CN109055708B - Heat treatment method for weld joint of eutectoid steel rail and hypereutectoid steel rail - Google Patents
Heat treatment method for weld joint of eutectoid steel rail and hypereutectoid steel rail Download PDFInfo
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- CN109055708B CN109055708B CN201810946975.1A CN201810946975A CN109055708B CN 109055708 B CN109055708 B CN 109055708B CN 201810946975 A CN201810946975 A CN 201810946975A CN 109055708 B CN109055708 B CN 109055708B
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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
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Abstract
The invention discloses a heat treatment method for a weld joint of a eutectoid steel rail and a hypereutectoid steel rail, relates to the technical field of railway steel rail manufacturing, and provides a heat treatment method for a weld joint, which is low in cost and good in mechanical property of the treated weld joint. The method comprises the following steps which are carried out in sequence: A. cooling the welding joint with the temperature of 1000-1400 ℃ in a first stage to reduce the surface temperature of the welding joint to 650-720 ℃, wherein the cooling in the first stage is air cooling at the cooling speed of 5.0-9.0 ℃/s; B. cooling the welded joint in the second stage to reduce the surface temperature of the welded joint to 170-230 ℃, wherein the cooling in the second stage is carried out by adopting a profiling cooling device, and the cooling speed is 1.5-2.5 ℃/s; C. and cooling the welded joint in the third stage to reduce the surface temperature of the welded joint to 10-30 ℃, wherein the cooling in the third stage is performed by adopting a profiling cooling device, and the cooling speed is 0.05-0.50 ℃/s.
Description
Technical Field
The invention relates to the technical field of railway steel rail manufacturing, in particular to a heat treatment method for a weld joint of a eutectoid steel rail and a hypereutectoid steel rail.
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% by weight, and the steel rails have the characteristics of good obdurability matching, moderate comprehensive mechanical property index and the like, and the metallographic structure is pearlite. With the rapid development of railways, heavy-duty lines with large axle loads have higher requirements on the service performance of steel rails. As the comprehensive mechanical property and the welding property of the traditional pearlitic steel rail are almost developed to the limit, in this case, the hypereutectoid steel rail with higher strength grade and taking good comprehensive properties such as wear resistance, contact fatigue and the like into consideration is produced at the same time, the carbon content of the steel rail is usually within the range of 0.90-1.10% by weight, and the metallographic structure is pearlite and a small amount of secondary cementite. At present, steel rail mobile flash welding has become the mainstream steel rail on-line welding technology in railway construction sites at home and abroad, and for two kinds of steel rails with different strength grades and materials, the difference between the properties of parent metals brings great challenges to the welding. Meanwhile, 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 width 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 of the welding and post-welding heat treatment process of hypereutectoid steel rails and eutectoid steel rails. CN201610909362.1 discloses a postweld heat treatment method for a hypereutectoid steel rail and PG4 heat treatment eutectoid pearlite steel rail welded joint, which comprises the steps of firstly cooling a steel rail welded joint to be cooled obtained by welding to below 400 ℃, then heating the steel rail welded joint after the first cooling to 860-930 ℃, and then carrying out second cooling until the tread temperature of the steel rail welded joint 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: flash welding is the test requirement for fatigue, tensile, impact and static bending tests. However, the invention relates to the process of normalizing heat treatment after welding the steel rail, and needs to adopt the heat treatment equipment after welding the steel rail to locally heat the welded joint of the steel rail, so that the operation and implementation processes are complex, and the cost is higher.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: provides a heat treatment method for the weld joint of the eutectoid steel rail and the hypereutectoid steel rail, which has lower cost and good mechanical property of the treated weld joint.
