CN108504848B - Heat treatment method of steel rail flash welding joint - Google Patents
Heat treatment method of steel rail flash welding joint Download PDFInfo
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- CN108504848B CN108504848B CN201810708275.9A CN201810708275A CN108504848B CN 108504848 B CN108504848 B CN 108504848B CN 201810708275 A CN201810708275 A CN 201810708275A CN 108504848 B CN108504848 B CN 108504848B
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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
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Abstract
The invention discloses a heat treatment method of a steel rail flash welding head, and belongs to the technical field of steel rail welding. The invention provides a heat treatment method of a steel rail flash welding joint, aiming at solving the technical problems of saddle-shaped abrasion and early fatigue fracture of the steel rail welding joint caused by low hardness of a welding area or abnormal microstructure of the joint in the line service process of a steel rail, wherein the steel rail welding joint is sequentially subjected to a first cooling stage, a second cooling stage and a third cooling stage, and the cooling speed and the temperature of each stage are controlled, so that abnormal structures such as martensite, bainite and the like do not exist in the metallographic structure of the steel rail welding joint, the saddle-shaped abrasion and early fatigue fracture of the steel rail welding joint caused by low hardness of the welding area or abnormal microstructure of the joint in the line service process of the steel rail are improved, and the running safety of the railway is ensured.
Description
Technical Field
The invention belongs to the technical field of steel rail welding, and particularly relates to a heat treatment method of a steel rail flash welding head.
Background
At present, heavy haul railway lines at home and abroad mostly adopt eutectoid pearlite steel rails, the carbon content of the steel rails is usually within the range of 0.72-0.82 wt%, and the steel rails have pearlite metallographic structures and have the characteristics of good obdurability matching, moderate comprehensive mechanical property index and the like. With the rapid development of railways, heavy-duty lines with large axle loads have higher requirements on the service performance of steel rails, and the comprehensive mechanical property and the welding property of the traditional pearlitic steel rails are almost developed to the limit. In this case, hypereutectoid steel rails having a higher strength grade and having good wear resistance and contact fatigue balance are produced, and the steel rails usually have a carbon content in the range of 0.90 to 1.10 wt%, and a pearlite + a small amount of secondary cementite as a metallographic structure. At present, the steel rail mobile flash welding has become the mainstream steel rail on-line welding technology in railway construction sites at home and abroad. For two kinds of steel rails with different strength grades and materials, the difference between the properties of the base metal brings great challenges to the welding. After the steel rail is subjected to the action of welding heat cycle, a hardening layer of a welding area disappears, and low-hardness areas with larger widths are formed on two sides of a welding line, so that the hardness of the welding line and a heat affected area is lower than that of a steel rail base metal. In the service process of a steel rail, saddle-shaped abrasion is easily formed on the head tread of a welded joint preferentially, so that the impact of a wheel rail is increased, the service life of the steel rail is seriously influenced, and even the driving safety is endangered. Therefore, the precondition for the application of the steel rail is that how to recover the mechanical property of the steel rail reduced by welding.
At present, relatively few reports and literature documents are available on the research on the welding and post-welding heat treatment process of hypereutectoid steel rails and eutectoid steel rails. CN201610909362.1 discloses a post-weld heat treatment method for hypereutectoid steel rails and PG4 heat-treated eutectoid pearlite steel rail welded joints, which comprises the steps of performing first cooling on the steel rail welded joints to be cooled obtained by welding to below 400 ℃, then heating the steel rail welded joints after the first cooling to 860-450 ℃, and then performing second cooling until the tread temperature of the steel rail welded joints is 410-450 ℃. The dissimilar steel rail welding joint obtained by the method can meet the current national railway industry standard TB/T1632.2-2014 steel rail welding part 2: testing requirements for fatigue, tension, impact and static bending tests in flash welding; however, the invention relates to the post-weld normalizing heat treatment of the steel rail, and needs to adopt post-weld heat treatment equipment of the steel rail to locally heat a welded joint of the steel rail, so that the operation and implementation processes are complex and the cost is high.
Disclosure of Invention
The invention provides a heat treatment method of a steel rail flash welding head, which aims to solve the technical problems of saddle-shaped abrasion and early fatigue fracture of the steel rail welding head caused by low hardness of a welding area or abnormal microstructure of the joint in the line service process of a steel rail, and comprises the following steps: and carrying out first-stage cooling on the welded steel rail welding joint to be cooled at a first cooling speed so as to reduce the surface temperature of the rail head of the steel rail welding joint to 650-720 ℃, then carrying out second-stage cooling on the steel rail welding joint at a second cooling speed so as to reduce the surface temperature of the rail head of the steel rail welding joint to 350-410 ℃, and finally carrying out third-stage cooling on the steel rail welding joint at a third cooling speed so as to reduce the surface temperature of the rail head of the steel rail welding joint to 10-30 ℃.
