High-alkalinity sintered flux for pressure steel pipe of pumped storage power station and preparation method of high-alkalinity sintered flux

Abstract

The invention discloses a high-alkalinity sintered flux for a pressure steel pipe of a pumped storage power station and a preparation method of the high-alkalinity sintered flux, and belongs to the technical field of welding. The problems that after the pressure steel pipe of the pumped storage power station is welded through the welding flux, a weld joint cannot have high strength and low-temperature toughness at the same time, and the slag detachability is poor are solved. The flux comprises mineral dry powder and a binder, wherein the mineral dry powder comprises the following components in percentage by mass: 6-16% of wollastonite, 10-20% of fused magnesite, 25-40% of bauxite, 25-40% of fluorite, 5-10% of feldspar, 1-5% of manganese ore and 1-5% of an alloying agent. A wollastonite-bauxite-fluorite-fused magnesite quaternary system is used for deep deoxidation through oxygen potential synergistic pressing and nucleation synergistic catalysis, formation of acicular ferrite is promoted, and the low-temperature impact toughness is improved. When the welding flux is used in cooperation with a high-strength steel welding wire, the welding seam formability is good, the welding seam structure components are uniform, high strength and low-temperature toughness are achieved, the surface of a welding bead is smooth, and the deslagging performance is good.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, specifically relating to a high-basicity sintering flux for pressure steel pipes in pumped storage power stations and its preparation method. Background Technology

[0002] As the core pressure-bearing structure of pumped-storage power station pressure steel pipes, which withstand ultra-high water head pressure (≥800m), high-frequency alternating loads, and complex geological stresses, the performance of its welded joints directly affects the safety and service life of the power station. Currently, submerged arc welding (SAW) has become the mainstream welding process in the large-scale pipe section manufacturing process, which demands both high efficiency and ultra-high weld quality, due to its advantages such as high production efficiency, high mechanization, and good and stable weld quality. However, pressure steel pipes have large diameters and thick walls, making them prone to problems such as high sensitivity to hydrogen-induced cracking, uneven slag coverage, and poor slag removal during welding, thus placing higher demands on the comprehensive performance of welding fluxes. Existing fluxes often struggle to simultaneously guarantee high strength, high and low temperature toughness, and excellent weld bead formation and slag removal performance. Therefore, there is an urgent need to develop a high-performance sintered flux to meet the dual requirements of weld quality and processability for pumped-storage power station pressure steel pipes. Summary of the Invention

[0003] To address the technical problems of existing flux welding of pressure steel pipes in pumped storage power stations failing to achieve both high strength and low-temperature toughness, and exhibiting poor slag removal properties, this invention provides a high-basicity sintering flux for pressure steel pipes in pumped storage power stations and its preparation method.

[0004] The present invention adopts the following technical solution: One objective of this invention is to provide a high-alkalinity sintering flux for pressure steel pipes in pumped storage power stations. The flux comprises mineral powder and a binder, wherein the mineral powder comprises, by mass percentage: 6%-16% wollastonite, 10%-20% fused magnesia, 25%-40% bauxite, 25%-40% fluorite, 5%-10% potassium feldspar, 1%-5% manganese ore, and 1%-5% alloying agent.

[0005] Further specifying, the alloying agent is at least one of ferrosilicon, ferromanganese, and ferrotitanium.

[0006] To further specify, the ferromanganese alloy is a medium-carbon ferromanganese alloy.

[0007] Furthermore, the binder should account for 18%-30% of the total mass of the mineral dry powder.

[0008] Further specifying, the binder is sodium potassium silicate.

[0009] Furthermore, the potassium-sodium ratio of sodium-potassium water glass is (1:1)-(3:1), the modulus is 2.91-2.93, and the Baumé degree is 42.

[0010] Further specified, the basicity of the sintering flux is >2.0.

