Pipe line steel resistance to hydrogen flux cored wire and its preparation method

Abstract

This invention discloses a hydrogen-resistant flux-cored welding wire for pipeline steel, consisting of an outer sheath and a flux core. The flux core is composed of the following raw materials by mass percentage: C: 0.10%–0.11%, Mn: 1.50%–2.00%, Si: 0.30%–0.90%, Ni: 1.90%–3.00%, Mo: 0.40%–0.80%, Cr: 0.25%–0.60%, Cu: 0.40%–0.50%, with the balance being Fe. The total content of all the above raw materials is 100%. The outer sheath is made of low-carbon steel strip. This invention also discloses a method for preparing the hydrogen-resistant flux-cored welding wire. The flux-cored welding wire obtained according to this invention exhibits a hydrogen resistance in the weld area that is no less than that of the base metal. After 15 hours of electrochemical hydrogen charging, its hydrogen embrittlement sensitivity can reach 4%–7.2%, which is 1.4–2.2 times that of the base metal, greatly improving the hydrogen resistance of the weld joint in pipeline steel.

Description

Technical Field

[0001] This invention belongs to the field of welding materials technology, and relates to hydrogen-resistant flux-cored welding wire for pipeline steel. This invention also relates to a method for preparing the above-mentioned flux-cored welding wire. Background Technology

[0002] Pipeline steel is a type of steel specifically designed for manufacturing oil and gas transmission pipelines, characterized by high strength, good toughness, and corrosion resistance. During oil and gas transportation, pipeline steel must withstand complex environments including high pressure, high temperature, low temperature, and hydrogen-containing conditions. Particularly in hydrogen-containing environments, pipeline steel is prone to hydrogen-induced cracking, leading to pipeline leaks, ruptures, and other safety accidents. Therefore, developing a flux-cored welding wire with excellent hydrogen resistance suitable for pipeline welding is of great significance for ensuring the safety and reliability of pipeline transportation.

[0003] Flux-cored welding wire, as a high-efficiency and high-quality welding material, is widely used in welding various structures. It achieves efficient and stable welding by filling the steel strip with flux powder to form a core, releasing a large amount of heat and gas during welding. Flux-cored welding wire also has broad application prospects in pipeline steel welding. However, traditional flux-cored welding wires have limitations in hydrogen resistance, making it difficult to meet the welding requirements of pipeline steel in hydrogen-containing environments. Currently, most pipeline steel flux-cored welding wires on the market exhibit excellent strength and toughness, but their hydrogen resistance still needs improvement. Traditional flux-cored welding wires are prone to forming hydrogen pores during welding, and hydrogen diffuses rapidly in the weld, easily leading to hydrogen-induced cracking and other problems.

[0004] Given the shortcomings of traditional flux-cored welding wires in hydrogen resistance and the urgent need for welding pipeline steel in hydrogen-containing environments, it is particularly important to develop a flux-cored welding wire for pipeline steel with excellent hydrogen resistance. By optimizing the composition and manufacturing process of the flux-cored welding wire, the hydrogen resistance of the wire can be effectively improved, the formation of hydrogen porosity can be reduced, and the diffusion rate of hydrogen in the weld can be slowed down, thereby preventing problems such as hydrogen-induced cracking. Summary of the Invention

[0005] The purpose of this invention is to provide a hydrogen-resistant flux-cored welding wire for pipeline steel, which produces a weld with good hydrogen resistance.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned hydrogen-resistant flux-cored welding wire for pipeline steel.

[0007] The technical solution adopted in this invention includes a core and an outer casing. The core is composed of the following raw material components by weight percentage: C: 0.10%~0.11%, Mn: 1.50%~2.00%, Si: 0.30%~0.90%, Ni: 1.90%~3.00%, Mo: 0.40%~0.80%, Cr: 0.25%~0.60%, Cu: 0.40%~0.50%, with the balance being Fe. The total content of all the above raw materials is 100%. The outer sheath is made of low-carbon steel strip.