In the heat treatment method of the steel rail flash welding joint, the steel rail welding joint is a dissimilar steel rail welding joint formed by welding a hypereutectoid steel rail and a eutectoid steel rail having the same rail type.
Preferably, in the method for the postweld heat treatment of the hypereutectoid steel rail and the eutectoid steel rail welded joint, the shape of the hypereutectoid steel rail is 60 to 75kg/m, and the shape of the eutectoid steel rail is 60 to 75 kg/m.
In the heat treatment method of the steel rail flash welding joint, the initial temperature of the steel rail welding joint is 1000-1400 ℃.
In the method for heat treatment of a steel rail flash welding joint, the first stage cooling mode is natural cooling in air.
In the heat treatment method of the steel rail flash welding joint, the first cooling speed is 5.0-9.0 ℃/s.
In the heat treatment method of the steel rail flash welding joint, the second stage of cooling adopts a steel rail head profiling cooling device, compressed air or water mist mixed gas is used as a cooling medium to cool the rail head tread and the rail head side face of the steel rail welding joint, and the distance between the cooling device and the steel rail head tread is 20-50 mm; the gas pressure of the compressed air or the water mist mixed gas ejected by the cooling device is 0.40-0.80 MPa.
In the heat treatment method of the steel rail flash welding joint, the second cooling speed is 1.5-2.5 ℃/s.
In the heat treatment method of the steel rail flash welding joint, the third-stage cooling adopts a steel rail head profiling cooling device, compressed air or water mist mixed gas is used as a cooling medium to cool the rail head tread and the rail head side face of the steel rail welding joint, and the distance between the cooling device and the steel rail head tread is 20-50 mm; the gas pressure of the compressed air or the water mist mixed gas ejected by the cooling device is 0.05-0.25 MPa.
Wherein, in the heat treatment method of the steel rail flash welding joint, the third cooling speed is 0.05-0.50 ℃/s.
In the heat treatment method of the steel rail flash welding joint, the steel rail welding joint is formed by welding a steel rail mobile flash welding machine.
The invention has the beneficial effects that:
the method can improve the saddle-shaped abrasion of the steel rail joint caused by low hardness of the welding area in the line service process of the steel rail, can ensure that the longitudinal hardness of the steel rail joint in the area which is +/-10 mm away from the center of the welding line respectively meets the +/-30 HV range of the average hardness of the corresponding eutectoid pearlite steel rail and hypereutectoid steel rail parent metal (the central line of the welding line which does not contain decarburization is influenced by the high temperature of the steel rail welding, the center of the welding line is decarburized and generates element burning loss to cause low hardness), and the widths of the softening areas at the two sides of the welding line of the joint are lower than 15 mm; meanwhile, the steel rail welded joint can be ensured to have no martensite, bainite and other abnormal structures in the metallographic structure, and the railway operation safety is favorably ensured.
Drawings
FIG. 1 is a graph showing the effect of longitudinal hardness at a position 3 to 5mm below the rail head tread of a welded joint of a hypereutectoid steel rail and a eutectoid pearlite steel rail under the condition of the post-weld heat treatment obtained by the method in example 1.
FIG. 2 is a graph showing the effect of longitudinal hardness at a position 3 to 5mm below the tread of the rail head of a welded joint between a hypereutectoid steel rail and a eutectoid pearlite steel rail under the condition of the post-weld heat treatment obtained by the method in example 2.
FIG. 3 is a graph showing the effect of longitudinal hardness at a position 3 to 5mm below the rail head tread of a welded joint of a hypereutectoid steel rail and a eutectoid pearlite steel rail under post-welding air-cooling conditions obtained by the method in comparative example 1.
FIG. 4 is a graph showing the effect of longitudinal hardness at a position 3 to 5mm below the tread of the rail head of a welded joint of a hypereutectoid steel rail and a eutectoid pearlite steel rail under the condition of post-weld heat treatment obtained by the method in comparative example 2.
FIG. 5 is a graph showing the effect of longitudinal hardness at a position 3 to 5mm below the rail head tread of a welded joint of a hypereutectoid steel rail and a eutectoid pearlite steel rail under the condition of post-weld heat treatment obtained by the method in comparative example 3.
FIG. 6 is a schematic diagram showing the longitudinal hardness measurement of the welded rail joint according to the present invention at a position 3-5mm below the tread of the rail head.
Fig. 7 is a schematic view of a metallographic specimen sampling position of a rail head tread of a rail joint according to the present invention.
