EP3199255B1 - Rail manufacturing method and rail manufacturing apparatus - Google Patents

Rail manufacturing method and rail manufacturing apparatus Download PDF

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Publication number
EP3199255B1
EP3199255B1 EP15845139.3A EP15845139A EP3199255B1 EP 3199255 B1 EP3199255 B1 EP 3199255B1 EP 15845139 A EP15845139 A EP 15845139A EP 3199255 B1 EP3199255 B1 EP 3199255B1
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EP
European Patent Office
Prior art keywords
rail
less
cooling
rolling
temperature
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EP15845139.3A
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German (de)
English (en)
French (fr)
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EP3199255A1 (en
EP3199255A4 (en
Inventor
Kenji OKUSHIRO
Hideo Kijima
Hiroyuki Fukuda
Moriyasu YAMAGUCHI
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JFE Steel Corp
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JFE Steel Corp
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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
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/08—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling structural sections, i.e. work of special cross-section, e.g. angle steel
    • B21B1/085—Rail sections
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • 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
    • 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

Definitions

  • the present invention relates to a method for manufacturing a pearlitic steel rail with excellent ductility obtained by performing rough rolling, finish rolling, and heat treatment of a heated bloom and particularly relates to a method and an apparatus for manufacturing a rail having ductility improved by refining the pearlite block or colony size.
  • a rail in which the structure of a head portion forms a pearlite structure is generally manufactured by the following manufacturing method.
  • a bloom cast by a continuous casting method is heated to 1100°C or more, and then hot-rolled into a predetermined rail shape by rough rolling and finish rolling.
  • a rolling method in each rolling process is performed combining caliber rolling and universal rolling.
  • the rolling is performed in a plurality of passes in the rough rolling or in a plurality of passes or a single pass in the finish rolling.
  • crops at end portions of the hot-rolled rail are sawn.
  • the length of the hot-rolled rail is 50 to 200 m. Therefore, when a heat treatment apparatus has a length limitation, the rail is sawn into a predetermined length, e.g., 25 m, simultaneously with the sawing of the crops.
  • the rail when the rail is required to have wear resistance, the rail is subjected to heat treatment by the heat treatment apparatus (heat treatment process) subsequent to the hot-rolling process.
  • heat treatment process heat treatment process
  • the wear resistance improves when the heat treatment start temperature is higher. Therefore, a re-heating process of heating the rail may be provided before the heat treatment process.
  • the rail In the heat treatment process, the rail is fixed with a restraining device, such as a clamp, and then a head portion, a foot portion, and, as necessary, an web portion are forcibly cooled using a cooling medium, such as air, water, and mist.
  • the forcible cooling is usually performed until the temperature of the head portion reaches 650°C or less.
  • the restraint of the rail by the clamp is released, and then the rail is conveyed to a cooling bed.
  • the rail is cooled until the temperature reaches 100°C or less.
  • a rail to be used under severe environments such as mining sites of natural resources, such as coal
  • a rail to be used under severe environments is demanded to have high wear resistance and high toughness. Therefore, when the rail to be used under severe environments is manufactured, the above-described heat treatment process is required.
  • processing such as bending processing, for example, later
  • the processing becomes difficult to achieve in some cases because the rail is excessively hardened when subjected to heat treatment, so that the ductility decreases. Therefore, a rail with high hardness and excellent ductility has been demanded.
  • JP 2013-14847 A discloses a method including setting the rolling temperature in finish rolling in a temperature range of Ar3 transformation point to 900°C, and then performing accelerated cooling of a rail to at least 550°C at a cooling rate of 2 to 30/sec within 150 sec after the end of the finish rolling to thereby increase the ductility of the rail.
  • JP 62-127453 A discloses a method including performing rolling at an area reduction ratio of 10% or more in a temperature range 800°C or less in hot-rolling to thereby improve the ductility of a rail.
  • JP 2001234238 A discloses a producing method for a high toughness rail by which toughness is moreover imparted to steel with a pearlitic structure of high carbon excellent in strength and wear resistance by suppressing the growth of recrystallized fine grains ⁇ in the process of rolling and after rolling.
  • continuous rolling in which rolling at a reduction of cross-sectional area by 5 to 30% per pass is applied for ⁇ 2 passes, and the time between the rolling passes is ⁇ 8 sec is performed at 850 to 1,000°C and the steel is successively cooled to 800 to 950°C at a cooling rate of 0.5 to 50°C/s and is thereafter subjected to air cooling or accelerated cooling.
  • WO 2005/085481 A1 discloses methods of producing steel rails having a high carbon content and being excellent in wear resistance and ductility from the slabs for rails.
  • One method involves producing a steel rail having a high content of carbon, comprising finish rolling the rail in two consecutive passes, with a reduction rate per pass of a cross-section of the rail of 2-30%, wherein the conditions of the finish rolling satisfy the following relationship: S ⁇ 800 / (C x T), wherein S is the maximum rolling interval time (seconds), C is the carbon content of the steel, wherein the carbon content is 0.85-1.40 mass%, and T is the maximum surface temperature (°C) of the rail head.