[0011] The second objective of this invention is to provide a method for preparing the high-basicity sintering flux for the pressure steel pipes of the above-mentioned pumped storage power station, comprising the following steps: Step 1, Mixing: Weigh each component according to the sintering flux composition ratio and mix to prepare a semi-solid wet mixture; Step 2, Granulation: Granulate the semi-solid wet mixture, pass it through a 12-40 mesh sieve to obtain a semi-finished product, and dry the semi-finished product; Step 3, Sintering: Sinter the dried semi-finished product; Step 4, sieving: Pass the sintered material through a 12-40 mesh sieve to obtain sintered flux for pressure steel pipes of pumped storage power stations.

[0012] Further specifying, the granulation time in step 2 is 3-5 minutes.

[0013] Further specifying, the drying temperature in step 2 is 200-350℃, and the time is 0.5-2h.

[0014] Further specifying, the sintering temperature in step 3 is 600-800℃, and the time is 0.5-2h.

[0015] The third objective of this invention is to provide a welding method that is used in conjunction with the above-mentioned flux. This method employs single-sided single-wire V-groove submerged arc welding with DC reverse polarity, a welding current of 500-550A, an arc voltage of 28-32V, and a welding speed of 400-500mm / min.

[0016] Furthermore, the flux must be dried at 300-500℃ for at least 1 hour before use.

[0017] The fourth objective of this invention is to provide an application of the above-mentioned welding method, using high-strength steel welding wire as welding material, for welding high-strength steel plates used in pressure steel pipes of pumped storage power stations.

[0018] Further specified, the high-strength steel welding wire is H12Mn2Ni2Mo, and the high-strength steel plate is 800Mpa grade high-strength steel.

[0019] The fifth objective of this invention is to provide a welded joint obtained by the above-mentioned application, with a tensile strength ≥780MPa, a yield strength ≥690MPa, a Charpy impact absorption energy ≥100J at -40℃, and an elongation ≥18%.

[0020] The beneficial effects of this invention are as follows: (1) In this invention, wollastonite is used to completely replace traditional marble as the core of flux calcium source, eliminating the high-temperature decomposition reaction of carbonate (CaCO3→CaO+CO2↑), and solving the weld indentation defect caused by CO2 release from the root. Wollastonite directly participates in the slag system reaction, reducing the overall sintering temperature of the flux slag system and reducing energy consumption. At the same time, the SiO2 network structure in wollastonite has a strong ability to adsorb hydrogen atoms, inhibiting H2O decomposition, reducing the content of diffuse hydrogen, and reducing the hydrogen-induced cracking rate. The natural TiO2 and Fe2O3 in bauxite form (Ti,Fe) composite oxide inclusions, which serve as the heterogeneous nucleation core of acicular ferrite, greatly increasing its proportion. In addition, SiO2 in bauxite will form a low-melting-point glass phase with alkali metal oxides (including sodium oxide, potassium oxide, magnesium oxide, calcium oxide, etc.), improving the slag removal performance. CaF2 in fluorite reduces the viscosity and surface tension of slag, which helps to achieve zero-residue slag removal in all-position welding. While increasing the basicity, MgO in fused magnesia can also refine the grains. The aforementioned quaternary system of wollastonite-bauxite-fluorite-fused magnesia undergoes deep deoxidation through synergistic suppression of oxygen potential and synergistic catalysis of nucleation, significantly promoting the formation of acicular ferrite and improving low-temperature impact toughness. Compared with traditional fluxes, the sintered flux of this invention has the advantages of ultra-low hydrogen content, high strength and toughness, and low energy consumption.

[0021] (2) When the flux of this invention is used in conjunction with low-alloy high-strength steel welding wire, it can ensure good weld formation and uniform weld microstructure, while also possessing excellent strength and low-temperature toughness. The resulting weld surface is smooth, has good slag removal performance, and is free of defects, fully meeting the performance and process requirements for pressure steel pipe welding. Attached Figure Description

[0022] Fig. 1 Optical micrograph of the cross-section of the weld joint formed by welding with sintered flux in Example 1; Fig. 2 Metallographic micrograph of the weld formed by welding with the sintered flux of Example 1; Fig. 3 The image shows the weld formation and slag shell morphology after welding with the sintered flux of Example 1. Detailed Implementation

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0025] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0026] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0027] In the following examples, the high-strength steel welding wire is H12Mn2Ni2Mo.

