JPH0734133A - Production of high-strength bainite steel rail having excellent surface damage resistance - Google Patents

Abstract

PURPOSE:To provide a process for production of the high-strength bainite steel rail imparted with the wear resistance of a GC part in addition to rolling fatigue damage resistance. CONSTITUTION:The top of the rail which consists of a steel contg. 0.15 to 0.45% C, 0.15 to 1.20% Si, 0.30 to 2.00% Mn and 0.50 to 3.00% Cr and at least one kind among Mo, Ni, Cu, Nb, V, Ti and B at need is cooled at 1 to 10 deg.C/sec from the temp of gamma region or above from the flanks thereof and the accelerated cooling is stopped between 500 and 350 deg.C; thereafter, the rail is cooled at 1 to 40 deg.C/min down to ordinary temp., by which the high-strength bainite steel rail having 300 to 400Hv hardness in the summit of the rail and >=400Hv hardness of the corner parts of the top and the excellent surface damage resistance is obtd. As a result, the surface damage resistance of the summit of the rail laid in a straight section of a heavy load railway and the corner parts at the top of a gentle curvilinear section is improved. The wear resistance of the corner parts of the top of the rail laid at the outer track of the rapidly curving section of the high-speed passage railway, etc., and the surface damage resistance of the rail top of the inner track are improved by the high-strength bainite structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of surface damage resistance of a rail top portion and a head corner portion of a gentle curve section laid in a straight section of a heavy-duty railway, and a sharp curve section of a high-speed passenger railway. The present invention relates to a high-strength bainite steel rail for the purpose of improving the wear resistance of the head corner portion of the rail laid on the outer gauge and the surface damage resistance of the inner rail head surface.

[0002]

2. Description of the Related Art In recent years, the energy efficiency and transportation efficiency of railway transportation have been re-recognized, and as a part of this, the tendency toward higher speed and heavier loading has become stronger than ever. In heavy-duty railways, we have aggressively worked to increase the strength and hardness of rail materials in order to deal with rail wear in sharp curves that accompany heavy loading. As a result, we achieved high strength and high hardness by refining the pearlite structure, and significantly improved rail wear in curved sections. On the other hand, however, further improvement in transportation efficiency is planned, and along with this, increase in rail wear and surface damage in straight sections and gentle curve sections has become a problem. Conventionally, in heavy-duty railways, the rail surface is ground and rectified at regular intervals in order to deal with such surface damage, and the cost required for track maintenance tends to increase more and more. Furthermore, from the viewpoint of track maintenance,
Improving the toughness of high-strength rails is also an important issue from the viewpoint of ensuring safety, and further labor saving and longer life of laying rails are of utmost concern.

In addition, not only the Shinkansen but also the conventional lines have been proposed for speeding up railway transportation, and along with this, damage to the surface of the rail head that occurs during high-speed operation in straight sections has occurred. Rail material has become an important issue. On the other hand, conventionally, high-strength heat-treated rails, which heat-treat ordinary carbon steel pearlite structure rails by heat treatment, have been used in the sharply curved sections of passenger railways. Local wear is generated at the corners of the parts, causing peeling damage at the boundary with the rail head surface where the wear is not so severe, causing noise and vibration. There was a problem that occurred.

[0004]

The rails laid in the straight section and the gently curved section, which have become apparent due to the heavy load of the heavy-duty railway, are frequently damaged by the surface. The frequency of rectification by the grinding of the rail surface that is being carried out is also extremely frequent, and in order to reduce the track maintenance work, the self-removal effect of the rolling fatigue layer that is the cause of the surface damage, that is, proper wear promotion is the cause of surface damage. It is a point to suppress the generation and reduce the grinding work. On the other hand, even for high-speed passenger railroads with relatively light loads, high-strength rails with a finer pearlite structure have been conventionally laid on the outer gauge rails in sharp curve sections, but wear of the head corners could be suppressed. However, there is a problem that peeling damage occurs due to damage being generated on the top surface side of the head and abrasion being suppressed also on the head surface of the inner rail.

