WO2012028111A1 - 用于高速和准高速铁路的钢轨及其制造方法 - Google Patents

用于高速和准高速铁路的钢轨及其制造方法 Download PDF

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Publication number
WO2012028111A1
WO2012028111A1 PCT/CN2011/079278 CN2011079278W WO2012028111A1 WO 2012028111 A1 WO2012028111 A1 WO 2012028111A1 CN 2011079278 W CN2011079278 W CN 2011079278W WO 2012028111 A1 WO2012028111 A1 WO 2012028111A1
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WIPO (PCT)
Prior art keywords
rail
cooling
less
rolling
equal
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PCT/CN2011/079278
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English (en)
French (fr)
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WO2012028111A8 (zh
Inventor
梅东生
邹明
韩振宇
徐权
郭华
邓勇
李大东
唐历
赵云
刘建华
Original Assignee
攀钢集团有限公司
攀钢集团攀枝花钢钒有限公司
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Priority to BR112013005163-9A priority Critical patent/BR112013005163B1/pt
Priority to US13/820,493 priority patent/US20130193223A1/en
Priority to EP11821137.4A priority patent/EP2612943A4/en
Publication of WO2012028111A1 publication Critical patent/WO2012028111A1/zh
Publication of WO2012028111A8 publication Critical patent/WO2012028111A8/zh

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Classifications

    • 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
    • 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
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • 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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • 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
    • C21D2211/005—Ferrite
    • 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
    • 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
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/4998—Combined manufacture including applying or shaping of fluent material
    • Y10T29/49988—Metal casting
    • Y10T29/49991—Combined with rolling

Definitions

  • the present invention relates to a rail material, and more particularly to a rail suitable for use on a high speed or quasi-high speed railway and a method of manufacturing the same. Background technique
  • the world railways mainly include three types of heavy-duty railways, high-speed railways, and passenger and cargo mixed railways.
  • heavy-duty railway rails because the train axle is large (usually 25t ⁇ 40t), the wheel-rail contact stress is large and the force is severe.
  • the C content is more than 0.75%, the tensile strength is above 1200MPa, and the whole pearlite structure is used.
  • Carbon rail or alloy rail to ensure excellent wear resistance of the rail.
  • high-speed railways because they are mainly used for passenger transportation, the axle weight is light, so high-speed railway rails are usually required to have excellent fatigue resistance.
  • the required rails must ensure certain wear resistance and certain anti-fatigue performance. It needs to be found between the two. balance point.
  • the body is mainly composed of a part of ferrite.
  • U71Mn hot-rolled rails with a tensile strength of 900 MPa are widely used, and their carbon content is 0.65%. -0.76% between.
  • the first method is to use a rail-polishing train to periodically grind the upper end of the rail.
  • the problem with this method is that the grinding of the train is expensive, and at the same time, the high-speed and quasi-high-speed railways have high driving density and insufficient grinding time.
  • Another method is to improve the wear rate of the rail surface, and remove the fatigue layer by continuous wear between the wheel and rail before the fatigue damage occurs.
  • the wear characteristics of the rail are governed by the hardness, and the hardness of the rail can be reduced in order to promote the wear.
  • simply lowering the hardness causes the upper surface of the rail to undergo plastic deformation after a certain period of operation, and often causes cracks such as cracks and peeling, which is also unfavorable for improving the service life and transportation safety of the rail.
  • Patent No. CN1074058C discloses a bainite series rail having excellent weldability and a method of manufacturing the same.
  • the bainite series rail contains 0.15% to 0.40% of C, 0.1% to 0.2% of Si, 0.15 to 1.10% of Mn, 0.035% or less of P and S, and further includes Cr, Nb, Mo, V, Elements such as Ni.
  • the steel rail with bainite structure especially the lower bainite structure, has a higher toughness and plasticity than the pearlite series of the same strength grade, and has an advantage in operational safety.
  • Theoretical and practical applications are not uniform in terms of wear and rolling contact fatigue performance. Since the bainite structure and properties are determined by the morphology and distribution of ferrite and carbide and the mode of action between them, such as the solid solution of carbides in ferrite or along the ferrite grain boundaries, it will lead to a huge difference in hardness.
  • the hardness directly determines the wear performance, which determines the extremely strict requirements for the process control and production process of the rail in order to obtain the desired microstructure.
  • bainitic rails if they are applied to high-speed or quasi-high-speed rails, the manufacturing cost is strict and requires the addition of a large amount of precious alloys, and the manufacturing cost is more than twice that of the existing pearlite rails. Promotional use is limited. In addition, whether the fatigue properties of bainitic rails are superior to existing pearlite rails requires further verification.
  • An object of the present invention is to solve the above problems in the prior art and to provide a rail suitable for high speed or quasi-high speed railway use having excellent rolling contact fatigue performance.
  • the present invention provides a rail for a high speed and quasi-high speed railway, the rail comprising a chemical composition of: 0.40% ⁇ 0.64% C, 0.10% ⁇ 1.00% Si, 0.30% ⁇ 1.50% by weight Mn, P of less than or equal to 0.025%, S of less than or equal to 0.025%, A1 of less than or equal to 0.005%, Re of more than 0 and less than or equal to 0.05%, V, Cr of total amount greater than 0 and less than or equal to 0.20% And at least one of Ti and the balance Fe and unavoidable impurities, wherein the head of the rail is a uniform mixed structure of pearlite and 15% to 50% ferrite at room temperature.
  • the rail comprises a chemical composition of: 0.45% to 0.60% C, 0.15% to 0.50% Si, 0.50% to 1.20% Mn, less than or equal to 0.025% P, less than a rare earth element equal to 0.025% S , less than or equal to 0.005% A1, greater than 0 and less than or equal to 0.05%, at least one of V, Cr and Ti in a total amount greater than 0 and less than or equal to 0.20%, and the balance Fe And inevitable impurities.
  • the rail may include at least one of 0.01% to 0.15% V, 0.02% to 0.20% Cr, and 0.01% to 0.05% Ti.
  • the rail may include at least one of 0.02% - 0.08% V, 0.10% - 0.15% Cr, and 0.01% - 0.05% Ti.
  • the head of the rail is a homogeneously mixed structure of pearlite and 15% to 30% ferrite at room temperature.
  • the present invention provides a method of manufacturing the above-described rail, the method comprising molten steel smelting and casting, rolling a rail, post-rolling controlled cooling, and air cooling placement, wherein the step of controlling the cooling after the rolling may include: erecting the rail to the rail Roller path, through the roller conveyor to drive the rail into the heat treatment unit, through the heat treatment unit to spray the cooling medium to the rail, thereby uniformly cooling the rail head at a cooling rate of 1 °C / s to 4 °C / s, to the top surface temperature of the rail head Stop cooling when it drops to 350 °C ⁇ 550 °C.
  • the method may further include: after performing the final rolling in the step of rolling the rail, cooling the rail to a temperature lower than the austenite phase region, and then at rC/s ⁇ 20 ° C / s The rate heats the rail to a temperature interval of the austenite phase zone and then performs the step of controlling the cooling after the rolling.
  • the cooling medium may be at least one of compressed air, a water vapor mixture, and an oil and gas mixture.
  • the step of smelting and casting the molten steel may include: smelting the molten steel by using a converter, an electric furnace or an open hearth, vacuum processing, cooling the molten steel into a square billet or a slab, or directly sending it to a heating furnace to raise the temperature.
  • the step of rolling the rail may include: heating the temperature to a certain temperature and keeping the temperature constant Time billets or slabs are fed into the mill to roll the rails into the desired section. In the step of rolling the rail, the rail can be heated to 1200 ° C ⁇ 1300 ° C and kept for 0.5 h ⁇ 2 h.
  • the method may further include: after controlling the cooling after rolling, the cooled rail is naturally cooled to room temperature in the air.
  • the toughness and yield strength of the rail are improved while maintaining the strength and hardness level of the existing high-speed railway rail, and the surface layer is formed on the rail.
  • the fatigue microcracks initiate and expand the required energy values, which can improve the rolling contact fatigue performance of the rail under the same conditions, and ultimately improve the service life and transportation safety of the rail.
  • Figure 1 is a schematic view showing the wear of a rail according to the present invention and a prior art rail;
  • FIG. 2 is a metallographic view of a rail head structure of a rail according to an embodiment of the present invention
  • Figure 3 is a metallographic view of the rail head structure of the rail according to the comparative example. detailed description
  • the toughness and the yield strength of the rail are improved while maintaining the strength and hardness level of the existing high-speed railway rail, and the formation is improved.
  • the fatigue microcracks on the surface of the rail initiate and expand the required energy values, so that under the same conditions, the rolling contact fatigue performance of the rail can be improved, and the service life and transportation safety of the rail are finally improved.
  • the present invention provides a rail for high speed and quasi-high speed railways having a chemical composition of: 0.40% to 0.64% C, 0.10% to 1.00% Si, 0.30% - by weight 1.50% of Mn, less than or equal to 0.025% of P, less than or equal to 0.025% of S, less than or equal to 0.005% of A1, greater than 0 and less than or equal to 0.05% of Re, total amount greater than 0 and less than or equal to 0.20% At least one of V, Cr and Ti, and the balance of Fe and unavoidable impurities.
  • the rail for high speed and quasi-high speed railway comprises a chemical composition of: 0.45% ⁇ 0.60% C, 0.15% ⁇ 0.50% Si, 0.50% ⁇ 1.20% Mn, less than or equal to 0.025 % P, less than or equal to 0.025% S, less than or equal to 0.005% A1, greater than 0 and less than or equal to 0.05% of rare earth elements, total amount greater than 0 and less than or equal to 0.20% of at least one of V, Cr and Ti, And the balance of Fe and inevitable impurities.
  • the contents of the materials mentioned are in percentage by weight unless otherwise stated.
  • Rails for high speed and quasi-high speed railways according to the present invention are organized into pearlite at room temperature and
  • C is one of the most important and cheapest elements for obtaining the proper strength, hardness and wear resistance of the rail.
