JP4828109B2 - Perlite steel rail - Google Patents

Description

  The present invention relates to a pearlite steel rail for the purpose of improving the wear resistance required for a rail head of a heavy-duty railway and improving the service life of the rail.

In overseas heavy-duty railways, in order to increase the efficiency of railway transport, cargo is being loaded more and more, especially on sharply curved rails, the GC section (gauge corner section) and the resistance to the head side section. Abrasion cannot be ensured sufficiently, and a decrease in the service life of the rail due to wear has become a problem. Against this background, there has been a demand for the development of a rail having wear resistance higher than that of a high-strength rail containing current eutectoid carbon steel. Conventionally, in order to solve these problems, the present inventors have developed a rail as shown below.
(1) Rail with excellent wear resistance using hypereutectoid steel (C: more than 0.85 to 1.20%) with increased cementite volume ratio in lamellae in pearlite structure (see Patent Document 1) ).
(2) Using hypereutectoid steel (C: more than 0.85 to 1.20%), increasing the cementite volume ratio in the lamellae in the pearlite structure, and at the same time, excellent in wear resistance with controlled hardness Rail (see Patent Document 2).

The rail characteristics obtained by these patent applications increase the carbon content of the steel, increase the volume ratio of the cemetite phase in the pearlite lamella, and further control the hardness of the pearlite structure of the rail head. The wear resistance was improved.
JP-A-8-144016 JP-A-8-246100

  In the rails according to these inventions shown in the above (1) and (2), by increasing the volume ratio of the cemetite phase in the pearlite lamella, that is, by increasing the carbon content of the steel, a certain level of resistance. Abrasion can be improved. In recent years, however, overseas heavy-duty railways have been increasing their freight capacity in order to further improve the efficiency of railway transportation. In the rails shown in (1) and (2) above, There was a problem that it was difficult to ensure the wear resistance of the head and the service life of the rail was greatly reduced.

Further, in order to solve this problem, if the amount of carbon in the steel is further increased, the ductility and toughness of the pearlite structure are remarkably lowered, and there is a problem that the rail breakage is liable to occur due to a head defect or the like. . Furthermore, there is a problem that a pro-eutectoid cementite structure which is harmful to the ductility and toughness of the rail is likely to be generated, and the rail is liable to break.
From such a background, in the high carbon content pearlite steel rail, it has been desired to provide a rail with further improved wear resistance without greatly increasing the carbon content of the steel.
That is, the present invention aims to improve the wear resistance required for the rail heads of recent heavy-duty railways and to improve the service life of the rails.

The present invention achieves the above object, and the gist thereof is as follows.
(1) The present invention is mass%, C: more than 0.85% to 1.40%, Co: 0.003 to less than 0.10%, Cr: 0.05 to 2.00% , the balance Is a steel rail composed of Fe and unavoidable impurities, starting from the head corner portion and the top surface of the steel rail, at least a depth of 20 mm is a pearlite structure, and its hardness is Hv300 ~ It is characterized by being in the range of 500.
(2) The present invention is in mass%, further, Mn: characterized in that it contains 0.10 to 2.00%.

(3) The steel rail according to the present invention described in the above (1) to (2) may further contain the components described in the following 1) to 9) in mass%. That is,
1) Cu: 0.05-1.00%,
2) Ni: 0.01 to 1.00%,
You can select a composition containing.

  According to the present invention, by adding a small amount of Co in a steel rail with a pearlite structure used in heavy-duty railways, the wear resistance of the rail head can be improved and the service life of the rail can be improved. it can.

The present invention will be described in detail below based on the best mode.
First, in order to clarify the factors governing the wear characteristics of rail steel, the present inventors have used the track surface of the rail head that has been used on a real track for a long period of time and is sufficiently worn by contact with the wheels. Visual tissue was observed. As a result, on the wear surface of the rail head, it should be confirmed that there is no pearlite structure of the rail before use, and that the structure is composed of a finely divided hard cementite phase and a fine ferrite structure. I was able to.
Furthermore, as a result of investigating the relationship between the fine ferrite structure and the wear of the rail, the present inventors have found that there is a linear correlation between the ferrite grain size of the wear surface of the rail head and the wear amount. It has been found that a small-sized rail has a small amount of wear, and the wear resistance of the rail is improved by making the ferrite grain size of the worn surface finer.

