A laser cladding process for repairing surface damage on rails

Abstract

This invention discloses a laser cladding process for repairing surface damage on rails, belonging to the field of metal powder laser cladding technology. The process includes the following steps: pre-treating the rail damage repair area; determining the laser cladding area based on the length, width, and depth of the damage repair area; using cobalt-based alloy powder as the cladding material, employing a pulsed waveform-current composite laser cladding process to clad the area with a cladding layer; and completing the repair after reaching a predetermined number of cladding layers. The calculation method for the number of cladding layers is as follows: This invention reduces the thermal energy difference between the bottom and top of the cladding layer, increasing the temperature of the substrate during laser cladding, achieving the superposition of temperature and electromagnetic fields, inhibiting the initiation of cracks in the rail cladding layer and the transformation of martensite in the heat-affected zone, thereby improving the efficiency of rail repair and the performance of the cladding layer.

Description

Technical Field

[0001] This invention relates to the field of metal powder laser cladding technology, specifically to a laser cladding process for repairing surface damage on rails. Background Technology

[0002] Steel rails are the basic load-bearing structure of railway tracks. With increasing axle load, the service life of steel rails decreases significantly, and their surfaces inevitably experience failures such as cracks, collapses, and wear. This seriously affects traffic smoothness and train operation safety. Furthermore, with the accumulation of time and the increasing demands of heavy-haul and high-speed trains on the tracks, rail failures are becoming increasingly severe. Therefore, in order to promote the development of the transportation industry and ensure the safety of train operation, extending the service life of steel rails and repairing damaged rails has become an urgent task.

[0003] Laser cladding technology, a novel surface modification technique, utilizes a high-energy laser beam as a heat source to melt the substrate surface and cladding powder. The cladding powder, carried by a flowing internal gas (such as argon), is injected into the molten pool through a powder nozzle. After solidification, the cladding material forms a superior metallurgical bonding layer on the substrate surface, thereby improving the durability of the rails and extending their service life. Compared with traditional repair methods, laser cladding technology features high energy density, a small heat-affected zone, high precision, and rapid heating and cooling, and is currently widely used in industrial manufacturing.

[0004] Laser cladding process parameters significantly influence the geometry and dilution rate of the cladding layer. Mismatched parameters can lead to defects such as porosity and cracks in the coating. Optimal process parameters improve the forming quality of the cladding layer and ensure a tight bond between the coating and the substrate, resulting in a strong metallurgical bond. Laser cladding process parameters control the geometric characteristics and mechanical properties of the cladding layer by affecting the thermal history during the cladding process. However, optimization of laser process parameters sometimes fails to produce satisfactory results and meet performance requirements.

[0005] Laser waveform has a significant impact on the quality of the cladding layer. Pulse shaping, by altering the waveform of the pulsed laser, controls the energy distribution of individual pulses, increasing the degree of control over the laser energy reaching the substrate, and thus controlling the melting process of the material. This plays a positive role in controlling cracks and martensite. Therefore, researchers choose pulsed lasers and control the duty cycle and laser frequency to change the heat input, thereby affecting the thermal history during laser cladding and consequently the mechanical properties of the cladding layer. Pulsed current, as an external physical field, generates skin effect, Joule effect, and Peltier effect when passing through a metallic conductor, attracting increasing attention in material modification and research. Laser cladding technology has broad application prospects in rail repair, but current research mainly focuses on the impact of process parameter optimization on the shape of the cladding layer, with less research and depth on pulse shaping, pulsed current, and pulse waveform-current composite processes. Therefore, this invention provides a process method for rail repair based on pulse waveform-current composite laser cladding technology. Summary of the Invention

