Welding process for surfacing Monel welding wire on surface of low alloy steel

Abstract

The invention discloses a welding process for surfacing a Monel welding wire on the surface of low alloy steel, and belongs to the field of hot wire TIG surfacing. The invention aims to solve the problem that welding slag is easy to generate when a Monel welding wire is subjected to surfacing on low-alloy pressure vessel steel. According to the method, a hot wire TIG welding method is used, welding is conducted in the vertical upper welding direction, pure nickel metal is selected as a transition layer material between low-alloy pressure vessel steel and a Monel cladding layer, accurate control over the interlayer temperature is achieved by effectively controlling welding process parameters and accurately adjusting welding heat input, and the welding quality is improved. A Ni-Fe system is formed between the pure nickel welding wire and the low-alloy pressure vessel steel, and the pure nickel welding wire and the low-alloy pressure vessel steel have good intersolubility and compatibility; and the Fe content is low, so that the problem of incompatibility of Fe and Cu is effectively avoided, and low-melting-point eutectic substances which are easy to cause welding slag are not easy to generate. And meanwhile, the viscosity, surface tension and fluidity of the molten pool are more uniform and controllable, stable escape of gas and impurities is facilitated, and the slag inclusion tendency is reduced. The overall metallurgical reaction is stable, and welding slag is eliminated.

Description

Technical Field

[0001] This invention belongs to the field of hot-wire TIG welding, specifically, it relates to a welding process for welding Monel wire onto the surface of low-alloy steel. Background Technology

[0002] In the chemical, nuclear power, and energy sectors, low-alloy pressure vessel steels (such as 16MnR, 15CrMo, and 20MnMo) are often used as the preferred material for pressure vessel shells due to their excellent strength, toughness, and weldability, as well as relatively low cost, effectively meeting pressure requirements. Monel welding wire, due to its high nickel-copper content, possesses unique properties, especially its excellent corrosion resistance, exhibiting superior resistance to flowing seawater, neutral salt solutions, alkalis, and various non-oxidizing acids (such as non-aerated room-temperature dilute hydrochloric acid, sulfuric acid, and hydrofluoric acid). Particularly due to its high nickel content, it is almost unaffected by chloride stress corrosion cracking. Furthermore, it has good crack resistance. Taking the most commonly used ERNiCu-7 welding wire as an example, its composition appropriately increases the manganese and titanium content, effectively inhibiting the formation of hot cracks and porosity during welding, ensuring weld quality. In addition, Monel weld metal possesses excellent mechanical properties. It not only boasts high strength (tensile strength typically ≥480 MPa) but also exhibits good plasticity and toughness, enabling it to withstand a wide range of operating temperatures from low to certain high levels. It is particularly suitable for marine engineering (such as ships and offshore platforms), petrochemicals (such as pipelines, heat exchangers, and containers), and other fields, demonstrating reliable performance in environments requiring resistance to seawater, salt, and various chemical corrosion.

[0003] However, due to the intense metallurgical reactions and changes in the physical properties of the molten pool caused by dissimilar metals, the weldability of Monel welding wire when cladding onto low-alloy pressure vessel steel is poor. This is because a complex Fe-Ni-Cu mixture forms in the molten pool. Fe and Cu are miscible in the liquid state, but their solubility in the solid state is extremely low, making them almost incompatible. This can lead to severe segregation and reactions in the molten pool. In the Fe-Ni-Cu system, Cu readily forms low-melting-point eutectic compounds or complex oxides with impurity elements (such as S and P) or alloying elements (such as Si and Mn) in the steel. The melting points of these substances are much lower than the solidification temperature of the weld metal. Towards the end of the molten pool solidification, these last-solidifying low-melting-point liquid substances are pushed to the grain boundaries and weld surface. When they reach the weld surface, they further react with oxygen in the air to form visible weld slag. This necessitates the use of a transition layer between the low-alloy pressure vessel steel and the Monel cladding layer. Nickel and its alloys are very suitable as a transition layer between low-alloy pressure vessel steel and Monel welding wire because they contain little or no Fe. However, nickel and its alloys are extremely sensitive to oxygen at high temperatures, and oxidation will occur in high-temperature welds and heat-affected zones.

