High-chromium cast iron surfacing flux-cored wire for shield tunneling machine and preparation method of high-chromium cast iron surfacing flux-cored wire

Abstract

The invention provides a high-chromium cast iron surfacing flux-cored wire for a shield tunneling machine and a preparation method of the high-chromium cast iron surfacing flux-cored wire. The high-chromium cast iron surfacing flux-cored wire is formed by wrapping powder with a steel belt, and the powder accounts for 33.0%-36.0% of the total weight of the flux-cored wire; the powder comprises, by mass, 3%-8% of reduced iron powder, 1%-3% of fluorite, 0.5%-1% of rare earth fluoride, 3%-8% of electrolytic manganese, 1%-5% of high silicon iron, 80%-85% of ferrochrome carbide, 5%-9% of graphite and 1%-3% of nickel powder. Wherein the rare earth fluoride is cerium fluoride. The high-chromium cast iron surfacing flux-cored wire for the shield tunneling machine is excellent in welding process, stable in electric arc, small in splashing, attractive in forming and capable of conducting all-position welding.

Description

Technical Field

[0001] This invention belongs to the field of welding materials technology, and in particular relates to a high-chromium cast iron flux-cored welding wire for tunnel boring machines and its preparation method. Background Technology

[0002] The cutterhead of a tunnel boring machine (TBM) is a core component of tunnel excavation. It endures high-intensity abrasive wear, impact wear, and combined wear over extended periods, especially in geological conditions such as hard rock and gravel. Its service life directly impacts project progress and cost. During excavation, the cutterhead comes into direct contact with rock and gravel. The hardness of the base material (e.g., Q235 steel) (HRC≈20-30) is much lower than the hardness of the rock (HRC≥50), making it prone to rapid wear. This shortens the cutterhead's service life, leads to frequent maintenance, increases maintenance costs, and significantly impacts work efficiency.

[0003] Flux-cored welding wire, with its fast cladding speed and high welding efficiency, is suitable for both semi-automatic and automatic welding. By adding specific alloying elements, the hardness of the cladding metal can be increased, providing a certain degree of wear resistance.

[0004] Traditional flux-cored welding wires for surfacing mainly consist of slag-forming agents, arc stabilizers, and alloying elements, with a focus on alloy content and hardness. They tend to exhibit significant spatter during welding and poor weld formation. In recent years, customers have increasingly demanded higher welding process specifications for flux-cored welding wires, requiring good welding performance while maintaining high alloy content and hardness. Metal powder thin-slag welding wires produce less slag, have higher cladding efficiency, less spatter, better arc stability, and superior cladding efficiency and crack resistance compared to ordinary flux-cored wires. Their low hydrogen content in the weld also contributes to improved crack resistance. Therefore, it is necessary to develop a high-chromium cast iron flux-cored welding wire for surfacing to improve welding processes. Summary of the Invention

[0005] In view of this, the present invention aims to provide a high-chromium cast iron flux-cored welding wire for tunnel boring machines and its preparation method. The cladding metal of the welding wire has a suitable surface hardness, good welding process, can be used for all-position welding, has high cladding efficiency, high surface hardness, and good crack resistance, and can be used for cladding welding of tunnel boring machine cutterheads.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows: A high-chromium cast iron flux-cored welding wire for tunnel boring machines, wherein the welding wire is composed of flux powder wrapped in steel strip, and the flux powder accounts for 33.0%-36.0% of the total weight of the welding wire; By mass fraction, the powder comprises the following components: 3%-8% reduced iron powder, 1%-3% fluorite, 0.5%-1% rare earth fluoride, 3%-8% electrolytic manganese, 1%-5% high silicon iron, 80%-85% chromium carbide, 5%-9% graphite, and 1%-3% nickel powder; among which, the rare earth fluoride is cerium fluoride, with a fluorine content of 30-40%, and impurity elements (such as Ca, Fe, Si, Al, etc.) <1%.

[0007] Among them, reduced iron powder has an Fe content of over 98%. The addition of reduced iron powder can significantly improve cladding efficiency, enhance process performance, increase the utilization rate of transition metal, and adapt to various welding positions. Metal powder-cored welding wire mainly relies on the addition of iron powder to optimize the welding process and improve welding efficiency.

[0008] Fluorite: Its main chemical component is CaF2. The addition of fluoride reduces the diffusible hydrogen content in the cladding metal. However, if the amount added is too high, it will affect the arc concentration, reduce the arc stability, and cause more spatter during welding. Therefore, the amount added must be strictly controlled.

[0009] Rare earth fluorides: The addition of rare earth elements inhibits grain growth and reduces the tendency to crack. Fluorides can remove hydrogen, reduce hydrogen content, and decrease susceptibility to cold cracking.

