Method for reinforcing rail by laser and auxiliary heat source efficient hybrid cladding

Abstract

The disclosure discloses a method for reinforcing a rail by laser and auxiliary heat source efficient hybrid cladding. The laser and the auxiliary heat source simultaneously apply on a region to be cladded of a rail surface. The laser serves as a main heat source to enable simultaneous and rapid fusion of an added metal powder and partial substrate material in the rail surface to form a molten pool. The auxiliary heat source moves with the laser heat source in the same direction at the same speed, and performs synchronous preheating and/or post-heating on the laser molten pool, the heat-affected zone and the surface layer of the rail substrate to reduce the temperature gradient, thereby reducing the cooling rate, and avoiding martensite transformation and cracking in the heat-affected zone.

1 . A method for reinforcing a rail by laser and auxiliary heat source efficient hybrid cladding, wherein in the method, a laser and an auxiliary heat source are utilized to simultaneously apply on a region to be cladded of a rail surface; the laser serves as a main heat source to enable rapid fusion of an added powder material and a partial substrate material on the rail surface to form a molten pool and then to form a cladded coating; the auxiliary heat source is located in front of or/and behind the main heat source, moves with the main heat source in the same direction at the same speed, and performs synchronous preheating and/or post-heating on the molten pool, a heat-affected zone and a surface layer of a rail substrate to reduce a temperature gradient between the molten pool and heat-affected zone and the rail substrate, thereby reducing a cooling rate of the molten pool and heat-affected zone, and avoiding martensite transformation in the laser-heat-affected zone and generation of cracks in the cladded coating and the heat-affected zone at a high laser scanning rate. 
     
     
         2 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 1 , wherein a thermal cycle process of the heat-affected zone under laser action is reasonably regulated by the combined action of the laser and the auxiliary heat source such that a cooling time of the heat-affected zone is larger than a critical cooling time of transformation from austenite to pearlite in a continuous cooling transformation (CCT) curve or a time-temperature-transformation (TTT) curve, thereby meeting critical conditions of complete transformation from austenite to pearlite, and allowing the heat-affected zone to be transformed into a fine lamellar pearlite structure which has an interlamellar spacing less than or equal to that of the rail substrate and has a hardness between hardnesses of the cladded coating and the rail substrate, so that mechanical properties between the cladded coating, the heat-affected zone and the rail substrate are reasonably matched, the hardness curve is smooth, and the overall fatigue performance is good. 
     
     
         3 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 1 , wherein the auxiliary heat source adopts any one of induction heating, oxyacetylene flame and propane torch, or any combination thereof. 
     
     
         4 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 1 , wherein a preheating temperature is 100-1000° C., and a post-heating temperature is 300-700° C. 
     
     
         5 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 1 , wherein the cladded coating obtained by single processing has a thickness of 0.1-2 mm, a width of 3-20 mm, and a hardness which is controlled within a range of HV250 to HV500 according to specific requirements of the rail. 
     
     
         6 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 1 , wherein the heat-affected zone has a width of less than 1 mm and a hardness of HV250 to HV400, and there is no martensite transformation in the heat-affected zone. 
     
     
         7 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 1 , wherein the method comprises following specific implementation steps of:
 (1) polishing the region to be cladded of the rail surface first to remove surface rust and contaminants;   (2) adjusting a defocusing distance of a laser beam to allow a laser spot to be a circular spot with a diameter of 3-20 mm or a rectangular spot with a size of (1-3) mm×(6-30) mm;   (3) adjusting relative position of the laser spot and the auxiliary heat source such that the laser spot is in front of, in the middle of or behind the auxiliary heat source;   (4) turning on the laser and the auxiliary heat source, and synchronously feeding or pre-placing a coating material into a laser irradiation region of the rail surface by using an automatic powder feeder, so that the molten pool is formed when the focused laser beam is incident on the rail substrate, and then the cladded coating is formed on the rail surface after the molten pool is solidified, wherein the auxiliary heat source plays a role of preheating and/or post-heating the rail, with a preheating temperature of 100-1000° C. and a post-heating temperature of 300-700° C.;   (5) after a layer of the cladded coating is formed, determining whether a thickness of the cladded coating meets working conditions, and if so, ending the cladding process; if not, repeating the above steps (2), (3) and (4) until the thickness requirements are met;   (6) after the cladding process is finished, inspecting the surface of the corrosion-resistant cladded coating by penetration or ultrasonic inspection, to ensure that there are no metallurgical defects in the cladded coating; and   (7) selectively performing cleaning and profile trimming on a rail tread to make its surface flat.   
     
     
         8 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 1 , wherein the method is integrated with a fixed processing platform to perform off-line processing of the rail, or integrated with an on-line mobile laser processing vehicle to perform on-line laser cladding reinforcement or repair of the rail at a railway site. 
     
