CN113305407A - Flash welding process of 75kg/m 1380MPa bainite steel rail - Google Patents
Flash welding process of 75kg/m 1380MPa bainite steel rail Download PDFInfo
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- CN113305407A CN113305407A CN202110659299.1A CN202110659299A CN113305407A CN 113305407 A CN113305407 A CN 113305407A CN 202110659299 A CN202110659299 A CN 202110659299A CN 113305407 A CN113305407 A CN 113305407A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/04—Flash butt welding
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/02—Iron or ferrous alloys
- B23K2103/04—Steel or steel alloys
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Abstract
The invention provides a flash welding process of 75kg/m 1380MPa bainite steel rails, which comprises a flash flattening stage, a preheating stage, a burning stage and a top burning stage which are continuous; the technological parameters of each stage are as follows: controlling time parameters in a flash stage and a preheating stage, wherein the total time of the two stages is 70s +/-5 s; the burning stage comprises a continuous initial burning stage and an accelerated burning stage, and displacement parameters are controlled; the initial stage of burning comprises four continuous steps, wherein the displacement of a steel rail in each step is 2mm-2.2mm, and the displacement of the steel rail in the accelerated burning stage is 4mm-4.8 mm; and the displacement parameters are controlled in the top forging stage, and the displacement of the steel rail is 10mm +/-1 mm. The connector welded by the flash welding process parameters of the bainite steel rail provided by the invention can realize more than 15 continuous drop hammer tests to be qualified, and each mechanical property of the connector meets the requirement of upper pavement.
Description
Technical Field
The invention belongs to the technical field of welding, particularly relates to the technical field of flash welding, and particularly relates to a flash welding process of a bainite steel rail with high tensile strength.
Background
The bainite steel has good wear resistance and stripping resistance, and theoretically, if the bainite steel is used for railway tracks, the service life of heavy-duty railway steel rails can be prolonged. But the bainite steel rail is only applied as a turnout part without welding at home and abroad. As the difficult problem of welding the bainite steel rail is not solved, no bainite steel rail seamless line is put into commercial operation so far.
The welding of the steel rail on the railway in China is mainly completed in a flash welding machine by adopting a flash welding method. During welding, the two butt steel rails move slowly in opposite directions, current is made to pass through the contact surfaces of the two steel rails, the resistances of the fine contact points on the two contact surfaces and the electric arcs on the contact surfaces generate heat to heat the butt joint surfaces, and after a proper time, pressure is applied to the butt joint to make the whole areas of the two butt joint surfaces be firmly combined at the same time.
Because the spark that surface oxide and other impurity become the splash is cleared away, will not mix into in the welding seam, the reliability of the flash welding seam is high. Flash welding is generally divided into four continuous stages, namely a flash flattening stage, a preheating stage, a burning stage and a top burning stage, wherein the burning stage can be divided into an early burning stage and an accelerated burning stage. In the flash leveling stage, the end face of the normal-temperature steel rail is just heated by current, and surface oxides become sparks which splash; in the preheating stage, the end face of the steel rail is continuously heated; in the burning stage, the end face of the steel rail is ablated due to high temperature, and the solid steel is partially softened at the end face and has certain fluidity; in the top forging stage, two end faces which are completely contacted are applied with opposite pressure, so that the whole areas of the two butt joint surfaces are firmly combined at the same time. Flash welding is generally carried out by means of a flash welder. During welding, one steel rail is clamped and fixed by a fixed end of a welding machine, and the other steel rail is clamped by a movable end of the welding machine; in the welding process, the moving end of the welding machine clamps the steel rail and can move along the length direction of the steel rail, so that flash heating and upsetting of the end face of the steel rail are realized. Generally, only time is controlled for the flash stage, preheat stage, and burn stage processes.
The bainite steel rails with high Si-high Mn and medium Si-high Mn in China have unsatisfactory weldability due to high alloy content, and are mainly expressed in the following 3 aspects: firstly, welding a superheat zone has more defects. The superheated zone of flash welding has component segregation along austenite grain boundary, not only the microstructure changes, the brittleness increases, and even the serious zone has inclusions or liquification cracks. ② the welding residual stress inside the flash welding head is high and is distributed unevenly. The toughness of the welding seam is reduced dramatically; in general, compared with the base material, the toughness of the welding seam is reduced by more than 1 time, and the advantage loss of the toughness is quite serious. Therefore, the two bainite steel rail flash welding joints in China hardly meet the qualified requirement of a 15-joint continuous drop hammer test.
