JP2002302738A - Low-segregation pearlitic rail with excellent wear resistance and resistance to internal fatigue damage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wear resistance and simultaneously prevent deterioration in the toughness of a rail pillar, to improve resistance to internal fatigue damage, and resultantly to prolong the service life of a rail by increasing the amount of carbon in steel, adding Zr and controlling the total number of Zr inclusions in the cross section in the rolling direction. SOLUTION: In the low-segregation pearlitic rail with excellent wear resistance and resistance to internal fatigue damage: the structure of the steel rail containing, by mass, >0.85-1.40% C and 0.0001-0.2000% Zr in the region ranging from the railhead corners and railhead surface to a position at a depth of at least 30 mm is composed of pearlite structure; and the total number of Zr inclusions of >10 μm major axis in the cross section in the rolling direction is made to <=500 pieces for every 100 mm<2> of inspection area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention improves the abrasion resistance required for rails of heavy-load railways, and at the same time, reduces segregation to prevent a reduction in the toughness of rail columns and further reduces internal fatigue damage. The present invention relates to a pearlite-based rail for the purpose of preventing occurrence.

[0002]

2. Description of the Related Art Overseas heavy-load railways have been designed to increase the speed of trains and increase the weight of trains as means for increasing the efficiency of rail transportation. 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. More specifically, G.R. C. (Gauge corners) and head side wear increased sharply, and it became a problem in terms of rail service life.

However, with the recent progress in heat treatment technology for increasing the strength, a high-strength (high-hardness) rail having a fine pearlite structure using eutectoid carbon steel as shown below has been invented. The rail life of the section 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). After rolling, or after reheating the rail head from the austenitic zone temperature to 850-500 ° C, 1-4 ° C / s
A method of manufacturing a high-strength rail of 130 kgf / mm ² or more that is accelerated and cooled by ec (Japanese Patent Publication No. 63-23244). The characteristics of these rails are eutectoid carbon-containing steel (carbon content: 0.7 to 0.
(8%), a high-strength rail exhibiting a fine pearlite structure, the purpose of which is to reduce the lamellar spacing in the pearlite structure and improve wear resistance.

[0004] However, in recent years, heavy-load railways abroad have been strongly promoting the loading of cargo in order to further increase the efficiency of rail transportation. G. C. The abrasion resistance of the part and the head side cannot be sufficiently secured, and the reduction of the rail life due to wear has become a problem. Against this background, the development of rails having wear resistance higher than that of the current high-strength eutectoid carbon steel rails has been required.

[0005] In order to solve these problems, the present inventors have developed the following rails. Using hypereutectoid steel (C: more than 0.85 to 1.20%) to increase the cementite density in the lamella in the pearlite structure and to provide a rail with excellent wear resistance (JP-A-8-144).
016 publication). A hypereutectoid steel (C: more than 0.85 to 1.20%) is used to increase the cementite density in the lamella in the pearlite structure, and at the same time, to control the hardness and to provide a rail with excellent wear resistance (JP-A-Hei. 8-246100). The features of these rails were to increase the carbon content of the steel, increase the density of the cemetite phase in the pearlite lamella, and improve the wear resistance of the pearlite structure by controlling the hardness.

[0006]

In the invention rail having the pearlite structure shown above, the wear resistance can be improved by increasing the carbon content. However, the above-mentioned invention rail is
Since the carbon content is higher than that of the existing high-strength rail containing eutectoid carbon, a segregation zone in which carbon and alloy elements are concentrated is likely to be formed in the center of the slab during the casting of molten steel. In particular, in the rail column portion after rolling shown by the hatched portion in FIG. 1, there was a problem that a large amount of proeutectoid cementite structure was generated along the segregation zone, and particularly the toughness of the column portion was greatly reduced.

As a method for preventing the formation of a segregation zone formed in the central portion of a slab, there is a method of making a solidified structure of a steel slab fine. For example, γ-Fe is a primary solidified high carbon (C> 0.
In a rail steel of 9 mass%), an oxide of Zr (ZrO ₂ ) having good lattice matching with γ-Fe acts very stably as a solidification nucleus, and proeutectoid cementite in a rail column portion is formed by refining the solidification structure. Suppress tissue generation. However, when a certain amount of Zr is added, generation of a pro-eutectoid cementite structure in a column portion can be suppressed, but there is a problem that rail service life is easily reduced due to occurrence of internal fatigue damage. .

