AU2015237464B2

AU2015237464B2 - Rail and method for manufacturing same

Info

Publication number: AU2015237464B2
Application number: AU2015237464A
Authority: AU
Inventors: Tatsumi Kimura; Yukio Takashima
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2014-03-24
Filing date: 2015-03-24
Publication date: 2018-02-01
Anticipated expiration: 2035-03-24
Also published as: EP3124636A1; CN106103772A; WO2015146150A1; JPWO2015146150A1; US20170101692A1; EP3124636A4; BR112016022007B1; CA2936780A1; EP3124636B1; CN106103772B; AU2015237464A1; JP6150008B2; CA2936780C; EP3124636B2

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

The present invention 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;

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.

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

I I:\s.xn\Intcrwovcn\NRPortbl\DCC\SXN\l 6275244_ I .docx-10/01/2018

2015237464 10 Jan 2018

-6removing 0.5 mm or greater of a decarburized layer using a grinder or the like.

[0014] In one embodiment, the chemical composition of the rail 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.

[0015] [Blank] [0016] [Blank] [0017] The present invention further 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 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 of900°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 l°C/s to 10°C/s, the cooling rate of the cooling exhibits variation of ±l°C/s or less in the rail length direction, 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.

I I:\sxn\Intcrwovcn\NRPortbl\DCC\SXN\l 6275244_ 1 .docx-10/01/2018

2015237464 10 Jan 2018

-7[0018] According to the rail manufacturing method, the chemical composition may further contain, 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.

[0019] [Blank] [0020] The present invention can enable 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.

DETAIFED DESCRIPTION [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 γ + 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%.

[0023] 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

PO144539-PCT-ZZ (8/23)

-90.001%.

[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%.

[0028] 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%.

[0029] 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

PO144539-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 O 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

PO144539-PCT-ZZ (10/23)

I I:\sxn\Interwoven\NRPortbl\DCC\SXN\l 6275244_ I .docx-10/01/2018

2015237464 10 Jan 2018

- 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 5 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 inNb and Ti of0.003% 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 10 points or less in the rail length direction. The reason for this is that a 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

- 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

PO144539-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).

PO144539-PCT-ZZ (13/23)

I I:\sxn\Intcrwovcn\NRPortbl\DCC\SXN\l 6275244_ I .docx-10/01/2018

2015237464 10 Jan 2018

- 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 l°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 l°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 l°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 exhibits variation of ±l°C/s or less in the rolling longitudinal direction. Restricting cooling rate variation to ±l°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.

I I:\sxn\Intcrwovcn\NRPortbl\DCC\SXN\l 6275244_ I .docx-10/01/2018

2015237464 10 Jan 2018

- 15 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 abovedescribed rolling and cooling, a pearlitic steel rail can be obtained that has a surface hardness of HB 400 or greater and that exhibits surface hardness variation of ±HB 10 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 1 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.

[0047] [Table 1]

Table 1

Remarks |

Example I

Comparative example |

<l> Ί & e o O

Comparative example |

<l> Ί & g o O

Example |

t,

00

rn

rsi

o

Ti

rsi

Ti

00

o

Ti

*

o

O

o

o'

o’

o

Ti

rsi

Ti

o

fTi

o

00

Ti

*

o

ό

o

z

o

o'

*H

rsl

rs)

o

O

o

o T

o’

rs)

*

o

O

Ή

o

o'

rs)

*

o

o'

rn

rsi r- o

o

>

o

ό

o'

o

rsi

2

o'

Ti

z

o'

1 ⁿ3

0.31

00

o

rsi

fTi

00

oo

fTi

o

l~-

rn

rsi

Ti

rsi

Ti

rsi

o

O

fTi

o’

rsi

o’

rr>

Ti

r—-

Ti

r-

Ti

oo

Ti

UQ

o

O

o

O

o

o’

o

00

rsi

Ti

00

rn

o

rs)

o

00

Ti

00

fTi

Ph

o

O

o

O

o

o'

o

rn

00

rsi

fTi

o

rs)

00

rsi

fTi

o

Vl

rsi

o

i--

rn

Ti

O

rsi

1--

o’

rn

00

o

rn

Ti

rn

00

Ti

fTi

Ti

fTi

00

UQ

t,

rsi

O

o

Ti

o

Ti

fTi

rsi

o'

r<|

o

T)

oo

rs)

T)

o

OO

rs)

r-

rs)

O

00

l~-

o

00

Vi

1--

00

o

00

o

00

o'

o

£

-

m

O

Q

ω

0

ffi

1—>

hJ

2

z

<L> <L>

a z

a <L>

g

O

O *

PO144539-PCT-ZZ (16/23)

- 17 [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 ±l°C/s or was less than or equal to ±l°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.

