CN108660306B - Postweld heat treatment method for hypereutectoid steel rail and eutectoid steel rail welded joint - Google Patents
Postweld heat treatment method for hypereutectoid steel rail and eutectoid steel rail welded joint Download PDFInfo
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- CN108660306B CN108660306B CN201810581145.3A CN201810581145A CN108660306B CN 108660306 B CN108660306 B CN 108660306B CN 201810581145 A CN201810581145 A CN 201810581145A CN 108660306 B CN108660306 B CN 108660306B
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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
- C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
- C21D9/505—Cooling thereof
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
Abstract
The invention discloses a postweld heat treatment method for a hypereutectoid steel rail and a eutectoid steel rail welding joint, and belongs to the technical field of steel rail welding. The invention provides a postweld heat treatment method of a hypereutectoid steel rail and a eutectoid steel rail welding joint, which aims to solve 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.
Description
Technical Field
The invention belongs to the technical field of steel rail welding, and particularly relates to a postweld heat treatment method for a hypereutectoid steel rail and a eutectoid steel rail welding joint.
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 postweld heat treatment method of a hypereutectoid steel rail and a eutectoid steel rail welding joint, which aims to solve the technical problems of saddle-shaped abrasion and early-stage 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, and comprises the following steps: and carrying out first-stage cooling on the welded steel rail welded joint to be cooled at a first cooling speed so as to reduce the surface temperature of the rail head of the steel rail welded joint to 570-640 ℃, then carrying out second-stage cooling on the steel rail welded joint at a second cooling speed so as to reduce the surface temperature of the rail head of the steel rail welded joint to 410-460 ℃, and finally carrying out third-stage cooling on the steel rail welded joint at a third cooling speed so as to reduce the surface temperature of the rail head of the steel rail welded joint to 10-30 ℃.
In the method for the postweld heat treatment of the hypereutectoid steel rail and eutectoid steel rail welded joint, the steel rail welded joint is formed by welding the hypereutectoid steel rail and the eutectoid steel rail with the same rail type.
Preferably, in the method for the post-weld heat treatment of a welded joint between a hypereutectoid steel rail and a eutectoid steel rail, the shape of the hypereutectoid steel rail is 60 or 68kg/m, and the shape of the eutectoid steel rail is 60 or 68 kg/m.
In the postweld heat treatment method for the hypereutectoid steel rail and eutectoid steel rail welded joint, the initial temperature of the steel rail welded joint is 1000-1350 ℃.
In the method for the postweld heat treatment of the hypereutectoid steel rail and the eutectoid steel rail welded joint, the first-stage cooling mode is natural cooling in the air.
In the method for the postweld heat treatment of the hypereutectoid steel rail and eutectoid steel rail welded joint, the first cooling speed is 3.0-5.0 ℃/s.
In the postweld heat treatment method for the hypereutectoid steel rail and the eutectoid steel rail welded joint, a steel rail head profiling cooling device is adopted in the second stage of 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 the steel rail welded 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.
In the method for the postweld heat treatment of the hypereutectoid steel rail and eutectoid steel rail welded joint, the second cooling speed is 1.5-2.5 ℃/s.
In the postweld heat treatment method for the hypereutectoid steel rail and the eutectoid steel rail welding joint, a steel rail head profiling cooling device is adopted in the third stage of 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 the 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 0.05-0.25 MPa.
In the method for the postweld heat treatment of the hypereutectoid steel rail and eutectoid steel rail welded joint, the third cooling speed is 0.05-0.50 ℃/s.
In the method for the postweld heat treatment of the hypereutectoid steel rail and eutectoid steel rail welded joint, the welded joint of the hypereutectoid steel rail and eutectoid steel rail is a welded joint of dissimilar steel rails welded by a rail moving flash welding machine.