[0008] From such a background, it has been required to develop a rail which reduces segregation in a high carbon content pearlite structure rail, prevents a decrease in column toughness, and at the same time prevents the occurrence of internal fatigue damage. Have been.

[0009] The present invention meets such a demand, and is intended to improve the wear resistance and reduce segregation of a high carbon content pearlite structure rail used in heavy load railways. An object of the present invention is to provide a rail that prevents a decrease in toughness of a column portion and further prevents occurrence of internal fatigue damage.

[0010]

The present invention attains the above-mentioned object, and its gist is as follows. (1) A steel rail containing, by mass%, C: more than 0.85 to 1.40%, with a depth of at least 3 starting from the head corner and top surface of the steel rail.
The range of 0 mm is the pearlite structure, and in the cross section in the rolling direction, the total number of Zr-based inclusions having a major axis of more than 10 μm is 500 or less per 100 mm ^{2 of the} test area. Low segregation pearlite rail with excellent internal fatigue damage. (2) The rail further has a depth of at least 3 starting from the head corner and top surface of the steel rail.
A range of 0 mm is a pearlite structure having a hardness of Hv320 or more. (3) The rail has a steel component in mass%, C: more than 0.85 to 1.40%, Zr: 0.0001 to
0.2000%, Si: 0.10-2.00%, M
n: 0.10 to 2.00%, with the balance being Fe and inevitable impurities.

(4) The rail of (3) may further contain the following components in mass%. Cr: 0.05 to 2.00%, Mo: 0.01 to
One or two of 0.50%, V: 0.005 to 0.50%, Nb: 0.002
One or two of 0.050%, B: 0.0001 to 0.0050%, Co: 0.10 to 2.00%, Cu: 0.05 to
One or two of 1.00%, Ni: 0.05 to 2.00%, Ti: 0.0050 to 0.0500%, Mg: 0.0005 to 0.0300%, Ca: 0.0010 One or more kinds of 0.0150%, Al: 0.0040 to 3.00%.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The present inventors first investigated the cause of the formation of a pro-eutectoid cementite structure along a segregation zone of a rail column portion in a high carbon content pearlite structure steel rail. As a result, a segregation zone in which carbon and alloying elements are concentrated is formed at the center of the slab during the casting of molten steel, and this segregation zone remains in the rail column after hot rolling, and the carbon concentration of the column segregation zone is mainly reduced. It was confirmed that a proeutectoid cementite structure was generated by increasing the amount.

Therefore, the present inventors have studied a method for preventing the formation of a segregation zone generated at the center of the slab. As a result, it was confirmed that the formation of a segregation zone at the center of the slab was suppressed by reducing the solidification structure of the slab, and the formation of a pro-eutectoid cementite structure harmful to the toughness of the rail could be prevented.

Next, the present inventors have studied a method for refining the solidification structure of a steel slab. As a result, it was confirmed that it was effective to increase the equiaxed crystallization rate of the solidified structure by adding a solidification nucleus when the molten steel was solidified.

Further, the present inventors have studied the optimum coagulation nucleus by experiments. As a result, in a high carbon (C> 0.9 mass%) rail steel in which γ-Fe is a primary solidification crystal, γ-Fe
It has been found that a solidification nucleus having a good lattice matching with the above is most effective, and among them, an oxide of Zr (ZrO ₂ ) acts extremely stably. Then, the present inventors set the optimum Zr
The amount of the oxide (ZrO ₂ ) was examined. As a result, by keeping the Zr addition amount within a certain range,
The amount of Zr oxide can be optimized. As a result, the equiaxed crystallization ratio of the solidified structure is improved, the formation of segregation zones in the center of the slab is suppressed, and the formation of a pro-eutectoid cementite structure harmful to the toughness of the rail is prevented. I confirmed that it could be prevented.

In addition to these studies, the present inventors investigated the cause of the reduction in the service life of the rail due to the occurrence of internal fatigue damage when a certain amount of Zr was added. as a result,
It was confirmed that a single Zr-based inclusion (ZrO ₂ ) or a MnS-based inclusion having this as a nucleus was present at the starting point of the internal fatigue damage of the rail head.

Next, the present inventors consider that Zr existing at the starting point
The morphology of system inclusions was investigated. As a result, in a high carbon content pearlite steel rail, the Zr-based inclusions have an elliptical shape in the cross section in the rolling direction, and the starting diameter of the Zr-based inclusions has a certain length. Confirmed that it exceeded.