  • Another method involves producing a steel rail with a high content of carbon, comprising: finish rolling the rail in three or more passes, with a reduction rate per pass of a cross-section of the rail of 2-30%, wherein the conditions of the finish rolling satisfy the following relationship: S ⁇ 2400 / (C x T x P), wherein S is the maximum rolling interval time (seconds), C is the carbon content of the steel rail, wherein the carbon content is 0.85 ⁇ 1.40 mass%, T is the maximum surface temperature (°C) of a rail head, and P is the number of passes, which is 3 or more.
  • controlled additional amounts of V, Nb, N may be added to the steel rail and/or controlled rapid cooling of the rail after rolling may be accomplished to provide further improvements.
  • JP 2002 226 915 A discloses manufacturing method of a rail of high toughness in which the growth of re-crystallized grain y during an after rolling is suppressed, a pearlite structure of the grain is obtained, and the toughness is provided in steel representing pearlite structure with high carbon content of excellent strength and wear resistance.
  • a steel slab containing, by mass, 0.6-1.20% C is subjected to rough rolling, and the intermediate rolling is performed by a reverse rolling mill at the surface temperature between 1,000 and 1, 050°C.
  • the steel slab is subjected to the cooling immediately after the rolling of each pass of the intermediate rolling so that the temperature of the surface of a rail head and the surface of the bottom center is dropped by 50-100°C.
  • the finish rolling is performed by a continuous rolling mill at the surface temperature between 850 and 1,000°C with at least two passes of reduction ratio per pass of 5-30% and ⁇ 10 seconds between rolling passes.
  • the steel slab is cooled to 800-950°C at the cooling speed of 0.5-50°C/s on the rail surface, and subjected to the natural or accelerated cooling.
  • JP 5 472 418 B discloses a method to control the composition of steel, the reaction force ratio during finish rolling and the heat treatment condition after finish rolling, the structure of the head of the rail is made finer, the hardness is kept within a predetermined range, Improve abrasion and ductility.
  • C 0.65 to 1.20%
  • Si 0.05 to 2.00%
  • Mn 0.05 to 2.00% are contained, the balance being Fe and unavoidable.
  • the amount of the unrecrystallized austenitic structure formed by rolling immediately after rolling in the temperature range of 900 ° C. or less to the A 3 transformation point or Ar cm transformation point is set to 40% or more and 70% or less in area ratio, Characterized in that the surface of the head of the rail after finish rolling is accelerated and cooled to at least 550 °C. at a cooling rate of 2 to 30 ° C./s within 150 seconds after completion of the finish rolling.
  • Patent Document 1 has had a problem in that the temperature control for a foot portion of a rail is not performed, and therefore the ductility of the foot portion does not improve.
  • JP 62-127453 A has had a problem in that the temperature adjustment conditions in rolling for a foot portion of a rail are not specified, and therefore the ductility of the foot portion does not improve.
  • the present invention has been made focusing on the problems described above. It is an object of the present invention to provide a method for manufacturing a rail having high ductility in both a head portion and a foot portion. Solution to the Problem
  • a method for manufacturing a rail according to the present invention is defined by claim 1.
  • Dependent claims relate to preferred embodiments.
  • a rail having high ductility in both a head portion and a foot portion is able to be manufactured.
  • % for chemical composition means % by mass.
  • the rail manufacturing apparatus 1 is a rolling line having a heating furnace 2, a roughing mill 3A, a finishing mill 3B, a rough cooling device 4, a finish cooling device 5, a re-heating device 6, a heat treatment apparatus 7, and a cooling bed 8.
  • the rail 9 is manufactured by rolling and heat-treating a steel rail material, such as a continuously cast bloom, by the manufacturing apparatus 1. As illustrated in FIG. 4 , the rail 9 extends in the width direction viewed in a cross section perpendicular to the longitudinal direction and has a head portion 91 and a foot portion 93 facing each other in the vertical direction and an web portion 92 connecting the head portion 91 disposed on the upper side and the foot portion 93 disposed on the lower side and extending in the vertical direction. As the rail 9, steel containing the following chemical composition is usable, for example.
  • C carbon
  • the lower limit is preferably set to 0.60% and more preferably set to 0.70% or more.
  • excessive content of C causes an increase in the cementite amount, and therefore an increase in hardness and strength is expectable but, contrarily, the ductility decreases.
  • the increase in the C content extends the temperature range of a ⁇ + ⁇ zone and promotes softening of a weld heat affected zone. Considering these adverse effects, the upper limit of the C content is preferably set to 1.05% and more preferably set to 0.97% or less.
  • Si 0.1% or more and 1.5% or less
  • Si silicon
  • the Si content is preferably 0.1% or more and more preferably 0.2% or more.
  • excessive content of Si promotes decarburization and promotes the generation of surface flaws of the rail 9, and therefore the upper limit of the Si content is preferably set to 1.5% and more preferably 1.3% or less.
  • Mn 0.01% or more and 1.5% or less
  • Mn manganese
  • Mn has an effect of lowering the pearlite transformation temperature and densifying the pearlite lamella intervals, and therefore Mn is effective for maintaining high hardness up to a rail inner region.
  • the Mn content is preferably 0.01% or more and more preferably 0.3% or more.