[0010] Electrolytic manganese: Manganese is a major deoxidizer and an important alloying agent for weld metal, reducing the oxygen content of the weld while increasing the strength and hardness of the weld metal.

[0011] High-silicon ferrometallurgy: Silicon is the main deoxidizer and alloying agent. When combined with manganese, silicon and manganese are used for deoxidation during welding, which increases the amount of acicular ferrite in the weld metal and improves the strength and hardness of the weld.

[0012] Ferrochromium carbide: The addition of carbon increases the carbon content of the weld metal, ensuring deoxidation and weld metal hardness. Meanwhile, chromium, as a major alloying element, enhances the strength and hardness of the weld metal.

[0013] Graphite: Its main component is carbon, which increases the hardness of the weld.

[0014] Nickel powder: Adding a small amount of nickel powder to the flux-cored welding wire helps to refine the grains, promote the formation of acicular ferrite, improve the toughness of the weld, and reduce the occurrence of cracks in the weld due to its high hardness.

[0015] By properly combining the above-mentioned powders, the arc is kept stable and good during the welding process, the weld is aesthetically pleasing, and it has high hardness to meet the needs of on-site welding.

[0016] Furthermore, by mass fraction, the chemical composition of the steel strip includes C: 0.01-0.04%, Mn: 0.19-0.26%, Si≤0.03%, S≤0.010%, P≤0.015%, Als: 0.010-0.045%, Ca≤0.003%, N≤0.005%, with the balance being Fe and unavoidable impurities.

[0017] Furthermore, the diameter of the welding wire is 1.6mm.

[0018] Furthermore, fluorite needs to be baked at 800℃ for 4 hours, while rare earth fluorides, electrolytic manganese, high silicon iron, ferrochrome carbide, and nickel powder need to be baked at 150℃ for 3 hours.

[0019] The present invention also provides a method for preparing the high-chromium cast iron flux-cored welding wire for tunnel boring machines as described above, the method comprising the following steps: (1) Weigh each component of the powder according to the proportion, and bake the fluorite, rare earth fluoride, electrolytic manganese, high silicon iron, chromium iron carbide and nickel powder. (2) Mix and stir the components of the baked medicinal powder; (3) Cut the steel strip to the required size; (4) The powder and steel strip are sent to the forming machine for rolling into semi-finished products; (5) Draw the rolled semi-finished product to the required size as required; (6) Vacuum package the finished welding wire.

[0020] Compared with existing technologies, the high-chromium cast iron flux-cored welding wire for tunnel boring machines and its preparation method described in this invention have the following advantages: (1) The high-chromium cast iron flux-cored welding wire for shield tunneling machines described in this invention has excellent welding process, stable arc, less spatter, beautiful shape and can be used for all-position welding.

[0021] (2) The high-chromium cast iron flux-cored welding wire for shield tunneling machines described in this invention has high hardness, strong wear resistance and good crack resistance after welding.

[0022] 3. The high-chromium cast iron flux-cored welding wire for tunnel boring machines described in this invention has high welding efficiency and can be used for surfacing welding with automated welding equipment. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1 A high-chromium cast iron flux-cored welding wire for tunnel boring machines, wherein the welding wire is composed of flux powder wrapped in steel strip, and the flux powder accounts for 35.0% of the total weight of the welding wire; By mass fraction, the powder comprises the following components: 4.5% reduced iron powder, 3% fluorite, 0.5% rare earth fluoride, 3% electrolytic manganese, 1% high silicon iron, 81% chromium carbide, 6% graphite, and 1% nickel powder; wherein the rare earth fluoride is cerium fluoride, with a fluorine content of 30-40% and impurity elements <1%.

[0026] The chemical composition of the steel strip, by mass fraction, includes C: 0.01-0.04%, Mn: 0.19-0.26%, Si≤0.03%, S≤0.010%, P≤0.015%, Als: 0.010-0.045%, Ca≤0.003%, N≤0.005%, with the balance being Fe and unavoidable impurities.

[0027] The preparation method of the high-chromium cast iron flux-cored welding wire for tunnel boring machines includes the following steps: (1) Weigh each component of the powder according to the proportion. Fluorite needs to be baked at 800℃ for 4 hours, and rare earth fluoride, electrolytic manganese, high silicon iron, ferrochrome carbide and nickel powder need to be baked at 150℃ for 3 hours. (2) Mix and stir the components of the baked medicinal powder; (3) Cut the steel strip to the required size; (4) The powder and steel strip are sent to the forming machine for rolling into semi-finished products; (5) Draw the rolled semi-finished product as required to make a welding wire with a diameter of 1.6 mm; (6) Vacuum package the finished welding wire.