In addition to these findings, the present inventors have confirmed the relationship between the form and amount of Zr-based inclusions in the steel rail and the occurrence of internal fatigue damage. As a result, even if the major axis of the Zr-based inclusion exceeds a certain length, damage does not necessarily occur, and the presence or absence of damage depends on the amount of the Zr-based inclusion in a certain test area, that is, the number thereof. I found that I was ruled.

As a result, in a steel rail having a pearlite structure with a high carbon content, the amount of Zr added is kept within a certain range, thereby preventing the formation of a pro-eutectoid cementite structure in a column portion and further, a certain length of a long diameter. It has been found that by keeping the number of Zr-based inclusions exceeding the predetermined range within a certain range, the wear resistance is improved, the toughness of the rail column is prevented from being lowered, and the internal fatigue damage resistance is further improved.

That is, according to the present invention, in a steel rail having a high carbon content pearlite structure used in heavy-load railways, a reduction in toughness of a column portion is prevented by improving wear resistance and simultaneously adding Zr. Furthermore, the purpose is to prevent the occurrence of fatigue damage inside the head caused by Zr-based inclusions, and to simultaneously achieve abrasion resistance, prevention of reduction in toughness of pillars, and improvement of internal fatigue damage resistance. is there.

Next, the reasons for limitation of the present invention will be described in detail. (1) Definition of major axis and total number of Zr-based inclusions in steel rail: First, the reason why the total number of Zr-based inclusions having a major axis of more than 10 μm is limited to 500 or less per 100 mm ^{2 of the} test area will be described. The Zr-based inclusion has an elliptical shape in a cross section in the rolling direction. Zr that became the starting point of internal fatigue damage
As a result of examining the system inclusions, the major axis was more than 10 μm. Therefore, the major axis of the Zr-based inclusion is limited to more than 10 μm. The Zr-based inclusions having a major axis of 10 μm or less do not serve as a starting point of fatigue damage, and mainly act as solidification nuclei during casting to contribute to the refinement of the solidification structure, and as a result, the formation of a proeutectoid cementite structure. Suppress and prevent the toughness of the rail column from lowering.

Next, the long diameter of 10 μm existing in the steel rail
The reason why the total number of excessive Zr-based inclusions is limited to 500 or less per 100 mm ^{2 of the} test area will be described. When the total number of Zr-based inclusions exceeds 500, fatigue damage occurs from the inside of the head of most of the rails examined, and the service life of the rails is significantly reduced.
The total number of Zr-based inclusions per mm ² was limited to 500 or less.

The Zr-based inclusions described here are a single elliptical ZrO ₂ , MnS, Zr having ZrO ₂ as a nucleus.
It refers to a composite of oxides of Si, Ca, and Mg with rO ₂ as a nucleus. In the case of MnS having ZrO ₂ as a nucleus,
In the analysis using X-rays or the like, those having an area ratio of ZrO ₂ of 50% or more in the cross section were evaluated as inclusions.

Further, in order to control the number of these Zr-based inclusions within the above-mentioned limited range, the amount of oxygen in the molten steel is kept within a certain range to suppress the generation of Zr-based inclusions. It is desirable to apply a method of bubbling molten steel with an inert gas or the like during refining to float coarse Zr-based inclusions generated in the steel by removing them in slag, or a technique combining these methods.

(2) The range and hardness of the pearlite structure in which the major axis and the total number of the Zr-based inclusions are controlled:
The reason why the range exhibited by the pearlite structure in which the major axis and the total number of the Zr-based inclusions are controlled is limited to a range of a depth of 30 mm starting from the head surface at the head corner and the top of the head will be described. If the depth is less than 30 mm, the area where the wear resistance and internal fatigue damage resistance of the rail head is required is small, and the effect of improving sufficient wear resistance and internal fatigue damage resistance cannot be obtained. is there. Further, if the range of the pearlite structure in which the major axis and the total number of the Zr-based inclusions are controlled is 40 mm or more starting from the head surface at the head corner and the head, if the depth is 40 mm or more, the wear resistance and the internal resistance are improved. The effect of improving fatigue damage is further increased, which is more desirable.

Next, the hardness of the pearlite structure controlled by the major axis and the total number of Zr-based inclusions within a range of 30 mm in depth starting from the head surface at the head corner and the crown is Hv3.
The reason why the number is limited to 20 or more will be described. When the hardness of the component system is less than Hv320, the rail head wears remarkably when the operating environment of the rail is severe, and in some cases, surface damage due to plastic deformation occurs. Furthermore, even if the number of Zr-based inclusions is controlled, fatigue damage is likely to occur from the inside of the rail head, and the abrasion resistance, surface damage resistance, and internal fatigue damage resistance required for heavy load railways are sufficiently secured. Therefore, the hardness of the pearlite structure was limited to Hv320 or more.

