallize and grow on the residual graphite. This high heat input allows for larger wire diameters, more flux, and higher weld efficiency, resulting in thicker, wear-resistant hardfacing alloys.

[0060] Graphite is the source of the self-lubricating function of the self-lubricating wear-resistant cladding alloy and is a necessary component phase. G When the graphite volume percentage content is >1%, it can show self-lubricating effect. G When the graphite content is >5%, the self-lubricating effect is obvious, but the hardness of the wear-resistant surfacing alloy itself decreases. G When the content exceeds 15%, graphite will seriously cut the alloy matrix, the brittleness of the wear-resistant cladding alloy will increase too much, the overall hardness of the wear-resistant cladding alloy will decrease a lot, and the wear life of the wear-resistant cladding alloy may decrease. G =5% to 15%, the self-lubricating and wear-resistant properties are the best. The self-lubricating and hardness required by the wear-resistant surfacing alloy can be determined according to the working conditions. For example, for deep wells, ultra-deep wells, horizontal wells, and large displacement wells, the casing is often required not to be worn by the drill bit, so the wear-resistant surfacing alloy is required to have good self-lubricating properties and low hardness, which requires a higher graphite content. On the contrary, for ordinary shallow wells, whether the casing is worn is not very important, so the wear-resistant surfacing alloy is required to have a higher hardness and better wear resistance to extend the life of the drill bit. Therefore, the wear-resistant surfacing alloy can contain less graphite. First, according to the drilling working conditions, the required graphite volume percentage C in the self-lubricating wear-resistant surfacing alloy must be determined. G .

[0061] According to the working condition requirements of the mechanical parts, after determining the graphite content of the wear-resistant cladding alloy, according to the type of cladding technology used, the burnout rate m and dilution rate n of the alloy elements in the welding wire can be determined, and then the formula C G (%) = 3(1-mn)C E , calculate the minimum graphite equivalent C that should be required in the flux-cored welding wire E Then according to the formula k[C%+0.4Si%+0.1(Ni%+Al%+Cu%+Co%)]≥C E, design the content of various alloy elements in the flux-cored welding wire, and finally determine the amount of various powders added to the core of the flux-cored welding wire according to the composition of various alloy powders, so as to manufacture a flux-cored welding wire that meets the performance requirements.

[0062] The key technology behind the self-lubricating, wear-resistant hardfacing alloy and flux-cored welding wire is to transfer graphite from the wire's flux core to the weld pool, allowing a portion to solidify in the pool. The remaining dissolved graphite then recrystallizes and grows to a sufficient volume using the remaining graphite as a core during the solidification process. This technology requires designing a flux-cored welding wire tailored to the hardfacing equipment and techniques. Specifically, sufficient graphite is incorporated into the flux core, along with various other alloying elements, such as silicon, that enhance graphite stability and promote graphitization.

[0063] The flux-cored wire is welded to the workpiece surface by tungsten inert gas arc welding (GTAW or TIG) or metal arc gas shielded welding (GMAW, MIG, MAG) to form the self-lubricating wear-resistant hardfacing alloy. The hardness is generally HRC40-55. The metallographic specimen is cut to observe the cross-sectional microstructure of the wear-resistant hardfacing alloy (such as Figure 3(a)-Figure 4(b) As shown in the figure, evenly dispersed graphite flakes or particles approximately 10 to 50 μm in size are visible. The microstructure of the tungsten inert gas arc hardfacing alloy is dominated by granular graphite, which is due to a large proportion of residual graphite and a small proportion of subsequent growth. The microstructure of the wear-resistant hardfacing alloy using metal-metal gas shielded hardfacing is primarily flake-shaped, with a small amount of granular graphite forming a network between dendrites. This is due to a small proportion of residual graphite and a large proportion of subsequent growth.

