AU2018271236B2 - Rail manufacturing method and rail manufacturing apparatus - Google Patents

Abstract

To provide a method and an apparatus for manufacturing a rail having high ductility in both a head portion and a foot portion. A heated steel rail material is hot-rolled, the temperature is adjusted by cooling the hot-rolled steel rail material, the steel rail material subjected to the temperature adjustment is processed into a rail shape by means of temperature-adjusted rolling at an area reduction ratio of 20% or more, and, in adjusting the temperature of the steel railmaterial, the surface portions ofthe steelrailmaterial corresponding to a head portion and a foot portion of the rail shape so that the temperatures of the surface portions reach 5000C or more and 1,000C or less.

Description

RAIL MANUFACTURING METHOD AND RAIL MANUFACTURING APPARATUS

This is a divisional of Australian Patent Application No.

2015323176, the entire contents of which are incorporated

herein by reference.

Technical Field

[0001]

The present invention relates to a method and an

apparatus for manufacturing a pearlitic steel rail with

excellent ductility obtained by performing rough rolling,

finish rolling, and heat treatment of a heated bloom and

particularly relates to a method and an apparatus for

manufacturing a rail having ductility improved by refining

the pearlite block or colony size.

Background Art

[0002]

A rail in which the structure of a head portion forms

a pearlite structure is generally manufactured by the

following manufacturing method.

First, a bloom cast by a continuous casting method is

heated to 11000C or more, and then hot-rolled into a

predetermined rail shape by rough rolling and finish rolling.

A rolling method in each rolling process is performed

combining caliber rolling and universal rolling. Herein,

the rolling is performed in a plurality of passes in the rough rolling or in a plurality of passes or a single pass in the finish rolling.

[0003]

-1A -

Then, crops at end portions of the hot-rolled rail are

sawn. The length of the hot-rolled rail is 50 to 200 m.

Therefore, when a heat treatment apparatus has a length

limitation, the railis sawninto apredeterminedlength, e.g.,

25 m, simultaneously with the sawing of the crops.

Furthermore, when the rail is required to have wear

resistance, the rail is subjected to heat treatment by the

heat treatment apparatus (heat treatment process) subsequent

to the hot-rolling process. Herein, the wear resistance

improves when the heat treatment start temperature is higher.

Therefore, a re-heating process of heating the rail may be

provided before the heat treatment process. In the heat

treatment process, the railis fixed with a restraining device,

such as a clamp, and then a head portion, a foot portion, and,

as necessary, an web portion are forcibly cooled using a

cooling medium, such as air, water, and mist. In the heat

treatment process, the forcible cooling is usually performed

until the temperature of the head portion reaches 650 0 C or

less.

[0004]

Thereafter, the restraint of the rail by the clamp is

released, and then the rail is conveyed to a cooling bed. On

the cooling bed, the rail is cooled until the temperature

reaches 100 0 C or less.

For example, a rail to be used under severe environments,

such as mining sites of natural resources, such as coal, is

demanded to have high wear resistance and high toughness.

Therefore, when the rail to be used under severe environments is manufactured, the above-described heat treatment process is required. However, when the rail manufactured by the process described above is subjected to processing, such as bending processing, for example, later, the processing becomes difficult to achieve in some cases because the rail is excessively hardened when subjected to heat treatment, so that the ductility decreases. Therefore, a rail with high hardness and excellent ductility has been demanded.

[0005]

For example, Patent Document 1 discloses a method

including setting the rolling temperature in finish rolling

in a temperature range of Ar3 transformation point to 900°C,

and then performing accelerated cooling of a rail to at least

550°C at a cooling rate of 2 to 30/sec within 150 sec after

the end of the finish rolling to thereby increase the

ductility of the rail.

Moreover, Patent Document 2 discloses amethodincluding

performing rolling at an area reduction ratio of 10% or more

in a temperature range 800°C or less in hot-rolling to thereby

improve the ductility of a rail.

Citation List

Patent Documents

[0006]

[Patent Document 1] JP 2013-14847 A

[Patent Document 2] JP 62-127453 A

[00071

However, the method described in Patent Document 1 has

had a problem in that the temperature control for a foot

portion of a rail is not performed, and therefore the

ductility of the foot portion does not improve.

The method described in Patent Document 2 has had a

problem in that the temperature adjustment conditions in

rolling for a foot portion of a rail are not specified, and

therefore the ductility of the foot portion does not improve.

Then, the present invention has been made focusing on

the problems described above. The present invention aims to

provide a method and an apparatus for manufacturing a rail

having high ductility in both a head portion and a foot

portion.

Summary of the Invention

[0008]

The present invention provides a rail manufacturing

method comprising: hot-rolling a heated steel rail material

by at least one first rolling mill; adjusting a temperature

by cooling the hot-rolled steel rail material; and rolling

the steel rail material subjected to the temperature

adjustment into a rail shape at the adjusted temperature at

an area reduction ratio of 20% or more by at least one second

rolling mill, wherein, in adjusting the temperature of the

steel rail material, a surface portion of the steel rail

material corresponding to a head portion and a foot portion

of the rail shape is cooled so that the temperatures of the

surface portion reaches 500°C or more and 1,000°C or less by a cooling device arranged between the at least one first rolling mill and the at least one second rolling mill, wherein: after the rolling by the at least one second rolling mill, heat-treating the railby forcibly coolingatan average cooling rate of 1°C/s or more and 10 °C/s or less from a surface temperature of 730°C or more until the surface temperature reaches 600°C or less; and wherein the steel material has a composition comprising 0.60% or more and 1.05% or less carbon

(C), 0.1% or more and 1.5% or less silicon (Si), 0.01% or more

and 1.5% or less manganese (Mn), 0.035% or less phosphorus

(P), 0.030% or less sulfur (S), 0.1% or more and 2.0% or less

chromium (Cr) , 0.5% or less antimony (Sb) , optionally at least

one of 0.01% or more and 0.5% or less copper (Cu), 0.01% or

more and 0.5% or less nickel (Ni), 0.01% or more and 0.5% or

less molybdenum (Mo), 0.001% or more and 0.15% or less

vanadium (V) , 0. 001% or more and 0. 30% or less niobium (Nb),

the balance being iron (Fe) and inevitable impurities. Also

described is a method for manufacturing a rail according to

one aspect of the present invention includes hot-rolling a

heated steel rail material, adjusting the temperature by

cooling the hot-rolled steel rail material, processing the

steel rail material subjected to the temperature adjustment

into a rail shape by means of temperature-adjusted rolling

at an area reduction ratio of 20% or more, and, in adjusting

the temperature of the steel rail material, cooling the

surface portions of the steel rail material corresponding to

a head portion and a foot portion of the rail shape to 500°C

or more and 1,000°C or less.

[0009]

An apparatus for manufacturing a rail according to one

aspect of the present invention has at least one first rolling

millrollinga steelrailmaterial, acoolingdevice adjusting

a temperature by cooling the steel rail material rolled with

the first rolling mill, and at least one second rolling mill

processing the steel rail material subjected to the

temperature adjustment into a rail shape by means of

temperature-adjusted rolling at an area reduction ratio of

20% or more, in which the cooling device cools the surface

portions of the steel rail material corresponding to a head

portion and a foot portion of the rail shape so that the

temperatures of the surface portions reach 500°C or more and

1,000°C or less.

[0010]

According to the method and the apparatus for

manufacturing a rail according to the present invention, a

rail having high ductility in both a head portion and a foot

portion can be manufactured.

Brief Description of the Drawings

[0011]

FIG. 1is a schematic view illustrating an apparatus for

manufacturing a rail according to one embodiment of the

present invention;

FIG. 2 is a cross-sectional view illustrating a rough

cooling device of one embodiment of the present invention;

- 5A -

FIG. 3 is a schematic view illustrating a heat treatment

apparatus of one embodiment of the present invention;

FIG. 4 is a cross-sectional view illustrating each

portion of a rail;

FIG. 5 is an explanatory view illustrating collection

positions of tensile test pieces evaluated in Examples; and

FIG. 6 is an explanatory view illustrating positions

where a Brinellhardness test evaluatedin Examples is carried

out.

