EP2343390B1 - Pearlite rail having superior abrasion resistance and excellent toughness - Google Patents

Pearlite rail having superior abrasion resistance and excellent toughness Download PDF

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Publication number
EP2343390B1
EP2343390B1 EP09823351.3A EP09823351A EP2343390B1 EP 2343390 B1 EP2343390 B1 EP 2343390B1 EP 09823351 A EP09823351 A EP 09823351A EP 2343390 B1 EP2343390 B1 EP 2343390B1
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EP
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Prior art keywords
rail
pearlite
sulfide
amount
range
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EP09823351.3A
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German (de)
English (en)
French (fr)
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EP2343390A1 (en
EP2343390A4 (en
Inventor
Masaharu Ueda
Kazunori Seki
Takuya Satou
Takeshi Yamamoto
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Nippon Steel Corp
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Nippon Steel and Sumitomo Metal Corp
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Priority to PL09823351T priority Critical patent/PL2343390T3/pl
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Publication of EP2343390A4 publication Critical patent/EP2343390A4/en
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    • 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
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0025—Adding carbon material
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/064—Dephosphorising; Desulfurising
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

  • the present invention relates to a pearlite rail used for freight railways in overseas in which both the abrasion resistance (wear resistance) and toughness are improved at the head portion.
  • the refinement of a pearlite structure specifically, grain refining in an austenite structure which is yet to be transformed into pearlite or the refinement of pearlite blocks is effective to improve the toughness of a pearlite steel.
  • the rolling temperature is decreased and the rolling reduction rate is increased and, furthermore, a heat treatment by low-temperature reheating after hot rolling of rails is implemented.
  • pearlite transformation starting from the inside of austenite grains is accelerated by utilizing transformation nuclei or the like.
  • Patent Document 1 discloses that a rail having high ductile can be provided by conducting 3 or more continual passes of rolling with a predetermined interval of time in the finish rolling of a high carbon steel rail.
  • Patent Document 2 discloses that a rail having superior wear resistance and high toughness can be provided by conducting two or more continual passes of rolling with a predetermined interval of time in the finish rolling of a high carbon steel rail, and furthermore, conducting accelerated cooling after the continuous rolling.
  • Patent Document 3 discloses that a rail having superior wear resistance and high toughness can be provided by conducting cooling between passes of rolling in the finish rolling of a high-carbon steel rail, and conducting accelerated cooling after the continuous rolling.
  • Patent Documents 1 to 3 can achieve the refinement of an austenite structure at a certain level and exhibit a slight improvement in toughness by the combination of the temperature, the number of rolling passes, and the interval of time between passes during the continuous hot rolling.
  • these technologies do not exhibit any effects in regard to fracture starting from inclusions present inside the steel; and thereby, the toughness is not fundamentally improved.
  • Patent Document 4 discloses a method for manufacturing a high-carbon silicon-killed high-cleanliness molten steel in which the added amount of Ca is optimized to fix S as CaS; and thereby, the amount of elongated MnS-based inclusions is reduced.
  • S which segregates and concentrates in a solidification process reacts with Ca which similarly segregates and concentrates or calcium silicate generated in the molten steel; and thereby, S is sequentially fixed as CaS.
  • the generation of elongated MnS inclusions is suppressed.
  • Patent Document 5 discloses a method for manufacturing a high-carbon high-cleanliness molten steel in which the amount of MnO inclusions is reduced; and thereby, the amount of elongated MnS inclusions precipitated from MnO is reduced.
  • a steel is tapped in a non-deoxidized or weakly deoxidized state after being melted in an atmosphere refining furnace, and then a vacuum treatment is conducted at a degree of vacuum of 1 Torr or less so as to make the dissolved oxygen content be in a range of 30 ppm or less.
  • Al and Si are added, and then Mn is added.
  • Patent Document 6 discloses a method for manufacturing a high-carbon high-cleanliness molten steel with reduced amounts of oxygen and Al in the molten steel.
  • a rail having superior damage resistance can be manufactured by limiting the total amount of oxygen based on the relationship between the total oxygen value in oxide-based inclusions and the damage property.
  • the damage resistance of rails can be further improved by limiting the amount of solid-soluted Al or the composition of inclusions in a preferable range.
  • Patent Documents 4 to 6 control the configurations and amounts of MnS and Al-based inclusions generated in a bloom stage.
  • the configuration of inclusions is altered during hot rolling in the rolling of rails.
  • Mn sulfide-based inclusions elongated in the lengthwise direction by rolling act as the starting points of fracture in rails; and therefore, there is a problem in that the damage resistance or toughness of rails cannot be stably improved in the case where only the inclusions in the bloom stage is controlled.
  • Patent Document 7 just achieves the refinement of an austenite structure. This technology has no effect on damages due to Mn sulfide-based inclusions elongated in the lengthwise direction by rolling; and therefore, there is a problem in that the damage resistance and the toughness of rails cannot be stably improved.
  • the present invention has been made in consideration of the above problems, and the object of the present invention is to provide a pearlite rail in which both wear resistance and toughness are improved at the head portion that are particularly in demand as a rail for freight railways in overseas.
  • a pearlite rail according to the present invention consists of a steel comprising, in terms of percent by mass, C: 0.65% to 1.20%, Si: 0.05% to 2.00%, Mn: 0.05% to 2.00%, P ⁇ 0.0150%, S ⁇ 0.0100%, Ca: 0.0005% to 0.0200%, and Fe and inevitable impurities as the balance.
  • a head surface portion which ranges from surfaces of head corner portions and a head top portion to a depth of 10 mm has a pearlite structure, and a hardness Hv of the pearlite structure is in a range of 320 to 500.
  • Mn sulfide-based inclusions having major lengths in a range of 10 to 100 ⁇ m are present at an amount per unit area in a range of 10 to 200/mm 2 in a cross-section (a cross-section parallel to the longitudinal direction of the rail) taken along a lengthwise direction in the pearlite structure.
  • Hv refers to the Vickers hardness defined by JIS B7774.
  • the steel further indudes, in terms of percent by mass, either one or both ofMg: 0.0005 to 0.0200% and Zr: 0.0005 to 0.0100%, and Mg-based oxides, Zr oxides, and Mn sulfide-based inclusions having grain diameters in a range of 5 nm to 100 nm may be present at an amount per unit area in a range of 500 to 50,000/mm 2 in a transverse cross-section (a cross-section parallel to the width direction of the rail) in the pearlite structure.