From the results studied by the inventors so far, it has been confirmed that an increase in the volume ratio of the hard cementite phase is effective in reducing the ferrite grain size on the wear surface. However, an increase in the volume ratio of the cementite phase, that is, an increase in the carbon content of the steel causes the above problems.
Therefore, the present inventors have studied a method for reducing the ferrite grain size on the wear surface without increasing the carbon content of the steel. As a result, by adding a small amount of Co, the ferrite grain size on the wear surface can be reduced. It has been found that the wear resistance of pearlite steel is further improved.

Therefore, the present inventors examined the amount of Co added to promote the refinement of ferrite grains on the rolling surface. As a result, it was confirmed that the wear resistance of the pearlite structure was stably improved by controlling the Co addition amount within a certain range.
That is, the present invention is a pearlite steel rail intended to improve the wear resistance of the pearlite structure and improve the service life of the steel rail by adding a small amount of Co to the steel rail having a high carbon content. It is about.

Next, the reason for limitation of the present invention will be described in detail.
(1) Reasons for limiting chemical components of steel rail First, the reasons for limiting the chemical components of rail steel as described in the claims will be described in detail.
C is an element effective in promoting pearlite transformation in the rail steel metal structure and at the same time ensuring wear resistance. If the C content is less than 0.65%, the wear resistance of the pearlite structure of the rail head cannot be ensured, and further, a pro-eutectoid ferrite structure that is harmful to the wear resistance is generated, and the service life of the rail is reduced. In addition, when the C content exceeds 1.40%, a pro-eutectoid cementite structure that is harmful to ductility and toughness is formed in the pearlite structure, and the density of the cementite phase in the pearlite structure increases, and the ductility of the pearlite structure decreases. In addition, the surface damage resistance of the rail head is greatly reduced. For this reason, the amount of C was limited to 0.65 to 1.40%. In order to further improve the wear resistance of the rail head and to sufficiently improve the wear resistance by adding Co, it is desirable that the C content be more than 0.85%.

  Co is an element that dissolves in the ferrite phase in the pearlite structure of the rail steel, further refines the fine ferrite structure formed by contact with the wheel on the wear surface of the rail head, and improves wear resistance. is there. If the Co content is less than 0.003%, the ferrite structure cannot be refined and the effect of improving wear resistance cannot be expected. Moreover, even if the amount of Co is added to 0.10% or more, the above effect is saturated, and the ferrite structure corresponding to the amount added cannot be refined. Moreover, the economical efficiency as a steel rail falls by the increase in alloy addition cost. For this reason, it is preferable to limit the amount of Co to 0.003 to less than 0.10%.

In addition, steel rails manufactured with the above-mentioned composition improve the hardness (strengthening) of the pearlite structure, improve the ductility of the pearlite structure, prevent softening of the heat affected zone, and control the cross-sectional hardness distribution inside the rail head. For the purpose of achieving the above, one or more of the elements of Si, Mn, Cr, Mo, V, Nb, B, Cu, Ni, Ti, Mg, Ca, Al, Zr, and N are used as necessary. Can be added.
Here, Si is an element that increases the hardness (strength) of the rail head by solid solution strengthening in the ferrite phase, suppresses the formation of proeutectoid cementite structure, and secures hardness and ductility. Mn is an element that secures the hardness of the pearlite structure by increasing the hardenability and reducing the pearlite lamella spacing. Cr and Mo increase the equilibrium transformation point of pearlite and ensure the hardness of the pearlite structure mainly by refining the pearlite lamella spacing. V and Nb improve the hardness of the pearlite structure by precipitation hardening with carbides and nitrides generated in the cooling process after hot rolling. In addition, carbides and nitrides are stably generated during reheating, and softening of the weld joint heat-affected zone is prevented. B refines the formation of a pro-eutectoid cementite structure, and at the same time, reduces the cooling rate dependence of the pearlite transformation temperature, improves the ductility of the rail, and further makes the hardness distribution of the rail head uniform.

