Method for manufacturing submerged arc welding wire for pure hydrogen transmission pipeline, and submerged arc welding method for pure hydrogen transmission pipeline

Abstract

The application discloses a preparation method of a submerged-arc welding wire for a pure hydrogen conveying pipeline and a submerged-arc welding method of the pure hydrogen conveying pipeline. In the preparation method of the welding wire, the chemical composition of the molten steel comprises C≤0.05%, Si 0.05~0.20%, Mn 0.70~0.90%, Cr 0.10~0.20%, Ni+Mo 0.10~0.20%, Ti 0.01~0.10%, Nb 0.01~0.10%, Cu≤0.10%, P≤0.005%, S≤0.005%, and the rest is Fe and impurities; in the billet forging process, the steel ingot is heated to 1150~1200 DEG C and then is kept for ≥1h, and then is forged to obtain a small square billet and is cooled to room temperature; in the rolling process, the heating temperature is 1050~1100 DEG C, the finish rolling inlet temperature is 890~920 DEG C, and the wire feeding temperature is 850~890 DEG C.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of welding materials, and particularly relates to a preparation method of a submerged-arc welding wire for a pure hydrogen conveying pipeline and a submerged-arc welding method of the pure hydrogen conveying pipeline. BACKGROUND

[0002] Hydrogen energy, as a clean and zero-carbon new energy, has broad application prospects. With the development of technology and the popularization and application of hydrogen energy, large-scale centralized hydrogen production and long-distance hydrogen conveying are indispensable links.

[0003] At present, the commonly used hydrogen conveying pipeline is mainly applied to the conveying of hydrogen mixed gas or low-pressure (less than 5 MPa) pure hydrogen, and the conveying pressure is relatively small, and the requirements for the welds of the conveying pipeline and the pipeline connection are low.

[0004] However, in the long-distance conveying process of high-pressure (greater than or equal to 5 MPa) pure hydrogen, the welds of the conveying pipeline and the pipeline connection are in long-time contact with high-pressure and high-purity hydrogen, which is easy to cause hydrogen embrittlement and hydrogen-induced cracking, thereby leading to failure. Especially, the welds of the pipeline connection are more prone to hydrogen embrittlement and hydrogen-induced cracking due to the characteristics of stress concentration, compared with the base steel plate and the heat-affected zone, which seriously affects the safety of pipeline transportation. SUMMARY

[0005] In view of the deficiencies in the prior art, the purpose of the present application is to provide a preparation method of a submerged-arc welding wire for a pure hydrogen conveying pipeline and a submerged-arc welding method of the pure hydrogen conveying pipeline.

[0006] To achieve the above-mentioned application purposes, an embodiment of the present application provides a preparation method of a submerged-arc welding wire, which comprises sequentially performed molten steel smelting, ingot casting, billet forging, rolling, surface treatment, drawing and copper plating processes;

[0007] The chemical composition of the molten steel obtained in the molten steel smelting process includes, in mass percent, C≤0.05%, Si 0.05~0.20%, Mn 0.70~0.90%, Cr 0.10~0.20%, Ni+Mo 0.10~0.20%, Ti 0.01~0.10%, Nb 0.01~0.10%, Cu≤0.10%, P≤0.005%, S≤0.005%, and the rest is Fe and unavoidable impurities;

[0008] In the ingot casting process, the molten steel obtained in the molten steel smelting process is injected into a mold to form an ingot;

[0009] In the billet forging process, the ingot is heated to 1150~1200℃ and then is kept for ≥1h, and then is forged to obtain a small square billet, and is cooled to room temperature;

[0010] In the rolling process, the billets are sequentially subjected to heating, rough rolling, finish rolling, wire laying, and cooling to obtain the wire rod; wherein the heating temperature is 1050-1100℃, the finish rolling inlet temperature is 890-920℃, and the wire laying temperature is 850-890℃.

[0011] In an embodiment, in the molten steel smelting process, a vacuum induction melting furnace is used to smelt the molten steel, and the vacuum degree in the vacuum induction melting furnace is controlled to be <0.15 mbar.

