A flux-cored wire for hot-rolling vertical roll surfacing and application thereof

Abstract

The application discloses a flux-cored wire for hot-rolling vertical roll surfacing and application thereof, and relates to the field of welding materials and surfacing technology. The flux-cored wire comprises a wire sheath and a flux core. The flux core comprises the following components: graphite 0.8-2.0%, manganese powder 1.8-4.5%, chromium powder 6.0-15%, molybdenum powder 1.0-2.5%, vanadium iron 0.2-0.5%, Nb-1Zr niobium-zirconium alloy 4.5-11.5%, metallic silicon 0.9-2.0%, nickel powder 2.5-6.3%, scandium earth 0.02-0.05% and active agent 1.0-2.5%, and the balance is iron. When the vertical roll is repaired by surfacing, Nb-Cr multi-element alloy is formed, which has the advantages of high wear resistance, red hardness and thermal strength. The single-time rolling amount of the remanufactured vertical roll is multiplied compared with the original half-steel vertical roll and the high-chromium cast iron vertical roll, and the vertical roll can be repaired by surfacing multiple times after normal dismounting, thereby reducing roll consumption and production cost.

Description

Technical Field

[0001] This invention belongs to the field of welding materials and surfacing technology, specifically relating to a flux-cored welding wire for surfacing hot-rolled vertical rolls and its application. Background Technology

[0002] The vertical rolls used in the E1 and E2 mills of the hot rolling production line are mainly used to control the width accuracy of the strip and ensure the flatness of the plate sides. The roll surface has a trapezoidal opening and weighs 10-20 tons. Traditional vertical rolls are made of semi-steel, alloy cast steel, or alloy forged steel, with a hardness of around 40-50 HSD. During use, they suffer from problems such as insufficient wear resistance, thermal crack resistance, indentation resistance, short roll change cycle, and high wear. With technological advancements, vertical rolls made of high-chromium cast iron and high-chromium cast steel have been researched, which have better wear resistance, but their thermal crack resistance is still insufficient.

[0003] Vertical rolls are used in the roughing zone of hot rolling production lines. The slabs are thick, and temperatures reach 1200-1250℃. Combined with the relatively slow rolling speed, the instantaneous temperature at the contact point between the vertical roll and the slab is around 1100℃. This temperature is essentially the limit of the metal material's operating temperature, leading to poor thermal cracking resistance during use. Currently, traditional vertical rolls suffer from short service life and require frequent replacement. The large workload involved in roll replacement and disassembly significantly impacts mill operating rates and rolling output. Summary of the Invention

[0004] To address the aforementioned shortcomings in the existing technology, this invention provides a flux-cored welding wire for hot-rolled vertical roll surfacing and its application. When surfacing repairs hot-rolled vertical rolls, an Nb-Cr multi-element alloy is formed, which has the advantages of high wear resistance, red hardness, and high heat strength. The single rolling capacity of the remanufactured vertical roll is several times higher than that of the original semi-steel vertical roll and high-chromium cast iron vertical roll. Moreover, it can be surfacing repaired multiple times after normal unloading, reducing roll consumption and production costs.

[0005] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is as follows: A flux-cored welding wire for hot-rolled vertical roll surfacing is provided, characterized in that it comprises a welding wire sheath with a mass percentage of 50-80% and a flux core of 20-50%; the flux core comprises the following components by mass percentage: graphite 0.8-2.0%, manganese powder 1.8-4.5%, chromium powder 6.0-15%, molybdenum powder 1.0-2.5%, ferrovanadium 0.2-0.5%, Nb-1Zr niobium-zirconium alloy 4.5-11.5%, metallic silicon 0.9-2.0%, nickel powder 2.5-6.3%, scandium 0.02-0.05%, and activator 1.0-2.5%, with the balance being iron.

[0006] Furthermore, based on the total mass percentage of the flux-cored wire, the flux core comprises the following components: 1.4% graphite, 3.15% manganese powder, 10.5% chromium powder, 1.75% molybdenum powder, 0.35% ferrovanadium, 7.88% Nb-1Zr niobium-zirconium alloy, 1.58% metallic silicon, 4.38% nickel powder, 0.04% scandium, and 1.75% activator, with the balance being iron.

[0007] Furthermore, the outer sheath of the welding wire is made of low-carbon steel strip.

