CA2936780C - Rail and method for manufacturing same - Google Patents
Rail and method for manufacturing same Download PDFInfo
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- CA2936780C CA2936780C CA2936780A CA2936780A CA2936780C CA 2936780 C CA2936780 C CA 2936780C CA 2936780 A CA2936780 A CA 2936780A CA 2936780 A CA2936780 A CA 2936780A CA 2936780 C CA2936780 C CA 2936780C
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- 238000004519 manufacturing process Methods 0.000 title claims description 19
- 238000000034 method Methods 0.000 title description 16
- 239000000126 substance Substances 0.000 claims abstract description 18
- 239000000203 mixture Substances 0.000 claims abstract description 17
- 239000012535 impurity Substances 0.000 claims abstract description 12
- 238000001816 cooling Methods 0.000 claims description 79
- 238000005096 rolling process Methods 0.000 claims description 69
- 229910000831 Steel Inorganic materials 0.000 claims description 28
- 239000010959 steel Substances 0.000 claims description 28
- 238000005098 hot rolling Methods 0.000 claims description 18
- 238000010438 heat treatment Methods 0.000 claims description 17
- 230000009467 reduction Effects 0.000 claims description 14
- 239000002994 raw material Substances 0.000 claims description 11
- 230000001186 cumulative effect Effects 0.000 claims description 7
- 230000001747 exhibiting effect Effects 0.000 claims description 4
- 230000002829 reductive effect Effects 0.000 abstract description 2
- 102100035793 CD83 antigen Human genes 0.000 abstract 1
- 101000946856 Homo sapiens CD83 antigen Proteins 0.000 abstract 1
- 238000012360 testing method Methods 0.000 description 25
- 230000000052 comparative effect Effects 0.000 description 23
- 230000000694 effects Effects 0.000 description 15
- 239000000463 material Substances 0.000 description 15
- 229910001562 pearlite Inorganic materials 0.000 description 14
- 230000009466 transformation Effects 0.000 description 12
- 229910000734 martensite Inorganic materials 0.000 description 10
- 229910001566 austenite Inorganic materials 0.000 description 9
- 230000007423 decrease Effects 0.000 description 9
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 8
- 239000003595 mist Substances 0.000 description 8
- 230000015572 biosynthetic process Effects 0.000 description 7
- 229910052758 niobium Inorganic materials 0.000 description 7
- 230000002441 reversible effect Effects 0.000 description 7
- 230000008859 change Effects 0.000 description 4
- 238000001953 recrystallisation Methods 0.000 description 4
- 238000009628 steelmaking Methods 0.000 description 4
- 229910001567 cementite Inorganic materials 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 238000009749 continuous casting Methods 0.000 description 3
- 238000005261 decarburization Methods 0.000 description 3
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 238000005065 mining Methods 0.000 description 3
- 238000007670 refining Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 229910001563 bainite Inorganic materials 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
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- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 102100022749 Aminopeptidase N Human genes 0.000 description 1
- 101710099461 Aminopeptidase N Proteins 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- 229910001208 Crucible steel Inorganic materials 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 239000004365 Protease Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 238000007872 degassing Methods 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
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- 229910052742 iron Inorganic materials 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
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Classifications
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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
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
-
- 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
-
- 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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- 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
-
- 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
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium 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
- C22C38/24—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
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
- C22C38/42—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
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
Abstract
Provided is a rail which has reduced fluctuations in hardness as measured in the length direction of the rail and also has ensured excellent wear resistance. A rail which has a chemical composition comprising 0.60 to 1.0% of C, 0.1 to 1.5% of Si, 0.01 to 1.5% of Mn, 0.035% or less of P, 0.030% or less of S, 0.1 to 2.0% of Cr, and a remainder made up by Fe and unavoidable impurities, wherein the fluctuations in surface hardness of the rail as measured in the length direction of the rail fall within the range of ± HB15 points or smaller.
Description
RAIL AND METHOD FOR MANUFACTURING SAME
TECHNICAL FIELD
[0001] The present disclosure relates to a rail, particularly a rail having high hardness and small hardness variation, and also to a method for manufacturing the rail.
BACKGROUND
TECHNICAL FIELD
[0001] The present disclosure relates to a rail, particularly a rail having high hardness and small hardness variation, and also to a method for manufacturing the rail.
BACKGROUND
[0002] Freight cars used on freight transportation and mining railways tend .. to have heavier loading weights than passenger cars, which results in heavy loads acting on the axles of the freight cars and a severe contact environment between the freight car wheels and rails. Rails used under these conditions are expected to exhibit wear resistance and are conventionally made from steel having a pearlite structure.
.. [0003] In recent years, there has been a trend toward even heavier loading weights of freight, minerals, and so forth in order to improve railway transport efficiency, which has led a further increase in rail wear and a decrease in rail service life. Accordingly, there is demand for improved rail wear resistance in order to extend rail service life and numerous high hardness rails have been proposed in which rail hardness is enhanced.
For example, PTL 1, PTL 2, PTL 3, and PTL 4 each disclose a hypereutectoid rail having increased cementite content and a manufacturing method thereof. Moreover, PTL 5, PTL 6, and PTL 7 each disclose a technique for increasing hardness by refining the lamellar spacing of a pearlite structure in steel containing the eutectoid level of carbon content.
[0004] With regards to a method for manufacturing a rail, PTL 8 proposes a method for manufacturing a high hardness rail having superior head internal fatigue resistance. In rolling of a rail steel slab in this method, finish rolling is performed at a head surface temperature of 850 C to 1050 C to leave final finishing, and after a time interval between passes of at least 3 seconds and no greater than 1 minute, one pass or a plurality of passes of final finish rolling are performed at a head surface temperature of 800 C to 950 C and with a rolling reduction of 10% or less per pass. Thereafter, accelerated cooling is started at a cooling rate of 2 C/s to 4 C/s for 0.1 seconds to 10 P0144539-PCT-ZZ (1/23) seconds to cool the temperature at less than 5 mm from the surface of the head and corner of the rail to the Ari transformation temperature or lower, and cooling is continued at a maximum surface cooling rate of at least 4 C/s and no greater than 30 C/s.
[0005] PTL 9 describes a method for manufacturing a high toughness rail that exhibits a pearlite metal structure. In this method, after rough rolling of a steel slab of low-alloy steel or carbon steel containing 0.60% to 1.00% of C into a rail shape, continuous finish rolling is performed for three or more rolling passes at a rail surface temperature of 850 C to 1000 C with a cross-section area reduction rolling reduction of 5% to 30% per pass and 10 seconds or less between rolling passes, and thereafter the rail is allowed to cool or is cooled from 700 C or higher to a temperature in a range of 500 C
to 700 C at a rate of 2 C/s to 15 C/s.
100061 Furthermore, PTL 10 discloses a method for manufacturing a pearlitic rail having superior wear resistance and ductility in which at least rough rolling and finish rolling are performed on a steel slab for rail rolling that contains, in mass%, 0.65% to 1.20% of C, 0.05% to 2.00% of Si, and 0.05% to 2.00% of Mn, the balance being Fe and incidental impurities. In the finish rolling, rolling is performed at a rail head surface temperature of no higher than 900 C and no lower than the Ar3 transformation point or the Arcm transformation point, a head cumulative area reduction rate of 20% or greater, and with a reaction force ratio of 1.25 or greater, which is a value obtained by dividing a reaction force value of the roller by a reaction force value for the same cumulative area reduction rate and a rolling temperature of 950 C. After the finish rolling, the rail head surface is cooled to 550 C
or lower at a cooling rate of 2 C/s to 30 C/s by accelerated cooling or natural cooling.
[0007] Rails used in high axle load railways, the main examples of which being railways for freight transportation and mining, are expected to have superior wear resistance in order to improve rail durability and, in response, there have been various proposals for rails, such as described above, that focus on increasing hardness.
CITATION LIST
P0144539-PCT-ZZ (2/23)
.. [0003] In recent years, there has been a trend toward even heavier loading weights of freight, minerals, and so forth in order to improve railway transport efficiency, which has led a further increase in rail wear and a decrease in rail service life. Accordingly, there is demand for improved rail wear resistance in order to extend rail service life and numerous high hardness rails have been proposed in which rail hardness is enhanced.
For example, PTL 1, PTL 2, PTL 3, and PTL 4 each disclose a hypereutectoid rail having increased cementite content and a manufacturing method thereof. Moreover, PTL 5, PTL 6, and PTL 7 each disclose a technique for increasing hardness by refining the lamellar spacing of a pearlite structure in steel containing the eutectoid level of carbon content.
[0004] With regards to a method for manufacturing a rail, PTL 8 proposes a method for manufacturing a high hardness rail having superior head internal fatigue resistance. In rolling of a rail steel slab in this method, finish rolling is performed at a head surface temperature of 850 C to 1050 C to leave final finishing, and after a time interval between passes of at least 3 seconds and no greater than 1 minute, one pass or a plurality of passes of final finish rolling are performed at a head surface temperature of 800 C to 950 C and with a rolling reduction of 10% or less per pass. Thereafter, accelerated cooling is started at a cooling rate of 2 C/s to 4 C/s for 0.1 seconds to 10 P0144539-PCT-ZZ (1/23) seconds to cool the temperature at less than 5 mm from the surface of the head and corner of the rail to the Ari transformation temperature or lower, and cooling is continued at a maximum surface cooling rate of at least 4 C/s and no greater than 30 C/s.
[0005] PTL 9 describes a method for manufacturing a high toughness rail that exhibits a pearlite metal structure. In this method, after rough rolling of a steel slab of low-alloy steel or carbon steel containing 0.60% to 1.00% of C into a rail shape, continuous finish rolling is performed for three or more rolling passes at a rail surface temperature of 850 C to 1000 C with a cross-section area reduction rolling reduction of 5% to 30% per pass and 10 seconds or less between rolling passes, and thereafter the rail is allowed to cool or is cooled from 700 C or higher to a temperature in a range of 500 C
to 700 C at a rate of 2 C/s to 15 C/s.
100061 Furthermore, PTL 10 discloses a method for manufacturing a pearlitic rail having superior wear resistance and ductility in which at least rough rolling and finish rolling are performed on a steel slab for rail rolling that contains, in mass%, 0.65% to 1.20% of C, 0.05% to 2.00% of Si, and 0.05% to 2.00% of Mn, the balance being Fe and incidental impurities. In the finish rolling, rolling is performed at a rail head surface temperature of no higher than 900 C and no lower than the Ar3 transformation point or the Arcm transformation point, a head cumulative area reduction rate of 20% or greater, and with a reaction force ratio of 1.25 or greater, which is a value obtained by dividing a reaction force value of the roller by a reaction force value for the same cumulative area reduction rate and a rolling temperature of 950 C. After the finish rolling, the rail head surface is cooled to 550 C
or lower at a cooling rate of 2 C/s to 30 C/s by accelerated cooling or natural cooling.
