AU2019219859B2

AU2019219859B2 - Corrosion-resistant rail and manufacturing method thereof

Info

Publication number: AU2019219859B2
Application number: AU2019219859A
Authority: AU
Inventors: Chongmu Chen; Zhenyu Han; Gongming Tao; Ming Zou
Original assignee: Pangang Group Panzhihua Iron and Steel Research Institute Co Ltd
Current assignee: Pangang Group Panzhihua Iron and Steel Research Institute Co Ltd
Priority date: 2018-08-27
Filing date: 2019-08-23
Publication date: 2020-09-24
Anticipated expiration: 2039-08-23
Also published as: CN109023058A; CN109023058B; AU2019219859A1

Abstract

The invention relates to a corrosion-resistant rail and a manufacturing method thereof, and belongs to the technical field of steel rolling and surface treatment. The technical problem to be solved by the invention is to provide a corrosion-resistant rail and a manufacturing method thereof for solving the problems of high manufacturing cost and low efficiency of corrosion-resistant rails in the prior art. The invention provides a corrosion-resistant rail and a manufacturing method thereof, and the rail consists of the following elements in percentage by weight: 0.70-0.90% of C, 0.10-0.80% of Si, 0.70-1.10% of Mn, 0.30-0.90% of Cr, at least one of the following three elements: 0.04%-0.15% of V, 0.02%-0.06% of Nb and 0.005%-0.05% of Ti, and the remaining elements are Fe and inevitable impurities. The rail prepared by the method of the invention has good corrosion resistance.

Description

Corrosion Resistant Rail and Manufacturing Method Thereof

Related Application This application claims priority from CN201810981152.2 filed on 27 August 2018, the contents of which are to be taken as incorporated herein by this reference.

Technical Field The invention belongs to the technical field of steel rolling and surface treatment, in particular to a corrosion-resistant rail and a manufacturing method thereof

Background As the world's largest rail producer, China has exported more than 500,000 tons of rails each year. High-strength rails are the key competitive products of various countries due to their strict implementation standards, excellent mechanical properties and high added value. For the vast majority of rails exported by China are transported by sea, they may be piled up in ports or transported by sea for several months. Being maintained in such a high-salt and high-humidity environment, rails get rusty easily, which not only inevitably impact their appearance, but also shorten their service life in severe case and even damage their mechanical property. thus affecting the safe operation of trains, and seriously affecting the market competitiveness and brand image of products. At present, two methods are used for protecting rails against corrosion: (1) improving the corrosion resistance of rail matrix by adding Cr, Ni, Cu and other alloy elements; (2) spraying zinc, aluminum alloy, polymer coating, grease, ointment and other protective coatings on the surface of rails to improve their corrosion resistance.

The patent document CN104060187B discloses a corrosion-resistant micro

alloyed rail, and the basic alloy system comprises the following alloy elements in

percentage by weight: 0.73%-0.85% of C, 0.30%-0.90% of Si, 0.80%-1.20% of Mn,

0.20%-0.40% of Cr, 0.30%-0.50% of Cu, Ni being 1/2-2/3 of Cu, 0.03%-0.05% of P,

S being not more than 0.025%, at least one of the following three elements:

0.04%-0.12% of V, 0.02%-0.06% of Nb and 0.005%-0.05% of Re; and the remaining

elements are Fe and inevitable impurities. The patent improves the corrosion

resistance of the rail matrix by adding the corrosion-resistant alloy elements like Cr,