  • Mg-based oxides, Zr oxides, and Mn sulfide-based inclusions having grain diameters in a range of 5 nm to 100 nm may be present at an amount per unit area in a range of 500 to 50,000/mm 2 in a transverse cross-section (a cross-section parallel to the width direction of the rail) in the pearlite structure.
  • the steel may further include, in terms of percent by mass, one or more of steel components described in the following (1) to (9).
  • the components, structure and hardness of a rail steel are controlled, and, in addition, the contents of P and S are reduced, Ca is added, and the number of Mn sulfide-based inclusions is controlled.
  • the wear resistance and toughness of a pearlite structure are improved; and as a result, it is possible to improve the usable period of a rail, particularly, for freight railways in overseas (overseas freight railways).
  • it is possible to further improve the toughness of the pearlite structure by adding Mg and Zr and controlling the number of fine Mn sulfide-based inclusions and Mg and Zr-based oxides; and as a result, it is possible to further improve the usable period.
  • FIG. 1 shows a cross-section perpendicular to the lengthwise direction of the pearlite rail having superior wear resistance and toughness according to the present invention.
  • a rail head portion 3 includes a head top portion 1 and head corner portions 2 situated at both ends of the head top portion 1.
  • One of the head corner portions 2 is a gauge corner (G. C.) portion that mainly comes into contact with wheels.
  • a portion ranging from surfaces of the head corner portions 2 and the head top portion 1 to a depth of 10 mm is called a head surface portion 3a (diagonal solid line area).
  • a portion ranging from the surfaces of the head corner portions 2 and the head top portion 1 to a depth of 20 mm is given a reference number 3b (diagonal dotted line area).
  • the inventors of the present invention studied a steel component system having a bad effect on the toughness of rails.
  • a test melting and a hot rolling test which simulated the equivalent hot rolling conditions for rails were conducted using steels of which the contents of P and S were varied while utilizing steels having a varied amount of carbon as a base; and thereby, prototypes of rails were manufactured.
  • the impact values of the prototypes were measured by an impact test, and the effects of the contents of P and S on the impact values were studied.
  • the inventors of the present invention clarified the generation mechanism of Mn sulfide-based inclusions elongated in the lengthwise direction.
  • a bloom is reheated to a temperature in a range of 1200°C to 1300°C, and then the bloom is subjected to hot rolling.
  • the inventors have investigated the relationship between the hot rolling conditions and the configuration of MnS. As a result, it was observed that, in the case where the rolling temperature was high or in the case where the rolling reduction rate was high during rolling, plastic deformation of soft Mn sulfide-based inclusions easily occurred; and thereby, the Mn sulfide-based inclusions were easily elongated in the lengthwise direction of rails.
  • the inventors of the present inventions studied methods to suppress the elongation of Mn sulfide-based inclusions.
  • Mn sulfide-base inclusions were generated from various kinds of oxides as nuclei.
  • the elongation could be suppressed by hardening inclusions which acted as the nuclei of the Mn sulfide-based inclusions.
  • the inventors of the present invention studied hard inclusions which acted as the nuclei of Mn sulfide-based inclusions. As a result of conducting a laboratory test using oxides with a high melting point, it was found that Ca with a relative high melting point formed sulfides and oxides, and formed CaO-CaS aggregates. In addition, the inventors have found that, since CaS has a high consistency with Mn sulfide-based inclusions, Mn sulfide-based inclusions were efficiently generated in the aggregates of the oxides and sulfides of Ca (CaO-CaS).
  • the consistency refers to a difference of lattice constants (interatomic distance) on crystal planes in the crystal structures of two metals. The smaller the difference is, the higher the consistency is. That is, it is considered that two metals are easily bonded.
  • the inventors of the present invention conducted test melting and a hot rolling test using steels including Ca in order to verify the above observation. As a result, it was observed that Mn sulfide-based inclusions generated from the aggregates of the oxides and sulfides of Ca (CaO-CaS) acting as the nuclei were rarely elongated after hot rolling; and consequently, the number of Mn sulfide-based inclusions elongated in the lengthwise direction was decreased.
  • the inventors of the present invention studied the relationship between the added amount of Ca and the added amount of S which enable oxides and sulfides to form aggregates by conducting test melting and a hot rolling test. As a result, it was observed that an appropriate number of Ca sulfides were generated and finely dispersed by controlling the ratio of the added amount of S and the added amount of Ca; and consequently, it was possible to further suppress the elongation of Mn sulfide-based inclusions after hot rolling.
  • the inventors of the present invention studied methods that suppress the grain growth of an austenite structure after hot rolling by using Mn sulfide-based inclusions and oxides. As a result of test melting and a hot rolling test, it was found that it is necessary to finely disperse nano-sized oxides and Mn sulfide-based inclusions, instead of alloy elements formerly used, in an austenite structure as pinning elements in order to stably suppress the grain growth of the austenite structure.
  • the inventors of the present invention studied methods that finely disperse oxides and Mn sulfide-based inclusions. As a result, it was observed that the oxides of Mg and Zr did not aggregate, but were finely and uniformly dispersed. Furthermore, it was observed that, since both Mg-based oxides and Zr oxides have a good consistency with Mn sulfide-based inclusions, Mn sulfide-based inclusions were also finely dispersed with the fine oxides as the nuclei.
  • the inventors of the present invention conducted a hot rolling test using steels including Mg and Zr. As a result, it was observed that nano-sized oxides and Mn sulfide-based inclusions were finely dispersed, and the grain growth of an austenite structure after hot rolling could be suppressed. Furthermore, as a result of conducting an impact test using these steels, it was observed that impact values were improved by the refinement of a pearlite structure in the steels including Mg and Zr.
  • the inventors of the present invention conducted a test melting of experimental steels by preparing steels including carbon at a content of 1.00% and P at a content in a range of 0.0150% or less, adding various contents of S, and further adding Ca, Mg and Zr.
  • the inventors conducted a laboratory rolling test which simulated the equivalent rolling conditions for rails so as to manufacture prototypes of rails.
  • the impact values of the prototypes were measured by an impact test, and the effects of the amount of S and the effects of the addition of Ca, Mg and Zr on the impact values were studied.
  • the hardness of the materials was set to an Hv level of 400 by controlling heat treatment conditions.