Detailed Description
The heat treatment method of the steel rail flash welding joint comprises the following steps: and carrying out first-stage cooling on the welded steel rail welding joint to be cooled at a first cooling speed so as to reduce the surface temperature of the rail head of the steel rail welding joint to 650-720 ℃, then carrying out second-stage cooling on the steel rail welding joint at a second cooling speed so as to reduce the surface temperature of the rail head of the steel rail welding joint to 350-410 ℃, and finally carrying out third-stage cooling on the steel rail welding joint at a third cooling speed so as to reduce the surface temperature of the rail head of the steel rail welding joint to 10-30 ℃.
The critical cooling rate of martensitic transformation during continuous cooling transformation of eutectoid pearlite rail steel is about 0.7-1.5 ℃/s, and the critical cooling rate of martensitic transformation during continuous cooling transformation of hypereutectoid rail steel is about 1.8-3.0 ℃/s. The Ms temperature (the starting temperature for the formation of martensite structure) of the eutectoid pearlitic rail is about 250 ℃ and the Ms temperature of the hypereutectoid rail is about 190 ℃. In order to avoid the occurrence of abnormal structures such as martensite in the welded joint of the steel rail, when the welded joint of the hypereutectoid steel rail and the eutectoid steel rail is subjected to postweld heat treatment, the final cooling temperature in the postweld heat treatment rapid cooling process needs to be controlled to be higher than the Ms temperature of the eutectoid pearlite steel rail. Meanwhile, the cooling rate during the post-weld heat treatment must be limited to eutectoid pearlitic rail steels with relatively low critical cooling rates, otherwise the joint will undergo premature fatigue fracture due to the hardened martensite structure.
Thus, the rail welding standard, AS specified in australian rail welding standard AS 1085.20-2012: for some steel rails with high strength grade, high carbon content and high alloy content, under the observation magnification of a metallographic microscope of 100x, the percentage content of a martensite structure in the most serious area of a steel rail welding joint is not higher than 5%, otherwise, the joint can be subjected to early fatigue fracture due to a large amount of hardened martensite structures, and the running safety of the railway is seriously influenced. Therefore, strict control of the martensite content in the welded structure of the steel rail is important for stable operation of the railway line. In addition, a small amount of secondary cementite is also present in the base material of the hypereutectoid steel rail, and in order to prevent the secondary cementite from being crystallized out in a net shape along the steel rail during the welding process, the joint needs to be rapidly cooled before the transformation from austenite to pearlite begins. Based on the above findings, the inventors have completed the present invention.
The invention realizes the post-welding heat treatment process of the steel rail by using the welding waste heat of the steel rail. And (3) performing post-welding accelerated cooling on the welded steel rail joint with higher residual temperature (1000-1400 ℃) so as to reduce the transformation temperature of the joint rail head from austenite to pearlite, thereby improving the hardness of an austenite recrystallization region. Based on the principle of metallurgy, the steel rail joint has certain dynamic supercooling degree under the high-temperature rapid cooling condition after welding, so that the phase transition temperature of transformation from austenite to pearlite in a non-equilibrium state moves downwards, and the phase transition temperature is gradually reduced along with the increase of the supercooling degree. Thus, even if the joint railhead is cooled in the second stage where the opening cooling temperature is relatively low, the structural transformation from austenite to pearlite can occur.
In the invention, the first cooling stage is natural cooling in the air (which can be carried out at room temperature), the cooling speed is 5.0-9.0 ℃/s, the control of the cooling speed of the first stage can be realized by adjusting the test environment temperature (such as adopting a central air conditioner for temperature control), and the final cooling temperature of the first stage cooling of the steel rail welding joint can be controlled to be 650-720 ℃ by adjusting the setting of a welding machine or manual operation; the opening cooling temperature of the second stage cooling is 650-720 ℃, and the final cooling temperature of the second stage cooling is higher than the martensite transformation starting temperature (Ms temperature) of hypereutectoid rail steel and eutectoid pearlite rail steel, the final cooling temperature of the second stage cooling is 350-410 ℃ in the invention, and the cooling speed is 1.5-2.5 ℃/s; when the steel rail joint is cooled in the third stage, in order to avoid the joint from generating a hardened martensite structure, the joint is slowly cooled at a cooling speed of 0.05-0.50 ℃/s which is lower than the martensite transformation critical cooling speed of the eutectoid pearlite steel rail, and the steel rail joint is cooled to room temperature (10-30 ℃); according to the invention, by adopting a cooling mode of three-step cooling, the cooling speed and the cooling temperature in different cooling stages are limited, the hardness of the steel rail welding joint can be improved, and the steel rail welding joint is ensured to have no martensite, bainite and other abnormal structures in the metal phase.
