U.S. patent application number 14/990407 was filed with the patent office on 2016-07-07 for high-strength and highly fatigue-resistant steel rail and production method thereof.
This patent application is currently assigned to PanGang Group Panzhihua Iron & Steel Research Institute Co., Ltd.. The applicant listed for this patent is PanGang Group Panzhihua Iron & Steel Research Institute Co., Ltd., Pangang Group Panzhihua Steel & Vanadium Co., Ltd.. Invention is credited to Yong Deng, Hua Guo, Zhenyu Han, Jihai Jia, Chunjian Wang, Jun Yuan, Ming Zou.
Application Number | 20160194729 14/990407 |
Document ID | / |
Family ID | 53078880 |
Filed Date | 2016-07-07 |
United States Patent
Application |
20160194729 |
Kind Code |
A1 |
Deng; Yong ; et al. |
July 7, 2016 |
HIGH-STRENGTH AND HIGHLY FATIGUE-RESISTANT STEEL RAIL AND
PRODUCTION METHOD THEREOF
Abstract
The present invention relates to a high-strength, highly
wear-resistant, and highly contact-fatigue-resistant steel rail and
a production method thereof, and belongs to the field of black
steel manufacturing technology. The present invention provides a
high-strength and highly fatigue-resistant steel rail, comprising
the following chemical components by weight percentage: C:
0.76%.about.0.86%; Si: 0.6%.about.1%; Mn: 0.7%.about.1.5%, Cr:
0.1%.about.0.5%, and 0.8%.ltoreq.Mn %+Cr %.ltoreq.1.6%; V:
0.05%.about.0.3%, Ni: 0.1%.about.0.35%, and 0.15%.ltoreq.V %+Ni
%.ltoreq.0.4%; Mo: .ltoreq.0.03%; P: .ltoreq.0.02%; S:
.ltoreq.0.015%; Fe and inevitable impurities: the remaining
content, wherein, the metallurgical structure of the steel rail is
fine pearlite+A, where, A is proeutectoid ferrite or proeutectoid
cementite, and A.ltoreq.2%. The tensile strength of the obtained
steel rail is 1,260 MPa.about.1,420 MPa.
Inventors: |
Deng; Yong; (Panzhihua,
CN) ; Guo; Hua; (Panzhihua, CN) ; Zou;
Ming; (Panzhihua, CN) ; Jia; Jihai;
(Panzhihua, CN) ; Wang; Chunjian; (Panzhihua,
CN) ; Han; Zhenyu; (Panzhihua, CN) ; Yuan;
Jun; (Panzhihua, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PanGang Group Panzhihua Iron & Steel Research Institute Co.,
Ltd.
Pangang Group Panzhihua Steel & Vanadium Co., Ltd. |
Panzhihua
Panzhihua |
|
CN
CN |
|
|
Assignee: |
PanGang Group Panzhihua Iron &
Steel Research Institute Co., Ltd.
Panzhihua
CN
Pangang Group Panzhihua Steel & Vanadium Co., Ltd.
Panzhihua
CN
|
Family ID: |
53078880 |
Appl. No.: |
14/990407 |
Filed: |
January 7, 2016 |
Current U.S.
Class: |
148/541 ;
148/335 |
Current CPC
Class: |
C22C 38/002 20130101;
C22C 38/48 20130101; B22D 11/00 20130101; C21D 6/004 20130101; C22C
38/02 20130101; B22D 11/001 20130101; C21D 8/005 20130101; C21D
1/60 20130101; C22C 38/04 20130101; C22C 38/50 20130101; C21D 6/008
20130101; C22C 33/04 20130101; C22C 38/46 20130101; C21D 1/613
20130101; C21D 9/04 20130101; C22C 38/44 20130101; C21D 6/005
20130101 |
International
Class: |
C21D 9/04 20060101
C21D009/04; C22C 38/48 20060101 C22C038/48; C22C 38/46 20060101
C22C038/46; C22C 38/44 20060101 C22C038/44; C22C 38/04 20060101
C22C038/04; B22D 11/00 20060101 B22D011/00; C22C 38/00 20060101
C22C038/00; C22C 33/04 20060101 C22C033/04; C21D 6/00 20060101
C21D006/00; C21D 8/00 20060101 C21D008/00; C21D 1/613 20060101
C21D001/613; C21D 1/60 20060101 C21D001/60; C22C 38/50 20060101
C22C038/50; C22C 38/02 20060101 C22C038/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 7, 2015 |
CN |
201510006016.8 |
Claims
1. A steel rail, comprising the following chemical components by
weight percentage: C: 0.76%.about.0.86%; Si: 0.60%.about.1.00%; Mn:
0.70%.about.1.50%, Cr: 0.10%.about.0.50%, and 0.80%.ltoreq.Mn %+Cr
%.ltoreq.1.60%; V: 0.05%.about.0.30%, Ni: 0.10%.about.0.35%, and
0.15%.ltoreq.V %+Ni %.ltoreq.0.40%; Mo: .ltoreq.0.03%; P:
.ltoreq.0.020%; S: .ltoreq.0.015%; Fe and inevitable impurities:
the remaining content, wherein, the metallurgical structure of the
steel rail is fine pearlite+A, where, A is proeutectoid ferrite or
proeutectoid cementite, and A.ltoreq.2%.