The technical scheme adopted for solving the problems is as follows: the heat treatment method for the weld joint of the eutectoid steel rail and the hypereutectoid steel rail comprises the following steps in sequence:
A. welding a welded joint formed by welding a eutectoid pearlite steel rail and a hypereutectoid steel rail and having the temperature of 1000-1400 ℃ for first-stage cooling, so that the surface temperature of the welded joint is reduced to 650-720 ℃, the first-stage cooling is natural cooling in air, and the cooling speed is 5.0-9.0 ℃/s;
B. cooling the welded joint in the second stage to reduce the surface temperature of the welded joint to 170-230 ℃, wherein the cooling in the second stage is performed by adopting a profiling cooling device, and the profiling cooling device sprays compressed air or water mist mixed gas to the welded joint at the cooling speed of 1.5-2.5 ℃/s;
C. and cooling the welded joint in the third stage to reduce the surface temperature of the welded joint to 10-30 ℃, wherein the cooling in the third stage is performed by adopting a profiling cooling device, and the profiling cooling device sprays compressed air or water mist mixed gas to the welded joint at the cooling speed of 0.05-0.50 ℃/s.
Further, the method comprises the following steps: in the step B, the distance between the profiling cooling device and the welding joint is 20-50 mm; the pressure of the compressed air or the water mist mixed gas ejected by the cooling device is 0.40-0.80 MPa.
Further, the method comprises the following steps: in the step C, the distance between the profiling cooling device and the welding joint is 20-50 mm; the pressure of the compressed air or the water mist mixed gas ejected by the cooling device is 0.05-0.25 MPa.
Further, the method comprises the following steps: the welded joint is formed by welding a eutectoid pearlite steel rail and a hypereutectoid steel rail which are identical in rail type and have the specification of 60-75 kg/m through a steel rail mobile flash welding machine.
The invention has the beneficial effects that: (1) the invention carries out heat treatment by utilizing the welding waste heat of the welding joint, and reheating is not needed in the heat treatment process, thereby simplifying the heat treatment process and reducing the cost.
(2) The method can control the percentage content of martensite structures possibly appearing in the metallographic structure of the steel rail joint within the range of less than or equal to 2 percent. Meanwhile, the longitudinal hardness of the steel rail joint in a region +/-10 mm from the center of the welding seam can meet the +/-30 HV range of the average hardness of the parent metals of the corresponding eutectoid pearlite steel rail and hypereutectoid steel rail (the central line of the welding seam, which does not contain decarburization, is influenced by high welding temperature of the steel rail, the center of the welding seam is decarburized, element burning loss is generated, and the hardness is low), 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 of the steel rail welding joint caused by low hardness of the welding area in the service process of the steel rail, and is beneficial to ensuring the running safety of the railway.
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 rail joint under the post-weld heat treatment conditions obtained by the method of example 1.
FIG. 2 is a graph showing the effect of longitudinal hardness at a position 3 to 5mm below the rail head tread of a welded rail joint under the post-weld heat treatment conditions obtained by the method of 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 for rails under post-weld air-cooling conditions obtained by the method of comparative example 1.
FIG. 4 is a graph showing the effect of longitudinal hardness at a position 3 to 5mm below the rail head tread of a welded rail joint under the post-weld heat treatment condition obtained by the method of comparative example 2.
Fig. 5 is a schematic view of each part or position according to the present invention.
Fig. 6 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 invention is further described with reference to the following figures and detailed description.
The welding joint is formed by welding a eutectoid pearlite steel rail and a hypereutectoid steel rail which have the same rail type and the specification of 60-75 kg/m through a steel rail mobile flash welding machine. The welded joint comprises a region with the length of 70-100 mm in the welding seam and/or the heat affected zone, and the center of the region is the welding seam. In the invention, the room temperature is 10-30 ℃.
In fig. 6, a is a eutectoid pearlite rail, b is a welded joint, c is an hypereutectoid steel rail, and d is a rail head tread. The weld center is at e in fig. 6 and 6. In fig. 6, f is a metallographic sample sampling position.
