WO2020238724A1 - 用于贝氏体钢轨焊后接头热处理的施工方法及其冷却装置 - Google Patents

用于贝氏体钢轨焊后接头热处理的施工方法及其冷却装置 Download PDF

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WO2020238724A1
WO2020238724A1 PCT/CN2020/091284 CN2020091284W WO2020238724A1 WO 2020238724 A1 WO2020238724 A1 WO 2020238724A1 CN 2020091284 W CN2020091284 W CN 2020091284W WO 2020238724 A1 WO2020238724 A1 WO 2020238724A1
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Prior art keywords
cooling
rail
bainite
welded
joint
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PCT/CN2020/091284
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English (en)
French (fr)
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白威
李大东
邓健
陆鑫
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攀钢集团攀枝花钢铁研究院有限公司
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Publication of WO2020238724A1 publication Critical patent/WO2020238724A1/zh

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    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
    • C21D9/505—Cooling thereof

Definitions

  • the invention relates to a construction method, in particular to a construction method for heat treatment of a joint after welding of a bainite rail, and belongs to the technical field of rail rolling production technology.
  • the invention also relates to a rail head profiling cooling device used in the construction method.
  • Bainite rail has been a research hotspot in countries all over the world in recent decades. Because of its high strength, toughness, wear resistance and long service life, it is expected to replace traditional pearlite rails. It is widely used in railway turnout components and small-scale heavy-duty lines. Radius curve segment. At this stage, seamless rails have become an inevitable trend. As an important process in the seamless process of rails, the quality of rail welding is directly related to the service life of railway lines and even driving safety. During the service process of the rail, the welding quality and the complexity of the actual operating conditions of the line make the fracture of the welded long rail mostly occur in the welded joint, so the welded joint has become the weak link of the seamless line.
  • the austenite grains in the superheated zone of the rail welding are coarse, resulting in the hardness of this zone being significantly lower than the base material.
  • the current domestic railway industry standards TB/T1632.2-2014 "Rail Welding Part 2: Flash Welding” and TB/T1632.4-2014 "Rail Welding Part 4: Air Pressure Welding” stipulate that for heat-treated rails, the welding area
  • the average hardness of the steel rail base metal shall not be less than 90% of the average hardness of the rail base metal, and the microstructure of the weld and heat-affected zone shall not contain harmful structures such as martensite or bainite.
  • the above two rail welding standards are all pearlitic rails, but there is no welding standard for bainite rails at home and abroad.
  • the chemical composition of bainite rails is generally: C content 0.20-0.30 wt%, Si content 0.8-1.8 wt%, Mn content 1.5-2.5 wt%, Cr content 0.50-1.60 wt%, Mo content 0.20-0.50 wt%.
  • the existing patent technology with the application number 201210394058.X and the invention name "Heat treatment method of bainite rail” discloses a heat treatment method of bainite rail.
  • the method includes natural cooling of the finished rail to make The surface temperature of the rail head is reduced to 460-490°C; the rail is forced to cool at a cooling rate of 2.0-4.0°C/s to reduce the surface temperature of the rail head to 250-290°C; the temperature of the rail naturally rises to the rail head The surface temperature reaches above 300°C; the steel rail is placed in a heating furnace with a furnace temperature of 300-350°C for tempering for 2-6 hours; the steel rail is air-cooled to room temperature.
  • the purpose of the invention is to obtain a bainite rail with good comprehensive mechanical properties, which belongs to a heat treatment process for rail production, and is not suitable for a post-weld heat treatment process method for a welded joint of a non-bainite rail.
  • the application number is 201810480790.6, and the existing patent technology with the title of “heat treatment type bainite rail welded joint post-weld heat treatment method” discloses a method for post-weld heat treatment of bainite welded joint. After cooling the joint tread surface temperature to the temperature range of 850 ⁇ 500°C, air-cool the rail head part of the joint. When the surface temperature of the tread surface cools to 270 ⁇ 210°C, the air cooling is finished and the joint is allowed to cool to room temperature naturally. In this invention, the joint is directly air-cooled after the bainite rail is welded. There is no heating process after the rail is welded, and the effect of heat treatment is open to question.
  • the bainite rail involved in the master's thesis "Research on the Microstructure and Damage of Bainite Rail Joints” by Zhao Guo of the Chinese Academy of railway Sciences belongs to a different composition system from the bainite rail of the present invention. It can be seen from the table below that the contents of Si, Ni, Cr, and Mo in the two kinds of bainite rail base materials are significantly different. For rails with different composition systems, the corresponding post-weld heat treatment processes are also completely different.
  • the railway engineering field urgently needs a post-weld heat treatment method to ensure the service life of the rail welded joint by controlling the tread hardness of the bainite rail welded joint within a reasonable range to ensure the bainite rail Service performance of welded joints and railway operation safety.
  • the technical problem to be solved by the present invention is to provide a construction method for heat treatment of the bainite rail welded joint that can control the tread hardness of the bainite rail welded joint within a reasonable range, and a construction method for the heat treatment of the bainite rail welded joint.
  • Rail head copy cooling device for construction method is provided.
  • the technical solution adopted to solve the above technical problems is: a construction method for heat treatment of the post-welded bainite rail joint, the construction method is to weld the bainite welded rail with a temperature not lower than 1100 °C Based on the joint, the post-weld heat treatment of the bainite rail welded joint is completed by successively cooling the bainite rail welded joint three times in sequence with the cooling rate gradually slowing down.
  • the second cooling adopts rapid cooling using compressed air or water mist mixture as the cooling medium.
  • the compressed air or water mist mixture is quickly sprayed to the surface of the welded joint through the rail head copy cooling device, and its spray pressure is at Between 0.40 ⁇ 0.80MPa, the distance between the nozzle and the rail head tread is between 20 ⁇ 50mm, and the final cooling temperature of the second cooling is 290 ⁇ 400°C, which is also the starting cooling temperature of the third cooling.
  • the final cooling temperature of the first cooling is 550-750°C, which is also the starting cooling temperature of the second cooling.
  • the preferred mode of the above solution is that both the first cooling and the third cooling adopt natural cooling in the air.
  • the cooling rate of the first cooling is 3.0 to 5.0°C/s
  • the cooling rate of the second cooling is 1.5 to 2.5°C/s
  • the cooling rate of the third cooling is 0.05 to 0.50°C/s.
  • the preferred mode of the above scheme is that the initial cooling temperature of the first cooling is 1100-1400°C, and the final cooling temperature of the third cooling is 10-30°C.
  • the starting cooling temperature and final cooling temperature are both the temperature of the rail head tread collected by an infrared thermometer.
  • the welded joint of the bainite rail is a flash welded joint or an air pressure welded joint
  • the rail type is a heavy rail with a rail type of 60-75 kg/m.
  • the rail head profiling cooling device includes a rail top spray cooling component and a rail head side spray cooling component, and the welds and heats of the rail welding joints that need cooling
  • the base material in the affected zone and its vicinity is rapidly cooled by the cooling medium sprayed by the rail top cooling nozzle of the rail top spray cooling module and the rail side cooling nozzle of the rail head side spray cooling module.
  • the rail top spray cooling assembly further includes a rail top refrigerant delivery pipe and a rectangular parallelepiped nozzle cavity, and the rail top refrigerant delivery pipe communicates with the rectangular parallelepiped nozzle cavity from the top.
  • the bottom surface of the rectangular parallelepiped nozzle cavity is provided with the rail top cooling nozzle, and the length of the rectangular parallelepiped nozzle cavity is greater than the sum of the length of the rail welded joint, the heat-affected zone and the nearby base materials that need to be cooled on both sides;
  • the rail head side spray cooling assembly also includes a rail-side refrigerant delivery pipe and a tubular nozzle cavity.
  • the rail-side refrigerant delivery pipe communicates with the tubular nozzle cavity from the top and faces the tubular nozzle cavity.
  • the rail side cooling nozzle is arranged on the side of the rail head side, and the length of the tube nozzle cavity is greater than the sum of the length of the rail welded joint, the heat-affected zone and the nearby base materials that need to be cooled on both sides .
  • the rail head profiling cooling device further includes a profiling frame, and the rail top spray cooling assembly and the rail head side spray cooling assembly are both arranged on the profiling frame.
  • the beneficial effect of the present invention is that the technical solution provided by the present application uses sequential cooling with a gradually slowing down three cooling rates during the heat treatment process to weld the completed bainite welded rail with a post-weld temperature of not less than 1100°C
  • the joint is heat-treated, so that the longitudinal hardness of the rail joint of the bainite rail welded joint within ⁇ 25mm from the center of the weld can be effectively controlled to 80-85% of the average hardness of the rail base material, and the joint welds on both sides
  • the width of the softened zone is less than 20.0mm; and can control the physical fatigue life of the bainite rail welded joint to be no less than 2.5 million times, which is higher than the TB/T1632.2-2014 and TB/T1632.4-2014 standards 2 million times, and control the percentage of martensite that may appear in the metallographic structure of the bainite rail welded joint to ⁇ 5%.