2. The steel rail according to claim 1, wherein, further comprising
the following components by weight percentage: Ti:
0.05%.about.0.30%, and Nb: 0.005%.about.0.10%.
3. The steel rail according to claim 1, wherein, A is
.ltoreq.1%.
4. The steel rail according to claim 2, wherein, A is
.ltoreq.1%.
5. The steel rail according to claim 1, wherein, tensile strength
of the steel rail is 1,260 MPa.about.1,420 MPa, hardness of the
rail head tread is 390HB.about.432HB, hardness of the part at 10 mm
below the surface of rail head is 380HB.about.420HB, and hardness
of the part at 24 mm below the surface of rail head is
370HB.about.401HB.
6. The steel rail according to claim 2, wherein, tensile strength
of the steel rail is 1,260 MPa.about.1,420 MPa, hardness of the
rail head tread is 390HB.about.432HB, hardness of the part at 10 mm
below the surface of rail head is 380HB.about.420HB, and hardness
of the part at 24 mm below the surface of rail head is
370HB.about.401HB.
7. The steel rail according to claim 3, wherein, tensile strength
of the steel rail is 1,260 MPa.about.1,420 MPa, hardness of the
rail head tread is 390HB.about.432HB, hardness of the part at 10 mm
below the surface of rail head is 380HB.about.420HB, and hardness
of the part at 24 mm below the surface of rail head is
370HB.about.401HB.
8. The steel rail according to claim 4, wherein, tensile strength
of the steel rail is 1,260 MPa.about.1,420 MPa, hardness of the
rail head tread is 390HB.about.432HB, hardness of the part at 10 mm
below the surface of rail head is 380HB.about.420HB, and hardness
of the part at 24 mm below the surface of rail head is
370HB.about.401HB.
9. A method for producing a steel rail, comprising the procedures
in turn: converter smelting-LF refining-RH vacuum
treatment-continuous casting-rolling-cooling-straightening,
wherein, finish rolling temperature in the rolling procedure is
controlled to be 930.degree. C..about.1,000.degree. C.; initial
cooling temperature in the cooling procedure is controlled to be
780.degree. C..about.880.degree. C., final cooling temperature is
controlled to be 300.degree. C..about.400.degree. C., and cooling
rate is controlled to be 4.0.degree. C..about.10.0.degree. C./s;
wherein, the steel rail comprises the following chemical components
by weight percentage: C: 0.76%.about.0.86%; Si: 0.60%.about.1.00%;
Mn: 0.70%.about.1.50%, Cr: 0.10%.about.0.50%, and 0.80%.ltoreq.Mn
%+Cr %.ltoreq.1.60%; V: 0.05%.about.0.30%, Ni: 0.10%.about.0.35%,
and 0.15%.ltoreq.V %+Ni %.ltoreq.0.40%; Mo: .ltoreq.0.03%; P:
.ltoreq.0.020%; S: .ltoreq.0.015%; Fe and inevitable impurities:
the remaining content, wherein, the metallurgical structure of the
steel rail is fine pearlite+A, where, A is proeutectoid ferrite or
proeutectoid cementite, and A.ltoreq.2%.
10. The method for producing the steel rail according to claim 9,
wherein, the steel rail further comprising the following components
by weight percentage: Ti: 0.05%.about.0.30%, and Nb:
0.005%.about.0.10%.
11. The method for producing the steel rail according to claim 9,
wherein, A is .ltoreq.1%.
12. The method for producing the steel rail according to claim 10,
wherein, A is .ltoreq.1%.
13. The method for producing the steel rail according to claim 9,
wherein, tensile strength of the steel rail is 1,260
MPa.about.1,420 MPa, hardness of the rail head tread is
390HB.about.432HB, hardness of the part at 10 mm below the surface
of rail head is 380HB420HB, and hardness of the part at 24 mm below
the surface of rail head is 370HB.about.401HB.
14. The method for producing the steel rail according to claim 10,
wherein, tensile strength of the steel rail is 1,260
MPa.about.1,420 MPa, hardness of the rail head tread is 390HB432HB,
hardness of the part at 10 mm below the surface of rail head is
380HB.about.420HB, and hardness of the part at 24 mm below the
surface of rail head is 370HB.about.401HB.
15. The method for producing the steel rail according to claim 11,
wherein, tensile strength of the steel rail is 1,260
MPa.about.1,420 MPa, hardness of the rail head tread is 390HB432HB,
hardness of the part at 10 mm below the surface of rail head is
380HB420HB, and hardness of the part at 24 mm below the surface of
rail head is 370HB.about.401HB.
