U.S. patent application number 12/663866 was filed with the patent office on 2010-07-29 for internal high hardness type pearlitic rail with excellent wear resistance, rolling contact fatigue resistance, and delayed fracture property and method for producing same.
This patent application is currently assigned to JFE STEEL CORPORATION. Invention is credited to Minoru Honjo, Tatsumi Kimura, Kimihiro Nishimura, Nobuo Shikanai, Shinichi Suzuki.
Application Number | 20100186857 12/663866 |
Document ID | / |
Family ID | 40549076 |
Filed Date | 2010-07-29 |
United States Patent
Application |
20100186857 |
Kind Code |
A1 |
Honjo; Minoru ; et
al. |
July 29, 2010 |
INTERNAL HIGH HARDNESS TYPE PEARLITIC RAIL WITH EXCELLENT WEAR
RESISTANCE, ROLLING CONTACT FATIGUE RESISTANCE, AND DELAYED
FRACTURE PROPERTY AND METHOD FOR PRODUCING SAME
Abstract
An internal high hardness type pearlitic rail has a composition
containing 0.73% to 0.85% by mass C, 0.5% to 0.75% by mass Si, 0.3%
to 1.0% by mass Mn, 0.035% by mass or less P, 0.0005% to 0.012% by
mass S, 0.2% to 1.3% by mass Cr, 0.005% to 0.12% by mass V, 0.0015%
to 0.0060% by mass N, and the balance being Fe and incidental
impurities, wherein the value of [% Mn]/[% Cr] is greater than or
equal to 0.3 and less than 1.0, where [% Mn] represents the Mn
content, and [% Cr] represents the Cr content, and the value of [%
V]/[% N] is in the range of 8.0 to 30.0, where [% V] represents the
V content, and [% N] represents the N content, and wherein the
internal hardness of a rail head is defined by the Vickers hardness
of a portion located from a surface layer of the rail head to a
depth of at least 25 mm and is greater than or equal to 380 Hv and
less than 480 Hv.
Inventors: |
Honjo; Minoru; (Tokyo,
JP) ; Kimura; Tatsumi; (Tokyo, JP) ; Suzuki;
Shinichi; (Tokyo, JP) ; Nishimura; Kimihiro;
(Tokyo, JP) ; Shikanai; Nobuo; (Tokyo,
JP) |
Correspondence
Address: |
IP GROUP OF DLA PIPER LLP (US)
ONE LIBERTY PLACE, 1650 MARKET ST, SUITE 4900
PHILADELPHIA
PA
19103
US
|
Assignee: |
JFE STEEL CORPORATION
Tokyo
JP
|
Family ID: |
40549076 |
Appl. No.: |
12/663866 |
Filed: |
March 25, 2008 |
PCT Filed: |
March 25, 2008 |
PCT NO: |
PCT/JP2008/056273 |
371 Date: |
December 10, 2009 |
Current U.S.
Class: |
148/584 ;
148/332; 148/333; 148/334 |
Current CPC
Class: |
C21D 8/005 20130101;
C21D 9/04 20130101; C21D 2221/02 20130101; C21D 6/00 20130101; C22C
38/24 20130101; C21D 6/005 20130101; C21D 2221/00 20130101; C22C
38/02 20130101; C21D 6/002 20130101; C21D 2211/009 20130101; B21B
1/085 20130101; C21D 1/02 20130101; C22C 38/04 20130101; C22C
38/001 20130101 |
Class at
Publication: |
148/584 ;
148/333; 148/332; 148/334 |
International
Class: |
C21D 9/04 20060101
C21D009/04; C22C 38/18 20060101 C22C038/18; C22C 38/20 20060101
C22C038/20; C22C 38/22 20060101 C22C038/22 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 10, 2007 |
JP |
2007-264826 |
Claims
1. An internal high hardness type pearlitic rail comprising a
composition containing 0.73% to 0.85% by mass C, 0.5% to 0.75% by
mass Si, 0.3% to 1.0% by mass Mn, 0.035% by mass or less P, 0.0005%
to 0.012% by mass S, 0.2% to 1.3% by mass Cr, 0.005% to 0.12% by
mass V, 0.0015% to 0.0060% by mass N, and the balance being Fe and
incidental impurities, wherein [% Mn]/[% Cr] is greater than or
equal to 0.3 and less than 1.0, where [% Mn] represents Mn content,
and [% Cr] represents Cr content, and [% V]/[% N] is in the range
of 8.0 to 30.0, where [% V] represents V content, and [% N]
represents N content, and wherein internal hardness of a rail head
is defined by Vickers hardness of a portion located from a surface
layer of the rail head to a depth of at least 25 mm and is greater
than or equal to 380 Hv and less than 480 Hv.
2. The internal high hardness type pearlitic rail according to
claim 1, wherein DI calculated from expression (1) is 5.6 to 8.6,
and C.sub.eq calculated from expression (2) is 1.04 to 1.27,
DI=(0.548[% C].sup.1/2).times.(1+0.64[% Si]).times.(1+4.1[%
Mn]).times.(1+2.83[% P]).times.(1-0.62[% S]).times.(1+2.23[%
Cr]).times.(1+1.82[% V]) (1); and C.sub.eq=[% C]+([% Si]/11)([%
Mn]/7)+([% Cr]/5.8)+[% V] (2) where [% C] represents C content, [%
Si] represents Si content, [% Mn] represents Mn content, [% P]
represents P content, [% S] represents S content, [% Cr] represents
Cr content, and [% V] represents V content of the composition.
3. The internal high hardness type pearlitic rail according to
claim 1, wherein [% Si]+[% Mn]+[% Cr] is 1.55% to 2.50, where [%
Si] represents Si content, [% Mn] represents Mn content, and [% Cr]
represents Cr content of the composition.
4. The internal high hardness type pearlitic rail according to
claim 1, wherein the composition further contains one or more
components selected from the group consisting of 1.0% by mass or
less Cu, 1.0% by mass or less Ni, 0.001% to 0.05% by mass Nb, and
0.5% by mass or less Mo.
5. The internal high hardness type pearlitic rail according to
claim 1, wherein lamellar spacing of a pearlite layer in a portion
located from a surface layer of the rail head to a depth of at
least 25 mm is 0.04 to 0.15 .mu.m.
6. A method of producing an internal high hardness type pearlitic
rail comprising: hot-rolling a steel material having the
composition according to claim 1 to form a rail in such a manner
that the finishing rolling temperature is in the range of
850.degree. C. to 950.degree. C.; and slack-quenching a surface of
the rail head from a temperature equal to or higher than a pearlite
transformation starting temperature to 400.degree. C. to
650.degree. C. at a cooling rate of 1.2 to 5.degree. C./s.
7. The internal high hardness type pearlitic rail according to
claim 2, wherein [% Si]+[% Mn]+[% Cr] is 1.55% to 2.50, where [%
Si] represents Si content, [% Mn] represents Mn content, and [% Cr]
represents Cr content of the composition.
8. The internal high hardness type pearlitic rail according to
claim 2, wherein the composition further contains one or more
components selected from the group consisting of 1.0% by mass or
less Cu, 1.0% by mass or less Ni, 0.001% to 0.05% by mass Nb, and
0.5% by mass or less Mo.
9. The internal high hardness type pearlitic rail according to
claim 3, wherein the composition further contains one or more
components selected from the group consisting of 1.0% by mass or
less Cu, 1.0% by mass or less Ni, 0.001% to 0.05% by mass Nb, and
0.5% by mass or less Mo.
10. The internal high hardness type pearlitic rail according to
claim 7, wherein the composition further contains one or more
components selected from the group consisting of 1.0% by mass or
less Cu, 1.0% by mass or less Ni, 0.001% to 0.05% by mass Nb, and
0.5% by mass or less Mo.
11. The internal high hardness type pearlitic rail according to
claim 2, wherein lamellar spacing of a pearlite layer in a portion
located from a surface layer of the rail head to a depth of at
least 25 mm is 0.04 to 0.15 .mu.m.
12. The internal high hardness type pearlitic rail according to
claim 3, wherein lamellar spacing of a pearlite layer in a portion
located from a surface layer of the rail head to a depth of at
least 25 mm is 0.04 to 0.15 .mu.m.
