CN112813348A - Air-cooled martensite and retained austenite complex-phase medium manganese rail steel and preparation method thereof - Google Patents
Air-cooled martensite and retained austenite complex-phase medium manganese rail steel and preparation method thereof Download PDFInfo
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- 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
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- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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Abstract
The invention discloses air-cooled martensite and residual austenite multiphase medium manganese rail steel and a preparation method thereof, belongs to the technical field of steel materials, and solves the problems that the rail steel in the prior art has poor comprehensive performance, complex production process, unstable performance of the rail steel after rolling or unstable welding structural performance of the rail steel and the like. The rail steel comprises the following chemical components in percentage by mass: 0.05 to 0.25 percent of C, 0.1 to 2.0 percent of Si, 3.00 to 5.00 percent of Mn, less than or equal to 1.00 percent of Cr, less than or equal to 1.00 percent of Ni, less than or equal to 0.50 percent of Mo, less than or equal to 0.015 percent of P, less than or equal to 0.01 percent of S, and the alloy also comprises the following components: one or more of Nb, Ti and V, wherein the total content of one or more of Nb, Ti and V is 0.01-0.20 percent by mass, the balance is Fe and inevitable impurities, the microstructure of the material comprises air-cooled martensite and retained austenite, and the volume fraction of the retained austenite is 5-15 percent. The air-cooled martensite and residual austenite complex phase medium manganese steel rail and the preparation method can be used for preparing steel rails.
Description
Technical Field
The invention belongs to the technical field of steel materials, and particularly relates to air-cooled martensite and retained austenite complex phase medium manganese rail steel for a heavy-load and high-speed development direction railway and a preparation method thereof.
Background
Railway transportation is the leading transportation mode in China, and steel rails are important bearing parts of railway transportation, and in the long-term load carrying process, abrasion, fatigue and the like inevitably occur, so that the steel rails are stripped, collapsed and even broken, and the like, and the safety and the operation efficiency of the railway transportation are seriously threatened. The development of rail steels at home and abroad goes through several courses such as common rail steels (ferrite + pearlite rail, alloy ferrite + pearlite rail, carbon pearlite rail), wear-resistant rail steels (alloy pearlite steel), high-grade wear-resistant rail steels (heat-treated sorbite rail, alloy transformed pearlite rail, bainite rail, austenite rail) and the like. With the rapid development of national economy, railway transportation develops towards heavy load and high speed, the heavy load transportation is an important way for improving the transportation capacity, correspondingly, the service conditions of the steel rail become severe, and the performance of the steel rail material needs to be improved so as to meet the development requirements of railway transportation.
Chinese patent application CN107675084 discloses a pearlite steel rail with high carbon content, high strength and toughness and a manufacturing method thereof, wherein a steel billet is hot-rolled into a steel rail, the finish rolling temperature is 900-1000 ℃, when the central temperature of the top surface of the steel rail is air-cooled to 800-850 ℃, cooling media are sprayed on the top surface of a railhead, two side surfaces of the railhead and two lower jaws of the railhead, the steel rail is cooled to the central temperature of the top surface of 480-530 ℃, and the steel rail is obtained by air-cooling to the room temperature. Although the above-described manufacturing method can obtain high strength, the heat treatment process is complicated and the elongation of the material is not high.
Chinese patent application CN111041345A discloses a 800MPa grade vanadium-containing low-carbon bainite complex phase steel and a production method thereof, wherein the production method comprises the working procedures of molten iron desulphurization, converter smelting, LF refining, RH vacuum degassing, slab continuous casting, slab heating, controlled rolling, controlled cooling and coiling. Although the steel grade can be used in the aspects of petroleum pipelines, ships, large-scale components, marine facilities and the like, the steel grade has some defects for railway transportation developed in heavy load and high speed directions, and the use requirements cannot be met.
The Chinese patent application CN110592496A discloses a pearlitic rail steel and a preparation method thereof, steel ingots with the same components as the pearlitic rail steel are sequentially rolled and controlled to be cooled to obtain the pearlitic rail steel, and the average lamellar spacing of the obtained nano-scale pearlitic microstructure is less than 60 nm. However, the specific properties of steel are not clear, and the requirements for heavy load and high-speed development are difficult to realize.
