JPH06316728A - Production of bainitic steel rail excellent in surface damage resistance - Google Patents

Abstract

PURPOSE:To produce a bainitic steel with surface damage resistance for rapid transit railway. CONSTITUTION:A steel, which has a composition containing 0.15-0.45% C, 0.15-1.00% Si, 0.32-2.00% Mn, and 0.20-2.00% Cr and containing, besides the above, one or >=2 elements among Mo, Cu, Ni, V, Nb, and B, if necessary, is used. The bainitic steel rail excellent in surface damage resistance can be produced by subjecting a high temp. rail having a temperature not lower than gamma-region temp., after the completion of hot rolling or after heating for the purpose of heat treatment, to accelerated cooling at a rate of (1 to 10) deg.C/sec from the side face of a railhead and regulating the hardness at the surface of a railhead corner part to >=Hv300. By this method, dark spot damage occurring in a rail for rapid transit railway, in a straight line section, can be removed by abrasive wear, and also the formation of flaking in a curve section can be prevented by applying heat treatment to a rail GC.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed rail, a rail head gauge corner where a wheel flange is strongly pressed, such as a damage generated on a rail head surface mainly in a straight section, and a high-speed meandering operation section or a gentle curve section. The present invention relates to a method for manufacturing a bainite steel rail having excellent surface damage resistance, which has resistance to surface damage generated on the surface of the portion.

[0002]

2. Description of the Related Art In recent years, railway transportation has been re-evaluated from the viewpoint of its energy efficiency or air pollution, and particularly in passenger railways, speeding up has been vigorously pursued as transportation efficiency. On the other hand, such improved transportation efficiency makes the rail usage environment harsh and requires radical improvement in rail material. That is, since the pearlite structure steel that has been conventionally used for straight sections of passenger railways has excellent wear resistance, fatigue damage accumulates on the rail surface without being removed by wear, and after a certain period of time, the crown surface is shelled. Or surface damage called dark spot damage occurs, which eventually causes rail breakage, which is the most important issue for ensuring safety in high-speed railways. As a countermeasure for this, a method of decreasing the hardness of a conventional pearlite structure rail to promote wear can be considered. However, due to the decrease in strength, rail head gauge corners (GC ) There is a problem that plastic deformation occurs on the surface, peeling damage called flaking is generated, and noise and vibration are generated.

[0003]

On the other hand, in the recently developed bainite steel as a rail material which has high strength and is easily worn, even if the hardness is higher than that of the conventional pearlite structure steel as shown in FIG. Fatigue damage on the top surface of the rail that accumulates due to repeated contact of the wheels in the straight section, because it has the feature of increasing the amount of wear, generates the bainite structure as it is rolled without performing special cooling control on the rail head. The layer is removed by abrasion, and in the curved section or the high-speed meandering operation section, the wheel flange is strongly pressed against the GC part, so that plastic deformation and plastic flow are generated, and resistance to surface damage based on it is also increased. A high alloy bainitic steel invention is disclosed. However,
Conventional bainite steel rails contain a large amount of Cr and Mo and, if necessary, one or more of Nb, V and Ti, and have a high hardness after rolling of Hv 370 or more. Therefore, there is a problem that the weldability is poor and the electric resistance is high, and the influence on the signal cannot be ignored.

The present invention prevents the occurrence of dark spot damage, which is rolling fatigue damage of rails laid in a straight section of a high-speed railway, in which the weldability is not impaired and the increase in electric resistance is minimized, and Prevents flaking damage on the rail GC surface in curved sections and straight sections caused by high-speed meandering operation, and is suitable for rails laid in high-speed sections of conventional line type trains whose train speed is slower than the Shinkansen. A method for manufacturing a bainite steel rail having excellent properties is provided.