16. The method for producing the steel rail according to claim 12,
wherein, tensile strength of the steel rail is 1,260
MPa.about.1,420 MPa, hardness of the rail head tread is 390HB432HB,
hardness of the part at 10 mm below the surface of rail head is
380HB420HB, and hardness of the part at 24 mm below the surface of
rail head is 370HB.about.401HB.
17. The method for producing the steel rail according to claim 9,
wherein, the cooling method is at least one selected from the group
consisting of air blast cooling, water mist cooling, and water
cooling.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to Chinese Application No.
201510006016.8, filed on Jan. 7, 2015, entitled "High-Strength and
Highly Fatigue-Resistant Steel Rail and Production Method Thereof",
which is specifically and entirely incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a high-strength, highly
wear-resistant, and highly contact-fatigue-resistant steel rail and
a production method thereof, and belongs to the field of black
steel manufacturing technology.
BACKGROUND OF THE INVENTION
[0003] With the rapid development of China's heavy haul railways,
the axle load on the freight railways in China has been increased
continuously. For example, the axle load on most mixed passenger
and freight transport railways is 21 tons or 23 tons, the axle load
on special major freight railways, such as Daqin Railway and
Shuohuang Railway, is 25 tons, and the axle load on the South
Central Channel, which has just be built up and put into trial run,
is 30 tons. It is foreseeable that increasing the axle load of
freight trains will be the most optimal and the most economical
method among the methods for further improving the efficiency of
railway freightage in China. In addition, as the axle load on
freight railways is increased continuously, the need for high wear
resistance performance and high contact fatigue resistance
performance of freight railways becomes more urgent. Therefore, it
is an urgent task to develop new rail steel to adapt to the new
railway transport pattern in China. Thus, in the present invention,
a heavy-duty steel rail with high wear resistance and high contact
fatigue resistance performance is developed, against the complex
and heavy-haul railway transportation conditions in China.
[0004] In recent years, considering the present situation of steel
rail production and railway operation in China, relevant domestic
and foreign steel rail manufacturers have applied for patents
related with steel rail techniques in China, such as
hyper-eutectoid steel rail production technique, low alloy steel
rail production technique, etc.
[0005] Relevant patent applications include as indicated below.
[0006] (1) Corus UK LIMITED applied for a patent for "Rail Steel
with an Excellent Combination of Wear Properties and Rolling
Contact Fatigue Resistance" (Application Publication No.
CN101946019A) in 2011, which related to a high-strength pearlitic
steel rail with an excellent combination of wear properties and
rolling contact fatigue resistance, comprising: C:
0.88.about.0.95%, Si: 0.75.about.0.92%, Mn: 0.80.about.0.95%, V:
0.05.about.0.14%, N: .ltoreq.0.008%, P: .ltoreq.0.030%, S:
0.008.about.0.030%, H: .ltoreq.2.5 ppm, Cr: .ltoreq.0.10%, Al:
.ltoreq.0.010%, 0: .ltoreq.20 ppm, and Fe and inevitable
impurities: the remaining content. The patented steel rail has RCF
resistance higher than 130,000 cycles under water lubricated
condition. [0007] (2) Baotou Steel Corporation (China) applied for
a patent for "High-Strength Rare Earth Steel Rail Containing Cr and
V" (Application Publication No. CN102517501A) in 2012, which
related to a high-strength and highly wear-resistant rare earth
steel rail and belongs to the technical field of metallurgical
products. The chemical components and their weight percentages in
the steel rail are: C: 0.65.about.0.82%, Si: 0.50.about.0.80%, Mn:
0.70.about.1.20%, P: .ltoreq.0.025%, S: .ltoreq.0.025%, Cr:
0.20.about.0.40%, V: .ltoreq.0.10%, RE (addition): .ltoreq.0.03%,
and Fe substrate and trace impurities: the remaining content. By
adding Cr and V alloys and rare earth (rare earth cored wires are
added after refining), the elements complement each other and
thereby the strength and wear resistance of the steel rail are
improved, and overall properties, welding performance, and heat
treatment performance of the steel rail are improved. Thus, the
steel rail is applicable to important heavy-haul trunk railways and
has extensive application prospects. [0008] (3) Baotou Steel
Corporation (China) applied for a patent for "Steel Special for
High-Strength and Heat-Treated Steel Rail" (Application Publication
No. CN103014486A) in 2013, which related to steel special for
high-strength and heat-treated steel rail, and the chemical
components of the steel by weight percentage include: C:
0.70.about.0.82%, Si: 0.13.about.0.60%, Mn: 0.65.about.1.25%, P or
S: .ltoreq.0.025%, Al: .ltoreq.0.007%, and Fe and inevitable
impurities: the remaining content. The steel has reasonable
composition proportion, the strength of the steel rail is improved