Cu dissolves in the ferrite in the pearlite structure and increases the hardness of the pearlite structure. Ni prevents embrittlement during hot rolling due to addition of Cu, and at the same time improves the hardness of pearlite steel and further prevents softening of the heat affected zone of the weld joint. Ti refines the structure of the heat-affected zone and prevents embrittlement of the weld joint. Mg and Ca make austenite grains finer during rail rolling, and at the same time promote pearlite transformation and improve the ductility of the pearlite structure. Al moves the eutectoid transformation temperature to the high temperature side, strengthens the pearlite structure, and improves the wear resistance of the rail. Furthermore, the amount of eutectoid carbon is moved to the high carbon side, and the formation of proeutectoid cementite structure is suppressed. Zr suppresses the formation of a segregation zone at the center of the slab by increasing the equiaxed crystallization rate of the solidified structure by the inclusion of ZrO ₂ inclusions as the solidification nucleus of the high carbon rail steel, and the thickness of the proeutectoid cementite structure To reduce the ductility of the rail. N is mainly intended to improve ductility by promoting pearlite transformation from the austenite grain boundary and making the pearlite structure fine.

The reasons for limiting these components will be described in detail below.
Si is an essential component as a deoxidizer during steelmaking. Moreover, it is an element which raises the hardness (strength) of a rail head by the solid solution strengthening to the ferrite phase in a pearlite structure | tissue. Furthermore, in hypereutectoid steel, it is an element that suppresses the formation of proeutectoid cementite structure and suppresses the decrease in ductility.
However, if the Si amount is less than 0.10%, these effects cannot be expected sufficiently. On the other hand, if the Si content exceeds 2.00%, many surface defects are generated during hot rolling, and weldability is deteriorated due to generation of oxides. Furthermore, the hardenability is remarkably increased and a martensite structure is generated which is detrimental to the wear resistance of the rail head. For this reason, it is preferable to limit the amount of Si to 0.10 to 2.00%.
Mn is an element that increases the hardenability and refines the pearlite lamella spacing, thereby ensuring the hardness of the pearlite structure and improving the wear resistance. However, if the amount of Mn is less than 0.10%, the effect is small, and it becomes difficult to ensure the wear resistance required for the rail. On the other hand, if the amount of Mn exceeds 2.00%, the hardenability is remarkably increased, and a martensite structure that is harmful to the wear resistance of the rail head is easily generated. For this reason, it is preferable to limit the amount of Mn to 0.10 to 2.00%.
Cr raises the equilibrium transformation point of pearlite and, as a result, refines the pearlite structure and contributes to higher hardness (strength), and at the same time, strengthens the cementite phase and improves the hardness (strength) of the pearlite structure. Although it is an element that improves wear resistance, the effect is small when the Cr content is less than 0.05%. On the other hand, if the Cr content exceeds 2.00%, the hardenability is remarkably increased, a large amount of martensite structure is generated, and the wear resistance of the rail head is lowered. For this reason, it is preferable to limit the amount of Cr to 0.05 to 2.00%.