[0004] Therefore, there is an urgent need to develop a process for overlaying Monel wire onto low-alloy pressure vessel steel, ensuring welding quality while maintaining good metallurgical compatibility with the steel and relatively controllable weldability. Summary of the Invention

[0005] This invention uses a hot-wire TIG welding method, performing welding in a vertical welding direction. Pure nickel metal is selected as the transition layer material between low-alloy pressure vessel steel and Monel cladding. By effectively controlling the welding process parameters and precisely adjusting the welding heat input, the interlayer temperature can be precisely controlled, thereby effectively solving the problem of oxidation that easily occurs when Monel welding wire is deposited on a pure nickel transition layer.

[0006] This invention utilizes pure nickel welding wire to form a Ni-Fe system with low-alloy pressure vessel steel, exhibiting excellent miscibility and compatibility. Furthermore, the low Fe content effectively avoids the Fe-Cu incompatibility problem. The molten pool has a uniform composition, making it less prone to forming low-melting-point eutectics that easily induce welding slag. Simultaneously, the viscosity, surface tension, and fluidity of the molten pool are more uniform and controllable, facilitating the smooth escape of gases and impurities and reducing the tendency for slag inclusions. The overall metallurgical reaction is stable, and welding slag is eliminated.

[0007] The process of this invention can ensure good weld formation and no welding defects when Monel is deposited on the surface of low alloy pressure vessel steel, and the process window is relatively wide.

[0008] To address the aforementioned technical problems, the present invention adopts the following technical solution: The purpose of this invention is to provide a welding process for depositing Monel welding wire onto the surface of low alloy steel. The process is characterized by employing a hot-wire pulsed TIG welding process, applied vertically, and includes the following steps: Grind the low-alloy pressure vessel steel to be welded until smooth and flat, and then wipe the surface with anhydrous ethanol. Then, under inert gas protection, pure nickel welding wire is deposited on the surface to be welded. After grinding until smooth and flat, the surface is wiped with anhydrous ethanol to form a pure nickel transition layer. Then, under inert gas protection, Monel alloy welding wire was deposited on the surface of the pure nickel transition layer. The welding process parameters are as follows: peak current time is 100-300 ms, base current time is 100-300 ms, peak current is 100-300 A, base current is 100-300 A, arc voltage is 10-20 V, hot wire current is 30-80 A, welding speed is 100-500 mm / min, and wire feed speed is 1000-2500 mm / min.

[0009] Further specify the welding process parameters for surfacing pure nickel welding wire as follows: peak current time is 100-300 ms, base current time is 100-300 ms, peak current is 100-300 A, base current is 100-300 A, arc voltage is 10-20 V, hot wire current is 30-80 A, welding speed is 100-500 mm / min, and wire feed speed is 1000-2500 mm / min.

[0010] Further specified, the inert gas is argon with a purity ≥99.99% (by volume) and a flow rate of 20 L / min.

[0011] Further specified, during the welding process of the pure nickel and Monel alloy welding wire, the distance between the tungsten electrode and the welding wire is 2.2 mm, the tungsten electrode tip angle is 30°, and the tungsten electrode tip platform is maintained at 1.5 mm.

[0012] Further specified, during the welding process of pure nickel and Monel alloy welding wire, after each weld seam is completed, the turntable rotation angle is set to 2° and the turntable speed is set to 40 mm / min.

[0013] Further specifying, during the welding process of the pure nickel and Monel alloy welding wires, the gas supply time in advance is 6 seconds, and the gas shutdown time is 6 seconds.

[0014] Further specified, during the welding process of pure nickel and Monel alloy welding wire, the equipment start-up delay is 0-3 s, the stop delay is 0-3 s, the wire feeding delay is 0-5 s, the equipment arc termination delay is set to 0-3 s, the wire feeding stop delay is 0-5 s, the wire drawing length after welding is 5-20 mm, the welding torch retraction delay is set to 0-3 s, and the welding torch retraction distance is set to 0-10 mm.

