JPWO2016047076A1 - Rail manufacturing method and manufacturing apparatus - Google Patents

Abstract

To provide a rail manufacturing method and a manufacturing apparatus having high ductility in both a head and a foot. The heated rail steel material is hot-rolled, and the temperature is adjusted by cooling the hot-rolled rail steel material, and the temperature-adjusted rail steel material is temperature-controlled and rolled with a reduction in area of 20% or more. Thus, when the rail steel material is processed and the temperature of the rail steel material is adjusted, the surface temperature of the portion of the rail steel material corresponding to the rail-shaped head and foot is cooled to 500 ° C. or higher and 1000 ° C. or lower.

Description

  The present invention relates to a method and an apparatus for manufacturing a pearlite rail excellent in ductility in which rough rolling, finish rolling and heat treatment are performed on a heated bloom, and in particular, by reducing the size of a pearlite block or colony, the ductility is improved. The present invention relates to an improved rail manufacturing method and manufacturing apparatus.

The rail in which the head tissue forms a pearlite structure is generally manufactured by the following manufacturing method.
First, the bloom cast by the continuous casting method is heated to 1100 ° C. or higher, and then hot-rolled into a predetermined rail shape by rough rolling and finish rolling. The rolling method in each rolling process is performed by combining caliber rolling and universal rolling. At this time, rolling is performed in a plurality of passes in rough rolling and in a plurality of passes or a single pass in finish rolling.

The crop at the end of the hot rolled rail is then sawn. The hot-rolled rail has a length of 50 to 200 m. For this reason, when the length of the heat treatment apparatus is limited, the rail is sawed to a predetermined length such as 25 m simultaneously with the saw cutting of the crop.
Further, when the rail is required to have wear resistance, the rail is subjected to heat treatment by a heat treatment apparatus following the hot rolling step (heat treatment step). At this time, since the wear resistance is improved as the heat treatment start temperature is higher, a reheating step for heating the rail may be provided before the heat treatment step. In the heat treatment step, the rail is fixed by a restraining device such as a clamp, and the head, feet, and, if necessary, the abdomen are forcibly cooled using a cooling medium such as air, water, and mist. In the heat treatment step, the forced cooling is usually performed until the head temperature becomes 650 ° C. or lower.

Thereafter, the restriction of the rail by the clamp is released, and the rail is conveyed to the cooling floor. In the cooling floor, the rail is cooled until it becomes 100 ° C. or lower.
For example, rails used in harsh environments such as natural resource mining sites such as coal are required to have high wear resistance and high toughness. For this reason, when manufacturing the rail used in a severe environment, said heat treatment process is needed. However, when the rail manufactured by the above-described process is subsequently subjected to processing such as bending, for example, when the heat treatment is performed, the rail becomes excessively hard and the ductility is lowered, so that processing becomes difficult. Cases arise. For this reason, a rail having high hardness and excellent ductility is required.

For example, Patent Document 1 discloses that the rolling temperature in finish rolling is in the temperature range of Ar3 transformation point to 900 ° C, and the rail is accelerated to at least 550 ° C at a cooling rate of 2 to 30 ° C / sec within 150 seconds after finishing rolling. Thus, a method for improving the ductility of the rail is disclosed.
Patent Document 2 discloses a method of improving the ductility of a rail by performing rolling with a reduction in area of 10% or more in a temperature range of 800 ° C. or lower when performing hot rolling.

JP 2013-14847 A JP 62-127453 A

However, the method described in Patent Document 1 has a problem that the ductility of the foot portion is not improved because temperature control is not performed on the foot portion of the rail.
Further, in the method described in Patent Document 2, there is a problem that the ductility of the foot portion is not improved for the foot portion of the rail because the conditions for temperature adjustment during rolling are not specified.
Then, this invention is made paying attention to said subject, and it aims at providing the manufacturing method and manufacturing apparatus of a rail which have high ductility in both a head and a foot | leg part.

  To achieve the above object, the rail manufacturing method according to one aspect of the present invention hot-rolls a heated rail steel material, adjusts the temperature by cooling the hot-rolled rail steel material, When the temperature-adjusted rail steel material is processed into a rail shape by temperature-adjusting and rolling at a reduction in area of 20% or more, it corresponds to the rail-shaped head and foot when the temperature of the rail steel material is adjusted. The surface temperature of the rail steel material part is cooled to 500 ° C. or higher and 1000 ° C. or lower.

  Moreover, the rail manufacturing apparatus according to one aspect of the present invention includes at least one first rolling mill that rolls the rail steel material, and temperature adjustment by cooling the rail steel material that is rolled by the first rolling mill. And at least one second rolling mill that processes the temperature-adjusted rail steel material into a rail shape by performing temperature-adjusted rolling with a reduction in area of 20% or more, and the cooling device is The surface temperature of the rail steel material corresponding to the rail-shaped head and feet is cooled to 500 ° C. or higher and 1000 ° C. or lower.

  According to the method and apparatus for manufacturing a rail according to the present invention, it is possible to manufacture a rail having high ductility in both the head and the foot.

It is a schematic diagram which shows the manufacturing apparatus of the rail which concerns on one Embodiment of this invention. It is sectional drawing which shows the rough cooling apparatus of one Embodiment of this invention. It is a schematic diagram which shows the heat processing apparatus of one Embodiment of this invention. It is sectional drawing which shows each site | part of a rail. It is explanatory drawing which shows the collection position of the tensile test piece evaluated in the Example. It is explanatory drawing which shows the implementation position of the Brinell hardness test evaluated in the Example.

DESCRIPTION OF EMBODIMENTS Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings. In addition, in the following description, all the% display regarding a chemical component means the mass%.
<Configuration of manufacturing equipment>
First, with reference to FIGS. 1-4, the manufacturing apparatus 1 of the rail 9 which concerns on one Embodiment of this invention is demonstrated. The rail manufacturing apparatus 1 according to the present embodiment includes a heating furnace 2, a rough rolling mill 3A, a finishing rolling mill 3B, a rough cooling apparatus 4, a finishing cooling apparatus 5, a reheating apparatus 6, and a heat treatment apparatus 7. And a cooling line having a cooling bed 8.

