A surface strengthening process for corrosion and wear resistant cross

Abstract

The application discloses a kind of corrosion and wear resistant four-way surface strengthening processes, belong to laser cladding technical field.The process specifically includes the following steps: (1) structure design and pretreatment;(2) laser cladding powder preparation;(3) laser cladding treatment;(4) inner wall post-processing.The application is according to the different degree of erosion and corrosion of different regions of four-way inner wall and flange, designs different cladding layer, and designs reasonable four-way structure and cladding material, maximizes the corrosion and wear resistant performance of four-way.

Description

Technical Field

[0001] This invention relates to the field of laser cladding technology, and more specifically to a corrosion-resistant and wear-resistant four-way surface strengthening process. Background Technology

[0002] In oil and gas field development operations, the four-way valve, as a critical manifold component, is subjected to the impact of large-volume, high-velocity, and high-pressure produced fluids for extended periods, operating in extremely harsh environments. The produced medium contains not only corrosive gases such as hydrogen sulfide and carbon dioxide, and high concentrations of chloride ions, but also solid hard particles such as formation gravel and drill cuttings. When this multiphase fluid flows through the four-way valve, the forced abrupt change in flow direction causes solid particles to continuously and violently impact the inner wall of the bypass due to inertia, resulting in significant erosion and wear. More seriously, erosion continuously strips away the protective corrosion product film from the material surface, accelerating the penetration of corrosive media; the corrosion process, in turn, weakens the base material, further exacerbating its erosion and loss. This synergistic effect of erosion and corrosion creates a vicious cycle, causing the four-way valve wall thickness to rapidly thin or even perforate far below its design life, leading to media leaks, production shutdowns, and even safety accidents, posing a serious threat to the safe production and economic benefits of oil and gas fields.

[0003] Currently, most protection technologies for cross joints focus on protecting against single wear or corrosion, making it difficult to effectively address the complex destructive mechanisms of the combined effects of erosion and corrosion in actual working conditions. While the commonly used welding technology can improve the corrosion and wear resistance of cross joints to some extent, its high heat input can easily lead to workpiece deformation and increased dilution rate, resulting in damage to the performance of the cladding layer. Furthermore, the surface of the weld overlay is rough, leading to higher subsequent processing costs.

[0004] Therefore, how to develop a new corrosion-resistant and wear-resistant strengthening process for four-way junction boxes is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a corrosion-resistant and wear-resistant surface strengthening process for four-way fittings to overcome the shortcomings of the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A corrosion-resistant and wear-resistant surface strengthening process for tee fittings specifically includes the following steps: (1) Structural design and pretreatment Based on the degree of erosion and corrosion, the four-way blank is divided into five areas: area I, area II, area III, area IV, and the sealing part of the flange; the material is uniformly removed from the sealing part of the flange to form the flange surface to be clad, and then cleaned and preheated. (2) Preparation of laser cladding powder Carbon powder, silicon powder, tungsten powder, chromium powder, nickel powder, cerium powder, chromium carbide powder, molybdenum powder, and cobalt powder are mixed evenly to obtain laser cladding powder; (3) Laser cladding treatment Laser cladding powder is fed into the laser cladding equipment. The laser nozzle is controlled to always be perpendicular to the inner curved surface of the four-way tube, maintaining a constant focusing distance and processing angle, so that the laser head moves along a predetermined path and performs laser cladding on the surface of each area. After the laser cladding powder melts, it forms a metallurgically bonded cladding layer with the substrate. (4) Post-treatment of the inner wall After cladding, the four-way valve undergoes slow cooling. Then, the sealing parts of the flange and other precision-required parts are precision-machined, and the dimensional and surface roughness requirements are met through a grinding process.

[0008] Furthermore, in step (1) above, the design formula for the thickness of the cladding layer is: T = (CR L K)+ζ, where T (mm) is the total design thickness of the cladding layer, CR (mm / h) is the predicted or experimentally measured thickness loss rate, L (h) is the design life, K is the safety factor, ζ (mm) is the compensation thickness, the range of the compensation thickness ζ is 1.5~2.5mm, and the safety factor K is greater than 1.05.

