JP2010018844A - Pearlite-based rail having excellent wear resistance and ductility - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the service life of a rail used for a heavy-load railroad by compositely adding Co and Ni as the components of a rail steel, and controlling an Ni/Co ratio to a fixed range, so as to improve the wear resistance and ductility of a pearlite texture, and controlling the texture and hardness, so as to improve the wear resistance and ductility of a pearlite texture. <P>SOLUTION: The pearlite-based rail having excellent wear resistance and ductility is characterized in that, in a steel rail comprising, by mass, 0.65 to 1.20% C, 0.05 to 2.00% Si, 0.05 to 2.00% Mn, 0.05 to 0.50% Co, 0.10 to 2.25% Ni and the balance Fe with inevitable impurities, the ratio of the Co content to the Ni content (Ni/Co) lies in the range of 2.0 to 4.5, and at least a part of the head surface part of the steel rail has a pearlite texture. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pearlite rail intended to simultaneously improve wear resistance and ductility of a head in a rail used in heavy-duty railways.

  In overseas heavy-duty railroads, we are increasing the load of freight in order to increase the efficiency of rail transport. Especially for sharply curved rails, sufficient wear resistance is ensured in the GC section and the head side. However, the deterioration of 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. In order to solve these problems, the following rails have been developed. The main features of these rails are to increase the carbon content of the steel, to increase the volume ratio of the cemetite phase in the pearlite lamella, and to control the hardness (for example, to improve wear resistance) (See Patent Documents 1 and 2).

  In the disclosed technique of Patent Document 1, a hypereutectoid steel (C: more than 0.85 to 1.20%) is used to increase the cementite volume ratio in the lamellae in the pearlite structure, and the rail has excellent wear resistance. Can be provided.

  Moreover, in the open technology of patent document 2, using hypereutectoid steel (C: more than 0.85 to 1.20%), the cementite volume ratio in the lamella in the pearlite structure is increased, and at the same time, the hardness is increased. The rail can be controlled and has excellent wear resistance.

  However, in the disclosed technologies of Patent Documents 1 and 2, a certain level of wear resistance can be improved by increasing the volume ratio of the cemetite phase in the pearlite structure, that is, by increasing the carbon content of the steel. However, there is a problem that the ductility of the pearlite structure itself is remarkably lowered and the rail breakage is liable to occur. Furthermore, there is a problem that a pro-eutectoid cementite structure which is harmful to the ductility of the rail is likely to be generated and the rail breakage is likely to occur.

JP-A-8-144016 JP-A-8-246100

  Against this background, it has been desired to provide a pearlite rail that has improved wear resistance of the pearlite structure and at the same time has improved wear resistance and ductility.

  Therefore, the present invention has been devised in view of the above-mentioned problems, and its object is to simultaneously improve the head wear resistance and ductility required for heavy-duty railroad rails. It is aimed at.

(1) By mass%, C: 0.65 to 1.20%, Si: 0.05 to 2.00%, Mn: 0.05 to 2.00%, Co: 0.05 to 0.50% In a steel rail containing Ni: 0.10 to 2.25% and the balance being Fe and inevitable impurities, Ni mass% / Co mass%, which is a ratio of Co content to Ni, is 2.0 to 4 A pearlite rail excellent in wear resistance and ductility, characterized in that at least part of the head surface of the steel rail has a pearlite structure.

(2) A pearlite rail excellent in wear resistance and ductility, characterized in that in the above (1), C is in the range of 0.90 to 1.20%.

(3) Moreover, the rail of said (1) or (2) can be made to selectively contain the following [1]-[8] further by the mass%.
[1] One or two of Cr: 0.01 to 2.00%, Mo: 0.01 to 0.50%,
[2] V: 0.005 to 0.50%, Nb: 0.002 to 0.050%, 1 type or 2 types,
[3] B: One of 0.0001 to 0.0050%,
[4] Cu: 0.05% to 1.00%,
[5] One or more of Ti: 0.0050 to 0.0500%, Mg: 0.0005 to 0.0200%, Ca: 0.0005 to 0.0150%,
[6] Al: one type of 0.0100 to 1.00%,
[7] Zr: one of 0.0001 to 0.2000%,
[8] N: one kind of 0.0060 to 0.0200%,
It consists of the remainder Fe and inevitable impurities.