  The rail 9 is manufactured by rolling and heat-treating a rail steel material such as bloom continuously cast by the manufacturing apparatus 1. As shown in FIG. 4, the rail 9 includes a head 91 and a foot 93 that extend in the width direction and face each other in the vertical direction in a cross-sectional view perpendicular to the longitudinal direction, and a head 91 disposed on the upper side. And an abdominal portion 92 extending in the vertical direction. Moreover, as the rail 9, for example, steel having the following chemical composition can be used.

C: 0.60% or more and 1.05% or less C (carbon) is an important element for forming cementite, increasing hardness and strength, and improving wear resistance in a pearlite rail. However, if the content is less than 0.60%, the effect is small, so the lower limit is preferably 0.60%, more preferably 0.70% or more. On the other hand, excessive content of C leads to an increase in the amount of cementite, and thus an increase in hardness and strength can be expected, but conversely, ductility is reduced. Further, the increase in the C content expands the temperature range of the γ + θ region, and promotes softening of the weld heat affected zone. Considering these adverse effects, the upper limit of the C content is preferably 1.05%, and more preferably 0.97% or less.

Si: 0.1% or more and 1.5% or less Si (silicon) is added for strengthening the deoxidizer and the pearlite structure, but if the content is less than 0.1%, these effects are small. The content is preferably 0.1% or more, and more preferably 0.2% or more. On the other hand, excessive content of Si promotes decarburization and promotes the formation of surface flaws on the rail 9, so the upper limit of Si content is preferably 1.5%, 1.3% or less More preferably.

Mn: 0.01% or more and 1.5% or less Mn (manganese) has an effect of lowering the pearlite transformation temperature and densifying the pearlite lamellar spacing, and is therefore an effective element for maintaining high hardness inside the rail. Since the effect is small if the content is less than 0.01%, the Mn content is preferably 0.01% or more, and more preferably 0.3% or more. On the other hand, when the Mn content exceeds 1.5%, the equilibrium transformation temperature (TE) of pearlite is lowered and the structure is likely to undergo martensitic transformation. For this reason, it is preferable to make the upper limit of Mn content into 1.5%, and 1.3% or less is more preferable.

P: 0.035% or less P (phosphorus) reduces toughness and ductility when the content exceeds 0.035%. Therefore, the P content is preferably suppressed to 0.035% or less, and more preferably 0.025% or less. In addition, when special refining etc. are performed in order to reduce P content as much as possible, the cost at the time of melting is increased, so the lower limit is preferably made 0.001%.

S: 0.030% or less S (sulfur) forms coarse MnS that extends in the rolling direction and reduces ductility and toughness. For this reason, the S content is preferably suppressed to 0.030% or less, and more preferably 0.015% or less. In addition, in order to reduce S content as much as possible, since the cost increase at the time of smelting, such as the time of smelting treatment and an increase in solvent, is significant, the lower limit is preferably set to 0.0005%.

Cr: 0.1% or more and 2.0% or less Cr (chromium) increases the equilibrium transformation temperature (TE), contributes to the refinement of the pearlite lamellar spacing, and increases the hardness and strength. In addition, the combined use effect with Sb is effective in suppressing the formation of the decarburized layer. Therefore, when Cr is contained, the content is preferably 0.1% or more, and more preferably 0.2% or more. On the other hand, when the Cr content exceeds 2.0%, the possibility of occurrence of weld defects increases, the hardenability increases, and the generation of martensite is promoted. Therefore, the upper limit of the Cr content is preferably 2.0%, and more preferably 1.5% or less.
The total content of Si and Cr is preferably 2.0% or less. This is because, when the total content of Si and Cr exceeds 2.0%, the adhesion of the scale is increased, so that peeling of the scale is hindered and decarburization may be promoted.

Sb: 0.005% or more and 0.5 or less Sb (antimony) has a remarkable effect of preventing decarburization during heating when the rail steel material is heated in a heating furnace. In particular, when added together with Cr, since the Sb content is 0.005% or more and there is an effect of reducing the decarburized layer, when Sb is contained, the content is preferably 0.005% or more, 0.01 % Or more is more preferable. On the other hand, if the Sb content exceeds 0.5%, the effect is saturated, so the upper limit is preferably 0.5%, and more preferably 0.3% or less.
In addition to the above chemical composition, Cu: 0.01% to 1.0%, Ni: 0.01% to 0.5%, Mo: 0.01% to 0.5%, V: One or more elements of 0.001% or more and 0.15% or less and Nb: 0.001% or more and 0.030% or less may be contained.

Cu: 0.01% or more and 1.0% or less Cu (copper) is an element capable of further increasing the hardness by solid solution strengthening. Cu is also effective in suppressing decarburization. In order to expect this effect, the Cu content is preferably 0.01% or more, and more preferably 0.05% or more. On the other hand, when the Cu content exceeds 1.0%, surface cracks due to embrittlement tend to occur during continuous casting or rolling. For this reason, it is preferable to make the upper limit of Cu content into 1.0%, and it is more preferable to set it as 0.6% or less.

Ni: 0.01% or more and 0.5% or less Ni (nickel) is an element effective for improving toughness and ductility. Moreover, since it is an element effective for suppressing Cu cracking by adding it in combination with Cu, it is desirable to add Ni when Cu is added. However, since these effects cannot be obtained when the Ni content is less than 0.01%, the lower limit is preferably 0.01%, and more preferably 0.05% or more. On the other hand, when the Ni content exceeds 0.5%, the hardenability is excessively increased and the generation of martensite is promoted. Therefore, the upper limit is preferably set to 0.5%, and is 0.3% or less. More preferably.

Mo: 0.01% or more and 0.5% or less Mo (molybdenum) is an element effective for increasing the strength. However, if the content is less than 0.01%, the effect is small, so the lower limit is 0.01%. And more preferably 0.05% or more. On the other hand, when the Mo content exceeds 0.5%, the hardenability is increased and martensite is generated, so that toughness and ductility are extremely lowered. Therefore, the upper limit of the Mo content is preferably 0.5%, and more preferably 0.3% or less.

V: 0.001% or more and 0.15% or less V (Vanadium) is an element that forms VC or VN and precipitates finely in ferrite and contributes to high strength through precipitation strengthening of ferrite. V also functions as a hydrogen trap site, and can be expected to suppress delayed fracture. For this purpose, the V content is preferably 0.001% or more, and more preferably 0.005% or more. On the other hand, the addition of V exceeding 0.15% causes the effect to saturate, but the increase in the alloy cost is significant, so the upper limit is preferably made 0.15%, 0.12% or less More preferably.