Cu and Ni on the basis of carbon rails and mixing P, Ni and Cu contents. Rails to be exported must be conform to technical standards of exporting countries or other international standards. However, since the world standards put forward strict requirements on the content of chemical elements, the technical route of improving the corrosion resistance of rails through alloying is greatly limited. The patent document CN1884616A discloses a corrosion-resistant rail for railways and a manufacturing method thereof The method requires previous shot blasting or sandblasting treatment on the rail produced on line, electric arc spraying of zinc, aluminum or zinc-aluminum alloy, and automatic spraying, roll painting or manual brushing of an organic sealing layer or pigment paint layer. The shot blasting or sandblasting treatment of rail has high energy consumption and low efficiency. Moreover, due to the weak adhesion between the low-temperature spraying coating and the rail, the low-temperature spraying coating is prone to local peeling during hoisting and transportation, resulting high manufacturing cost, low efficiency and poor effect. Thus, the method mentioned above cannot be widely promoted and applied from the perspective of cost, efficiency and effectiveness. A reference herein to a patent document or any other matter identified as prior art, is not to be taken as an admission that the document or other matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims. Summary of the Invention It is desirable to provide a corrosion-resistant rail and a manufacturing method thereof for solving the problem of high manufacturing cost and/or low efficiency of corrosion-resistant rails in the prior art, or provide a useful choice. An aspect of the invention provides a corrosion-resistant rail, wherein an oxide film is coated on the corrosion-resistant rail, the oxide film is 15tm - 35pim thick, and a section Fe 3 04 thereof has an average area of 65-80%. In terms of chemical compositions, the corrosion-resistant rail matrix consists of the following elements in percentage by weight: 0.70-0.90% of C, 0.10-0.80% of Si, 0.70-1.10% of Mn and 0.30-0.90% of Cr, at least one of the following three elements: 0.04%-0.15% of V, 0.02%-0.06% of Nb, and 0.005%-0.05% of Ti, the remaining elements are Fe and inevitable impurities; the tensile strength of the corrosion-resistant rail is more than

1200MPa, and the elongation thereof is not less than 10%.

A further aspect of the invention provides a manufacturing method of the

corrosion-resistant rail as described in the preceding paragraph, wherein a billet is

prepared from blast furnace molten iron through converter smelting, LF refining,

electric heating and continuous casting, the billet is heated to be deformable, descaled

with high-pressure water until the scale area on the surface of the billet is less than

%, rolled and formed in a break-down mill, and made into a rail through rough

rolling, medium rolling and finish rolling in a universal mill; the medium rolling and

rough rolling sequentially adopt high-reduction rolling at low temperature, then the

compressed air is used to remove the scales again until they are completely descaled

from the rail surface accelerated cooling of the austenite area of the rail below 570 C

with compressed air, natural cooling to room temperature, and small deformation

straightening of the rail the scales are iron scales on the surface of billet or rail.

According to an embodiment of the manufacturing method of the

corrosion-resistant rail, the billet is heated at 1150 C - 1220 C for 2.5 - 3 h.

According to an embodiment of the manufacturing method of the

corrosion-resistant rail, the relative reduction of medium rolling is 18%-23% in the

universal mill and the medium rolling temperature is 850 C - 900 C.

According to an embodiment of the manufacturing method of the

corrosion-resistant rail, the relative reduction of finish rolling is 13%-17%in the

universal mill and the finish rolling temperature is 820 C - 870 C.

According to an embodiment of the manufacturing method of the

corrosion-resistant rail, the rail is subjected to secondary descaling with compressed

air at 15-20 MPa.

According to an embodiment of the manufacturing method of the

corrosion-resistant rail, the cooling speed is 1.5-5 °C/s in the cooling process, and the

rail is naturally cooled when the cooling temperature reaches 540 C - 570 C.