Description of Embodiments

[0012]

Hereinafter, aspects for carrying out the present

invention (hereinafter also referred to as "embodiment") are

described in detail with reference to the drawings. In the

following description, % for chemical composition means % by

mass.

<Configuration of manufacturing apparatus>

First, a manufacturing apparatus 1 of a rail 9 according

to one embodiment of the present invention is described with

reference to FIG. 1 to FIG. 4. The rail manufacturing

apparatus 1 according to this embodiment is a rolling line

having a heating furnace 2, a roughing mill 3A, a finishing

mill 3B, a rough cooling device 4, a finish cooling device

5, a re-heating device 6, a heat treatment apparatus 7, and

a cooling bed 8.

[0013]

The rail 9 is manufactured by rolling and heat-treating

a steel rail material, such as a continuously cast bloom, by the manufacturing apparatus 1. As illustrated in FIG. 4, the rail 9 extends in the width direction viewed in a cross section perpendicular to the longitudinal direction and has a head portion 91 and a foot portion 93 facing each other in the vertical direction and an web portion 92 connecting the head portion 91 disposed on the upper side and the foot portion

93 disposed on the lower side and extending in the vertical

direction. As the rail 9, steel containing the following

chemical composition is usable, for example.

[0014]

C: 0.60% or more and 1.05% or less

C (carbon) is an important element which forms cementite

to increase hardness and strength and increases wear

resistance in a pearlitic steel rail. However, when the

contentis less than0.60%, these effects are low. Therefore,

the lower limit is preferably set to 0.60% and more preferably

set to 0.70% or more. On the other hand, excessive content

of C causes an increase in the cementite amount, and therefore

an increase in hardness and strength is expectable but,

contrarily, the ductility decreases. The increase in the C

content extends the temperature range of a y+O zone and

promotes softening of a weld heat affected zone. Considering

these adverse effects, the upper limit of the C content is

preferably set to 1.05% and more preferably set to 0.97% or

less.

[0015]

Si: 0.1% or more and 1.5% or less

Si (silicon) is added as a deoxidizer and for reinforcing

the pearlite structure. When the content is less than 0.1%,

these effects are low. Therefore, the Si content is

preferably 0.1% or more and more preferably 0.2% or more. On

the other hand, excessive content of Si promotes

decarburization and promotes the generation of surface flaws

of the rail 9, and therefore the upper limit of the Si content

is preferably set to 1.5% and more preferably 1.3% or less.

[0016]

Mn: 0.01% or more and 1.5% or less

Mn (manganese) has an effect of lowering the pearlite

transformation temperature and densifying the pearlite

lamella intervals, and therefore Mn is effective for

maintaining high hardness up to a rail inner region. When

the contentis less than 0.01%, the effectis low. Therefore,

the Mn content is preferably 0.01% or more andmore preferably

0.3% or more. On the other hand, when the Mn content exceeds

1.5%, the equilibrium transformation temperature (TE) of

pearlite is lowered and martensite transformation easily

occurs in the structure. Therefore, the upper limit of the

Mn content is preferably set to 1.5% and more preferably set

to 1.3% or less.

[0017]

P: 0.035% or less

When the content of P (phosphorus) exceeds 0.035%, the

toughness and the ductility are lowered. Therefore, the P

content is preferably suppressed to 0.035% or less and more

preferably limited to 0.025% or less. When special refinement and the like are performed in order to reduce the

P content as much as possible, the cost increase in smelting

is caused. Therefore, the lower limit is preferably set to

0.001%.

[0018]

S: 0.030% or less

S (sulfur) extends in the rolling direction to form

coarse MnS reducing ductility and toughness. Therefore, the

S content is preferably suppressed to 0.030% or less and more

preferably suppressed to 0.015% or less. In order to reduce

the S content as much as possible, the cost increase in

smelting, such as an increase in smelting processing time and

a flux, is remarkable. Therefore, the lower limit is

preferably set to 0.0005%.

[0019]

Cr: 0.1% or more and 2.0% or less

Cr (chromium) increases the equilibrium transformation

temperature (TE) and contributes to the reduction in the

pearlite lamella intervals to increase the hardness and the

strength. Furthermore, the use of Cr in combination with Sb

is effective for inhibition of the generation of a

decarburized layer. Therefore, when Cr is compounded, the

content is preferably set to 0.1% or more and more preferably

set to 0.2% or more. On the other hand, when the Cr content

exceeds 2.0%, a possibility of the generation of welding

defectsincreases, the quenchingpropertiesincrease, and the

generation of martensite is promoted. Therefore, the upper limit of the Cr content is preferably set to 2.0%, and more preferably set to 1.5% or less.

The total content of Si and Cr is desirably set to 2.0%

or less. This is because, when the total content of Si and

Cr exceeds 2.0%, the adhesiveness of a scale increases, and

therefore the peeling of the scale may be inhibited and

decarburization may be promoted.

[0020]

Sb: 0.005% or more and 0.5 or less

When a steel rail material is heated with a heating

furnace, Sb (antimony) has a remarkable effect of preventing

decarburization during the heating. In particular, when Sb

is added together with Cr, an effect of reducing a

decarburized layer is demonstrated when the Sb content is

0.005% ormore. Therefore, whenSbis compounded, the content

is preferably 0.005% ormore andmore preferably 0.01% ormore.

On the otherhand, when the Sb content exceeds 0.5%, the effect

is saturated. Therefore, the upper limit is preferably set

to 0.5% and more preferably set to 0.3% or less.

In addition to the chemicalcomposition described above,

one or two or more elements of Cu: 0.01% or more and 1.0% or

less, Ni: 0.01% or more and 0.5% or less, Mo: 0.01% or more

and 0.5% or less, V: 0.001% or more and 0.15% or less, and

Nb: 0.001% or more and 0.030% or less may be compounded.

[0021]

Cu: 0.01% or more and 1.0% or less

Cu (copper) is an element capable of further increasing

the hardness by solid solution strengthening. Cu is effective also for decarburization control. In order to expect the effect, the Cu content is preferably 0.01% or more and more preferably 0.05% or more. On the other hand, when the Cu content exceeds 1.0%, surface cracks due to embrittlement in continuous casting and rolling is easily generated. Therefore, the upper limit of the Cu content is preferablyset to1.0% andmore preferably set to0.6% orless.

[0022]

Ni: 0.01% or more and 0.5% or less

Ni (nickel) is an element effective for increasing

toughness and ductility. Moreover, by adding Ni in

combination with Cu, Ni is an element effective also for

preventing Cu cracks. Therefore, it is preferable to add Ni

when adding Cu. However, when the Ni content is less than

0.01%, these effects are not obtained. Therefore, the lower

limit is preferably set to 0.01% and more preferably set to

0.05% or more. On the other hand, when the Ni content exceeds

0.5%, hardenability excessively increases and the generation

of a martensite is promoted. Therefore, the upper limit is

preferably set to0.5% andmore preferably set to 0.3% or less.

[0023]

Mo: 0.01% or more and 0.5% or less

Mo (molybdenum) is an element effective for increasing

strength. When the content is less than 0.01%, the effect

is low. Therefore, the lower limitispreferablyset to 0.01%

and more preferably set to 0.05% or more. On the other hand,

when the Mo content exceeds 0.5%, hardenability increases and

a martensite is generated, and therefore the toughness and the ductility extremely decrease. Therefore, the upper limit of the Mo content is preferably set to 0.5% and more preferably set to 0.3% or less.