Nb: 0.001% or more and 0.030% or less Nb (niobium) raises the non-recrystallization temperature of austenite and is effective for refinement of pearlite colonies and block sizes by introducing processing strain into austenite during rolling Therefore, it is an effective element for improving ductility and toughness. In order to acquire the said effect, it is preferable that Nb content is 0.001% or more, and it is more preferable that it is 0.003% or more. On the other hand, when the Nb content exceeds 0.030%, Nb carbonitrides crystallize during the solidification process during the casting of the rail steel material, and lowers the cleanliness. Therefore, the upper limit is preferably 0.030%. And 0.025% or less is more preferable.

  The balance other than the above components is Fe (iron) and inevitable impurities. As unavoidable impurities, N (nitrogen) can be mixed up to 0.015%, O (oxygen) up to 0.004%, and H (hydrogen) up to 0.0003%. Moreover, in order to suppress the deterioration of rolling fatigue characteristics due to hard AlN or TiN, it is desirable that the Al content is 0.001% or less and the Ti content is 0.001% or less.

The heating furnace 2 is a continuous or batch-type heating furnace, and heats a rail steel material such as bloom continuously cast to a predetermined temperature.
The rough rolling mill 3A is a universal rolling mill that hot-rolls a steel material at a predetermined area reduction rate, and a plurality of the rolling mills are provided. In the example shown in FIG. 1, the manufacturing apparatus 1 has n rough rolling mills 3A1 to 3An. Of the rough rolling mills 3A1 to 3An, a rough cooling device 4 is provided between the kth rough rolling mill 3Ak and the (k + 1) th rough rolling mill 3Ak + 1 in the rail 9 conveyance direction.

  The finish rolling mill 3B is a universal rolling mill that finally processes the roughly rolled rail 9 into a target rail shape by further hot rolling. In this embodiment, the area reduction rate of the rail 9 rolled between the k + 1th rough rolling mill 3Ak + 1 and the finishing rolling mill 3B, which is a rolling process after the rough cooling device 4, is 20% or more. Here, the area reduction rate in the present embodiment indicates the area reduction rate of the cross-sectional area perpendicular to the longitudinal direction of the rail steel material, and the amount of reduction in the cross-sectional area accompanying rolling relative to the cross-sectional area in the state before rolling such as bloom. Indicates the ratio.

As shown in FIG. 2, the coarse cooling device 4 includes a head cooling nozzle 41, a foot cooling nozzle 42, a head thermometer 43, a foot thermometer 44, a transfer table 45, and guides 46a and 46b. And a control unit 47.
The head cooling nozzle 41 cools the head 91 by injecting a cooling medium onto the head 91 of the rail 9. The foot cooling nozzle 42 cools the foot 93 by injecting a cooling medium onto the foot 93 of the rail 9. The cooling medium sprayed from the head cooling nozzle 41 and the foot cooling nozzle 42 is spray water. The head cooling nozzle 41 and the foot cooling nozzle 42 are respectively provided above the head 91 and the foot 93 on the positive y-axis direction side, and are inclined to the head 91 and the foot 93 with a tilt in the y-axis direction. Are injected respectively. A plurality of head cooling nozzles 41 and foot cooling nozzles 42 are provided side by side in the z-axis direction perpendicular to the xy plane that is the longitudinal direction of the rail 9.

The head thermometer 43 and the foot thermometer 44 are non-contact type thermometers that respectively measure the surface temperatures of the head 91 and the foot 93 of the rail 9 to which the cooling medium is injected. The portions 93 are provided to face each other in the x-axis direction. The measurement results of the head thermometer 43 and the foot thermometer 44 are transmitted to the control unit 47.
The conveyance table 45 is a conveyance roll extending in the x-axis direction, and a plurality of conveyance tables 45 are provided side by side in the z-axis direction. The guides 46a and 46b are plate-like members and are provided extending in the z-axis direction. Further, the guides 46 a and 46 b are arranged on the y-axis positive direction side that is above the conveyance table 45 and on both ends in the longitudinal direction of the conveyance table 45. Further, the guides 46a and 46b are provided with openings 461a and 461b, respectively, at positions where the head thermometer 43 and the foot thermometer 44 are disposed.

The control unit 47 controls the conditions of the cooling medium ejected from the head cooling nozzle 41 and the foot cooling nozzle 42 based on the measurement results of the head thermometer 43 and the foot thermometer 44, so that the rail 9 Is cooled to a predetermined surface temperature. The cooling medium spraying conditions are, for example, the cooling medium spraying amount, the spraying pressure, the moisture amount, the spraying time, and the like.
The rough cooling device 4 having the above configuration is provided between the k-th rough rolling mill 3Ak and the k + 1-th rough rolling mill 3Ak + 1 among the plurality of rough rolling mills 3A arranged in the rolling direction of the rail 9, and the k-th The surface temperature of the head portion 91 and the foot portion 93 of the rail 9 that is rolled by the rough rolling mill 3Ak is controlled.

The finish cooling device 5 is provided immediately before the finish rolling mill 3B, and controls the surface temperatures of the head portion 91 and the foot portion 93 of the rail 9 rolled by the finish rolling mill 3B. The finish cooling device 5 has the same configuration as the rough cooling device 4 shown in FIG.
In addition, the rail 9 is conveyed and rolled in a falling posture as shown in FIG. 2 when being rolled or cooled by the rough rolling mill 3A, the rough cooling device 4, the finishing cooling device 5 and the finishing rolling mill 3B.