Chinese patent application CN105695849B discloses a method for manufacturing nano bainite steel rail by using rare earth La element, which uses La to improve hardenability of steel, and the rolling process inhibits recrystallization, refines crystal grains, etc., to obtain steel rail with high strength performance. However, the steel grade has high requirements on the subsequent cooling process, and certain requirements exist on the stable control of quality in the actual production process, especially large components with complex sections and the like.
By summarizing, the conventional pearlitic rail steel can relieve the deterioration of plasticity, toughness and weldability caused by the increase of carbon content by optimizing the heat treatment process to refine grains, but cannot fundamentally improve the comprehensive performance of the pearlitic rail. The bainite steel rail which is a hot point in research at present has the defects that the performance of the steel rail after rolling is greatly influenced by the environment during cooling, the steel rail after rolling cannot be subjected to heat treatment in time, the stability of the product performance is influenced, the performance of a steel rail welding joint is unstable, and the like.
Disclosure of Invention
In view of the analysis, the invention aims to provide the air-cooled martensite and residual austenite complex phase medium manganese rail steel and the preparation method thereof, and solves the problems that the rail steel in the prior art has poor comprehensive performance, complex production process, unstable performance of the rail steel after rolling, unstable welding structure performance of the rail steel and the like.
The purpose of the invention is mainly realized by the following technical scheme:
the invention provides air-cooled martensite and retained austenite multiphase medium manganese rail steel, which comprises the following chemical components in percentage by mass: 0.05 to 0.25 percent of C, 0.1 to 2.0 percent of Si, 3.00 to 5.00 percent of Mn, less than or equal to 1.00 percent of Cr, less than or equal to 1.00 percent of Ni, less than or equal to 0.50 percent of Mo, less than or equal to 0.015 percent of P, less than or equal to 0.01 percent of S, and the alloy also comprises the following components: the steel comprises one or more of Nb, Ti and V, wherein the total content of one or more of Nb, Ti and V is 0.01-0.20 percent by mass, and the balance is Fe and inevitable impurities, wherein the microstructure of the air-cooled martensite and residual austenite complex phase medium manganese rail steel comprises air-cooled martensite and residual austenite, the volume fraction of the residual austenite is 5-15 percent, and the air-cooled martensite is 85-95 percent.
Furthermore, the tensile strength of the air-cooled martensite and residual austenite complex phase medium manganese rail steel is 1200-1400 MPa, the yield strength is 900-1100 MPa, and the elongation is more than or equal to 16%.
Further, the air-cooled martensite and retained austenite complex phase medium manganese rail steel comprises the following chemical components in percentage by mass: 0.05 to 0.25 percent of C, 0.50 to 2.0 percent of Si, 3.00 to 4.50 percent of Mn, 0.65 to 1.00 percent of Cr, 0.50 to 1.00 percent of Ni, 0.35 to 0.43 percent of Mo, less than or equal to 0.015 percent of P, less than or equal to 0.01 percent of S, 0.05 to 0.16 percent of total content of Nb, Ti and V, and the balance of Fe and inevitable impurities.
Further, the air-cooled martensite and retained austenite complex phase medium manganese rail steel comprises the following chemical components in percentage by mass: 0.20 to 0.25 percent of C, 1.5 to 2.0 percent of Si, 3.5 to 4.5 percent of Mn, 0.65 to 0.75 percent of Cr, 0.5 to 1.0 percent of Ni, 0.36 to 0.43 percent of Mo, less than or equal to 0.004 percent of P, less than or equal to 0.005 percent of S, 0.15 to 0.16 percent of total content of Nb, Ti and V, and the balance of Fe and inevitable impurities.
The invention also provides a preparation method of the air-cooled martensite and residual austenite complex phase medium manganese rail steel, which comprises the following steps: obtaining a casting blank with a target component design range through smelting and external refining, heating the casting blank, and performing repeated forging, multi-pass rolling and air cooling treatment to obtain the air-cooled martensite and residual austenite complex phase medium manganese rail steel.
Further, the heating temperature of the casting blank is 1100-1200 ℃.
Furthermore, the initial rolling temperature is 1100-1200 ℃, and the final rolling temperature is 800-850 ℃.
Further, the cooling rate of the air cooling treatment is 1 ℃/s-3 ℃/s.
Further, the air cooling treatment further comprises the following steps:
and tempering the forged piece after air cooling.
