A laser surface remelting method to improve the corrosion resistance of low alloy steel welds

Abstract

The present invention relates to a laser surface remelting method for improving the corrosion resistance of low-alloy steel welds, and belongs to the field of metal surface treatment and protection technology. The method comprises the following steps: (1) preparing a low-alloy steel weld by metal arc welding; (2) grinding the low-alloy steel weld, immersing the weld in a treatment liquid, ultrasonically treating, cleaning, and drying to obtain a treated low-alloy steel weld; (3) performing laser surface remelting treatment on the weld surface of the treated low-alloy steel weld by using a fiber laser. The laser surface remelting technology described in the present invention is simple in process, reduces the influence of oxides and impurities on the weld surface on the weld quality by layer-by-layer treatment, is highly efficient and pollution-free, and effectively improves the corrosion resistance of the treated low-alloy steel weld.

Description

Technical Field

[0001] The invention belongs to the technical field of metal surface treatment and protection, and relates to a laser surface remelting method for improving the corrosion resistance of low alloy steel welds. Background Art

[0002] Low-alloy steel structural parts have the advantages of low cost and easy construction, and have been widely used in marine and coastal engineering structures. However, the corrosion of low-alloy steel is a major problem that plagues building quality. Every year, the degradation of materials caused by corrosion causes considerable economic losses, especially for steel structural components used in marine and coastal projects. The marine atmospheric environment will aggravate the corrosion problem of steel structures. Low-alloy steel structural parts are usually connected by welding, but welding has the characteristics of high heating temperature, fast heating rate, and local cooling. This causes the weld metal to undergo phase change during the welding process, which in turn causes problems such as uneven microstructure and coarse grains. Therefore, the weld is usually the weakest point in marine steel structural parts, and corrosion often occurs first in these places.

[0003] Currently used corrosion protection methods include sacrificial anodes, impressed current cathodic protection, anti-corrosion coatings, and weathering steel technologies. However, sacrificial anodes and impressed current cathodic protection suffer from low current efficiency and difficulty replacing spent anodes. Anti-corrosion coatings are relatively mature and economical, but they require high surface quality, and secondary maintenance is cumbersome and complex. Weathering steel offers excellent corrosion resistance, but is expensive and has low economic benefits. Laser surface remelting technology can rapidly melt and solidify the material surface, producing a fine, uniform microstructure and thus improving the material's corrosion resistance. Compared with other corrosion protection technologies, laser surface remelting offers advantages such as simplicity, high efficiency, and a green, pollution-free design. Therefore, combining laser surface remelting with improving the corrosion resistance of low-alloy steel welds has significant scientific research value and engineering application prospects. Summary of the Invention

[0004] The object of the present invention is to provide a laser surface remelting method for improving the corrosion resistance of low-alloy steel welds. The laser surface remelting method described in the present invention has a simple process, reduces the influence of weld surface oxides and impurities on weld quality through layer-by-layer treatment, is highly efficient and pollution-free, and effectively improves the corrosion resistance of the low-alloy steel welds obtained by treatment.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A laser surface remelting method for improving the corrosion resistance of low alloy steel welds, the method comprising the following steps:

[0007] (1) Preparation of low alloy steel welds using gas metal arc welding;

[0008] (2) After the low alloy steel weld is polished, the weld is immersed in the treatment liquid, ultrasonically treated for 1-2 hours, washed with deionized water three times, and dried to obtain the treated low alloy steel weld;

[0009] (3) A fiber laser is used to perform laser surface remelting treatment on the weld surface of the treated low alloy steel weld.

[0010] Furthermore, the shielding gas used in the metal arc welding in step (1) is a mixed gas consisting of 80-84% argon and 16-20% carbon dioxide, and the flow rate of the shielding gas is 15-25 L / min.

[0011] Furthermore, the welding parameters of the metal arc welding in step (1) are: welding voltage of 28.2-29V, welding current of 200-400A, and welding speed of 0.3-0.5m / min.

[0012] Furthermore, the parameters of the grinding process in step (2) are: grinding along the weld direction, grinding particle size of 150-250 mesh, grinding pressure of 30-50% of the maximum pressure of the grinder, grinding speed of 3500-5500 rpm, and grinding time of 3-5 min.