  • FIG. 2 shows the relationship between the amount of S (ppm) and the impact value.
  • the steels including C at a content of 1.00% ⁇ marks
  • the impact values were improved if the content of S was reduced to 0.0100% or less.
  • the results of the steels including Ca ⁇ marks
  • the generation of the elongated Mn sulfide-based inclusions were suppressed by the addition of Ca; and thereby, the impact values were improved.
  • Si is an essential element as a deoxidizing material.
  • Si is an element that increases the hardness (strength) of a rail head portion by solid solution strengthening in the ferrite phase in a pearlite structure.
  • Si is an element that suppresses the generation of proeutectoid cementite structures in hypereutectoid steels; and thereby, a decrease in toughness is suppressed.
  • the amount of Si is less than 0.05%, it is not possible to sufficiently expect such effects.
  • the amount of Si exceeds 2.00%, a number of surface defects are generated during hot rolling and weldability is degraded due to the generation of oxides.
  • the amount of Si is limited to be in a range of 0.05% to 2.00%.
  • the amount of Si is in a range of 0.20% to 1.30% in order to ensure hardenability and suppress the generation of martensite structure which is harmful to wear resistance or toughness.
  • Mn is an element that increases hardenability and refines pearlite lamellar spacing; and thereby, the hardness of the pearlite structure is ensured and wear resistance is improved.
  • the amount of Mn is less than 0.05%, such effects become small, and it becomes difficult to ensure wear resistance necessary for rails.
  • the amount of Mn exceeds 2.00%, hardenability is remarkably increased, and martensite structure is easy to generate which is harmful to wear resistance or toughness. Therefore, the amount of Mn added is limited to be in a range of 0.05% to 2.00%.
  • the amount of Mn is in a range of 0.40% to 1.30% in order to ensure hardenability and suppress the generation of martensite structure which is harmful to wear resistance or toughness.
  • the amount of P is an element inevitably included in steels.
  • the amount of P has a relationship with toughness, and, if the amount of P increases, the pearlite structure is embrittled due to the embrittlement of ferrite phases, and brittle fracture, that is, rail fracture is easy to occur. Therefore, the amount of P is desirably small in order to improve toughness.
  • the impact value As a result of experimentally observing the relationship between the impact value and the amount of P, it was observed that, in the case where the amount of P was reduced to 0.0150% or less, the segregation of P was remarkably reduced, the embrittlement of the pearlite structure which was the starting point of fracture was suppressed; and thereby, impact values were greatly improved.
  • the amount of P is limited to be in a range of 0.0150% or less.
  • the lower limit of the amount of P is not specified; however, about 0.0020% is considered to be the lower limit of the amount of P when actually manufacturing rails in view of dephosphorization capability in a refining process.
  • the amount of P is in a range of 0.0030% to 0.0100% in order to stably improve impact values.
  • the amount of S is an element inevitably included in steels.
  • the amount of S has a relationship with toughness, and if the amount of S increases, stress concentration occurs due to the coarsening of MnS or the increase of density of MnS; and thereby, brittle fracture, that is, rail damage is easy to occur. Therefore, the amount of S is desirably small in order to improve toughness.
  • the amount of S is limited to be in a range of 0.0100% or less.
  • the lower limit of the amount of S is not specified; however, about 0.0010% is considered to be the lower limit of the amount of S when actually manufacturing rails in view of desulfurization capability in a refining process.
  • the amount of S is in a range of 0.0060% or less in order to suppress generation of elongated Mn sulfide-based inclusions and stably improve impact values.
  • the amount of S is in a range of 0.0020% to 0.0035% in order to stably generate fine Mn sulfide-based inclusions which pin the austenite structure and to suppress the generation of elongated Mn sulfide-based inclusions.
  • Ca is a deoxidizing and desulfurizing element, and aggregates of the oxides and sulfides of calcium (CaO-CaS) are generated by the addition of Ca. These aggregates act as nuclei for the generation of Mn sulfide-based inclusions; and thereby, the elongation of Mn sulfide-based inclusions is suppressed after hot rolling. Furthermore, nano-sized Mn sulfide-based inclusions are formed from these aggregates as nuclei (formed by utilizing the aggregates as nuclei). Ca is an element having such functional effects.
  • the amount of Ca is less than 0.0005%, such effects become small, and the aggregates cannot sufficiently act as nuclei for the generation of Mn sulfide-based inclusions.
  • the amount of Ca exceeds 0.0200%, the amount of independent hard CaO which does not act as the nuclei for Mn sulfide-based inclusions is increased depending on the amount of oxygen in a steel. As a result, the toughness of a rail steel is greatly degraded. Therefore, the amount of Ca is limited to be in a range of 0.0005% to 0.0200%.
  • the amount of Ca is in a range of 0.0015% to 0.0150% in order to improve impact values by stably suppressing the generation of elongated Mn sulfide-based inclusions and by suppressing in advance the generation of hard CaO which does not act as the nuclei for Mn sulfide-based inclusions and is harmful to toughness.
  • S and Ca generate the aggregates of the oxides and sulfides (CaO-CaS). These aggregates act as nuclei for Mn sulfide-based inclusions; and therefore, the aggregates greatly affect the elongation of Mn sulfide-based inclusions. Therefore, it is important to control the amount of S and the amount of Ca. In view of these circumstances, steels with varied amounts of S and Ca were test-melted, and a hot rolling test was conducted.
  • the value of S/Ca is less than 0.45
  • the amount of independent hard CaO which does not act as nuclei for Mn sulfide-based inclusions is slightly increased.
  • the toughness of rail steels is degraded.
  • the value of S/Ca exceeds 3.00
  • the number of the aggregates of sulfides (CaO-CaS) which act as nuclei for Mn sulfide-based inclusions is reduced; and thereby, the elongation of Mn sulfide-based inclusions is promoted.
  • the ratio of S/Ca is in a range of 0.45 to 3.00.
  • the present invention preferably includes either one or both of Mg and Zr.
  • Mg is a deoxidizing element that is mainly bonded with O to form a complex of fine nano-sized oxides (MgO) and sulfides (MgS). Nano-sized Mn sulfide-based inclusions are formed from the complexes as nuclei (formed by utilizing the complexes as nuclei). As a result, the grain growth of an austenite structure after hot rolling is suppressed; and thereby, the structure of rail steel is refined. As a result, it is possible to improve the toughness of a pearlite structure.
