RU2139946C1 - Rails from low-alloyed heat-treated perilit steel featuring high wear resistance and weldability and method of their production - Google Patents

Abstract

FIELD: rails made from perlitic steel featuring considerably improved wear resistance and weldability and meeting requirements of main railroads, and processes of rail production. SUBSTANCE: rail steel contains, wt.%: C 0.85-1.20; Si 0.10-1.00; Mn 0.20-1.50; Cr 0.50-1.00; or contains C 0.85-1.20; Si 0.40-1.00; Mn 0.20-0.40; Cr 0.35-0.50. In this case, total content of Si/4+Mn/2+Cr ranges from 0.8 to 1.8 wt.%. Rail steel contains one or, at least, two elements taken from group including Mo, V, Nb and B, the balance iron and inevitable impurities. Steel rails has perlitic structure to depth of, at least, 20 mm from angle and upper surface of rail head as initial point. Perlitic structure features Vickers hardness of, at least, 320, and difference between Vickers hardness of main metal and metal of welded joint does not exceed 30 to prevent wear depression resulted from local wear of rail upper part in point of weld without affecting its weldability. EFFECT: higher efficiency. 7 cl, 12 dwg, 16 tbl

Description

 The invention relates to pearlitic steel rails having significantly improved wear resistance and weldability (welding performance, weld characteristics), which are required for rails used on main railways, as well as a method for their production.

 The present invention relates in particular to rails in which a difference in hardness between a rail weld and a base metal of a rail can be controlled in a predetermined range so that recesses can be prevented from being caused by wear of the surface of the rail head at the weld point without compromising while the weldability of the rail, as well as the production process of these rails.

BACKGROUND OF THE INVENTION
To further increase the efficiency of rail transportation, an increase in the speed and weight of trains is taking place. Such efficient rail transport means toughening the operating conditions of the rails, which in turn requires further improvement of the materials from which the rails are made. In particular, overseas rails laid in curved sections of the main railway tracks experienced a sharp increase in wear, which caused concern over the service life of the rails. However, due to recent advances in the field of hardening heat treatment processes, the high-strength (high hardness) rails described below were obtained using eutectoid steel with a fine-grained pearlite structure. This led to a significant increase in the service life of rails on curved sections of the track of the main railways.

(1) Heat treated rails for extra heavy loads having a sorbitol structure or fine-grained pearlite structure of the rail head (Publication of the Examined Japanese Patent (Kokoku) N 54-25490); and
(2) The manufacturing process of high-strength rails with a strength of at least 130 kgf / mm ² , including the operation of accelerated cooling of the rail head, subjected to finish rolling or re-heating, from the temperature of austenization to a temperature of from 850 to 500 ^o C at a speed of from 1 to 4 ^o C / s (Publication of the Japanese Examined Patent (Kokoku) N 63-23244).

 The features of these rails, which are high-strength rails, are associated with the use of eutectoid carbon steel for their manufacture, and the rails must have wear resistance by reducing the distance between the plates in the pearlite structure.

 On the other hand, rail joints are welded in order to prevent the possibility of destruction and reduce the cost of maintenance and control. As a result, in practice, rails are used in the form of long rails. However, it is known that in a welded joint that has been reheated to an austenitizing temperature, the cooling rate after welding is completed is slower than the cooling rate of the head subjected to heat treatment during rail production, resulting in a decrease in the hardness of the welded joint with the formation of a softer section. The softer section has a tendency to local wear upon contact with train wheels, which leads to the appearance of wear depressions on the upper surface of the rail. The consequence is serious problems associated with noise and vibration arising from the passage of trains, and these problems include deterioration in the quality of railway tracks.

The following method is used as a countermeasure:
the welded joint of the rail immediately after welding or after reheating is subjected to heat treatment with accelerated cooling so that its hardness rises to approximately the level inherent in the base metal of the rail. However, this raises a new problem associated with this method, which consists in increasing the duration of the welding operation and reducing the production efficiency. Accordingly, a softer portion on the welded joint of the rail immediately after welding is not allowed, as described below. As a result, it was possible not only to improve - wear resistance, but also weldability (welding performance).

 (3) The production process of heat-treated rails made of low alloy steel with increased wear resistance and improved weldability (welding performance, weld characteristics) with the addition of alloying elements such as Cr, Nb, etc. (Publication of the Examined Japanese Patent (Kokoku) N 59-19173).

 However, in recent years, in connection with the desire to further improve the efficiency of rail transportation, the load on the rails of the main railways continued to grow. As a result, even in the case of using the rails described above, it is impossible to provide wear resistance and prevent the occurrence of wear depressions on the upper surface of the rail heads under the influence of local wear of welded joints, which is associated with an increase in the contact pressure of the wheels. As a result, shortening the service life, the occurrence of noise and vibration in welded joints, and the deterioration of railway tracks become serious problems again.

 Under such conditions, there is a need to create wear-resistant rails with the same wear resistance as existing high-strength rails made of eutectoid carbon steel, capable of preventing local wear of welded joints and possessing excellent weldability.

