AU2023319321A1 - Medium-strength steel rail having high yield strength and production method therefor - Google Patents
Medium-strength steel rail having high yield strength and production method therefor Download PDFInfo
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- 238000004519 manufacturing process Methods 0.000 title claims abstract description 33
- 229910000831 Steel Inorganic materials 0.000 title abstract description 18
- 239000010959 steel Substances 0.000 title abstract description 18
- 238000010438 heat treatment Methods 0.000 claims abstract description 30
- 238000001816 cooling Methods 0.000 claims description 71
- 229910001562 pearlite Inorganic materials 0.000 claims description 22
- 239000000203 mixture Substances 0.000 claims description 14
- 238000005096 rolling process Methods 0.000 claims description 14
- 239000000126 substance Substances 0.000 claims description 11
- 229910052804 chromium Inorganic materials 0.000 claims description 9
- 229910052717 sulfur Inorganic materials 0.000 claims description 9
- 229910052748 manganese Inorganic materials 0.000 claims description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 7
- 239000003595 mist Substances 0.000 claims description 6
- 238000003723 Smelting Methods 0.000 claims description 5
- 239000002826 coolant Substances 0.000 claims description 5
- 238000009749 continuous casting Methods 0.000 claims description 4
- 238000012545 processing Methods 0.000 claims description 4
- 238000007670 refining Methods 0.000 claims description 4
- 238000009489 vacuum treatment Methods 0.000 claims description 4
- 238000000034 method Methods 0.000 abstract description 16
- 230000008569 process Effects 0.000 abstract description 8
- 229910045601 alloy Inorganic materials 0.000 abstract description 3
- 239000000956 alloy Substances 0.000 abstract description 3
- 230000002708 enhancing effect Effects 0.000 abstract 1
- 230000000052 comparative effect Effects 0.000 description 12
- 230000000694 effects Effects 0.000 description 6
- 239000012535 impurity Substances 0.000 description 6
- 229910000734 martensite Inorganic materials 0.000 description 4
- 150000001247 metal acetylides Chemical class 0.000 description 4
- 230000009466 transformation Effects 0.000 description 4
- 229910052782 aluminium Inorganic materials 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 230000006872 improvement Effects 0.000 description 3
- 239000007769 metal material Substances 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- 238000010998 test method Methods 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 230000002159 abnormal effect Effects 0.000 description 2
- 229910001563 bainite Inorganic materials 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000007689 inspection Methods 0.000 description 2
- 238000009413 insulation Methods 0.000 description 2
- 229910052758 niobium Inorganic materials 0.000 description 2
- 238000004321 preservation Methods 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- 238000010583 slow cooling Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 229910052720 vanadium Inorganic materials 0.000 description 2
- 229910000859 α-Fe Inorganic materials 0.000 description 2
- 238000007546 Brinell hardness test Methods 0.000 description 1
- 238000007550 Rockwell hardness test Methods 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 229910052729 chemical element Inorganic materials 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
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- E—FIXED CONSTRUCTIONS
- E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
- E01B—PERMANENT WAY; PERMANENT-WAY TOOLS; MACHINES FOR MAKING RAILWAYS OF ALL KINDS
- E01B5/00—Rails; Guard rails; Distance-keeping means for them
- E01B5/02—Rails
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/08—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling structural sections, i.e. work of special cross-section, e.g. angle steel
- B21B1/085—Rail sections
-
- 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
- C21D11/00—Process control or regulation for heat treatments
- C21D11/005—Process control or regulation for heat treatments for cooling
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
-
- 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
- C21D9/04—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rails
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
-
- 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
-
- 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
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
-
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Metallurgy (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Structural Engineering (AREA)
- Civil Engineering (AREA)
- Architecture (AREA)
- Heat Treatment Of Articles (AREA)
Abstract
The present invention belongs to the field of steel rail production, and particularly relates to a medium-strength steel rail having high yield strength and a production method therefor. The medium-strength steel rail having high yield strength in the present invention has a yield strength larger than or equal to 820 MPa, a tensile strength in the range of 1200-1300 MPa, and an elongation larger than or equal to 10%. Without the addition of various alloy elements, the medium-strength steel rail to which the present invention relates achieves high yield strength by means of online heat treatment process design, such that the probability of contact fatigue damages caused in use of passenger and freight mixed transportation lines can be effectively reduced, which effectively improves the service performance and prolongs the service life of steel rails, thus enhancing operation safety of trains; and meanwhile, the production method for the medium-strength steel rail having high yield strength provided in the present application is simple and easy to operate, facilitating large-scale popularization and application thereof in the passenger and freight mixed transportation lines.