The reheating device 6 is an induction heating type heating device, and heats the head 91 of the rail 9 to a predetermined temperature.
As shown in FIG. 3, the heat treatment apparatus 7 includes head cooling headers 71 a to 71 c, a foot cooling header 72, a head thermometer 73, and a control unit 74. The head cooling headers 71a to 71c are provided to face the top surface of the head 91 and the side surfaces of both sides, respectively, and cool the head 91 by injecting a cooling medium onto the top surface and both sides of the head. The foot portion cooling header 72 is provided to face the foot back surface of the foot portion 93, and cools the foot portion 93 by injecting a cooling medium onto the foot back surface. Air, water, mist, or the like is used as a cooling medium sprayed from the head cooling headers 71 a to 71 c and the foot cooling header 72. A plurality of head cooling headers 71 a to 71 c and a foot cooling header 72 are provided side by side in the longitudinal direction of the rail 9. The head thermometer 73 is a non-contact thermometer and measures the surface temperature of the head 91. The temperature measurement result of the head thermometer 73 is transmitted to the control unit 74. The control unit 74 controls the cooling of the rail 9 by controlling the injection conditions of the cooling medium injected from the head cooling headers 71 a to 71 c and the foot cooling header 72 according to the temperature measurement result of the head thermometer 73. Control the speed. The heat treatment apparatus 7 having the above configuration cools the rail 9 at a predetermined cooling rate until a predetermined surface temperature is reached. The heat treatment apparatus 7 has a clamp (not shown). The clamp is a device that restrains by clamping the foot portion of the rail 9.
The cooling floor 8 is a facility that naturally cools the rail 9, and includes, for example, a pedestal that supports the rail 9.

<Rail manufacturing method>
Next, the manufacturing method of the rail 9 which concerns on one Embodiment of this invention is demonstrated.
First, bloom, which is a rail steel material cast by the continuous casting method, is carried into the heating furnace 2 and heated until it reaches 1100 ° C. or higher.
Next, the heated rail steel material is rolled so as to have a substantially rail shape by the rough rolling mills 3Aa to 3Ak on the upstream side in the transport direction from the rough cooling device 4. In addition, below, what is in the middle of hot rolling is also called a rail steel material.

Furthermore, the rail steel material rolled by the rough rolling mills 3Aa to 3Ak is until the surface temperature of the portion corresponding to the head portion 91 and the foot portion 93 of the rail 9 becomes 500 ° C. or higher and 1000 ° C. or lower in the rough cooling device 4. Cooling (temperature adjustment). At this time, the control unit 47 cools the rail steel material by controlling the injection amount, the injection pressure, the moisture amount, the injection time, and the like of the cooling medium.
When the rail steel material is heated to 1100 ° C. or higher, the entire structure is transformed into austenite. In the austenite structure at 1000 ° C. or higher, the grain boundary is easy to move, and recrystallization causes coarsening of crystal grains. On the other hand, when rolling is performed, the crystal grains are distorted, and the crystal grains are divided and refined. At this time, when the temperature at the time of rolling is 1000 ° C. or less, recrystallization and coarsening of crystal grains hardly occur. For this reason, the crystal grain refined | miniaturized by rolling becomes difficult to coarsen by making the temperature of the rail steel raw material at the time of rolling into 1000 degrees C or less.

  Further, when the rail steel material is cooled by the coarse cooling device 4, it is preferable to adjust the temperature until the surface temperature of the portion corresponding to the head portion 91 and the foot portion 93 becomes 500 ° C. or higher and 730 ° C. or lower. When the rail steel material is cooled to 730 ° C. or less, a part of the structure undergoes pearlite transformation, so that the structure of the rail steel material becomes a two-phase structure of untransformed austenite and pearlite. When austenite and pearlite are compared, since the yield strength of austenite is low, most of the strain enters austenite grains, and the structure becomes finer than when the structure during rolling is a single austenite phase. The final pearlite colony size and block size are affected by the crystal grain size of the austenite pre-transformation structure. For this reason, when the austenite grain is coarse, the pearlite colony size and the block size are also coarsened, so that the ductility is lowered. On the other hand, when the austenite grains are fine, the pearlite colony size and the block size are miniaturized, thereby improving ductility.

Furthermore, when the temperature of the rail 9 during rolling is less than 500 ° C., the structure undergoes pearlite transformation completely, so that austenite grains do not exist. Therefore, the pearlite colony size and block size are not miniaturized, and improvement in ductility cannot be expected.
Since the above phenomenon occurs regardless of the portion of the rail 9, the toughness and ductility can be improved by performing rolling after adjusting the temperature at the portion corresponding to the head portion 91 and the foot portion 93. .

Thereafter, the rail steel material whose temperature has been adjusted by the coarse cooling device 4 is further rolled by the coarse rolling mills 3Ak + 1 to 3An.
Next, the rail steel material roughly rolled by the rough rolling mills 3A1 to 3An is cooled by the finish cooling device 5 as necessary, and then rolled by the finish rolling mill 3B, and the rail 9 having a desired shape is obtained. Become. Note that rolling in the rough rolling mills 3Ak + 1 to 3An and the finishing mill 3B after the temperature adjustment is also referred to as temperature adjustment rolling. The reduction in area of the rail steel material that is temperature-rolled is 20% or more. By setting the area reduction rate to 20% or more, the inside of the rail steel material can be strained, so that the inside of the rail 9 can be miniaturized. On the other hand, when the area reduction rate is less than 20%, the strain entering the surface of the rail steel material is large, but the strain entering the interior is small. For this reason, it becomes difficult to miniaturize the inside of the rail 9, and the amount of improvement in ductility is reduced.

Furthermore, the rail 9 hot-rolled by the rough rolling mill 3A and the finish rolling mill 3B is conveyed to the reheating device 6 and heated until the surface temperature of the head 91 becomes 730 ° C. or higher and 900 ° C. or lower.
Thereafter, the heated rail 9 is transported to the heat treatment apparatus 7 where it is forcibly cooled (heat treatment) until the surface temperature of the head 91 becomes 600 ° C. or lower in a state of being restrained by a clamp. The At this time, the control unit 74 calculates the cooling rate of the rail 9 from the temperature measurement result of the head thermometer 73, and the head cooling header so that the average cooling rate is 1 ° C./second or more and 10 ° C./second or less. The injection conditions of the cooling medium injected from 71a-71c are controlled. Moreover, the control part 74 is controlled so that it may become the same conditions as either of the head cooling headers 71a-71c also about the injection conditions of the cooling medium injected from the leg cooling header 72. FIG.