[0007] Rails used in high axle load railways, the main examples of which being railways for freight transportation and mining, are expected to have superior wear resistance in order to improve rail durability and, in response, there have been various proposals for rails, such as described above, that focus on increasing hardness.
CITATION LIST
P0144539-PCT-ZZ (2/23)
- 3 -Patent Literature [0008] PTL 1: JP 4272385 B
PTL 2: JP 3078461 B
PTL 3: JP 3081116 B
PTL 4: JP 3513427 B
PTL 5: JP 4390004 B
PTL 6: JP 2009-108396 A
PTL 7: JP 2009-235515 A
PTL 8: JP 3423811 B
PTL 9: JP 3113137 B
PTL 10: JP 2008-50687 A
SUMMARY
(Technical Problem) [0009] A rail is manufactured by hot rolling a steel raw material to a length of as long as 100 m or greater and, hardness of the rail exhibits variation in the rail length direction that is dependent on the method of manufacture. Consequently, the rail may experience uneven wear when laid and thus may be unable to sufficiently demonstrate its effects. Although it is extremely important, therefore, to reduce hardness variation in the longitudinal direction of rolling, PTL 1-10 make no mention of this hardness variation.
[0010] In consideration of the above, an objective of the present disclosure is to provide a rail that exhibits excellent wear resistance and reduced hardness variation in the rail length direction, and also a method for manufacturing the rail.
(Solution to Problem) [0011] The present disclosure provides a rail comprising a chemical composition containing, in mass%:
0.60% to 1.0% of C;
0.1% to 1.5% of Si;
0.01% to 1.5% of Mn;
0.035% or less of P;
PTL 2: JP 3078461 B
PTL 3: JP 3081116 B
PTL 4: JP 3513427 B
PTL 5: JP 4390004 B
PTL 6: JP 2009-108396 A
PTL 7: JP 2009-235515 A
PTL 8: JP 3423811 B
PTL 9: JP 3113137 B
PTL 10: JP 2008-50687 A
SUMMARY
(Technical Problem) [0009] A rail is manufactured by hot rolling a steel raw material to a length of as long as 100 m or greater and, hardness of the rail exhibits variation in the rail length direction that is dependent on the method of manufacture. Consequently, the rail may experience uneven wear when laid and thus may be unable to sufficiently demonstrate its effects. Although it is extremely important, therefore, to reduce hardness variation in the longitudinal direction of rolling, PTL 1-10 make no mention of this hardness variation.
[0010] In consideration of the above, an objective of the present disclosure is to provide a rail that exhibits excellent wear resistance and reduced hardness variation in the rail length direction, and also a method for manufacturing the rail.
(Solution to Problem) [0011] The present disclosure provides a rail comprising a chemical composition containing, in mass%:
0.60% to 1.0% of C;
0.1% to 1.5% of Si;
0.01% to 1.5% of Mn;
0.035% or less of P;
- 4 -0.030% or less of S; and 0.1% to 2.0% of Cr, the balance being Fe and incidental impurities, wherein surface hardness of a head of the rail exhibits variation of HB 10 points or less in a length direction of the rail, and the surface hardness of the head of the rail is HB 400 or greater.
[0012] The present disclosure also provides a rail manufacturing method comprising:
heating to 1200 C or higher, a steel raw material having a chemical composition containing, in mass%:
0.60% to 1.0% of C, 0.1% to 1.5% of Si, 0.01% to 1.5% of Mn, 0.035% or less of P, 0.030% or less of S, and 0.1% to 2.0% of Cr, the balance being Fe and incidental impurities;
hot rolling the steel raw material after the heating, the hot rolling being performed such that rolling in a rail length direction in a temperature region not exceeding 1000 C is performed over a plurality of passes in one direction with a time interval between passes exhibiting variation of 15 s or less in the rail length direction, a cumulative area reduction rate of 40% or greater for a portion forming a rail head, and a finisher delivery temperature of 900 C or higher; and cooling the rail head after the hot rolling from a cooling start temperature of 800 C or higher to a cooling stop temperature of 600 C or lower at a cooling rate of 1 C/s to 10 C/s, wherein the cooling rate exhibits a variation of 1 C/s or less in the rail length direction, a surface hardness of a head of the rail exhibits a variation of +11B 10 .. points or less in the rail length direction, and the surface hardness of the head of the rail is HB 400 or greater.
[0012] The present disclosure also provides a rail manufacturing method comprising:
heating to 1200 C or higher, a steel raw material having a chemical composition containing, in mass%:
0.60% to 1.0% of C, 0.1% to 1.5% of Si, 0.01% to 1.5% of Mn, 0.035% or less of P, 0.030% or less of S, and 0.1% to 2.0% of Cr, the balance being Fe and incidental impurities;
hot rolling the steel raw material after the heating, the hot rolling being performed such that rolling in a rail length direction in a temperature region not exceeding 1000 C is performed over a plurality of passes in one direction with a time interval between passes exhibiting variation of 15 s or less in the rail length direction, a cumulative area reduction rate of 40% or greater for a portion forming a rail head, and a finisher delivery temperature of 900 C or higher; and cooling the rail head after the hot rolling from a cooling start temperature of 800 C or higher to a cooling stop temperature of 600 C or lower at a cooling rate of 1 C/s to 10 C/s, wherein the cooling rate exhibits a variation of 1 C/s or less in the rail length direction, a surface hardness of a head of the rail exhibits a variation of +11B 10 .. points or less in the rail length direction, and the surface hardness of the head of the rail is HB 400 or greater.
- 5 -[0013] Specifically, primary features of the present disclosure are as follows.
(1) A rail comprising a chemical composition containing (consisting of), in mass%:
0.60% to 1.0% of C;
0.1% to 1.5% of Si;
0.01% to 1.5% of Mn;
0.035% or less of P;
0.030% or less of S; and 0.1% to 2.0% of Cr, the balance being Fe and incidental impurities, wherein surface hardness of a head of the rail exhibits variation of +I-1B 15 points or less in a length direction of the rail.
Herein, the surface hardness variation in the rail length direction refers to the difference between an average value of Brinell hardness of the top of the rail head calculated from measurements made at intervals of 5 m in a rolling length direction along the entire length of the rail (for example, 25 m to 100 m) and the value of Brinell hardness measured at each of the measurement points. In other words, surface hardness variation of HB 15 points or less in the rail length direction signifies that when an average value for Brinell hardness is calculated from all hardness values measured at 5 m intervals (i.e., values measured at 6 points in the case of a total length of 25 m, 11 points in the case of a total length of 50 m, and 21 points in the case of a total length of 100 m), the maximum difference in Brinell hardness between the average value and the values for the measurement points is +15 points or less. Note that Brinell hardness is measured after removing 0.5 mm or greater of a decarburized layer using a grinder or the like.
[0014] (2) The rail described in (1), wherein the chemical composition further contains, in mass%, one or more of:
1.0% or less of Cu;
0.5% or less of Ni;
0.5% or less of Mo; and 0.15% or less of V.
(1) A rail comprising a chemical composition containing (consisting of), in mass%:
0.60% to 1.0% of C;
0.1% to 1.5% of Si;
0.01% to 1.5% of Mn;
0.035% or less of P;
0.030% or less of S; and 0.1% to 2.0% of Cr, the balance being Fe and incidental impurities, wherein surface hardness of a head of the rail exhibits variation of +I-1B 15 points or less in a length direction of the rail.
Herein, the surface hardness variation in the rail length direction refers to the difference between an average value of Brinell hardness of the top of the rail head calculated from measurements made at intervals of 5 m in a rolling length direction along the entire length of the rail (for example, 25 m to 100 m) and the value of Brinell hardness measured at each of the measurement points. In other words, surface hardness variation of HB 15 points or less in the rail length direction signifies that when an average value for Brinell hardness is calculated from all hardness values measured at 5 m intervals (i.e., values measured at 6 points in the case of a total length of 25 m, 11 points in the case of a total length of 50 m, and 21 points in the case of a total length of 100 m), the maximum difference in Brinell hardness between the average value and the values for the measurement points is +15 points or less. Note that Brinell hardness is measured after removing 0.5 mm or greater of a decarburized layer using a grinder or the like.
[0014] (2) The rail described in (1), wherein the chemical composition further contains, in mass%, one or more of:
1.0% or less of Cu;
0.5% or less of Ni;
0.5% or less of Mo; and 0.15% or less of V.
-6-100151 (3) The rail described in (1) or (2), wherein the surface hardness of the head of the rail is HB 400 or greater.
[0016] (4) The rail described in any one of (1) to (3), wherein the variation of the surface hardness is HB 10 points or less.
[0017] (5) A rail manufacturing method comprising:
heating to 1200 C or higher, a steel raw material having a chemical composition containing (consisting of), in mass%, 0.60% to 1.0% of C, 0.1% to 1.5% of Si, 0.01% to 1.5% of Mn, 0.035% or less of P, 0.030% or less of S, and 0.1% to 2.0% of Cr, the balance being Fe and incidental impurities;
hot rolling the steel raw material after the heating, the hot rolling being performed such that rolling in a rail length direction in a temperature region not exceeding 1000 C is performed over a plurality of passes with a time interval between passes exhibiting variation of 15 s or less in the rail length direction, a cumulative area reduction rate of 40% or greater for a portion forming a rail head, and a finisher delivery temperature of 900 C or higher; and cooling the rail head after the hot rolling from a cooling start temperature of 800 C or higher to a cooling stop temperature of 600 C or lower at a cooling rate of 1 C/s to 10 C/s.
[0018] (6) The rail manufacturing method described in (5), wherein the chemical composition further contains, in mass%, one or more of:
1.0% or less of Cu;
0.5% or less of Ni;
0.5% or less of Mo; and 0.15% or less of V.
[0016] (4) The rail described in any one of (1) to (3), wherein the variation of the surface hardness is HB 10 points or less.
[0017] (5) A rail manufacturing method comprising:
heating to 1200 C or higher, a steel raw material having a chemical composition containing (consisting of), in mass%, 0.60% to 1.0% of C, 0.1% to 1.5% of Si, 0.01% to 1.5% of Mn, 0.035% or less of P, 0.030% or less of S, and 0.1% to 2.0% of Cr, the balance being Fe and incidental impurities;
hot rolling the steel raw material after the heating, the hot rolling being performed such that rolling in a rail length direction in a temperature region not exceeding 1000 C is performed over a plurality of passes with a time interval between passes exhibiting variation of 15 s or less in the rail length direction, a cumulative area reduction rate of 40% or greater for a portion forming a rail head, and a finisher delivery temperature of 900 C or higher; and cooling the rail head after the hot rolling from a cooling start temperature of 800 C or higher to a cooling stop temperature of 600 C or lower at a cooling rate of 1 C/s to 10 C/s.