[0009] The thicknesses of the cladding layer in regions I, II, III, and IV are as follows: the starting thickness T1 of the cladding layer in region I is 2.5~3mm; the starting thickness T2 of the cladding layer in region II is 3~3.5mm; the starting thickness T3 of the cladding layer in region III is 3.5~4mm; and the thickness T4 of the cladding layer in region IV is 4~4.5mm. The positional relationship between Region I, Region II, Region III, and Region IV is as follows: bypass central axis m The distance S from the sealing surface of the main flange of the four-way main section is defined as the distance from the sealing surface of the main flange of the four-way main section. Region I extends inward from the sealing surface of the main flange of the four-way main section to the distance from the centerline of the bypass. m The inner wall region of the main pipe section, which is 1.25 times the inner diameter D1 of the main pipe, has an axial length L1 = S - 1.25D2; Regions II and III together constitute the main body of the bypass pipe inner wall that receives the fluid from Region I, and its axial range is: from the centerline of the main pipe... l Starting from the point on the inner wall of the bypass pipe at a vertical distance of 1.25 times the bypass pipe diameter D2, and ending at the plane of the bypass flange port on the same side, within this range, the area located on the central axis of the bypass pipe... m The inner wall of the lower half is designated as II, located on the central axis. m The inner wall of the upper part is designated as III; region IV is the area covered by rectangle A, which is a rectangular region with a length q equal to 1.5 times the main pipe diameter D1 and a width p equal to 2 times the bypass pipe diameter D2, with the centroid of the rectangle being the two central axes. m and lAt point O, the sealing surface of the flange consists of the sealing surface of the flange and the sealing groove of the flange.

[0010] To ensure a smooth transition in the inner wall flow channel, the cladding thickness varies linearly within each region. In Region I, the cladding thickness gradually changes from T1 at the starting end to T4 at the end adjacent to Region IV; in Region II, it changes from T2 at the starting end to T4 at the end adjacent to Region IV; and in Region III, it changes from T3 at the starting end to T4 at the end adjacent to Region IV. The thickness at the bypass port gradually changes from the top thickness T3 to the bottom thickness T2. The flow cross-sections of Regions I, II, and III are all circular and connect to Region IV. The cross-section a1 at the junction of Region I and Region IV and the cross-section a2 at the flange end of Region I are located on the vertical main pipe axis. l The projection of the surfaces is a concentric circle with a radius difference of T4-T1. The center of the section b1 at the junction of regions II, III, and IV is Ob1. The port section b2 at the flange end of regions II and III is circular, and the radius difference between b1 and b2 is T4-(T2-T3) / 2. b1 and b2 are perpendicular to the bypass centerline. m In the projection of the surface, the center Ob1 of section b1 at the junction of regions II, III, and IV, and the center Ob2 of section b2 at the flange end of regions II and III, are both located on the central axis. l Above, Ob1 is above Ob2, and the distance db between the center Ob1 and the center Ob2 is (T3-T2) / 2; the laser cladding layer on the flange cladding base surface has a geometric contour conforming to the base surface, and the laser cladding position and shape of the flange port are consistent with the position and shape of the part of the four-way blank that has been cut off.

[0011] The further beneficial effect of the above-mentioned method is that, based on the actual differences in the degree of erosion and corrosion in different areas inside the four-way connector, the thickness of the protective layer is designed in a gradient manner, thereby improving material utilization efficiency and enhancing overall economy while ensuring the protective effect.

[0012] Furthermore, in step (1) above, the sealing part of the flange includes the sealing surface of the flange and the sealing groove area located on the sealing surface of the flange.

[0013] Furthermore, in step (1) above, the material is uniformly removed from the sealing part of the flange by machining, and the removal depth d is 1~2mm.

[0014] Furthermore, in step (1) above, the preheating temperature is 150~200℃.

[0015] Furthermore, in step (2) above, the mass percentage of each raw material in the laser cladding powder is as follows: carbon powder 0.2%~0.34%, silicon powder 0.2%~0.4%, tungsten powder 5%~8%, chromium powder 20%~23.6%, nickel powder 8.1%~9.7%, cerium powder 0.02%~0.06%, chromium carbide powder 7%~8.4%, molybdenum powder 2.3%~3.6%, and cobalt powder as the balance.

[0016] Furthermore, in step (2) above, the particle size of the laser cladding powder is 20~105μm, and the sphericity is 0.85~0.95. Specifically, the particle size of each raw material in the laser cladding powder is different. Among them, the particle size of tungsten powder, chromium powder, chromium carbide powder and molybdenum powder is 75~105μm, the particle size of nickel powder and cobalt powder is 45~85μm, and the particle size of carbon powder, silicon powder and cerium powder is 20~50μm.

