A submerged arc welding wire and flux for 9Cr-1Mo-V steel of hydrogenation equipment and a preparation method thereof

Abstract

The application discloses a 9Cr-1Mo-V steel submerged arc welding wire for hydrogenation equipment, a welding flux and a preparation method thereof, and belongs to the technical field of welding materials and preparation thereof. The application solves the problems of the existing conventional 9Cr-1Mo-V steel submerged arc welding material, such as insufficient improvement of low-temperature impact toughness at 0 DEG C, difficulty in balancing strength and toughness, and restriction of the purification ability of the welding flux by the component system. The application changes the component of the welding wire, specifically reduces the content of C and Si to improve the toughness, maintains the strength of the welding seam through the strengthening effect of Mo, V, Nb and N, and further utilizes the synergistic design of the component of the welding wire and the welding flux system, so that the tensile strength and yield strength of the welding seam metal meet the use requirements of the 9Cr-1Mo-V steel welding structure. Specifically, the 0 DEG C V-type notch impact absorption energy of the submerged arc welding seam metal is more than 47J, and the brittle fracture resistance of the welding joint under the low-temperature impact condition is improved.

Description

Technical Field

[0001] This invention relates to a 9Cr-1Mo-V steel submerged arc welding wire and flux for hydrogenation equipment, and their preparation method, belonging to the technical field of welding materials and their preparation. Background Technology

[0002] P91 steel (10Cr9Mo1VNb) is an improved 9Cr-1Mo martensitic heat-resistant steel with high high-temperature strength, creep resistance, and structural stability. It has been widely used in power plant boilers, high-temperature steam pipelines, headers, and related thick-walled pressure-bearing structures. With the increasing demands for higher design temperatures and longer operating cycles in processes such as heavy oil hydrogenation and coal-to-oil, the application of 9Cr-1Mo-V steel in hydrogenation equipment has certain technical value. However, issues such as the matching of strength and toughness in welded joints and the stability of low-temperature impact performance still need to be addressed.

[0003] For thick-walled pressure-bearing structures such as hydrogenation equipment, weld metal typically needs to meet strength, toughness, and process stability requirements simultaneously after post-weld heat treatment. Among these, the V-notch impact toughness at 0°C directly relates to the welded joint's resistance to brittle fracture under start-up, maintenance, hydrostatic testing, and low-temperature service or exposure conditions. Conventional P91 submerged arc welding wire / flux systems are primarily designed around strength and high-temperature performance, with limited room for improvement in 0°C low-temperature impact toughness.

[0004] However, existing improvement schemes mostly focus on adjusting single alloying elements or increasing flux basicity, lacking a synergistic design between key elements in the welding wire and the flux's purification capabilities. Simply reducing the C content may lead to a decrease in weld strength; increasing the Mn or Ni content to improve toughness may cause grain boundary segregation, austenite stabilization, or temper brittleness; if the proportion of oxidizing components in the flux is not properly controlled, oxide inclusions in the weld are difficult to control effectively. These factors collectively limit further improvement in the 0℃ low-temperature impact toughness of 9Cr-1Mo-V steel submerged arc welds.

[0005] Therefore, it is necessary to provide a 9Cr-1Mo-V steel submerged arc welding wire / flux combination that forms a synergistic match between the alloying elements of the welding wire and the composition of the flux, so as to improve the low-temperature impact toughness of the weld metal at 0℃ while ensuring the weld strength and welding process performance. Summary of the Invention

[0006] To address the problems of insufficient low-temperature impact toughness improvement at 0℃, difficulty in balancing strength and toughness, and limitations on flux purification capacity due to the composition system in existing conventional 9Cr-1Mo-V steel submerged arc welding materials, this invention provides a 9Cr-1Mo-V steel submerged arc welding wire for hydrogenation equipment, a flux, and a method for its preparation.

[0007] The technical solution of the present invention: One objective of this invention is to provide a 9Cr-1Mo-V steel submerged arc welding wire for hydrogenation equipment. The chemical composition of this welding wire, by weight percentage, includes: C: 0.06-0.11%, Mn: 0.3-0.7%, Ni: 0.3-0.5%, Mo: 0.85-1.05%, Cr: 8.0-9.5%, V: 0.15-0.25%, Nb: 0.03-0.08%, N: 0.02-0.06%, Si≤0.15%, S≤0.010%, P≤0.010%, with the balance being Fe and unavoidable impurities.