[0008] The invention is further characterized by: The outer skin is made of H08A steel.

[0009] The outer skin has a width of 7–7.5 mm and a thickness of 0.25–0.3 mm.

[0010] Another technical solution adopted in this invention is a method for preparing hydrogen-resistant flux-cored welding wire for pipeline steel, which is implemented according to the following steps: Step 1: Weigh the following raw materials according to their mass percentages: C: 0.10%~0.11%, Mn: 1.50%~2.00%, Si: 0.30%~0.90%, Ni: 1.90%~3.00%, Mo: 0.40%~0.80%, Cr: 0.25%~0.60%, Cu: 0.40%~0.50%, with the balance being Fe. The total content of all the above raw materials should be 100%. Step 2: Grind each of the raw materials selected in Step 1 into powder; Step 3: Mix and stir the raw material powder formed by grinding in Step 2 for 2-3 hours, then heat it to 150-200℃ in a vacuum tube furnace and keep it at that temperature for 2-2.5 hours to form core powder; Step 4: Roll the outer skin into a U-shape along its length; Step 5: Fill the groove of the U-shaped outer skin with the core powder, and then make it into welding wire after passing through the closed forming roller.

[0011] Another feature of the technical solution of the present invention is that: In step 2, all raw materials are ground into powder of 80-100 mesh.

[0012] In step 3, the powder is mixed using a V-type powder mixer.

[0013] In step 3, the raw material powder is heated and kept warm in a vacuum tube furnace under an argon atmosphere.

[0014] In step 5, the filling rate of the drug core powder is 23% to 27%.

[0015] The beneficial effects of this invention are: This invention provides a hydrogen-resistant flux-cored welding wire for pipeline steel. The weld formed by this wire exhibits a higher concentration of fine ferrite, providing more diffusion sites for hydrogen atoms. This reduces the likelihood of hydrogen accumulation and lowers the hydrogen pressure within the phase structure, thus minimizing the formation of deep and large corrosion pits. Simultaneously, enhanced dislocation transport further reduces hydrogen atom accumulation, resulting in lower internal hydrogen pressure and reducing the likelihood of hydrogen-induced corrosion. As a weak point in pipeline steel, the weld exhibits hydrogen resistance comparable to or greater than that of the base metal. After 15 hours of electrochemical hydrogen embrittlement, its hydrogen embrittlement susceptibility reaches 4%–7.2%, which is 1.4–2.2 times that of the base metal. Attached Figure Description

[0016] Figure 1 This is a microstructure diagram of the weld formed by welding pipeline steel with hydrogen-resistant flux-cored wire according to the present invention. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0018] This invention relates to a hydrogen-resistant flux-cored welding wire for pipeline steel, comprising a flux core and an outer sheath. The flux core is composed of the following raw material components by weight percentage: C: 0.10%~0.11%, Mn: 1.50%~2.00%, Si: 0.30%~0.90%, Ni: 1.90%~3.00%, Mo: 0.40%~0.80%, Cr: 0.25%~0.60%, Cu: 0.40%~0.50%, with the balance being Fe. The total content of all the above raw materials is 100%. The outer sheath is made of low-carbon steel strip.

[0019] The invention is further characterized by: The outer skin is made of H08A steel.

[0020] The outer skin has a width of 7–7.5 mm and a thickness of 0.25–0.3 mm.

[0021] The roles of each component in the hydrogen-resistant flux-cored welding wire for pipeline steel of the present invention are as follows: C: Carbon enhances the strength and hardness of welds, but high-carbon welds are more prone to forming brittle, hard structures. These structures are more sensitive to hydrogen diffusion and accumulation, increasing the risk of hydrogen-induced cracking. To improve hydrogen resistance in hydrogen-resistant welding wires, the carbon content needs to be properly controlled. An appropriate amount of carbon ensures the weld has sufficient strength and hardness while avoiding hydrogen-induced cracking caused by excessive carbon content. In hydrogen-resistant welding wires, carbon typically works with other alloying elements (such as manganese, silicon, chromium, and nickel) to help reduce the hydrogen content and diffusion rate in the weld, thereby improving its hydrogen resistance.