[0008] The raw material for the outer sheath of the welding wire is high-quality cold-rolled steel strip such as SPCC and H08A. The S and P content of the steel strip is strictly controlled during the selection process.

[0009] Furthermore, the diameter of the welding wire is 2.5-4.0mm.

[0010] The cross-section of the flux-cored welding wire is O-shaped or E-shaped, and the wire diameter is usually 2.5mm, 3.2mm, or 4.0mm. Due to the large diameter of the vertical roller, in order to improve the welding efficiency and to ensure the control of the welding formation on the vertical wall, the wire diameter is selected as 3.2mm.

[0011] Furthermore, the particle size of each component in the core is 80-150 mesh.

[0012] Furthermore, the preparation method is as follows: the outer sheath of the welding wire is rolled into a U-shape, then a uniformly mixed flux core is filled in, and then the outer sheath of the welding wire is rolled closed.

[0013] The activator is a commercially available, conventional product. Its main purposes are twofold: first, it acts as a diluent, facilitating the escape of gases from the weld; second, it desulfurizes, allowing sulfur to combine with hydrogen and volatilize, reducing the tendency for white spots. If fluorite is used as the activator, too much should be added, as the fluorine in fluorite is a highly ionizing element that can affect arc stability. After welding with this flux-cored wire, the deposited metal will contain trace amounts of unavoidable impurities such as Mn, Si, S, and P, but these are all within permissible limits.

[0014] The beneficial effects of adopting the solution of this invention are:

[0015] (1) Nb-1Zr niobium-zirconium alloy has good processing and welding performance. It contains medium and high strength carbide forming elements such as W, Mo, Ti, V and Nb. During the surfacing process and post-weld heat treatment, it can form a variety of hard carbide phases to ensure the hardness and strength of the working layer metal. Moreover, the niobium alloy has the highest specific strength in the range of 1093-1427℃, which matches the slab temperature and meets the oxidation resistance, corrosion resistance, thermal fatigue resistance and intermetallic wear resistance required by vertical rolls in high temperature environment.

[0016] (2) Chromium powder and graphite are selected to provide sufficient chromium and carbon elements for welding. Cr mainly improves the hardenability of steel, thereby affecting the depth of the hardened layer of the roll body. The C provided by graphite forms medium- and high-strength carbide hard phases with Cr and elements such as Mo, V, Nb, Ti, and W in the niobium-zirconium alloy. This invention does not use chromium carbide to add chromium because when chromium carbide is added, the structure of the weld metal after tempering increases with the tempering temperature, the structure of the weld metal becomes coarser and the amount of carbide precipitation increases, and the dislocation density decreases. This leads to a decrease in the high-temperature tensile strength and hardness of the weld metal under the service conditions of a contact temperature of 1100℃, and the wear resistance deteriorates. At the same time, the addition of graphite can make the weld metal form a graphitized structure, improve the lubrication effect, reduce the friction of the contact surface during rolling, and reduce the amount of wear.

[0017] (3) Molybdenum metal is mainly used for alloying. It has a stronger ability to form carbides than Cr and W, and has higher wear resistance than W. At the same time, it increases the red hardness of steel, eliminates the brittleness of steel, and significantly improves the impact toughness. Adding a small amount of vanadium is to supplement the insufficient amount of vanadium in niobium-zirconium alloy. In addition, Nb has a stronger carbon-extraction ability than V, allowing more V to dissolve in the matrix and play a role in precipitation strengthening. The carbides of V and Ti are beneficial to reduce segregation and generate refractory carbides, refine the grains, and improve strength and toughness. Nickel powder can improve the toughness, strength and corrosion resistance of weld metal. Adding an appropriate amount of Ni can also greatly improve its thermal sensitivity.

[0018] (4) Manganese and silicon are both basic elements of steel. The reasonable addition of Mn and Si serves two purposes: first, to ensure the alloy content of each element in the weld metal and to give full play to their respective properties; and second, to deoxidize and desulfurize during the welding process. The Al contained in the material and the added scandium both help to remove impurities during the welding process, making the weld metal cleaner and better able to perform the properties of the weld metal.

[0019] (5) When scandium is added to an alloy as a transition element and a rare earth element, it can not only significantly refine the grains of the cast alloy and increase the recrystallization temperature, thereby improving the strength and toughness of the scandium alloy, but also significantly improve the weldability, heat resistance and corrosion resistance of the alloy.

