CN108570550B - Postweld heat treatment method for heat-treatment type bainite steel rail welded joint - Google Patents
Postweld heat treatment method for heat-treatment type bainite steel rail welded joint Download PDFInfo
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- CN108570550B CN108570550B CN201810480790.6A CN201810480790A CN108570550B CN 108570550 B CN108570550 B CN 108570550B CN 201810480790 A CN201810480790 A CN 201810480790A CN 108570550 B CN108570550 B CN 108570550B
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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
Abstract
The invention relates to a heat treatment type bainite steel rail welded joint postweld heat treatment method, and belongs to the technical field of steel rail welding. The invention solves the technical problem of low hammer resistance of heat treatment type bainite. The technical scheme includes that after the surface temperature of a tread of a joint to be cooled obtained through welding is cooled to a temperature range of 850-500 ℃, air cooling is conducted on a rail head portion of the joint, and when the surface temperature of the tread is cooled to 270-210 ℃, air cooling is finished, and the joint is naturally cooled to the room temperature. The welded joint after heat treatment meets the technical requirements of impact, hardness, softening area width and hammer resistance of the heat treatment type bainite steel rail welded joint, and can be popularized and used in domestic heavy-duty line steel rail welding bases or on-line welding construction units.
Description
Technical Field
The invention belongs to the technical field of railway rail welding, and particularly relates to a postweld heat treatment method for a heat treatment type bainite steel rail welding joint.
Background
No matter the welding rail is based on ground flash welding, or on-site thermite welding or air pressure welding, the steel rail generally needs to be welded to form a seamless line, so that the smoothness of the railway is improved, and the stable running of a train is ensured. Years of data statistics show that the probability of rail damage accidents of a steel rail welding joint is far higher than that of a steel rail base metal, and the steel rail welding joint relates to the safety of railway transportation, so that the quality of the steel rail welding joint is always a major technical problem concerned by railway engineering departments. Bainite steel rails are new varieties researched and developed in recent years, are divided into two main categories of hot rolling type and heat treatment type at present, are mainly applied to producing steel rails and turnouts used by railway users, and are increasingly concerned by manufacturers and railway users due to high tensile strength and hardness, excellent fatigue performance and excellent wear resistance.
At present, after welding of domestic steel rails by flash welding or gas pressure welding, a postweld normalizing heat treatment process is usually carried out at about 900 ℃ according to the TB/1632 standard requirement, namely, medium-frequency induction electric heating or oxyacetylene flame heating is adopted to reach the peak temperature of 900 ℃, then air cooling is carried out to the room temperature, and in order to further improve the tread hardness, an air cooling process can be adopted after normalizing treatment.
The heat treatment type bainite steel rail has serious joint hardness softening after welding, so that the first task is to adopt a reasonable postweld heat treatment process to accelerate cooling and recover the joint hardness, reduce the width of a softening region and avoid the joint from low collapse in the service process on the upper road to influence the driving stability. However, after the heat treatment type bainite steel rail is subjected to full-section medium frequency or flame heating to 900-940 ℃ peak temperature heat treatment after welding, the tread hardness is difficult to reach 0.90HpThe soft area usually exceeds 20mm, and no matter be air cooling or adopt the gushing air to handle and accelerate cooling rate moreover, the fracture of welded joint in the drop hammer inspection all is the brittle fracture of parallel and level, and the joint hammer resistance is low, and the drop hammer inspection is difficult to pass through, and hammer resistance direct reaction connects the welding comprehensive quality.
Patent CN103898310B discloses a postweld heat treatment method for a bainite steel rail welded joint, which comprises the steps of carrying out first cooling on a joint to be cooled obtained by welding to a first temperature of 320-380 ℃, then heating the joint after the first cooling to a temperature higher than the first temperature and not higher than 510 ℃, and then carrying out second cooling.
Disclosure of Invention
The invention solves the technical problem of low hammer resistance of the heat treatment type bainite steel rail welding joint.
