WO2019144843A1 - 一种激光-辅助热源高效复合熔覆强化钢轨的方法 - Google Patents

一种激光-辅助热源高效复合熔覆强化钢轨的方法 Download PDF

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WO2019144843A1
WO2019144843A1 PCT/CN2019/072300 CN2019072300W WO2019144843A1 WO 2019144843 A1 WO2019144843 A1 WO 2019144843A1 CN 2019072300 W CN2019072300 W CN 2019072300W WO 2019144843 A1 WO2019144843 A1 WO 2019144843A1
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Prior art keywords
laser
rail
heat source
cladding
steel rail
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PCT/CN2019/072300
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English (en)
French (fr)
Inventor
曾晓雁
孟丽
王邓志
胡乾午
郭平华
许晓明
牛莅
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华中科技大学
武汉新瑞达激光工程有限责任公司
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Priority to US16/639,746 priority Critical patent/US20200199698A1/en
Publication of WO2019144843A1 publication Critical patent/WO2019144843A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C24/00—Coating starting from inorganic powder
    • C23C24/08—Coating starting from inorganic powder by application of heat or pressure and heat
    • C23C24/10—Coating starting from inorganic powder by application of heat or pressure and heat with intermediate formation of a liquid phase in the layer
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C24/00—Coating starting from inorganic powder
    • C23C24/08—Coating starting from inorganic powder by application of heat or pressure and heat
    • C23C24/10—Coating starting from inorganic powder by application of heat or pressure and heat with intermediate formation of a liquid phase in the layer
    • C23C24/103—Coating with metallic material, i.e. metals or metal alloys, optionally comprising hard particles, e.g. oxides, carbides or nitrides
    • C23C24/106—Coating with metal alloys or metal elements only
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/06—Surface hardening
    • C21D1/09—Surface hardening by direct application of electrical or wave energy; by particle radiation
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/04—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rails
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite

Definitions

  • the invention belongs to the field of material processing, and particularly relates to a method for efficiently preparing a metal cladding layer on a rail surface by using a laser-assisted heat source composite cladding.
  • the method can be used to improve the wear resistance and contact fatigue performance of the rail, and can also be used to solve the problem of poor railway shunt and repair of damaged rails.
  • Thermal spraying, electroplating and surfacing are the main methods currently used to prepare metal coatings on rail surfaces.
  • the thermal spray coating and the electroplating coating are mechanically combined with the rail substrate, and the bonding force is weak, and it is easy to fall off during the wheel-rail friction process.
  • the surfacing layer and the rail substrate are metallurgically bonded, but the heat input and heat affected zone are large, the microstructure and performance uniformity of the surfacing layer are poor, and the martensite structure is easily induced inside the rail matrix.
  • laser cladding Compared with plasma arc and arc surfacing, laser cladding has the advantages of high energy density, small heat affected zone, low heat input, low residual stress, small substrate penetration depth and high cladding efficiency. It is widely used for surface strengthening coating of metal parts.
  • Layer preparation and additive manufacturing Chinese invention patent [CN 107099793 A] discloses a laser cladding cobalt alloy coating to improve the wear resistance of heavy-duty wheel rails, which uses a high power laser to melt cobalt alloy powder Cover the surface of the wheel rail to reduce the surface friction coefficient, improve wear resistance and extend its service life.
  • a high carbon needle martensite structure is generated in the heat affected zone of the rail.
  • the martensite structure has high hardness, but the toughness is low, which is easy to cause the risk of breakage. Therefore, the martensite structure in the rail has been prohibited in the railway industry standard TB/T2344-2003.
  • the martensite structure in the rail has been prohibited in the railway industry standard TB/T2344-2003.
  • the high laser scanning rates due to the high cooling rate of the cladding layer and the heat-affected zone and the large temperature gradient with the rail substrate, cracks in the cladding layer and the heat-affected zone are easily caused, which affects the safe operation of the train.
  • the patent document discloses an automatic powder feeding laser induction composite cladding method and device, which adopts laser and induction heat source composite processing, can not only greatly improve the cladding efficiency, but also can solve the alloying material with poor weldability.
  • the problem of easy cracking during laser cladding does not consider how to reduce and avoid the martensitic transformation in the heat-affected zone when cladding the coating on large high carbon steel substrates (such as rails), as well as in specific service environments (roller-rail rolling contact) Under the technical problems of the cladding layer, the heat affected zone and the mechanical properties of the substrate.
  • the invention provides a method for efficiently preparing a high-performance cladding layer on a rail surface by using a laser-assisted heat source to achieve the purpose of strengthening and repairing the surface of the rail.
  • the laser and the auxiliary heat source simultaneously act on the rail to be processed, which not only avoids the cracking phenomenon of the cladding layer and the heat-affected zone at high scanning rate, but also avoids the generation of harmful structures such as martensite in the heat-affected zone, ensuring melting.
  • the mechanical properties of the coating, heat affected zone and matrix are well matched.
  • the invention can be used for preparing the high-performance cladding layer on the rail surface to improve the wear resistance and contact fatigue performance of the rail, and can also be used for solving problems such as poor railway shunt and repair of damaged rail.
  • the invention provides a laser-assisted heat source high-efficiency composite cladding reinforced steel rail method, which utilizes a laser and an auxiliary heat source to simultaneously act on a surface of a rail surface to be welded, and the laser as a main heat source enables the cladding layer material and the surface material of the rail surface portion to be fast.
  • the auxiliary heat source is located in front of or/and behind the laser heat source, moves at the same speed as the laser heat source, and synchronously preheats or/and afterheats the laser molten pool, the laser heat affected zone and the surface layer of the rail base to Reduce the cooling rate of the laser bath and heat affected zone, avoid the martensite transformation in the heat affected zone and the cracking of the cladding and heat affected zone at high laser scanning rate.
  • the laser and the auxiliary heat source can reasonably adjust the temperature cycle curve of the heat affected zone of the laser through a composite action, so that the cooling time is greater than the continuous cooling curve (CCT curve) and the isothermal transition curve (TTT curve) of the rail material.
  • the critical cooling time of the transition of austenite to pearlite satisfies the critical condition of complete transformation of austenite to pearlite.
  • the microstructure of the heat-affected zone is transformed into a sheet-like pearlite with a sheet spacing less than or equal to the base of the rail, and the hardness is between cladding. Between the layer and the substrate, the mechanical properties between the cladding layer, the heat affected zone and the substrate are reasonably matched, the hardness curve is distributed smoothly, and the overall fatigue performance is good.