  • C% ⁇ 0.40% (wt) since the amount of carbide in the structure is small, it is difficult to gather under the rail head tread, and the wear performance is lowered, resulting in the rail being lowered due to excessive wear. Lifetime; At the same time, due to the reduction of hardness, the rail tread forms a plastic rheological zone, and is prone to defects such as flash, which jeopardizes the safety of high-speed trains.
  • the strength and hardness of the rail will be too high by the subsequent heat treatment process, and on the other hand, the crack can be expanded due to the crack that has not been generated in time, thereby making the rail transverse
  • the tendency to break is enhanced; on the other hand, the excessive hardness of the rails accelerates the wear rate of the wheels and seriously reduces the service life of the train.
  • the improvement of the strength of the rail will be accompanied by a decrease in the ductile plasticity, which also fails to meet the safety requirements.
  • the C content is limited to between 0.40% and 0.64%, which can better satisfy the required rigidity of the rail, and at the same time, match the hardness of the wheel and rail and improve the safety of the rail.
  • the C content is limited to between 0.45% and 0.60%.
  • the main additive element of Si as steel is usually present in solid solution in ferrite and austenite to increase the strength of the structure.
  • the rail according to the present invention when Si% ⁇ 0.10% (wt) in the rail, the low solid solution amount will result in inconspicuous effect; when Si% > 1.00% (wt), the ductility of the steel will be made. And extension Reduced sex.
  • the high Si content in the steel severely reduces the lateral properties of the steel, which is not conducive to the safety of the rail. Therefore, in the present invention, the Si content is limited to be between 0.10% and 1.00%, and particularly when 0.15wt% ⁇ Si% ⁇ 0.50% by weight, the effect is remarkable.
  • Mn is a carbide forming element. After entering the cementite, it can partially replace the Fe atom, increase the hardness of the carbide, and finally increase the hardness of the steel.
  • Mn% ⁇ 0.50% (wt) in the rail the strengthening effect is not satisfactory, and the performance of the steel is slightly improved only by solid solution; when Mn% > 1.20% (wt), the steel The hardness of the medium carbide is too high, so that the rail can not obtain the ideal toughness and coordination.
  • the Mn content is limited to between 0.30% and 1.50%, particularly when 0.50% by weight ⁇ Mn% ⁇ 1.20% by weight, the effect is remarkable.
  • A1 is easily combined with oxygen in steel to form ⁇ 1 2 0 3 or other complex oxides. If it is not fully floated, it will remain in the steel.
  • the inclusion as a heterogeneous phase will destroy the continuity of the matrix. Under the action of cyclic stress, a fatigue crack source is formed, and further expansion will increase the tendency of the rail to be brittle. Therefore, in order to improve the purity of the rail and ensure the safety of use, the content of niobium is not more than 0.005%.
  • RE rare earth element
  • RE also reduces the damage of steel, such as 8, As and other impurities, and improves the fatigue properties of steel rail steel.
  • RE% > 0.05% it tends to promote the formation of coarse inclusions and seriously deteriorate the properties of the steel.
  • the range in which RE is added is limited to be less than or equal to 0.05%, particularly when 0.010 wt% ⁇ Re% ⁇ 0.020 wt%, the effect is remarkable.
  • the total amount of V+Cr+Ti is required to be ⁇ 0.20% for the following reasons:
  • C is the main strengthening element of steel, and its content directly determines the structure and properties of the rail, and the content of ferrite in the structure decreases with the decrease of C content.
  • the proportion gradually increases, the proportion of pearlite decreases, and ferrite is a soft phase in steel, which is difficult to withstand repeated wear of the wheel. Even by heat treatment, the strength of the ferrite matrix is limited. Therefore, it is necessary to add an alloying element such as V, Cr, and/or Ti to strengthen the ferrite matrix, thereby improving the toughness and plasticity of the rail while improving the wear performance.
  • an alloying element such as V, Cr, and/or Ti
  • the V in steel has a very low solubility at room temperature, usually forming V(C,N) with C and N in steel, fine
  • the grain formation which enhances the toughness and plasticity while strengthening the matrix, is one of the commonly used strengthening elements in carbon steel.
  • the rail according to the present invention when ⁇ % ⁇ 0.15%, the effect is more obvious; when the V content is further increased, the strength is further increased and the toughness, particularly the impact property, is significantly lowered, that is, the ability of the rail to resist impact. Weakened, this is inconsistent with the high safety required for rails for high-speed railways; if ⁇ % ⁇ 0.01%, it is difficult to exert a strengthening effect due to the limited amount of V precipitation. Therefore, when V is added alone, the V content is limited to 0.01% to 0.15%. Especially when 0.02% ⁇ V% ⁇ 0.08%, the effect is more remarkable.
  • Cr and Fe form a continuous solid solution and form a variety of carbides with C, which is also one of the main strengthening elements in steel.
  • Cr can uniform the distribution of carbides in the steel and improve the wear properties of the steel. Compared with V, the biggest advantage of Cr is economics. However, a higher Cr content will have a detrimental effect on the weldability.
  • the Cr content is limited to 0.02% to 0.20%, especially when 0.10% ⁇ Cr% ⁇ 0.15%, the effect is more remarkable.
  • the main role of Ti in steel is to refine the austenite grains during heating, rolling and cooling, ultimately increasing the toughness and stiffness of the structure.
  • Ti% > 0.05% on the one hand, since Ti is a strong carbonitride forming element, the excessive TiC generated will cause the rail hardness to be too high; on the other hand, the TiC will be excessively segregated.
  • the enrichment forms coarse carbides, which not only reduces the ductile plasticity, but also makes the contact surfaces of the rails susceptible to cracking and fracture under the impact load.
  • Ti% ⁇ 0.01% the amount of the carbonitride compound formed is limited and it is difficult to function, so in the present invention, the Ti content is limited to 0.01% to 0.05%.
  • a method of manufacturing a rail for a high speed and quasi-high speed railway includes the following steps: (1) molten steel smelting and casting
  • the molten steel containing the following components is smelted by a converter, an electric furnace or a flat furnace: 0.40% ⁇ 0.64% C, 0.10% ⁇ 1.00% Si, 0.30% ⁇ 1.50% Mn, P less than or equal to 0.025%, less than or equal to 0.025 % S, less than or equal to 0.005% of A1, greater than 0 and less than or equal to 0.05% of Re,
  • the total amount is greater than 0 and less than or equal to 0.20% of at least one of V, Cr and Ti, and the balance of Fe and unavoidable impurities.
  • LF Ladle Furnace
  • furnace refining ie, refining outside the furnace
  • vacuum treatment cooling of the molten steel into billet or slab, or directly sent to the furnace to raise the temperature.
  • the continuous casting billet which is heated to a certain temperature (preferably 1200 ° C to 1300 ° C) and kept for 0.5 to 2 h is fed to a rolling mill to be rolled into a rail of a desired section.
  • the rail After the final rolling, the rail is usually kept at a temperature above 800 °C. At this time, by controlling the cooling rate of the rail head, the rail can obtain different performance.
  • the rails which have residual heat after rolling due to the rolling characteristics of the rolling mill, usually the rails contact the roller table with the corners of the side rails and the side of the rail head, and the rails actually used only have the rail head portion.
  • the process of controlling the cooling is as follows: First, the rail is erected on the roller table, and the rail is driven to enter the heat treatment unit by the rotation of the roller.
  • the heat treatment unit used to cool the top surface of the rail head and the nozzles on both sides had begun to spray a cooling medium with an appropriate pressure and flow rate, typically 2 kPa to 15 KPa in the atmosphere.
  • a cooling medium typically 2 kPa to 15 KPa in the atmosphere.
  • the accelerated cooling medium may be at least one of a compressed air, a water vapor mixture, and an oil and gas mixture.
  • a compressed air a compressed air
  • water vapor mixture a water vapor mixture
  • oil and gas mixture an oil and gas mixture.
  • the rail head temperature reaches the end accelerated cooling temperature range in the present invention, the rail is naturally cooled in the air and subjected to subsequent processing.
  • an in-line heat treatment process is employed.
  • an off-line heat treatment process can also be employed.
  • the off-line heat treatment is a process in which the rail is cooled to room temperature after being rolled, and then heated by an induction heating device to austenite phase region temperature, usually 900 ° C to 1100 ° C, and the rail head portion is accelerated and cooled.
  • the rail is naturally cooled to a temperature lower than the austenite phase region, and then the rail is reheated to austenite phase region or a temperature of 800 ° C or higher.
  • the product of the present invention can also be obtained by taking the process in the step (3).
  • the billet when the billet is rolled into a rail to be cooled to a temperature lower than the austenite phase region At the rate of 1 °C / s ⁇ 20 °C / s, the rail is heated to a temperature range of 800 °C ⁇ 1000 °C, and then the process of step (3) is repeated, that is, 1 °C / s ⁇ 4
  • the cooling rate of °C/s is evenly cooled when the rail head is cooled to 350 ° C ⁇ 550 ° C, and then naturally cooled to room temperature in the air.
  • the rail when the naturally cooled rail is reheated to the austenite phase zone temperature, different heating rates can be used depending on factors such as specific equipment conditions, for example, the rail can be slowly heated at 1 ° C/s.
  • the temperature to the austenite phase zone can also be rapidly heated to a temperature in the austenite phase zone at 20 °C/s.
  • the method of manufacturing a rail according to the present invention is substantially the same as the method of manufacturing a rail of the prior art except for the step of controlling the cooling after rolling, and therefore, the same content is not described in detail herein.
  • the head of the rail is uniformly cooled at a cooling rate of 1 ° C / s ⁇ 4 ° C / s, until the temperature of the rail head is lowered to 350 ° C ⁇ 550 ° C Stop cooling. Since the choice of the cooling process will determine the performance of the final product, in the present invention, the rail containing the above components cannot be used to refine the ferrite and pearlite grains in the structure when the cooling rate is less than 1 °C/s.
  • the insufficient strength of the ferrite matrix may cause the vertical load of the train to be unbearable during use, resulting in excessive wear and tear, and the top surface of the rail head may be deformed due to plastic flow. It not only reduces the service life of the rail but also jeopardizes the safety of driving.
  • the cooling rate exceeds 4 ° C / s, the diffusion rate of carbide in the steel decreases, increasing the production of bainite and martensite. Tendency, while the latter two organizations are explicitly forbidden in the pearl system rail.