The invention has the beneficial effects that:
the method can ensure that the longitudinal hardness of the steel rail joint in a region +/-10 mm away from the center of the welding seam respectively meets the +/-30 HV range (excluding the center line of the decarburized welding seam) of the average hardness of the base materials of the corresponding eutectoid pearlite steel rail and hypereutectoid steel rail on the premise that the steel rail welding joint has no martensite, bainite and other abnormal structures, and the widths of the softening zones at two sides of the welding seam of the joint are lower than 15 mm; the invention is beneficial to improving 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 service process of a steel rail.
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 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 4.
FIG. 7 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. 8 is a schematic view of a metallographic specimen sampling site on a rail head tread of a rail joint according to the present invention.
Detailed Description
The postweld heat treatment method for the hypereutectoid steel rail and the eutectoid steel rail welded joint comprises the following steps of: and carrying out first-stage cooling on the welded steel rail welded joint to be cooled at a first cooling speed so as to reduce the surface temperature of the rail head of the steel rail welded joint to 570-640 ℃, then carrying out second-stage cooling on the steel rail welded joint at a second cooling speed so as to reduce the surface temperature of the rail head of the steel rail welded joint to 410-460 ℃, and finally carrying out third-stage cooling on the steel rail welded joint at a third cooling speed so as to reduce the surface temperature of the rail head of the steel rail welded joint to 10-30 ℃.
The critical cooling speed of martensite transformation in the continuous cooling transformation process of the eutectoid rail steel is about 0.7-1.5 ℃/s, and the critical cooling speed of martensite transformation in the continuous cooling transformation process of the 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 and the like in a steel rail welding joint, when the postweld heat treatment is carried out on the hypereutectoid steel rail and the welding joint of the eutectoid steel rail, the final cooling temperature in the postweld heat treatment rapid cooling process is 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. 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 rail 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.
In the invention, post-welding accelerated cooling is carried out on the welded steel rail joint with higher residual temperature (1000-1350 ℃) 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 air (which can be carried out at room temperature), the cooling speed is 3.0-5.0 ℃/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 570-640 ℃ by adjusting the setting of a welding machine or manual operation; the opening cooling temperature of the second stage cooling is 570-640 ℃, 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 410-460 ℃, 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, and the purposes of improving the hardness of the steel rail welding joint and ensuring that no martensite, bainite and other abnormal structures exist in the metal phase of the steel rail welding joint can be achieved.
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 method for the postweld heat treatment of the hypereutectoid steel rail and eutectoid steel rail welded joint, the third cooling rate is much lower than the second cooling rate.
In the method for the postweld heat treatment of the hypereutectoid steel rail and eutectoid steel rail welded joint, the welded joint of the hypereutectoid steel rail and eutectoid steel rail is a welded joint of dissimilar steel rails welded by a rail moving flash welding machine.
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 or 68kg/m, and the steel rail welding joint is a welding joint formed by welding by 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.
The welded joints of the examples and comparative examples of the present invention were 68kg/m hypereutectoid steel rails and 68kg/m eutectoid steel rail welded joints.
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 7, 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
And after the steel rail is subjected to upsetting and beading in the moving flash welding process, performing postweld heat treatment on the joint obtained by welding. Firstly, carrying out first-stage cooling on a welded steel rail joint with the residual temperature of 1100 ℃ at a first cooling speed of 4.0 ℃/s so as to reduce the surface temperature of a rail head of the steel rail joint to 630 ℃, then carrying out second-stage cooling on the steel rail joint at a second cooling speed of 2.0 ℃/s so as to reduce the surface temperature of the rail head of the steel rail joint to 450 ℃, and finally carrying out third-stage cooling on the steel rail joint at a third cooling speed of 0.4 ℃/s so as to reduce the surface temperature of the rail head of the steel rail joint to the room temperature of 25 ℃, thereby obtaining the welded steel rail joint subjected to postweld heat treatment;
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 the rail head tread and the rail head side surface of the 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 0.60 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 8mm, 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. 8, 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
And after the steel rail is subjected to upsetting and beading in the moving flash welding process, performing postweld heat treatment on the joint obtained by welding. Firstly, carrying out first-stage cooling on a welded steel rail joint with the residual temperature of 1000 ℃ at a first cooling speed of 5.0 ℃/s so as to reduce the surface temperature of a rail head of the steel rail joint to 610 ℃, then carrying out second-stage cooling on the steel rail joint at a second cooling speed of 2.2 ℃/s so as to reduce the surface temperature of the rail head of the steel rail joint to 440 ℃, and finally carrying out third-stage cooling on the steel rail joint at a third cooling speed of 0.10 ℃/s so as to reduce the surface temperature of the rail head of the steel rail joint to the room temperature of 25 ℃, thereby obtaining the welded dissimilar material steel rail joint subjected to postweld heat treatment;
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 8mm, 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. 8, 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.