  • the upper limit of the Mn content is preferably set to 1.5% and more preferably set to 1.3% or less.
  • the content of P phosphorus
  • the toughness and the ductility are lowered. Therefore, the P content is preferably suppressed to 0.035% or less and more preferably limited to 0.025% or less.
  • the lower limit is preferably set to 0.001%.
  • the S content is preferably suppressed to 0.030% or less and more preferably suppressed to 0.015% or less.
  • the lower limit is preferably set to 0.0005%.
  • Cr chromium
  • TE equilibrium transformation temperature
  • the use of Cr in combination with Sb is effective for inhibition of the generation of a decarburized layer. Therefore, when Cr is compounded, the content is preferably set to 0.1% or more and more preferably set to 0.2% or more.
  • the Cr content exceeds 2.0%, a possibility of the generation of welding defects increases, the quenching properties increase, and the generation of martensite is promoted. Therefore, the upper limit of the Cr content is preferably set to 2.0%, and more preferably set to 1.5% or less.
  • the total content of Si and Cr is desirably set to 2.0% or less. This is because, when the total content of Si and Cr exceeds 2.0%, the adhesiveness of a scale increases, and therefore the peeling of the scale may be inhibited and decarburization may be promoted.
  • Sb antimony
  • the content is preferably 0.005% or more and more preferably 0.01% or more.
  • the upper limit is preferably set to 0.5% and more preferably set to 0.3% or less.
  • one or two or more elements of Cu 0.01% or more and 1.0% or less, Ni: 0.01% or more and 0.5% or less, Mo: 0.01% or more and 0.5% or less, V: 0.001% or more and 0.15% or less, and Nb: 0.001% or more and 0.030% or less may be compounded.
  • Cu copper
  • Cu is an element capable of further increasing the hardness by solid solution strengthening. Cu is effective also for decarburization control.
  • the Cu content is preferably 0. 01% or more and more preferably 0.05% or more.
  • the upper limit of the Cu content is preferably set to 1.0% and more preferably set to 0.6% or less .
  • Ni 0.01% or more and 0.5% or less
  • Ni nickel
  • Ni nickel
  • the lower limit is preferably set to 0.01% and more preferably set to 0.05% or more.
  • the upper limit is preferably set to 0. 5% and more preferably set to 0.3% or less.
  • Mo mobdenum
  • the lower limit is preferably set to 0.01% and more preferably set to 0.05% or more.
  • the upper limit of the Mo content is preferably set to 0.5% and more preferably set to 0.3% or less.
  • V 0.001% or more and 0.15% or less
  • V vanadium
  • VN vanadium
  • V content is preferably 0.001% or more and more preferably 0.005% or more.
  • the upper limit is preferably set to 0.15% and more preferably set to 0.12% or less.
  • Nb 0.001% or more and 0.030% or less
  • Nb niobium
  • the Nb content is preferably 0.001% or more and more preferably 0.003% or more.
  • the upper limit is preferably set to 0.030% and more preferably set to 0.025% or less.
  • the remainder other than the components described above includes Fe (iron) and inevitable impurities.
  • Fe iron
  • inevitable impurities the mixing of N (nitrogen) up to 0.015%, the mixing of O (oxygen) up to 0.004%, and the mixing of H (hydrogen) up to 0.0003% are acceptable.
  • the Al content is desirably set to 0.001% or less and the Ti content is desirably set to 0.001% or less.
  • the heating furnace 2 is a continuation type or batch type heating furnace and heats steel rail materials, such as a continuously cast bloom, to a predetermined temperature.
  • the roughing mill 3A is a universal mill which hot-rolls a steel material at a predetermined area reduction ratio and two or more of the roughing mills 3A are provided.
  • the manufacturing apparatus 1 has n pieces of roughing mills 3A1 to 3An.
  • the rough cooling device 4 is provided between a k-th roughing mill 3Ak and a (K+1) -th roughing mill 3Ak+1 among the roughing mills 3A1 to 3An along the conveyance direction of the rail 9.
  • the finishing mill 3B is a universal mill which further hot-rolls the rough-rolled rail 9 to thereby finally process the same into a target rail shape.
  • the area reduction ratio of the rail 9 to be rolled from the (k+1)-th roughing mill 3Ak+1 to the finishing mill 3B as the rolling process after the rough cooling device 4 is set to 20% or more.
  • the area reduction ratio in this embodiment shows the area reduction ratio of a cross-sectional area perpendicular to the longitudinal direction of the steel rail material and shows the ratio of the reduction in the cross-sectional area during the rolling to the cross-sectional area before the rolling of the bloom and the like.
  • the rough cooling device 4 has a head portion cooling nozzle 41, a foot portion cooling nozzle 42, a head portion thermometer 43, a foot portion thermometer 44, a conveyance table 45, guides 46a and 46b, and a control unit 47 as illustrated in FIG. 2 .
  • the head portion cooling nozzle 41 cools the head portion 91 of the rail 9 by ejecting a cooling medium to the head portion 91.
  • the foot portion cooling nozzle 42 cools the foot portion 93 of the rail 9 by ejecting a cooling medium to the foot portion 93.
  • the cooling medium ejected from the head portion cooling nozzle 41 and the foot portion cooling nozzle 42 is spray water.