In the method, a steel rail head profiling cooling device is adopted for the second-stage cooling and the third-stage cooling, compressed air or water mist mixed gas is used as a cooling medium to cool a rail head tread and a rail head side face of a steel rail welding joint, and the distance between the cooling device and the rail head tread is 20-50 mm; the gas pressure of the compressed air or the water mist mixed gas ejected by the second-stage cooling device is 0.40-0.80 MPa, and the gas pressure of the compressed air or the water mist mixed gas ejected by the third-stage cooling device is 0.05-0.25 MPa.
In the invention, the hypereutectoid steel rail and the eutectoid steel rail for welding are both in the same specification, in particular to the specification of 60-75 kg/m, and the steel rail welding joint is a dissimilar welding joint formed by welding through a steel rail mobile flash welding machine by adopting the same welding process.
In the present invention, unless otherwise stated, the "welded rail joint" is a welded region having a length of 70 to 100mm including a weld and/or a heat-affected zone, and the center of the region is the weld of the rail.
According to the invention, an infrared thermometer is adopted to collect temperature signals of a steel rail head tread, wherein the steel rail head tread is a contact part of a wheel and a steel rail; the hardness value corresponding to the softening area width measurement line in the longitudinal hardness curve of the steel rail joint is the hardness obtained by subtracting 25HV from the average hardness of the steel rail base metal; the width of the softened region in the hardness curve is the intercept of the hardness curve and the measurement line of the width of the softened region.
The present invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.
When the embodiment and the comparative example are used for testing the hardness of the steel rail welding joint, the hardness sample sampling position of the longitudinal section of the welding joint is shown in figure 6, a welding seam is positioned in the center of the length of the sample, the hardness value of the longitudinal section of the steel rail welding joint is tested, measuring points are symmetrically arranged towards the left side and the right side by taking the welding seam as the center, and the distance between the measuring points is 2 mm; the Vickers hardness of the longitudinal section of the welded joint is detected, the test method is carried out according to the regulation of GB/T4340.1-2009, and the test force value is 294.2N; the recrystallization zone is a zone which is +/-10 mm away from the center of the welding seam; the hardness detection should cover the whole area of the welded joint, including the base material, the heat affected zone and the welding line, and extend to the area of 20mm of the base material of the steel rail on each side of the welded joint.
Example 1
After the upsetting and the push-button in the process of moving flash welding are finished on the steel rail with the specification of 60kg/m, the post-welding heat treatment is carried out on the joint obtained by welding. Firstly, the steel rail joint with the residual temperature of 1100 ℃ obtained by welding is subjected to first-stage cooling at a first cooling speed of 7.0 ℃/s so as to reduce the surface layer temperature of the rail head of the steel rail joint to 660 ℃, then the steel rail joint is subjected to second-stage cooling at a second cooling speed of 2.0 ℃/s so as to reduce the surface layer temperature of the rail head of the steel rail joint to 400 ℃, and finally the steel rail joint is subjected to third-stage cooling at a third cooling speed of 0.4 ℃/s so as to reduce the surface layer temperature of the rail head of the steel rail joint to the room temperature of 25 ℃, so that the steel rail welded joint subjected to postweld heat treatment is obtained.
In the postweld heat treatment process, the first cooling is natural cooling in the air; in the second cooling process and the third cooling process, a steel rail head profiling cooling device is adopted to cool a rail head tread and a rail head side surface of a steel rail joint by taking compressed air as a cooling medium, and the distance between the cooling device and the steel rail head tread is 42 mm; in the second cooling process, the gas pressure of the compressed air sprayed by the cooling device is 0.62 MPa; in the third cooling process, the gas pressure of the compressed air injected by the cooling device is 0.20 MPa. And monitoring the tread temperature of the rail head of the steel rail by adopting an infrared thermometer.
The post-weld heat treated rail joint obtained in this example was machined into a longitudinal hardness test specimen. A hardness sample is subjected to longitudinal Vickers hardness detection by using a Bravicer hardness tester (general factory of testing machines in Laizhou, Shandong, model HBV-30A) at a position 4mm below a rail head tread of a steel rail at a measuring point interval of 2mm, and measuring points are symmetrically arranged towards the left side and the right side by taking a welding line as a center. The Vickers hardness test method refers to GB/T4340.1-2009 part 1 of metal Vickers hardness test: test methods "were performed using HV scale. The hardness test data are shown in Table 1, and the effect of the distribution of the longitudinal hardness of the joint is shown in FIG. 1.