  • the auxiliary heat source adopts any one or a combination of induction heating, oxyacetylene flame and propane torch; the preheating temperature is 100-1000 ° C, and the post-heating temperature is 300-700 ° C;
  • the thickness of the metal cladding layer obtained by single processing is 0.1-2mm and the width is 3-20mm.
  • the hardness of the cladding layer can be adjusted within the range of HV250-HV500 according to the specific requirements of the track; the width of the laser heat affected zone is less than 1mm.
  • the hardness is HV250-HV400, which can avoid martensite transformation in the heat-affected zone; the induction heating is realized by induction power supply and induction coil.
  • the induction coil is bent and welded by a copper tube, and a magnet is embedded in the copper tube of the working area.
  • the lower surface of the copper tube is parallel to the rail cladding surface, and the gap is 0.5-15 mm; the heating surface is “long” along the length of the rail.
  • the font structure has a length of 10-500mm.
  • the laser and the auxiliary heat source use the automatic powder feeder to synchronously feed or preset the coating material on the laser irradiation area of the rail surface.
  • the laser beam is focused, it is incident on the rail substrate to form a molten pool.
  • the molten pool is solidified,
  • the surface of the rail forms a cladding layer;
  • the auxiliary heat source acts on the rail for preheating, postheating and preheating + postheating, the preheating temperature is 100-1000 ° C, and the post-heating temperature is 300-700 ° C;
  • the surface of the corrosion-resistant cladding layer is inspected by using penetration or ultrasonic flaw detection to ensure that the cladding layer has no metallurgical defects;
  • the rail tread is cleaned and profiled to make the surface smooth.
  • the above cladding material may be an iron-based alloy, and the main chemical composition is (Wt.%): (0.01-0.60) C, (10-40) Cr, (5-18) Ni, (0.1-3.0) Si, ( 0-3) B, (0-3) Mo, (1-3) Mn, Fe balance;
  • the above cladding material may be a nickel-based alloy, and the main chemical composition is (Wt.%): (0.01-0.50) C, (20-30) Cr, (5-10) W, (3-5) Si, ( 0-3) B, (5-10) Fe, Ni balance;
  • the above cladding material may be a cobalt-based alloy, and the main chemical composition is (Wt.%): (0.01-0.5) C, (20-35) Cr, (1-10) Ni, (1-3) Si, ( 5-15) W, (0-3) B, (0.5-2) Mn, Co balance.
  • the laser and the auxiliary heat source act on the surface of the rail to be welded at the same time.
  • the high-energy laser beam causes the cladding material and the thin surface material of the rail surface to be rapidly melted to form a molten pool, and the auxiliary heat source is applied to the laser molten pool, the heat affected zone and the rail base surface.
  • Synchronous preheating and post-heating are performed to reduce the temperature gradient of the molten pool, the heat-affected zone and the rail matrix, thereby reducing the cooling rate and avoiding cracking and spalling of the metal cladding layer and the heat-affected zone under high-speed laser scanning;
  • the temperature cycle curve of the heat affected zone can be reasonably controlled, and the cooling time is greater than the CCT curve and the TTT curve.
  • the critical cooling time of the body-to-pearl transformation, satisfying the critical condition of complete transformation of austenite to pearlite, and the heat-affected zone is transformed into a fine-grained pearlite structure with a sheet spacing less than or equal to the rail base, and the hardness is between the cladding layer and Between the substrates, the mechanical properties between the cladding layer, the heat-affected zone and the substrate are reasonably matched, the hardness curve is smooth, and the overall fatigue performance is good.
  • the laser energy density is high and the heat affected zone is small.
  • the heating width and depth of the induction coil and other auxiliary heat sources are only larger than the heat affected zone width to eliminate the martensite structure.
  • the heat input is small, the residual stress and deformation of the rail processing are small, and the stability is high; the device has good flexibility and high processing precision, and can repair the damaged rails with different degrees.
  • the cladding layer has a low dilution rate, especially for thinner coatings.
  • the thickness of the cladding layer is less than 0.5 mm, the dilution ratio of the coating is less than 5%, and the wear resistance and corrosion resistance of the cladding layer can be ensured.
  • the energy required to form the molten pool is greatly reduced.
  • the deposition rate of the cladding layer can reach 10-250 g/min, and the scanning speed reaches 0.4-30 m/min.
  • the deposition efficiency is increased by 3-15 times;
  • the invention has strong versatility, and can directly prepare a wear-resistant, corrosion-resistant cladding layer and a fatigue-resistant cladding layer with uniform composition and mechanical properties matching on the surface of the rail, and can also repair the locally damaged rail.
  • the hardness distribution curve of the strengthened or repaired rail along the depth direction is smooth, the mechanical properties of the cladding layer, the heat affected zone and the substrate are matched with each other, and the overall fatigue performance is good, and the coating peeling phenomenon does not occur during the service.
  • the various process components used in the method of the invention have high integration degree and are easy to integrate with related processing platforms, and can be used for fixed laser processing machines, offline processing, and mobile laser processing equipment (for example, mobile lasers). Processing car), in-line processing reinforcement or repair at the railway site.
  • FIG. 1 is a top view of a laser-inductive post-thermal composite cladding of a rail surface prior to induction heating of a laser spot;
  • FIG. 2 is a top view of laser-inductive preheating + post-induction thermal composite cladding of a rail surface in which the laser spot is positioned in the middle of induction heating;
  • Figure 3 is a top view of the surface of the rail surface laser-induction heating + oxyacetylene flame (or laser-induction heating + propane torch) heating composite cladding;
  • Figure 4 is a top view of a composite cladding of a laser-oxyacetylene flame (or laser-propane torch) on a rail surface;
  • FIG. 5 is a hardness distribution diagram of a Fe-based metal cladding layer rail prepared in a depth direction after laser-induction thermal composite cladding;
  • FIG. 6 is a hardness distribution diagram of a Ni-based metal clad layer rail prepared by laser-induction preheating + post-induction thermal composite cladding in a depth direction;
  • FIG. 7 is a hardness distribution diagram of a Co-based metal clad layer rail prepared by laser-induction heating + oxyacetylene flame (or laser-induction heating + propane torch) heating composite cladding.