[0012] In an embodiment, in the molten steel smelting process, carbon particles, electrolytic nickel, metallic chromium, molybdenum strips, and niobium strips are fed into the vacuum induction melting furnace for electric melting, and during the melting, metallic manganese, polysilicon, and titanium sponge are added for composition adjustment; after the molten steel is smelted to the target chemical composition and reaches the target temperature, the molten steel is tapped, wherein the target temperature is controlled to be 1590-1610℃.

[0013] In an embodiment, the surface treatment process includes sequentially performed mechanical peeling, abrasive belt polishing, online pickling and water washing, and boronizing steps.

[0014] In an embodiment, the cross-sectional size of the billet obtained in the billet forging process is 53mm x 53mm, the diameter of the wire rod obtained in the rolling process is 6.5mm, and the diameter of the welding wire is 4.0mm.

[0015] To achieve the above-mentioned application purposes, an embodiment of the present application provides a submerged arc welding method, which covers the electric arc by a flux, forms a protective slag, continuously feeds a welding wire into the electric arc area, and melts the welding wire with a workpiece to form a weld seam, and the molten slag forms a slag shell after cooling.

[0016] The welding wire is prepared by the preparation method of the submerged arc welding wire as described above.

[0017] In an embodiment, the basicity of the flux is ≥2.0.

[0018] In an embodiment, the chemical composition of the flux includes, in terms of mass percentage, P≤0.005%, S≤0.005%, CaF220-30%, SiO2+TiO210-20%, Al2O3+MnO 6-10%, and CaO+MgO 35-45%.

[0019] In an embodiment, the submerged arc welding method uses a V-shaped groove with a groove angle of 45-60°, a root face thickness of 1.5-4mm, and an assembly gap of 2-3mm; the welding current is 500-600A, the arc voltage is 30-40V, and the welding speed is 300-350mm / min.

[0020] In an embodiment, the microstructure of the weld metal formed by welding is a composite structure of ferrite + pearlite, wherein the proportion of ferrite is ≥80%, and the grain size of the ferrite structure is ≥9.5 grade.

[0021] In an embodiment, the tensile strength Rm of the weld metal formed by welding is ≥510 MPa, the yield strength Rp is ≥410 MPa, the elongation after fracture A is ≥23%, the impact energy Akv at -20℃ is ≥100 J, and the hardness HV 10 ≤210.

[0022] Compared with the prior art, the application has the following beneficial effects:

[0023] (1) By reasonably designing the chemical composition and content, in the design scheme of the chemical composition, the design idea of low C + low Mn + low P + low S is adopted, wherein the lower C content can reduce the center segregation and effectively inhibit the formation of carbides, thereby reducing the risk of hydrogen-induced cracking of the weld; the appropriate amount of Mn can reduce the formation of MnS and eliminate the MnS segregation, thereby reducing the risk of hydrogen-induced cracking of the weld; further, by adding an appropriate amount of Si, the deoxidation capacity in the welding process can be ensured, thereby improving the Mn / Si ratio; the low P and low S control can effectively reduce the generation of inclusions and segregation, thereby improving the hydrogen embrittlement resistance of the weld; in addition, by adding appropriate amounts of alloying elements Mo and Ni and micro-alloying elements Ti and Nb, the strength, impact toughness and corrosion resistance of the weld metal can be improved.

[0024] (2) The welding wire prepared by the preparation method of the application can be used for welding of pure hydrogen conveying pipelines, and has good compatibility with hydrogen and is suitable for high-pressure environments with a pipeline conveying pressure of ≥5 MPa.

[0025] (3) The submerged-arc welding method of the application uses the welding wire prepared by the above preparation method, the microstructure of the weld metal formed by welding is a composite structure of ferrite + trace pearlite, wherein the proportion of ferrite is ≥80%, and the grain size of the ferrite structure is ≥9.5 grade; the weld metal formed by welding has excellent mechanical properties, and has good hydrogen compatibility, can be applied to high-pressure environments with a pipeline conveying pressure of ≥5 MPa, and can be applied to the conveying of pure hydrogen. DETAILED DESCRIPTION

[0026] The technical solutions of the application will be further described below in combination with specific embodiments, but the scope of protection is not limited to the description.

[0027] The application provides a submerged-arc welding wire. The submerged-arc welding wire can be used for welding of pure hydrogen conveying pipelines, and has good compatibility with hydrogen and is suitable for high-pressure environments with a pipeline conveying pressure of ≥5 MPa.