Description
Description
Moderate-strength rail with high yield strength and production method therefor
Technical Field
The present invention relates to the field of rail production, and in particular to a moderate-strength rail with high yield strength and a production method therefor.
Background Art
In China, railway is in a high-speed development stage. Passenger dedicated lines and heavy-haul freight lines are increasing greatly. For the all-round development of the railway field, existing mixed passenger and freight transportation lines are also upgrading, with higher requirements for freight volume, passenger safety and overall operational stability. This trend leads to the increase of surface contact fatigue damage, such as stripping and chipping of rails, which seriously affects service performance and service life of rail and makes it difficult to ensure the efficiency and safety of railway transportation.
At present, in order to improve the service performance and service life of rail, high-performance heat-treated pearlite rail is mainly applied at home and abroad. Through on-line or off-line heat treatment, tensile strength and hardness of the rail are increased to improve wear resistance and contact fatigue resistance. However, for existing moderate-strength pearlite heat-treated rail, little consideration has been given to the improvement of plastic deformation resistance caused by high yield strength and the effect of fundamentally reducing surface contact fatigue damage. However, the high-strength heat-treated pearlite rail with high yield strength is difficult to balance the safety degradation caused by the increase of wheel wear from the excessive tensile strength and hardness when it is used in the mixed passenger and freight transportation lines.
Patent CN 106086622A "Heat treatment production method of rail for mixed passenger and freight transportation railway, and obtained rail" discloses a rail for mixed passenger and freight transportation and a production method therefor. The chemical composition of the rail includes, by weight percentage, C: 0.71-0.82%, Si: 0.13-0.60%, Mn: 0.65-1.25%, Cr: 0.05-0.25%, P: < 0.020%, S: < 0.015%, Al: < 0.1%, the balance being Fe and inevitable impurities. The patent uses an on-line heat treatment method to sequentially perform accelerated cooling, slow cooling and air cooling on the center of the tread of the rail head, both sides of the rail head and the center of the rail bottom of the rail. The accelerated cooling has a starting cooling temperature of 650-950°C, a cooling rate of 2.5-7°C/s, and a final cooling temperature of 400-630°C. The slow cooling has a cooling rate of 0.1-1.5°C/s, and a final cooling temperature of 180-300°C. The rail has a high aluminum content, which is easy to cause core damage and fracture of the rail. Also, the production method of the rail requires accelerated cooling of the rail bottom and high equipment requirements, and is complicated.
Patent CN 104988405A "Rail for mixed passenger and freight transportation and a production method and application thereof' discloses a rail for mixed passenger and freight transportation and a preparation method thereof. The chemical composition of the rail includes C: 0.71-0.78%, Si: 0.30-0.80%, Mn: 0.80-1.1%, Cr: 0.1-0.3%, V: 0.04-0.2%, P: < 0.020%, S: < 0.015%, and the balance being Fe and inevitable impurities. According to the on-line heat treatment method of the rail, the rail after the final rolling is rapidly cooled. Then the rail gauge corner is rapidly heated and insulated. The conditions for rapid cooling include a starting cooling temperature of 800-880°C, a cooling rate of 2-6°C/s, and a final cooling temperature of 430-470°C. The conditions for rapidly heating and heat preservation include raising the rail gauge corner temperature to 700-800°C at a heating rate of 3.0-4.0°C/s and performing heat preservation for 2-4 min. The rail described in the patent requires the addition of high-valent alloy elements such as V, and the cost is high. Also, the rail head is heated several times in the rail production process, and the production method is complicated. The secondary heating has a great negative impact on the performance stability of the rail head, and seriously affects the service safety performance of the rail line.