[0020] The present invention also provides the application of the flux-cored welding wire described above for hot-rolled vertical roll surfacing in the surfacing repair of hot-rolled vertical rolls.

[0021] Furthermore, the welding method includes the following steps in sequence:

[0022] (1) Heat the vertical roller to 420-440℃ for 16-20 hours, and then perform submerged arc automatic welding. For each weld thickness of 23-27mm, perform an intermediate heat treatment.

[0023] (2) After the vertical roll is welded, heat it to 420-440℃ and keep it for 3 hours. Then heat it to 490-510℃ and keep it for 3-5 hours. Then heat it to 530-540℃ and keep it for 12-16 hours. Finally, cool it to room temperature and turn it to obtain the remanufactured vertical roll.

[0024] Furthermore, in step (1), the vertical roller is a new roller with a forged steel 45 core or an old roller with a base material of other materials. The base material of the old roller is mostly 60CrNiMo cast steel or medium-high carbon alloy forged steel. The surface of the old roller needs to be inspected by colorimetric testing or magnetic particle testing, and the inside of the roller body needs to be inspected by ultrasonic testing. Defects inside that affect the use are not repaired by welding.

[0025] Furthermore, in step (1), the intermediate heat treatment involves placing the vertical roller into the furnace at the interlayer temperature, heating it to 500-510℃ at a rate of ≤30℃ / h, and then holding it at that temperature for 12-16h.

[0026] Furthermore, in step (2), the parameters of the submerged arc automatic surfacing welding include: the power supply polarity is DC reverse polarity; the welding wire diameter is 3.2mm; the welding current is 350-420A; the welding voltage is 30-33V; the welding speed is 300-500mm / min; the dry extension is 25-35mm; the eccentricity is 30-40mm; the overlap between adjacent weld passes is 60-70%; and the interpass temperature is 380-420℃.

[0027] Furthermore, in step (2), the temperature is increased to 420-440℃ at a heating rate of ≤30℃ / h and held for 3h, then increased to 490-510℃ at a heating rate of ≤30℃ / h and held for 3-5h, then increased to 530-540℃ at a heating rate of ≤20℃ / h and held for 12-16h, and finally cooled to room temperature at a cooling rate of ≤20℃ / h.

[0028] The beneficial effects of adopting the solution of this invention are:

[0029] (1) When the submerged arc welding flux-cored wire produced by this invention is used with the corresponding flux for hot rolling vertical roll surfacing, the surfacing metal has high red hardness and wear resistance. During use, the roll body surface does not stick to steel, which also changes the method used by some domestic and foreign manufacturers to produce vertical rolls using cast iron and semi-steel materials.

[0030] (2) This application method is a traditional submerged arc automatic welding method, which is easy to master and operate. It eliminates the need for a heat preservation welding transition layer and can directly weld the working layer. The newly manufactured vertical rollers are of high quality, solving the problems of surface cracking, scabbing, chipping and severe wear of traditional vertical rollers.

[0031] (3) The new roller core used for overlay welding is made of high-quality carbon steel, and the old roller base is made of medium-high carbon alloy steel. Both have good weldability after preheating. When the base has no defects that affect overlay welding or use, the fatigue layer can be machined off and then overlay welding can be performed multiple times to remanufacture the vertical roller. This overcomes the problem that cast iron vertical rollers and semi-steel rollers cannot be repaired by overlay welding, and better reduces roller consumption and production costs.

[0032] In summary, the present invention has the following advantages:

[0033] 1. In order to ensure the wear resistance, red hardness, and heat strength of the weld metal, the flux-cored wire used in the hot-rolled vertical roll surfacing of this invention requires, on the one hand, controlling the content of harmful elements S and P in the raw materials to avoid their adverse effects on the weld metal; on the other hand, it is important to consider that the weld metal contains a high content of refractory metals, taking advantage of their good high-temperature strength, high density, good thermal conductivity, small coefficient of linear expansion, high elastic modulus, and excellent corrosion resistance.

