A flux-cored wire for hardfacing of high corrosion-resistant pipe fittings and a preparation method thereof

Abstract

The present application relates to the technical field of welding wire, especially to a flux-cored wire for high corrosion-resistant pipe fitting surfacing and a preparation method thereof, which comprises obtaining the material and thickness of the target pipe fitting, determining the theoretical welding heat interval and upper and lower limits for surfacing; determining the theoretical diameter interval of the flux-cored wire according to the theoretical welding heat interval; determining the target diameter through the depth-height ratio; when the diameter is adjusted to the interval limit and still does not meet the standard, optimizing the flux-cored wire adhesion degree according to the depth-height ratio difference; detecting the corrosion resistance by surfacing with the target welding wire, and adjusting the theoretical welding heat interval reversely. The present application determines the theoretical diameter interval of the flux-cored wire through the theoretical welding heat interval, determines the target diameter of the flux-cored wire based on the actual depth-height ratio, and determines the theoretical welding heat interval based on the actual parameters of corrosion resistance to form an effective surfacing layer when surfacing the pipe fitting.

Description

Technical Field

[0001] This invention relates to the field of welding wire technology, and in particular to a flux-cored welding wire for high corrosion-resistant pipe overlay welding and its preparation method. Background Technology

[0002] Flux-cored welding wire, also known as powder-cored welding wire or tubular welding wire, is divided into two main categories: gas-shielded and non-gas-shielded. The surface of flux-cored welding wire is the same as that of solid welding wire. It is made of materials such as low-carbon steel or low-alloy steel with good plasticity. The manufacturing method is to first roll the steel strip into a U-shaped cross section, then fill the U-shaped steel strip with welding powder prepared according to the dosage, press it tightly with a rolling mill, and finally draw it into flux-cored welding wire of different specifications.

[0003] Chinese Patent Publication No. CN118023760A discloses a flux-cored welding wire and its preparation method. The flux-cored welding wire includes a steel strip and a flux core, wherein the flux core is filled in the steel strip. The flux core comprises the following raw materials in the following mass percentages: 7%-10% micro-carbon ferrochrome, 3%-5% high-carbon ferrochrome, 7%-10% metallic manganese, 5%-7% ferromolybdenum, 4%-6% rutile, 40%-55% fluorite, 3%-5% quartz, 1%-2% potassium feldspar, 1%-2% potassium fluorozirconate, 2%-3% calcium silicate powder, 3%-5% magnesium powder, 3%-4% 45% ferrosilicon, and the balance being atomized iron powder. The flux-cored welding wire provided by this invention can improve the fluidity of molten slag, reduce slag spatter, and enhance arc stability during welding, thereby optimizing the welding process performance. On the other hand, it can improve the high-temperature oxidation resistance and corrosion resistance of high-melt metal, giving the weld excellent resistance to hot cracking and low-temperature toughness, thus making the weld of heat-resistant steel more adaptable to harsh environments of high temperature, high pressure, and steam corrosion.

[0004] Therefore, the existing technology has the following problems: In the preparation process of flux-cored welding wire, due to the lack of a process to determine the theoretical diameter range of flux-cored welding wire through the theoretical welding heat range, to determine the target diameter of flux-cored welding wire based on the actual depth-to-height ratio, and to determine the theoretical welding heat range based on the actual corrosion resistance parameters, the flux-cored welding wire cannot form an effective weld overlay layer on the surface of the pipe fitting when it is used for welding. Summary of the Invention

[0005] To address this issue, the present invention provides a flux-cored welding wire for high corrosion-resistant pipe surfacing and its preparation method, thereby overcoming the problem in the prior art where, during the preparation of flux-cored welding wire, the theoretical diameter range of the flux-cored welding wire is not determined by the theoretical welding heat range, the target diameter of the flux-cored welding wire is determined based on the actual depth-to-height ratio, and the theoretical welding heat range is determined based on the actual corrosion resistance parameters. This results in the flux-cored welding wire failing to form an effective weld overlay layer on the surface of the pipe fitting when surfacing it.

[0006] To achieve the above objectives, the present invention provides a method for preparing flux-cored welding wire for high corrosion-resistant pipe fittings, comprising:

[0007] Obtain the pipe material and thickness of the target pipe fitting, preset welding parameters based on the pipe material and thickness and perform overlay welding, monitor the melting degree of the pipe fitting substrate to determine the corresponding welding heat, determine the theoretical welding heat range that the pipe fitting can withstand based on the welding heat and melting degree determination results, and determine the upper limit and lower limit of heat input of the flux-cored welding wire based on the theoretical welding heat range.

[0008] The upper limit of the diameter of the flux-cored wire is determined based on the upper limit of the heat input, the lower limit of the diameter of the flux-cored wire is determined based on the lower limit of the heat input, and the theoretical diameter range of the flux-cored wire is determined based on the upper limit and the lower limit of the diameter.

[0009] The diameter of the appropriate flux-cored wire is determined based on the median value of the theoretical diameter range. A welding operation is performed based on the diameter of the appropriate flux-cored wire to obtain the fusion depth and height of the weld overlay. The actual depth-to-height ratio is obtained based on the ratio of the fusion depth to the height of the weld overlay. The target diameter of the flux-cored wire is determined based on the actual depth-to-height ratio and the depth-to-height ratio threshold range.

[0010] If the actual depth-to-height ratio still does not fall into the depth-to-height ratio threshold range after the theoretical diameter of the flux-cored wire is adjusted to the upper or lower limit of the theoretical diameter range, then the target flux-cored wire fit is determined based on the difference between the actual depth-to-height ratio and the extreme value of the depth-to-height ratio threshold range.

[0011] The target flux-cored welding wire is obtained based on the target flux-cored fit and the target diameter. The pipe is then subjected to a welding operation based on the target flux-cored welding wire to obtain the actual corrosion resistance parameters of the weld overlay. The theoretical welding heat range is then adjusted based on the comparison between the actual corrosion resistance parameters and the threshold range of the actual corrosion resistance parameters.

[0012] The fusion depth is the maximum melting depth of the pipe fitting base material when the pipe fitting surface is melted by electric arc to form a molten pool of base material, and the molten pool of base material forms a metallurgical bond with the flux-cored wire deposited metal. The weld overlay height is the height of the deposited metal layer that is higher than the surface of the pipe fitting base material after weld overlay.

[0013] Furthermore, the process of determining the theoretical welding heat range that the pipe fitting can withstand during surfacing welding includes:

[0014] The pipe fitting is overlay welded based on preset welding parameters. The melting degree of the substrate on the pipe fitting surface is monitored in real time, and the corresponding welding heat is determined based on the melting degree. The theoretical welding range is determined based on the welding heat.

[0015] The welding parameters include target current, target voltage, and target wire feed speed.

[0016] Furthermore, the process of determining the theoretical upper limit of the flux-cored wire diameter includes:

[0017] The maximum welding current is determined based on the target voltage, preset welding speed, and upper limit of heat input. The upper limit of the diameter of the flux-cored wire is then determined based on the maximum welding current.

[0018] Furthermore, the process of determining the theoretical lower limit of the flux-cored wire diameter includes:

[0019] The minimum welding current is determined based on the target voltage, preset welding speed, and lower limit of heat input. The lower limit of the diameter of the flux-cored wire is then determined based on the minimum welding current.

[0020] Furthermore, the process of obtaining the fusion depth and height of the weld overlay includes:

[0021] The pipe fitting after the overlay welding operation is divided to obtain the cross-section of the overlay layer. The fusion depth is obtained by measuring the distance from the surface of the pipe fitting to the metallization layer formed by the flux-cored wire weld metal and the pipe fitting substrate in the cross-section of the overlay layer.

[0022] The weld overlay height is determined by the height of the weld metal layer that extends above the surface of the pipe substrate after welding.

[0023] Furthermore, the process of determining the target diameter of the flux-cored wire includes:

[0024] Based on the fact that the actual depth-to-height ratio is less than the minimum value of the depth-to-height ratio threshold range, the diameter of the flux-cored welding wire is reduced according to the difference between the minimum value of the depth-to-height ratio threshold range and the actual depth-to-height ratio.

[0025] Based on the actual depth-to-height ratio being within the depth-to-height ratio threshold range, the current flux-cored wire diameter is maintained.