Table 1 example 1 hardness test data for rail welded joint
As is apparent from Table 1 and FIG. 1, the longitudinal hardness of the welded joint of steel rails treated according to the present invention in the region of. + -.10 mm from the center of the weld line satisfies. + -.30 HV range of the average hardness of the base materials of the corresponding eutectoid pearlite steel rail and hypereutectoid steel rail, respectively (excluding the center line of the weld line which is decarburized: the center line of the weld line which is decarburized under the influence of high temperature during welding of the steel rail and generates element burnout, resulting in lower hardness). The width of a softening zone at one side of the eutectoid pearlite steel rail of a joint welding seam is 10mm, the width of a softening zone at one side of the hypereutectoid steel rail is 6mm, and the widths of the softening zones at two sides of the joint welding seam are both lower than 15 mm.
Referring to the sampling method shown in FIG. 7, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 metal microstructure examination method, etching is carried out on the metallographic structure sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope. The result shows that the metallographic phase of the joint has no abnormal structures such as martensite, bainite and the like.
Example 2
After the upsetting and the push-button in the process of moving flash welding are finished on the steel rail with the specification of 68kg/m, the post-welding heat treatment is carried out on the joint obtained by welding. Firstly, the rail joint with the residual temperature of 1000 ℃ obtained by welding is subjected to first-stage cooling at a first cooling speed of 6.5 ℃/s so as to reduce the surface temperature of the rail head of the rail joint to 680 ℃, then the rail joint is subjected to second-stage cooling at a second cooling speed of 2.2 ℃/s so as to reduce the surface temperature of the rail head of the rail joint to 380 ℃, and finally the rail joint is subjected to third-stage cooling at a third cooling speed of 0.10 ℃/s so as to reduce the surface temperature of the rail head of the rail joint to the room temperature of 25 ℃, so that the welded and heat-treated dissimilar material steel rail welded joint is obtained.
In the postweld heat treatment process, the first cooling is natural cooling in the air; in the second cooling process and the third cooling process, a rail head profiling cooling device is adopted to cool a rail head tread and a rail head side face of a rail joint by taking water-mist mixed gas as a cooling medium, and the distance between the cooling device and the rail head tread is 40 mm; in the second cooling process, the gas pressure of the water mist mixed gas sprayed by the cooling device is 0.65 MPa; in the third cooling process, the gas pressure of the water mist mixed gas sprayed by the cooling device is 0.09 MPa. And monitoring the tread temperature of the rail head of the steel rail by adopting an infrared thermometer.
The post-weld heat treated rail joint obtained in this example was machined into a longitudinal hardness test specimen. A hardness sample is subjected to longitudinal Vickers hardness detection by using a Bravicer hardness tester (general factory of testing machines in Laizhou, Shandong, model HBV-30A) at a position 4mm below a rail head tread of a steel rail at a measuring point interval of 2mm, and measuring points are symmetrically arranged towards the left side and the right side by taking a welding line as a center. The Vickers hardness test method refers to GB/T4340.1-2009 part 1 of metal Vickers hardness test: test methods "were performed using HV scale. The hardness test data are shown in Table 2, and the effect of the longitudinal hardness distribution of the joint is shown in FIG. 2.
Table 2 example 2 hardness test data for rail welded joint
As is apparent from Table 2 and FIG. 2, the longitudinal hardness of the welded joint of steel rails treated according to the present invention in the region of. + -.10 mm from the center of the weld line satisfies. + -.30 HV range of the average hardness of the base materials of the corresponding eutectoid pearlite steel rail and hypereutectoid steel rail, respectively (excluding the center line of the weld line which is decarburized, the center of the weld line is decarburized and the element is burned, and the hardness is low). The width of a softening zone at one side of the eutectoid pearlite steel rail of the joint welding seam is 8mm, the width of a softening zone at one side of the hypereutectoid steel rail is 6mm, and the widths of the softening zones at two sides of the joint welding seam are both lower than 15 mm.
Referring to the sampling method shown in FIG. 7, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 Metal microstructure examination method, etching is carried out on the metallographic sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope. The result shows that the joint gold phase has no abnormal structures such as martensite, bainite and the like.
Comparative example 1
After the upsetting and the push-button in the process of moving flash welding are finished on the steel rail with the specification of 68kg/m, directly air-cooling the steel rail joint with the residual temperature of 1100 ℃ to the room temperature (about 25 ℃) so as to obtain the steel rail welded joint under the air-cooling (natural cooling) condition.