[0034] 2. The flux-cored welding wire of this invention for hot-rolled vertical roll surfacing is based on material properties and adopts a multi-element alloying method, utilizing trace elements such as W, Ti, V, Zr, and Ni to achieve micro-alloying for strengthening and toughening. When matched with a suitable flux, the resulting metal alloy system is an Nb-Cr system, specifically an Nb-Cr-Ti-W-Ni-V multi-element alloy, which possesses advantages such as high wear resistance, red hardness, and high heat resistance.

[0035] 3. The single rolling capacity of remanufactured vertical rolls is several times greater than that of the original semi-steel vertical rolls and high-chromium cast iron vertical rolls. Moreover, after normal removal from the machine, under the premise of ensuring the quality of the base material, multiple welding repairs can be carried out, further reducing roll consumption and production costs. Attached Figure Description

[0036] Figure 1 This is a diagram of the roller surface of a traditional vertical roller mill.

[0037] Figure 2 A diagram of the roller surface from the remanufacturing vertical roller. Detailed Implementation

[0038] Example 1

[0039] A flux-cored welding wire for hot-rolled vertical roll surfacing comprises a wire sheath of 80% by mass and a flux core of 20% by mass. The flux core, by mass percentage of the total flux-cored wire, comprises the following components: 0.8% graphite, 1.8% manganese powder, 6.0% chromium powder, 1.0% molybdenum powder, 0.2% ferrovanadium, 4.5% Nb-1Zr niobium-zirconium alloy, 0.9% metallic silicon, 2.5% nickel powder, 0.02% scandium, and 1.0% activator, with the balance being iron. The wire sheath is H08A steel strip.

[0040] Example 2

[0041] A flux-cored welding wire for hot-rolled vertical roll surfacing comprises a wire sheath of 65% by mass and a flux core of 35% by mass. The flux core, by mass percentage of the total flux-cored wire, comprises the following components: 1.4% graphite, 3.15% manganese powder, 10.5% chromium powder, 1.75% molybdenum powder, 0.35% ferrovanadium, 7.88% Nb-1Zr niobium-zirconium alloy, 1.58% metallic silicon, 4.38% nickel powder, 0.04% scandium, and 1.75% activator, with the balance being iron. The wire sheath is SPCC steel strip.

[0042] Example 3

[0043] A flux-cored welding wire for hot-rolled vertical roll surfacing comprises a wire sheath of 50% by mass and a flux core of 50% by mass. The flux core, by mass percentage of the total flux-cored wire, comprises the following components: 2.0% graphite, 4.5% manganese powder, 15% chromium powder, 2.5% molybdenum powder, 0.5% ferrovanadium, 11.5% Nb-1Zr niobium-zirconium alloy, 2.0% metallic silicon, 6.3% nickel powder, 0.05% scandium, and 2.5% activator, with the balance being iron. The wire sheath is SPCC steel strip.

[0044] Example 4

[0045] The hot-rolled vertical roll is welded using the flux-cored welding wire obtained in Example 2, and the steps are as follows:

[0046] (1) The new roll of forged steel 45 roll core is heated to 430℃ for 18h and then submerged arc automatic surfacing is carried out. The main parameters of submerged arc automatic surfacing include: the power supply polarity is DC reverse polarity; the welding wire diameter is 3.2mm; the welding current is 380A; the welding voltage is 32V; the welding speed is 400mm / min; the dry extension is 30mm; the eccentricity is 35mm; the overlap of adjacent welds is 65%; the interpass temperature is 400℃; during submerged arc automatic surfacing, every 25mm thick surfacing is heated to 500℃ at a rate of 30℃ / h and then held for 12h for intermediate heat treatment.

[0047] (2) After the vertical roll is welded, heat it to 430℃ at a heating rate of 30℃ / h and keep it at that temperature for 3h. Then heat it to 500℃ at a heating rate of 30℃ / h and keep it at that temperature for 4h. Then heat it to 535℃ at a heating rate of 20℃ / h and keep it at that temperature for 15h. Finally, cool it down to room temperature at a cooling rate of 20℃ / h and then turn it to obtain the remanufactured vertical roll.

[0048] The surface hardness of the remanufactured vertical roll obtained in Example 4 is HS72-78 (or 56HRC±2).