through heat treatment, and the steel can meet the requirements for
steel rails on the coal transport railways and curve steel rail in
Indonesia. [0009] (4) Baotou Steel Corporation (China) applied for
a patent for "Steel special for Low-Alloy and Medium-Strength Steel
Rail" (Application Publication No. CN103014506A) in 2013, which
related to steel special for low-alloy and medium-strength steel
rail, and the chemical components of the steel by weight percentage
include: C: 0.72.about.0.82%, Si: 0.35.about.1.00%, Mn:
0.80.about.1.25%, Cr: 0.40.about.0.70%, P: .ltoreq.0.020%, S:
.ltoreq.0.020%, Al: .ltoreq.0.005%, and Fe and inevitable
impurities: the remaining content. The steel has reasonable
composition proportion and low alloying element content, the steel
rail has higher strength and higher hardness when compared with
ordinary hot-rolled steel rails, and the steel can meet the use
requirements for steel rails on curve railways and heavy-haul
railways. [0010] (5) Nippon Steel & Sumitomo Metal Corporation
(Japan) applied for a patent for "Steel Rail and Production Method
Thereof" (Application Publication No. CN102985574A) in 2013, which
provided a steel rail comprising the following components by weight
percentage: C: >0.85 and .ltoreq.1.20%, Si: 0.05.about.2.00%,
Mn: 0.05.about.0.50%, Cr: 0.05.about.0.60%, P: .ltoreq.0.0150%, and
Fe and inevitable impurities: the remaining content, wherein, 97%
or more of a head surface portion, which is in a range from a
surface of a head corner portion and a head top portion as a
starting point to a depth of 10 mm, has a pearlite structure,
wherein, the Vickers hardness of the pearlite structure is
Hv320.about.500, and a CMn/FMn value which is a value obtained by
dividing CMn [at. %] that is a Mn concentration of a cementite
phase in the pearlite structure by FMn [at. %] that is a Mn
concentration of a ferrite is .gtoreq.1.0 and .ltoreq.5.0. [0011]
(6) Voest-Alpine Stahl AG (Austria) applied for a patent for
"Method for Heat Treatment of Rails" (Application Publication No.
CN1085258A) in 1993, which related to a method for the thermal
treatment of steel rail, in particular of the rail head, in which
cooling is carried out in a cooling medium that contains a
synthetic cooling agent additive, starting at temperatures above
720.degree. C. In order to prevent the rail web from hardening
while maintaining optimum cooling speeds for the rail head,
immersion in the cooling medium is continued until a surface
temperature between 450.degree. C. and 550.degree. C. is obtained
after drawing the submerged areas of the rails without temperature
equalization over the whole cross section. [0012] (7) Nippon Steel
Corporation (Japan) applied for a patent for "Pearlite-Based
High-Carbon Steel Rail with Excellent Ductility and Method for
Manufacturing the Same" (Application Publication No. CN102803536A)
in 2012, which related to a pearlite-based high-carbon steel rail
with excellent ductility, comprising the following components by
mass percentage: C: more than 0.85 to 1.40%, Si: 0.10 to 2.00%, Mn:
0.10 to 2.00%, Ti: 0.001 to 0.01%, V: 0.005 to 0.20%, N: less than
0.0040%, and Fe and inevitable impurities: the remaining content;
the contents of Ti and V meet the following formula (1), and the
rail head part is a pearlite structure: 5.ltoreq.[V (% by
mass)]/[Ti (% by mass)].ltoreq.20. [0013] (8) BNSF Railway Co.,
Ltd. (USA) applied for a patent for "High-Strength and
Damage-Resistant Steel Rail and Method for Manufacturing the Same"
(Application Publication No. CN1063916A) in 1991. The patent puts
forth a high-strength and damage-resistant steel rail, comprising
the following components by weight percentage: C:
(0.60.about.0.85)%, Si: (0.1.about.1.0)%, Mn: (0.5.about.1.5)%, P:
.ltoreq.0.035%, S: .ltoreq.0.040%, Al: .ltoreq.0.05%, and Fe and
inevitable impurities: the remaining content. The hardness of the
corner part 2 and head side part 3 of rail is HB341.about.HB405,
and the hardness of the head top part is not more than 90% of the
hardness of the corner part and head side part of rail. With that
invention, injuries of the top part of rail head resulted from
excessive contact pressure incurred by scuffs on the head part can
be inhibited, and the service life of the steel rail can be
prolonged. [0014] (9) Nippon Kokan Co., Ltd. (Japan) applied for a
patent for "Wear-Resistant Steel Rail Capable for Preventing
Propagation of Unstable Fracture" (Application Publication No.
CN86106894A) in 1986, in which the steel rail comprises the
following components by weight percentage: C: 0.50.about.0.85%, Si:
0.10.about.1.0%, Mn: 0.50.about.1.50%, P: <0.035%, S:
<0.035%, Al: <0.050%, and Fe and inevitable impurities: the
remaining content. The structure of the rail web is high-ductility
tempered bainite structure or mixed structure of bainite and
martensite. The steel rail may further comprises one or more of the
following elements by weight percentage: Cr: 0.05.about.1.50%, Mo:
0.05.about.0.20%, V: 0.03.about.0.10%, Ni: 0.10.about.1.00%, and
Nb: 0.005.about.0.050%.