 In order to improve the wear resistance of ordinary rail steel having a pearlite structure with a carbon content corresponding to eutectoid carbon steel, a method of increasing hardness is applied by reducing the distances between the plates in the pearlite structure.

 However, an existing rail steel with a pearlite structure with a carbon content corresponding to eutectoid carbon steel has an upper Vickers hardness of 420. When, in order to increase hardness, the cooling rate is increased during heat treatment or the number of alloying elements added, a bainitic or martensitic structure is formed in the pearlite structure causing a decrease in wear resistance and viscosity of rails.

 In addition, another way to solve the problem can be recognized as the method of using as a rail steel a material having a metal structure exhibiting higher wear resistance than that of a pearlite structure. However, so far it has not been possible to find material that would be cheaper and superior in wear resistance to a fine-grained pearlite structure under rolling wear conditions observed on rails and wheels.

 A pearlite structure having a carbon component corresponding to eutectoid carbon steel of a conventional rail steel has a lamellar structure of a ferritic phase having low hardness and a harder cementite phase. As a result of the analysis of the wear mechanism of the pearlite structure, the authors of the present invention made sure that the wear resistance is improved as follows: first, the wheels passing along the rails squeeze the soft ferrite phase, then the remaining solid cementite phase is split into thin layers directly under the rolling surfaces.

 The authors of the present invention experimentally revealed that the wear resistance can be significantly improved by increasing the percentage of harder cementite in pearlite, which leads to an increase in the hardness of pearlite and, therefore, wear resistance and that causes an increase in carbon content, increasing wear resistance, since the density of the cementite phase directly below the surface increases rolling.

 In FIG. 1 shows a comparison of the relationship between the carbon content and the degree of wear performed during the experiments. The degree of wear decreases with increasing carbon content, when the hardness of the steel remains the same. Thus, it is confirmed that the use of high-carbon steel (hypereutectoid steel) contributes to a significant increase in wear resistance compared to conventional eutectoid steel grades (carbon content from 0.7 to 0.8%).

 Paying attention to the influence that the carbon content has on the characteristics of pearlite transformation, the inventors of the present invention have developed a heat treatment method for the stable formation of a pearlite structure in high carbon steel. In FIG. 2 shows the relationship between the carbon content and the characteristics of pearlite transformation with reference to the transformation diagram under continuous cooling (thermokinetic diagram). It was confirmed that with increasing carbon content, the inflection of the pearlite transformation curve shifts to the left compared to conventional eutectoid steels (carbon content from 0.7 to 0.8%), so that pearlite transformation is easily carried out in the range of rapid cooling.

 This means that the heat treatment method designed for high carbon rail steel (hypereutectoid steel) is as follows: the inventors of the present invention have found that even with an additional increase in the increased cooling rate during the heat treatment compared to conventional eutectoid steels, abnormal formation does not occur structures, such as martensite, with the stable formation of a pearlite structure, so that rail steel can acquire additional strength.

 In addition, it was found that the formation of hypereutectoid cementite, which has a negative effect on ductility and toughness, which is a disadvantage of high-carbon steel (hypereutectoid steel), can be prevented by accelerated cooling during heat treatment with the aim of strong hardening of the steel and that wear resistance can be improved without deteriorating ductility and toughness in the production of high carbon steel.

SUMMARY OF THE INVENTION
In addition to the previous invention, the inventors of the present invention investigated a method for preventing wear seizure caused by local wear on a head top surface of a welded joint without impairing weldability (welding performance). In order to prevent local wear of the welded joint of the rails, it is necessary to reduce as much as possible the difference in hardness between the welded joint heated to the austenization temperature and the base metal. First, the authors of the present invention experimentally determined the effect that additives have on the hardness of a welded joint of high carbon steel (hypereutectoid steel). As a result, the inventors confirmed that the amount of added chromium and silicon affects the hardness of the welded joint of high carbon steel (hypereutectoid steel), although silicon is not as effective as chromium, and found that controlling the amount of additives can prevent a decrease in the hardness of the welded joint.

 Therefore, the inventors used high-carbon steels (hypereutectoid steels), in which the amount of added chromium, the element that most effectively prevents a decrease in the hardness of the welded joint, varies, and in the course of the experiments revealed an interdependence between the amount of added chromium and the hardness of the welded rail immediately after welding (without heat treatment ) As a result, the hardness of the welded joint increased when the amount of added chromium exceeded 0.50%, and a hardness comparable to that of the main rail was provided.

 In addition, since the carbon content in the hypereutectoid steel is high, segregation of manganese, chromium, and the like occurs. in addition to carbon in the columnar part of the rail, and in the segregation area, a tendency is observed to form a martensitic structure that adversely affects viscosity. The authors of the present invention, therefore, have studied a method of limiting the amount of added manganese and chromium to certain values in order to eliminate segregation and prevent a decrease in the hardness of the welded joint. As a result, they found that in high-carbon steels (hypereutectoid steels), controlling the amount of added silicon, which is essentially not segregated, in the columnar part of the rail prevents the reduction of the weld hardness in the same way as chromium.