[0018] (6) The rail manufacturing method described in (5), wherein the chemical composition further contains, in mass%, one or more of:
1.0% or less of Cu;
0.5% or less of Ni;
0.5% or less of Mo; and 0.15% or less of V.
- 7 -[0019] (7) The rail manufacturing method described in (5) or (6), wherein the cooling rate in the cooling exhibits variation of 1 C/s or less in the rail length direction.
(Advantageous Effect) [0020] The present disclosure enables minimization of hardness variation in a rail length direction and effectively improves rail durability (extends rail life), particularly in the case of a rail that is laid in a high axle load environment such as a heavy freight railway or a mining railway, and thus demonstrates a significant effect in industrial use.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In the accompanying drawings:
FIG. 1 is a graph illustrating a relationship between the rail material hardness and wear;
FIG. 2 illustrates a Nishihara type wear test piece of which wear resistance is evaluated, wherein (a) is a plan view and (b) is a side view; and FIG. 3 is a cross-sectional view of a rail head illustrating sampling positions of Nishihara type wear test pieces.
DETAILED DESCRIPTION
[0021a] The inventors sampled test pieces from steel materials having pearlite structures corresponding to rails of differing hardness and conducted a rail wear test with respect to the test pieces in order to investigate a relationship between hardness and wear. The results of the investigation are shown in FIG. 1.
The wear test was a comparative test in which actual contact conditions between a pearlite steel rail and a wheel were simulated using a Nishihara type wear test apparatus that enables wear resistance evaluation in a short period of time. The test was conducted as illustrated in FIG. 2 by rotating a Nishihara type wear test piece 1 of 30 mm in outer diameter, sampled from a rail head, in contact with a tire test piece 2. The arrows in FIG. 2 indicate the rotation directions of the Nishihara type wear test piece 1 and the tire test piece 2, respectively. The tire test piece was - 7a -obtained by sampling a round bar of 32 mm in diameter from a normal rail head stipulated by JIS E1101, subjecting the round bar to heat treatment such as to have a tempered martensite structure and a Brinell hardness (Brinell load 29.4 kN) of HB 370, and subsequently processing the round bar into the shape illustrated in FIG. 2. Nishihara type wear test pieces 1 were sampled from two locations in a rail head 3 as illustrated in FIG. 3. A test piece sampled from a surface layer of the rail head 3 is denoted Nishihara type wear test piece la and a test piece sampled from an inner part of the rail head 3 is denoted Nishihara type wear test piece lb.
The center, in a longitudinal direction, of the Nishihara type wear test piece lb sampled from the inner part of the rail head 3 is located at a depth of from 24 mm to 26 mm (average value 25 mm) from an upper surface of the rail head 3. The test was conducted in dry ambient conditions and the wear was measured after 1.8 x105 rotations under conditions of a contact pressure of 1.2 GPa, a slip ratio of ¨10%, and a rotational speed of 750 rpm (tire test piece: 750 rpm). The wear was calculated from the difference in the mass of the test piece measured before and after the test.
[0021b] As illustrated in FIG. 1, wear resistance increases with increasing hardness.
For example, wear resistance of a rail having a hardness of HB 400 or higher can be improved by 15% compared to an ordinary heat treated rail (HB 370). However, if the hardness exhibits a large amount of variation in the rail length direction, a difference in wear behavior arises for hard portions and soft portions. For example, in a situation in which the hardness is HB 415 points and exhibits variation of 15 or less (i.e., the hardness varies within a range from at least HB 400 to no greater than HB 430), the wear changes from 0.37 g to 0.3 g and accordingly exhibits variation of 20% or less. On the other hand, in a situation in which the hardness is HB 415 points and exhibits variation of 30 (i.e., the hardness varies in a range from at least HB 385 to no greater than HB 445), the wear changes from 0.40 g to 0.27 g and accordingly exhibits variation of 33%. In consideration of the above, reducing hardness variation in the longitudinal direction of a rail in accompaniment to increasing rail hardness enables uniform rail wear and contributes to improving rail life. It is preferable for wear to be as uniform as possible in the length direction because wear proceeds due to contact between the rail and wheels during use.
- 7b -Taking into account the results of the test described above, hardness variation in the rail length direction is preferably of a level such that wear variation is 20%
or less.
The inventors discovered that surface hardness variation of HB 15 or less ensures superior wear resistance along the length direction and contributes to improved rail life. This discovery led to the present disclosure.
[0022] Firstly, the reasons for limitations on each component in the chemical composition of a rail will be explained. When components are expressed in "%", this refers to "mass%" unless otherwise specified.
C: 0.60% to 1.0%
=
(Advantageous Effect) [0020] The present disclosure enables minimization of hardness variation in a rail length direction and effectively improves rail durability (extends rail life), particularly in the case of a rail that is laid in a high axle load environment such as a heavy freight railway or a mining railway, and thus demonstrates a significant effect in industrial use.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In the accompanying drawings:
FIG. 1 is a graph illustrating a relationship between the rail material hardness and wear;
FIG. 2 illustrates a Nishihara type wear test piece of which wear resistance is evaluated, wherein (a) is a plan view and (b) is a side view; and FIG. 3 is a cross-sectional view of a rail head illustrating sampling positions of Nishihara type wear test pieces.
DETAILED DESCRIPTION
[0021a] The inventors sampled test pieces from steel materials having pearlite structures corresponding to rails of differing hardness and conducted a rail wear test with respect to the test pieces in order to investigate a relationship between hardness and wear. The results of the investigation are shown in FIG. 1.
The wear test was a comparative test in which actual contact conditions between a pearlite steel rail and a wheel were simulated using a Nishihara type wear test apparatus that enables wear resistance evaluation in a short period of time. The test was conducted as illustrated in FIG. 2 by rotating a Nishihara type wear test piece 1 of 30 mm in outer diameter, sampled from a rail head, in contact with a tire test piece 2. The arrows in FIG. 2 indicate the rotation directions of the Nishihara type wear test piece 1 and the tire test piece 2, respectively. The tire test piece was - 7a -obtained by sampling a round bar of 32 mm in diameter from a normal rail head stipulated by JIS E1101, subjecting the round bar to heat treatment such as to have a tempered martensite structure and a Brinell hardness (Brinell load 29.4 kN) of HB 370, and subsequently processing the round bar into the shape illustrated in FIG. 2. Nishihara type wear test pieces 1 were sampled from two locations in a rail head 3 as illustrated in FIG. 3. A test piece sampled from a surface layer of the rail head 3 is denoted Nishihara type wear test piece la and a test piece sampled from an inner part of the rail head 3 is denoted Nishihara type wear test piece lb.
The center, in a longitudinal direction, of the Nishihara type wear test piece lb sampled from the inner part of the rail head 3 is located at a depth of from 24 mm to 26 mm (average value 25 mm) from an upper surface of the rail head 3. The test was conducted in dry ambient conditions and the wear was measured after 1.8 x105 rotations under conditions of a contact pressure of 1.2 GPa, a slip ratio of ¨10%, and a rotational speed of 750 rpm (tire test piece: 750 rpm). The wear was calculated from the difference in the mass of the test piece measured before and after the test.
[0021b] As illustrated in FIG. 1, wear resistance increases with increasing hardness.
For example, wear resistance of a rail having a hardness of HB 400 or higher can be improved by 15% compared to an ordinary heat treated rail (HB 370). However, if the hardness exhibits a large amount of variation in the rail length direction, a difference in wear behavior arises for hard portions and soft portions. For example, in a situation in which the hardness is HB 415 points and exhibits variation of 15 or less (i.e., the hardness varies within a range from at least HB 400 to no greater than HB 430), the wear changes from 0.37 g to 0.3 g and accordingly exhibits variation of 20% or less. On the other hand, in a situation in which the hardness is HB 415 points and exhibits variation of 30 (i.e., the hardness varies in a range from at least HB 385 to no greater than HB 445), the wear changes from 0.40 g to 0.27 g and accordingly exhibits variation of 33%. In consideration of the above, reducing hardness variation in the longitudinal direction of a rail in accompaniment to increasing rail hardness enables uniform rail wear and contributes to improving rail life. It is preferable for wear to be as uniform as possible in the length direction because wear proceeds due to contact between the rail and wheels during use.
- 7b -Taking into account the results of the test described above, hardness variation in the rail length direction is preferably of a level such that wear variation is 20%
or less.
The inventors discovered that surface hardness variation of HB 15 or less ensures superior wear resistance along the length direction and contributes to improved rail life. This discovery led to the present disclosure.
[0022] Firstly, the reasons for limitations on each component in the chemical composition of a rail will be explained. When components are expressed in "%", this refers to "mass%" unless otherwise specified.
C: 0.60% to 1.0%
=
- 8 -C is an important element in a pearlitic rail for forming cementite, increasing hardness and strength, and improving wear resistance. However, these effects are small when C content is less than 0.60% and therefore the lower limit for the C content is 0.60%. On the other hand, although an increase in the C content, and thus an increase in cementite content, is expected to lead to higher hardness and strength, an increase in the C
content also decreases ductility. Furthermore, an increase in the C content broadens the y + 0 temperature range and promotes softening of a heat-affected zone. Taking into account these influences, the upper limit for the C content is 1.0%. The C content is preferably in a range of 0.73% to 0.85%.
100231 Si: 0.1% to 1.5%
Si is added to the rail material as a deoxidizing material and in order to raise the equilibrium transformation temperature (TE) and reinforce the pearlite structure (increase hardness by refining the lamellar structure).
However, these effects are small when Si content is less than 0.1%. On the other hand, an increase in the Si content promotes decarburization and promotes formation of rail surface defects. Therefore, the upper limit for the Si content is 1.5%. The Si content is preferably in a range of 0.5% to 1.3%.
[0024] Mn: 0.01% to 1.5%
Mn has an effect of lowering the actual pearlite transformation temperature and narrowing pearlite lamellar spacing, and is an effective element for achieving high hardness. However, these effects are small when Mn content is less than 0.01%. On the other hand. addition of greater than 1.5% of Mn to improve hardenability facilitates transformation to bainite or martensite. Therefore, the upper limit for the Mn content is 1.5%. The Mn content is preferably in a range of 0.3% to 1.2%.
[0025] P: 0.035% or less P content of greater than 0.035% decreases toughness and ductility.
Therefore, the upper limit for the P content is 0.035%. A preferable range for the P content has an upper limit of 0.025%. On the other hand, taking into consideration the increased cost of steelmaking when special refining or the like is performed, the lower limit for the P content is preferably P0144539-PCT-ZZ (8/23)
content also decreases ductility. Furthermore, an increase in the C content broadens the y + 0 temperature range and promotes softening of a heat-affected zone. Taking into account these influences, the upper limit for the C content is 1.0%. The C content is preferably in a range of 0.73% to 0.85%.