13. The internal high hardness type pearlitic rail according to
claim 4, wherein lamellar spacing of a pearlite layer in a portion
located from a surface layer of the rail head to a depth of at
least 25 mm is 0.04 to 0.15 .mu.m.
14. The internal high hardness type pearlitic rail according to
claim 7, wherein lamellar spacing of a pearlite layer in a portion
located from a surface layer of the rail head to a depth of at
least 25 mm is 0.04 to 0.15 .mu.m.
15. The internal high hardness type pearlitic rail according to
claim 10, wherein lamellar spacing of a pearlite layer in a portion
located from a surface layer of the rail head to a depth of at
least 25 mm is 0.04 to 0.15 .mu.m.
Description
RELATED APPLICATIONS
[0001] This is a .sctn.371 of International Application No.
PCT/JP2008/056273, with an international filing date of Mar. 25,
2008 (WO 2009/047926 A1, published Apr. 16, 2009), which is based
on Japanese Patent Application No. 2007-264826, filed Oct. 10,
2007, the subject matter of which is incorporated by reference.
TECHNICAL FIELD
[0002] This disclosure relates to an internal high hardness type
pearlitic rail with excellent wear resistance and rolling contact
fatigue (RCF) resistance and a method for producing the same.
Specifically, the disclosure relates to an internal high hardness
type pearlitic rail having excellent wear resistance, rolling
contact fatigue resistance, and delayed fracture properties and
achieving longer operating life of rails used under severe
high-axle load conditions like foreign mining railways in which
freight cars are heavy and high curve lines are often present, and
to a method for producing the internal high hardness type pearlitic
rail.
BACKGROUND
[0003] In high-axle load railways mainly transporting mineral ores,
a load on an axle of a freight car is significantly higher than
that of a passenger car, and the use environment of rails is also
severe. Rails used in such an environment have been mainly composed
of steel having a pearlitic structure from the viewpoint of
significant concern of wear resistance. To enhance the efficiency
of railway transport, progress has recently been made in increasing
carrying capacity. Thus, there is a need for further improvement in
wear resistance and rolling contact fatigue resistance. High-axle
load railways are used to indicate railways in which trains and
freight cars have a large carrying capacity (for example, a
carrying capacity of about 150 ton or more per freight car).
[0004] In recent years, various studies have been conducted to
further improve wear resistance. For example, in Japanese
Unexamined Patent Application Publication Nos. 8-109439 and
8-144016, the C content is increased to more than 0.85% and 1.20%
by mass or less. In Japanese Unexamined Patent Application
Publication Nos. 8-246100 and 8-246101, the C content is increased
to more than 0.85% to 1.20% by mass or less and a rail head is
subjected to heat treatment. In this way, for example, a technique
for improving wear resistance by increasing the C content to
increase the cementite ratio has been used.
[0005] Meanwhile, rails placed in curved sections of high-axle load
railways are subjected to rolling stress due to wheels and slip
force due to centrifugal force, causing severe wear of rails and
fatigue damage due to slippage. As described above, in the case
where the C content is simply more than 0.85% and 1.20% by mass or
less, a proeutectoid cementite structure is formed depending on
heat treatment conditions, and the amount of a cementite layer in a
brittle lamellar pearlitic structure is also increased. Hence,
rolling contact fatigue resistance is not improved. Japanese
Unexamined Patent Application Publication No. 2002-69585 thus
discloses a technique for inhibiting the formation of proeutectoid
cementite by addition of Al and Si to improve rolling contact
fatigue resistance. The addition of Al, however, causes the
formation of an oxide acting as a starting point of fatigue damage,
for example. It is thus difficult to satisfy both wear resistance
and rolling contact fatigue resistance of a rail having a pearlitic
structure.
[0006] To improve the operating life of rails, in Japanese
Unexamined. Patent Application Publication No. 10-195601, a portion
located from the surface of corners and of the top of the head of
the rail to a depth of at least 20 mm have a hardness of 370 HV or
more, thereby improving the operating life of the rail. In Japanese
Unexamined Patent Application Publication No. 2003-293086, by
controlling a pearlite block, a portion located from the surface of
corners and of the top of the head of the rail to a depth of at
least 20 mm have a hardness of 300 HV to 500 HV, thereby improving
the operating life of the rail.
[0007] Further strengthening of a rail increases the risk of
causing a delayed fracture. In Japanese Unexamined Patent
Application Publication Nos. 8-109439, 8-144016, 8-246100,
8-246101, 2002-69585, 10-195601, and 2003-293086, the effect of
preventing the delayed fracture is not sufficient.
[0008] As a technique for preventing a delayed fracture of a rail
composed of pearlitic steel (hereinafter, referred to as a
"pearlitic rail"), for example, Japanese Patent No. 3648192 and
Japanese Unexamined Patent Application Publication No. 5-287450
disclose, a technique for improving delayed fracture properties by
subjecting high-strength pearlitic steel to heavy drawing. In the
case of applying the technique to rails, disadvantageously, the use
of heavy drawing increases the production cost of rails.
[0009] The control of the figure and volume of A-type inclusions
disclosed in Japanese Unexamined Patent Application Publication
Nos. 2000-328190 and 6-279928, Japanese Patent No. 3323272, and
Japanese Unexamined Patent Application Publication No 6-279929 is
also known to be effective as a technique for improving delayed
fracture properties. In Japanese Unexamined Patent Application
Publication Nos. 2000-328190 and 6-279928, Japanese Patent. No.
3323272, and Japanese Unexamined Patent Application Publication No.
6-279929, however, the figure and volume of A-type inclusions are
controlled to improve the toughness and ductility of rails. For
example, in Japanese Unexamined Patent Application Publication No.
6-279928, A-type inclusions are controlled so as to have a size of
0.1 to 20 .mu.m and in such a manner that the number of the A-type
inclusions is 25 to 11,000 per square millimeter, thereby improving
the toughness and ductility of a rail. Thus, this technique does
not necessarily provide satisfactory delayed fracture
properties.
[0010] The use environment of pearlitic rails, however, has been
increasingly severe. To improve the operating life of pearlitic
rails, there has been a challenge for higher hardness, the
expansion of the range of quench hardening depth, and improvement
in delayed fracture properties.
SUMMARY
[0011] We found that the addition of Si, Mn, Cr, V, and N improves
the quench hardenability index (hereinafter, referred to as "DI")
and the carbon equivalent (hereinafter, referred to as "C.sub.eq"),
and keeping the values of [% Mn]/[% Cr] and [% V]/[% N], where [%
Mn] represents the Mn content, [% Cr] represents the Cr content, [%
V] represents the V content, and [% N] represents the N content,
within proper ranges increase the hardness of a portion located
from the surface of a rail head to a depth of at least 25 mm, as
compared with hypoeutectoid-, eutectoid-, and hypereutectoid-type
pearlitic rails in the related art, thereby providing an internal
high hardness type pearlitic rail with excellent wear resistance,
rolling contact fatigue resistance, and delayed fracture
properties. We also provide a preferred method for producing the
internal high hardness type pearlitic rail.
[0012] We produced pearlitic rails with different proportions of
Si, Mn, Cr, V, and N and have conducted intensive studies on the
structure, hardness, wear resistance, rolling contact fatigue
resistance, and delayed fracture properties. As a result, we found
that, in, the case where the value of [% Mn]/[% Cr], which is
calculated from the Mn content [% Mn] and the Cr content [% Cr], is
greater than or equal to 0.3 and less than 1.0 and where the value
of [% V]/[% N], which is calculated from the V content [% V] and
the N content [% N], is in the range of 8.0 to 30.0, the spacing of
the lamella (lamellar spacing) of a pearlite layer (hereinafter,
also referred to simply as a "lamella") is reduced, and the
internal hardness of a rail head that is defined by the Vickers
hardness of a portion located from a surface layer of the rail head
to a depth of at least 25 mm is greater than or equal to 380 Hv and
less than 480 Hv, thereby improving wear resistance, rolling
contact fatigue resistance, and delayed fracture properties.
Furthermore, we found that in the case where the quench
hardenability index (i.e., the DI value) is in the range of 5.6 to
8.6, the carbon equivalent (i.e., the C.sub.eq value) is in the
range of 1.04 to 1.27, and the value of [% Si]+[% Mn]+[% Cr], which
is calculated from the Mn content [% Mn], the Cr content [% Cr],
and the Si content [% Si], is in the range of 1.55% to 2.50% by
mass, the effect of improving wear resistance and rolling contact
fatigue resistance can be stably maintained.