[0017] Furthermore, in step (3) above, the process parameters for laser cladding are: laser power 1800~3400W, powder feeding speed 12~18g / min, scanning speed 600~800mm / min, spot diameter 2~3mm, overlap rate 45%~60%, and the protective gas is high-purity argon with a purity ≥99.99%.

[0018] The further beneficial effects of employing the aforementioned technologies lie in the fact that laser cladding technology, with its concentrated energy and precise controllable heat input, exhibits advantages such as a small heat-affected zone and low dilution rate. It not only effectively maintains the dimensional stability of the substrate and the properties of the cladding material but also yields a dense, smooth cladding layer. Therefore, laser cladding technology demonstrates great potential in improving the corrosion and wear resistance of four-way connectors.

[0019] Furthermore, in step (4) above, the slow cooling operation is as follows: the clad four-way valve is placed in a heat treatment furnace under a protective argon atmosphere, heated to 570-590°C at a rate of 80-100°C / h, held for 1.5-2.5h, then cooled to below 300°C at a rate of ≤50°C / h, and finally removed from the furnace and air-cooled to room temperature.

[0020] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention innovatively divides the four-way valve into five regions based on the internal flow field simulation of the erosion and corrosion laws: region I, region II, region III, region IV, and the sealing part of the flange. Correspondingly, a cladding layer thickness is designed with a linear gradient from thin to thick, so that the distribution of the protective layer thickness is precisely matched with the actual erosion and corrosion risk field, changing the traditional extensive mode of uniform cladding.

[0021] 2. This invention ensures that the erosion and corrosion areas obtain the best reinforcement layer to extend the overall component life, while significantly reducing the amount of expensive cladding material used in low-wear areas, thereby significantly reducing manufacturing costs and achieving a dual improvement in product life and economy.

[0022] 3. Laser cladding technology enables a high-strength metallurgical bond between the cladding layer and the substrate, with a bonding strength far exceeding that of traditional welding technology and mechanical bonding methods such as thermal spraying.

[0023] In summary, this invention designs different cladding layers based on the different erosion and corrosion levels of different areas of the inner wall of the tee and the flange, and designs a reasonable tee structure and cladding material to maximize the corrosion and wear resistance of the tee. Attached Figure Description