100231 Si: 0.1% to 1.5%
Si is added to the rail material as a deoxidizing material and in order to raise the equilibrium transformation temperature (TE) and reinforce the pearlite structure (increase hardness by refining the lamellar structure).
However, these effects are small when Si content is less than 0.1%. On the other hand, an increase in the Si content promotes decarburization and promotes formation of rail surface defects. Therefore, the upper limit for the Si content is 1.5%. The Si content is preferably in a range of 0.5% to 1.3%.
[0024] Mn: 0.01% to 1.5%
Mn has an effect of lowering the actual pearlite transformation temperature and narrowing pearlite lamellar spacing, and is an effective element for achieving high hardness. However, these effects are small when Mn content is less than 0.01%. On the other hand. addition of greater than 1.5% of Mn to improve hardenability facilitates transformation to bainite or martensite. Therefore, the upper limit for the Mn content is 1.5%. The Mn content is preferably in a range of 0.3% to 1.2%.
[0025] P: 0.035% or less P content of greater than 0.035% decreases toughness and ductility.
Therefore, the upper limit for the P content is 0.035%. A preferable range for the P content has an upper limit of 0.025%. On the other hand, taking into consideration the increased cost of steelmaking when special refining or the like is performed, the lower limit for the P content is preferably P0144539-PCT-ZZ (8/23)
- 9 -0.001%.
[0026] S: 0.030% or less S forms coarse MnS extending in the rolling direction and decreases ductility and toughness. Therefore, the upper limit for S content is 0.030%.
On the other hand, restricting the S content to less than 0.0005% requires a significant increase in steel making cost due to, for example, a large increase in steelmaking process time. Therefore, the lower limit for the S
content is preferably 0.0005%. The S content is preferably 0.001% to 0.015%.
[0027] Cr: 0.1% to 2.0%
Cr raises the equilibrium transformation temperature (TE), contributes to refinement of pearlite lamellar spacing, and increases hardness and strength. In order to obtain such effects, it is necessary to add 0.2% or greater of Cr. On the other hand, adding greater than 2.0% of Cr increases occurrence of welding defects while also increasing hardenability and promoting martensite formation. Therefore, the upper limit for Cr content is 2.0%. The Cr content is more preferably in a range of 0.26% to 1.00%.
100281 Besides the chemical components described above, one or more of 1.0% or less of Cu, 0.5% or less of Ni, 0.5% or less of Mo, and 0.15% or less of V may be added.
Cu: 1.0% or less Cu is an element that can provide even higher hardness through solid solution strengthening. Cu also has an effect of suppressing decarburization. In order to obtain these effects, 0.01% or greater of Cu is preferably added. On the other hand, adding greater than 1.0% of Cu makes surface cracking more likely to occur during continuous casting or rolling.
Therefore, the upper limit for Cu content is preferably 1.0%. Moreover, the Cu content is more preferably in a range of 0.05% to 0.6%.
10029] Ni: 0.5% or less Ni is an effective element for improving toughness and ductility. Ni is also an effective element for inhibiting Cu cracking through combined addition with Cu. Therefore, in a situation in which Cu is added, Ni is preferably also added. However, these effects are not noticeable when Ni P0144539-PCT-ZZ (9/23)
[0026] S: 0.030% or less S forms coarse MnS extending in the rolling direction and decreases ductility and toughness. Therefore, the upper limit for S content is 0.030%.
On the other hand, restricting the S content to less than 0.0005% requires a significant increase in steel making cost due to, for example, a large increase in steelmaking process time. Therefore, the lower limit for the S
content is preferably 0.0005%. The S content is preferably 0.001% to 0.015%.
[0027] Cr: 0.1% to 2.0%
Cr raises the equilibrium transformation temperature (TE), contributes to refinement of pearlite lamellar spacing, and increases hardness and strength. In order to obtain such effects, it is necessary to add 0.2% or greater of Cr. On the other hand, adding greater than 2.0% of Cr increases occurrence of welding defects while also increasing hardenability and promoting martensite formation. Therefore, the upper limit for Cr content is 2.0%. The Cr content is more preferably in a range of 0.26% to 1.00%.
100281 Besides the chemical components described above, one or more of 1.0% or less of Cu, 0.5% or less of Ni, 0.5% or less of Mo, and 0.15% or less of V may be added.
Cu: 1.0% or less Cu is an element that can provide even higher hardness through solid solution strengthening. Cu also has an effect of suppressing decarburization. In order to obtain these effects, 0.01% or greater of Cu is preferably added. On the other hand, adding greater than 1.0% of Cu makes surface cracking more likely to occur during continuous casting or rolling.
Therefore, the upper limit for Cu content is preferably 1.0%. Moreover, the Cu content is more preferably in a range of 0.05% to 0.6%.
10029] Ni: 0.5% or less Ni is an effective element for improving toughness and ductility. Ni is also an effective element for inhibiting Cu cracking through combined addition with Cu. Therefore, in a situation in which Cu is added, Ni is preferably also added. However, these effects are not noticeable when Ni P0144539-PCT-ZZ (9/23)
- 10 -content is less than 0.01%. Therefore, in a situation in which Ni is added, the lower limit for the Ni content is preferably 0.01% or greater. On the other hand, adding greater than 0.5% of Ni increases hardenability and promotes formation of martensite. Therefore, the upper limit for the Ni content is preferably 0.5%. The Ni content is more preferably in a range of 0.05% to 0.50%.
[0030] Mo: 0.5% or less Mo is an effective element for increasing strength, but this effect is small when Mo content is less than 0.01%. Therefore, the lower limit for the Mo content is preferably 0.01%. On the other hand, adding greater than 0.5% of Mo causes formation of martensite as a result of increased hardenability and dramatically decreases toughness and ductility. Therefore, the upper limit for the Mo content is preferably 0.5%. The Mo content is more preferably in a range of 0.05% to 0.30%.
[0031] V: 0.15% or less V forms VC, VN, or the like as a fine precipitate in ferrite and is an element that contributes to achieving high hardness through precipitation strengthening of ferrite. The solvation temperature of VC or VN is sufficiently lower than that of Ti or Nb such as to have little influence on recrystallization behavior of austenite during rolling and therefore has little influence on variation of properties in the rail length direction. Moreover, V
also acts as a hydrogen trapping site and can be expected to exhibit an effect of inhibiting delayed fracture. Therefore, 0.001% or greater of V is preferably added. On the other hand, when greater than 0.15% of V is added, the above-described effects reach saturation and the alloying cost increases dramatically. Therefore, the upper limit for V content is preferably 0.15%.
The V content is more preferably in a range of 0.005% to 0.12%.
[0032] The balance excluding the aforementioned components is Fe and incidental impurities.
For example, up to 0.006% of N and 0.003% of 0 may be allowed as incidental impurities. Furthermore, although Al is effective as a deoxidizing material, Al forms cluster-shaped AIN, which significantly decreases rolling fatigue characteristics. Therefore, Al content is preferably 0.003%
or less. Nb and Ti are also contained as incidental impurities as described P0144539-PCT-ZZ (10/23) =
[0030] Mo: 0.5% or less Mo is an effective element for increasing strength, but this effect is small when Mo content is less than 0.01%. Therefore, the lower limit for the Mo content is preferably 0.01%. On the other hand, adding greater than 0.5% of Mo causes formation of martensite as a result of increased hardenability and dramatically decreases toughness and ductility. Therefore, the upper limit for the Mo content is preferably 0.5%. The Mo content is more preferably in a range of 0.05% to 0.30%.
[0031] V: 0.15% or less V forms VC, VN, or the like as a fine precipitate in ferrite and is an element that contributes to achieving high hardness through precipitation strengthening of ferrite. The solvation temperature of VC or VN is sufficiently lower than that of Ti or Nb such as to have little influence on recrystallization behavior of austenite during rolling and therefore has little influence on variation of properties in the rail length direction. Moreover, V
also acts as a hydrogen trapping site and can be expected to exhibit an effect of inhibiting delayed fracture. Therefore, 0.001% or greater of V is preferably added. On the other hand, when greater than 0.15% of V is added, the above-described effects reach saturation and the alloying cost increases dramatically. Therefore, the upper limit for V content is preferably 0.15%.
The V content is more preferably in a range of 0.005% to 0.12%.
[0032] The balance excluding the aforementioned components is Fe and incidental impurities.
For example, up to 0.006% of N and 0.003% of 0 may be allowed as incidental impurities. Furthermore, although Al is effective as a deoxidizing material, Al forms cluster-shaped AIN, which significantly decreases rolling fatigue characteristics. Therefore, Al content is preferably 0.003%
or less. Nb and Ti are also contained as incidental impurities as described P0144539-PCT-ZZ (10/23) =
- 11 -below.
[0033] Nb: 0.003% or less Ti: 0.003% or less Nb and Ti are effective elements for improving hardness and wear resistance due to forming carbides or carbonitrides that strengthen the matrix. However, Nb and Ti are harmful elements that promote hardness variation of the rail in the longitudinal direction and are therefore not generally added, although incidentally mixed in Nb and Ti of 0.003% or less is allowable. Specifically, addition of Nb or Ti causes hardness to change to a greater extent in accordance with material heating, rolling, or cooling conditions and thus causes changes in hardness in the rolling length direction to be more sensitively associated with variation in these conditions. In metallurgical terms, inhomogeneity of heated austenite particles is promoted and, at the same time, inhibition of recrystallization of austenite during rolling and a change in pearlite transformation temperature associated therewith are greatly increased compared to steel in which Nb and Ti are not added, and this may promote hardness variation.
[0034] In addition to the chemical composition described above, it is essential that surface hardness exhibits variation of HB 15 points or less in the rail length direction. The reason for this is that the change in rail wear reaches 20% or greater if the hardness variation is greater than HB 15 points. Furthermore, it is more preferable that the surface hardness exhibits variation of HB 10 points or less in the rail length direction because hardness variation of HB 10 points or less enables restriction of the change in rail wear to less than 15%.
[0035] The following provides a specific description of rail manufacture conditions.
First, the steel raw material that is used is preferably continuous-cast steel obtained through continuous casting of molten steel that has been adjusted to the chemical composition described above through steelmaking processes such as a process in a blast furnace, molten iron pretreatment, a process in a converter, and RH degassing.
[0036] The steel raw material is hot rolled to form a rail shape by ordinary caliber rolling or universal rolling. The following explains the reasons for P0144539-PCT-ZZ (11/23)
[0033] Nb: 0.003% or less Ti: 0.003% or less Nb and Ti are effective elements for improving hardness and wear resistance due to forming carbides or carbonitrides that strengthen the matrix. However, Nb and Ti are harmful elements that promote hardness variation of the rail in the longitudinal direction and are therefore not generally added, although incidentally mixed in Nb and Ti of 0.003% or less is allowable. Specifically, addition of Nb or Ti causes hardness to change to a greater extent in accordance with material heating, rolling, or cooling conditions and thus causes changes in hardness in the rolling length direction to be more sensitively associated with variation in these conditions. In metallurgical terms, inhomogeneity of heated austenite particles is promoted and, at the same time, inhibition of recrystallization of austenite during rolling and a change in pearlite transformation temperature associated therewith are greatly increased compared to steel in which Nb and Ti are not added, and this may promote hardness variation.