[0028] Example 2 A high-chromium cast iron flux-cored welding wire for tunnel boring machines, wherein the welding wire is composed of flux powder wrapped in steel strip, and the flux powder accounts for 34% of the total weight of the welding wire; By mass fraction, the powder comprises the following components: 3% reduced iron powder, 2% fluorite, 1% rare earth fluoride, 3% electrolytic manganese, 2% high silicon iron, 81% chromium carbide, 7% graphite, and 1% nickel powder; wherein the rare earth fluoride is cerium fluoride, with a fluorine content of 30-40% and impurity elements <1%.

[0029] The chemical composition of the steel strip, by mass fraction, includes C: 0.01-0.04%, Mn: 0.19-0.26%, Si≤0.03%, S≤0.010%, P≤0.015%, Als: 0.010-0.045%, Ca≤0.003%, N≤0.005%, with the balance being Fe and unavoidable impurities.

[0030] The method for preparing the welding wire is the same as in Example 1.

[0031] Example 3 A high-chromium cast iron flux-cored welding wire for tunnel boring machines, wherein the welding wire is composed of a steel strip wrapped with flux powder, and the flux powder accounts for 34.0% of the total weight of the welding wire; The powder comprises the following components by mass fraction: 3.5% reduced iron powder, 3% fluorite, 0.5% rare earth fluoride, 4% electrolytic manganese, 1% high silicon iron, 81.5% chromium carbide, 5% graphite, and 1.5% nickel powder; wherein the rare earth fluoride is cerium fluoride, with a fluorine content of 30-40% and impurity elements <1%.

[0032] The chemical composition of the steel strip, by mass fraction, includes C: 0.01-0.04%, Mn: 0.19-0.26%, Si≤0.03%, S≤0.010%, P≤0.015%, Als: 0.010-0.045%, Ca≤0.003%, N≤0.005%, with the balance being Fe and unavoidable impurities.

[0033] The method for preparing the welding wire is the same as in Example 1.

[0034] Example 4 A high-chromium cast iron flux-cored welding wire for tunnel boring machines, wherein the welding wire is composed of flux powder wrapped in steel strip, and the flux powder accounts for 33.0% of the total weight of the welding wire; By mass fraction, the powder comprises the following components: 3% reduced iron powder, 2% fluorite, 1% rare earth fluoride, 3.5% electrolytic manganese, 2% high silicon iron, 82% chromium carbide, 5% graphite, and 1.5% nickel powder; wherein the rare earth fluoride is cerium fluoride, with a fluorine content of 30-40% and impurity elements <1%.

[0035] The chemical composition of the steel strip, by mass fraction, includes C: 0.01-0.04%, Mn: 0.19-0.26%, Si≤0.03%, S≤0.010%, P≤0.015%, Als: 0.010-0.045%, Ca≤0.003%, N≤0.005%, with the balance being Fe and unavoidable impurities.

[0036] The method for preparing the welding wire is the same as in Example 1.

[0037] Comparative Example 1: Increased content of rare earth fluorides A high-chromium cast iron flux-cored welding wire for tunnel boring machines, wherein the welding wire is composed of flux powder wrapped in steel strip, and the flux powder accounts for 35.0% of the total weight of the welding wire; By mass fraction, the powder comprises the following components: 4% reduced iron powder, 3% fluorite, 2% rare earth fluoride, 3% electrolytic manganese, 1% high silicon iron, 80% chromium carbide, 6% graphite, and 1% nickel powder; wherein the rare earth fluoride is cerium fluoride.

[0038] The chemical composition of the steel strip, by mass fraction, includes C: 0.01-0.04%, Mn: 0.19-0.26%, Si≤0.03%, S≤0.010%, P≤0.015%, Als: 0.010-0.045%, Ca≤0.003%, N≤0.005%, with the balance being Fe and unavoidable impurities.

[0039] Comparative Example 2: Cerium fluoride replaced with lanthanum fluoride A high-chromium cast iron flux-cored welding wire for tunnel boring machines, wherein the welding wire is composed of flux powder wrapped in steel strip, and the flux powder accounts for 35.0% of the total weight of the welding wire; By mass fraction, the powder comprises the following components: 4.5% reduced iron powder, 3% fluorite, 0.5% rare earth fluoride, 3% electrolytic manganese, 1% high silicon iron, 81% chromium ferrocarbide, 6% graphite, and 1% nickel powder; wherein the rare earth fluoride is lanthanum fluoride.

[0040] The chemical composition of the steel strip, by mass fraction, includes C: 0.01-0.04%, Mn: 0.19-0.26%, Si≤0.03%, S≤0.010%, P≤0.015%, Als: 0.010-0.045%, Ca≤0.003%, N≤0.005%, with the balance being Fe and unavoidable impurities.