Mo, like Cr, is an element that raises the equilibrium transformation point of pearlite and contributes to the increase in hardness (strength) by making the pearlite structure fine, and improves the hardness (strength) of pearlite structure. If the amount is less than 0.01%, the effect is small, and the effect of improving the hardness of the rail steel is not seen at all. On the other hand, if the Mo content exceeds 0.50%, the transformation rate of the pearlite structure is remarkably reduced, and a martensite structure that is harmful to the wear resistance of the rail head is easily generated. For this reason, it is preferable to limit Mo addition amount to 0.01 to 0.50%.
V is an element effective for increasing the hardness (strength) of the pearlite structure by precipitation hardening due to V carbide and V nitride generated in the cooling process after hot rolling. In addition, it is an element effective in preventing V softening of the weld joint heat affected zone by generating V carbide and V nitride in a relatively high temperature range in the heat affected zone reheated to a temperature range below Ac1 point. is there. However, if the amount of V is less than 0.005%, the effect cannot be sufficiently expected, and improvement in the hardness of the pearlite structure and improvement in ductility are not recognized. On the other hand, if the V content exceeds 0.50%, coarse V carbides and V nitrides, which are the starting points of fatigue cracks, are generated, and the internal fatigue damage resistance of the rail head is reduced. For this reason, it is preferable to limit the amount of V to 0.005 to 0.50%.

Nb is an element effective in increasing the hardness (strength) of the pearlite structure by precipitation hardening with Nb carbide and Nb nitride generated in the cooling process after hot rolling. Moreover, in the heat affected zone reheated to a temperature range below the Ac1 point, Nb carbide and Nb nitride are stably generated from the low temperature range to the high temperature range, and the weld joint heat affected zone is prevented from being softened. It is an effective element. However, the effect cannot be expected when the Nb content is less than 0.002%, and no improvement in the hardness of the pearlite structure or improvement in the ductility is observed. On the other hand, if the Nb content exceeds 0.050%, coarse Nb carbides and Nb nitrides that are the starting points of fatigue cracks are generated, and the internal fatigue damage resistance of the rail head is reduced. For this reason, it is preferable to limit the amount of Nb to 0.002 to 0.050%.
B forms iron boride at the prior austenite grain boundaries, refines the formation of proeutectoid cementite structure, and at the same time reduces the cooling rate dependence of the pearlite transformation temperature and makes the head hardness distribution uniform. Therefore, it is an element that prevents the deterioration of the ductility of the rail and extends the life. If the amount of B is less than 0.0001%, the effect is not sufficient, and no improvement is observed in the formation of proeutectoid cementite structure and the hardness distribution of the rail head. On the other hand, if the amount of B exceeds 0.0050%, coarse iron carbon borides that become the starting point of fatigue cracks are generated at the prior austenite grain boundaries, and the internal fatigue damage resistance of the rail head is greatly reduced. Therefore, it is preferable to limit the B amount to 0.0001 to 0.0050%.

Cu is an element that dissolves in the ferrite in the pearlite structure and improves the hardness (strength) of the pearlite structure by solid solution strengthening. If the amount of Cu is less than 0.05%, the effect cannot be expected. On the other hand, when the Cu content exceeds 1.00%, a martensite structure that is harmful to the wear resistance of the rail head is likely to be generated due to a marked improvement in hardenability. Furthermore, the ductility of the ferrite phase in the pearlite structure is significantly reduced, and the surface damage resistance of the rail head is reduced. For this reason, it is preferable to limit the amount of Cu to 0.05 to 1.00%.
Ni is an element that prevents embrittlement during hot rolling due to the addition of Cu, and at the same time, increases the hardness (strength) of pearlite steel by solid solution strengthening in ferrite. Further, in the weld heat affected zone, Ni ₃ Ti intermetallic compound is finely precipitated in combination with Ti, and is an element that suppresses softening by precipitation strengthening. If the amount of Ni is less than 0.01%, the effect is remarkably small. On the other hand, if the Ni content exceeds 1.00%, the ductility of the ferrite phase in the pearlite structure is remarkably lowered, and the surface damage resistance of the rail head is lowered. For this reason, it is preferable to limit the amount of Ni to 0.01 to 1.00%.