As shown in FIG. 1, the recently developed bainite steel rail having high strength and being easily worn has a feature that the wear amount is larger than that of the conventional pearlite steel rail even if the hardness is higher. The bainite structure is generated in the as-rolled state without special cooling control on the rail head, and the fatigue damage layer on the rail head surface accumulated by repeated contact of the wheels in the straight section is removed by abrasion. In the high-speed meandering operation section, the plastic deformation generated because the wheel flange is strongly pressed against the rail corner,
A high-strength, high-alloy bainite steel rail that prevents surface damage due to plastic flow is disclosed. This rail is C; 0.15-0.45% by weight%, Si; 0.15-
1.20%, Mn; 0.30 to 1.00%, Cr; 2.
In a steel rail containing 0 to 4.00%, Mo; 0.20 to 0.60%, and if necessary, one or more of Nb, V, and Ti, the hardness after rolling is Hv370.
Although it is characterized by having the above, it is laid in a straight section of a heavy-duty railway and has almost proper hardness to prevent surface damage generated on the rail top surface, but it has a gentle curve or this In a meandering section with a driving condition close to, the hardness of the rail head corner is insufficient, so there is a problem that surface damage at the rail head corner cannot be completely prevented. There is a problem in that the peeling damage generated on the surface of the is not completely suppressed.

On the other hand, even in a sharp curve section of a high-speed passenger railway, in order to completely prevent the damage generated on the head surface of the inner rail, it is necessary to pick up the buds of the surface damage due to the wear according to the curvature. Yes, wear control with proper hardness is required. In the outer rail, the head corners are less likely to wear, and the rail top surface needs to be worn to some extent in order to completely prevent surface damage. From this point of view, as a rail for a sharp curve section of an ultra-high-speed passenger railway, the outer rail rail head corner portion is less likely to wear, and the head surface side corner portion surface has a lower hardness to promote wear to some extent. Need to control.

In order to solve such problems, the rail of the present invention eliminates rolling fatigue damage, which causes surface damage by ensuring proper wear, and increases the strength of the rail head. It is intended to suppress the occurrence of surface damage caused by plastic deformation.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to improving the surface damage resistance of the crown and head corners of a heavy-duty railway rail laid in a straight section and the outer gauge of a curved section such as a high-speed passenger railway. The present invention provides a method for producing a high-strength bainite steel rail for the purpose of improving the wear resistance of the head corners of the rail laid on the rail and the surface damage resistance of the inner rail head surface. 0.15 to 0.45%,
Si; 0.15 to 1.20%, Mn; 0.30
2.00%, Cr; 0.50 to 3.00%, and optionally Mo; 0.10 to 0.60%, Ni;
0.05 to 4.00%, Cu; 0.05 to 0.50%,
Nb: 0.01 to 0.05%, V: 0.05 to
0.30%, Ti; 0.01 to 0.05%, B;
Steel containing 0.0005 to 0.0050% of one kind or two or more kinds, and the balance being iron and unavoidable impurities,
A high temperature rail that holds heat above the austenite region temperature, which has been heated for the purpose of finishing hot rolling or heat treatment, is accelerated and cooled at 1 to 10 ° C / sec from the side of the rail head,
The accelerated cooling is stopped between 500 and 350 ° C., and then the temperature is cooled to room temperature at 1 to 40 ° C./min. The rail top hardness is Vickers hardness Hv300 to 400, and the head corner hardness is Vickers hardness Hv400 or more. Is a method of manufacturing a high-strength bainite steel rail having excellent surface damage resistance. That is, the present invention promotes wear by suppressing the hardness of the rail top portion, prevents the rail top surface from being damaged, and reduces the hardness of the rail head corner portion to Hv400.
By the above, a rail is provided which suppresses wear of the rail head corner portion laid in a curved section and a laying environment equivalent to this, and prevents surface damage.

