CN110616368B - Method for controlling R260 steel rail flash welding joint martensite structure - Google Patents
Method for controlling R260 steel rail flash welding joint martensite structure Download PDFInfo
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- CN110616368B CN110616368B CN201910702888.6A CN201910702888A CN110616368B CN 110616368 B CN110616368 B CN 110616368B CN 201910702888 A CN201910702888 A CN 201910702888A CN 110616368 B CN110616368 B CN 110616368B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
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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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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B2201/00—Special rolling modes
- B21B2201/06—Thermomechanical rolling
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- Machines For Laying And Maintaining Railways (AREA)
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Abstract
The invention relates to a method for controlling R260 steel rail flash welding joint martensite structure, belonging to the technical field of railway steel rail welding. The invention solves the technical problem that the R260 steel rail flash welding joint is easy to have martensite structure after air cooling after welding. The technical scheme of the invention is a method for controlling R260 steel rail flash welding joint martensite structure, comprising the steps of controlling the chemical components of R260 steel rail base metal, controlling a hot rolling process, controlling a welding process and controlling cooling after welding, wherein the Mn content of the R260 steel rail base metal is controlled to be 1.10-1.25% in percentage by weight, the C content is controlled to be at the middle lower limit, and the Si content is controlled to be less than or equal to 0.30%. According to the invention, martensite structures can be prevented from appearing at the specified inspection positions of the rail head central plane and the rail foot, various mechanical property indexes of the joint are ensured, the technical requirements of EN14587-2:2009 standard are met, and the rail joint has good popularization and application prospects.
Description
Technical Field
The invention belongs to the technical field of railway steel rail welding, and particularly relates to a method for controlling R260 steel rail flash welding joint martensite structure.
Background
The EN R260 steel rail is one of steel grades which are exported to southeast Asia countries such as Malaysia, Thailand and the like most frequently every year, and is exported by about 2-4 million tons every year. The chemical components of the finished steel rail of R260 produced according to the standard requirement of EN13674-1:2011 < Railway applications-Track-Railpart 1: Vignole Railway rails 46 kg/and above >: 0.60 to 0.82 percent of C, 0.65 to 1.25 percent of Mn, 0.13 to 0.60 percent of Si, P, S to less than or equal to 0.030 percent, Cr to less than or equal to 0.15 percent, V to less than or equal to 0.030 percent, the rest of Mo, Ni, Cu, Sn, Pb and the like are control elements, and the general content is required to be controlled to be 0.02 to 0.15 percent. Meanwhile, the EN standard requires that the tensile strength Rm of the mechanical property of the R260 steel rail is more than or equal to 880MPa, the elongation A after fracture is more than or equal to 10 percent, and the tread hardness is 260-300 HB.
In order to ensure that the strength and tread hardness of the R260 steel rail meet the standard requirements, the steel rail manufacturer raises the Mn content to an upper limit range to ensure that the steel rail after normal rolling meets EN standards under air cooling conditions: rm is not less than 880MPa, and the tread hardness is 260-300 HB. However, C, Mn is a segregation element, when the content of Mn in the steel rail is increased to the upper limit, the steel rail base metal with high Mn content tends to cause Mn micro-region segregation, the chemical component with high content in the segregation region causes the CCT curve to move to the right severely, and particularly, the spot martensite structure appears in the air cooling process of the welded joint, which cannot pass the weld type detection of EN standard.
Disclosure of Invention
The invention solves the technical problem that the R260 steel rail flash welding joint is easy to have martensite structure after air cooling after welding.
The technical scheme for solving the technical problems is to provide a method for controlling R260 steel rail flash welding joint martensite structure, which comprises the following steps: controlling chemical components of R260 steel rail base metal, controlling a hot rolling process, controlling a welding process and controlling cooling after welding, wherein the Mn content of the R260 steel rail base metal is controlled to be 1.10-1.25% in percentage by weight, the C content is controlled to be at a middle lower limit, and Si is controlled to be less than or equal to 0.30%.
Wherein the mechanical property of the steel rolling rail can meet the condition that Rm is more than or equal to 880MPa and tread hardness is more than or equal to 260HB under the control of the hot rolling process.
Furthermore, the hot rolling process adopts a universal rolling production line for hot rolling.
Wherein the welding process is controlled to keep the welding upset amount at 14.0-15.0 mm.
Furthermore, the welding process adopts 8.5-9.5 MJ high heat input pulsation or preheating flash welding.
And performing postweld cooling control when the joint is air-cooled to 590-570 ℃ after the joint push beading is finished in the welding process control.
Wherein, the post-welding cooling is controlled to be carried out when the temperature of the joint is kept and cooled to be below 250 ℃, and then the joint is air-cooled to the room temperature.