Here, FIG. 2 requires the designation of the pearlite-based rail of the present invention in which the major axis and the total number of the Zr-based inclusions are controlled at the cross-sectional surface position of the head, the wear resistance and the resistance to internal fatigue damage. Indicates the region to be used. In the rail head, 1 is a crown, 2 is a head corner, and one of the head corners 2 is a gauge corner (GC) part mainly in contact with wheels. If the pearlite structure is arranged at least in the oblique lines in the drawing, it is possible to improve the wear resistance and the internal fatigue damage resistance of the rail.

Further, if the hardness of the pearlite structure in the hatched area in the figure is Hv320 or more, it is possible to sufficiently secure the abrasion resistance and the internal fatigue damage resistance particularly required for heavy load railways. Become. Therefore, it is desirable to arrange the pearlite structure in which the major axis and the total number of the Zr-based inclusions are controlled in the vicinity of the surface of the rail head where the wheel and the rail mainly contact each other, and the other parts are metal structures other than the pearlite structure. Is also good.

The metal structure of the rail of the present invention is preferably a pearlite structure as described above. However, depending on the component system of the rail and the heat treatment manufacturing method, even in the present component system added with Zr, a trace amount of proeutectoid ferrite structure, proeutectoid cementite structure, A bainite structure or a martensite structure may be mixed. However, even if these structures are mixed, the rail does not have a significant adverse effect on the wear resistance, toughness, internal fatigue damage resistance, etc. of the rail. The structure of the rail includes a slight mixture of a proeutectoid ferrite structure, a proeutectoid cementite structure, a bainite structure, and a martensite structure.

(3) Chemical composition of steel rail: First, the reason why the chemical composition of the steel rail is limited as described above in the present invention will be described. C is an element that promotes the pearlite transformation, increases the density of the cementite phase, and secures abrasion resistance. As a normal rail steel, the C content is 0.
60 to 0.85%, but the C content is 0.85%.
% Or less, the density of the cementite phase in the pearlite structure for improving the wear resistance cannot be secured, and the wear resistance cannot be improved. If the C content exceeds 1.40%, Zr
In addition to this component system, proeutectoid cementite structure is formed in the pearlite structure on the head surface and inside the head, in addition to the rail column, which reduces the toughness of the rail and the internal fatigue damage on the head Is more likely to occur. Furthermore, since the density of the cementite phase in the pearlite structure increases and the ductility required for the rail cannot be sufficiently secured, the C content is limited to more than 0.85 to 1.40%.

Zr is an oxide of Zr (ZrO_Two) Is γ-
Because of good lattice matching with Fe, γ-Fe
It becomes the solidification nucleus of a certain high carbon rail steel and the equiaxed
The segregation zone at the center of the slab by increasing the
Suppresses the proeutectoid cementite structure that is harmful to rail toughness.
It is an element that suppresses generation. 0.0001% of Zr content
At full, the solidification nucleus oxide (ZrO_TwoSmall)
And the equiaxed crystallization rate of the solidified structure decreases,
The toughness of the rail column decreases due to the formation of the structure. Also Z
When the amount of r exceeds 0.2000%, extremely coarse Zr
Oxide (ZrO _Two) Is formed, starting from the oxide of Zr.
Not only is the internal fatigue damage likely to occur,
The toughness of the rails sharply and shorten the service life of the rails
Therefore, the amount of Zr is limited to 0.0001 to 0.2000%
did.

Si is an element that increases the hardness (strength) of the rail head by solid solution hardening into the ferrite phase in the pearlite structure, and at the same time, suppresses the pro-eutectoid cementite structure, thereby improving the toughness and the internal fatigue damage resistance of the rail. If it is less than 0.10%, its effect cannot be expected sufficiently. If it exceeds 2.00%, many surface flaws are generated at the time of hot rolling or oxides are generated. The weldability decreases. Further, not only the pearlite structure itself is embrittled and ductility and toughness of the rail are reduced, but also surface damage such as spalling occurs and the service life of the rail is reduced. %.

Mn is an element that enhances the hardenability and reduces the pearlite lamella spacing to secure the strength of the pearlite structure and improve the wear resistance.
If the content is less than 10%, the effect is small, and it becomes difficult to secure the wear resistance and internal fatigue damage resistance required for the rail. If it exceeds 2.00%, the hardenability is remarkably increased, a martensite structure harmful to wear resistance and toughness is easily generated, and segregation is promoted even in the present Zr-added component system. Since a pro-eutectoid cementite structure is formed in columns and the like and the toughness of the rail is reduced, the Mn content is reduced to 0.10.
To 2.00%.