According to an embodiment of the manufacturing method of the

corrosion-resistant rail, during small deformation straightening of the rail, the rolling reduction of the second roller of the horizontal straightener is 12-16 mm, and the total rolling reduction of the four upper rollers is 30-40 mm. According to an embodiment of the manufacturing method of the corrosion-resistant rail, the total rolling deformation of the break-down mill is 35-55%, and the total deformation of rough rolling of the universal mill is 25-40%. One embodiment provides a corrosion-resistant rail, formed of a chemical composition matrix and including an oxide fil coating, wherein: the oxide film is 15um - 35um thick and a section Fe304 thereof has an average area of 6 5 -8 0 %; wherein the chemical composition matrix consists of the following elements in percentage by weight: 0.70-0.90% of C, 0.10-0.80% of Si, 0.70-1.10% of Mn and 0.30-0.90% of Cr, at least one of the following three elements: 0.04%-0.15% of V, 0.02%-0.06% of Nb, and 0.005%-0.05% of Ti, the remaining elements are Fe and inevitable impurities; wherein the tensile strength of the corrosion-resistant rail is more than 1200MPa, and the elongation thereof is not less than 10%; and wherein the corrosion-resistant rail is manufactured by a method comprising: the steps: a billet of rail base composition is heated to be deformable, descaled with high-pressure water until the scale area on a surface of the billet is less than 10%, rolled and formed in a break-down mill, and made into a rail through rough rolling, medium rolling and finish rolling in a universal mill; the medium rolling and rough rolling adopt high-reduction rolling at low temperature, then the compressed air is used to remove the scales again until they are completely descaled from the rail surface, accelerated cooling of the austenite area of the rail below 540-570 C with compressed air, natural cooling to room temperature, the cooling speed is 1.5-5 C/s, and small deformation straightening of the rail; the billet is prepared from blast furnace molten iron through converter smelting, LF refining, electric heating and continuous casting; the scales are iron scales on the surface of billet or rail; the billet is heated at 1150 °C - 1220 °C for 2.5 - 3 h; the relative reduction of medium rolling is 18%-23% in a universal mill and the medium rolling temperature is 850 °C - 900 °C; and the relative reduction of finish rolling is 13%-17% in the universal mill and the finish rolling temperature is 820 °C - 870 °C.

The beneficial effects of embodiments of the invention may be as follows:

The method of the invention can form a dense oxide film on the surface of rail

through billet heating, high-pressure water descaling, breakdown rolling, rough

rolling, medium rolling and finish rolling in a universal mill, secondary descaling and

cooling process. The thickness of the oxide film is 15 m-35 m. Since the average

area of a section Fe304 of the oxide film is 65-80%, the oxide film has higher

adhesion and compactness than that on the surface of common rail, which enables

rails to have good corrosion resistance in the transportation and stacking process. For

the corrosion-resistant rail prepared by the method of the invention, the surface

corrosion area is less than 10% of total surface area after the neutral salt spray test

with 5% of NaCl for 144h.The method of the invention does not require spraying

polymer coating, zinc, aluminum alloy and other parting agent on the surface of rail,

thus reducing environmental pollution and meeting the environmental protection

requirements. In addition, the method of the invention does not require any major

change to the rail manufacturing process and equipment, and matches with the

production schedule of rail, thus saving time and improving work efficiency. The

product of the invention is corrosion-resistant due to the oxide film on the surface of

rail, and the compositions of rail are easily controlled considering that elements such

as Ni and Cu are not added, which greatly save the cost.

Detailed Description of the Preferred Embodiment

The raw materials and equipment used in the preferred embodiment of the

invention are all known and commercially available.

The existing method for improving the corrosion resistance of rails includes adding alloy elements such as Ni, Cu and the like, spraying zinc, aluminum alloy, polymer coating, grease, ointment and other protective coatings on the surface of rail, or connecting Zn blocks with the rail to form a corrosion couple for protecting the rail by sacrificing Zn anode. However, these methods cannot be widely promoted and applied from the perspective of cost, efficiency and effectiveness. Through a great deal of researches, the inventors have found that a layer of dense oxide film can be formed on the surface of rail through billet heating, high-pressure water descaling, breakdown rolling, rough rolling, medium rolling and finish rolling in a universal mill, secondary descaling and cooling process. The oxide film may have higher adhesion and compactness than that on the surface of common rail so as to achieve the purpose of preventing the rail from rusting during transportation and stacking.

An embodiment of the invention provides a corrosion-resistant rail, whose

surface is covered with an oxide-film with a tickness of 15km - 35[tm, and a section

Fe 3 04 of the oxide film has an average area of 65-80%. In addition to Fe304, the oxide

film contains Fe203 and FeO. The oxide film has good corrosion resistance due to

dense structure, stable crystal form and strong adhesion.