Patent CN 112301205A "Pearlite rail with high yield ratio and preparation method thereof' discloses a pearlite rail with a high yield ratio and a preparation method thereof. The components of the rail include, by weight percent, C: 0.70-0.85%, Si: 0.2-0.8%, Mn: 0.8-1.1%, Cr: 0.5-0.7%, Cu: 0.01-0.1%, Nb: 0.01-0.05%, P: < 0.020%, S: < 0.015%, Al < 0.005%, and the balance being Fe and inevitable impurities. According to the on-line heat treatment method of the rail, the heat treatment is a multi-stage cooling process, with the rail cooled from 850°C-950°C to room temperature at different cooling rates. The rail described in the patent has a high yield strength, but its tensile strength exceeds 1,300 MPa. Thus, it is easy to cause rapid wheel wear in the use of low axle load mixed passenger and freight transportation line and increase the line maintenance cost. Meanwhile, the rail contains much Cr, Cu, Nb and other alloy elements. Thus, it has a high production cost and is difficult to promote production.
In the current patents of heat-treated pearlite rail and its production method, although the rail disclosed in most of the patents has good strength and hardness, the study on the yield strength of the rail is rough. The improvement of the yield strength is mainly driven by the improvement of the overall tensile properties, without considering the reduced service safety caused by the excessive tensile strength in the application process of the rail low axle load line. The obtained heat-treated pearlite rail still cannot fully meet the performance requirements of the mixed passenger and freight transportation line after upgrading. The chemical composition system and production process are complicated. It is difficult to achieve large scale applications.
Summary of the Invention
In view of the drawbacks and deficiencies of the prior art, it is an object of the present invention to provide a moderate-strength rail with high yield strength and a production method therefor, so as to meet the requirements of standard sound insulation and shock absorption, with the advantages of faster construction speed, stronger adhesion, lower cost and more stable sound insulation effects.
In order to achieve the purpose, the invention provides the following technical solution.
A moderate-strength rail with high yield strength is provided. The moderate-strength rail has a yield strength > 820 MPa, a tensile strength of 1200-1300 MPa, and an elongation rate > 10%.
In one or more embodiments, the moderate-strength rail has a rail head containing full pearlite microstructure.
In one or more embodiments, the moderate-strength rail has a running surface hardness of 350-390 HB, and has a sectional hardness of 35.5-41.0 HRC at a depth of 10 mm at the rail top surface and a rail gauge corner.
In one or more embodiments, the rail includes the following chemical composition, by weight percentage, C: 0.65-0.85%, Si: 0.15-0.60%, Mn: 0.50-1.30%, Cr: 0.05-0.20%, P: < 0.020%, S: < 0.015%, and the balance being
Fe.
The invention also provides a production method for a moderate-strength rail with high yield strength, comprising converter smelting, LF furnace refining, RH vacuum treatment, obtaining billets by continuous casting, rolling the billets, on-line heat treatment and processing in sequence.
In one or more embodiments, the on-line heat treatment comprises:
a, a first-stage of cooling: performing cooling treatment on the rail after finishing rolling, wherein the cooling treatment comprises performing accelerated cooling treatment on running surface of the rail, two upper rounded corners of a rail head, both side surfaces of the rail head and two lower rounded corners of the rail head until the top surface of the rail has a temperature of 630-750°C;
b, a second-stage of cooling: subjecting the rail cooled in Step a to accelerated cooling treatment at a cooling rate of 3.0-6.0°C/s on the running surface of the rail, the two upper rounded corners of the rail head, the both side surfaces of the rail head and the two lower rounded corners of the rail head until the temperature of the running surface of the rail is 400-500°C; and
c, a third-stage of cooling: placing the rail cooled in Step b on a cooling bed, and air-cooling the rail to room temperature.
In one or more embodiments, at least one of water mist, compressed air, and a mixture of compressed air and water mist is used as a cooling medium for the on-line heat treatment.
In one or more embodiments, in Step a, a cooling treatment is performed when the temperature of the running surface of the rail after the finishing rolling is 800-950 0 C.
In one or more embodiments, the temperature is lowered at a cooling rate of 1.0-3.0C/s in the cooling treatment.
In one or more embodiments, compressed air is used as a cooling medium for the on-line heat treatment.
Compared with the prior art, the invention has the following beneficial effects.
The present invention adopts a method for controlling the chemical composition of a rail and an on-line heat treatment process to obtain a moderate-strength rail with high yield strength having a yield strength > 820 MPa, a tensile strength of 1200-1300 MPa, and an elongation rate > 10% without adding various alloying elements. Thus, the moderate-strength rail of the present invention may effectively reduce the occurrence probability of contact fatigue damage in the use of a mixed passenger and freight transportation line, and can effectively improve the service performance and service life of the rail and improve the train operation safety. Meanwhile, the method for producing a moderate-strength rail with high yield strength provided by the present patent is simple and easy to operate, which is beneficial to the large-scale promotion and application of the rail in the mixed passenger and freight transportation line.