  • the amount of Mg is less than 0.0005%, the generated amount of the complexes of fine oxides (MgO) and sulfides (MgS) is small; and thereby, the effect of suppressing the grain growth of an austenite structure after hot rolling cannot be sufficiently obtained.
  • the amount of Mg exceeds 0.0200%, the coarse oxides of Mg are generated; and thereby, the toughness of rails is degraded, and simultaneously, fatigue damage occurs from the coarse oxides. Therefore, the amount of Mg is limited to be in a range of 0.0005% to 0.0200%.
  • the amount of Mg is in a range of 0.0010% to 0.0050% in order to improve impact values by sufficiently ensuring the generated amount of fine oxides (MgO) which pin an austenite structure and the generated amount of the complexes of the oxides (MgO) and sulfides (MgS) which form nano-sized Mn sulfide-based inclusions, and by sufficiently suppressing the generation of coarse oxides which are harmful to fatigue damage.
  • MgO fine oxides
  • MgS sulfides
  • Zr is a deoxidizing element that is mainly bonded with O so as to form fine nano-sized oxides (ZrO 2 ). These oxides are dispersed finely and uniformly, and furthermore, nano-sized Mn sulfide-based inclusions are formed from the oxides as nuclei (formed by utilizing the oxides as nuclei). As a result, the grain growth of an austenite structure after hot rolling is suppressed; and thereby, the structure of a rail steel is refined. As a result, it is possible to improve the toughness of a pearlite structure.
  • the amount of Zr is less than 0.0005%, the generated amount of fine oxides (ZrO 2 ) is small; and thereby, the effect of suppressing the grain growth of an austenite structure after hot rolling cannot be sufficiently obtained.
  • the amount of Zr exceeds 0.0100%, the coarse oxides of Zr are generated; and thereby, the toughness of rails is degraded, and simultaneously, fatigue damage occurs from the coarse precipitates. Therefore, the amount of Zr added is limited to be in a range of 0.0005% to 0.0100%.
  • the amount of Mg is in a range of 0.0010% to 0.0050% in order to improve impact values by sufficiently ensuring the generated amount fine oxides (ZrO 2 ) which pin an austenite structure and the generated amount of oxides (ZrO 2 ) which form nano-sized Mn sulfide-based inclusions, and by sufficiently suppressing the generation of coarse oxides which are harmful to fatigue damage.
  • rails manufactured in the above-described component composition preferably include one or more elements selected from the group consisting of Co, Cr, Mo, V, Nb, B, Cu, Ni, Ti, Al and N for the purpose of the improvement in the hardness (strength) of a pearlite structure or a proeutectoid ferrite structure, the improvement in toughness, the prevention of softening in weld heat-affected zones, and the control of the cross-sectional hardness distribution inside the rail head portion.
  • Co refines a lamellar structure in a rolling contact surface and decreases ferrite grain diameter; and thereby, the wear resistance of a pearlite structure is increased.
  • Cr and Mo increase the equilibrium transformation point, and mainly refine pearlite lamellar spacing; and thereby, the hardness of a pearlite structure is ensured.
  • V and Nb generate carbides and nitrides in a hot rolling process and a subsequent cooling process; and thereby, the growth of austenite grains is suppressed. Furthermore, V and Nb precipitate and harden in a ferrite structure and a pearlite structure; and thereby, the toughness and hardness of a pearlite structure are improved.
  • V and Nb stably generate carbides and nitrides; and thereby, the softening of welded joint heat-affected zones is prevented.
  • B reduces the dependency of the pearlite transformation temperature on a cooling rate; and thereby, the hardness distribution in the rail head portion is made uniform.
  • Cu is solid-solubilized in a ferrite structure and in a ferrite phase in a pearlite structure; and thereby, the hardness of the pearlite structure is increased.
  • Ni improves the toughness and hardness of a ferrite structure and a pearlite structure, and simultaneously, Ni prevents the softening of welded joint heat-affected zones.
  • Ti refines the structure in weld heat-affected zones and prevents the embrittlement of welded joint heat-affected zones.
  • Al raises the eutectoid transformation temperature to a higher temperature, and increases the hardness of a pearlite structure.
  • N segregates in austenite grain boundaries; and thereby, pearlite transformation is accelerated. In addition, N refines the size of pearlite blocks; and thereby, toughness is improved.
  • Co is solid-solubilized in a ferrite phase in a pearlite structure.
  • fine ferrite structure formed by the contact with wheels at the rolling contact surface of the rail head portion is further refined; and as a result, wear resistance is improved.
  • the amount of Co is less than 0.01%, the refinement of ferrite structure is not achieved; and therefore, it is not possible to expect the effect of improving the wear resistance.
  • the amount of Co exceeds 1.00%, the above-described effect is saturated; and therefore, the refinement of ferrite structure corresponding to the added amount of Co is not achieved.
  • an increase in the cost for adding alloy elements degrades economic efficiency. Therefore, the amount of Co is limited to be in a range of 0.01% to 1.00%.
  • Cr increases the equilibrium transformation temperature, and consequently Cr refines ferrite structure and pearlite structure; and thereby, Cr contributes to an increase of hardness (strength). At the same time, Cr strengthens cementite phase; and thereby, the hardness (strength) of pearlite structure is improved.
  • the amount of Cr is less than 0.01 %, such an effect becomes small, and the effect of improving the hardness of a rail steel is not observed at all.
  • Cr is excessively added at an amount of more than 2.00%, hardenability is increased, and martensite structure is generated. Thereby, spalling damage starting from the martensite structure occurs in the head corner portions and the head top portion; and as a result, resistance to surface damages is degraded. Therefore, the amount of Cr is limited to be in a range of 0.01 % to 2.00%.
  • Mo similarly to Cr, increases the equilibrium transformation temperature, and consequently Mo refines ferrite structure and pearlite structure; and thereby, Mo contributes to an increase of hardness (strength). Therefore, Mo is an element that improves hardness (strength).
  • the amount of Mo is less than 0.01%, such an effect becomes small, and the effect of improving the hardness of rail steels is not observed at all.
  • Mo is excessively added at an amount of more than 0.50%, transformation rate is remarkably degraded. Thereby, spalling damage starting from the martensite structure occurs in the head corner portions and the head top portion; and as a result, resistance to surface damages is degraded. Therefore, the amount of Mo is limited to be in a range of 0.01% to 0.50%.