[0013] Furthermore, the preparation method of the treatment liquid in step (2) is:

[0014] After mixing dihydroxysuccinic acid and deionized water, potassium phosphate buffer solution was added dropwise to adjust the pH to 5-6, and then modified nano-titanium dioxide solution and sodium lauryl sulfate were added, and stirred at a speed of 20-40 rpm for 40-50 minutes to obtain a treated solution;

[0015] Wherein, the preparation method of the modified nano titanium dioxide solution is:

[0016] After mixing nano-titanium dioxide, polyethylene glycol and deionized water, stirring at 40-50° C. and 30-60 rpm for 20-30 minutes, a modified nano-titanium dioxide solution is obtained.

[0017] Furthermore, by mass percentage, the dihydroxysuccinic acid accounts for 5-10wt% of the treatment liquid, the modified nano-titanium dioxide solution accounts for 3-6wt% of the treatment liquid, and the sodium lauryl sulfate accounts for 1-5wt% of the treatment liquid; the concentration of the potassium phosphate buffer solution is 0.1-0.3mol / L.

[0018] Furthermore, in terms of mass percentage, the nano-titanium dioxide accounts for 0.6-1.5wt% of the modified nano-titanium dioxide solution, and the polyethylene glycol accounts for 0.9-1.8wt% of the modified nano-titanium dioxide solution; the particle size of the nano-titanium dioxide is 60-100nm; and the molecular weight of the polyethylene glycol is 400-3600Da.

[0019] Furthermore, the parameters of the ultrasonic treatment in step (2) are: ultrasonic frequency of 20-40 kHz, ultrasonic power of 100-300 W, and ultrasonic temperature of 30-40°C.

[0020] Furthermore, the protective gas required for laser surface remelting in step (3) is 99.9% argon, and the protective gas flow rate is 10-30 L / min.

[0021] Furthermore, the parameters of the laser during the laser surface remelting process in step (3) are: laser power of 1500-2500 W, spot diameter of 3-6 mm, scanning speed of 0.5-1.5 m / min, defocus of 0-5 mm, and overlap rate of 40-60%.

[0022] Beneficial effects of the present invention:

[0023] After the polishing treatment, the present invention immerses the weld with the treatment liquid to ensure that the treatment liquid can contact the weld surface more evenly and remove the stubborn oxide layer and impurities; further, the dihydroxysuccinic acid in the treatment liquid can react with the metal oxide on the weld surface, dissolve the oxide layer on the weld surface, reduce the binding force between the oxide and the metal substrate, and make it easy to remove; the sodium dodecyl sulfate molecules are arranged on the weld surface, with the hydrophilic end facing the water phase and the hydrophobic end facing the air or pollutants, forming a monomolecular layer, which can significantly reduce the surface tension of the liquid, enhance the wettability of the treatment liquid on the weld surface, help to penetrate deeper into the weld, and remove hidden impurities and gases in micropores; further, the polymer in the modified nano titanium dioxide solution Ethylene glycol interacts with the hydroxyl groups or acidic sites on the surface of nano-titanium dioxide, and the hydrophobic groups in the polyethylene glycol molecules are physically adsorbed with the hydroxyl groups on the surface of nano-titanium dioxide, thereby improving the binding force between the two and forming a stable modified layer, thereby improving the uniform dispersion of nano-titanium dioxide in the treatment fluid, reducing agglomeration, and enhancing the contact efficiency between the treatment fluid and the weld surface; finally, the shock wave generated by the bursting of tiny bubbles generated by ultrasound can help disperse and dissolve pollutants on the weld surface, effectively remove the oxide layer and impurities on the weld surface, reduce the active points of corrosion, namely the oxides at the grain boundaries, thereby synergistically reducing the probability of corrosion. In addition, it also helps the formation and flow of the molten pool during subsequent laser remelting, thereby improving the welding quality.