The rail joint obtained in the comparative example under the air cooling condition after welding is processed into a longitudinal hardness sample. A hardness sample is subjected to longitudinal Vickers hardness detection by using a Bravicer hardness tester (general plant of testing machines in Laizhou, Shandong, model HBV-30A) at a position 5mm below a rail head tread of a steel rail at a measuring point interval of 2mm, and measuring points are symmetrically arranged towards the left side and the right side by taking a welding line as a center. The Vickers hardness test method refers to GB/T4340.1-2009 part 1 of metal Vickers hardness test: test methods "were performed using HV scale. The hardness test data are shown in Table 3, and the effect of the longitudinal hardness distribution of the joints is shown in FIG. 3.
TABLE 3 comparative example 1 Steel Rail weld Joint hardness test data
As is apparent from table 3 and fig. 3, the welded joint of the steel rail which was not treated by the post-weld heat treatment method according to the present invention exhibited a softened state in the entire welded region as compared with the hardness of the steel rail base metal on both sides of the weld. The longitudinal hardness of the steel rail joint in the area which is +/-10 mm away from the center of the welding seam can not meet the range of +/-30 HV of the average hardness of the corresponding eutectoid pearlite steel rail and hypereutectoid steel rail base metals (excluding the center line of the decarburized welding seam: the center line of the welding seam is influenced by the high welding temperature of the steel rail, the center of the welding seam is decarburized, element burning loss is generated, and the hardness is lower). The width of the softening zone on the side of the eutectoid pearlite rail of the joint weld joint is 17mm, and the width of the softening zone on the side of the hypereutectoid steel rail is 18 mm. In the service process of the line, the welded joint obtained by the comparative example is easy to preferentially form low-collapse steel rail head tread in a softening area on one side of the hypereutectoid steel rail of the joint weld, and the smoothness and the driving safety of the line are influenced.
Referring to the sampling method shown in FIG. 7, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 metal microstructure examination method, etching is carried out on the metallographic structure sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope. The result shows that the metallographic structure of the joint is normal and abnormal structures such as martensite, bainite and the like do not exist.
Comparative example 2
After the upsetting and the push-button in the process of moving flash welding are finished on the steel rail with the specification of 75kg/m, the post-welding heat treatment is carried out on the joint obtained by welding. Firstly, the rail joint with the residual temperature of 1050 ℃ obtained by welding is subjected to first-stage cooling at a first cooling speed of 6.0 ℃/s so as to reduce the rail head surface layer temperature of the rail joint to 680 ℃, then the rail joint is subjected to second-stage cooling at a second cooling speed of 2.8 ℃/s so as to reduce the rail head surface layer temperature of the rail joint to 220 ℃, and finally the rail joint is subjected to third-stage cooling at a third cooling speed of 0.10 ℃/s so as to reduce the rail head surface layer temperature of the rail joint to room temperature of 25 ℃, so that the post-welding heat-treated dissimilar material steel rail welded joint of the comparative example is obtained.
In the postweld heat treatment process, the first cooling is natural cooling in the air; in the second cooling process and the third cooling process, a steel rail head profiling cooling device is adopted to cool a rail head tread and a rail head side face of a steel rail joint by taking compressed air as a cooling medium, and the distance between the cooling device and the steel rail head tread is 45 mm; in the second cooling process, the gas pressure of the compressed air sprayed by the cooling device is 0.90 MPa; in the third cooling process, the gas pressure of the compressed air injected by the cooling device is 0.13 MPa. And monitoring the tread temperature of the rail head of the steel rail by adopting an infrared thermometer.
The rail joint obtained in the comparative example under the air cooling condition after welding is processed into a longitudinal hardness sample. A hardness sample is subjected to longitudinal Vickers hardness detection by using a Bravicer hardness tester (general factory of testing machines in Laizhou, Shandong, model HBV-30A) at a position 4mm below a rail head tread of a steel rail at a measuring point interval of 2mm, and measuring points are symmetrically arranged towards the left side and the right side by taking a welding line as a center. The Vickers hardness test method refers to GB/T4340.1-2009 part 1 of metal Vickers hardness test: test methods "were performed using HV scale. The hardness test data are shown in Table 4, and the effect of the longitudinal hardness distribution of the joints is shown in FIG. 4.
TABLE 4 comparative example 2 hardness test data for rail welded joints
As is apparent from Table 4 and FIG. 4, the resulting welded joint of rails which had not been treated by the post-weld heat treatment method according to the present invention had a softened region width on the eutectoid rail side of 12mm and a softened region width on the hypereutectoid rail side of 10 mm. The hardness of one side of the eutectoid pearlite steel rail of the joint welding seam is higher, the hardness of the position 2mm away from the center of the welding seam reaches 476HV, and the average hardness exceeds 36HV of the base metal of the eutectoid pearlite steel rail. In the service process of the line, because the hardness of one side of the hypereutectoid steel rail of a joint welding line is relatively low, the tread of the rail head of the steel rail is easy to collapse preferentially in a softening area of the side, saddle-shaped abrasion of the joint is caused, and the smoothness of the line is influenced.