By utilizing the fact that Ti carbide and Ti nitride precipitated during reheating during welding are not dissolved, the structure of the heat-affected zone heated to the austenite region is refined and brittleness of the welded joint is achieved. It is an effective ingredient for preventing oxidization. However, when the amount of Ti is less than 0.0050%, the effect is small. In addition, if the Ti content exceeds 0.0500%, coarse Ti carbide and Ti nitride, which are the starting points of fatigue cracks, are generated, and the internal fatigue damage resistance of the rail head is greatly reduced. It is preferable to limit the amount of Ti to 0.0050 to 0.0500%.
Mg combines with O, S, Al, etc. to form fine oxides, suppresses grain growth during reheating during rail rolling, refines austenite grains, It is an effective element for improving the ductility of the steel. In addition, MgO and MgS finely disperse MnS, forming a thin Mn band around MnS, contributing to the generation of pearlite transformation, and as a result, by reducing the pearlite block size, the ductility of the pearlite structure It is an effective element for improving However, if the amount of Mg is less than 0.0005%, the effect is weak. On the other hand, if the Mg content exceeds 0.0200%, a coarse oxide of Mg that becomes the starting point of fatigue cracks is generated and the internal fatigue damage resistance of the rail head is reduced. It is preferable to limit to 0.0200%.

Ca has a strong binding force with S and forms a sulfide as CaS. Further, CaS finely disperses MnS, forms a Mn dilute band around MnS, and contributes to the generation of pearlite transformation. As a result, it is an effective element for improving the ductility of the pearlite structure by reducing the pearlite block size. However, when the Ca content is less than 0.0005%, the effect is weak. However, if the Ca content exceeds 0.0150%, a coarse oxide of Ca that becomes the starting point of fatigue cracks is generated, and the internal fatigue damage resistance of the rail head is reduced. It is preferable to limit to 0.0150%.
Al is an essential component as a deoxidizer during steelmaking. In addition, it is an element that moves the eutectoid transformation temperature to the higher temperature side and the amount of eutectoid carbon to the higher carbon side, and is an effective element for increasing the strength of the pearlite structure and suppressing the formation of the proeutectoid cementite structure. However, when the Al content is 0.0100% or less, the effect is weak. Also, if the Al content exceeds 1.00%, it becomes difficult to make a solid solution in the steel, and coarse alumina inclusions that become the starting point of fatigue cracks are generated, resulting in resistance to internal fatigue damage of the rail head. Decreases. Moreover, since an oxide produces | generates at the time of welding and weldability falls remarkably, it is preferable to limit Al amount to 0.0100 to 1.00%.

Zr has a good lattice matching with γ-Fe because ZrO ₂ inclusions have a good lattice matching with γ-Fe, so that γ-Fe becomes a solidification nucleus of high-carbon rail steel that is a solidification primary crystal and increases the equiaxed crystallization rate of the solidification structure. An element that suppresses the formation of a segregation zone at the center of a slab and suppresses the formation of a pro-eutectoid cementite structure generated in a rail segregation portion. However, when the amount of Zr is 0.0001% or less, the number of ZrO ₂ inclusions is small, and a sufficient action as a solidification nucleus is not exhibited. As a result, a pro-eutectoid cementite structure is generated in the segregation part, and the ductility of the rail is lowered. On the other hand, if the amount of Zr exceeds 0.2000%, a large amount of coarse Zr-based inclusions that become the starting point of fatigue cracks are generated, and the internal fatigue damage resistance of the rail head is reduced. For this reason, it is preferable to limit the amount of Zr to 0.0001 to 0.2000%.
N is an element effective for improving the ductility of the pearlite structure by promoting segregation at the austenite grain boundary to promote pearlite transformation from the austenite grain boundary and by reducing the pearlite block size. However, if the N content is less than 0.0060%, the effect is weak. When the N content exceeds 0.0200%, it becomes difficult to make a solid solution in the steel, and bubbles that become the starting point of fatigue damage are generated, so that the internal fatigue damage resistance of the rail head is lowered. For this reason, it is preferable to limit N amount to 0.0060 to 0.0200%.
In the rail steel, N is contained as a maximum of about 0.0050% as an impurity. Therefore, to obtain the above effect, N needs to be added in an amount of at least 0.0060%.