And controlling the cooling speed of the joint in a phase transition temperature range from austenite to pearlite to be 0.6-0.3 ℃/s.
Specifically, the cooling speed of the joint is controlled to be 0.6-0.3 ℃/s within the range of 620-500 ℃.
Wherein, the post-welding cooling control adopts a heat preservation device for slow cooling, and the heat preservation device adopts a railhead heat preservation device or a full-section steel rail heat preservation device with a hinge structure embedded with aluminosilicate cellucotton.
Further, the length of the heat preservation device is 230 mm-250 mm; the thickness of the aluminosilicate cellucotton is 40 mm. .
The invention has the beneficial effects that:
according to the invention, by comprehensively controlling the chemical components, the hot rolling process, the welding process and the post-welding cooling of the R260 steel rail, under the condition that the Mn content of the component of the R260 steel rail is 1.10-1.25%, the flash welding head can avoid martensite structures from appearing at the specified inspection positions of the central plane of the rail head and the rail foot, so that various mechanical property indexes of the joint are ensured, and the technical requirements of EN14587-2:2009 standard are met; the invention adopts a simple rail head heat preservation device or a full-section steel rail heat preservation device to carry out heat preservation and cooling control, and the length and the thickness of the heat preservation device are set, so that the cooling speed after welding is well controlled; the invention has simple control process, can solve the major welding technical problem of the EN R260 steel rail on the popularization and application roads in a matching way, and has good popularization and application prospect.
Drawings
FIG. 1 is a schematic diagram of a microstructure inspection position specified in EN14587-2:2009 standard, where 1 and 2 are the microstructure inspection positions;
FIG. 2 is a schematic view of the heat-insulating structure of the railhead heat-insulating device according to the present invention, wherein a is the length of the heat-insulating device;
FIG. 3 is a schematic view of the thermal insulation of the full-face thermal insulation apparatus according to the present invention;
FIG. 4 is a metallographic structure diagram of a joint in example 1 of the present invention.
Detailed Description
The rail welding method and the inspection standard required by the foreign EN, AREMA and other standards are different from the standard of the China TB/T1632-2014 rail welding series. The biggest difference of the welding method is that the joint post-welding heat treatment is not carried out by adopting a post-welding normalizing air cooling process after welding, but a post-welding air cooling or air straightening process is generally adopted. The R260 steel rail is generally welded and accepted in AS standard abroad before, but in recent years, strict acceptance is required according to EN14587-2:2009 standard. In particular, EN14587-2:2009 "Rail way applications-Track-Flash building welding of rails, part 2: New R220R 260R 260Mn and R350HT grade rails by mobile welding machines at sites other than a fixed plant" standard provides for examining the microstructure of the position of the vertical central plane of 0 mm-20 mm under the tread of the R260 Rail Flash welding air-cooled joint as shown in FIG. 1. The vertical central plane of the steel rail is the central crystal plane of the continuous casting billet and is the most serious region of element segregation such as C, Mn and the like.
The invention provides a method for controlling R260 steel rail flash welding joint martensite structure, which comprises the following steps: controlling chemical components of R260 steel rail base metal, controlling a hot rolling process, controlling a welding process and controlling cooling after welding, wherein the Mn content of the R260 steel rail base metal is controlled to be 1.10-1.25% in percentage by weight, the C content is controlled to be at a middle lower limit, and Si is controlled to be less than or equal to 0.30%. The C content is controlled between 0.70-0.75% in the middle and lower limits.
Wherein the mechanical property of the steel rolling rail can meet the condition that Rm is more than or equal to 880MPa and tread hardness is more than or equal to 260HB under the control of the hot rolling process. The hot rolling process of the steel rail base metal can adopt the conventional hot rolling technology, so that the mechanical property of the steel rail after hot rolling can meet the condition that Rm is more than or equal to 880MPa and tread hardness is more than or equal to 260 HB. Preferably, the hot rolling process adopts a universal rolling production line for hot rolling.
Wherein the welding process is controlled to keep the welding upset amount at 14.0-15.0 mm. After hot rolling, the method enters a welding process control stage, wherein the upsetting amount is particularly controlled, and because the upsetting amount is too small, oxides which are not completely extruded exist in a welding seam, the performance of the joint is reduced; an excessive upset amount results in a cold joint, and the performance is also reduced. In practice, the best upsetting amount needs to be confirmed through a large number of static bending or stretching experiments.
Specifically, the steel rail mobile flash welding machine or the fixed flash welding machine is used for performing high heat input pulsation or preheating flash welding of 8.5-9.5 MJ. The larger the heat input, the slower the cooling speed of the joint after welding, which is beneficial to reducing the area percentage content of martensite structure.