(4) In the rail of any one of the above (1) to (3), at least a range of 20 mm in depth is a pearlite structure starting from the head corner portion and the top surface of the steel rail, and its hard A pearlite rail excellent in wear resistance and ductility, characterized in that the length is in the range of Hv 320 to 500.

  Rail steel components, ie, Co and Ni, are added together to keep the Ni / Co ratio within a certain range, thereby improving the wear resistance and ductility of the pearlite structure and controlling the structure and hardness. By doing so, it becomes possible to improve the service life of the rail used for heavy-duty railway.

  Hereinafter, a pearlite rail excellent in wear resistance and ductility will be described in detail as an embodiment of the present invention. Hereinafter, the mass in the composition is simply described as%.

  First, in order to clarify the factors governing the wear characteristics of rail steel, the inventors first used a rail head that has been used for a long time on an actual track as described above and was sufficiently worn by contact with the wheel. The microstructure of the worn surface was observed. As a result, the lamellar structure of the ferrite phase and cementite phase of the base pearlite structure becomes fine on the wear surface of the rail head, and in addition, the lamellar structure disappears partially, and the crushed hard cementite phase and fine ferrite It was confirmed that the organization was composed of organizations.

  Furthermore, the present inventors investigated the relationship between rail wear and structural changes. As a result, it was confirmed that the structure of the wear surface of the rail head having excellent wear resistance has a fine lamella structure and a fine ferrite particle size.

  From previous laboratory studies, it has been confirmed that increasing the volume ratio of the hard cementite phase is effective in refining these structures. However, an increase in the volume ratio of the cementite phase, that is, an increase in the amount of carbon greatly reduces the ductility of the steel. Therefore, the present inventors have studied a method for refining the structure of the wear surface without increasing the carbon content of the steel. As a result of examining various alloy elements, it was found that the addition of a certain amount of Co refines the lamellar structure and ferrite grain size of the wear surface and further improves the wear resistance of pearlite steel.

  Therefore, the transformation characteristics of the Co-added steel were evaluated in the laboratory. Based on rail steel having a carbon content of 1.00% C, a material in which the amount of Co was changed was melted, and a heating / cooling experiment simulating rolling conditions corresponding to the rail was conducted to investigate the transformation characteristics. As a result, it was confirmed that Co-added steel promotes pearlite transformation and at the same time suppresses the formation of proeutectoid cementite structure, which is a cause of embrittlement of high-carbon steel. It was found that steel is an extremely effective alloy as an element that stabilizes wear resistance and pearlite transformation characteristics.

  Furthermore, the ductility of the Co-added steel was evaluated experimentally. Based on rail steel with a carbon content of 0.65 to 1.20% C, a material with 0.20% Co added was melted, and a laboratory rolling experiment simulating rolling conditions equivalent to the rail was conducted. investigated. The hardness of the material was adjusted to the Hv400 level by controlling the heat treatment conditions.

  FIG. 1 shows the relationship between the amount of carbon and the total elongation value. It was confirmed that the total elongation value decreased by adding Co at any carbon content.

  Furthermore, the present inventors examined a method for improving the decrease in the total elongation value due to the addition of Co. First, the cause of ductility reduction due to Co addition was clarified. As a result of observing the structure of the tensile test piece, it was confirmed that a number of cracks were present in the ferrite phase, and the ferrite phase of the pearlite structure was embrittled by the addition of Co.

  Therefore, a method for suppressing embrittlement of the ferrite phase was examined. Based on rail steel with 0.65 to 1.20% carbon and 0.20% Co added, the alloy-altered material was melted, and lab rolling experiments were performed simulating rolling conditions equivalent to rails. The ductility was evaluated by a tensile test. The hardness of the material was adjusted to the Hv400 level by controlling the heat treatment conditions.

  FIG. 1 also shows the results of steel obtained by adding 0.50% Ni to the above materials. It was confirmed that by adding a certain amount of Ni, embrittlement of the ferrite phase due to the addition of Co is suppressed, and a decrease in the total elongation value can be prevented.

  Furthermore, the present inventors examined the optimal range of said Ni addition amount. Based on steel with carbon content of 1.00% and steel with 1.00% C added with 0.05%, 0.20% and 0.50% Co, the material with varying Ni content was melted. Then, lab rolling experiments simulating rolling conditions equivalent to rails were conducted, tensile tests and wear tests were conducted, and the effects of Ni addition on ductility and wear resistance were investigated. The hardness of the material was adjusted to the Hv400 level by controlling the heat treatment conditions.