[0006] To address the problems of wear, fatigue, and other failure modes that occur in existing rails after long-term use, this invention provides a laser cladding process for repairing rail surface damage. The energy distribution of a single laser pulse is controlled by a periodic, linearly ramped waveform to influence melting and solidification behavior. Simultaneously, the skin effect, Joule heating effect, and Peltier effect generated during the passage of pulsed current through the metal substrate are utilized to reduce the thermal energy difference between the bottom and top of the cladding layer, increasing the substrate temperature during laser cladding. This achieves the superposition of temperature and electromagnetic fields, refining the solidification structure, inhibiting the initiation of cracks in the rail cladding layer and the transformation of martensite in the heat-affected zone, thereby improving the efficiency of rail repair and the performance of the cladding layer.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] The purpose of this invention is to provide a laser cladding process for repairing surface damage on rails, comprising the following steps:

[0009] Pre-treatment is performed on the rail damage repair area; the laser cladding area is determined according to the length, width and depth of the damage repair area; cobalt-based alloy powder is used as the cladding material, and a pulse waveform-current composite laser cladding process is used to clad the cladding layer in the cladding area. The repair is completed after the determined number of cladding layers is reached.

[0010] The method for calculating the number of cladding layers is as follows:

[0011] ;

[0012] N= ;

[0013] in, W The width of a single coating layer during stable operation of the pulse waveform-current composite laser cladding process;

[0014] d The distance between the center points of adjacent melt channels;

[0015] R 0 Overlap rate;

[0016] D is the width of the cladding area;

[0017] N represents the number of cladding layers.

[0018] Preferably, the pulse waveform is a rising wave laser shape, the pulse current frequency is 3000Hz, the current duty cycle is 20~50%, and the current value is 5~10A; the laser power of the laser cladding is 1000~1400W, the spot diameter is 3mm, the scanning speed is 4~8mm / s, the defocusing amount is -1~1mm, and the overlap rate is 20~40%.

[0019] Preferably, when the laser pulse waveform is a periodic linear ramp-up mode, with each period being 0~50ms, and within each period, the laser power is gradually increased from 0W to 1000~1400W in a linear trend, and the laser cladding is performed in a cyclical manner until the repair is completed.

[0020] Preferably, during the laser cladding process, cobalt-based alloy powder is fed by carrying it with an inert gas at a feeding rate of 3~6 g / min.

[0021] Preferably, the inert gas is argon, and the flow rate of argon is 400 L / h.

[0022] Preferably, the rail is U71Mn with dimensions of 120mm×60mm×15mm; the pretreatment method is to grind the damaged repair area, clean it with acetone and ethanol solution, and dry it to remove oil stains.

[0023] Preferably, after the repair is completed, the surface is polished, and ultrasonic cleaning and drying are performed using acetone and ethanol.

[0024] Preferably, after the repair is completed, the sum of the thicknesses of all cladding layers is 0.7~1mm.

[0025] Preferably, determining the pulse waveform-current composite laser cladding process based on the laser cladding area includes the following steps: conducting a single-pass cladding pre-test using cladding material in the cladding area to determine the range of parameters for the pulse waveform-current composite laser cladding process; designing orthogonal experiments based on the parameter range values ​​to determine the geometry and dilution rate of the single-pass cladding layer, thereby determining the pulse waveform-current composite laser cladding process parameters; wherein the dilution rate is calculated as follows:

[0026] 00%,

[0027] Where h is the melting depth and H is the melting height.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) This invention proposes a new rail repair process based on pulsed current composite laser cladding to improve the performance of cobalt-based cladding layers. The energy distribution of a single pulse is controlled by the periodic linear ramp of the laser pulse waveform to influence the melting and solidification behavior. At the same time, the skin effect, Joule heating effect, Peltier effect and other effects generated during the pulsed current passing through the metal substrate are utilized to reduce the thermal energy difference between the bottom and top of the cladding layer and increase the temperature of the substrate during laser cladding. This achieves the superposition of temperature field and electromagnetic field, refines the solidification structure, inhibits the initiation of cracks in the rail cladding layer and the transformation of martensite in the heat-affected zone, and improves the efficiency of rail repair and the performance of the cladding layer.