[0034] In addition to the chemical composition described above, it is essential that surface hardness exhibits variation of HB 15 points or less in the rail length direction. The reason for this is that the change in rail wear reaches 20% or greater if the hardness variation is greater than HB 15 points. Furthermore, it is more preferable that the surface hardness exhibits variation of HB 10 points or less in the rail length direction because hardness variation of HB 10 points or less enables restriction of the change in rail wear to less than 15%.
[0035] The following provides a specific description of rail manufacture conditions.
First, the steel raw material that is used is preferably continuous-cast steel obtained through continuous casting of molten steel that has been adjusted to the chemical composition described above through steelmaking processes such as a process in a blast furnace, molten iron pretreatment, a process in a converter, and RH degassing.
[0036] The steel raw material is hot rolled to form a rail shape by ordinary caliber rolling or universal rolling. The following explains the reasons for P0144539-PCT-ZZ (11/23)
- 12 -limitations placed on conditions during the heating and rolling described above and also conditions during subsequent cooling.
[0037] [Heating temperature prior to hot rolling: 1200 C or higher]
Heating of the produced steel raw material is required to 1200 C or higher. This is performed with the main objective of sufficiently reducing deformation resistance so as to enable use of a lighter rolling load and also with the objective of homogenization. In order to sufficiently obtain these effects, the heating temperature is required to be 1200 C or higher.
Although it is not necessary to set a specific upper limit, the heating temperature is preferably 1300 C or lower from a viewpoint of suppressing scale loss and decarburization.
[0038] [Rolling in a rail length direction in a temperature region not exceeding 1000 C is performed over a plurality of passes with a time interval between passes exhibiting variation of 15 s or less in the rail length direction]
The steel raw material heated as described above is shaped into a rail shape by hot rolling. In the hot rolling, it is important that a plurality of rolling passes at temperatures not exceeding 1000 C are performed by rolling repeatedly in a single direction in order to minimize variation in a time interval between passes. Note that the time interval between passes refers to the interval between a time when a given portion in the longitudinal direction (rolling direction) of a rolled rail material is bitten by a roller and a time when the given portion is next bitten by the roller. The time interval between passes differs the most for the top (leading end) of the rolled rail material and the bottom (trailing end) of the rolled rail material.
[0039] In conventional reverse rolling, during an interval between a rolled top portion (leading end) being bitten by the roller in a given pass and starting to be bitten in a next pass, the next pass is performed in order by first feeding a rolled bottom portion (trailing end) to the roller, which lengthens the time interval between passes for the rolled top portion. On the other hand, after the rolled bottom portion (trailing end) has passed through in a given pass, the bottom portion is bitten first by the roller in the next pass, which shortens the time interval between passes. The difference in the P0144539-PCT-ZZ (12/23) =
[0037] [Heating temperature prior to hot rolling: 1200 C or higher]
Heating of the produced steel raw material is required to 1200 C or higher. This is performed with the main objective of sufficiently reducing deformation resistance so as to enable use of a lighter rolling load and also with the objective of homogenization. In order to sufficiently obtain these effects, the heating temperature is required to be 1200 C or higher.
Although it is not necessary to set a specific upper limit, the heating temperature is preferably 1300 C or lower from a viewpoint of suppressing scale loss and decarburization.
[0038] [Rolling in a rail length direction in a temperature region not exceeding 1000 C is performed over a plurality of passes with a time interval between passes exhibiting variation of 15 s or less in the rail length direction]
The steel raw material heated as described above is shaped into a rail shape by hot rolling. In the hot rolling, it is important that a plurality of rolling passes at temperatures not exceeding 1000 C are performed by rolling repeatedly in a single direction in order to minimize variation in a time interval between passes. Note that the time interval between passes refers to the interval between a time when a given portion in the longitudinal direction (rolling direction) of a rolled rail material is bitten by a roller and a time when the given portion is next bitten by the roller. The time interval between passes differs the most for the top (leading end) of the rolled rail material and the bottom (trailing end) of the rolled rail material.
[0039] In conventional reverse rolling, during an interval between a rolled top portion (leading end) being bitten by the roller in a given pass and starting to be bitten in a next pass, the next pass is performed in order by first feeding a rolled bottom portion (trailing end) to the roller, which lengthens the time interval between passes for the rolled top portion. On the other hand, after the rolled bottom portion (trailing end) has passed through in a given pass, the bottom portion is bitten first by the roller in the next pass, which shortens the time interval between passes. The difference in the P0144539-PCT-ZZ (12/23) =
- 13 -time interval between passes for the leading end and the trailing end described above, which is a characteristic of reverse rolling, influences the state of the austenite structure and also influences hardness variation after transformation to pearlite. In contrast, when continuous rolling is performed in a single direction, the difference in the time interval between passes for a leading end and a trailing end of a rolled material is fundamentally small. Therefore, inhomogeneity of the austenite structure arising from the above-described difference in the time interval between passes can be resolved. It is therefore necessary for the aforementioned difference in the time interval between passes to be 15 s or less. In other words, a difference in the time interval between passes of 15 s or less can suppress hardness variation in the rail length direction. The difference in the time interval between passes is preferably 12 s or less.
[0040] The above stipulations are conditions to be applied to rolling performed at 1000 C or lower in the hot rolling. Reverse rolling may be used for rolling performed in a temperature region exceeding 1000 C, a representative example of which is rough rolling. In other words, so long as rolling at 1000 C or lower is performed continuously in a single direction, a preceding stage of rolling in a temperature region exceeding 1000 C may be performed freely. In the hot rolling, two to seven passes of rolling are preferably performed at 1000 C or lower. The reason for this is that single pass rolling requires a large rolling load and makes shaping difficult, whereas more than seven passes tends to cause a fairly inhomogeneous austenite state and increase hardness variation.
[0041] [Cumulative area reduction rate of 40% or greater for a portion forming a rail head]
The cumulative area reduction rate of rolling performed at 1000 C
or lower is required to be 40% or greater. The reason for this is that it is necessary to perform 40% or greater of area reduction processing at 1000 C
or lower in order to promote recrystallization refinement of austenite. If the area reduction rate for rolling at 1000 C or lower is less than 40%, recrystallization refinement of austenite is insufficient and coarse austenite may partially remain, which results in increased hardness variation in the rail length direction (rolling direction).
P0144539-PCT-ZZ (13/23)
[0040] The above stipulations are conditions to be applied to rolling performed at 1000 C or lower in the hot rolling. Reverse rolling may be used for rolling performed in a temperature region exceeding 1000 C, a representative example of which is rough rolling. In other words, so long as rolling at 1000 C or lower is performed continuously in a single direction, a preceding stage of rolling in a temperature region exceeding 1000 C may be performed freely. In the hot rolling, two to seven passes of rolling are preferably performed at 1000 C or lower. The reason for this is that single pass rolling requires a large rolling load and makes shaping difficult, whereas more than seven passes tends to cause a fairly inhomogeneous austenite state and increase hardness variation.
[0041] [Cumulative area reduction rate of 40% or greater for a portion forming a rail head]
The cumulative area reduction rate of rolling performed at 1000 C
or lower is required to be 40% or greater. The reason for this is that it is necessary to perform 40% or greater of area reduction processing at 1000 C
or lower in order to promote recrystallization refinement of austenite. If the area reduction rate for rolling at 1000 C or lower is less than 40%, recrystallization refinement of austenite is insufficient and coarse austenite may partially remain, which results in increased hardness variation in the rail length direction (rolling direction).
P0144539-PCT-ZZ (13/23)
- 14 -[0042] [Finisher delivery temperature of 900 C or higher]
When performing continuous rolling in a single direction in order to reduce variation in the time interval between passes along the whole length of the rolled material, a finisher delivery temperature of 900 C or higher is preferable. The reason for this it that if the finisher delivery temperature is lower than 900 C, overall hardness decreases and variation thereof increases due to reasons such as a decrease in the cooling start temperature of on-line heat treatment performed consecutively after rolling and promotion of transformation to pearlite (transformation at higher temperature). Therefore, the finisher delivery temperature is preferably 900 C or higher in order to prevent a decrease in hardness such as described above.
[0043] Cooling is performed consecutively after the hot rolling under the following conditions.
[Cooling of the rail head from a cooling start temperature of 800 C
or higher to a cooling stop temperature of 600 C or lower at a cooling rate of 1 C/s to 10 C/s]
Firstly, the cooling start temperature is preferably 800 C or higher.
Specifically, a cooling start temperature of lower than 800 C may not enable sufficient supercooling or allow sufficient surface hardness to be obtained. The cooling stop temperature is required to be 600 C or lower.
Sufficient hardness cannot be obtained if the cooling stop temperature is greater than 600 C. Although no specific lower limit is given, saturation is reached in terms of hardness once cooling is performed to 400 C or lower and productivity is adversely affected by increased cooling time. Therefore, cooling is preferably stopped at 400 C or higher.
The cooling rate is in a range of 1 C/s to 10 C/s. A cooling rate of greater than 10 C/s does not allow sufficient time for pearlite transformation, causes formation of bainite and martensite, and thus reduces toughness, ductility, and fatigue resistance. On the other hand, a cooling rate of less than 1 C/s does not allow sufficient hardness to be obtained. The cooling rate is preferably in a range of 2 C/s to 8 C/s.
Moreover, the cooling rate preferably exhibits variation of 1 C/s or less in the rolling longitudinal direction. Restricting cooling rate P0144539-PCT-ZZ (14/23)
When performing continuous rolling in a single direction in order to reduce variation in the time interval between passes along the whole length of the rolled material, a finisher delivery temperature of 900 C or higher is preferable. The reason for this it that if the finisher delivery temperature is lower than 900 C, overall hardness decreases and variation thereof increases due to reasons such as a decrease in the cooling start temperature of on-line heat treatment performed consecutively after rolling and promotion of transformation to pearlite (transformation at higher temperature). Therefore, the finisher delivery temperature is preferably 900 C or higher in order to prevent a decrease in hardness such as described above.
[0043] Cooling is performed consecutively after the hot rolling under the following conditions.
[Cooling of the rail head from a cooling start temperature of 800 C
or higher to a cooling stop temperature of 600 C or lower at a cooling rate of 1 C/s to 10 C/s]
Firstly, the cooling start temperature is preferably 800 C or higher.
Specifically, a cooling start temperature of lower than 800 C may not enable sufficient supercooling or allow sufficient surface hardness to be obtained. The cooling stop temperature is required to be 600 C or lower.