[0022] Mn: The addition of manganese can improve weld morphology and reduce the incidence of welding deformation and cracking. In hydrogen-resistant welding wire, manganese, through its unique chemical properties, reacts with other elements in the weld to form stable compounds, thereby optimizing the weld's microstructure. This structural optimization helps improve the weld's strength and toughness, making the welded joint more robust and reliable. This is particularly important for welded structures operating in high-hydrogen environments.

[0023] Silicon (Si): Silicon is a commonly used deoxidizing element in welding wire. It effectively prevents iron from combining with oxides and reduces FeO in the molten pool, thereby reducing oxide inclusions in the weld. This effect is crucial for improving weld purity and quality. Since hydrogen-resistant welding wires require extremely low hydrogen content in the weld, silicon's deoxidizing effect helps reduce hydrides that may be generated during welding, thus lowering the hydrogen content in the weld. Although silicon itself does not directly reduce the hydrogen content in the weld, it can indirectly affect it through its combined action with other elements such as manganese. The combined silicon-manganese deoxidation can generate silicate compounds, which help reduce hydrogen diffusion and penetration in the weld, thereby improving the weld's hydrogen resistance to some extent.

[0024] Ni (Ni): Nickel significantly improves the resistance of welded joints to hydrogen corrosion. In hydrogen-containing environments, welded joints are susceptible to hydrogen corrosion, leading to decreased joint performance or even failure. The addition of Ni effectively inhibits the diffusion and penetration of hydrogen atoms in the weld metal, thereby reducing the risk of hydrogen corrosion. Ni can also optimize the microstructure of the weld metal, giving it a more uniform and finer grain structure. This structure of weld metal is better able to resist the penetration and diffusion of hydrogen atoms when subjected to external forces, thus reducing the risk of hydrogen embrittlement. In addition, Ni can improve the strength and toughness of the weld metal, giving the welded joint higher load-bearing capacity and stability in hydrogen-containing environments.

[0025] Molybdenum (Mo): Molybdenum significantly improves the corrosion resistance of weld metal, particularly its resistance to hydrogen corrosion. In hydrogen-containing environments, weld metal is susceptible to hydrogen erosion, leading to performance degradation. The addition of molybdenum forms stable compounds that protect the weld metal from hydrogen erosion, thereby enhancing its resistance to hydrogen corrosion. Simultaneously, molybdenum enhances the toughness of the weld metal, reducing its susceptibility to hydrogen-induced cracking. This role of molybdenum is particularly important in hydrogen-resistant welding wires, giving the weld metal higher crack resistance in hydrogen-containing environments, thus ensuring the quality and reliability of the weld joint.

[0026] Cr: Chromium can combine with oxygen in the weld structure to form a dense chromium oxide layer. This oxide layer covers the weld surface and effectively prevents further corrosion damage from corrosive media such as oxygen and water, including the penetration and diffusion of hydrogen atoms. Therefore, adding chromium to hydrogen-resistant welding wire can significantly improve the hydrogen corrosion resistance of the weld, enabling it to maintain good stability in harsh hydrogen-containing environments.

[0027] Cu (Copper): The addition of copper alters the physical properties of the welding wire, most notably lowering its melting point. This characteristic reduces the heat required during welding, thus simplifying the process and increasing efficiency. Simultaneously, the lower melting point facilitates rapid weld formation, reducing potential defects. Furthermore, the addition of Cu enhances the toughness of the weld metal and reduces its susceptibility to hydrogen-induced cracking. In hydrogen-resistant welding wires, this effect of Cu contributes to higher crack resistance in hydrogen-containing environments, ensuring the quality and reliability of the weld joint.