 Accordingly, the authors of the present invention experimentally determined the relationship between the amount of added silicon and the hardness of the welded rail immediately after welding (without heat treatment) in order to prevent segregation when using high-carbon steels (hypereutectoid steels), in which the amount of added silicon varies, while the amount of added manganese and chromium is limited by the specified limits. As a result, when the amount of added silicon exceeds 0.40%, the hardness of the welded joint is improved even with a slight addition of manganese and chromium, and a hardness comparable to that of the main rail is provided.

 Based on the results of the experiments, the inventors found that the following method is effective way to reduce the difference in hardness between a welded joint heated to austenitic temperature and the base metal as much as possible: in various grades of steel used as the main material of rails and produced under heat treatment conditions corresponding to the claims stated above, the hardness is mainly affected by the number of added alloying elements of chromium, m manganese and silicon, and the control of the added amount of manganese in addition to the control of the added amounts of chromium and silicon, which helps to increase the hardness of the welded joints, is effective in controlling the differences in hardness between the base metal and the corresponding welded joints. Therefore, the authors of the present invention investigated the relationship between the difference in hardness between the base metal of the rail and the welded joint, on the one hand, and the added amounts of silicon, chromium and manganese, on the other. The contribution of chromium to hardness is taken equal to 1, and the results are arranged in such a way as to bring out the contribution of three elements to it. As a result, when silicon, manganese and chromium are added in equal amounts, it was found that the contribution of individual elements is as follows Si: 1/4; Mn: 1/2. Thus, it was found that in order to ensure that the difference in hardness between the welded joint and the base metal remains in a certain range so as to prevent destruction caused by local wear of the upper head surface of the welded joint without compromising weldability (welding performance), the total the content in weight percent of chromium, one fourth of the content in weight percent of silicon and one second content in weight percent of manganese should be in a certain range.

 The object of the present invention is to provide rails with significantly improved wear resistance and weldability (welding performance, characteristics of welded joints), which, according to the study, are required for main railways.

The present invention achieves the task, and the object of the present invention are:
pearlitic steel rails with excellent wear resistance and weldability, obtained as described below:
the head of the hot-rolled steel rails contains high-temperature thermal energy or the steel rail is heated to high temperature for the purpose of heat treatment, and the steel rail contains, by weight:
from more than 0.85 to 1.20% C, from 0.10 to 1.00% Si, from 0.20 to 1.50% Mn, from more than 0.50 to 1.00% Cr, or
from more than 0.85 to 1.20% C, from 0.40 to 1.00% Si, from 0.20 to less than 0.40% Mn, from 0.35 to 0.50% Cr, and the sum the content of Si / 4 + Mn / 2 + Cr should be by weight from 0.8 to 1.8%,
and further contains, in weight percent, one or at least two elements selected from the group that contains:
from 0.01 to 0.20% Mn, from 0.02 to 0.30% V, from 0.002 to 0.050% Nb, from 0.10 to 2.00% Co and from 0.0005 to 0.005% B, and the rest is accounted for by Fe and inevitable impurities,
rails subjected to accelerated cooling or controlled cooling in one of the following ways: (1) the head is subjected to accelerated cooling from the austenitizing temperature with a cooling rate in the range from 1 to 10 ^° C / sec, and accelerated cooling stops when the temperature of the steel rail reaches from 700 to 500 ^o C; (2) the head is subjected to accelerated cooling from the austenitizing temperature with a cooling rate in the range of 10 to 30 ^° C./sec, and accelerated cooling is stopped at the moment when the pearlite transformation of the steel rail accounts for 70% of the total transformation; and (3) the head is subjected to accelerated cooling from an austenitizing temperature to a temperature of from 750 to 600 ^° C. with a cooling rate of more than 10 to 30 ^° C./sec, and then subjected to controlled cooling with a cooling rate of from 1 to less than 10 ^° C. temperature range from 750-600 ^o C to 550-450 ^o C;
steel rails having a pearlite structure to a depth of at least 20 mm from the angle of the head and the upper surface of the head as a starting point, the pearlite structure having a Vickers hardness of at least 320, and the difference in Vickers hardness of the base metal and the welded joint of steel rail reaches 30; and
method of manufacturing these rails.

Brief Description of the Drawings
In FIG. 1 graphically shows the relationship between the carbon content and the degree of wear;
in FIG. 2 graphically shows the relationship between carbon content and pearlite conversion characteristics;
in FIG. 3 is a view showing the names of the positions of the cross section of the rail head, and numerical positions 1 and 2 indicate the upper surface of the head and the angle of the head, respectively;
in FIG. 4 shows a schematic representation of a Nishihara wear measuring device, and numerical positions 3, 4, and 5 denote a test rail sample, supplementing the material and cooling nozzle, respectively.
in FIG. 5 graphically shows the relationship between hardness and the degree of wear according to Example 1;
in FIG. 6 graphically shows the distribution of hardness of the head in a welded joint according to Example 1;
in FIG. 7 graphically shows the relationship between hardness and the degree of wear according to Example 2;
in FIG. 8 graphically shows the distribution of hardness of the head in a welded joint according to Example 2;
in FIG. 9 graphically shows the relationship between hardness and wear according to Example 3;
in FIG. 10 graphically shows the distribution of hardness of the head in a welded joint according to Example 3;
in FIG. 11 graphically shows a different relationship between hardness and wear according to Example 3;
in FIG. 12 graphically shows a different distribution of hardness of the head in a welded joint according to Example 2.

