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WO2024202408A1 - Rail et son procédé de fabrication - Google Patents

Rail et son procédé de fabrication Download PDF

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Publication number
WO2024202408A1
WO2024202408A1 PCT/JP2024/001017 JP2024001017W WO2024202408A1 WO 2024202408 A1 WO2024202408 A1 WO 2024202408A1 JP 2024001017 W JP2024001017 W JP 2024001017W WO 2024202408 A1 WO2024202408 A1 WO 2024202408A1
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WIPO (PCT)
Prior art keywords
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rail
center
cooling
rail bottom
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PCT/JP2024/001017
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English (en)
Japanese (ja)
Inventor
稔 本庄
佳祐 安藤
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JFE Steel Corp
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JFE Steel Corp
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Priority to CN202480020000.XA priority Critical patent/CN121079446A/zh
Priority to EP24778554.6A priority patent/EP4667604A1/fr
Priority to AU2024245086A priority patent/AU2024245086A1/en
Priority to JP2024527864A priority patent/JPWO2024202408A1/ja
Publication of WO2024202408A1 publication Critical patent/WO2024202408A1/fr
Anticipated expiration legal-status Critical
Pending legal-status Critical Current

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    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • 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
    • 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

  • the present invention relates to rails and their manufacturing methods.
  • rail transport is highly efficient and environmentally friendly, so there has been active effort to increase transport capacity by increasing operating speeds, increasing freight car loads, and congesting timetables.
  • the number of wheels passing over the rails is also increasing, and repeated tensile and compressive stresses are being applied to the rails, causing them to break from the bottom, and the frequency of rail replacement is gradually increasing, becoming a problem. For this reason, there is a growing demand for rail steel that is less susceptible to breakage from the bottom.
  • Patent Document 1 discloses a steel rail with a pearlite structure containing 0.65 to 1.40% C, in which at least a portion of the area extending from the bottom surface to a depth of 10 mm contains 200 or more pearlite blocks with grain sizes of 1 to 15 ⁇ m per 0.2 mm2 of an examination area.
  • Patent Document 2 discloses a rail in which the rail head is accelerated from the austenite region after rolling, while the rail bottom is accelerated to between 800 and 450°C at a cooling rate of 1 to 5°C/sec, resulting in an average pearlite hardness at the rail bottom of HB 320 or more.
  • Patent Document 3 discloses a rail that contains, by mass, 0.65-1.20% C, 0.05-2.00% Si, 0.05-2.00% Mn, with the remainder being Fe and unavoidable impurities, with 97% or more of the head and bottom surfaces being pearlite structures, with the surface hardness of the pearlite structure being in the range of Hv320-500, the maximum surface roughness being 180 ⁇ m or less, and the ratio of the surface hardness to the maximum surface roughness being 3.5 or more.
  • JP 2006-57127 A Japanese Patent Application Laid-Open No. 1-139724 International Publication No. 2011/021582
  • Patent Documents 1 to 3 mentioned above can control the structure of the rail bottom and increase the strength of the rail bottom, but this alone is not enough to prevent cracks from occurring at the rail bottom or to reduce the rate at which cracks grow due to tensile stress, and there is a risk of breakage from the rail bottom.
  • the present invention has been made to solve this problem, and provides a rail that can prevent breakage from the bottom of the rail by controlling the component composition of the rail and by controlling the 0.2% proof stress at the center of the rail bottom, the longitudinal residual stress at the center of the rail bottom, and the crack propagation speed within predetermined ranges, together with a manufacturing method for the rail.
  • the gist and configuration of the present invention are as follows. [1] In mass%, C: 0.60% or more but less than 0.90% Si: 0.10% or more and 1.20% or less, Mn: 0.10% or more and 1.50% or less, Cr: 0.05% or more and 2.00% or less, Al: 0.0002% or more and 0.005% or less, P: 0% or more and 0.035% or less, S: 0% or more and 0.020% or less, V: 0% or more and 0.30% or less, Cu: 0% or more and 1.0% or less, Ni: 0% or more and 1.0% or less, Nb: 0% or more and 0.05% or less, Mo: 0% or more and 0.5% or less, B: 0% or more and 0.0050% or less, Ti: 0% or more and 0.01% or less, Mg: 0% or more and 0.01% or less, Ca: 0% or more and 0.02% or less, W: 0% or more and 0.10% or less, Sb: 0% or more and
  • the longitudinal residual stress at the center of the rail bottom is less than 200 MPa, And the fatigue crack propagation rate when the stress intensity factor range ⁇ K at the center of the rail bottom is 15MPa m 1/2 is 5.0 ⁇ 10 ⁇ 8 m/cycle or less. rail.