  When the surface temperature of the head 91 is lower than 730 ° C. before the heat treatment, part or all of the tissue undergoes pearlite transformation. Before the heat treatment, the pearlite lamellar spacing becomes coarse due to natural cooling and a slow cooling rate. Therefore, by performing reheating so that the surface temperature of the head 91 becomes 730 ° C. or higher before the heat treatment, the pearlite structure is reversely transformed into the austenite structure, and the lamellar structure can be recreated again. On the other hand, the higher the surface temperature of the head 91, the more hardened the decarburized layer on the surface and the higher the cooling rate inside the rail, so that the wear resistance can be improved. However, when the surface temperature of the head 91 is higher than 900 ° C., the above effect is reduced. Furthermore, when the surface temperature of the head 91 is higher than 1000 ° C., recrystallization and coarsening of austenite grains occur, which is not preferable. Therefore, considering the saving of energy required for reheating and the effect of improving wear resistance, the upper limit of the surface temperature during reheating before heat treatment is preferably set to 900 ° C.

In order to achieve high wear resistance, it is effective to reduce the pearlite lamellar spacing. In order to achieve finer pearlite lamellar spacing, heat treatment at a high cooling rate is required. Therefore, the surface temperature and the average cooling rate are preferably performed within the above ranges. When the cooling rate is less than 1 ° C./second, the pearlite lamellar spacing becomes coarse and the wear resistance decreases. On the other hand, when the cooling rate exceeds 10 ° C./second, the transformation structure becomes a structure such as bainite or martensite, which has a significantly reduced toughness and ductility, which is not preferable. In this embodiment, the average cooling rate is a cooling rate obtained from the temperature change amount and the heat treatment time from the start to the end of the heat treatment. For this reason, the heat history from the start to the end of the heat treatment includes heat generation due to transformation heat and isothermal holding due to patenting. When the surface temperature of the head 91 at the end of the heat treatment exceeds 600 ° C., the lamellar structure is partially spheroidized after the end of the heat treatment, so that the lamellar spacing becomes coarse and wear resistance decreases.
Next, the accelerated and cooled rail 9 is conveyed to the cooling floor 8 and naturally cooled until it reaches about 100 ° C. or less. After cooling in the cooling floor 8, the rail 9 is corrected as necessary when there is a bend or the like. By passing through the above process, the rail 9 excellent in ductility and abrasion resistance is manufactured.

<Modification>
The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  For example, in the above embodiment, the cooling method in the coarse cooling device 4 and the finish cooling device 5 is spray cooling using spray water as a cooling medium, but the present invention is not limited to such an example. For example, the cooling method in the coarse cooling device 4 and the finish cooling device 5 includes spray cooling using mist as a cooling medium, mist cooling, or mist cooling using mist and air as cooling medium and blast cooling. Mixed cooling may be used. Further, instead of spray cooling in the rough cooling device 4 and the finish cooling device 5, natural cooling, immersion cooling, blast cooling, water column cooling, and the like may be performed. In natural cooling and blast cooling, since the cooling rate is slow, the time until cooling to a predetermined temperature becomes long. For this reason, when it is desired to increase the rolling pitch, other cooling methods such as spray cooling, immersion cooling, and water column cooling can be considered. However, since the water column cooling is too fast, it is difficult to adjust the cooling rate. Furthermore, when the rail 9 is transported in a falling posture, water accumulates in the abdomen 92 of the rail 9 and a portion where the cooling rate is excessively high is generated. there's a possibility that. On the other hand, spray cooling has an advantage that it can secure a somewhat high cooling rate and can easily limit cooling points. For this reason, it is preferable to use spray cooling for the cooling method in the rough cooling device 4 and the finish cooling device 5.

  Furthermore, in the said embodiment, although temperature-controlled rolling was performed by the rolling pass after rough rolling mill 3Ak + 1, this invention is not limited to the example which concerns. The temperature-adjusted rolling may be performed by any roughing mill 3A or later as long as the area reduction rate can be secured by 20% or more. At this time, the rough cooling device 4 is provided immediately before the rough rolling mill 3A where the temperature adjustment rolling is started. Moreover, temperature-controlled rolling may be performed at the time of finish rolling by the finish rolling mill 3B. At this time, the rail manufacturing apparatus 1 is not provided with the coarse cooling device 4, and the temperature may be adjusted only by the finishing cooling device 5. In addition, when temperature control rolling is performed by finish rolling, since it is necessary to finish-roll with a large area reduction ratio of 20% or more, the shape of the rail 9 may be deteriorated. For this reason, it is preferable that temperature control rolling is performed at the time of rolling by a part of rough rolling mill 3A and the finishing mill 3B.

Furthermore, in the said embodiment, although rough rolling mill 3A and finishing rolling mill 3B were universal rolling mills, this invention is not limited to this example. For example, the coarse rolling mill 3A and the finishing rolling mill 3B may be caliber rolling mills. Since the universal rolling method enables rolling from a plurality of directions as compared with the caliber rolling method, the rolling load can be reduced. In particular, in the present invention, the rolling operation capable of obtaining a large reduction in area at low temperatures is performed, so that the load on the roll and the rolling mill is excessively increased and the risk of equipment trouble is increased. For this reason, it is preferable that at least one of the rough rolling mill 3A and the plurality of finish rolling mills 3B is a universal rolling mill.
Further, a plurality of finish rolling mills 3B may be provided.

Furthermore, in the said embodiment, although the reheating apparatus 6 was set as the induction heating type heating apparatus, this invention is not limited to this example. For example, the reheating device 6 may be a burner type heating device. In addition, since the induction heating type reheating device 6 can reduce the size of the equipment as compared with the burner type, it is preferable to install it in-line.
Moreover, in the said embodiment, although the reheating apparatus 6 heated the head 91, this invention is not limited to this example. For example, the reheating device 6 may be configured to heat the entire rail 9. In addition, when the rail 9 is used, since the part which contacts a wheel will be worn out, especially in the head 91, abrasion resistance is required. Therefore, when reheating, the configuration in which only the head 91 is reheated is economically superior because energy required for heating can be reduced.