[0028] Example 1 The sintered welding flux for the pressure steel pipe of the pumped storage power station in this embodiment is prepared from mineral dry powder and binder. The mineral dry powder is composed of the following components by mass percentage: wollastonite 8%, fused magnesia 15%, bauxite 35%, fluorite 35%, feldspar 5%, manganese ore 1%, and alloying agent 1%. The alloying agent includes 75# ferrosilicon alloy and medium-carbon ferromanganese, with a mass ratio of 1:3 between the 75# ferrosilicon alloy and the medium-carbon ferromanganese.

[0029] The preparation method of sintered welding flux for pressure steel pipes in pumped storage power stations according to this embodiment includes the following steps: Step 1, Mixing: (1) According to the mineral dry powder ratio of the sintered welding flux for the pressure steel pipe of the pumped storage power station, accurately weigh each raw material and place it in a mixing container, stir until the powder is evenly mixed, and obtain dry mixed raw material. (2) Add water glass at 18% of the mass of the dry mixed raw materials and wet mix to prepare a semi-solid wet mixture; wherein, the water glass is a potassium-sodium 1:1 mixed water glass with a modulus of 2.93 and a Baume degree of 42. Step 2, Granulation: (1) Pour the semi-solid wet mixture into a granulator for granulation for 5 minutes, and then pass it through a 12-40 mesh sieve to obtain 12-40 mesh granules as a semi-finished product. (2) Crush particles smaller than 12 mesh, regranulate particles larger than 40 mesh, and then return to step 2 (2) until all particles become 12-40 mesh semi-finished products. The semi-finished products obtained in this step are wet particles. (3) To evaporate the water adhering to the surface of the wet material particles, the semi-finished product is dried at 200℃ for 1 hour; Step 3, sintering: The dried semi-finished product was placed in a box-type resistance furnace for sintering at a temperature of 650℃ for 2 hours. Step 4, sieve: The sintered material is passed through a 12-40 mesh sieve to obtain sintered welding flux for pressure steel pipes of pumped storage power stations.

[0030] The sintered flux for the pressure steel pipes of the pumped storage power station prepared in this embodiment needs to be dried in a drying oven at 300℃ for 2 hours before welding. Then, the dried flux is used in conjunction with high-strength steel welding wire to weld 800MPa grade high-strength steel Q690. The welding method is as follows: single-sided single-wire V-groove submerged arc welding with DC reverse polarity, welding current 550A, arc voltage 30V, and welding speed 450mm / min.

[0031] The welded joint has the following properties: tensile strength of 825 MPa, yield strength of 716 MPa, Charpy impact energy at -40℃ of 108 J, and elongation of 26%. An optical micrograph of the welded joint's cross-section is shown below. Fig. 1 As shown, the metallographic micrograph of the weld is as follows: Fig. 2 As shown in the figure, the weld formation and slag shell morphology are as follows: Fig. 3 As shown. From Figs. 1-3 It can be seen that the welding process using the flux of this embodiment is good, the weld formation is beautiful, the weld composition is uniform, and the slag removal performance is good.

[0032] Example 2 The difference between this embodiment and Embodiment 1 is that the mineral powder by mass percentage is: 8% wollastonite, 15% fused magnesia, 35% bauxite, 35% fluorite, 5% feldspar, 1% manganese ore, and 1% alloying agent; the water glass in step 1 (2) is... Potassium-sodium 3:1 mixed water glass with a modulus of 2.91 and a Baume degree of 42, and the amount of water glass used is 21% of the mass of the dry mixed raw materials; the drying temperature in step 2 (3) is 300℃; the sintering temperature in step 3 is 700℃ and the time is 1h; the obtained flux is dried at 350℃ for 1h before welding, and the remaining operation steps and parameter settings are the same as in Example 1.

[0033] The welded joint has the following properties: tensile strength of 822MPa, yield strength of 719MPa, Charpy impact energy at -40℃ of 116J, elongation of 25%, good weldability, beautiful weld formation, uniform weld composition, and good slag removal performance.