  FIG. 2 shows the relationship between the Ni addition amount and the total elongation value. When the Ni addition amount is small, no significant change is observed in the total elongation value, and when the Ni addition amount exceeds a certain amount, it is confirmed that the total elongation value increases and the ductility is improved. It became clear that there was a lower limit on the amount. Further, when attention is paid to the ratio between the Co addition amount and the Ni addition amount, the total elongation value is not improved when the Ni / Co ratio is less than 2.0 at any Co addition amount, and the Ni / Co ratio is It was confirmed that the total elongation value was improved at 2.0 or more.

  Next, the present inventors examined wear characteristics. FIG. 3 shows the relationship between the Ni addition amount and the wear amount. The wear test was performed under the same conditions using the wear tester shown in the examples of the present invention. When the amount of added Ni is small, no significant change is observed in the amount of wear, and it was confirmed that when the amount of added Ni exceeds a certain amount, the amount of wear increases greatly and wear resistance decreases. This is because when Ni is added, the lamellar structure on the rolling surface and the refinement of the ferrite grain size are suppressed, and work hardening is suppressed. From these results, it became clear that there is an upper limit for the amount of Ni added to ensure wear resistance. Further, when attention is paid to the ratio of the Co addition amount and the Ni addition amount, no decrease in wear resistance is observed when the Ni / Co ratio is 4.5 or less at any Co addition amount. It was confirmed that when the ratio exceeds 4.5, the wear resistance is lowered.

  From the results of these material tests, it was confirmed that the addition of Ni is effective for improving the ductility in the Co-added steel. However, in order to reliably improve the ductility and ensure the wear resistance, Ni It has been newly found that there is an optimum range for the addition amount, and that the optimum range can be controlled by keeping the Ni / Co ratio within a certain range.

  That is, the present invention improves the wear resistance and ductility of the pearlite structure by adding Co and Ni in a high carbon content steel rail and keeping the Ni / Co ratio within a certain range. The present invention relates to a pearlite rail for the purpose of improving the service life of the steel.

  Next, the reason for limitation of the present invention will be described in detail. Hereinafter, the mass% in the composition is simply described as%.

(1) Reason for limitation of chemical component In claim 1, the reason why the chemical component of the rail steel is limited to the above-mentioned claims will be described in detail.

C is an effective element that promotes pearlite transformation and ensures wear resistance. If the amount of C is less than 0.65%, the minimum strength and wear resistance required for the rail cannot be maintained. On the other hand, if the C content exceeds 1.20%, a large amount of coarse pro-eutectoid cementite structure is generated, and the wear resistance and ductility are lowered. For this reason, C addition amount was limited to 0.65-1.20%.
When the C content is 0.90% or more, the wear resistance is further improved, and the service life of the rail is further improved. For this reason, in order to further improve the wear resistance of the rail and increase the life in a track under severe usage conditions, the C addition amount is 0.90 to 1.20% as shown in claim 3. It is desirable to limit to.

Si is an essential component as a deoxidizing material. 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, when the Si content is less than 0.05%, 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. Further, the hardenability is remarkably increased, and a martensite structure that is harmful to the wear resistance and ductility of the rail is generated. For this reason, Si addition amount was limited to 0.05 to 2.00%.
Mn is an element that increases the hardenability and refines the pearlite lamella spacing to ensure the hardness of the pearlite structure and improve the wear resistance. However, if the amount of Mn is less than 0.05%, the effect is small, and it is difficult to ensure the wear resistance required for the rail. Moreover, when the amount of Mn exceeds 2.00%, hardenability will increase remarkably and it will become easy to produce | generate the martensitic structure harmful to abrasion resistance and ductility. For this reason, Mn addition amount was limited to 0.05 to 2.00%.

  Co is an element that dissolves in the ferrite phase in the pearlite structure, further refines the fine ferrite structure formed by contact with the wheel on the wear surface of the rail head, and improves the wear resistance. If the amount of Co is less than 0.05%, the lamellar structure and the ferrite grain size cannot be reduced, and the effect of improving wear resistance cannot be expected. On the other hand, if the Co content exceeds 0.50%, the ductility of the pearlite structure is significantly reduced. In addition, the economic efficiency decreases due to the increase in the alloy addition cost. For this reason, the amount of Co added is limited to 0.05 to 0.50%.