[0028] The application also provides a preparation method of the submerged arc welding wire. The preparation method comprises sequentially performed molten steel smelting, ingot casting, billet forging, rolling, surface treatment, drawing and copper plating processes.

[0029] The preparation method of the submerged arc welding wire of the application is obtained according to a large number of experimental researches, and each process in the preparation method is further described sequentially as follows.

[0030] Each process is described in detail as follows.

[0031] (1) Molten steel smelting process

[0032] The chemical composition of the molten steel obtained by the molten steel smelting process includes, in mass percentage: C≤0.05%, Si 0.05~0.20%, Mn 0.70~0.90%, Cr 0.10~0.20%, Ni+Mo 0.10~0.20%, Ti 0.01~0.10%, Nb 0.01~0.10%, Cu≤0.10%, P≤0.005%, S≤0.005%, and the balance of Fe and unavoidable impurities.

[0033] It can be understood that the chemical composition of the molten steel obtained by the molten steel smelting process is the same as the chemical composition of the ingot obtained by the subsequent ingot casting process, the chemical composition of the billet obtained by the subsequent billet forging process, the chemical composition of the wire rod obtained by the subsequent rolling process, and the chemical composition of the finally obtained welding wire, all of which are consistent with the chemical composition described above, and will not be described here.

[0034] Specifically, the chemical composition of each element is as follows:

[0035] C: The increase of C content can effectively improve the strength of the weld metal, but when the content is too high, the welding cold crack sensitivity increases, the low temperature impact toughness and the welding performance are poor; an appropriate amount of carbon can reduce the central segregation and effectively inhibit the formation of carbides, thereby reducing the risk of hydrogen-induced cracking of the weld.

[0036] Si: Si is the main deoxidizing element in the welding process, which can improve the deoxidizing capacity in the welding process.

[0037] Mn: An appropriate amount of Mn can reduce the formation of MnS and eliminate MnS segregation, thereby reducing the risk of hydrogen-induced cracking of the weld.

[0038] Cr: Cr can significantly improve the strength and hardness of the weld metal, and also improve the oxidation resistance and corrosion resistance of the weld metal.

[0039] Ni: Ni can significantly improve the toughness of the weld metal, especially the low temperature impact toughness, and reduce the brittle transition temperature; in addition, Ni can also expand the austenite region, thereby improving the tensile strength and hardness of the weld metal.

[0040] Mo: can significantly improve the strength and hardness of the weld metal, while refining the grain, improving the toughness of the weld metal.

[0041] Ti: is a strong deoxidizer, which can refine the grain size of the weld, improve the toughness and crack resistance of the weld metal.

[0042] Nb: can refine the grain, improve the crack resistance of the grain boundary, and improve the low temperature toughness of the weld metal.

[0043] Cu: will form copper-containing precipitates, reducing the toughness and plasticity of the weld metal.

[0044] P, S as impurity elements in the welding wire, low P, low S can effectively reduce the inclusion and segregation, and further improve the hydrogen embrittlement resistance of the weld.

[0045] In summary, the chemical composition design scheme of the submerged arc welding wire of the present application adopts the design idea of low C + medium-low Mn + low P + low S, wherein the lower C content can reduce the core segregation and effectively inhibit the formation of carbides, thereby reducing the risk of hydrogen-induced cracking of the weld; appropriate amount of Mn can reduce the formation of MnS and eliminate MnS segregation, reduce the risk of hydrogen-induced cracking of the weld, and further add appropriate amount of Si to ensure a certain Mn / Si ratio, thereby improving the deoxidation capacity during welding; low P and low S control can effectively reduce the inclusion and segregation to improve the hydrogen embrittlement resistance of the weld; in addition, by adding appropriate amount of alloying elements Mo, Ni and micro-alloying elements Ti, Nb, the strength, impact toughness and corrosion resistance of the weld metal can be improved.

[0046] Preferably, in the molten steel smelting process, a vacuum induction melting furnace is used for molten steel smelting, and the vacuum degree in the vacuum induction melting furnace is controlled to be <0.15 mbar. By controlling the vacuum degree, the N content in the molten steel can be reduced to ensure the impact toughness of the weld metal.