  • the components are, in mass %, V: 0.001% or more and 0.30% or less, Cu: 0.001% or more and 1.0% or less, Ni: 0.001% or more and 1.0% or less, Nb: 0.001% or more and 0.05% or less, Mo: 0.001% or more and 0.5% or less, B: 0.0001% or more and 0.0050% or less, Ti: 0.001% or more and 0.01% or less, Mg: 0.0005% or more and 0.01% or less, Ca: 0.0005% or more and 0.02% or less, W: 0.001% or more and 0.10% or less, Sb: 0.001% or more and 0.05% or less, Sn: 0.001% or more and 0.05% or less, and Co: Contains one or more selected from the group consisting of 0.001% to 1.0% [1] Rail.
  • a method for manufacturing a rail according to [1] or [2] After hot rolling a steel slab having the chemical composition described in [1] or [2], the average cooling rate during cooling of the center of the bottom of the rail from the cooling start point T1 to the cooling end point T2 is set to 0.4°C/sec or more and 6.0°C/sec or less, the average cooling rates of both rail bottom toes during cooling of the rail bottom center from the cooling start point T1 to the cooling stop point T2 are equal to or less than the average cooling rate of the rail bottom center,
  • T1 is a temperature in the range of 650°C to 800°C
  • T2 is a temperature in the range of 400°C to 600°C.
  • the 0.2% proof stress at the center of the rail bottom, the longitudinal residual stress at the center of the rail bottom, and the fatigue crack propagation rate when the stress intensity factor range ⁇ K at the center of the rail bottom is 15 MPa m 1/2 may be values measured by the methods described in the Examples.
  • the present invention can provide a rail that can suppress the occurrence of cracks at the bottom of the rail, and, if a crack exists at the bottom of the rail, can reduce the speed of crack propagation when a mechanical load is applied, thereby suppressing breakage from the bottom of the rail, together with a manufacturing method thereof.
  • FIG. FIG. 2 is a diagram showing the cross-sectional area and thickness of the bottom of the rail.
  • FIG. 2 is a schematic diagram of an example of accelerated cooling in a manufacturing method for a rail.
  • FIG. 13 is a schematic diagram of another example of accelerated cooling in a rail manufacturing method.
  • FIG. 2 is a diagram showing the positions at which tensile test specimens were taken.
  • FIG. 1 is a diagram showing dimensions of a tensile test specimen.
  • FIG. 2 is a diagram showing the positions at which fatigue crack propagation test specimens were taken.
  • FIG. 2 is a diagram showing the dimensions of a fatigue crack propagation test specimen.
  • FIG. 1 is a diagram showing a method for measuring residual stress by a strain gauge cutting method.
  • ⁇ Rail parts> The designations of the various parts of a rail according to the present invention will be described with reference to the rail cross-sectional view of Figure 1.
  • reference numeral 11 denotes a head portion
  • 12 denotes a web portion
  • 13 denotes a bottom portion (foot portion).
  • W the width of the bottom surface of the rail
  • the center of the rail bottom (bottom center) is the center in the width direction of the back surface of the bottom, located 0.5 x W from each end.
  • the rail bottom foot (bottom foot) is located 0.15 x W from each end in the width direction of the back surface of the bottom.
  • C 0.60% or more and less than 0.90%
  • C is an essential element for forming cementite in pearlite structure and ensuring 0.2% proof stress, and the 0.2% proof stress improves with increasing content. If the C content is less than 0.60%, it is difficult to obtain excellent 0.2% proof stress and fracture toughness values. Therefore, the C content is set to 0.60% or more, preferably 0.63% or more, and more preferably 0.70% or more. Furthermore, if it is 0.90% or more, proeutectoid cementite is generated at the austenite grain boundary during transformation after hot rolling, and cracks tend to propagate along the generated proeutectoid cementite, so that the speed of crack propagation increases significantly. Therefore, the C content is set to less than 0.90%, preferably 0.89% or less, and more preferably 0.85% or less.
  • Si 0.10% or more and 1.20% or less
  • Si is a deoxidizing agent and a strengthening element of pearlite structure, and 0.10% or more is necessary to obtain its effect sufficiently.
  • the Si content is preferably 0.15% or more, more preferably 0.20% or more. If the Si content exceeds 1.20%, martensite structure is likely to be generated, and the 0.2% proof stress increases and the oxide of Si also increases, so the speed of crack propagation increases significantly. Therefore, the Si content is 1.20% or less, preferably 1.10% or less, and more preferably 1.00% or less.
  • Mn 0.10% or more and 1.50% or less
  • Mn is a strengthening element for pearlite structure, and 0.10% or more is necessary to obtain its effect sufficiently.
  • the Mn content is preferably 0.20% or more, more preferably 0.30% or more. If the Mn content exceeds 1.50%, the high hardenability of Mn makes it easy for martensite structure to occur, and the 0.2% proof stress increases and the speed of crack propagation increases significantly. Therefore, the Mn content is 1.50% or less, preferably 1.40% or less, and more preferably 1.30% or less.
  • the P content is set to 0.035% or less, and preferably 0.020% or less.