[0030] (2) Based on the interaction between temperature field and electromagnetic field in the pulse shaping-current composite laser cladding process, this invention has conducted in-depth research on its repair mechanism and determined the composite laser cladding process with pulse current intensity, pulse laser waveform and frequency. It can open up new ways for rail repair, service life extension and environmental benefits improvement, and has high practical application value. Attached Figure Description

[0031] Figure 1 This is a circuit diagram of the pulse waveform-current composite laser cladding process of the present invention;

[0032] Figure 2 This is a schematic diagram of the upward-sloping laser waveform of the present invention;

[0033] Figure 3 Metallographic images showing the microstructure of the cobalt-based cladding layer in Examples 1-3 and Comparative Example 1 of this invention;

[0034] Figure 4 Metallographic images showing the microstructure of the cobalt-based cladding layer in Examples 1-3 and Comparative Example 1 of this invention;

[0035] Figure 5These are Tafel polarization curves of the cobalt-based cladding layers in Examples 1-3 and Comparative Example 1 of the present invention;

[0036] Figure 6 These are surface wear marks on the cobalt-based cladding layers of Examples 1-3 and Comparative Example 1 of the present invention. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0038] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0039] The following embodiments all use a coaxial powder feeding laser cladding system, and the equipment setup is as follows: Figure 1 As shown, the main components include a semiconductor laser (LMD 4000-100, LaserLine, Germany), a six-axis industrial robot (ZH 30 / 60III, KUKA, Germany), a coaxial laser cladding head (YC52, Precitec, Germany), a dual-hopper negative pressure pneumatic powder feeder (RC-PGF-D, Yucheng, China), a precision water chiller (MCWL-150T-01AK1S4, Tongfei Refrigeration, China), and a pulse power supply device to assist in laser cladding (G22, Jiaman, China). This equipment offers a high degree of freedom; the laser waveform can be selected by changing parameters through programming. It employs a fully automated and intelligent repair method, achieving comprehensive computer control. Furthermore, 3D scanning analysis enables precise control of the repair path. Its flexible processing performance and high efficiency significantly reduce manufacturing costs and time.

[0040] A laser cladding process for repairing surface damage on rails includes the following steps:

[0041] Pre-treatment is performed on the rail damage repair area; the laser cladding area is determined according to the length, width and depth of the damage repair area; cobalt-based alloy powder is used as the cladding material, and a pulse waveform-current composite laser cladding process is used to clad the cladding layer in the cladding area. The repair is completed after the determined number of cladding layers is reached.

[0042] The method for calculating the number of cladding layers is as follows:

[0043] ;

[0044] N= ;

[0045] in, W The width of a single coating layer during stable operation of the pulse waveform-current composite laser cladding process;

[0046] d The distance between the center points of adjacent melt channels;

[0047] R 0 Overlap rate;

[0048] D is the width of the cladding area;

[0049] N represents the number of cladding layers.

[0050] By controlling the energy distribution of a single pulse through laser pulse shaping, the melting and solidification behavior can be influenced. At the same time, by utilizing the skin effect, Joule heating effect, and Peltier effect generated during the pulsed current passing through the metal substrate, the thermal energy difference between the bottom and top of the cladding layer is reduced, increasing the temperature of the substrate during laser cladding. This achieves the superposition of temperature and electromagnetic fields, refines the solidification structure, inhibits the initiation of cracks in the rail cladding layer and the transformation of martensite in the heat-affected zone, and improves the efficiency of rail repair and the performance of the cladding layer.