  • the cooling rate is too high, the strength of the rail will be greatly increased. Although the energy of crack initiation and expansion is simultaneously increased, the cracks that have been generated cannot be removed by wheel and rail wear, which is also unfavorable for driving safety.
  • the end temperature of the accelerated cooling is 350 ° C to 550 ° C for the reason that: the rail containing the above components is accelerated from the austenite phase region, and the surface of the rail and the surface are at least 15 mm below about 550 ° C.
  • the internal transformation has been completed; at this time, the heat stored inside the rail head will be transferred outwards, such as the end of accelerated cooling, which may cause the formation of the refined structure to be roughened due to the increase of the surface temperature due to heat conduction, which is not conducive to the internal organization of the rail head.
  • the transformation is completed under a large degree of subcooling, and the effect of the heat treatment cannot be fully exerted. If the accelerated cooling temperature is lower than 350 °C, it has entered the bainite transformation zone, which is not conducive to obtaining stable pearlite and ferrite structure, and increasing the tendency of abnormal tissue generation.
  • the rail rail waist and the rail bottom position are naturally air-cooled to room temperature for the following reasons:
  • the rail rail waist serves as a joint between the head and the bottom, and indirectly receives the weight from the train, and requires a certain rigidity. At the same time, it also bears the normal force generated by the steering of the train; the bottom of the rail directly acts on the sleeper, determines the running track of the train, and finally transfers the load to the track bed.
  • columns The axle weight (l lt ⁇ 14t) is lower than the passenger-carried mixed line or heavy-duty line (25t ⁇ 40t) and the curve curve radius is large (usually > 1000m).
  • the rail waist and the rail bottom are limited by vertical force and normal force.
  • accelerated cooling has limited impact on toughness and plasticity index compared to air cooling, and has no significant effect on the safety of rail use.
  • a rail with a fine pearlite + (15% to 50%) fine ferrite mixed structure can be obtained, and the strength of the rail reaches the existing high-speed or quasi-high-speed railway rail.
  • the same strength level significantly improves the ductility and yield strength of the rail, improves the crack initiation and expansion energy of the rail surface, improves the rail's ability to resist impact loads, and finally improves the rolling contact fatigue performance of the rail to ensure the safety of railway transportation.
  • it is not necessary to renovate existing equipment in the production process and the production process is simple, and the operation cylinder is flexible.
  • the converter is smelted into the steels listed in Table 2 below, and then subjected to LF furnace refining, vacuum degassing, billet continuous casting, billet heating furnace heating, rail rolling, finishing temperature of 903 ° C, after 40 s.
  • the top surface temperature of the rail head drops to 800 °C and the compressed air is blown.
  • the head of the rail is uniformly cooled at a cooling rate of 3.1 °C/s.
  • the top surface temperature of the rail head is 520 °C, the rail waist and the rail bottom. The temperature was greater than 600 ° C, and then the rail was placed in the air and naturally cooled to room temperature to obtain Sample 1.
  • the steel rail was manufactured in the same manner as in the method of Example 1, except for the step of controlling the cooling after rolling. Specifically, in this example, the finishing temperature is 910 ° C, and after 45 s of placement, the top surface temperature of the rail head drops to 780 ° C to start blowing compressed air and oil and gas mixture, and is uniformly cooled at a cooling rate of 2.9 ° C / s.
  • the temperature of the top surface of the rail head is 514 ° C
  • the temperature of the rail waist and the bottom of the rail is greater than 600 ° C, and then the rail is naturally cooled to room temperature in the air to obtain sample 2.
  • the steel rail was manufactured in the same manner as in the method of Example 1, except for the step of controlling the cooling after rolling. Specifically, in this example, the finishing temperature is 900 °C. After 42 seconds, the top surface temperature of the rail head drops to 770 °C, and the oil and gas mixture is sprayed to uniformly cool the rail head at a cooling rate of 2.7 °C/s. After the injection, the temperature of the top surface of the rail head is 530 ° C, the temperature of the rail waist and the bottom of the rail is greater than 600 ° C, and then the rail is placed in the air and naturally cooled to room temperature to obtain sample 3.
  • the finish rolling temperature is 890 ° C.
  • the top surface temperature of the rail head is lowered to 790 ° C to start blowing the water vapor mixture and the oil and gas mixture, and uniformly cooling at a cooling rate of 3.0 ° C / s.
  • the temperature of the top surface of the rail head is 495 ° C
  • the temperature of the rail waist and the bottom of the rail is greater than 550 ° C, and then the rail is placed in the air and naturally cooled to room temperature to obtain the sample 4 .
  • the steel rail was manufactured in the same manner as in the method of Example 1, except for the step of controlling the cooling after rolling. Specifically, in this example, the finishing temperature is 915 ° C, after 50 s of placement, the top surface temperature of the rail head drops to 780 ° C to start blowing compressed air, and the rail head is uniformly cooled at a cooling rate of 2.8 ° C / s. After the injection is completed, the temperature of the top surface of the rail head is 528 ° C, the temperature of the rail waist and the bottom of the rail is greater than 600 ° C, and then the rail is placed in the air and naturally cooled to room temperature to obtain the sample 5 .
  • the finishing temperature is 915 ° C
  • the top surface temperature of the rail head drops to 780 ° C to start blowing compressed air
  • the rail head is uniformly cooled at a cooling rate of 2.8 ° C / s.
  • the temperature of the top surface of the rail head is 528 ° C
  • the steel rail was manufactured in the same manner as in the method of Example 1, except for the step of controlling the cooling after rolling. Specifically, in this example, the finishing temperature is 922 ° C. After standing for 53 s, the top surface temperature of the rail head is lowered to 795 ° C to start blowing compressed air, and the rail head is uniformly cooled at a cooling rate of 2.1 ° C / s. After the injection, the temperature of the top surface of the rail head is 519 ° C, the temperature of the rail waist and the bottom of the rail is greater than 600 ° C, and then the rail is placed in the air and naturally cooled to room temperature to obtain the sample 6.
  • the steel rail was manufactured in the same manner as in the method of Example 1, except for the step of controlling the cooling after rolling. Specifically, in this example, the finish rolling temperature is 918 ° C. After standing for 49 s, the top surface temperature of the rail head is lowered to 800 ° C to start blowing compressed air, and the rail head is uniformly cooled at a cooling rate of 2.2 ° C / s. After the injection is completed, the temperature of the top surface of the rail head is 531 °C, the temperature of the rail waist and the bottom of the rail is greater than 600 °C, and then the rail is placed in the air and naturally cooled to room temperature to obtain the sample 7.
  • the steel rail was manufactured in the same manner as in the method of Example 1, except for the step of controlling the cooling after rolling. Specifically, in this example, the finishing temperature is 907 ° C, after 48 s of placement, the top surface temperature of the rail head drops to 785 ° C, and the compressed air and water vapor mixture is injected to be uniformly cooled at a cooling rate of 2.3 ° C / s. At the head of the rail, after the injection, the temperature of the top surface of the rail head is 526 ° C, the temperature of the rail waist and the bottom of the rail is greater than 600 ° C, and then the rail is placed in the air and naturally cooled to room temperature to obtain a sample 8 .
  • the rail was manufactured in the same manner as the method of Example 1 except for the step of controlling the cooling after rolling. Specifically, in this example, the finishing temperature is 895 ° C, first air cooled to room temperature, and then The rail head was reheated to 900 °C at a rate of 5 °C/s using a power frequency induction heating device. When the rail head was naturally air cooled to 760 °C, the water vapor mixture and compressed air were sprayed at 2.2 °C/ The cooling rate of s is evenly cooled to the head of the rail.
  • the temperature of the top surface of the rail head is 510 ° C
  • the temperature of the rail waist and the bottom of the rail is greater than 600 ° C
  • the rail is placed in the air and naturally cooled to room temperature to obtain a sample 9 .
  • the steel rail was manufactured in the same manner as in the method of Example 1, except for the step of controlling the cooling after rolling. After obtaining the required section rail, it is directly placed in the air and cooled to room temperature to obtain the existing high speed or quasi-high speed railway rail, that is, Comparative Example 1.
  • the strength of the rails of 1 is at the same level, but the elongation is increased by about 50%.
  • the tensile strength (R m ) of the example 2 and the example 8 rail according to the present invention is slightly lower than that of the rail of the comparative example 1, but the yield strength (R el ) is high, and under the same conditions, the fatigue crack of the surface layer in the rail is effectively prevented.
  • the high-speed railway rails are currently in use due to low wheel-rail contact stress and slight wear, which can meet the wear requirements.
  • the steel rail according to Example 2 of the present invention has a post-break elongation which is higher than that of the rail of Comparative Example 1 by about 75%, and the use safety is improved.
  • Example 4 With respect to Comparative Example 1, the strength and hardness of Example 4, Example 6, Example 7, and Example 8 of the present invention were also improved while the plasticity was improved, and the overall performance was improved.
  • Example 9 since the ferrite grains are refined, the performance also satisfies the requirements for rails for high speed or quasi-high speed railways.
  • FIG. 2 is a metallographic view of a rail head structure of a rail according to Example 1 of the present invention.
  • Figure 3 is a metallographic view of the rail head structure of the rail according to Comparative Example 1.
  • the rail produced according to the method of the present invention has a structure in which the pearlite and the ferrite are uniformly arranged in comparison with the rail according to the comparative example 1, and therefore, in the present invention
  • the wear properties of the rails can be improved by the cementite in the pearlite, and the toughness and fatigue properties of the rails can be improved by the strengthened ferrite. Therefore, for high-speed and quasi-high-speed railway rails,
  • the rail of the present invention has better wear resistance and fatigue contact resistance than prior art rails.
  • the impact toughness of the rails produced according to the method of the present invention at normal temperature and low temperature is significantly improved as compared with the rails manufactured by the prior art.
  • Examples 2 and 8 are due to the low carbon content and Microalloying treatment nearly doubles the toughness.