[0047] Specifically, carbon particles, electrolytic nickel, metallic chromium, molybdenum strips, niobium strips are sent into the vacuum induction melting furnace for power melting, and metal manganese, polysilicon and sponge titanium are added for composition adjustment during melting. After the molten steel is smelted to the target chemical composition and reaches the target temperature, the molten steel is tapped, wherein the target temperature is controlled to be 1590-1610℃. The appropriate tapping temperature can avoid excessive solidification shrinkage during pouring of the ingot, which can cause serious shrinkage and porosity, and can also improve the surface quality of the ingot.

[0048] Tapping refers to discharging molten steel from the vacuum induction melting furnace to the container of the next process.

[0049] (2) Ingot pouring process

[0050] The molten steel obtained in the molten steel smelting process is injected into a mold to form a steel ingot.

[0051] Specifically, after the molten steel in the molten steel smelting process reaches the target chemical composition and the temperature of the molten steel is 1590-1610℃, the molten steel is tapped and injected into a steel ingot mold to form a steel ingot. Then the steel ingot is cut and ground to obtain a steel ingot without surface defects. In this way, the surface quality of the subsequent wire rod and welding wire can be ensured.

[0052] (3) Billet forging process

[0053] After the steel ingot is heated to 1150-1200℃ and held for ≥1h, it is forged to obtain a small billet, which is then cooled to room temperature.

[0054] Specifically, after the small billet is obtained, it is slowly cooled to room temperature at a cooling rate <1℃ / s. By slow cooling, the stress generated during forging can be released to avoid cracking of the small billet.

[0055] Preferably, the cross-sectional size of the small billet is 53mm x 53mm.

[0056] (4) Rolling process

[0057] The small billet is sequentially heated, rough rolled, finished rolled, wire-drawing, and cooled to obtain a wire rod with a diameter of 6.5mm. The heating temperature is 1050-1100℃, the finishing rolling inlet temperature is 890-920℃, and the wire-drawing temperature is 850-890℃.

[0058] Using a higher finishing rolling inlet temperature and wire-drawing temperature can coarsen the microstructure grains of the wire rod, reduce the strength of the wire rod, and be beneficial to subsequent drawing.

[0059] (5) Surface treatment process

[0060] Preferably, the surface treatment process includes sequentially performed mechanical descaling, abrasive belt grinding, online pickling and water washing, and boronizing steps. In this way, the oxide scale on the surface of the wire rod can be effectively removed, making the surface of the wire rod shiny and metallic, which provides good surface conditions for subsequent drawing and copper plating.

[0061] The mechanical descaling removes the hot-rolled oxide scale and slight scratches, roll marks, and adhered impurities on the surface of the wire rod by bending and straightening and shot blasting.

[0062] Bending and straightening is to pass the wire rod through a group of staggered straightening rollers to undergo repeated bending deformation. This bending stress causes brittle oxide scale to crack and peel off from the ductile metal matrix.

[0063] Shot peening uses centrifugal force to propel a large number of fine metal pellets or abrasive particles (such as stainless steel shot) at high speed onto the surface of wire rods. These metal pellets violently impact the surface of the wire rods, thereby completely breaking down and peeling off the oxide scale.

[0064] Belt grinding is performed on a production line equipped with large belt grinding heads. The grinding heads are driven by a motor and have annular abrasive belts that rotate at extremely high linear speeds. The wire rod passes under tension, tightly against the support rollers beneath the grinding head. As the annular abrasive belts rotate, they grind the surface of the wire rod to achieve specific surface roughness and gloss, and remove microscopic defects.

[0065] Depending on the product requirements, different grit sizes of abrasive belts can be used for multiple passes of abrasive belt grinding. The grinding sequence is based on the grit size of the abrasive belt from largest to smallest.

[0066] In the online pickling and washing process, the wire rod first passes continuously through one or more closed pickling tanks containing sulfuric acid. After pickling, the wire rod immediately enters a multi-stage washing tank, where it is repeatedly rinsed with circulating pure water or hot water to ensure that the surface is neutral. The multi-stage washing tank includes a spray tank and an immersion tank. After that, it is dried.