Further, the tempering treatment is medium-low temperature tempering, and the tempering temperature is 200-300 ℃.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
a) the air-cooled martensite and retained austenite complex phase medium manganese rail steel provided by the invention adopts a medium manganese steel system, Mn is used as an element for improving hardenability, the air-cooled martensite and retained austenite complex phase medium manganese rail steel is particularly important for obtaining a martensite structure through air cooling, and the air-cooled martensite and retained austenite can be finally obtained through adjusting various components of the rail steel. The basic structure of the air-cooled martensite can ensure that the material has certain strength and hardness, and the basic structure of the matrix of the material is ensured; austenite is a soft phase, and the retained austenite in the structure not only can obviously improve the toughness and plasticity of the material, but also can effectively prevent fatigue crack from expanding. Therefore, the structure of the air-cooled martensite and the residual austenite has excellent comprehensive performance, thereby meeting the development requirements of heavy load and high-speed transportation, greatly improving the service life of the existing rail steel, preventing and reducing the rail failure of the rail caused by fatigue or abrasion and the like, and bringing remarkable economic value and huge social benefit.
b) In the prior art, the cooling process of the rail steel usually adopts quenching tempering or a Q-P process, and requires a higher cooling speed. The invention can effectively reduce the requirement of the required cooling speed by reasonably adjusting the chemical components and the preparation process, so that the complex phase rail steel with the air-cooled martensite and the residual austenite, which meets the requirement, can be obtained under the air-cooled condition.
c) In the preparation method of the air-cooled martensite and residual austenite complex phase medium manganese rail steel, if the medium manganese steel material adopts the traditional high-temperature reverse phase transformation annealing method, the method has the advantages that the austenite with higher volume fraction can be obtained, and the defect that the strength of the steel is low due to high-temperature annealing; the preparation method of the air-cooled martensite and residual austenite complex phase medium manganese rail steel provided by the invention not only can keep the steel with high enough strength, but also can obtain a certain proportion of stable residual austenite. The medium manganese air-cooled martensite/austenite complex phase steel provided by the invention has super hardenability, a martensite structure can be obtained even under the air-cooled condition, and the air-cooled process is actually an element redistribution process, so that the steel can obtain a certain proportion of retained austenite when the steel is air-cooled to room temperature. Meanwhile, in the research, the volume fraction difference of the obtained retained austenite in a certain cooling speed range is not large, the cooling process window is not very narrow, and the method can be implemented on site.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The drawings are only for purposes of illustrating the particular invention and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout the figures.
FIG. 1 is a metallographic structure photograph of an air-cooled martensite and retained austenite complex phase medium manganese rail steel provided in example 5 of the present invention;
fig. 2 shows the shape of the retained austenite of the air-cooled martensite and retained austenite complex phase medium manganese rail steel provided in embodiment 5 of the present invention under a transmission electron microscope.
Detailed Description
The preferred invention will now be described in detail with reference to the accompanying drawings, which form a part hereof, and which together with the description serve to explain the principles of the invention.
The invention provides air-cooled martensite and retained austenite multiphase medium manganese rail steel, which comprises the following chemical components in percentage by mass: 0.05 to 0.25 percent of C, 0.1 to 2.0 percent of Si, 3.00 to 5.00 percent of Mn, less than or equal to 1.00 percent of Cr, less than or equal to 1.00 percent of Ni, less than or equal to 0.50 percent of Mo, less than or equal to 0.015 percent of P, less than or equal to 0.01 percent of S, and the alloy also comprises the following components: the steel comprises one or more of Nb, Ti and V, wherein the total content of one or more of Nb, Ti and V is 0.01-0.20 percent by mass, and the balance is Fe and inevitable impurities, wherein the microstructure of the air-cooled martensite and residual austenite complex phase manganese rail steel comprises air-cooled martensite and residual austenite, and the volume fraction of the residual austenite is 5-15 percent.
Compared with the prior art, the air-cooled martensite and retained austenite complex phase medium manganese rail steel provided by the invention adopts a medium manganese steel system, Mn is used as an element for improving hardenability, the air-cooled martensite and retained austenite complex phase medium manganese rail steel is particularly important for obtaining a martensite structure through air cooling, and the air-cooled martensite and retained austenite can be finally obtained through adjusting all components of the rail steel. The basic structure of the air-cooled martensite can ensure that the material has certain strength and hardness, and the basic structure of the matrix of the material is ensured; austenite is a soft phase, and the retained austenite in the structure not only can obviously improve the toughness and plasticity of the material, but also can effectively prevent fatigue crack from expanding. Therefore, the structure of the air-cooled martensite and the residual austenite has excellent comprehensive performance, thereby meeting the development requirements of heavy load and high-speed transportation, greatly improving the service life of the existing rail steel, preventing and reducing the rail failure of the rail caused by fatigue or abrasion and the like, and bringing remarkable economic value and huge social benefit.