  • the lower limit of the P content there is no particular restriction on the lower limit of the P content, and it may be 0%, but to set it to less than 0.001%, an increase in steelmaking costs is unavoidable, so the P content may be set to 0.001% or more.
  • S 0% or more and 0.020% or less S is an element that exists in steel mainly in the form of A-type inclusions, but if the S content exceeds 0.020%, the amount of these inclusions increases significantly, and at the same time, coarse inclusions are generated, which deteriorates the cleanliness of the rail steel and significantly increases the crack propagation speed of the rail. Therefore, the S content is set to 0.020% or less, preferably 0.015% or less, and more preferably 0.010% or less.
  • the lower limit of the S content is not particularly limited and may be 0%, but if it is less than 0.0005%, the steelmaking cost will be unavoidably increased, so it may be set to 0.0005% or more.
  • Cr 0.05% or more and 2.00% or less Cr is an element that increases the pearlite equilibrium transformation temperature and contributes to refinement of lamellar spacing. At the same time, by including Cr, it is possible to further increase the 0.2% proof stress by solid solution strengthening. If the Cr content is less than 0.05%, sufficient 0.2% proof stress cannot be obtained, so the Cr content is set to 0.05% or more, preferably 0.10% or more, and more preferably 0.15% or more. If the Cr content exceeds 2.00%, the hardenability increases and martensite structure is easily formed, which increases the 0.2% proof stress and significantly increases the speed of crack propagation. Therefore, the Cr content is set to 2.00% or less, preferably 1.60% or less, and more preferably 1.40% or less.
  • Al 0.0002% to 0.005%
  • Al is a deoxidizing agent and strengthens the pearlite structure, and 0.0002% or more is necessary to fully obtain its effects. If the Al content exceeds 0.005%, the 0.2% proof stress increases and the amount of Al oxide also increases, significantly increasing the speed of crack propagation. Therefore, the Al content is set to 0.0002% to 0.005%.
  • the component composition of the rail of the present invention may contain, in addition to the above basic components, one or more components selected from the following: V: 0% to 0.30%, Cu: 0% to 1.0%, Ni: 0% to 1.0%, Nb: 0% to 0.05%, Mo: 0% to 0.5%, B: 0% to 0.0050%, Ti: 0% to 0.01%, Mg: 0% or more and 0.01% or less, Ca: 0% or more and 0.02% or less, W: 0% or more and 0.10% or less, Sb: 0% or more and 0.05% or less, Sn: 0% or more and 0.05% or less, and Co: 0% or more and 1.0% or less.
  • V 0% to 0.30%
  • Cu 0% to 1.0%
  • Ni 0% to 1.0%
  • Nb 0% to 0.05%
  • Mo 0% to 0.5%
  • B 0% to 0.0050%
  • Ti 0% to 0.01%
  • Mg 0% or more and 0.01% or less
  • Ca 0%
  • V 0.001% or more and 0.30% or less
  • V is an element that forms carbonitrides in steel, disperses and precipitates in the matrix, and improves the fracture toughness value through the improvement of the 0.2% proof stress. Since this effect is exhibited when the V content is 0.001% or more, when V is contained, the V content is preferably 0.001% or more, and more preferably 0.005% or more. On the other hand, when the V content exceeds 0.30%, the 0.2% proof stress increases and the fracture toughness value decreases. In addition, the alloy cost increases, and the cost of the rail steel increases. Therefore, when V is contained, the V content is preferably 0.30% or less, and more preferably 0.29% or less.
  • Cu 0.001% or more and 1.0% or less Like Cr, Cu is an element that can further increase strength through solid solution strengthening. If the Cu content is less than 0.001%, the effect is small, while if it exceeds 1.0%, Cu cracking is likely to occur. Therefore, if Cu is contained, the Cu content is preferably 0.001% or more and 1.0% or less.
  • Ni 0.001% to 1.0%
  • Ni is an element that can increase strength without deteriorating ductility.
  • Nb 0.001% or more and 0.05% or less
  • Nb is an element that combines with C in steel to precipitate as carbides during and after rolling, improving the 0.2% yield strength and thereby improving the fracture toughness value, but if the Nb content is less than 0.001%, the effect is small, and even if it is contained in excess of 0.05%, an effect commensurate with the content cannot be obtained. Therefore, when Nb is contained, the Nb content is preferably 0.001% or more and 0.05% or less.
  • Mo 0.001% to 0.5%
  • Mo is an element that can further increase strength through solid solution strengthening, but if it is less than 0.001%, the effect is small, while if it exceeds 0.5%, the hardenability increases, martensite is formed, and the speed of crack propagation tends to increase significantly. Therefore, if Mo is contained, the Mo content is preferably 0.001% to 0.5%.
  • B 0.0001% or more and 0.0050% or less B is an element that precipitates as a nitride and can further increase the strength of a rail through precipitation strengthening. If the B content is less than 0.0001%, the effect is small, while if it exceeds 0.0050%, the alloy cost increases. Therefore, when B is contained, the B content is preferably 0.0001% or more and 0.0050% or less.