  • FIG. 8 is a hardness distribution diagram of a Fe-based metal clad layer rail prepared by laser-oxyacetylene flame (or laser-propane torch) composite cladding in the depth direction;
  • the invention uses the laser as the main heat source to weld the alloy material on the surface of the rail, and the auxiliary heat source preheats or/and heats the rail to reduce the cooling rate of the cladding layer and the heat affected zone, and can be efficiently prepared on the surface of the rail with wear resistance. Functional coating for fatigue and corrosion resistance or repair of damaged rails.
  • the thickness of the cladding layer obtained in a single process is 0.1-2 mm.
  • the hardness can be adjusted in the range of HV250-HV500 according to the specific requirements of the track.
  • the invention provides a laser-assisted heat source high-efficiency composite cladding method for reinforcing steel rails, and the auxiliary heat source can be combined with induction heating, oxyacetylene flame, propane torch or induction heating and oxyacetylene flame (or propane torch).
  • the invention method can be integrated with the fixed laser processing equipment, and the steel rail can be processed offline, or integrated with the vehicle-mounted laser processing platform, and the rail can be processed or strengthened or repaired on the railway site.
  • the implementation steps include:
  • the laser and auxiliary heat source and use the automatic powder feeder to synchronously feed (or preset) the alloy powder material into the laser irradiation area of the rail surface.
  • the laser beam After the laser beam is focused, it is incident on the rail substrate to form a molten pool, and the molten pool is solidified.
  • the auxiliary heat source acts on the rail for preheating, postheating and preheating + postheating, the preheating temperature is 100-1000 ° C, and the post-heating temperature is 300-700 ° C;
  • the surface of the corrosion-resistant cladding layer is inspected by using penetration or ultrasonic flaw detection to ensure that the cladding layer has no metallurgical defects;
  • the rail tread surface is cleaned and profiled to make the surface flat, that is, the finished product is obtained.
  • Embodiment 1 Railway online laser-induction thermal efficient composite cladding
  • the service rail is efficiently strengthened and repaired at the railway site, induction heating is used as an auxiliary heat source, and the machining motion and position control unit adopts an industrial manipulator or a three-dimensional motion axis.
  • the area to be welded on the rail surface is heated by the induction heating assembly and the temperature control mechanism, as well as the control of the heating temperature and time.
  • the induction heating component comprises an inductive power supply and an induction coil
  • the temperature control mechanism comprises an infrared thermometer and a temperature controller, an induction coil and an inductive power connection, an infrared thermometer and a temperature controller, and the temperature controller and the inductive power supply are connected through the data line. .
  • the detection signal of the infrared thermometer is input to the temperature controller.
  • the temperature controller After the calculation, the temperature controller outputs a control signal to adjust the output power of the induction heating power source to realize the control of the rail induction heating temperature.
  • the laser spot is focused on the front of the induction coil, as shown in Figure 1.
  • the metal cladding layer is prepared on the surface of the rail by laser-induction post-thermal composite cladding. The basic implementation steps are as follows:
  • the laser spot is a circular spot with a diameter of 3 mm
  • the powder feeding amount of the powder feeder is 10 g/min
  • the laser power is 1 kW
  • the laser scanning speed is 0.4 m/min.
  • the automatic powder feeder is used to synchronously feed the powder material (or preset) to the laser irradiation area of the rail surface. After the laser beam is focused, it is incident on the rail substrate to form a molten pool. After the molten pool is solidified, a metal coating is formed on the surface of the rail. ;
  • the surface of the metal coating is detected by penetration or ultrasonic inspection to ensure that the cladding layer has no metallurgical defects
  • the rail treads are cleaned and profiled to make the surface flat, that is, the finished product is obtained.
  • the thickness of the iron-based metal cladding layer prepared in this example is 0.1 mm, and the mechanical properties between the cladding layer, the heat-affected zone and the rail substrate are reasonably matched, and the hardness distribution along the depth direction of the rail is as shown in FIG.
  • Example 2 Railway online laser-induction preheating + induction heat efficient composite cladding
  • the service rail is efficiently strengthened and repaired at the railway site, and induction heating is used as an auxiliary heat source.
  • the induction heating control mechanism is the same as that of the first embodiment, and the machining movement and position control unit adopts an industrial robot or a three-dimensional motion axis.
  • the laser spot is focused on the middle of the induction coil.
  • the metal cladding layer is prepared on the surface of the rail by laser-induction preheating + post-induction thermal composite cladding.
  • Nickel-based alloy powder as cladding material, the main chemical composition is (Wt.%): (0.01-0.50)C, (20-30)Cr, (5-10)W, (3-5)Si , (0-3) B, (5-10) Fe, Ni balance;
  • the laser spot is a rectangle of 1 ⁇ 6 mm
  • the powder feeding amount of the powder feeder is 50 g/min
  • the laser power is 5 kW
  • the laser scanning speed is 2 m/min.
  • the automatic powder feeder is used to synchronously feed the powder material (or preset) to the laser irradiation area of the rail surface. After the laser beam is focused, it is incident on the rail substrate to form a molten pool. After the molten pool is solidified, a metal cladding layer is formed on the surface of the rail. ;
  • the surface of the metal coating is detected by penetration or ultrasonic inspection to ensure that the cladding layer has no metallurgical defects
  • the rail tread is cleaned and profiled to make the surface flat, that is, the finished product is obtained.
  • the induction coil consists of two parts, 4(a) and 4(b), which are connected by copper tubes, 4(a) acts to preheat the rails, and 4(b) acts to delay the cooling of the rails.
  • the role of the rate In practical applications, under the premise of reasonable matching of mechanical properties, the cladding efficiency can be effectively improved, which is conducive to energy conservation.
  • the thickness of the obtained nickel-based metal cladding layer is 0.5 mm, and the mechanical properties between the cladding layer, the heat-affected zone and the rail substrate are reasonably matched, and the hardness distribution along the depth direction of the rail is as shown in FIG. 6.
  • Example 3 Off-line rail surface laser-induction heating + oxyacetylene flame (propane torch) heating efficient composite cladding
  • This example provides off-line reinforcement and repair of the rail, induction heating and oxyacetylene flame (or propane torch) as an auxiliary heat source.
  • the laser spot is focused on the front of the induction coil, and the oxyacetylene flame (or propane torch) preheats the rail to be welded.
  • the laser and the induction coil move in the same direction at the same speed, and the induction heating is applied to the rail laser molten pool.