  Ni is an element that improves the ductility of the ferrite phase in the pearlite structure, suppresses the decrease in ductility due to the addition of Co, and at the same time increases the hardness (strength) by solid solution strengthening. When the amount of Ni is less than 0.10%, the effect is remarkably small. When the amount of Ni exceeds 2.25%, the ductility of the ferrite phase in the pearlite structure is significantly reduced, and the wear resistance of the pearlite structure. Decrease greatly. For this reason, Ni addition amount was limited to 0.10-2.25%.

  In addition, the rail manufactured with the above component composition improves the hardness (strengthening) of the pearlite structure and pro-eutectoid ferrite structure, improves the ductility, prevents softening of the weld heat affected zone, and the cross-sectional hardness distribution inside the rail head. For the purpose of control, elements of Cr, Mo, V, Nb, B, Cu, Ti, Mg, Ca, Al, Zr, and N are added as necessary.

Here, Cr and Mo increase the equilibrium transformation point of pearlite, and ensure the hardness of the pearlite structure mainly by reducing the pearlite lamella spacing. V, Nb suppresses the growth of austenite grains by carbides and nitrides generated in the hot rolling and subsequent cooling process, and further precipitates and hardens in the ferrite structure and pearlite structure. Improve hardness. In addition, carbides and nitrides are stably generated, and the weld joint heat-affected zone is prevented from being softened. B reduces the cooling rate dependence of the pearlite transformation temperature and makes the hardness distribution of the rail head uniform. Cu dissolves in the ferrite in the ferrite structure or pearlite structure, and increases the hardness of the pearlite structure. Ti refines the structure of the heat-affected zone and prevents embrittlement of the weld joint. Mg and Ca reduce the austenite grains during rail rolling, and at the same time, promote ferrite and pearlite transformation and improve toughness. Al moves the eutectoid transformation temperature to the high temperature side and increases the hardness of the pearlite structure. Zr suppresses the formation of segregation zone at the center of the slab and prevents the deterioration of the ductility of the rail by increasing the equiaxed crystallization rate of the solidification structure by the inclusion of ZrO ₂ inclusions as the solidification nucleus of the high carbon rail steel. . 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.
Cr increases the equilibrium transformation temperature, and as a result, refines the ferrite structure and pearlite structure to contribute to higher hardness (strength), and at the same time, strengthens the cementite phase and improves the hardness (strength) of the pearlite structure. However, when the Cr content 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. Moreover, if excessive addition exceeding Cr content of 2.00% is performed, the hardenability increases, a martensite structure is generated, and the sprig damage starting from the martensite structure occurs at the head corner or the top of the head. , Surface damage resistance is reduced. For this reason, Cr addition amount was limited to 0.01 to 2.00%.
Mo, like Cr, is an element that increases the equilibrium transformation temperature and, as a result, contributes to higher hardness (strength) by making the ferrite structure and pearlite structure finer, and improves hardness (strength). 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. In addition, when the Mo amount exceeds 0.50%, the transformation rate is remarkably reduced, and sprig damage starting from the martensite structure occurs at the head corner and the top of the head, resulting in surface damage resistance. Decreases. For this reason, Mo addition amount was limited to 0.01 to 0.50%.

  V is a V carbide or V nitride produced by a cooling process after hot rolling by refining austenite grains due to the pinning effect of V carbide or V nitride when heat treatment is performed at a high temperature. It is an element effective for improving the ductility by increasing the hardness (strength) of ferrite structure and pearlite structure by precipitation hardening. 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 no improvement in the hardness or ductility of the ferrite structure or pearlite structure is observed. If the V content exceeds 0.50%, the precipitation and hardening of V carbides and nitrides will be excessive, the ductility of the ferrite structure and pearlite structure will be reduced, and sprig damage will occur at the head corner and the top of the head. , Surface damage resistance is reduced. For this reason, V addition amount was limited to 0.005-0.50%.

  Nb, like V, is refined by the pinning effect of Nb carbide or Nb nitride when heat treatment is performed at a high temperature, and further Nb produced in the cooling process after hot rolling. It is an element effective for improving the ductility as well as increasing the hardness (strength) of ferrite structure and pearlite structure by precipitation hardening with carbide and Nb nitride. 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, when the Nb content is less than 0.002%, the effect cannot be expected, and no improvement in hardness or toughness of the ferrite structure or pearlite structure is observed. If the Nb content exceeds 0.050%, the precipitation hardening of Nb carbides and nitrides becomes excessive, the ductility of the ferrite structure and pearlite structure decreases, and the sprig damage occurs at the head corner and the top of the head. , Surface damage resistance is reduced. For this reason, the amount of Nb added is limited to 0.002 to 0.050%.