[0024]

V: 0.001% or more and 0.15% or less

V (vanadium) is an element which forms VC, VN, or the

like and is minutely precipitated into ferrite to contribute

to an increase in the strength through precipitation

strengthening of the ferrite. Moreover, V functions also as

a trap site of hydrogen, and thus an effect of preventing

delayed fracture is also expectable. To that end, the V

content is preferably 0.001% or more and more preferably

0.005% or more. On the other hand, when V is added in a

proportion exceeding 0.15%, the alloy cost extremely

increases while the effects are saturated. Therefore, the

upper limit is preferably set to 0.15% and more preferably

set to 0.12% or less.

[0025]

Nb: 0.001% or more and 0.030% or less

Nb (niobium) increases the non-recrystallization

temperature of austenite and is effective for reducing the

pearlite colony or block size by introduction of processing

strain into the austenite in rolling. Therefore, Nb is an

effective element for an improvement of ductility and

toughness. In order to obtain the effect, the Nb content is

preferably 0.001% or more andmore preferably 0.003% or more.

On the other hand, when the Nb content exceeds 0.030%, Nb

carbonitride is crystallized in a solidification process in casting of a steel rail material to reduce cleanliness.

Therefore, the upper limit is preferably set to 0.030% and

more preferably set to 0.025% or less.

[0026]

The remainder other than the components described above

includes Fe (iron) and inevitable impurities. As the

inevitable impurities, themixingofN (nitrogen) up to 0.015%,

the mixing of 0 (oxygen) up to 0.004%, and the mixing of H

(hydrogen) up to 0.0003% are acceptable. In order to prevent

a reduction in rolling fatigue properties due to hard AlN or

TiN, the Al content is desirably set to 0.001% or less and

the Ti content is desirably set to 0.001% or less.

[0027]

The heating furnace 2 is a continuation type or batch

type heating furnace and heats steel rail materials, such as

a continuously cast bloom, to a predetermined temperature.

The roughing mill 3Ais a universal mill which hot-rolls

a steel material at a predetermined area reduction ratio and

two or more of the roughing mills 3A are provided. In the

example illustrated in FIG. 1, the manufacturing apparatus

1has npieces ofroughingmills 3A1 to 3An. The roughcooling

device 4 is provided between a k-th roughing mill 3Ak and a

(K+1)-th roughing mill 3Ak+1 among the roughing mills 3A1 to

3An along the conveyance direction of the rail 9.

[0028]

The finishing mill 3B is a universal mill which further

hot-rolls the rough-rolled rail 9 to thereby finally process

the same into a target rail shape. In this embodiment, the area reduction ratio of the rail 9 to be rolled from the

(k+1)-th roughing mill 3Ak+1 to the finishing mill 3B as the

rolling process after the rough cooling device 4 is set to

20% or more. Herein, the area reduction ratio in this

embodiment shows the area reduction ratio of a

cross-sectional area perpendicular to the longitudinal

direction of the steel rail material and shows the ratio of

the reduction in the cross-sectional area during the rolling

to the cross-sectional area before the rolling of the bloom

and the like.

[0029]

The rough cooling device 4 has a head portion cooling

nozzle 41, a foot portion cooling nozzle 42, a head portion

thermometer 43, a foot portion thermometer 44, a conveyance

table 45, guides 46a and 46b, and a control unit 47 as

illustrated in FIG. 2.

The head portion cooling nozzle 41 cools the head portion

91 of the rail 9 by ejecting a cooling medium to the head

portion 91. The foot portion cooling nozzle 42 cools the foot

portion 93 of the rail 9 by ejecting a cooling medium to the

foot portion 93. The cooling medium ejected from the head

portion cooling nozzle 41 and the foot portion cooling nozzle

42 is spray water. The head portion cooling nozzle 41 and

the foot portion cooling nozzle 42 are provided above the head

portion 91 and the foot portion 93, respectively, on the

y-axis positive direction side and eject a cooling medium to

each of the head portion 91 and the foot portion 93 with an

inclination with respect to the y axial direction. Moreover, two or more of the head portion cooling nozzles 41 and the foot portion cooling nozzles 42 are provided along the z axis direction perpendicular to the x-y plane as the longitudinal direction of the rail 9.

[0030]

The head portion thermometer 43 and the foot portion

thermometer 44 are noncontact thermometers which measure the

surface temperature of each of the head portion 91 and the

foot portion 93 of the rail 9, respectively, to which the

cooling medium is ejected and are provided facing the head

portion 91 and the foot portion 93, respectively, in the x

axis direction. The measurement results of the head portion

thermometer 43 and the foot portion thermometer 44 are

transmitted to the control unit 47.

The conveyance table 45 is a conveyance roll extending

in the x axis direction and two or more of the conveyance tables

45 are provided side by side along the z axis direction. The

guides 46a and 46b are plate-like members and are provided

extending in the z axis direction. The guides 46a and 46b

are individually disposed on the upper side relative to the

conveyance table 45 on the y-axis positive direction side and

on both end sides in the longitudinal direction of the

conveyance table 45. Furthermore, the guides 46a and 46b are

further provided with openings 461a and 461b at the positions

where the head portion thermometer 43 and the foot portion

thermometer 44 are disposed, respectively.

[0031]

The control unit 47 controls the conditions of the

cooling medium ejected from the head portion cooling nozzle

41 and the foot portion cooling nozzle 42 based on the

measurement results of the head portion thermometer 43 and

the foot portion thermometer 44 to thereby cool the rail 9

to a predetermined surface temperature. The ejection

conditions of the coolingmediuminclude the ejection amount,

the ejection pressure, the moisture amount, the ejection time,

and the like of the cooling medium, for example.

The roughcoolingdevice 4 ofthe configuration described

above is provided between the k-th roughing mill 3Ak and the

(k+1)-th roughing mill 3Ak+1 among the plurality of roughing

mills 3A located side by side in the rolling direction of the

rail 9 and controls the surface temperature of the head

portion 91 and the foot portion 93 of the rail 9 to be rolled

with the k-th roughing mill 3Ak.

[0032]

The finish cooling device 5 is provided immediately

before the finishing mill 3B and controls the surface

temperature of the head portion 91 and the foot portion 93

of the rail 9 to be rolled with the finishing mill 3B. The

finish cooling device 5 has the same configuration as that

of the rough cooling device 4 illustrated in FIG. 2.

The rail9is conveyed androlledwithanoverturned state

as illustrated in FIG. 2 when rolled or cooled with the

roughing mills 3A, the rough cooling device 4, the finish

cooling device 5, and the finishing mill 3B.

[0033]

The re-heating device 6 is an induction heating type

heating device and heats the head portion 91 of the rail 9

to a predetermined temperature.

The heat treatment apparatus 7 has head portion cooling

headers 71a to 71c, a foot portion cooling header 72, a head

portion thermometer 73, and a control unit 74 as illustrated

in FIG. 3. The head portion cooling headers 71a to 71c are

provided facing each of the head top surface and both head

side surfaces of the head portion 91 and cool the head portion

91 by ejecting a cooling medium to the head top surface and

both the head side surfaces. The foot portion cooling header

72 is provided facing the underside of the foot portion 93

and cools the foot portion 93 by ejecting a cooling medium

to the underside of the foot. For the cooling medium ejected

from the head portion cooling headers 71a to 71c and the foot

portion cooling header 72, air, water, mist, and the like are

used. Two or more of the head portion cooling headers 71a

to 71c and the foot portion cooling headers 72 are provided

side by side along the longitudinal direction of the rail 9.

The head portion thermometer 73 is a non-contact-type

thermometer and measures the surface temperature of the head

portion 91. The temperature measurement results of the head

portion thermometer 73 are transmitted to the control unit

74. The control unit 74 controls the ejection conditions of

the cooling medium ejected from the head portion cooling

headers 71a to 71c and the foot portion cooling header 72

according to the temperature measurement results of the head

portion thermometer 73 to thereby control the cooling rate of the rail 9. The heat treatment apparatus 7 of the configuration described above cools the rail 9 at a predetermined cooling rate until the surface temperature reaches a predetermined surface temperature. The heat treatment apparatus 7 has a clamp (not illustrated). The clamp is a device restraining the foot portion of the rail

9 by holding the same.