[0028] The manufacturing method of the hydrogen-resistant flux-cored welding wire for pipeline steel of the present invention is carried out according to the following steps: Example 1: Step 1: Weigh the following raw materials according to their mass percentages: C: 0.10%, Mn: 1.60%, Si: 0.40%, Ni: 2.00%, Mo: 0.50%, Cr: 0.3%, Cu: 0.40%, balance Fe; Step 2: Grind each of the raw materials selected in Step 1 into a 100-mesh powder; Step 3: Mix the raw material powder formed by grinding in Step 2 in a V-type mixer for 2 hours, then heat it to 150°C in a vacuum tube furnace and keep it at that temperature for 2 hours to form core powder. Step 4: Roll the 7mm wide and 0.25mm thick outer skin along its length into a U-shaped low-carbon steel strip; Step 5: Fill the groove of the U-shaped low carbon steel strip with the core powder, with a filling rate of 23%, and then make it into welding wire after passing through the closed forming roller.

[0029] Example 2: Step 1: Weigh the following raw materials according to their mass percentages: C: 0.10%, Mn: 1.50%, Si: 0.30%, Ni: 2.50%, Mo: 0.60%, Cr: 0.3%, Cu: 0.45%, balance Fe; Step 2: Grind each of the raw materials selected in Step 1 into a 90-mesh powder; Step 3: Mix the raw material powder formed by grinding in Step 2 in a V-type mixer for 2.1 hours, then heat it to 160°C in a vacuum tube furnace and keep it at that temperature for 2.1 hours; Step 4: Roll the 7.1mm wide and 0.26mm thick outer skin along its length into a U-shaped low-carbon steel strip; Step 5: Fill the groove of the U-shaped low carbon steel strip with the core powder, with a filling rate of 25%, and then make it into welding wire after passing through the closed forming roller.

[0030] Example 3: Step 1: Weigh the following raw materials according to their mass percentages: C: 0.10%, Mn: 1.80%, Si: 0.60%, Ni: 2.10%, Mo: 0.70%, Cr: 0.5%, Cu: 0.40%, balance Fe; Step 2: Grind each of the raw materials selected in Step 1 into an 80-mesh powder; Step 3: Mix the raw material powder formed by grinding in Step 2 in a V-type mixer for 2.2 hours, then heat it to 170°C in a vacuum tube furnace and keep it at that temperature for 2.2 hours; Step 4: Roll the 7.2mm wide and 0.27mm thick outer skin along its length into a U-shaped low-carbon steel strip; Step 5: Fill the groove of the U-shaped low carbon steel strip with the core powder, with a filling rate of 26%, and then make it into welding wire after passing through the closed forming roller.

[0031] Example 4: Step 1: Weigh the following raw materials according to their mass percentages: C: 0.10%, Mn: 2.0%, Si: 0.80%, Ni: 3.00%, Mo: 0.80%, Cr: 0.6%, Cu: 0.40%, balance Fe; Step 2: Grind each of the raw materials selected in Step 1 into a 100-mesh powder; Step 3: Mix the raw material powder formed by grinding in Step 2 in a V-type mixer for 2.3 hours, then heat it to 180°C in a vacuum tube furnace and keep it at that temperature for 2.3 hours. Step 4: Roll the 7.3mm wide and 0.28mm thick outer skin along its length into a U-shaped low-carbon steel strip; Step 5: Fill the groove of the U-shaped low carbon steel strip with the core powder, with a filling rate of 27%, and then make it into welding wire after passing through the closed forming roller.