[0051] The pulse waveform-current composite laser cladding process is determined based on the laser cladding area, including the following steps: Prepare a U71Mn rail steel substrate. The chemical composition of the U71Mn rail is shown in Table 1. Cut the rail steel substrate into appropriately sized small pieces. Conduct a single-pass cladding pre-test on the rail material to determine the optimal process parameters, including the range of laser power, powder feeding rate, and scanning speed. Within this range, select parameter levels to design orthogonal experiments. Perform a comprehensive analysis of the orthogonal experimental results to study the influence of process parameters on the geometry and dilution rate of the single-pass cladding layer. The dilution rate is an indicator of the bonding strength between the cladding layer and the rail. Too low a rate will cause the cladding layer to easily detach, while too high a rate will affect the performance of the cladding layer. The dilution rate can be determined using the formula: The calculation is performed with 00% accuracy, where h is the melt depth and H is the melt height. The melt height and melt depth are obtained by measuring the geometry of the cladding layer, and the dilution rate ranges from 10% to 15%. The influence of process parameters on the geometry and dilution rate of a single-pass cladding layer is determined through calculation, and the optimal parameter combination is identified. The geometry parameters of a single-pass cladding layer under these parameters are obtained, providing process parameter values ​​for the pulse waveform-current composite laser cladding process in the laser cladding region in the following embodiments.

[0052] Table 1 Chemical composition (wt.%) of U71Mn steel rails

[0053]

[0054] Example 1

[0055] A laser cladding process for repairing surface damage on rails includes the following steps:

[0056] The damaged area of ​​the rail was pretreated by grinding to remove surface rust and oxide film, and ultrasonic cleaning and drying were performed with acetone and ethanol to remove oil stains. The rail was U71Mn rail steel with dimensions of 120mm×60mm×15mm. The chemical composition of U71Mn rail is shown in Table 1.

[0057] Based on the length L=80mm and width D=40mm of the damaged repair area, the area of ​​the laser cladding area is determined. Cobalt-based alloy powder is used as the cladding material. The powder is fed by argon gas at a feeding rate of 0.078g / s and an argon gas flow rate of 400 L / h. The pulse waveform-current composite laser cladding process is used to clad the rail in the cladding area to repair the rail repair area.

[0058] The cobalt-based alloy powder comprises the following components by weight percentage: 1.16% carbon, 29.1% chromium, 1.2% silicon, 4.6% tungsten, 3.1% iron, 1.1% molybdenum, 3.1% nickel, 1.1% Mn, with the balance being cobalt.

[0059] The process parameters for pulse waveform-current composite laser cladding are: laser power of 1400W, scanning speed of 4mm / s, spot diameter of 3mm, defocusing amount of -1mm, and overlap rate of 30%.

[0060] The pulse waveform is a rising laser shape. The current value, current frequency value, and current duty cycle value can be set by adjusting the programmable DC pulse power supply. The pulse current frequency is 3000Hz, the current duty cycle is 20%, and the current value is 5A.

[0061] During laser cladding performed using pulsed waveform-current composite laser cladding, the width of a single coating layer is measured when the process reaches a steady state. W The overlap is 2.3mm, and the overlap rate is... R 0 The overlap rate is 30%. The number of weld overlaps required to repair the cladding damage area is calculated using the overlap rate formula. ,in, W To determine the width of a single-pass coating during stable operation of the pulse waveform-current composite laser cladding process, the spacing between the center points of adjacent cladding passes is determined. d The thickness is 1.61 mm. Based on the expected cladding area width D of 40 mm, according to N = The number of cladding layers N is determined to be 24;

[0062] Employing pulse waveform-current composite laser cladding technology, Figure 2A schematic diagram of the waveform of a ramp-rising pulsed laser, as shown below. Figure 2 As shown, when the laser pulse waveform is a ramp-up, each 0~50ms is a cycle, and within each cycle, the laser power is gradually increased from 0W to 1400W in a linear trend to carry out the laser cladding process. The cladding layer (the number of cladding layers N is 24) is clad in the cladding area of ​​the rail to repair the cladding area of ​​the rail. After the repair is completed, the cladding surface is polished smooth, and ultrasonic cleaning and drying are performed using acetone and ethanol. The sum of the thicknesses of the cladding layers is 1mm.

[0063] Example 2

[0064] A laser cladding process for repairing surface damage on rails includes the following steps:

[0065] S1. Pre-treatment of the damaged area of ​​the rail is carried out. The damaged area is ground to remove surface rust and oxide film. Ultrasonic cleaning and drying with acetone and ethanol are used to remove oil stains. The rail is U71Mn rail steel with dimensions of 120mm×60mm×15mm. The chemical composition of U71Mn rail is shown in Table 1.