The cooling bed 8 is a device which naturally cools the

rail 9 and contains, for example, a base supporting the rail

9.

[0034]

<Rail manufacturing method>

Next, a method for manufacturing the rail 9 according

to one embodiment of the present invention is described.

First, a bloom which is a steel rail material cast by

a continuous casting method is carried into the heating

furnace 2 to be heated to reach 1100 0 C or more.

Subsequently, the heated steel rail material is rolled

to have an almost rail shape by the roughing mills 3Aa to 3Ak

on the upstream side in the conveyance direction relative to

the rough cooling device 4. Hereinafter, a steel material

in the hot-rolling process is also referred to as a steel rail

material.

[0035]

Furthermore, the steel rail material rolled with the

roughing mills 3Aa to 3Ak is cooled (temperature adjustment)

with the rough cooling device 4 until the surface temperature

of portions corresponding to the head portion 91 and the foot portion 93 of the rail 9 reaches 500 0C or more and 1000 0 C or less. Herein, the control unit 47 controls the ejection amount, the ejection pressure, the moisture amount, the ejection time, and the like of the cooling medium to thereby cool the steel rail material.

When the steel rail material is heated to 11000 C or more,

the entire structure is transformed into austenite. In the

austenite structure of 1000 0 C or more, the grain boundary

easily moves and re-crystallization occurs, so that the

crystal grains are coarsened. On the other hand, when the

rolling is performed, strain is generated in the crystal

grains, and thus the crystal grains are divided, and then

refined. Herein, when the temperature in the rolling is

1000 0 C or less, the re-crystallization and the coarsening of

the crystal grains are difficult to occur. Therefore, by

setting the temperature of the steel rail material in the

rolling to 1000 0 C or less, the coarsening of the crystal grains

refined by the rolling is difficult to occur.

[0036]

When the steel rail material is cooled with the rough

cooling device 4, the temperature adjustment is preferably

performed until the surface temperature of the portions

corresponding to the head portion 91 and the foot portion 93

reach 500 0C or more and 730 0 C or less. When the steel rail

material is cooled to 7300 C or less, the structure partially

causes pearlite transformation. Therefore, the structure of

the steel rail material has a two phase structure containing

untransformed austenite and pearlite. When the austenite and the pearlite are compared with each other, the yield strength of the austenite is lower, and therefore most of strainis introducedin the austenite grains and the structure in the rolling is refined as compared with the case where the structure in the rolling is an austenite single phase. The colony size and the block size of the pearlite as the final structure are affected by the crystal grain diameter of the austenite which is the structure before transformation.

Therefore, when the austenite grains are coarse, the colony

size and the block size of the pearlite are also coarsened,

and therefore the ductility decreases. On the other hand,

when the austenite grains are fine, the colony size and the

block size of the pearlite are refined, and therefore the

ductility improves.

[0037]

When the temperature of the rail 9 in the rolling reaches

less than 5000 C, the structure completely causes pearlite

transformation, and therefore the austenite grains are not

present. Therefore, the colony size and the block size of

the pearlite do not become smaller, and thus an improvement

of ductility cannot be expected.

The phenomenon described above occurs irrespective of

portions of the rail 9. Therefore, by performing the rolling

after the temperature adjustment is performed in the portions

corresponding to the head portion 91 and the foot portion 93,

toughness and ductility is improved.

[0038]

Thereafter, the steel rail material subjected to the

temperature adjustment with the rough cooling device 4 is

further rolled with the roughing mills 3Ak+1 to 3An.

Subsequently, the steel railmaterial rough-rolled with

the roughingmills 3A1 to 3Anis cooledwith the finishcooling

device 5 as necessary, and then rolled with the finishingmill

3B tobe formedinto the rail9ofadesired shape. The rolling

in the roughing mills 3Ak+1 to 3An and the finishing mill 3B

after the temperature adjustment is also referred to as

temperature-adjusted rolling. The area reduction ratio of

the steel rail material to be subjected to the

temperature-adjusted rolling is 20% or more. By setting the

area reduction ratio to 20% or more, strain can be generated

also in the steel rail material, and therefore the inside

structure of the rail 9 can be refined. On the other hand,

when the area reduction ratio is less than 20%, a large number

of strains are generated in the surface of the steel rail

material but the number of strains generated inside the steel

rail material decreases. Therefore, the refinement of the

inside structure of the rail 9 becomes difficult to achieve,

so that a ductility improvement degree decreases.

[0039]

Furthermore, the rail 9 hot-rolled with the roughing

mills 3A and the finishing mill 3B is conveyed to the

re-heatingdevice 6 tobe heateduntil the surface temperature

of the head portion 91 reaches 7300 C or more and 9000 C or less.

Thereafter, the heated rail 9 is conveyed to the heat

treatment apparatus 7 to be forcibly cooled (heat treatment) with the heat treatment apparatus 7 in the state of being restrained by the clamp until the surface temperature of the head portion 91 reaches 600 0C or less. Herein, the control unit 74 calculates the cooling rate of the rail 9 from the temperature measurement results of the head portion thermometer 73, and then controls the ejection conditions of the cooling medium ejected from the head portion cooling headers 71a to 71c so that the average cooling rate is 1°C/s or more and 10°C/s or less. Moreover, the control unit 74 controls the ejection conditions of the cooling medium ejected from the foot portion cooling header 72 in such a manner as to be the same as any one of the ejection conditions of the cooling medium ejected from the head portion cooling headers 71a to 71c.

[0040]

When the surface temperature of the head portion 91 is

less than 7300 C before the heat treatment, the structure

partially or entirely causes pearlite transformation.

Before the heat treatment, the rail 9 is naturally cooled and

the cooling rate is low. Therefore, the pearlite lamella

intervals is coarse. Therefore, by performing re-heating so

that the surface temperature of the head portion 91 reaches

7300 C or more before the heat treatment, the pearlite

structure is reversely transformed to the austenite structure,

and thus the lamella structure is able to be formed again.

On the other hand, when the surface temperature of the head

portion 91is higher, the hardening of the decarburized layer

on the surface and the hardening due to an improvement of the cooling rate inside the rail are achieved, so that the wear resistance is improved. However, when the surface temperature of the head portion 91 exceeds 900C, the effect described above is lowered. Furthermore, when the surface temperature of the head portion 91 exceeds 1000 0 C, the re-crystallization and the coarseningof the austenite grains occur, which is not preferable. Therefore, considering the saving of the energy required for the re-heating and the wear resistance improvement effect, the upper limit of the surface temperature in the re-heating before the heat treatment is preferably set to 900 0 C.

[0041]

In order to achieve high wear resistance properties, the

reductionin the pearlite lamellaintervalsis effective. In

order to reduce pearlite lamella intervals, heat treatment

at a high cooling rate is required. Therefore, the heat

treatment is preferably performed at a surface temperature

and at an average cooling rate within the ranges mentioned.

When the cooling rate is less than 1°C/s, the pearlite lamella

intervals are coarse and the wear resistance decreases. On

the other hand, when the cooling rate exceeds 10°C/s, the

structure after transformation is such as bainite and

martensite that are poor in toughness and ductility, and this

is not preferable. In this embodiment, the average cooling

rate is acoolingrate determined from the temperature changes

and the heat treatment time from the start of the heat

treatment to the end of the heat treatment. Therefore, the

thermal history from the start of the heat treatment to the end of the heat treatment also includes the heat generation of the phase transformation heat and isothermal-holding by patenting treatment. When the surface temperature of the head portion 91 at the end of the heat treatment exceeds 600C, the lamella structure is partially spheroidized after the end of the heat treatment, and therefore the lamella intervals are coarse and the wear resistance decreases.

Subsequently, the rail 9 subjected to accelerated

cooling is conveyed to the cooling bed 8, and then naturally

cooled until the temperature reaches about 100 0 C or less.