  • the head portion cooling nozzle 41 and the foot portion cooling nozzle 42 are provided above the head portion 91 and the foot portion 93, respectively, on the y-axis positive direction side and eject a cooling medium to each of the head portion 91 and the foot portion 93 with an inclination with respect to the y axial direction.
  • two or more of the head portion cooling nozzles 41 and the foot portion cooling nozzles 42 are provided along the z axis direction perpendicular to the x-y plane as the longitudinal direction of the rail 9.
  • the head portion thermometer 43 and the foot portion thermometer 44 are noncontact thermometers which measure the surface temperature of each of the head portion 91 and the foot portion 93 of the rail 9, respectively, to which the cooling medium is ejected and are provided facing the head portion 91 and the foot portion 93, respectively, in the x axis direction.
  • the measurement results of the head portion thermometer 43 and the foot portion thermometer 44 are transmitted to the control unit 47.
  • the conveyance table 45 is a conveyance roll extending in the x axis direction and two or more of the conveyance tables 45 are provided side by side along the z axis direction.
  • the guides 46a and 46b are plate-like members and are provided extending in the z axis direction.
  • the guides 46a and 46b are individually disposed on the upper side relative to the conveyance table 45 on the y-axis positive direction side and on both end sides in the longitudinal direction of the conveyance table 45.
  • the guides 46a and 46b are further provided with openings 461a and 461b at the positions where the head portion thermometer 43 and the foot portion thermometer 44 are disposed, respectively.
  • the control unit 47 controls the conditions of the cooling medium ejected from the head portion cooling nozzle 41 and the foot portion cooling nozzle 42 based on the measurement results of the head portion thermometer 43 and the foot portion thermometer 44 to thereby cool the rail 9 to a predetermined surface temperature.
  • the ejection conditions of the cooling medium include the ejection amount, the ejection pressure, the moisture amount, the ejection time, and the like of the cooling medium, for example.
  • the rough cooling device 4 of the configuration described above is provided between the k-th roughing mill 3Ak and the (k+1) -th roughing mill 3Ak+1 among the plurality of roughing mills 3A located side by side in the rolling direction of the rail 9 and controls the surface temperature of the head portion 91 and the foot portion 93 of the rail 9 to be rolled with the k-th roughing mill 3Ak.
  • the finish cooling device 5 is provided immediately before the finishing mill 3B and controls the surface temperature of the head portion 91 and the foot portion 93 of the rail 9 to be rolled with the finishing mill 3B.
  • the finish cooling device 5 has the same configuration as that of the rough cooling device 4 illustrated in FIG. 2 .
  • the rail 9 is conveyed and rolled with an overturned state as illustrated in FIG. 2 when rolled or cooled with the roughing mills 3A, the rough cooling device 4, the finish cooling device 5, and the finishing mill 3B.
  • the re-heating device 6 is an induction heating type heating device and heats the head portion 91 of the rail 9 to a predetermined temperature.
  • the heat treatment apparatus 7 has head portion cooling headers 71a to 71c, a foot portion cooling header 72, a head portion thermometer 73, and a control unit 74 as illustrated in FIG. 3 .
  • the head portion cooling headers 71a to 71c are provided facing each of the head top surface and both head side surfaces of the head portion 91 and cool the head portion 91 by ejecting a cooling medium to the head top surface and both the head side surfaces.
  • the foot portion cooling header 72 is provided facing the underside of the foot portion 93 and cools the foot portion 93 by ejecting a cooling medium to the underside of the foot.
  • the head portion thermometer 73 is a non-contact-type thermometer and measures the surface temperature of the head portion 91. The temperature measurement results of the head portion thermometer 73 are transmitted to the control unit 74.
  • the control unit 74 controls the ejection conditions of the cooling medium ejected from the head portion cooling headers 71a to 71c and the foot portion cooling header 72 according to the temperature measurement results of the head portion thermometer 73 to thereby control the cooling rate of the rail 9.
  • the heat treatment apparatus 7 of the configuration described above cools the rail 9 at a predetermined cooling rate until the surface temperature reaches a predetermined surface temperature.
  • the heat treatment apparatus 7 has a clamp (not illustrated).
  • the clamp is a device restraining the foot portion of the rail 9 by holding the same.
  • the cooling bed 8 is a device which naturally cools the rail 9 and contains, for example, a base supporting the rail 9.
  • a bloom which is a steel rail material cast by a continuous casting method is carried into the heating furnace 2 to be heated to reach 1100°C or more.
  • the heated steel rail material is rolled to have an almost rail shape by the roughing mills 3Aa to 3Ak on the upstream side in the conveyance direction relative to the rough cooling device 4.
  • a steel material in the hot-rolling process is also referred to as a steel rail material.
  • the steel rail material rolled with the roughing mills 3Aa to 3Ak is cooled (temperature adjustment) with the rough cooling device 4 until the surface temperature of portions corresponding to the head portion 91 and the foot portion 93 of the rail 9 reaches 500°C or more and 1000°C or less.
  • the control unit 47 controls the ejection amount, the ejection pressure, the moisture amount, the ejection time, and the like of the cooling medium to thereby cool the steel rail material.