[0067] Online pickling and washing can remove the extremely thin oxide layer and embedded metal particles remaining on the surface of the wire rod after mechanical peeling and belt grinding, thus activating and cleaning the wire rod surface.

[0068] During boronizing, the wire rod first passes through a boronizing agent coating device, using roller coating or immersion to uniformly coat the surface of the wire rod with a layer of boronizing agent film. Then, it is sent into a heating furnace for heat treatment at 500~900℃. During the heat treatment process, boron diffuses to the surface of the wire rod and reacts with iron to form a hard and porous Fe2B layer. The Fe2B layer can still maintain excellent lubrication effect under high pressure and high temperature, thereby reducing friction and wear, extending the life of stamping or drawing dies, and reducing defects such as scratches and cracks in the workpiece during processing. The Fe2B layer can also prevent "cold welding" or adhesion between metals under extreme deformation conditions.

[0069] (6) Drawing and copper plating processes

[0070] Specifically, the wire rod is drawn to a diameter of 4.0 mm through four rounds of die drawing, then copper plating is performed, and the wire is wound in layers to obtain a copper-plated welding wire with a diameter of 4.0 mm.

[0071] The welding wire prepared by the above method can be used for welding pure hydrogen transportation pipelines. It not only has good compatibility with hydrogen, but is also suitable for high-pressure environments with pipeline transportation pressures above 5 MPa.

[0072] This application also provides a submerged arc welding method.

[0073] Submerged Arc Welding (SAW) is an automatic welding method in which the electric arc burns under a layer of flux.

[0074] The SAW welding method of the present application covers the electric arc with flux, forms a protective slag, continuously feeds the welding wire into the arc area, and melts to form a weld with the workpiece. The slag forms a slag shell after cooling.

[0075] The welding wire is prepared by the method described above. The weld metal after welding has excellent hydrogen compatibility.

[0076] The SAW welding method not only has the advantages of high efficiency, stability, and high quality, but also can reduce defects such as pores and cracks. Moreover, it can be used for welding pure hydrogen transmission pipelines, and the microstructure and mechanical properties of the weld metal formed by welding are excellent.

[0077] Preferably, the basicity of the flux used in the SAW welding method is ≥2.0. In this way, the oxygen content in the weld can be reduced, the inclusions in the weld can be reduced, and the low-temperature impact toughness of the weld metal can be improved. The hydrogen resistance of the weld metal is improved.

[0078] The basicity of the flux is calculated by the following formula:

[0079] .

[0080] [CaO] is the mass percentage of CaO in the flux, for example, if the mass percentage of CaO in the flux is 20%, then [CaO] is 20. [MgO], [CaF2], [MnO], [SiO2], [Al2O3], [TiO2] and so on.

[0081] Preferably, the chemical composition of the flux used in the SAW welding method includes, by mass percentage: P≤0.005%, S≤0.005%, CaF2 20~30%, SiO2+TiO2 10~20%, Al2O3+MnO 6~10%, CaO+MgO 35~45%.

[0082] The specific description of each component in the chemical composition of the flux is as follows.

[0083] P, S: Low P and low S can improve the hydrogen embrittlement resistance of the weld metal and improve the hydrogen compatibility of the weld metal.

[0084] CaF2: can promote gas escape and avoid pore defects in the weld metal.

[0085] SiO2+TiO2: can supplement the Si and Ti burned in the welding wire, avoid the Si and Ti in the molten pool forming slag and being stripped, and thus the Si and Ti content in the weld metal cannot reach the target content.

[0086] Al2O3+MnO: can improve the high-temperature stability of the slag and the formability of the weld.

[0087] CaO+MgO: can capture non-metallic inclusions and improve the purity of the weld metal.

[0088] In summary, by using high-alkalinity, ultra-low phosphorus content, ultra-low sulfur content, ultra-low fluorine content, and low-hydrogen alkaline sintered flux, not only can the oxygen content in the weld be reduced, the inclusions in the weld can be reduced, thereby improving the low-temperature impact toughness of the weld metal, improving the hydrogen resistance performance of the weld metal, and the ultra-low phosphorus content, sulfur content control can further improve the hydrogen embrittlement resistance of the weld metal, and improve the hydrogen compatibility of the weld metal.