The domestic research on the bainite steel rail welding process mainly focuses on the postweld tempering heat treatment process. For example, the improvement of the tempering process is thought to greatly reduce the occurrence of horizontal cracks of welding seams (Dingwei, et al. study of bainite steel rail flash welding technology [ J ] railway construction, 2019, 59 (12): 142-. When the welding equipment is fixed, the control of welding defects mainly depends on optimizing the welding process. However, there are few reports and disclosures of this aspect.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a flash welding process of 75kg/m and 1380MPa bainite steel rails. By the flash welding process, the success of continuous drop hammer tests of 15 joints is realized, the welding defects are effectively controlled, and various performances of the welding joints meet the requirements of upper pavement.
Therefore, the invention adopts the following technical scheme:
a flash welding process of 75kg/m 1380MPa grade bainite steel rail, two bainite steel rails to be welded adopt the flash welding machine, one is fixed, another moves along the length direction of the steel rail; the flash welding comprises a flash flattening stage, a preheating stage, a burning stage and a top calcining stage which are continuous; the technological parameters of each stage are as follows:
controlling time parameters in a flash stage and a preheating stage, wherein the total time of the two stages is 70s +/-5 s;
the burning stage comprises a continuous initial burning stage and an accelerated burning stage, and displacement parameters are controlled; the initial stage of burning comprises four continuous steps, wherein the displacement of a steel rail in each step is 2mm-2.2mm, and the displacement of the steel rail in the accelerated burning stage is 4mm-4.8 mm;
and the displacement parameters are controlled in the top forging stage, and the displacement of the steel rail is 10mm +/-1 mm.
Preferably, the flash phase time is 15s-25s, the remainder being preheat phase time.
Preferably, the voltage of the accelerated burn-up phase is 400V ± 5V.
As a preferred embodiment, the flash welding process provided by the invention further comprises controlling the heat input amount to be 10.7MJ-11.7 MJ.
Alternatively, the current, voltage, feed or reverse speed values for the flash-flat and preheat phases may be set according to the welder equipment conditions.
Alternatively, the current, feed or reverse speed values for the burn phase may be set according to the welder equipment conditions.
Optionally, the live upsetting time of the upsetting stage can be set according to the condition of the welding machine equipment.
In the burning stage, the end faces of the two rails to be welded are ablated due to high temperature, so the displacement of the rails in the stage is to compensate for the ablated rails.
The connector welded by the flash welding process provided by the invention can realize more than 15 continuous drop hammer tests to be qualified, so that the welding defects are effectively controlled, and all mechanical properties of the connector meet the requirements of upper laying.
The flash welding process provided by the invention is suitable for various types of flash welding machines.
Drawings
The present application is further described below with reference to the accompanying drawings.
FIG. 1 is a plot of the flash welding process profile for the bainitic rail of example 1. In the figure:
the record of reference number 1 is that the current changes continuously; the record numbered 2 is a continuous change in voltage; the horizontal segment of the broken line with the reference number 3 shows the time length of each stage of flash welding, wherein the horizontal segments with the reference numbers of (I), (II), (III) and (III) are the time lengths of four continuous steps of the initial burning stage respectively (the broken line with the reference number 3 only sees an abscissa, and the ordinate has no practical significance); the continuous variation of pressure is recorded at reference numeral 4; the record 5 is the continuous variation of the displacement of the rail at the moving end.
In addition, designated as I is a flash-leveling stage, designated as II is a preheat stage, designated as III is a burn stage, designated as III-1 is an initial burn stage, designated as III-2 is an accelerated burn stage, and designated as IV is a top burn stage.
FIG. 2 is a plot of flash welding process recordings of bainitic steel rails of comparative example 1. In the figure:
the record of reference number 1 is that the current changes continuously; the record numbered 2 is a continuous change in voltage; the horizontal segment of the broken line with the reference number 3 shows the time length of each stage of flash welding, wherein the horizontal segments with the reference numbers of (I), (II), (III) and (III) are the time lengths of four continuous steps of the initial burning stage respectively (the broken line with the reference number 3 only sees an abscissa, and the ordinate has no practical significance); the continuous variation of pressure is recorded at reference numeral 4; the record 5 is the continuous variation of the displacement of the rail at the moving end.
In addition, designated as I is a flash-leveling stage, designated as II is a preheat stage, designated as III is a burn stage, designated as III-1 is an initial burn stage, designated as III-2 is an accelerated burn stage, and designated as IV is a top burn stage.