[0013] We thus provide an internal high hardness type pearlitic
rail with excellent wear resistance, rolling contact fatigue
resistance, and delayed fracture properties has a composition
containing 0.73% to 0.85% by mass C, 0.5% to 0.75% by mass Si, 0.3%
to 1.0% by mass Mn, 0.035% by mass or less P, 0.0005% to 0.012% by
mass S, 0.2% to 1.3% by mass Cr, 0.005% to 0.12% by mass V, 0.0015%
to 0.0060% by mass N, and the balance being Fe and incidental
impurities, in which the value of [% Mn]/[% Cr] is greater than or
equal to 0.3 and less than 1.0, where [% Mn] represents the Mn
content, and [% Cr] represents the Cr content, and the value of [%
V]/[% N] is in the range of 8.0 to 30.0, where [% V] represents the
V content, and [% N] represents the N content, and in which the
internal hardness of a rail head is defined by the Vickers hardness
of a portion located from a surface layer of the rail head to a
depth of at least 25 mm and is greater than or equal to 380 Hv and
less than 480 Hv.
[0014] In the internal high hardness type pearlitic rail,
preferably, the value of DI calculated from expression (1) is in
the range of 5.6 to 8.6, and the value of C.sub.eq calculated from
expression (2) is in the range of 1.04 to 1.27,
DI=(0.548[% C].sup.1/2).times.(1+0.64[% Si]).times.(1+4.1[%
Mn]).times.(1+2.83[% P]).times.(1-0.62[% S]).times.(1+2.23[%
Cr]).times.(1+1.82[% V]) (1); and
C.sub.eq[% C]+([% Si]/11)+([% Mn]/7)+([% Cr]/5.8)+[% V] (2)
where [% C] represents the C content, [% Si] represents the Si
content, [% Mn] represents the Mn content, [% P] represents the P
content, [% S] represents the S content, [% Cr] represents the Cr
content, and [% V] represents the V content of the composition.
[0015] Preferably, the value of [% Si]+[% Mn]+[% Cr] is in the
range of 1.55% to 2.50, where [% Si] represents the Si content, [%
Mn] represents the Mn content, and [% Cr] represents the Cr content
of the composition. Preferably, the composition further contains
one or two or more selected from 1.0% by mass or less Cu, 1.0% by
mass or less Ni, 0.001% to 0.05% by mass Nb, and 0.5% by mass or
less Mo.
[0016] In the internal high hardness type pearlitic rail,
preferably, the lamellar spacing of a pearlite layer in the portion
located from the surface layer of the rail head to a depth of at
least 25 mm is in the range of 0.04 to 0.15 .mu.m.
[0017] Furthermore, a method for producing an internal high
hardness type pearlitic rail with excellent wear resistance,
rolling contact fatigue resistance, and delayed fracture properties
includes hot-rolling a steel material having the composition
described above to form a rail in such a manner that the finishing
rolling temperature is in the range of 850.degree. C. to
950.degree. C., and then slack-quenching the surface of the rail
head from a temperature equal to or higher than a pearlite
transformation starting temperature to 400.degree. C. to
650.degree. C. at a cooling rate of 1.2 to 5.degree. C./s.
[0018] A pearlitic rail having excellent wear resistance, rolling
contact fatigue resistance, and delayed fracture properties can be
stably produced compared with pearlitic rails in the related art.
This contributes to longer operating life of pearlitic rails used
for high-axle load railways and to the prevention of railway
accidents, providing industrially beneficial effects.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIGS. 1A and 1B show a Nishihara-type rolling contact test
piece used for evaluation of wear resistance; FIG. 1A is a plan
view, and FIG. 1B is a side view.
[0020] FIG. 2 is a cross-sectional view of a rail head and
illustrates positions where Nishihara-type rolling contact test
pieces are taken.
[0021] FIGS. 3A and 3B show a Nishihara-type rolling contact test
piece used for evaluation of rolling contact fatigue resistance;
FIG. 3A is a plan view, and FIG. 3B is a side view.
[0022] FIG. 4 is a cross-sectional view of a rail head and
illustrates a position where a slow strain rate technique (SSRT)
test piece is taken.
[0023] FIG. 5 is a cross-sectional view of the shape and dimensions
of the SSRT test piece.
[0024] FIG. 6 is a graph showing the relationship between the [%
V]/[% N] value and the rate of improvement in delayed fracture
susceptibility.
REFERENCE NUMERALS
[0025] 1 Nishihara-type rolling contact test piece taken from
pearlitic rail [0026] 1a Nishihara-type rolling contact test piece
taken from surface layer of rail head [0027] 1b Nishihara-type
rolling contact test piece taken from inside of rail head [0028] 2
tire specimen [0029] 3 rail head [0030] 4 SSRT test piece
DETAILED DESCRIPTION
[0031] Reasons for the conditions of an internal high hardness type
pearlitic rail including the composition will now be described.
C: 0.73% to 0.85% by Mass
[0032] C is an essential element to form cementite in a pearlitic
structure to ensure wear resistance. The wear resistance is
improved as the C content is increased. At a C content of less than
0.73% by mass, however, it is difficult to provide high wear
resistance compared with heat treatment-type pearlitic rails in the
conventional art. A C content exceeding 0.85% by mass results in
the formation of proeutectoid cementite in austenite grain
boundaries during transformation after hot rolling, thereby
significantly reducing rolling contact fatigue resistance. Thus,
the C content is set in the range of 0.73% to 0.85% by mass and
preferably 0.75% to 0.85% by mass.
Si: 0.5% to 0.75% by Mass
[0033] Si is an element serving as a deoxidizer and strengthening a
pearlitic structure and needed in an amount of 0.5% by mass or
more. A Si content exceeding 0.75% by mass results in a
deterioration in weldability due to high bond strength of Si with
oxygen. Further more, high quench hardenability of Si facilitates
the formation of a martensitic structure in a surface layer of the
internal high hardness type pearlitic rail. Thus, the Si content is
set in the range of 0.5% to 0.75% by mass and preferably 0.5% to
0.70% by mass.
Mn: 0.3% to 1.0% by Mass
[0034] Mn reduces a pearlite transformation starting temperature to
reduce a lamellar spacing. Thus, Mn contributes to higher strength
and higher ductility of the internal high hardness type pearlitic
rail. An excessive amount of Mn added reduces the equilibrium
transformation temperature of pearlite to reduce the degree of
supercooling, increasing the lamellar spacing. A Mn content of less
than 0.3% by mass does not result in a sufficient effect. A Mn
content exceeding 1.0% by mass facilitates the formation of a
martensitic structure, so that hardening and embrittlement occur
during heat treatment and welding, thereby readily reducing the
quality of the material. Furthermore, even if the pearlitic
structure is formed, the equilibrium transformation temperature is
reduced, thereby increasing the lamellar spacing. Thus, the Mn
content is set in the range of 0.3% to 1.0% by mass and preferably
0.3% to 0.8% by mass.
P: 0.035% by Mass or Less
[0035] A P content exceeding 0.035% results in a deterioration in
ductility. Thus, the P content is set to 0.035% by mass or less and
preferably 0.020% by mass or less.
S: 0.0005% to 0.012% by Mass
[0036] S is present in steel mainly in the form of A-type
inclusions. A S content exceeding 0.012% by mass results in a
significant increase in the amount of the inclusions and also
results in the formation of coarse inclusions, thereby reducing
cleanliness of steel. A S content of less than 0.0005% by mass
leads to an increase in steelmaking cost. Thus, the S content is
set in the range of 0.0005% to 0.012% by mass and preferably
0.0005% to 0.008% by mass.
Cr: 0.2% to 1.3% by Mass
[0037] Cr is an element that increases the equilibrium
transformation temperature of pearlite to contribute to a reduction
in lamellar spacing and that further increases the strength by
solid-solution hardening. However, a Cr content of less than 0.2%
by mass does not result in sufficient internal hardness. A Cr
content exceeding 1.3% by mass results in excessively high quench
hardenability, forming martensite to reduce wear resistance and
rolling contact fatigue resistance. Thus, the Cr content is set in
the range of 0.2% to 1.3% by mass, preferably 0.3% to 1.3% by mass,
and more preferably 0.5% to 1.3% by mass.