Further, in the welding process, when the joint is air-cooled to 590-570 ℃ after the joint push beading is finished, post-welding cooling control is performed.
The post-welding cooling control is particularly important, and the invention carries out cooling control in a heat preservation cooling mode, controls the temperature of the joint to be cooled to below 250 ℃ in a heat preservation manner, and then carries out air cooling to the room temperature.
The invention reduces the cooling speed in a heat preservation cooling (slow cooling) mode, thereby avoiding the occurrence of martensite structure. Specifically, the cooling speed of the joint in a phase transition temperature range from austenite to pearlite is controlled to be 0.6-0.3 ℃/s. A large number of tests verify that the cooling speed of the connector at the temperature of 620-500 ℃ is controlled to be 0.6-0.3 ℃/s after welding, and the critical martensite transformation speed can be avoided being exceeded.
Specifically, the post-welding cooling control adopts a heat preservation device for slow cooling, and the heat preservation device adopts a rail head heat preservation device (figure 2) or a full-section steel rail heat preservation device (figure 3) with a hinge type structure and embedded with aluminosilicate cellucotton.
The length and thickness of the heat preservation device greatly influence the heat preservation cooling, and in order to better control the cooling speed, the length of the heat preservation device is preferably 230 mm-250 mm, and the thickness of the aluminate cellucotton is preferably 40 mm.
The present invention is further illustrated by the following examples.
In the invention, the welding joint is a welded area which contains a welding seam and has a length of 70-110 mm, and the center of the area is a steel rail welding seam. The joint temperature related by the invention is the rail head surface layer temperature of a welding joint, namely the rail head tread temperature, an infrared thermometer is adopted to collect temperature signals, and the rail head tread is the contact part of a wheel and a rail. The full section refers to the whole section of the steel rail welding joint including the welding seam and having the length of about 70-110 mm, and comprises a rail head, a rail web and a rail bottom.
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, 3 percent nitric acid alcohol solution is adopted to carry out etching on the metallographic structure sample of the steel rail joint, and a German Leica MeF3 optical microscope is adopted to observe the metallographic structure of the steel rail joint. And the static bending load, the deflection and the microscopic structure inspection position of the joint are performed according to EN14587-2:2009 standard.
Example 1
Controlling Mn content in R260 steel rail base metal components to be 1.10% Mn, other chemical components to be middle and lower limits, keeping Si to be less than or equal to 0.30%, enabling mechanical properties of a hot-rolled steel rail produced and rolled normally by a universal line to meet Rm of not less than 880MPa, enabling tread hardness of not less than 260HB, utilizing a steel rail mobile flash welding machine or a steel rail fixed flash welding machine, adopting 8.5MJ large heat input quantity pulsation or preheating flash welding, keeping actual welding upsetting quantity to be 14.0mm, after joint beading is completed, air-cooling to 570 ℃, carrying out slow cooling by adopting a rail head heat preservation device or a full-section steel rail heat preservation device with a hinge type structure embedded with aluminosilicate fiber cotton with the thickness of 40mm, wherein the length of the heat preservation slow cooling device is 230mm, and when the slow cooling temperature is below 250 ℃, removing the heat preservation device, and air-cooling the joint to room.
Through tests, no martensite structure is confirmed through inspection according to the specified positions of the rail head and the rail foot required by EN14587-2:2009 standard, the corresponding metallographic structure is shown in figure 4, the static bending load of the continuous 5-branch R260 steel rail joint of the embodiment reaches 1610kN, the deflection is 25.0mm, and the EN standard requirement is met.
Example 2
Controlling Mn content in R260 steel rail base metal components to be 1.15% Mn, other chemical components to be middle and lower limits, keeping Si to be less than or equal to 0.30%, enabling mechanical properties of a hot-rolled steel rail produced and rolled normally by a universal line to meet Rm of more than or equal to 880MPa, enabling tread hardness of more than or equal to 260HB, utilizing a steel rail mobile flash welding machine or a steel rail fixed flash welding machine, adopting large heat input pulsation of 8.5MJ or preheating flash welding, keeping actual welding upsetting amount to be 14.0mm, after joint beading is finished, air-cooling to 580 ℃, carrying out slow cooling by adopting a rail head heat preservation device or a full-section steel rail heat preservation device with a hinge type structure embedded with aluminosilicate fiber cotton with the thickness of 40mm, wherein the length of the heat preservation slow cooling device is 240mm, and when the slow cooling temperature is below 250 ℃, removing the heat preservation device, and enabling the joint.