In terms of chemical compositions, the corrosion-resistant rail matrix of the

invention consists of the following elements in percentage by weight: 0.70-0.90% of

C, 0.10-0.80% of Si, 0.70-1.10% of Mn and 0.30-0.90% of Cr, and at least one of the

following three elements: 0.04%-0.15% of V, 0.02%-0.06% of Nb, and

0.005%-0.05% of Ti, the remaining elements are Fe and inevitable impurities; the

tensile strength of the corrosion-resistant rail is more than 1200MPa, and the

elongation thereof is not less than 10%.

An embodiment of the invention further provides a manufacturing method of a

corrosion-resistant rail, comprising the following steps: a billet is prepared from blast

furnace molten iron through converter smelting, LF refining, electric heating and

continuous casting, the billet is heated to be deformable, descaled with high-pressure

water until the scale area on the surface of billet is less than 10%, rolled and formed in

a break-down mill, and made into a rail through rough rolling, medium rolling and

finish rolling in a universal mill; the medium rolling and rough rolling sequentially adopts high-reduction rolling at low temperature, accelerated cooling of the austenite area of the rail below 570 °C with compressed air, natural cooling to room temperature, and small deformation straightening of the rail.

According to the manufacturing method of the corrosion-resistant rail, the billet

is prepared from blast furnace molten iron through converter smelting, LF refining,

electric heating and continuous casting by the methods known to those skilled in the

art; and the scales are iron scales on the surface of billet or rail. The iron scales are

oxides formed by chemical reaction of iron elements on the surface of billet or rail

with oxidizing gas in the environment, as well as further diffusion of oxygen from the

surface to the inside of the billet.

is heated at 1150 °C - 1220 °C for 2.5 - 3 h.

According to the manufacturing method of the corrosion-resistant rail, the

relative reduction of medium rolling is 18%-23% in the universal mill and the

medium rolling temperature is 850 °C - 900 °C.

According to the manufacturing method of the corrosion-resistant rail, the

relative reduction of finish rolling is 13%-17% in the universal mill and the finish

rolling temperature is 820 °C - 870 °C.

In the medium rolling and finish rolling steps of the invention, the lower the

medium rolling and finish rolling temperature in the universal mill; the larger the

rolling reduction. As a result, the scale on the surface of the rolled piece (secondary

scale) is to be broken and peeled off in the rolling process, and removed in the

subsequent secondary descaling process. The finally obtained oxide films (third scale)

are all generated after finish rolling. The thinner the film is, the better the integrity is.

However, large rolling reduction and low temperature may cause large rolling

load of the mill and serious wear of rollers, which will adversely affect the safety of

the equipment and the surface quality of the rail. Therefore, the medium rolling

temperature is controlled to be 850 °C - 900 °C in a universal mill, with the relative

rolling reduction of 18%-23%; whereas, the finish rolling temperature is controlled to

be 820 °C - 870 °C in a universal mill, with the relative rolling reduction of

13%-17%.The maximum load of the mill is 88% of the rated load thereof, and single rolling amount of the roller is 90% of the rolling amount of common process, which not only meets the requirements of the rolling process, but also ensures the safety of equipment and the production efficiency. The oxide film will be thickened at extremely high medium rolling and finish rolling temperature in a universal mill. According to the manufacturing method of the corrosion-resistant rail, the rail is subjected to the second descaling with compressed air to completely remove the scale (secondary scale) remaining on the surface after finish rolling. Meanwhile, the descaling point is located within 6m of the inlet of the accelerated cooling device, and the descaling pressure is 15-20 MPa to inhibit the growth of scale thickness. High pressure water can also be used for the second descaling. In the invention, the heated billet isfirstly descaled with high-pressure water until the surface scale area of the billet is less than 10%. The secondary scale (FeO oxide film) will be generated on the surface of rail after breakdown rolling, rough rolling, medium rolling and finish rolling. The purpose of secondary descaling is to completely remove the scales on the surface of rail, which cannot be achieved in actual operation; and the secondary descaling area is more than 95% in the invention. According to the manufacturing method of the corrosion-resistant rail, the cooling speed is 1.5-5 °C/s in the cooling process, and the rail will be naturally cooled when the cooling temperature reaches 540 °C - 570 °C. In an embodiment, the initial accelerated cooling temperature of rail is 680 °C 820 °C, and accelerated cooling with compressed air can improve the transformation undercooling of austenite and reduce the austenite-to-pearlite transformation temperature, thus reducing the interlaminar spacing of pearlite. In general, the faster the cooling speed is; the smaller the interlaminar spacing of pearlite is and the higher the strength of steel is. When the cooling speed is more than 5°C/s, the internal segregation of rail is inevitable. Abnormal structures such as martensite, bainite and the like are easily generated in local areas when C and Mn occur segregation due to excessive cooling speed, resulting in scrap of rails. When the cooling rate is less than 1.5°C/s, the strength of rail will be affected. In the invention, when the cooling speed is 1.5-5°C/s, the strength of rail can be more than 1200MPa.