[0089] Preferably, in the submerged arc welding method, a V-shaped groove is used, the groove angle is 45-60°, the root face thickness is 1.5-4mm, and the assembly gap is 2-3mm; the welding current is 500-600A, the arc voltage is 30-40V, and the welding speed is 300-350mm / min. By reasonably controlling the heat input, the cooling speed after welding can be ensured, and thus the weld metal has good plasticity and toughness.

[0090] After detection, the weld metal formed by welding has a composite structure of ferrite + pearlite, wherein the proportion of ferrite is ≥80%, the content of pearlite is small, and the grain size of ferrite structure is ≥9.5 level.

[0091] The tensile strength Rm of the weld metal formed by welding is ≥510MPa, the yield strength Rp is ≥410MPa, the elongation A after fracture is ≥23%, the impact energy Akv at -20℃ is ≥100J, and the hardness HV 10 ≤210, which can meet the performance requirements of the matching welding material of L360MH grade pure hydrogen conveying pipeline steel plate.

[0092] Further referring to GB / T 34542.2-2018 "Hydrogen storage and conveying system Part 2: Test method for compatibility of metal materials and hydrogen environment", the weld metal formed by welding is tested for slow strain rate tensile test, fracture toughness test, and fatigue life test under 6.3MPa high pressure environment + pure hydrogen atmosphere and 6.3MPa high pressure environment + pure nitrogen atmosphere respectively. The tensile strength Rm of the weld metal formed by welding is ≥490MPa, the elongation A after fracture is ≥20%, the reduction of area Ψ is ≥67%, the fracture toughness is ≥130MPa·m 1 / 2 , and the fatigue life is ≥8300 / number of times.

[0093] Under the high pressure environment of 6.3 MPa, compared with the pure nitrogen atmosphere, under the pure hydrogen atmosphere, the loss of the tensile strength, the elongation after fracture, the reduction of area, the fracture toughness and the fatigue life of the weld metal formed by welding are smaller, which shows that the weld metal has good hydrogen compatibility and can be applied to the high pressure environment with the pipeline transportation pressure above 5 MPa and applied to the pure hydrogen transportation.

[0094] The specific embodiments of the present application are further described below through 10 examples and 4 comparative examples.

[0095] The processes of the preparation method of the welding wire are specifically as follows.

[0096] (1) Molten steel smelting process

[0097] The vacuum induction melting furnace is used for molten steel smelting, and the vacuum degree in the vacuum induction melting furnace is controlled to be <0.15 mbar.

[0098] Specifically, the carbon particles, electrolytic nickel, metal chromium, molybdenum bar and niobium bar are sent into the vacuum induction melting furnace for power smelting, and the metal manganese, polysilicon and sponge titanium are added during smelting for composition adjustment, and after the molten steel is smelted to the target chemical composition and reaches the target temperature, the molten steel is tapped, wherein the target temperature is controlled to be 1590-1610℃.

[0099] The chemical composition of the molten steel obtained by the molten steel smelting process is shown in Table 1 in terms of mass percentage. The molten steel is tapped when it reaches the target chemical composition and tapping temperature of Table 1. The tapping temperature is shown in Table 2.

[0100] Table 1

[0101]

[0102] (2) Ingot casting process

[0103] The molten steel is poured into the ingot mold to form an ingot. Then the ingot is cut head and tail and the surface is ground, and the ingot surface is bright and smooth without visible defects.

[0104] It can be understood that the chemical composition of the obtained ingot is also shown in Table 1.

[0105] (3) Billet forging process

[0106] After the ingot is heated and kept, the heating temperature and the holding time are shown in Table 2, and then it is forged to obtain a small square billet with a cross-sectional size of 53mmx53mm. The small square billet is slowly cooled to room temperature at a cooling rate of <1℃ / s.

[0107] It can be understood that the chemical composition of the obtained small square billet is also shown in Table 1.

[0108] (4) Rolling process

[0109] The small billets were sequentially heated, rough-rolled, finish-rolled, wire-rolled, and cooled to obtain a wire rod with a diameter of 6.5 mm. The heating temperature, the finish-rolling inlet temperature, and the wire-rolling temperature are shown in Table 2.