  B forms iron boride (Fe23 (CB) 6) at the austenite grain boundary, reduces the cooling rate dependence of the pearlite transformation temperature due to the accelerating effect of the pearlite transformation, and has a more uniform hardness from the head surface to the inside. An element that imparts a distribution to the rail and prolongs the life of the rail. However, if the amount of B is less than 0.0001%, the effect is not sufficient, and the hardness distribution of the rail head is not improved. On the other hand, if the amount of B exceeds 0.0050%, a coarse borohydride is formed, resulting in a decrease in ductility and toughness. For this reason, B addition amount was limited to 0.0001 to 0.0050%.

  Cu is an element that dissolves in the ferrite phase in the ferrite structure and pearlite structure and improves the hardness (strength) of the pearlite structure by solid solution strengthening, but the effect is expected when the Cu content is less than 0.05%. Can not. Further, if the Cu content exceeds 1.00%, martensite structure harmful to ductility is generated due to remarkable hardenability improvement, and sprig damage occurs in the head corner portion and the top of the head, and the surface damage resistance decreases. . For this reason, the amount of Cu was limited to 0.05 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, if the Ti amount is less than 0.0050%, the effect is small, and if the Ti amount exceeds 0.0500%, coarse Ti carbides and Ti nitrides are generated, and at the same time, the toughness of the rail is lowered. Fatigue damage occurs from coarse precipitates. For this reason, Ti addition amount was limited to 0.0050 to 0.050%.

  Mg combines with O, S, Al, or the like to form a fine oxide, suppresses grain growth during reheating during rail rolling, refines austenite grains, and produces a ferrite structure It is an element effective for improving the ductility of pearlite structure. Furthermore, MgO, MgS finely disperses MnS, forms a thin Mn band around MnS, contributes to the generation of ferrite and pearlite transformation, and as a result, mainly by reducing the pearlite block size, It is an element effective for improving the ductility of the pearlite structure. However, if the amount of Mg is less than 0.0005%, the effect is weak. If the amount of Mg exceeds 0.0200%, a coarse oxide of Mg is generated, and the toughness of the rail is lowered, and at the same time, fatigue is caused from coarse precipitates. Damage will occur. For this reason, Mg addition amount was limited to 0.0005 to 0.0200%.

  Ca has a strong binding force with S and forms a sulfide as CaS. Furthermore, CaS finely disperses MnS, forming a Mn dilute band around MnS, contributing to the generation of ferrite and pearlite transformation. As a result, the element is effective in improving the ductility of the pearlite structure mainly by reducing the pearlite block size. However, when the Ca content is less than 0.0005%, the effect is weak. When the Ca content exceeds 0.0150%, a coarse oxide of Ca is generated and the toughness of the rail is reduced. It was limited to 0005 to 0.0150%.

  Al is an essential component as a deoxidizing material. Moreover, although it is an element which moves a eutectoid transformation temperature to the high temperature side and contributes to high hardness (strength) of a pearlite structure | tissue, the effect is weak if Al amount is less than 0.0100%. Also, if the Al content exceeds 1.00%, it becomes difficult to make a solid solution in the steel, coarse alumina inclusions are generated, the toughness of the rail is lowered, and at the same time fatigue damage is caused from the coarse precipitates. appear. Furthermore, since oxides are generated during welding and weldability is remarkably reduced, the amount of Al added is limited 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 band at the center of the slab and improves the characteristics of the segregation. 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. On the other hand, when the amount of Zr exceeds 0.2000%, a large amount of coarse Zr-based inclusions are generated, and the toughness is lowered, and at the same time, fatigue damage occurs from the coarse precipitates. For this reason, the amount of Zr was limited to 0.0001 to 0.2000%.

  N is an element effective for improving ductility by mainly segregating at the austenite grain boundary to promote ferrite and pearlite transformation from the austenite grain boundary and mainly 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, and fatigue damage occurs inside the rail head. For this reason, N addition amount was limited to 0.0060-0.0200%.

  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, continuously cast, or hot. It is manufactured as a rail after rolling.

(2) Limited range of ratio of Ni to Co content (Ni / Co, mass%) Next, the ratio of Ni to Co content (Ni / Co, mass%) is set to a range of 2.0 to 4.5. The reason for the limitation will be described.