[0066] Based on the length L=80mm and width D=40mm of the damaged repair area, the expected laser cladding area is determined. Cobalt-based alloy powder is used as the cladding material. The powder is fed by argon gas at a rate of 0.078g / s and a flow rate of 400 L / h. The pulse waveform-current composite laser cladding process is used to clad the rail in the rail repair area.

[0067] The cobalt-based alloy powder comprises the following components by weight percentage: 1.16% carbon, 29.1% chromium, 1.2% silicon, 4.6% tungsten, 3.1% iron, 1.1% molybdenum, 3.1% nickel, 1.1% Mn, with the balance being cobalt.

[0068] The process parameters for pulse waveform-current composite laser cladding are as follows: laser power is 1400W, scanning speed is 4mm / s, spot diameter is 3mm, defocusing amount is -1mm, and overlap rate is 30%. The pulse waveform is an upward wave laser shape. The current value, current frequency, and current duty cycle are controlled by adjusting the programmable DC pulse power supply. The pulse current frequency is 3000Hz, the current duty cycle is 50%, and the current value is 5A.

[0069] During laser cladding performed using pulsed waveform-current composite laser cladding, the width of a single coating layer is measured when the process reaches a steady state. W The overlap is 2.3mm, and the overlap rate is... R 0The overlap rate is 30%. The number of weld overlaps required to repair the cladding damage area is calculated using the overlap rate formula. ,in, W To determine the width of a single-pass coating during stable operation of the pulse waveform-current composite laser cladding process, the spacing between the center points of adjacent cladding passes is determined. d The thickness is 1.61 mm. Based on the expected cladding area width D of 40 mm, according to N = The number of cladding layers N is determined to be 24;

[0070] Employing pulse waveform-current composite laser cladding technology, such as Figure 2 As shown, when the laser pulse waveform is a ramp-up, each 0~50ms is a cycle, and within each cycle, the laser power is gradually increased from 0W to 1400W in a linear trend to perform laser cladding. A cladding layer (the number of cladding layers N is 24) is clad in the cladding area of ​​the rail to repair the cladding area. After the repair is completed, the cladding surface is polished smooth, and ultrasonic cleaning and drying are performed using acetone and ethanol. The sum of the thicknesses of the cladding layers is 0.7mm.

[0071] Example 3

[0072] A laser cladding process for repairing surface damage on rails includes the following steps:

[0073] The damaged area of ​​the rail was pretreated by grinding to remove surface rust and oxide film, and ultrasonic cleaning and drying were performed with acetone and ethanol to remove oil stains. The rail was U71Mn rail steel with dimensions of 120mm×60mm×15mm. The chemical composition of U71Mn rail is shown in Table 1.

[0074] Based on the length L=80mm and width D=40mm of the damaged repair area, the expected laser cladding area is determined. Cobalt-based alloy powder is used as the cladding material. The powder is fed by argon gas at a rate of 0.078g / s and a flow rate of 400 L / h. The pulse waveform-current composite laser cladding process is used to clad the rail in the rail repair area.

[0075] The cobalt-based alloy powder comprises the following components by weight percentage: 1.16% carbon, 29.1% chromium, 1.2% silicon, 4.6% tungsten, 3.1% iron, 1.1% molybdenum, 3.1% nickel, 1.1% Mn, with the balance being cobalt.

[0076] The process parameters for pulse waveform-current composite laser cladding are as follows: laser power is 1400W, scanning speed is 4mm / s, spot diameter is 3mm, defocusing amount is -1mm, and overlap rate is 30%. The pulse waveform is an upward wave laser shape. The current value, current frequency, and current duty cycle are controlled by adjusting the programmable DC pulse power supply. The pulse current frequency is 3000Hz, the current duty cycle is 50%, and the current value is 10A.