[0026] Based on the fact that the actual depth-to-height ratio is greater than the maximum value of the depth-to-height ratio threshold range, the diameter of the flux-cored wire is increased according to the difference between the actual depth-to-height ratio and the maximum value of the depth-to-height ratio threshold range.

[0027] Furthermore, the process of determining the target flux-cored wire fit includes:

[0028] Based on the fact that the actual depth-to-height ratio is less than the minimum value of the depth-to-height ratio threshold range, the core-to-drug fit is increased according to the difference between the minimum value of the depth-to-height ratio threshold range and the actual depth-to-height ratio to obtain the target core-to-drug fit.

[0029] Based on the actual depth-to-height ratio being within the depth-to-height ratio threshold range, the current core-to-drug fit is maintained as the target core-to-drug fit.

[0030] Based on the fact that the actual depth-to-height ratio is greater than the maximum value of the depth-to-height ratio threshold range, the core-to-drug fit is reduced according to the difference between the actual depth-to-height ratio and the maximum value of the depth-to-height ratio threshold range to obtain the target core-to-drug fit.

[0031] The core-coating fit refers to the fit between the core welding wire and the inner wall of the pipe.

[0032] Furthermore, the process of adjusting the theoretical welding heat range includes:

[0033] Based on the fact that the actual corrosion resistance parameter is less than the minimum value of the threshold range of the actual corrosion resistance parameter, the actual corrosion resistance difference is obtained according to the difference between the actual corrosion resistance parameter and the minimum value of the threshold range of the actual corrosion resistance parameter. Based on the actual corrosion resistance difference and the threshold range of the corrosion resistance difference, the adjustment method of the theoretical welding heat range is determined.

[0034] Based on the actual corrosion resistance parameters being within the threshold range of the actual corrosion resistance parameters, the current theoretical welding heat range is maintained;

[0035] Based on the fact that the actual corrosion resistance parameter is greater than the maximum value of the threshold range of the actual corrosion resistance parameter, the actual corrosion resistance difference is obtained according to the difference between the actual corrosion resistance parameter and the maximum value of the threshold range of the actual corrosion resistance parameter. Based on the actual corrosion resistance difference and the threshold range of the corrosion resistance difference, the adjustment method of the theoretical welding heat range is determined.

[0036] The actual parameters of corrosion resistance are positively correlated with the corrosion resistance performance.

[0037] Furthermore, the process of determining the adjustment method for the theoretical welding heat range includes:

[0038] Based on the fact that the actual corrosion resistance parameter is less than the minimum value of the threshold range of the actual corrosion resistance parameter;

[0039] Based on the fact that the actual difference is less than the minimum value of the corrosion resistance difference threshold range, the lower limit of the theoretical welding heat range is adjusted upward according to the difference between the minimum value of the corrosion resistance difference threshold range and the actual difference, while the upper limit of the theoretical welding heat range is maintained.

[0040] Based on the actual difference being within the corrosion resistance difference threshold range, the upper limit of the theoretical welding heat range is simultaneously lowered and the lower limit of the theoretical welding heat range is simultaneously raised according to the initial adjustment value.

[0041] Based on the fact that the actual difference is greater than the maximum value of the corrosion resistance difference threshold range, the upper limit of the theoretical welding heat range is lowered according to the difference between the actual difference and the maximum value of the corrosion resistance difference threshold range, while the lower limit of the theoretical welding heat range is maintained.

[0042] The present invention also provides a flux-cored welding wire for high corrosion-resistant pipe overlay welding, comprising a low-carbon steel strip shell and a flux core filled in the low-carbon steel strip shell;

[0043] The chemical composition by mass percentage of the low-carbon steel strip shell is as follows: C≤0.12%, Mn0.30%-0.60%, Si≤0.30%, Cr0.5-1.2%, P≤0.035%, S≤0.035%, with the remainder being Fe and unavoidable impurities;

[0044] The core is composed of the following raw materials in the indicated weight percentages: titanium dioxide 28%-35%, silicon dioxide 2%-10%, zirconium dioxide 0-2%, aluminum oxide 0.5%-4%, iron oxide 1%-3.5%, sodium oxide 0-1.5%, potassium oxide 0-1.2%, fluoride 0.5%-8%, manganese 10%-14%, silicon 2%-5%, aluminum 0-1.5%, magnesium 0.25-3%, and iron 11.3%-55.75%.

[0045] Compared with existing technologies, the beneficial effects of this invention are as follows: In implementation, by focusing on the core parameters of pipe material and thickness to determine the theoretical welding heat range, it avoids the blindness of traditional general heat parameters. The material determines the heat conduction characteristics and melting threshold of the pipe, while the thickness is related to the heat carrying capacity. The combination of these two factors allows the heat range to match the essential characteristics of the pipe, fundamentally avoiding the risks of incomplete fusion or excessive melting. The clear upper and lower limits of heat input further realize the refinement of heat control, ensuring that the base material of the pipe can be fully melted during welding to form a reliable metallurgical bond, while preventing excessive heat input from causing excessive melting of the base material and exceeding the dilution rate limit. This lays a key foundation for subsequent matching of welding wire diameter and ensuring corrosion resistance. This invention has good versatility and adaptability, and the heat range can be flexibly adjusted according to the characteristics of pipes with different materials and thicknesses, breaking through the limitations of a single pipe specification and expanding the scope of application of the method. In addition, the intermediate value verification step strengthens the reliability of the range, providing a stable benchmark for subsequent process parameter optimization and improving the controllability and stability of the overall welding process.

[0046] Furthermore, in implementation, the maximum and minimum welding currents are derived from the upper and lower limits of heat input, establishing a quantitative matching logic between current and welding wire diameter. This avoids the empirical and blind selection of traditional diameters, ensuring that the selected diameter can stably bear the corresponding welding current, guaranteeing arc stability and welding process continuity. In diameter selection, factors such as deposition amount, dilution rate, burn-through risk, and weld coverage requirements are comprehensively considered. This eliminates specifications with insufficient or excessive load-bearing capacity and avoids weld defects caused by inappropriate diameters, achieving a balance between welding quality and efficiency. It also enables precise matching between flux-cored wire diameter and welding process and pipe characteristics, providing reliable consumable specification support for high corrosion-resistant weld overlay.

[0047] Furthermore, during implementation, standardized cross-sectional preparation, corrosion, and testing processes enabled precise quantification of fusion depth and weld overlay height. Sampling locations focused on the stable section of the weld overlay, coupled with refined cutting and corrosion processes, ensuring that the test data accurately reflected the metallurgical bonding state between the weld overlay and the substrate. This provided a reliable basis for depth-to-height ratio calculations and avoided subsequent parameter misadjustments due to testing errors. Based on the comparison between the actual depth-to-height ratio and the threshold range, the difference quantification guided the targeted adjustment of the welding wire diameter. This ensured that the diameter matched the forming requirements of the weld overlay, avoiding excessive dilution or insufficient bonding strength caused by improper flux-cored wire diameter, while also ensuring that the depth-to-height ratio was within the optimal range. This balanced metallurgical bonding quality and corrosion resistance. Efficient optimization was achieved through standardized steps, significantly improving process controllability.

[0048] Furthermore, in practice, for scenarios where the diameter of the flux-cored wire, even adjusted to the theoretical limit, still cannot meet the depth-to-height ratio requirement, the depth-to-height ratio difference is used as a quantitative basis. By increasing or decreasing the flux-cored wire adhesion, the problem of uneven or excessive heat conduction is precisely solved. When the flux-cored wire adhesion is insufficient, increasing the adhesion can optimize the contact tightness between the flux-cored wire and the tubing, improve the uniformity of heat conduction, and avoid insufficient fusion caused by energy dispersion in the molten pool. When the flux-cored wire adhesion is too high, appropriately reducing the adhesion can disperse the excessively concentrated energy, prevent the substrate from melting excessively, and achieve precise calibration of the depth-to-height ratio. The adjustment of the adhesion is achieved by optimizing industrially feasible process parameters such as vibration filling time and drawing reduction rate, ensuring the feasibility and repeatability of the technical solution. Through targeted adjustment of the flux-cored wire adhesion, the depth-to-height ratio is further guaranteed to be within the optimal threshold range, laying a solid process foundation for high corrosion-resistant surfacing welding.