Sufficient hardness cannot be obtained if the cooling stop temperature is greater than 600 C. Although no specific lower limit is given, saturation is reached in terms of hardness once cooling is performed to 400 C or lower and productivity is adversely affected by increased cooling time. Therefore, cooling is preferably stopped at 400 C or higher.
The cooling rate is in a range of 1 C/s to 10 C/s. A cooling rate of greater than 10 C/s does not allow sufficient time for pearlite transformation, causes formation of bainite and martensite, and thus reduces toughness, ductility, and fatigue resistance. On the other hand, a cooling rate of less than 1 C/s does not allow sufficient hardness to be obtained. The cooling rate is preferably in a range of 2 C/s to 8 C/s.
Moreover, the cooling rate preferably exhibits variation of 1 C/s or less in the rolling longitudinal direction. Restricting cooling rate P0144539-PCT-ZZ (14/23)
- 15 -variation to 1 C/s or less reduces variation in pearlite lamellar spacing, enables hardness variation of HB 10 or less to be achieved, and reduces wear resistance variation and fatigue resistance variation in the rail longitudinal direction.
The cooling performed consecutively after the hot rolling is preferably performed by air blast cooling or mist cooling. Air blast cooling is accelerated cooling in which air is forcefully blown against the rail head.
Mist cooling involves mixing air and water and blowing a water mist against the rail head.
[0044] In order to control and minimize cooling rate variation in the rolling longitudinal direction, in the case of air blast cooling, for example, it is necessary to control air pressure at intervals of 5 m or less (preferably 3 m or less), adjust air pressure on-line in accordance with temperature variation of the rail in the longitudinal direction measured before the cooling, and perform control such that the cooling rate is constant in the length direction. In the case of mist cooling, cooling is preferably performed by controlling the amount of water and pressure in the longitudinal direction in the same way as described above.
[0045] Through the above-described chemical composition and performance of the above-described rolling and cooling, a pearlitic steel rail can be obtained that has a surface hardness of preferably HB 400 or greater and that exhibits surface hardness variation of HB 15 points or less in the rail length direction. In other words, a homogeneous and high-hardness pearlitic steel rail that exhibits little hardness variation in the rolling length direction can be obtained.
EXAMPLES
[0046] Steels having the chemical compositions shown in Table I were made and cast steels obtained through continuous casting thereof were subjected to heating, hot rolling, and cooling to manufacture a 136-pound rail or a 141-pound rail for each steel. The manufacture conditions are shown together with investigation results for surface hardness and variation thereof in Table 2.
P0144539-PCT-ZZ (15/23) _ .
. .
Table 1 Steel symbol C Si Mn P S Cr Cu Ni Mo V Nb*
Ti* sol AP N* 0* Remarks 0 A.
A 0.82 0.53 0.56 0.016 0.004 0.76 - - - -0.001 0.001 0.002 0.0041 0.0015 Example ---1 ,--, R 0_80 1.28 0.23 0.018 0.003 0.38 - 0.053 0.001 0.001 0.002 0.0029 0.0018 Example C 0.89 0.26 1.43 0.012 , 0.005 0.26 - . 0.12 - 0.002 0.001 0.001 0.0040 0.0018 Example H
D 0.76 1.43 0.93 0.015 0.007 0.53 0.31 0.15 -0.072 0.001 0.002 0.001 0.0045 0.0013 Example - -P
Cr E 0.98 0.63 0.78 0.018 0.005 0.22 - - 0.001 0.001 0.001 0.0042 0.0012 Example CD
F 0.82 0.95 0.48 0.013 0.004 1.43 - - - 0.036 0.001 0.001 0.002 0.0055 0.0016 Example =--, G 0.56 , 0.53 1.32 0.016 0.005 0.53 - - - -0.002 0.001 0.002 0.0035 0.0015 Comparative example H 0.79 1.58 0.13 002 0.007 0.23 . - , - - 0.001 , 0.002 0.001 0.0051 0.0015 Comparative example 1 0.81 0.05 1.59 0.016 0.005 0.23 - - - -0.001 0.001 0.002 0.0040 0.0012 Comparative example J 0.68 0.43 1.62 0.021 0.008 0.18 - - 0.001 0.001 0.002 0.0033 0.0012 Comparative example K 0.81 0.55 0.48 0.018 0.005 0.08 - - - 0.001 0.002 0.001 0.0043 0.0015 Comparative example -.
L 0.82 0.43 0.22 0.015 0.003 2.03 - - - .
0.001 0.001 0.003 0.0060 0.0018 , Comparative example M 1.07 0.38 0.73 0.018 0.005 0.33 - - - -0.001 0.001 0.002 0.0038 0.0016 Comparative example R
N 0.82 1.24 0.10 0.013 0.004 1.36 - - - 0.001 0.002 0.002 0.0045 0.0015 Example u, 0., *Contents ofNb, Ti, sol Al, N, and 0 are as incidental impurities ..., o o i o ,-.
1-, CN
cm I
0...]
H
µ., -11-:
-r--i.6 c.., u.rD
AV
(...) N
N
-237., 1,5 L., .._, =
[0048] Herein, the variation in the time interval between passes in the rolling conditions indicates the difference between the time elapsing from a leading end of a rolled material being rolled to the leading end being next rolled and the time elapsing from a trailing end of the rolled material being rolled to the trailing end being next rolled. As explained further above, when rolling is performed by conventional reverse rolling, the time interval between passes is extended for a rolled top portion and shortened for a rolled bottom portion. Thus, the difference in the time interval between passes for the leading end (top portion) and the trailing end (bottom portion) of the rolled material is particularly evident in reverse rolling. In contrast, the difference in the time interval between passes associated with a leading end and a trailing end of a rolled material is smaller in continuous rolling in a single direction and therefore inhomogeneity of a produced structure can be resolved as shown in Table 2.
[0049] Note that the cooling start temperature and the cooling stop temperature are results for surface temperature of a rail corner measured by a thermoviewer. The rail cooling rate is an average value of cooling rates measured from cooling start and end temperatures and cooling times measured at 5 m intervals in the length direction. With regards to cooling rate variation in the length direction, it was determined whether the difference between a largest value and a smallest value in variation of the cooling rates was greater than 1 C/s or was less than or equal to 1 C/s.
Furthermore, the rail head surface hardness and microstructure of each of the manufactured rails was evaluated. The rail head surface hardness was evaluated by removing 0.5 mm or greater of a decarburized layer using a grinder and measuring the Brinell hardness of points at 5 m intervals in the rail length direction. In the same way, microscope samples were cut out and the microstructures thereof were observed.
The evaluation results are shown in Table 2.
P0144539-PCT-ZZ (17/23) _ -_ .
Table 2 Heating Rolling conditions Cooling conditions Erna hardness of surface 0 t/11 Area 0 Variation in Length reduction Finisher Cooling Average Surface Steel Use of continuous rolling at time ntcrval Cooling direction Start Stop Cooling No. symbol Temperature rate at delivery rate surface hardness Remarks 1000 C or lower between method cooling temperature temperature rate H
1000 C or temperature variation hardness variation Po passes control lower 1=1"
1 C) (s) (%) ( C) 1 C) ( C) ( C/s) ( c/s) (H13) (HB) CD
1 A 1240 Reverse rolling 25 45 950 Air blast No 760 430 3.4 >1 422 23 Conventional exnnsple "
2 A 1230 Reverse rolling 22 45 970 Air blast No 780 470 3.5 >1 426 18 Comparative example 3 A 1220 Single-direction continuous 12 45 950 Air blast No 820 450 3.3 >1 420 13 Example 4 A 1180 Single-direction continuous 12 45 920 Air blast No 770 450 2.8 >1 398 17 Comparative example A 1220 Single-direction continuous 10 45 930 Air blast Yes 820 450 3.4 01 420 8 Example 6 A 1240 Single-ditection continuous 12 45 940 Mist No 820 430 6.7 >1 439 14 Example 7 A 1230 Single-direction continuous 8 45 900 Air blast Yes 800 430 3.3 01 416 7 Example 8 A 1220 Single-direction continuous 12 37 950 Air blast No 810 450 3.5 >1 422 18 Comparative example R .
9 A 1240 Single-direction conthuous 10 45 880 Air blast No 830 450 3.4 >1 403 17 Comparative example o ND
A 1230 Single-direction continuous 17 45 910 Air blast No 810 460 3.4 >1 400 17 Comparative example gi L., 11 A 1250 Single-direction continuous 12 45 920 Air blast Yes 820 430 3.5 01 435 7 Example a, ..., 12 A 1230 Single-direction continuous 12 45 920 Mist Yes 830 400 7.0 .1 455 9 Example 0>
i 13 A 1250 Single-direction continuous 12 45 910 Air blast Yes 820 620 3.7 .1 373 7 Comparative example ni 14 A , 1250 Singe-direction continuous 12 45 910 Air blast Yes 810 430 0.5 5.1 351 7 Comparative example I--e, A 1250 Single-direction continuous 12 45 920 Mist Yes 820 400 12 61 789 82 Comparative example in ...]
I Martensite formation 6, Length direction cooling control. No ¨> Variation > 1 C/s Length direction cooling control Yes ¨> Variation 6 1 Cis *0 -7:
-r¨
Ln, ,...., 'F' -v (-) N
N
,¨, e7'e t,..) ,..,, ,.....
...
-. -Table 2 (contd) Heating Rolling conditions Cooling conditions Brinell hardness of surface Area Variation in Length reduction Finisher Cooling Average Surface Steel Use of continuous rolling at time interval Cooling direction Start Stop Cooing No.
s,yinbol Temperature rate at delivery rate surface hardness Remarks 1000 C or lower between method cooling temperature temperature rate 1000 C or temperature variation hardness variation passes control lower CC) (s) (%) CC) CC) ( C) ( C/s) CC/s) (11B) (HB)
The cooling performed consecutively after the hot rolling is preferably performed by air blast cooling or mist cooling. Air blast cooling is accelerated cooling in which air is forcefully blown against the rail head.
Mist cooling involves mixing air and water and blowing a water mist against the rail head.
[0044] In order to control and minimize cooling rate variation in the rolling longitudinal direction, in the case of air blast cooling, for example, it is necessary to control air pressure at intervals of 5 m or less (preferably 3 m or less), adjust air pressure on-line in accordance with temperature variation of the rail in the longitudinal direction measured before the cooling, and perform control such that the cooling rate is constant in the length direction. In the case of mist cooling, cooling is preferably performed by controlling the amount of water and pressure in the longitudinal direction in the same way as described above.
[0045] Through the above-described chemical composition and performance of the above-described rolling and cooling, a pearlitic steel rail can be obtained that has a surface hardness of preferably HB 400 or greater and that exhibits surface hardness variation of HB 15 points or less in the rail length direction. In other words, a homogeneous and high-hardness pearlitic steel rail that exhibits little hardness variation in the rolling length direction can be obtained.