[0077] During laser cladding performed using pulsed waveform-current composite laser cladding, the width of a single coating layer is measured when the process reaches a steady state. W The overlap is 2.3mm, and the overlap rate is... R 0 The overlap rate is 30%. The number of weld overlaps required to repair the cladding damage area is calculated using the overlap rate formula. ,in, W To determine the width of a single-pass coating during stable operation of the pulse waveform-current composite laser cladding process, the spacing between the center points of adjacent cladding passes is determined. d The thickness is 1.61 mm. Based on the expected cladding area width D of 40 mm, according to N = The number of cladding passes N is determined to be 24;

[0078] Cobalt-based alloy powder is used as the cladding material. The cobalt-based alloy powder comprises the following components by weight percentage: 1.16% carbon, 29.1% chromium, 1.2% silicon, 4.6% tungsten, 3.1% iron, 1.1% molybdenum, 3.1% nickel, 1.1% Mn, and the balance is cobalt.

[0079] Employing pulsed waveform-current composite laser cladding technology, such as Figure 2 As shown, when the laser pulse waveform is a ramp-up, each 0~50ms is a cycle, and within each cycle, the laser power is gradually increased from 0W to 1400W in a linear trend to carry out the laser cladding process. The cladding layer (the number of cladding layers N is 24) is clad in the cladding area of ​​the rail. After the repair is completed, the cladding surface is polished smooth, and ultrasonic cleaning and drying are performed using acetone and ethanol. The sum of the thicknesses of the cladding layers is 0.8mm.

[0080] Comparative Example 1

[0081] A laser cladding process for repairing surface damage on rails includes the following steps:

[0082] S1. Pre-treatment of the damaged area of ​​the rail is carried out. The damaged area is ground to remove surface rust and oxide film. Ultrasonic cleaning and drying with acetone and ethanol are used to remove oil stains. The rail is U71Mn rail steel with dimensions of 120mm×60mm×15mm. The chemical composition of U71Mn rail is shown in Table 1.

[0083] Based on the length L=80mm and width D=40mm of the damaged repair area, the expected laser cladding area is determined. Cobalt-based alloy powder is used as the cladding material. The powder is fed by argon gas at a rate of 0.078g / s and a flow rate of 400 L / h. The laser cladding process is used to clad the rail in the rail repair area.

[0084] The cobalt-based alloy powder comprises the following components by weight percentage: 1.16% carbon, 29.1% chromium, 1.2% silicon, 4.6% tungsten, 3.1% iron, 1.1% molybdenum, 3.1% nickel, 1.1% Mn, with the balance being cobalt.

[0085] The laser cladding process parameters are: laser power of 1400W, scanning speed of 4mm / s, spot diameter of 3mm, defocusing amount of -1mm, and overlap rate of 30%.

[0086] When laser cladding is performed under determined process parameters, the width of a single coating layer is measured when the process reaches a steady state. W The overlap is 2.3mm, and the overlap rate is... R 0 The overlap rate is 30%. The number of weld overlaps required to repair the cladding damage area is calculated using the overlap rate formula. Determine the spacing between the center points of adjacent melt channels. d The thickness is 1.61 mm. Based on the expected cladding area width D of 40 mm, according to N = The number of cladding layers N is determined to be 24;

[0087] Laser cladding technology is used to repair the cladding area of ​​the rail by cladding layers (N is 24). After the repair is completed, the cladding surface is polished and ultrasonically cleaned and dried using acetone and ethanol. The total thickness of the cladding layers is 0.7 mm.