[0049] Furthermore, in implementation, a closed-loop optimization mechanism for the theoretical welding heat range based on corrosion resistance feedback enables refined and targeted control of heat parameters. This mechanism uses the actual corrosion resistance parameters and their differences as quantitative criteria to distinguish between two core scenarios: insufficient and excessive corrosion resistance. Differentiated adjustment methods are then matched according to the magnitude of the difference, avoiding the blindness and uniformity of traditional heat adjustment. This ensures that the heat range always adapts to the core requirements of high corrosion resistance surfacing. In scenarios with insufficient corrosion resistance, precise control through adjusting the lower limit, bidirectional fine-tuning, and lowering the upper limit solves both the fusion defects caused by excessively low heat input and avoids the burn-off of corrosion-resistant elements caused by excessively high heat input, achieving a balance between metallurgical bonding quality and corrosion resistance. In scenarios with excessive corrosion resistance, production efficiency is optimized while ensuring that corrosion resistance does not deteriorate, avoiding resource waste, by maintaining the range or moderately increasing the range. Attached Figure Description

[0050] Figure 1 This is a flowchart illustrating the preparation method of flux-cored welding wire for high corrosion-resistant pipe overlay welding according to an embodiment of the present invention.

[0051] Figure 2This is a flowchart illustrating the process of determining the target diameter of the flux-cored wire according to an embodiment of the present invention.

[0052] Figure 3 This is a flowchart illustrating the process of determining the target flux-cored wire fit in an embodiment of the present invention.

[0053] Figure 4 This is a flowchart illustrating the process of adjusting the theoretical welding heat range according to an embodiment of the present invention. Detailed Implementation

[0054] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0055] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0056] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0057] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0058] Please see Figure 1 As shown, Figure 1 This is a flowchart illustrating the preparation method of flux-cored welding wire for high corrosion-resistant pipe overlay welding according to an embodiment of the present invention.

[0059] This invention provides a method for preparing flux-cored welding wire for high corrosion-resistant pipe fittings, comprising:

[0060] Step S1: Obtain the pipe material and pipe thickness of the target pipe fitting; preset welding parameters based on the pipe material and pipe thickness and perform overlay welding operation; monitor the melting degree of the pipe fitting substrate to determine the corresponding welding heat; determine the theoretical welding heat range that the pipe fitting can withstand based on the welding heat and melting degree determination results; and determine the upper limit and lower limit of heat input of the flux-cored welding wire based on the theoretical welding heat range.

[0061] Step S2: Determine the upper limit of the diameter of the flux-cored wire based on the upper limit of the heat input, determine the lower limit of the diameter of the flux-cored wire based on the lower limit of the heat input, and determine the theoretical diameter range of the flux-cored wire based on the upper limit and the lower limit of the diameter.

[0062] Step S3: Determine the diameter of the appropriate flux-cored wire based on the median value of the theoretical diameter range; perform a welding operation based on the appropriate flux-cored wire diameter to obtain the fusion depth and height of the weld overlay; obtain the actual depth-to-height ratio based on the ratio of the fusion depth to the height of the weld overlay; and determine the target diameter of the flux-cored wire based on the actual depth-to-height ratio and the depth-to-height ratio threshold range.

[0063] Step S4: If the actual depth-to-height ratio still does not fall into the depth-to-height ratio threshold range after the theoretical diameter of the flux-cored wire is adjusted to the upper or lower limit of the theoretical diameter range, then the target flux-cored wire fit is determined based on the difference between the actual depth-to-height ratio and the extreme value of the depth-to-height ratio threshold range.

[0064] Step S5: Obtain the target flux-cored welding wire based on the target flux-cored wire fit and the target diameter; perform a welding operation on the pipe based on the target flux-cored welding wire to obtain the actual corrosion resistance parameters of the weld overlay; adjust the theoretical welding heat range based on the comparison results between the actual corrosion resistance parameters and the threshold range of the actual corrosion resistance parameters.

[0065] The fusion depth is the maximum melting depth of the pipe fitting base material when the pipe fitting surface is melted by electric arc to form a molten pool of base material, and the molten pool of base material forms a metallurgical bond with the flux-cored wire deposited metal. The weld overlay height is the height of the deposited metal layer that is higher than the surface of the pipe fitting base material after weld overlay.

[0066] Specifically, the process of determining the theoretical welding heat range that the pipe fitting can withstand during overlay welding includes:

[0067] The pipe fitting is overlay welded based on preset welding parameters. The melting degree of the substrate on the pipe fitting surface is monitored in real time, and the corresponding welding heat is determined based on the melting degree. The theoretical welding range is determined based on the welding heat.

[0068] The welding parameters include target current, target voltage, and target wire feed speed.

[0069] In this embodiment of the invention, in step S1, the pipe fitting is made of 304 stainless steel, which is a low-carbon austenitic stainless steel with a chemical composition of Cr 18-20%, Ni 8-12%, C ≤ 0.08% and a pipe fitting thickness of 10mm.

[0070] The pipe fittings are 50mm in outer diameter and 200mm in length. The surface is sandblasted to remove oil and oxide scale residue. During the welding process, an infrared thermometer is used to detect the temperature range.

[0071] Based on 1.2mm high corrosion-resistant flux-cored welding wire, three sets of preset welding parameters were designed: target current, target voltage, and target wire feed speed, covering low, medium, and high heat input scenarios, with the welding speed fixed at 12mm / s.

[0072] Table 1 presents the three sets of preset welding parameters:

[0073] ;

[0074] For each set of parameters, a 100mm long weld overlay is performed on the surface of the target pipe fitting, avoiding the two ends of the pipe fitting by 20mm to ensure the representativeness of the data;

[0075] During the surfacing process, based on the 1.2mm high corrosion-resistant flux-cored welding wire, the welding parameter recorder collects current, voltage, and wire feed speed data in real time to ensure that the parameter fluctuation is ≤±5%; the thermometer is aimed at the center area of ​​the molten pool and records the molten pool temperature every 100ms; the high-speed camera simultaneously captures the molten pool morphology to observe whether there is any lack of fusion or burn-through.

[0076] After the welding is completed, a sample with a size of 5mm×10mm is cut along the vertical interface of the weld layer. After grinding and etching with 2% nitric acid alcohol solution for 8-12s, the melting depth of the substrate is observed and measured by metallographic microscope. That is, the vertical depth of the substrate surface that is melted, which is used as a quantitative indicator of the degree of melting.

[0077] Table 2 presents the results of the three groups of melting degree determination tables:

[0078] ;

[0079] The standard heat input calculation formula is adopted: Heat input = (current × voltage × 60) / (welding speed × 1000) in kJ / mm, where 60 is the conversion factor between seconds and minutes, and 1000 is the conversion factor between millimeters and meters;

[0080] Calculation results of welding heat for each group:

[0081] Low-calorie group: Heat input = (218 × 25.8 × 60) / (12 × 1000) ≈ 28.12 kJ / mm;

[0082] Medium heat group: Heat input = (248 × 27.9 × 60) / (12 × 1000) ≈ 34.60 kJ / mm;

[0083] High-calorie group: Heat input = (298 × 29.8 × 60) / (12 × 1000) ≈ 44.40 kJ / mm;

[0084] The current and voltage are derived from the actual collected parameters in Table 2;

[0085] In this embodiment, the lower limit of heat input is 28.12 kJ / mm for the low heat group, which is insufficient for melting and requires increasing the heat input to just enough for complete melting. Combined with the medium heat group of 34.60 kJ / mm, the lower limit of the theoretical welding heat range is determined to be 30.00 kJ / mm, which is slightly higher than the low heat group to avoid insufficient melting.

[0086] Upper limit of heat input: The high heat group is 44.40 kJ / mm, which is excessive melting. The heat input needs to be reduced to just the point where there is no excessive melting. Combined with the medium heat group of 34.60 kJ / mm, the upper limit of the theoretical welding heat range is determined to be 40.00 kJ / mm, which is slightly lower than the high heat group to avoid exceeding the dilution rate.