Detailed Description of the Invention
The technical solutions of the present invention are described in further detail below with reference to specific embodiments.
The present invention provides a moderate-strength rail with high yield strength, the moderate-strength rail having a high yield strength > 820 MPa, a tensile strength of 1200-1300 MPa, and an elongation rate > 10%.
Further, the moderate-strength rail has a rail head containing full pearlite microstructure.
Further, the moderate-strength rail has a running surface hardness of 350-390 HB, and has a sectional hardness of 35.5-41.0 HRC at a depth of 10 mm at the rail top surface and a rail gauge corner.
Further, the moderate-strength rail with high yield strength includes the following chemical composition, by weight percentage, C: 0.65-0.85%, Si: 0.15-0.60%, Mn: 0.50-1.30%, Cr: 0.05-0.20%, P: < 0.020%, S: < 0.015%, and the balance being Fe.
Preferably, the chemical composition of the rail includes, by weight percentage, C: 0.70-0.85%, Si: 0.30-0.60%, Mn: 0.95-1.25%, Cr: 0.05-0.20%, P: < 0.020%, S: < 0.015%, and the balance being Fe and inevitable impurities. Reasons for defining the contents of the main chemical elements of the rail in the present invention are described in detail below.
C is the most important and cheapest element for pearlite rail to obtain good comprehensive mechanical properties and promote pearlite transformation. When the content of C is less than 0.65%, under the production process of the present invention, it cannot ensure that the rail has a suitable strength and hardness and contact fatigue resistance. When the content of C is more than 0.85%, under the production process of the present invention, the rail has a high proportion of carbides, excessive tensile strength, and excess strength index, which reduces the contact fatigue resistance of the rail during service and adversely affects the safe use of the rail. Therefore, the content of carbon in the present invention is limited to 0 . 6 5 -0 .8 5 %.
Si in steel has a main role to inhibit the formation of cementite and serves as a solid solution strengthening element so as to increase the hardness of ferrite matrix and improve the strength and hardness of steel. When the content of Si is less than 0.15%, the strengthening effect is not obvious due to the low solid solution content and the abnormal structure such as martensite is easy to appear in the rail. When the content of Si is more than 0.60%, local segregation is easy to occur, which will reduce the toughness and ductility and weldability of steel, and will have a negative impact on the safe use of rail. Therefore, the content of
Si in the present invention is limited to 0.15-0.60%.
Mn is essential to increase the strength of ferrite and austenite in the steel. When the content of Mn is less than 0.50%, it is difficult to achieve the effect of increasing the carbide hardness and thus increasing the strength and hardness of the steel. When the content of Mn is more than 1.30%, the grain size is coarsened, which affects the microstructure change of rail during heat treatment, and obviously decreases the toughness and plasticity of steel. Meanwhile, the effect of Mn on the diffusion of C in steel is significant. The abnormal microstructure such as bainite or martensite may be formed in the Mn segregation region, which affects the welding performance of rail. Therefore, the content of Mn in the present invention is limited to 0.50-1.30%.
Cr, as a carbide-forming element, may form a variety of carbides with carbon in steel. Also, Cr may evenly distribute the carbides in steel, reduce the size of carbides and improve the wear resistance of rail. When the content of Cr is less than 0.05%, the hardness and proportion of carbide formed are lower. When the content of Cr is more than 0.20%, the hardenability of the rail is too high, which makes the rail produce harmful bainite or martensite structures. While reducing the mechanical properties of the rail, the rail cannot be guaranteed to be a full pearlite structure. Therefore, the content of Cr in the present invention is limited to 0.05-0.20%.
P and S are impurity elements which cannot be completely removed from the rail. P segregates at the grain boundaries of the rail structure, seriously reducing the toughness of the rail. S is easy to form MnS inclusion in steel, which is harmful to the wear resistance and contact fatigue resistance of rail. Therefore, the content of P in the present invention needs to be controlled to 0.020% or below. The content of S should be controlled to 0.015% below.