  • the hardness of the bainite rail welded joint and its adjacent tread after the post-weld heat treatment construction method of this application is between 80-85% of the average hardness of the rail base material, and the width of the softened zone on both sides of the joint weld All are controlled to be less than 20.0mm, which can also effectively avoid the "saddle-shaped" wear and wheel-rail impact of the rail during long-term use, thereby eliminating the accumulation factors that seriously affect the service life of the rail, so as to extend the service life of the rail and ensure the railway The purpose of operational safety.
  • Figure 1 is an effect diagram of longitudinal hardness at a position 5mm below the rail head tread of a rail welded joint under post-weld heat treatment conditions obtained by using the method in Example 1;
  • Figure 2 is an effect diagram of longitudinal hardness at a position 5mm below the rail head tread of a rail welded joint under post-weld heat treatment conditions obtained by using the method in Example 2;
  • Figure 3 is an effect diagram of longitudinal hardness at a position 5mm below the rail head tread of a bainite rail welded joint under air-cooling conditions after welding obtained by using the method in Comparative Example 1;
  • Figure 4 is an effect diagram of longitudinal hardness at a position 5mm below the rail head tread of a bainite rail welded joint under the conditions of post-weld heat treatment obtained by using the method in Comparative Example 2;
  • Fig. 5 is a schematic diagram of longitudinal hardness detection at a position 5mm below the rail head tread of the bainite rail welded joint of the present invention
  • Fig. 6 is a schematic diagram of the sampling position of the metallographic sample of the rail head tread of the rail welding joint of the present invention.
  • Fig. 7 is a schematic diagram and a three-dimensional structure diagram of the rail head profiling cooling device used in the present invention.
  • the device only cools the rail head tread and the side surface of the rail head, and its aperture can be designed and processed according to actual needs to achieve different cooling strengths.
  • the pressure of the gas flowing through the compressed air or water mist mixture channel 1 and the compressed air or water mist mixture channel 2 can be monitored by the relevant pressure detection device, and flows through the compressed air or water mist mixture channel 1 and the compressed air or water mist
  • the gas pressure of the mixed gas channel 2 is adjusted according to actual needs.
  • the left side is a schematic diagram of the rail head profiling cooling device, and the right side is a three-dimensional structure diagram of the rail head profiling cooling device.
  • the cuboid structure on the top surface of the rail in the original drawing is the above-mentioned cuboid shape.
  • the compressed air channel connected to the rectangular nozzle cavity in the figure is the above-mentioned rail top refrigerant delivery pipe; the long tube structure located on the side of the rail head in the original picture is the above-mentioned tubular nozzle cavity.
  • the compressed air channel connected to the tubular nozzle cavity in the figure is the above-mentioned rail head side refrigerant delivery pipe; in the original drawing, the rectangular parallelepiped nozzle cavity and the tubular nozzle cavity are connected into a four-claw structure. It is the above-mentioned copy frame.
  • the present invention provides a construction method for heat treatment of the bainite rail welded joint that can control the tread hardness of the bainite rail welded joint within a reasonable range.
  • the said construction method is based on the bainite welded rail welded joint with a temperature not lower than 1100°C obtained by welding, and the post-welding of the bainite welded rail welded joint is completed by successively cooling the welded joints of the bainite steel rails successively through three successive cooling speeds.
  • the final cooling temperature of the second cooling is 290-400°C, which is also the starting cooling temperature of the third cooling.
  • the technical solution provided by this application uses sequential cooling with the three cooling rate gradually slowed down during the heat treatment process to heat the welded bainite welded rail welded joints with a post-weld temperature of not less than 1100°C.
  • the hardness of the bainite rail welded joint and its adjacent tread after the post-weld heat treatment construction method of this application is between 80-85% of the average hardness of the rail base material, and the width of the softened zone on both sides of the joint weld All are controlled to be less than 20.0mm, which can also effectively avoid the "saddle-shaped" wear and wheel-rail impact of the rail during long-term use, thereby eliminating the accumulation factors that seriously affect the service life of the rail, so as to extend the service life of the rail and ensure the railway
  • the bainite rail base metal structure is usually a complex structure composed of bainite and martensite, which results in the inevitable process of rapid heating and rapid cooling during the welding of bainite rails. The formation of martensite.
  • the brittle and hard martensite structure is harmful to the service performance of the rail, but the influence of martensite on the service performance of the bainite rail is still inconclusive. Therefore, usually by adjusting the rail welding and post-weld heat treatment process to minimize the brittle and hard martensite structure may have a negative impact on the service performance of the bainite rail.
  • the welded joint based on the bainite rail is a flash welded joint or an air pressure welded joint, and the rail type is 60 ⁇ 75kg/m
  • the specific requirements of each process step in this application are as follows.
  • the final cooling temperature of the first cooling is 550-750°C, which is also the starting cooling temperature of the second cooling; both the first cooling and the third cooling are carried out in air Natural cooling; secondary cooling is rapid cooling using a cooling medium; the cooling medium is compressed air or water mist mixture; the compressed air or water mist mixture is quickly sprayed to the welding through the rail head profile cooling device
  • the spray pressure on the joint surface is between 0.40 ⁇ 0.80MPa, and the distance between the nozzle and the rail head tread is between 20 ⁇ 50mm;
  • the cooling rate of the first cooling is 3.0 ⁇ 5.0°C/s, and the cooling rate of the second cooling is 1.5 ⁇ 2.5 °C/s, the cooling rate of the triple cooling is 0.05 ⁇ 0.50°C/s;
  • the initial cooling temperature is 1100 ⁇ 1400°C, and the final cooling temperature of the triple cooling is 10 ⁇ 30°C; in each cooling stage, the cooling Both the cold temperature and the final cold temperature are the temperatures of the rail head treads collected by an infrared thermometer.
  • using the welding heat treatment construction method of the present application to process the welded joint of the bainite rail can achieve the purpose of ensuring the fatigue life of the rail welded joint by reasonably controlling the longitudinal hardness of the rail head tread of the welded joint. This helps to improve the "saddle-shaped" wear and wheel-rail impact caused by the low hardness of the rail welding area during the railway operation process, prolong the service life of the rail and ensure the safety of railway operation.
  • the longitudinal hardness of the rail head tread of the post-weld heat-treated bainite rail welded joint is controlled within a reasonable range of 80-85% of the average hardness of the rail base material.
  • heat-treated bainite rails have low tread hardness and poor toughness in the welding area after welding. Normalizing heat treatment is usually required to improve joint performance. However, after normalizing, the welded joint has low hardness and widened softening zone, which is easy to cause "saddle-shaped" wear during the service process of the welded joint, resulting in poor service performance. Based on this, the work of the present invention finds and designs a post-weld heat treatment method for heat-treated bainite rails, which not only ensures the hardness of the joint tread, but also ensures the service life of the rail joint.
  • the "rail welded joint” is a welded welded seam and/or heat-affected zone including a region with a length ranging from 70 to 100 mm. The center of the region It is the weld of the rail.
  • the "room temperature” is a temperature in the range of 10 to 30°C.
  • the present invention provides a method for post-welding heat treatment of bainitic steel rails.
  • the method includes: performing a first stage cooling on a welded rail joint with a temperature above 1100°C at a first cooling rate to make the rail head surface of the rail joint The temperature is reduced to 570 ⁇ 750°C, and then the rail joint is cooled in the second stage at the second cooling rate to reduce the surface temperature of the rail head of the rail joint to 290 ⁇ 400°C, and finally the rail joint is carried out at the third cooling rate
  • the third stage of cooling is to reduce the surface temperature of the rail head surface of the rail joint to a room temperature of 10-30°C; wherein, the first cooling rate is 3.0-5.0°C/s, and the second cooling rate is 1.5-2.5°C/s. s, the third cooling rate is 0.05 to 0.50°C/s.
  • the object of the present invention is to provide a post-weld heat treatment method for bainitic steel rails, the method comprising: performing a first stage cooling of the welded rail joints with a temperature above 1100°C at a first cooling rate to make the rails of the rail joints
  • the head surface temperature is reduced to 550 ⁇ 750°C
  • the rail joint is cooled in the second stage at the second cooling rate to reduce the rail head surface temperature of the rail joint to 290 ⁇ 400°C
  • the rail joint is cooled at the third cooling rate
  • the third stage cooling is carried out to reduce the surface temperature of the rail head surface of the rail joint to a room temperature of 10-30°C.