[0064] The friction and wear properties and friction coefficient of the self-lubricating hardfacing alloy described above were compared with those of conventional hardfacing alloys using an HT-1000 high-temperature friction and wear tester. Ten parallel specimens were used for each test. In the friction and wear tests, a disc specimen made of oil well cementing casing material, measuring 20×30×5 mm, was used as the disc specimen. A drill pipe hardfacing alloy was used as the pin specimen. The end face of the pin specimen was rubbed against the disc specimen under a load of 10 N and a pressure of approximately 1.4 MPa at the wear contact surface. The tests were conducted at room temperature, using water as the test medium. The test duration was 40 minutes, the rotation speed was 224 rpm, and the wear scar radius was 5.5 mm. The tester automatically monitored the friction coefficient in real time. After the friction and wear tests were completed and the friction coefficient data was exported, the wear scar profile of the disc specimen (casing) was measured using a surface profilometer. The volumetric wear of the disc specimen (casing) was calculated using the integral method, and thus the volumetric wear rate. The mass of the pin specimen before and after wear was measured using an electronic balance, and the mass wear rate of the pin specimen (drill pipe hardfacing alloy) was calculated. Test results show that the friction coefficient between the self-lubricating wear-resistant cladding alloy and the oil cementing casing is 40-50% lower than that of ordinary wear-resistant cladding alloys, reducing the casing wear rate by nearly 10 times, while its own wear resistance is equivalent to or improved with that of ordinary wear-resistant cladding alloys.

[0065] Table 1 Friction and wear test results of wear-resistant surfacing alloy and casing

[0066]

[0067] The present invention will be further described below with reference to the embodiments.

[0068] Example 1

[0069] The guide rails of a certain equipment are worn and need to be repaired. The hardness of the wear-resistant cladding alloy is required to be higher, the wear resistance is better, and it has a certain degree of self-lubrication. According to the working conditions, the volume percentage of graphite required in the self-lubricating wear-resistant cladding alloy is C G Reaching 5% will meet the requirement.

[0070] The construction company uses tungsten inert gas welding (GTAW or TIG) to weld wear-resistant alloys, using argon as the shielding gas. The estimated alloy element burnout rate m is 10%, and the alloy element dilution rate n is 10%. According to the formula C G (%) = 3(1-mn)C E , calculate the graphite equivalent C in the flux-cored welding wire E It should be at least 2.1%.

[0071] The diameter of the tungsten inert gas arc welding flux-cored wire is selected as 1.0mm, and the flux core filling rate k is selected as 10%. According to the formula C E=k[C%+0.4Si%+0.1(Ni%+Al%+Cu%+Co%)]≥2.1%, it is deduced that the amount of carbon and silicon elements added should satisfy C%+0.4Si%+0.1(Ni%+Al%+Cu%+Co%)≥21%. If the amount of graphite added in the core is C%=12%, according to the principle that the weight percentage content of silicon element should be more than twice the content of carbon element, then the amount of silicon element added can be selected as Si%=26%, which is equivalent to 62% of ferrosilicon alloy powder. Nickel powder Ni%=15%, aluminum powder Al%=5%, Cu%=4%, Co%=2% are added. The amount of these powders added has reached 100%, and there is no need to add iron powder.

[0072] The manufactured flux-cored wire was welded onto the guide rail surface using a tungsten inert gas (GTAW) welder, using argon as the shielding gas. The wear-resistant alloy was welded to a thickness of approximately 2 mm, completing the guide rail repair. Samples were taken for testing, revealing a hardness of HRC 47-52 and a graphite volume content of 4-6%.

[0073] Example 2

[0074] The wells in a certain oil field are very deep, the working conditions are complex, and the casing wear is serious. It is hoped that on the basis of protecting the drilling tools, the casing wear can be reduced. Therefore, the drilling tool wear-resistant cladding alloy is required to have good self-lubrication and low hardness. According to the drilling working conditions, the volume percentage of graphite C required in the self-lubricating wear-resistant cladding alloy is G Should reach 15%.