The present invention also provides a production method for the moderate-strength rail with high yield strength as described above, comprising converter smelting, LF furnace refining, RH vacuum treatment, obtaining billets by continuous casting, rolling the billets, on-line heat treatment and processing in sequence.
Further, according to the production method for the moderate-strength rail with high yield strength, the on-line heat treatment includes:
a, a first-stage of cooling: when the temperature of the running surface of the rail after finishing rolling is between 800-950°C, performing accelerated cooling treatment on running surface of the rail, two upper rounded corners of the rail head, both side surfaces of the rail head and two lower rounded corners of the rail head until the temperature of the funning surface of the rail is 630-750°C; and
b, a second-stage of cooling: subjecting the rail cooled in Step a to accelerated cooling treatment at a cooling rate of 3.0-6.0°C/s on the running surface of the rail, the two upper rounded corners of the rail head, the both side surfaces of the rail head and the two lower rounded corners of the rail head until the temperature of the running surface of the rail is 400-500°C; and
c, a third-stage of cooling: placing the rail cooled in Step b on a cooling bed, and air-cooling the rail to room temperature.
Further, at least one of water mist, compressed air, and a mixture of compressed air and water mist is used as a cooling medium for the on-line heat treatment of the present invention.
The inventors of the present invention have found through extensive studies that:
(1) For the first-stage of cooling of the on-line heat treatment procedure, when the temperature of rail head tread is 800-950°C, the rail has not started pearlite transformation. In order to obtain the rail with high yield strength without excessively increasing the tensile strength of the rail, it is necessary to adopt a low cooling rate to make the temperature of the rail decrease uniformly. In order to ensure the rail head temperature decrease uniformly, it is necessary to control the cooling rate between 1.0-3.0°C/s.
(2) For the second-stage of cooling of the on-line heat treatment procedure, when the temperature of the rail head tread is cooled to 630-750°C in the first stage, the pearlite phase transformation of the rail has already occurred. Considering the heat transfer from the non-accelerated cooling part of the rail to the rail head, a higher cooling rate needs to be used in order to obtain the rail with high yield strength, and the cooling rate needs to be controlled between 3.0-6.0°C/s in the second-stage of cooling.
(3) For the third-stage of cooling, after the first two cooling stages have ended, the internal temperature of the rail head is in the range of 400-500°C, at which point the rail has completed the pearlite phase transformation process. It has no obvious significance to continue the accelerated cooling, and the rail can be air-cooled to room temperature for subsequent procedure treatment.
The complete production process of the production method for the moderate-strength rail with high yield strength according to the invention may be as follows. The low-sulfur vanadium-containing molten steel is smelted by a converter or an electric furnace, followed by LF refining, RH or VD vacuum treatment, bloom protection and continuous casting, heating by a billet heating furnace, high-pressure water descaling before billet rolling, rolling by a universal rolling mill, an on-line heat treatment, stepping cold bed room temperature air cooling, horizontal and vertical composite straightening, rail specification inspection, a processing line treatment, surface inspection and warehousing.
Hereinafter, the present invention will be described in detail by way of examples, but the scope of the present invention is not limited thereto.
The rails with following chemical composition numbers 1-3 are selected accordingly in Examples 1-3 and Comparative Examples 1-3. The manufacturing process is the same as described above, and the specific chemical composition is shown in Table 1.
Table 1
No. C Si Mn Cr P S
1 0.80 0.50 1.09 0.08 0.011 0.006
2 0.74 0.55 1.02 0.15 0.017 0.012
3 0.78 0.48 0.99 0.11 0.009 0.003
The balance is Fe and inevitable impurities.
Heat treatment process parameters of Examples 1-3 and Comparative Examples 1-3 are as shown in Table 2. The difference between the smelting process and the rolling process of Examples and Comparative Examples is negligible.