  • the laser beam is a rectangle of 3 ⁇ 30 mm, the powder feeding amount of the powder feeder is 250 g/min, the laser power is 20 kW, and the laser scanning speed is 30 m/min;
  • the surface of the metal coating is detected by penetration or ultrasonic inspection to ensure that the cladding layer has no metallurgical defects
  • the rail tread is cleaned and profiled to make the surface flat, that is, the finished product is obtained.
  • the thickness of the cobalt-based metal cladding layer prepared in this example is 2 mm, and the mechanical properties between the cladding layer, the heat-affected zone and the rail substrate are reasonably matched, and the hardness distribution along the depth direction of the rail is as shown in FIG.
  • Example 4 Off-line rail surface laser-oxyacetylene flame (propane torch) heating efficient composite cladding
  • the rail is strengthened and repaired off-line, and an oxyacetylene flame (or propane torch) is selected as an auxiliary heat source.
  • a metal cladding layer is prepared on the surface of the rail by laser-oxyacetylene flame (or laser-propane torch) composite cladding, as shown in FIG. 4, and the basic implementation steps are as follows:
  • thermometer using an oxyacetylene flame/propane torch to preheat the rail surface to be welded, the infrared thermometer is aimed at the heating surface of the rail surface, and the preheating temperature of the rail surface is monitored to be 800 ° C - 1000 ° C;
  • the laser use the automatic powder feeder to synchronously feed (or preset on) the laser irradiation area of the rail surface, and focus the laser beam on the rail substrate to form a molten pool.
  • the surface of the rail is formed with a metal coating; at the same time, the oxyacetylene flame/propane torch is used to heat the rail after the surface is welded, and the infrared temperature is monitored after the infrared thermometer is 300-400 ° C, and the oxyacetylene flame/propane torch is turned off after the holding time is reached;
  • the surface of the metal coating is detected by penetration or ultrasonic inspection to ensure that the cladding layer has no metallurgical defects
  • the rail tread surface is cleaned and profiled to make the surface flat, that is, the finished product is obtained.
  • the thickness of the iron-based metal cladding layer prepared in this example is 2 mm, and the mechanical properties between the cladding layer, the heat-affected zone and the rail substrate are reasonably matched, and the hardness distribution along the depth direction of the rail is as shown in FIG.

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Abstract