  • V refines austenite grains due to the pinning effect of V carbides and V nitrides in the case where a heat treatment is conducted at high temperatures. Furthermore, V increases the hardness (strength) of ferrite structure and pearlite structure due to the precipitation hardening of V carbides and V nitrides generated in the cooling process after hot rolling, and simultaneously, V improves toughness. V is an effective element to obtain those effects. In addition, in heat-affected portions that are reheated to a temperature in a range of Ac1 or less, V is an effective element to prevent the softening of welded joint heat-affected zones by generating V carbides and V nitrides in a relatively high temperature range.
  • the amount of V is less than 0.005%, such an effect cannot be sufficiently expected, and the improvement in the hardness and the toughness of the ferrite structure and the pearlite structure is not observed.
  • the amount of V exceeds 0.50%, the precipitation hardening of the carbides and nitrides of V becomes excessive, and the toughness of the ferrite structure and the pearlite structure is degraded. Thereby, spalling damage occurs in the head corner portions and the head top portion; and as a result, resistance to surface damages is degraded. Therefore, the amount of V is limited to be in a range of 0.005% to 0.50%.
  • Nb similarly to V, refines austenite grains due to the pinning effect of Nb carbides and Nb nitrides in the case where a heat treatment is conducted at high temperatures. Furthermore, Nb increases the hardness (strength) of ferrite structure and pearlite structure due to the precipitation hardening ofNb carbides and Nb nitrides generated in the cooling process after hot rolling, and simultaneously, Nb improves toughness. Nb is an effective element to obtain those effect.
  • Nb is an effective element to prevent the softening of welded joint heat-affected zones by stably generating the carbides of Nb and the nitrides of Nb from a low temperature range to a high temperature range.
  • the amount of Nb is less than 0.002%, such an effect cannot be expected, and the improvement in the hardness and the the toughness of the ferrite structure and the pearlite structure is not observed.
  • the amount ofNb exceeds 0.050%, the precipitation hardening of the carbides and nitrides ofNb becomes excessive, and the toughness of ferrite structure and the pearlite structure is degraded. Thereby, spalling damage occurs in the head corner portions and the head top portion; and as a result, resistance to surface damages is degraded. Therefore, the amount ofNb is limited to be in a range of 0.002% to 0.050%.
  • B forms iron borocarbides (Fe 23 (CB) 6 ) in austenite grain boundaries, and B accelerates pearlite transformation.
  • This effect of accelerating pearlite transformation reduces the dependency of the pearlite transformation temperature on a cooling rate; and thereby, more uniform hardness distribution is achieved from the head surface portion to the inside portion of a rail. Therefore, it is possible to extend the usable period of the rail.
  • the amount of B is less than 0.0001 %, those effects are not sufficient, and improvement of the hardness distribution in the rail head portion is not observed.
  • the amount of B exceeds 0.0050%, coarse iron borocarbides are generated; and thereby, toughness is degraded. Therefore, the amount of B is limited to be in a range of 0.0001% to 0.0050%.
  • Cu is an element that is solid-solubilized in a ferrite structure and in a ferrite phase in a pearlite structure, and Cu improves the hardness (strength) of the pearlite structure due to solid solution strengthening.
  • the amount of Cu is less than 0.01%, those effects cannot be expected.
  • the amount of Cu exceeds 1.00%, martensite structure, which is harmful to toughness, is generated by the remarkable improvement of hardenability. Thereby, spalling damage occurs in the head corner portions and the head top portion; and as a result, resistance to surface damages is degraded. Therefore, the amount of Cu is limited to be in a range of 0.01 % to 1.00%.
  • Ni is an element that improves toughness of a ferrite structure and a pearlite structure, and simultaneously, Ni increases hardness (strength) by solid solution strengthening. Furthermore, Ni finely precipitates intermetallic compound of Ni 3 Ti, which is a complex compound with Ti, in weld heat-affected zones; and thereby, softening is suppressed by precipitation strengthening. In the case where the amount of Ni is less than 0.01 %, those effects are extremely small. In the case where the amount of Ni exceeds 1.00%, toughness of a ferrite structure and a pearlite structure is remarkably degraded. Thereby, spalling damage occurs in the head corner portions and the head top portion; and as a result, resistance to surface damages is degraded. Therefore, the amount ofNi is limited to be in a range of 0.0 1 % to 1.00%.
  • Ti is an effective element that refines the structure of heat-affected zones which are heated to an austenite range by utilizing the fact that carbides of Ti and nitrides of Ti, which are precipitated during the reheating in welding, are not melted; and thereby, Ti prevents the embrittlement of welded joint portions.
  • the amount of Ti is less than 0.0050%, those effects are small, and in the case where the amount of Ti exceeds 0.0500%, coarse carbides of Ti and nitrides of Ti are generated; and thereby, toughness of a rail is degraded. At the same time, fatigue damage occurs due to coarse precipitates. Therefore, the amount of Ti is limited to be in a range of 0.0050% to 0.050%.
  • Al is an essential element as a deoxidizing material.
  • Al is an element that raises the eutectoid transformation temperature to a higher temperature, and Al contributes to an increase in the hardness (strength) of a pearlite structure.
  • the amount of Al is 0.0100% or less, those effects are small.
  • the amount of Al exceeds 1.00%, it becomes difficult to solid-solubilize Al in a steel; and thereby, coarse alumina-based inclusions are generated. Thereby, toughness of a rail is degraded, and simultaneously, fatigue damage occurs due to coarse precipitates. Furthermore, oxides are generated during welding; and thereby, weldability is degraded remarkably. Accordingly, the amount of Al is limited to be in a range of more than 0.0100% to 1.00%.
  • N segregates in austenite grain boundaries; and thereby, N accelerates ferrite transformation and pearlite transformation from the austenite grain boundaries.
  • the size of pearlite blocks is mainly refined; and thereby, it is possible to improve toughness.
  • the amount of N is less than 0.0060%, those effects are small.
  • the amount ofN exceeds 0.0200%, it becomes difficult to solid-solubilize N in a steel. As a result, air bubbles which act as the starting points of fatigue damage are generated; and thereby, fatigue damage occurs inside the rail head portion. Therefore, the amount ofN is limited to be in a range of 0.0060% to 0.0200%.
  • the head surface portion 3 a of a rail includes a pearlite structure and the hardness Hv thereof is limited to be in a range of 320 to 500 will be described.