  • the first stage cooling and the third cooling method are natural cooling in the air.
  • the second cooling is to use the rail head copy cooling device as shown in FIG. 7 to cool the rail head tread and the side surface of the rail joint with compressed air or water mist mixture as the cooling medium.
  • the cooling method of the first cooling and the third cooling is natural cooling in the air
  • the second cooling is a rail head profiling cooling device using compressed air or water mist mixture as cooling
  • the medium cools the rail head tread and the side of the rail head of the rail joint.
  • the distance between the cooling device and the rail head tread is 20-50mm; the compressed air or water mist mixture sprayed by the cooling device has a gas pressure of 0.05-0.5MPa.
  • an infrared thermometer is used to collect the temperature signal of the rail head tread, and the rail head tread is the contact part of the wheel and the rail.
  • the hardness value (0.9Hp) corresponding to the softening zone width measurement line in the longitudinal hardness curve of the rail joint is 90% of the average hardness Hp of the rail base material.
  • the softening zone width in the hardness curve is the intercept between the hardness curve and the softening zone width measurement line.
  • the bainite rails used for welding have the same rail shape, specifically a specification of 60-75kg/m, and the rail welded joint is a welded joint welded by a rail mobile flash welder using the same welding process .
  • the bainite steel rails are of the online heat treatment type, which are all produced by a certain steel group.
  • the cooling method for performing the first cooling and the third cooling is air cooling in which the welded joints of the bainite rails are directly placed in the air for natural cooling.
  • the second cooling method is rapid cooling using compressed air or water mist mixture as the cooling medium.
  • the invention uses the welding waste heat of the steel rail to realize the post-weld heat treatment process of the steel rail, and implements post-weld accelerated cooling for the steel rail joints with higher residual temperature obtained by welding, so as to reduce the phase transition temperature of the joint rail head area and improve the austenite recrystallization zone hardness.
  • the phase change The temperature gradually decreases. Therefore, even in the second stage of cooling when the cooling temperature is relatively low, the joint rail head can still undergo tissue transformation.
  • the first cooling is natural cooling in the air, which can be controlled by adjusting the temperature of the test environment (such as using central air-conditioning to control the temperature, etc.), and by adjusting the welding machine settings. Or manual operation is used to control the final cooling temperature of the first cooling of the rail welding joint at 550-750°C, and the opening cooling temperature of the second cooling is 550-750°C.
  • the final cooling temperature of the second cooling is lower than the martensite transformation start temperature (Ms temperature) of the bainite rail steel, and the final cooling temperature of the second cooling in the present invention is 290-400°C.
  • the cooling methods of the first cooling, the second cooling, and the second cooling may be cooling methods such as air cooling and air cooling.
  • the first cooling and the third cooling in the present invention preferably adopt air cooling
  • the second cooling method preferably adopts air cooling.
  • the post-weld heat treatment method for bainite rails of the present invention can be used for welded joints of bainite rails obtained by welding at various temperatures.
  • the present invention prefers the initial temperature of the welded joints of bainite rails obtained by welding. It is 1100-1400°C.
  • the model of the bainite rail is a PB2 online heat-treated bainite rail, which is produced by a certain steel group.
  • the post-weld heat treatment process method of the bainite rail welded joint of the present invention refers to TB/T1632.2-2014 "Rail Welding Part 2: Flash Welding” and TB/T1632.4-2014 "Rail Welding” Part 4: Air Pressure Welding
  • the rail welded joints are machined into longitudinal section hardness samples, and the longitudinal section Rockwell hardness test of the welded joints is performed at a position 5mm under the tread.
  • the measuring points are arranged symmetrically to the left and right sides with the weld as the center. , The measuring point spacing is 5mm, the Rockwell hardness method is carried out in accordance with GB/T230.1-2009, and the HRC scale is adopted.
  • Hp represents the average hardness of the rail base material
  • Hj represents the average hardness of the joint
  • the joint hardness is less than 0.9
  • the position of Hp indicates the softened area.
  • the MTS-FT310 fatigue testing machine is used to conduct three-point bending fatigue test on rail welded joints, and the pulsating bending fatigue test mode is adopted.
  • the load frequency is 7 Hz
  • the load ratio is 0.2
  • the maximum fatigue stress of the welded joint is 300 MPa.
  • the test target is that no fatigue fracture of the welded joint occurs when the cyclic load is loaded 3 million times.
  • the welded joint is subjected to post-weld heat treatment.
  • the welded rail joint with a residual temperature of 1100°C is cooled in the first stage at a first cooling rate of 4.5°C/s to reduce the surface temperature of the rail head of the rail joint to 700°C, and then the rail joint is heated to 2.0°C
  • the second cooling rate of 0.4°C/s performs the second stage cooling to reduce the surface temperature of the rail head of the rail joint to 200°C
  • the third stage cooling of the rail joint is performed at the third cooling rate of 0.4°C/s to reduce the temperature of the rail joint.
  • the surface temperature of the rail head is reduced to a room temperature of 25°C, thereby obtaining the post-weld heat-treated steel rail welded joint of the present invention.
  • the first cooling and the third cooling are natural cooling in the air
  • the second cooling is the use of a rail head profiling cooling device using compressed air or water mist mixture as the cooling medium for the rail head treads and rail joints.
  • the cooling device is 40mm away from the tread of the rail head.
  • the gas pressure of the compressed air or water mist mixture sprayed by the cooling device is 0.30 MPa.
  • An infrared thermometer is used to monitor the temperature of the rail head tread.
  • the bainite rail joint obtained in this example was machined into a longitudinal hardness sample, and the longitudinal Rockwell hardness test was performed on the welded joint at a position 5mm below the tread.
  • the measuring points were symmetrically arranged to the left and right sides with the weld as the center.
  • the dot pitch is 5mm.
  • the Rockwell hardness test method is carried out in accordance with GB/T 230.1-2009, and the HRC scale is adopted.
  • the longitudinal hardness data at the position 5mm below the rail head tread of the welded joint is shown in Table 1, and the longitudinal hardness distribution effect is shown in Figure 1.
  • the longitudinal hardness of the rail joint within ⁇ 25 mm from the weld center reaches 88% of the average hardness of the rail base material.
  • the width of the softening zone on both sides of the joint weld is 18.0mm, and the width of the softening zone on both sides of the joint weld is less than 20.0mm.
  • the welded joint is subjected to post-weld heat treatment.
  • the welded rail joints with a residual temperature of 1200°C are cooled in the first stage at a first cooling rate of 4.5°C/s to reduce the surface temperature of the rail head of the rail joint to 650°C, and then the rail joints are heated to 2.5°C.
  • the second cooling rate of 0.10°C/s is used for the second stage of cooling to reduce the surface temperature of the rail head of the rail joint to 180°C, and the third stage of cooling is performed at the third cooling rate of 0.10°C/s to reduce the temperature of the rail joint.
  • the surface temperature of the rail head is reduced to a room temperature of 25°C, thereby obtaining the post-weld heat-treated steel rail welded joint of the present invention.
  • the first cooling and the third cooling are natural cooling in the air
  • the second cooling is the use of a rail head profiling cooling device using compressed air or water mist mixture as the cooling medium for the rail head treads and rail joints.
  • the cooling device is 40mm away from the tread of the rail head.
  • the gas pressure of the water mist mixture sprayed by the cooling device is 0.60 MPa.
  • An infrared thermometer is used to monitor the temperature of the rail head tread.
  • the bainite rail welded joint obtained in this example was machined into a longitudinal hardness sample, and the welded joint was tested for longitudinal Rockwell hardness at a position 5mm below the tread.
  • the measuring points were symmetrically arranged to the left and right sides with the weld as the center.
  • the measuring point spacing is 5mm.
  • the Rockwell hardness test method is carried out in accordance with GB/T 230.1-2009, and the HRC scale is adopted.
  • the longitudinal hardness data at the position 5mm below the rail head tread of the welded joint is shown in Table 2, and the longitudinal hardness distribution effect is shown in Figure 2.
  • the longitudinal hardness of the rail joint in the area of ⁇ 25 mm from the weld center reaches 90% of the average hardness of the rail base material.
  • the width of the softening zone on both sides of the joint weld is 15mm on the left and 17.0mm on the right.
  • the width of the softening zone on both sides of the joint weld is less than 20.0mm.
  • the obtained rail joint is within ⁇ 25mm from the center of the weld.
  • the average hardness is 39.0HRC, which is 90% of the average hardness of the rail base material.
  • the width of the softening zone on both sides of the joint weld is 15mm on the left and 17.0mm on the right.