[0015] Furthermore, during the welding process of the pure nickel and Monel alloy welding wires, the hot wire power delay is set to 0-5 seconds.

[0016] Further specifying, during the welding process of the pure nickel and Monel alloy welding wire, the pre-melting current is set to 100-200A for 0.1-3s, the power supply current decay time is 1-10s, and the decay current value is 5-40A.

[0017] The present invention also provides a method for overlaying Monel welding wire onto the surface of low alloy pressure vessel steel using any of the above-described processes.

[0018] Based on one specific implementation method, Monel wire is deposited on the surface of low-alloy pressure vessel steel using a hot-wire TIG welding method in a vertically upward welding direction. The transition layer metal is made of pure nickel wire (ERNi-1) with a specification of 1.2 mm. The base material main pipe has an outer diameter of 268 mm, a thickness of 70 mm, and a height of 300 mm; the Monel wire used is NiCu-7 wire with a specification of 1.2 mm.

[0019] The welding steps are as follows: Step 1: Clean the surface of the low alloy pressure vessel steel to be welded. Use an angle grinder to remove the surface oxide scale and wipe it with anhydrous ethanol to ensure that the surface is free of oil and rust and reaches a smooth and flat state.

[0020] Step 2: Adjust the welding torch angle so that the angle between the tungsten electrode tip and the workpiece surface is maintained at 20°-40°.

[0021] Step 3: Adjust the distance between the tungsten electrode and the welding wire before welding to ensure that the distance between the tungsten electrode and the welding wire is 2-2.5 mm.

[0022] Step 4: Ensure the tungsten electrode tip angle. Use a tungsten electrode grinding machine to grind the tungsten electrode tip to ensure the tungsten electrode tip angle is 20°-40° and the tungsten electrode tip platform is maintained at 1-2 mm.

[0023] Step 5: The welding shielding gas is argon with a purity of ≥99.99%. The flow rate of the welding shielding gas during welding is 20~25 L / min. An alarm is set when the flow rate of the shielding gas is lower than 18 L / min.

[0024] Step 6: After each weld is completed, set the turntable rotation angle to 0-5°. Set the turntable speed to 20-100 mm / min.

[0025] Step 7: Set the gas supply advance time to 5-10 s and the gas shutdown delay time to 5-20 s before welding.

[0026] Step 8: Set the equipment start delay to 0-3 s, stop delay to 0-3 s, wire feeder wire feeding delay to 0-5 s, equipment arc termination delay to 0-3 s, wire feeder wire stop delay to 0-5 s, wire pulling length after welding to 5-20 mm, welding torch retraction delay to 0-3 s, and welding torch retraction distance to 0-10 mm. Step 9: After welding begins, the hot wire power delay is set to 0-5 seconds, meaning the hot wire machine will start working after 0-5 seconds.

[0027] Step 10: Set the pre-melting current to 100-200 A for 0.1-3 s, the power supply current decay time to 1-10 s, and the decay current value to 5-40 A.

[0028] Step 11: Set the arc start position and stop position of the welding torch.

[0029] Step 12: The welding process adopts hot-wire pulse TIG welding technology to deposit pure nickel on the surface of the low-alloy pressure vessel steel to be welded. The number of welding layers is single layer. The welding process parameters are as follows: peak current time is 100-300 ms, base current time is 100-300 ms, peak current is 100-300 A, base current is 100-300 A, arc voltage is 10-20 V, hot wire current is 30-80 A, welding speed is 100-500 mm / min, and wire feed speed is 1000-2500 mm / min. After grinding with an angle grinder, the surface is wiped with anhydrous ethanol to ensure that the surface is free of oil and rust and that the outer wall is smooth and flat.