SUMMARY OF THE INVENTION
[0015] The technical problem to be solved in the present invention
is to provide a high-strength, highly wear-resistant, and highly
contact-fatigue-resistant steel rail and a production method
thereof.
[0016] The technical solution of the present invention is as
indicated below.
[0017] A high-strength and highly fatigue-resistant steel rail,
comprising the following chemical components by weight percentage:
C: 0.76%.about.0.86%; Si: 0.60%.about.1.00%; Mn: 0.70%.about.1.50%,
Cr: 0.10%.about.0.50%, and 0.80%.ltoreq.Mn %+Cr %.ltoreq.1.60%; V:
0.05%.about.0.30%, Ni: 0.10%.about.0.35%, and 0.15%.ltoreq.V %+Ni
%.ltoreq.0.40%; Mo: .ltoreq.0.03%; P: .ltoreq.0.020%; S:
.ltoreq.0.015%; Fe and inevitable impurities: the remaining
content, wherein, the metallurgical structure of the steel rail is
fine pearlite+A, where, A is proeutectoid ferrite or proeutectoid
cementite, and A.ltoreq.2%.
[0018] The steel rail further comprises the following components by
weight percentage: Ti: 0.05%.about.0.30%, and Nb:
0.005%.about.0.10%.
[0019] Preferably, A is proeutectoid ferrite or proeutectoid
cementite, and A.ltoreq.1%.
[0020] The tensile strength of the steel rail is 1,260
MPa.about.1,420 MPa, the hardness of the rail head tread is
390HB.about.432HB, the hardness of the part at 10 mm below the
surface of rail head is 380HB.about.420HB, and the hardness of the
part at 24 mm below the surface of rail head is
370HB.about.401HB.
[0021] The present invention further provides a method for
producing the high-strength and highly fatigue-resistant steel
rail, comprising the procedures in turn: converter smelting-LF
refining-RH vacuum treatment-continuous
casting-rolling-cooling-straightening, wherein, the finish rolling
temperature in the rolling procedure is controlled to be
930.degree. C..about.1,000.degree. C.; the initial cooling
temperature in the cooling procedure is controlled to be
780.degree. C..about.880.degree. C., the final cooling temperature
is controlled to be 300.degree. C..about.400.degree. C., and the
cooling rate is controlled to be 4.0.degree. C..about.10.0.degree.
C./s.
[0022] Preferably, the cooling method is at least one selected from
the group consisting of air blast cooling, water mist cooling and
water cooling.
[0023] The present invention has the following beneficial effects.
Compared with the inventions reported in the prior art, in the
present invention, the second-phase structure (e.g., proeutectoid
ferrite and proeutectoid cementite) is less, and the full rail
profile is pearlite structure; especially, there is no martensite
or bainite structure in tempered state in the rail web; thus, the
risk of occurrence of horizontal cracks in the rail web in the
service life of the steel rail is avoided. In addition, the present
invention has the following advantages. [0024] (1) The production
process of the steel rail is compact and the operation is easier to
control; a secondary heating procedure is eliminated, when compared
with an offline heat treatment process; thus, energy and production
time are saved. [0025] (2) Through the process described above, the
cooling of the rail head is more uniform, and the depth of hardened
layer in the rail head is greater.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a structural representation of hardness testing
positions on the steel rail tread, where, L=10 mm, and B=24 mm. At
the hardness testing position A0 on the rail tread, when the steel
rail tread is tested, the surface layer of the rail tread must be
ground off by 0.50 mm, before Brinell hardness test can be carried
out for the surface; A1, B1 and C1 are hardness testing points at
10 mm distance from the surface of rail head, A2, B2 and C2 are
hardness testing points at 24 mm distance from the surface of rail
head.
[0027] FIG. 2 is a partially enlarged view of part A in FIG. 1.
[0028] FIG. 3 shows the typical metallurgical structure of the
sample obtained in example 1, and the metallurgical structure is
pearlite+0.8% trace proeutectoid ferrite.
DETAILED DESCRIPTION OF EMBODIMENTS
[0029] The present invention provides a high-strength and highly
fatigue-resistant steel rail, comprising the following chemical
components by weight percentage: C: 0.76%.about.0.86%; Si:
0.60%.about.1.00%; Mn: 0.70%.about.1.50%, Cr: 0.10%.about.0.50%,
and 0.80%.ltoreq.Mn %+Cr %.ltoreq.1.60%; V: 0.05%.about.0.30%, Ni:
0.10%.about.0.35%, and 0.15%.ltoreq.V %+Ni %.ltoreq.0.40%; Mo:
.ltoreq.0.03%; P: .ltoreq.0.020%; S: .ltoreq.0.015%; Fe and
inevitable impurities: the remaining content, wherein, the
metallurgical structure of the steel rail is fine pearlite+A,
where, A is proeutectoid ferrite or proeutectoid cementite (also
referred to as secondary cementite), and A.ltoreq.2%.