PO144539-PCT-ZZ (17/23)

H:\sxn\Interwoven\NRPortbl\DCC\SXN\i6275244_l.docx-10/01/2018

2015237464 10 Jan 2018

- 18100501 TTable 21

Table 2 (coitt'd)

Remarks

w

W

w

W

w

g s © Ί 13 g © 0

Comparative example Martensite formation

g s © Ί 13 g © 0

Comparative example Martensite formation

g s © Ί 13 g © 0

Comparative example Martensite formation

Comparative example Low ductility

Example I

Brinell hardness of surface |

Surface hardness variation (HB)

Cx)

r-

00

Cx)

00

-

Cx)

r-

00

0

IKS <ΎΊ

Γ-

SO <7S

OS

0

00

r-

Average surface hardness (HB)

| 441 |

| 436 |

| 455 |

IKS

| 430 |

420 |

| 432 |

| 458 |

| 367 |

486

382 |

483

| 362 |

503

433

| 421 |

Cooling conditions

Cooling rate variation (°C/s)

Λ

VI

Λ

VI

Λ

VI

Cooling rate (°C/s)

r- <Ύ3

0

OO CS

IKS CS

00 CS

IKS CS

<ΎΊ CS

<7S

Cv)

so <7S

IKS CS

SO

n 06

Cx)

C*S

IKS <rs

Cx)

Stop temperature (°C)

| 450 |

420 |

460 |

| 450 |

| 470 |

1 450 I

440 |

480 |

460 |

450

| 470 |

460

| 450 |

430

| 410 |

Start temperature (°C)

850 |

840 |

820 |

830 |

820 |

| 810 |

1 810 1

820 |

830 |

820 |

800

820 |

830

| 008

810

820

820 |

Length direction cooling control

| No |

Yes |

| No |

Yes |

| No |

1 No 1

Yes |

| No |

Yes

Yes |

Yes

Yes |

Yes

Yes |

Cooling method

to -© • b

Air blast |

Air blast

Air blast |

Mist

Air blast |

Air blast

Air blast |

Rolling conditions

Finisher delivery temperature (°C)

| 950

970

| 950

930

| 950

930

940

920

910

930

920

930

920

930

Area reduction rate at 1000°C or lower (%)

IKS

0

IKS

0

IKS

Γ- <Ύ3

IKS

in

IKS

Variation in time interval between passes (s)

<7S

0 Cx)

Cx)

00

IKS

<ΎΊ

©

IKS

00

0

IKS

Cx)

Heating |

Use of continuous rolling at 1000°C or lower

Single-direction continuous |

Single-direction continuous

Single-direction continuous |

Single-direction continuous

Single-direction continuous |

Single-direction continuous

Single-direction continuous |

Temperature (°C)

1220 |

1250 |

1230 |

1200 |

1230 |

1220 |

1240 |

1250 |

1230 |

1240

1230 |

1250

1250 |

1220

1230

1250 |

Steel syntrol

CQ

0

Q

M

Uh

0

-

fQ

s

z

No.

so

r-

00

OS

0 Cx)

Cx)

Cx) Cx)

<ΎΊ Cv)

Cx)

IKS

SO

Γ-

00

OS

0 <rs

<rs

Cx) <rs

PO144539-PCT-ZZ (19/23)

I I:\sxn\Intcrwovcn\NRPortbl\DCC\SXN\l 6275244_ I .docx-1 0/01/2018

2015237464 10 Jan 2018

-20[0051] The hardness of rails according to the present disclosure exhibited extremely small variation of ±HB 10 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 10.

[0052] The reference in this specification to any prior publication (or information derived from it), 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.

[0053] 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.

-20 [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.

PO144539-PCT-ZZ (20/23)

I I:\sxn\Interwoven\NRPortbl\DCC\SXN\l 6275244_ I .docx-10/01/2018

2015237464 10 Jan 2018

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1/2

Rail material wear (g)

FIG. 1

Wear resistance

P0144539-K0

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:

0.60% to 1.0% of C,

0.1% to 1.5% of Si,

0.01% to 1.5%ofMn,

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

I I:\s.xn\Intcrwovcn\NRPortbl\DCC\SXN\l 6275244_ I .docx-10/01/2018

2015237464 10 Jan 2018

-22performed 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 of900°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 l°C/s to 10°C/s, the cooling rate of the cooling exhibits variation of ±l°C/s or less in the rail length direction, 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.

4. The rail manufacturing method of claim 3, wherein the chemical composition further contains, in mass%, one or more of:

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%ofMn;

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:

2/2

FIG. 3

P0144539-K0