[0024] The present invention first uses metallurgical electrode gas shielded welding to prepare low-alloy steel welds, which reduces the contact between the molten pool and the air and reduces the risk of oxidation and nitridation. The stable arc and gas protection help to reduce defects such as pores and slag inclusions, thereby producing well-formed welds and reducing the difficulty of subsequent processing; finally, laser surface remelting technology is used to modify the surface of the treated low-alloy steel welds. During the laser remelting process, the local rapid heating of the weld causes the metal to expand, and then the rapid cooling causes the metal to shrink. This thermal cycle helps to release residual stress and reduce stress concentration inside the weld. Laser heating causes the grains of the weld metal to re-nucleate to achieve the goal of refining the surface grain size of the weld, so that the grain boundary area is relatively reduced, and the chemical composition of the grain boundary is more uniform, which is not easy to form a local battery effect, thereby improving corrosion resistance. In addition, it also helps to form a continuous and dense passivation film on the weld surface, thereby improving the corrosion resistance of the low-alloy steel weld surface.

[0025] The laser surface remelting technology described in the present invention has a simple process and reduces the influence of oxides and impurities on the weld surface on the weld quality through layer-by-layer treatment. It is highly efficient and pollution-free, and the corrosion resistance of the low-alloy steel weld obtained by the treatment is effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] To facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0027] Figure 1 The experimental device required for a laser surface remelting method for improving the corrosion resistance of low alloy steel welds includes: (1) a fiber laser, (2) a laser surface remelting workbench, (3) a low alloy steel weld specimen block, (4) a laser control console, and (5) a control cabinet for providing shielding gas;

[0028] Figure 2 This is the cross-sectional morphology of the low alloy steel weld after laser surface remelting treatment in Example 1;

[0029] Figure 3 This is the cross-sectional morphology of the low alloy steel weld after laser surface remelting treatment in Example 2;

[0030] Figure 4 This is the cross-sectional morphology of the low alloy steel weld after laser surface remelting treatment in Example 3. DETAILED DESCRIPTION

[0031] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0032] Example 1

[0033] A laser surface remelting method for improving the corrosion resistance of low alloy steel welds, the method of this embodiment comprises the following steps:

[0034] (1) Preparation of low alloy steel welds using gas metal arc welding;

[0035] (2) After the low alloy steel weld is polished, the weld is immersed in the treatment liquid, ultrasonically treated for 1 hour, washed with deionized water three times, and dried to obtain the treated low alloy steel weld;

[0036] (3) A fiber laser is used to perform laser surface remelting treatment on the weld surface of the treated low alloy steel weld.

[0037] The shielding gas used in the metal arc welding in step (1) of this embodiment is a mixed gas consisting of 82% argon and 18% carbon dioxide. The flow rate of the shielding gas in this embodiment is 20 L / min.

[0038] The welding parameters of the gas metal arc welding in step (1) of this embodiment are: welding voltage of 28.6 V, welding current of 300 A, and welding speed of 0.4 m / min.

[0039] The parameters of the grinding process in step (2) of this embodiment are: grinding along the weld direction, grinding particle size of 150 mesh, grinding pressure of 30% of the maximum pressure of the grinder, grinding speed of 3500 rpm, and grinding time of 3 minutes.

[0040] The preparation method of the treatment liquid in step (2) of this embodiment is:

[0041] After mixing dihydroxysuccinic acid and deionized water, potassium phosphate buffer solution was added dropwise to adjust the pH to 5, and then modified nano-titanium dioxide solution and sodium lauryl sulfate were added, and stirred at 20 rpm for 40 minutes to obtain a treated solution;

[0042] The preparation method of the modified nano-titanium dioxide solution of this embodiment is as follows:

[0043] Nano-titanium dioxide, polyethylene glycol and deionized water were mixed and stirred at 40° C. and 30 rpm for 20 minutes to obtain a modified nano-titanium dioxide solution.

[0044] In terms of mass percentage, the dihydroxysuccinic acid of this embodiment accounts for 5wt% of the treatment liquid, the modified nano-titanium dioxide solution of this embodiment accounts for 3wt% of the treatment liquid, and the sodium lauryl sulfate of this embodiment accounts for 1wt% of the treatment liquid; the concentration of the potassium phosphate buffer solution of this embodiment is 0.1mol / L.