  • Examples 4 and 6 which have a high carbon content and no alloying, the impact toughness is also improved by 25%. It can be seen that it is advantageous to reduce the carbon content and control the cooling method after rolling to improve the toughness of the rail. Therefore, the rail manufactured according to the method of the present invention will provide a more effective guarantee for the safety of the train when the high-speed railway in the cold region is damaged due to irregularities or other causes.
  • Test horse full machine name MM-200 type
  • Sample size thickness 10mm, inner diameter 10mm, eve diameter 36mm;
  • the wear performance of the example 8 rail in the present invention was slightly lower than that of the rail of Comparative Example 1. Due to the light axle weight of the high-speed train and the low wear rate of the rail, it is beneficial to remove the fatigue cracks generated on the surface of the rail head by wear, which is very beneficial to improve the rolling contact fatigue performance. For Examples 5 and 6, the wear performance is comparable to that of Comparative 1 and is equally applicable to high speed or quasi-high speed rail applications.
  • the fatigue crack growth rate of the rail according to the present invention and the prior art rail is shown in Table 6 below.
  • a crack propagation rate tester model ISTRON 8801 was used to study the law of crack length (or depth) along the direction perpendicular to the stress direction. The slower the crack growth rate, the better it is to prevent crack propagation under the same conditions. Crack propagation rate of rails of the present invention and comparative examples
  • the crack propagation rate of the rail manufactured by the method according to the present invention is lower than that of the steel of Comparative Example 1, so that it is advantageous to prevent crack propagation under the same conditions.
  • the fracture toughness (K IC ) of the rail according to the present invention and the prior art rail at low temperature (-20 ° C) and normal temperature (20 ° C) is shown in Table 7 below.
  • the fracture toughness of the rail was measured using a fracture toughness tester model ISTRON 8801.
  • Fracture toughness K IC is a mechanical property index that measures the ability of a material to resist crack propagation. The higher the K IC value, the stronger the ability of the rail to resist crack propagation, and the more favorable it is for driving safety.
  • the fracture toughness of the rail manufactured by the method according to the present invention is higher than that of the rail of Comparative Example 1 at both normal temperature and low temperature.
  • the fracture toughness increases remarkably. Therefore, lowering the carbon content in the rail is advantageous for obtaining higher fracture toughness.
  • the rails produced according to the method of the present invention and the rails manufactured according to the prior art both meet the standard requirements, and the fatigue limit of the rail according to the present invention is higher than that of the rails manufactured according to the prior art. Fatigue limit.
  • the head of the rail is a large amount of pearlite and smaller than
  • the rail for high speed and quasi-high speed railway provided according to the present invention can make the head of the rail at room temperature by reducing the carbon content in the rail and controlling the cooling after rolling. It is a homogeneous mixed structure of pearlite + 15% ⁇ 50% ferrite.
  • the advantages of increasing the proportion of ferrite in the rails of high-speed railways to 15% to 50% in the microstructure are as follows: (1) The existing high-speed railway rails are mainly pearlite, containing less than 5% of ferrite structure. After a certain period of operation, it was found that the wear between the high-speed train and the rail hardly occurred, which made the pearlite structure, which is known for its good wear performance, difficult to function.