[0087] Final theoretical welding heat range: 30.00-40.00 kJ / mm;

[0088] Using the midpoint of the theoretical welding heat range of 35.00 kJ / mm, and setting the welding parameters as follows: current 250 A, voltage 28 V, wire feed speed 5.5 m / min, and welding speed 12 mm / s, a welding test was conducted again, and the melting depth of the pipe substrate was found to be 1.1 mm, indicating that the pipe was fully melted.

[0089] The molten pool temperature stabilized at 1540℃ within the optimal range of 1500-1600℃;

[0090] The bonding rate between the weld overlay and the pipe substrate is 98.6%, and the dilution rate is 3.2%, which meets the requirements for high corrosion resistance and has no defects such as incomplete fusion or burn-through.

[0091] In this embodiment of the invention, the theoretical welding heat range for 304 stainless steel, 10mm thick pipe fittings is determined to be 30.00-40.00 kJ / mm. If the target pipe fitting material is changed to carbon steel such as Q235 and the thickness is adjusted to 8mm, the theoretical welding heat range needs to be adjusted accordingly to 25.00-35.00 kJ / mm. The reason is that carbon steel has better thermal conductivity than 304 stainless steel, so the heat input needs to be slightly reduced to avoid insufficient fusion caused by rapid heat conduction. At the same time, with the pipe fitting thickness reduced, in order to prevent the risk of burn-through, the upper and lower limits of the heat input range need to be further lowered to ensure the safety and reliability of the welding process.

[0092] In implementation, by focusing on the core parameters of pipe material and thickness to determine the theoretical welding heat range, the blindness of traditional general heat parameters is avoided. The material determines the heat conduction characteristics and melting threshold of the pipe, while the thickness is related to the heat carrying capacity. The combination of the two allows the heat range to match the inherent characteristics of the pipe, fundamentally avoiding the risks of incomplete fusion or excessive melting. The clear upper and lower limits of heat input further realize the refinement of heat control, ensuring that the base material of the pipe can be fully melted during surfacing to form a reliable metallurgical bond, while preventing excessive heat input from causing excessive melting of the base material and exceeding the dilution rate limit. This lays a key foundation for subsequent matching of welding wire diameter and ensuring corrosion resistance. This invention has good versatility and adaptability, and the heat range can be flexibly adjusted according to the characteristics of pipes with different materials and thicknesses, breaking through the limitations of a single pipe specification and expanding the scope of application of the method. In addition, the intermediate value verification link strengthens the reliability of the range, provides a stable benchmark for subsequent process parameter optimization, and improves the controllability and stability of the overall surfacing process.

[0093] Specifically, the process of determining the theoretical upper limit of the diameter of the flux-cored wire includes:

[0094] The maximum welding current is determined based on the target voltage, preset welding speed, and upper limit of heat input. The upper limit of the diameter of the flux-cored wire is then determined based on the maximum welding current.

[0095] In this embodiment of the invention, the target voltage is set to 28V, which is the commonly used voltage for high corrosion-resistant surfacing welding, and is matched with 1.2-1.6mm flux-cored welding wire, with voltage fluctuation ≤±1V; the preset welding speed is 12mm / s;

[0096] Based on the formula for calculating heat input, the maximum welding current can be calculated as: (upper limit of heat input × voltage × 1000) / (voltage × 60).

[0097] The maximum welding current is (40×12×1000) / (28×60)≈285.7A, rounded to the nearest integer 286A. The current adjustment accuracy of the welding equipment is 1A.

[0098] Based on historical data, the current range for stable welding corresponding to different flux-cored wire diameters is shown in Table 3.

[0099] Table 3 presents the applicable heat input range corresponding to the diameter of the flux-cored welding wire:

[0100] ;

[0101] The maximum welding current is 286A. It must be less than or equal to the maximum stable welding current of the welding wire, and excessive deposition and dilution rate due to excessive diameter must be avoided.

[0102] The maximum current carrying capacity of the 1.0mm welding wire is 260A < 286A, which is insufficient to carry the current, so it is excluded.

[0103] The 1.2mm welding wire has a maximum current carrying capacity of 300A ≥ 286A and a heat input limit of 40kJ / mm, which is within its applicable range and meets the requirements.

[0104] Although the 1.6mm welding wire has a maximum current carrying capacity of 330A ≥ 286A, its larger diameter results in a higher deposition rate than the 1.2mm welding wire. Combined with the 10mm pipe thickness, this can easily lead to excessive weld overlay and excessive dilution rate, so it is excluded.

[0105] For 10mm thick-walled pipe fittings, the risk of burn-through due to excessive diameter should be avoided. The penetration depth of 1.2mm welding wire at 286A current is approximately 2.2mm, which is less than 1 / 4 of the pipe fitting thickness, i.e., 2.5mm. There is no risk of burn-through. Further confirmation of compatibility determines that the upper limit of the diameter of the flux-cored welding wire is 1.2mm.

[0106] Specifically, the process of determining the theoretical lower limit of the flux-cored wire diameter includes:

[0107] The minimum welding current is determined based on the target voltage, preset welding speed, and lower limit of heat input. The lower limit of the diameter of the flux-cored wire is then determined based on the minimum welding current.

[0108] In this embodiment of the invention, the target voltage is set to 28V, which is the commonly used voltage for high corrosion-resistant surfacing welding, and is matched with 1.2-1.6mm flux-cored welding wire, with voltage fluctuation ≤±1V; the preset welding speed is 12mm / s;

[0109] Based on the formula for calculating heat input, the maximum welding current can be calculated as follows: (Upper limit of heat input × Voltage × 1000) / (Voltage × 60).

[0110] The maximum welding current is (30×12×1000) / (28×60)≈214.3A, rounded to the nearest integer 214A. The current adjustment accuracy of the welding equipment is 1A.

[0111] The suitability of the minimum welding current of 214A is analyzed in conjunction with Table 3;

[0112] The minimum stable current of 1.0mm welding wire is 200A≤214A. Although it can withstand the current, the deposition amount is low. A single welding pass cannot cover the surface of the substrate and multiple welding passes are required, which is inefficient. In addition, the low flux filling rate affects the adhesion. Therefore, it is excluded.

[0113] The minimum stable current of the 1.2mm welding wire is 220A≈214A with a deviation of only 2.7%. The arc can be stabilized by fine-tuning the voltage, and the deposition amount can meet the requirements of single-pass welding coverage.

[0114] The minimum stable current of 1.6mm welding wire is 250A > 214A, so stable welding cannot be achieved at 214A current.

[0115] With a minimum welding current of 214A and a wire feed speed of 5.0m / min, the 1.2mm welding wire can achieve a single weld layer height of approximately 2.0mm and a width of approximately 8mm, which can completely cover the surface of the 304 stainless steel pipe fitting without any risk of incomplete welding and meets the coverage requirements. Therefore, the lower limit of the diameter of the flux-cored welding wire was finally determined to be 1.2mm.

[0116] Through the above process, the theoretical diameter range of flux-cored welding wire is determined to be 1.2mm-1.2mm. That is, for 10mm 304 stainless steel pipe fittings, the optimal suitable flux-cored welding wire diameter is a single specification of 1.2mm. There is no need to iteratively adjust the diameter. It can be understood that in the embodiments of the present invention, the 304 stainless steel specification of the pipe fitting is only one of the pipe fitting raw materials. Multiple key raw materials can be obtained for the surfacing operation.

[0117] In implementation, the maximum and minimum welding currents are derived from the upper and lower limits of heat input, establishing a quantitative matching logic between current and welding wire diameter. This avoids the empirical and blind selection of traditional diameters, ensuring that the selected diameter can stably bear the corresponding welding current, guaranteeing arc stability and welding process continuity. In diameter selection, factors such as deposition amount, dilution rate, burn-through risk, and weld coverage requirements are comprehensively considered. This eliminates specifications with insufficient or excessive load-bearing capacity and avoids weld defects caused by inappropriate diameters, achieving a balance between welding quality and efficiency. It also enables precise matching between flux-cored wire diameter and welding process and pipe characteristics, providing reliable consumable specification support for high corrosion-resistant weld overlay.

[0118] Specifically, the process of obtaining the fusion depth and height of the weld overlay includes:

[0119] The pipe fitting after the overlay welding operation is divided to obtain the cross-section of the overlay layer. The fusion depth is obtained by measuring the distance from the surface of the pipe fitting to the metallization layer formed by the flux-cored wire weld metal and the pipe fitting substrate in the cross-section of the overlay layer.

