JP3078461B2 - High wear-resistant perlite rail - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high abrasion resistant perlite rail having abrasion resistance required for rails in a curved section of a high axle heavy railway.

[0002]

2. Description of the Related Art As means for increasing the efficiency of rail transportation, train speed has been increased and train load weight has been increased. Such an increase in the efficiency of rail transportation implies a severer use environment for rails, and further improvements in rail materials have been required. Specifically, the wear of rails laid on curved sections of heavy-duty railways abroad has rapidly increased, and this has become a problem in extending the life of rails.

However, with the recent improvement in the heat treatment technology for increasing the strength of rails, the following high-strength (high-hardness) rails exhibiting a fine pearlite structure using eutectoid carbon steel have been developed, and have been developed for heavy load railways. Rail life in curved sections has been dramatically improved. Heat treatment rail for ultra-high load with sorbite head or fine pearlite head (Japanese Patent Publication No. 54-2549)
No. 0). A method for producing a low-alloy heat-treated rail in which an alloy such as Cr or Nb is added to improve not only wear resistance but also a decrease in hardness of a welded portion (Japanese Patent Publication No. 59-19173).

The characteristics of these rails are high-strength (high-hardness) rails exhibiting a fine pearlite structure made of eutectoid carbon-containing steel. The purpose of the rails is to improve wear resistance. However, in recent years, overseas heavy-duty railways have been aggressively pursuing higher axle load (increase in train loading weight) in order to further increase the efficiency of rail transport. Even if a rail is used, wear resistance cannot be ensured, and a reduction in rail life due to wear has become a problem. Against this background, it has been required to develop a rail having wear resistance higher than that of the current eutectoid carbon steel high-strength rail.

[0005]

The pearlite structure of the eutectoid carbon component conventionally used as a rail steel has a layered structure of a ferrite structure having a low hardness and a plate-like hard cementite structure. As a method of improving abrasion, generally, a method of reducing the lamellar spacing in a pearlite structure: λ [λ = (ferrite thickness: t ₁ ) + (cementite thickness: t ₂ )] to improve hardness. There is. For example, Metallurgical transac-tions Vol.7A
(1976) As shown in Fig. 1 on page 1217, when the lamellar spacing in the pearlite structure is reduced, the hardness is greatly improved. However, the current pearlite hardness is the upper limit for high hardness rails exhibiting the fine pearlite structure of eutectoid carbon steel, and the pearlite lamella spacing is further refined by increasing the heat treatment cooling rate and adding alloys with the aim of improving hardness. If this is attempted, there is a problem that a hard martensite structure is generated in the pearlite structure, and the toughness and wear resistance of the rail are reduced.

As another solution, a method of using a material exhibiting a metal structure having higher wear resistance than the pearlite structure as the rail steel can be considered. However, in the case of rolling wear such as rails and wheels, a fine pearlite structure is used. At present, no material that is less expensive and has excellent wear resistance has not been found.

As a wear mechanism in the pearlite structure, first, a soft ferrite structure is squeezed out by passing through a wheel, and thereafter, only hard cementite is stacked immediately below the rolling surface, and work hardening is added thereto to secure wear resistance. Was confirmed by experiments. Therefore,
The present inventors refined the pearlite lamella spacing in order to obtain strength (hardness), and at the same time, increased the ratio of a plate-like hard cementite structure which increased the carbon content to ensure the wear resistance of the pearlite structure, By increasing the cementite density just below the surface, without impairing toughness and ductility,
Experiments have shown that the wear resistance is dramatically improved. That is, an object of the present invention is to provide a low-cost rail having excellent wear resistance required for a high axle heavy railway or a rail in a curved section.

[0008]

The present invention attains the above object, and its gist is that (1) by weight%, C: more than 0.85% and 1.20% or less At least a portion of the steel rail, or at least a range from the rail head surface to a depth of 20 mm from the rail head surface as a starting point, exhibits a pearlite structure, and the pearlite lamella spacing: λ [λ = (Ferrite thickness:
t ₁ ) + (cementite thickness: t ₂ )] is 100 nm or less and the ferrite thickness (t ₁ ) in the pearlite structure
Ratio of cementite thickness (t ₂ ) to Rc: Rc (Rc =
(t ₂ / t ₁ ) is 0.15 or more, a highly wear-resistant pearlitic rail, and (2) weight%
, C: more than 0.85 to 1.20%, Si: 0.
10 to 1.00%, Mn: 0.40 to 1.50%, and if necessary, Cr: 0.05 to 0.50%.
%, Mo: 0.01 to 0.20%, V: 0.
02 to 0.30%, Nb: 0.002 to 0.0
5%, a steel rail containing one or more of Co: 0.10 to 2.00%, the balance being iron and unavoidable impurities, at least a part of the steel rail or at least the rail A pearlite structure is present in a range of a depth of 20 mm from the head surface as a starting point, and a pearlite lamella spacing: λ [λ = (ferrite thickness: t ₁ ) + (cementite thickness: t ₂ )] is 100 nm or less, and And the ratio of the cementite thickness (t ₂ ) to the ferrite thickness (t ₁ ) in the pearlite structure: R _c (R _c = t ₂ / t ₁ ) is 0.1
5 is a high wear-resistant pearlite-based rail characterized by being 5 or more.