  • the entire structure is transformed into austenite.
  • the austenite structure of 1000°C or more the grain boundary easily moves and re-crystallization occurs, so that the crystal grains are coarsened.
  • strain is generated in the crystal grains, and thus the crystal grains are divided, and then refined.
  • the temperature in the rolling is 1000°C or less, the re-crystallization and the coarsening of the crystal grains are difficult to occur. Therefore, by setting the temperature of the steel rail material in the rolling to 1000°C or less, the coarsening of the crystal grains refined by the rolling is difficult to occur.
  • the temperature adjustment is preferably performed until the surface temperature of the portions corresponding to the head portion 91 and the foot portion 93 reach 500°C or more and 730°C or less.
  • the structure partially causes pearlite transformation. Therefore, the structure of the steel rail material has a two phase structure containing untransformed austenite and pearlite.
  • the yield strength of the austenite is lower, and therefore most of strain is introduced in the austenite grains and the structure in the rolling is refined as compared with the case where the structure in the rolling is an austenite single phase.
  • the colony size and the block size of the pearlite as the final structure are affected by the crystal grain diameter of the austenite which is the structure before transformation. Therefore, when the austenite grains are coarse, the colony size and the block size of the pearlite are also coarsened, and therefore the ductility decreases. On the other hand, when the austenite grains are fine, the colony size and the block size of the pearlite are refined, and therefore the ductility improves.
  • the steel rail material subjected to the temperature adjustment with the rough cooling device 4 is further rolled with the roughing mills 3Ak+1 to 3An.
  • the steel rail material rough-rolled with the roughing mills 3A1 to 3An is cooled with the finish cooling device 5 as necessary, and then rolled with the finishing mill 3B to be formed into the rail 9 of a desired shape.
  • the rolling in the roughing mills 3Ak+1 to 3An and the finishing mill 3B after the temperature adjustment is also referred to as temperature-adjusted rolling.
  • the area reduction ratio of the steel rail material to be subjected to the temperature-adjusted rolling is 20% or more. By setting the area reduction ratio to 20% or more, strain can be generated also in the steel rail material, and therefore the inside structure of the rail 9 can be refined.
  • the rail 9 hot-rolled with the roughing mills 3A and the finishing mill 3B is conveyed to the re-heating device 6 to be heated until the surface temperature of the head portion 91 reaches 730°C or more and 900°C or less.
  • the heated rail 9 is conveyed to the heat treatment apparatus 7 to be forcibly cooled (heat treatment) with the heat treatment apparatus 7 in the state of being restrained by the clamp until the surface temperature of the head portion 91 reaches 600°C or less.
  • the control unit 74 calculates the cooling rate of the rail 9 from the temperature measurement results of the head portion thermometer 73, and then controls the ejection conditions of the cooling medium ejected from the head portion cooling headers 71a to 71c so that the average cooling rate is 1°C/s or more and 10°C/s or less.
  • control unit 74 controls the ejection conditions of the cooling medium ejected from the foot portion cooling header 72 in such a manner as to be the same as any one of the ejection conditions of the cooling medium ejected from the head portion cooling headers 71a to 71c.
  • the structure When the surface temperature of the head portion 91 is less than 730°C before the heat treatment, the structure partially or entirely causes pearlite transformation. Before the heat treatment, the rail 9 is naturally cooled and the cooling rate is low. Therefore, the pearlite lamella intervals is coarse. Therefore, by performing re-heating so that the surface temperature of the head portion 91 reaches 730°C or more before the heat treatment, the pearlite structure is reversely transformed to the austenite structure, and thus the lamella structure is able to be formed again. On the other hand, when the surface temperature of the head portion 91 is higher, the hardening of the decarburized layer on the surface and the hardening due to an improvement of the cooling rate inside the rail are achieved, so that the wear resistance is improved.
  • the upper limit of the surface temperature in the re-heating before the heat treatment is preferably set to 900°C.
  • the reduction in the pearlite lamella intervals is effective.
  • heat treatment at a high cooling rate is required. Therefore, the heat treatment is preferably performed at a surface temperature and at an average cooling rate within the ranges mentioned.
  • the cooling rate is less than 1°C/s, the pearlite lamella intervals are coarse and the wear resistance decreases.
  • the cooling rate exceeds 10°C/s, the structure after transformation is such as bainite and martensite that are poor in toughness and ductility, and this is not preferable.
  • the average cooling rate is a cooling rate determined from the temperature changes and the heat treatment time from the start of the heat treatment to the end of the heat treatment.
  • the thermal history from the start of the heat treatment to the end of the heat treatment also includes the heat generation of the phase transformation heat and isothermal-holding by patenting treatment.
  • the surface temperature of the head portion 91 at the end of the heat treatment exceeds 600°C, the lamella structure is partially spheroidized after the end of the heat treatment, and therefore the lamella intervals are coarse and the wear resistance decreases.
  • the rail 9 subjected to accelerated cooling is conveyed to the cooling bed 8, and then naturally cooled until the temperature reaches about 100°C or less.
  • shape correction of the rail 9 is performed as necessary when the rail 9 is bent or the like.