  When Ni / Co is less than 2.0, as shown in FIG. 2, embrittlement of the ferrite phase can be suppressed. As a result, the effect of improving ductility is not recognized, and the ductility of the Co-added steel is not improved. Moreover, when Ni / Co exceeds 4.5, as shown in FIG. 3, the lamellar structure on the rolling surface and the refinement of the ferrite grain size are suppressed, and as a result, work hardening is suppressed, and the Co-added steel is suppressed. The wear resistance of the material is greatly reduced. For this reason, Ni / Co was limited to the range of 2.0-4.5.

  The ratio of Ni content to Ni (Ni / Co, mass%) is more preferably in the range of 2.0 to 4.2, and still more preferably in the range of 2.3 to 4.2. The reason for this is as follows. When Ni / Co is controlled in the range of 2.0 to 4.2, the effect of improving ductility and wear resistance is stably obtained, and when Ni / Co is controlled in the range of 2.3 to 4.2, The effect of improving ductility and wear resistance can be obtained more stably, and the balance between the wear resistance and ductility of the rail becomes the best.

(3) Hardness of pearlite structure of rail head and reason for limitation of the range Next, a pearlite structure having a depth of at least 20 mm and a hardness of Hv320 to 500 starting from the head corner and the top surface. The reason for the limitation will be described.

First, the reason why the range of the pearlite structure having a hardness of Hv 320 to 500 is limited 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 where the pearlite structure having a hardness of Hv 320 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 Hv320-500 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 the hardness of the pearlite structure in the depth range of 20 mm starting from the head surface at the head corner and the top of the head is limited to the range of Hv 320 to 500 will be described.
In this component system, when the hardness of the pearlite structure is less than Hv320, 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, 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 the pearlite structure is remarkably lowered, the spalling damage of the rolling surface is generated, and the surface damage resistance of the rail head is lowered. For this reason, the hardness of the pearlite structure | tissue was limited to the range of Hv320-500.

  Here, FIG. 4 shows the designation of the pearlite rail excellent in wear resistance and ductility according to the present invention at the head cross-sectional surface position, and the region where the pearlite structure having a hardness of Hv 320 to 500 is required. In the rail head portion, 1 is a top portion, 2 is a head corner portion, and one of the head corner portions 2 is a gauge corner (GC) portion that mainly contacts a wheel.

  The rail head surface portion indicates a range up to a depth of 5 mm starting from the head corner portion and the top surface, and if the pearlite structure having the above component range is disposed at least in this portion, the rail has wear resistance. Can be improved.

  In addition, the pearlite structure having a hardness of Hv320 to 500 has a wear resistance of the rail as long as the pearlite structure is arranged in a range up to a depth of 20 mm starting from the head corner portion and the top surface, that is, at least within the oblique line in the figure. Is further secured, and the service life of the rail can be improved.

  Therefore, the pearlite structure having a hardness of Hv 320 to 500 is desirably arranged in the vicinity of the rail head surface where the wheel and the rail mainly contact each other, and the other part may be a metal structure other than the pearlite structure.

  As a method for obtaining a pearlite structure having a hardness of Hv 320 to 500 in the rail head, 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.

  The head metal structure of the rail of the present invention is desirably a pearlite structure as described above. However, depending on the component system of the rail and the heat treatment production method, a trace amount of pro-eutectoid ferrite structure, pro-eutectoid cementite structure, bainite structure and martensite structure of 5% or less may be mixed in the pearlite structure. However, even if these structures are mixed, there is no significant adverse effect on the wear resistance and ductility of the rail head, so a pearlite rail structure with excellent wear resistance and ductility is a trace amount of 5% or less. Also included is a pro-eutectoid ferrite structure, pro-eutectoid cementite structure, bainite structure, and martensite structure. In other words, 95% or more of the head metal structure of the rail of the present invention may be a pearlite structure. In order to sufficiently secure wear resistance and ductility, 98% or more of the head metal structure is a pearlite structure. It is desirable to do. In Tables 1 and 2, the amount of 5% or less in the column of microstructure in the column means the amount of 5% or less, and the amount not exceeding 5% in the tissue other than the pearlite structure. means.