  Furthermore, in the said embodiment, although it reheated with the reheating apparatus 6 after hot rolling, the reheating with the reheating apparatus 6 does not need to be performed. At this time, the hot-rolled rail 9 is conveyed to the heat treatment apparatus 7 and subjected to heat treatment in the heat treatment apparatus 7. Even if reheating is not performed, the ductility improvement effect of the head portion 91 and the foot portion 93 can be obtained, but when the temperature of the rail 9 after the end of hot rolling (after the end of temperature adjustment rolling) is low, Hardness is lower than when it is high. In addition to the reheating, the heat treatment in the heat treatment apparatus 7 can be omitted. At this time, the hot-rolled rail 9 is conveyed to the cooling bed 8 and cooled to about 100 ° C. or less. Even if reheating and heat treatment are not performed, the effect of improving the ductility of the head portion 91 and the foot portion 93 can be obtained, but the hardness is reduced as compared with the case where reheating and heat treatment are performed.

<Effect of embodiment>
(1) The manufacturing method of the rail 9 which concerns on the said embodiment is temperature-controlled by hot-rolling the heated rail steel raw material, cooling the rail steel raw material hot-rolled, and temperature-controlled rail steel. When the material is processed into a rail shape by temperature-adjusting rolling with a reduction in area of 20% or more, when the temperature of the rail steel material is adjusted, the part of the rail steel material corresponding to the rail-shaped head and foot parts The surface temperature is cooled to 500 ° C. or higher and 1000 ° C. or lower.
According to the said structure, a crystal grain can be parted and refined | miniaturized, preventing the coarsening of the crystal grain by recrystallization in an austenite temperature range at the time of temperature control rolling. For this reason, the toughness and ductility of the head 91 and the foot 93 of the rail 9 can be improved.

(2) After the temperature adjustment rolling, the rail 9 is heat-treated at an average cooling rate of 1 ° C./second or more and 10 ° C./second or less until the head surface temperature of the rail 9 becomes 600 ° C. or less.
According to the said structure, the pearlite lamellar space | interval of the head 91 of the rail 9 can be refined | miniaturized, and abrasion resistance can be improved. In addition, since the spherical structure of the lamellar structure after the heat treatment can be prevented, wear resistance is improved.

(3) Before heat-treating the rail 9, when the head surface temperature of the rail 9 is lower than 730 ° C., the rail is reheated to 730 ° C. or higher.
According to the above configuration, the pearlite structure is reversely transformed into the austenite structure, and the lamellar structure can be recreated again. Therefore, the hardness and wear resistance of the rail 9 can be improved.
(4) When the rail 9 is reheated, only the head portion 91 of the rail 9 is reheated.
According to the said structure, the energy concerning heating can be decreased compared with the case where the whole rail 9 is reheated.

(5) The rail 1 manufacturing apparatus 1 according to the above embodiment includes at least one first rolling mill 3A1 to 3Ak that rolls a rail steel material, and a rail steel material that is rolled by the first rolling mill 3A1 to 3Ak. The cooling device 4 that adjusts the temperature by cooling the steel, and at least one second rolling mill 3Ak + 1 that processes the temperature-adjusted rail steel material into a rail shape by performing temperature-adjusted rolling at a reduction in area of 20% or more. The cooling device 4 cools the surface temperature of the portion of the rail steel material corresponding to the rail-shaped head portion 91 and the foot portion 93 to 500 ° C. or more and 1000 ° C. or less.
According to the said structure, the effect similar to (1) can be acquired.

Next, Example 1 performed by the present inventors will be described.
In Example 1, the rail manufacturing apparatus 1 described in FIG. 1 was used to manufacture the rail 9 under different component conditions and rolling conditions, and the total elongation of the manufactured rail 9 was measured.
Table 1 shows the chemical component conditions of the rail 9 used in Example 1. The balance is iron and inevitable impurities. Table 2 shows the rolling conditions and the measurement results of total elongation in Example 1.

In Example 1, first, the continuously cast bloom was heated in the heating furnace 2 to 1100 ° C. As shown in Table 2, the chemical component of the bloom used in Example 1 was any one of Component A to Component G in Table 1.
Next, the heated bloom was extracted from the heating furnace 2 and hot-rolled with a roughing mill 3A and a finishing mill 3B. A plurality of rolling mills combining a universal rolling mill and a caliber rolling mill were used as the rough rolling mill 3A. The rolling rail 9 is rolled and transported in a falling posture. In addition, when performing hot rolling, temperature adjustment was performed by either the rough cooling device 4 or the finish cooling device 5 until the surface temperatures of the head portion 91 and the foot portion 93 became 500 ° C. or higher and 1000 ° C. or lower. Table 2 shows the temperature adjustment method, the time from the start of temperature adjustment rolling to the end of hot rolling, and the number of temperature adjustment rolling passes. The temperature-adjusted rolling refers to hot rolling after adjusting the temperature.

  As shown in Table 2, in Example 1, the temperature was adjusted by any one of spray cooling, blast cooling, and natural cooling. In the case of spray cooling, the water density and the cooling time are adjusted, and in the case of natural cooling, the cooling time is controlled without using the rough cooling device 4 and the finish cooling device 5, so that the head 91 and the foot 93 are controlled. The surface temperature of was adjusted.

  Further, the number of temperature-adjusted rolling passes shown in Table 2 indicates the number of passes that have been rolled after the temperature is adjusted by any of the methods described above. For example, when the number of temperature-adjusted rolling passes is 1, it indicates that only finish rolling is performed after temperature adjustment. When the number of temperature-adjusted rolling passes is n (n ≧ 2) times, n-1 times after temperature adjustment. It shows that rough rolling and one finish rolling were performed. In addition, when the number of temperature-adjusted rolling passes is 1, the temperature is adjusted using the finishing cooling device 5, and when the number of temperature-adjusted rolling passes is n, the temperature is adjusted using the coarse cooling device 4. went.

  After hot rolling, the rail 9 was forcibly cooled by the heat treatment device 7. The surface temperatures of the head 91 and the foot 93 when starting forced cooling were the conditions shown in Table 2. When forced cooling was performed, the average cooling rate was 3 ° C./second, and cooling was performed until the surface temperature reached 400 ° C. Moreover, when performing forced cooling, mist was used for the cooling medium. In Example 1, the reheating process using the reheating device 6 was not performed after the hot rolling.