In the cooling process, the third scale will be formed on the surface of rail,

namely an oxide film with high adhesion, compactness and corrosion resistance

according to the invention. Since FeO can be converted to Fe304 at approximately

540-570 °C, the final accelerated cooling temperature is controlled to 540-570 °C.

Due to large temperature difference between the surface and the core of rail, the heat

of core will be transferred to the surface, and the surface temperature will rise in the

accelerated cooling process. In order to convert most of FeO to Fe304, the surface

temperature of rail shall be kept at 540 - 570 °C for a long time. The rail is naturally

cooled when it is subjected to accelerated cooling below 570 °C. Further, the natural

cooling occurs after accelerated cooling below 540 - 570 °C.

According to the manufacturing method of the corrosion-resistant rail, during

small deformation straightening of the rail, the rolling reduction of the second roller

of the horizontal straightener is 12-16mm and the total rolling reduction of the four

upper rollers is 30-40mm. The invention adopts a 9-roller straightener for the

straightening purpose, wherein the roller system consists of 4 upper straightening

rollers and 5 lower straightening rollers arranged in a staggered way, and the

straightening rollers from the upper inlet to the outlet of the straightener are

respectively numbered as 2, 4, 6 and 8. In order to reduce the cracking and peeling-off

of the oxide film on the rail surface during straightening, a small deformation process

is adopted for composite horizontal and vertical roll straightening, wherein the rolling

reduction of 2 rollers of horizontal straighteners is 12-16mm and the total rolling

reduction of 4 upper rollers is 30-40mm. The smaller the deformation of rail during

straightening is; the less likely the oxide film on the surface of rail will crack and peel

off. However, an important purpose of rail straightening is to make the rail straight,

which cannot be guaranteed in case of too small deformation. Therefore, when the

rolling reduction of the second straightening roller for horizontal straightener is

12-16mm and the total rolling reduction of the four upper rollers is 30-40mm, the

oxide film on the surface of rail may basically not crack and peel off, and the

straightness of rail can meet the standard requirements.

In an example, the average area of the oxide film section Fe304 refers to the

content of the oxide film section Fe304 obtained by image tool software after

analyzing the oxide film; and the thickness of the oxide film refers to the average

thickness of the oxide film on the surface of rail.

The invention will be further described in detail in combination with preferred

embodiments.

The billets in this example and comparative example are prepared from blast

continuous casting by the methods known to those skilled in the art.

Example 1

In terms of the chemical compositions, the rail matrix in this example consists of

the following elements in percentage by weight: 0.80% of C, 0.75% of Si, 0.95% of

Mn, 0.50% of Cr and 0.07% of V, and the remaining elements are Fe and other

inevitable impurities.

The chemical composition of billet is the same as that of rail matrix in this

example.

The billet is heated to 1170 °C in a heating furnace for 3 hours, descaled to 5%

by high-pressure water, rolled and formed by breakdown rolling in a break-down mill

and rough rolling in a universal mill, wherein the total rolling deformation of

breakdown rolling is 42-48% and the total rolling deformation of rough rolling is

2 7 - 32 % respectively. Then, the billet is subjected to the medium rolling in a universal

mill at 880 °C with the relative rolling reduction of 22%, as well as finish rolling in a

universal mill at 850°C with the relative rolling reduction of 14.5%. The secondary

scale (FeO oxide film) formed in the rolling process become brittle at the medium

rolling and finish rolling temperature of this example, and are fully crushed and

peeled off from the rail matrix due to large deformation in the rolling deformation

process, thus creating conditions for descaling with compressed air after finish rolling.