[0032] Example 5: Step 1: Weigh the following raw materials according to their mass percentages: C: 0.10%, Mn: 1.7%, Si: 0.50%, Ni: 2.40%, Mo: 0.80%, Cr: 0.35%, Cu: 0.40%, balance Fe; Step 2: Grind each of the raw materials selected in Step 1 into a 90-mesh powder; Step 3: Mix the raw material powder formed by grinding in Step 2 in a V-type mixer for 2.4 hours, then heat it to 190°C in a vacuum tube furnace and keep it at that temperature for 2.4 hours. Step 4: Roll the 7.4mm wide and 0.29mm thick outer skin along its length into a U-shaped low-carbon steel strip; Step 5: Fill the groove of the U-shaped low carbon steel strip with the core powder, with a filling rate of 24%, and then make it into welding wire after passing through the closed forming roller.

[0033] Example 6: Step 1: Weigh the following raw materials according to their mass percentages: C: 0.11%, Mn: 1.5%, Si: 0.85%, Ni: 2.60%, Mo: 0.65%, Cr: 0.55%, Cu: 0.50%, balance Fe; Step 2: Grind each of the raw materials selected in Step 1 into an 80-mesh powder; Step 3: Mix the raw material powder formed by grinding in Step 2 in a V-type mixer for 2.5 hours, then heat it to 200°C in a vacuum tube furnace and keep it at that temperature for 2.5 hours. Step 4: Roll the 7.5mm wide and 0.3mm thick outer skin along its length into a U-shaped low-carbon steel strip; Step 5: Fill the groove of the U-shaped low carbon steel strip with the core powder, with a filling rate of 24%, and then make it into welding wire after passing through the closed forming roller.

[0034] The flux-cored welding wires prepared in Examples 1 to 6 were used for welding, and the welds were inspected. The inspection results are as follows: Example 1: The welding arc is stable, the weld formation is beautiful, and there are no defects such as cracks or porosity, nor are there any defects such as incomplete fusion or incomplete penetration. The resulting weld has a tensile strength of up to 670 MPa, an elongation of up to 29.1%, and a hydrogen embrittlement susceptibility of 7.2%, which is 1.4 times that of the base metal, demonstrating excellent hydrogen resistance.

[0035] Example 2: The welding arc is stable, the weld formation is beautiful, and there are no defects such as cracks or porosity. Furthermore, there are no defects such as incomplete fusion or incomplete penetration. The resulting weld has a tensile strength of up to 649.7 MPa, an elongation of up to 30.4%, and a hydrogen embrittlement susceptibility of 6.2%, which is 1.5 times that of the base metal, demonstrating excellent hydrogen resistance.

[0036] Example 3: The welding arc is stable, the weld formation is beautiful, and there are no defects such as cracks or porosity. Furthermore, there are no defects such as incomplete fusion or incomplete penetration. The resulting weld has a tensile strength of 663.9 MPa, an elongation of 28.4%, and a hydrogen embrittlement susceptibility of 5.2%, which is 1.78 times that of the base metal, demonstrating excellent hydrogen resistance.

[0037] Example 4: The welding arc is stable, the weld formation is aesthetically pleasing, and there are no defects such as cracks or porosity. Furthermore, there are no defects such as incomplete fusion or incomplete penetration. The resulting weld has a tensile strength of up to 656.9 MPa, an elongation of up to 32.8%, and a hydrogen embrittlement susceptibility of 4%, which is 2.2 times that of the base metal. It exhibits excellent hydrogen resistance.

[0038] Example 5: The welding arc is stable, the weld formation is aesthetically pleasing, and there are no defects such as cracks or porosity. Furthermore, there are no defects such as incomplete fusion or incomplete penetration. The resulting weld has a tensile strength of 682.1 MPa, an elongation of 31.8%, and a hydrogen embrittlement susceptibility of 4.8%, which is 2.05 times that of the base metal. It exhibits excellent hydrogen resistance.

[0039] Example 6: The welding arc is stable, the weld formation is aesthetically pleasing, and there are no defects such as cracks or porosity. Furthermore, there are no defects such as incomplete fusion or incomplete penetration. The resulting weld has a tensile strength of 666.8 MPa, an elongation of 24.8%, and a hydrogen embrittlement susceptibility of 10.2%, which is 1.38 times that of the base metal. It exhibits excellent hydrogen resistance.