[0024] Figure 1 This is a cross-sectional view of the blank for the four-way connector of the present invention; Figure 2 This is a cross-sectional view of the part of the blank of the four-way connector of the present invention that has been removed; Figure 3 This is an enlarged view of point B in the cross-sectional view of the part of the four-way blank to be cut off in this invention; Figure 4 This is a diagram showing the distribution of different regions on the inner wall of the four-way connector of the present invention; Figure 5 This is a cross-sectional view of the laser cladding process of the present invention; Figure 6 This is an enlarged view of point M in the cross-sectional view after laser cladding according to the present invention; Figure 7 This is a diagram showing the positional relationship of the projections of circles Ob1 and Ob2 of the present invention onto the plane where the four-way bypass flange is located; Figure 8 This is a diagram showing the positional relationship of the projections of circles Oa1 and Oa2 on the plane containing the four-way main pipe section of the present invention. Wherein, 1-Tee blank, 2-Pre-treated tee blank, 3-Flange removed portion, 4-Tee bypass upper wall surface, 5-Tee bypass lower wall surface, 6-Tee main pipe upper inner wall surface, 7-Tee main pipe lower inner wall surface, 8-Projection of the tee blank bypass onto the bypass flange port plane, 9-Projection of the tee blank main pipe onto the main pipe flange port plane, 10-Flange sealing surface, 11-Flange sealing groove, 12-Flange sealing portion. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1 The surface strengthening process for corrosion-resistant and wear-resistant four-way fittings includes the following steps: (1) Structural design and pretreatment Prepare a tee blank FS11-05 with a nominal diameter of 280mm, a bypass inner diameter of 102mm, and tee material of A694 F65. Based on the degree of erosion and corrosion, divide the tee blank into five areas: area I, area II, area III, area IV, and the sealing part of the flange. Area IV has the most severe erosion and corrosion, while area I has a relatively lighter degree of erosion and corrosion. On the sealing part of the flange (sealing surface and sealing groove), material with a depth d of 1.5mm is uniformly removed by machining to form a new flange surface to be clad. The blank is cleaned and preheated at a temperature of 170℃. (2) Preparation of laser cladding powder Weigh out 8.3g of carbon powder, 10g of silicon powder, 250g of tungsten powder, 884.8g of chromium powder, 360g of nickel powder, 1.5g of cerium powder, 324g of chromium carbide powder, 100.5g of molybdenum powder, and 2029.6g of cobalt powder. After mixing evenly, a laser cladding powder with a particle size of 24~103μm and a sphericity of 0.90 is obtained. Among them, the particle size of tungsten powder, chromium powder, chromium carbide powder and molybdenum powder is 80~103μm, the particle size of nickel powder and cobalt powder is 48~76μm, and the particle size of carbon powder, silicon powder and cerium powder is 24~41μm. (3) Laser cladding treatment Laser cladding powder is fed into the laser cladding equipment. The laser nozzle is controlled to always be perpendicular to the inner wall curved surface of the four-way, maintaining a constant focusing distance and processing angle, so that the laser head moves along a predetermined path and performs laser cladding on the inner wall and flange surfaces to be clad in each area. After the laser cladding powder melts, it forms a metallurgically bonded cladding layer with the substrate. The laser cladding process parameters are as follows: laser power 2400W, powder feeding speed 12g / min, scanning speed 650mm / min, spot diameter 2mm, overlap rate 55%, and the protective gas is high-purity argon with a purity ≥99.99%. The thickness of the cladding layer in different regions is as follows: the thickness of the cladding layer in region I changes linearly from 2.5 mm at the beginning to 4.5 mm at the end adjacent to region IV; the thickness of the cladding layer in region II changes linearly from 3 mm at the beginning to 4.5 mm at the end adjacent to region IV; the thickness of the cladding layer in region III changes linearly from 3.5 mm at the beginning to 4.5 mm at the end adjacent to region IV; the thickness of the bypass port gradually changes from 3.5 mm at the top to 3 mm at the bottom; and the cladding thickness of the sealing part of the flange is 1.5 mm. (4) Post-treatment of the inner wall The clad four-way valve is placed in a heat treatment furnace under a protective argon atmosphere. It is first heated to 580°C at a rate of 93°C / h and held at that temperature for 2 hours. Then, it is cooled in the furnace to 100°C at a rate of 40°C / h. Finally, it is removed from the furnace and air-cooled to room temperature. The sealing part of the flange is then precision-machined using a grinding process to meet the dimensional and surface roughness requirements. (Structural diagrams of the four-way valve in each treatment step are shown in the figure.) Figure 1-8 (As shown).