[0045] In terms of mass percentage, the nano-titanium dioxide of this embodiment accounts for 0.6 wt % of the modified nano-titanium dioxide solution, and the polyethylene glycol of this embodiment accounts for 0.9 wt % of the modified nano-titanium dioxide solution; the particle size of the nano-titanium dioxide of this embodiment is 60 nm; and the molecular weight of the polyethylene glycol of this embodiment is 400 Da.

[0046] The parameters of the ultrasonic treatment in step (2) of this embodiment are: ultrasonic frequency of 20 kHz, ultrasonic power of 100 W, and ultrasonic temperature of 30°C.

[0047] The protective gas required for laser surface remelting in step (3) of this embodiment is 99.9% argon, and the protective gas flow rate is 20 L / min.

[0048] The parameters of the laser during the laser surface remelting process in step (3) of this embodiment are: laser power of 1500 W, spot diameter of 4 mm, scanning speed of 1 m / min, defocus of 0 mm, and overlap rate of 50%.

[0049] The cross-sectional morphology of the low alloy steel weld sample after laser surface remelting treatment is as follows: Figure 2 shown.

[0050] Example 2

[0051] A laser surface remelting method for improving the corrosion resistance of low alloy steel welds, the method of this embodiment comprises the following steps:

[0052] (1) Preparation of low alloy steel welds using gas metal arc welding;

[0053] (2) After the low alloy steel weld is polished, the weld is immersed in the treatment liquid, ultrasonically treated for 1.5 hours, washed with deionized water three times, and dried to obtain the treated low alloy steel weld;

[0054] (3) A fiber laser is used to perform laser surface remelting treatment on the weld surface of the treated low alloy steel weld.

[0055] The shielding gas used in the metal arc welding in step (1) of this embodiment is a mixed gas consisting of 82% argon and 18% carbon dioxide. The flow rate of the shielding gas in this embodiment is 20 L / min.

[0056] The welding parameters of the gas metal arc welding in step (1) of this embodiment are: welding voltage of 28.6 V, welding current of 300 A, and welding speed of 0.4 m / min.

[0057] The parameters of the grinding process in step (2) of this embodiment are: grinding along the weld direction, grinding particle size of 200 mesh, grinding pressure of 40% of the maximum pressure of the grinder, grinding speed of 4500 rpm, and grinding time of 4 minutes.

[0058] The preparation method of the treatment liquid in step (2) of this embodiment is:

[0059] After mixing dihydroxysuccinic acid and deionized water, potassium phosphate buffer solution was added dropwise to adjust the pH to 5.5, and then modified nano-titanium dioxide solution and sodium lauryl sulfate were added, and stirred at 30 rpm for 45 minutes to obtain a treated solution;

[0060] The preparation method of the modified nano-titanium dioxide solution of this embodiment is as follows:

[0061] After nano-titanium dioxide, polyethylene glycol and deionized water are mixed, the mixture is stirred at 45° C. and 45 rpm for 25 minutes to obtain a modified nano-titanium dioxide solution.

[0062] In terms of mass percentage, the dihydroxysuccinic acid of this embodiment accounts for 7.5wt% of the treatment liquid, the modified nano-titanium dioxide solution of this embodiment accounts for 4.5wt% of the treatment liquid, and the sodium lauryl sulfate of this embodiment accounts for 3wt% of the treatment liquid; the concentration of the potassium phosphate buffer solution of this embodiment is 0.2mol / L.

[0063] In terms of mass percentage, the nano-titanium dioxide of this embodiment accounts for 1.05wt% of the modified nano-titanium dioxide solution, and the polyethylene glycol of this embodiment accounts for 1.35wt% of the modified nano-titanium dioxide solution; the particle size of the nano-titanium dioxide of this embodiment is 80nm; and the molecular weight of the polyethylene glycol of this embodiment is 2000Da.

[0064] The parameters of the ultrasonic treatment in step (2) of this embodiment are: ultrasonic frequency of 30 kHz, ultrasonic power of 200 W, and ultrasonic temperature of 35°C.

[0065] The protective gas required for laser surface remelting in step (3) of this embodiment is 99.9% argon, and the protective gas flow rate is 20 L / min.