  Rail steel composed of the above components is melted in a commonly used melting furnace such as a converter, electric furnace, etc., and this molten steel is ingot-bundled or continuously cast, and further hot-rolled. After that, it is manufactured as a steel rail of the desired shape. Next, by applying accelerated cooling to the hot-rolled steel rail that retains high-temperature heat, or the rail head that has been reheated to a high temperature for the purpose of heat treatment, Can be stably generated.

(2) Hardness of pearlite structure of rail head and reason for limitation of the range Next, starting from the head corner and head surface of the steel rail, at least a range of 20 mm in depth is a range of hardness Hv300 to 500 The reason why it is preferable to limit to the pearlite structure is described below.
First, the reason why it is preferable to limit the range of the pearlite structure in the range of hardness Hv 300 to 500 to a range of at least a depth of 20 mm starting from the head corner and the top surface will be described.
If the range in which the pearlite structure having a hardness of Hv 300 to 500 exists is less than 20 mm in depth starting from the head surface at the corner of the head and the top of the head, in order to maintain wear resistance in the rail of heavy-duty railways It is too small to improve the service life of the rail. Moreover, if the range where the pearlite structure | tissue of hardness Hv300-500 exists is 30 mm or more in depth starting from this head surface of a head corner part and a head part, a rail service life will improve further and it is more desirable.

Next, the reason why it is preferable to limit the hardness of the pearlite structure having a depth of 20 mm to the range of Hv 300 to 500 starting from the head surface at the head corner and the top of the head will be described.
In the rail steel component system according to the present invention, when the hardness of the pearlite structure is less than Hv300, it is difficult to ensure the wear resistance of the rail head, and the service life of the rail is reduced. Further, flaking damage caused by plastic deformation occurs on the rolling surface of the steel rail that comes into contact with the vehicle wheel, and the surface damage resistance of the rail head is greatly reduced. Further, when the hardness of the pearlite structure exceeds Hv500, the ductility of pearlite damage is remarkably reduced, the spalling damage of the rolling surface is generated, and the surface damage resistance of the rail head is lowered. For this reason, it is preferable to limit the hardness of a pearlite structure to the range of Hv300-500.

Here, in FIG. 1, the designation at the head cross-sectional surface position and the pearlite structure of hardness Hv 300 to 500 in the first embodiment of the high carbon pearlite steel rail excellent in wear resistance of the present invention are required. Indicates the area.
The steel rail A according to this embodiment includes a rail head B, a pedestal C, and a leg D. In the rail head B, 1 is formed on the top of the head, and 2 is formed on both sides of the top 1 of the head. It is a head corner portion, and one of the head corner portions 2 is a gauge corner (GC) portion that mainly contacts the wheel.
The rail head surface defined in the specification of the present application (specified in claims 1 and 2) means a range up to a depth of 5 mm starting from the surface of the head corner 2 and the top 1 and at least at this part. If the pearlite structure in the above component range is arranged, the wear resistance of the steel rail A can be improved.

Further, the pearlite structure (defined in claim 12) having a hardness Hv of 300 to 500 defined in the specification of the present application is a range up to a depth of 20 mm starting from the surfaces of the head corner portion 2 and the head top portion 1, that is, at least in the figure. If it arrange | positions in the range shown with the oblique line in 1, the abrasion resistance as the steel rail A will be ensured further, and the service life of the steel rail A will be improved.
Therefore, it is desirable to arrange the pearlite structure having a hardness of Hv 300 to 500 in the vicinity of the rail head surface where the wheel and the steel rail A mainly contact, and the other part may be a metal structure other than the pearlite structure. It is not particularly limited.
In addition, as a method for obtaining a pearlite structure having a hardness of Hv 300 to 500 in the rail head B, it is desirable to perform accelerated cooling on a high-temperature rail head having an austenite region after rolling or after reheating. As a method of accelerated cooling, a predetermined structure and hardness can be obtained by performing heat treatment by a method as described in JP-A-8-246100, JP-A-9-111352 and the like.