[0030] Proeutectoid ferrite: it means ferrite precipitating from
austenite lower than the eutectoid composition as the austenite is
cooled down from a high temperature before eutectoid transformation
(eutectoid transition) takes place.
[0031] Proeutectoid cementite: it is also referred to as secondary
cementite, which refers to Fe.sub.3C precipitating from austenite
A. The secondary cementite precipitates from austenite along the
grain boundaries as the carbon content changes during temperature
drop. It appears in hypereutectoid steel in most cases and is
usually in mesh form. In view that the secondary cementite meshes
have adverse effects to the performance of the steel, they can be
broken by normalization to improve performance.
[0032] Preferably, 0.05%.about.0.30% Ti and 0.005%.about.0.10% Nb
may be added, depending on the requirement for strengthening.
Hereinafter, the design and control ranges of the elements will be
described.
[0033] C is a positive element for improving wear resistance of
steel rail. However, if the carbon content is too high, a large
amount of proeutectoid cementite (also referred to as secondary
cementite) may appear; if the carbon content is too low, a large
amount of proeutectoid ferrite may precipitate; both cases have
adverse effects to the contact fatigue resistance of the steel
rail. Hence, in the present invention, the carbon content is
controlled to be within a range of 0.76%.about.0.86%, so that
proeutectoid ferrite and proeutectoid cementite can be controlled
to be 2.0% or lower.
[0034] Si is a major element for solution strengthening, and can
improve the strength and wear resistance of steel rail. In
addition, in eutectoid steel rails, Si is an element that promotes
the precipitation of ferrite, and has a function of inhibiting the
precipitation of cementite. However, if the Si content is too high,
the plasticity and toughness of the steel rail will be decreased;
consequently, the contact fatigue resistance of the steel rail will
be decreased. Hence, in the present invention, the Si content is
controlled to be within a range of 0.60%.about.1.00%.
[0035] Mn and Cr are strong-hardenability alloying elements, an
optimal effect can be attained if both elements are added at the
same time. In addition, Mn and Cr are maj or elements for improving
wear resistance of steel rail. However, if the Mn content and Cr
content are too high, harmful bainite and martensite structures may
appear in the steel rail. Therefore, the total addition amount of
Mn and Cr must be controlled strictly. Hence, in the present
invention, to ensure the structure of the steel rail is pearlite
structure, the Mn content is controlled to be within a range of
0.70%.about.1.50%, the Cr content is controlled to be within a
range of 0.10%.about.0.50%, and 0.80%.ltoreq.Mn %+Cr
%.ltoreq.1.60%.
[0036] Mo is an element that can strongly increase hardenability;
especially, when Mn and Cr are used in combination, even a small
amount of Mo can result in mixed bainite and martensite structure
in the rail web, which is quite harmful to the performance of the
rail web. For example, in the Mn, Cr and Mo alloy system described
in the patent document CN86106894A, typical bainite structure
appears in the rail web. In the present invention, microalloy
elements Mn and Cr are mainly utilized to ensure hardenability
performance. Hence, in the present invention, the Mo content is
controlled to be lower than 0.03%.
[0037] V and Ni are elements that can improve the
strength-toughness of steel rail without compromising the
plasticity of steel rail. However, excessive V and Ni have little
contribution to further improvement of toughness but have adverse
effects, and result in significantly increased production cost at
the same time. Hence, in the present invention, the V content is
controlled to be within a range of 0.05%.about.0.30%, the Ni
content is controlled to be within a range of 0.10%.about.0.35%,
and 0.15%.ltoreq.V %+Ni %.ltoreq.0.40%.
[0038] Both P and S are elements that can not be eliminated
completely. P segregates at the grain boundaries in the steel rail
structure, which is very harmful to the toughness of the steel
rail; S mainly produces MnS inclusion in the steel, which is
harmful to the contact fatigue resistance of the steel rail. Hence,
in the present invention, according to the actual production
control ability of the manufacturer, the P content is controlled to
be lower than 0.020%, and the S content is controlled to be lower
than 0.015%.
[0039] In addition, to improve the strength and wear resistance of
the rail steel, prevent the welding heat affected zone from
softening, and improve the strength and hardness of welded joints,
Ti and Nb elements can be added for grain refining. However, if the
Ti content and Nb content are too high, a second phase such as TiC
or NbC will precipitate in the steel rail at a high temperature. In
the precipitation process of the above second phase, the content of
cementite lamellas in the pearlite structure of the steel rail will
be reduced, because the content of carbon dissolved in the steel
rail is decreased actually. Consequently, the strength and hardness
of the steel will be decreased instead. Hence, in the present
invention, only a very small amount of Ti and Nb can be added. The
Ti content is controlled to be within a range of 0.05%.about.0.30%,
and the Nb content is controlled to be within a range of
0.005%.about.0.10%.
[0040] The tensile strength of the obtained steel rail is 1,260
MPa.about.1,420 MPa, and the testing positions are shown in FIG. 1;
the hardness of the rail head tread is 390HB.about.432HB, and the
testing positions are shown in FIG. 2; the hardness of the part at
10 mm below the surface of rail head is 380HB.about.420HB, and the
testing positions are shown in FIG. 2; the hardness of the part at
24 mm below the surface of rail head is 370HB.about.401HB, and the
testing positions are shown in FIG. 2.