[0066] The parameters of the laser during the laser surface remelting process in step (3) of this embodiment are: laser power of 2000 W, spot diameter of 4 mm, scanning speed of 0.5 m / min, defocus of 0 mm, and overlap rate of 50%.

[0067] The cross-sectional morphology of the low alloy steel weld sample after laser surface remelting treatment is as follows: Figure 3 shown.

[0068] Example 3

[0069] A laser surface remelting method for improving the corrosion resistance of low alloy steel welds, the method of this embodiment comprises the following steps:

[0070] (1) Preparation of low alloy steel welds using gas metal arc welding;

[0071] (2) After the low alloy steel weld is polished, the weld is immersed in the treatment liquid, ultrasonically treated for 2 hours, washed with deionized water three times, and dried to obtain the treated low alloy steel weld;

[0072] (3) A fiber laser is used to perform laser surface remelting treatment on the weld surface of the treated low alloy steel weld.

[0073] The shielding gas used in the metal arc welding in step (1) of this embodiment is a mixed gas consisting of 82% argon and 18% carbon dioxide. The flow rate of the shielding gas in this embodiment is 20 L / min.

[0074] The welding parameters of the gas metal arc welding in step (1) of this embodiment are: welding voltage of 28.6 V, welding current of 300 A, and welding speed of 0.4 m / min.

[0075] The parameters of the grinding process in step (2) of this embodiment are: grinding along the weld direction, grinding particle size of 250 mesh, grinding pressure of 50% of the maximum pressure of the grinder, grinding speed of 5500 rpm, and grinding time of 5 min.

[0076] The preparation method of the treatment liquid in step (2) of this embodiment is:

[0077] After mixing dihydroxysuccinic acid and deionized water, potassium phosphate buffer solution was added dropwise to adjust the pH to 6, and then modified nano-titanium dioxide solution and sodium lauryl sulfate were added, and stirred at 40 rpm for 50 minutes to obtain a treated solution;

[0078] The preparation method of the modified nano-titanium dioxide solution of this embodiment is as follows:

[0079] After nano-titanium dioxide, polyethylene glycol and deionized water are mixed, the mixture is stirred at 50° C. and 60 rpm for 30 minutes to obtain a modified nano-titanium dioxide solution.

[0080] In terms of mass percentage, the dihydroxysuccinic acid of this embodiment accounts for 10wt% of the treatment liquid, the modified nano-titanium dioxide solution of this embodiment accounts for 6wt% of the treatment liquid, and the sodium lauryl sulfate of this embodiment accounts for 5wt% of the treatment liquid; the concentration of the potassium phosphate buffer solution of this embodiment is 0.3mol / L.

[0081] In terms of mass percentage, the nano-titanium dioxide of this embodiment accounts for 0.6-1.5wt% of the modified nano-titanium dioxide solution, and the polyethylene glycol of this embodiment accounts for 0.9-1.8wt% of the modified nano-titanium dioxide solution; the particle size of the nano-titanium dioxide of this embodiment is 100nm; the molecular weight of the polyethylene glycol of this embodiment is 3600Da.

[0082] The parameters of the ultrasonic treatment in step (2) of this embodiment are: ultrasonic frequency of 40 kHz, ultrasonic power of 300 W, and ultrasonic temperature of 40°C.

[0083] The protective gas required for laser surface remelting in step (3) of this embodiment is 99.9% argon, and the protective gas flow rate is 20 L / min.

[0084] The parameters of the laser during the laser surface remelting process in step (3) of this embodiment are: laser power of 2500 W, spot diameter of 4 mm, scanning speed of 1 m / min, defocus of 0 mm, and overlap rate of 50%.

[0085] The cross-sectional morphology of the low alloy steel weld sample after laser surface remelting treatment is as follows: Figure 4 shown.

[0086] Comparative Example 1

[0087] On the basis of Example 2, the treatment liquid treatment step in step (2) was removed, and other conditions were consistent with Example 2.

[0088] Comparative Example 2

[0089] On the basis of Example 2, the modified nano-titanium dioxide solution in the treatment liquid was removed and replaced with an equal weight of deionized water. Other conditions were the same as those in Example 2.

[0090] Comparative Example 3

[0091] On the basis of Example 2, the polishing process in step (2) was removed, and other conditions were consistent with those in Example 2.