  • the hardness Hv of the pearlite structure in the case where the hardness Hv of the pearlite structure is less than 320, it becomes difficult to ensure the wear resistance of the head surface portion 3a of the rail; and thereby, the usable period of the rail is reduced. In addition, flaking damage occurs in the rolling contact surface due to plastic deformation; and thereby, the resistance to surface damages in the rail head surface portion 3a is greatly degraded. In addition, in the case where the hardness Hv of a pearlite structure exceeds 500, the toughness of the pearlite structure is greatly degraded; and thereby, the damage resistance in the rail head surface portion 3a is degraded. Therefore, the hardness Hv of the pearlite structure is limited to be in a range of 320 to 500.
  • the head surface portion 3a of a rail refers to, as shown in FIG. 1 , a portion ranging from surfaces of the head corner portions 2 and the head top portion 1 to a depth of 10 mm (diagonal solid line area). If a pearlite structure having the above-described components is disposed in the head surface portion 3a, abrasion due to the contact with wheels is suppressed; and thereby, the wear resistance of the rail is improved.
  • a pearlite structure having a hardness Hv in a range of 320 to 500 at or in the vicinity of the surface of the rail head portion 3, with which the wheels mainly contact, and other portions may be a metallographic structure other than the pearlite structure.
  • the metallographic structure in the head surface portion 3 a or in the portion 3b which ranging to a depth of 20 mm and including the head surface portion 3a consists of the above-described pearlite structure.
  • the pearlite structure is mixed with proeutectoid ferrite structure, proeutectoid cementite structure, bainite structure and martensite structure at a small amount, for example, an area ratio of 5% or less.
  • the above-described pearlite structure may include structures mixed with proeutectoid ferrite structure, proeutectoid cementite structure, bainite structure, martensite structure or the like at an area ratio of 5% or less.
  • 95% or more of the metallographic structure in the head surface portion 3a or the portion 3b ranging to a depth of 20 mm and including the head surface portion 3a needs to be a pearlite structure, and it is preferable that 98% or more of the metallographic structure in the head portion be a pearlite structure in order to sufficiently ensure wear resistance and toughness.
  • the description 'small amount' refers to a content of 5% or less, and structures other than a pearlite structure without the description 'small amount' mean that the structures are included at an amount of more than 5% (out of the range of the present invention).
  • the length of the major axis (major length) of Mn sulfide-based inclusions in an arbitrary cross-section taken along the lengthwise direction, which are evaluation subjects, is limited to be in a range of 10 ⁇ m to 100 ⁇ m will be described in detail.
  • Mn sulfide-based inclusions having a long length of the major axis, in which stress concentration occurs remarkably, have a large effect on damage resistance
  • Mn sulfide-based inclusions having a short length of the major axis have a small effect on the damage resistance.
  • Mn sulfide-based inclusions having a length exceeding 100 ⁇ m which are not suitable to identify the characteristics of the steels.
  • Mn sulfide-based inclusions having a length of less than 10 ⁇ m have a small effect on the damage resistance. Therefore, Mn sulfide-based inclusions having the above-described lengths of the major axis (major lengths) are used as evaluation subjects.
  • the total number (per unit area) of Mn sulfide-based inclusions having major lengths in a range of 10 ⁇ m to 100 ⁇ m is less than 10 /mm 2
  • trap sites which absorb inevitable hydrogen remaining in the steel are remarkably reduced.
  • the possibility of inducing hydrogenous defects (hydrogen embrittlment) increases; and thereby, the damage resistance of the rail is impaired.
  • the total number (per unit area) of Mn sulfide-based inclusions having major lengths in a range of 10 ⁇ m to 100 ⁇ m is limited to be in a range of 10 /mm 2 to 200 /mm 2 .
  • the Mn sulfide-based inclusions refer to both of Mn sulfide-based inclusions generated from aggregates of oxides and sulfides of calcium (CaO-CaS) as nuclei and other Mn sulfide-based inclusions as evaluation subjects.
  • a sample is taken from a cross-section taken along the lengthwise direction of the rail head portion 3, in which the rail damage becomes obvious as shown in FIG. 3 , and the measurement of sulfide-based inclusions is conducted.
  • the cross-section in the lengthwise direction of the rail of each of the taken samples is mirror-polished, and Mn sulfide-based inclusions are investigated on an arbitrary cross-section with an optical microscope. Then, the number of inclusions having the above-limited sizes is counted and calculated as the number per unit cross-section area.
  • the typical value of each rail steel is obtained from the average value of the numbers per unit cross-section area of these 20 viewing fields.
  • the location (portion) to be used to investigate Mn sulfide-based inclusions is not particularly limited; however, it is preferable to observe a portion ranging from the surface of the rail head portion 3, which acts as the starting point of damage, to a depth of 3 to 10 mm.
  • Mn sulfide-based inclusions which act as the starting points of fracture and by suppressing hydrogenous defects in advance
  • Mg-based oxides, Zr oxides, and Mn sulfide-based inclusions having grain diameters in a range of 5 nm to 100 nm are present at an amount per unit area in a range of 500/mm 2 to 50,000/mm 2 in an arbitrary transverse cross-section.
  • the grain diameters of Mg-based oxides, Zr oxides and Mn sulfide-based inclusions is in a range of from 5 nm to 100 nm, a sufficient pinning effect is obtained in grain boundaries when they are generated in an austenite structure. Thereby, it was observed that, without adversely affecting the damage resistance of a rail, consequently, a pearlite structure was refined; and thereby, toughness was reliably improved. Therefore, the grain diameters of Mg-based oxides, Zr oxides and Mn sulfide-based inclusions eligible for the evaluation subjects is limited to be in a range of 5 nm to 100 nm.
  • Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of less than 5 nm it is extremely difficult to measure the number thereof.
  • Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of more than 100 nm the above-described pinning effect cannot be obtained. Therefore, Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having the above-described grain diameters are used as evaluation subjects.
  • the reason why the amount (number) (per mm 2 ) of Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of 5 nm to 100 nm in an arbitrary cross-section in the lengthwise direction is limited to be in a range of 500 to 50,000 will be described in detail.
  • the pinning effect is not sufficiently obtained in an austenite structure after hot rolling. As a result, a pearlite structure becomes coarsened, and toughness of the rail is not improved.