FIG. 3 is a photograph showing the fracture morphology of the weld of the bainitic rail welded according to example 1. The photographs show that the fractures are good and the welding defects are effectively controlled.
Figure 4 is a photograph showing the weld fracture morphology of the welded bainitic rail of comparative example 1. Within the photo circle is a gray spot defect that causes the joint to break.
Detailed Description
The invention is illustrated below with reference to specific examples. It will be understood by those skilled in the art that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention in any way.
The experimental procedures in the following examples are conventional unless otherwise specified. The raw materials used in the following examples are all commercially available products unless otherwise specified.
Wherein, the flash welding machine: YHF1200K (produced by Beijing Zhongxike New Material technology Co., Ltd.)
75kg/m, 1380MPa grade bainite steel rail: saddle Steel group Co.
Example 1Flash welding process of 75kg/m 1380MPa bainite steel rail
The flash welding process described in this embodiment includes a flash flattening stage (I), a preheating stage (II), a burning stage (III), and a top burning stage (IV) in succession, and the parameter records of each stage are shown in fig. 1.
Clamping and fixing a 75kg/m 1380MPa bainite steel rail to be welded by a fixed end of a flash welding machine, and clamping the other steel rail by a movable end of the welding machine; in the welding process, the moving end of the welding machine clamps the steel rail and can move along the length direction of the steel rail, so that flash heating and upsetting of the end face of the steel rail are realized.
After the flash stage (I) is carried out for 15 seconds, the preheating stage (II) is automatically switched to. And (3) voltage, current, advancing or retreating speed and displacement value of the steel rail in the flash leveling stage (I) are according to parameters automatically set by the welding machine.
The preheating stage (II) was carried out for 55 seconds, and the initial burning stage (III-1) was automatically carried out. And (3) the voltage, the current, the advancing or retreating speed and the displacement value of the steel rail in the preheating stage (II) are according to the parameters automatically set by the welding machine.
The initial stage of burning (III-1) comprises four successive steps, the duration of which corresponds to the horizontal sections marked by (1), (ii), (III) and (iv) in figure 1, each step advancing the rail by 2mm to compensate for the 2mm burned. Therefore, after the initial burn stage (III-1) is completed, the rail should burn off 8mm at this stage, and this amount of burn needs to be accurately controlled.
After 8mm of the rail is burnt in the initial burning stage (III-1), the accelerated burning stage (III-2) is started immediately. In the accelerated burning stage (III-2), the voltage is set to 400V, so that the burning speed is increased continuously, and the upsetting stage (IV) is started immediately when the rail is burnt by about 4mm in the accelerated burning stage (III-3).
And (3) the current in the burning stage (III) and the advancing or retreating speed of the steel rail are according to parameters automatically set by the welding machine.
In the upset forging stage (IV), the design upset amount is 8mm, and the actual upset amount achieved is about 2.5mm greater than the design value, so the actual displacement value of the rail is about 10.5 mm. The inventors have surprisingly found that the presence of this difference adaptively achieves the best match of the heating effect to the amount of upset.
And (3) the voltage, the current and the advancing speed of the steel rail in the burning stage (III) are automatically set according to parameters of a welding machine.
And (4) after the top calcining stage (IV) is finished, carrying out the operations of pushing the tumor and maintaining the pressure after pushing the tumor according to the conventional operation.
The heat input during the entire flash welding process was 11.2 MJ.
Comparative example 1Flash welding process of 75kg/m 1380MPa bainite steel rail
The flash welding machine used in this comparative example is the same as that used in example 1, and the welding process also includes a flash flattening stage (I), a preheating stage (II), a burning stage (III) and a top burning stage (IV) in succession, and the parameter records of each stage are shown in fig. 2. The difference between the welding process parameters of the comparative example and the welding process parameters of the example 1 is as follows:
the flash stage (I) time is set to 30 seconds, the preheating stage (II) time is set to 58 seconds, the burning stage (III) time is set to 12 seconds, the top end amount of the top forging stage (IV) is designed to be 10.5mm, and the actual displacement value is 12.7 mm. The heat input throughout the flash welding process was 12.1 MJ.