V: 0.005% to 0.12% by Mass
[0038] V forms a carbonitride that is dispersively precipitated in
a matrix, improving wear resistance and delayed fracture
properties. At a V content of less than 0.005% by mass, the effect
is reduced. A V content exceeding 0.12% by mass results in an
increase in alloy cost, thereby increasing the cost of the internal
high hardness type pearlitic rail. Thus, the V content is in the
range of 0.005% to 0.12% by mass and preferably 0.012% to 0.10% by
mass.
N: 0.0015% to 0.0060% by Mass
[0039] N forms a nitride that is dispersively precipitated in a
matrix, improving wear resistance and delayed fracture properties.
At a N content of less than 0.0015% by mass, the effect is reduced.
A N content exceeding 0.0060% by mass results in the formation of
coarse nitrides in the internal high hardness type pearlitic rail,
thereby reducing rolling contact fatigue resistance and delayed
fracture properties. Thus, the N content is in the range of 0.0015%
to 0.060% by mass and preferably 0.0030% to 0.0060%.
[% Mn]/[% Cr]: Greater than or Equal to 0.3 and Less than 1.0
[0040] Mn and Cr are additive elements to increase the hardness of
the internal high hardness type pearlitic rail. In the case where
an appropriate balance between the Mn content [% Mn] and the Cr
content [% Cr] is not achieved, however, martensite is formed in a
surface layer of the internal high hardness type pearlitic rail.
Note that the units of [% Mn] and [% Cr] are percent by mass. When
the value of [% Mn]/[% Cr] is less than 0.3, the Cr content is
high. This facilitates the formation of martensite in the surface
layer of the internal high hardness type pearlitic rail due to high
quench hardenability of Cr. When the value of [% Mn]/[% Cr] is 1.0
or more, the Mn content is high. This also facilitates the
formation of martensite in the surface layer of the internal high
hardness type pearlitic rail due to high quench hardenability of
Mn. In the case where the Mn content and the Cr content are set in
the above ranges respectively and where the value of [% Mn]/[% Cr]
is greater than or equal to 0.3 and less than 1.0, the internal
hardness of the head of the rail (hardness of a portion located
from the surface layer of the head of the internal high hardness
type pearlitic rail to a depth of at least 25 mm) can be controlled
within a range described below while the formation of martensite in
the surface layer is being prevented. Thus, the value of [% Mn]/[%
Cr] is greater than or equal to 0.3 and less than 1.0 and
preferably in the range of 0.3 to 0.9.
[% V]/[% N]: 8.0 to 30.0
[0041] V and N are important elements that form a V-based nitride
serving as a hydrogen-trapping site. To form the V-based nitride,
the amounts thereof added must be controlled. The units of [% V]
and [% N] are percent by mass. At a [% V]/[% N] value of less than
8.0, the V-based nitride is not sufficiently formed, thereby
reducing the number of the hydrogen-trapping sites. Thus, it is
unlikely that delayed fracture properties will be significantly
improved. At a [% V]/[% N] value exceeding 30.0, the amount of V
added is increased to increase the alloy cost, thereby increasing
the cost of the internal high hardness type pearlitic rail.
Furthermore, it is unlikely that delayed fracture properties will
be significantly improved. Thus, the [% V]/[% N] value is in the
range of 8.0 to 30.0 and preferably 8.0 to 22.0.
Internal Hardness of Rail Head (Hardness of Portion Located from
Surface Layer of Head of Internal High Hardness Type Pearlitic Rail
to Depth of at Least 25 mm): Greater than or Equal to 380 Hv and
Less than 480 Hv
[0042] An internal hardness of the rail head of less than 380 Hv
results in a reduction in wear resistance, thereby reducing the
operating life of the internal high hardness type pearlitic rail.
An internal hardness of the rail head of 480 Hv or more results in
the formation of martensite, thereby reducing the rolling contact
fatigue resistance of the internal high hardness type pearlitic
rail. Thus, the internal hardness of the rail head is greater than
or equal to 380 Hv and less than 480 Hv. The reason the internal
hardness of the rail head is defined by the hardness of the portion
located from the surface layer of the head of the internal high
hardness type pearlitic rail to a depth of at least 25 mm is as
follows: at a depth of less than 25 mm, the wear resistance of the
internal high hardness type pearlitic rail is reduced with
increasing distance from the surface layer of the rail head toward
the inside, reducing the operating life. Preferably, the internal
hardness of the rail head is greater than 390 Hv and less than 480
Hv.
DI: 5.6 to 8.6
[0043] The value of DI is calculated from expression (1) described
below:
DI=(0.548[% C].sup.1/2).times.(1+0.64[% Si]).times.(1+4.1[%
Mn]).times.(1+2.83[% P]).times.(1-0.62[% S]).times.(1+2.23[%
Cr]).times.(1+1.82[% V]) (1)
where [% C] represents the C content, [% Si] represents the Si
content, [% Mn] represents the Mn content, [% P] represents the P
content, [% S] represents the S content, [% Cr] represents the Cr
content, and [% V] represents the V content. Note that the units of
[% C], [% Si], [% Mn], [% P], [% S], [% Cr], and [% V] are percent
by mass.
[0044] The DI value indicates quench hardenability and is used as
an index to determine whether quench hardenability is good or not.
The DI value is used as an index to prevent the formation of
martensite in the surface layer of the internal high hardness type
pearlitic rail and to achieve a target value of the internal
hardness of the rail head. The DI value is preferably maintained
within a suitable range. At a DI value of less than 5.6, although a
desired internal hardness is provided, the internal hardness is
close to the lower limit of the target hardness range. Thus, it is
unlikely that the wear resistance, rolling contact fatigue
resistance, and delayed fracture properties will be further
improved. A DI value exceeding 8.6 results in an increase in the
quench hardenability of the internal high hardness type pearlitic
rail, facilitating the formation of martensite in the surface layer
of the rail head. Thus, the DI value is preferably in the range of
5.6 to 8.6 and more preferably 5.6 to 8.2.
C.sub.eq: 1.04 to 1.27
[0045] The value of C.sub.eq is calculated from expression (2)
described below:
C.sub.eq=[% C]+([% Si]/11)+([% Mn]/7)+([% Cr]/5.8)+[% V] (2)
where [% C] represents the C content, [% Si] represents the Si
content, [% Mn] represents the Mn content, [% Cr] represents the Cr
content, and [% V] represents the V content. Note that the units of
[% C], [% Si], [% Mn], [% Cr], and [% V] are percent by mass.
[0046] The C.sub.eq value is used to estimate the maximum hardness
and weldability from proportions of the alloy components added. The
C.sub.eq value is used as an index to prevent the formation of
martensite in the surface layer of the internal high hardness type
pearlitic rail and to achieve a target value of the internal
hardness of the rail head. The C.sub.eq value is preferably
maintained within a suitable range. At a C.sub.eq value of less
than 1.04, although a desired internal hardness is provided, the
internal hardness is close to the lower limit of the target
hardness range. Thus, it is unlikely that the wear resistance and
rolling contact fatigue resistance will be further improved. A
C.sub.eq value exceeding 1.27 results in an increase in the quench
hardenability of the internal high hardness type pearlitic rail,
facilitating the formation of martensite in the surface layer of
the rail head. Thus, the C.sub.eq value is preferably in the range
of 1.04 to 1.27 and more preferably 1.04 to 1.20.
[% Si]+[% Mn]+[% Cr]: 1.55% to 2.50
[0047] When the sum of the Si content [% Si], the Mn content [%
Mn], and the Cr content [% Cr] (=[% Si]+[% Mn]+[% Cr]) is less than
1.55, it is difficult to satisfy an internal hardness of the rail
head greater than or equal to 380 Hv and less than 480 Hv. When the
sum exceeds 2.50, a martensitic structure is formed because of high
quench hardenability of Si, Mn, and Cr. This is liable to cause a
reduction in ductility and toughness. Thus, the value of [% Si]+[%
Mn]+[% Cr] is preferably in the range of 1.55 to 2.50 and more
preferably 1.55 to 2.30. The units of [% Si], [% Mn], and [% Cr]
are percent by mass.
[0048] The composition described above may further contain one or
two or more selected from 1.0% by mass or less Cu, 1.0% by mass or
less Ni, 0.001% to 0.05% by mass Nb, and 0.5% by mass or less Mo,
as needed.