  • the method of increasing the strength of the matrix is nothing more than three kinds of methods, namely, alloying element solid solution, precipitation strengthening and heat treatment fine grain strengthening, and relying solely on the heat treatment process, the ferrite matrix will be improved. At the same time, the strengthening effect of the cementite is enhanced, and the strength is too high. Therefore, the addition of a part of the microalloying element is mainly to strengthen the ferrite matrix, and at the same time, the toughness and plasticity are slightly improved. In addition, if the ferrite ratio exceeds 50%, the proportion of pearlite will be lowered, and a certain degree of wear performance cannot be ensured, and the same cannot be applied to a high-speed line. (2) The increase of the proportion of ferrite in the rail means that the toughness is greatly improved, and the higher elongation and impact toughness will greatly reduce the probability of the rail breaking under the same impact load, ensuring the driving. Extremely safe Lee.

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Abstract

本发明公开了一种用于高速和准高速铁路的钢轨及其制造方法。通过降低碳含量，并配合轧后控制冷却的方式，得到具有优良的滚动接触疲劳性能的钢轨，所述钢轨包含的化学成分以重量计为：0.40%～0.64%的C，0.10%～.00%的Si，0.30%～1.50%的Mn，少于等于0.025%的P，少于等于0.025%的S，少于等于0.005%的Al，大于0少于等于0.05%的稀土元素，总量大于0且小于等于0.20%的V、Cr和Ti中的至少一种，以及余量的Fe和不可避免的杂质。根据本发明的方法制造的钢轨保持了现有高速铁路的钢轨的强度和硬度的同时提高了钢轨的韧塑性和屈服强度，并提高了形成在钢轨表层的疲10劳微裂纹萌生及扩展所需的能量值，从而在相同条件下可以改善钢轨的滚动接触疲劳性能，最终提高钢轨的使用寿命和运输安全性。

Description

说 明 书 用于高速和准高速铁路的钢轨及其制造方法 技术领域
本发明涉及一种钢轨材料， 特别涉及一种适于在高速或准高速铁路上使 用的钢轨及其制造方法。 背景技术
目前， 世界铁路主要包括重载铁路、 高速铁路以及客货混运铁路三种类 型。 对于重载铁路用钢轨， 由于列车轴重大（通常为 25t ~ 40t ), 轮轨接触应 力大， 受力苛刻， 通常选用 C含量大于 0.75%、 抗拉强度在 1200MPa以上、 具有全珠光体组织的碳素轨或合金轨， 以保证钢轨具有优良的耐磨性。 对于 高速铁路， 由于其主要用于承担客运， 列车轴重轻， 所以通常要求高速铁路 用钢轨具有优良的抗疲劳性能。 对于客货混运铁路， 由于其既承担客运， 又 要保证货物运输的特殊性， 要求选用的钢轨既要保证一定的耐磨损性能， 又 要求一定的抗疲劳性能， 需在两者间找到平衡点。 在客货混运铁路使用的钢 轨选用上， 通常为碳含量 0.70% ~ 0.80%, 抗拉强度 900MPa ~ HOOMPa之间 的热轧或热处理钢轨， 部分小半径曲线可选用 1200MPa钢轨， 组织一般以珠 光体为主， 部分包含微量铁素体。 对于高速铁路和准高速铁路， 由于二者均 要求钢轨具有一定的抗疲劳性能， 所以对于高速及准高速铁路， 当前广泛应 用的是抗拉强度 900MPa的 U71Mn热轧钢轨，其碳含量在 0.65%-0.76%之间。
然而， 实际应用表明， 由于高速列车轴重较轻（通常为 llt ~ 14t ), 实际 运营中轮轨间几乎没有磨损， 导致已产生于钢轨轨头表面或侧面的裂纹难以 磨去， 经轮轨间接触力往复作用， 反而加剧了裂纹扩展导致钢轨断裂的倾向 性， 严重危及列车的行车安全； 另一方面， 如果通过单纯降低钢轨的强度和 硬度的方法来提高钢轨的磨耗速率不仅会使钢轨表层产生塑性流变导致钢轨 断面尺寸偏差， 使列车无法沿钢轨行进， 还将由于钢轨磨损过快而缩短其使 用寿命。 因此， 在高速及准高速铁路中， 以珠光体组织为主的热轧钢轨在磨 损与滚动接触疲劳两者间难以寻找平衡点。
为了改善高速及准高速铁路钢轨的滚动接触疲劳性能， 目前主要有两种 方法。 第一种方法是利用钢轨打磨列车对钢轨上端进行定期研磨， 但这种方 法存在的问题是， 打磨列车费用昂贵， 同时， 高速及准高速铁路行车密度高， 没有充分的研磨时间。 另一种方法是改善钢轨表面的磨损速率， 在疲劳伤损 出现之前， 通过轮轨间不断的磨耗去除疲劳层。 钢轨的磨损特性受硬度支配， 为了促进磨耗降低钢轨的硬度即可。 然而， 单纯降低硬度会导致钢轨的上表 面在运行一定时间后出现塑性变形，并常发生伴随而来的龟裂及剥离等伤损， 同样不利于提高钢轨的使用寿命和运输安全性。
近年来， 为改善高速铁路钢轨的抗接触疲劳伤损性能， 发展了一种以贝 氏体组织为主， 同时包含部分马氏体和残余奥氏体的钢轨。 专利号为 CN1074058C 的专利公开了一种焊接部结合性优良的贝氏体系列钢轨及其制 造方法。该贝氏体系列钢轨含有 0.15% ~ 0.40%的 C、 0.1% ~ 0.2%的 Si、 0.15 ~ 1.10%的 Mn、 小于等于 0.035%的 P和 S, 此外还包含 Cr、 Nb、 Mo、 V、 Ni 等元素。
然而， 从理论上分析， 具有贝氏体组织特别是下贝氏体组织的钢轨与同 等强度级别的珠光体系列钢轨相比， 韧塑性较大幅度提高， 在运行的安全性 方面占有优势， 但在磨损及滚动接触疲劳性能方面， 理论与实际应用并未统 一。 由于贝氏体组织和性能由铁素体与碳化物的形态、 分布和彼此间作用方 式决定， 如碳化物固溶于铁素体或沿铁素体晶界分布， 将导致硬度的巨大差 异， 而硬度直接决定磨损性能， 这就决定了为获得理想的组织形态， 对钢轨 的过程控制和生产工艺有极其严格的要求。 此外， 对于专利 CN1074058C中 所公开的贝氏体系列钢轨， 要获得理想的贝氏体组织， 除要求严格的控制工 艺外， 还需添加大量的贵重元素， 导致钢轨的制造成本远高于现有的珠光体 系列钢轨， 即使性能优良， 也难于大批量推广使用。
因此， 对于贝氏体钢轨， 如果将其应用于高速或准高速铁路， 则由于其 制造工艺要求严格且需要添加大量的贵重合金， 制造成本相当于现有珠光体 钢轨的两倍以上而使得批量推广使用受到限制。 此外， 贝氏体钢轨的疲劳性 能是否优于现有珠光体钢轨还需进一步验证。
因此， 亟需一种制造成本较低且同时具有优良的耐磨损性和抗疲劳伤损 性能的珠光体系列钢轨， 以适宜于高速或准高速铁路应用。 发明内容 本发明的目的在于解决现有技术中存在的上述问题， 提供一种具有优良 的滚动接触疲劳性能的适于高速或准高速铁路使用的钢轨。
本发明提供了一种用于高速和准高速铁路的钢轨， 所述钢轨包含的化学 成分以重量计为： 0.40% ~ 0.64%的 C, 0.10% ~ 1.00%的 Si, 0.30% ~ 1.50%的 Mn, 少于等于 0.025%的 P, 少于等于 0.025%的 S, 少于等于 0.005%的 A1, 大于 0且少于等于 0.05%的 Re, 总量大于 0且小于等于 0.20%的 V、 Cr和 Ti 中的至少一种， 以及余量的 Fe和不可避免的杂质， 其中， 所述钢轨的头部在 室温下为珠光体和 15% ~ 50%铁素体的均匀混合组织。
根据本发明的一个实施例， 所述钢轨包含的化学成分以重量计为： 0.45% ~ 0.60% C, 0.15% ~ 0.50% Si, 0.50% ~ 1.20% Mn, 少于等于 0.025% P, 少于等于 0.025% S , 少于等于 0.005% A1, 大于 0且少于等于 0.05%的稀土元 素， 总量大于 0且小于等于 0.20%的 V、 Cr和 Ti中的至少一种， 以及余量的 Fe和不可避免的杂质。根据本发明的另一实施例，所述钢轨可以包含 0.01% ~ 0.15% V、 0.02% ~ 0.20% Cr和 0.01% ~ 0.05% Ti中的至少一种。 根据本发明 的又一实施例， 所述钢轨可以包含 0.02% - 0.08% V、 0.10% ~ 0.15% Cr和 0.01% ~ 0.05% Ti中的至少一种。
根据本发明的一个实施例， 所述钢轨的头部在室温下为珠光体和 15% ~ 30%铁素体的均匀混合组织。
本发明提供了一种制造上述钢轨的方法，所述方法包括钢水冶炼及浇铸、 轧制钢轨、 轧后控制冷却和空冷放置， 其中， 所述轧后控制冷却的步骤可以 包括： 将钢轨直立于辊道， 通过辊道转运带动钢轨进入热处理机组， 通过热 处理机组向钢轨喷吹冷却介质， 从而以 1 °C /s至 4 °C /s的冷却速率均匀冷却钢 轨头部， 至轨头顶面温度降至 350°C ~ 550 °C时停止冷却。
根据本发明， 所述方法还可以包括： 在轧制钢轨的步骤中进行终轧后， 先将钢轨冷却至低于奥氏体相区的温度， 然后以 rC/s ~ 20°C/s的速率将钢轨 加热至奥氏体相区的温度区间， 然后再执行所述轧后控制冷却的步骤。
根据本发明的一个实施例，所述冷却介质可以为压缩空气、水汽混合物、 油气混合物中的至少一种。
根据本发明， 所述钢水冶炼及浇铸的步骤可以包括： 采用转炉、 电炉或 平炉冶炼钢水， 真空处理， 在将钢水浇铸为方形坯或板坯后冷却或直接送至 加热炉升温。 所述轧制钢轨的步骤可以包括： 将升温至一定温度并保温一定 时间的钢坯或连铸坯送入轧机， 以轧制为所需断面的钢轨。 在所述轧制钢轨 的步骤中， 可以将钢轨升温至 1200 °C ~ 1300 °C , 并保温 0.5h ~ 2h。
根据本发明， 所述方法还可以包括： 在轧后控制冷却之后， 将冷却后的 钢轨置于空气中自然冷却至室温。
在本发明中，通过降低钢轨中的碳元素含量， 配合轧后控制冷却的方式， 在保持现有高速铁路钢轨的强度、 硬度级别的同时提高钢轨的韧塑性和屈服 强度， 提高形成于钢轨表层的疲劳微裂纹萌生及扩展所需能量值， 从而在相 同条件下可以改善钢轨的滚动接触疲劳性能， 最终提高钢轨的使用寿命和运 输安全性。 附图说明
通过下面结合示例性地示出一例的附图进行的描述， 本发明的上述和其 他目的和特点将会变得更加清楚， 其中：
图 1是根据本发明的钢轨和现有技术的钢轨的磨损示意图；