  • the total number (per unit area) of Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of 5 nm to 100 nm exceeds 50,000/mm 2 , precipitation occurs excessively, and a pearlite structure becomes embrittled; and thereby, the toughness of the rail is degraded. Therefore, the total number (per unit area) of Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of 5 nm to 100 nm is limited to be in a range of 500/mm 2 to 50,000/mm 2 .
  • the Mg-based oxides and the Zr oxides refer to oxides partially including complex oxides such as Mn sulfide or the like.
  • the Mn sulfide-based inclusions refer to inclusions generated from fine oxides such as Mg oxides, Zr oxides, Ca oxides or the like, as nuclei.
  • the grain diameter and the number of the Mg-based oxides, the Zr oxides and the Mn sulfide-based inclusions are observed and measured in the following manner.
  • a thin film is taken from an arbitrary transverse cross-section shown in FIG. 4 , and the thin film is observed at a magnification of 50,000 to 500,000 using a transmission electron microscope.
  • the grain diameter of precipitates is obtained by measuring the area of each precipitate through observation and calculating the diameter of a circle having the same area as that of the precipitate.
  • the precipitates are observed at 20 viewing fields, and the number of precipitates having diameters in a predetermined range of 5 nm to 100 nm is counted, and the number per unit area is calculated from the counted number.
  • the typical value of a rail steel is obtained from the average value of these 20 viewing fields.
  • the location (portion) to be used to investigate the Mg-based oxides, the Zr oxides, and the Mn sulfide-based inclusions is not particularly limited; however, it is preferable to observe a portion ranging from the surface of the rail head surface portion 3a to a depth of 3 mm to 10 mm, which requires toughness.
  • the method for manufacturing the rail steel according to the present invention including the above-described component composition and microstructure is not particularly limited; however, in general, the rail steel is manufactured by the following method. At first, melting is conducted so as to obtain molten steel with a commonly used melting furnace such as a converter furnace, an electric furnace or the like. Then, the molten steel is subjected to an ingot-making and blooming method or a continuous casting method so as to manufacture a bloom (a steel ingot) for rolling. Furthermore, the bloom is reheated to 1200°C or more, and then, the bloom is subjected to several passes of hot rolling, and molded into rails. Thereafter, heat treatments (reheating and cooling) are conducted so as to manufacture a rail.
  • a commonly used melting furnace such as a converter furnace, an electric furnace or the like.
  • the molten steel is subjected to an ingot-making and blooming method or a continuous casting method so as to manufacture a bloom (a steel ingot) for rolling. Furthermore, the bloom is
  • the hot metal step it is preferable to conduct general dephosphorization treatment and desulfurization treatment in a careful manner to achieve the reduction of the amounts of P and S.
  • the addition of CaO is a method conducted in the case where S is reduced from a hot metal having an extremely large amount of S. Unlike the addition of CaO-Si alloy, which is added to generate aggregates of oxides and sulfides of calcium (CaO-CaS), as described below, this method has no influence.
  • dephosphorization it is preferable, in refining in a converter furnace, to eject slag in the middle of refining in order to prevent P from being melted again from the slag including P (P 2 O 5 or the like) separated by dephosphorization.
  • a preferable adding method of Ca is either adding Ca alloy (Ca-Si alloy or the like) wires or Ca alloy ingots in a ladle or injecting a Ca alloy powder.
  • the Ca alloy As the Ca alloy, a Ca-Si alloy (50Ca-50Si or the like), a Fe-Si-Ca alloy (Fe-30Si-30Ca or the like) and a Ni-Ca alloy (90Ni-10Ca or the like) are used. Since the vapor pressure of Ca is high, if pure Ca is added, splashing occurs in a molten steel, or slag on the surface of the molten steel is involved into the molten steel; and thereby, the purity of the molten steel is degraded. In addition, the yield rate becomes low. Consequently, the addition of a Ca alloy, for example, a Ca-Si alloy is widely conducted. Compared with pure Ca, the activity of Ca is lowered in the Ca alloy. Therefore, in the case of adding the Ca alloy, vaporization during the addition becomes relatively gentle, and the yield rate is also improved.
  • Ca may be added to a tundish in a casting process, instead of the refining process. It is necessary to adjust the addition rate of a Ca alloy depending on the throughput during casting (the casting amount per hour). In this case, since the stirring of the molten steel after the addition of Ca is conducted inside the tundish or a casting mold, the uniformity of the concentration of Ca is slightly worse than that in the case of adding Ca in the ladle.
  • the amount of oxygen in the molten steel so as to suppress the generation of an excessive amount of CaO.
  • Mg alloy Fe-Si-Mg, Fe-Mn-Mg, Fe-Si-Mn-Mg and Si-Mg
  • Zr alloy Fe-Si-Zr, Fe-Mn-Mg-Zr and Fe-Si-Mn-Mg-Zr
  • the temperature at which the final molding is conducted is preferably in a range of 900°C to 1000°C from the viewpoint of ensuring the shape and material.
  • the heat treatment after the hot rolling it is preferable to conduct accelerated cooling on a rail head portion 3 at high temperatures including austenite regions after hot rolling or reheating in order to obtain a pearlite structure with a hardness Hv of 320 to 500 in the rail head portion 3.
  • accelerated cooling method by conducting the heat treatment (and cooling) with a method described in Patent Document 8 (Japanese Unexamined Patent Application, Publication No. H08-246100 ) or Patent Document 9 (Japanese Unexamined Patent Application, Publication No. H09-111352 ), it is possible to obtain a structure and hardness in predetermined ranges.
  • Tables 1 to 6 show the chemical components of tested rail steels. Here, the balance consists of Fe and inevitable impurities. Rail steels having the component compositions shown in Tables 1 to 6 were manufactured in the following manner.
  • Dephosphorization and desulfurization were conducted in a hot metal step, and, furthermore, sufficient dephosphorization and desulfurization were conducted in a commonly used melting furnace such as a converter furnace, an electric furnace or the like so as to obtain molten steel.
  • Ca was added to the molten steel so as to control Mn sulfide-based inclusions, or Mg and Zr were further added so as to finely disperse nano-sized oxides and Mn sulfide-based inclusions.
  • a steel ingot was manufactured by a continuous casting method, and hot rolling was conducted on the steel ingot. Thereafter, a heat treatment was conducted so as to manufacture a rail.
  • FIG. 3 shows a location at which Mn sulfide-based inclusions were observed in the rail steel.
  • FIG. 4 shows a location at which Mn sulfide-based inclusions, Mg-based oxides and Zr oxides were observed in the rail steel.