Next, the forcibly cooled rail 9 was transported to the cooling floor 8 and cooled to 100 ° C. or lower, and then correction such as bending was performed.
After manufacturing the rail 9 by the above process, specimens were collected from four ends of the rail 9 in the longitudinal direction, 1/4 position, 1/2 position, and 3/4 position, and various physical properties were measured. . As shown in FIG. 5, samples 9a and 9b were collected from the head 91 and the foot 93, respectively, of the test specimens collected at each position in the longitudinal direction. The sample 9a is a JIS No. 4 test piece taken from a position where the distance d2 = 12.7 mm from the upper end of the head 91 and the distance d1 = 24.6 mm from the center in the width direction. The sample 9b is a JIS No. 4 test piece collected from the lower end of the foot portion 93 at a distance d3 = 12.7 mm and from the center in the width direction.

In Example 1, as an example in which the chemical composition, the temperature adjustment method, the number of temperature-adjusted rolling passes, the surface temperature, and the area reduction rate are different, the rail 9 is manufactured under 28 kinds of conditions of Examples 1-1 to 1-28, Total elongation was evaluated.
As shown in Table 2, as Comparative Examples, Comparative Examples 1-1 to 1-5 in which the surface temperature and the area reduction rate during temperature-adjusted rolling are outside the range of the above-described embodiment are also described in Examples 1-1 to 1-1. Rail 9 was manufactured under the same conditions as 1-28, and the total elongation was evaluated. In addition, the value of the total elongation shown in Table 2 shows the average value of a total of 4 samples of 1 sample each collected from the test piece collected from 4 places.

  In all the conditions of Examples 1-1 to 1-28, it was confirmed that the total elongation of the head 91 and the foot 93 was 12% or more as a target. In addition, Examples 1-14, 1-15, 1-19, and 1-20 in which the surface temperature of either the head 91 or the foot 93 during temperature-adjusted rolling is 730 ° C. or lower are the heads having a low surface temperature. It was confirmed that the elongation of the portion 91 or the foot portion 93 was as high as 17% or more. Furthermore, in Example 1-8 in which the surface temperatures of both the head 91 and the foot 93 during temperature-controlled rolling are 730 ° C. or less, the total elongation of the head 91 and the foot 93 is as high as 19% or more. It was confirmed.

  On the other hand, in Comparative Example 1-1 in which the surface temperature of the foot part 93 during temperature-adjusted rolling exceeds 1000 ° C. and Comparative Example 1-2 in which the area reduction rate of the foot part 93 during temperature-adjusted rolling is less than 20% The elongation of the foot portion 93 was less than 12%, which was lower than those of Examples 1-1 to 1-28. Further, Comparative Examples 1-3 and 1-4 in which the surface temperature during temperature-controlled rolling is less than 500 ° C. or over 1000 ° C., and Comparative Example 1 in which the rolling reduction of the head 91 during temperature-controlled rolling is less than 20%. In −5, the elongation of the head 91 was less than 12%, which was lower than those of Examples 1-1 to 1-28.

Next, Example 2 implemented by the present inventors will be described.
In Example 2, the influence on the total elongation, the hardness, and the surface structure due to the heat treatment conditions was confirmed by changing the chemical components, the temperature-adjusted rolling and the heat treatment conditions. Table 3 shows the chemical composition, surface temperature during temperature-adjusted rolling, heat treatment (forced cooling) conditions, measurement results of total elongation, measurement results of hardness, and observation results of the head surface structure in Example 2.

  In Example 2, as temperature control rolling, a total of four passes of rolling consisting of three universal rolling mills and one caliber rolling mill were performed so that the head portion 91 and the foot portion 93 had a reduction in area of 30%. The surface temperature of the head portion 91 and the foot portion 93 during the temperature-adjusted rolling, and the start temperature, the cooling rate, and the end temperature during the heat treatment were as shown in Table 3. When the heat treatment was performed, air was used as a cooling medium when the cooling rate was 3 ° C./second or less, and air and mist were mixed into the cooling medium when the cooling rate exceeded 3 ° C./second. Other manufacturing conditions were the same as in Example 1.

  About the total elongation of the rail 9, the test piece was extract | collected by the method similar to Example 1, and the total elongation was measured. As for the hardness of the rail 9, the head shown in FIG. 6 is obtained from a test piece having a thickness of about 20 mm that is cut from four ends of the longitudinal end, the 1/4 position, the 1/2 position, and the 3/4 position of the rail 9. A sample 9c was taken from the part surface position and a sample 9d was taken from the head internal position. The sample 9c was taken from the center of the upper end surface of the head 91 of the test piece polished to remove the surface irregularities. Sample 9d was collected from the center in the width direction of the test piece polished to remove the irregularities on the surface and from a position d4 = 20 mm away from the upper end of the head 91. Next, the hardness of the collected samples 9c and 9d was measured by a Brinell hardness test. Regarding the surface texture, the surface texture of the sample 9c collected was observed.

  In Example 2, as an example in which the chemical composition, the surface temperature during temperature-adjusted rolling, and the conditions during heat treatment are different, the rail 9 is manufactured under 21 types of conditions of Examples 2-1 to 2-21, and the total elongation and The hardness was measured and the surface texture was further observed. In Example 2-13, heat treatment was not performed, and the rail 9 after hot rolling was transported to the cooling bed 8 and cooled to 100 ° C. or lower. After the rail 9 became 100 ° C. or lower, the bending or the like was corrected.

  Moreover, as shown in Table 3, as Comparative Examples, the same conditions as in Examples 2-1 to 2-21 were also applied to Comparative Examples 2-1 to 2-3 in which the cooling rate during the heat treatment exceeded the range of the above embodiment. The rail 9 was manufactured by measuring the total elongation and hardness, and the surface structure was observed. The values of total elongation and hardness shown in Table 3 are average values of 4 samples collected from test pieces collected from 4 locations.

In Examples 2-1 to 2-21 which were heat-treated at a cooling rate of 0.5 ° C./second or more and 10 ° C./second or less, the total elongation of the head 91 and the foot 93 was 12% in all conditions. It was confirmed that this was the case.
In Examples 2-2 and 2-3, the surface temperature of the head 91 at the time of temperature-adjusted rolling was low compared to other conditions, so the surface temperature at the start of heat treatment was also low, and the total elongation of the head 91 was 15 % And higher than other conditions. However, in Examples 2-2 and 2-3, the hardness of the head 91 was 380 HB or less, which was lower than that in Example 2-1.