[0110] It can be understood that the chemical composition of the obtained wire rod is also shown in Table 1.

[0111] Table 2

[0112]

[0113] (5) Surface treatment process

[0114] After the wire rod was stored at room temperature for three days, it was loaded into a wire feeding frame for wire drawing treatment to eliminate the stress of the wire rod. Then the wire rod was sequentially subjected to mechanical peeling, abrasive belt polishing, online pickling and water washing, and boronizing steps to remove the oxide skin on the surface of the wire rod.

[0115] After the surface treatment, the wire rod was high-temperature dried, and the surface of the wire rod was metallic.

[0116] (6) Drawing and copper plating process

[0117] Through four-pass die drawing, the wire rod was drawn into a steel wire with a diameter of 4.0 mm, then copper plating was performed, and layer winding was performed to obtain a copper-plated welding wire with a diameter of 4.0 mm.

[0118] It can be understood that the chemical composition of the obtained welding wire is also shown in Table 1.

[0119] In the submerged arc welding method, the workpiece to be welded is an L360MH steel plate with a thickness of 14 mm; the welding wire is obtained by the above preparation method; the chemical composition of the welding flux includes, by mass percent: P 0.004%, S 0.003%, CaF2 20%, SiO2+TiO2 12%, Al2O3+MnO 8%, CaO+MgO 40%, and the basicity of the welding flux is 2.0.

[0120] By covering the electric arc with the welding flux, a protective slag is formed, the welding wire is continuously fed into the electric arc area, and is fused with the workpiece to form a weld, and the slag is cooled to form a slag shell.

[0121] The groove adopts a V-shaped groove with a groove angle of 45-60° and a root face thickness of 1.5-4 mm, and the assembly gap is 2-3 mm; the welding current, the arc voltage, and the welding speed are shown in Table 3.

[0122] Table 3

[0123]

[0124] The microstructure of the weld metal is a composite structure of ferrite + pearlite, wherein the proportion of ferrite is ≥80%, and the content of pearlite is small.

[0125] The microstructure and mechanical properties of the weld formed after welding are tested, specifically including:

[0126] a. The tensile properties are tested according to GB / T 228.1 “Metallic Materials Tensile Test Part 1: Room Temperature Test Method”, and the tensile strength, yield strength Rp, and elongation after fracture A of the weld metal are measured as shown in Table 4;

[0127] b. The impact test is performed according to GB / T 229 “Metallic Materials Charpy Pendulum Impact Test Method”, and the -20℃ impact energy Akv of the weld metal is measured as shown in Table 4;

[0128] c. The hardness test is performed according to GB / T 2654-2008 “Welded Joint Hardness Test Method”, and the hardness HV of the weld metal is measured as shown in Table 4; 10 as shown in Table 4;

[0129] d. The grain size test is performed according to GB / T 6394-2017 “Metallic Average Grain Size Determination Method”, wherein the grain size level of the ferrite structure is shown in Table 4.

[0130] Table 4

[0131]

[0132] According to GB / T 34542.2-2018 “Hydrogen Storage and Transportation System Part 2: Test Method for Compatibility of Metal Materials and Hydrogen Environment”, slow strain rate tensile test, fracture toughness test, and fatigue life test are performed on the weld metal formed by welding under 6.3MPa high pressure environment + pure hydrogen atmosphere and 6.3MPa high pressure environment + pure nitrogen atmosphere, respectively. The loading stress of the fatigue life test is 500MPa, and the frequency is 1Hz.

[0133] The tensile strength Rm, elongation after fracture A, reduction of area Ψ, fracture toughness, and fatigue life of the weld metal formed by welding are measured as shown in Table 5.

[0134] Table 5

[0135]

[0136] With pure nitrogen atmosphere as the reference benchmark, it can be seen from Table 5 that under pure hydrogen atmosphere, the loss of tensile strength, elongation after fracture, reduction of area, fracture toughness, and fatigue life of the weld metal of the 10 examples is small, indicating that the weld metal has good hydrogen compatibility.

[0137] The tensile strength, elongation at break, reduction of area, fracture toughness and fatigue life of the weld metal of the four comparative examples are greatly lost, which indicates that the hydrogen compatibility of the weld metal is poor.