[0092] Comparative Example 4

[0093] On the basis of Example 2, the ultrasonic treatment step in step (2) was changed to stirring at room temperature, and the other conditions were consistent with Example 2.

[0094] Comparative Example 5

[0095] On the basis of Example 2, the welding current of the metal electrode gas shielded welding in step (1) was changed to 100 A, and the other conditions were consistent with those in Example 2.

[0096] Comparative Example 6

[0097] On the basis of Example 2, the welding current of the metal electrode gas shielded welding in step (1) was changed to 500 A, and the other conditions were consistent with those in Example 2.

[0098] Comparative Example 7

[0099] On the basis of Example 2, the welding speed of the metal arc welding in step (1) was changed to 0.2 m / min, and the other conditions were consistent with those in Example 2.

[0100] Comparative Example 8

[0101] On the basis of Example 2, the welding speed of the metal arc welding in step (1) was changed to 0.6 m / min, and the other conditions were consistent with those in Example 2.

[0102] Comparative Example 9

[0103] On the basis of Example 2, the laser power in the laser surface remelting process in step (3) was changed to 1200 W, and the other conditions were consistent with Example 2.

[0104] Comparative Example 10

[0105] On the basis of Example 2, the laser power in the laser surface remelting process in step (3) was changed to 3000 W, and the other conditions were consistent with Example 2.

[0106] Comparative Example 11

[0107] On the basis of Example 2, the tower connection rate in the laser surface remelting process in step (3) was changed to 70%, and the other conditions were consistent with Example 2.

[0108] A 10*10*3 mm sample block was cut from the low-alloy steel weld after laser surface remelting in Examples 1-3 and Comparative Examples 1-11 using a wire cutting process. The sample blocks of this embodiment were ground, polished, and corroded according to a standard metallographic sample preparation method. A 3.5 wt% sodium chloride solution was prepared with deionized water and analytical grade sodium chloride. The sample blocks were immersed in the sodium chloride solution for 15 minutes every 2 hours at a constant temperature of 40±1°C. A corrosion resistance test was conducted for a total of half a month, and the average weight gain per unit area (including the weight of rust that fell off during the recording process) was recorded. At the same time, "#" was used to indicate that the outer oxide layer at the weld had bulged, and "##" was used to indicate that the outer oxide layer at the weld had fallen off. The recorded table data is shown in Table 1 below.

[0109]

[0110] As can be seen from Table 1 above, the corrosion resistance of the low alloy steel welds obtained in Examples 1-3 of the present invention is significantly better than that in Comparative Examples 1-11, and Example 2 is the best, because the layer-by-layer treatment of metal gas shielded welding preparation, grinding, ultrasonic treatment of the treatment liquid, and laser surface remelting effectively reduces the influence of oxides and impurities on the weld quality on the weld surface, thereby achieving the effect of refining the grain size of the weld surface and promoting the formation of a continuous and dense passivation film on the weld surface. As a result, the weld precipitates less in a long-term high-salt environment, and the outer oxide layer at the weld does not bulge or fall off, reflecting good corrosion resistance.

[0111] In contrast, in Examples 1-3, changes are made to the grinding, treatment liquid treatment, and ultrasonic treatment. Some oxides, spatters, or other impurities exist on the surface of the weld treated with metallurgical gas shielded welding. The changes in the first two steps directly affect the flatness of the weld surface and the subsequent laser surface remelting treatment. The ultrasound in Example 4 only increases the penetration of the treatment liquid, which has less impact on the subsequent process and less impact on the corrosion resistance than the first two. Therefore, no bulging or falling off occurs at 15 days. In contrast, in Examples 5-8, changes are made to the preparation steps of metallurgical gas shielded welding. The reduction in current in Example 5 may directly affect the deposition rate and integrity of the weld, while the increase in current in Example 6 and the reduction in welding speed in Example 7 may both lead to Although it will cause overheating of the weld, the increase in speed in Example 8 may cause the molten pool to cool too quickly, which will also increase the risk of oxidation and nitriding, but the subsequent grinding and treatment liquid treatment steps can help reduce the interference of impurities such as oxides, so the impact is weaker than that of Example 5; Comparative Examples 9-11 change the laser surface remelting step. Although the reduction in power in Example 9 will affect the weld deposition rate and integrity, and the increase in power in Example 10 will cause the weld temperature to be too high, both may lead to the formation of more oxides and nitrides, thereby affecting the corrosion resistance of the weld. The increase in the tower rate in Example 11 may cause excessive stress concentration and deformation, and it is impossible to form a continuous, uniform and dense passivation film on the weld surface, thereby reducing the corrosion resistance.