[0030] Step 13: Repeat steps 1-11 to deposit Monel wire onto the transition layer metal. The welding process parameters are as follows: peak current time is 100-300 ms, base current time is 100-300 ms, peak current is 100-300 A, base current is 100-300 A, arc voltage is 10-20 V, hot wire current is 30-80 A, welding speed is 100-500 mm / min, and wire feed speed is 1000-2500 mm / min.

[0031] Compared with the prior art, the present invention has the following beneficial effects: The weld formation quality is excellent. This process can achieve a smooth surface and smooth transition of the weld overlay, with no weld slag and a clean weld bead. It is free from common defects such as undercut, lack of fusion, rough weld bead, and cracks. Both the internal and external quality meet the high standard welding requirements. The process has strong stability and reliability. By precisely controlling parameters such as shielding gas flow rate, welding sequence, hot wire delay, and current attenuation, the system has good process stability and repeatability, which is conducive to ensuring the consistency of quality in mass production.

[0032] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0033] Figure 1 It is formed by overlaying pure nickel welds on the surface of low alloy pressure vessel steel; Figure 2 It is a process of overlaying Monel wire onto the transition layer surface of low alloy pressure vessel steel to form a weld seam. Detailed Implementation

[0034] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0035] Example 1 Monel wire was used for overlay welding on 20MnMo low-alloy pressure vessel steel. The main body of the base material had an outer diameter of 268 mm, a thickness of 70 mm, and a height of 300 mm. The main element mass percentage range was as follows: Carbon (C): 0.19%, Silicon (Si): 0.23%, Manganese (Mn): 1.19%, Molybdenum (Mo): 0.24%, Phosphorus (P): 0.012%, Sulfur (S): 0.005%, Chromium (Cr): 0.09%, Copper (Cu): 0.07%, Nickel (Ni): 0.05%. NiCu-7 welding wire with a diameter of 1.2 mm was used for the Monel welding. Pure nickel welding wire (ERNi-1) with a diameter of 1.2 mm was used for the transition layer metal.

[0036] The welding steps are as follows: Step 1: Clean the surface of the low alloy pressure vessel steel to be welded. Use an angle grinder to grind off the oxide scale on the surface and wipe the surface with anhydrous ethanol to ensure that the surface is free of oil and rust and that the outer wall is smooth and flat. Step 2: Adjust the welding torch angle so that the angle between the tungsten electrode tip and the workpiece surface is maintained at 20°; Step 3: Adjust the gap between the tungsten electrode and the welding wire before welding to ensure that the gap between the tungsten electrode and the welding wire is 2.2 mm; Step 4: Ensure the tungsten electrode tip angle. Use a tungsten electrode grinding machine to grind the tungsten electrode tip to ensure that the tungsten electrode tip angle is 30° and the tungsten electrode tip platform is maintained at 1.5 mm. Step 5: The welding shielding gas is argon gas with a purity of 99.99% (by volume). The flow rate of the welding shielding gas during welding is 20 L / min. An alarm is set when the flow rate of the shielding gas is lower than 18 L / min. Step 6: After each weld is completed, the turntable rotation angle is set to 2° and the turntable speed is set to 40 mm / min; Step 7: Set the gas supply advance time to 6 seconds and the gas shutdown delay time to 6 seconds before welding. Step 8: Set the equipment start delay to 0.5 s, stop delay to 0 s, wire feeder wire feeding delay to 0.5 s, equipment arc termination delay to 1 s, wire feeder wire stop delay to 2 s, welding wire pull-out length after welding to 10 mm, welding torch retraction delay to 1 s, and welding torch retraction distance to 2 mm. Step 9: After welding begins, the hot wire power delay is set to 0.5 s, meaning the hot wire machine starts working after 0.5 s. Step 10: Set the pre-melting current to 120 A for 0.1 s, the power supply current decay time to 3 s, and the decay current value to 20 A.