Cu: 1.0% by Mass or Less
[0049] Like Cr, Cu is an element that further increases the
strength by solid-solution hardening. To provide the effect, the Cu
content is preferably 0.005% by mass or more. A Cu content
exceeding 1.0% by mass, however, is liable to cause Cu cracking.
Thus, in the case where Cu is added, the Cu content is preferably
1.0% by mass or less and more preferably 0.005% to 0.5% by
mass.
Ni: 1.0% by Mass or Less
[0050] Ni is an element that increases the strength without
reducing ductility. Furthermore, the addition of Ni together with
Cu suppresses Cu cracking. Thus, when Cu is added, preferably, Ni
is also added. To provide the effect, the Ni content is preferably
0.005% or more. The Ni content exceeding 1.0% by mass, however,
results in an increase in quench hardenability, forming martensite.
This is liable to cause a reduction in wear resistance and rolling
contact fatigue resistance. In the case where Ni is added, thus,
the Ni content is preferably 1.0% by mass or less and more
preferably 0.005% to 0.5% by mass.
Nb: 0.001% to 0.05% by Mass
[0051] Nb is combined with C in steel to precipitate as a carbide
during and after rolling and contributes to a reduction in pearlite
colony size. This leads to significant improvement in wear
resistance, rolling contact fatigue resistance and ductility and
significant contribution to longer operating life of the internal
high hardness type pearlitic rail. To provide the effects, a Nb
content of 0.001% by mass or more is preferred. At a Nb content of
less than 0.001% by mass, the effect is not sufficiently provided.
At a Nb content exceeding 0.05% by mass, the effect of improving
wear resistance and rolling contact fatigue resistance is
saturated, the effect is not worth the amount added. In the case
where Nb is added, thus, the Nb content is preferably in the range
of 0.001% to 0.05% by mass and more preferably 0.001% to 0.03% by
mass.
Mo: 0.5% by Mass or Less
[0052] Mo is an element that increases the strength by
solid-solution hardening. To provide the effect, the Mn content is
preferably 0.005% by mass or more. A Mo content exceeding 0.5% by
mass is liable to cause the formation of a bainitic structure and
to reduce wear resistance. In the case where Mo is added, thus, the
Mo content is preferably 0.5% by mass or less and more preferably
0.005% to 0.3% by mass.
Lamellar spacing of pearlite layer in portion located from surface
layer of rail head to depth of at least 25 mm: 0.04 to 0.15
.mu.m
[0053] A reduction in the lamellar spacing of a pearlite layer
increases the hardness of the internal high hardness type pearlitic
rail, which is advantageous from the viewpoint of improving wear
resistance and rolling contact fatigue resistance. A lamellar
spacing exceeding 0.15 .mu.m does no result in sufficient
improvement in these properties. Thus, the lamellar spacing is
preferably 0.15 .mu.m or less. On the other hand, for reducing the
lamellar spacing to less than 0.04 .mu.m, a technique for reducing
the lamellar spacing by improving quench hardenability is to be
used. This is liable to cause the formation of martensite in the
surface layer, thereby adversely affecting rolling contact fatigue
resistance. Thus, the lamellar spacing is preferably 0.04 .mu.m or
more.
[0054] We also provide other trace elements in place of part of the
usual balance of Fe in the composition. Examples of impurities
include P and O. A P content of up to 0.035% by mass is allowable
as described above. An O content of up to 0.004% by mass is
allowable. Furthermore, a Ti content of up to 0.0010% is allowable,
Ti being contained as an impurity. In particular, Ti forms an oxide
to reduce rolling contact fatigue resistance, which is a basic
property of the rail. Thus, the Ti content is preferably controlled
so as to be up to 0.0010%.
[0055] The internal high hardness type pearlitic rail is preferably
produced by hot-rolling a steel material with a composition to form
a rail shape in such a manner that the finishing rolling
temperature is in the range of 850.degree. C. to 950.degree. C.,
and slack-quenching at least the head of the rail article from a
temperature equal to or higher than a pearlite transformation
starting temperature to 400.degree. C. to 650.degree. C. at a
cooling rate of 1.2 to 5.degree. C./s. The reason for a finishing
rolling temperature (roll finishing temperature) of 850.degree. C.
to 950.degree. C., a cooling rate of the slack quenching of 1.2 to
5.degree. C./s, and a cooling stop temperature of 400.degree. C. to
650.degree. C. is described below.
Finishing Rolling Temperature: 850.degree. C. to 950.degree. C.
[0056] In the case of a finishing rolling temperature of less than
850.degree. C., rolling is performed to a low-temperature austenite
range. This not only introduces processing strain in the austenite
grains, but also causes a significantly high degree of extension of
the austenite grains. The introduction of dislocation and an
increase in austenite grain boundary area results in an increase in
the number of pearlite nucleation sites. Although the pearlite
colony size is reduced, the increase in the number of pearlite
nucleation sites increases a pearlite transformation starting
temperature, thereby increasing the lamellar spacing of the
pearlite layer to cause a significant reduction in wear resistance.
Meanwhile, a finishing rolling temperature exceeding 950.degree. C.
increases the austenite grain size, thereby increasing the final
pearlite colony size to cause a reduction in rolling contact
fatigue resistance. Thus, the finishing rolling temperature is
preferably in the range of 850.degree. C. to 950.degree. C.
Cooling Rate from Temperature Equal to or Higher than Pearlite
Transformation Starting Temperature: 1.2 to 5.degree. C./s
[0057] A cooling rate of less than 1.2.degree. C./s results in an
increase in pearlite transformation starting temperature, thereby
increasing the lamellar spacing of the pearlite layer to cause a
significant reduction in wear resistance and rolling contact
fatigue resistance. Meanwhile, a cooling rate exceeding 5.degree.
C./s results in the formation of a martensitic structure, thereby
reducing ductility and toughness. Thus, the cooling rate is
preferably in the range of 1.2 to 5.degree. C./s and more
preferably 1.2 to 4.6.degree. C./s. Although the pearlite
transformation starting temperature varies depending on the cooling
rate, the pearlite transformation starting temperature is referred
to as an equilibrium transformation temperature. In the composition
range, the cooling rate within the above range may be used at
720.degree. C. or higher.
Cooling Stop Temperature: 400.degree. C. to 650.degree. C.
[0058] In the case of the composition and the cooling rate, to
obtain a uniform pearlitic structure at a cooling rate of 1.2 to
5.degree. C./s, it is preferable to ensure a cooling stop
temperature of at least about 70.degree. C. lower than the
equilibrium transformation temperature. A cooling stop temperature
of less than 400.degree. C., however, results in an increase in
cooling time, leading to an increase in the cost of the internal
high hardness type pearlitic rail. Thus, the cooling stop
temperature is preferably in the range of 400.degree. C. to
650.degree. C. and more preferably 450.degree. C. to 650.degree.
C.
[0059] Next, methods for measuring and evaluating wear resistance,
rolling contact fatigue resistance, delayed fracture properties,
the internal hardness of the rail head, and the lamellar spacing
will be described.
(Wear Resistance)
[0060] With respect to wear resistance, most preferably, the
internal high hardness type pearlitic rail is actually placed and
evaluated. In this case, disadvantageously, it takes a long time to
conduct a test. Thus, evaluation is made by a comparative test
performed under simulated real conditions of rail and wheel contact
with a Nishihara-type rolling contact test machine that can
evaluate wear resistance in a short time. A Nishihara-type rolling
contact test piece 1 having an external diameter of 30 mm is taken
from the rail head. The test is performed by contacting the test
piece 1 with a tire specimen 2 and rotating them as shown in FIG.