EXAMPLES
[0046] Steels having the chemical compositions shown in Table I were made and cast steels obtained through continuous casting thereof were subjected to heating, hot rolling, and cooling to manufacture a 136-pound rail or a 141-pound rail for each steel. The manufacture conditions are shown together with investigation results for surface hardness and variation thereof in Table 2.
P0144539-PCT-ZZ (15/23) _ .
. .
Table 1 Steel symbol C Si Mn P S Cr Cu Ni Mo V Nb*
Ti* sol AP N* 0* Remarks 0 A.
A 0.82 0.53 0.56 0.016 0.004 0.76 - - - -0.001 0.001 0.002 0.0041 0.0015 Example ---1 ,--, R 0_80 1.28 0.23 0.018 0.003 0.38 - 0.053 0.001 0.001 0.002 0.0029 0.0018 Example C 0.89 0.26 1.43 0.012 , 0.005 0.26 - . 0.12 - 0.002 0.001 0.001 0.0040 0.0018 Example H
D 0.76 1.43 0.93 0.015 0.007 0.53 0.31 0.15 -0.072 0.001 0.002 0.001 0.0045 0.0013 Example - -P
Cr E 0.98 0.63 0.78 0.018 0.005 0.22 - - 0.001 0.001 0.001 0.0042 0.0012 Example CD
F 0.82 0.95 0.48 0.013 0.004 1.43 - - - 0.036 0.001 0.001 0.002 0.0055 0.0016 Example =--, G 0.56 , 0.53 1.32 0.016 0.005 0.53 - - - -0.002 0.001 0.002 0.0035 0.0015 Comparative example H 0.79 1.58 0.13 002 0.007 0.23 . - , - - 0.001 , 0.002 0.001 0.0051 0.0015 Comparative example 1 0.81 0.05 1.59 0.016 0.005 0.23 - - - -0.001 0.001 0.002 0.0040 0.0012 Comparative example J 0.68 0.43 1.62 0.021 0.008 0.18 - - 0.001 0.001 0.002 0.0033 0.0012 Comparative example K 0.81 0.55 0.48 0.018 0.005 0.08 - - - 0.001 0.002 0.001 0.0043 0.0015 Comparative example -.
L 0.82 0.43 0.22 0.015 0.003 2.03 - - - .
0.001 0.001 0.003 0.0060 0.0018 , Comparative example M 1.07 0.38 0.73 0.018 0.005 0.33 - - - -0.001 0.001 0.002 0.0038 0.0016 Comparative example R
N 0.82 1.24 0.10 0.013 0.004 1.36 - - - 0.001 0.002 0.002 0.0045 0.0015 Example u, 0., *Contents ofNb, Ti, sol Al, N, and 0 are as incidental impurities ..., o o i o ,-.
1-, CN
cm I
0...]
H
µ., -11-:
-r--i.6 c.., u.rD
AV
(...) N
N
-237., 1,5 L., .._, =
[0048] Herein, the variation in the time interval between passes in the rolling conditions indicates the difference between the time elapsing from a leading end of a rolled material being rolled to the leading end being next rolled and the time elapsing from a trailing end of the rolled material being rolled to the trailing end being next rolled. As explained further above, when rolling is performed by conventional reverse rolling, the time interval between passes is extended for a rolled top portion and shortened for a rolled bottom portion. Thus, the difference in the time interval between passes for the leading end (top portion) and the trailing end (bottom portion) of the rolled material is particularly evident in reverse rolling. In contrast, the difference in the time interval between passes associated with a leading end and a trailing end of a rolled material is smaller in continuous rolling in a single direction and therefore inhomogeneity of a produced structure can be resolved as shown in Table 2.
[0049] Note that the cooling start temperature and the cooling stop temperature are results for surface temperature of a rail corner measured by a thermoviewer. The rail cooling rate is an average value of cooling rates measured from cooling start and end temperatures and cooling times measured at 5 m intervals in the length direction. With regards to cooling rate variation in the length direction, it was determined whether the difference between a largest value and a smallest value in variation of the cooling rates was greater than 1 C/s or was less than or equal to 1 C/s.
Furthermore, the rail head surface hardness and microstructure of each of the manufactured rails was evaluated. The rail head surface hardness was evaluated by removing 0.5 mm or greater of a decarburized layer using a grinder and measuring the Brinell hardness of points at 5 m intervals in the rail length direction. In the same way, microscope samples were cut out and the microstructures thereof were observed.
The evaluation results are shown in Table 2.
P0144539-PCT-ZZ (17/23) _ -_ .
Table 2 Heating Rolling conditions Cooling conditions Erna hardness of surface 0 t/11 Area 0 Variation in Length reduction Finisher Cooling Average Surface Steel Use of continuous rolling at time ntcrval Cooling direction Start Stop Cooling No. symbol Temperature rate at delivery rate surface hardness Remarks 1000 C or lower between method cooling temperature temperature rate H
1000 C or temperature variation hardness variation Po passes control lower 1=1"
1 C) (s) (%) ( C) 1 C) ( C) ( C/s) ( c/s) (H13) (HB) CD
1 A 1240 Reverse rolling 25 45 950 Air blast No 760 430 3.4 >1 422 23 Conventional exnnsple "
2 A 1230 Reverse rolling 22 45 970 Air blast No 780 470 3.5 >1 426 18 Comparative example 3 A 1220 Single-direction continuous 12 45 950 Air blast No 820 450 3.3 >1 420 13 Example 4 A 1180 Single-direction continuous 12 45 920 Air blast No 770 450 2.8 >1 398 17 Comparative example A 1220 Single-direction continuous 10 45 930 Air blast Yes 820 450 3.4 01 420 8 Example 6 A 1240 Single-ditection continuous 12 45 940 Mist No 820 430 6.7 >1 439 14 Example 7 A 1230 Single-direction continuous 8 45 900 Air blast Yes 800 430 3.3 01 416 7 Example 8 A 1220 Single-direction continuous 12 37 950 Air blast No 810 450 3.5 >1 422 18 Comparative example R .
9 A 1240 Single-direction conthuous 10 45 880 Air blast No 830 450 3.4 >1 403 17 Comparative example o ND
A 1230 Single-direction continuous 17 45 910 Air blast No 810 460 3.4 >1 400 17 Comparative example gi L., 11 A 1250 Single-direction continuous 12 45 920 Air blast Yes 820 430 3.5 01 435 7 Example a, ..., 12 A 1230 Single-direction continuous 12 45 920 Mist Yes 830 400 7.0 .1 455 9 Example 0>
i 13 A 1250 Single-direction continuous 12 45 910 Air blast Yes 820 620 3.7 .1 373 7 Comparative example ni 14 A , 1250 Singe-direction continuous 12 45 910 Air blast Yes 810 430 0.5 5.1 351 7 Comparative example I--e, A 1250 Single-direction continuous 12 45 920 Mist Yes 820 400 12 61 789 82 Comparative example in ...]
I Martensite formation 6, Length direction cooling control. No ¨> Variation > 1 C/s Length direction cooling control Yes ¨> Variation 6 1 Cis *0 -7:
-r¨
Ln, ,...., 'F' -v (-) N
N
,¨, e7'e t,..) ,..,, ,.....
...
-. -Table 2 (contd) Heating Rolling conditions Cooling conditions Brinell hardness of surface Area Variation in Length reduction Finisher Cooling Average Surface Steel Use of continuous rolling at time interval Cooling direction Start Stop Cooing No.
s,yinbol Temperature rate at delivery rate surface hardness Remarks 1000 C or lower between method cooling temperature temperature rate 1000 C or temperature variation hardness variation passes control lower CC) (s) (%) CC) CC) ( C) ( C/s) CC/s) (11B) (HB)
16 B 1220 Single-direction continuous 13 45 950 Air blast No 850 450 3.7 >1 441 12 Example
17 B 1250 Single-direction continuous 20 40 970 Al blast Yes 840 420 4.0 41 436 7 Example
18 B 1230 Single-direction continuous 12 45 950 Air blast Yes 820 460 3.8 41 455 8 Example
19 C 1200 Single-direction continuous 18 45 950 Air blast No , 830 450 3.5 >1 415 12 Example ,
20 C 1230 Single-direction continuous 18 40 930 Air blast Yes 820 470 3.8 61 430 8 Example
21 D 1220 Single-direction continuous 15 45 950 Air blast No 810 470 3.5 >1 430 11 Example
22 E 1240 Single-direction continuous 13 45 930 Air blast No 810 450 3.3 >1 420 12 Example
23 E 1240 Single-direction continuous 10 37 940 Air blast Yes , 820 440 3.4 41 432 7 Example R
24 F 1250 Sirwle-direction continuous 15 45 920 Air blast No 830 480 4.2 41 458 8 Example in
25 G 1230 Single-direction continuous 18 45 920 Air blast No 820 460 3.6 <I 367 10 Comparative example ND
l.0 U.1
l.0 U.1
26 H 1240 Single-direction continuous 10 45 910 Air blast Yes 800 450 3.5 41 486 35 Comparative example a, .., , Martensite formation o, in t
27 1 1230 Single-direction continuous 12 45 930 Air blast Yes 820 470 2.6 41 382 7 Comparative example st in
28 J 1250 Single-direction continuous 12 45 930 Mist Yes 830 460 8.2 41 483 36 Comparative example 1.---a, Martensite kin-nation in 1
29 K 1250 Single-direction continuous 15 45 920 Air blast Yes 800 450 4.2 41 362 9 Comparative example vi i 1-, Comparative example it
30 L 1220 Single-direction continuous 12 45 930 Air blast Yes 810 430 4.3 .1 503 20 Martensite fannation
31 M 1230 Single-direction continuous 12 45 920 Air blast Yes 820 430 3.5 41 433 8 Comparative example Low ductility
32 N 1250 Single-direction continuous 12 45 930 Air blast Yes 820 410 4.2 41 421 7 Example Length direction cooling control: No ¨. Variation > 1 C/s Length direction cooling control Yes --.), Variation 4 1 C/s =;:.
4.
tal t..., Sc C.-) '7,-N
N
tza F..) i.....t ,_, [0051] The hardness of rails according to the present disclosure exhibited extremely small variation of HB 15 or less in the rail length direction, whereas the hardness of rails that deviated from the scope of the present disclosure in terms of either or both of chemical composition and rolling conditions exhibited variation of greater than HB 15.
P0144539-PCT-ZZ (20/23)
4.
tal t..., Sc C.-) '7,-N
N
tza F..) i.....t ,_, [0051] The hardness of rails according to the present disclosure exhibited extremely small variation of HB 15 or less in the rail length direction, whereas the hardness of rails that deviated from the scope of the present disclosure in terms of either or both of chemical composition and rolling conditions exhibited variation of greater than HB 15.