Table 2
Accelerated First stage First stage Second stage Second stage cooling accelerated accelerated accelerated accelerated cooling No. initial cooling final cooling rate cooling rate final temperature temperature temperature /°C/s /°C/s /s /°C /s
Example 1 857 1.05 749 4.51 451
Example 2 908 2.21 685 3.09 482
Example 3. 833 1.83 721 3.99 437
Start cooling First stage First stage Second stage Second stage
No. temperature accelerated accelerated accelerated accelerated cooling
/C cooling rate cooling final cooling rate final temperature
/°C/s temperature /°C/s /s
/s
Comparative 780 2.01 637 3.42 420 Example 1
Comparative 842 3.08 695 2.11 432 Example 2
Comparative 866 2.91 455
/ Example 3
According to GB/T 228.1, Tensile test of metallic materials, Part 1: Room temperature test method, the yield strength, tensile strength and elongation rate after fracture of rail shall be tested. According to GB/T 230.1, Rockwell hardness test of metallic materials, Part 1: Test method, the test is conducted on the cross-sectional hardness of rail at 10 mm position. According to GB/T 231.1, Brinell hardness test of metallic materials, Part 1: Test method, the surface hardness of the top surface of rail is tested. The tensile properties, rail top surface hardness, and sectional hardness at 10 mm position of Examples 1-3 and Comparative Examples 1-3 are shown in Table 3.
Table 3
Sectional
hardness at 10 Yield Tensile Elongation Surface Metallographic No. mm strength/MPa strength/MPa rate/% hardness/HB structure
Example 851 1255 11.5 365 39.3 Pearlite
Example 2 879 1293 10.5 383 40.6 Pearlite
Example 3 828 1270 11.5 370 38.9 Pearlite
Comparative 767 1230 12.0 360 37.5 Pearlite Example 1
Comparative Pearlite
+ 819 1301 10.0 390 41.7 Example 2 Martensite
Comparative 908 1411 10.5 405 42.5 Pearlite Example 3
It can be seen by comparing Examples with Comparative Examples that, in the Examples according to the present invention, under the same chemical composition and smelting process, the difference in the on-line heat treatment mode of the rail after rolling has a significant effect on the final properties of the rail. The rail obtained by using the method according to the present invention has a high yield strength, with a yield strength > 820MPa, a tensile strength of 1200-1300 MPa and an elongation rate > 10%. However, the yield strength, tensile strength or microstructure of the rail in the Comparative Example does not meet the requirements.
Although the preferred examples of the present invention have been described in detail, the present invention is not limited to the above embodiments. It will be apparent to those skilled in the art to make various changes without departing from the spirit of the present invention.
Claims (10)
1. A moderate-strength rail with high yield strength, characterized in that the moderate-strength rail has a yield strength > 820MPa, a tensile strength of 1200-1300 MPa, and an elongation rate > 10%.
2. The moderate-strength rail with high yield strength according to claim 1, characterized in that the moderate-strength rail has a rail head containing full pearlite microstructure.
3. The moderate-strength rail with high yield strength according to claim 1 or 2, characterized in that the moderate-strength rail has a running surface hardness of 350-390 HB, and has a sectional hardness of 35.5-41.0 HRC at a depth of 10 mm at the rail top surface and a rail gauge corner.
4. The moderate-strength rail with high yield strength according to claim 3, characterized in that the rail includes the following chemical composition, by weight percentage, C: 0.65-0.85%, Si: 0.15-0.60%, Mn: 0.50-1.30%, Cr: 0.05-0.20%, P: < 0.020%, S: < 0.015%, and the balance being Fe.
5. A production method for a moderate-strength rail with high yield strength, characterized by comprising converter smelting, LF furnace refining, RH vacuum treatment, obtaining billets by continuous casting, rolling the billets, on-line heat treatment and processing in sequence.
6. The production method according to claim 5, characterized in that the on-line heat treatment comprises:
a, a first-stage of cooling: performing cooling treatment on the rail after finishing rolling, wherein the cooling treatment comprises performing accelerated cooling treatment on running surface of the rail, two upper rounded corners of a rail head, both side surfaces of the rail head and two lower rounded corners of the rail head until the running surface of the rail has a temperature of 630-750°C; b, a second-stage of cooling: subjecting the rail cooled in Step a to accelerated cooling treatment at a cooling rate of 3.0-6.0°C/s on the running surface of the rail, the two upper rounded corners of the rail head, the both side surfaces of the rail head and the two lower rounded corners of the rail head until the temperature of the running surface of the rail is 400-500°C; and c, a third-stage of cooling: placing the rail cooled in Step b on a cooling bed, and air-cooling the rail to room temperature.
7. The production method according to claim 6, characterized in that at least one of water mist, compressed air, and a mixture of compressed air and water mist is used as a cooling medium for the on-line heat treatment.