Next, examples of the present invention will be described.
Table 1 shows the chemical composition of the test rail steel, the Ni / Co value, the microstructure of the rail head, and the hardness. The microstructure and hardness are data at a position 2 mm below the head surface. The pearlite in the microstructure means that the area ratio is 95% or more of the pearlite structure, and the trace amount of the tissue other than the pearlite structure is the area ratio. Is 5% or less. Furthermore, the test piece was sampled from the position shown in FIG. 5, the result of the abrasion test conducted by the method shown in FIG. 6, and the result of the tensile test conducted by collecting the test specimen from the position shown in FIG.

  Table 2 shows the chemical composition, the Ni / Co value, the microstructure of the rail head, and the hardness of the comparative rail steel. Note that the microstructure and hardness are data at a position 2 mm below the head surface, and the structure other than the pearlite structure in the microstructure means that the area ratio is more than 5%, but the trace amount of the tissue other than the pearlite structure is the area. It means that the rate is 5% or less. Furthermore, the test piece was sampled from the position shown in FIG. 5, the result of the abrasion test conducted by the method shown in FIG. 6, and the result of the tensile test conducted by collecting the test specimen from the position shown in FIG.

(1) Invention rail (33) Reference numerals 1 to 33
A pearlite rail excellent in wear resistance and ductility within a range of the present invention component and having a Ni / Co value, a microstructure of a rail head, and a hardness within a specified range.

(2) Comparison rail (28) Reference numerals 34 to 61
Steel: 34-43: Rail whose component range is outside the scope of the present invention.
Steel: 44-55: Rail whose component range is within the scope of the present invention, but whose Ni / Co value is outside the scope of the present invention.
Steel: 56-58: Rail whose component range is within the scope of the present invention but whose head microstructure is outside the scope of the present invention.
Steel: 59 to 61: A rail whose component range is within the scope of the present invention, but whose head hardness is outside the scope of the present invention.

(3) Evaluation method
[1] Head tensile tester: Universal small tensile tester Test piece shape: JIS No. 4 similar parallel part length: 30 mm, parallel part diameter: 6 mm, distance between elongation measurement scores: 25 mm
Test piece sampling position: 6mm below the rail head surface (see Fig. 7)
Tensile speed: 10 mm / min, test temperature: normal temperature (20 ° C.)

[2] Head wear tester: Nishihara type wear tester (see Fig. 6)
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. 5)
Test load: 686 N (contact surface pressure 640 MPa)
Slip rate: 20%
Opposite material: Pearlite steel (Hv380)
Atmosphere: Air cooling: Forced cooling with compressed air (flow rate: 100 Nl / min)
Repeat count: 700,000 times

  As shown in Table 1 and Table 2, the rail steel of the present invention (steel: 1 to 33) is compared with the comparative rail steel (steel: 34 to 39), by keeping the chemical composition of the steel within a limited range. It is possible to stably obtain a pearlite structure within a certain hardness range without generating a structure such as a pro-eutectoid cementite structure, a martensite structure, and a bainite structure that adversely affects ductility and wear resistance.

  As shown in Tables 1 and 2, the rail steel of the present invention (steel: 1 to 33) has an added amount of Co and Ni within the limited range compared to the comparative rail steel (steel: 40 to 43). Thus, the wear resistance can be improved without reducing the ductility.

  As shown in Table 1, Table 2, and FIG. 8, the rail steel of the present invention (steel: 1 to 33) is compared with the comparative rail steel (steel: 42, 45, 46, 49, 50, 53, 54). By keeping the value of Ni / Co within a certain range, it is possible to improve the ductility of the rail of the pearlite structure.

  As shown in Table 1, Table 2, and FIG. 9, the present invention rail steel (steel: 1 to 33) is compared with comparative rail steel (steel: 43, 44, 47, 48, 51, 52, 55). By keeping the value of Ni / Co within a certain range, it is possible to improve the wear resistance of the rail of the pearlite structure.

  As shown in Tables 1 and 2, the rail steel of the present invention (steel: 1 to 33) has a wear resistance by making the microstructure a pearlite structure compared to the comparative rail steel (steel: 56 to 58). And ductility can be secured.

  As shown in Tables 1 and 2, the rail steel of the present invention (steel: 1 to 33) has a pearlite structure hardness within a certain range as compared with the comparative rail steel (steel: 59 to 61). Thus, wear resistance and ductility can be ensured.

  Further, as shown in Table 1, Table 2, and FIG. 10, the rail steel of the present invention (steel: 1 to 33) dramatically improves the wear resistance by setting the carbon content to 0.90% or more. .