P0144539-PCT-ZZ (20/23)
Claims (4)
1. A rail comprising a chemical composition containing, in mass%:
0.60% to 1.0% of C;
0.1% to 1.5% of Si;
0.01% to 1.5% of Mn;
0.035% or less of P;
0.030% or less of S; and 0.1% to 2.0% of Cr, the balance being Fe and incidental impurities, wherein surface hardness of a head of the rail exhibits variation of ~HB 10 points or less in a length direction of the rail, and the surface hardness of the head of the rail is HB 400 or greater.
0.60% to 1.0% of C;
0.1% to 1.5% of Si;
0.01% to 1.5% of Mn;
0.035% or less of P;
0.030% or less of S; and 0.1% to 2.0% of Cr, the balance being Fe and incidental impurities, wherein surface hardness of a head of the rail exhibits variation of ~HB 10 points or less in a length direction of the rail, and the surface hardness of the head of the rail is HB 400 or greater.
2. The rail of claim 1, wherein the chemical composition further contains, in mass%, one or more of:
1.0% or less of Cu;
0.5% or less of Ni;
0.5% or less of Mo; and 0.15% or less of V.
1.0% or less of Cu;
0.5% or less of Ni;
0.5% or less of Mo; and 0.15% or less of V.
3. A rail manufacturing method comprising:
heating to 1200°C or higher, a steel raw material having a chemical composition containing, in mass%:
0.60% to 1.0% of C, 0.1% to 1.5% of Si, 0.01% to 1.5% of Mn, 0.035% or less of P, 0.030% or less of S, and 0.1% to 2.0% of Cr, the balance being Fe and incidental impurities;
hot rolling the steel raw material after the heating, the hot rolling being performed such that rolling in a rail length direction in a temperature region not exceeding 1000°C is performed over a plurality of passes in one direction with a time interval between passes exhibiting variation of 15 s or less in the rail length direction, a cumulative area reduction rate of 40% or greater for a portion forming a rail head, and a finisher delivery temperature of 900°C or higher; and cooling the rail head after the hot rolling from a cooling start temperature of 800°C or higher to a cooling stop temperature of 600°C or lower at a cooling rate of 1°C/s to 10°C/s, wherein the cooling rate exhibits a variation of ~1°C/s or less in the rail length direction, a surface hardness of a head of the rail exhibits a variation of ~HB 10 points or less in the rail length direction, and the surface hardness of the head of the rail is HB 400 or greater.
heating to 1200°C or higher, a steel raw material having a chemical composition containing, in mass%:
0.60% to 1.0% of C, 0.1% to 1.5% of Si, 0.01% to 1.5% of Mn, 0.035% or less of P, 0.030% or less of S, and 0.1% to 2.0% of Cr, the balance being Fe and incidental impurities;
hot rolling the steel raw material after the heating, the hot rolling being performed such that rolling in a rail length direction in a temperature region not exceeding 1000°C is performed over a plurality of passes in one direction with a time interval between passes exhibiting variation of 15 s or less in the rail length direction, a cumulative area reduction rate of 40% or greater for a portion forming a rail head, and a finisher delivery temperature of 900°C or higher; and cooling the rail head after the hot rolling from a cooling start temperature of 800°C or higher to a cooling stop temperature of 600°C or lower at a cooling rate of 1°C/s to 10°C/s, wherein the cooling rate exhibits a variation of ~1°C/s or less in the rail length direction, a surface hardness of a head of the rail exhibits a variation of ~HB 10 points or less in the rail length direction, and the surface hardness of the head of the rail is HB 400 or greater.
4. The rail manufacturing method of claim 3, wherein the chemical composition further contains, in mass%, one or more of:
1.0% or less of Cu;
0.5% or less of Ni;
0.5% or less of Mo; and 0.15% or less of V.
1.0% or less of Cu;
0.5% or less of Ni;
0.5% or less of Mo; and 0.15% or less of V.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2014060786 | 2014-03-24 | ||
| JP2014-060786 | 2014-03-24 | ||
| PCT/JP2015/001659 WO2015146150A1 (en) | 2014-03-24 | 2015-03-24 | Rail and method for manufacturing same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2936780A1 CA2936780A1 (en) | 2015-10-01 |
| CA2936780C true CA2936780C (en) | 2018-10-02 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2936780A Active CA2936780C (en) | 2014-03-24 | 2015-03-24 | Rail and method for manufacturing same |
Country Status (8)
| Country | Link |
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| US (1) | US20170101692A1 (en) |
| EP (1) | EP3124636B2 (en) |
| JP (1) | JP6150008B2 (en) |
| CN (1) | CN106103772B (en) |
| AU (1) | AU2015237464B2 (en) |
| BR (1) | BR112016022007B1 (en) |
| CA (1) | CA2936780C (en) |
| WO (1) | WO2015146150A1 (en) |
Families Citing this family (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BR112016022007B1 (en) | 2014-03-24 | 2021-05-11 | Jfe Steel Corporation | rail and manufacturing method |
| WO2015182743A1 (en) * | 2014-05-29 | 2015-12-03 | 新日鐵住金株式会社 | Rail and production method therefor |
| CN106636891A (en) * | 2016-11-17 | 2017-05-10 | 马鞍山市银鼎机械制造有限公司 | Preparation method of ball milling cast iron for shock resisting railway steel rail |
| CN107326302B (en) * | 2017-05-26 | 2018-10-19 | 北京交通大学 | A kind of anti-corrosion bainitic steel, rail and preparation method |
| WO2019102258A1 (en) * | 2017-11-27 | 2019-05-31 | Arcelormittal | Method for manufacturing a rail and corresponding rail |
| EP3778961B1 (en) * | 2018-03-30 | 2022-03-09 | JFE Steel Corporation | Rail and method for manufacturing same |
| BR112020019343A2 (en) | 2018-03-30 | 2021-01-05 | Jfe Steel Corporation | RAIL |
| JP6822575B2 (en) * | 2018-03-30 | 2021-01-27 | Ｊｆｅスチール株式会社 | Rails and their manufacturing methods |
| JP6852761B2 (en) * | 2018-10-26 | 2021-03-31 | Ｊｆｅスチール株式会社 | Rails and their manufacturing methods |
| SE543919C2 (en) * | 2019-05-17 | 2021-09-21 | Husqvarna Ab | Steel for a sawing device |
| CN112575137B (en) * | 2020-10-26 | 2022-03-25 | 邯郸钢铁集团有限责任公司 | Method for direct tapping during high-speed rail steel converter smelting |
| MX2023005664A (en) * | 2020-11-17 | 2023-05-26 | Arcelormittal | Steel for rails and a method of manufacturing of a rail thereof. |
| CN114058824B (en) * | 2021-11-26 | 2023-12-08 | 武汉钢铁有限公司 | Production method for improving hardness uniformity of heat-treated steel rail tread and steel rail obtained by production method |
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| US2773867A (en) * | 1954-05-17 | 1956-12-11 | Glidden Co | Process for dehalogenating steroids |
| JPS6289818A (en) * | 1985-10-14 | 1987-04-24 | Nippon Kokan Kk <Nkk> | Heat treatment of rail |
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| JPH01104721A (en) * | 1987-10-19 | 1989-04-21 | Nippon Steel Corp | Method for cooling high-temperature rail |
| JP2773867B2 (en) * | 1987-10-19 | 1998-07-09 | 新日本製鐵株式会社 | Hot rail cooling |
| BR9406250A (en) | 1993-12-20 | 1996-01-02 | Nippon Steel Corp | Perlitic steel rails with high wear resistance and toughness and their manufacturing methods |
| JPH07216454A (en) | 1994-01-31 | 1995-08-15 | Nippon Steel Corp | Heat treatment of rail |
| US6804795B1 (en) * | 1999-04-02 | 2004-10-12 | Sony Corporation | Electronic device and its repairing method |
| JP2001234238A (en) * | 2000-02-18 | 2001-08-28 | Nippon Steel Corp | Producing method for highly wear resistant and high toughness rail |
| EP1493831A4 (en) * | 2002-04-05 | 2006-12-06 | Nippon Steel Corp | Pealite based rail excellent in wear resistance and ductility and method for production thereof |
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| CN1754973A (en) | 2004-09-27 | 2006-04-05 | 铁道科学研究院 | Heat treating rail iron containing Cr |
| JP5145795B2 (en) * | 2006-07-24 | 2013-02-20 | 新日鐵住金株式会社 | Method for producing pearlitic rails with excellent wear resistance and ductility |
| CN101646795B (en) * | 2007-03-28 | 2011-04-27 | 杰富意钢铁株式会社 | Pearlite steel rail of high internal hardness type excellent in wear resistance and fatigue failure resistance and process for production of the same |
| JP5282506B2 (en) * | 2008-09-25 | 2013-09-04 | Ｊｆｅスチール株式会社 | Internal high hardness type pearlitic steel rail with excellent wear resistance and fatigue damage resistance and method for manufacturing the same |
| AU2009308639B2 (en) * | 2008-10-31 | 2015-07-02 | Nippon Steel Corporation | Pearlite rail having superior abrasion resistance and excellent toughness |
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| AU2010216990B2 (en) * | 2009-02-18 | 2015-08-20 | Nippon Steel Corporation | Pearlitic rail with excellent wear resistance and toughness |
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| BR112016022007B1 (en) | 2014-03-24 | 2021-05-11 | Jfe Steel Corporation | rail and manufacturing method |
-
2015
- 2015-03-24 BR BR112016022007-2A patent/BR112016022007B1/en active IP Right Grant
- 2015-03-24 WO PCT/JP2015/001659 patent/WO2015146150A1/en active Application Filing
- 2015-03-24 CN CN201580013144.3A patent/CN106103772B/en active Active
- 2015-03-24 JP JP2016510035A patent/JP6150008B2/en active Active
- 2015-03-24 AU AU2015237464A patent/AU2015237464B2/en active Active
- 2015-03-24 EP EP15768893.8A patent/EP3124636B2/en active Active
- 2015-03-24 CA CA2936780A patent/CA2936780C/en active Active
- 2015-03-24 US US15/128,267 patent/US20170101692A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| EP3124636A1 (en) | 2017-02-01 |
| CN106103772A (en) | 2016-11-09 |
| WO2015146150A1 (en) | 2015-10-01 |
| JPWO2015146150A1 (en) | 2017-04-13 |
| US20170101692A1 (en) | 2017-04-13 |
| AU2015237464B2 (en) | 2018-02-01 |
| EP3124636A4 (en) | 2017-02-01 |
| BR112016022007B1 (en) | 2021-05-11 |
| CA2936780A1 (en) | 2015-10-01 |
| EP3124636B1 (en) | 2019-03-06 |
| CN106103772B (en) | 2018-05-22 |
| AU2015237464A1 (en) | 2016-08-11 |
| JP6150008B2 (en) | 2017-06-21 |
| EP3124636B2 (en) | 2023-05-17 |
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