一种激光-辅助热源高效复合熔覆强化钢轨的方法，激光与辅助热源同时作用于钢轨表面待熔覆区域，激光作为主要热源使熔覆层材料和钢轨表面部分基底材料同时快速熔融形成熔池，辅助热源与激光热源同向同速移动，对激光熔池、热影响区及钢轨基底表层进行同步预热或/和后热，降低其温度梯度，从而降低其冷却速率，避免了热影响区马氏体转变以及开裂现象，可在铁路钢轨现场表面在线熔覆金属层，也可在生产车间对钢轨表面实现熔覆加工。

Description

一种激光-辅助热源高效复合熔覆强化钢轨的方法 【技术领域】
本发明属于材料加工领域，具体涉及一种采用激光-辅助热源复合熔覆在钢轨表面高效制备金属熔覆层的方法。该方法可用于提高钢轨耐磨性和接触疲劳性能，也可用于解决铁路分路不良以及损伤钢轨的修复等。
【背景技术】
我国轨道交通发展迅速，截至2016年底，全国铁路运营里程达12.4万公里。随着铁路运输量和列车速度及轴重的增加，钢轨的损伤问题日益凸显，如钢轨磨损、滚动接触疲劳和钢轨腐蚀等。钢轨的损伤主要发生在表面，所以在钢轨的表面制备覆层对于延长其使用寿命具有重要的意义。
热喷涂、电镀和堆焊是目前在钢轨表面制备金属覆层的主要方法。热喷涂和电镀涂层与钢轨基底呈机械结合，结合力弱，在轮轨摩擦过程中容易脱落。堆焊层与钢轨基底为冶金结合，但是该方法热输入和热影响区大，堆焊层组织结构与性能均匀性差，且在钢轨基体内部易诱发马氏体组织。
与等离子弧和电弧堆焊相比，激光熔覆具有能量密度高、热影响区小、热输入小、残余应力低、基底熔深小、熔覆效率高等优点，广泛应用于金属零件表面强化涂层的制备以及增材制造等，中国发明专利[CN 107099793 A]公开了一种激光熔覆钴合金涂层提高重载轮轨耐磨性的方法，该方法利用高功率激光将钴合金粉末熔覆在轮轨的表面，以降低其表面摩擦系数，提高耐磨性，延长其使用寿命。但是，由于激光的快速加热和快速冷却作用，在钢轨热影响区会产生高碳针状马氏体组织。马氏体组织硬度高，但是韧性低，易导致断轨风险，所以在铁路行业标准TB/T2344-2003中一直禁止钢轨中存在马氏体组织。其次，在高激光扫描速率下，由于熔覆层与热影响区冷却速率高及与钢轨基底的温度梯度大，容易导致熔覆层和热影 响区产生裂纹，影响列车的安全运营。
将高能激光束和辅助热源结合起来，实现复合加工，可以有效解决上述问题。专利文献(公开号CN101125394 A)公开了一种自动送粉激光感应复合熔覆方法及装置，采用激光和感应热源复合加工，不但可以大幅度提高熔覆效率，还可以解决焊接性差的合金材料在激光熔覆过程中易开裂的难题。但是，该方法并未考虑在大型高碳钢基底(如钢轨)上熔覆涂层时，如何减少和避免热影响区马氏体相变的问题，以及在特定的服役环境(轮轨滚动接触)下，熔覆层、热影响区和基底力学性能匹配等技术问题。
【发明内容】
本发明提供了一种采用激光-辅助热源在钢轨表面高效制备高性能熔覆层的方法，以实现钢轨表面强化以及修复等目的。激光与辅助热源同时作用于钢轨待熔覆加工面，不仅可避免在高扫描速率下熔覆层及热影响区的开裂现象，还可避免在热影响区产生马氏体等有害组织，确保熔覆层、热影响区及基体力学性能匹配良好。本发明可用于钢轨表面高性能熔覆层的制备，以提高钢轨耐磨性能和接触疲劳性能，也可以用于解决铁路分路不良和损伤钢轨的修复等问题。
本发明提供的一种激光-辅助热源高效复合熔覆强化钢轨的方法，利用激光与辅助热源同时作用于钢轨表面待熔覆区域，激光作为主要热源使熔覆层材料和钢轨表面部分基底材料快速熔融形成熔池，辅助热源位于激光热源的前方或/和后方，与激光热源同向同速移动，对激光熔池、激光热影响区及钢轨基底表层进行同步预热或/和后热，以降低激光熔池和热影响区的冷却速率，避免热影响区马氏体转变以及高激光扫描速率下熔覆层及热影响区的开裂现象。
作为上述技术方案的改进，所述激光与辅助热源通过复合作用合理调控激光作用热影响区的温度循环曲线，使其冷却时间大于钢轨材料连续冷 却曲线(CCT曲线)和等温转变曲线(TTT曲线)中奥氏体向珠光体转变的临界降温时间，满足奥氏体向珠光体完全转变的临界条件，热影响区组织转变为片间距小于或等于钢轨基底的片状珠光体，硬度介于熔覆层和基底之间，使熔覆层、热影响区和基底三者之间力学性能合理匹配，硬度曲线分布光滑，整体疲劳性能良好。
作为上述技术方案的进一步改进，辅助热源采用感应加热、氧乙炔焰和丙烷喷灯中的任一种或任几种的组合；预热温度为100-1000℃，后热温度为300-700℃；单次加工获得的金属熔覆层厚度为0.1-2mm，宽度为3-20mm，熔覆层硬度可以根据轨道的具体要求，在HV250-HV500范围内可调；激光热影响区的宽度小于1mm，硬度为HV250-HV400，可避免热影响区马氏体转变；所述感应加热采用感应电源和感应线圈实现。其中，感应线圈由铜管弯折、焊接而成，工作区铜管上嵌有导磁体，铜管下表面与钢轨熔覆面平行，间隙为0.5-15mm；加热面沿着钢轨长度方向呈“一”字型结构，长度为10-500mm。
本发明方法的具体实现步骤为：
(1)先将钢轨表面待熔覆区域进行打磨处理，去除表面锈迹和污染物；
(2)调整激光束离焦量，将激光光斑设置为直径3～10mm的圆形或为(1～3)mm×(6～30)mm的矩形；
(3)调整激光光斑与辅助热源的相对位置，使光斑在辅助热源的前方、中间或后方；
(4)开启激光器和辅助热源，采用自动送粉器将涂层材料同步送入或预置于钢轨表面激光辐照区域，激光束聚焦后入射到钢轨基体上形成熔池，熔池凝固后在钢轨表面形成熔覆层；辅助热源对钢轨起到预热、后热和预热+后热的作用，预热温度为100-1000℃，后热温度为300-700℃；
(5)熔覆完一层金属熔覆层后，判断熔覆层厚度是否达到工况需求，如 果是，则结束熔覆过程；如果否，则重复上述步骤(2)(3)和(4)，直至达到满足需求的厚度；
(6)熔覆完之后采用渗透或者超声探伤检测耐蚀熔覆层表面，保证熔覆层无冶金缺陷；
(7)根据应用需求，选择对钢轨踏面进行清理和廓形修整，使表面平整。
上述熔覆层材料可以是铁基合金，主要化学成分为(Wt.％):(0.01-0.60)C,(10-40)Cr,(5-18)Ni,(0.1-3.0)Si,(0-3)B,(0-3)Mo,(1-3)Mn,Fe余量；