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. In some national rail welding standards, such AS specified in australian rail welding standard AS1085.20-2012, for some high-strength-grade, high-carbon-content and high-alloy-content rails, under an observation magnification of a metallographic microscope of 100x, for the most severe region where martensite appears in a rail welded joint, the percentage content of martensite structure is not higher than 5%, otherwise the joint will cause premature fatigue fracture due to a large amount of hardened martensite structure, and the operation safety of the rail is seriously affected. 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, because a small amount of secondary cementite exists in the hypereutectoid steel rail base metal, in order to avoid the crystallization of the secondary cementite in a net shape along the steel rail welding process, the joint needs to be rapidly cooled before the transformation from austenite to pearlite begins.
Based on the above findings, the present invention is as follows: the heat treatment method for the weld joint of the eutectoid steel rail and the hypereutectoid steel rail comprises the following steps in sequence: A. welding a welded joint formed by welding a eutectoid steel rail and a hypereutectoid steel rail and having the temperature of 1000-1400 ℃ for first-stage cooling, so that the surface temperature of the welded joint is reduced to 650-720 ℃, the first-stage cooling is natural cooling in air, and the cooling speed is 5.0-9.0 ℃/s; B. cooling the welded joint in the second stage to reduce the surface temperature of the welded joint to 170-230 ℃, wherein the cooling in the second stage is performed by adopting a profiling cooling device, and the profiling cooling device sprays compressed air or water mist mixed gas to the welded joint at the cooling speed of 1.5-2.5 ℃/s; C. and cooling the welded joint in the third stage to reduce the surface temperature of the welded joint to 10-30 ℃, wherein the cooling in the third stage is performed by adopting a profiling cooling device, and the profiling cooling device sprays compressed air or water mist mixed gas to the welded joint at the cooling speed of 0.05-0.50 ℃/s.
The invention realizes the post-welding heat treatment process of the steel rail by using the welding waste heat of the steel rail. And performing post-welding accelerated cooling on the welded rail joint with high residual temperature to reduce the transformation temperature of the joint rail head from austenite to pearlite, so as to improve the hardness of an austenite recrystallization zone. 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-stage cooling is natural cooling in air, and the control of the first-stage cooling speed can be realized by adjusting the test environment temperature (for example, adopting a central air conditioner for temperature control). The reason why the temperature drop rate is still high in this stage though air cooling is because the temperature difference between the welded joint and the air is large.
The starting cooling temperature of the second cooling stage is 650-720 ℃. In the present invention, the final cooling temperature of the second cooling is higher than the martensite start temperature (Ms temperature) of the hypereutectoid rail steel and the eutectoid pearlite rail steel, and the final cooling temperature of the second cooling is 170 to 230 ℃. In the step B, the following method can be adopted to ensure that the cooling speed is 1.5-2.5 ℃/s: the distance between the profiling cooling device and the welding joint is 20-50 mm; the pressure of the compressed air or the water mist mixed gas ejected by the cooling device is 0.40-0.80 MPa.
When the rail joint is cooled in the third stage, in order to avoid the hardened martensite structure of the joint, the invention selects the cooling speed of 0.05-0.50 ℃/s lower than the martensite transformation critical cooling speed of the eutectoid pearlite rail steel to carry out slow cooling on the joint. The following method can be adopted to ensure the cooling speed of 0.05-0.50 ℃/s: the distance between the profiling cooling device and the welding joint is 20-50 mm; the pressure of the compressed air or the water mist mixed gas ejected by the cooling device is 0.05-0.25 MPa.
The present invention will be described in detail below by way of specific examples. In the following examples, hypereutectoid steel rails and eutectoid pearlite steel rails were produced from Pan Steel group.