Specifically, the mechanism of action of the above elements is briefly described below.
C: is the most basic element in steel, contributes to the expansion of an austenite phase region, and is also an element having a strong solid solution strengthening effect. If the C content in the steel is lower, the hardness of the product is insufficient; the carbon content is too high, the product hardness is higher, and the toughness and the welding performance are poorer. Usually has an important function for stabilizing the retained austenite in the steel, and is often added in combination with Mn element. Comprehensively considering, the steel grade needs to be matched with excellent obdurability, so the carbon content is controlled to be 0.05-0.25 percent.
Si: without forming carbide, the hardenability and tempering resistance of the steel can be improved. In the present invention, the most important role is Si, which is capable of suppressing Fe3C forms and stabilizes (eta) carbide, ensures carbon distribution, has important significance for obtaining high-strength and high-toughness tissues, and obviously improves the strength and the hardness of the steel. The invention controls the silicon content to be 0.10-2.0%.
Mn: is an austenite forming element and is also an important strengthening and toughening element. The toughness and plasticity of the steel can be improved by improving the thermodynamic stability of austenite, obviously improving the hardenability of the steel, obtaining more retained austenite and reversing transformed austenite. However, too high Mn content increases the hardenability of steel, affects weldability and toughness, and if too low, the martensite structure cannot be obtained under air-cooling conditions, resulting in insufficient hardenability of steel. The invention controls the manganese content to be 3.00-5.00%.
Cr: ferrite forming elements can also strongly improve hardenability, and have the functions of reducing A3 temperature and improving the stability of undercooled austenite, medium carbide forming elements can enter cementite to obtain alloy cementite to improve the stability and refine the alloy cementite, and a sigma phase is formed when the content is high, so that the toughness of steel is obviously damaged. The invention controls the chromium content to be less than or equal to 1.00 percent.
Ni: is an austenite forming element and exists only in a solid solution state, obviously improves the hardenability of the steel by improving the thermodynamic stability of austenite, obtains more retained austenite and reverse transformed austenite, and particularly improves the toughness by releasing the stress at the micro-crack tip of the austenite soft phase and obviously increasing the phase interface. The invention controls the nickel content to be less than or equal to 1.00 percent.
Mo: can strongly improve the hardenability of steel, and can form an alloy carbide Mo with a hexagonal crystal structure by using a medium carbide forming element2C, M forming a complex crystal structure at higher contents6C, can enter MC phase and M23C6And the method plays an important role in improving the tempering stability of the steel and obviously reducing the tempering brittleness. The invention controls the content range of molybdenum to be less than or equal to 0.50 percent.
Nb/V/Ti: both are strong carbide forming elements and ferrite forming elements, improve hardenability during solid solution, and also play a role in refining grain size and obviously increasing toughness. The invention controls the total content range of niobium, vanadium and titanium to be 0.01-0.20%.
P, S is a foreign element that seriously impairs the toughness and plasticity of steel, and S is also liable to form sulfide inclusions. Therefore, the content of P is controlled to be less than or equal to 0.015 percent, and the content of S is controlled to be less than or equal to 0.01 percent.
In order to further improve the comprehensive performance of the air-cooled martensite and residual austenite complex phase medium manganese rail steel, the chemical components comprise the following components in percentage by mass: 0.05 to 0.25 percent of C, 0.50 to 2.0 percent of Si, 3.00 to 4.50 percent of Mn, 0.65 to 1.00 percent of Cr, 0.50 to 1.00 percent of Ni, 0.35 to 0.43 percent of Mo, less than or equal to 0.015 percent of P, less than or equal to 0.01 percent of S, 0.05 to 0.16 percent of total content of Nb, Ti and V, and the balance of Fe and inevitable impurities.