1. Arrows in FIG. 1 indicate rotational directions of the
Nishihara-type rolling contact test piece 1 and the tire specimen
2. With respect to the tire specimen, a round bar with a diameter
of 32 mm is taken from the head of a standard rail (Japanese
industrial standard rail) described in JIS E1101. The round bar is
subjected to heat treatment to have a Vickers hardness of 390 HV
(load: 98 N) and a tempered martensitic structure. Then the round
bar is processed to have a shape shown in FIG. 1, resulting in the
tire specimen. Note that the Nishihara-type rolling contact test
piece 1 is taken from each of two portions of a rail head 3 as
shown in FIG. 2. A piece taken from a surface layer of the rail
head 3 is referred to as a Nishihara-type rolling contact test
piece 1a. A piece taken from the inside is referred to as a
Nishihara-type rolling contact test piece 1b. The center of the
Nishihara-type rolling contact test piece 1b, which is taken from
the inside of the rail head 3, in the longitudinal direction is
located at a depth of 24 to 26 mm (mean value: 25 mm) below the top
face of the rail head 3. The test is performed in a dry state at a
contact pressure of 1.4 GPa, a slip ratio of -10%, and a rotation
speed of 675 rpm (750 rpm for the tire specimen). The wear amount
at 100,000 rotations is measured. A heat-treated pearlitic rail is
employed as reference steel used in comparing wear amounts. It is
determined that the wear resistance is improved when the wear
amount is at least 10% smaller than that of the reference steel.
Note that the rate of improvement in wear resistance is calculated
from {(wear amount of reference steel-wear amount of test
piece)/(wear amount of reference steel)}.times.100.
(Rolling Contact Fatigue Resistance)
[0061] With, respect to rolling contact fatigue resistance, the
Nishihara-type rolling contact test piece 1 having an external
diameter of 30 mm and a curved contact surface with a radius of
curvature of 15 mm is taken from the rail head. A test is performed
by contacting the test piece 1 with the tire specimen 2 and
rotating them as shown in FIG. 3. Arrows in FIG. 3 indicate
rotational directions of the Nishihara-type rolling contact test
piece 1 and the tire specimen 2. Note that the Nishihara-type
rolling contact test piece 1 is taken from each of two portions of
a rail head 3 as shown in FIG. 2. The tire specimen and each
portion where the Nishihara-type rolling contact test piece 1 is
taken are the same as above. Hence, the description is omitted. The
test is performed under an oil-lubricated condition at a contact
pressure of 2.2 GPa, a slip ratio of -20%, and a rotation speed of
600 rpm (750 rpm for the tire specimen). The surface of each test
piece is observed every 25,000 rotations. The number of rotations
at the occurrence of a crack with a length of 0.5 mm or more is
defined as rolling contact fatigue life. A heat-treated pearlitic
rail is employed as reference steel used in comparing rolling
contact fatigue life. It is determined that the rolling contact
fatigue resistance is improved when the rolling contact fatigue
life is at least 10% longer than that of the reference steel. Note
that the rate of improvement in rolling contact fatigue resistance
is calculated from {(number of rotations at occurrence of fatigue
damage of test piece-number of rotation at occurrence of fatigue
damage of reference steel)/(number of rotations at occurrence of
fatigue damage of reference steel)}.times.100.
(Delayed Fracture Property)
[0062] As shown in FIG. 4, a slow strain rate technique (SSRT) test
piece 4 having the center 25.4 mm below the top face of the rail
head 3 is taken. The SSRT test piece 4 has dimensions and a shape
shown in FIG. 5. The test piece is subjected to three triangle mark
finish, except for screw sections and round sections. Parallel
sections are polished with emery paper (up to #600). The SSRT test
piece is mounted on an SSRT test apparatus and then subjected to an
SSRT test at a strain rate of 3.3.times.10.sup.-6/s and a
temperature of 25.degree. C. in the atmosphere, obtaining
elongation E.sub.0 of the SSRT test piece in the atmosphere. An
SSRT test piece is subjected to an SSRT test in a 20 mass %
ammonium thiocyanate (NH.sub.4SCN) solution at a strain rate of
3.3.times.10.sup.-6/s and a temperature of 25.degree. C., obtaining
elongation E.sub.1 of the SSRT test piece in the ammonium
thiocyanate solution. Delayed fracture susceptibility (i.e., DF)
used as an index to evaluate delayed fracture properties is
calculated from DF(%)=100.times.(1-E.sub.1/E.sub.0). It is
determined that the delayed fracture properties are improved when
the rate of improvement in delayed fracture susceptibility is at
least 10% higher than that of a reference steel (i.e., a heat
treatment-type pearlitic rail having a C content of 0.68% by mass).
Note that the rate of improvement in delayed fracture
susceptibility is calculated from {(delayed fracture susceptibility
of test piece-delayed fracture susceptibility of reference
steel)/(delayed fracture susceptibility of reference
steel}.times.100.
(Internal Hardness of Rail Head)
[0063] The Vickers hardness of a portion located from the surface
layer of the rail head of to a depth of 25 mm is measured at a load
of 98 N and a pitch of 1 mm. Among all hardness values, the minimum
hardness value is defined as the internal hardness of the rail
head.
(Lamellar Spacing)
[0064] Random five fields of view of each of a portion (at a depth
of about 1 mm) close to the surface layer of the rail head and a
portion located at a depth of 25 mm are observed with a scanning
electron microscope (SEM) at a magnification of 7,500.times.. In
the case where a portion with the minimum lamellar spacing is
present, the portion is observed at a magnification of
20,000.times., and the lamellar spacing in the field of view is
measured. In the case where no small lamellar spacing is observed
in a field of view at a magnification of 7,500.times. or where the
cross-section of a lamellar structure is not perpendicular to a
lamellar plane but is obliquely arranged, the measurement is
performed in another field of view. The lamellar spacing is
evaluated by the mean value of the lamellar spacing measurements in
the five fields of view.
EXAMPLES
Example 1
[0065] Steel materials with compositions shown in Table 1 were
subjected to rolling and cooling under conditions shown in Table 2
to produce pearlitic rails. Cooling was performed only at heads of
the rails. After termination of the cooling, the pearlitic rails
were subject to natural cooling. The resulting pearlitic rails were
evaluated for Vickers hardness, lamellar spacing, wear resistance,
rolling contact fatigue resistance, and delayed fracture
properties. Table 3 shows the results. The finishing rolling
temperature shown in Table 2 indicates a value obtained by
measuring a temperature of the surface layer of a side face of each
rail head on the entrance side of a final roll mill with a
radiation thermometer. The cooling stop temperature indicates a
value obtained by measuring a temperature of the surface layer of a
side face of each rail head on the exit side of a cooling apparatus
with a radiation thermometer. The cooling rate was defined as the
rate of change in temperature between the start and end of
cooling.
[0066] The values of [% V]/[% N] were calculated from the V content
and the N content in 1-B to 1-N shown in Table 1. FIG. 6 shows the
relationship between the resulting [% V]/[% N] values and the rate
of improvement in delayed fracture susceptibility shown in Table
3.
[0067] The results demonstrated the following: In the case where
the [% Mn]/[% Cr] value was greater than or equal to 0.3 and less
than 1.0 and where the [% V]/[% N] value was in the range of 8.0 to
30.0, the portion located from the surface layer of the rail head
to a depth of at least 25 mm had a hardness greater than or equal
to 380 Hv and less than 480 Hv, so that the wear resistance and the
rolling contact fatigue resistance were improved, and the delayed
fracture properties are improved by 10% or more. In each of 1-F and
1-I, the [% V]/[% N] value exceeded 30. In this case, further
significant improvement in delayed fracture properties was not
achieved.
Example 2
[0068] Steel materials with compositions shown in Table 4 were
subjected to rolling and cooling under conditions shown in Table 5
to produce pearlitic rails. Cooling was performed only at heads of
the rails. After termination of the cooling, the pearlitic rails
were subject to natural cooling. Like Example 1, the resulting
pearlitic rails were evaluated for Vickers hardness, lamellar
spacing, wear resistance, rolling contact fatigue resistance, and
delayed fracture properties. Table 6 shows the results.
[0069] The results demonstrated the following: In each of 2-B to
2-L and 2-V to 2-X, in the case where the amounts of Si, Mn, Cr, V,
and N added were optimized, the [% Mn]/[% Cr] value was greater
than or equal to 0.3 and less than 1.0, the [% V]/[% N] value was
in the range of 8.0 to 30.0, and one or two or more components
selected from Cu, Ni, Nb, and Mo were added in proper amounts, the
wear resistance, rolling contact fatigue resistance, and delayed
fracture properties were improved. Among these examples, in each of
2-B to 2-H and 2-V to 2-X, i.e., in the case where of a DI value of
5.6 to 8.6 and a C.sub.eq of 1.04 to 1.27, the wear resistance and
the rolling contact fatigue resistance were improved compared with
2-I to 2-L. In 2-U, i.e., in the case of adding Ti, the rolling
contact fatigue resistance was reduced.