[0088] Microstructure analysis: The microstructure of the cobalt-based cladding layers in Examples 1-3 and Comparative Example 1 was tested. Figure 3 The images show the metallographic structure of the cobalt-based cladding layers in Examples 1-3 and Comparative Example 1 of this invention. Figure 3 In the examples, a represents Comparative Example 1, b represents Example 1, c represents Example 2, and d represents Example 3. Figure 3 As shown in Figure a, the cladding microstructure of laser cladding process mainly consists of dendrites at the bottom and equiaxed crystals in the middle and upper parts, and the grains are relatively coarse and irregular. Figure 3As shown in bd, most of the cladding parts assisted by pulse waveform-current in Examples 1-3 are mainly distributed with cellular and equiaxed crystals. It can be clearly observed that the crystal structure is finer and more regular, indicating that adding pulse waveform-current during laser cladding can improve the nucleation rate of crystal structure, thereby refining the structure.

[0089] Further observation of the organization reveals that Figure 3 Traditional cladding without pulse waveform-current assistance will produce some porosity, while Figure 3 The pulsed waveform-current assisted cladding process used in Examples 1-3 significantly reduced the number of pores in the cladding parts. The introduction of pulsed current is equivalent to applying an electromagnetic force to the molten pool. This electromagnetic force can both expel gas and provide timely shrinkage, and in Example 2, with pulsed waveform-current assistance, almost no pores were generated. The introduction of pulsed waveform-current technology during laser cladding greatly improved the quality of the clad parts.

[0090] Mechanical property testing: The hardness of the cobalt-based cladding layers in Examples 1-3 and Comparative Example 1 was tested respectively. Figure 4 Metallographic images showing the microstructure of the cobalt-based cladding layers in Examples 1-3 and Comparative Example 1 of this invention. Figure 4 It can be seen that the hardness of the cobalt-based cladding layer in Examples 1-3 and Comparative Example 1 is 375.9 HV, 393.9 HV, 385.2 HV and 338 HV, respectively. The hardness of the rail cladding layer assisted by pulse waveform-current is higher than that of the rail cladding layer without pulse assistance. Among them, the hardness of the cladding layer in Example 2 is 16.54% higher than that in Comparative Example 1, and 39.85% higher than that of the substrate.

[0091] Corrosion resistance test: The corrosion resistance of the cobalt-based cladding layers of Examples 1-3 and Comparative Example 1 were tested respectively. The self-corrosion potential refers to the potential at which the corrosion reaction occurs, which reflects the degree of hot corrosion of the material. The larger the value, the less likely the material is to be corroded. The self-corrosion current density reflects the uniform corrosion rate of the material. The larger the value, the faster the corrosion rate of the material. Figure 5 These are Tafel polarization curves of the cobalt-based cladding layers in Examples 1-3 and Comparative Example 1 of the present invention. Figure 5 It can be seen that, for Example 2 > Example 3 > Example 1 > Comparative Example 1; For Example 2 < Example 3 < Example 1 < Comparative Example 1. In this invention, the self-corrosion potential and self-corrosion current density of Example 2 are -0.35536 V and 4.3005 A·cm, respectively. -2 It exhibits the best corrosion resistance, and the comparison also demonstrates that adding pulse waveform-current during the laser cladding process can improve the corrosion resistance of the cladding layer.

[0092] Friction resistance test: The friction and wear performance of the cobalt-based cladding layers in Examples 1-3 and Comparative Example 1 were tested. Given the complex working environment of the rails, strict requirements are placed on the wear resistance of the rails themselves. The wear loss was determined by the amount of mass loss of the cladding before and after the wear test. The less the loss, the better the wear resistance of the workpiece surface. As shown in Table 2, it can be seen that in this invention, the wear amounts of the cladding before and after Examples 1-3 were 7.6 mg, 4.9 mg, and 6.5 mg, respectively, while the wear amount of the traditional cladding without pulse waveform-current assistance in Comparative Example 1 reached 11.8 mg. This indicates that the pulse waveform-current process proposed in this invention significantly improves the performance of the cladding.

[0093] Table 2 shows the wear measurement results of the cladding parts before and after cladding.