[0120] The weld overlay height is determined by the height of the weld metal layer that extends above the surface of the pipe substrate after welding.

[0121] Please see Figure 2 The diagram shown is a flowchart illustrating the process of determining the target diameter of the flux-cored wire according to an embodiment of the present invention.

[0122] Specifically, the process of determining the target diameter of the flux-cored wire includes:

[0123] Based on the fact that the actual depth-to-height ratio is less than the minimum value of the depth-to-height ratio threshold range, the diameter of the flux-cored welding wire is reduced according to the difference between the minimum value of the depth-to-height ratio threshold range and the actual depth-to-height ratio.

[0124] Based on the actual depth-to-height ratio being within the depth-to-height ratio threshold range, the current flux-cored wire diameter is maintained.

[0125] Based on the fact that the actual depth-to-height ratio is greater than the maximum value of the depth-to-height ratio threshold range, the diameter of the flux-cored wire is increased according to the difference between the actual depth-to-height ratio and the maximum value of the depth-to-height ratio threshold range.

[0126] In the middle 50mm area of ​​the weld overlay section, mark a cutting line perpendicular to the weld length direction with a marker pen at 40mm from the start end and 10mm from the end end of the weld overlay to ensure that the cross-section completely includes the three-layer structure of the pipe base material, the fusion zone and the weld overlay layer.

[0127] A slow wire EDM machine was used, with the following cutting parameters set: electrode wire diameter 0.18 mm, cutting speed 5 mm / min, and emulsion cooling pressure 0.3 MPa. After cutting, a cuboid sample was obtained with dimensions of 10 mm pipe thickness × 15 mm width × 8 mm weld overlay length. The 10 mm × 15 mm cross-section was the core inspection surface.

[0128] The polished sample was placed with its cross-section facing down and vertically immersed in a 2% nitric acid alcohol solution. It was etched at room temperature (25°C) for 10 seconds. Preliminary experiments verified that the interface clarity was optimal at 10 seconds. This avoids insufficient etching leading to a blurred interface or excessive etching leading to surface pitting. After removing the sample, it was immediately rinsed with deionized water for 30 seconds to remove any residual etching solution. Then, it was dehydrated with anhydrous ethanol for 10 seconds and finally dried with a cold air blower at a speed of 3 m / s to prevent residual moisture from causing secondary oxidation.

[0129] When the cross-section is observed with the naked eye, the three-layer structure can be clearly distinguished: the light gray base material area is the 304 stainless steel body, the light white transition fusion area is the mixed area of ​​the pipe base material and the deposited metal, and the gray-white overlay layer area is the flux-cored wire deposited metal. The three-layer boundary is a continuous straight line, and the absence of a blurred transition zone indicates that the corrosion is qualified.

[0130] The etched sample was placed on the stage of a metallographic microscope. The magnification was adjusted to 200x, and the focus was on the critical interface. Using the original surface of the pipe substrate as a baseline, the un-welded area of ​​the pipe substrate was observed through the microscope. The baseline was calibrated to a horizontal state to ensure a consistent measurement reference. The maximum depth of the metallurgical bond formed after the flux-cored wire weld metal melts with the pipe substrate, i.e., the boundary between the fusion zone and the substrate, appears as a continuous dark line after etching. Three measurement points were evenly selected on the cross-section, one on the left, one in the center, and one on the right, with a spacing of 3mm, avoiding local defects. The vertical distance from the original surface of the pipe substrate to the metallurgical bond surface was measured using the microscope's digital display scale. The data were recorded as follows:

[0131] The fusion depth at measurement point 1 is 1.09 mm; the fusion depth at measurement point 2 is 1.11 mm; and the fusion depth at measurement point 3 is 1.10 mm.

[0132] The average value of the three measurement points is taken as the final fusion depth. Fusion depth = (1.09 + 1.11 + 1.10) / 3 = 1.10 mm;

[0133] Measure the vertical distance from the original surface of the pipe fitting substrate to the highest point of the weld overlay, where the highest point of the weld overlay is the natural accumulation vertex of the deposited metal, avoiding minor surface protrusions. Record the data as follows:

[0134] Measurement point 1: 2.18mm; Measurement point 2: 2.22mm; Measurement point 3: 2.20mm;

[0135] The average value of the three measurement points is taken as the final weld overlay height. Weld overlay height = (2.18 + 2.22 + 2.20) / 3 = 2.20 mm;

[0136] In this embodiment of the invention, the depth-to-height ratio threshold range is set to [0.33, 0.67]. The key to high corrosion resistance welding is to control the dilution rate of the pipe substrate to ≤5%. The dilution rate is directly positively correlated with the depth-to-height ratio. The greater the fusion depth, the higher the dilution rate. The greater the height of the weld overlay, the lower the dilution rate. The depth-to-height ratio threshold range of 0.33-0.67 corresponds to a dilution rate of 2.5%-4.8%, which fully meets the corrosion resistance requirements and is determined based on historical data.

[0137] Welding was performed using flux-cored wire with an initial diameter of 1.6mm, with a length of 100mm following preset parameters. Samples were taken to test the fusion depth and weld layer height.

[0138] Fusion depth: 1.05mm, excessive deposition of 1.6mm diameter flux-cored wire, resulting in slow growth of fusion depth due to weld overlay accumulation;

[0139] Fusion depth: 3.75mm. The large diameter of the flux-cored wire resulted in a high deposition rate, which significantly increased the weld overlay.

[0140] Actual depth-to-height ratio = fusion depth / fusion depth = 1.05 / 3.75 = 0.28 < 0.33, which is the minimum value in the depth-to-height ratio threshold range.

[0141] The depth-to-height ratio difference is 0.33-0.28=0.05, so the standard step of the welding wire diameter needs to be reduced by 0.2mm. The initial diameter of 1.6mm is adjusted to 1.4mm, and the welding is inspected again.

[0142] Adjusted parameters: current 260A, voltage 28.5V, wire feed speed 6.5m / min, welding speed 12mm / s, matching heat input 35kJ / mm;

[0143] Final adjustment: 1.6mm to 1.2mm, actual depth-to-height ratio 0.5 in [0.33, 0.67], therefore the target diameter is 1.2mm;

[0144] Welding was performed using flux-cored wire with an initial diameter of 1.0 mm and according to preset parameters. The fusion depth was measured to be 1.35 mm. The 1.0 mm diameter flux-cored wire has a high current density, concentrated molten pool energy, and significantly increased fusion depth.

[0145] The weld overlay height is 1.80 mm, the flux core diameter is small, the deposition amount is low, and the weld overlay growth is slow.

[0146] The actual depth-to-height ratio is 1.35 / 1.80 = 0.75 > 0.67, which is the maximum value within the threshold range for the depth-to-height ratio.

[0147] The difference between the depth and height ratio is 0.75-0.67=0.08; the diameter of the flux-cored wire needs to be increased, with a standard step of 0.2mm. The initial flux-cored wire diameter of 1.0mm should be adjusted to 1.2mm, and the welding should be inspected again.

[0148] Adjusted parameters: current 250A, voltage 28V, wire feed speed 5.5m / min, welding speed 12mm / s, matching heat input 35kJ / mm;

[0149] Test results: The fusion depth is 1.10mm, the weld overlay height is 2.20mm, and the depth-to-height ratio is 0.5, which is within the depth-to-height ratio threshold range. After adjustment, the depth-to-height ratio falls into the threshold range, so the target diameter is 1.2mm.

[0150] In implementation, standardized cross-sectional preparation, corrosion, and testing processes enabled precise quantification of fusion depth and weld overlay height. Sampling was focused on the stable section of the weld overlay, and refined cutting and corrosion processes ensured that the test data accurately reflected the metallurgical bonding state between the weld overlay and the substrate, providing a reliable basis for depth-to-height ratio calculation and avoiding subsequent parameter misadjustments due to testing errors. Based on the comparison between the actual depth-to-height ratio and the threshold range, the difference was quantified to guide the targeted adjustment of the welding wire diameter. This ensured that the diameter matched the forming requirements of the weld overlay, avoiding excessive dilution or insufficient bonding strength caused by improper flux-cored wire diameter, while ensuring that the depth-to-height ratio was within the optimal range, balancing metallurgical bonding quality and corrosion resistance. Efficient optimization was achieved through standardized steps, significantly improving process controllability.