  • Ti 0.001% or more and 0.01% or less Ti is an element that precipitates as carbide, nitride, or carbonitride, and can further increase the strength of rails through precipitation strengthening. If the Ti content is less than 0.001%, the effect is small, while if it exceeds 0.01%, it will lead to an increase in alloy costs. Therefore, when Ti is contained, the Ti content is preferably 0.001% or more and 0.01% or less.
  • Mg 0.0005% or more and 0.01% or less Mg is an element that can combine with oxygen to precipitate MgO and further increase strength. If the Mg content is less than 0.0005%, the effect is small, while if it exceeds 0.01%, the increase in MgO tends to significantly increase the speed of crack propagation. Therefore, when Mg is contained, the Mg content is preferably 0.0005% or more and 0.01% or less.
  • Ca 0.0005% or more and 0.02% or less
  • Ca is an element that can combine with oxygen to precipitate CaO and further increase strength. If the Ca content is less than 0.0005%, the effect is small, while if it exceeds 0.02%, the increase in CaO tends to significantly increase the speed of crack propagation. Therefore, if Ca is contained, the Ca content is preferably 0.0005% or more and 0.02% or less.
  • W 0.001% to 0.10%
  • W is an element that precipitates as carbide and can further increase the strength of rails through precipitation strengthening. If the W content is less than 0.001%, the effect is small, while if it exceeds 0.10%, it leads to an increase in alloy costs. Therefore, if W is contained, the W content is preferably 0.001% to 0.10%.
  • Sb 0.001% or more and 0.05% or less Sb has a remarkable effect of preventing decarburization of steel during reheating of rail steel pieces in a heating furnace before hot rolling. If the Sb content exceeds 0.05%, it has a negative effect on the ductility and toughness of the steel. Therefore, if Sb is contained, the Sb content is preferably 0.05% or less. On the other hand, if Sb is contained, the Sb content is preferably 0.001% or more in order to exert the effect of reducing the decarburized layer.
  • Sn 0.001% or more and 0.05% or less
  • Sn is an element that has a remarkable effect of preventing decarburization of steel during reheating of rail steel pieces in a heating furnace before hot rolling. If the Sn content exceeds 0.05%, it has a negative effect on the ductility and toughness of the steel, so if Sn is contained, the Sn content is preferably 0.05% or less. On the other hand, if Sn is contained, the Sn content is preferably 0.001% or more in order to exert the effect of reducing the decarburized layer.
  • Co 0.001% or more and 1.0% or less
  • Co is an element that can increase the pearlite equilibrium transformation temperature and refine the lamellar spacing, thereby further increasing the strength of the steel. Co also has the effect of suppressing the precipitation of proeutectoid cementite. If the Co content exceeds 1.0%, martensite is formed in the steel, and as a result, ductility decreases. From these points of view, when the composition contains Co, the Co content is preferably 1.0% or less.
  • the lower limit of the Co content is not particularly limited, but it is preferably 0.001% or more in order to increase the strength. A more preferable range of the Co content is 0.001 to 0.5%.
  • the balance of the above essential and optional components consists of Fe and unavoidable impurities.
  • unavoidable impurities include N and O, with N being permitted up to 0.008% and O being permitted up to 0.004%.
  • impurities other than N and O may be unavoidably mixed into the steel depending on the conditions of the raw materials, materials, manufacturing equipment, etc. Examples of raw materials include iron ore, reduced iron, and scrap. The above impurities are permitted to be mixed in as long as they do not impede the objectives of the present invention.
  • impurities other than N and O include Pb, Zr, Bi, Zn, Se, As, Te, Tl, Cd, Hf, Ag, Hg, Ga, Ge, REM, etc.
  • the microstructure of the rail of the present invention is pearlite at an area ratio of 95% or more at the rail bottom.
  • the remaining structure other than pearlite is permissible as long as the total area ratio is 5% or less since it does not significantly affect the characteristics of the present invention.
  • Examples of the remaining structure include ferrite and bainite.
  • the microstructure can be identified by the method described in the Examples.
  • the 0.2% yield strength at the center of the rail bottom is more than 500 MPa and less than 1100 MPa. If the 0.2% yield strength is 500 MPa or less, resistance to cracking when a wheel passes over is weak, and cracks are more likely to occur at the rail bottom due to stress generated within the rail. On the other hand, if the 0.2% yield strength is 1100 MPa or more, the strength of the rail bottom becomes high, which in turn increases sensitivity to crack growth after crack initiation, making the rail more likely to break. For this reason, the 0.2% yield strength at the center of the rail bottom is more than 500 MPa, preferably 550 MPa or more. Moreover, the 0.2% yield strength at the center of the rail bottom is less than 1100 MPa, preferably 1000 MPa or less.