[0008] Furthermore, the sum of the mass fractions of Mn and Ni is not greater than 1.2%.

[0009] Further specified, C: 0.065–0.085%, Mo: 0.98–1.03%, Si ≤ 0.12%.

[0010] The second objective of this invention is to provide a method for preparing 9Cr-1Mo-V steel submerged arc welding wire for hydrogenation equipment. The method is as follows: weigh each component according to the proportion, and sequentially pass it through vacuum induction furnace melting, refining, forging, heat treatment, drawing, surface treatment and layer winding processes to obtain the finished welding wire.

[0011] The third objective of this invention is to provide a 9Cr-1Mo-V steel submerged arc welding flux for hydrogenation equipment. This flux is used in conjunction with the aforementioned 9Cr-1Mo-V steel submerged arc welding wire for thick-walled pressure-bearing structures. The chemical composition of this flux, by weight percentage, includes: CaO: 2-10%, CaF2: 20-40%, Al2O3: 15-30%, MgO: 15-25%, SiO2: 7-13%, MnO: 1-2%, rare earth ferrosilicon: 1-2%, and composite deoxidizer: 1-3%.

[0012] Further specified, the total content of CaO, CaF2 and MgO is 52-66%, the total content of SiO2 and MnO is 8-15%, and the rare earth elements in rare earth ferrosilicon include La and / or Ce, and the total mass fraction of rare earth elements is not less than 20%.

[0013] Further specified, CaF2 is 30-34%, CaO is 5-10%, MgO is 20-22%, and SiO2 is 7-10%.

[0014] Further specifying, the composite deoxidizer is a mixture of ferrosilicon, ferromanganese and silicon-calcium alloy in a mass ratio of 2:1:1.

[0015] The fourth objective of this invention is to provide a method for preparing a submerged arc welding flux for 9Cr-1Mo-V steel used in hydrogenation equipment. The method is as follows: CaO, CaF2, Al2O3, MgO, SiO2 and MnO are mixed and sintered at 800-850°C for 30-60 minutes, and then rare earth ferrosilicon and composite deoxidizer are added and mixed evenly. Alternatively, rare earth ferrosilicon coated with oxidation resistant material and composite deoxidizer can be mixed with CaO, CaF2, Al2O3, MgO, SiO2 and MnO and sintered at 800-850℃ for 30-60 minutes.

[0016] The fifth objective of this invention is to provide a submerged arc welding process for a hydrogenation equipment, wherein the submerged arc welding uses the aforementioned welding wire and flux.

[0017] Further specify that the base material for welding is 9Cr-1Mo-V steel used in hydrogenation equipment, pressure vessels, power plant boilers, or high-temperature pipelines.

[0018] Further, the weld metal shall be tempered at 740-770℃ for 3-5 hours after welding. The treated weld metal shall have an impact absorption energy of not less than 47J at 0℃ and a V-notch, a tensile strength of not less than 640MPa, and a yield strength of not less than 540MPa.

[0019] Beneficial effects: This invention improves toughness by modifying the welding wire composition, specifically reducing the C and Si content, while maintaining weld strength through the strengthening effects of Mo, V, Nb, and N. Furthermore, by utilizing the synergistic design of the welding wire composition and flux system, the tensile strength and yield strength of the weld metal meet the requirements for 9Cr-1Mo-V steel welded structures. Specifically, the submerged arc weld metal achieves an impact absorption energy of over 47J at 0℃ with a V-notch, enhancing the weld joint's resistance to brittle fracture under low-temperature impact conditions. In addition, the use of a flux system with a high combined content of CaO, CaF2, and MgO, and controlled SiO2 and MnO content, helps reduce the level of oxide inclusions in the weld, improves slag removal and weld formation quality, and reduces the risk of defects such as porosity, slag inclusions, and undercut. Detailed Implementation