[0041] Comparative Example 3: Reduced iron powder replaced with rutile. A high-chromium cast iron flux-cored welding wire for tunnel boring machines, wherein the welding wire is composed of flux powder wrapped in steel strip, and the flux powder accounts for 35.0% of the total weight of the welding wire; The powder comprises the following components by mass fraction: rutile 4.5%, fluorite 3%, rare earth fluoride 0.5%, electrolytic manganese 3%, high silicon iron 1%, ferrochrome carbide 81%, graphite 6%, and nickel powder 1%; wherein the rare earth fluoride is cerium fluoride.

[0042] The chemical composition of the steel strip, by mass fraction, includes C: 0.01-0.04%, Mn: 0.19-0.26%, Si≤0.03%, S≤0.010%, P≤0.015%, Als: 0.010-0.045%, Ca≤0.003%, N≤0.005%, with the balance being Fe and unavoidable impurities.

[0043] The welding wires obtained in the examples and comparative examples were welded using a mixed gas of 80% Ar + 20% CO2, and the welded cladding metal was analyzed.

[0044] Table 1. Chemical composition of the flux-cored wire cladding metal prepared in each example and comparative example. Table 2 Welding process testing of welding wires prepared in each embodiment and comparative example Cladding efficiency is the percentage of the weight of the cladding metal to the weight of the welding wire consumed. The higher the cladding efficiency, the less welding wire is needed to obtain the same amount of cladding metal, and the higher the production efficiency per unit.

[0045] As can be seen from the table above, the welding wires prepared according to Examples 1-4 of the present invention have good weld formation and smooth weld surface, which meets the requirements for use on the cutterhead of the tunnel boring machine.

[0046] Comparative Example 1 exhibited significant spatter during welding, moderate arc stability, poor weld formation, and severe post-weld cracking, making it impossible to perform vertical and overhead welding.

[0047] Comparative Example 2 showed significant spatter during welding, poor arc stability, and unsatisfactory weld formation, making it impossible to perform vertical and overhead welding.

[0048] Comparative Example 3 showed good welding process, but the post-weld hardness was slightly low and the cladding efficiency was not high.

[0049] In summary, the flux-cored welding wire described in this invention offers excellent welding technology, stable arc, minimal spatter, and aesthetically pleasing weld formation, enabling all-position welding. The cladding metal produced by the flux-cored welding wire exhibits high hardness and strong wear resistance. Furthermore, the flux-cored welding wire offers high welding efficiency, allowing for surfacing welding using automated welding equipment.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-chromium cast iron flux-cored welding wire for tunnel boring machines, characterized in that: The welding wire consists of a steel strip wrapped with flux powder, and the flux powder accounts for 33.0%-36.0% of the total weight of the welding wire. By mass fraction, the powder comprises the following components: 3%-8% reduced iron powder, 1%-3% fluorite, 0.5%-1% rare earth fluoride, 3%-8% electrolytic manganese, 1%-5% high silicon iron, 80%-85% chromium carbide, 5%-9% graphite, and 1%-3% nickel powder; among which, the rare earth fluoride is cerium fluoride, with a fluorine content of 30-40% and impurity elements <1%.

2. The high-chromium cast iron flux-cored welding wire for tunnel boring machines according to claim 1, characterized in that: The chemical composition of the steel strip, by mass fraction, includes C: 0.01-0.04%, Mn: 0.19-0.26%, Si≤0.03%, S≤0.010%, P≤0.015%, Als: 0.010-0.045%, Ca≤0.003%, N≤0.005%, with the balance being Fe and unavoidable impurities.

3. The high-chromium cast iron flux-cored welding wire for tunnel boring machines according to claim 1, characterized in that: The welding wire diameter is 1.6mm.

4. The high-chromium cast iron flux-cored welding wire for tunnel boring machines according to claim 1, characterized in that: Fluorite needs to be baked at 800℃ for 4 hours, while rare earth fluorides, electrolytic manganese, high silicon iron, ferrochrome carbide, and nickel powder need to be baked at 150℃ for 3 hours.

5. A method for preparing a high-chromium cast iron flux-cored welding wire for tunnel boring machines as described in any one of claims 1-4, characterized in that: The method includes the following steps: (1) Weigh each component of the powder according to the proportion, and bake the fluorite, rare earth fluoride, electrolytic manganese, high silicon iron, chromium iron carbide and nickel powder. (2) Mix and stir the components of the baked medicinal powder; (3) Cut the steel strip to the required size; (4) The powder and steel strip are sent to the forming machine for rolling into semi-finished products; (5) Draw the rolled semi-finished product to the required size as required; (6) Vacuum package the finished welding wire.

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