[0151] Please see Figure 3 This is a flowchart illustrating the process of determining the target flux-cored wire fit in an embodiment of the present invention.

[0152] Specifically, the process of determining the target flux-cored wire fit includes:

[0153] Based on the fact that the actual depth-to-height ratio is less than the minimum value of the depth-to-height ratio threshold range, the core-to-drug fit is increased according to the difference between the minimum value of the depth-to-height ratio threshold range and the actual depth-to-height ratio to obtain the target core-to-drug fit.

[0154] Based on the actual depth-to-height ratio being within the depth-to-height ratio threshold range, the current core-to-drug fit is maintained as the target core-to-drug fit.

[0155] Based on the fact that the actual depth-to-height ratio is greater than the maximum value of the depth-to-height ratio threshold range, the core-to-drug fit is reduced according to the difference between the actual depth-to-height ratio and the maximum value of the depth-to-height ratio threshold range to obtain the target core-to-drug fit.

[0156] The core-coating fit refers to the fit between the core welding wire and the inner wall of the pipe.

[0157] In this embodiment of the invention, the initial value of the core fit is set to 95%, and three sets of test conditions are designed to cover three scenarios: the actual depth-to-height ratio is less than the minimum value of the depth-to-height ratio threshold range; the actual depth-to-height ratio is within the depth-to-height ratio threshold range; and the actual depth-to-height ratio is greater than the maximum value of the depth-to-height ratio threshold range. The depth-to-height ratio anomaly is simulated by adjusting the initial fit, and then the target fit is determined according to the rules. Please refer to Table 4, which shows the fit of the three different conditions.

[0158] Table 4 presents the test objectives for the three operating conditions:

[0159] ;

[0160] The welding test results were obtained using a 1.2mm flux-cored wire with an initial fit of 93%.

[0161] The fusion depth was 0.88 mm, and the gap caused the energy of the molten pool to be dispersed, resulting in insufficient melting of the pipe fitting substrate;

[0162] The weld overlay height is 2.70mm, with localized accumulation of flux core and uneven deposition, resulting in an excessively thick weld overlay.

[0163] The actual depth-to-height ratio of 0.88 / 2.70 ≈ 0.327 is less than the minimum value in the threshold range for the depth-to-height ratio.

[0164] The difference between depth and height is 0.01;

[0165] The initial fit was adjusted from 90% to 91%, and the process was optimized: vibration filling time was 35 minutes, and the drawing reduction rate was 11.5%. A second welding inspection was then conducted.

[0166] Test results: The fusion depth is 1.05mm, the weld overlay height is 2.33mm, and the actual depth-to-height ratio of 0.45 falls within the threshold range for depth-to-height ratio.

[0167] If the depth-to-height ratio difference is 0.05, the core adhesion will increase from 90% to 95%. Optimized process: vibration filling time 45 min, drawing diameter reduction rate 11%, actual depth-to-height ratio 0.45 falls within the depth-to-height ratio threshold range [0.33, 0.67], therefore the target core adhesion is 95%.

[0168] Welding with 1.2mm flux-cored wire with 99% initial adhesion was used. Excessive flux-cored adhesion resulted in excessive tightness between the flux-cored wire and the inner wall of the pipe, leading to concentrated energy in the molten pool.

[0169] The fusion depth was 1.38 mm, and the energy concentration led to a significant increase in the fusion depth of the pipe substrate during the melting transition.

[0170] The weld overlay height is 2.00mm, the flux core is too tightly bonded, and the deposition amount is uniform but the total amount is slightly low, resulting in a smaller weld overlay height.

[0171] The actual depth-to-height ratio is 1.38 / 2.00 = 0.69 > 0.67, which is the maximum value within the threshold range for the depth-to-height ratio.

[0172] The difference between the depth and height is 0.69 - 0.67 = 0.02;

[0173] In this embodiment, the required step size for reducing the core adhesion is set to 2%, the initial adhesion is adjusted from 99% to 97%, the process vibration filling time is optimized to 50 minutes, the drawing diameter reduction rate is 11%, and a second welding inspection is performed.

[0174] Adjusted parameters: current 250A, voltage 28V, wire feed speed 5.5m / min, welding speed 12mm / s;

[0175] The fusion depth was 1.25 mm, and the reduced adhesion of the drug core led to slightly dispersed heat conduction and a reduced fusion depth.

[0176] The weld overlay height is 2.16mm, the flux core compactness is moderate, and the weld overlay height has increased slightly.

[0177] The actual depth-to-height ratio of 1.25 / 2.16 ≈ 0.59 falls within the threshold range of [0.33, 0.67] for the depth-to-height ratio.

[0178] After adjustment, the depth-to-height ratio falls within the threshold range, therefore the target core fit is 97%.

[0179] In practice, for scenarios where the diameter of the flux-cored wire, even adjusted to the theoretical limit, still cannot meet the depth-to-height ratio requirement, the depth-to-height ratio difference is used as a quantitative basis. By increasing or decreasing the flux-cored wire adhesion, the problem of uneven or excessive heat conduction is precisely solved. When the flux-cored wire adhesion is insufficient, increasing the adhesion optimizes the contact tightness between the flux-cored wire and the tubing, improves the uniformity of heat conduction, and avoids insufficient fusion caused by energy dispersion in the molten pool. When the flux-cored wire adhesion is too high, appropriately reducing the adhesion can disperse the excessively concentrated energy, prevent over-melting of the substrate, and achieve precise calibration of the depth-to-height ratio. The adjustment of the adhesion is achieved by optimizing industrially feasible process parameters such as vibration filling time and drawing reduction rate, ensuring the feasibility and repeatability of the technical solution. Through targeted adjustments to the flux-cored wire adhesion, the depth-to-height ratio is further guaranteed to be within the optimal threshold range, laying a solid process foundation for high corrosion-resistant surfacing welding.

[0180] Please see Figure 4 The diagram shown is a flowchart illustrating the process of adjusting the theoretical welding heat range according to an embodiment of the present invention.

[0181] Specifically, the process of adjusting the theoretical welding heat range includes:

[0182] Based on the fact that the actual corrosion resistance parameter is less than the minimum value of the threshold range of the actual corrosion resistance parameter, the actual corrosion resistance difference is obtained according to the difference between the actual corrosion resistance parameter and the minimum value of the threshold range of the actual corrosion resistance parameter. Based on the actual corrosion resistance difference and the threshold range of the corrosion resistance difference, the adjustment method of the theoretical welding heat range is determined.

[0183] Based on the actual corrosion resistance parameters being within the threshold range of the actual corrosion resistance parameters, the current theoretical welding heat range is maintained;

[0184] Based on the fact that the actual corrosion resistance parameter is greater than the maximum value of the threshold range of the actual corrosion resistance parameter, the actual corrosion resistance difference is obtained according to the difference between the actual corrosion resistance parameter and the maximum value of the threshold range of the actual corrosion resistance parameter. Based on the actual corrosion resistance difference and the threshold range of the corrosion resistance difference, the adjustment method of the theoretical welding heat range is determined.

[0185] The actual parameters of corrosion resistance are positively correlated with the corrosion resistance performance.

[0186] Specifically, the process of determining the adjustment method for the theoretical welding heat range includes:

[0187] Based on the fact that the actual corrosion resistance parameter is less than the minimum value of the threshold range of the actual corrosion resistance parameter;

[0188] Based on the fact that the actual difference is less than the minimum value of the corrosion resistance difference threshold range, the lower limit of the theoretical welding heat range is adjusted upward according to the difference between the minimum value of the corrosion resistance difference threshold range and the actual difference, while the upper limit of the theoretical welding heat range is maintained.

[0189] Based on the actual difference being within the corrosion resistance difference threshold range, the upper limit of the theoretical welding heat range is simultaneously lowered and the lower limit of the theoretical welding heat range is simultaneously raised according to the initial adjustment value.

[0190] Based on the fact that the actual difference is greater than the maximum value of the corrosion resistance difference threshold range, the upper limit of the theoretical welding heat range is lowered according to the difference between the actual difference and the maximum value of the corrosion resistance difference threshold range, while the lower limit of the theoretical welding heat range is maintained.