[0037] Step 11: Set the arc start position and stop position of the welding torch; Step 12: The welding process uses hot-wire pulse TIG welding to deposit pure nickel on the 20MnMo base material. The welding layer is a single layer. The welding process parameters are as follows: peak current time is 100 ms, base current time is 230 ms, peak current is 260 A, base current is 140 A, arc voltage is 12.5 V, hot wire current is 50 A, welding speed is 120 mm / min, and wire feed speed is 1100 mm / min. After grinding with an angle grinder, the surface is wiped with anhydrous ethanol to ensure that the surface is free of oil and rust and that the outer wall is smooth and flat. Step 13: Repeat steps 2-11 to deposit Monel wire onto the transition layer metal. The welding process parameters are as follows: peak current time is 120 ms, base current time is 220 ms, peak current is 200 A, base current is 160 A, arc voltage is 13 V, hot wire current is 60 A, welding speed is 180 mm / min, and wire feed speed is 1500 mm / min.

[0038] Figure 1 shows the formation of a pure nickel weld overlay on the surface of low-alloy pressure vessel steel. Figure 1 As shown; the weld formation of the Monel wire overlay on the transition layer surface of low alloy pressure vessel steel is as follows. Figure 2 As shown, the post-weld visual inspection, radiographic inspection, penetrant testing, and mechanical property testing (bending) all passed.

[0039] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. A welding process for overlaying Monel welding wire onto the surface of low alloy steel, characterized in that, The hot-wire pulse TIG welding process, applied vertically, includes the following steps: Grind the low-alloy pressure vessel steel to be welded until smooth and flat, and then wipe the surface with anhydrous ethanol. Then, under inert gas protection, pure nickel welding wire is deposited on the surface to be welded. After grinding until smooth and flat, the surface is wiped with anhydrous ethanol to form a pure nickel transition layer. Then, under inert gas protection, Monel alloy welding wire was deposited on the surface of the pure nickel transition layer. The welding process parameters are as follows: peak current time is 100-300 ms, base current time is 100-300 ms, peak current is 100-300 A, base current is 100-300 A, arc voltage is 10-20 V, hot wire current is 30-80 A, welding speed is 100-500 mm / min, and wire feed speed is 1000-2500 mm / min.

2. The process according to claim 1, characterized in that, The welding process parameters for surfacing pure nickel welding wire are as follows: peak current time is 100-300 ms, base current time is 100-300 ms, peak current is 100-300 A, base current is 100-300 A, arc voltage is 10-20 V, hot wire current is 30-80 A, welding speed is 100-500 mm / min, and wire feed speed is 1000-2500 mm / min.

3. The process according to claim 1, characterized in that, The inert gas is argon with a purity of ≥99.99% and a flow rate of 20 L / min.

4. The process according to claim 1, characterized in that, During the welding process, the distance between the tungsten electrode and the welding wire is 2.2 mm, the angle of the tungsten electrode tip is 30°, and the tungsten electrode tip platform is maintained at 1.5 mm.

5. The process according to claim 1, characterized in that, During the welding process, after each weld seam is completed, the turntable rotation angle is set to 2° and the turntable speed is set to 40 mm / min.

6. The process according to claim 1, characterized in that, During the welding process, the gas supply time is 6 seconds in advance and the gas shutdown time is 6 seconds in delay.

7. The process according to claim 1, characterized in that, During the welding process, the equipment start-up delay is 0-3 s, the stop delay is 0-3 s, the wire feeder wire feeding delay is 0-5 s, the equipment arc termination delay is set to 0-3 s, the wire feeder wire stop delay is 0-5 s, the wire drawing length after welding is 5-20 mm, the welding torch retraction delay is set to 0-3 s, and the welding torch retraction distance is set to 0-10 mm.

8. The process according to claim 1, characterized in that, During the welding process, the hot wire power delay is set to 0-5 seconds.

9. The process according to claim 1, characterized in that, During the welding process, the pre-melting current is set to 100-200A and lasts for 0.1-3s. The power supply current decay time is 1-10s and the decay current value is 5-40A.

10. A process according to any one of claims 1-9 for overlaying Monel wire onto the surface of low-alloy pressure vessel steel.

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