[0020] The chemical composition of the 9Cr-1Mo-V steel submerged arc welding wire for hydrogenation equipment provided by this invention, by weight percentage, includes: C: 0.06-0.11%, Mn: 0.3-0.7%, Ni: 0.3-0.5%, Mo: 0.85-1.05%, Cr: 8.0-9.5%, V: 0.15-0.25%, Nb: 0.03-0.08%, N: 0.02-0.06%, Si≤0.15%, S≤0.010%, P≤0.010%, with the balance being Fe and unavoidable impurities. Further, the sum of the mass fractions of Mn and Ni is not greater than 1.2%. Further, C: 0.065-0.085%, Mo: 0.98-1.03%, Si≤0.12%. The chemical composition of the flux, by weight percentage, includes: CaO: 2-10%, CaF2: 20-40%, Al2O3: 15-30%, MgO: 15-25%, SiO2: 7-13%, MnO: 1-2%, rare earth ferrosilicon: 1-2%, and composite deoxidizer: 1-3%.

[0021] The rationale for setting the chemical composition range of the 9Cr-1Mo-V steel submerged arc welding wire / flux used in this invention is as follows: Low C content is synergistically controlled with V, Nb, and N. Keeping the C content of the welding wire within a low range can reduce the precipitation of coarse M23C6 type carbides at grain boundaries and the tendency for grain boundary embrittlement, which is beneficial to improving low-temperature impact toughness. At the same time, retaining an appropriate amount of C allows it to form fine and dispersed MX type carbonitrides with V, Nb, and N, thereby maintaining the necessary precipitation strengthening and grain refinement strengthening effects while reducing the tendency for embrittlement.

[0022] The total amount of Mn and Ni is controlled. Controlling Mn and Ni within an appropriate range and keeping Mn+Ni≤1.2% can improve hardenability and reduce the ductile-brittle transition temperature, while suppressing the risks of segregation, excessive austenite stability, and temper brittleness caused by excessive Mn or Ni content.

[0023] Mo compensation strengthening. By controlling the Mo content to 0.85–1.05%, preferably 0.98–1.03%, it is possible to compensate for the strength loss that may be caused by low C design through solid solution strengthening, improved tempering stability, and participation in the precipitation of Mo-rich carbides, so that the weld metal can still maintain high strength after tempering.

[0024] Low-Si welding wire and flux have synergistic purification capabilities. A Si content of ≤0.15% in the welding wire reduces the tendency for temper brittleness. The flux has a high combined content of CaO, CaF2, and MgO, while the SiO2 and MnO content is controlled, which helps reduce flux oxidizability, decrease oxide inclusions, and improve weld purity, thereby enhancing 0℃ impact toughness. Rare earth ferrosilicon and composite deoxidizers further promote inclusion modification, flotation, and removal, and improve slag removal performance.

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[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] The chemical compositions of the 9Cr-1Mo-V steel submerged arc welding wires and fluxes provided in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1 and Table 2, respectively.

[0028] Table 1 Table 2 The composite deoxidizers are mixtures of ferrosilicon, ferromanganese, and silicon-calcium alloy in a mass ratio of 2:1:1; the rare earth elements in the rare earth ferrosilicon include La and Ce, and the total mass fraction of rare earth elements is not less than 20%. The sintering conditions of the basic mineral components in the fluxes of the examples and comparative examples are 800℃×40min, 820℃×45min, and 850℃×50min, respectively; the rare earth ferrosilicon and the composite deoxidizer are added after the basic mineral components are sintered.

[0029] The same welding process was used under the following conditions: base material was 20mm thick P91 steel plate; groove type was V-groove; welding current was 360A; welding voltage was 30V; welding speed was 42cm / min; interpass temperature was 200-250℃; post-weld tempering temperature was 760℃; and tempering time was 4h. The weld metal properties were tested according to the conventional test methods for the mechanical properties of welded joints and weld metals, including a 0℃ V-notch impact test. The test results are shown in Table 3.

[0030] Table 3 As shown in the table above, the impact absorption energy of the weld metal obtained in Examples 1-3 at 0℃ is 62-65 J, which is significantly higher than the 24-35 J of Comparative Examples 1-3. Meanwhile, the tensile strength of the weld metal in these examples is 650-655 MPa, and the yield strength is 545-555 MPa, which meets the strength requirements of 9Cr-1Mo-V steel welded structures.