[0005]

That is, the gist of the present invention is, by weight, C; 0.15 to 0.45% Si; 0.15.
~ 1.00% Mn; 0.30-2.00% Cr; 0.20
.About.2.00% and, if necessary, Mo; 0.10 to 0.60% Cu; 0.05
~ 0.50% Ni; 0.05-2.00% Ti; 0.01
~ 0.05% V; 0.05-0.30% Nb; 0.01
.About.0.05% B; 0.0005 to 0.0050% of one or two or more types, the balance of which is iron and inevitable impurities, and is heated for the purpose of finishing hot rolling or heat treatment. In addition, the high-temperature rail that retains heat above the austenite region temperature is accelerated and cooled from the side of the rail head at 1-10 ° C / sec to make the hardness of the rail head corner surface Hv300 or higher. It is an excellent method of manufacturing bainite steel rails. That is, in order to deal with flaking damage which may occur due to a decrease in strength of the rail GC portion due to the low alloying, the GC portion is strengthened by heat treatment,
The rail top surface is intended to promote wear and prevent dark spot damage by not increasing strength on the contrary.

The present invention is limited to the above chemical steel components produced in a converter or an electric furnace. The reasons for limiting the respective chemical components will be described below. C is an important element for securing a certain hardness and stably generating a bainite structure, and if it is 0.15% or less, it becomes difficult to secure the hardness of the rail steel and plastic deformation is caused. A ferrite structure with low resistance is mixed in,
If it is 0.45% or more, the wear resistance of the rail top surface is improved, and a pearlite structure harmful to rolling fatigue damage damage accumulation is generated.
Limited to.

Si is an element that increases the strength by forming a solid solution in the base material in the bainite structure, and 0.15%
The effect cannot be expected below, and if it exceeds 1.00%, an island-like martensite structure is formed in the bainite structure and the toughness is deteriorated, so the content is limited to 0.15 to 1.00%.

Like C, Mn is an element that inexpensively increases the rail hardness. If it is less than 0.3%, its 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 the strength.
If it is less than 0.2%, the effect cannot be expected, and if it is 2.00% or more, the carbides become too fine to improve the wear resistance of the rail top surface, which is harmful to the removal of fatigue damage and heat treatment. 0.20 to 2.0 in order to improve the hardenability of the applied GC part and to easily generate a martensite structure.
Limited to 0%.

Further, in the present invention, one or more kinds of Mo, Cu, Ni, Ti, V, Nb, B, etc. are added to the above-mentioned component composition, 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 the added amount is
If it is 0.10 to 0.60% and 0.10% or less, the effect cannot be expected, and if it is 0.60% or more, the transformation rate of the bainite structure is extremely reduced, and the martensite in the bainite structure is reduced. Since the site structure is generated, it is limited to 0.10 to 0.60%.

Cu and Ni are also elements that stably generate a bainite structure, and both Cu and Ni are effective in improving the hardness of the bainite matrix by solution hardening.
If Cu is less than 0.05%, its effect is small and 0.50.
% Is more than 0.05% because it causes red heat brittleness.
It was limited to 0.50%. Ni is known as an element that relaxes the red hot embrittlement of Cu, but if it is 0.05% or less, its effect and solution hardening cannot be expected, and if it is 2.00% or more, the bainite transformation rate decreases due to the stabilization of austenite. In order to facilitate the formation of a martensite structure, the content is limited to 0.05 to 2.00%.

Further, by adding an austenite grain refining element such as Ti, V or Nb, the bainite structure can be made fine and the toughness and ductility of the rail steel can be secured. At this time, the effective Ti addition amount is 0.01
% Or more, and when it exceeds 0.05%, Ti carbonitrides coarsely precipitate and become the starting point of fatigue damage from the inside of the rail, so the content was limited to 0.01 to 0.05%. V is V (C,
The precipitation of N) can strengthen the bainite structure, and since this precipitation hardening does not contribute to wear, it is effective in generating surface damage due to the plastic flow of the metal structure. The lower limit of the amount of addition of this effect is 0.05%.
When it exceeds 30%, V (C, N) is coarsened to cause embrittlement, so the content is limited to 0.05 to 0.30%. Nb also has the same effect as V, but 0.01
% Is the lower limit, and when it exceeds 0.05%, an intermetallic compound of Nb is formed, which rather causes embrittlement.
Limited to ~ 0.05%.