After finish rolling in a universal mill, the billet is subjected to secondary

descaling with compressed air. The descaling point is located within 6m of the inlet of

the heat treatment unit and the descaling pressure is 17MPa. The area of secondary scale to be removed is more than 95%. The austenitic area (770°C-800°C) of rail is subjected to accelerated cooling to 550 °C with compressed air at 3.5 °C/s, and then natural cooling. When the rail is cooled to room temperature, a small deformation process is adopted for composite horizontal and vertical roll straightening of rail, wherein the rolling reduction of the second straightening roller for horizontal roll straightening of rail is 13mm, and the total rolling reduction of the four upper straightening rollers is 32 mm.

The straightened rail is completely covered except for partial peeling of the rail

head tread, and no obvious crack is observed on the surface. After passing the on-line

automatic detection, ultrasonic flaw detection of internal quality, surface defect eddy

current flaw detection, processing and the like, the straightened rail is turned into the

finished product. Then, the tensile property test is performed as described in GB/T228

and the result indicated that the tensile strength of rail is 1286MPa and the elongation

is 10.5%. The section of oxide film on the rail surface is observed when preparing

metallographic specimens, and the average thickness of oxide film is 35 m. Based on

image tool software, the average area of the oxide film section Fe304 is 76%. After

the rail is subjected to neutral salt spray test with 5% of NaCl for 144 h, the surface

corrosion area of rail accounts for 7% of total surface area.

Example 2

the following elements in percentage by weight: 0.70% of C, 0.15% of Si, 0.75% of

Mn, 0.30% of Cr and 0.10% of V, and the remaining elements are Fe and other

inevitable impurities.

The chemical composition of billet is the same as that of rail matrix in this

example.

The billet is heated to 1150°C in a heating furnace for 2.5 hours, descaled to 4%

and rough rolling in a universal mill, wherein the total rolling deformation of

breakdown rolling is 38-44% and the total rolling deformation of rough milling is

33-39% respectively. Then, the billet is subjected to the medium rolling in a universal mill at 850 °C with the relative rolling reduction of 19%, as well as finish rolling in a universal mill at 820 °C with the relative rolling reduction of 16%. The secondary scale (FeO oxide film) formed in the rolling process become brittle at the medium rolling and finish rolling temperature of this example, and are fully crushed and peeled off from the rail matrix due to large deformation in the rolling deformation process, thus creating conditions for complete descaling with compressed air after finish rolling. After finish rolling in a universal mill, the billet is subjected to secondary descaling with compressed air. The area of secondary scale to be removed is more than 95%. The descaling point is located within 6m of the inlet of the heat treatment unit and the descaling pressure is 15MPa. The austenitic area (750 °C - 780 °C) of rail is subjected to accelerated cooling to 540 °C with compressed air at 1.5 °C/s, and then natural cooling. When the rail is cooled to room temperature, a small deformation process is adopted for composite horizontal and vertical roll straightening of rail, wherein the rolling reduction of the second straightening roller for horizontal roll straightening of rail is 14mm, and the total rolling reduction of the four upper straightening rollers is 33mm.

and the result indicated that the tensile strength of rail is 1289MPa and the elongation

is 10.8%. The section of oxide film on the rail surface is observed when preparing

metallographic specimens, and the average thickness of oxide film is 30 m. Based on

image tool software, the average area of the oxide film section Fe304 is 74%. After

corrosion area of rail accounts for 8% of total surface area.

Example 3

In terms of the chemical compositions, the rail matrix in this example consists of the following elements in percentage by weight: 0.90% of C, 0.80% of Si, 1.0% of

Mn, 0.80% of Cr and 0.11% of V, and the remaining elements are Fe and other

inevitable impurities.

The chemical composition of billet is the same as that of rail matrix in this

example.