  • ⁇ Fatigue crack propagation rate is 5.0 ⁇ 10-8 m/cycle or less when the stress intensity factor range ⁇ K at the center of the rail bottom is 15MPa m1 /2 >
  • the fatigue crack propagation rate at the center of the rail bottom is 5.0 ⁇ 10 ⁇ 8 m/cycle or less when the stress intensity factor range ⁇ K is 15 MPa m 1/2 . If the fatigue crack propagation rate at the stress intensity factor range ⁇ K of 15 MPa m 1/2 (hereinafter also referred to as fatigue crack propagation rate) exceeds 5.0 ⁇ 10 ⁇ 8 m/cycle, when a crack is present at the rail bottom, the crack will grow too fast, increasing the possibility of the rail breaking before regular inspection or replacement.
  • the fatigue crack propagation rate at the center of the rail bottom is set to 5.0 ⁇ 10 ⁇ 8 m/cycle or less, preferably 4.8 ⁇ 10 ⁇ 8 m/cycle or less.
  • the lower limit of the fatigue crack propagation rate at the center of the rail bottom is not particularly limited, but it can be set to 1.0 ⁇ 10 ⁇ 8 m/cycle or more from the viewpoint of lamellar spacing that can be industrially refined.
  • ⁇ Longitudinal residual stress at the center of the rail bottom is less than 200 MPa>
  • the longitudinal residual stress at the center of the rail bottom is less than 200 MPa. If the residual stress at the center of the rail bottom is less than 200 MPa, it is easy to avoid a situation in which a large tensile residual stress acts on the rail bottom, accelerating the rate of fatigue crack growth and leading to rail breakage.
  • the residual stress at the center of the rail bottom is more preferably 150 MPa or less.
  • the residual stress at the center of the rail bottom is preferably -100 MPa or more.
  • the shape of the rail in the present invention is not particularly limited, and may be any shape described in JIS E 1101:2001, BS EN13674-1:2011, American Railway Engineering and Maintenance-of-Way Association (AREMA), or the like.
  • AREMA American Railway Engineering and Maintenance-of-Way Association
  • the rail of the present invention is prepared by hot rolling a steel bloom having the above-mentioned chemical composition, and then cooling the center of the rail bottom from the cooling start point T1 to the cooling stop point T2 at an average cooling rate of 0.4°C/sec to 6.0°C/sec, and the average cooling rates of both rail bottom foot tips during the cooling of the center of the rail bottom from the cooling start point T1 to the cooling stop point T2 are equal to or lower than the average cooling rate of the center of the rail bottom.
  • the cooling start point T1 is a temperature in the range of 650°C or more and 800°C or less.
  • the cooling start point T1 and the cooling stop point T2 are surface temperatures at the center of the bottom of the rail measured with a radiation thermometer, and the average cooling rate at the center of the bottom of the rail is the difference between the cooling start point T1 and the cooling stop point T2 at the center of the bottom divided by the time required for cooling.
  • the average cooling rate of the base tip of the rail bottom is calculated by dividing the difference in temperatures at the points corresponding to the cooling start point T1 and the cooling stop point T2 at the center of the rail bottom, based on the surface temperatures at the base tip of the rail bottom measured with a radiation thermometer, by the time required to cool the center of the rail bottom to the cooling start point T1 and the cooling stop point T2 .
  • the two rail bottom toes are usually cooled so that they have the same thermal history.
  • the temperatures of the rail bottom toes corresponding to the cooling start point T1 and the cooling end point T2 at the center of the rail bottom are usually the same, and the average cooling rates of the rail bottom toes are also usually the same.
  • the steel blooms used as rail materials have the above-mentioned rail composition and can be produced by any method. They can be produced by casting, particularly continuous casting. For example, steel can be smelted in a converter or electric furnace, and if necessary, secondary refining such as degassing is performed to adjust the steel composition to the above range, and the smelted steel can then be continuously cast into a cast bloom.
  • the slab can be heated to 1200°C to 1350°C in a heating furnace and then hot rolled.
  • hot rolling can be performed using a breakdown rolling mill, a rough rolling mill, and a finishing rolling mill.
  • the austenite grains that have become coarse due to heating can be refined by rolling in the recrystallization temperature range and recrystallization, or the structure after pearlite transformation can be refined by introducing strain in the non-recrystallization temperature range.
  • the rolling end temperature of the bottom (foot) part during hot rolling is 800°C or higher and 1000°C or lower.
  • the hot rolling is preferably carried out at a temperature of 1050° C. or less so that the area reduction rate of the bottom part is 11% or more, more preferably 13% or more.
  • the area reduction rate can be 20% or less, preferably 18% or less.
  • the reduction rate (thickness reduction rate) in the thickness direction of the bottom is the same as or larger than the cross-sectional area reduction rate of the pass.
  • the cross-sectional area reduction rate in the finish rolling is 11%
  • the thickness reduction rate at the center of the bottom in the finish rolling is 15% or more. This allows a large strain to be introduced into the bottom, which can further promote the refinement of the structure after pearlite transformation, and can effectively increase the fatigue strength of the back surface of the bottom.