After the cooling on the cooling bed 8, shape correction of

the rail 9 is performed as necessary when the rail 9 is bent

orthelike. Bypassing through the processes described above,

the rail 9 excellent in ductility and wear resistance is

manufactured.

[0042]

<Modification>

Hitherto, the preferable embodiments of the present

invention are described in detail with reference to the

accompanying drawings but the present invention is not

limited to such examples. It is apparent that a person who

has ordinary knowledge in the technical field to which the

present invention belongs can perceive various changes or

modifications within the scope of the technical thoughts

described in claims. It should be understood that these

changes or modifications also naturally belong to the

technical scope of the present invention.

[0043]

For example, the cooling method in the rough cooling

device 4 and the finish cooling device 5 is spray cooling

employingspraywater for the coolingmediumin the embodiment

described above but the present invention is not limited to

the example. For example, mist cooling as spray cooling

employing mist as a cooling medium or mixed cooling of mist

cooling and air blast cooling employing mist and air as a

cooling medium maybe used for the cooling method in the rough

cooling device 4 and the finish cooling device 5.

Alternatively, natural cooling, immersion cooling, air blast

cooling, water column cooling, and the like may be performed

in place of the spray cooling with the rough cooling device

4 and the finish cooling device 5. In the natural cooling

and the air blast cooling, the cooling rate is low, and

therefore the time until the rail 9 is cooled to a

predetermined temperature is prolonged. Therefore, when the

rolling pitch is to be increased, other cooling methods, such

as spray cooling, immersion cooling, and water column cooling,

are able to be employed. However, the cooling rate in the

water column cooling is excessively high, and therefore the

cooling rate is difficult to adjust. Furthermore, when the

rail 9 is conveyed with an overturned state, water is stored

in the web portion 92 of the rail 9, resulting in the generation

of aportion with an excessively high cooling rate. Therefore,

the structure may be transformed to a structure having low

toughness and ductility, such as bainite and martensite. On

the other hand, the spray cooling has advantages in that a

somewhat high cooling rate is able to be secured and the cooling portion is easily localized. Therefore, the spray cooling is preferably used for the cooling method in the rough cooling device 4 and the finish cooling device 5.

[0044]

Furthermore, the temperature-adjusted rolling is

performed in the rolling pass after the roughing mill 3Ak+1

in the embodiment described above but the present invention

is not limited to the example. The temperature-adjusted

rolling may be performed after any roughing mill 3A insofar

as an areareduction ratio of20% ormore is able tobe secured.

Herein, the rough cooling device 4 is provided immediately

before the roughing mill 3A with which the

temperature-adjusted rolling is started. The

temperature-adjusted rolling may be performed in finish

rolling by the finishing mill 3B. Herein, the rough cooling

device 4 may not be provided in the rail manufacturing

apparatus 1 and the temperature adjustment may be performed

only the finish cooling device 5. When the

temperature-adjusted rolling is performedin finish rolling,

the finish rolling needs to be performed at a large area

reduction ratio of 20% or more, and therefore the shape of

the rail 9 may deteriorates. Therefore, the

temperature-adjusted rolling is preferably performed in the

rolling with some of the roughing mills 3A and with the

finishing mill 3B.

[0045]

Furthermore, the roughingmills 3Aand the finishingmill

3B are universal mills in the embodiment described above but the present invention is not limited to the example. For example, the roughing mills 3A and the finishing mill 3B may be caliber rolling mills. In a universal rolling method, rolling from aplurality ofdirections is achieved as compared with a caliber rolling method, and therefore the rolling load can be reduced. In particular, in the present invention, a rolling operation capable of obtaining a large area reduction ratio at alow temperature is performed, and therefore rolling is performed under an overload and the load to the rolling mills becomes high, so that the risk of a facility trouble becomes high. Therefore, at least any one of the roughing mills3Aandtwoormoreofthe finishingmills3Bispreferably a universal mill.

Furthermore, two or more of the finishing mills 3B may

be provided.

[0046]

Furthermore, the re-heating device 6 is the induction

heating type heating device in the embodiment described above

but the present invention is not limited to the example. For

example, the re-heating device 6 may be a burner type heating

device. In the induction heating type re-heating device 6,

the size of the facility is able to be made small as compared

with the burner type. Therefore, the induction heating type

re-heating device 6 is preferable when disposed in-line.

The re-heating device 6 heats the head portion 91 in the

embodiment described above but the present invention is not

limited to the example. For example, the re-heating device

6 may have a configuration ofheating the entire rail 9. When the rail 9 is used, portions contacting wheels are worn out, and therefore particularly the head portion 91 is required to have wear resistance. Therefore, a configuration of re-heating only the head portion 91 in re-heating is economically excellent because energy required for the heating is able to be reduced.

[0047]

Furthermore, the re-heating is performed with the

re-heating device 6 after the hot-rolling in the embodiment

described above but the re-heating with the re-heating device

6 may not be performed. Herein, the hot-rolled rail 9 is

conveyed to the heat treatment apparatus 7, and then

heat-treated with the heat treatment apparatus 7. Even when

the re-heating is not performed, the ductility improvement

effect of the head portion 91 and the foot portion 93 is able

to be obtained. However, when the temperature of the rail

9 after the end of the hot-rolling (after the end of the

temperature-adjusted rolling) is low, the hardness decreases

as compared with the case where the temperature is high. In

addition to the re-heating, the heat treatment with the heat

treatment apparatus 7 is also omissible. Herein, the

hot-rolled rail 9 is conveyed to the cooling bed 8, and then

cooled until the temperature reaches about 100 0 C or less.

Even when the re-heating and the heat treatment are not

performed, the ductility improvement effect of the head

portion 91 and the foot portion 93 is able to be obtained.

However, the hardness decreases as compared with the case

where the re-heating and the heat treatment are performed.

[0048]

(1) The method for manufacturing the rail 9 according to the

embodiment described above includes hot-rolling a heated

steel railmaterial, adjusting the temperature by cooling the

hot-rolled steel rail material, processing the steel rail

material subjected to the temperature adjustment into a rail

shape by means of temperature-adjusted rolling at an area

reduction ratio of 20% or more, and, in adjusting the

temperature of the steel rail material, cooling the surface

portions of the steel rail material corresponding to a head

portion and a foot portion of the rail shape so that the

temperatures of the surface portions reach 500°C or more and

1,000°C or less.

According to the configuration described above, crystal

grains are able to be divided and refined while preventing

the coarsening of the crystal grains due to the

re-crystallization in the austenite temperature range in the

temperature-adjusted rolling. Therefore, the toughness and

the ductility of the head portion 91 and the foot portion 93

of the rail 9 are able to be increased.

[0049]

(2) After performing the temperature-adjusted rolling,

the rail 9 is heat-treated until the surface temperature of

the head portion of the rail 9 reaches 600°C or less at an

average cooling rate of 1 °C/s or more and 10 °C/s or less.

According to the configuration described above, the

pearlite lamella intervals of the head portion 91 of the rail

9canbe refinedand the wear resistance is able tobeincreased.

Moreover, the spheroidization of the lamella structure after

the end of the heat treatment is able to be prevented, and

therefore the wear resistance improves.

[0050]

(3) Before heat-treating the rail 9, the rail is

re-heated to 730 0 C or more when the surface temperature of

the head portion of the rail 9 is less than 730 0 C.

According to the configuration described above, the

pearlite structure is able to be reversely transformed to the

austenite structure, so that the lamella structure is able

to be re-created again. Therefore, the hardness and the wear

resistance of the rail 9 are able to be increased.

(4) In re-heating the rail 9, only the head portion 91

of the rail 9 is re-heated.

According to the configuration described above, the

energy required for the heating is able to be reduced as

compared with the case where the entire rail 9 is re-heated.