[0112] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A laser surface remelting method for improving the corrosion resistance of low alloy steel welds, characterized by: The method comprises the following steps: (1) Preparation of low alloy steel welds using gas metal arc welding; (2) After the low alloy steel weld is polished, the weld is immersed in the treatment liquid, ultrasonically treated for 1-2 hours, washed with deionized water three times, and dried to obtain the treated low alloy steel weld; (3) Using a fiber laser to perform laser surface remelting treatment on the weld surface of the treated low alloy steel weld; The preparation method of the treatment liquid in step (2) is: After mixing dihydroxysuccinic acid and deionized water, potassium phosphate buffer solution is added dropwise to adjust the pH to 5-6, and then modified nano-titanium dioxide solution and sodium lauryl sulfate are added, and stirred at a speed of 20-40 rpm for 40-50 minutes to obtain a treatment liquid; in terms of mass percentage, the dihydroxysuccinic acid accounts for 5-10wt% of the treatment liquid, the modified nano-titanium dioxide solution accounts for 3-6wt% of the treatment liquid, and the sodium lauryl sulfate accounts for 1-5wt% of the treatment liquid; the concentration of the potassium phosphate buffer solution is 0.1-0.3 mol / L; Wherein, the preparation method of the modified nano titanium dioxide solution is: After mixing nano-titanium dioxide, polyethylene glycol and deionized water, stirring at 40-50° C. and 30-60 rpm for 20-30 minutes, a modified nano-titanium dioxide solution is obtained; in terms of mass percentage, the nano-titanium dioxide accounts for 0.6-1.5wt% of the modified nano-titanium dioxide solution, and the polyethylene glycol accounts for 0.9-1.8wt% of the modified nano-titanium dioxide solution; the particle size of the nano-titanium dioxide is 60-100nm; and the molecular weight of the polyethylene glycol is 400-3600Da.

2. The laser surface remelting method for improving the corrosion resistance of low alloy steel welds according to claim 1, characterized in that: The shielding gas used in the metal arc welding in step (1) is a mixed gas consisting of 80-84% argon and 16-20% carbon dioxide, and the flow rate of the shielding gas is 15-25 L / min.

3. The laser surface remelting method for improving the corrosion resistance of low alloy steel welds according to claim 1, characterized in that: The welding parameters of the metal arc welding in step (1) are: welding voltage of 28.2-29V, welding current of 200-400A, and welding speed of 0.3-0.5m / min.

4. The laser surface remelting method for improving the corrosion resistance of low alloy steel welds according to claim 1, characterized in that: The parameters of the grinding process in step (2) are: grinding along the weld direction, grinding particle size of 150-250 mesh, grinding pressure of 30-50% of the maximum pressure of the grinder, grinding speed of 3500-5500 rpm, and grinding time of 3-5 min.

5. The laser surface remelting method for improving the corrosion resistance of low alloy steel welds according to claim 1, characterized in that: The parameters of the ultrasonic treatment in step (2) are: ultrasonic frequency of 20-40 kHz, ultrasonic power of 100-300 W, and ultrasonic temperature of 30-40°C.

6. The laser surface remelting method for improving the corrosion resistance of low alloy steel welds according to claim 1, characterized in that: The protective gas required for laser surface remelting in step (3) is 99.9% argon, and the protective gas flow rate is 10-30 L / min.

7. The laser surface remelting method for improving the corrosion resistance of low alloy steel welds according to claim 1, characterized in that: The parameters of the laser during the laser surface remelting process in step (3) are: laser power of 1500-2500W, spot diameter of 3-6mm, scanning speed of 0.5-1.5m / min, defocus of 0-5mm, and overlap rate of 40-60%.

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