8. The production method according to claim 6, characterized in that in Step a, a cooling treatment is performed when the temperature of the running surface of the rail after the finishing rolling is 800-950°C.
9. The production method according to claim 6, characterized in that the temperature is lowered at a cooling rate of 1.0-3.0°C/s in the cooling treatment.
10. The production method according to claim 6, characterized in that compressed air is used as a cooling medium for the on-line heat treatment.
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| CN202210941427.6A CN115233503A (en) | 2022-08-05 | 2022-08-05 | Medium-strength steel rail with high yield strength and production method thereof |
| CN202210941427.6 | 2022-08-05 | ||
| PCT/CN2023/093537 WO2024027264A1 (en) | 2022-08-05 | 2023-05-11 | Medium-strength steel rail having high yield strength and production method therefor |
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| JPH08109440A (en) * | 1994-10-07 | 1996-04-30 | Nippon Steel Corp | High toughness rail with pearlitic metallic structure |
| CN1041443C (en) * | 1993-12-20 | 1998-12-30 | 新日本制铁株式会社 | Rail of high abrasion resistance and high tenacity having pearlite metalographic structure and method of manufacturing the same |
| CN101818312B (en) * | 2010-01-19 | 2012-07-25 | 钢铁研究总院 | Corrosion resistant heavy rail steel with excellent strength-toughness, fatigue resistance and abrasive resistance |
| CN102220545B (en) * | 2010-04-16 | 2013-02-27 | 攀钢集团有限公司 | High-carbon and high-strength heat-treated steel rail with high wear resistance and plasticity and manufacturing method thereof |
| US10253397B2 (en) * | 2013-03-27 | 2019-04-09 | Jfe Steel Corporation | Pearlitic rail and method for manufacturing pearlitic rail |
| CN104060075B (en) * | 2014-07-14 | 2016-05-04 | 攀钢集团攀枝花钢铁研究院有限公司 | Improve the heat treatment method of rail hardening layer depth |
| CN104060065B (en) * | 2014-07-14 | 2016-04-06 | 攀钢集团攀枝花钢铁研究院有限公司 | The rail of resistance to marine environment |
| CN104480390B (en) * | 2015-01-07 | 2016-10-19 | 攀钢集团攀枝花钢铁研究院有限公司 | The rail of high impact toughness and production method thereof |
| CN107674960A (en) * | 2017-10-10 | 2018-02-09 | 攀钢集团研究院有限公司 | Passenger-cargo mixed fortune Rail for railway and its manufacture method |
| CN107475616B (en) * | 2017-10-10 | 2019-01-04 | 攀钢集团研究院有限公司 | High-strength tenacity pearlite steel rail and its manufacturing method |
| CN110578041B (en) * | 2019-09-12 | 2021-10-08 | 内蒙古科技大学 | Corrosion-resistant superfine pearlite material added with rare earth Ce and Nb elements |
| CN111607738B (en) * | 2020-06-30 | 2021-12-17 | 武汉钢铁有限公司 | Corrosion-resistant high-strength pearlitic steel rail and preparation method thereof |
| CN112301205B (en) * | 2020-10-19 | 2022-04-29 | 攀钢集团攀枝花钢铁研究院有限公司 | Pearlite steel rail with high yield ratio and preparation method thereof |
| CN112195413A (en) * | 2020-10-19 | 2021-01-08 | 攀钢集团攀枝花钢铁研究院有限公司 | Fatigue-resistant steel rail of freeze-thaw circulating line and production method thereof |
| CN112501512A (en) * | 2020-11-30 | 2021-03-16 | 武汉钢铁有限公司 | Controlled rolling and controlled cooling high-strength pearlitic steel rail and production method thereof |
| CN113637914A (en) * | 2021-08-18 | 2021-11-12 | 攀钢集团攀枝花钢铁研究院有限公司 | High-strength and high-toughness steel rail and preparation method thereof |
| CN114672730A (en) * | 2022-03-18 | 2022-06-28 | 武汉钢铁有限公司 | Rolling contact fatigue resistant steel rail for passenger-cargo mixed transportation railway and production method thereof |
| CN115233503A (en) * | 2022-08-05 | 2022-10-25 | 攀钢集团攀枝花钢铁研究院有限公司 | Medium-strength steel rail with high yield strength and production method thereof |
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