The reason why the present invention is limited to each chemical component as described above will be explained below. C is an important element for securing a certain hardness and stably generating a bainite structure, and if the content is less than 0.15%, it becomes difficult to secure the hardness of the rail steel. Or, a ferrite structure with low resistance to plastic deformation is mixed, and if it exceeds 0.45%, the wear resistance of the rail crown surface is rather improved, and a pearlite structure harmful to the accumulation of rolling fatigue damage damage is formed. 0.15 because it will be generated
Limited to ~ 0.45%. Si is an element that increases the strength by forming a solid solution in the base material in the bainite structure, and if less than 0.15%, its effect cannot be expected, and if it exceeds 1.20%, island-like martensite is contained in the bainite structure. 0.15 because site structure is generated and deteriorates toughness
Limited to ~ 1.20%.

Similar to C, Mn is an element that inexpensively increases the rail hardness. If it is less than 0.3%, these effects are small, and if it exceeds 2.00%, the rolling fatigue damage damage of the rail top surface is similar to C. Therefore, a pearlite structure that is harmful to the accumulation of Pd is generated, so the content is limited to 0.30 to 2.00%. Cr is an important element for finely dispersing the carbide in the bainite structure and ensuring strength, but 0.5%
If it is less than 3.0%, the effect cannot be expected, and if it exceeds 3.00%, the fine carbide rather improves the wear resistance, which is not only harmful to the removal of fatigue damage but also improves the hardenability. , Because a martensite structure is generated in the rail head corner where heat treatment is applied, 0.5
It was limited to 0 to 2.00%.

Further, in the present invention, one or more kinds of Mo, Ni, Cu, Nb, V, Ti, B and the like are added to the above-mentioned composition of components, if necessary. Mo is an important element for stable formation of the bainite structure, and is used for stabilizing the bainite structure depending on the combination of chemical components or heat treatment conditions. The range of addition amount is 0.1
If it is 0 to 0.60% and less than 0.10%, the effect cannot be expected, and if it exceeds 0.60%, the bainite transformation rate is extremely decreased, and a martensite structure is formed in the bainite structure. 0.10 to 0.60%
Limited to. Ni and Cu are also elements that stably generate a bainite structure, and both Ni and Cu are effective in improving the hardness of the bainite structure base by solid solution hardening.
If Cu is less than 0.05%, its effect is small, and 0.50.
%, The red hot brittleness is generated, so 0.05 to 0.
Limited to 50%. Ni is known as an element that relaxes the red hot embrittlement of Cu, but if it is less than 0.05%, its effect and solid solution hardening cannot be expected, and if it exceeds 4.00%, the bainite transformation rate is lowered due to the stabilization of austenite. 0.0 to generate martensitic structure
It was limited to 5 to 4.00%.

Further, by adding an austenite grain refiner such as Nb or Ti, the bainite structure can be refined and the toughness and ductility of the rail steel can be improved. Nb is known as an austenite recrystallization suppressing element, and by combining with controlled rolling during rail rolling, the bainite structure can be further refined. However, the lower limit of addition at which this effect can be expected is 0.
If it is 01% or more, and if it exceeds 0.05%, coarse N
Since the carbonitride of b is generated and rather causes embrittlement,
It was limited to 0.01 to 0.05%. Ti is known as an element for making austenite grains fine during heating during rail rolling, and the effective lower limit addition amount at this time is 0.01%, and if it exceeds 0.05%, Ti carbonitrides become coarse. Turned into
It is harmful because it becomes the starting point of fatigue cracks generated from inside the rail head. Therefore, the addition range of Ti is 0.01 to 0.0
Limited to 5%. V has the action of strengthening the bainite structure material by the precipitation of V (C, N), and this precipitation hardening is effective in preventing the damage generated on the rail head corner surface due to the plastic flow of the metal structure, Since this precipitation hardening does not contribute to the improvement of wear resistance, it is an element which is convenient for promoting wear and preventing the generation of rail crown surface damage intended to remove the rolling fatigue layer. The lower limit of addition of this effect is 0.05%, and if it exceeds 0.30%, V (C,
Since the coarsening of N) causes rather embrittlement,
It was limited to 0.05 to 0.30%. B has an effect of suppressing the generation of ferrite generated from austenite grain boundaries, and is an effective element for stably generating a bainite structure. If it is less than 0.0005%, the effect is weak, and 0.0050%. If added in excess of 0.005, a coarse compound of B is produced and the rail material is deteriorated, so 0.0005-
It was limited to 0.0050%.