  • the thickness reduction rate in the finish rolling is preferably 4% or more and 8% or less, and more preferably 5% or more and 7% or less.
  • finish rolling refers to one pass of final rolling performed with the final rolling groove of one final rolling mill. Finish rolling under such conditions makes it easier to manufacture rails in which the 0.2% proof stress at the bottom part is more than 500 MPa and less than 1100 MPa and the fatigue crack propagation rate at the rail bottom part is 5.0 ⁇ 10-8 m/cycle or less when the stress intensity factor range ⁇ K is 15 MPa m1 /2 . These conditions are also effective in achieving a longitudinal residual stress of less than 200 MPa at the width center of the rail bottom surface.
  • the cross-sectional area of the bottom of the rail is the area of the shaded portion marked with S in the cross-sectional view of the rail in Figure 2, and the thickness of the bottom of the rail is the height marked with H in the same figure.
  • the cooling start point T1 of the accelerated cooling is a temperature in the range of 650°C to 800°C. If the cooling start temperature is less than 650°C, the pearlite transformation temperature will be high and the 0.2% proof stress will decrease. On the other hand, if cooling is performed from above 800°C, martensite is likely to form at the bottom of the rail, and the 0.2% proof stress will increase, which will tend to accelerate the crack growth rate. For this reason, the cooling start temperature is set to 650°C to 800°C.
  • the cooling end point T2 is a temperature in the range of 400°C to 600°C. If the cooling end temperature is less than 400°C, cooling will continue even after the pearlite transformation is complete, which increases the cooling time and reduces productivity. On the other hand, if the cooling end temperature is more than 600°C, cooling will be stopped before the pearlite transformation is complete, which will result in a decrease in 0.2% yield strength. Therefore, the cooling end temperature is set to 400°C to 600°C.
  • the average cooling rate from the cooling start point T1 to the cooling end point T2 is 0.4°C/sec or more and 6.0°C/sec or less. If the average cooling rate is less than 0.4°C/sec, the 0.2% proof stress of the rail base decreases, the tensile residual stress increases, and the fatigue crack growth rate increases. On the other hand, if the average cooling rate exceeds 6.0°C/sec, the 0.2% proof stress of the rail base increases, and the fatigue crack growth rate increases. Therefore, the average cooling rate during accelerated cooling is preferably 0.4°C/sec or more and 6.0°C/sec or less, and more preferably 0.4°C/sec or more and 2.9°C/sec or less.
  • the rail bottom center is thicker than the other parts of the rail bottom, and is prone to hot spots, so that when cooling is completed and the temperature returns to normal, a large residual stress acting as tension in the longitudinal direction is relatively likely to occur in the rail bottom center, which may increase the fatigue crack propagation rate in the rail bottom.
  • it is effective to cool the rail bottom center more strongly than the foot toes, which are thinner than the other parts of the rail bottom, and to make the average cooling rate at the rail bottom center equal to or higher than the corresponding average cooling rate at each of the rail bottom toes.
  • the average cooling rate at both rail bottom toes during the period from the cooling start point T1 to the cooling stop point T2 of the rail bottom center is set to be equal to or lower than the cooling rate at the rail bottom center.
  • the average cooling rate at each of the rail bottom toes is preferably 0.4°C/s or more and 2.5°C/s or less. It is preferable that the average cooling rate at the center of the rail bottom is V1 , and the average cooling rate at the toes of each rail bottom is ( V1 - 0)°C/sec to ( V1 - 1.5)/sec.°C.
  • the accelerated cooling method is not particularly limited, and can be, for example, a cooling method using online heat treatment equipment.
  • the cooling medium is not particularly limited, and can be one or more selected from air, spray water, mist, etc., but it is preferable to use air.
  • the rail bottom center can be cooled more actively than each rail bottom foot.
  • the refrigerant can be sprayed directly onto an area that is 1/5 of the rail bottom width W (0.2 times W) by using nozzles 21 to sandwich the rail bottom center, and other parts of the bottom, such as the rail bottom foot, can be cooled by the refrigerant flowing along the bottom surface.
  • the area directly sprayed with the refrigerant is set to an area that is 1/5 of the rail bottom width W, but the area directly sprayed with the refrigerant can be changed to a range of about 0.1 to 0.5 times W by selecting the nozzle.
  • a method in which the refrigerant is sprayed from the rail body side toward the rail bottom center by using nozzles 22 is also effective.
  • the cooling of other parts of the rail is not particularly limited, and may be allowed to cool naturally or may undergo accelerated cooling.
  • the rail material may be subjected to known treatments, for example, cold roller straightening.
  • a steel slab having the chemical composition shown in Table 1 was heated to 1250°C and then hot rolled into a rail shape at the rolling finish temperature shown in Table 2.