  • the cooling method in the rough cooling device 4 and the finish cooling device 5 is spray cooling employing spray water for the cooling medium in the embodiment described above but the present invention is not limited to the example.
  • mist cooling as spray cooling employing mist as a cooling medium or mixed cooling of mist cooling and air blast cooling employing mist and air as a cooling medium may be used for the cooling method in the rough cooling device 4 and the finish cooling device 5.
  • natural cooling, immersion cooling, air blast cooling, water column cooling, and the like may be performed in place of the spray cooling with the rough cooling device 4 and the finish cooling device 5. In the natural cooling and the air blast cooling, the cooling rate is low, and therefore the time until the rail 9 is cooled to a predetermined temperature is prolonged.
  • the rolling pitch is to be increased, other cooling methods, such as spray cooling, immersion cooling, and water column cooling, are able to be employed.
  • the cooling rate in the water column cooling is excessively high, and therefore the cooling rate is difficult to adjust.
  • the structure may be transformed to a structure having low toughness and ductility, such as bainite and martensite.
  • the spray cooling has advantages in that a somewhat high cooling rate is able to be secured and the cooling portion is easily localized. Therefore, the spray cooling is preferably used for the cooling method in the rough cooling device 4 and the finish cooling device 5.
  • the temperature-adjusted rolling is performed in the rolling pass after the roughing mill 3Ak+1 in the embodiment described above but the present invention is not limited to the example.
  • the temperature-adjusted rolling may be performed after any roughing mill 3A insofar as an area reduction ratio of 20% or more is able to be secured.
  • the rough cooling device 4 is provided immediately before the roughing mill 3A with which the temperature-adjusted rolling is started.
  • the temperature-adjusted rolling may be performed in finish rolling by the finishing mill 3B.
  • the rough cooling device 4 may not be provided in the rail manufacturing apparatus 1 and the temperature adjustment may be performed only the finish cooling device 5.
  • the temperature-adjusted rolling is preferably performed in the rolling with some of the roughing mills 3A and with the finishing mill 3B.
  • the roughing mills 3A and the finishing mill 3B are universal mills in the embodiment described above but the present invention is not limited to the example.
  • the roughing mills 3A and the finishing mill 3B may be caliber rolling mills.
  • a universal rolling method rolling from a plurality of directions is achieved as compared with a caliber rolling method, and therefore the rolling load can be reduced.
  • a rolling operation capable of obtaining a large area reduction ratio at a low temperature is performed, and therefore rolling is performed under an overload and the load to the rolling mills becomes high, so that the risk of a facility trouble becomes high. Therefore, at least any one of the roughing mills 3A and two or more of the finishing mills 3B is preferably a universal mill.
  • finishing mills 3B may be provided.
  • the re-heating device 6 is the induction heating type heating device in the embodiment described above but the present invention is not limited to the example.
  • the re-heating device 6 may be a burner type heating device.
  • the size of the facility is able to be made small as compared with the burner type. Therefore, the induction heating type re-heating device 6 is preferable when disposed in-line.
  • the re-heating device 6 heats the head portion 91 in the embodiment described above but the present invention is not limited to the example.
  • the re-heating device 6 may have a configuration of heating the entire rail 9. When the rail 9 is used, portions contacting wheels are worn out, and therefore particularly the head portion 91 is required to have wear resistance. Therefore, a configuration of re-heating only the head portion 91 in re-heating is economically excellent because energy required for the heating is able to be reduced.
  • the re-heating is performed with the re-heating device 6 after the hot-rolling in the embodiment described above but the re-heating with the re-heating device 6 may not be performed.
  • the hot-rolled rail 9 is conveyed to the heat treatment apparatus 7, and then heat-treated with the heat treatment apparatus 7. Even when the re-heating is not performed, the ductility improvement effect of the head portion 91 and the foot portion 93 is able to be obtained.
  • the temperature of the rail 9 after the end of the hot-rolling (after the end of the temperature-adjusted rolling) is low, the hardness decreases as compared with the case where the temperature is high.
  • the hot-rolled rail 9 is conveyed to the cooling bed 8, and then cooled until the temperature reaches about 100°C or less. Even when the re-heating and the heat treatment are not performed, the ductility improvement effect of the head portion 91 and the foot portion 93 is able to be obtained. However, the hardness decreases as compared with the case where the re-heating and the heat treatment are performed.
  • rails 9 were manufactured using the rail manufacturing apparatus 1 described in FIG. 1 under various chemical composition conditions and rolling conditions, and then the total elongation of the manufactured rails 9 was measured.
  • Table 1 shows the chemical composition of the rail 9 used in Examples 1. The remainder includes iron and inevitable impurities.
  • Table 2 shows the rolling conditions and the measurement results of the total elongation in Examples 1.
  • Example 1 first, a continuously cast bloom was heated with the heating furnace 2 until the temperature reached 1100°C.
  • the chemical composition of the bloom used in Examples 1 was any one of the composition A to the composition G of Table 1 as shown in Table 2.
  • the heated bloom was collected from the heating furnace 2, and then hot-rolled with the roughing mills 3A and the finishing mill 3B.
  • the roughing mills 3A a plurality of rolling mills in which a universal mill and a caliber rolling mill were combined was used.
