CN117660736A - Heat treatment method for 350HB grade steel rail welded joint - Google Patents
Heat treatment method for 350HB grade steel rail welded joint Download PDFInfo
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- CN117660736A CN117660736A CN202311480886.XA CN202311480886A CN117660736A CN 117660736 A CN117660736 A CN 117660736A CN 202311480886 A CN202311480886 A CN 202311480886A CN 117660736 A CN117660736 A CN 117660736A
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 61
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 57
- 239000010959 steel Substances 0.000 title claims abstract description 57
- 238000000034 method Methods 0.000 title claims abstract description 32
- 238000001816 cooling Methods 0.000 claims abstract description 37
- 230000006698 induction Effects 0.000 claims abstract description 14
- 238000003466 welding Methods 0.000 claims description 41
- 238000005507 spraying Methods 0.000 claims description 13
- 229910052799 carbon Inorganic materials 0.000 claims description 5
- 229910045601 alloy Inorganic materials 0.000 claims description 4
- 239000000956 alloy Substances 0.000 claims description 4
- 239000012535 impurity Substances 0.000 claims description 3
- 239000000126 substance Substances 0.000 claims description 3
- 230000008569 process Effects 0.000 abstract description 16
- 229910000734 martensite Inorganic materials 0.000 abstract description 4
- 230000007704 transition Effects 0.000 abstract description 2
- 239000010953 base metal Substances 0.000 description 5
- 238000005096 rolling process Methods 0.000 description 4
- 238000009826 distribution Methods 0.000 description 3
- 241001391944 Commicarpus scandens Species 0.000 description 2
- 230000009471 action Effects 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 230000008520 organization Effects 0.000 description 2
- 230000035882 stress Effects 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 238000003723 Smelting Methods 0.000 description 1
- 229910001563 bainite Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000010835 comparative analysis Methods 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000006355 external stress Effects 0.000 description 1
- 230000004927 fusion Effects 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical group C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
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Abstract
The invention discloses a heat treatment method of a 350HB grade steel rail welded joint, which comprises the steps of air-cooling a high-temperature welded joint to below 200 ℃ to ensure that each position of the joint is completely phase-changed; induction heating treatment is carried out by using a joint double-frequency normalizing machine, and joint low-frequency induction heating is carried out firstly: heating the joint from 0-200 ℃ to 825-845 ℃, stopping heating, and immediately performing high-frequency induction heating on the joint after the joint reaches the target temperature: heating the joint from 825-845 ℃ to 880-920 ℃; and (3) adopting air-jet cooling, adjusting the air pressure to 0.28-0.35 MPa, controlling the final air-jet cooling temperature of the joint to be between 450 and 485 ℃, stopping air-jet cooling, and naturally cooling to room temperature. The invention aims to solve the problem that the hardness of the welded joint is low due to the fact that harmful tissues such as martensite are generated in the cooling process of the steel rail welded joint because the local cooling speed is higher than the critical transition temperature.
Description
Technical Field
The invention relates to the technical field of steel rail welding, in particular to a heat treatment method for a 350HB grade steel rail welding joint.
Background
The steel rail welding has the characteristics of high heating temperature, high heating speed, short high-temperature residence time, uneven temperature distribution, continuous cooling under the air cooling condition and the like, is easy to generate coarse structure in a heat affected zone, has the grain size of about 1-2 levels, and also generates harmful structures such as martensite, bainite and the like, so that the phenomena of hardening, embrittlement and the like at the joints of the steel rail are caused; meanwhile, the welded joint generates internal stress, and is extremely easy to break under the action of complex external stress, so that the welded joint becomes a weak link for line operation. Therefore, the welded joint of the steel rail needs to be subjected to heat treatment, the microstructure of the welded joint is thinned, and the grain size of the steel rail is increased, so that the toughness of the welded joint of the steel rail is improved
The steel rail flash welding process and the joint heat treatment process directly influence the joint organization performance and the service state. The defects of over-burning, unwelded joint, excessive gray spots, liquefied cracks and the like of the joint can be caused by improper flash welding process, and the joint performance is poor. The weld joint is subjected to normalizing heat treatment, the microstructure of the weld joint is obviously refined, the grain size is increased from level 1 to more than level 8, the toughness of the flash welding joint is well improved, but the weld joint heat treatment process is improper, such as the characteristics of high and low heating temperature, high and low heating speed, nonuniform high-temperature residence time, nonuniform temperature distribution, continuous cooling under air cooling conditions and the like, the joint, especially a heat affected zone, is easy to have coarse structure, even easy to form martensite and other harmful structures, the joint is easy to have hardening, embrittlement and other phenomena, and the joint is extremely easy to break under the action of wheel rail stress in the line service process, thus becoming a weak link of line operation.