[0070] A pearlitic rail having excellent wear resistance, rolling
contact fatigue resistance, and delayed fracture properties
compared with pearlitic rails in the related art can be stably
produced. This contributes to longer operating life of pearlitic
rails used for high-axle load railways and to the prevention of
railway accidents, providing industrially beneficial effects.
INDUSTRIAL APPLICABILITY
[0071] A pearlitic rail having excellent wear resistance, rolling
contact fatigue resistance, and delayed fracture properties
compared with pearlitic rails in the related art can be stably
produced. This contributes to longer operating life of pearlitic
rails used for high-axle load railways and to the prevention of
railway accidents, providing industrially beneficial effects.
TABLE-US-00001 TABLE 1 (mass % excluding mass ratio, DI, and Ceq)
[% Si] + Steel [% Mn]/ [% V]/ [% Mn] + No. C Si Mn P S Cr V N [%
Cr] [% N] DI Ceq [% Cr] Remarks 1-A 0.68 0.18 1.00 0.014 0.016 0.20
0.000 0.0024 5.0 0.0 3.8 0.87 1.38 Reference material 1-B 0.81 0.52
0.71 0.011 0.006 0.82 0.073 0.0035 0.9 20.9 8.5 1.17 2.05 Example
1-C 0.84 0.53 0.53 0.011 0.003 0.79 0.061 0.0056 0.7 10.9 6.7 1.16
1.85 1-D 0.84 0.61 0.66 0.012 0.004 0.88 0.017 0.0021 0.8 8.1 8.2
1.16 2.15 1-E 0.83 0.51 0.68 0.010 0.004 0.84 0.092 0.0031 0.8 29.7
8.6 1.21 2.03 1-F 0.81 0.51 0.71 0.012 0.005 0.8 0.089 0.0020 0.9
44.5 8.5 1.18 2.02 Comparative 1-G 0.82 0.51 0.73 0.013 0.004 0.79
0.011 0.0039 0.9 2.8 7.7 1.12 2.03 example 1-H 0.81 0.66 0.69 0.011
0.005 0.83 0.015 0.0022 0.8 6.8 8.1 1.13 2.18 1-I 0.82 0.59 0.68
0.010 0.006 0.77 0.072 0.0022 0.9 32.7 8.2 1.18 2.04 1-J 0.76 0.51
0.69 0.011 0.003 0.82 0.072 0.0042 0.8 17.1 8.0 1.12 2.02 Example
1-K 0.83 0.70 0.63 0.013 0.003 0.79 0.055 0.0050 0.8 11.0 8.1 1.17
2.12 1-L 0.84 0.69 0.59 0.010 0.004 0.99 0.030 0.0030 0.6 10.0 8.6
1.19 2.27 1-M 0.82 0.52 0.46 0.011 0.004 1.20 0.063 0.0035 0.4 18.0
8.0 1.20 2.18 1-N 0.85 0.70 0.55 0.011 0.003 0.83 0.090 0.0045 0.7
20.0 8.1 1.23 2.08
TABLE-US-00002 TABLE 2 Finishing Cooling rolling stop Cooling
temperature temperature rate Steel No. (.degree. C.) (.degree. C.)
(.degree. C./s) Remarks 1-A 900 500 2.0 Reference material 1-B 900
500 1.6 Example 1-C 950 550 2.3 1-D 900 450 2.2 1-E 850 600 3.2 1-F
900 550 1.4 Comparative 1-G 950 500 2.2 example 1-H 950 550 1.9 1-I
850 500 1.6 1-J 900 500 2.6 Example 1-K 950 550 3.2 1-L 900 500 2.3
1-M 850 450 2.5 1-N 900 550 3.3
TABLE-US-00003 TABLE 3 Surface layer of rail Number of rotations at
occurrence of Rate of rolling improvement Rate of contact in
rolling Inside of rail 25 mm Hardness improvement fatigue contact
Hardness of Lamellar Wear in wear defect fatigue of Lamellar Steel
rail spacing Micro- amount resistance (.times.10.sup.5 resistance
rail spacing Micro- No. (HV) (.mu.m) structure (g) (%) rotations)
(%) (HV) (.mu.m) structure 1-A 370 0.16 P 1.37 -- 8.10 -- 340 0.23
P 1-B 431 0.06 P 1.10 19.7 9.90 22.2 410 0.08 P 1-C 420 0.08 P 1.14
16.8 9.68 19.5 403 0.09 P 1-D 433 0.06 P 1.12 18.2 9.90 22.2 399
0.10 P 1-E 442 0.05 P 1.09 20.4 10.13 25.1 415 0.08 P 1-F 430 0.06
P 1.10 19.7 9.90 22.2 412 0.08 P 1-G 409 0.09 P 1.16 15.3 9.23 14.0
382 0.14 P 1-H 411 0.08 P 1.14 16.8 9.23 14.0 384 0.14 P 1-I 436
0.05 P 1.10 19.7 9.90 22.2 402 0.09 P 1-J 435 0.06 P 1.12 18.2 9.90
22.2 402 0.09 P 1-K 440 0.06 P 1.11 19.0 9.90 22.2 401 0.10 P 1-L
439 0.06 P 1.12 18.2 9.68 19.5 403 0.10 P 1-M 441 0.05 P 1.12 18.2
9.90 22.2 409 0.09 P 1-N 433 0.06 P 1.14 16.8 9.68 19.5 399 0.10 P
Inside of rail 25 mm Number of rotations at occurrence Rate of of
improvement Rate of Rate of rolling in improvement improvement
contact rolling in in fatigue contact Delayed delayed Wear wear
defect fatigue fracture fracture Steel amount resistance
(.times.10.sup.5 resistance susceptibility susceptibility No. (g)
(%) rotations) (%) (%) (%) Remarks 1-A 1.40 -- 7.65 -- 85.0 0.0
Reference material 1-B 1.16 17.1 9.23 20.7 73.7 13.3 Example 1-C
1.18 15.7 9.00 17.6 75.0 11.8 1-D 1.17 16.4 9.00 17.6 76.1 10.5 1-E
1.16 17.1 9.00 17.6 72.6 14.6 1-F 1.17 16.4 9.23 20.7 72.4 14.8
Comparative 1-G 1.26 10.0 8.55 11.8 78.1 8.1 example 1-H 1.26 10.0
8.55 11.8 76.9 9.5 1-I 1.19 15.0 9.23 20.7 72.3 14.9 1-J 1.19 15.0
9.00 17.6 73.9 13.1 Example 1-K 1.18 15.7 9.00 17.6 75.2 11.5 1-L
1.19 15.0 9.00 17.6 75.6 11.1 1-M 1.17 16.4 9.00 17.6 75.3 11.4 1-N
1.19 15.0 9.00 17.6 74.8 12.0 P represents pearlite, and M
represents martensite.