B has an effect of suppressing the formation of ferrite generated from austenite grain boundaries, and is an effective element for stably forming a bainite structure.
If it is 005% or less, its effect is weak, and if it is added in an amount of 0.0050% or more, a coarse compound of B is formed and the rail material is deteriorated, so the content is limited to 0.0005 to 0.0050%.

A bainite steel rail having the above-described composition was played on the side surface of the rail head from a high temperature which retains heat above the austenite region temperature, which is heated for the purpose of finishing hot rolling or heat treatment. A pair of nozzles continuously cools the rail side surface including the rail GC to room temperature at a cooling rate of 1 to 10 ° C./sec so that the surface of the rail GC becomes Hv 300 or more. At this time, at a cooling rate of 1 ° C / sec or less, the GC part cannot obtain the desired high hardness of Hv300 or more, and at 10 ° C / sec or more, G
Since the martensite structure is generated in the C part, the cooling rate range is limited to 1 to 10 ° C / sec. Furthermore, the reason why the hardness of the GC part is limited to Hv300 or higher is that the hardness of less than this causes flaking damage in the GC part of the conventional wire, which is an improvement compared with the conventional pearlitic steel. Therefore, the hardness of the GC part is limited to Hv 300 or more. By this heat treatment method, a high-strength bainite steel excellent in surface damage resistance in a conventional wire can be manufactured at a relatively low cost, and the purpose can be achieved by ensuring a hardness of Hv300 or more.

[0015]

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. In addition, Table 2 shows the results of the evaluation test performed on the bainite steel rail of the present invention and the conventional pearlite rail as a comparative steel and the comparative steel bainite. In the evaluation test, a predetermined heat treatment is applied to a position corresponding to a rail head corner of a rail disk test piece that has been scaled down to 1/4,
Similarly, the comparison result of the surface damage occurrence life of the rail test piece after the water lubrication test by the disk test piece having the wheel shape that has been reduced to 1/4 is shown. As a test condition, the contact condition between the rail and the wheel is reproduced in a straight line section to contact the rail head surface with the wheel center to evaluate the dark spot damage characteristics, and the contact condition in a curved section is reproduced to contact the rail corner portion and the wheel flange. Then, an evaluation test of flaking damage was performed.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

As is apparent from the above examples, according to the present invention, in the bainite steel having the hardness of the GC portion of Hv300 or more, the dark spot damage generation straight line reproduction life is longer than that of the pearlite steel rail of the comparative steel. In the reproduction life of flaking damage generation curve, a significant improvement effect was recognized as compared with the comparative rail having a bainite structure deviating from the steel composition of the present invention.

[Brief description of drawings]

FIG. 1 shows the relationship between the amount of wear in a wear tester and the hardness of a rail material, showing a comparison between a pearlite structure rail material and a bainite structure material.

Claims (2)

[Claims] 1. By weight C; 0.15 to 0.45% Si; 0.15 to 1.00% Mn; 0.30 to 2.00% Cr; 0.20 to 2.00% , The balance is steel consisting of iron and unavoidable impurities, and a high temperature rail that retains heat above the austenite region temperature, which has been heated for the purpose of finishing hot rolling or heat treatment, is installed at 1-10 ° C from the side of the rail head. A method for manufacturing a bainite steel rail with excellent surface damage resistance, characterized by increasing the hardness of the rail head corner surface to Hv300 or more by accelerated cooling at / sec. 2. By weight C; 0.15 to 0.45% Si; 0.15 to 1.00% Mn; 0.30 to 2.00% Cr; 0.20 to 2.00% , Mo; 0.10 to 0.60% Cu; 0.05 to 0.50% Ni; 0.05 to 2.00% Ti; 0.01 to 0.05% V; 0.05 to 0. 30% Nb; 0.01 to 0.05% B; 0.0005 to 0.0050% of one or more kinds of steel, the balance of which is iron and inevitable impurities. Alternatively, a high temperature rail that retains heat above the temperature of the austenite zone heated for the purpose of heat treatment is accelerated and cooled from the side of the rail head at 1 to 10 ° C / sec, and the hardness of the rail head corner surface is Hv300. The bainite steel rail with excellent surface damage resistance characterized by the above Method.