[0051]

(5) The apparatus 1 for manufacturing the rail 9

according to the embodiment has at least one first rolling

mills 3A1 to 3AK rolling a steel rail material, a cooling

device 4 adjusting a temperature by cooling the steel rail

material rolled with the first rolling mills 3A1 to 3AK, and

at least one second rolling mills 3AK+1 to 3An and 3B

processing the steel rail material subjected to the

temperature adjustment into a rail shape by means of

temperature-adjusted rolling at an area reduction ratio of

20% or more, in which the cooling device 4 cools the surface

portions of the steel railmaterial corresponding to the head

portion 91 and the foot portion 93 of the rail shape so that

the temperatures of the surface portions reach 5000 C or more

and 1,000°C or less.

According to the configuration described above, the same

effects as those obtained in (1) are able to be obtained.

Examples

[Example 1]

[0052]

Next, Examples 1 performed by the present inventors are

described.

In Examples 1, rails 9 were manufactured using the rail

manufacturing apparatus 1 described in FIG. 1 under various

chemical composition conditions and rolling conditions, and

then the total elongation of the manufactured rails 9 was

measured.

Table 1 shows the chemical composition of the rail 9 used

in Examples 1. The remainder includes iron and inevitable

impurities. Table 2 shows the rolling conditions and the

measurement results of the total elongation in Examples 1.

[0053]

[Table 1]

Composition C[%] Si[%] Mn[%] P[%] S[%] Cr[%] Sb[%] Al[%] Ti[%] Others A 0.83 0.52 0.51 0.015 0.008 0.192 0.00010.0005 0.001 B 0.83 0.52 1.11 0.015 0.008 0.192 0.00010.0005 0.001 C 1.03 0.52 1.11 0.015 0.008 0.192 0.00010.0005 0.001 D 0.84 0.54 0.55 0.018 0.004 0.784 0.00010.0000 0.002 V[%]: 0.058 E 0.82 0.23 1.26 0.018 0.005 0.155 0.0360 0.0001 0.001 Cu[%] 0.11, F 0.83 0.66 0.26 0.015 0.005 0.896 0.1200 0.0005 0.001 Ni[%] 0.12, Mo[%]: 0.11

G 0.82 0.55 1.13 0.012 0.002 0.224 0.0001 0.0000 0.000 Nb[%] 0.009

0 4

0j 0 0-m~0 ' 0 )0 G 0-) 0-) 0-) 0-) 0-) 0-) 0-) N~ N' P- m 0-) 0-) N' N' 0-) 0-) 0-) () CD (0) () ()

44~ 0

0 t0 2

00

01 0 C-H 10 C'J M CD ~Q~~' )~ CDCD' )f Q

44~ 0

0 00,

a) 4-,u m 0t -H d

0 0 0 a)

00 -4 -4 0-A

0 4

0

0 )

Z50

S0 ~ )

- 10H

wt 0 00

0.

00

0 0 0' 0))'J-0

S0 -H10"

(11 (1 (11 4 " (1 (1 (1 O CO C O C O C O C 0 0 4 ( 0 ( 0 ( 0 C O C -H-H-H4Z--] H 14H -11 -H- H- H- H - H- -1 -H -4 -H -H -H -H -H -H -H -H -H ~~~~~~ 00 0000 0 I0 1 1 1 14 0- 8 0 - 1 ,-1 ],]

U)~~ U) C) 0- -H U)O M) M) 0 HCD~ )U U 0-U) 0 C) U)O M)U )U)U

0 0000.

[0055]

In Examples 1, first, a continuously cast bloom was

heated with the heating furnace 2 until the temperature

reached 11000 C. The chemical composition of the bloom used

in Examples 1 was any one of the composition A to the

composition G of Table 1 as shown in Table 2.

Subsequently, the heated bloom was collected from the

heating furnace 2, and thenhot-rolledwith the roughingmills

3A and the finishing mill 3B. For the roughing mills 3A, a

plurality of rolling mills in which a universal mill and a

caliber rolling mill were combined was used. The rail 9

during the rolling was rolled and conveyed with an overturned

state. When the hot-rolling was performed, the temperature

adjustment was performed until the surface temperatures of

the head portion 91 and the foot portion 93 reached 5000 C or

more and 1000 0 C or less with either the rough cooling device

4 or the finish cooling device 5. The temperature adjustment

method, the time from the start of the temperature-adjusted

rolling to the end of the hot-rolling, and the number of

temperature-adjusted rolling passes are individually shown

in Table 2. The temperature-adjusted rolling refers to

hot-rolling after the temperature adjustment was performed.

[0056]

As shown in Table 2, in Examples 1, the temperature

adjustment was performed by any one of the spray cooling, air

blast cooling, and naturally cooling methods. The surface

temperatures of the head portion 91 and the foot portion 93

were adjusted by adjusting the water amount density and the cooling time in the case of the spray coolingor by controlling the cooling time without using the rough cooling device 4 and the finishcoolingdevice 5in the case of the naturalcooling.

[0057]

The number of the temperature-adjusted rolling passes

shown in Table 2 shows the number of rolling passes after the

temperature adjustment was performed by any one of the methods

described above. For example, the number of times of the

temperature-adjustedrollingpasses was 1 time indicates that,

after the temperature adjustment, only the finish rolling was

performed and the number of times of the temperature-adjusted

rolling passes was n (n 2) times indicates that, after the

temperature adjustment, n-i times of rough rolling and one

finish rolling were performed. When the number of times of

the temperature-adjusted rolling passes was 1 time, the

temperature adjustment was performedusing the finish cooling

device 5. When the number of times of the

temperature-adjusted rolling passes was n times, the

temperature adjustment was performed using the rough cooling

device 4.

[0058]

After the hot-rolling was performed, the rail 9 was

forcibly cooled with the heat treatment apparatus 7. The

surface temperatures of the head portion 91 and the foot

portion 93 in starting the forcible cooling were set as shown

in the conditions shown in Table 2. When the forcible cooling

was performed, the average cooling rate was set to 3C/s. The

cooling was performed until the surface temperature reached

400 0 C. When the forcible cooling was performed, mist was used

for a cooling medium. In Examples 1, the re-heat treatment

employing the re-heating device 6 was not performed after the

hot-rolling.

[0059]

Subsequently, the forcibly cooled rail 9 was conveyed

to the cooling bed 8, the temperature was reduced to 100 0 C

or less by cooling, and then the railwas straightened. After

the rail 9 was manufactured in the processes described above,

test pieces were collected from fourplaces of an endportion,

the 1/4 position, the 1/2 position, and the 3/4 position in

the longitudinal direction of the rail 9, and then various

physical properties were measured. As illustrated in FIG.

5, a sample 9a was collected from the head portion 91 and a

sample 9b was collected from the foot portion 93 of the test

pieces collected at each position in the longitudinal

direction. The sample 9a is a JIS No. 4 test piece collected

from a position having a distance d2 = 12.7 mm from the upper

end of the head portion 91 and having a distance dl = 24.6

mm from the center in the width direction. The sample 9b is

a JIS No. 4 test piece collected from a position having a

distance d3 = 12.7 mm from the lower end of the foot portion

93 and at the center in the width direction.

[0060]

In Examples 1, as examples different in the chemical

composition, the temperature adjustment method, the number

of temperature-adjusted rolling passes, the surface

temperature, and the area reduction ratio, rails 9 were manufactured under 28 kinds of conditions of Examples 1-1 to

1-28, and then the total elongation was evaluated.

Moreover, as shown in Table 2, rails 9 were manufactured

as comparative examples under the same conditions as those

of Examples 1-1 to 1-28, and then the total elongation was

evaluated also for Comparative Examples 1-1 to 1-5 with the

surface temperature and the area reduction ratio in the

temperature-adjusted rolling outside the ranges of the

embodiment described above. The total elongation values

shown in Table 2 show the average value of the four samples,

i.e., the sum of one sample collected from each of the test

pieces collected from each of the four places.