Test example 1Bainite Steel weld Joint Performance measurement of example 1 and comparative example 1
1. Drop weight test
15 joints welded in example 1 and comparative example 1 were each subjected to a drop weight test in accordance with the method of TB/T1632. Example 1 achieved that 15 continuous joints drop weight tests were acceptable, comparative example 1 broke off when the drop weight test was performed on the 3 rd joint, and it was not meaningful to continue to perform the welding test according to the welding parameters of the comparative example, so that the trial welding of the comparative example failed, and the subsequent performance test was terminated. A photograph of the welded rail joint discontinuity of example 1 is shown in fig. 3, which shows that the discontinuity is good and the weld defect is effectively controlled. Comparative example 1 a photograph of a welded rail joint discontinuity is shown in figure 4 which shows the presence of a gray spot defect (darker areas of the area indicated by the circles in the figure) which results in the fracture of the joint.
2. Fatigue test
The joint obtained by welding in the embodiment 1 takes 3 joints, and the fatigue test is carried out according to the method in TB/T1632, and the result meets the requirement of the joint of the 75kg/m steel rail in TB/T1632.
3. Tensile test of welded joint
Example 1 the welded joint was tested in tension by the method of TB/T1632, and the results of the tension test are shown in Table 1.
TABLE 1 weld joint tensile test results
4. Weld joint impact test
Example 1 the welded joint was 1-point tested by the method of TB/T1632 and the results are shown in Table 2.
TABLE 2 weld joint impact test results
The tests prove that the flash welding of 75kg/m and 1380MPa bainite steel rails by the welding process can effectively control the welding defects and has stable and reliable welding quality.
Finally, it should be noted that the above embodiments are only intended to illustrate the technical solution of the present invention and not to limit the technical method, the present invention can be extended in application to other modifications, variations, applications and embodiments according to different welding apparatuses, and all such modifications, variations, applications, embodiments are therefore considered to be within the spirit and teaching of the present invention.
Claims (7)
1. A flash welding process of 75kg/m 1380MPa grade bainite steel rail, two bainite steel rails to be welded adopt the flash welding machine, one is fixed, another moves along the length direction of the steel rail; the flash welding comprises a flash flattening stage, a preheating stage, a burning stage and a top calcining stage which are continuous; the technological parameters of each stage are as follows:
controlling time parameters in a flash stage and a preheating stage, wherein the total time of the two stages is 70s +/-5 s;
the burning stage comprises a continuous initial burning stage and an accelerated burning stage, and displacement parameters are controlled; the initial stage of burning comprises four continuous steps, wherein the displacement of a steel rail in each step is 2mm-2.2mm, and the displacement of the steel rail in the accelerated burning stage is 4mm-4.8 mm;
and the displacement parameters are controlled in the top forging stage, and the displacement of the steel rail is 10mm +/-1 mm.
2. The flash welding process of claim 1, wherein the flash phase time is 15-25 s, the remainder being preheat phase time.
3. Flash welding process according to claim 1, characterized in that the voltage of the accelerated burn phase is 400V ± 5V.
4. The flash welding process according to any of the claims 1 to 3, characterized in that the heat input is controlled to be 10.7MJ-11.7 MJ.
5. Flash welding process according to one of the claims 1 to 4, characterized in that the current, voltage, feed or back speed values for the flash-leveling phase and the preheating phase can be set according to the welder equipment.
6. Flash welding process according to one of the claims 1 to 5, characterized in that the current, feed or back speed values of the burn phase can be set according to the welder equipment conditions.
7. Flash welding process according to any of claims 1 to 6, characterized in that the live upsetting time of the upsetting stage can be set according to the welder equipment conditions.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115488482A (en) * | 2022-11-03 | 2022-12-20 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for reducing width of heat affected zone of high-strength pearlite steel rail flash welding head |
| CN115780977A (en) * | 2022-11-24 | 2023-03-14 | 攀钢集团攀枝花钢铁研究院有限公司 | Flash welding method for medium-carbon low-alloy steel rail |
| CN115922042A (en) * | 2023-01-31 | 2023-04-07 | 江苏科技大学 | Preheating flash butt welding method |
| WO2024168975A1 (en) * | 2023-02-14 | 2024-08-22 | 江苏科技大学 | Intelligent preheating flash butt welding method considering temperature field change at welding seam |
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| CN115488482A (en) * | 2022-11-03 | 2022-12-20 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for reducing width of heat affected zone of high-strength pearlite steel rail flash welding head |
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| CN115780977A (en) * | 2022-11-24 | 2023-03-14 | 攀钢集团攀枝花钢铁研究院有限公司 | Flash welding method for medium-carbon low-alloy steel rail |
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| WO2024168975A1 (en) * | 2023-02-14 | 2024-08-22 | 江苏科技大学 | Intelligent preheating flash butt welding method considering temperature field change at welding seam |
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