The best option of the invention
Compared to conventional rail steels, the rail steel of the present invention has a high carbon content, exhibits a reduction in wear at the same hardness, and has significantly higher wear resistance. In addition, stable formation of a pearlite structure with excellent wear resistance is possible without the simultaneous formation of martensite, bainite and hypereutectoid cementite, which contribute to the deterioration of ductility, toughness and wear resistance of rails, by selecting the appropriate chemical composition and choosing suitable heat treatment conditions.

 In addition, the decrease in hardness of the fusion line is reduced, and abnormal structures such as martensite are not formed in the welded joint (region reheated to austenitization temperature). The difference in Vickers hardness between the welded joint and the base metal reaches 30, and as a result, partial wear, such as a notch of local wear caused by wear of the upper surface of the head of the welded joint immediately after welding, can be prevented (without heat treatment).

 According to the present invention, rails with excellent wear resistance and weldability (welding performance, characteristics of welded joints) can be proposed as rails intended for heavy loads.

 The present invention will now be described in detail.

(1) Chemical compositions
The reasons for the above chemical limitations of the rails of the present invention will be described in detail. C is an element that effectively promotes pearlite transformation and ensures wear resistance. It is added to ordinary rail steel in an amount of 0.60 to 0.85%. However, when the C content is below 0.85%, it is not possible to ensure the density of the cementite phase in the pearlite structure in order to improve wear resistance and, in addition, there is a tendency to the formation of intergranular ferrite, which can become the starting point of fatigue fracture in the rail head. Moreover, when the C content exceeds 1.20%, a lot of hypereutectoid cementite is formed in the rail head after heat treatment, which significantly reduces ductility and toughness. Thus, the C content should exceed 0.85% but be less than 1.20%.

 Si is an element that increases the hardness (strength) of the base metal of the rail and the welded joint, reheated to the temperature of austenization, by hardening a solid solution of the ferrite phase in a pearlite structure. Si is also an element that concentrates in the pearlite structure at the boundaries between ferrite and cementite, and the Si concentration zone prevents the spheroidization of cementite in the heat affected zone, which is heated to the austenization temperature during welding. As a result, Si prevents the decrease in hardness in the heat affected zone, i.e., Si increases the resistance of the steel to softening during tempering. With a Si content of less than 0.10%, such results cannot be expected. In addition, when the Si content exceeds 1.00%, many surface defects appear during hot rolling. Along with this, embrittlement of the rail and deterioration of weldability occur. Thus, the Si content is limited to a range of 0.10 to 1.00%. In addition, in a rail chemical composition system in which the Mn and Cr content is limited to certain values in order to reduce segregation in the columnar portion of the rail, it is necessary that the Si content be limited to at least 0.40% to ensure the hardness of the base metal of the rail and welded joints .

 Mn is an element that contributes to the achievement of high hardness (strength) of the rail by lowering the temperature of pearlite transformation and increase hardenability, as well as preventing the formation of hypereutectoid cementite. When the Mn content is less than 0.20%, its effect is insignificant, and there is a tendency to form in the rail head after heat treatment of hypereutectoid cementite. On the other hand, when the Mn content exceeds 1.50%, there is a tendency to form a martensitic structure that has a negative effect on the viscosity of the rail. In this regard, the content of Mn is limited to a range of 0.20-1.50%. In addition, in order to weaken the segregation in the columnar part of the rail and prevent the formation of a martensitic structure that has a negative effect on the viscosity of the steel, the Mn content should be in the range from 0.20 to less than 0.40%.

 Cr is an element that helps to increase the equilibrium point of pearlite transformation, which makes the pearlite structure fine-grained. Thus, Cr imparts greater hardness (strength) to the base metal of the rail, improves the hardness of the welded joint reheated to the austenization temperature, and reduces the difference in hardness between the base metal of the rail and the welded joint. In addition, Cr is an element that forms Cr carbides and thus hardens cementite in a pearlite structure. As a result, Cr not only increases the wear resistance, but also prevents the softening of cementite in the heat affected zone, which is reheated during the welding process to a temperature close to the austenization temperature. Although the base metal of the rail can be significantly hardened with a Cr content of less than 0.50%, the hardness of the weld cannot be satisfactorily provided, and the difference in hardness between the base metal of the rail and the weld becomes significant. As a result, due to local wear, a wear recess is formed on the weld joint. In addition, when Cr is added in an amount exceeding 1.00%, i.e. in excess, bainitic and martensitic structures are formed, which reduce the wear resistance and viscosity of the rails. Accordingly, the Cr content is limited to a range of 0.50-1.00%. In addition, in order to eliminate segregation in the columnar part of the rail and prevent the formation of a martensitic structure that adversely affects the viscosity of the rail, the added amount of Cr can be limited to a range of 0.20 to less than 0.40% due to the addition of a large amount of Si .