According to the present invention, the bainite steel rail having the above-described composition is subjected to hot rolling or heat treatment for the purpose of heat treatment, and from the high temperature which retains heat above the austenite region temperature, the rail head side surface Accelerated cooling at a cooling rate of 1-10 ° C / sec with a pair of nozzles
After cooling is stopped at 500 to 300 ° C., the temperature is cooled to room temperature at 1 to 40 ° C./min, the hardness of the rail top is Vickers hardness Hv300 to 400, and the hardness of the head corner is Vickers hardness Hv400 or more. The high-strength bainite steel rail with excellent surface damage resistance is manufactured. That is, the rail top surface damage generated in the straight section of a heavy-duty railway is promoted and prevented by suppressing the hardness, and the rail head corner surface generated in the relaxation curve section is hardened by increasing the hardness. Suppresses
Further, it is possible to manufacture a rail that suppresses the wear of the outer rail rail head corner portion in the sharp curve section of the high-speed passenger railway and prevents the generation of surface damage on the inner rail top portion.

At this time, the reason for limiting the cooling rate for accelerating cooling the side surface of the high temperature rail to 1 to 10 ° C./sec is 1 ° C./s.
If the cooling rate is slower than ec, it is not possible to make the hardness higher than the target Hv400 at the rail head corner, and if the cooling rate is higher than 10 ° C / sec, the surface of the rail head corner may be overcooled to cause local hardness. Since a martensite structure is generated, it is limited to 1 to 10 ° C / sec.

Here, the hardness of the rail head corner is Hv
The reason for limiting to 400 or more is that in the gentle curve section of the heavy-duty railway, the rail head corner surface damage generated because the wheel is pressed against the rail head corner portion, bainite with the same hardness and greater wear than the pearlite steel. A hardness of Hv 400 or more is required to prevent the structure, and the wear rate is not so large as to cause a problem. Also, when laid on a sharp curve section on a passenger railway with a relatively light load,
A hardness of Hv 400 or higher is required to exert sufficient wear resistance on the outer rail rail corner portion. In addition,
The reason why the hardness of the rail crown is limited to Hv300 to 400 is that if the hardness is less than Hv300, the hardness is insufficient, so that not only surface damage is generated on the crown surface of the inner rail in the curved section, but also wavy wear is generated to improve the speed of the high-speed railway. There is concern that the generation of corrugated wear may occur even in a straight section of a heavy-duty railway. If the rail crown exceeds Hv400, the rolling crown fatigue layer is not removed due to wear to prevent damage to the rail crown surface of heavy-duty railways, and rail crown surface damage is generated early. The hardness range was limited to Hv 300-400.

The cooling stop temperature after accelerated cooling is set to 500
The reason for limiting the temperature to ~ 350 ° C is that if cooling is stopped at a high temperature exceeding 500 ° C, the bainite transformation temperature on the rail head surface will rise due to subsequent heat recovery from inside the rail head, and It becomes impossible to secure the hardness of the top portion and the corner portion. Furthermore, the cooling stop temperature is 3
When the temperature is lower than 50 ° C, not only the martensite structure is generated on the rail head corner surface due to overcooling but also the martensite structure is generated inside the rail head, which reduces the toughness of the rail head and stops cooling. Temperature 500
The range was limited to 350 ° C.

By subjecting the rail head to the heat treatment as described above, damage to the top surface of the rail laid in a straight section in a heavy-duty railway is prevented, and wear of the rail head corner section in a gently curved section is suppressed. At the same time, it is possible to prevent the occurrence of damage on the surface of the corner portion by promoting appropriate wear. In addition, it is possible to provide a long-life rail that simultaneously achieves abrasion control of the outer rail rail head corner portion and damage prevention of the inner rail head surface, which are problems in a sharp curve section of a high-speed railway such as the Shinkansen.