The rail manufactured with the above-mentioned composition has an improved abrasion resistance by strengthening a pearlite structure, prevents a decrease in toughness by suppressing the formation of a proeutectoid cementite structure, and softens and embrittles a heat-affected zone of a welded portion. Cr, Mo, V, Nb, B, Co, Cu, and N for the purpose of preventing cracking, improving ductility and toughness of pearlite structure, and preventing coarsening of alumina-based inclusions.
Elements of i, Ti, Mg, Ca, and Al are added as needed.

Here, the main purposes of adding these elements are as follows. Cr and Mo raise the equilibrium transformation point of pearlite and mainly secure the strength of the pearlite structure by reducing the pearlite lamellar spacing to improve the wear resistance. V, Nb suppresses the growth of austenite grains by carbides and nitrides generated during hot rolling and subsequent cooling processes, and further increases the strength of the pearlite structure by precipitation hardening, thereby improving the wear resistance and ductility of the pearlite structure. Improve.

B forms iron carbide borides, suppresses the formation of proeutectoid cementite, further promotes pearlite transformation, and aims to improve the wear resistance of the rails and prevent a decrease in toughness. Co and Cu aim to improve wear resistance mainly by solid solution strengthening of the base ferrite. Ni improves wear resistance mainly by solid solution strengthening of the base ferrite, and also increases softening resistance of the heat-affected zone during rail welding heat. Ti refines the structure of the heat-affected zone, which is heated to the austenite region during rail welding heat, and prevents the welding joint from becoming brittle.

Mg and Ca finely disperse MnS by generating fine oxides and sulfides, and improve ductility and toughness of the rail by promoting pearlite transformation and miniaturizing the pearlite block size. Al shifts the eutectoid transformation temperature to the high temperature side, and at the same time shifts the eutectoid carbon concentration to the high carbon side, strengthens the pearlite structure and suppresses the formation of proeutectoid cementite, improves the wear resistance of the rail and decreases the toughness. To prevent it.

Each of these components will be described in detail below. 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, If it is less than 0.05%, the effect is small, and it is 2.00.
%, The amount of Cr is limited to 0.05 to 2.00%, since a large amount of martensite structure is generated to reduce the wear resistance and toughness of the veil.

Mo is an element that, like Cr, raises the equilibrium transformation point of pearlite and reduces the pearlite lamella spacing, thereby contributing to an increase in the strength of the pearlite structure and improving wear resistance. %, The effect is small, and when excessive addition exceeding 0.50% is performed, Zr
In the present component system to which is added, segregation is promoted, the pearlite transformation rate is further reduced, and a martensite structure is generated in a column portion and the like, and the toughness of the rail is reduced. %.

V increases the strength by precipitation hardening by carbides of V and nitrides of V generated in a cooling process during hot rolling, and further suppresses the growth of crystal grains during heat treatment at a high temperature. Austenite grains are refined by action,
Although it is an effective element for improving the strength, ductility and toughness of the pearlite structure, its effect cannot be expected sufficiently if it is less than 0.005%, and if it is added more than 0.50%,
Since coarse V carbides and V nitrides are generated and the toughness of the rail and the resistance to internal fatigue damage are reduced, the amount of V is set to 0.005.
~ 0.50%.

Like V, Nb increases the strength by precipitation hardening with carbides of Nb and nitrides of Nb, and further suppresses the growth of crystal grains during heat treatment at a high temperature. And the effect of suppressing austenite grain growth is higher in the temperature range than V (1200
(Approx. ° C.) to improve the ductility and toughness of the pearlite structure. If the effect is less than 0.002%, it cannot be expected. If it exceeds 0.050%, coarse Nb
Carbides and nitrides of Nb are generated, and the toughness of the rail and the resistance to internal fatigue damage are reduced.
Limited to 0.050%.

B is an element which forms iron carbide borides to suppress the formation of proeutectoid cementite, promotes pearlite transformation at the same time, and prevents the wear resistance and toughness of the rail from decreasing. When the content is less than 0.0050%, the effect is not at all. When added in excess of 0.0050%, coarse iron borides are formed, and ductility, toughness, and internal fatigue damage resistance are greatly reduced. , B amount 0.000
It was limited to 1 to 0.0050%.