[0191] In this embodiment of the invention, the actual corrosion resistance parameter threshold range is set to [0.25V, 0.4V]; the corrosion resistance difference threshold range is [0.02V, 0.05V].

[0192] The initial heat input range is 30.00-40.00 kJ / mm, and the welding parameters are: current 250A, voltage 28V, wire feed speed 5.5m / min, and heat input is 35kJ / mm.

[0193] Corrosion resistance test: After 48 hours of neutral salt spray test, the pitting potential was 0.235V < 0.25V;

[0194] The actual difference is 0.25V - 0.235V = 0.015V < 0.02V, which is the minimum value in the corrosion resistance difference threshold range.

[0195] In this embodiment of the invention, the adjustment logic is to increase the range by 3% based on the difference between the minimum value of the corrosion resistance difference threshold range and the actual difference; keep the upper limit of the theoretical welding heat range unchanged at 40.00 kJ / mm, and after adjusting the lower limit by 3%, the upper limit of the theoretical welding heat range is 30.00 kJ / mm × (1 + 3%) = 30.90 kJ / mm; the adjusted theoretical welding heat range is 30.90-40.00 kJ / mm.

[0196] The initial heat input range is 30.00-40.00 kJ / mm, and the pitting potential detected after welding is 0.22V < 0.25V.

[0197] The actual difference is 0.25V - 0.22V = 0.03V, which falls within the corrosion resistance difference threshold range of [0.02V, 0.05V].

[0198] The adjustment logic is that if the actual difference is within the corrosion resistance difference threshold range, the upper limit of the theoretical welding heat range is simultaneously lowered and the lower limit of the theoretical welding heat range is simultaneously raised by ±3% of the initial adjustment value.

[0199] The upper limit of the theoretical welding heat range is lowered by 3% to 40.00×(1-3%)=38.80kJ / mm, and the lower limit of the theoretical welding heat range is raised by 3% to 30.00×(1+3%)=30.90kJ / mm; the adjusted theoretical welding heat range is 30.90-38.80kJ / mm.

[0200] The initial heat input range is 30.00-40.00 kJ / mm, and the pitting potential detected after welding is 0.19V < 0.25V.

[0201] The actual difference is 0.25V - 0.19V = 0.06V > 0.05V, which is the maximum value in the corrosion resistance difference threshold range.

[0202] In this embodiment, the adjustment logic is a difference of 0.06V - 0.05V = 0.01V, corresponding to a downward adjustment of 5%.

[0203] The lower limit of the theoretical welding heat range remains unchanged at 30.00 kJ / mm, while the upper limit of the theoretical welding heat range is lowered by 5% to 40.00 × (1 - 5%) = 38.00 kJ / mm;

[0204] The initial heat input range is 30.00-40.00 kJ / mm, and the pitting potential detected after welding is 0.41V > 0.4V.

[0205] The actual difference is 0.41V - 0.4V = 0.01V < 0.02V;

[0206] In this embodiment, the actual difference in the adjustment logic is small, the corrosion resistance is slightly excessive, the theoretical welding heat range of 30.00-40.00kJ / mm is kept unchanged, and only the wire feeding speed is increased by 5%, from 5.5m / min to 5.75m / min to improve production efficiency;

[0207] The initial heat input range is 30.00-40.00 kJ / mm, and the pitting potential detected after welding is 0.43V > 0.4V.

[0208] The actual difference is 0.43V - 0.4V = 0.03V, which falls within the corrosion resistance difference threshold range of [0.02V, 0.05V].

[0209] In this embodiment of the invention, the adjustment logic is that when the actual difference is within the difference range, the upper and lower limits are simultaneously increased by 3% to optimize production efficiency without affecting corrosion resistance.

[0210] The upper limit of the theoretical welding heat range is increased by 3% to 40.00×1.03=41.20kJ / mm, and the lower limit of the theoretical welding heat range is increased by 3% to 30.00×1.03=30.90kJ / mm; the adjusted theoretical welding heat range is 30.90-41.20kJ / mm.

[0211] The initial heat input range was 30.00-40.00 kJ / mm, and the pitting potential after welding was detected to be 0.47V > 0.4V.

[0212] The actual difference is 0.47V - 0.4V = 0.07V > 0.05V;

[0213] In this embodiment, the adjustment logic is that the actual difference is large and the corrosion resistance is seriously excessive, so the upper limit of the theoretical welding heat range is increased by 5% to maximize efficiency.

[0214] The lower limit of the theoretical welding heat range remains unchanged at 30.00 kJ / mm, while the upper limit is increased by 5% to 40.00 × 1.05 = 42.00 kJ / mm; the adjusted theoretical welding heat range is 30.00-42.00 kJ / mm.

[0215] In implementation, a closed-loop optimization mechanism for the theoretical welding heat range based on corrosion resistance feedback enables refined and targeted control of heat parameters. This mechanism uses the actual corrosion resistance parameters and their differences as quantitative criteria to distinguish between two core scenarios: insufficient and excessive corrosion resistance. Differentiated adjustment methods are then matched according to the magnitude of the difference, avoiding the blindness and uniformity of traditional heat adjustment. This ensures that the heat range always adapts to the core requirements of high corrosion resistance surfacing. In scenarios with insufficient corrosion resistance, precise control through adjusting the lower limit, bidirectional fine-tuning, and lowering the upper limit solves both the fusion defects caused by excessively low heat input and avoids the burn-off of corrosion-resistant elements caused by excessively high heat input, achieving a balance between metallurgical bonding quality and corrosion resistance. In scenarios with excessive corrosion resistance, production efficiency is optimized while ensuring that corrosion resistance does not deteriorate, avoiding resource waste.

[0216] This invention also provides a flux-cored welding wire for high corrosion-resistant pipe overlay welding, comprising a low-carbon steel strip shell and a flux core filled within the low-carbon steel strip shell;

[0217] The chemical composition by mass percentage of the low-carbon steel strip shell is as follows: C≤0.12%, Mn0.30%-0.60%, Si≤0.30%, Cr0.5-1.2%, P≤0.035%, S≤0.035%, with the remainder being Fe and unavoidable impurities;

[0218] The core is composed of the following raw materials in the indicated weight percentages: titanium dioxide 28%-35%, silicon dioxide 2%-10%, zirconium dioxide 0-2%, aluminum oxide 0.5%-4%, iron oxide 1%-3.5%, sodium oxide 0-1.5%, potassium oxide 0-1.2%, fluoride 0.5%-8%, manganese 10%-14%, silicon 2%-5%, aluminum 0-1.5%, magnesium 0.25-3%, and iron 11.3%-55.75%.

[0219] In this invention, the flux-cored wire has a flux-cored mass filling rate of 18%-25%, meaning the flux-cored mass accounts for 18%-25% of the total mass of the wire, and the low-carbon steel strip shell accounts for 75%-82% of the total mass. For example, the 1.2mm diameter flux-cored wire used in the embodiment has a flux-cored mass filling rate of 20%, corresponding to a shell mass ratio of 80%, ensuring a stable wire structure and a balance between deposition efficiency and corrosion resistance.

[0220] The specific parameters for the welding test are: overall diameter of 1.2 mm including shell and core, core mass filling rate of 20%, after the core melts, it mixes with the molten metal of the low carbon steel strip shell to form the corrosion-resistant metal matrix of the welding layer, which is the core component of the welding layer.