In addition, in order to increase the strength, ductility and viscosity of the rail, which is supposed to be produced with the chemical composition mentioned above, one or at least two elements selected from the following elements are additionally added:
Mo: from 0.01 to 0.20%, V: from 0.02 to 0.30%, Nb: from 0.002 to 0.050%, Co: from 0.10 to 2.00%, and B: from 0.0005 up to 0.005%.

 Next, the reasons for determining the chemical composition as described above will be explained.

 Mo is similar to Cr in that it increases the equilibrium point of pearlite transformation and as a result makes the pearlite structure fine-grained, which contributes to a significant hardening of rail steel and an increase in wear resistance. When added in an amount of less than 0.01%, the effect is negligible. When Mo is added in an amount in excess of 0.20%, i.e. in excess, Mo reduces the rate of pearlite transformation and, as a result, promotes the formation of a martensitic structure that has a negative effect on viscosity. In this regard, the Mo content is limited to a range from 0.01 to 0.20%.

 V is a component that contributes to an increase in strength due to dispersion hardening, and vanadium carbonitrides formed during cooling during hot rolling contribute to the grinding of austenite grains by suppressing grain growth during heat treatment in the form of heating steel to a high temperature, which contributes to an increase in strength and ductility and the viscosity required from the rails. However, results are difficult to expect if the V content is less than 0.02%. In addition, the result cannot be expected if V is added in an amount in excess of 0.30%. Therefore, the content of V is limited to a range from 0.02 to 0.30%.

Nb is similar to V in that it is an element that contributes to the grinding of austenite grains due to the formation of niobium carbonitrides. Nb affects the suppression of the growth of austenite grains at higher temperatures compared to V, approaching 1200 ^o C, and helps to improve the ductility and viscosity of the rails. The result cannot be expected if the Nb content is less than 0.002%. In addition, if Nb is added in an amount in excess of 0.050%, i.e. in excess, an additional effect cannot be expected. Accordingly, the Nb content is limited to a range of 0.002 to 0.050%.

 Co is an element that increases strength by increasing the energy of pearlite transformation with the aim of grinding the structure of perlite. However, the effect cannot be expected when its content is less than 0.10%. When Co is added in an amount in excess of 2.00%, i.e. in excess, saturation occurs in the absence of an additional effect. Accordingly, the Co content is limited to a range of 0.10 to 2.00%.

 B is an element that affects the suppression of the formation of hypereutectoid cementite from the former boundaries of austenitic grain and which contributes to the stable formation of a pearlite structure. However, when its content is less than 0.0005%, the effect is weak. When B is added in an amount in excess of 0.0050%, coarse boron carbides are formed, reducing the ductility and toughness of the rails. Accordingly, the content of B is limited to a range of 0.0005 to 0.0050%.

 In addition, we explain the reasons for limiting the sum of the indicators of the Si / 4 + Mn / 2 + Cr content from 0.8 to 1.8 wt.%. When the sum of the indicators of the Si / 4 + Mn / 2 + Cr content is less than 0.8 wt.%, The hardness of the welded joint of the rails after welding, such as flash butt welding, is significantly reduced compared to the hardness of the base metal of the rail, and the difference in hardness between increases by the welded joint and the base metal, which does not satisfy the requirement that the difference in Vickers hardness should not exceed 30, a condition that allows local rail wear on the upper surface of the head to be prevented in the welded joint . In addition, when the sum of the indicators of the content of Si / 4 + Mn / 2 + Cr exceeds 1.8 wt.%, The hardness of the welded joint of the rails increases significantly compared to the base metal, which does not allow to satisfy the requirement that the difference in Vickers hardness must not exceed 30, a condition that prevents local wear of the rail on the upper surface of the head in a welded joint. In addition to unsatisfactory abnormalities, abnormal structures such as martensite form in the welded joint, and the viscosity and fatigue strength of the rail welded joint are significantly reduced. In accordance with this, the sum of the indicators of the content of Si / 4 + Mn / 2 + Cr is limited to a range from 0.8 to 1.8 wt.%. In addition, in order to prevent segregation in the columnar part of the rail, in a system of components in which the content of Mn and Cr decreases, and Si is added in large quantities in order to prevent segregation in the columnar part of the rail, abnormal structures like martensite are not formed in welded joint even at the maximum permissible content of Mn, Cr and Si, and the difference in Vickers hardness between the welded joint and the base metal does not exceed 30. Accordingly, the sum of the indicators of the content of Si / 4 + Mn / 2 + Cr is limited value of 0.95.