[0041] The present invention further provides a method for
producing the above high-strength and highly fatigue-resistant
steel rail, comprising the procedures in trun: converter
smelting-LF refining-RH vacuum treatment-continuous
casting-rolling-cooling-straightening-test-surface inspection,
wherein, the finish rolling temperature in the rolling procedure is
controlled to be 930.degree. C..about.1,000.degree. C.; the initial
cooling temperature in the cooling procedure is controlled to be
780.degree. C..about.880.degree. C., the final cooling temperature
is controlled to be 300.degree. C..about.400.degree. C., and the
cooling rate is controlled to be 4.0.degree. C..about.10.0.degree.
C./s.
[0042] The steel rail is treated by in-line heat treatment.
Usually, the finish rolling temperature of the steel rail is
930.degree. C..about.1,000.degree. C. Forced cooling (including a
combination of one or more selected from the group consisting of
air blast cooling, water mist cooling, and water cooling) is
required in the high-temperature stage in order to inhibit the
precipitation of proeutectoid ferrite or proeutectoid cementite in
the steel rail, and the initial cooling temperature of the steel
rail is controlled to be between 780.degree. C..about.880.degree.
C. Moreover, in view of the high initial cooling temperature, high
cooling efficiency is required, so that the core part of rail head
can be quenched fully. Usually, the cooling is controlled at
4.0.degree. C./s.about.10.0.degree. C./s cooling rate, till the
temperature at the center of the rail head surface drops to
300.degree. C..about.400.degree. C. Finally, the hardness of the
part at 24 mm below the rail head surface reaches 370HB or more,
while the hardness of the rail head surface increased to 390HB.
EXAMPLE
[0043] The production procedures include: rail steel smelting in a
converter-refining in a LF furnace and molten steel heating-RH
composition control and homogenization-bloom continuous casting
under six-strand protection-bloom heating-7-stand universal
rolling-feeding the rolled steel with ends into heat treatment
equipment for forced cooling-discharging from the heat-treatment
equipment at 300.degree. C..about.400.degree. C. final cooling
temperature-cooling on walking beam cooler-combined vertical and
horizontal straightening-non-destructive test, cross sectional
dimension and straightness inspection-combined cutting and
drilling, and cutting to specified length-surface
inspection-warehousing.
[0044] The temperature of the rolled part is 930.degree.
C..about.1,000.degree. C. when the rolled part is discharged from
the UF finish rolling section. To ensure the initial cooling
temperature is 780.degree. C..about.880.degree. C., the running
speed of the roller way must be increased, and relevant pause
procedures must be cancelled, so that the rolled part enters into
the heat treatment equipments at a desired temperature. The range
of adjustment is 4.0.degree. C./s.about.10.0.degree. C./s,
according to the composition of the steel rail in smelting and the
cooling rate of the steel rail controlled by temperature.
[0045] Hereinafter, some examples will be described with reference
to the above embodiment. The chemical composition of the rail steel
in smelting in Examples 1-10 is shown in Table 1, wherein the
remaining is Fe and inevitable impurities; the process conditions
controlled in Examples 1-10 as shown in Table 2; the properties and
metallurgical structure of the finished product in Examples 1-10
are shown in Table 3. In the examples and comparative examples of
the present invention, the properties of the steel rail, including
tensile strength, specific elongation, and hardness of tread, etc.,
are respectively tested as per GB/T228.1 "Metallic
Materials-Tensile Testing-Part 1: Method of Test at Room
Temperature", and GB/T 231.1 "Metallic Materials-Brinell Hardness
Test-Part 1: Test Method".
Comparative Examples 1-4
[0046] The chemical compositions of the steel rails in smelting in
the comparative examples 1-4 are shown in Table 4, wherein the
remaining is Fe and inevitable impurities. The production
procedures involved in comparative examples are the same as those
in the examples, and the process conditions involved in comparative
examples 1-4 are the same as those in Example 1.
Comparative Examples 5-7
[0047] The process conditions involved in comparative examples 5-7
are shown in Table 5. The chemical compositions of the steel rails
in smelting in the comparative examples 5-7 are respectively the
same as those involved in Example 5-7.