  • the rail 9 during the rolling was rolled and conveyed with an overturned state.
  • the temperature adjustment was performed until the surface temperatures of the head portion 91 and the foot portion 93 reached 500°C or more and 1000°C or less with either the rough cooling device 4 or the finish cooling device 5.
  • the temperature adjustment method the time from the start of the temperature-adjusted rolling to the end of the hot-rolling, and the number of temperature-adjusted rolling passes are individually shown in Table 2.
  • the temperature-adjusted rolling refers to hot-rolling after the temperature adjustment was performed.
  • the temperature adjustment was performed by any one of the spray cooling, air blast cooling, and naturally cooling methods.
  • the surface temperatures of the head portion 91 and the foot portion 93 were adjusted by adjusting the water amount density and the cooling time in the case of the spray cooling or by controlling the cooling time without using the rough cooling device 4 and the finish cooling device 5 in the case of the natural cooling.
  • the number of the temperature-adjusted rolling passes shown in Table 2 shows the number of rolling passes after the temperature adjustment was performed by any one of the methods described above.
  • the number of times of the temperature-adjusted rolling passes was 1 time indicates that, after the temperature adjustment, only the finish rolling was performed and the number of times of the temperature-adjusted rolling passes was n (n ⁇ 2) times indicates that, after the temperature adjustment, n-1 times of rough rolling and one finish rolling were performed.
  • the number of times of the temperature-adjusted rolling passes was 1 time the temperature adjustment was performed using the finish cooling device 5.
  • the number of times of the temperature-adjusted rolling passes was n times the temperature adjustment was performed using the rough cooling device 4.
  • the rail 9 was forcibly cooled with the heat treatment apparatus 7.
  • the surface temperatures of the head portion 91 and the foot portion 93 in starting the forcible cooling were set as shown in the conditions shown in Table 2.
  • the average cooling rate was set to 3°C/s.
  • the cooling was performed until the surface temperature reached 400°C.
  • mist was used for a cooling medium.
  • the re-heat treatment employing the re-heating device 6 was not performed after the hot-rolling.
  • the forcibly cooled rail 9 was conveyed to the cooling bed 8, the temperature was reduced to 100°C or less by cooling, and then the rail was straightened.
  • test pieces were collected from four places of an end portion, the 1/4 position, the 1/2 position, and the 3/4 position in the longitudinal direction of the rail 9, and then various physical properties were measured. As illustrated in FIG. 5 , a sample 9a was collected from the head portion 91 and a sample 9b was collected from the foot portion 93 of the test pieces collected at each position in the longitudinal direction.
  • the sample 9a is a JIS No.
  • Example 1 as examples different in the chemical composition, the temperature adjustment method, the number of temperature-adjusted rolling passes, the surface temperature, and the area reduction ratio, rails 9 were manufactured under 28 kinds of conditions of Examples 1-1 to 1-28, and then the total elongation was evaluated.
  • rails 9 were manufactured as comparative examples under the same conditions as those of Examples 1-1 to 1-28, and then the total elongation was evaluated also for Comparative Examples 1-1 to 1-5 with the surface temperature and the area reduction ratio in the temperature-adjusted rolling outside the ranges of the embodiment described above.
  • the total elongation values shown in Table 2 show the average value of the four samples, i.e., the sum of one sample collected from each of the test pieces collected from each of the four places.
  • Example 1-8 in which the surface temperatures of both the head portion 91 and the foot portion 93 in the temperature-adjusted rolling were 730°C or less, the total elongations of the head portion 91 and the foot portion 93 were as high as 19% or more.
  • Examples 2 influences on the total elongation, the hardness, and the surface structure depending on the heat treatment conditions were confirmed by varying the chemical composition and the conditions in the temperature-adjusted rolling and the heat treatment.
  • Table 3 shows the chemical composition, the surface temperature in temperature-adjusted rolling, the conditions of heat treatment (forcible cooling), the measurement results of the total elongation, the measurement results of the hardness, and the observation results of a head portion surface structure in Examples 2.
  • Example 2 as the temperature-adjusted rolling, rolling in four passes in total containing three universal mills and one caliber rolling mill was performed so that the area reduction ratios of the head portion 91 and the foot portion 93 were 30%.
  • the surface temperatures of the head portion 91 and the foot portion 93 in the temperature-adjusted rolling and the start temperature, the cooling rate, and the end temperature in the heat treatment were set as shown in the conditions shown in Table 3.
  • air was used for a cooling medium under the condition where the cooling rate was 3°C/s or less and a mixture of air and mist was used for a cooling medium under the condition where the cooling rate exceeded 3°C/s.
  • the other manufacturing conditions were the same as those of Examples 1.
  • test pieces were collected, and then the total elongation was measured by the same method as that of Examples 1.
  • a sample 9c was collected from a position of the head portion surface illustrated in FIG. 6 and a sample 9d was collected from a position inside the head portion from the test pieces of about 20 mm thickness sawn from four places of an end portion, the 1/4 position, the 1/2 position, and the 3/4 position in the longitudinal direction of the rail 9.
  • the sample 9c was collected from the center of the upper end surface of the head portion 91 of the test pieces polished in order to remove surface unevenness.