  • the width of the softening zone on both sides of the joint weld is less than 20.0mm.
  • the bainite rail welded joint sample obtained from this embodiment can pass the fatigue test with 2.3 million cycles, which is higher than the 2 million specified in TB/T1632.2-2014.
  • the rail joint with a residual temperature of 1200°C is directly air-cooled to room temperature (about 25°C), so as to obtain the air cooling (natural cooling) condition Rail welded joints.
  • the entire welded area is in a softened state compared with the hardness of the rail base material on both sides of the weld.
  • the average hardness of the obtained rail joint within ⁇ 25mm from the weld center is 35.8HRC, which reaches 83% of the average hardness of the rail base material, which is lower than the range of 80-85% of the average hardness of the rail base material.
  • the left and right sides of the joint weld
  • the width of the softened zone is 25.0mm.
  • the welded joint obtained from this comparative example tends to preferentially form a low rail head tread collapse in the softened area of the rail welded joint during line service, which affects the smoothness of the line and driving safety.
  • the welded joint is subjected to post-weld heat treatment.
  • the welded rail joint with a residual temperature of 1150°C is cooled in the first stage at a first cooling rate of 4.0°C/s to reduce the surface temperature of the rail head of the rail joint to 620°C, and then the rail joint is heated to 2.5°C.
  • the second cooling rate of 0.10°C/s is used for the second stage of cooling to reduce the surface temperature of the rail head surface of the rail joint to 130°C, and finally the rail joint is subjected to the third stage of cooling at a third cooling rate of 0.10°C/s to reduce the temperature of the rail joint.
  • the surface temperature of the rail head is reduced to a room temperature of 25°C, thereby obtaining the post-weld heat-treated steel rail welded joint of the present invention.
  • the first cooling and the third cooling are natural cooling in the air;
  • the second cooling is the use of rail head profile cooling device to use compressed air as the cooling medium to the rail head tread and rail head of the rail joint
  • the cooling device is 40mm away from the rail head tread; in the second cooling process, the gas pressure of the compressed air injected by the cooling device is 0.60MPa.
  • An infrared thermometer is used to monitor the temperature of the rail head tread.
  • the process method provided by the present invention can reduce the percentage of martensite structure that may appear in the metallographic structure of the bainite rail welded joint. Control it to ⁇ 5%, control the longitudinal hardness of the rail joint within ⁇ 25mm from the center of the weld to 80-85% of the average hardness of the rail base material, and the width of the softening zone on both sides of the joint weld is less than 20.0mm, which is helpful To improve the "saddle-shaped" wear of the rail welded joint caused by the low hardness of the welded area during the service of the rail. At the same time, the fatigue life of the bainite rail joint can be maintained at more than 2.5 million times, and the purpose of ensuring a higher fatigue life of the joint is achieved while ensuring the higher hardness of the joint.

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Abstract