Referring to the sampling method shown in FIG. 7, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 Metal microstructure examination method, etching is carried out on the metallographic sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope. The results show that the quenched martensite structures appear in the welding heat affected zone of the hypereutectoid steel rail and the eutectoid pearlite steel rail, which is not beneficial to the running safety of railways.
Comparative example 3
After the upsetting and the push-button in the process of moving flash welding are finished on the steel rail with the specification of 75kg/m, the post-welding heat treatment is carried out on the joint obtained by welding. Firstly, the rail joint with the residual temperature of 1050 ℃ obtained by welding is subjected to first-stage cooling at a first cooling speed of 7.0 ℃/s so as to reduce the rail head surface layer temperature of the rail joint to 670 ℃, then the rail joint is subjected to second-stage cooling at a second cooling speed of 2.4 ℃/s so as to reduce the rail head surface layer temperature of the rail joint to 390 ℃, and finally the rail joint is subjected to third-stage cooling at a third cooling speed of 2.5 ℃/s so as to reduce the rail head surface layer temperature of the rail joint to room temperature of 25 ℃, so that the post-welding heat-treated dissimilar material steel rail welded joint of the comparative example is obtained.
In the postweld heat treatment process, the first cooling is natural cooling in the air; in the second cooling process and the third cooling process, a steel rail head profiling cooling device is adopted to cool a rail head tread and a rail head side face of a steel rail joint by taking compressed air as a cooling medium, and the distance between the cooling device and the steel rail head tread is 40 mm; in the second cooling process, the gas pressure of the compressed air sprayed by the cooling device is 0.65 MPa; in the third cooling process, the gas pressure of the compressed air injected by the cooling device is 0.80 MPa. And monitoring the tread temperature of the rail head of the steel rail by adopting an infrared thermometer.
The rail joint obtained in the comparative example under the air cooling condition after welding is processed into a longitudinal hardness sample. A hardness sample is subjected to longitudinal Vickers hardness detection by using a Bravicer hardness tester (general factory of testing machines in Laizhou, Shandong, model HBV-30A) at a position 4mm below a rail head tread of a steel rail at a measuring point interval of 2mm, and measuring points are symmetrically arranged towards the left side and the right side by taking a welding line as a center. The Vickers hardness test method refers to GB/T4340.1-2009 part 1 of metal Vickers hardness test: test methods "were performed using HV scale. The hardness test data are shown in Table 5, and the effect of the longitudinal hardness distribution of the joints is shown in FIG. 5.
TABLE 5 comparative example 3 hardness test data for rail welded joints
As is apparent from Table 5 and FIG. 5, the resulting welded joint of rails which had not been treated by the post-weld heat treatment method according to the present invention had a softened region width on the eutectoid rail side of 12mm and a softened region width on the hypereutectoid rail side of 11 mm. The hardness of one side of the eutectoid pearlite steel rail of the joint welding seam is higher, and the hardness of the position +/-10 mm away from the center of the welding seam exceeds the average hardness of parent materials of the eutectoid pearlite steel rail and the hypereutectoid steel rail by 30 HV. In the service process of the line, because the hardness of one side of the hypereutectoid steel rail of a joint welding line is relatively low, the tread of the rail head of the steel rail is easy to collapse preferentially in a softening area of the side, saddle-shaped abrasion of the joint is caused, and the smoothness of the line is influenced.
Referring to the sampling method shown in FIG. 7, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 Metal microstructure examination method, etching is carried out on the metallographic sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope. Metallographic examination results show that a large amount of massive martensite appears in welding heat affected zones of the hypereutectoid steel rail and the eutectoid pearlite steel rail, which is not beneficial to the running safety of railways.
As can be seen by comparing the weld joint railhead tread longitudinal stiffness and joint softening zone width in fig. 1-5: by adopting the postweld heat treatment method provided by the invention to carry out postweld heat treatment on the hypereutectoid steel rail and the eutectoid pearlite steel rail welding joint, the longitudinal hardness of the steel rail joint in a region +/-10 mm from the center of a welding seam can respectively meet the range +/-30 HV of the average hardness of the corresponding base metal of the eutectoid pearlite steel rail and the hypereutectoid steel rail (the center line of the welding seam, which does not contain decarburization, is influenced by the high temperature of steel rail welding, the center of the welding seam is decarburized and generates element burning loss, so that the hardness is low), and the widths of softening zones at two sides of the welding seam of the. Meanwhile, the gold phase of the welding joint has no martensite, bainite and other abnormal structures, and the safety of the line driving is ensured.