Comparative example 1
After the steel rail is subjected to upset forging and push-button in the moving flash welding process, directly air-cooling the steel rail joint with the residual temperature of 1000 ℃ to 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 one side of the eutectoid pearlite steel rail of the joint weld joint is 8mm, and the width of the softening zone on one 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. 8, 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
And after the steel rail is subjected to upsetting and beading in the moving flash welding process, performing postweld heat treatment on the joint obtained by welding. Firstly, carrying out first-stage cooling on a welded steel rail joint with the residual temperature of 1100 ℃ at a first cooling speed of 5.0 ℃/s so as to reduce the surface temperature of a rail head of the steel rail joint to 620 ℃, then carrying out second-stage cooling on the steel rail joint at a second cooling speed of 3.0 ℃/s so as to reduce the surface temperature of the rail head of the steel rail joint to 220 ℃, and finally carrying out third-stage cooling on the steel rail joint at a third cooling speed of 0.10 ℃/s so as to reduce the surface temperature of the rail head of the steel rail joint to the room temperature of 25 ℃, thereby obtaining the welded dissimilar material steel rail joint subjected to postweld heat treatment;
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 0.90 MPa; in the third cooling process, the gas pressure of the compressed air injected 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 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 10mm 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 475HV, and the average hardness exceeds 35HV 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. 8, 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 results show that the hypereutectoid steel rail and the eutectoid pearlite steel rail of the joint have hardened martensite structures, and the operation safety of the line is influenced.
Comparative example 3
And after the steel rail is subjected to upsetting and beading in the moving flash welding process, performing postweld heat treatment on the joint obtained by welding. Firstly, carrying out first-stage cooling on a steel rail joint with the residual temperature of 1050 ℃ obtained by welding at a first cooling speed of 4.5 ℃/s so as to reduce the surface temperature of a rail head of the steel rail joint to 620 ℃, then carrying out second-stage cooling on the steel rail joint at a second cooling speed of 2.2 ℃/s so as to reduce the surface temperature of the rail head of the steel rail joint to 440 ℃, and finally carrying out third-stage cooling on the steel rail joint at a third cooling speed of 2.5 ℃/s so as to reduce the surface temperature of the rail head of the steel rail joint to the room temperature of 25 ℃, thereby obtaining the welded dissimilar material steel rail welding joint subjected to postweld heat treatment;
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 10 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. 8, 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 on one side of the hypereutectoid steel rail of the joint welding seam has a hardened martensite structure, and the operation safety of the line is influenced.
Comparative example 4
And after the steel rail is subjected to upsetting and beading in the moving flash welding process, performing postweld heat treatment on the joint obtained by welding. Firstly, carrying out first-stage cooling on a steel rail joint with the residual temperature of 1050 ℃ obtained by welding at a first cooling speed of 4.5 ℃/s so as to reduce the surface temperature of a rail head of the steel rail joint to 620 ℃, then carrying out second-stage cooling on the steel rail joint at a second cooling speed of 2.2 ℃/s so as to reduce the surface temperature of the rail head of the steel rail joint to 440 ℃, and finally carrying out third-stage cooling on the steel rail joint at a third cooling speed of 3.5 ℃/s so as to reduce the surface temperature of the rail head of the steel rail joint to the room temperature of 20 ℃, thereby obtaining the welded dissimilar material steel rail welding joint subjected to postweld heat treatment;
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 1.10 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 6, and the effect of the longitudinal hardness distribution of the joints is shown in FIG. 6.