Co is an element that forms a solid solution with ferrite in the pearlite structure and improves the wear resistance of the pearlite structure by solid solution strengthening, and further increases the transformation energy of the pearlite to make the pearlite structure fine. Is less than 0.10%, the effect cannot be expected, and even if excessive addition exceeding 2.00%, the effect reaches a saturation range.
The amount of Co was limited to 0.10 to 2.00%.

Cu is an element which forms a solid solution with the ferrite in the pearlite structure and improves the wear resistance of the pearlite structure by solid solution strengthening, and its effect is 0.05 to 0.50%.
, And more than 1.00% tends to cause red-hot embrittlement.
Limited to 00%.

Ni is an element that improves the ductility and toughness of the pearlite steel and at the same time increases the strength of the pearlite steel by solid solution strengthening. Furthermore, in the heat affected zone, Ti
Intermetallic compound of Ni ₃ Ti composite is finely precipitated, is an element of suppressing the softening by precipitation strengthening, 0.05%
If it is less than 10%, the effect is extremely small, and even if an excessive addition exceeding 1.00% is performed, no further effect can be expected. Therefore, the amount of Ni was limited to 0.05 to 1.00%.

Titanium is used to reduce the structure of the heat-affected zone heated to the austenite region by utilizing the fact that Ti carbide and Ti nitride precipitated during reheating during welding do not dissolve, and the welding joint is used. It is an effective component for preventing embrittlement of a part. However, if the content is less than 0.0050%, the effect is small, and if the content exceeds 0.0500%, coarse Ti carbides and Ti nitrides are formed and the toughness of the rail is reduced. Limited to ~ 0.050%.

Mg combines with O, S, Al, etc. to form a fine oxide, suppresses the growth of crystal grains during reheating during rail rolling, and refines austenite grains. It is an element effective for improving the ductility and toughness of the pearlite structure. Further, MgO and MgS are replaced with MnS
Is finely dispersed and forms a rare band of Mn around MnS, thereby contributing to the generation of pearlite transformation. As a result, the pearlite block size is reduced, thereby improving the ductility and toughness of the pearlite structure. Element.
However, when the content is less than 0.0005%, the effect is weak.
If it is added in excess of 300%, a coarse oxide of Mg is formed and the ductility and toughness of the rail and the resistance to internal fatigue damage are reduced.
Limited to.

Ca has a strong bonding force with S, forms sulfides as CaS, and CaS finely disperses MnS, forms a thin Mn band around MnS, and contributes to the formation of pearlite transformation. However, as a result, it is an element effective for improving the ductility and toughness of the pearlite structure by reducing the pearlite block size. But 0.0
If it is less than 010%, the effect is weak. If it is added more than 0.0150%, a coarse oxide of Ca is generated and the ductility and toughness of the rail and the resistance to internal fatigue damage are reduced. It was limited to 0.0010 to 0.0150%.

Al is an essential component as a deoxidizing material.
Further, it is an element that moves the eutectoid transformation temperature to the high temperature side and simultaneously shifts the eutectoid carbon concentration to the high carbon side, and is an element that suppresses the increase in the strength of the pearlite structure and the generation of the proeutectoid cementite structure. If it is less than 0.0040%, the effect is weak, and if it exceeds 3.00%, it is difficult to form a solid solution in steel, and coarse alumina-based inclusions serving as a starting point of fatigue damage are generated, and the toughness and the toughness of the rail are reduced. Since the internal fatigue damage resistance is reduced, or an oxide is generated during welding, and the weldability is significantly reduced, the Al content is 0.0040 to 3.00%
Limited to.

The rail steel having the above composition is melted in a commonly used melting furnace, such as a converter or an electric furnace, and the molten steel is subjected to ingot-bulking or continuous casting.
Further, it is manufactured as a rail through hot rolling. next,
By applying heat treatment to this hot-rolled rail that holds high-temperature heat or to the rail head that has been reheated to a high temperature for the purpose of heat treatment, a pearlite structure with high hardness is generated stably on the rail head. It is possible to do.

[0051]

Next, an embodiment of the present invention will be described. Table 1 shows the chemical composition, microstructure (head, column), total number of Zr-based inclusions, and hardness of the rail head of the rail steel of the present invention. Table 1 also shows the wear amount after 700,000 repetitions of the Nishihara-type wear test under forced cooling conditions shown in FIG. 3, the impact test results, and the rolling fatigue test results shown in FIG.
Table 2 shows the chemical composition, microstructure (head, column), total number of Zr-based inclusions, and hardness of the rail head of the comparative rail steel. Table 2 also shows the wear amount after 700,000 repetitions of the Nishihara-type wear test under forced cooling conditions shown in FIG. 3, the impact test results, and the rolling fatigue test results shown in FIG.