The billet is heated to 1210°C in a heating furnace for 3 hours, descaled to 3% by

high-pressure water, rolled and formed by breakdown rolling in a break-down mill

and rough rolling in a universal mill, wherein the total rolling deformation of

breakdown rolling is 47-53% and the total rolling deformation of rough rolling is

-31% respectively. Then, the billet is subjected to the medium rolling in a universal

mill at 890 °C with the relative rolling reduction of 23%, as well as finish rolling in a

universal mill at 870 °C with the relative rolling reduction of 16.0%. After finish

rolling in a universal mill, the billet is subjected to secondary descaling with

compressed air. The descaling point is located within 6m of the inlet of the heat

treatment unit and the descaling pressure is 18MPa. The area of secondary scale to be

removed is more than 95%. The austenitic area (780°C-810 °C) of rail is subjected to

accelerated cooling to 560 °C with compressed air at 4 °C/s, and then natural cooling.

When the rail is cooled to room temperature, a small deformation process is adopted

for composite horizontal and vertical roll straightening of rail, wherein the rolling

reduction of the second straightening roller for horizontal roll straightening of rail is

mm, and the total rolling reduction of the four upper straightening rollers is 35mm.

The straightened rail is completely coated except for partial peeling of the rail

automatic detection, ultrasonic flaw detection of internal quality, eddy current flaw

detection of surface defect, processing and the like, the straightened rail is turned into

the finished product. Then, the tensile property test is performed as described in

GB/T228 and the result indicated that the tensile strength of rail is 1290MPa and the

elongation is 11.2%. The section of oxide film on the rail surface is observed when

preparing metallographic specimen, and the average thickness of oxide film is 33 m.

Based on image tool software, the average area of the oxidefilm section Fe304 is 79%.

After the rail is subjected to neutral salt spray test with 5% of NaCl for 144 h, the

surface corrosion area of rail accounts for 8% of total surface area.

Comparative example 1

In terms of chemical compositions, the rail matrix in this comparative example

consists of the following elements in percentage by weight: 0.82% of C, 0.79% of Si,

0.92% of Mn, 0.58% of Cr and 0. 0 7 % of V, and the remaining elements are Fe and

other inevitable impurities.

The chemical composition of billet is the same as that of rail matrix in this

comparative example 1.

In comparative example 1, the billet heating, first descaling, breakdown rolling

and straightening processes are the same as those currently implemented by domestic

and foreign manufacturers. The medium rolling temperature of billet is 965°C, with

the relative reduction of 14.3%, and the finish rolling temperature of billet is 923°C,

with the relative reduction of 8.7%. The secondary scale (FeO oxide film) formed at

the medium rolling temperature of 965°C and at the finish rolling temperature of

923°C had high plasticity. In the case of small rolling deformation, the secondary

scale on the rail surface had good plasticity, and the breakage and peeling area is very

small. After finish rolling, about 90% of the area of the secondary scale remained on

the rail surface, resulting in the secondary scale mainly on the surface of the finished

rail.

High pressure blast descaling (i.e. compressed air descaling) would not be

carried out after finish rolling. The rail is cooled at 4 °C/s with compressed air within

the range of 790°C to 820°C, and natural cooling is carried out after cooling to 560°C.

After being cooled to room temperature, the rail is straightened. The rolling reduction

of the second straightening roller for horizontal roll straightening of the rail is 23mm,

the rolling reduction of the fourth straightening roller is 18.5mm, and the total rolling

reduction of the four upper straightening rollers is 56 mm. The thickness of the

secondary scale in the rail rolling process is generally more than 50tm and is

relatively loose. In case of large straightening deformation, the secondary scale is