[0221] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0222] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing flux-cored welding wire for high corrosion-resistant pipe fittings overlay welding, characterized in that, include: Obtain the pipe material and thickness of the target pipe fitting, preset welding parameters based on the pipe material and thickness and perform overlay welding, monitor the melting degree of the pipe fitting substrate to determine the corresponding welding heat, determine the theoretical welding heat range that the pipe fitting can withstand based on the welding heat and melting degree determination results, and determine the upper limit and lower limit of heat input of the flux-cored welding wire based on the theoretical welding heat range. The upper limit of the diameter of the flux-cored wire is determined based on the upper limit of the heat input, the lower limit of the diameter of the flux-cored wire is determined based on the lower limit of the heat input, and the theoretical diameter range of the flux-cored wire is determined based on the upper limit and the lower limit of the diameter. The diameter of the appropriate flux-cored wire is determined based on the median value of the theoretical diameter range. A welding operation is performed based on the diameter of the appropriate flux-cored wire to obtain the fusion depth and height of the weld overlay. The actual depth-to-height ratio is obtained based on the ratio of the fusion depth to the height of the weld overlay. The target diameter of the flux-cored wire is determined based on the actual depth-to-height ratio and the depth-to-height ratio threshold range. If the actual depth-to-height ratio still does not fall into the depth-to-height ratio threshold range after the theoretical diameter of the flux-cored wire is adjusted to the upper or lower limit of the theoretical diameter range, then the target flux-cored wire fit is determined based on the difference between the actual depth-to-height ratio and the extreme value of the depth-to-height ratio threshold range. The target flux-cored welding wire is obtained based on the target flux-cored fit and the target diameter. The pipe is then subjected to a welding operation based on the target flux-cored welding wire to obtain the actual corrosion resistance parameters of the weld overlay. The theoretical welding heat range is then adjusted based on the comparison between the actual corrosion resistance parameters and the threshold range of the actual corrosion resistance parameters. The fusion depth is the maximum melting depth of the pipe fitting base material when the pipe fitting surface is melted by electric arc to form a molten pool of base material, and the molten pool of base material forms a metallurgical bond with the flux-cored wire deposited metal. The weld overlay height is the height of the deposited metal layer that is higher than the surface of the pipe fitting base material after weld overlay.

2. The method for preparing flux-cored welding wire for high corrosion-resistant pipe fittings according to claim 1, characterized in that, The process of determining the theoretical welding heat range that the pipe fitting can withstand during surfacing welding includes: The pipe fitting is overlaid with welding based on preset welding parameters. The melting degree of the substrate on the surface of the pipe fitting is monitored in real time, and the corresponding welding heat is determined based on the melting degree. The theoretical welding heat range is determined based on the welding heat. The welding parameters include target current, target voltage, and target wire feed speed.

3. The method for preparing flux-cored welding wire for high corrosion-resistant pipe fittings according to claim 2, characterized in that, The process of determining the theoretical upper limit of the diameter of the flux-cored welding wire includes: The maximum welding current is determined based on the target voltage, preset welding speed, and upper limit of heat input. The upper limit of the diameter of the flux-cored wire is then determined based on the maximum welding current.

4. The method for preparing flux-cored welding wire for high corrosion-resistant pipe fittings according to claim 3, characterized in that, The process of determining the theoretical lower limit of the flux-cored welding wire includes: The minimum welding current is determined based on the target voltage, preset welding speed, and lower limit of heat input. The lower limit of the diameter of the flux-cored wire is then determined based on the minimum welding current.

5. The method for preparing flux-cored welding wire for high corrosion-resistant pipe fittings according to claim 4, characterized in that, The process of obtaining the fusion depth and height of the weld overlay includes: The pipe fitting after the overlay welding operation is divided to obtain the cross-section of the overlay layer. The fusion depth is obtained by measuring the distance from the surface of the pipe fitting to the metallization layer formed by the flux-cored wire weld metal and the pipe fitting substrate in the cross-section of the overlay layer. The weld overlay height is determined by the height of the weld metal layer that extends above the surface of the pipe substrate after welding.

6. The method for preparing flux-cored welding wire for high corrosion-resistant pipe fittings according to claim 5, characterized in that, The process of determining the target diameter of the flux-cored welding wire includes: Based on the fact that the actual depth-to-height ratio is less than the minimum value of the depth-to-height ratio threshold range, the diameter of the flux-cored welding wire is reduced according to the difference between the minimum value of the depth-to-height ratio threshold range and the actual depth-to-height ratio. Based on the actual depth-to-height ratio being within the depth-to-height ratio threshold range, the current flux-cored wire diameter is maintained. Based on the fact that the actual depth-to-height ratio is greater than the maximum value of the depth-to-height ratio threshold range, the diameter of the flux-cored wire is increased according to the difference between the actual depth-to-height ratio and the maximum value of the depth-to-height ratio threshold range.

7. The method for preparing flux-cored welding wire for high corrosion-resistant pipe fittings according to claim 6, characterized in that, The process of determining the target flux-cored wire fit includes: Based on the fact that the actual depth-to-height ratio is less than the minimum value of the depth-to-height ratio threshold range, the core-to-drug fit is increased according to the difference between the minimum value of the depth-to-height ratio threshold range and the actual depth-to-height ratio to obtain the target core-to-drug fit. Based on the actual depth-to-height ratio being within the depth-to-height ratio threshold range, the current core-to-drug fit is maintained as the target core-to-drug fit. Based on the fact that the actual depth-to-height ratio is greater than the maximum value of the depth-to-height ratio threshold range, the core-to-drug fit is reduced according to the difference between the actual depth-to-height ratio and the maximum value of the depth-to-height ratio threshold range to obtain the target core-to-drug fit. The core-coating fit refers to the fit between the core welding wire and the inner wall of the pipe.

8. The method for preparing flux-cored welding wire for high corrosion-resistant pipe fittings according to claim 7, characterized in that, The process of adjusting the theoretical welding heat range includes: Based on the fact that the actual corrosion resistance parameter is less than the minimum value of the threshold range of the actual corrosion resistance parameter, the actual corrosion resistance difference is obtained according to the difference between the actual corrosion resistance parameter and the minimum value of the threshold range of the actual corrosion resistance parameter. Based on the actual corrosion resistance difference and the threshold range of the corrosion resistance difference, the adjustment method of the theoretical welding heat range is determined. Based on the actual corrosion resistance parameters being within the threshold range of the actual corrosion resistance parameters, the current theoretical welding heat range is maintained; Based on the fact that the actual corrosion resistance parameter is greater than the maximum value of the threshold range of the actual corrosion resistance parameter, the actual corrosion resistance difference is obtained according to the difference between the actual corrosion resistance parameter and the maximum value of the threshold range of the actual corrosion resistance parameter. Based on the actual corrosion resistance difference and the threshold range of the corrosion resistance difference, the adjustment method of the theoretical welding heat range is determined. The actual parameters of corrosion resistance are positively correlated with the corrosion resistance performance.

9. The method for preparing flux-cored welding wire for high corrosion-resistant pipe fittings according to claim 8, characterized in that, The process of determining the adjustment method for the theoretical welding heat range includes: Based on the fact that the actual corrosion resistance parameter is less than the minimum value of the threshold range of the actual corrosion resistance parameter; Based on the fact that the actual difference is less than the minimum value of the corrosion resistance difference threshold range, the lower limit of the theoretical welding heat range is adjusted upward according to the difference between the minimum value of the corrosion resistance difference threshold range and the actual difference, while the upper limit of the theoretical welding heat range is maintained. Based on the actual difference being within the corrosion resistance difference threshold range, the upper limit of the theoretical welding heat range is simultaneously lowered and the lower limit of the theoretical welding heat range is simultaneously raised according to the initial adjustment value. Based on the fact that the actual difference is greater than the maximum value of the corrosion resistance difference threshold range, the upper limit of the theoretical welding heat range is lowered according to the difference between the actual difference and the maximum value of the corrosion resistance difference threshold range, while the lower limit of the theoretical welding heat range is maintained.

10. A flux-cored welding wire prepared using the method for preparing high corrosion-resistant pipe welding wire according to any one of claims 1-9, characterized in that, It includes a low-carbon steel strip shell and a core filled inside the low-carbon steel strip shell; The chemical composition by mass percentage of the low-carbon steel strip shell is as follows: C≤0.12%, Mn0.30%-0.60%, Si≤0.30%, Cr0.5-1.2%, P≤0.035%, S≤0.035%, with the remainder being Fe and unavoidable impurities; The core is composed of the following raw materials in the indicated weight percentages: titanium dioxide 28%-35%, silicon dioxide 2%-10%, zirconium dioxide 0-2%, aluminum oxide 0.5%-4%, iron oxide 1%-3.5%, sodium oxide 0-1.5%, potassium oxide 0-1.2%, fluoride 0.5%-8%, manganese 10%-14%, silicon 2%-5%, aluminum 0-1.5%, magnesium 0.25-3%, and iron 11.3%-55.75%. The core filler content is 20%.

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