[0027] Example 2 The surface strengthening process for corrosion-resistant and wear-resistant four-way fittings includes the following steps: (1) Structural design and pretreatment Prepare a 4-way blank FS23-35 with a nominal diameter of 230mm, a bypass inner diameter of 102mm, and a 4-way material of 316L. Based on the degree of erosion and corrosion, divide the 4-way blank into five areas: area I, area II, area III, area IV, and the sealing part of the flange. Area IV has the most severe erosion and corrosion, while area I has a relatively lighter degree of erosion and corrosion. On the sealing part of the flange (sealing surface and sealing groove), the material with a depth of 1.5mm is uniformly removed by machining to form a new flange surface to be fused and clad. The blank is cleaned and preheated at a temperature of 200℃. (2) Preparation of laser cladding powder Weigh out 8.8g of carbon powder, 10.4g of silicon powder, 268g of tungsten powder, 878.4g of chromium powder, 373.6g of nickel powder, 1.5g of cerium powder, 316.8g of chromium carbide powder, 116g of molybdenum powder, and 2022.4g of cobalt powder. After mixing evenly, a laser cladding powder with a particle size of 27~95μm and a sphericity of 0.90 is obtained. Among them, the particle size of tungsten powder, chromium powder, chromium carbide powder and molybdenum powder is 75~95μm, the particle size of nickel powder and cobalt powder is 50~72μm, and the particle size of carbon powder, silicon powder and cerium powder is 27~48μm. (3) Laser cladding treatment Laser cladding powder is fed into the laser cladding equipment. The laser nozzle is controlled to always be perpendicular to the inner curved surface of the four-way, maintaining a constant focusing distance and processing angle, so that the laser head moves along a predetermined path and performs laser cladding in each area of ​​the four-way. After the laser cladding powder melts, it forms a metallurgically bonded cladding layer with the substrate. The laser cladding process parameters are as follows: laser power 2300W, powder feeding speed 11g / min, scanning speed 630mm / min, spot diameter 2.5mm, overlap rate 50%, and the protective gas is high-purity argon with a purity ≥99.99%. The thickness of the cladding layer in different regions is as follows: the thickness of the cladding layer in region I changes linearly from 2.7 mm at the beginning to 4.1 mm at the end adjacent to region IV; the thickness of the cladding layer in region II changes linearly from 3.2 mm at the beginning to 4.1 mm at the end adjacent to region IV; the thickness of the cladding layer in region III changes linearly from 3.5 mm at the beginning to 4.1 mm at the end adjacent to region IV; the thickness of the bypass port gradually changes from 3.1 mm at the top to 2.7 mm at the bottom; and the cladding thickness of the sealing part of the flange is 1.5 mm. (4) Post-treatment of the inner wall The clad four-way valve is placed in a heat treatment furnace under a protective argon atmosphere. It is first heated to 570°C at a rate of 90°C / h and held at that temperature for 1.5 hours. Then, it is cooled to 100°C in the furnace at a rate of 45°C / h. Finally, it is removed from the furnace and air-cooled to room temperature. The sealing part of the flange is then precision-machined using a grinding process to meet the dimensional and surface roughness requirements. (A structural diagram of the four-way valve in each processing step is shown in the figure.) Figure 1-8 (As shown).

[0028] Performance testing 1. Element detection Elemental analysis was performed on the cladding portions of the four-way connectors in Examples 1 and 2, and the results are shown in Table 1.

[0029] Table 1. Material content (wt.%) of the cladding portion of the four-way connector in Examples 1 and 2.

[0030] As shown in Table 1, the present invention can form a uniform cladding layer on the complex inner wall structure of the four-way junction. Comparing the original ratio of the laser cladding powder with the composition of the final cladding layer, it can be seen that the proportion of alloying elements is basically consistent, indicating that the process parameters adopted effectively reduce element burn-off and achieve efficient transition from laser cladding powder to cladding layer, thus forming the expected alloy system.

[0031] The above experiments demonstrate that the inner wall of the four-way valve formed in Examples 1 and 2 has good erosion and corrosion resistance, effectively resisting wear and corrosion, and has high promotional value.

[0032] 2. Erosion resistance test The erosion resistance test was conducted on the four-way valves of Examples 1 and 2, and the steps are as follows: (1) Using wire cutting technology, three samples were taken from each of the four-way junctions in regions I, II, III and IV. A control group was set up according to Example 1 and Example 2 to compare the erosion resistance of the four-way junctions with those with thermal spray WC coating and those without surface reinforcement. Five samples were taken from each four-way junction with thermal spray WC coating and those without surface reinforcement. The length of each sample was 15 mm, the arc length was 20 mm and the thickness was 2 mm. In Examples 1 and 2, the four-way valves with thermally sprayed WC coatings were model FS11-05 and FS23-35, respectively, with nominal diameters of 280mm and 230mm, and bypass inner diameters of 102mm. The materials were A694, F65, and 316L, respectively. The preparation method was as follows: high-speed flame spraying technology was used, with an oxygen flow rate of 68 m³ / h. 3 The spraying distance is 260 mm, the powder feeding speed is 55 g / min, and a 110-120 μm WC coating is formed on the inner surface of the tee and the flange surface. The coating is then polished to a relatively smooth finish with a thickness of about 90 μm using a polishing machine. The non-surface-reinforced four-way valves are model FS11-05 and FS23-35, with nominal diameters of 280mm and 230mm respectively, bypass inner diameter of 102mm for both, and materials of A694F65 and 316L respectively. (2) Use acetone and ethanol for ultrasonic cleaning. After cleaning, dry the sample with cold air. Then weigh it accurately (accurate to 0.1 mg) before the test and record the initial weight of the cladding layer (M1). (3) Securely mount the sample on the fixture of the air jet erosion tester and adjust the impact angle to the sampling angle; the nozzle pressure is 0.5 MPa, the abrasive flow rate is 7 g / min, the distance from the nozzle outlet to the sample surface is 15 mm, the abrasive is silica sand, the fixed total abrasive amount is 250 g, and the particle size is 100-200 μm; the parameters need to be monitored and recorded during the test to ensure their stability. (4) After the test, carefully remove the sample and gently remove the loose abrasive and debris adhering to the sample surface with a soft brush or airflow. Clean it slightly with acetone or ethanol, blow it dry, accurately weigh the weight of the sample cladding layer after erosion (M2), and calculate the erosion rate (EW): EW=(M1-M2) / total abrasive.