TABLE-US-00004 TABLE 4 (mass % excluding mass ratio, DI, and Ceq)
Steel No. C Si Mn P S Cr V N Nb Cu Ni 2-A 0.68 0.18 1.00 0.014
0.016 0.20 0.000 0.0032 2-B 0.84 0.55 0.55 0.012 0.004 0.77 0.050
0.0021 0.03 2-C 0.84 0.65 0.39 0.011 0.008 0.78 0.051 0.0055 0.01
0.05 0.05 2-D 0.84 0.55 0.33 0.011 0.004 1.09 0.120 0.0043 0.05
0.05 2-E 0.82 0.52 0.66 0.015 0.003 0.83 0.050 0.0051 0.02 2-F 0.82
0.54 0.77 0.013 0.005 0.83 0.029 0.0031 0.02 2-G 0.82 0.66 0.47
0.016 0.002 1.15 0.013 0.0016 0.01 0.05 2-H 0.81 0.53 0.72 0.012
0.007 0.86 0.055 0.0051 0.03 0.07 2-I 0.83 0.51 0.51 0.010 0.005
0.65 0.031 0.0032 0.02 2-J 0.81 0.52 0.44 0.011 0.003 0.69 0.062
0.0044 0.01 2-K 0.81 0.52 0.44 0.012 0.004 0.75 0.042 0.0032 0.02
2-L 0.79 0.51 0.31 0.011 0.003 0.70 0.033 0.0019 0.01 2-M 0.78 0.31
0.72 0.011 0.004 1.08 0.044 0.0048 0.04 0.03 0.03 2-N 0.70 0.62
0.81 0.012 0.004 0.89 0.031 0.0022 0.02 2-P 1.05 0.51 0.58 0.009
0.003 0.63 0.027 0.0031 0.02 2-Q 0.84 0.94 0.63 0.009 0.008 0.81
0.044 0.0042 0.02 0.05 0.05 2-R 0.83 0.62 0.31 0.007 0.003 1.25
0.021 0.0045 0.01 2-S 0.76 0.53 1.16 0.011 0.004 0.50 0.081 0.0042
2-T 0.80 0.51 0.36 0.013 0.007 1.35 0.051 0.0041 0.05 0.05 2-U 0.79
0.73 0.55 0.011 0.004 0.75 0.055 0.0055 0.02 2-V 0.77 0.62 0.61
0.010 0.004 0.72 0.025 0.0031 0.01 2-W 0.84 0.51 0.51 0.014 0.003
0.71 0.053 0.0055 2-X 0.82 0.70 0.31 0.013 0.004 1.11 0.048 0.0059
0.01 0.01 [% Si] + Steel [% Mn]/ [% V]/ [% Mn] + No. Mo Ti [% Cr]
[% N] DI Ceq [% Cr] Remarks 2-A 5.0 0.0 3.8 0.87 1.38 Reference
material 2-B 0.7 23.8 6.8 1.15 1.87 Example 2-C 0.5 9.3 5.7 1.14
1.82 2-D 0.05 0.3 27.9 6.9 1.25 1.97 2-E 0.03 0.8 9.8 7.9 1.15 2.01
2-F 0.03 0.9 9.4 8.6 1.15 2.14 2-G 0.4 8.1 7.9 1.16 2.28 2-H 0.15
0.8 10.8 8.6 1.16 2.11 2-I 0.8 9.7 5.4 1.09 1.67 2-J 0.08 0.6 14.1
5.4 1.10 1.65 2-K 0.6 13.1 5.5 1.09 1.71 2-L 0.4 17.4 4.1 1.03 1.52
2-M 0.7 9.2 8.7 1.14 2.11 Comparative 2-N 0.9 14.1 9.0 1.06 2.32
Example 2-P 0.04 0.9 8.7 6.5 1.31 1.72 2-Q 0.8 10.5 8.9 1.20 2.38
2-R 0.16 0.2 4.7 6.3 1.17 2.18 2-S 0.05 2.3 19.3 9.2 1.14 2.19 2-T
0.03 0.3 12.4 7.3 1.18 2.22 2-U 0.01 0.7 10.0 7.0 1.12 2.03 2-V 0.8
8.1 6.6 1.06 1.95 Example 2-W 0.01 0.7 9.6 6.1 1.13 1.73 2-X 0.3
8.1 6.4 1.17 2.12
TABLE-US-00005 TABLE 5 Finishing rolling Cooling stop temperature
temperature Cooling rate Steel No. (.degree. C.) (.degree. C.)
(.degree. C./s) Remarks 2-A 900 500 2.0 Reference material 2-B 900
500 2.3 Example 2-C 900 500 1.9 2-D 950 550 1.3 2-E 900 500 2.2 2-F
900 500 1.9 2-G 950 500 2.3 2-H 900 600 2.0 2-I 950 500 2.0 2-J 850
550 2.1 2-K 950 450 2.8 2-L 950 550 2.0 2-M 900 500 2.1 Comparative
2-N 900 550 2.0 example 2-P 950 500 2.2 2-Q 900 500 2.3 2-R 850 450
3.1 2-S 850 650 2.4 2-T 850 550 3.2 2-U 900 600 2.2 2-V 850 550 2.6
Example 2-W 900 500 2.4 2-X 900 600 2.6
TABLE-US-00006 TABLE 6 Surface layer of rail Number of rotations at
Rate of occurrence of Rate of improvement rolling contact
improvement in Inside of rail 25 mm Lamellar Wear in wear fatigue
defect rolling contact Lamellar Steel Hardness spacing Micro-
amount resistance (.times. 10.sup.5 fatigue Hardness spacing No. of
rail (HV) (.mu.m) structure (g) (%) rotations) resistance (%) of
rail (HV) (.mu.m) 2-A 370 0.16 P 1.37 -- 8.10 -- 340 0.23 2-B 425
0.08 P 1.10 19.7 9.68 19.5 399 0.10 2-C 429 0.07 P 1.11 19.0 9.68
19.5 395 0.11 2-D 431 0.06 P 1.10 19.7 9.68 19.5 401 0.10 2-E 428
0.07 P 1.11 19.0 9.90 22.2 400 0.10 2-F 434 0.06 P 1.10 19.7 9.90
22.2 398 0.10 2-G 459 0.05 P 1.07 21.9 10.58 30.6 417 0.09 2-H 438
0.05 P 1.10 19.7 10.35 27.8 412 0.09 2-I 419 0.11 P 1.15 16.1 9.23
14.0 381 0.15 2-J 422 0.12 P 1.14 16.8 9.00 11.1 381 0.15 2-K 425
0.08 P 1.10 19.7 9.90 22.2 383 0.14 2-L 411 0.09 P 1.14 16.8 9.23
14.0 380 0.15 2-M 411 0.11 P 1.17 14.6 9.00 11.1 377 0.17 2-N 409
0.11 P 1.14 16.8 9.00 11.1 373 0.19 2-P 432 0.05 P + .theta. 1.11
19.0 8.78 8.4 378 0.17 2-Q 488 -- P + M 1.12 18.2 8.55 5.6 421 0.08
2-R 483 -- P + M 1.12 18.2 8.55 5.6 432 0.07 2-S 495 -- P + M 1.18
13.9 8.55 5.6 440 0.06 2-T 500 -- P + M 1.18 13.9 8.55 5.6 437 0.06
2-U 412 0.11 P 1.17 14.6 8.78 8.4 388 0.15 2-V 421 0.09 P 1.13 17.5
9.68 19.5 395 0.11 2-W 435 0.08 P 1.11 19.0 9.68 19.5 403 0.10 2-X
439 0.07 P 1.10 19.7 9.68 19.5 409 0.09 Inside of rail 25 mm Number
of rotations at Rate of Rate of occurrence of Rate of improvement
in improvement in rolling contact improvement in Delayed delayed
Wear wear fatigue defect rolling contact fracture fracture Steel
Micro- amount resistance (.times. 10.sup.5 fatigue susceptibility
susceptibility No. structure (g) (%) rotations) resistance (%) (%)
(%) Remarks 2-A P 1.40 -- 7.65 -- 85.0 0.0 Reference material 2-B P
1.17 16.4 9.00 17.6 72.4 14.8 Example 2-C P 1.18 15.7 9.00 17.6
72.2 15.1 2-D P 1.17 16.4 9.00 17.6 73.1 14.0 2-E P 1.17 16.4 9.00
17.6 74.2 12.7 2-F P 1.18 15.7 9.00 17.6 74.2 12.7 2-G P 1.15 17.9
9.45 23.5 75.1 11.6 2-H P 1.16 17.1 9.45 23.5 75.1 11.6 2-I P 1.25
10.7 8.55 11.8 74.8 12.0 2-J P 1.25 10.7 8.55 11.8 74.5 12.4 2-K P
1.25 10.7 8.55 11.8 74.1 12.8 2-L P 1.26 10.0 8.55 11.8 73.9 13.1
2-M P 1.31 6.4 8.33 8.9 74.3 12.6 Comparative 2-N P 1.33 5.0 8.33
8.9 74.3 12.6 example 2-P P 1.31 6.4 8.33 8.9 74.0 12.9 2-Q P 1.14
18.6 9.45 23.5 76.2 10.4 2-R P 1.10 21.4 9.68 26.5 76.2 10.4 2-S P
1.08 22.9 9.68 26.5 76.5 10.0 2-T P 1.10 21.4 9.45 23.5 76.3 10.2
2-U P 1.19 15.0 7.88 3.0 76.3 10.2 2-V P 1.21 13.6 8.78 14.8 73.9
13.1 Example 2-W P 1.17 16.4 9.00 17.6 74.1 12.8 2-X P 1.15 17.9
9.23 20.7 74.1 12.8 P represents pearlite, .theta. represents
proeutectoid cementite, and M represents martensite.
* * * * *