Patent publication No. CN109022749A discloses a post-weld heat treatment method for U71MnH rail welded joint. The invention provides a post-welding heat treatment method of a U71MnH steel rail welding joint, which comprises the following steps: and (3) after butt welding, heating the welding seam area of the U71MnH steel rail welding joint cooled to below 300 ℃ to 865-925 ℃, stopping heating, adopting air-jet cooling, stopping air-jet cooling after the tread temperature of the steel rail joint is reduced to 458-475 ℃, and naturally cooling to room temperature. However, the study object is a U71Mn steel rail, and is not suitable for a heat treatment steel rail with a medium strength level.
Disclosure of Invention
The invention aims to provide a heat treatment method for a 350HB grade steel rail welding joint, which solves the problem that the hardness of the welding joint is low due to the fact that the local cooling speed of the steel rail welding joint is higher than the critical transition temperature and harmful tissues such as martensite are generated in the cooling process.
In order to solve the technical problems, the invention adopts the following technical scheme:
the invention relates to a heat treatment method of a 350HB grade steel rail welding joint, which comprises the following steps:
air cooling the high-temperature welded joint to below 200 ℃ to ensure that each position of the joint is completely phase-changed; induction heating treatment is carried out by using a joint double-frequency normalizing machine, and joint low-frequency induction heating is carried out firstly: heating the joint for 80-92 s by using 57-65 kW low-frequency power, stopping heating after the joint is heated to 825-845 ℃ from 0-200 ℃, and immediately performing high-frequency induction heating on the joint after the joint reaches the target temperature: the normalizing machine is adjusted to 67-60 kW high-frequency power to heat for 88-100 s, and the joint is heated to 880-920 ℃ from 825-845 ℃; and (3) adopting air-jet cooling, adjusting the air pressure to 0.28-0.35 MPa, controlling the final air-jet cooling temperature of the joint to be between 450 and 485 ℃, stopping air-jet cooling, and naturally cooling to room temperature.
Further, the high temperature weld joint is properly cooled at a temperature of less than 300 ℃.
Further, the steel rail takes C, S i, mn and Cr as main alloy elements, and the weight percentage of the chemical components of the steel rail is C:0.72 to 0.82 percent, S i:0.30 to 0.60 percent, 0.90 to 1.20 percent of Mn, less than or equal to 0.3 percent of Cr, less than or equal to 0.01 percent of V, less than or equal to 0.02 percent of P, less than or equal to 0.02 percent of S, and the balance of Fe and unavoidable impurities.
Further, the welding seam area heating mode of the steel rail welding joint adopts a double-frequency normalizing machine to carry out induction heating treatment, the welding seam area heating is controlled to be 110-130s, the welding seam jointing amount of the steel rail is controlled to be 10-12 mm, the air outlet of the air spraying cooling is 20-30 mm away from the rail top surface, 40-50 mm away from the rail head side surface, 50-60 mm away from the rail web, 50-70 mm away from the rail bottom, and the air pressure of the air spraying is 0.3+/-0.05 MPa.
Further, the air outlet is 28mm away from the rail top surface, 45mm away from the rail head side surface, 55mm away from the rail web and 66mm away from the rail bottom; the air-jet time is 120s.
Compared with the prior art, the invention has the beneficial technical effects that:
the invention can effectively improve the mechanical properties of the medium-strength steel rail fixing flash welding head, and improve the strength, hardness and toughness of the high-hardness steel rail joint, so that the high-hardness steel rail joint is matched with the properties of a base metal. The ratio of the average hardness HJ of the joint to the average hardness HP of the base material is more than or equal to 0.90; the ratio of the average hardness HJ1 of the joint soft points to the average hardness HP of the base metal is more than or equal to 0.80; the softening area is smaller than 20mm, and meets the standard requirement. Meanwhile, the organization performance is normal, and the method has good popularization and application prospects, and can be popularized and used in domestic heavy-duty line steel rail welding bases or on-line welding construction units.
Drawings
The invention is further described with reference to the following description of the drawings.