[0033] The results are shown in Table 2-4.

[0034] Table 2 Erosion rates of laser cladding samples from Examples 1 and 2

[0035] Table 3 Erosion rate of thermally sprayed WC coating samples

[0036] Table 4 Erosion rate of unreinforced specimens

[0037] As shown in Tables 2-4, the erosion rates of the laser cladding samples in Examples 1 and 2 are much lower than those of the thermally sprayed WC coating samples and the standard unreinforced samples.

[0038] The above tests demonstrate that the four-way valves of Examples 1 and 2 exhibit excellent erosion resistance in the erosion environment of oil and gas field pipelines, and can meet the application conditions of oil and gas field operations.

[0039] 3. Corrosion resistance test The corrosion resistance test was conducted on the inner wall of the four-way valves of Examples 1 and 2, and the steps are as follows: (1) Using wire cutting technology, three samples were taken from each of the four-way regions IV and II in Examples 1 and 2. A control group was set up according to Examples 1 and 2 to compare the corrosion resistance of the four-way with the thermal spray WC coating and the four-way without surface reinforcement. Six samples were taken from each four-way with thermal spray WC coating and the four-way without surface reinforcement. The length of each sample was 25 mm, the arc length was 20 mm, and the thickness was 2 mm. Using wire cutting technology, three samples were taken from the sealing part of the flange of the four-way in Examples 1 and 2. The length of each sample was 5 mm, the arc length was 10 mm, and the thickness was 1 mm. In Examples 1 and 2, the four-way valves with thermally sprayed WC coatings were model FS11-05 and FS23-35, respectively, with nominal diameters of 280mm and 230mm, and bypass inner diameters of 102mm. The materials were A694, F65, and 316L, respectively. The preparation method was as follows: high-speed flame spraying technology was used, with an oxygen flow rate of 68 m³ / h. 3 The spraying distance is 260 mm, the powder feeding speed is 55 g / min, and a 110-120 μm WC coating is formed on the inner surface of the tee and the flange surface. The coating is then polished to a relatively smooth finish with a thickness of about 90 μm using a polishing machine. The non-surface-reinforced four-way valves are model FS11-05 and FS23-35, with nominal diameters of 280mm and 230mm respectively, bypass inner diameter of 102mm for both, and materials of A694F65 and 316L respectively. (2) Use acetone and ethanol in sequence for ultrasonic cleaning for 15 minutes to thoroughly remove oil and impurities. After cleaning, dry the sample with cold air. (3) Place the prepared sample into a high-temperature and high-pressure reactor, add the prepared deionized water solution of 3.5 wt% NaCl + 0.5 wt% CH3COOH, then seal the high-temperature and high-pressure reactor, first introduce nitrogen to remove oxygen, then introduce CO2 to the partial pressure of 5 MPa, start the stirring and heating system, slowly raise the temperature to 90℃, the total pressure is 35.0 MPa, and the test time is 720h; (4) After the test, the sample was taken out and cleaned with deionized water and ethanol in sequence. After drying with cold air, it was weighed and the corrosion rate was calculated. Then, a stereomicroscope was used to observe whether there were holes and cracks on the sample surface.

[0040] The results are shown in Table 5-7.

[0041] Table 5. Corrosion rate and surface condition of laser cladding samples from Examples 1 and 2.

[0042] Table 6 Corrosion rate and surface condition of thermally sprayed WC coating samples

[0043] Table 7 Corrosion rate and surface condition of unreinforced specimens

[0044] As shown in Tables 5-7, the corrosion rates of the laser cladding samples in Examples 1 and 2 were lower than those of the thermally sprayed WC coating samples and the samples without surface strengthening. At the same time, the surfaces of the samples were bright, and no pores or cracks were found.