Having described preferred embodiments of the present invention in detail, while the post weld heat treatment method for steel rails according to the present invention has been described with reference to specific examples, those skilled in the art will recognize that various modifications and combinations can be made therein without departing from the spirit and scope of the invention.
Claims (8)
1. The heat treatment method of the steel rail flash welding joint is characterized in that: the method comprises the following steps: carrying out first-stage cooling on a welded joint of a steel rail to be cooled obtained by welding at a first cooling speed so as to reduce the temperature of the surface layer of the railhead of the welded joint of the steel rail to 650-720 ℃, then carrying out second-stage cooling on the welded joint of the steel rail at a second cooling speed so as to reduce the temperature of the surface layer of the railhead of the welded joint of the steel rail to 350-410 ℃, and finally carrying out third-stage cooling on the welded joint of the steel rail at a third cooling speed so as to reduce the temperature of the surface layer of the railhead of the welded joint of the steel rail to 10-30 ℃; the steel rail welding joint is a dissimilar steel rail welding joint formed by welding a hypereutectoid steel rail with the same rail type and a eutectoid steel rail; the third cooling speed is 0.05-0.50 ℃/s.
2. The method for heat-treating a flash welded steel rail joint according to claim 1, wherein: the initial temperature of the steel rail welding joint is 1000-1400 ℃.
3. The method for heat-treating a flash welded steel rail joint according to claim 1, wherein: the first stage cooling mode is natural cooling in air.
4. The method for heat-treating a flash welded steel rail joint according to claim 1, wherein: the first cooling speed is 5.0-9.0 ℃/s.
5. The method for heat-treating a flash welded steel rail joint according to claim 1, wherein: the second stage of cooling adopts a steel rail head profiling cooling device, compressed air or water mist mixed gas is used as a cooling medium to cool a rail head tread and a rail head side face of a steel rail welding joint, and the distance between the cooling device and the rail head tread is 20-50 mm; the gas pressure of the compressed air or the water mist mixed gas ejected by the cooling device is 0.40-0.80 MPa.
6. A method for heat treating a flash welded joint for steel rails according to claim 5, wherein: the second cooling speed is 1.5-2.5 ℃/s.
7. The method for heat-treating a flash welded steel rail joint according to claim 1, wherein: the third stage of cooling adopts a steel rail head profiling cooling device, compressed air or water mist mixed gas is used as a cooling medium to cool the rail head tread and the rail head side face of the steel rail welding joint, and the distance between the cooling device and the steel rail head tread is 20-50 mm; the gas pressure of the compressed air or the water mist mixed gas ejected by the cooling device is 0.05-0.25 MPa.
8. A method for heat treating a flash welded joint for steel rails according to any one of claims 1 to 7, characterized by comprising: the steel rail welding joint is formed by welding a steel rail mobile flash welding machine.
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| CN201810708275.9A CN108504848B (en) | 2018-07-02 | 2018-07-02 | Heat treatment method of steel rail flash welding joint |
| AU2019204691A AU2019204691B2 (en) | 2018-07-02 | 2019-07-01 | Heat treatment method for rail flash butt welding joint |
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| CN112226609B (en) * | 2020-10-23 | 2022-03-22 | 攀钢集团攀枝花钢铁研究院有限公司 | Construction method for heat treatment of post-welded joints of dissimilar steel rails |
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| CN113458568B (en) * | 2021-08-09 | 2022-10-21 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for welding medium carbon steel rail in field |
| CN114891967B (en) * | 2022-06-20 | 2023-10-13 | 攀钢集团攀枝花钢铁研究院有限公司 | Welding method for medium-low carbon pearlite steel rail |
| CN115478149B (en) * | 2022-10-18 | 2023-08-25 | 包头钢铁（集团）有限责任公司 | Bainite steel rail and pearlite steel rail welding joint heat treatment process for heavy haul railway |
| CN115679079A (en) * | 2022-11-03 | 2023-02-03 | 攀钢集团攀枝花钢铁研究院有限公司 | Method and device for improving hardness of hypereutectoid steel rail joint re-austenitizing area |
| CN115488482B (en) * | 2022-11-03 | 2023-12-22 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for reducing width of heat affected zone of high-strength pearlitic steel rail flash welding head |
| CN116237624B (en) * | 2023-02-09 | 2024-10-29 | 包头钢铁（集团）有限责任公司 | 75Kg/m hypereutectoid steel rail fixed flash welding and joint heat treatment method for heavy haul railway |
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| CN106544933B (en) * | 2016-10-19 | 2019-05-03 | 攀钢集团攀枝花钢铁研究院有限公司 | The method that a kind of pair of steel rail weld joint carries out post weld heat treatment |
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