图 2是根据本发明的一个实施例的钢轨的轨头组织的金相图；
图 3是根据对比例的钢轨的轨头组织的金相图。 具体实施方式
高速及准高速铁路的发展要求钢轨具有优异的综合性能， 以保证高速铁 路的安全性与长寿化。 列车沿钢轨高速行驶， 除要求钢轨的外观具有高平直 度、 高几何尺寸精度且无任何缺陷外， 还要求钢轨具有良好的韧塑性和滚动 接触疲劳性能。 对于现阶段高速及准高速铁路使用的钢轨， 要保证其具有长 寿命， 需尽可能减少由于轮轨接触摩擦造成钢轨表面的磨损； 同时， 为保证 已产生于钢轨表面的微裂纹在向内扩展之前能够被及时磨掉， 还需保证一定 的磨损速率， 这就形成了提高钢轨使用寿命以提高磨耗速率为代价的矛盾， 无法从根本上解决降低磨损与改善滚动接触疲劳性能的问题。
因此， 在本发明中， 通过降低钢轨中的 C元素含量， 配合轧后控制冷却 的方式， 在保持现有高速铁路钢轨的强度、 硬度级别的同时提高钢轨的韧塑 性和屈服强度， 提高形成于钢轨表层的疲劳微裂纹萌生及扩展所需能量值， 从而在相同条件下可以改善钢轨的滚动接触疲劳性能， 最终提高钢轨的使用 寿命和运输安全性。 具体地讲， 本发明提供了一种用于高速和准高速铁路的钢轨， 该钢轨包 含的化学成分以重量计为： 0.40% ~ 0.64%的 C, 0.10% ~ 1.00%的 Si, 0.30% - 1.50%的 Mn, 少于等于 0.025%的 P, 少于等于 0.025%的 S, 少于等于 0.005% 的 A1, 大于 0且少于等于 0.05%的 Re, 总量大于 0且小于等于 0.20%的 V、 Cr和 Ti中的至少一种， 以及余量的 Fe和不可避免的杂质。 优选地， 根据本 发明的用于高速和准高速铁路的钢轨包含的化学成分以重量计为： 0.45% ~ 0.60% C, 0.15% ~ 0.50% Si, 0.50% ~ 1.20% Mn, 少于等于 0.025% P, 少于等 于 0.025% S, 少于等于 0.005% A1, 大于 0且少于等于 0.05%的稀土元素， 总 量大于 0且小于等于 0.20%的 V、 Cr和 Ti中的至少一种， 以及余量的 Fe和 不可避免的杂质。 在下面的描述中， 除非另有说明， 否则所提到的物质的含 量均按重量百分比计。
根据本发明的用于高速和准高速铁路的钢轨在室温下组织为珠光体和
15% ~ 50%铁素体（优选地为珠光体和 15% ~ 30%铁素体 ) 的均匀混合组织， 断后延伸率≥15% , 屈服强度 （ RE1 ) >550MPa , -20 °C时的断裂韧性 KIC≥40MPam1/2。
C是使钢轨获得适宜强度、 硬度及耐磨性能的一种最重要也是最廉价的 元素。 在根据本发明的钢轨中， 当 C% < 0.40%(wt)时， 由于组织中的碳化物 数量少， 在钢轨轨头踏面下方难以聚集， 降低磨损性能， 导致钢轨因磨损过 快而降低使用寿命； 同时， 由于硬度的降低， 使钢轨踏面形成塑性流变区， 并易于产生飞边等缺陷， 危及高速列车的行车安全。 在根据本发明的钢轨中， 当 C% > 0.64%(wt)时， 通过后续热处理工序， 将使钢轨强度、 硬度过高， 一 方面由于已产生的裂纹无法及时磨耗而扩展， 从而使钢轨横向断裂的倾向性 增强； 另一方面， 钢轨硬度过高使车轮磨耗速率加快， 严重降低列车的使用 寿命。 此外， 在相同条件下， 钢轨强度的提高必将伴随韧塑性的降低， 同样 无法满足安全性要求。 因此，在本发明中， C含量限定在 0.40% ~ 0.64%之间， 可以更好地满足钢轨所需刚度， 同时， 使轮轨硬度匹配并提高钢轨使用的安 全性。 优选地， C含量限定在 0.45% ~ 0.60%之间。
Si作为钢的主要添加元素通常以固溶形式存在于铁素体和奥氏体中提高 组织的强度。 在根据本发明的钢轨中， 当钢轨中 Si% < 0.10%(wt)时， 固溶量 偏低将导致强化效果不明显； 当 Si% > 1.00%(wt)时， 将使钢的韧塑性和延展 性降低。 此外， 钢中的 Si含量偏高时严重降低钢材的横向性能， 不利于钢轨 使用的安全性。 因此， 在本发明中， Si含量限定在 0.10% ~ 1.00%之间， 特别 当 0.15wt% < Si% < 0.50wt%时， 效果显著。
Μη可以和 Fe形成固溶体， 提高铁素体和奥氏体的强度。 同时， Mn又 是碳化物形成元素， 进入渗碳体后可部分替代 Fe原子， 增加碳化物的硬度， 最终增加钢的硬度。 在根据本发明的钢轨中， 当钢轨中 Mn% < 0.50%(wt)时， 强化效果不理想，仅通过固溶作用使钢的性能略微提高； 当 Mn% > 1.20%(wt) 时， 钢中碳化物的硬度过高， 使钢轨无法获得理想的强韧性配合， 更重要的 是， 由于 Mn具有拖拽溶质原子的作用， 在制造钢轨过程中的控冷阶段， 由 于冷却速率较快， 奥氏体状态下的 C原子由于 Mn的作用而无法充分扩散， 最终形成饱和或过饱和状态， 易于产生贝氏体和马氏体等异常组织， 而后两 者是珠光体系列钢轨中禁止出现的。 因此， 在本发明中， Mn含量限定在 0.30% ~ 1.50%之间， 特别是当 0.50wt% < Mn% < 1.20wt%时， 效果显著。
A1在钢中易与氧结合，形成 Α1203或其它复杂氧化物，如未能充分上浮， 将存留于钢中， 在钢轨使用时该夹杂物作为异质相将破坏基体的连续性， 在 循环应力的作用下， 形成疲劳裂纹源， 进一步扩展将增加钢轨横向脆断的趋 势。因此，为提高钢轨的纯净度，确保使用安全，ΑΙ的含量规定不超过 0.005%。
RE (稀土元素）在钢中的作用是促进非金属夹杂物变形， 同时提高钢质 纯净度。 此外， RE还有降低8、 As等杂质对钢材性能的危害， 改善钢轨钢的 疲劳性能。 然而， 当 RE% > 0.05%时， 易促进粗大夹杂物生成， 严重恶化钢 材性能。 对于高速或准高速铁路用钢轨， 提高钢质纯净度， 减少非金属夹杂 物对钢质基体的破坏十分重要。 因此， 在本发明中， 添加 RE 的范围限定为 小于或等于 0.05%, 特别当 0.010wt% < Re% < 0.020wt%时， 效果显著。
在本发明中， V+Cr+Ti总量要求≤0.20%, 原因如下： C作为钢的主要强 化元素， 其含量高低直接决定钢轨的组织与性能， 随 C含量的降低， 组织中 铁素体的比例逐步扩大， 珠光体比例降低， 铁素体作为钢中的软质相， 难以 承受车轮反复磨耗， 即使通过热处理， 对铁素体基体强度的提高也很有限。 因此， 需要添加如 V、 Cr和 /或 Ti等合金元素来强化铁素体基体， 从而在改 善磨损性能的同时改善钢轨的韧塑性。 以下具体说明上述三种合金元素的添 加目的和范围。
钢中的 V在室温下溶解度很低， 通常与钢中的 C和 N形成 V(C,N), 细 化晶粒， 在强化基体的同时提高韧塑性， 是目前碳钢中常用的强化元素之一。 在根据本发明的钢轨中， 当 ¥% < 0.15%时， 这种效果较为明显； 当进一步提 高 V含量时， 强度将进一步提高而韧性特别是沖击性能显著下降， 即钢轨抵 抗沖击的能力减弱， 这与高速铁路用钢轨所需的高安全性不符； 如果 ¥% < 0.01%, 由于 V析出的数量有限， 难以发挥强化效果， 故单独添加 V时， V 含量限定在 0.01% ~ 0.15%, 特别是当 0.02%≤V%≤0.08%时， 效果更加显著。
Cr与 Fe能形成连续固溶体并与 C形成多种碳化物， 也是钢中的主要强 化元素之一。 此外， Cr能均匀钢中碳化物的分布， 改善钢材的磨损性能。 与 V相比， Cr最大的优势即经济性。 然而， Cr含量较高时将对焊接性能带来不 利影响。 在本发明中， 由于 C含量的降低， 使得钢中铁素体比例扩大， 需要 添加固溶强化元素以提高铁素体的强度， 保证钢轨使用中的磨损性能， 同时， 由于高速或准高速列车轴重轻， 磨耗有限， 因此， Cr含量限定在 0.02% ~ 0.20%, 特别是当 0.10%≤Cr%≤0.15%时， 效果更加显著。
Ti在钢中的主要作用是细化加热、 轧制及冷却时奥氏体的晶粒， 最终增 加组织的韧塑性和刚度。 在根据本发明的钢轨中， 当 Ti% > 0.05%时， 一方面 由于 Ti是强碳氮化物形成元素， 产生的 TiC偏多将使钢轨硬度过高； 另一方 面， TiC 偏多将偏聚富集形成粗大碳化物， 不仅降低韧塑性， 还使得钢轨在 沖击载荷作用下接触面易于开裂并导致断裂。在根据本发明的钢轨中，当 Ti% < 0.01%时， 形成的碳氮化物化物数量有限， 难以发挥作用， 故在本发明中， Ti含量限定在 0.01% ~ 0.05%。
由于高速或准高速铁路钢轨强度较低， 所需 V、 Cr和 Ti等元素的固溶 强化、 析出强化作用有限； 同时， 由于本发明中碳含量的降低， 韧塑性已显 著改善， 仅依靠上述合金元素改善钢轨的磨损性能。 因此， 本发明中限定 0<V+Cr+Ti≤0.20%。
以下， 将详细说明根据本发明的用于高速和准高速铁路的钢轨的制造方 法。
根据本发明， 制造用于高速和准高速铁路的钢轨的方法包括以下步骤： ( 1 )钢水冶炼及浇铸
首先， 采用转炉、 电炉或平炉对包含如下成分的钢水进行冶炼： 0.40% ~ 0.64% C, 0.10% ~ 1.00% Si, 0.30% ~ 1.50% Mn, 少于等于 0.025%的 P, 少于 等于 0.025%的 S, 少于等于 0.005%的 A1, 大于 0且少于等于 0.05%的 Re, 总量大于 0且小于等于 0.20%的 V、 Cr和 Ti中的至少一种， 以及余量的 Fe 和不可避免的杂质。 然后， 进行 LF ( Ladle Furnace ) 炉精炼 （即炉外精炼）、 真空处理， 在将钢水浇铸为方坯或板坯后冷却或直接送至加热炉升温。
( 2 )钢轨轧制
将升温至一定温度（优选为 1200 °C ~ 1300 °C )并保温 0.5 ~ 2h的连铸坯 送入轧机， 以轧制为所需断面的钢轨。
( 3 )轧后控制冷却
终轧后， 钢轨通常保持在 800 °C以上的温度， 此时通过控制钢轨轨头冷 却速率， 可以使钢轨获得不同的性能。 对于轧制后尚有余热的钢轨， 由于轧 机的轧制特点， 通常钢轨以一侧轨底角部和轨头侧面接触辊道， 而实际使用 的钢轨只有轨头部位。 在本发明中， 控制冷却的过程如下： 首先将钢轨直立 于辊道， 通过辊道转动带动钢轨进入热处理机组。 在此之前， 热处理机组用 于冷却钢轨轨头顶面和两个侧面的喷嘴已开始喷吹具有适当压力和流量， 通 常为大气环境下 2kPa ~ 15KPa的冷却介质。 当钢轨在辊道的带动下经过连续 布置的喷嘴时， 以 1 °C/s ~ 4°C/s的冷却速率对钢轨的轨头部位进行均匀冷却， 当位于热处理机组上方的红外温度探测装置探知轨头顶面表层温度降至