TABLE 6 comparative example 4 hardness test data for rail welded joint
As is apparent from Table 6 and FIG. 6, 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 8mm and a softened region width on the hypereutectoid rail side of 10 mm. The hardness of the joint weld seam eutectoid pearlite steel rail is not greatly different from that of the hypereutectoid steel rail. In the eutectoid pearlite rail, the hardness at a position 10mm from the center of the weld is only 350HV, which is 90HV lower than the average hardness of the base material of the eutectoid pearlite rail.
Referring to the sampling method shown in FIG. 8, 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 results show that the joint weld seam eutectoid pearlite steel rail and hypereutectoid steel rail have quenched martensite structures in the gold phase, and the operation safety of the line is influenced.
As can be seen by comparing the weld joint railhead tread longitudinal stiffness and joint softening zone width in fig. 1-6: 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 (excluding the center line of the decarburized welding seam), and the widths of softening zones at two sides of the welding seam of the joint are lower than 15 mm. 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 (5)
1. The postweld heat treatment method for the hypereutectoid steel rail and the eutectoid steel rail welded joint is characterized by comprising the following steps of: 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 570-640 ℃, 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 410-460 ℃, 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 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; 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; the first cooling speed is 3.0-5.0 ℃/s; the second cooling speed is 1.5-2.5 ℃/s; the third cooling speed is 0.05-0.50 ℃/s.
2. The method for the post-weld heat treatment of a hypereutectoid steel rail and a eutectoid steel rail welded joint according to claim 1, characterized in that: the steel rail welding joint is formed by welding hypereutectoid steel rails with the same rail type and eutectoid steel rails.
3. The method for the post-weld heat treatment of a hypereutectoid steel rail and a eutectoid steel rail welded joint according to claim 1, characterized in that: the initial temperature of the steel rail welding joint is 1000-1350 ℃.
4. The method for the post-weld heat treatment of a hypereutectoid steel rail and a eutectoid steel rail welded joint according to claim 1, characterized in that: the first stage cooling mode is natural cooling in air.
5. The method for the postweld heat treatment of a hypereutectoid steel rail and a eutectoid steel rail welded joint according to any one of claims 1 to 4, characterized in that: the hypereutectoid steel rail and the eutectoid steel rail are welded by a steel rail mobile flash welding machine to form a welding joint of dissimilar steel rails.
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| CN110016544A (en) * | 2019-05-28 | 2019-07-16 | 攀钢集团攀枝花钢铁研究院有限公司 | Construction method for the heat treatment of bainite rail postwelding connector |
| CN112251592B (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 dissimilar steel rail flash welded joint |
| CN112251587B (en) * | 2020-10-23 | 2022-03-22 | 攀钢集团攀枝花钢铁研究院有限公司 | Heat treatment method for welded joint of bainite steel rail and eutectoid pearlite steel rail |
| CN113414480B (en) * | 2021-07-23 | 2022-10-11 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for eliminating overburning defect of mobile flash welding head of hypereutectoid steel rail of 75kg/m |
| CN113755670B (en) * | 2021-08-24 | 2022-10-25 | 中铁宝桥集团有限公司 | Quenching and cooling method for bainitic steel frog point rail |
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| JPH09316598A (en) * | 1996-03-27 | 1997-12-09 | Nippon Steel Corp | Pearlitic rail, excellent in wear resistance and weldability, and its production |
| JP4105909B2 (en) * | 2002-07-10 | 2008-06-25 | 新日本製鐵株式会社 | Heat treatment method for pearlitic rails to improve toughness of welded joints |
| EP2578716B1 (en) * | 2010-06-07 | 2019-09-11 | Nippon Steel Corporation | Steel rail |
| CN103160736B (en) * | 2011-12-14 | 2015-09-02 | 鞍钢股份有限公司 | A kind of high strength bainite steel rail and thermal treatment process thereof |
| CN106086370B (en) * | 2016-06-24 | 2018-10-09 | 成都先进金属材料产业技术研究院有限公司 | A kind of method reducing rail residual stress and gained rail and its application |
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