一种用于贝氏体钢轨焊后接头热处理的施工方法及钢轨轨头仿型冷却装置，属于钢轨轧制生产工艺技术领域。以焊接获得的温度不低于1100℃的贝氏体焊接钢轨焊接接头为基础，先后分别通过三次冷却速度逐渐减慢的顺序冷却完成所述贝氏体钢轨焊接接头的焊后热处理工作，其中，二冷采用以压缩空气或水雾混合气为冷却介质的快速冷却，所述的压缩空气或水雾混合气通过钢轨轨头仿型冷却装置快速的喷射到焊接接头表面，其喷射压力在0.40～0.80MPa之间，喷嘴距轨头踏面的距离为20～50mm之间，二冷的终冷温度为290～400℃，该温度也是三冷的起冷温度。所述冷却装置包括轨顶喷冷组件和轨头侧面喷冷组件。所述方法能将贝氏体钢轨焊接接头的踏面硬度控制在合理范围内。

Description

用于贝氏体钢轨焊后接头热处理的施工方法及其冷却装置 技术领域
本发明涉及一种施工方法，尤其是涉及一种用于贝氏体钢轨焊后接头热处理的施工方法，属于钢轨轧制生产工艺技术领域。本发明还涉及一种用于所述施工方法的轨头仿型冷却装置。
背景技术
贝氏体钢轨为近几十年世界各国的研究热点，因其强韧性高、耐磨损及使用寿命长等特性而有望取代传统珠光体钢轨，广泛应用于铁路道岔部件及重载线路的小半径曲线段。现阶段，钢轨无缝化已成为必然趋势。作为钢轨无缝化环节中的一道重要工序，钢轨焊接的质量直接关系到铁路线路服役寿命，甚至行车安全。钢轨服役过程中，受焊接质量及线路实际运营条件复杂性的影响，使得焊接长轨条的断裂大多发生在焊接接头上，因而焊接接头成为了无缝线路的薄弱环节。
受熔化过程及高温影响，钢轨焊接过热区奥氏体晶粒粗大，导致该区域的硬度明显低于母材。软化后的钢轨焊接接头在服役过程中，易优先在接头轨头踏面部位形成“马鞍型”磨耗，增加了轮轨冲击，影响钢轨使用寿命，甚至危及行车安全。因此，国内现行铁道行业标准TB/T1632.2-2014《钢轨焊接 第2部分：闪光焊接》及TB/T1632.4-2014《钢轨焊接 第4部分：气压焊接》规定，对于热处理钢轨，焊接区域的平均硬度不得低于钢轨母材平均硬度的90％，且焊缝和热影响区的微观组织中不应有马氏体或贝氏体等有害组织。上述两项钢轨焊接标准所涉及的对象均为珠光体钢轨，而目前国内外尚无适用于贝氏体钢轨的焊接标准。因而，完全遵照国内现行钢轨焊接技术标准对贝氏体钢轨焊接接头的力学性能进行评估是不合适的，并且过高的焊接接头轨头踏面纵向硬度即高于钢轨母材平均硬度的90％的纵向硬度将导致接头疲劳性能下降，发生早期断裂。
贝氏体钢轨的化学成分一般为：C含量0.20-0.30重量％，Si含量0.8-1.8重量％，Mn含量1.5-2.5重量％，Cr含量0.50-1.60重量％，Mo含量0.20-0.50重量％。采用热处理工艺技术，基于细晶强化原理生产制造的贝氏体钢轨受焊接热循环作用后，焊缝区域的淬硬层消失并出现一较宽的低硬度区，导致焊缝及热影响区的硬度远低于钢轨母材，因而对贝氏体钢轨焊接接头进行焊后热处理就成了恢复钢轨焊接区域硬度的最有效手段。
目前，国内钢轨焊接完成后一般遵照TB/T1632.2-2014《钢轨焊接 第2部分：闪光 焊接》及TB/T1632.4-2014《钢轨焊接 第4部分：气压焊接》标准进行焊后正火热处理，以中频感应电加热或氧乙炔火焰加热作为热源将钢轨焊接接头加热至奥氏体化温度以上温度后，采取空冷或风冷工艺进一步提升钢轨焊接区域的踏面硬度。
申请号为201210394058.X，发明名称“贝氏体钢轨的热处理方法”的现有专利技术，公开了一种贝氏体钢轨的热处理方法，该方法包括将终轧后的钢轨自然冷却，以使钢轨轨头表层温度降至460-490℃；将钢轨以2.0-4.0℃/s的冷却速度强制冷却，以使钢轨轨头表层温度降至250-290℃；使钢轨温度自然回升直至钢轨轨头表层温度达到300℃以上；将钢轨置于炉膛温度为300-350℃的加热炉内回火处理2-6h；将钢轨空冷至室温。该发明的目的是为了获得综合力学性能良好的贝氏体钢轨，属于钢轨生产热处理工艺，其并不适合于非贝氏体钢轨焊接接头的焊后热处理工艺方法。
申请号为201810480790.6，发明名称“热处理型贝氏体钢轨焊接接头焊后热处理方法”的现有专利技术，公开了一种贝氏体焊接接头焊后热处理方法，该方法具体为将焊接得到的待冷却接头踏面表面温度冷却到850～500℃的温度区间后对接头的轨头部分进行风冷，当踏面表面温度冷却至270～210℃后结束风冷，让接头自然冷却至室温。该发明是在贝氏体钢轨完成焊接后直接对接头实施风冷，钢轨焊后无加热过程，热处理效果有待商榷。
中国铁道科学研究院赵国的硕士学位论文“贝氏体钢轨接头微观组织及伤损研究”中涉及的贝氏体钢轨与本发明中贝氏体钢轨属于不同的成分体系。由下表可见两种贝氏体钢轨母材成分中的Si、Ni、Cr和Mo含量明显不同。对于不同成分体系的钢轨，对应的焊后热处理工艺也就截然不同。
表贝氏体钢轨化学成分对比(质量分数％)
分类 C Si Mn Ni Cr Mo V Al P、S
对比文件 0.1～0.3 0.5～0.9 1.0～2.3 0.30～0.75 0.6～1.3 0.2～0.7 / 0.004 ≤0.015
本发明钢轨 0.15～0.30 1.0～1.8 1.5～2.5 / 0.2～0.6 0.05～0.10 / ≤0.005 ≤0.010
注释：“/”为不含该种元素。
综上所述，铁路工程领域亟需一种通过将贝氏体钢轨焊接接头的踏面硬度控制在合理范围内的方式达到保证钢轨焊接接头使用寿命的焊后热处理方法工艺，以保证贝氏体钢轨焊接接头的服役性能及铁路运行安全。
发明内容
本发明所要解决的技术问题是：提供一种能将贝氏体钢轨焊接接头的踏面硬度控制在合理范围内的用于贝氏体钢轨焊后接头热处理的施工方法，以及一种用于所述施工方 法的轨头仿型冷却装置。
为解决上述技术问题所采用的技术方案是：一种用于贝氏体钢轨焊后接头热处理的施工方法，所述的施工方法以焊接获得的温度不低于1100℃的贝氏体焊接钢轨焊接接头为基础，先后分别通过三次冷却速度逐渐减慢的顺序冷却完成所述贝氏体钢轨焊接接头的焊后热处理工作，
其中，二冷采用以压缩空气或水雾混合气为冷却介质的快速冷却，所述的压缩空气或水雾混合气通过钢轨轨头仿型冷却装置快速的喷射到焊接接头表面，其喷射压力在0.40～0.80MPa之间，喷嘴距轨头踏面的距离为20～50mm之间，二冷的终冷温度为290～400℃，该温度也是三冷的起冷温度。
进一步的是，一冷的终冷却温度为550～750℃，该温度也是二冷的起冷温度。
上述方案的优选方式是，一冷和三冷均采用在空气中进行的自然冷却。
进一步的是，一冷的冷却速度为3.0～5.0℃/s，二冷的冷却速度为1.5～2.5℃/s，三冷的冷却速度为0.05～0.50℃/s。
上述方案的优选方式是，一冷的起冷温度为1100～1400℃，三冷的终冷温度为10～30℃。
进一步的是，在各个冷却阶段中，所述的起冷温度和终冷温度均为采用红外测温仪采集的钢轨轨头踏面的温度。
上述方案的优选方式是，所述贝氏体钢轨的焊接接头为闪光焊接接头或气压焊接接头，轨型为60～75kg/m的重型钢轨。
一种用于所述施工方法的轨头仿型冷却装置，所述的轨头仿型冷却装置包括轨顶喷冷组件和轨头侧面喷冷组件，需要冷却的钢轨焊接接头的焊缝、热影响区及其附近的母材，分别通过轨顶喷冷组件的轨顶冷却喷头和轨头侧面喷冷组件的轨侧冷却喷头喷出的冷却介质快速冷却。
上述方案的优选方式是，所述轨顶喷冷组件还包括轨顶冷媒输送管和长方体型喷头腔，所述的轨顶冷媒输送管从顶部与所述的长方体型喷头腔连通，在所述长方体型喷头腔的底面上设置有所述的轨顶冷却喷头，所述长方体型喷头腔的长度大于钢轨焊接接头、热影响区以及两侧需要冷却的附近母材的长度之和；所述的轨头侧面喷冷组件还包括轨侧冷媒输送管和管式喷头腔体，所述的轨侧冷媒输送管从顶部与所述的管式喷头腔体连通，在所述管式喷头腔体朝向钢轨轨头侧面的那一个侧面上设置有所述的轨侧冷却喷头，所述的管式喷头腔体的长度大于钢轨焊接接头、热影响区以及两侧需要冷却的附 近母材的长度之和。
进一步的是，所述的轨头仿型冷却装置还包括仿型架，所述的轨顶喷冷组件和所述的轨头侧面喷冷组件均布置在所述的仿型架上。
本发明的有益效果是：本申请提供的技术方案由于在热处理过程中采用的是三次冷却速度逐渐减慢的顺序冷却来对焊接完成的焊后温度不低于1100℃的贝氏体焊接钢轨焊接接头进行热处理的，从而可以有效果的将贝氏体钢轨焊接接头在距焊缝中心±25mm区域内的钢轨接头纵向硬度控制在钢轨母材平均硬度的80-85％，且接头焊缝两侧的软化区宽度均低于20.0mm；并能控制该贝氏体钢轨焊接接头的实物疲劳寿命不低于250万次，高于TB/T1632.2-2014及TB/T1632.4-2014标准规定的200万次，以及将贝氏体钢轨焊接接头金相组织中可能出现的马氏体组织百分含量控制在≤5％。由于通过本申请的焊后热处理施工方法处理后的贝氏体钢轨焊接接头及其附近踏面的硬度为钢轨母材平均硬度的80-85％之间，以及将接头焊缝两侧的软化区宽度均控制得低于20.0mm，还可以有效的避免钢轨在长期使用过程中出现“马鞍型”磨耗及轮轨冲击，进而消除严重影响钢轨服役寿命的消积因素，达到延长钢轨使用寿命及保证铁路运行安全的目的。