Hereinafter, the present invention will be described in detail. First, the reason why the chemical components of the rail are limited as described above in the present invention will be described. C is an effective element for generating a pearlite structure and securing wear resistance. Usually, a C content of 0.60 to 0.85% is used as a rail steel, but the C content is 0.85% or less. In the above, the ratio of the cementite thickness (t ₂ ) to the ferrite thickness (t ₁ ) in the pearlite structure ensuring the wear resistance: R _c (R _c = t ₂ /
t ₁ ) cannot be secured to 0.15 or more, and the lamellar spacing in the pearlite structure formula is set to 100 due to the decrease in hardenability.
It cannot be smaller than nm. In addition, the C content is 1.20%
If the content exceeds 1, the amount of pro-eutectoid cementite at the austenite grain boundary increases, and the ductility and toughness are greatly reduced.

Next, the elements other than the above C will be described. Si is an element that improves the strength by solid solution hardening into the ferrite phase in the pearlite structure and slightly improves the toughness of the rail steel. However, if it is less than 0.10%, its effect cannot be sufficiently expected. If it exceeds .20%, it causes embrittlement and lowers the weldability.
It was limited to 0 to 1.20%.

Mn, like C, lowers the pearlite transformation temperature and enhances the hardenability, thereby contributing to an increase in strength. Further, Mn is an element that suppresses the formation of proeutectoid cementite. The effect is small in the content, and when the content exceeds 1.50%, the Mn content is set to 0.40 to 0.4 in order to easily form a martensite structure in the segregated portion.
Limited to 1.50%.

Further, one or two or more of the following elements are added to a rail manufactured with the above component composition as required for the purpose of improving strength, ductility and toughness. Cr: 0.
05 to 0.50%, Mo: 0.01 to 0.20%,
V: 0.02 to 0.30%, Nb: 0.002 to
0.050%, Co: 0.10-2.00%

Next, the reason why these chemical components are determined as described above will be described. Cr is an element that raises the equilibrium transformation point of pearlite and consequently refines the pearlite structure to contribute to high strength, and at the same time, enhances the wear resistance by strengthening the cementite phase in the pearlite structure. When the content is less than 0.05%, the effect is small. When the content exceeds 0.50%, a martensitic structure is formed and the steel is embrittled. Therefore, the Cr content is limited to 0.05 to 0.50%. .

Mo is an element that raises the equilibrium transformation point of pearlite like Cr, and consequently refines the perato structure, contributing to higher strength and improving wear resistance.
If it is less than 01%, the effect is small, and if it exceeds 0.20%, excessive addition lowers the pearlite transformation rate and generates a martensite structure harmful to toughness. Limited to.

V is V generated in a cooling process during hot rolling.
Precipitation hardening by charcoal and nitride enhances plastic deformability, suppresses austenite grain growth when heat treatment is performed at high temperature, refines austenite grains, strengthens pearlite structure after cooling Although it is an effective component for improving the strength and toughness required for rails, its effect cannot be expected if it is less than 0.03%, and conversely, if it exceeds 0.30%, it will be more Therefore, the amount of V was limited to 0.03 to 0.30% because the effect of (1) cannot be expected.

Nb, like V, is an effective element for forming Nb charcoal and nitride to reduce the size of austenite grains, and the effect of suppressing austenite grain growth is higher than V (1%).
Effect up to around 200 ° C) and improve the ductility and toughness of the rail. The effect cannot be expected with a small content of less than 0.002%, and no further effect can be expected with an excessive content exceeding 0.050%. Therefore, the amount of Nb was limited to 0.002 to 0.050%.

Co is an element that increases the transformation energy of pearlite to improve the strength by making the pearlite structure finer, but its effect cannot be expected with a small content of less than 0.10%. With an excessive addition exceeding 0.000%, the effect of strengthening reaches the saturation range,
The amount was limited to 0.10-2.00%.