[0138] It should be understood that, although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the present specification is described in this way only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.

[0139] The detailed description listed above is only a specific description of the feasible embodiments of the present application, and is not used to limit the protection scope of the present application, and equivalent embodiments or changes made without departing from the spirit of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing submerged arc welding wire, characterized in that, This includes the sequential processes of steel smelting, casting steel ingots, forging steel billets, rolling, surface treatment, drawing, and copper plating. The chemical composition of the molten steel obtained from the steelmaking process, by mass percentage, includes: C≤0.05%, Si 0.05~0.20%, Mn 0.70~0.90%, Cr 0.10~0.20%, Ni+Mo 0.10~0.20%, Ti 0.01~0.10%, Nb 0.01~0.10%, Cu≤0.10%, P≤0.005%, S≤0.005%, with the remainder being Fe and unavoidable impurities; In the process of casting steel ingots, molten steel obtained from steel smelting is poured into a mold to form steel ingots; In the billet forging process, the steel ingot is heated to 1150~1200℃ and held for ≥1h, then forged to obtain a small square billet, and cooled to room temperature at a cooling rate of <1℃ / s. In the rolling process, the small square billet is sequentially heated, rough rolled, finish rolled, wire rod produced, and cooled to obtain wire rod; wherein the heating temperature is 1050~1100℃, the finish rolling inlet temperature is 890~920℃, and the wire rod producing temperature is 850~890℃.

2. The method for preparing submerged arc welding wire according to claim 1, characterized in that, In the steel smelting process, a vacuum induction melting furnace is used for steel smelting, and the vacuum degree in the vacuum induction melting furnace is controlled to be <0.15mbar.

3. The method for preparing submerged arc welding wire according to claim 1, characterized in that, In the steel smelting process, carbon particles, electrolytic nickel, metallic chromium, molybdenum bars, and niobium bars are fed into a vacuum induction melting furnace and smelted by electricity. During the smelting process, metallic manganese, polycrystalline silicon, and sponge titanium are added to adjust the composition. After the molten steel reaches the target chemical composition and the target temperature, it is tapped. The target temperature is controlled at 1590~1610℃.

4. The method for preparing submerged arc welding wire according to claim 1, characterized in that, The surface treatment process includes mechanical peeling, belt sanding, online pickling and washing, and boronizing steps performed in sequence.

5. The method for preparing submerged arc welding wire according to claim 1, characterized in that, The cross-sectional dimensions of the small square billet obtained by the billet forging process are 53mm × 53mm, the diameter of the wire rod obtained by the rolling process is 6.5mm, and the diameter of the welding wire is 4.0mm.

6. A submerged arc welding method, characterized in that, The flux covers the electric arc to form a protective slag. The welding wire is continuously fed into the arc zone and fuses with the workpiece to form a weld. After the slag cools, it forms a slag shell. The welding wire is prepared using the method for preparing submerged arc welding wire as described in any one of claims 1 to 5.

7. The submerged arc welding method according to claim 6, characterized in that, The basicity of the flux is ≥2.

0.

8. The submerged arc welding method according to claim 7, characterized in that, The chemical composition of the flux, by mass percentage, includes: P≤0.005%, S≤0.005%, CaF2 20~30%, SiO2+TiO2 10~20%, Al2O3+MnO 6~10%, CaO+MgO 35~45%.

9. The submerged arc welding method according to claim 6, characterized in that, The welding process employs a V-groove with a groove angle of 45~60°, a blunt edge thickness of 1.5~4mm, and an assembly gap of 2~3mm. The welding current is 500~600A, the arc voltage is 30~40V, and the welding speed is 300~350mm / min.

10. The submerged arc welding method according to claim 8, characterized in that, The weld metal formed by welding has a composite structure of ferrite and pearlite, wherein the proportion of ferrite is ≥80% and the grain size of the ferrite structure is ≥9.

5.

11. The submerged arc welding method according to claim 8, characterized in that, The weld metal formed by welding has the following properties: tensile strength Rm ≥ 510 MPa, yield strength Rp ≥ 410 MPa, elongation after fracture A ≥ 23%, impact energy Akv ≥ 100 J at -20℃, and hardness HV. 10 ≤210.

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