附图说明
图1为采用实施例1中的方法所得到的焊后热处理条件下的钢轨焊接接头的轨头踏面以下5mm位置的纵向硬度效果图；
图2为采用实施例2中的方法所得到的焊后热处理条件下的钢轨焊接接头的轨头踏面以下5mm位置的纵向硬度效果图；
图3为采用对比例1中的方法所得到的焊后空冷条件下的贝氏体钢轨焊接接头的轨头踏面下5mm位置的纵向硬度效果图；
图4为采用对比例2中的方法所得到的焊后热处理条件下的贝氏体钢轨焊接接头的轨头踏面下5mm位置的纵向硬度效果图；
图5为本发明的贝氏体钢轨焊接接头的轨头踏面下5mm位置的纵向硬度检测示意图；
图6为本发明的钢轨焊接接头的轨头踏面金相试样取样位置示意图。
图7为本发明涉及到的钢轨轨头仿型冷却装置使用的示意图和三维结构示意图。该装置仅对钢轨轨头踏面及轨头侧面实施冷却，其孔径可根据实际需求进行设计加工，从而实现不同的冷却强度。流经压缩空气或水雾混合气通道一和压缩空气或水雾混合气通道二的气体压力可通过相关压力检测装置监控，且流经压缩空气或水雾混合气通道一和 压缩空气或水雾混合气通道二的气体压力根据实际需要进行调节。其中左侧为钢轨轨头仿型冷却装置使用的示意图，右侧为钢轨轨头仿型冷却装置的三维结构示意图，其中原附图中位于钢轨轨顶面的长方体形结构即为上述的长方体型喷头腔，图中与该长方体型喷头腔连接的压缩空气通道即为上述的轨顶冷媒输送管；原附图中位于钢轨轨头侧面的长管式结构即为上述的管式喷头腔体，图中与该管式喷头腔体连接的压缩空气通道即为上述的轨头侧面冷媒输送管；原附图中将长方体型喷头腔和管式喷头腔体连接为一体的呈四爪形的结构即为上述的仿型架。
具体实施方式
为了解决现有技术存在的上述技术问题，本发明提供的一种能将贝氏体钢轨焊接接头的踏面硬度控制在合理范围内的用于贝氏体钢轨焊后接头热处理的施工方法。所述的施工方法以焊接获得的温度不低于1100℃的贝氏体焊接钢轨焊接接头为基础，先后分别通过三次冷却速度逐渐减慢的顺序冷却完成所述贝氏体钢轨焊接接头的焊后热处理工作，
其中，二冷的终冷温度为290～400℃，该温度也是三冷的起冷温度。本申请提供的技术方案由于在热处理过程中采用的是三次冷却速度逐渐减慢的顺序冷却来对焊接完成的焊后温度不低于1100℃的贝氏体焊接钢轨焊接接头进行热处理的，从而可以有效果的将贝氏体钢轨焊接接头在距焊缝中心±25mm区域内的钢轨接头纵向硬度控制在钢轨母材平均硬度的80-85％，且接头焊缝两侧的软化区宽度均低于20.0mm；并能控制该贝氏体钢轨焊接接头的实物疲劳寿命不低于250万次，高于TB/T1632.2-2014及TB/T1632.4-2014标准规定的200万次，以及将贝氏体钢轨焊接接头金相组织中可能出现的马氏体组织百分含量控制在≤8％。由于通过本申请的焊后热处理施工方法处理后的贝氏体钢轨焊接接头及其附近踏面的硬度为钢轨母材平均硬度的80-85％之间，以及将接头焊缝两侧的软化区宽度均控制得低于20.0mm，还可以有效的避免钢轨在长期使用过程中出现“马鞍型”磨耗及轮轨冲击，进而消除严重影响钢轨服役寿命的消积因素，达到延长钢轨使用寿命及保证铁路运行安全的目的
基于中国铁道行业钢轨焊接标准TB1632-2014中规定的钢轨焊缝和热影响区显微组织中不应有马氏体或贝氏体等有害组织的要求。以及国外钢轨焊接标准，如澳洲钢轨焊接标准AS1085.20-2012中规定：对于某些高强度等级、高含碳量及高合金含量的钢轨，在金相显微镜100x观察倍率下，对于钢轨焊接马氏体出现的最严重区域，其马氏体百分含量不得高于5％，否则接头将会由于大量淬硬的马氏体而导致过早疲劳断裂，影响铁 路运行安全的规定。因此，严格控制钢轨焊接马氏体含量对于铁路线路的稳定运行而言至关重要。需要指出的是，上述标准针对的是传统珠光体钢轨。与珠光体钢轨组织不同，贝氏体钢轨母材组织通常为由贝氏体、马氏体组成的复相组织，这就造成了在贝氏体钢轨焊接的快速加热及快速冷却过程中不可避免的形成马氏体。此外，对传统珠光体钢轨而言，脆硬的马氏体组织有害于钢轨服役性能，但马氏体对贝氏体钢轨服役性能的影响尚无定论。因此，通常通过调整钢轨焊接和焊后热处理工艺来尽量降低脆硬的马氏体组织可能对贝氏体钢轨服役性能造成的负面影响。基于上述发现，申请人完成了本申请上述的技术方案。
上述实施方式中，为了更加精准的控制热处理过程，提高热处理效果，同时又方便操作，基于所述贝氏体钢轨的焊接接头为闪光焊接接头或气压焊接接头，轨型为60～75kg/m的重型钢轨的特点，本申请各个工步中的具体要求如下，一冷的终冷却温度为550～750℃，该温度也是二冷的起冷温度；一冷和三冷均采用在空气中进行的自然冷却；二冷为采用冷却介质的快速冷却；所述的冷却介质为压缩空气或水雾混合气；所述的压缩空气或水雾混合气通过钢轨轨头仿型冷却装置快速的喷射到焊接接头表面，其喷射压力在0.40～0.80MPa之间，喷嘴距轨头踏面的距离为20～50mm之间；一冷的冷却速度为3.0～5.0℃/s，二冷的冷却速度为1.5～2.5℃/s，三冷的冷却速度为0.05～0.50℃/s；一次的起冷温度为1100～1400℃，三冷的终冷温度为10～30℃；在各个冷却阶段中，所述的起冷温度和终冷温度均为采用红外测温仪采集的钢轨轨头踏面的温度。
综上所述，采用本申请的焊接热处理施工方法来处理贝氏体钢轨的焊接接头能够通过合理控制焊接接头轨头踏面纵向硬度的方式达到保证钢轨焊接接头疲劳寿命的目的。从而有助于改善铁路运营过程中因钢轨焊接区域硬度偏低而导致的“马鞍型”磨耗及轮轨冲击，延长钢轨使用寿命及保证铁路运行安全。经焊后热处理的贝氏体钢轨焊接接头的轨头踏面纵向硬度控制在钢轨母材平均硬度的80-85％之间的合理范围。可以控制贝氏体钢轨焊接接头的实物疲劳寿命不低于250万次，远高于TB/T1632.2-2014及TB/T1632.4-2014标准规定的200万次，使焊接接头金相组织中可能出现的马氏体组织百分含量控制在≤5％的范围内。
实施例
按照常规手段，热处理型贝氏体钢轨焊后存在焊接区域踏面硬度偏低，韧性差等现象，通常需要进行正火热处理以改善接头性能。但经正火后焊接接头又出现了硬度低塌、软化区变宽，容易造成焊接接头服役过程中“马鞍形”磨耗，导致服役性能变差。本发 明的工作正是基于此，找到并设计了一种热处理型贝氏体钢轨的焊后热处理方法，在保证了接头踏面硬度的同时，保证了钢轨接头服役寿命。
以下对本发明的具体实施方式进行详细说明。应当理解的是，此处所描述的具体实施方式仅用于说明和解释本发明，并不用于限制本发明。
本发明中，在未作相反说明的情况下，所述“钢轨焊接接头”为经焊接得到的包含焊缝和/或热影响区在内的长度为70～100mm范围的区域，该区域的中心为钢轨的焊缝。本发明中，所述“室温”为10～30℃范围的温度。
本发明提供了一种贝氏体钢轨焊后热处理方法，该方法包括：将焊接得到的温度在1100℃以上的钢轨接头在第一冷却速度下进行第一阶段冷却以使钢轨接头的轨头表层温度降至570～750℃，接着使钢轨接头在第二冷却速度下进行第二阶段冷却以使钢轨接头的轨头表层温度降至290～400℃，最后使钢轨接头在第三冷却速度下进行第三阶段冷却以使钢轨接头的轨头表层温度降至10～30℃的室温；其中，所述第一冷却速度为3.0～5.0℃/s，所述第二冷却速度为1.5～2.5℃/s，所述第三冷却速度为0.05～0.50℃/s。
本发明的目的为提供一种贝氏体钢轨焊后热处理方法，该方法包括：将焊接得到的温度在1100℃以上的钢轨接头在第一冷却速度下进行第一阶段冷却以使钢轨接头的轨头表层温度降至550～750℃，接着使钢轨接头在第二冷却速度下进行第二阶段冷却以使钢轨接头的轨头表层温度降至290～400℃，最后使钢轨接头在第三冷却速度下进行第三阶段冷却以使钢轨接头的轨头表层温度降至10～30℃的室温。其中，第一阶段冷却和第三冷却的方式为在空气中的自然冷却。第二冷却为采用如图7所示的钢轨轨头仿型冷却装置，以压缩空气或水雾混合气作为冷却介质对钢轨接头的轨头踏面及轨头侧面进行的冷却。