Further, in order to optimize the comprehensive performance of the air-cooled martensite and retained austenite complex phase medium manganese rail steel as far as possible, the chemical components comprise the following components in percentage by mass: 0.20 to 0.25 percent of C, 1.5 to 2.0 percent of Si, 3.5 to 4.5 percent of Mn, 0.65 to 0.75 percent of Cr, 0.5 to 1.0 percent of Ni, 0.36 to 0.43 percent of Mo, less than or equal to 0.004 percent of P, less than or equal to 0.005 percent of S, 0.15 to 0.16 percent of total content of Nb, Ti and V, and the balance of Fe and inevitable impurities.
The invention also provides a preparation method of the air-cooled martensite and residual austenite complex phase medium manganese rail steel, which comprises the following steps: obtaining a casting blank with a target component design range through smelting and external refining, heating the casting blank to 1100-1200 ℃, and performing repeated forging, multi-pass rolling and air cooling treatment to obtain the air-cooled martensite and residual austenite complex phase medium manganese rail steel.
Compared with the prior art, the beneficial effects of the preparation method of the air-cooled martensite and residual austenite complex phase medium manganese rail steel provided by the invention are basically the same as those of the air-cooled martensite and residual austenite complex phase medium manganese rail steel provided by the invention, and the detailed description is omitted here.
It should be noted that, in the prior art, the rail steel cooling process usually adopts quenching and tempering or a Q-P process, and requires a relatively fast cooling speed. The invention can effectively reduce the requirement of the required cooling speed by reasonably adjusting the chemical components and the preparation process, so that the complex phase rail steel with the air-cooled martensite and the residual austenite, which meets the requirement, can be obtained under the air-cooled condition.
In addition, it should be noted that if the traditional high-temperature reverse phase transformation annealing method is adopted for the medium manganese steel material, the medium manganese steel material has the advantages that austenite with higher volume fraction can be obtained, and the defect that the high-temperature annealing causes the low strength of the steel; the preparation method of the air-cooled martensite and residual austenite complex phase medium manganese rail steel provided by the invention not only can keep the steel with high enough strength, but also can obtain a certain proportion of stable residual austenite. The medium manganese air-cooled martensite/austenite complex phase steel provided by the invention has super hardenability, a martensite structure can be obtained even under the air-cooled condition, and the air-cooled process is actually an element redistribution process, so that the steel can obtain a certain proportion of retained austenite when the steel is air-cooled to room temperature. Meanwhile, in the research, the volume fraction difference of the retained austenite obtained in a certain cooling speed range (1 ℃/s-3 ℃/s) is not large, the cooling process window is not very narrow, and the method can be implemented on site.
Specifically, the steel blank is heated to austenitizing temperature, the initial rolling temperature is controlled to be 1100-1200 ℃, the final rolling temperature is controlled to be 800-850 ℃, and after multi-pass rolling, the steel is subjected to an air cooling process to obtain the prototype rail steel with an air-cooled martensite structure and a certain proportion of retained austenite.
In order to further improve the toughness and plasticity, the method also comprises the following steps after the air cooling treatment:
and tempering the forged piece after air cooling.
Thus, the toughness and plasticity of the medium manganese steel are significantly improved by air-cooling the steel and then performing medium-low temperature tempering, and the stability of the retained austenite can be further improved by diffusion of the element C in the retained austenite. Illustratively, the tempering treatment is medium-low temperature tempering, and the tempering temperature is 200-300 ℃.
The air-cooled martensite and retained austenite complex phase medium manganese rail steel and the preparation method thereof according to the present invention will be further described with reference to the following specific examples.
The chemical compositions of the air-cooled martensite and retained austenite complex phase medium manganese rail steels of examples 1 to 5 of the present invention are shown in table 1 below.
Table 1 chemical composition (wt.%) of the medium manganese rail steels of examples 1 to 5
Table 2 shows the preparation process of the steel of the invention: smelting and casting the steel blank by a converter to obtain a steel blank, heating the steel blank to the austenitizing temperature of 1150-1210 ℃, controlling the initial rolling temperature of 1130-1200 ℃ and the final rolling temperature of 800-850 ℃, and after multi-pass rolling, carrying out an air cooling heat treatment process on the steel to obtain the prototype rail steel with an air cooling martensite structure and a certain proportion of retained austenite.
Table 2 preparation process of inventive steel
Table 3 shows the mechanical properties of the steel, the tensile strength of the steel is 1200-1400 MPa, the yield strength is 900-1100 MPa, the elongation is more than or equal to 16%, and the volume fraction of the retained austenite of the steel is 5-15%.