[0075] The pipe company uses a metal arc welding machine to weld wear-resistant alloys, using carbon dioxide as the shielding gas. The alloy element burnout rate m is expected to be 25%, and the alloy element dilution rate n is 25%. According to the formula C G (%) = 3(1-mn)C E , it is deduced that the graphite equivalent in the flux-cored wire should be at least C E =10%.

[0076] The diameter of flux-cored wire for gas metal arc welding is 1.6mm. A sufficient amount of flux core powder must be added to the wire to meet the technical requirements, so the flux core filling rate k is selected as 35%. Since the volume percentage of graphite required in the wear-resistant cladding alloy is very high, sufficient graphite powder must be added to the flux core of the wire first. Therefore, the flux core should be mainly composed of graphite and silicon elements. According to the formula

[0077] C E= k[C% + 0.4Si% + 0.1(Ni% + Al% + Cu% + Co%)] ≥ 10%. The calculated carbon and silicon additions should satisfy C% + 0.4Si% + 0.1(Ni% + Al% + Cu% + Co%) ≥ 29%. If the graphite addition in the flux core is 15% C%, and according to the principle that the silicon content by weight should be at least twice the carbon content, the silicon addition is 35% Si, which translates to 85% ferrosilicon powder. Since the graphite and ferrosilicon powder additions reach 100%, no other alloying elements or iron powder are required in the flux core. The resulting flux-cored wire was welded onto the surface of a drill pipe joint using a gas metal arc welding machine, using carbon dioxide as the shielding gas. The wear-resistant alloy was welded to a thickness of approximately 3mm. Test specimens were taken and tested, revealing a wear-resistant alloy hardness of 35-40 HRC and a graphite volume content of 13-18%, meeting design requirements.

[0078] Example 3

[0079] The wells in a certain oil field are deep, and the casing is sometimes worn by the drill pipe. The drilling company wants to protect the drill tools while reducing the wear of the casing, so it requires the drill tool wear-resistant cladding alloy to have high hardness and good self-lubrication. According to the drilling conditions, the required graphite volume percentage C in the self-lubricating wear-resistant cladding alloy is G Reaching 10% will meet the requirements.

[0080] The pipe company uses a metal arc welding machine to weld wear-resistant cladding alloy. The shielding gas is a mixture of argon and carbon dioxide, with an argon content of 80%. The alloy element burnout rate m is expected to be 15%, and the alloy element dilution rate n is 15%. According to the formula C G (%) = 3(1-mn)C E , calculate the graphite equivalent C in the flux-cored wire E The minimum should be 5%.

[0081] The diameter of the flux-cored wire for gas metal arc welding is 1.6 mm, the flux core filling rate k is 25%, and the flux core is mainly added with graphite powder and ferrosilicon alloy powder, and then added with appropriate amounts of nickel, aluminum, copper, and cobalt powder, and the balance is iron powder. According to the design formula C E=k[C% + 0.4Si% + 0.1(Ni% + Al% + Cu% + Co%)] ≥ 5%. It is calculated that the amounts of various alloying elements should satisfy C% + 0.4Si% + 0.1(Ni% + Al% + Cu% + Co%) ≥ 20%. If the graphite content in the core is C% = 10%, and according to the principle that the weight percentage of silicon should be at least twice the carbon content, the silicon content is selected to be Si% = 25%, which converts to 60% ferrosilicon alloy powder. In addition, 20% nickel powder, 5% aluminum powder, 4% copper powder, and 1% cobalt powder are added. The total powder content reaches 100%, so there is no need to add iron powder.

[0082] The manufactured flux-cored wire was welded onto the surface of a drill pipe joint using a gas metal arc welding machine. A mixture of argon and carbon dioxide was used as the shielding gas, with 80% argon. The thickness of the welded wear-resistant alloy was approximately 3 mm. Samples were taken for testing, revealing a hardness of HRC 50-55 and a graphite volume content of 8-12%.