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, the post-welding heat treatment is carried out on the joint obtained by welding. Firstly, the rail joint with the residual temperature of 1100 ℃ 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 2.0 ℃/s so as to reduce the surface temperature of the rail head of the rail joint to 220 ℃, and finally the rail joint is subjected to third-stage cooling at a third cooling speed of 0.4 ℃/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 rail joint subjected to postweld heat treatment is obtained. In the postweld heat treatment process, the first cooling is natural cooling carried out in the air, the second cooling and the third cooling process adopt the steel rail railhead profiling cooling device to cool the railhead tread and the railhead side surface of the steel rail joint by taking compressed air or water mist mixed gas as a cooling medium, and the distance between the cooling device and the steel rail railhead tread is 40 mm. In the second cooling process, the gas pressure of the compressed air or the water mist mixed gas sprayed by the cooling device is 0.60 MPa; in the third cooling process, the gas pressure of the compressed air or the water mist mixed gas sprayed 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:
as can be seen 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 the softening zone at one side of the eutectoid pearlite steel rail of the joint welding seam is 8.5mm, the width of the softening zone at one side of the hypereutectoid steel rail is 6.4mm, 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. 6, 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 test result shows that: a small amount of martensite structure appears in the heat affected zone on the side of the welded joint eutectoid rail. Under the observation magnification of a metallographic microscope of 100x, the percentage content of the martensite structure is 1.3% by statistics for the most severe region where the martensite structure appears. Meanwhile, the metallographic structure of the welding heat affected zone at one side of the hypereutectoid steel rail of the welding joint is normal, and abnormal structures such as martensite and bainite do not appear.
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 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 1000 ℃ obtained by welding is subjected to first-stage cooling at a first cooling speed of 6.0 ℃/s so as to reduce the surface 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 2.3 ℃/s so as to reduce the surface temperature of the rail head of the steel rail joint to 180 ℃, and finally the steel 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 steel 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 0.66 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:
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 the softening zone on one side of the joint eutectoid pearlite steel rail is 7.1mm, the width of the softening zone on one side of the hypereutectoid steel rail is 6.4mm, and the widths of the softening zones on two sides of the joint welding line are both lower than 15 mm.
Referring to the sampling method shown in FIG. 6, 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 test results show that martensite structures with different degrees appear in the welding heat affected zone of the hypereutectoid steel rail and the eutectoid pearlite steel rail. Under the observation magnification of a metallographic microscope of 100x, for the most serious area in which the martensite structure appears in the joint, the percentage content of the martensite structure on one side of the eutectoid steel rail is 1.8% through statistics, and the percentage content of the martensite structure on one side of the hypereutectoid steel rail is 1.0%. The percentage content of martensite structures on two sides of the steel rail welding joint is less than 2.0%, which is beneficial to ensuring the railway operation safety.
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 this comparative example under air cooling after welding was processed into a longitudinal hardness test specimen. 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:
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. 6, 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 test result shows that the metallographic structure of the welded 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 68kg/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 1050 ℃ 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 steel rail joint to 670 ℃, then the steel 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 steel rail joint to 250 ℃, and finally the steel rail joint is subjected to third-stage cooling 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 ℃, 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 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 4, and the effect of the longitudinal hardness distribution of the joints is shown in FIG. 4.
Table 4:
as can be seen from Table 4 and FIG. 4, the resulting welded joint of rails which had not been treated by the post-weld heat treatment method of the present invention had a softened region width on the eutectoid rail side of 9.0mm and a softened region width on the hypereutectoid rail side of 9.0 mm. The hardness of one side of the eutectoid pearlite steel rail of the welding joint is higher, and the hardness of the positions 2mm and 4mm away from the welding seam exceeds the average hardness of the base metal of the eutectoid pearlite steel rail by more than 30 HV.
Referring to the sampling method shown in FIG. 6, 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 test results show that martensite appears in different degrees in the welding heat affected zone of the hypereutectoid steel rail and the eutectoid pearlite steel rail. Under the observation magnification of a metallographic microscope of 100x, for the most serious area with the martensite structure in the joint, statistics shows that the percentage content of the martensite structure of the joint eutectoid steel rail reaches 14%, and the percentage content of the martensite structure of the joint hypereutectoid steel rail reaches 9%. The percentage content of martensite structures on both sides of the joint exceeds 5 percent, which is not beneficial to the railway operation safety.