  For example, as an example of the method described in JP-A-8-246100, the head of the steel rail A heated to a high temperature is 1-10 ° C. between the austenite region temperature and the cooling stop temperature 700-500 ° C. By selecting the conditions for accelerated cooling at / sec, the coarse and low hardness pearlite structure and the martensite structure that is harmful to toughness and wear resistance are not generated. A condition for generating a high pearlite structure can be selected.

  In addition, the metal structure of the rail head according to the present invention is desirably a pearlite structure as described above. However, a trace amount of pro-eutectoid ferrite structure, pro-eutectoid cementite structure, bainite structure, and martensite structure may be mixed in the pearlite structure depending on the rail component system and heat treatment manufacturing method. However, even if these structures are mixed, since it does not have a large adverse effect on the wear resistance of the rail head, as the structure of the pearlite rail excellent in wear resistance of the present application, some proeutectoid ferrite structures, It also includes a mixture of proeutectoid cementite structure, bainite structure, and martensite structure.

Next, examples of the present invention will be described.
Table 1 shows the chemical composition of each rail steel according to the present invention, the microstructure of the rail head (2 mm below the head surface, 20 mm), and the hardness of the rail head (2 mm below the head surface, 20 mm). Table 1 also shows the amount of wear of the rail head material after 700,000 repetitions in the Nishihara type abrasion test under the forced cooling condition shown in FIG.
In Table 1, Steel A to Steel F , Steel H and I, and Steel K to Steel N are all reference examples.
Moreover, in FIG. 2, 3 is a rail test piece, 4 is a counterpart material (wheel material), 5 is a cooling nozzle which can eject refrigerants, such as compressed air.
FIG. 3 shows the positions where the test pieces used in the wear tests shown in Tables 1 and 2 were taken from the rail head B. FIG.

  Table 2 shows the chemical composition of each rail steel as a comparative example, the microstructure of the rail head (2 mm below the head surface, 20 mm), and the hardness of the rail head (2 mm below the head surface, 20 mm). Table 2 also shows the amount of wear of the rail head material after 700,000 repetitions in the Nishihara type abrasion test under the forced cooling condition shown in FIG.

In addition, the structure of each rail steel applied in order to obtain the test result shown in Tables 1 and 2 is as follows.
○ Invention rail steel (14). It shows with the code | symbol A-N in Table 1 (steel A-steel F , steel H, I, and steel K-steel N are reference examples).
A pearlitic steel rail excellent in wear resistance and ductility, characterized in that at least a part of a rail head surface portion has a pearlite structure within the above-mentioned component range.
○ Comparison rail steel (12 pieces). Table 2 shows the symbols O to Z.
Reference signs O to Q: Comparative rail steels (additions of C, Si and Mn) outside the above claims.
Reference signs R to Z: Comparative rail steel (9) in which the amount of Co added is outside the above-mentioned claims.

FIG. 4 shows the relationship between the amount of carbon and the amount of wear in the wear test results of the rail steel of the present invention shown in Table 1 (symbol: A to N) and the comparative rail steel shown in Table 2 (symbol: R to Z). is there.
The various tests were as follows.
○ Abrasion test Tester: Nishihara type wear tester (see Fig. 2)
Test piece shape: disk-shaped test piece (outer diameter: 30 mm, thickness: 8 mm)
Test piece sampling position: 2mm below the rail head surface (see Fig. 3)
Test load: 686 N (contact surface pressure 640 MPa)
Slip rate: 20%
Opposite material: Pearlite steel (Hv380)
Atmosphere: In the air Cooling: Forced cooling with compressed air (flow rate: 100 Nl / min)
Repeat count: 700,000 times

As shown in Tables 1 and 2, the rail steels according to the present invention (signs: A to N, where Steel A to Steel F , Steel H and I, and Steel K to Steel N are reference examples) are comparative rails. Compared to steel (code: O to Q), by adding the amount of C, Si, Mn within a certain range, proeutectoid cementite structure or martensite structure that adversely affects the wear resistance and ductility of the rail, etc. It was possible to obtain a pearlite structure excellent in wear resistance.