  • the hardness of the collected samples 9c and 9d was measured by a Brinell hardness test. With respect to the surface structure, the surface structure of the collected samples 9c was observed.
  • Examples 2 as examples different in the chemical composition, the surface temperature in the temperature-adjusted rolling, and conditions in the heat treatment, rails 9 were manufactured under 21 kinds of conditions of Examples 2-1 to 2-21, and then the total elongation and the hardness were measured and further the surface structure was observed.
  • Example 2-13 the heat treatment was not performed and the rail 9 after the hot-rolling was conveyed to the cooling bed 8, and then cooled until the temperature reached 100°C or less. After the rail 9 reached 100°C or less, the rail was straightened.
  • Example 2-2 and 2-3 the surface temperature of the head portion 91 in the temperature-adjusted rolling was lower than that in other conditions, the surface temperature in starting the heat treatment was also low and the total elongation of the head portion 91 was 15% or more, which was higher than that in other conditions.
  • the hardness of the head portion 91 was 380 HB or less, which was lower than that in Example 2-1.
  • Examples 2-1, 2-7 to 2-10, and 2-14 to 2-21 in which the conditions except the cooling rate in the heat treatment were the same and, further, in Examples 2-14 to 2-21 in which the composition is different, the hardness of the surface and inside of the head portion 91 improved when the cooling rate was higher.
  • Examples 2-1, 2-7 to 2-10, and 2-14 to 2-21 and Comparative Examples 2-1 to 2-3 in which the conditions except the cooling rate in the heat treatment were the same and, further, in Comparative Examples 2-1 to 2-3 in which the cooling rate exceeded 10°C/s, the cooling rate was excessively high, and therefore the structure was partially transformed into a martensite and the total elongation was as very low as 3%.
  • Example 2-13 in which the heat treatment was not performed, the total elongations of the head portion 91 and the foot portion 93 were 12% or more but the hardness of the surface and inside of the head portion 91 was the lowest in all the conditions.
  • the pearlite structure was partially spheroidized.
  • Example 3 in order to confirm influences on the hardness and the surface structure by re-heat treatment, re-heating was performed before the heat treatment with respect to the condition of Example 2-3 in which the hardness was low.
  • manufacturing conditions other than the surface temperature of the head portion 91 in the temperature-adjusted rolling and performing re-heating were the same as those of Example 2-3.
  • Table 4 individually shows the chemical composition, the surface temperature in the temperature-adjusted rolling, the conditions in the re-heating and the heat treatment, the measurement results of the total elongation, the measurement results of the hardness, and the observation results of the head portion surface structure in Example 3.
  • the total elongation values and the hardness shown in Table 4 show the average value of the four samples, i.e., the sum of one sample collected from each of the test pieces collected from each of the four places .
  • Table 4 Condition Composition In temperature-adjusted rolling Re-heating In heat treatment Total elongation Hardness Head portion surface structure Head portion temperature [°C] Foot portion temperature [°C] Presence or absence Position Start temperature [°C] Cooling rate [°C/s] End temperature [°C] Head portion [%] Foot portion [%] Head portion surface [HB] Head portion inner region [HB] Ex. 3-1 A 650 900 Not performed 630 3 400 18 13 380 360 Coarse pearlite Ex.
  • the head portion 91 or the entire rail 9 was re-heated with the re-heating device 6 after the hot-rolling.
  • the re-heating device 6 is an induction heating type heating device and is able to heat the head portion 91 or the entire rail 9 according to the conditions shown in Table 4.
  • the surface temperature of the head portion 91 after the re-heating is the start temperature in the heat treatment shown in Table 4.
  • Examples 3 rails 9 were manufactured under 9 kinds of conditions of Examples 3-1 to 3-9 different in the surface temperature of the head portion 91 in the temperature-adjusted rolling and the re-heating conditions, and then the total elongation and the hardness were measured and further the surface structure was observed.
  • a method for collecting samples for the total elongation and the hardness and a method for collecting samples for observing the surface structure are the same as those of Examples 2.
  • Example 3-1 is the condition in which the re-heating was not performed and has the same manufacturing conditions as those of Example 2-3.
  • Example 3-1 in which the re-heating was not performed, the surface temperature in starting the temperature-adjusted rolling was low, and therefore the surface temperature of the head portion 91 in starting the heat treatment was as low as 630°C and the hardness of the surface and inside of the head portion 91 was low.
  • Example 3-2 and 3-6 the re-heating was performed and the surface temperature of the head portion 91 in starting the heat treatment was set to 700°C but the surface temperature was as low as 730°C or less, and therefore the hardness of the surface and inside of the head portion 91 was low as in Example 3-1.

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  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
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  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Articles (AREA)
  • Metal Rolling (AREA)
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EP15845139.3A 2014-09-22 2015-09-10 Rail manufacturing method and rail manufacturing apparatus Active EP3199255B1 (en)

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JPS62127453A (ja) * 1985-11-26 1987-06-09 Nippon Kokan Kk <Nkk> 延性及び靭性に優れた高性能レールの製造方法
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CN106714990A (zh) 2017-05-24
BR112017005296A2 (pt) 2017-12-12
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