FIG. 5 shows the microstructure observation positions and head hardness measurement positions shown in Tables 1 and 2. FIG.
Fig. 2 illustrates the test specimen collection positions in the wear tests shown in Tables 1 and 2. FIG. 7 illustrates the test specimen sampling positions in the impact tests shown in Tables 1 and 2. FIG. 8 shows the relationship between the head hardness and the wear amount in the wear test results of the rail steel of the present invention shown in Table 1 and the comparative rail steel (eutectoid carbon-containing steel, code: M to O) shown in Table 2. It is.
In FIG. 3, 3 is a rail test piece, 4 is a mating material, and 5 is a cooling nozzle. In FIG. 4, reference numeral 6 denotes a rail moving slider on which a rail 7 is installed.
Reference numeral 10 denotes a load load device that controls the left-right movement and load of the wheel 8 rotated by the motor 9. In the test, wheels 8 roll on rails 7 moving left and right.

The configuration of the rail is as follows. -Rail steel of the present invention (12) Symbols A to L In the above component ranges, at least a range of 30 mm in depth starting from the head corner portion and the top surface of the steel rail,
Abrasion resistance and wear resistance characterized in that the total number of Zr-based inclusions having a major axis of more than 10 μm is 500 or less per 100 mm ^{2 of a} test area in a pearlite structure having a hardness of Hv320 or more and a cross section in a rolling direction thereof. Low segregation pearlite rail with excellent internal fatigue damage.・ Comparative rail steel (12 pieces) Codes M to X Codes M to O: Comparative rail steel (3) made of eutectoid carbon-containing steel
Book). Symbols P to U: Comparative rail steel (6
Book). Symbols V to X: chemical components within the above-mentioned claims, and the area to be detected 1
Comparative rail steel (three) made of hypereutectoid carbon-containing steel whose total number of Zr-based inclusions per 00 mm ² is out of the above-mentioned claims.

The wear test conditions were as follows. Tester: Nishihara type abrasion tester (see Fig. 3) Test specimen shape: disk-shaped test specimen (outer diameter: 30mm, thickness: 8mm) Test specimen sampling position: 2mm below the rail head surface (see Fig. 6) Test load : 686 N (contact surface pressure: 640 MPa) Sliding rate: 20% Counterpart material: Pearlite steel (Hv380) Atmosphere: Air cooling: Forced cooling with compressed air (flow rate: 10)
0Nl / min) Number of repetitions: 700,000 times

The conditions of the impact test were as follows. Test piece: JIS No. 3 2mm U notch Charpy impact test piece Test piece sampling position: Rail column (see Fig. 7) Test temperature: Normal temperature (+ 20 ° C)

The conditions for the rolling fatigue test were as follows. Testing machine: rolling fatigue test machine (see Fig. 4) Specimen shape Rail: 136 lb rail x 2m Wheel: AAR type (diameter 920mm) Load condition (reproduction of heavy load railway) Radial load: 147000N (15 tons) Thrust load : 9800N (1 ton) Lubrication condition Dry + oil (intermittent lubrication)

As shown in FIG. 8, the rail steel of the present invention has a higher carbon content than the comparative rail steels (symbols: M to O), so that the amount of wear is small at the same hardness and the wear resistance is greatly improved. are doing. Further, as shown in the rail steel of the present invention in Table 1, by adding the added amounts of C and Zr in an appropriate range, the rails as confirmed in the comparative rail steel (signs: P to S) in Table 2 were obtained. The formation of the pro-eutectoid cementite structure and coarse Zr-based inclusions in the column was suppressed, and the reduction in toughness and the occurrence of internal fatigue damage in the rail column could be prevented.

Further, by setting the addition amount of Si or Mn within an appropriate range, the comparative rail steels (symbols: T to
U) The formation of a martensite structure or a bainite structure in the head as confirmed in U) was suppressed, a decrease in the toughness of the pearlite structure was suppressed, and abrasion resistance was maintained and a decrease in the toughness of the rail column was able to be prevented. . In addition to these effects, as shown in the rail steel of the present invention in Table 1, the amount of generated Zr-based inclusions is kept within an appropriate range to confirm the comparative rail steels in Table 2 (symbols: V to X). As a result, the occurrence of fatigue damage from the inside of the rail head as described above was suppressed, and the internal fatigue damage resistance was improved.