上述熔覆层材料可以是镍基合金，主要化学成分为(Wt.％)：(0.01-0.50)C,(20-30)Cr,(5-10)W,(3-5)Si,(0-3)B,(5-10)Fe,Ni余量；
上述熔覆层材料可以是钴基合金，主要化学成分为(Wt.％)：(0.01-0.5)C，(20-35)Cr,(1-10)Ni,(1-3)Si,(5-15)W,(0-3)B,(0.5-2)Mn,Co余量。
本发明具有以下优点：
①激光与辅助热源同时作用于钢轨表面待熔覆区域，高能激光束使熔覆层材料和钢轨表面薄层材料同时快速熔融形成熔池，辅助热源对激光熔池、热影响区及钢轨基底表面进行同步预热及后热作用，降低熔池、热影响区和钢轨基体的温度梯度，从而降低其冷却速率，避免金属熔覆层及热影响区在激光高速扫描下的开裂及剥落现象；
②通过调整激光与辅助热源的相对位置、激光加工功率、激光扫描速率以及辅助热源对钢轨的加热温度，可合理控制热影响区温度循环曲线，使其冷却时间大于CCT曲线和TTT曲线中奥氏体向珠光体转变的临界降温时间，满足奥氏体向珠光体完全转变的临界条件，热影响区转变为片间距小于或等于钢轨基底的细片状珠光体组织，硬度介于熔覆层和基底之间，使熔覆层、热影响区和基底三者之间力学性能合理匹配，硬度曲线分布光滑，整体疲劳性能良好。
③与等离子弧和电弧等其他方法相比，激光能量密度高、热影响区小， 感应线圈及其他辅助热源的加热宽度及深度仅大于其热影响区宽度即可消除其马氏体组织，整体热输入小，使钢轨加工残余应力和变形小、稳定性高；装置柔性好，加工精度高，可对不同程度损伤钢轨进行修复。
④熔覆层稀释率低，尤其是对于较薄涂层熔覆时更有效。当熔覆层厚度小于0.5mm时，涂层稀释率小于5％，能够保证熔覆层的耐磨性和耐蚀性。
⑤由于辅助热源的引入，形成熔池所需能量大大降低。当激光功率为1-20kW时，熔覆层的沉积速率可达到10-250g/min，扫描速度达到0.4-30m/min。与单纯激光熔覆工艺相比，沉积效率提高3-15倍；
本发明通用性强，可直接在钢轨表面高效制备成分均匀、力学性能匹配的耐磨、耐蚀熔覆层以及耐疲劳熔覆层等，也可进行局部损伤钢轨的修复。强化或修复后的钢轨沿深度方向硬度分布曲线平滑，熔覆层、热影响区和基底的力学性能相互匹配，整体疲劳性能良好，在服役过程中不会发生涂层脱落现象。同时，本发明方法所采用的各个工艺组件集成度高，便于和相关的加工平台集成，既可用于固定式激光加工机床，进行离线加工，也可应用于移动式激光加工设备(例如移动式激光加工车)，在铁路现场进行在线加工强化或修复。
【附图说明】
图1为激光光斑定位在感应加热前的钢轨表面激光-感应后热复合熔覆俯视图；
图2为激光光斑定位在感应加热中间的钢轨表面激光-感应预热+感应后热复合熔覆俯视图；
图3为钢轨表面激光-感应加热+氧乙炔焰(或激光-感应加热+丙烷喷灯)加热复合熔覆俯视图；
图4为钢轨表面激光-氧乙炔焰(或激光-丙烷喷灯)加热复合熔覆俯 视图；
图5为激光-感应后热复合熔覆制备的Fe基金属熔覆层钢轨沿深度方向的硬度分布图；
图6为激光-感应预热+感应后热复合熔覆制备的Ni基金属熔覆层钢轨沿深度方向的硬度分布图；
图7为激光-感应加热+氧乙炔焰(或激光-感应加热+丙烷喷灯)加热复合熔覆制备的Co基金属熔覆层钢轨沿深度方向的硬度分布图。
图8为激光-氧乙炔焰(或激光-丙烷喷灯)复合熔覆制备的Fe基金属熔覆层钢轨沿深度方向的硬度分布图；
图中，1、激光光斑，2、感应加热线圈，2(a)、感应预热线圈，2(b)、感应后热线圈，3、氧乙炔(或丙烷喷灯)火焰。
【具体实施方式】
下面结合附图对本发明的具体实施方式作进一步说明。在此需要说明的是，对于这些实施方式的说明用于帮助理解本发明，但并不构成对本发明的限定。此外，下面所描述的本发明各个实施方式中所涉及到的技术特征只要彼此之间未构成冲突就可以相互组合。
本发明以激光为主要热源在钢轨表面熔覆合金材料，辅助热源对钢轨进行预热或/和后热以降低熔覆层及热影响区的冷却速率，可在钢轨表面高效制备具有耐磨、耐疲劳和耐蚀性能的功能覆层或进行损伤钢轨的修复，单次加工获得的熔覆层厚度为0.1-2mm，硬度可以根据轨道的具体要求，在HV250-HV500范围可调。同时，采用本发明提出的技术路线，在钢轨的热影响区不会产生马氏体，熔覆层与钢轨基底力学性能合理匹配，使钢轨得到强化修复的同时，具有较好的弯曲疲劳和接触疲劳性能。下面结合附图和实例对本发明做进一步说明。
本发明提出的一种激光-辅助热源高效复合熔覆强化钢轨的方法，辅助 热源可采用感应加热、氧乙炔焰、丙烷喷灯或者感应加热与氧乙炔焰(或丙烷喷灯)组合等。该发明方法既可与固定式激光加工装备集成，对钢轨进行离线加工，也可与车载式激光加工平台集成，在铁路现场对钢轨进行在线加工强化或修复等。其实施步骤包括：
(1)先将钢轨表面待熔覆区域进行打磨处理，去除表面锈迹和污染物；
(2)调整激光束离焦量，将激光光斑设置为直径3～20mm的圆形或为(1～3)mm×(6～30)mm的矩形；
(3)调整激光光斑与辅助热源的相对位置，使光斑在辅助热源的前方、中间或后方；
(4)开启激光器和辅助热源，采用自动送粉器将合金粉末材料同步送入(或预置于)钢轨表面激光辐照区域，激光束聚焦后入射到钢轨基体上形成熔池，熔池凝固后在钢轨表面形成金属涂层；辅助热源对钢轨起到预热、后热和预热+后热的作用，预热温度为100-1000℃，后热温度为300-700℃；
(5)熔覆完一层金属熔覆层后，判断熔覆层厚度是否达到工况需求，如果是，则结束熔覆过程；如果否，则重复上述步骤(2)(3)和(4)，直至满足需求的厚度；
(6)熔覆完之后采用渗透或者超声探伤检测耐蚀熔覆层表面，保证熔覆层无冶金缺陷；
(7)根据应用需求选择对钢轨踏面进行清理和廓形修整，使表面平整，即得到成品。
实例：
实施例一：铁路在线激光-感应后热高效复合熔覆
本实例在铁路现场对服役钢轨进行高效强化和修复，感应加热作为辅助热源，加工运动与位置控制单元采用工业机械手或三维运动轴。通过感应加热组件和温度控制机构对钢轨表面待熔覆区域进行加热，以及加热温 度和时间的控制。感应加热组件包括感应电源和感应线圈，温度控制机构包括红外测温仪和温度控制器，感应线圈和感应电源连接，红外测温仪和温度控制器连接，温度控制器与感应电源通过数据线相连。红外测温仪的检测信号输入温度控制器，经过运算后，温度控制器输出控制信号对感应加热电源的输出功率进行调节，实现对钢轨感应加热温度的控制。激光光斑聚焦于感应线圈的前方，如图1所示。通过激光-感应后热复合熔覆在钢轨表面制备金属熔覆层，其基本实施步骤如下：