 Rail steel with the chemical composition described above is smelted in a conventional steelmaking unit, such as a converter or an electric furnace. The resulting liquid steel is poured into ingots, followed by rolling into blooms, or continuous casting, and the resulting billets are then hot rolled into rails. Hot rolled rails with high thermal energy at high temperature, or rails heated to high temperature, are subjected to accelerated cooling of the head part for heat treatment to increase the hardness of the pearlite structure of the rail head.

(2) Hardness of a pearlite structure and its range
First, the reasons for limiting the hardness of a pearlite structure according to Vickers to a level of at least 320 should be explained. When the Vickers hardness is below 320, the following problems arise: it becomes difficult to ensure that the components in this system have the wear resistance that is required for rails of modern main railways; in addition, at a bend of a rail track with a sharp bend under the influence of tight contact between the rail and the wheels, a metal flow occurs, entailing the appearance of surface defects such as cracks in the head or peeling. In this regard, the Vickers hardness of the pearlite structure should be at least 320.

 Next, we explain the reasons for limiting the distribution of a pearlite structure having a Vickers hardness of at least 320 and a depth of at least 20 mm from the angle of the head and the upper surface of the head. When the depth is less than 20 mm, it is small compared to that which the wear-resistant area of the rail head should have, and due to the continued wear of the rail, it is impossible to achieve a sufficient extension of the rail service life. On the other hand, when the propagation depth of the aforementioned pearlite structure reaches at least 30 mm from the angle of the head and the upper surface of the head, there is a further amplification of the effect of increasing the service life of the rail. Accordingly, the indicated range is desired.

 In FIG. 3 shows the names of the surface positions of the transverse section of the rail head, which is the subject of the present invention and has excellent wear resistance and weldability. In the rail head, numeral positions 1 and 2 indicate the upper part of the head and the angles of the head, respectively. One of the corners of the 2 heads is the corner of the canvas (G.C.), most in contact with the wheels.

 Next, the reasons for limiting the difference in Vickers hardness between the base metal of the rail and the welded joint to no more than 30 will be explained. When the difference in Vickers hardness between the welded joint and the base metal exceeds 30, partial wear occurs on the upper surface of the rail head at the place of the welded joint form of notch wear. As a result, noise and vibration occur during the passage of the train, and there is a noticeable deterioration in the quality of the railway track. In this regard, the difference in Vickers hardness between the base metal of the rail and the welded joint is limited to not more than 30. In addition, the difference in hardness is limited by the difference in the distribution of head hardness between the welded joint of the rail reheated to the austenization temperature and the base metal. The difference in hardness does not mean a difference in hardness between the heat affected zone formed around the welded joint or the area with reduced hardness formed by decarburization along the welding line and the base metal. In addition, the difference in hardness is, first of all, an indicator of the absolute decrease in the hardness of the welded joint compared to the hardness of the base metal. The hardness of the welded joint sometimes increases and, depending on the system of components and the welding conditions, becomes comparable with the hardness of the base metal. However, since the hardness reaching such a high level does not significantly affect the characteristics of the weld, and the difference in hardness determines when the hardness of the weld is low compared to the base metal or when the hardness of the weld is large compared to it.

(3) Production conditions
Next, the reasons for the limitation of each of the cooling conditions during the above-mentioned rail production according to paragraphs 4-6 of the claims will be examined in detail.

According to paragraph 4, the steel rail is subjected to accelerated cooling from the temperature of austenization at a cooling rate of from 1 to 10 ^o C / sec, and cooling stops when the temperature of the steel rails reaches from 700 to 500 ^o C. The reasons for limiting the cooling conditions will be explained below. In addition, cooling conditions are heat treatment conditions in which air or a mixture containing mainly air and fog is used as the cooling medium.

First, we explain the reasons for limiting the temperature of termination of accelerated cooling and the speed of accelerated cooling during the operation of accelerated cooling of a steel rail from the temperature of austenization to a temperature of from 700 to 500 ^o C.

When accelerated cooling stops at a temperature in excess of 700 ^° C., immediately after accelerated cooling, pearlite transformation begins to form a large amount of pearlite structure having low hardness. As a result, the Vickers hardness of the rail head is below 320, which does not guarantee the necessary wear resistance. In this regard, the termination temperature of accelerated cooling is limited to not more than 700 ^o C. In addition, if accelerated cooling is carried out to a temperature of less than 500 ^o C, after the completion of accelerated cooling, it is impossible to expect a sufficient return of energy from the inner regions of the rail, and in the segregation area the formation of a martensitic structure that has a negative effect on the viscosity and wear resistance of the rail occurs. In this regard, the termination temperature of accelerated cooling should be at least 500 ^o C.

Explain the reasons for limiting the speed of accelerated cooling in the range from 1 to 10 ^o C.