easily cracked and peeled off, thus making the scale on the rail surface lose the ability to prevent the rail matrix from being exposed to air and corrosive medium. After the rail is straightened, the iron oxide on the surface of rail head tread, the joint between the rail head and the rail web, and the joint between the rail web and the leg is peeled off, and the scale of the rail web is densely cracked. After passing the on-line automatic detection, ultrasonic flaw detection of internal quality, surface defect eddy current flaw detection, processing and the like, the straightened rail is turned into the finished product. Then, the tensile property test is performed as described in GB/T228 and the result indicated that the tensile strength of rail is 1293MPa and the elongation is 11.0%. The section of oxide film on the rail surface is observed by preparing metallographic specimens, and the average thickness of the oxide film is 63pm (maximum value) and 31 m (minimum value) respectively. Based on image tool software, the average area of the oxide film section Fe304 is 52%. After the rail is subjected to neutral salt spray test with 5% of NaCl for 144 h, the surface corrosion area of rail accounts for 65% of total surface area. Based on examples 1 to 3 and comparative example 1, it is known that the rail prepared by the method of the invention has good corrosion resistance and the surface corrosion area of the rail accounts for less than 10% of the total area after the neutral salt spray test with 5% of NaCl for 144 h. Where any or all of the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components.

Claims

The claims defining the invention are as follows:

1. A corrosion-resistant rail, formed of a chemical composition matrix and

including an oxide fil coating, wherein:

the oxide film is 15km - 35tm thick and a section Fe304 thereof has an

average area of 65-80%;

wherein the chemical composition matrix consists of the following elements

in percentage by weight: 0.70-0.90% of C, 0.10-0.80% of Si, 0.70-1.10% of

Mn and 0.30-0.90% of Cr, at least one of the following three elements:

0.04%-0.15% of V, 0.02%-0.06% of Nb, and 0.005%-0.05% of Ti, the

remaining elements are Fe and inevitable impurities;

wherein the tensile strength of the corrosion-resistant rail is more than

1200MPa, and the elongation thereof is not less than 10%; and

wherein the corrosion-resistant rail is manufactured by a method comprising:

the steps:

a billet of rail base composition is heated to be deformable, descaled

with high-pressure water until the scale area on a surface of the billet is

less than 10%, rolled and formed in a break-down mill, and made into a

rail through rough rolling, medium rolling and finish rolling in a

universal mill;

the medium rolling and rough rolling adopt high-reduction rolling at low

temperature, then the compressed air is used to remove the scales again

until they are completely descaled from the rail surface, accelerated

cooling of the austenite area of the rail below 540-570 °C with

compressed air, natural cooling to room temperature, the cooling speed is

1.5-5 °C/s, and small deformation straightening of the rail;

the billet is prepared from blast furnace molten iron through converter

smelting, LF refining, electric heating and continuous casting;

the scales are iron scales on the surface of billet or rail;

the billet is heated at 1150 °C - 1220 °C for 2.5 - 3 h;

the relative reduction of medium rolling is 18%-23% in a universal mill and the medium rolling temperature is 850 °C - 900 °C; and the relative reduction of finish rolling is 13%-17% in the universal mill and the finish rolling temperature is 820 °C - 870 °C.

2. A manufacturing method of the corrosion-resistant rail according to claim 1, wherein a billet is prepared from blast furnace molten iron through converter smelting, LF refining, electric heating and continuous casting, the billet is heated to be deformable, descaled with high-pressure water until the scale area on the surface of the billet is less than 10%, rolled and formed in a break-down mill, and made into a rail through rough rolling, medium rolling and finish rolling in a universal mill; the medium rolling and rough rolling adopt high-reduction rolling at low temperature, then the compressed air is used to remove the scales again until they are completely descaled from the rail surface, accelerated cooling of the austenite area of the rail below 570 °C with compressed air, natural cooling to room temperature, and small deformation straightening of the rail; the scales are iron scales on the surface of billet or rail.

3. The manufacturing method of the corrosion-resistant rail according to claim 2, wherein the rail is subjected to secondary descaling with compressed air at 15-20 MPa.

4. The manufacturing method of the corrosion-resistant rail according to any one of claims 2 to 3, wherein, during small deformation straightening of the rail, the rolling reduction of the second roller of the horizontal straightener is 12-16 mm, and the total rolling reduction of the four upper rollers is 30-40 mm.

5. The manufacturing method of the corrosion-resistant rail according to any one of claims 2 to 4, wherein the total rolling deformation of the break-down mill is -55%, and the total deformation of rough rolling of the universal mill is 25-40%.