本发明中，所述第一冷却和第三冷却的冷却方式为在空气中进行的自然冷却，所述第二冷却为采用钢轨轨头仿型冷却装置，以压缩空气或水雾混合气作为冷却介质对钢轨接头的轨头踏面及轨头侧面进行冷却，冷却装置距离钢轨轨头踏面为20～50mm；冷却装置所喷射出的压缩空气或水雾混合气的气体压力为0.05～0.5MPa。
本发明中，采用红外测温仪采集钢轨轨头踏面的温度信号，所述钢轨轨头踏面为车轮与钢轨的接触部分。
需要说明的是，钢轨接头纵向硬度曲线中的软化区宽度测量线所对应的硬度值(0.9Hp)为钢轨母材平均硬度Hp的90％。硬度曲线中的软化区宽度为硬度曲线与软化区宽度测量线的截距。
本发明中，用于焊接的贝氏体钢轨具有相同的轨型，具体为60～75kg/m的规格，所述钢轨焊接接头为采用同一焊接工艺由钢轨移动闪光焊机焊接而成的焊接接头。
以下将通过具体实施例对本发明进行详细描述。以下实施例中，贝氏体钢轨为在线热处理型，皆由某钢集团生产。
本发明所述的一种贝氏体钢轨焊后热处理方法中，进行第一冷却和第三冷却的冷却方式为直接将贝氏体钢轨焊接接头放置在空气中进行自然冷却的空冷。
本发明所述的一种贝氏体钢轨焊后热处理方法中，进行第二冷却的冷却方式为以喷射压缩空气或水雾混合气作为冷却介质的快速冷却。
本发明利用钢轨的焊接余热实现钢轨的焊后热处理过程，针对焊接得到的余温较高的钢轨接头实施焊后加速冷却，以降低接头轨头区域相变温度，提高奥氏体再结晶区的硬度。基于金属学原理，钢轨接头在焊后高温快速冷却条件下存在一定的动态过冷度，致使非平衡状态下奥氏体转变的相变温度下移且随着过冷度的增大，相变温度逐渐降低。因此，即使在开冷温度相对较低的第二阶段冷却，接头轨头仍能发生组织转变。
本发明中，所述第一冷却为在空气中进行的自然冷却，可通过调节试验环境温度(如采用中央空调控温等)实现对第一阶段冷却速度的控制，并可通过调节焊机设置或人工操作来将钢轨焊接接头第一冷却的终冷温度控制在550～750℃，所述第二冷却的开冷温度为550～750℃。本发明中，所述第二冷却的终冷温度低于贝氏体轨钢的马氏体转变开始温度(Ms温度)，本发明中第二冷却的终冷温度为290～400℃。
优选情况下，本发明所述的一种贝氏体钢轨焊后热处理方法中，所述第一冷却、所述第二冷却和所述第二冷却的冷却方法可以采用空冷和风冷等冷却方法中的至少一种，但为了将焊接接头的踏面纵向硬度控制在合理范围内，本发明中第一冷却和第三冷却的冷却方式优选采用空冷，第二冷却的冷却方式优选采用风冷。
本发明所述的一种贝氏体钢轨焊后热处理方法可以用于各种温度的焊接得到的贝氏体钢轨焊接接头，本发明优选所述焊接得到的贝氏体钢轨焊接接头的起始温度为1100-1400℃。
以下将通过具体实施例对本发明进行详细描述。以下实施例中，贝氏体钢轨的型号为PB2在线热处理型贝氏体钢轨，产自某钢集团。
本发明所述的一种贝氏体钢轨焊接接头的焊后热处理工艺方法，参照TB/T1632.2-2014《钢轨焊接 第2部分：闪光焊接》及TB/T1632.4-2014《钢轨焊接 第4部分：气压焊接》标准将钢轨焊接接头机加工成纵断面硬度试样，并在踏面下5mm位 置对焊接接头进行纵断面洛氏硬度检测，测点以焊缝为中心向左右两侧对称排列，测点间距为5mm，洛氏硬度方法按GB/T230.1-2009规定进行，采用HRC标尺，以Hp表示钢轨母材的硬度平均值，Hj表示接头的硬度平均值，接头硬度低于0.9Hp的位置表示软化区域。
采用MTS-FT310型疲劳试验机对钢轨焊接接头实物进行三点弯曲疲劳试验，采用脉动弯曲疲劳试验模式。载荷频率7Hz，载荷比0.2，焊接接头最大疲劳应力为300MPa，以循环载荷加载300万次时焊接接头不发生疲劳断裂为试验目标。
实施例一
规格为68kg/m的钢轨完成移动闪光焊接过程中的顶锻和推瘤后，对焊接得到的接头进行焊后热处理。首先，将焊接得到的余温在1100℃的钢轨接头以4.5℃/s的第一冷却速度进行第一阶段冷却以将钢轨接头的轨头表层温度降至700℃，接着使钢轨接头以2.0℃/s的第二冷却速度进行第二阶段冷却以将钢轨接头的轨头表层温度降至200℃，最后使钢轨接头以0.4℃/s的第三冷却速度进行第三阶段冷却以将钢轨接头的轨头表层温度降至25℃的室温，从而得到本发明的经焊后热处理的钢轨焊接接头。其中，第一冷却和第三冷却为在空气中进行的自然冷却，第二冷却为采用钢轨轨头仿型冷却装置以压缩空气或水雾混合气作为冷却介质对钢轨接头的轨头踏面及轨头侧面进行的冷却，冷却装置距离钢轨轨头踏面40mm。第二冷却过程中，冷却装置喷射的压缩空气或水雾混合气的气体压力为0.30MPa。采用红外测温仪监控钢轨轨头踏面温度。
将本实施例得到的贝氏体钢轨接头机加工成纵向硬度试样，并在踏面下5mm位置对焊接接头进行纵向洛氏硬度检测，测点以焊缝为中心向左右两侧对称排列，测点间距为5mm。洛氏硬度检验方法按GB/T 230.1-2009规定进行，采用HRC标尺。焊接接头的轨头踏面下5mm位置的纵向硬度数据见表1，纵向硬度的分布效果如图1所示。
表1
Figure PCTCN2020091284-appb-000001
由表1和图1可知，对于经本发明处理的贝氏体钢轨焊接接头，在距焊缝中心±25mm区域内的钢轨接头纵向硬度达到了钢轨母材平均硬度的88％。接头焊缝两侧的软化区宽度均为18.0mm，接头焊缝两侧的软化区宽度均低于20.0mm。
参照图7所示的取样方法按GB/T 13298-2015《金属显微组织检验方法》对钢轨接头金相试样进行金相组织检验，采用3％硝酸酒精溶液对钢轨接头金相试样开展浸蚀，采用德国徕卡MeF3光学显微镜对钢轨接头金相组织进行观察。检验结果表明：钢轨接头焊缝两侧的热影响区中均出现了少量的马氏体组织。在金相显微镜的100x观察倍率下，对于马氏体组织出现的最严重区域，经统计，马氏体组织的百分含量为6％。
由表1和图1可知，采用本发明提供的焊后热处理工艺方法处理闪光焊焊接得到的温度在1500℃的贝氏体钢轨的焊接接头时，所得钢轨接头距离焊缝中心±25mm区域内的硬度平均值为38.2HRC，达到了钢轨母材平均硬度的88％。接头焊缝两侧的软化区宽度均为18.0mm，接头焊缝两侧的软化区宽度均低于20.0mm。由本实施例得到的贝氏体钢轨焊接接头试样可通过循环次数为260万次的疲劳试验，高于TB/T1632.2-2014中规定的200万次。
实施例二
规格为60kg/m的钢轨完成移动闪光焊接过程中的顶锻和推瘤后，对焊接得到的接头进行焊后热处理。首先，将焊接得到的余温在1200℃的钢轨接头以4.5℃/s的第一冷却速度进行第一阶段冷却以将钢轨接头的轨头表层温度降至650℃，接着使钢轨接头以2.5℃/s的第二冷却速度进行第二阶段冷却以将钢轨接头的轨头表层温度降至180℃，最后使钢轨接头以0.10℃/s的第三冷却速度进行第三阶段冷却以将钢轨接头的轨头表层温度降至25℃的室温，从而得到本发明的经焊后热处理的钢轨焊接接头。其中，第一冷却和第三冷却为在空气中进行的自然冷却，第二冷却为采用钢轨轨头仿型冷却装置以压缩空气或水雾混合气作为冷却介质对钢轨接头的轨头踏面及轨头侧面进行的冷却，冷却装置距离钢轨轨头踏面40mm。第二冷却过程中，冷却装置喷射的水雾混合气的气体压力为0.60MPa。采用红外测温仪监控钢轨轨头踏面温度。
将本实施例得到的贝氏体钢轨焊接接头机加工成纵向硬度试样，并在踏面下5mm位置对焊接接头进行纵向洛氏硬度检测，测点以焊缝为中心向左右两侧对称排列，测点间距为5mm。洛氏硬度检验方法按GB/T 230.1-2009规定进行，采用HRC标尺。焊接接头的轨头踏面下5mm位置的纵向硬度数据见表2，纵向硬度的分布效果如图2所示。
表2
Figure PCTCN2020091284-appb-000002
由表2和图2可知，对于经本发明处理的贝氏体钢轨焊接接头，在距焊缝中心±25mm区域内的钢轨接头纵向硬度达到了钢轨母材平均硬度的90％。接头焊缝两侧的软化区宽度左侧为15mm，右侧为17.0mm，接头焊缝两侧的软化区宽度均低于20.0mm。
参照图5、图6所示的取样方法按GB/T13298-2015《金属显微组织检验方法》对钢轨接头金相试样进行金相组织检验，采用3％硝酸酒精溶液对钢轨接头金相试样开展浸蚀，采用德国徕卡MeF3光学显微镜对钢轨接头金相组织进行观察。检验结果表明：钢轨接头焊缝两侧的热影响区中均出现了少量的马氏体组织。在金相显微镜的100x观察倍率下，对于马氏体组织出现的最严重区域，经统计，马氏体组织的百分含量为5％。由本实施例得到的贝氏体钢轨焊接接头试样可通过循环次数为230万次的疲劳试验。