When the accelerated cooling rate is less than 1 ^° C./sec, during accelerated cooling in the high temperature region, pearlite transformation begins and a large amount of pearlite structure having low hardness is formed. As a result, the hardness of the rail head according to Vickers is less than 320, which does not guarantee the necessary wear resistance. In addition, in large quantities, hypereutectoid cementite is formed, which has a negative effect on the viscosity and ductility of the rail. In this regard, the accelerated cooling rate must be at least 1 ^o C / sec. Further, in the case of using air or a medium containing mainly air, fog, etc. as the cooling medium, which medium has stable characteristics during the heat treatment, it is not possible to provide a stable cooling rate in excess of 10 ^° C./sec. Therefore, the accelerated cooling rate is limited to a range from 1 to 10 ^o C.

 In addition, the accelerated cooling rate is defined as the average cooling rate from the moment it begins to the end of cooling. Temporary temperature rises are sometimes possible due to heat generation during pearlite transformation or natural heat transfer during accelerated cooling from the inner rail region. However, when the average cooling rate from the beginning to the end of accelerated cooling is within the limits set above, there is no noticeable effect on the characteristics of the pearlitic steel rail of the present invention. Therefore, the conditions for accelerated cooling of rails according to the present invention include a decrease in the cooling rate caused by a temporary increase in temperature during cooling.

A predetermined cooling rate in the range of 1 to 10 ^° C. can be achieved using air or a cooling medium containing air, mainly fog, or the like, or a combination of air and cooling medium.

In accordance with the foregoing, in order to obtain a rail with a pearlite structure with a Vickers hardness of at least 320 and excellent wear resistance and weldability, the steel rail head is subjected to accelerated cooling from the austenization temperature at a cooling rate of 1 to 10 ^° C. with air or a cooling medium, consisting mainly of air, fog, etc., and accelerated cooling stops when the temperature of the steel rail reaches from 700 to 500 ^o C, so that the formation of a pearlite page is not allowed in the rail head a low hardness structure and no abnormal structures are formed, such as a hypereutectoid cementite structure and a martensitic structure, which adversely affect ductility, toughness and wear resistance. As a result, a pearlite structure having high hardness can be stably formed.

 Although a pearlite structure is desirable as a rail metal structure, an insignificant amount of hypereutectoid cementite is sometimes formed depending on the component system, accelerated cooling rate, and segregation rate of the steel material. However, even with the formation of a small amount of hypereutectoid cementite, this hypereutectoid cementite does not have a noticeable effect on ductility, toughness, wear resistance, and strength. The pearlitic steel rail structure of the present invention may therefore comprise a certain amount of hypereutectoid cementite structure.

We will further explain the reasons for determining the following cooling conditions according to claim 5: the steel rail head is subjected to accelerated cooling from the austenization temperature with a cooling rate of more than 10 to 30 ^° C / sec, and accelerated cooling is stopped at the moment when the pearlite transformation of the steel rail accounts for 70% of the total conversion. In addition, these cooling conditions are heat treatment conditions in which a cooling medium is used that contains mainly water, such as fog or water spray.

As shown in FIG. 2 mentioned above, when the accelerated cooling rate is less than 10 ^° C./sec, the cooling curve constantly crosses the inflection point of the pearlite transformation curve and the pearlite transformation in most cases is completed during continuous cooling. However, when the accelerated cooling rate exceeds 10 ^o C / sec, it is found that the cooling curve crosses the inflection point of the pearlite transformation curve only when steels containing at least a certain amount of C are used. In addition, when the accelerated cooling rate exceeds 10 ^o C / sec, continued cooling to temperatures of only about 300 ^° C. leads to the formation of a large amount of martensitic structure in the pearlite structure. This has a negative effect on the wear resistance and toughness of the rail.

 However, when the steel rail is cooled at such a high cooling rate, a significant degree of subcooling becomes during pearlite transformation. When pearlite transformation occurs during cooling in certain sizes, the cessation of accelerated cooling in a certain temperature region during the transformation causes heat to be released during pearlite transformation and natural heat transfer from the inner region of the rail head, which leads to the temporary occurrence of a state similar to isothermal transformation. As a result, the pearlite transformation can be completed in the entire rail head.

 Detailed experiments were carried out, which confirmed that in order to complete the pearlite transformation in the rail head by using the heat of pearlite transformation and the natural heat transfer from the inner region of the rail head, after accelerated cooling, the minimum required pearlite transformation is at least 70% of the total transformations.

The concept of the aforementioned manufacturing process is shown in the continuous cooling transformation diagram (thermokinetic diagram), the steel of FIG. 2 containing 1.0% C. In this example, the steel is subjected to accelerated cooling (from more than 10 ^° C. to 30 ^° C.) of the austenitizing temperature, and accelerated cooling is stopped when the pearlite transformation becomes at least 75% of the total transformation. The cooling rate becomes less than 10 ^o C / sec after the termination of accelerated cooling due to the heat of pearlite transformation and natural heat transfer from the inner region of the rail itself. Thus, the pearlite transformation can be stably completed.

First, we explain the reasons for limiting the speed of accelerated cooling to a range of more than 10 to 30 ^o C / sec.