[0094]

[0095] Figure 6 These are surface wear mark morphology images of the cobalt-based cladding layers in Examples 1-3 and Comparative Example 1 of the present invention. Figure 6 In the examples, a represents Comparative Example 1, b represents Example 1, c represents Example 2, and d represents Example 3. Figure 6 As shown, the cladding surfaces of Examples 1-3 and Comparative Example 1 all exhibit furrows aligned with the wear direction, demonstrating significant furrowing and plastic deformation; from Figure 6 As can be seen from a, obvious peeling and severe wear were observed in the cladding layer wear marks of Comparative Example 1; from Figure 6 As can be seen from bd, the plowing and peeling in the wear marks of the clad parts assisted by pulse waveform-current are significantly reduced, there are no obvious tear marks, local plastic deformation occurs, and the wear is mainly smooth abrasive wear. The width and depth of the grooves on the surface of the clad layer in Example 2 are further widened and narrowed compared to Examples 1 and 3, and there is almost no adhesive wear, which shows superior wear resistance.

[0096] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0097] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A laser cladding process for repairing surface damage on rails, characterized in that, Includes the following steps: Pre-treatment is performed on the rail damage repair area; the laser cladding area is determined according to the length, width and depth of the damage repair area; cobalt-based alloy powder is used as the cladding material, and a pulse waveform-current composite laser cladding process is used to clad the cladding layer in the cladding area. The repair is completed after the required number of cladding layers is reached. The method for calculating the number of cladding layers is as follows: ； N= ； in, W The width of a single coating layer during stable operation of the pulse waveform-current composite laser cladding process; d The distance between the center points of adjacent melt channels; R 0 Overlap rate; D is the width of the cladding area; N is the number of cladding layers; The pulse waveform is a rising laser shape, the pulse current frequency is 3000Hz, the current duty cycle is 20~50%, and the current value is 5~10A. The laser cladding process has a laser power of 1000~1400W, a spot diameter of 3mm, a scanning speed of 4~8mm / s, a defocusing amount of -1~1mm, and an overlap rate of 20~40%. When the laser pulse waveform is a periodic linear ramp-up mode, with each period being 0~50ms, and within each period, the laser power is gradually increased from 0W to 1000~1400W in a linear trend, and the laser cladding is performed in a cyclical manner until the repair is completed.

2. The laser cladding process for repairing surface damage of rails according to claim 1, characterized in that, During the laser cladding process, cobalt-based alloy powder is fed by inert gas at a rate of 3-6 g / min.

3. The laser cladding process for repairing surface damage of rails according to claim 2, characterized in that, The inert gas is argon, and the argon flow rate is 400 L / h.

4. The laser cladding process for repairing surface damage of rails according to claim 1, characterized in that, The rail is U71Mn, with dimensions of 120mm×60mm×15mm; the pretreatment method is to grind the damaged repair area, clean it with acetone and ethanol solution, and dry it to remove oil stains.

5. The laser cladding process for repairing surface damage of rails according to claim 1, characterized in that, After repair, the surface is polished, and ultrasonic cleaning and drying are performed using acetone and ethanol.

6. The laser cladding process for repairing surface damage of rails according to claim 5, characterized in that, After the repair is completed, the sum of the thicknesses of all cladding layers is 0.7~1mm.

7. The laser cladding process for repairing surface damage of rails according to claim 1, characterized in that, The cobalt-based alloy powder is composed of the following components by weight percentage: 1.16% carbon, 29.1% chromium, 1.2% silicon, 4.6% tungsten, 3.1% iron, 1.1% molybdenum, 3.1% nickel, 1.1% Mn, with the balance being cobalt.

8. The laser cladding process for repairing surface damage of rails according to claim 1, characterized in that, The pulse waveform-current composite laser cladding process is determined based on the laser cladding area, including the following steps: A single-pass cladding pre-test is conducted in the cladding area using cladding material to determine the range of parameters for the pulse waveform-current composite laser cladding process. Orthogonal experiments are designed horizontally based on the parameter range values ​​to determine the geometry and dilution rate of the single-pass cladding layer, thereby determining the pulse waveform-current composite laser cladding process parameters. The method for calculating the dilution rate is as follows: 00%, where h is the melting depth and H is the melting height.

Images