  • the rail shape was that of a 60 kg rail as specified in JIS E 1101:2001.
  • the area reduction rate of the bottom part in rolling at 1050°C or less was set to satisfy the value shown in Table 2.
  • the reduction rate (thickness reduction rate) in the thickness direction of the bottom part was set to 15% or more, which is a value larger than the area reduction rate of the corresponding pass.
  • the obtained rail was transported to an online heat treatment facility, and the center of the bottom of the rail was cooled at the average cooling rate shown in Table 2.
  • the rail was further transported to a cooling bed, and allowed to cool to room temperature.
  • the cooling of the foot was performed by intensively spraying the coolant onto an area of 0.1 ⁇ W to 0.5 ⁇ W of the bottom width W by appropriately selecting air nozzles so as to sandwich the center of the rail bottom as shown in Fig. 3.
  • the coolant was sprayed onto almost the entire bottom surface.
  • the cooling was performed from the abdomen side as well as shown in Fig. 4.
  • the cooling start point and cooling stop point in Table 2 are the surface temperatures at the corresponding positions measured using a two-dimensional radiation thermometer capable of measuring the temperature distribution at the center of the rail bottom, and the average cooling rate is the average cooling rate between these temperatures.
  • the average cooling temperature of the rail base tip is the value obtained by measuring the temperature of one of the rail base tips (at a position 0.15 x W from one tip) with a spot thermometer and dividing the temperature by the accelerated cooling time. Since the cooling conditions of the rail base are uniform on both sides of the rail center, the measured value of one of the rail base tips was used.
  • the rails obtained as described above were subjected to tensile tests, fatigue crack propagation tests, residual stress tests and fatigue tests as described below.
  • ⁇ Tensile test> As shown in Figure 5, tensile test specimens were taken from the center of the bottom of the rail and subjected to tensile tests in accordance with JIS Z2241. The shape of the test specimen is shown in Figure 6. After the tensile test, the 0.2% proof stress was calculated.
  • a test piece for fatigue crack propagation test was taken from a position including the center of the rail bottom.
  • the shape of the test piece is shown in Fig. 8.
  • the residual stress of the rail was measured by the strain gauge cutting method. Specifically, a 2 m long rail was taken, and a strain gauge with a gauge length of 3 mm, resistance of 120 ⁇ , and gauge factor of 2 was attached to the width center of the bottom surface of the rail shown in Figure 9 at a position 1 m from the center in the longitudinal direction, and the initial strain was measured. Next, the rail was sawed at the position shown in Figure 9, and the strain after sawing was measured. The residual stress in the longitudinal direction of the rail was calculated from the change in strain before and after sawing. If the residual stress in the longitudinal direction of the rail is less than 200 MPa, the residual stress can be determined to be good.
  • the fatigue test was evaluated as follows.
  • the obtained rails were cut to 1500 mm and repeatedly subjected to three-point bending tests in a head-up position with the rail head on top and the rail bottom on the bottom using Mayekawa Testing Machinery's Pulsator 250PUS.
  • three-point bending was performed 3.5 million times under the following conditions: test load: 1000 kN, repetition speed: 600 rpm, bending support interval: 1000 mm, and the presence or absence of breakage was confirmed visually.
  • test load 1000 kN
  • repetition speed 600 rpm
  • bending support interval 1000 mm
  • An unfractured rail can be judged to have good fatigue properties, and is therefore a rail that can be prevented from breaking from the rail bottom.
  • a rail with no visible cracks has excellent properties.
  • the rails of the examples of the invention have good properties, with the 0.2% proof stress at the rail bottom center being more than 500 MPa and less than 1,100 MPa, the longitudinal residual stress at the rail bottom center being less than 200 MPa, and the fatigue crack propagation rate being 5.0 ⁇ 10-8 m/cycle or less when the stress intensity factor range ⁇ K at the rail bottom center is 15 MPa m1 /2 .
  • the present invention can provide a rail that can suppress the occurrence of cracks at the bottom of the rail, and, if a crack exists at the bottom of the rail, can reduce the speed of crack propagation when a mechanical load is applied, thereby suppressing breakage from the bottom of the rail, together with a manufacturing method thereof.

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Articles (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

L'invention concerne un rail capable de supprimer la rupture d'une partie inférieure de rail. Ledit rail a une composition de composant contenant, en termes de % en masse, 0,60 % ou plus et moins de 0,90 % de C, 0,10 à 1,20 % de Si, 0,10 à 1,50 % de Mn, 0,05 à 2,00 % de Cr, 0,0002 à 0,005 % d'Al, 0 à 0,035 % de P, 0 à 0,020 % de S, 0 à 0,30 % de V, 0 à 1,0 % de Cu, 0 à 1,0 % de Ni, 0 à 0,05 % de Nb, 0 à 0,5 % de Mo, 0 à 0,0050 % de B, 0 à 0,01 % de Ti, 0 à 0,01 % de Mg, 0 à 0,02 % de Ca, 0 à 0,10 % de W, 0 à 0,05 % de Sb, 0 à 0,05 % de Sn, et 0 à 1,0 % de Co, le reste étant du Fe et des impuretés inévitables, la limite d'élasticité à 0,2 % d'une partie inférieure de rail étant supérieure à 500 MPa et inférieure à 1 100 MPa, la contrainte résiduelle dans la direction longitudinale au centre de la partie inférieure de rail étant inférieure à 200 MPa, et la vitesse de propagation de fissure de fatigue lorsque la plage de facteur d'intensité de contrainte ΔK au centre de la partie inférieure de rail est de 15 MPa m1/2 est de 5,0 × 10-8 m/cycle ou moins.