As can be seen by comparing the weld joint railhead tread longitudinal stiffness and joint softening zone width in fig. 1-4: 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 percentage content of martensite structures possibly appearing in the metallographic structure of the steel rail joint can be controlled within the range of less than or equal to 2 percent, and the railway driving safety can be ensured.
Claims (4)
1. A heat treatment method for a weld joint of a eutectoid steel rail and a hypereutectoid steel rail is characterized by comprising the following steps of: comprises the following steps which are carried out in sequence:
A. welding a welded joint formed by welding a eutectoid pearlite steel rail and a hypereutectoid steel rail and having the temperature of 1000-1400 ℃ for first-stage cooling, so that the surface temperature of the welded joint is reduced to 650-720 ℃, the first-stage cooling is natural cooling in air, and the cooling speed is 5.0-9.0 ℃/s;
B. cooling the welded joint in the second stage to reduce the surface temperature of the welded joint to 170-230 ℃, wherein the cooling in the second stage is performed by adopting a profiling cooling device, and the profiling cooling device sprays compressed air or water mist mixed gas to the welded joint at the cooling speed of 1.5-2.5 ℃/s;
C. and cooling the welded joint in the third stage to reduce the surface temperature of the welded joint to 10-30 ℃, wherein the cooling in the third stage is performed by adopting a profiling cooling device, and the profiling cooling device sprays compressed air or water mist mixed gas to the welded joint at the cooling speed of 0.05-0.50 ℃/s.
2. The heat treatment method for the weld joint of the eutectoid steel rail and the hypereutectoid steel rail according to claim 1, characterized in that: in the step B, the distance between the profiling cooling device and the welding joint is 20-50 mm; the pressure of the compressed air or the water mist mixed gas ejected by the cooling device is 0.40-0.80 MPa.
3. The heat treatment method for the weld joint of the eutectoid steel rail and the hypereutectoid steel rail according to claim 1, characterized in that: in the step C, the distance between the profiling cooling device and the welding joint is 20-50 mm; the pressure of the compressed air or the water mist mixed gas ejected by the cooling device is 0.05-0.25 MPa.
4. The heat treatment method for the weld joint of the eutectoid steel rail and the hypereutectoid steel rail according to claim 1, characterized in that: the welded joint is formed by welding a eutectoid pearlite steel rail and a hypereutectoid steel rail which are identical in rail type and have the specification of 60-75 kg/m through a steel rail mobile flash welding machine.
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| CN201810946975.1A CN109055708B (en) | 2018-08-20 | 2018-08-20 | Heat treatment method for weld joint of eutectoid steel rail and hypereutectoid steel rail |
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| CN201810946975.1A CN109055708B (en) | 2018-08-20 | 2018-08-20 | Heat treatment method for weld joint of eutectoid steel rail and hypereutectoid steel rail |
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| CN110358906A (en) * | 2019-08-23 | 2019-10-22 | 攀钢集团攀枝花钢铁研究院有限公司 | The heat treatment method of steel rail weld joint |
| CN110358905A (en) * | 2019-08-23 | 2019-10-22 | 攀钢集团攀枝花钢铁研究院有限公司 | The heat treatment method of steel rail weld joint |
| CN112359179B (en) * | 2020-10-23 | 2022-07-19 | 攀钢集团攀枝花钢铁研究院有限公司 | Steel rail postweld heat treatment construction method |
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| JPS54148124A (en) * | 1978-05-12 | 1979-11-20 | Nippon Steel Corp | Manufacture of high strength rall of excellent weldability |
| CN1648263A (en) * | 2004-01-30 | 2005-08-03 | 哈尔滨铁路工务器材有限公司 | Heat treatment process after full length quenching steel rail welding |
| CN104862466B (en) * | 2015-06-11 | 2017-01-18 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for postweld heat treatment on hyper-eutectoid steel rail welding connector |
| 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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