[0031] The strength of the example was slightly lower than that of the comparative example, but the low-temperature impact toughness was significantly improved, indicating that the low C, controlled Mn / Ni, Mo compensation strengthening, and low Si design can effectively improve the strength-toughness matching relationship. The flux had a high total content of CaO, CaF2, and MgO, while the SiO2 and MnO contents were controlled, which further improved the weld formation, slag removal performance, and process stability.

[0032] In summary, this invention improves the low-temperature impact toughness at 0℃ while maintaining the necessary strength of the 9Cr-1Mo-V steel weld by synergistically matching the alloying elements of the welding wire and the purification capabilities of the flux, thus solving the problem of limited low-temperature toughness improvement in conventional 9Cr-1Mo-V steel submerged arc welding materials.

[0033] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A 9Cr-1Mo-V steel submerged arc welding wire for hydrogenation equipment, characterized in that, The chemical composition, by weight percentage, includes: C: 0.06–0.11%, Mn: 0.3–0.7%, Ni: 0.3–0.5%, Mo: 0.85–1.05%, Cr: 8.0–9.5%, V: 0.15–0.25%, Nb: 0.03–0.08%, N: 0.02–0.06%, Si≤0.15%, S≤0.010%, P≤0.010%, with the balance being Fe and unavoidable impurities.

2. The 9Cr-1Mo-V steel submerged arc welding wire for hydrogenation equipment according to claim 1, characterized in that, The sum of the mass fractions of Mn and Ni is no greater than 1.2%.

3. The 9Cr-1Mo-V steel submerged arc welding wire for hydrogenation equipment according to claim 1, characterized in that, C: 0.065~0.085%, Mo: 0.98~1.03%, Si≤0.12%.

4. A method for preparing 9Cr-1Mo-V steel submerged arc welding wire for hydrogenation equipment according to any one of claims 1 to 3, characterized in that, Weigh each component according to the proportions, and then sequentially process them through vacuum induction furnace melting, refining, forging, heat treatment, drawing, surface treatment, and layer winding to obtain the finished welding wire.

5. A submerged arc welding flux for 9Cr-1Mo-V steel used in hydrogenation equipment, characterized in that, This flux is used in conjunction with the 9Cr-1Mo-V steel submerged arc welding wire for thick-walled pressure-bearing structures as described in claim 1. The chemical composition of this flux, by weight percentage, includes: CaO: 2-10%, CaF2: 20-40%, Al2O3: 15-30%, MgO: 15-25%, SiO2: 7-13%, MnO: 1-2%, rare earth ferrosilicon: 1-2%, and composite deoxidizer: 1-3%.

6. The 9Cr-1Mo-V steel submerged arc welding flux for hydrogenation equipment according to claim 5, characterized in that, The total content of CaO, CaF2 and MgO is 52-66%, and the total content of SiO2 and MnO is 8-15%. Rare earth elements in rare earth ferrosilicon include La and / or Ce, and the total mass fraction of rare earth elements is not less than 20%.

7. The 9Cr-1Mo-V steel submerged arc welding flux for hydrogenation equipment according to claim 5, characterized in that, The composition of CaF2 is 30-34%, CaO is 5-10%, MgO is 20-22%, and SiO2 is 7-10%.

8. The 9Cr-1Mo-V steel submerged arc welding flux for hydrogenation equipment according to claim 5, characterized in that, The composite deoxidizer is made by mixing ferrosilicon, ferromanganese and silicon-calcium alloy in a mass ratio of 2:1:

1.

9. A method for preparing a submerged arc welding flux for 9Cr-1Mo-V steel used in a hydrogenation equipment as described in any one of claims 5 to 8, characterized in that, The method is as follows: CaO, CaF2, Al2O3, MgO, SiO2 and MnO are mixed and sintered at 800-850℃ for 30-60 minutes, and then rare earth ferrosilicon and composite deoxidizer are added and mixed evenly. Alternatively, rare earth ferrosilicon coated with oxidation resistant material and composite deoxidizer can be mixed with CaO, CaF2, Al2O3, MgO, SiO2 and MnO and sintered at 800-850℃ for 30-60 minutes.

10. A submerged arc welding process for a hydrogenation equipment, characterized in that, The submerged arc welding uses the welding wire described in claim 1 and the flux described in claim 4.

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