[0034] Example 3 The difference between this embodiment and embodiment 1 is that: the mineral dry powder by mass percentage is: 12% wollastonite, 20% fused magnesia, 30% bauxite, 30% fluorite, 5% feldspar, 1% manganese ore, and 1% alloying agent; the amount of water glass used in step 1 (2) is 25% of the mass of the dry mixed raw materials; the drying temperature in step 2 (3) is 350℃ and the time is 0.5h; the sintering temperature in step 3 is 750℃ and the time is 0.5h; the obtained flux is dried at 350℃ for 1h before welding; and the remaining operation steps and parameter settings are the same as in embodiment 1.

[0035] The welded joint has the following properties: tensile strength of 828 MPa, yield strength of 723 MPa, Charpy impact energy at -40℃ of 111 J, elongation of 26.5%, good weldability, beautiful weld formation, uniform weld composition, and good slag removal performance.

[0036] Example 4 The difference between this embodiment and embodiment 2 is that the mineral dry powder is as follows by mass percentage: 10% wollastonite, 18% fused magnesia, 20% bauxite, 40% fluorite, 8% feldspar, 2% manganese ore, and 2% alloying agent; the amount of water glass used in step 1 (2) is 20% of the mass of the dry mixed raw materials; the sintering temperature in step 3 is 750℃, and the obtained flux is dried at 350℃ for 1 hour before welding. The remaining operation steps and parameter settings are the same as in embodiment 1.

[0037] The welded joint has the following properties: tensile strength of 831 MPa, yield strength of 735 MPa, Charpy impact energy at -40℃ of 120 J, elongation of 26%, good weldability, beautiful weld formation, uniform weld composition, and good slag removal performance.

[0038] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-basicity sintering flux for pressure steel pipes in pumped storage power stations, characterized in that, The flux consists of mineral powder and binder; The mineral powder comprises, by mass percentage: 6%-16% wollastonite, 10%-20% fused magnesia, 25%-40% bauxite, 25%-40% fluorite, 5%-10% potassium feldspar, 1%-5% manganese ore, and 1%-5% alloying agent.

2. The sintering flux according to claim 1, characterized in that, The binder accounts for 18%-30% of the total mass of the mineral dry powder, and the binder is sodium potassium water glass.

3. The sintering flux according to claim 1, characterized in that, The potassium-sodium ratio of sodium-potassium water glass is (1:1)-(3:1), the modulus is 2.91-2.93, and the Baumé degree is 42; the basicity of the sintering flux is greater than 2.

0.

4. A method for preparing the flux according to any one of claims 1-3, characterized in that, The preparation method includes: Step 1, Mixing: Weigh each component according to the sintering flux composition ratio and mix to prepare a semi-solid wet mixture; Step 2, Granulation: Granulate the semi-solid wet mixture, pass it through a 12-40 mesh sieve to obtain a semi-finished product, and dry the semi-finished product; Step 3, Sintering: Sinter the dried semi-finished product; Step 4, sieving: Pass the sintered material through a 12-40 mesh sieve to obtain sintered flux for pressure steel pipes of pumped storage power stations.

5. The preparation method according to claim 4, characterized in that, In step 2, the granulation time is 3-5 minutes, the drying temperature is 200-350℃, and the drying time is 0.5-2 hours.

6. The preparation method according to claim 4, characterized in that, In step 3, the sintering temperature is 600-800℃ and the time is 0.5-2h.

7. A welding method used in conjunction with the flux according to any one of claims 1-3, characterized in that, This method uses single-sided single-wire V-groove submerged arc welding with DC reverse polarity, welding current of 500-550A, arc voltage of 28-32V, and welding speed of 400-500mm / min.

8. An application of the welding method according to claim 7, characterized in that, High-strength steel welding wire is used as welding material for welding high-strength steel plates used in pressure steel pipes of pumped storage power stations.

9. The application according to claim 8, characterized in that, The high-strength steel welding wire is H12Mn2Ni2Mo, and the high-strength steel plate is 800MPa grade high-strength steel.

10. A welded joint obtained by the application of claim 8 or 9, characterized in that, Tensile strength ≥780MPa, yield strength ≥690MPa, Charpy impact energy at -40℃ ≥100J, elongation ≥18%.

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