The technical scheme for solving the technical problems is to provide a postweld heat treatment method for a heat treatment type bainite steel rail welding joint, which comprises the following steps: and after the surface temperature of the welded joint tread of the steel rail to be cooled obtained by welding is cooled to a temperature range of 850-500 ℃, air cooling is carried out on the rail head part of the joint, and the air cooling is finished after the surface temperature of the tread is cooled to 270-210 ℃, so that the joint is naturally cooled to the room temperature.
Specifically, the air cooling is to perform air spraying cooling on the welding seams on the tread of the joint and the two sides of the rail head and within 50-100 mm of each of the two sides of the welding seams, namely, the air spraying cooling is performed on the welding seams and the two sides of the welding seams which are 100-200 mm in total.
Further, the air cooling is to perform air-jet cooling on the welding seam on the tread of the joint and the two sides of the railhead and the range within 100mm of each of the two sides of the welding seam, namely, the air-jet cooling is performed on the welding seam and the range within 200mm of the two sides of the welding seam.
Further, the air cooling is to cool the joint tread and the two sides of the railhead simultaneously, the existing railhead air cooling device can be adopted, the cooling device can simultaneously cool the joint tread and the two sides of the railhead, and is provided with an air pressure adjusting device and a display instrument, and the distance from the air injection port to the tread and the air injection length can be adjusted according to requirements.
Wherein the air pressure of the air-jet cooling is 0.10-0.25 MPa.
Furthermore, the air pressure of the air-jet cooling is 0.10-0.15 MPa.
Wherein the welded joint is obtained by flash welding or gas pressure welding.
The invention has the beneficial effects that:
the postweld heat treatment method for the heat treatment type bainite steel rail welding joint does not need to adopt a normalizing process of postweld medium-frequency induction electric heating or oxyacetylene flame heating, thereby simplifying the process and reducing the energy consumption; secondly, the average value of the impact work of the full-section welding seam of the joint reaches more than 17J, and the ratio H of the hardness of the longitudinal section of the joint to the hardness of the parent metalJ/HpThe steel plate reaches 0.86-0.93, the width of a softening region is less than 20mm, and the technical requirements of impact and hardness of a welded joint of the bainite steel rail subjected to heat treatment and the width of the softening region are met; finally, the full-section fracture of the steel rail of the welded joint is in a tough-plastic tearing shape in drop hammer test, and the hammer resistance of the joint is improved; the invention has good popularization and application prospect, and can be popularized and used in domestic heavy-duty line steel rail welding bases or on-line welding construction units.
Drawings
FIG. 1 is a test curve of the hardness of a welded joint in a longitudinal section obtained by the method of example 2 of the present invention.
FIG. 2 is a test curve of the hardness of a welded joint in a longitudinal section obtained by the method of example 4 of the present invention.
FIG. 3 is a test curve of the hardness of a welded joint in a longitudinal section obtained by the air cooling method after welding according to comparative example 1.
FIG. 4 is a hardness test curve of a welded joint in a vertical section obtained by the normalizing process method of comparative example 2.
FIG. 5 is a graph of the drop hammer fracture morphology of the welded joint obtained by the method of example 2 of the present invention.
FIG. 6 is a plot of the drop-weight fracture morphology of a welded joint obtained by the post-weld air-cooling method of comparative example 1.
FIG. 7 is a chart of the drop hammer fracture morphology of the welded joint obtained by the normalizing process method of comparative example 2.
Fig. 8 shows a rail head air-cooling device used in the embodiment.
Fig. 9 is a schematic diagram of the operation of the railhead air-cooling device.
Detailed Description
According to the conventional means, the tread hardness of the heat treatment type bainite steel rail welding joint needs to be restored through normalizing treatment, but fractures of the normalized welding joint in drop hammer test are all parallel and level brittle fractures, the hammer resistance of the joint is low, and the drop hammer test is not easy to pass.