[0049] The roll surface diagrams of the conventional vertical roll and the remanufactured vertical roll obtained in Example 4 are shown below. Figure 1 and Figure 2As shown, traditional vertical rolls have a throughput of 400,000-450,000 tons / cycle, while remanufactured vertical rolls have a throughput of 1,350,000-1,600,000 tons / cycle, which is 3-4 times that of traditional vertical rolls. At the same time, the wear and re-grinding of traditional vertical rolls reaches 6-7 mm per cycle, while that of remanufactured vertical rolls is only 1.5-2 mm. Remanufactured vertical rolls significantly increase the number of times they can be used on the mill from the maximum roll diameter to the minimum roll diameter, and significantly reduce the number of roll changes and the labor and material consumption required for roll changes, thereby improving the mill's operating rate and increasing output.

[0050] In summary, the flux-cored welding wire of the present invention for hot rolling vertical roll surfacing exhibits excellent metal properties after surfacing. The generated hard phase ensures that the working layer metal has good high-temperature strength, high-temperature hardness, and stable microstructure. During use, it exhibits good thermal fatigue performance, a smooth roll surface, and good roll pass retention. It also has a high single-pass rolling yield and stable product quality.

[0051] Although specific embodiments of the present invention have been described in detail with reference to the accompanying drawings, this should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A flux-cored welding wire for hot-rolled vertical roll surfacing, characterized in that, The welding wire comprises a wire sheath of 50-80% by mass and a flux core of 20-50% by mass. The flux core, by mass percentage of the total flux-cored welding wire, comprises the following components: 0.8-2.0% graphite, 1.8-4.5% manganese powder, 6.0-15% chromium powder, 1.0-2.5% molybdenum powder, 0.2-0.5% ferrovanadium, 4.5-11.5% Nb-1Zr niobium-zirconium alloy, 0.9-2.0% metallic silicon, 2.5-6.3% nickel powder, 0.02-0.05% scandium, and 1.0-2.5% activator, with the balance being iron. The wire sheath is made of low-carbon steel strip, and the wire diameter is 2.5-4.0 mm.

2. The flux-cored welding wire for hot-rolled vertical roll surfacing as described in claim 1, characterized in that, The flux-cored wire comprises the following components by weight percentage: 1.4% graphite, 3.15% manganese powder, 10.5% chromium powder, 1.75% molybdenum powder, 0.35% ferrovanadium, 7.88% Nb-1Zr niobium-zirconium alloy, 1.58% metallic silicon, 4.38% nickel powder, 0.04% scandium, and 1.75% activator, with the balance being iron.

3. The flux-cored welding wire for hot-rolled vertical roll surfacing as described in claim 1, characterized in that, The particle size of each component in the core is 80-150 mesh.

4. The flux-cored welding wire for hot-rolled vertical roll surfacing as described in claim 1, characterized in that, The preparation method is as follows: roll the outer sheath of the welding wire into a U-shape, then fill it with a uniformly mixed flux core, and then roll the outer sheath of the welding wire to close it.

5. The application of the flux-cored welding wire for hot-rolled vertical roll surfacing as described in any one of claims 1-4 in the surfacing repair of hot-rolled vertical rolls.

6. The application as described in claim 5, characterized in that, The welding method includes the following steps in sequence: (1) Heat the vertical roller to 420-440℃ for 16-20 h, and then perform submerged arc automatic welding. Perform an intermediate heat treatment once for every 23-27 mm thick weld. (2) After the vertical roller is welded, heat it to 420-440℃ and keep it for 3 hours. Then heat it to 490-510℃ and keep it for 3-5 hours. Then heat it to 530-540℃ and keep it for 12-16 hours. Finally, cool it to room temperature and turn it to obtain the remanufactured vertical roller.

7. The application as described in claim 6, characterized in that, In step (1), the intermediate heat treatment involves placing the vertical roller into the furnace at the interlayer temperature, heating it to 500-510℃ at a rate of ≤30℃ / h, and then holding it at that temperature for 12-16 h.

8. The application as described in claim 6, characterized in that, In step (1), the parameters of the submerged arc automatic surfacing welding include: the power supply polarity is DC reverse polarity; the welding wire diameter is 3.2 mm; the welding current is 350-420 A; the welding voltage is 30-33 V; the welding speed is 300-500 mm / min; the dry extension is 25-35 mm; the eccentricity is 30-40 mm; the overlap between adjacent welds is 60-70%; and the interpass temperature is 380-420℃.

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