     
         9 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 3 , wherein the induction heating is implemented by an induction power supply and an induction coil; wherein the induction coil is formed by bending and welding a copper tube, a magnet is embedded on the copper tube in a working area, a lower surface of the copper tube is parallel to a cladded surface of the rail, with a gap of 0.5-15 mm; a heating zone on the rail surface has a linear structure, which is parallel to a longitudinal direction of the rail and has a length of 10-500 mm. 
     
     
         10 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 1 , wherein the added powder material is an iron-based alloy, main chemical compositions of which are: 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 and Fe balance; or
 the added powder material is a nickel-based alloy or a cobalt-based alloy, wherein main chemical compositions of the nickel-based alloy are: 0.01-0.50% C, 20-30% Cr, 5-10% W, 3-5% Si, 0-3% B, 5-10% Fe and Ni balance; and main chemical compositions of the cobalt-based alloy are: 0.01-0.5% C, 20-35% Cr, 1-10% Ni, 1-3% Si, 5-15% W, 0-3% B, 0.5-2% Mn and Co balance.   
     
     
         11 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 2 , wherein the auxiliary heat source adopts any one of induction heating, oxyacetylene flame and propane torch, or any combination thereof. 
     
     
         12 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 2 , wherein a preheating temperature is 100-1000° C., and a post-heating temperature is 300-700° C. 
     
     
         13 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 2 , wherein the cladded coating obtained by single processing has a thickness of 0.1-2 mm, a width of 3-20 mm, and a hardness which is controlled within a range of HV250 to HV500 according to specific requirements of the rail. 
     
     
         14 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 2 , wherein the heat-affected zone has a width of less than 1 mm and a hardness of HV250 to HV400, and there is no martensite transformation in the heat-affected zone. 
     
     
         15 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 2 , wherein the method comprises following specific implementation steps of:
 (1) polishing the region to be cladded of the rail surface first to remove surface rust and contaminants;   (2) adjusting a defocusing distance of a laser beam to allow a laser spot to be a circular spot with a diameter of 3-20 mm or a rectangular spot with a size of (1-3) mm×(6-30) mm;   (3) adjusting relative position of the laser spot and the auxiliary heat source such that the laser spot is in front of, in the middle of or behind the auxiliary heat source;   (4) turning on the laser and the auxiliary heat source, and synchronously feeding or pre-placing a coating material into a laser irradiation region of the rail surface by using an automatic powder feeder, so that the molten pool is formed when the focused laser beam is incident on the rail substrate, and then the cladded coating is formed on the rail surface after the molten pool is solidified, wherein the auxiliary heat source plays a role of preheating and/or post-heating the rail, with a preheating temperature of 100-1000° C. and a post-heating temperature of 300-700° C.;   (5) after a layer of the cladded coating is formed, determining whether a thickness of the cladded coating meets working conditions, and if so, ending the cladding process; if not, repeating the above steps (2), (3) and (4) until the thickness requirements are met;   (6) after the cladding process is finished, inspecting the surface of the corrosion-resistant cladded coating by penetration or ultrasonic inspection, to ensure that there are no metallurgical defects in the cladded coating; and   (7) selectively performing cleaning and profile trimming on a rail tread to make its surface flat.   
     
     
         16 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 2 , wherein the method is integrated with a fixed processing platform to perform off-line processing of the rail, or integrated with an on-line mobile laser processing vehicle to perform on-line laser cladding reinforcement or repair of the rail at a railway site. 
     
     
         17 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 11 , wherein the induction heating is implemented by an induction power supply and an induction coil; wherein the induction coil is formed by bending and welding a copper tube, a magnet is embedded on the copper tube in a working area, a lower surface of the copper tube is parallel to a cladded surface of the rail, with a gap of 0.5-15 mm; a heating zone on the rail surface has a linear structure, which is parallel to a longitudinal direction of the rail and has a length of 10-500 mm. 
     
     
         18 . The method for reinforcing the rail by laser and auxiliary heat source efficient hybrid cladding according to  claim 2 , wherein the added powder material is an iron-based alloy, main chemical compositions (by weight percentage) of which are: 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 and Fe balanc; or
 the added powder material is a nickel-based alloy or a cobalt-based alloy, wherein main chemical compositions (by weight percentage) of the nickel-based alloy are: 0.01-0.50% C, 20-30% Cr, 5-10% W, 3-5% Si, 0-3% B, 5-10% Fe and Ni balance; and main chemical compositions (by weight percentage) of the cobalt-based alloy are: 0.01-0.5% C, 20-35% Cr, 1-310% Ni, 1-3% Si, 5-15% W, 0-3% B, 0.5-2% Mn and Co balance.