(1)选择铁基合金粉末为熔覆材料，主要化学成分为(Wt.％):(0.01-0.60)C,(10-40)Cr,(5-18)Ni,(0.1-3.0)Si,(0-3)B,(0-3)Mo,(1-3)Mn,Fe余量。
(2)先将钢轨表面熔覆区域进行打磨处理，去除表面锈迹和污染物；
(3)调整感应线圈的位置，使其下表面与钢轨表面待熔覆区域平行，间隙为5mm；红外测温仪瞄准铁轨表面感应加热区域，红外测温仪与温度控制器和感应电源连接，对感应加热温度进行检测和控制，设置感应加热温度为700℃；
(4)调整激光束离焦量以及激光光斑与感应线圈的相对位置，使激光光斑聚焦于感应线圈前方的钢轨表面。激光光斑为直径3mm的圆形光斑，送粉器送粉量为10g/min，激光功率为1kW，激光扫描速度为0.4m/min。
(5)开启运动控制单元、激光器和感应加热电源。采用自动送粉器将熔覆材料同步送粉(或预置于)钢轨表面激光辐照区域，激光束聚焦后入射到钢轨基体上形成熔池，熔池凝固后即在钢轨表面形成金属涂层；
(6)熔覆一层后，判断熔覆层厚度是否达到工况需求，如果是，则结束熔覆过程；如果否，则重复上述(2)(3)(4)(5)过程，直至满足厚度要求；
(7)熔覆完之后采用渗透或者超声探伤检测金属涂层表面，保证熔覆层无冶金缺陷；
(8)根据应用需求，对钢轨踏面进行清理和廓形修整，使表面平整，即 得到成品。
该实例中制得的铁基金属熔覆层厚度为0.1mm，熔覆层、热影响区和钢轨基底之间力学性能合理匹配，沿钢轨深度方向的硬度分布如图5所示。
实施例二：铁路在线激光-感应预热+感应后热高效复合熔覆
本实例在铁路现场对服役钢轨进行高效强化和修复，感应加热作为辅助热源，感应加热控制机构与实施例一相同，加工运动与位置控制单元采用工业机械手或三维运动轴。激光光斑聚焦于感应线圈的中间，如图2所示，通过激光-感应预热+感应后热复合熔覆在钢轨表面制备金属熔覆层，其基本实施步骤如下：
(1)选择镍基合金粉末为熔覆材料，主要化学成分为(Wt.％)：(0.01-0.50)C,(20-30)Cr,(5-10)W,(3-5)Si,(0-3)B,(5-10)Fe,Ni余量；
(2)先将钢轨表面熔覆区域进行打磨处理，去除表面锈迹和污染物；
(3)调整感应线圈的位置，使其下表面与钢轨表面待熔覆区域平行，间隙为0.5mm；红外测温仪瞄准铁轨表面感应加热区域，红外测温仪与温度控制器和感应电源连接，对感应加热温度进行检测和控制，设置感应加热温度为500℃；
(4)调整激光束离焦量以及激光光斑与感应线圈的相对位置，使激光光斑聚焦于感应线圈前方的钢轨表面。激光光斑为1×6mm的矩形，送粉器送粉量为50g/min，激光功率为5kW，激光扫描速度为2m/min。
(5)开启运动控制单元、激光器和感应加热电源。采用自动送粉器将熔覆材料同步送粉(或预置于)钢轨表面激光辐照区域，激光束聚焦后入射到钢轨基体上形成熔池，熔池凝固后在钢轨表面形成金属熔覆层；
(6)熔覆完一层后，判断熔覆层厚度是否达到工况需求，如果是，则结束熔覆过程；如果否，则重复上述(2)(3)(4)(5)过程，直至满足厚度要求；
(7)熔覆完之后采用渗透或者超声探伤检测金属涂层表面，保证熔覆层 无冶金缺陷；
(8)根据应用需求，对钢轨踏面进行清理和廓形修整，使表面平整，即得到成品。
该实例中，感应线圈由4(a)和4(b)两个部分组成，两者由铜管连接，4(a)起到对钢轨预热的作用，4(b)起到延缓钢轨降温速率的作用。在实际应用中，在力学性能合理匹配的前提下，可以有效的提高熔覆效率，利于节能。制得的镍基金属熔覆层厚度为0.5mm，熔覆层、热影响区和钢轨基底之间力学性能合理匹配，沿钢轨深度方向的硬度分布如图6所示。
实施例三：离线式钢轨表面激光-感应加热+氧乙炔焰(丙烷喷灯)加热高效复合熔覆
本实例对钢轨进行离线式强化和修复，感应加热和氧乙炔焰(或丙烷喷灯)作为辅助热源。激光光斑聚焦于感应线圈的前方，氧乙炔焰(或丙烷喷灯)对钢轨待熔覆面进行预热，如图3所示，激光与感应线圈同向同速运动，感应加热对钢轨激光熔池和热影响区进行同步后热，其基本实施步骤如下：
(1)选择钴基合金粉末为熔覆材料，主要化学成分为(Wt.％)：(0.01-0.5)C，(20-35)Cr,(1-10)Ni,(1-3)Si,(5-15)W,(0-3)B,(0.5-2)Mn,Co余量；
(2)先将钢轨表面熔覆区域进行打磨处理，去除表面锈迹和污染物；
(3)调整感应线圈的位置，使其下表面与钢轨表面待熔覆区域平行，间隙为15mm；红外测温仪瞄准铁轨表面感应加热区域，红外测温仪与温度控制器和感应电源连接，对感应加热温度进行检测和控制，设置感应加热温度为300℃；
(4)调整激光束离焦量以及激光光斑与感应线圈的相对位置，使激光光斑聚焦于感应线圈前方的钢轨表面。激光光束为3×30mm的矩形，送粉器送粉量为250g/min，激光功率为20kW，激光扫描速度为30m/min；
(5)采用氧乙炔焰/丙烷喷灯对钢轨待熔覆面预热，红外测温仪6-2瞄准钢轨表面加热区域，监测钢轨表面预热温度达到100℃-200℃后，关闭氧乙炔焰/丙烷喷灯装置；
(6)开启激光器和感应加热电源，采用自动送粉器将熔覆材料同步送粉(或预置于)钢轨表面激光辐照区域，激光束聚焦后入射到钢轨基体上形成熔池，熔池凝固后在钢轨表面形成金属熔覆层；
(7)熔覆完一层后，判断熔覆层厚度是否达到工况要求。如果是，则结束熔覆过程；如果否，则重复上述(3)(4)(5)(6)过程，直至满足需求的厚度；
(8)熔覆完之后采用渗透或者超声探伤检测金属涂层表面，保证熔覆层无冶金缺陷；
(9)根据应用需求，对钢轨踏面进行清理和廓形修整，使表面平整，即得到成品。
该实例中制得的钴基金属熔覆层厚度为2mm，熔覆层、热影响区和钢轨基底之间力学性能合理匹配，沿钢轨深度方向的硬度分布如图7所示。
实施例四：离线式钢轨表面激光-氧乙炔焰(丙烷喷灯)加热高效复合熔覆
本实例对钢轨进行离线式强化和修复，选择氧乙炔焰(或丙烷喷灯)作为辅助热源。通过激光-氧乙炔焰(或激光-丙烷喷灯)复合熔覆在钢轨表面制备金属熔覆层，如图4所示，其基本实施步骤如下：