[0040] like Figure 1 As shown, the weld microstructure formed by welding the flux-cored wire prepared in Example 4 consists of polygonal ferrite, acicular ferrite, and pearlite. In the figure, the acicular ferrite AF has a high density of dislocations, forming parallel, elongated, acicular ferrite with a non-equiaxed morphology through shear and diffusion phase transformations. Compared to the polygonal ferrite microstructure, the acicular ferrite microstructure is finer and is the ductile phase in the weld. The inner weld is composed of smaller, intersecting acicular ferrite AF and fine pearlite P. This structural distribution gives the joint weld good toughness. The abundance of fine ferrite in the weld provides more diffusion sites for hydrogen atoms, making hydrogen less likely to accumulate. The hydrogen pressure within the phase microstructure is lower, reducing the likelihood of deep and large corrosion pits. Simultaneously, enhanced dislocation transport and reduced hydrogen atom accumulation result in lower internal hydrogen pressure, making hydrogen-induced corrosion less likely. This improves its hydrogen resistance.

Claims

1. A hydrogen-resistant flux-cored welding wire for pipeline steel, characterized in that, It includes a core and an outer sheath, wherein the core is composed of the following raw materials in percentage by weight. composition: C: 0.10%~0.11%, Mn: 1.50%~2.00%, Si: 0.30%~0.90%, Ni: 1.90%~3.00%, Mo: 0.40%~0.80%, Cr: 0.25%~0.60%, Cu: 0.40%~0.50%, with the balance being Fe. The total content of all the above raw materials is 100%. The outer sheath is made of low-carbon steel strip.

2. The hydrogen-resistant flux-cored welding wire for pipeline steel according to claim 1, characterized in that, The outer skin is made of H08A steel.

3. The hydrogen-resistant flux-cored welding wire for pipeline steel according to claim 2, characterized in that, The outer skin has a width of 7-7.5 mm and a thickness of 0.25-0.3 mm.

4. A method for preparing hydrogen-resistant flux-cored welding wire for pipeline steel, characterized in that, The material described in any one of claims 1 to 3 is used, and the process is carried out according to the following steps: Step 1: Weigh the following raw materials according to their mass percentages: C: 0.10%~0.11%, Mn: 1.50%~2.00%, Si: 0.30%~0.90%, Ni: 1.90%~3.00%, Mo: 0.40%~0.80%, Cr: 0.25%~0.60%, Cu: 0.40%~0.50%, with the balance being Fe. The total content of all the above raw materials should be 100%. Step 2: Grind each of the raw materials selected in Step 1 into powder; Step 3: Mix and stir the raw material powder formed by grinding in Step 2 for 2-3 hours, then heat it to 150-200℃ in a vacuum tube furnace and keep it at that temperature for 2-2.5 hours to form core powder; Step 4: Roll the outer skin into a U-shape along its length; Step 5: Fill the groove of the U-shaped outer skin with the core powder, and then make it into welding wire after passing through the closed forming roller.

5. The method for preparing hydrogen-resistant flux-cored welding wire for pipeline steel according to claim 4, characterized in that, In step 2, each raw material is ground into powder of 80-100 mesh.

6. The method for preparing hydrogen-resistant flux-cored welding wire for pipeline steel according to claim 4, characterized in that, In step 3, the powder is mixed using a V-type powder mixer.

7. The method for preparing hydrogen-resistant flux-cored welding wire for pipeline steel according to claim 4, characterized in that, In step 3, the raw material powder is heated and kept warm in a vacuum tube furnace under an argon atmosphere.

8. The method for preparing hydrogen-resistant flux-cored welding wire for pipeline steel according to claim 4, characterized in that, In step 5, the filling rate of the core powder is 23% to 27%.

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