  In Examples 2-1 and 2-7 to 2-10 having the same conditions except for the cooling rate during the heat treatment, and in Examples 2-14 to 2-21 having different components, the faster the cooling rate, the higher the head The surface and internal hardness of 91 improved. Moreover, the conditions except the cooling rate at the time of heat processing are the same as in Examples 2-1, 2-7 to 2-10, 2-14 to 2-21, and the cooling rate is higher than 10 ° C./second. In Examples 2-1 to 2-3, since the cooling rate was excessively high, part of the structure was transformed into martensite, and the total elongation was very low at 3%.

In Examples 2-1, 11-12, and 12-12 under the same conditions except for the end temperature at the time of heat treatment, the hardness of the surface and the inside of the head 91 improved as the cooling stop temperature decreased. In Example 2-11 in which the end temperature during the heat treatment was 650 ° C., part of the pearlite structure was spheroidized.
In Example 2-13 where heat treatment was not performed, the total elongation of the head 91 and the foot 93 was 12% or more, but the hardness of the surface and the inside of the head 91 was the lowest among all conditions. . Furthermore, in Example 2-13, a part of the pearlite structure was spheroidized.

Next, Example 3 performed by the present inventors will be described.
In Example 3, in order to confirm the influence of the reheating treatment on the hardness and the surface structure, reheating was performed before the heat treatment under the conditions of Example 2-3 in which the hardness was low. Example 3 was the same as Example 2-3 except for the surface temperature of the head 91 at the time of temperature-adjusted rolling and reheating. Table 4 shows the chemical composition, surface temperature during temperature-controlled rolling, conditions during reheating and heat treatment, measurement results of total elongation, measurement results of hardness, and observation results of the head surface structure in Example 3. In addition, the value of the total elongation and hardness shown in Table 4 shows the average value of a total of 4 samples of each 1 sample each collected from the test piece extract | collected from 4 places.

In Example 3, the head 91 or the entire rail 9 was reheated by the reheating device 6 after hot rolling. The reheating device 6 is an induction heating type heating device, and can heat the head 91 or the entire rail 9 according to the conditions shown in Table 4. The surface temperature of the head 91 after reheating is the start temperature during the heat treatment shown in Table 4.
In Example 3, the rail 9 was manufactured under nine types of conditions of Examples 3-1 to 3-9, in which the surface temperature of the head 91 during temperature-controlled rolling and the reheating conditions were different, and the total elongation and hardness were measured. Further, the surface texture was observed. The sample collection method for total elongation and hardness and the sample collection method for surface texture observation are the same as in Example 2. In addition, Example 3-1 is the conditions which did not implement reheating, and is the same manufacturing conditions as Example 2-3.

As shown in Table 4, in all the conditions of Examples 3-1 to 3-9, it was confirmed that the total elongation of the head 91 and the foot 93 was 12% or more as a target.
In Example 3-1, in which reheating was not performed, the surface temperature at the start of temperature-adjusting rolling was low, so the surface temperature of the head 91 at the start of heat treatment was as low as 630 ° C. The hardness was low.

In Examples 3-2 and 3-6, although reheating was performed and the surface temperature of the head 91 at the start of the heat treatment was set to 700 ° C., the surface temperature was as low as 730 ° C. or less, and thus similar to Example 3-1. Further, the hardness of the surface and the inside of the head 91 was low.
In Examples 3-3 to 3-5 in which the entire rail 9 was reheated and Examples 3-7 to 3-9 in which only the head 91 was reheated, Example 3-2 in which the temperature after reheating was low , 3-6, it was confirmed that the hardness of the surface of the head 91 was improved by 20 HB or more and by 5 HB or more inside. Further, it was confirmed that there is no difference in the effect of improving the hardness of the head 91 between when the entire rail 9 is reheated and when only the head 91 is reheated. Furthermore, when Examples 3-4, 3-5, 3-8, and 3-9 were compared, there was no difference in the hardness of the head 91, so reheating was performed when the surface temperature after reheating reached 900 ° C or higher. It was confirmed that there was no difference in the hardness improvement effect by.
From the above results, according to the rail manufacturing method and manufacturing apparatus according to the present invention, it was confirmed that the rail 9 having high ductility in both the head 91 and the foot 93 can be manufactured.

DESCRIPTION OF SYMBOLS 1: Manufacturing apparatus 2: Heating furnace 3A, 3A1-3An: Rough rolling mill 3B: Finish rolling mill 4: Rough cooling apparatus 41: Head cooling nozzle 42: Foot cooling nozzle 43: Head thermometer 44: Foot temperature Total 45: Transfer table 46a, 46b: Guide 461a, 461b: Opening 5: Finishing cooling device 6: Reheating device 7: Heat treatment device 71a-71c: Head cooling header 72: Foot cooling header 73: Head thermometer 74: Control unit 8: Cooling floor 9: Rail 91: Head 92: Abdomen 93: Foot

Claims (5)

Hot rolled steel rail material,
The temperature is adjusted by cooling the rail steel material that has been hot-rolled,
The temperature-adjusted rail steel material is processed into a rail shape by temperature-adjusting rolling at a surface reduction rate of 20% or more,
When the temperature of the rail steel material is adjusted, the surface temperature of the portion of the rail steel material corresponding to the rail-shaped head and feet is cooled to 500 ° C. or higher and 1000 ° C. or lower. Method.   After the temperature adjustment rolling, the rail is heat-treated at an average cooling rate of 1 ° C / second or more and 10 ° C / second or less until the surface temperature of the head portion of the rail becomes 600 ° C or less. Item 2. A method for manufacturing a rail according to Item 1.   The rail manufacturing method according to claim 2, wherein the rail is reheated to 730 ° C. or higher when the surface temperature of the head of the rail is 730 ° C. or lower before heat-treating the rail.   The rail manufacturing method according to claim 3, wherein only the head of the rail is reheated when the rail is reheated. At least one first rolling mill for rolling rail steel material;
A cooling device for adjusting the temperature by cooling the rail steel material rolled by the first rolling mill;
At least one second rolling mill that processes the rail-steel material that has been temperature-adjusted into a rail shape by performing temperature-adjusted rolling at a reduction in area of 20% or more;
Have
The said cooling device cools the surface temperature of the site | part of the said rail steel raw material corresponded to the said rail-shaped head and leg | foot to 500 to 1000 degreeC, The manufacturing apparatus of the rail characterized by the above-mentioned.

Images