JP4415735B2 - Cooling method of high temperature rail - Google Patents

Description

  The present invention relates to a method for cooling a high-temperature rail, particularly to a high-temperature rail immediately after hot rolling or a high-temperature rail heated to austenite temperature or higher for heat treatment after hot rolling. The present invention relates to a method for cooling a high-temperature rail in which a portion is forcibly cooled by a cooling medium such as air or water in order to satisfy a target strength of the material.

  In order to make the rail head the target strength on the material and to improve its wear resistance and toughness, the high-temperature rail immediately after hot rolling or after hot rolling to a temperature above the austenite temperature for heat treatment A heat treatment (SQ) for forcibly cooling the heated high-temperature rail with a cooling medium such as air or water in a state of being restrained by a clamp is performed.

  From the viewpoint of making the rail head the target strength on the material, it is only necessary to forcibly cool only the rail head. However, if only the rail head is forcibly cooled, the temperature difference between the top and bottom of the rail is large. As a result of the relatively large residual stress inside the rail, when the rail clamp is removed, the rail will bend significantly and a subsequent pressing process for shape correction will be required. The problem of harming arises.

  In order to prevent such a problem, for example, in Patent Document 1 and Patent Document 2, as shown in FIG. 1, an upper header 2 provided on the head 1 a side of the rail 1 and a sole portion of the rail 1 are provided. A method is disclosed in which the sole 1b is forcibly cooled after the head 1a of the rail 1 is forcibly cooled by a cooling medium injected from the lower header 3 provided on the 1b side. Patent Document 3 also discloses a method of forcibly cooling only the sole 1b with a cooling medium for a predetermined time and then forcibly cooling the head 1a (hereinafter referred to as the prior art).

Japanese Patent Laid-Open No. 61-60827 JP 63-114923 A JP-A-10-130730

  According to the prior art, the residual bending after cooling can be reduced as compared with the case where only the rail head is cooled. However, a device that detects the bending of the rail during the forced cooling of the head 1a of the rail 1 and controls the cooling of the rail sole 1b by the lower header 3 is expensive, or the lower header When the strong cooling is performed to shorten the cooling time of the rail sole 1b due to 3, the cooling rate of the rail foot becomes too fast, and there is a problem that an abnormal structure such as martensite is generated in the rail foot.

  Therefore, the equipment cost becomes high, or the rail sole 1b has to be cooled for a long time with extremely slow cooling, and only the sole 1b is cooled in advance. The problem remains that production efficiency is hindered.

  As described above, with the technology disclosed in the preceding patent document, it is difficult to improve the production efficiency beyond the current level while suppressing the equipment cost.

  An object of the present invention is to provide a method for cooling a high-temperature rail that can improve the production efficiency beyond the current level without incurring equipment costs.

  The present invention has been made to achieve the above-described object, and is characterized by the following.

  Invention of Claim 1 is a steel composition heated more than the austenite temperature, and is mass%, C: 0.65-0.90%, Si: 0.1-0.9%, Mn: 0.5 to 2.0%, P: 0.035% or less, S: 0.035% or less, Nb: 0.005 to 0.1%, the balance: a high-temperature rail substantially made of Fe , And simultaneously start forced cooling with a cooling medium for the rail foot and the rail head, and at this time, the rail head is strongly cooled compared to the rail foot and the rail foot and Cooling of both of the rail heads is performed until the transformation of the rail heads is completed, and thus the heads are made to have a target strength on the material while minimizing the bending of the rails. It is.

  In addition to the composition described in claim 1, the invention described in claim 2 further includes, in mass%, Cr: 1% or less, Cu: 1% or less, Ni: 1% or less, Mo: 0.5% or less. V: Contains one or more of 0.2% or less, and the remainder: a high-temperature rail substantially made of Fe, and simultaneously forcibly cooling the rail sole and the rail head with a cooling medium. At this time, the rail head is strongly cooled compared to the rail sole, and both the rail sole and the rail head are cooled until the transformation of the rail head is completed. Thus, the present invention is characterized in that the head is made to have a target strength on the material while minimizing the bending of the rail.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein air is used as a cooling medium, and the cooling air volume of the rail foot is within a range of 40 to 80% of the cooling air volume of the rail head. It has the characteristics in that.

  According to the method of the present invention, the forcible forced cooling of the sole is unnecessary, the bending generated in the rail after releasing the clamp restraint is extremely small, and the bending in the subsequent cooling process hardly occurs. This eliminates the need for a pressing process for correction, improves production efficiency at a low cost, and is extremely useful industrially.

  In the present invention, a high-temperature rail heated to a temperature higher than that of the austenite region is fixed by a bending restraining clamp, and as shown in FIG. 1, it is injected from the lower header 3 provided on the sole 1b side. The forced cooling of the rail head portion 1a by the upper header 2 provided on the rail head portion 1a side together with the rail foot portion 1b is simultaneously started by the cooling medium such as air or water, and the head portion 1a and the sole portion As shown in FIG. 2, the cooling of both 1b is performed for a time until the transformation of the head is completed, so that the rail head 1a has a target strength on the material. Then, the clamp for restraining the bending of the rail is removed.