The invention provides a post-welding heat treatment method for a heat treatment type bainite steel rail welding joint, which is characterized in that after the surface temperature of a tread of a steel rail welding joint to be cooled obtained by welding is cooled to a temperature range of 850-500 ℃, the rail head part of the joint is subjected to air cooling, and after the surface temperature of the tread is cooled to 270-210 ℃, the air cooling is finished, and the joint is naturally cooled to room temperature.
As shown in figure 5, the I-shaped steel rail comprises a rail head, a rail waist and a rail bottom, and researches show that if the I-shaped steel rail comprises the rail waist and the rail bottom in air cooling, the steel rail can have a brittle and hard martensite structure, so that the risk of rail breakage accidents is increased, and the position corresponding to the air cooling is the rail head part.
After the push-up after welding is finished, the temperature of the joint is up to 1300 ℃, the phase transition temperature of the heat treatment type bainite steel rail is about 400 ℃, theoretically, the joint structure can generate phase transition effect only by air cooling above the phase transition point, and the hardness of the joint can be improved by accelerating cooling. Considering the air cooling effect and the feasibility of the implementation process, the stability of the air cooling process is influenced due to too short cabin, and the air cooling is started at 850-500 ℃.
In the research process, the hardness of the joint can be improved to more than 0.90Hp after the final cooling temperature is lower than 210 ℃, but a large amount of banded martensite structures appear in the joint, and the martensite structures belong to brittle structures, so that the impact and fatigue properties of the joint are not facilitated, and the comprehensive mechanical properties of the joint are seriously reduced; when the final cooling temperature is higher than 270 ℃, the joint has no martensite structure, but the hardness of the joint is below 0.85Hp, so that the low-collapse phenomenon is easy to occur. Based on the reasons, the final cooling temperature of 270-210 ℃ is selected, so that the hardness of the joint is ensured, and meanwhile, the better comprehensive mechanical property can be obtained.
And air cooling is carried out on the welding seams on the tread of the joint and the two side surfaces of the railhead and the range within 50-100 mm of each of the two sides of the welding seam, and room-temperature compressed air is adopted for air cooling. In research, it is found that when the air is sprayed and cooled to the welding seams on the tread of the joint and two side surfaces of the rail head and the range of the two sides of the welding seams within less than 50mm, the good cooling effect on the welding seams of the joint and the heat affected zone can not be generated.
Preferably, the air cooling is performed by blowing air to the weld seam on the tread of the joint and both sides of the rail head and within 100mm of each of both sides of the weld seam
Preferably, the air cooling is performed by using the existing railhead air cooling device as shown in fig. 8, the air cooling device can simultaneously air cool the railhead tread and the two sides of the railhead, and is provided with an air pressure adjusting device and a display instrument, the distance from an air injection port to the tread and the air injection length can be adjusted according to needs, and the cooling speed can be improved by simultaneously air cooling the railhead tread and the two sides of the railhead.
Wherein the air pressure of the air-jet cooling is 0.10-0.25 MPa. When the air pressure of the air jet cooling is too high, the temperature difference between the surface and the core of the rail head of the steel rail is large, the outer part of the joint is cooled to 210 ℃, but the core temperature can be over 300 ℃, and finally, the inspection hardness can be less than 0.85Hp, and the error is large.
Preferably, when the air pressure of the air-jet cooling is 0.1-0.15 MPa, the temperature difference between the surface and the center of the joint is small, and the hardness of the joint is more accurately checked.
Wherein the welded joint is obtained by flash welding or gas pressure welding.
In the invention, when not particularly described, the welded joint is a welded region having a length of 80 to 120mm including a weld and a heat affected zone, the center of the welded region is a rail weld, and the room temperature is a temperature range of 0 to 45 ℃.
The present invention is further illustrated by the following examples.
The bainitic rail used in the following examples is a new test product developed for Pan Steel, under the designation PB 2.