PCT/JP2024/001017 2023-03-24 2024-01-16 Rail et son procédé de fabrication Pending WO2024202408A1 (fr)

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CN202480020000.XA CN121079446A (zh) 2023-03-24 2024-01-16 导轨及其制造方法
EP24778554.6A EP4667604A1 (fr) 2023-03-24 2024-01-16 Rail et son procédé de fabrication
AU2024245086A AU2024245086A1 (en) 2023-03-24 2024-01-16 Rail and method of producing same
JP2024527864A JPWO2024202408A1 (fr) 2023-03-24 2024-01-16

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JPS63128123A (ja) * 1986-11-17 1988-05-31 Nkk Corp 靭性の優れた高強度レ−ルの製造方法
JPH01139724A (ja) 1987-11-27 1989-06-01 Nippon Steel Corp 耐落重特性に優れた鋼レールの熱処理方法
JP2006057127A (ja) 2004-08-18 2006-03-02 Nippon Steel Corp 耐落重破壊特性に優れたパーライト系レール
JP2010185106A (ja) * 2009-02-12 2010-08-26 Jfe Steel Corp 耐摩耗性レールおよびその製造方法
WO2011021582A1 (fr) 2009-08-18 2011-02-24 新日本製鐵株式会社 Rail en perlite
WO2016047076A1 (fr) * 2014-09-22 2016-03-31 Ｊｆｅスチール株式会社 Procédé de fabrication de rail et appareil de fabrication de rail
WO2016117692A1 (fr) * 2015-01-23 2016-07-28 新日鐵住金株式会社 Rail
WO2018168969A1 (fr) * 2017-03-15 2018-09-20 Ｊｆｅスチール株式会社 Dispositif de refroidissement et procédé de fabrication d'un rail
CN112239831A (zh) * 2020-10-19 2021-01-19 攀钢集团攀枝花钢铁研究院有限公司 高韧高寒铁路钢轨及其生产方法
CN112676347A (zh) * 2020-12-01 2021-04-20 攀钢集团攀枝花钢铁研究院有限公司 一种控制高性能钢轨轨底中心残余应力的方法
WO2022004247A1 (fr) * 2020-06-29 2022-01-06 Ｊｆｅスチール株式会社 Rail présentant d'excellentes caractéristiques de résistance à la propagation de fissures par fatigue, et son procédé de production

Patent Citations (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63128123A (ja) * 1986-11-17 1988-05-31 Nkk Corp 靭性の優れた高強度レ−ルの製造方法
JPH01139724A (ja) 1987-11-27 1989-06-01 Nippon Steel Corp 耐落重特性に優れた鋼レールの熱処理方法
JP2006057127A (ja) 2004-08-18 2006-03-02 Nippon Steel Corp 耐落重破壊特性に優れたパーライト系レール
JP2010185106A (ja) * 2009-02-12 2010-08-26 Jfe Steel Corp 耐摩耗性レールおよびその製造方法
WO2011021582A1 (fr) 2009-08-18 2011-02-24 新日本製鐵株式会社 Rail en perlite
WO2016047076A1 (fr) * 2014-09-22 2016-03-31 Ｊｆｅスチール株式会社 Procédé de fabrication de rail et appareil de fabrication de rail
WO2016117692A1 (fr) * 2015-01-23 2016-07-28 新日鐵住金株式会社 Rail
WO2018168969A1 (fr) * 2017-03-15 2018-09-20 Ｊｆｅスチール株式会社 Dispositif de refroidissement et procédé de fabrication d'un rail
WO2022004247A1 (fr) * 2020-06-29 2022-01-06 Ｊｆｅスチール株式会社 Rail présentant d'excellentes caractéristiques de résistance à la propagation de fissures par fatigue, et son procédé de production
CN112239831A (zh) * 2020-10-19 2021-01-19 攀钢集团攀枝花钢铁研究院有限公司 高韧高寒铁路钢轨及其生产方法
CN112676347A (zh) * 2020-12-01 2021-04-20 攀钢集团攀枝花钢铁研究院有限公司 一种控制高性能钢轨轨底中心残余应力的方法

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Title
See also references of EP4667604A1

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EP4667604A1 (fr) 2025-12-24

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