350°C ~ 550°C时， 冷却停止， 完成钢轨轨头的控制冷却。
在本发明中， 加速冷却介质可以为压缩空气、 水汽混合物和油气混合物 中的至少一种。 在本发明的指导下， 本领域技术人员可以根据实际需要来确 定所采用的加速冷却介质。 具体地讲， 在采用压缩空气和水汽混合物作为加 速冷却介质的情况下， 可以根据常规选择来确定二者之间的比例。
( 4 ) 空冷放置
当钢轨轨头温度达到本发明中的终止加速冷却温度范围后， 将钢轨置于 空气中自然冷却， 并进行后续工序处理。
此外， 在上述步骤（3 ) 中， 采用的是在线热处理工艺。 然而， 对于本发 明， 也可以采用离线热处理工艺。 离线热处理是钢轨轧后先空冷至室温， 再 由感应加热装置加热至奥氏体相区温度， 通常为 900°C ~ 1100°C , 再对轨头 部位进行加速冷却的过程。 具体地讲， 在通过前述步骤将钢坯轧制成钢轨之 后， 将钢轨自然冷却至低于奥氏体相区的温度， 然后再将钢轨重新加热至奥 氏体相区或 800°C以上的温度并采取步骤（3 ) 中的工艺， 同样可得到本发明 中的产品。 在本发明中， 当将钢坯轧制成钢轨冷却至低于奥氏体相区的温度 时， 以 1 °C /s ~ 20 °C /s的速率将钢轨加热至 800 °C ~ 1000 °C的温度区间， 然后 重复步骤（ 3 ) 的工艺， 即， 以 1 °C/s ~ 4°C/s的冷却速率均匀冷却钢轨头部至 350°C ~ 550°C时停止冷却， 其后在空气中自然冷却至室温。 这里， 需要注意 的是， 将自然冷却的钢轨重新加热至奥氏体相区温度时， 可以根据具体的设 备条件等因素采用不同的加热速率，例如，可以以 l °C/s将钢轨緩慢加热至奥 氏体相区的温度， 也可以以 20 °C/s将钢轨急速加热至奥氏体相区的温度。
除了轧后控制冷却的步骤之外， 根据本发明的制造钢轨的方法与现有技 术的制造钢轨的方法基本相同， 因此， 在此未对相同的内容进行详细的描述。 在本发明中， 在终轧后， 以 l °C/s ~ 4°C/s的冷却速率对钢轨的头部进行均匀 冷却， 待钢轨头部的温度降至 350°C ~ 550°C时停止冷却。 由于冷却工艺的选 择将决定最终产品的性能， 因此， 在本发明中， 采用含有上述成分的钢轨， 当冷却速率不足 l °C/s时，无法通过细化组织中铁素体及珠光体晶粒达到与现 有高速或准高速铁路钢轨同等的强度， 铁素体基体强度不足可能导致使用中 难以承受列车的垂直载荷， 产生过快磨损的同时使轨头顶面因塑性流变， 尺 寸发生偏差， 不仅降低钢轨的使用寿命， 还同时危及行车安全； 另一方面， 当冷却速率超过 4°C/s时，碳化物在钢中的扩散速率降低，增加产生如贝氏体、 马氏体组织的倾向性， 而后两种组织是珠光体系钢轨中明确禁止出现的。 此 夕卜， 冷却速率过高将大幅提高钢轨的强度， 尽管同时提高了裂纹萌生及扩展 的能量， 但同时对于已产生的裂纹无法通过轮轨磨耗去除， 同样不利于行车 安全。
在本发明中， 加速冷却的终止温度为 350°C ~ 550°C , 理由是： 采用包含 上述成分的钢轨自奥氏体相区加速冷却， 约 550°C时钢轨表面及表面下至少 15mm 范围内转变已完成； 此时， 轨头内部存有的热量将向外传递， 如终止 加速冷却， 可能由于热传导导致表层温度升高使已形成的细化组织粗糙化， 不利于轨头内部组织在较大的过冷度下完成转变， 无法充分发挥热处理的效 果。 如果加速冷却温度低于 350°C , 则已进入贝氏体转变区， 不利于获得稳 定的珠光体、 铁素体组织， 增加异常组织产生的倾向性。
在本发明中只对钢轨头部加速冷却而轨腰和轨底部位以自然空冷至室温 的原因如下： 钢轨轨腰作为头部和底部的连接体， 间接承受来自列车的重量， 需要一定刚度， 同时还承受列车转向产生的法向力； 轨底直接作用于轨枕， 决定列车运行轨迹， 并将载荷最终传递至道床。 对于高速及准高速铁路， 列 车轴重 （l lt ~ 14t )低于客货混运线路或重载线路（25t ~ 40t )且线路曲线半 径大（通常 > 1000m ), 轨腰和轨底受垂直力和法向力有限。 此外， 加速冷却 与空冷相比， 对韧塑性指标影响有限， 对钢轨使用的安全性无显著影响。
采用本发明的制造钢轨的方法， 可以得到轨头部位为细珠光体 + ( 15%~50% ) 细铁素体混合组织的钢轨， 该钢轨强度达到现有高速或准高速 铁路用钢轨的同等强度级别的同时显著提高了钢轨的韧塑性和屈服强度， 在 提高钢轨表层裂纹萌生及扩展能量的同时提高了钢轨抵抗沖击载荷的能力， 最终改善钢轨的滚动接触疲劳性能， 保障铁路运输安全。 同时， 在生产过程 中无需对现有设备改造， 生产工艺筒单， 操作筒便、 灵活。
下面， 将结合具体的实施例来更详细地描述本发明。 这些示例只是出于 举例说明的目的， 而不意图限制本发明的范围。
示例 1
采用转炉冶炼组成如下面的表 2中所列的钢， 然后进行 LF炉精炼、 真 空除气、 方坯连铸、 钢坯加热炉加热、 钢轨轧制， 终轧温度为 903 °C , 放置 40s后， 轨头顶面温度降至 800°C开始喷吹压缩空气， 以 3.1 °C/s的冷却速率 均匀冷却钢轨头部， 喷吹完毕后钢轨轨头顶面温度为 520 °C , 轨腰及轨底温 度大于 600°C , 然后将钢轨置于空气中自然冷却至室温， 得到样品 1。
示例 2
除了轧后控制冷却的步骤之外， 采用与示例 1的方法相同的方法制造钢 轨。 具体地讲， 在该示例中， 终轧温度为 910°C , 放置 45s后， 轨头顶面温度 降至 780°C开始喷吹压缩空气和油气混合物， 以 2.9°C/s的冷却速率均匀冷却 钢轨头部， 喷吹完毕后钢轨轨头顶面温度为 514°C , 轨腰及轨底温度大于 600 °C , 然后将钢轨置于空气中自然冷却至室温， 得到样品 2。
示例 3
除了轧后控制冷却的步骤之外， 采用与示例 1的方法相同的方法制造钢 轨。 具体地讲， 在该示例中， 终轧温度为 900 °C , 放置 42s后， 轨头顶面温度 降至 770 °C开始喷吹油气混合物， 以 2.7°C/s的冷却速率均匀冷却钢轨头部， 喷吹完毕后钢轨轨头顶面温度为 530°C , 轨腰及轨底温度大于 600 °C , 然后将 钢轨置于空气中自然冷却至室温， 得到样品 3。
示例 4
除了轧后控制冷却的步骤之外， 采用与示例 1的方法相同的方法制造钢 轨。 具体地讲， 在该示例中， 终轧温度为 890°C, 放置 35s后， 轨头顶面温度 降至 790°C开始喷吹水汽混合物和油气混合物， 以 3.0°C/s的冷却速率均匀冷 却钢轨头部， 喷吹完毕后钢轨轨头顶面温度为 495°C, 轨腰及轨底温度大于 550 °C, 然后将钢轨置于空气中自然冷却至室温， 得到样品 4。
示例 5
除了轧后控制冷却的步骤之外， 采用与示例 1的方法相同的方法制造钢 轨。 具体地讲， 在该示例中， 终轧温度为 915°C, 放置 50s后， 轨头顶面温度 降至 780°C开始喷吹压缩空气， 以 2.8°C/s的冷却速率均匀冷却钢轨头部， 喷 吹完毕后钢轨轨头顶面温度为 528°C, 轨腰及轨底温度大于 600 °C, 然后将钢 轨置于空气中自然冷却至室温， 得到样品 5。
示例 6
除了轧后控制冷却的步骤之外， 采用与示例 1的方法相同的方法制造钢 轨。 具体地讲， 在该示例中， 终轧温度为 922°C, 放置 53s后， 轨头顶面温度 降至 795°C开始喷吹压缩空气， 以 2.1°C/s的冷却速率均匀冷却钢轨头部， 喷 吹完毕后钢轨轨头顶面温度为 519°C, 轨腰及轨底温度大于 600 °C, 然后将钢 轨置于空气中自然冷却至室温， 得到样品 6。
示例 7
除了轧后控制冷却的步骤之外， 采用与示例 1的方法相同的方法制造钢 轨。 具体地讲， 在该示例中， 终轧温度为 918°C, 放置 49s后， 轨头顶面温度 降至 800°C开始喷吹压缩空气， 以 2.2°C/s的冷却速率均匀冷却钢轨头部， 喷 吹完毕后钢轨轨头顶面温度为 531 °C, 轨腰及轨底温度大于 600 °C, 然后将钢 轨置于空气中自然冷却至室温， 得到样品 7。
示例 8
除了轧后控制冷却的步骤之外， 采用与示例 1的方法相同的方法制造钢 轨。 具体地讲， 在该示例中， 终轧温度为 907°C, 放置 48s后， 轨头顶面温度 降至 785°C开始喷吹压缩空气与水汽混合物， 以 2.3°C/s的冷却速率均匀冷却 钢轨头部， 喷吹完毕后钢轨轨头顶面温度为 526°C, 轨腰及轨底温度大于 600 °C, 然后将钢轨置于空气中自然冷却至室温， 得到样品 8。
示例 9
除了轧后控制冷却的步骤之外， 采用与示例 1的方法相同的方法制造钢 轨。 具体地讲， 在该示例中， 终轧温度为 895°C, 首先空冷至室温， 然后采 用工频感应加热装置以 5 °C/s的速率将钢轨头部重新加热至 900°C , 当钢轨头 部自然空冷至 760°C时， 喷吹水汽混合物和压缩空气， 以 2.2°C/s的冷却速率 均匀冷却钢轨头部， 喷吹完毕后钢轨轨头顶面温度为 510°C , 轨腰及轨底温 度大于 600°C , 然后将钢轨置于空气中自然冷却至室温， 得到样品 9。
对比例 1
除了轧后控制冷却的步骤之外， 采用与示例 1的方法相同的方法制造钢 轨。 得到所需断面钢轨后将其直接置于空气中冷却至室温， 得到现有高速或 准高速铁路用钢轨， 即对比例 1。
本发明的钢轨与对比例的钢轨的化学组成
Figure imgf000014_0001
实验示例 1
下面的表 3中示出了根据本发明的钢轨和现有技术的钢轨的力学性能。 表 3 本发明的钢轨和对比例的钢轨的力学性能
Figure imgf000015_0001
由上面的表 3可以看出， 根据本发明的示例 1与示例 3的钢轨与对比例
1 的钢轨的强度处于同一级别， 但延伸率提高约 50%。 根据本发明的示例 2 与示例 8钢轨的抗拉强度（Rm )略低于对比例 1的钢轨， 但屈服强度（Rel ) 较高， 同等条件下将有效阻止钢轨使用中表层疲劳裂纹的萌生； 同时， 目前 高速铁路钢轨在使用中由于轮轨接触应力低， 磨损轻微， 能够满足磨耗要求。 此外， 根据本发明的示例 2的钢轨断后延伸率高出对比例 1的钢轨约 75%, 使用安全性得以提高。 相对于对比例 1 , 本发明中示例 4、 示例 6、 示例 7与 示例 8的强度、 硬度提高的同时塑性也明显改善， 综合性能得以提升。 对于 采用二次加热的示例 9 , 由于铁素体晶粒得到细化， 性能同样满足高速或准 高速铁路用钢轨要求。