  First, the reason for limiting the steel composition in this invention will be described. In addition,% of a component composition shows the mass%.

C: 0.65-0.90%
C is a basic element for ensuring wear resistance as a whole pearlite structure. If it is less than 0.65%, the entire pearlite structure cannot be formed, or a cementite fraction sufficient to ensure wear resistance cannot be secured. On the other hand, if it exceeds 0.90%, pro-eutectoid cementite is generated in a part of the rail, and the toughness may be significantly impaired. Therefore, the C content is in the range of 0.65 to 0.90%.

Si: 0.1 to 1%
Si is contained in an amount of 0.1% or more as a deoxidizing material, but if it exceeds 1%, weldability is remarkably impaired. Therefore, the Si amount is set to 0.1 to 1%.

Mn: 0.5 to 2.0%
Mn not only has a deoxidizing effect, but also has the effect of lowering the temperature at which it transforms from austenite to pearlite, reducing the pearlite layer spacing to increase strength, and improving wear resistance and fatigue damage resistance. If it is less than 0.5%, the desired effect cannot be sufficiently obtained. On the other hand, if it exceeds 2.0%, martensite is produced in the segregated part during SQ, and martensite is produced during cooling after welding, which impairs the quality. Therefore, the amount of Mn is set to a range of 0.5 to 2.0%.

P: 0.035% or less When P exceeds 0.035%, toughness deteriorates. The amount of P is limited to 0.035% or less.

S: 0.035% or less When S exceeds 0.035%, the amount of non-metallic inclusions increases, and the quality such as toughness and fatigue damage resistance is remarkably impaired. S amount is limited to 0.035% or less.

Nb: 0.005 to 0.1%
Nb combines with C to precipitate finely as carbide during hot rolling or after hot rolling, refine the austenite structure, and then refine the pearlite structure obtained by transformation. Since the austenite structure is refined, it has the effect of increasing the transformation temperature, and suppresses the formation of martensite and provides the desired material properties without the need for extremely slow cooling for a long time. Obtainable.

  In order to obtain desired mechanical properties, Cr: 1% or less, Cu: 1% or less, Ni: 1% or less, Mo: 0.5% or less, V: 0.2% or less More seeds can be added.

Cr: 1% or less Cr basically improves the strength and hardness by solid solution strengthening. However, if added over 1%, the weldability is impaired, and martensite is generated during cooling after welding, and the material is damaged. Therefore, the Cr content is limited to 1% or less.

Cu: 1% or less Cu, like Cr, basically improves strength and hardness by solid solution strengthening. However, when it is added in excess of 1%, cracking of the slab becomes particularly remarkable, making it difficult to obtain a product. Therefore, the amount of Cu is limited to 1% or less.

Ni: 1% or less Ni also basically improves the strength, hardness and toughness by solid solution strengthening. However, even if added in excess of 1%, the effects of improving strength, hardness and toughness are saturated, but the economic efficiency is remarkably impaired. Therefore, the amount of Ni is limited to 1% or less.

Mo: 0.5% or less Mo also has an effect of improving strength and hardness basically by solid solution strengthening. However, if added over 0.5%, not only martensite is produced during cooling after welding, but the economy is impaired. Therefore, the Mo amount is limited to 0.5% or less.

V: 0.2% or less V has the effect of improving strength and hardness by solid solution strengthening and bonding with C to form carbides and precipitation strengthening. However, if added over 0.2%, the weldability is impaired. Therefore, the V amount is limited to 0.2% or less.

  In addition to the elements described above, adding other elements as long as the effects of the present invention are not impaired does not cause a significant difference.

  Next, the reasons for limiting the cooling conditions will be described.

  As the cooling medium, mist or the like can be used as appropriate at a cooling rate within a range in which martensite and bainite are not generated in the rail head, including air.

  The forced cooling by the cooling medium for the rail sole and the rail head starts simultaneously. Prior to this, it is not necessary to cool the soles slowly, and the production efficiency can be improved.

  Cooling is performed until the pearlite transformation of the head is completed. This makes it possible to obtain material properties such as desired strength, toughness, and wear resistance as a rail. At this time, it is necessary to make the cooling of the rail sole portion weaker than the cooling of the head. In particular, the foot portion is thin in appearance and has a small heat capacity. Therefore, it is necessary to cool down the head more so as to suppress the formation of martensite.

  In particular, when air is used as the cooling medium, it is necessary that the cooling air volume at the sole is 40% to 80% of the cooling air volume at the head. If the amount of cooling air at the soles is less than 40% of the amount of cooling air at the head, the desired cooling effect cannot be obtained. As a result, it is necessary to cool for a long time, which impairs production efficiency. On the other hand, if it is larger than 80%, martensite may be generated particularly at the toe portion. Therefore, particularly when air is used as the cooling medium, the cooling air volume at the sole is limited to 40% or more and 80% or less of the cooling air volume at the head.

  As described above, by limiting the rail steel composition and cooling conditions described above, it is possible to produce a pearlite steel rail that has good production efficiency, minimizes bending, and has no abnormal structure such as martensite. .