The weld joint hardness test of the following examples was according to TB/T1632.2-2014 Rail weld part 2: flash welding, machining a steel rail welding joint into a longitudinal section hardness sample, performing longitudinal section Rockwell hardness detection on the welding joint at a position 5mm below a tread, symmetrically arranging measuring points to the left and right sides by taking a welding seam as a center, wherein the distance between the measuring points is 5mm, performing the Rockwell hardness method according to GB/T230.1-2009 regulations, and taking H as the standardpDenotes the average hardness of the base material of the rail, HjRepresenting the average value of the hardness of the joint, the hardness of the joint is lower than 0.9HpThe location of (b) represents a softened region.
Example 1
After the heat-treated bainite steel rail joint is subjected to flash welding or gas pressure welding, upsetting and push-welding, a special rail head air-cooling device is adopted when the welded joint is cooled to 850 ℃, and the joint tread and the rail head are buttedThe welding seams on the two side surfaces and the range within 70mm of each welding seam on the two sides are subjected to air blast cooling, the air pressure is 0.25MPa, the air cooling is finished after the surface temperature of the tread is cooled to 210 ℃, the joint is naturally cooled to the room temperature, the average value of the impact energy of the welding seams on the full section of the joint is more than 17J, and the ratio H of the hardness of the longitudinal section of the joint to the hardness of the base metal isJ/HpThe drop hammer fracture morphology is tough-plastic tearing at 0.86-0.93.
Example 2
After the heat treatment bainite steel rail joint is subjected to flash welding or gas pressure welding upsetting and push welding, a special rail head air cooling device is adopted when the welding joint is cooled to 750 ℃, air blasting cooling is simultaneously carried out on welding seams on a tread of the joint and two side surfaces of the rail head and the range within 100mm of each welding seam, the air pressure is 0.20MPa, air cooling is finished when the surface temperature of the tread is cooled to 220 ℃, the joint is naturally cooled to the room temperature, the average value of the impact work of the welding seam on the whole section of the joint is more than 17J, the hardness test curve of the longitudinal section of the joint is shown in figure 1, and the ratio H of the hardness of the longitudinal section of the joint to the hardness of a base metal isJ/Hp0.921, softening zone width: the left side is 15.0mm, the right side is 15.0mm, and the drop hammer fracture morphology is shown in FIG. 5.
Example 3
After the heat treatment bainite steel rail joint is subjected to flash welding or gas pressure welding upsetting and push welding, a special rail head air cooling device is adopted when the welding joint is cooled to 650 ℃, air blasting cooling is carried out on welding seams on a tread of the joint and two side surfaces of the rail head and the range within 80mm of each welding seam, the air pressure is 0.15MPa, air cooling is finished when the surface temperature of the tread is cooled to 250 ℃, the joint is naturally cooled to the room temperature, the average value of the impact power of the welding seam on the full section of the joint is more than 17J, and the ratio H of the hardness of the longitudinal section of the joint to the hardness of a base metal is HJ/HpThe drop hammer fracture morphology is tough-plastic tearing at 0.86-0.93.
Example 4
After the heat treatment bainite steel rail joint is subjected to flash welding or gas pressure welding upsetting and push welding, a special rail head air cooling device is adopted when the welding joint is cooled to 800 ℃, and the welding seams on the tread of the joint and two side surfaces of the rail head and two sides of the welding seam are respectively 100mmCooling with air jet within the range of 0.12MPa, cooling to 270 deg.C, cooling to room temperature, naturally cooling to obtain joint with average impact energy of 17J or more, testing the hardness of the longitudinal section of the joint as shown in FIG. 2, and comparing the hardness of the longitudinal section with that of the base materialJ/Hp0.865, softening zone width: the left side is 25.0mm, the right side is 22.5mm, and the drop hammer fracture appearance is in a tough-plastic tearing shape.
Comparative example 1
And (4) postweld air cooling is adopted, namely the joint is naturally cooled in the air after the push button of the steel rail is welded. The hardness test curve of the joint profile is shown in FIG. 3, from which it can be seen that the ratio H of the hardness of the weld joint profile to the hardness of the base metal of this comparative exampleJ/Hp0.841, softening zone width: the left side is 40.0mm, the right side is 40.0mm, and the drop hammer fracture morphology is shown in FIG. 6.