[0059]

[Table 1]

[0060]

[Table 2]

[0061]

As described above, according to the present invention, there is provided a heavy-load railway rail having improved abrasion resistance, at the same time preventing reduction in toughness of the rail column portion and preventing occurrence of internal fatigue damage. Therefore, since the service life of the rail can be improved, the industrial effect is great.

[Brief description of the drawings]

FIG. 1 is a view showing a region where a pro-eutectoid cementite structure is formed along a segregation zone.

FIG. 2 is a diagram showing a region where a pearlite structure is required in which the name and the total number of Zr-based inclusions are controlled at the position of the head cross section surface of the rail steel according to the present invention.

FIG. 3 is a schematic view of a Nishihara type abrasion tester.

FIG. 4 is a schematic diagram of a rolling fatigue tester.

FIG. 5 is a diagram showing a microstructure observation position and a head hardness measurement position.

FIG. 6 is a view showing a test piece sampling position in a wear test.

FIG. 7 is a diagram showing a test piece sampling position in an impact test.

FIG. 8 is a graph showing the relationship between the hardness of the head and the wear amount in the wear test results of the rail steel of the present invention and a comparative rail steel (eutectoid carbon-containing steel, code: M to O).

[Explanation of symbols]

 1: Top of head 2: Head corner 3: Rail test piece 4: Counter material 5: Cooling nozzle 6: Rail moving slider 7: Rail 8: Wheel 9: Motor 10: Load load device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naohisa Honda 1-1 Tobata-cho, Tobata-ku, Kitakyushu Nippon Steel Corporation Yawata Works (72) Inventor Koichiro Matsushita 1-1, Tobata-cho, Tobata-ku, Kitakyushu New Nippon Steel Corporation Yawata Works

Claims (10)

[Claims] 1. A steel rail containing, by mass%, C: more than 0.85 to 1.40%, wherein at least a depth of 3 mm starting from the head corner and top surface of the steel rail.
The range of 0 mm is the pearlite structure, and in the cross section in the rolling direction, the total number of Zr-based inclusions having a major axis of more than 10 μm is 500 or less per 100 mm ^{2 of the} test area. Low segregation pearlite rail with excellent internal fatigue damage. 2. A pearlite structure having a hardness of Hv320 or more at least in a range of a depth of 30 mm from a head corner portion and a top surface of the steel rail as a starting point. Low-segregation pearlite rail with excellent wear resistance and internal fatigue damage resistance. 3. In mass%, C: more than 0.85 to 1.40%, Zr: 0.0001 to 0.2000%, Si: 0.10 to 2.00%, Mn: 0.10 to 2 The low-segregation pearlitic rail according to claim 1 or 2, wherein the low segregation pearlite rail has excellent wear resistance and internal fatigue damage resistance. 4. The method according to claim 3, further comprising one or two types of Cr: 0.05 to 2.00% and Mo: 0.01 to 0.50% by mass%. A low-segregation pearlite rail with excellent wear resistance and internal fatigue damage resistance as described. 5. The composition according to claim 3, further comprising one or two of V: 0.005 to 0.50% and Nb: 0.002 to 0.050% by mass%.
Or a low-segregation pearlite-based rail excellent in wear resistance and internal fatigue damage resistance described in 4. 6. The method according to claim 3, further comprising: B: 0.0001 to 0.0050% by mass%.
A low-segregation pearlitic rail excellent in wear resistance and internal fatigue damage resistance described in the paragraph. 7. The composition according to claim 3, further comprising one or more of Co: 0.10 to 2.00% and Cu: 0.05 to 1.00% by mass%.
7. A low-segregation pearlite-based rail excellent in wear resistance and internal fatigue damage resistance according to any one of Items 1 to 6. 8. The method according to claim 3, further comprising: Ni: 0.05 to 1.00% by mass%.
A low-segregation pearlitic rail excellent in wear resistance and internal fatigue damage resistance described in the paragraph. 9. In mass%, one or more of Ti: 0.0050 to 0.0500%, Mg: 0.0005 to 0.0300%, Ca: 0.0010 to 0.0150% The low-segregation pearlitic rail according to any one of claims 3 to 8, which is excellent in wear resistance and internal fatigue damage resistance. 10. The method according to claim 3, further comprising: Al: 0.0040 to 3.00% by mass%.
A low-segregation pearlitic rail excellent in wear resistance and internal fatigue damage resistance described in the paragraph.