TABLE-US-00001 TABLE 1 Composition in Smelting in Examples 1-10
Chemical Composition in Smelting/wt % Example C Si Mn Cr V Ni Mo Ti
Nb P S 1 0.76 0.65 1.12 0.32 0.11 0.12 0.02 0.11 0.005 0.019 0.013
2 0.77 0.90 1.36 0.14 0.15 0.16 0.02 0.06 0.01 0.013 0.011 3 0.78
0.71 0.96 0.21 0.06 0.18 0.01 0.08 0.005 0.017 0.010 4 0.80 0.66
0.95 0.25 0.14 0.11 0.02 0.07 0.02 0.018 0.014 5 0.82 0.75 1.06
0.30 0.16 0.17 0.01 0.06 0.008 0.018 0.010 6 0.84 0.84 0.95 0.31
0.20 0.19 0.01 0.05 0.03 0.011 0.008 7 0.86 0.80 1.05 0.25 0.08
0.10 0.02 0.06 0.01 0.018 0.010 8 0.77 0.90 1.36 0.14 0.15 0.16
0.02 0 0 0.012 0.009 9 0.76 0.65 1.12 0.32 0.11 0.12 0.02 0 0.005
0.019 0.013 10 0.80 0.66 0.95 0.25 0.14 0.11 0.02 0.07 0 0.018
0.014
TABLE-US-00002 TABLE 2 Cooling Rates and Process Conditions in
Examples 1-10 Cooling Final cooling rate/ Finish Rolling Initial
cooling temperature/ Example .degree. C./s Temperature/.degree. C.
temperature/.degree. C. .degree. C. 1 7.5 971 831 368 2 8.0 978 838
373 3 6.5 948 808 360 4 7.2 960 820 365 5 5.0 942 802 354 6 9.2 995
855 380 7 8.5 990 850 378 8 7.9 975 835 371 9 7.5 972 830 365 10
7.2 961 819 364
TABLE-US-00003 TABLE 3 Performance Indexes in Examples 1-10
Hardness Hardness at 10 mm Hardness at 24 mm Tensile Specific of
tread below surface/HB below surface/HB Metallurgical Example
strength/MPa elongation/% A0/HB A1 B1 C1 A2 B2 C2 structure 1 1283
12.2 393 385 383 385 373 375 373 P + 0.8% .alpha. 2 1355 13.0 406
398 395 395 385 388 388 P 3 1298 12.3 395 385 388 385 375 375 373 P
4 1345 11.5 404 395 393 393 385 385 383 P 5 1340 11.0 401 393 393
390 383 380 380 P 6 1395 12.3 420 409 412 409 393 395 395 P + 0.1
wt % FeC 7 1386 13.1 417 406 404 404 390 388 390 P + 0.3 wt % FeC 8
1355 11.0 406 398 395 395 385 388 388 P 9 1270 11.7 390 383 383 383
373 373 373 P + 0.3 wt % .alpha. 10 1325 11.3 398 390 390 390 380
383 383 P
[0048] In the Table 3, P represents pearlite, a represents
proeutectoid ferrite, and FeC represents proeutectoid cementite
(also referred to as secondary cementite).
TABLE-US-00004 TABLE 4 Composition in Smelting in Comparative
Examples 1-4 Comparative Chemical Composition in Smelting/wt %
example C Si Mn Cr V Ni Mo Ti Nb P S 1 0.77 0.9 1.36 0.30 0.15 0.16
0.02 0.06 0.01 0.012 0.013 2 0.78 0.71 0.70 0.05 0.06 0.18 0.01
0.08 0.005 0.016 0.01 3 0.84 0.84 0.95 0.31 0.20 0.25 0.01 0.05
0.03 0.011 0.008 4 0.86 0.8 1.05 0.25 0.05 0.05 0.02 0.06 0.01
0.018 0.01
TABLE-US-00005 TABLE 5 Cooling Rates and Process Conditions in
Comparative Examples 5-7 Finish Rolling Initial cooling Final
cooling Comparative Cooling rate/ Temperature/ temperature/
temperature/ example .degree. C./s .degree. C. .degree. C. .degree.
C. 5 3 1100 970 465 6 12 1200 1070 605 7 8 900 770 298
TABLE-US-00006 TABLE 6 Performance Indexes in Comparative Examples
1-7 Hardness Hardness at 10 mm Hardness at 24 mm Comparative
Tensile Specific of tread below surface/HB below surface/HB
Metallurgical example strength/MPa elongation/% A0/HB A1 B1 C1 A2
B2 C2 structure 1 1373 8.0 412 401 398 398 393 390 390 P + dot-like
M 2 1252 10.4 383 373 370 373 361 363 363 P 3 1420 9.5 423 412 415
412 395 395 398 P + 0.1 wt % FeC + dot-like M 4 1355 10.5 406 395
395 393 383 383 380 P + 0.3 wt % FeC 5 1260 11.1 385 378 378 375
366 366 368 P 6 1230 10.8 373 366 366 368 345 343 343 P + 1.2 wt %
FeC 7 1425 9.3 426 417 417 415 398 401 401 P + 0.1 wt % FeC +
dot-like M
[0049] In the Table 6, P represents pearlite, at represents
proeutectoid ferrite, and FeC represents proeutectoid cementite
(also referred to as secondary cementite), M represents
martensite.
[0050] It can be seen from Table 1 to 6 that the second-phase
structure (e.g., proeutectoid ferrite and proeutectoid cementite)
is less and the steel rail in the present invention has
high-strength, highly wear-resistant, and highly
contact-fatigue-resistant performance.
* * * * *