[0061]

It was confirmed that the total elongations of the head

portion 91 and the foot portion 93 were 12% or more as the

target total elongation under all the conditions of Examples

1-1 to 1-28. It was also confirmed that, in Examples 1-14,

1-15, 1-19, and 1-20 in which the surface temperature of

either the head portion 91 or the foot portion 93 was 7300 C

or less in the temperature-adjusted rolling, the elongation

ofthe headportion91or the footportion93 withalow surface

temperature was as high as 17% or more. Furthermore, it was

confirmed that, in Example 1-8 in which the surface

temperatures of both the head portion 91 and the foot portion

93 in the temperature-adjusted rolling were 730 0 C or less,

the total elongations of the head portion 91 and the foot

portion 93 were as high as 19% or more.

[0062]

On the other hand, in Comparative Example 1-1 in which

the surface temperature of the foot portion 93 in the

temperature-adjusted rolling exceeded1000°C and Comparative

Example 1-2 in which the area reduction ratio of the foot

portion 93 in the temperature-adjusted rolling was less than

20%, the elongation of the foot portion 93 was less than 12%

and decreased as compared with those of Examples 1-1 to 1-28.

In Comparative Examples 1-3 and 1-4 in which the surface

temperature in the temperature-adjusted rollingwas less than

500°C or exceeded 1000°C and Comparative Example 1-5 in which

the rolling reduction of the head portion 91 in the

temperature-adjusted rolling was less than 20%, the

elongation of the head portion 91 was less than 12% and

decreased as compared with those of Examples 1-1 to 1-28.

[Example 2]

[0063]

Next, Examples 2 performed by the present inventors are

described.

In Examples 2, influences on the total elongation, the

hardness, and the surface structure depending on the heat

treatment conditions were confirmed by varying the chemical

composition and the conditions in the temperature-adjusted

rolling and the heat treatment. Table 3 shows the chemical

composition, the surface temperature in

temperature-adjusted rolling, the conditions of heat

treatment (forcible cooling), the measurement results of the

total elongation, the measurement results of the hardness, and the observation results of a head portion surface structure in Examples 2.

[0064]

[Table 3]

10 a)a 0

rd rj4jd j rd rd rd1 rd rd rd rd rd rd rd rd r drd r drd r d r

O o u o [ r1 r1 r1 o -- -- -- - 000 --1rd--1- -1--1rd--1--1--1--1 -r1 -r4-1 Z5. o )o 00~- )o[ 4 0~0 04y~~

001

-H4 0 00 0 0 0 0 F1) [1) [1) 0 [1) 0 0d 0 d [1) [1) 0 d 0 F114 l 0 1 m -- HH--HH--HS1

0 O U U 0 -H M 0000000 o 000 0 0 0 0 o Ot o 00 O 0 0 0

rd 0 i 0 0 4 0 ol M -i0 __. 00T T T T T00 0 TO ir) l 00 T TT TT T

-- r) LH CrNm0)m r)) 0 ..0 O4 O

H 0

S- -r

l - 0

Z5 0 d 41-c-1c 4j 00 0 00 0 0 0, 0 , 0 0,0,0,000, c rd OSO OD 0 0 00 mmmmo 00 00 00 00 00 omm.-me .0) *ma mmmo o e 01

(40 ed y 00 u a)

A 00

Z5 S 0 M0 0 0 Mm m m 0 00000 0 0 0 4 0 -r-H

-r-41 | | | ||1

1A Cl 0 -r- -1F M 0 ~~~~ ~ ~ CDC DC DC C DC D C D D C DC DC CD D CD~O~0 0 CD CD CD d O Z5l r [0o m r rr)

Clll~~1lll ~Clo ml CD 'A 'A Cl,~l

0 0 0

[0065]

In Examples 2, as the temperature-adjusted rolling,

rolling in four passes in total containing three universal

mills and one caliber rolling mill was performed so that the

area reduction ratios of the head portion 91 and the foot

portion 93 were 30%. The surface temperatures of the head

portion 91and the foot portion 93 in the temperature-adjusted

rolling and the start temperature, the cooling rate, and the

end temperature in the heat treatment were set as shown in

the conditions shown in Table 3. When the heat treatment was

performed, air was used for a cooling medium under the

condition where the cooling rate was 3 0 C/s or less and a

mixture of air and mist was used for a cooling medium under

the condition where the cooling rate exceeded 3 0 C/s. The

other manufacturing conditions were the same as those of

Examples 1.

[0066]

With respect to the total elongation of the rail 9, test

pieces were collected, and then the total elongation was

measured by the same method as that of Examples 1. With

respect to the hardness of the rail 9, a sample 9cwas collected

from a position of the head portion surface illustrated in

FIG. 6 and a sample 9d was collected from a position inside

the head portion from the test pieces of about 20 mm thickness

sawn from four places of an end portion, the 1/4 position,

the 1/2 position, and the 3/4 position in the longitudinal

direction of the rail 9. The sample 9c was collected from

the center of the upper end surface of the head portion 91 of the test pieces polished in order to remove surface unevenness. The sample 9d was collected from a position at the center in the width direction and having a distance d4

= 20 mm from the upper end of the head portion 91 of the test

pieces polished in order to remove surface unevenness. Next,

the hardness of the collected samples 9c and 9d was measured

by a Brinell hardness test. With respect to the surface

structure, the surface structure of the collected samples 9c

was observed.

[0067]

In Examples 2, as examples different in the chemical

composition, the surface temperature in the

temperature-adjusted rolling, and conditions in the heat

treatment, rails 9 were manufactured under 21 kinds of

conditions of Examples 2-1 to 2-21, and then the total

elongation and the hardness were measured and further the

surface structure was observed. In Example 2-13, the heat

treatment was not performed and the rail 9 after the

hot-rollingwas conveyed to the coolingbed 8, and then cooled

until the temperature reached 100 0 C or less. After the rail

9 reached 100 0 C or less, the rail was straightened.

[0068]

Also in Comparative Examples 2-1 to 2-3 in which the

cooling rate in the heat treatment exceeded the ranges of the

embodiment described above, rails 9 were manufactured as

comparative examples under the same conditions as those of

Examples 2-1 to 2-21, and then the total elongation and the

hardness were measured and further the surface structure was observed as shown in Table 3. The values of the total elongation and the hardness shown in Table 3 show the average value of the four samples individually collected from the test pieces collected from the four places.

[0069]

It was confirmed that, in Examples 2-1 to 2-21 in which

the heat treatment was performed at a cooling rate of 0.5C/s

or more and 10°C/s or less, the total elongations of the head

portion 91 and the foot portion 93 were 12% or more as the

target total elongation in all the conditions.

In Examples 2-2 and 2-3, the surface temperature of the

head portion 91in the temperature-adjusted rolling was lower

than that in other conditions, the surface temperature in

starting the heat treatment was also low and the total

elongation of the head portion 91 was 15% or more, which was

higher than that in other conditions. However, in Examples

2-2 and 2-3, the hardness of the head portion 91 was 380 HB

or less, which was lower than that in Example 2-1.

[0070]

In Examples 2-1, 2-7 to 2-10, and 2-14 to 2-21 in which

the conditions except the cooling rate in the heat treatment

were the same and, further, in Examples 2-14 to 2-21 in which

the composition is different, the hardness of the surface and

inside of the head portion 91 improved when the cooling rate

was higher. In Examples 2-1, 2-7 to 2-10, and 2-14 to 2-21

and Comparative Examples 2-1 to 2-3 in which the conditions

except the cooling rate in the heat treatment were the same

and, further, in Comparative Examples 2-1 to 2-3 in which the coolingrate exceeded10°C/s, the coolingrate was excessively high, and therefore the structure was partially transformed into a martensite and the total elongation was as very low as 3%.

[0071]

In Examples 2-1, 2-11, and 2-12 in which the conditions

except the end temperature in the heat treatment were the same,

the hardness of the surface and inside of the head portion

91 improved when the cooling stop temperature was lower. In

Example 2-11 in which the end temperature in the heat

treatment was set to 650 0 C, the pearlite structure was

partially spheroidized.