Comparative example 2
Normalizing and air cooling after welding, namely after the welding of the steel rail finishes the push button, normalizing the joint and spraying air for cooling, wherein the normalizing process is shown in Table 1, the hardness test curve of the longitudinal section of the joint is shown in figure 4, and the ratio H of the hardness of the longitudinal section of the joint to the hardness of the base metal is shown in figure 4J/Hp0.87, softening zone width: the left side is 7.5mm, the right side is 20mm, and the drop hammer fracture morphology is shown in FIG. 7.
TABLE 1
From the above examples and comparative examples, H of joints after welding if only air cooling treatment is employed as in comparative example 1J/HpThe thickness is 0.841 low, the width of a softening zone is large, the appearance of a drop hammer fracture is brittle and level, and the hammer resistance is low; if the post-welding is treated by the conventional normalizing process as in comparative example 2, H of the jointJ/HpWhen the width of the right softening area is 0.87, the width of the right softening area reaches 20mm, the appearance of the drop hammer fracture is brittle and level, and the hammer resistance is low; with the post-weld heat treatment method of the present invention as in example 1, H of the jointJ/Hp0.921, softening zone width: the left side is 15.0mm, the right side is 15.0mm, the drop hammer fracture morphology is tough-plastic tearing, and the hammer resistance is good, which indicates that the welded joint obtained by the postweld heat treatment method of the invention meets the technical requirements of hardness and width of a softening zone, and meanwhile, the hammer resistance is improved.
Claims (5)
1. The postweld heat treatment method for the heat treatment type bainite steel rail welding joint is characterized by comprising the following steps of: and after the surface temperature of the welded joint tread of the steel rail to be cooled obtained by welding is cooled to a temperature range of 850-500 ℃, carrying out air spraying cooling on the welding seams on the tread of the joint and two sides of the rail head and the range within 50-100 mm of each of two sides of the welding seams, wherein the air pressure of air cooling is 0.10-0.25 MPa, finishing air cooling after the surface temperature of the tread is cooled to 270-210 ℃, and then naturally cooling the joint to room temperature.
2. The method for the post-weld heat treatment of the heat-treated welded bainitic rail joint as claimed in claim 1, wherein: and the air cooling is to spray air to the welding seams on the tread of the joint and two sides of the railhead and the range within 100mm of each welding seam.
3. The method for the post-weld heat treatment of the heat-treated welded bainitic rail joint as claimed in claim 1, wherein: and the air cooling is to cool the joint tread and two side surfaces of the railhead simultaneously.
4. The method for the post-weld heat treatment of the heat-treated welded bainitic steel rail joint according to any one of claims 1 to 3, characterized in that: the air pressure of the air cooling is 0.10-0.15 MPa.
5. The method for the post-weld heat treatment of the heat-treated welded bainitic rail joint as claimed in claim 1, wherein: the welded joint is obtained by flash welding or gas pressure welding.
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| 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 |
| CN115488485B (en) * | 2022-11-03 | 2023-07-25 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for reducing width of annealing zone of hypereutectoid steel rail joint |
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Effective date of registration: 20220628 Address after: 610306 Chengdu City, Chengdu, Sichuan, China (Sichuan) free trade test zone, Chengdu City, Qingbaijiang District, xiangdao Boulevard, Chengxiang Town, No. 1509 (room 13, A District, railway port mansion), room 1319 Patentee after: Chengdu advanced metal material industry technology Research Institute Co.,Ltd. Patentee after: Panzhihua Iron and Steel Group Panzhihua iron and Steel Research Institute Co., Ltd. Address before: 617000 Taoyuan street, East District, Panzhihua, Sichuan Province, No. 90 Patentee before: PANGANG GROUP PANZHIHUA IRON & STEEL RESEARCH INSTITUTE Co.,Ltd. |
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