由表2和图2可知，采用本发明提供的焊后热处理工艺方法处理闪光焊焊接得到的温度在1500℃的贝氏体钢轨的焊接接头时，所得钢轨接头距离焊缝中心±25mm区域内的硬度平均值为39.0HRC，达到了钢轨母材平均硬度的90％。接头焊缝两侧的软化区宽度左侧为15mm，右侧为17.0mm，接头焊缝两侧的软化区宽度均低于20.0mm。由本实施例得到的贝氏体钢轨焊接接头试样可通过循环次数为230万次的疲劳试验，高于TB/T1632.2-2014中规定的200万次。
对比例一
规格为68kg/m的钢轨完成移动闪光焊接过程中的顶锻和推瘤后，将余温在1200℃的钢轨接头直接空冷至室温(约25℃)，从而得到空冷(自然冷却)条件下的钢轨焊接接头。
取本对比例得到的焊后空冷条件下的钢轨接头加工成纵向硬度试样，并在踏面下5mm位置对焊接接头进行纵向洛氏硬度检测，测点以焊缝为中心向左右两侧对称排列，测点间距为5mm。洛氏硬度检验方法按GB/T 230.1-2009规定进行，采用HRC标尺。焊接接头的轨头踏面下5mm位置的纵向硬度数据见表3，纵向硬度的分布效果如图3所示。
表3
Figure PCTCN2020091284-appb-000003
由表3和图3可知，对于未采用本发明提供的焊后热处理方法处理的钢轨焊接接头，与焊缝两侧的钢轨母材硬度相比，整个焊接区域呈现为软化状态。所得钢轨接头距离焊缝中心±25mm区域内的硬度平均值为35.8HRC，达到了钢轨母材平均硬度的83％，低于钢轨母材平均硬度的80-85％范围，接头焊缝左右两侧的软化区宽度均为25.0mm。由该对比例得到的焊接接头在线路服役过程中，易优先在钢轨焊接接头的软化区形成钢轨轨头踏面低塌，影响线路平顺性及行车安全。
参照图5、图6所示的取样方法按GB/T 13298-2015《金属显微组织检验方法》对钢轨接头金相试样进行金相组织检验，采用3％硝酸酒精溶液对钢轨接头金相试样开展浸蚀，采用德国徕卡MeF3光学显微镜对钢轨接头金相组织进行观察。结果表明，焊接接头金相组织正常，无马氏体、贝氏体等异常组织。由此对比例得到的贝氏体钢轨焊接接头试样在循环次数为170万次时发生疲劳试验。
对比例二
规格为75kg/m的钢轨完成移动闪光焊接过程中的顶锻和推瘤后，对焊接得到的接头进行焊后热处理。首先，将焊接得到的余温在1150℃的钢轨接头以4.0℃/s的第一冷却速度进行第一阶段冷却以将钢轨接头的轨头表层温度降至620℃，接着使钢轨接头以2.5℃/s的第二冷却速度进行第二阶段冷却以将钢轨接头的轨头表层温度降至130℃，最后使钢轨接头以0.10℃/s的第三冷却速度进行第三阶段冷却以将钢轨接头的轨头表层温度降至25℃的室温，从而得到本发明的经焊后热处理的钢轨焊接接头。焊后热处理过程中，第一冷却和第三冷却为在空气中进行的自然冷却；第二冷却为采用钢轨轨头仿型冷却装置以压缩空气作为冷却介质对钢轨接头的轨头踏面及轨头侧面进行的冷却，冷却装置距离钢轨轨头踏面40mm；第二冷却过程中，冷却装置喷射的压缩空气的气体压力为0.60MPa。采用红外测温仪监控钢轨轨头踏面温度。
取本对比例得到的焊后空冷条件下的钢轨接头加工成纵向硬度试样，并在踏面下5mm位置对焊接接头进行纵向洛氏硬度检测，测点以焊缝为中心向左右两侧对称排列，测点间距为5mm。洛氏硬度检验方法按GB/T 230.1-2009规定进行，采用HRC标尺。焊接接头的轨头踏面下5mm位置的纵向硬度数据见表4，纵向硬度的分布效果如图4所示。
表4
Figure PCTCN2020091284-appb-000004
由表4和图4可知，对于未采用本发明提供的焊后热处理方法处理的钢轨焊接接头，所得钢轨接头距离焊缝中心±25mm区域内的硬度平均值为40.6HRC，达到了钢轨母材平均硬度的94％，超出钢轨母材平均硬度的80-85％范围，接头焊缝左右两侧无明显软化区。
参照图5、图6所示的取样方法按GB/T 13298-2015《金属显微组织检验方法》对钢轨接头金相试样进行金相组织检验，采用3％硝酸酒精溶液对钢轨接头金相试样开展浸蚀，采用德国徕卡MeF3光学显微镜对钢轨接头金相组织进行观察。结果表明，钢轨焊接热影响区中均出现了不同程度的马氏体组织。在金相显微镜的100x观察倍率下，对于接头中马氏体组织出现的最严重区域，经统计，马氏体组织百分含量为10％。由此对比例得到的贝氏体钢轨焊接接头试样在循环次数为120万次时发生疲劳断裂。
通过对比图1至图4中的焊接接头轨头踏面纵向硬度分布可以看出：采用本发明提供的工艺方法能够将贝氏体钢轨焊接接头金相组织中可能出现的马氏体组织百分含量控制在≤5％，将距焊缝中心±25mm区域内的钢轨接头纵向硬度控制在钢轨母材平均硬度的80-85％且接头焊缝两侧的软化区宽度均低于20.0mm，有助于改善钢轨在线路服役过程中因焊接区域硬度偏低而导致的钢轨焊接接头“鞍型”磨耗。同时，可使贝氏体钢轨接头疲劳寿命保持在250万次以上，在保证接头具有较高硬度的同时达到了保证接头较高疲劳寿命的目的。
以上详细描述了本发明的优选实施方式，虽然已参照具体实施例描述了根据本发明的贝氏体钢轨的焊后热处理工艺方法，但本领域技术人员将认识到，在不脱离本发明的 思想和范围的情况下，在此可以对本发明做出各种修改和组合。

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  1. 一种用于贝氏体钢轨焊后接头热处理的施工方法，其特征在于：所述的施工方法以焊接获得的温度不低于1100℃的贝氏体焊接钢轨焊接接头为基础，先后分别通过三次冷却速度逐渐减慢的顺序冷却完成所述贝氏体钢轨焊接接头的焊后热处理工作，
    其中，二冷采用以压缩空气或水雾混合气为冷却介质的快速冷却，所述的压缩空气或水雾混合气通过钢轨轨头仿型冷却装置快速的喷射到焊接接头表面，其喷射压力在0.40～0.80MPa之间，喷嘴距轨头踏面的距离为20～50mm之间，二冷的终冷温度为290～400℃，该温度也是三冷的起冷温度。
  2. 根据权利要求1所述的用于贝氏体钢轨焊后接头热处理的施工方法，其特征在于：一冷的终冷却温度为550～750℃，该温度也是二冷的起冷温度。
  3. 根据权利要求1或2所述的用于贝氏体钢轨焊后接头热处理的施工方法，其特征在于：一冷和三冷均采用在空气中进行的自然冷却。
  4. 根据权利要求1或2所述的用于贝氏体钢轨焊后接头热处理的施工方法，其特征在于：一冷的冷却速度为3.0～5.0℃/s，二冷的冷却速度为1.5～2.5℃/s，三冷的冷却速度为0.05～0.50℃/s。
  5. 根据权利要求4所述的用于贝氏体钢轨焊后接头热处理的施工方法，其特征在于：一冷的起冷温度为1100～1400℃，三冷的终冷温度为10～30℃。
  6. 根据权利要求1所述的用于贝氏体钢轨焊后接头热处理的施工方法，其特征在于：在各个冷却阶段中，所述的起冷温度和终冷温度均为采用红外测温仪采集的钢轨轨头踏面的温度。
  7. 根据权利要求6所述的用于贝氏体钢轨焊后接头热处理的施工方法，其特征在于：所述贝氏体钢轨的焊接接头为闪光焊接接头或气压焊接接头，轨型为60～75kg/m的重型钢轨。
  8. 一种用于权利要求1所述施工方法的轨头仿型冷却装置，其特征在于：所述的轨头仿型冷却装置包括轨顶喷冷组件和轨头侧面喷冷组件，需要冷却的钢轨焊接接头的焊缝、热影响区及其附近的母材，分别通过轨顶喷冷组件的轨顶冷却喷头和轨头侧面喷冷组件的轨侧冷却喷头喷出的冷却介质快速冷却。
  9. 根据权利要求8所述的轨头仿型冷却装置，其特征在于：所述轨顶喷冷组件还包括轨顶冷媒输送管和长方体型喷头腔，所述的轨顶冷媒输送管从顶部与 所述的长方体型喷头腔连通，在所述长方体型喷头腔的底面上设置有所述的轨顶冷却喷头，所述长方体型喷头腔的长度大于钢轨焊接接头、热影响区以及两侧需要冷却的附近母材的长度之和；所述的轨头侧面喷冷组件还包括轨侧冷媒输送管和管式喷头腔体，所述的轨侧冷媒输送管从顶部与所述的管式喷头腔体连通，在所述管式喷头腔体朝向钢轨轨头侧面的那一个侧面上设置有所述的轨侧冷却喷头，所述的管式喷头腔体的长度大于钢轨焊接接头、热影响区以及两侧需要冷却的附近母材的长度之和。
  10. 根据权利要求8所述的轨头仿型冷却装置，其特征在于：所述的轨头仿型冷却装置还包括仿型架，所述的轨顶喷冷组件和所述的轨头侧面喷冷组件均布置在所述的仿型架上。
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