The rail steel having the above-mentioned composition is melted in a commonly used melting furnace such as a converter or an electric furnace, and the molten steel is subjected to an ingot-forming / disassembling method or a continuous casting method.
Further, it is manufactured as a rail through hot rolling. next,
The head of the hot-rolled rail having high temperature heat or the rail heated to a high temperature for the purpose of heat treatment is accelerated and cooled to make the lamellar spacing of the pearlite structure of the rail head fine.

Next, the range in which the pearlite structure is exhibited is preferably at least a depth of 20 mm from the surface of the rail head starting from the surface of the head. This is because a sufficient rail life extension effect cannot be obtained. When the range of the pearlite structure is from the rail head surface to the depth of 30 mm or more from the head surface as a starting point, it is more preferable to obtain a sufficient long life effect. The rail head surface is a top portion of the rail and a side portion of the rail head, that is, a portion particularly in contact with a wheel tread surface and a flange of the train.

Next, the pearlite lamellar spacing: λ (λ = ferrite thickness: t ₁ + cementite thickness: t ₂ ), the ratio of the cementite thickness to the ferrite thickness in the pearlite structure: R _c (R _c = t ₂ / t ₁ ) will be described below. First, the reason why the pearlite lamella spacing: λ is limited to 100 nm or less will be described. When the lamellar spacing than 100 nm, it is difficult to secure the hardness of the pearlite structure, the ratio of the cementite thickness: be reserved _{R c (R c = t 2} / t 1) of 0.15 or more wheel load 15 tons It is not possible to secure the abrasion resistance required for the extremely curved rails of overseas heavy load railways. Further, in order to induce surface damage such as creaking due to plastic deformation on the rail head surface, the pearlite lamella spacing: λ was limited to 100 nm or less.

Next, the ratio of the cementite thickness (t ₂ ) to the ferrite thickness (t ₁ ) in the pearlite structure: R _c
The reason why (R _c = t ₂ / t ₁ ) is limited to 0.15 or more is that when R _{c is set} to 0.15 or less, the cementite density immediately below the rolling surface that secures the wear resistance of the pearlite steel is reduced. This is because it is difficult to increase the wear resistance compared to conventional eutectoid rails.
Therefore, R _c was limited to 0.15 or more.

The pearlite lamella spacing: λ, ferrite thickness: t _1, and cementite thickness: t ₂ were measured by etching with a predetermined corrosive liquid such as nital or piclar, and in some cases, two steps from the corroded sample surface. Collect a replica. Further, these are observed in 10 visual fields with a scanning electron microscope, λ, t ₁ , and t ₂ are measured in each visual field, and averaged.

The metal structure of the rail is desirably a pearlite structure, but a small amount of proeutectoid cementite may be generated in the pearlite structure depending on the cooling method of the rail and the segregation state of the material. However, even if minute pro-eutectoid cementite is formed in the pearlite structure, it does not significantly affect the wear resistance, strength and toughness of the rail. It also includes a mixture.

[0024]

Next, an embodiment of the present invention will be described. Table 1 shows the chemical components of the pearlite-structured rail steel and the comparative rail steel according to the present invention. Table 2 shows the lamella spacing of these materials: λ [λ = (ferrite thickness: t ₁ ) + (cementite thickness: t ₂ )], and the ratio of cementite thickness (t ₂ ) to ferrite thickness (t ₁ ). Ratio: R _c (R _c = t ₂ /
t ₁ ) and the wear measurement results after 500,000 repetitions under dry conditions in the Nishihara abrasion test.

Further, FIG. 1 shows the relationship between the lamellar spacing (λ) and the wear amount of the comparative rail steel and the rail steel of the present invention, and FIG. 2 shows an example of a microstructure 10,000 times as large as that of the rail steel of the present invention (symbol: H). . FIG. 2 shows the rail steel of the present invention etched with a 5% nital solution and observed with a scanning electron microscope. The white part in the figure is a cementite layer and the black part is a ferrite layer.

The configuration of the rail is as follows. · Present invention rails (ten) code A-J: In the above composition range, the pearlite lamellar spacing: lambda (lambda = ferrite thickness: t ₁ + cementite thickness: t ₂₎ is at 100nm or less, and pearlite Medium ferrite thickness (t ₁ )
Ratio of cementite thickness (t ₂ ) to Rc: R _c (R _c =
(t ₂ / t ₁ ) A heat-treated rail with accelerated cooling applied to the head with a head of 0.15 or more. -Comparative rails (six) Symbols K to P: comparative rails made of eutectoid carbon-containing steel.