图 2是根据本发明的示例 1的钢轨的轨头组织的金相图。 图 3是根据对 比例 1的钢轨的轨头组织的金相图。 由图 2和图 3可以看出， 与根据对比例 1 的钢轨相比， 根据本发明的的方法制得的钢轨具有是珠光体和铁素体混合 均勾排列的组织， 因此， 在本发明的钢轨中， 可以通过珠光体中的渗碳体提 高钢轨的磨损性能， 同时可以通过已强化的铁素体提高钢轨的韧性和疲劳性 能， 所以， 对于高速和准高速铁路用钢轨而言， 根据本发明的钢轨具有比现 有技术的钢轨要好的耐磨损性和抗疲劳接触性。 实验示例 2
下面的表 4中出了根据本发明的钢轨和现有技术的钢轨的在不同温度下 的沖击功 （Aku )。
表 4 本发明和对比例的钢轨在不同温度下的沖击功
Figure imgf000016_0001
由上面的表 4可以看出， 与现有技术制造的钢轨相比， 根据本发明的方 法制造的钢轨在常温和低温下的沖击韧性明显提高， 示例 2与示例 8由于采 用低碳含量及微合金化处理， 韧性提高将近一倍。 对于碳含量较高且无合金 化的示例 4和示例 6, 沖击韧性也提高了 25%。 由此可见， 采用降低碳含量 并配合轧后控制冷却方式对提高钢轨的韧性较为有利。 因此， 根据本发明的 方法制造的钢轨将为寒冷地区高速铁路因不平顺或其它原因导致轮轨沖击时 列车的使用安全性提供更有效的保障。
实马全示例 3
下面的表 5中示出了根据本发明的钢轨和现有技术的钢轨的磨损性能。 通过滚滑磨损的方式对比钢轨在相同条件下的磨损性能， 对磨样为对比 例 1的钢轨。 具体试验条件及参数如下：
试马全机名称： MM-200型；
试样尺寸： 厚度 10mm, 内径 10mm, 夕卜径 36mm;
试验载荷： 980N;
滑差： 10%; 试验环境： 常温、 风冷；
转速： 200r/min;
对磨总转数： 20万；
试验数量： 3对（取其算术平均值表示结果）
磨损试验结果见表 5 , 磨损示意图见图 1。
表 5 本发明部分实施例和对比例的钢轨的磨损性能
Figure imgf000017_0001
由上面的表 5可以看出， 本发明中的示例 8钢轨的磨损性能略低于对比 例 1 的钢轨。 由于高速列车轴重较轻， 钢轨磨耗速率较低， 有利于将钢轨轨 头表面萌生的疲劳裂纹通过磨耗去除， 对改善滚动接触疲劳性能极为有利。 对于示例 5与示例 6, 其磨损性能与对比例 1相当， 同样适用于高速或准高 速铁路应用。
实马全示例 4
下面的表 6中示出了根据本发明的钢轨和现有技术的钢轨的疲劳裂纹扩 展速率。采用型号为 ISTRON 8801的裂纹扩展速率试验机，研究裂纹长度（或 深度） 沿垂直于应力方向扩展速率的规律。 裂纹扩展速率越慢， 相同条件下 越有利于阻止裂纹扩展。 本发明和对比例的钢轨的裂纹扩展速率
Figure imgf000018_0001
由上面的表 6可以看出， 通过与对比例 1的钢轨相比， 根据本发明的方 法制造的钢轨的裂纹扩展速率较低，从而相同条件下越有利于阻止裂纹扩展。 下面的表 7 中示出了根据本发明的钢轨和现有技术的钢轨在低温 （-20 °C )和常温（20°C ) 时的断裂韧性（KIC )。 采用型号为 ISTRON 8801的断裂 韧性试验机测量了钢轨的断裂韧性。 断裂韧性 KIC是衡量材料抵抗裂纹扩展 能力的力学性能指标。 KIC值越高， 表明钢轨抵抗裂纹扩展的能力越强， 越有 利于行车安全。
表 7 本发明和对比例钢轨的断裂韧性
Figure imgf000018_0002
由上面的表 7可以看出， 在相同条件下， 根据本发明的方法制造的钢轨 的断裂韧性无论常温或低温均高于对比例 1 的钢轨。 通过比较发现， 随着钢 中碳含量的降低， 断裂韧性显著提高。 因此， 降低钢轨中的碳含量有利获得 更高的断裂韧性。
实验示例 6
下面的表 8中示出了根据本发明的钢轨和对比例 1的钢轨的轴向疲劳性 能对比。采用型号为 PQ-6弯曲疲劳试验机采用应力幅升降法测量了钢轨的轴 向疲劳极限， 试验条件： 在总应变幅为 1350με时， 每组试样的疲劳寿命均大 于 5 x 106的要求。 表 8 本发明和对比例的钢轨的轴向疲劳极限
Figure imgf000019_0001
由上面的表 8可以看出， 根据本发明的方法制造的钢轨和根据现有技术 制造的钢轨均满足标准要求， 并且根据本发明的钢轨的疲劳极限要高于根据 现有技术制造的钢轨的疲劳极限。
在现有的高速和准高速铁路用钢轨中， 钢轨的头部为大量珠光体和小于
5%的铁素体的组织， 而根据本发明提供的用于高速和准高速铁路的钢轨， 通 过钢轨中的降低碳含量， 配合轧后控制冷却的方式， 可以使钢轨的头部在室 温下为珠光体 + 15%~50%铁素体的均匀混合组织。 高速铁路用钢轨中铁素体 在组织中比例提高至 15% ~ 50%的优点在于： （1 )现有高速铁路钢轨中组织 以珠光体为主， 包含少于 5%的铁素体组织， 经过一定时间的运营后发现， 高 速列车与轨道间的磨损几乎不发生， 致使以良好磨损性能著称的珠光体组织 难以发挥作用， 相反， 由于无磨损， 产生于轨头表层轮轨接触面的微裂纹将 难以去除， 经车轮的往复作用， 将使裂纹向钢轨内部扩展， 最终形成裂纹、 掉块等接触疲劳伤损， 继续发展将有断轨的危险。 当铁素体组织的比例提高 后， 由于铁素体属于钢中的软质相， 其磨损性能不如珠光体， 将使钢轨在使 用中产生一定磨损， 以确保钢轨表层的裂纹能够被及时磨去。 然而， 如果单 纯降级钢中的 C含量来获得一定比例的铁素体， 将会由于磨损过快同样影响 钢轨的使用寿命。 只有通过强化铁素体基体来达到目的， 而提高基体强度的 方法无外乎三种， 即合金元素固溶、 析出强化和热处理细晶强化， 而单纯依 靠热处理工艺，将在提高铁素体基体强度的同时渗碳体的强化作用同比增强， 会使强度过高， 因此， 添加部分微合金化元素以强化铁素体基体为主， 同时 还能略微提高韧塑性。 此外， 如果铁素体比例超过 50%,将使得珠光体比例降 低， 无法保证一定的磨损性能， 同样无法应用于高速线路。 （2 )钢轨中铁素 体比例的提高意味着韧塑形的大幅提升， 更高的延伸率与沖击韧性将使钢轨 在受到相同沖击载荷的条件下断轨的几率大幅降低， 对确保行车安全极为有 利。
综上所述， 通过对本发明的钢轨与现有高速铁路用钢轨的金相组织、 常 规力学性能及特殊力学性能在不同条件下的对比可以看出， 在本发明中， 通 过降低钢轨中的碳元素含量， 配合轧后控制冷却的方式， 保持了现有高速铁 路钢轨的强度、 硬度级别， 与此同时， 钢轨的韧塑性和屈服强度均显著提高， 即提高形成于钢轨表层的疲劳微裂纹萌生及扩展所需能量值， 从而在相同条 件下可以改善钢轨的滚动接触疲劳性能， 最终提高钢轨的使用寿命和运输安 全性。
本发明不限于上述实施例， 在不脱离本发明范围的情况下， 可以进行各 种变形和爹改。

Claims

1、 一种用于高速和准高速铁路的钢轨，所述钢轨包含的化学成分以重量 计为： 0.40% - 0.64% C, 0.10% ~ 1.00% Si, 0.30% ~ 1.50% Mn, 少于等于 0.025% P,少于等于 0.025% S,少于等于 0.005% A1,大于 0且少于等于 0.05% 的稀土元素， 总量大于 0且小于等于 0.20%的 V、 Cr和 Ti中的至少一种， 以 及余量的 Fe和不可避免的杂质，
其中， 所述钢轨的头部在室温下为珠光体和 15% ~ 50%铁素体的均匀混 合组织。
2、 如权利要求 1所述的钢轨， 其特征在于， 所述钢轨包含的化学成分以 重量计为： 0.45% ~ 0.60% C, 0.15% ~ 0.50% Si, 0.50% ~ 1.20% Mn, 少于等 于 0.025% P, 少于等于 0.025% S, 少于等于 0.005% A1, 大于 0且少于等于 0.05%的稀土元素， 总量大于 0且小于等于 0.20%的 V、 Cr和 Ti中的至少一 种， 以及余量的 Fe和不可避免的杂质。
3、 如权利要求 1或 2所述的钢轨， 其特征在于， 所述钢轨包含 0.01% ~
0.15% V、 0.02% ~ 0.20% Cr和 0.01% ~ 0.05% Ti中的至少一种。
4、如权利要求 3所述的钢轨，其特征在于，所述钢轨包含 0.02% ~ 0.08% V、 0.10% ~ 0.15% Cr和 0.01 % ~ 0.05% Ti中的至少一种。
5、 如权利要求 1所述的钢轨， 其特征在于， 所述钢轨的头部在室温下为 珠光体和 15% ~ 30%铁素体的均匀混合组织。
6、一种制造如权利要求 1所述的钢轨的方法，所述方法包括钢水冶炼及 浇铸、 轧制钢轨、 轧后控制冷却和空冷放置， 其特征在于， 所述轧后控制冷 却的步骤包括： 将钢轨直立于辊道， 通过辊道转运带动钢轨进入热处理机组， 通过热处理机组向钢轨喷吹冷却介质， 从而以 l °C/s至 4°C/s的冷却速率均匀 冷却钢轨头部， 至轨头顶面温度降至 350°C ~ 550 °C时停止冷却。
7、 如权利要求 6所述的方法， 其特征在于， 所述方法还包括： 在轧制钢 轨的步骤中进行终轧后， 先将钢轨冷却至低于奥氏体相区的温度， 然后以 1 °C/s ~ 20°C/s的速率将钢轨加热至奥氏体相区的温度区间，然后再执行所述轧 后控制冷却的步骤。
8、 如权利要求 6所述的方法， 其特征在于， 所述冷却介质为压缩空气、 水汽混合物、 油气混合物中的至少一种。
9、 如权利要求 6所述的方法， 其特征在于， 最终所得的钢轨的头部在室 温下为珠光体和 15% ~ 30%铁素体的均匀混合组织。
10、 如权利要求 6所述的方法， 其特征在于， 所述钢水冶炼及浇铸的步 骤包括： 采用转炉、 电炉或平炉冶炼钢水， 真空处理， 在将钢水浇铸为方形 坯或板坯后冷却或直接送至加热炉升温。
11、 如权利要求 6所述的方法， 其特征在于， 所述轧制钢轨的步骤包括： 将升温至一定温度并保温一定时间的钢坯或连铸坯送入轧机， 以轧制为所需 断面的钢轨。
12、如权利要求 11所述的方法，其特征在于，在所述轧制钢轨的步骤中， 将钢轨升温至 1200 °C ~ 1300 °C , 并保温 0.5h ~ 2h。
13、 如权利要求 6所述的方法， 其特征在于， 所述方法还包括： 在轧后 控制冷却之后， 将冷却后的钢轨置于空气中自然冷却至室温。
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