[0045] The above tests demonstrate that the four-way connectors of Examples 1 and 2 exhibit excellent corrosion resistance in harsh acidic environments and can meet application requirements.

[0046] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A surface strengthening process for corrosion-resistant and wear-resistant four-way fittings, characterized in that, Specifically, the following steps are included: (1) Structural design and pretreatment Based on the degree of erosion and corrosion, the four-way blank is divided into five areas: area I, area II, area III, area IV, and the sealing part of the flange; the material is uniformly removed from the sealing part of the flange to form the flange surface to be clad, and then cleaned and preheated. (2) Preparation of laser cladding powder Carbon powder, silicon powder, tungsten powder, chromium powder, nickel powder, cerium powder, chromium carbide powder, molybdenum powder, and cobalt powder are mixed evenly to obtain laser cladding powder; (3) Laser cladding treatment Laser cladding powder is fed into the laser cladding equipment. The laser nozzle is controlled to always be perpendicular to the inner curved surface of the four-way tube, maintaining a constant focusing distance and processing angle, so that the laser head moves along a predetermined path and performs laser cladding on the surface of each area. After the laser cladding powder melts, it forms a metallurgically bonded cladding layer with the substrate. (4) Post-treatment of the inner wall After cladding, the four-way valve undergoes slow cooling, and then the sealing part of the flange is ground to meet the dimensional and surface roughness technical requirements.

2. The surface strengthening process for corrosion-resistant and wear-resistant four-way fittings according to claim 1, characterized in that, In step (1), the thicknesses of the cladding layer in regions I, II, III and IV are as follows: the starting thickness T1 of the cladding layer in region I is 2.5~3mm; the starting thickness T2 of the cladding layer in region II is 3~3.5mm; the starting thickness T3 of the cladding layer in region III is 3.5~4mm; and the thickness T4 of the cladding layer in region IV is 4~4.5mm.

3. The surface strengthening process for corrosion-resistant and wear-resistant four-way fittings according to claim 1, characterized in that, In step (1), the sealing part of the flange includes the sealing surface of the flange and the sealing groove area located on the sealing surface of the flange.

4. The surface strengthening process for corrosion-resistant and wear-resistant four-way fittings according to claim 1, characterized in that, In step (1), the material is uniformly removed from the sealing part of the flange by machining, and the removal depth d is 1~2mm.

5. The surface strengthening process for corrosion-resistant and wear-resistant four-way fittings according to claim 1, characterized in that, In step (1), the preheating temperature is 150~200℃.

6. The surface strengthening process for corrosion-resistant and wear-resistant four-way fittings according to claim 1, characterized in that, In step (2), the mass percentage of each raw material in the laser cladding powder is as follows: carbon powder 0.2%~0.34%, silicon powder 0.2%~0.4%, tungsten powder 5%~8%, chromium powder 20%~23.6%, nickel powder 8.1%~9.7%, cerium powder 0.02%~0.06%, chromium carbide powder 7%~8.4%, molybdenum powder 2.3%~3.6%, and cobalt powder as the balance.

7. The surface strengthening process for corrosion-resistant and wear-resistant four-way fittings according to claim 6, characterized in that, In step (2), the particle size of the laser cladding powder is 20~105μm and the sphericity is 0.85~0.95; the particle size of the tungsten powder, chromium powder, chromium carbide powder and molybdenum powder is 75~105μm; the particle size of the nickel powder and cobalt powder is 45~85μm; and the particle size of the carbon powder, silicon powder and cerium powder is 20~50μm.

8. The surface strengthening process for corrosion-resistant and wear-resistant four-way fittings according to claim 1, characterized in that, In step (3), the laser cladding process parameters are: laser power 1800~3400W, powder feeding speed 12~18g / min, scanning speed 600~800mm / min, spot diameter 2~3mm, overlap rate 45%~60%, and the protective gas is high-purity argon with a purity ≥99.99%.

9. The surface strengthening process for corrosion-resistant and wear-resistant four-way fittings according to claim 1, characterized in that, In step (4), the slow cooling process is specifically performed as follows: the clad four-way valve is placed in a heat treatment furnace under a protective argon atmosphere, heated to 570-590°C at a rate of 80-100°C / h, held for 1.5-2.5h, then cooled to below 300°C at a rate of ≤50°C / h, and finally removed from the furnace and air-cooled to room temperature.

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