  Next, the present invention will be further described with reference to examples.

  A long rail that has been hot-rolled at 910 ° C. is divided into 25 m lengths, the rails thus divided are loaded into a heat treatment (SQ) device, and the rails are clamped to restrain bending. Fixed. Table 1 shows the chemical composition of the steel composition of the rail used at this time.

Next, from the state where the temperature of the rail head portion 1a is 780 ° C., the cooling air volume of the rail foot 1b relative to the cooling air volume of the rail head portion 1a by the air as the cooling medium injected from the lower header 3 shown in FIG. The ratio and the cooling times t ₁ and t ₂ shown in FIG. 2 were set as shown in Table 2, and cooling was started. In either case, t ₂ is the time required for the target intensity on the material of the rail head. After cooling for ₂ hours, air injection from the upper header 2 and the lower header 3 is stopped, and then the rail is removed from the clamp and the rail is taken out of the heat treatment (SQ) device, and then the rail is naturally cooled on the cooling floor. . Table 2 shows the hardness (Hv) of the depth of 1 mm from the surface layer of the foot sole in the center of the rail sole 1b after natural cooling, the form of the structure of the rail sole 1b, and the rail of the 25 m rail in a state where it is laid down Also shows the vertical bending of the rail.

In the first and second embodiments according to the present invention, both the rail head 1a and the rail sole 1b are forcibly cooled by setting the cooling time t ₁ = 0 seconds and t ₂ = 150 seconds shown in FIG. . In both cases, the rail bent out of the 25 m rail after the rail is taken out of the heat treatment (SQ) device and naturally cooled in the cooling floor without causing abnormal structure in the rail sole 1b is within 50 mm above and is good. Met. This can also be applied to specifications that regulate downward bending. Comparative Example 3 is the result of forced cooling of the rail rolled from the comparative steel C by setting the cooling time in the same manner as in Example 1 and Example 2, but the bending of the 25 m rail was good at 60 mm above. However, a martensite structure occurred in the rail sole 1b. Comparative Example 4 compares the flow rate of cooling air to the rail sole 1b so that the martensite structure of the rail sole 1b that occurs in Comparative Example 3 is prevented and the bending of the 25m rail is within 100 mm. This is a reduction from Example 4. If the flow rate of the cooling air with respect to the rail sole 1b is reduced, the bend of the 25 m rail increases, so that it is necessary to set t ₁ = 30 seconds. Comparative Example 1 and Comparative Example 2 are obtained by applying the cooling conditions implemented in Comparative Example 4 to the steel of the present invention. In either case, the 25 m rail could be bent within 100 mm without generating a martensite structure in the rail sole 1b, but it was necessary to set t ₁ = 30 seconds. Moreover, since all became a downward curve, it cannot adapt to the specification which controls the downward curve.

  In Comparative Example 1, Comparative Example 2, and Comparative Example 4, the 25 m rail can be bent within 100 mm without generating a martensite structure in the rail sole 1b. Since the cooling time was longer than 30 seconds, the productivity was lowered. In addition, it cannot be applied to specifications that regulate downward bending.

  This heat treatment condition is for making the rail head 1a in the heavy load rail have a target strength in material, and all the steel types used in the rail of the present invention generate an abnormal structure in the rail sole 1b. It has been found that a rail with few bends can be manufactured without heat treatment and with a short heat treatment.

It is a layout view of a rail cooling header used in the method of the present invention. It is a figure which shows the time change of the air flow rate for rail cooling.

Explanation of symbols

1: Rail 1a: Rail head 1b: Rail sole 2: Upper header 3: Lower header

Claims (3)

As a steel composition heated above the austenite temperature,
C: 0.65-0.90%,
Si: 0.1-0.9%
Mn: 0.5 to 2.0%
P: 0.035% or less,
S: 0.035% or less,
Nb: 0.005 to 0.1%
Containing
The rest: substantially Fe
Constraining the high-temperature rail consisting of, and simultaneously starting forced cooling by the cooling medium for the rail foot and the rail head, at this time, strongly cooling the rail head compared to the rail foot, The cooling of both the rail foot and the rail head is performed until the transformation of the rail head is completed, and thus the head is made to have a target strength on the material while minimizing the bending of the rail. A method for cooling a high-temperature rail. In addition to the composition of claim 1,
Cr: 1% or less Cu: 1% or less Ni: 1% or less Mo: 0.5% or less V: 0.2% or less containing 1 type or 2 types or more,
The rest: substantially Fe
Constraining the high-temperature rail consisting of, and simultaneously starting forced cooling by the cooling medium for the rail foot and the rail head, at this time, strongly cooling the rail head compared to the rail foot, The cooling of both the rail foot and the rail head is performed until the transformation of the rail head is completed, and thus the head is made to have a target strength on the material while minimizing the bending of the rail. A method for cooling a high-temperature rail.   The air according to claim 1 or 2, wherein air is used as the cooling medium, and a cooling air volume of the rail sole is within a range of 40 to 80% of a cooling air volume of the rail head. Cooling method for high temperature rails.

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