Based on rail steel with carbon content of 0.65 to 1.20% C, rolling condition equivalent to rail was simulated using steel with 0.20% Co added and steel with 0.50% Ni added. The figure which showed the result of having done the laboratory rolling experiment and having done the tension test by the relationship between the carbon content of steel, and the total elongation value. Rolling conditions equivalent to rails using steel with a carbon content of 1.00% and steel with 0.05%, 0.20%, and 0.50% addition of Co, and with varying amounts of Ni. The figure which showed the result of having done the lab rolling experiment which simulated NO, and having done the tension test by the relationship between Ni addition amount and total elongation value. The figure which showed the result of having done the abrasion test using the steel shown in FIG. 2 by the relationship between Ni addition amount and abrasion amount. The figure which showed the name in the head cross-section surface position of the rail of this invention. The figure which illustrated the test piece collection position in the abrasion test shown in Table 1 and Table 2. FIG. The figure which showed the outline | summary of the abrasion test shown in Table 1 and Table 2. FIG. The figure which showed specimen collection in the tension test shown in Table 1 and Table 2. FIG. The figure which showed the relationship of carbon amount and the total elongation value as a result of the head tension test of the present invention rail steel shown in Table 1 and the comparative rail steel shown in Table 2 (Ni / Co value is out of range). The figure which showed the result of the head tension test of this invention rail steel shown in Table 1, and the comparison rail steel shown in Table 2 (the value of Ni / Co is out of range) in relation to the amount of carbon and the amount of wear. The figure which showed the result of the head abrasion test of this invention rail steel, and showed the relationship between carbon amount and wear amount.

Explanation of symbols

1: head part 2: head corner part 3: head side part 4: rail test piece 5: mating material 6: cooling nozzle

Claims (11)

  In mass%, C: 0.65 to 1.20%, Si: 0.05 to 2.00%, Mn: 0.05 to 2.00%, Co: 0.05 to 0.50%, Ni: In steel rails containing 0.10 to 2.25% and the balance being Fe and inevitable impurities, the ratio of Ni content% / Co mass% relative to Ni is 2.0 to 4.5. A pearlite rail excellent in wear resistance and ductility, characterized in that at least a part of a head surface portion of the steel rail has a pearlite structure.   The pearlite rail excellent in wear resistance and ductility according to claim 1, wherein C is in a range of 0.90 to 1.20%.   3. The composition according to claim 1, further comprising at least one of Cr: 0.01 to 2.00% and Mo: 0.01 to 0.50% in mass%, with the balance being Fe and inevitable. A pearlitic rail with excellent wear resistance and ductility, characterized by impurities.   The composition according to any one of claims 1 to 3, further comprising one or two of V: 0.005 to 0.50% and Nb: 0.002 to 0.050% in mass%, and the balance A pearlite rail excellent in wear resistance and ductility, characterized by comprising Fe and inevitable impurities.   The wear resistance according to any one of claims 1 to 4, further comprising, in mass%, B: 0.0001 to 0.0050%, and the balance consisting of Fe and inevitable impurities. Perlite rail with excellent ductility.   The wear resistance according to any one of claims 1 to 5, further comprising Cu: 0.05 to 1.00% by mass and the balance comprising Fe and inevitable impurities. Perlite rail with excellent ductility.   In any 1 item | term of Claims 1-6, in mass%, Ti: 0.0050-0.0500%, Mg: 0.0005-0.0200%, Ca: 0.0005-0.0150% A pearlite rail excellent in wear resistance and ductility, characterized in that it contains one or two of the following, and the balance consists of Fe and inevitable impurities.   The wear resistance according to any one of claims 1 to 7, further comprising Al: 0.0100 to 1.00% in mass%, and the balance comprising Fe and inevitable impurities. Perlite rail with excellent ductility.   The wear resistance according to any one of claims 1 to 8, further comprising, in mass%, Zr: 0.0001 to 0.2000%, and the balance comprising Fe and inevitable impurities. Perlite rail with excellent ductility.   The wear resistance according to any one of claims 1 to 9, further comprising N: 0.0060 to 0.0200% in mass%, and the balance being composed of Fe and inevitable impurities. Perlite rail with excellent ductility.   In any one of Claims 1-10, the range of at least 20 mm in depth is a pearlite structure | tissue from the head corner part and head top surface in the said steel rail, and the hardness is Hv320-500 A pearlite rail with excellent wear resistance and ductility characterized by being in a range.

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