FIG. 1 shows the profile hardness distribution of a medium strength rail joint.
Detailed Description
A postweld heat treatment method for a medium strength grade steel rail welded joint comprises the following steps: the flash welded medium strength steel rail takes C, S i, mn and Cr as main alloy elements, and the weight percentage of the chemical components of the steel rail is C:0.72 to 0.82 percent, S i:0.30 to 0.60 percent, 0.90 to 1.20 percent of Mn, less than or equal to 0.3 percent of Cr, less than or equal to 0.01 percent of V, less than or equal to 0.02 percent of P, less than or equal to 0.02 percent of S, and the balance of Fe and unavoidable impurities.
The components are subjected to smelting, continuous casting, slow cooling of steel billets, rolling, heat treatment and the like to produce the steel rail. The size of the steel rail continuous casting blank is 280mm multiplied by 380mm, the rolling section is 60N, and the rolling compression ratio of the steel rail is greater than or equal to 11: and 1, the final rolling temperature of the steel rail is not higher than 980 ℃, the high-temperature welding state joint is cooled to below 200 ℃ in an air mode, the complete phase change of each position of the joint is ensured, the temperature of the joint is lower than 300 ℃, the cooled welding joint can be properly cooled in an accelerating mode, the cooled welding joint is heated to 880-920 ℃ and then stopped, after the joint reaches the target temperature, the high-frequency induction heating joint is immediately subjected to air-spraying and final cooling, the air-spraying and cooling are stopped after the temperature of the high-frequency induction heating joint is controlled to be 450-485 ℃, and the high-frequency induction heating joint is naturally cooled to the room temperature.
When the joint temperature is less than 300 ℃, the welding seam area of the medium-strength steel rail is heated to 880-920 ℃, and the normalizing process is adopted in the process, so that the joint structure form is changed, the grain size is refined, the welding seam hardness is improved, and the performance state is improved.
When the surface of the rail head of the steel rail reaches the required range, the interior of the steel rail, especially the temperature of the core part, can not be ensured to reach the required temperature, and the temperature can not be too low in order to ensure that the temperature of the core part can reach the required temperature; when the temperature is too high, on one hand, the temperature at the rail bottom of the relatively thin steel rail is higher than the actual measured temperature, and the risk of tissue overheating exists, on the other hand, the heating coil is a source of heat, heat is conducted to the two ends of the steel rail by taking the heating coil as the center, the width of a heat affected zone can be widened, and even the standard requirement is not met.
And after the joint subjected to normalizing heat treatment reaches the target temperature of 880-920 ℃, stopping heating, immediately performing air-jet accelerated cooling treatment on the joint, the rail web and the rail bottom, wherein an air-jet opening is 28mm away from the rail top surface, 45mm away from the rail head side surface, 55mm away from the rail web and 66mm away from the rail bottom. The air-jet time is 120s. The air-spraying final cooling temperature of the joint is controlled between 450 ℃ and 485 ℃, then the air-spraying cooling is stopped, and the joint is naturally cooled to the room temperature.
The process is compared in the implementation process:
the carbon content of the strength steel rail in 60N for heavy haul railways can reach about 0.78%, the alloy content of the steel rail is higher, element segregation such as C, mn and the like, microstructure defects and secondary cementite are easy to generate in a fusion line and a overheat area in the fixed flash welding process, therefore, the invention is carried out aiming at the parameters of a high-hardness steel rail welding process and a joint heat treatment process, and the 60kg/m high-hardness steel rail flash welding process and the joint heat treatment process are determined by combining the key parameters such as normalizing temperature, final cooling temperature and the like with the comparative analysis of the mechanical property of the joint, the drop hammer result and the like.
Example 1:
and heating the welding joint welding seam area of the 60kg/m medium-strength steel rail by adopting a high-frequency heating mode to 895 ℃, and stopping heating for 130s. After heating is stopped, when the tread temperature of the rail joint is reduced to 745 ℃, air-spraying cooling is carried out, the air-spraying opening is 28mm away from the surface of the rail joint, the air-spraying pressure is 0.2+/-0.05 MPa, when the tread temperature of the joint is reduced to 478 ℃, air-spraying cooling is stopped, and then the rail joint is naturally cooled to room temperature.
The hardness of 5mm Rockwell on the tread of the rail head on the longitudinal section was measured by using an HR-150A Rockwell hardness tester with reference to the TB/T1632.2-2014 standard.