In Example 2-13 in which the heat treatment was not

performed, the total elongations of the head portion 91 and

the foot portion 93 were 12% or more but the hardness of the

surface and inside of the head portion 91 was the lowest in

all the conditions. In Example 2-13, the pearlite structure

was partially spheroidized.

[Example 3]

[0072]

Next, Examples 3 performed by the present inventors are

described.

In Examples 3, in order to confirm influences on the

hardness and the surface structure by re-heat treatment,

re-heating was performed before the heat treatment with

respect to the condition of Example 2-3 in which the hardness

was low. In Examples 3, manufacturing conditions other than

the surface temperature of the head portion 91 in the temperature-adjusted rolling and performing re-heating were the same as those ofExample 2-3. Table 4 individually shows the chemical composition, the surface temperature in the temperature-adjusted rolling, the conditions in the re-heating and the heat treatment, the measurement results of the total elongation, the measurement results of the hardness, and the observation results of the head portion surface structure in Example 3. The total elongation values and the hardness shown in Table 4 show the average value of the four samples, i.e., the sum of one sample collected from eachof the testpieces collected fromeachof the fourplaces.

[0073]

[Table 4]

O U

E 0 Z5 4 0 CO00 ( (00 F 0 0 0 F 0 00 C

-r- 44 O .-. O 4 CO LC) 4 A (0O O4 4 4 LA O4 d

On C CCIn o o f 0 0 0 to 0 0

0 O -O 0 H-H H rd

o t0 0 00 A A -A 0'

- 0 0 0 0 0 00 0 0 0 0.r

0.

0

o o ._. A rA r o A r r o A

- 0 0 -]

-- 0 C C C C CCC C

00 O r'' M0 o o 0 o o o to 0 0 o 0 0 0 0 0 0 0

| o- -A o - o -H -] 4000A)000 0 0O -H -H--HI-H 0

0 0 yn L n L n L n

rd '-- D oD oD D oD D oD D CD 0

0 ° 0 0 0 0 000 0 0

0 0 0 0 0C 0 r0 0 0 -r- O 0| 0| 0 | |0| | H M M0 M0 M0 0 -r-oI 3 -]-H & N &N- 3 O- A MM MM

[0074]

In Examples 3, the head portion 91 or the entire rail

9 was re-heated with the re-heating device 6 after the

hot-rolling. The re-heating device 6 is aninductionheating

type heating device and is able to heat the head portion 91

or the entire rail9 according to the conditions shownin Table

4. The surface temperature of the head portion 91 after the

re-heating is the start temperature in the heat treatment

shown in Table 4.

In Examples 3, rails 9 were manufactured under 9 kinds

of conditions of Examples 3-1 to 3-9 different in the surface

temperature of the head portion 91 in the

temperature-adjusted rolling and the re-heating conditions,

and then the total elongation and the hardness were measured

and further the surface structure was observed. Amethod for

collecting samples for the total elongation and the hardness

and a method for collecting samples for observing the surface

structure are the same as those of Examples 2. Example 3-1

is the condition in which the re-heating was not performed

and has the same manufacturing conditions as those of Example

2-3.

[0075]

As shown in Table 4, it was confirmed that, in all the

conditions of Examples 3-1 to 3-9, the total elongations of

the head portion 91 and the foot portion 93 were 12% or more

as the target total elongation.

In Example 3-1inwhich the re-heatingwas not performed,

the surface temperature in starting the temperature-adjusted rolling was low, and therefore the surface temperature of the head portion 91 in starting the heat treatment was as low as

630C and the hardness of the surface and inside of the head

portion 91 was low.

[0076]

In Examples 3-2 and 3-6, the re-heating was performed

and the surface temperature of the head portion 91in starting

the heat treatmentwas set to7000 Cbut the surface temperature

was as low as 7300 C or less, and therefore the hardness of

the surface and inside of the head portion 91 was low as in

Example 3-1.

It was confirmed that, in Examples 3-3 to 3-5 in which

the entire rail 9 was re-heated and Examples 3-7 to 3-9 in

which only the head portion 91 was re-heated, the hardness

improved by 20 HB or more on the surface of the head portion

91 and 5 HB or more inside the head portion 91 as compared

with Examples 3-2 and 3-6 in which the temperature after the

re-heating was low. Moreover, it was confirmed that there

is no difference in the hardness improvement effect of the

head portion 91 between the case where the entire rail 9 was

re-heated and the case where only the head portion 91 was

re-heated. Furthermore, it was confirmed that there is no

difference in the hardness of the head portion 91 when

Examples 3-4, 3-5, 3-8, and 3-9 are compared, and therefore

there is no difference in the hardness improvement effect by

re-heating when the surface temperature after the re-heating

was 900 0 C or more.

It was confirmed from the results described above that

the rail 9 having high ductility in both the head portion 91

and the foot portion 93 is able to be manufactured according

to the method and the apparatus for manufacturing a rail

according to the present invention.

Reference Signs List

[0077]

1: manufacturing apparatus

2: heating furnace

3A, 3A1 to 3An: roughing mill

3B: finishing mill

4: rough cooling device

41: head portion cooling nozzle

42: foot portion cooling nozzle

43: head portion thermometer

44: foot portion thermometer

45: conveyance table

46a, 46b: guide

461a, 461b: opening

5: finish cooling device

6: re-heating device

7: heat treatment apparatus

71a to 71c: head portion cooling header

72: foot portion cooling header

73: head portion thermometer

74: control unit

8: cooling bed

9: rail

91: head portion

92: web portion

93: foot portion

[0078]

The reference in this specification to any prior

publication (orinformation derived fromit), or to any matter

which is known, is not, and should not be taken as an

acknowledgment or admission or any form of suggestion that

that prior publication (or information derived from it) or

known matter forms part of the common general knowledge in

the field of endeavour to which this specification relates.

Throughout this specification and the claims which

follow, unless the context requires otherwise, the word

"comprise", and variations such as "comprises" and

"comprising", will be understood to imply the inclusion of

a stated integer or step or group of integers or steps but

not the exclusion of any other integer or step or group of

integers or steps.

Claims (3)

1. A rail manufacturing method comprising:

hot-rolling a heated steel rail material by at least one

first rolling mill;

adjusting a temperature by cooling the hot-rolled steel

rail material; and

rolling the steel rail material subjected to the

temperature adjustment into a rail shape at the adjusted

temperature at an area reduction ratio of 20% or more by at

least one second rolling mill, wherein,

in adjusting the temperature of the steel railmaterial,

a surface portion of the steel rail material corresponding

to a head portion and a foot portion of the rail shape is cooled

so that the temperatures of the surface portion reaches 500°C

or more and 1,000°C or less by a cooling device arranged

between the at least one first rolling mill and the at least

one second rolling mill, wherein:

after the rollingby the at least one second rollingmill,

heat-treating the rail by forcibly cooling at an average

coolingrate of1°C/s ormore and10°C/s orless froma surface

temperature of 730°C or more until the surface temperature

reaches 600°C or less; and wherein

the steel material has a composition comprising 0.60%

or more and 1.05% or less carbon (C), 0.1% or more and 1.5%

or less silicon (Si), 0.01% or more and 1.5% or less manganese

(Mn), 0.035% or less phosphorus (P), 0.030% or less sulfur

(S), 0.1% or more and 2.0% or less chromium (Cr), 0.5% or less

antimony (Sb), optionally at least one of 0.01% or more and

0.5% or less copper (Cu), 0.01% or more and 0.5% or less nickel

(Ni), 0.01% or more and 0.5% or less molybdenum (Mo), 0.001%

or more and 0.15% or less vanadium (V), 0.001% or more and

0.30% or less niobium (Nb), the balance being iron (Fe) and

inevitable impurities.

2. The rail manufacturing method according to Claim

1 comprising:

before the heat-treating the rail, re-heating the rail

to 730°C or more when the surface temperature of the head

portion of the rail is 730°C or less.

3. The rail manufacturing method according to Claim

2, wherein,

in the re-heating the rail, only the head portion of the

rail is reheated.