Through tests, the rail head and rail foot specified positions required by EN14587-2:2009 are checked and confirmed to have no martensite structure, and the static bending load of the continuous 5-branch R260 steel rail joint of the embodiment reaches 1610kN, the deflection is 25.6mm, and the EN standard requirement is met.
Example 3
Controlling the Mn content in the R260 steel rail base metal to be 1.20% Mn, the other chemical components to be middle and lower limits and Si to be less than or equal to 0.30%, wherein the mechanical property of the hot rolled steel rail produced and rolled normally by a universal line meets the condition that Rm is more than or equal to 880MPa and the tread hardness is more than or equal to 260HB, utilizing a steel rail mobile flash welding machine or a fixed flash welding machine, adopting a 9.0MJ large heat input quantity pulse or preheating flash welding, keeping the actual welding upsetting quantity at 14.5mm, when the joint is air-cooled to 580 ℃ after the end of the knob pushing, adopting a rail head heat preservation device or a full-section steel rail heat preservation device with a hinge type structure embedded with aluminosilicate fiber cotton with the thickness of 40mm for slow cooling, keeping the length of the slow cooling device at 240mm, and removing the heat preservation device when the slow cooling temperature is below 250 ℃ to ensure that.
Through tests, the rail head and rail foot specified positions required by EN14587-2:2009 are checked and confirmed to have no martensite structure, and the static bending load of the continuous 5-branch R260 steel rail joint of the embodiment reaches 1610kN, the deflection is 24.0mm, and the EN standard requirement is met.
Example 4
Controlling the Mn content in the R260 steel rail base metal to be 1.25% Mn, the other chemical components to be middle and lower limits and Si to be less than or equal to 0.30%, wherein the mechanical property of the hot rolled steel rail produced and rolled normally by a universal line meets the condition that Rm is more than or equal to 880MPa and the tread hardness is more than or equal to 260HB, utilizing a steel rail mobile flash welding machine or a fixed flash welding machine, adopting a 9.5MJ large heat input quantity pulse or preheating flash welding, keeping the actual welding upsetting quantity at 15.0mm, when the joint is air-cooled to 590 ℃ after the end of the knob pushing, adopting an air-cooled hinge type rail head heat preservation device or a full-section steel rail heat preservation device with 40 mm-thickness aluminosilicate fiber cotton embedded in the structure to carry out slow cooling, wherein the length of the heat preservation slow cooling device is 250mm, and removing the heat preservation device when the slow cooling temperature is below.
Through tests, the rail head and rail foot specified positions required by EN14587-2:2009 are checked and confirmed to have no martensite structure, and the static bending load of the continuous 5-branch R260 steel rail joint of the embodiment reaches 1610kN, the deflection is 26.0mm, and the EN standard requirement is met.
The invention has good popularization and application prospect, and particularly, the steel climbing EN R260 steel rail is directly popularized and used in international railways and subway lines on-line welding construction units abroad.
Claims (3)
1. A method for controlling R260 steel rail flash welding joint martensite structure is characterized by comprising the following steps: controlling chemical components of R260 steel rail base metal, controlling a hot rolling process, controlling a welding process, and controlling heat preservation and cooling after welding, wherein the Mn content of the R260 steel rail base metal is controlled to be 1.10-1.25% by weight, the C content is controlled to be 0.70-0.75% by weight, and the Si content is controlled to be less than or equal to 0.30%; the welding process is controlled to keep the welding upset forging amount at 14.0-15.0 mm; the welding process control is that after the joint is subjected to push beading, air cooling is carried out to 590-570 ℃, and cooling control after welding is carried out; after welding, cooling, keeping the temperature of the joint, cooling to below 250 ℃, and then air cooling to room temperature; the welding process adopts 8.5-9.5 MJ high heat input pulsation or preheating flash welding; and the post-welding cooling control adopts a heat preservation device to carry out heat preservation and cooling, and the heat preservation device adopts a rail head heat preservation device or a full-section steel rail heat preservation device with a hinge type structure and embedded with aluminosilicate cellucotton.
2. The method for controlling R260 steel rail flash welding joint martensite structure according to claim 1, wherein: the mechanical property Rm of the rolled steel rail is not less than 880MPa and the tread hardness is not less than 260HB under the control of the hot rolling process.
3. The method for controlling R260 steel rail flash welding joint martensite structure according to claim 1 or 2, wherein: the length of the heat preservation device is 230 mm-250 mm; the thickness of the aluminosilicate cellucotton is 40 mm.
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| CN115488482B (en) * | 2022-11-03 | 2023-12-22 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for reducing width of heat affected zone of high-strength pearlitic steel rail flash welding head |
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