Claims

1. Self-lubricating wear-resistant surfacing flux-cored welding wire, characterized in that: The flux-cored welding wire includes a flux core wrapped in an outer sheath, the flux core including graphite powder and ferrosilicon alloy powder, with the balance being iron powder; the amount of each powder added should ensure that the weight percentage content of silicon in the flux-cored welding wire is more than twice the weight percentage content of carbon; the outer sheath of the flux-cored welding wire is a low-carbon steel strip; the flux core filling rate of the flux-cored welding wire is 10% to 35%; The weight percentage content of various powders in the flux core of the flux cored welding wire is as follows: graphite powder 10% to 15%, ferrosilicon alloy powder 35% to 85%, nickel powder 0% to 30%, aluminum powder 0% to 20%, copper powder 0% to 10%, cobalt powder 0% to 5%, and the balance is iron powder; According to the required graphite volume percentage C in the self-lubricating wear-resistant cladding alloy G , according to formula C G (%) = 3 (1- mn) C E , calculate the minimum graphite equivalent C required for the flux-cored wire E ; Then according to the formula k[C%+0.4Si%+0.1(Ni%+ Al%+Cu%+Co%)]≥C E , determining the addition amount of various alloying elements and their powders in the flux core of the flux cored welding wire; The volume percentage of graphite in the self-lubricating wear-resistant cladding alloy is calculated as follows: G (%) = 3 (1-mn) C E , where m is the burnout rate of the alloy element in the welding arc, and m is 0.10 to 0.25; n is the dilution rate of the alloy element in the wear-resistant surfacing alloy, and n is 0.10 to 0.25; C E is the graphite equivalent of the flux-cored wire; C E =k[C%+0.4Si%+0.1(Ni%+Al%+Cu%+Co%)], where k is the core filling rate of the flux-cored welding wire, and C%, Si%, Ni%, Al%, Cu% and Co% represent the contents of C, Si, Ni, Al, Cu and Co elements in the flux core, respectively.

2. The self-lubricating wear-resistant surfacing flux-cored welding wire according to claim 1, characterized in that: One or more of nickel powder, aluminum powder, copper powder and cobalt powder can also be added to the core.

3. The method for preparing the self-lubricating wear-resistant surfacing flux-cored welding wire according to any one of claims 1 to 2, characterized in that: The specific steps are as follows: Step 1: Weigh the following powders by mass percentage: graphite powder 10% to 15%, ferrosilicon alloy powder 35% to 85%, nickel powder 0% to 30%, aluminum powder 0% to 20%, copper powder 0% to 10%, cobalt powder 0% to 5%, and the balance iron powder; Step 2: placing the graphite powder, ferrosilicon alloy powder, nickel powder, aluminum powder, copper powder, cobalt powder and iron powder weighed in step 1 in a vacuum heating furnace for drying; placing the dried powder in a powder mixer for mixing to obtain a mixed powder; Step 3: Fill the mixed powder into the U-shaped groove of the low-carbon steel strip and make flux-cored welding wire after closed rolling; The addition amount of various powders should ensure that the weight percentage content of silicon element in the flux-cored welding wire reaches more than twice the weight percentage of carbon element; the flux core filling rate of the flux-cored welding wire is 10% to 35%.

4. A method for preparing a cladding alloy using the flux-cored welding wire according to any one of claims 1 to 2, characterized in that: Using tungsten inert gas arc welding or metal arc gas shielded welding to build up the flux-cored wire on the surface of the workpiece to form a build-up alloy; Among them, when using metal arc welding, a mixture of carbon dioxide and argon is used as the shielding gas; When using tungsten inert gas welding, argon is used as the shielding gas; During the welding process, the alloy element burnout rate m is: 0.10≤m≤0.25; the alloy dilution rate n is: 0.10≤n≤0.25.

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