TABLE 3 mechanical Properties of inventive steels and residual Austenite volume fraction (%)
A metallographic structure photograph of the air-cooled martensite and residual austenite complex phase medium manganese rail steel provided in the embodiment 5 of the invention is shown in fig. 1; the appearance of the residual austenite of the air-cooled martensite and residual austenite complex phase medium manganese rail steel provided in the embodiment 5 of the invention under a transmission electron microscope is shown in fig. 2. As can be seen from fig. 1, the basic structure of the air-cooled martensite and retained austenite complex phase medium manganese rail steel of example 5 is martensite, and as can be seen from fig. 2, a part of the retained austenite structure exists in the air-cooled martensite and retained austenite complex phase medium manganese rail steel of example 5.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. The air-cooled martensite and retained austenite complex phase medium manganese rail steel is characterized by comprising the following chemical components in percentage by mass: 0.05 to 0.25 percent of C, 0.1 to 2.0 percent of Si, 3.00 to 5.00 percent of Mn, less than or equal to 1.00 percent of Cr, less than or equal to 1.00 percent of Ni, less than or equal to 0.50 percent of Mo, less than or equal to 0.015 percent of P, less than or equal to 0.01 percent of S, and the alloy also comprises the following components: one or more of Nb, Ti and V, wherein the total content of one or more of Nb, Ti and V is 0.01-0.20 percent by mass, and the balance is Fe and inevitable impurities.
2. The air-cooled martensite and retained austenite complex phase medium manganese rail steel of claim 1, wherein the air-cooled martensite and retained austenite complex phase medium manganese rail steel has a tensile strength of 1200-1400 MPa, a yield strength of 900-1100 MPa, and an elongation of not less than 16%.
3. The air-cooled martensite and retained austenite complex phase medium manganese rail steel of claim 1, wherein the microstructure of the air-cooled martensite and retained austenite complex phase medium manganese rail steel comprises air-cooled martensite and retained austenite, and the volume fraction of the retained austenite is 5-15%.
4. The air-cooled martensite and retained austenite complex phase medium manganese rail steel of claim 1, wherein the chemical composition comprises, in mass percent: 0.05 to 0.25 percent of C, 0.50 to 2.0 percent of Si, 3.00 to 4.50 percent of Mn, 0.65 to 1.00 percent of Cr, 0.50 to 1.00 percent of Ni, 0.35 to 0.43 percent of Mo, less than or equal to 0.015 percent of P, less than or equal to 0.01 percent of S, 0.05 to 0.16 percent of total content of Nb, Ti and V, and the balance of Fe and inevitable impurities.
5. The air-cooled martensite and retained austenite complex phase medium manganese rail steel of claim 4, wherein the chemical composition comprises, by mass percent: 0.20 to 0.25 percent of C, 1.5 to 2.0 percent of Si, 3.5 to 4.5 percent of Mn, 0.65 to 0.75 percent of Cr, 0.5 to 1.0 percent of Ni, 0.36 to 0.43 percent of Mo, less than or equal to 0.004 percent of P, less than or equal to 0.005 percent of S, 0.15 to 0.16 percent of total content of Nb, Ti and V, and the balance of Fe and inevitable impurities.
6. A method for manufacturing an air-cooled martensite and retained austenite complex phase medium manganese rail steel according to claims 1 to 5, comprising the steps of:
obtaining a casting blank with a target component design range through smelting and external refining, heating the casting blank, and performing repeated forging, multi-pass rolling and air cooling treatment to obtain the air-cooled martensite and residual austenite complex phase medium manganese rail steel.
7. The method for preparing the air-cooled martensite and residual austenite complex phase medium manganese rail steel according to claim 6, wherein the casting blank heating temperature is 1100-1200 ℃.
8. The method for preparing the air-cooled martensite and residual austenite complex phase medium manganese rail steel according to claim 6, wherein the start rolling temperature is 1100-1200 ℃ and the finish rolling temperature is 800-850 ℃.
9. The method for preparing the air-cooled martensite and retained austenite complex phase medium manganese rail steel as claimed in claim 6, wherein the cooling rate of the air-cooling treatment is 1 ℃/s-3 ℃/s.
10. The method for producing air-cooled martensite and retained austenite complex phase medium manganese rail steel according to any one of claims 6 to 9, further comprising the following steps after the air-cooling treatment:
and tempering the forged piece after air cooling.
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