In addition, as shown in Tables 1 and 2, the rail steel of the present invention (signs: A to N , where Steel A to Steel F , Steel H, I Steel K to Steel N are reference examples) is a comparative rail steel. Compared with (symbol: R to Z), by keeping the amount of Co within a certain range, it was possible to further improve the wear resistance of the rail exhibiting a pearlite structure.

When the results of the above wear test are summarized by correlation with the carbon content of the steel, as shown in FIG. 4, at the same carbon content, a small amount of Co is added compared to the rail steel having a Co addition amount of less than 0.003%. It was confirmed that the rail steel added with (0.003 to 0.10 mass%) has a small amount of wear and the wear resistance is remarkably improved.
The relationship shown in FIG. 4 is plotted by paying attention to the carbon amount and wear amount of each sample shown in Table 1 and the carbon amount and wear amount of each sample shown in Table 2.

The element contents and test results of each sample shown in Table 1 and Table 2 will be described. Sample O in Table 2 is a sample containing more C than the preferred range (0.65-1.40%). Although the pro-eutectoid cementite is precipitated and the hardness is increased, the sample P is a sample in which Si is increased from the preferable range (0.10 to 2.00%), but martensite is precipitated and the hardness is increased. The sample Q was a sample in which Mn was increased from the preferred range (0.10 to 2.00%), but the hardness increased and the wear amount was large.
Samples R to Z are samples in which the Co content is made lower than the preferred range (less than 0.003 to less than 0.10%), the C amount is increased or decreased within the preferred range, and the Si and Mn amounts are also preferred. However, in all the samples, the wear amount increased.
On the other hand, all of the samples shown in Table 1 satisfying the preferred range of the present invention for C, Co, Si and Mn are structures mainly composed of pearlite, or structures having some pro-eutectoid ferrite or pro-eutectoid cementite. However, all of them are organizations mainly composed of the target perlite.

FIG. 1 shows the designation of the head cross-sectional surface position in one embodiment of the pearlite steel rail excellent in wear resistance according to the present invention, and the region where a high hardness pearlite structure is required in the steel rail. FIG. FIG. 2 is an explanatory view showing a schematic configuration of the Nishihara type abrasion tester. FIG. 3 is a view showing the sampling positions of the test pieces used in the abrasion tests of Examples and Comparative Examples shown in Tables 1 and 2 with respect to the steel rail. FIG. 4 shows the carbon content in the individual wear test results of the steel rail test pieces (reference characters: A to N) according to the present invention shown in Table 1 and the steel rail test pieces of the comparative example shown in Table 2 (reference characters: R to Z). It is a figure which shows the relationship between a wear amount.

Explanation of symbols

A: Steel rail,
B: Rail head,
C: pedestal,
D: Leg,
1: the top of the head,
2: Head corner,
3: Rail test piece,
4: Opponent material,
5: Nozzle for cooling,

Claims (4)

% By mass
C: Steel rail containing more than 0.85% to 1.40%, Co: 0.003 to less than 0.10%, Cr: 0.05 to 2.00% , the balance being Fe and inevitable impurities The steel rail has a pearlite structure with a depth of at least 20 mm starting from the head corner and the top surface of the steel rail, and its hardness is in the range of Hv 300 to 500. Perlite steel rail. In mass% ,
The pearlite steel rail according to claim 1, containing Mn: 0.10 to 2.00%. In mass%, further, Cu: pearlitic steel rail according to any one of claims 1-2, characterized in that it contains 0.05 to 1.00%. In mass%, further, Ni: 0.01 to 1.00% pearlitic steel rail according to any one of claims 1 to 3, characterized in that it contains.

Images