In the embodiment, the ratio of the average hardness HJ of the heat-treated joint after welding to the average hardness HP of the base metal of the 60kg/m medium-strength steel rail is 0.83, the ratio of the average hardness HJ1 of the soft point of the joint to the average hardness HP of the base metal is 0.90, the width of the softening area on the left side of the joint is 17.0mm, the width of the softening area on the right side of the joint is 11.0mm, and the standard requirement is met.
TABLE 1 example 1 results of Joint vertical section (test line 1) test
TABLE 2 example 1 flash bond tensile Property
TABLE 3 example 2 flash bond impact Properties
From the above table, it can be seen that: the flash welding head of example 1 meets the standard requirements for tensile properties and impact properties, and the joint has a large performance margin. The invention can effectively improve the mechanical properties of the steel rail fixing flash welding head with the strength grade in 60N for heavy haul railways, and improve the strength, hardness and toughness of the steel rail joint so as to match the properties of the base metal.
The above embodiments are only illustrative of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention, and various modifications and improvements made by those skilled in the art to the technical solutions of the present invention should fall within the protection scope defined by the claims of the present invention without departing from the design spirit of the present invention.
Claims (5)
1. A heat treatment method for a 350HB grade steel rail welding joint is characterized by comprising the following steps: the method comprises the following steps:
air cooling the high-temperature welded joint to below 200 ℃ to ensure that each position of the joint is completely phase-changed; induction heating treatment is carried out by using a joint double-frequency normalizing machine, and joint low-frequency induction heating is carried out firstly: heating the joint for 80-92 s by using 57-65 kW low-frequency power, stopping heating after the joint is heated to 825-845 ℃ from 0-200 ℃, and immediately performing high-frequency induction heating on the joint after the joint reaches the target temperature: the normalizing machine is adjusted to 67-60 kW high-frequency power to heat for 88-100 s, and the joint is heated to 880-920 ℃ from 825-845 ℃; and (3) adopting air-jet cooling, adjusting the air pressure to 0.28-0.35 MPa, controlling the final air-jet cooling temperature of the joint to be between 450 and 485 ℃, stopping air-jet cooling, and naturally cooling to room temperature.
2. The heat treatment method for the 350 HB-level steel rail welded joint according to claim 1, wherein: and properly accelerating cooling when the high-temperature welding state joint temperature is less than 300 ℃.
3. The heat treatment method for the 350 HB-level steel rail welded joint according to claim 1, wherein: the steel rail takes C, si, mn, cr as a main alloy element, and comprises the following chemical components in percentage by weight: 0.72 to 0.82 percent, si:0.30 to 0.60 percent, 0.90 to 1.20 percent of Mn, less than or equal to 0.3 percent of Cr, less than or equal to 0.01 percent of V, less than or equal to 0.02 percent of P, less than or equal to 0.02 percent of S, and the balance of Fe and unavoidable impurities.
4. The heat treatment method for the 350 HB-level steel rail welded joint according to claim 1, wherein: the heating mode of the welding seam area of the steel rail welding joint adopts the induction heating treatment of a double-frequency normalizing machine, the heating of the welding seam area is controlled to be 110-130s, the joint seam quantity of the steel rail welding seam is controlled to be 10-12 mm, the air outlet of the air spraying cooling is 20-30 mm away from the rail top surface, 40-50 mm away from the rail head side surface, 50-60 mm away from the rail web, 50-70 mm away from the rail bottom, and the air pressure of the air spraying is 0.3+/-0.05 MPa.
5. The heat treatment method for the 350HB grade steel rail welded joint according to claim 4, wherein: the air spraying opening is 28mm away from the rail top surface, 45mm away from the rail head side surface, 55mm away from the rail web and 66mm away from the rail bottom; the air-jet time is 120s.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311480886.XA CN117660736A (en) | 2023-11-08 | 2023-11-08 | Heat treatment method for 350HB grade steel rail welded joint |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311480886.XA CN117660736A (en) | 2023-11-08 | 2023-11-08 | Heat treatment method for 350HB grade steel rail welded joint |
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| CN117660736A true CN117660736A (en) | 2024-03-08 |
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| CN202311480886.XA Pending CN117660736A (en) | 2023-11-08 | 2023-11-08 | Heat treatment method for 350HB grade steel rail welded joint |
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