The wear test conditions were as follows.・ Testing machine: Nishihara type abrasion testing machine ・ Specimen shape: disk-shaped specimen (outer diameter: 30 mm, thickness: 8)
・ Test load: 686 N ・ Slip ratio: 9% ・ Material: Tempered martensitic steel (HV35
0)-Atmosphere: in the air-Cooling: Forced cooling with compressed air (flow rate: 100)
Nl (liter) / min) · Number of repetitions: 700,000 times

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

As shown in Table 1, the rail steel of the present invention makes the lamella spacing (λ) finer, and at the same time, the ratio of the cementite thickness (t ₂ ) to the ferrite thickness (t ₁ ) as compared with the comparative rail steel. : By increasing R _c (R _c = t ₂ / t ₁ ), the wear amount is smaller at the same lamella interval than the comparative rail, and the wear resistance is dramatically improved. As described above, according to the present invention, it is possible to provide a rail having excellent wear resistance even in a curved section of a high axle heavy railway.

[Brief description of the drawings]

FIG. 1 is a comparison of the results of wear tests of a comparative rail steel and the rail steel of the present invention in relation to the lamella spacing and the wear amount.

FIG. 2 shows an example of a cementite / ferrite layer interval of the rail steel of the present invention.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-8-109439 (JP, A) JP-A-8-49019 (JP, A) JP-A-7-173530 (JP, A) 158227 (JP, A) JP-A-5-335956 (JP, A) JP-A-62-161917 (JP, A) JP-A-51-2616 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) C22C 38/00 301 C22C 38/04 C22C 38/30

Claims (6)

(57) [Claims] Claims 1. In weight%, C: more than 0.85%.
A steel rail containing 20% or less, wherein at least a part of the steel rail has a pearlite structure, a pearlite lamella spacing of the pearlite structure is 100 nm or less, and a ferrite thickness in the pearlite structure. A high wear-resistant pearlite rail, wherein the ratio of cementite thickness to thickness is 0.15 or more. 2. In% by weight, C: more than 0.85 and 1.2
A steel rail containing 0% or less, wherein at least a range from the rail head surface to a depth of 20 mm starting from the head surface of the steel rail exhibits a pearlite structure, and the pearlite lamella spacing of the pearlite structure is 100 nm or less. And a ratio of the thickness of cementite to the thickness of ferrite in the pearlite structure is 0.15 or more. 3. The composition according to claim 1, wherein the content of C is more than 0.85% and not more than 1.20%, Si is 0.10-1.00%, and Mn is 0.40-1.50%. The remainder is a steel rail consisting of iron and unavoidable impurities, at least a part of the steel rail presents a pearlite structure, the pearlite lamella spacing of the pearlite structure is 100 nm or less,
A highly wear-resistant pearlitic rail, wherein the ratio of the thickness of cementite to the thickness of ferrite in the pearlite structure is 0.15 or more. 4. In% by weight, C: more than 0.85 and 1.20% or less, Si: 0.10 to 1.00%, Mn: 0.40 to 1.50%, the balance being Is a steel rail made of iron and unavoidable impurities, a range of a depth of 20 mm from the surface of at least the rail head from the surface of the head of the steel as a starting point exhibits a pearlite structure, and the pearlite lamella spacing of the pearlite structure is A highly wear-resistant pearlite rail characterized by being 100 nm or less and having a ratio of cementite thickness to ferrite thickness in the pearlite structure of 0.15 or more. 5. In% by weight, C: more than 0.85 and 1.20% or less, Si: 0.10 to 1.00%, Mn: 0.40 to 1.50%, Cr: 0.05 to 0.50%, Mo: 0.01 to 0.20%, V: 0.02 to 0.30%, Nb: 0.002 to 0.05%, Co: 0.10 to 0 A steel rail containing 2.00% or more of one type or two or more types and a balance of iron and unavoidable impurities, wherein at least a part of the steel rail has a pearlite structure, and a pearlite lamella having the pearlite structure. A highly wear-resistant pearlitic rail characterized by having an interval of 100 nm or less and a ratio of a cementite thickness to a ferrite thickness in a pearlite structure of 0.15 or more. 6. In% by weight, C: more than 0.85 and 1.20% or less, Si: 0.10 to 1.00%, Mn: 0.40 to 1.50%, Cr: 0.05 to 0.50%, Mo: 0.01 to 0.20%, V: 0.02 to 0.30%, Nb: 0.002 to 0.05%, Co: 0.10 to 0 A steel rail containing 2.00% of one or more kinds, the balance being iron and unavoidable impurities, wherein the steel rail has a depth from at least the rail head surface to the head surface. A range of 20 mm exhibits a pearlite structure, the pearlite lamella spacing of the pearlite structure is 100 nm or less, and the ratio of the cementite thickness to the ferrite thickness in the pearlite structure is 0.15 or more. Wear perlite rail.