(1)选择铁基合金粉末为熔覆材料，主要化学成分为(Wt.％):(0.01-0.60)C,(10-40)Cr,(5-18)Ni,(0.1-3.0)Si,(0-3)B,(0-3)Mo,(1-3)Mn,Fe余量；
(2)先将钢轨表面熔覆区域进行打磨处理，去除表面锈迹和污染物；
(3)调整激光束为直径20mm的圆形，激光器的功率为15kW，送粉速率为180g/min，扫描速度为10m/min；
(4)采用氧乙炔焰/丙烷喷灯对钢轨待熔覆面预热，红外测温仪瞄准铁轨表面加热区域，监测钢轨表面预热温度为800℃-1000℃；
(5)开启激光器，采用自动送粉器将合金粉末材料同步送入(或预置于)钢轨表面激光辐照区域，激光束聚焦后入射到钢轨基体上形成熔池，熔池凝固后即在钢轨表面形成金属涂层；同时，采用氧乙炔焰/丙烷喷灯对钢轨熔覆面后热，红外测温仪监测后热温度为300-400℃，达到保温时间后关闭氧乙炔焰/丙烷喷灯；
(6)熔覆完一层后，判断熔覆层厚度是否达到工况需求，如果是，则结束熔覆过程；如果否，则重复上述(3)(4)(5)过程，直至满足厚度要求；
(7)熔覆完之后采用渗透或者超声探伤检测金属涂层表面，保证熔覆层无冶金缺陷；
(8)根据应用需求选择对钢轨踏面进行清理和廓形修整，使表面平整，即得到成品。
该实例中制得的铁基金属熔覆层厚度为2mm，熔覆层、热影响区和钢轨基底之间力学性能合理匹配，沿钢轨深度方向的硬度分布如图8所示。
以上所述为本发明的较佳实施例而已，但本发明不应该局限于该实施例和附图所公开的内容。所以凡是不脱离本发明所公开的精神下完成的等效或修改，都落入本发明保护的范围。

Claims (10)

  1. 一种激光-辅助热源高效复合熔覆强化钢轨的方法，其特征在于，该方法利用激光与辅助热源同时作用于钢轨表面待熔覆区域，激光作为主要热源使所添加的粉末材料和钢轨表面部分基底材料同时快速熔融形成熔池并形成熔覆层，辅助热源位于激光热源的前方或/和后方，与激光热源同向同速移动，对激光熔池、激光热影响区及钢轨基底表层进行同步预热或/和后热，降低激光熔池和热影响区与钢轨基底间的温度梯度，从而降低其冷却速率，避免激光热影响区马氏体转变以及高激光扫描速率下熔覆层及热影响区的开裂现象。
  2. 根据权利要求1所述的一种激光-辅助热源高效复合熔覆强化钢轨的方法，其特征在于：所述激光与辅助热源通过复合作用合理调控激光作用热影响区的热循环过程，使其在冷却时间大于CCT曲线或TTT曲线中奥氏体向珠光体转变的临界降温时间，满足奥氏体向珠光体完全转变的临界条件，热影响区转变为片间距小于或等于钢轨基底的细片状珠光体组织，硬度介于熔覆层和基底之间，使熔覆层、热影响区和基底三者之间力学性能合理匹配，硬度曲线分布光滑，整体疲劳性能良好。
  3. 根据权利要求1或2所述的一种激光-辅助热源高效复合熔覆强化钢轨的方法，其特征在于：辅助热源采用感应加热、氧乙炔焰和丙烷喷灯中的任一种或任几种的组合。
  4. 根据权利要求1或2所述的一种激光-辅助热源高效复合熔覆强化钢轨的方法，其特征在于：预热温度为100-1000℃，后热温度为300-700℃。
  5. 根据权利要求1或2所述的一种激光-辅助热源高效复合熔覆强化钢轨的方法，其特征在于：单次加工获得的金属熔覆层厚度为0.1-2mm，宽度为3-20mm，熔覆层硬度根据轨道的具体要求，在HV250-HV500范围内调控。
  6. 根据权利要求1或2所述的一种激光-辅助热源高效复合熔覆强化钢轨的方法，特征在于：激光热影响区的宽度小于1mm，硬度为HV250-HV400，热影响区内没有马氏体转变。
  7. 根据权利要求1或2所述的一种激光-辅助热源高效复合熔覆强化钢轨的方法，其特征在于：该方法的具体实现步骤为：
    (1)先将钢轨表面待熔覆区域进行打磨处理，去除表面锈迹和污染物；
    (2)调整激光束离焦量，将激光光斑设置为直径3～20mm的圆形或为(1～3)mm×(6～30)mm的矩形；
    (3)调整激光光斑与辅助热源的相对位置，使光斑在辅助热源的前方、中间或后方；
    (4)开启激光器和辅助热源，采用自动送粉器将涂层材料同步送入或预置于钢轨表面激光辐照区域，激光束聚焦后入射到钢轨基体上形成熔池，熔池凝固后在钢轨表面形成金属熔覆层；辅助热源对钢轨起到预热、后热和预热+后热的作用，预热温度为100-1000℃，后热温度为300-700℃；
    (5)熔覆完一层金属熔覆层后，判断熔覆层厚度是否达到工况需求，如果是，则结束熔覆过程；如果否，则重复上述步骤(2)(3)和(4)，直至达到满足需求的厚度；
    (6)熔覆完之后采用渗透或者超声探伤检测耐蚀熔覆层表面，保证熔覆层无冶金缺陷；
    (7)根据应用需求，选择对钢轨踏面进行清理和廓形修整，使表面平整。
  8. 根据权利要求1或2所述的一种激光-辅助热源高效复合熔覆强化钢轨的方法，其特征在于：该方法与固定式加工平台集成，实现钢轨的离线加工，或者与钢轨在线移动激光加工车集成，在铁路现场对钢轨进行在线激光熔覆强化或修复。
  9. 根据权利要求3所述的一种激光-辅助热源高效复合熔覆强化钢轨 的方法，其特征在于，所述感应加热通过采用感应电源和感应线圈实现。其中，感应线圈由铜管弯折、焊接而成，工作区铜管上嵌有导磁体，铜管下表面与钢轨熔覆面平行，间隙为0.5-15mm；加热面呈“一”字型结构，与钢轨长度方向平行，长度为10-500mm。
  10. 根据权利要求1或2所述的一种激光-辅助热源高效复合熔覆强化钢轨的方法，其特征在于，所述熔覆材料为铁基合金，主要化学成分为(Wt.％):(0.01-0.60)C,(10-40)Cr,(5-18)Ni,(0.1-3.0)Si,(0-3)B,(0-3)Mo,(1-3)Mn,Fe余量；或者
    所述熔覆材料为镍基合金或钴基合金，镍基合金的主要化学成分为(Wt.％)：(0.01-0.50)C,(20-30)Cr,(5-10)W,(3-5)Si,(0-3)B,(5-10)Fe,Ni余量；钴基合金的主要化学成分为(Wt.％)：(0.01-0.5)C，(20-35)Cr,(1-10)Ni,(1-3)Si,(5-15)W,(0-3)B,(0.5-2)Mn,Co余量。
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