[0018]

EXAMPLES Next, examples of the present invention will be described. Table 1
Shows typical chemical components and heat treatment conditions of the steel of the present invention. Fig. 2 shows the designated parts of the surface position of the cross section of the head of the JIS 60 kilorail, where 1 is the top of the rail and 2 is the top of the rail.
Is the head corner. FIG. 3 shows the hardness distribution in the cross section of the rail head according to the embodiment of the present invention. The hardness of the head corner is higher than the hardness of the crown. The rail of the present invention has a Vickers hardness of Hv300 at the crown.
~ 400, the hardness of the crown is Hv400 or more. FIG. 4 is an experimental evaluation tester (patent registration number 1183162) for evaluating various surface damages on the rail head.
Table 2 shows a schematic view of the invention. In Table 2, the conventional rails of pearlite structure and the comparative steel bainite steel rails of the present invention and the comparative steel bainite steel rails are subjected to predetermined heat treatment, and the bending rails 3 shown in FIG. In the laboratory evaluation test in which the wheel 4 rotates while contacting the head of the above, the test results of obtaining the surface damage occurrence life under the wheel contact condition corresponding to the curved section will be shown. Table 3 shows the test results in which the contact conditions of the wheels corresponding to the straight line section were similarly given. The laboratory evaluation test was carried out by using a wheel used in an actual Shinkansen by bending a rail that had been subjected to a predetermined heat treatment to 6 m with the head inside. The test condition is that the contact condition between the rail and the wheel is reproduced as a contact condition in a curved section, lateral pressure is applied to the wheel, and the wheel flange is pressed against the corner of the rail head to evaluate the damage generated on the surface of the corner of the rail head. In the test, the rail top surface and the wheel center were brought into contact with each other to reproduce the straight section, and the top surface damage occurrence characteristics were evaluated. In addition,
The damage occurrence life is displayed as the cumulative tonnage of trains actually being used on the railway.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

[0022]

According to the present invention, as can be seen from the above examples, the hardness of the rail head corner portion is set to Hv 400 or more, whereby the damage occurrence life of the corner portion surface is significantly improved as compared with the comparative steel. Further, by controlling the hardness of the rail top surface to Hv 300 to 400, the occurrence of surface damage on the rail top surface can be suppressed.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a wear amount, a rail material structure and hardness in a Nishihara-type wear tester.

FIG. 2 is a view showing nominal portions of a rail head cross-sectional surface position.

FIG. 3 is a diagram showing a cross-sectional hardness distribution of the head of an example of the present invention.

FIG. 4 is a schematic view of a surface damage evaluation test machine for a bent rail of an actual rail.

[Explanation of symbols]

 1 Rail top 2 Rail head corner 3 Bending rail 4 Wheel

Claims (2)

[Claims] 1. By weight% C: 0.15 to 0.45% Si; 0.15 to 1.20% Mn; 0.30 to 2.00% Cr; 0.50 to 3.00% However, the balance is steel consisting of iron and unavoidable impurities, and a high temperature rail that retains heat above the austenite region temperature, which is heated for the purpose of finishing hot rolling or heat treatment, is installed from 1 to 10 from the side of the rail head. Cool at ℃ / sec,
The accelerated cooling is stopped between 500 and 350 ° C., and then the temperature is cooled to room temperature at 1 to 40 ° C./min. The rail top hardness is Vickers hardness Hv300 to 400, and the head corner hardness is Vickers hardness Hv400 or more. A method for producing a high-strength bainite steel rail having excellent surface damage resistance, which is characterized by: 2. C-0.15 to 0.45% Si; 0.15 to 1.20% Mn; 0.30 to 2.00% Cr; 0.50 to 3.00% by weight Mo; 0.10 to 0.60% Ni; 0.05 to 4.00% Cu; 0.05 to 0.50% Nb; 0.01 to 0.05% V; 0.05 to 0 30% Ti; 0.01 to 0.05% B; 0.0005 to 0.0050%, one or more, and the balance being iron and inevitable impurities. , Or a high temperature rail that retains heat above the temperature of the austenite region heated for the purpose of heat treatment
Cooling at 0 ° C./sec, stopping accelerated cooling at 500 to 350 ° C., and then cooling to room temperature at 1 to 40 ° C./min, the hardness of the rail top is Vickers hardness Hv 300 to 40
0, Vickers hardness of the head corner is Hv400
A method for producing a high-strength bainite steel rail having excellent surface damage resistance, which is characterized by the above.