  • the number (per unit area) (inclusions/mm 2 ) of Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of 5 nm to 100 nm was obtained by the above-described method.
  • a sample was cut off from a portion situated at a depth of 4 mm from the surface of the rail head portion 3. Thereafter, a surface to be observed was polished, and then the surface was etched with nital etching fluid. The microstructure in the surface to be observed was observed using an optical microscope in accordance with JIS G 0551.
  • the Vickers hardness Hv of the cut-off sample was measured.
  • the Vickers hardness was measured while a diamond indenter was loaded on the sample at a load of 98 N (10 kgf).
  • the Vickers hardness is expressed as (Hv, 98N) in Tables.
  • the 'Head portion material *1' refers to a material in a portion situated at a depth of 4 mm from the surface of the rail head portion 3.
  • Table 7 Rail Steel Number of Mn sulfide-based inclusions having major lengths in a range of 10 ⁇ m to 100 ⁇ m (/mm 2 ) Number of Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of 5 nm to 100 nm (/mm 2 )
  • FIG. 5 shows a location from which a test specimen for the wear test was taken, and the numeric values in the drawing show dimensions (mm).
  • a disk-like test specimen was cut off from a portion including the head surface portion 3a in the rail steel.
  • two opposing rotation axes were prepared, the disk-like test specimen (rail test specimen 4) was disposed at one of the rotation axis, and an opponent material 5 was disposed at the other rotation axis.
  • the rail test specimen 4 and the opponent material 5 were brought into contact in a state where a predetermined load was applied to the rail test specimen 4.
  • the two rotation axes were rotated at a predetermined speed while cooling the test specimen by supplying a compressed air from a cooling nozzle 6.
  • the reduced amount (abraded amount) of the weight of the rail test specimen 4 was measured.
  • FIG. 7 shows a location from which a test specimen for the impact test was taken.
  • a test specimen was cut off along the rail width direction (transverse cross-section) in the transverse cross-section of the rail steel so that a portion including the head surface portion 3a forms the bottom of a notch. Then, the obtained test specimen was subjected to an impact test under the following conditions; and thereby, impact values (J/cm 2 ) were measured.
  • the obtained results are shown in Tables 13 to 15.
  • the 'Wear test results *2' refer to the results of the above-described wear test, and the reduced amount (g) of the weight of the rail test specimen 13 is expressed as the abraded amount.
  • the 'Impact test results *3' refer to the results of the above-described impact test of the head portion and show impact values (J/cm 2 ). Meanwhile, a larger impact value (J/cm 2 ) means a more superior toughness.
  • Rails according to the present invention 47 rails
  • pearlite rails having superior wear resistance and toughness which have the chemical compositions within the above-described limited range of the present invention and of which the number of Mn sulfide-based inclusions having major lengths (lengths of major axes) in a range of 10 ⁇ m to 100 ⁇ m, the microstructure of the rail head portion and the hardness are within the limited ranges of the present invention.
  • pearlite rails having superior wear resistance and toughness which have the chemical compositions within the above-described limited range of the present invention and of which the number of Mn sulfide-based inclusions having major lengths (lengths of major axes) in a range of 10 ⁇ m to 100 ⁇ m, the number of Mg-based oxides, Zr oxides and Mn sulfide-based inclusions having grain diameters in a range of 5 nm to 100 nm, the microstructure of the rail head portion and the hardness are within the limited ranges of the present invention.
  • the rail steels according to the present invention include C, Si and Mn at contents within the limited ranges of the present invention. Therefore, it is possible to stably obtain a pearlite structure having a hardness within the limited range of the present invention without generating eutectoid ferrite structure, eutectoid cementite structure and martensite structure, which adversely affect the wear resistance and the toughness.
  • the rail steels according to the present invention include a pearlite structure in the microstructure of the head portion, and the hardness of the pearlite structure is within the limited range of the present invention. As a result, it is possible to improve the wear resistance and the toughness of the rail.
  • FIG. 8 shows the results of the wear test of the rail steels according to the present invention (Steel Nos. 1 to 47) and Comparative rail steels (Steel Nos. 48, 50, 51, 52, 53, 64, 66 and 67).
  • FIG. 9 shows the results of the impact test of the rail steels according to the present invention (Steel Nos. 1 to 47) and Comparative rail steels (Steel Nos. 49, 51, 53, 65, 66 and 68).
  • the rail steels according to the present invention include P, S and Ca at amounts within the limited ranges of the present invention. Thereby, it is possible to greatly improve the toughness of the pearlite rails with any amount of carbon.
  • the rail steels according to the present invention include Ca, and furthermore, the added amount of Ca is optimized.
  • Mn sulfide-based inclusions are controlled so that the number thereof is within the limited range of the present invention. As a result, it is possible to improve the toughness of the pearlite rail.
  • oxides and Mn sulfide-based inclusions are finely dispersed so that the number of Mg-based oxides, Zr oxides and Mn sulfide-based inclusions is made to be in a range of 500/mm 2 to 50,000/mm 2 . Thereby, it is possible to further improve the toughness of the pearlite rail.
  • the pearlite rail according to the present invention has wear resistance and toughness superior to those of a high-strength rail in current use. Therefore, the present invention can be preferably applied to rails used in an extremely severe track environment, such as rails for freight railways that transport natural resources mined from regions with severe natural environments.

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EP09823351.3A 2008-10-31 2009-10-30 Pearlite rail having superior abrasion resistance and excellent toughness Not-in-force EP2343390B1 (en)

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RU2461639C1 (ru) 2012-09-20
BRPI0918859B1 (pt) 2021-05-04
ES2550793T3 (es) 2015-11-12
CN102137947A (zh) 2011-07-27
JPWO2010050238A1 (ja) 2012-03-29
AU2009308639B2 (en) 2015-07-02
PL2343390T3 (pl) 2016-01-29
BRPI0918859A2 (pt) 2015-12-01
KR101263102B1 (ko) 2013-05-09
JP4757957B2 (ja) 2011-08-24
EP2343390A1 (en) 2011-07-13
WO2010050238A1 (ja) 2010-05-06
CA2734980C (en) 2014-10-21
CN102137947B (zh) 2013-03-20
CA2734980A1 (en) 2010-05-06
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EP2343390A4 (en) 2014-06-25
US20110155821A1 (en) 2011-06-30

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