When the steel rail is cooled with a cooling medium other than air, and mainly containing water, such as fog and water spray, at a high cooling rate below 10 ^o C / sec, the uniformity of cooling is completely insufficient in the region of such low cooling rates, which with very high cooling capacity, which makes cooling control difficult. In addition, with unstable cooling, the hardness varies and it becomes difficult to consistently achieve that the Vickers hardness of the rail head is at least 320. In this regard, the accelerated cooling rate must exceed 10 ^o C / sec. In addition, as shown in the continuous cooling transformation diagram (thermokinetic diagram) in FIG. 2, when the accelerated cooling rate exceeds 30 ^o C / sec, the cooling curve does not sufficiently intersect the inflection point of the pearlite transformation curve during accelerated cooling, and a martensitic structure is formed that adversely affects the viscosity and wear resistance of the rail. In addition, even when the cooling curve crosses the inflection point of the pearlite transformation curve sufficiently during accelerated cooling, it is not possible to expect a pearlite transformation corresponding to at least 70% of the entire transformation, and as a result, the pearlite transformation in the entire rail head does not complete. The result is the formation of a martensitic structure that has a negative effect on the viscosity and wear resistance of the rail. Therefore, the accelerated cooling rate is limited to a range of from more than 10 to 30 ^o C / sec.

 In addition, the accelerated cooling rate is defined as the average cooling rate from the moment it begins to the end of cooling. Temporary temperature rises are sometimes possible due to heat generation during pearlite transformation or natural heat transfer during accelerated cooling from the inner rail region. However, when the average cooling rate from the beginning to the end of accelerated cooling is within the limits set above, there is no noticeable effect on the characteristics of the pearlitic steel rail of the present invention. The conditions for accelerated cooling of the rails according to the present invention include a decrease in the cooling rate caused by a temporary increase in temperature during cooling.

Further, methods for achieving a predetermined cooling rate in the range of more than 10 to 30 ^° C./sec include the following: injection cooling with a mixture of water and air or a combination thereof, the rail head or the entire rail is immersed in oil, hot water, a mixture of polymer and water or salt bath.

 Now we will explain the reasons for the cessation of accelerated cooling at the moment of achieving 70% of the entire pearlite transformation.

 If less than 70% of the total pearlite transformation is achieved at the time of termination of accelerated cooling, the amount of heat generated during pearlite transformation after the termination of cooling is small, and as a result, pearlite transformation cannot be completed along the entire rail head. In this regard, a large amount of martensite is formed in the rail head. Moreover, if there are sections of microliquation in the rail head, these sections are cooled further without transformation, which leads to the appearance of islands, each of which has a martensitic structure. All this leads to a significant deterioration in the viscosity and wear resistance of the rail.

 The development of pearlite transformation at the moment of termination of accelerated cooling is therefore limited by a value of not more than 70%. The development of pearlite transformation can be determined by the change in temperature of the rail head during accelerated cooling. At the beginning of the pearlite transformation, a site of heat generation caused by the transformation is clearly observed. According to the results of detailed experiments, the state of the rail immediately before the completion of the temperature rise in the heat generation area corresponds to the temperature at which 70% of the entire pearlite transformation is completed. In addition, as a simple way to control the amount of conversion, it is most desirable to control this value based on the duration of cooling during accelerated cooling.

In accordance with the foregoing, in order to produce a rail with a pearlite structure and with a Vickers hardness of at least 320, as well as excellent wear resistance and weldability, the rail head is subjected to accelerated cooling with a cooling rate of more than 10 to 30 ^o C / sec cooling medium other than air and containing mainly water, such as fog and water sprays, and accelerated cooling stops at the moment when the pearlite transformation in the steel rail reaches 70% of the total transformation. As a result, it is possible the stable formation of a pearlite structure with high hardness.

 Although a pearlite structure is desirable as a rail metal structure, an insignificant amount of hypereutectoid cementite is sometimes formed depending on the component system, accelerated cooling rate, and segregation rate of the steel material. However, even with the formation of a small amount of hypereutectoid cementite, this hypereutectoid cementite does not have a noticeable effect on ductility, toughness, wear resistance, and strength. The pearlitic steel rail structure of the present invention may therefore comprise a certain amount of hypereutectoid cementite structure.

Let us further explain the reasons for limiting the following cooling conditions according to claim 6: the steel rail head is subjected to accelerated cooling from the austenization temperature to a temperature of 750 to 600 ^o C with a cooling rate of more than 10 to 30 ^o C / sec and subsequent controlled cooling with a cooling rate of 1 to less than 10 ^o C / s in the temperature range from 750-600 ^o C to 550-450 ^o C. In addition, the cooling conditions are heat treatment conditions when water is used in the form of fog or water spray during initial cooling, and when subsequent cooling - a cooling medium containing air or, mainly, air and fog.

As shown in FIG. 2, when the accelerated cooling rate is less than 10 ^° C./sec, the cooling curve constantly crosses the inflection point of the pearlite transformation curve, and the pearlite transformation is completed mostly during continuous cooling. When the accelerated cooling rate exceeds 10 ^° C./sec, it is found that the cooling curve crosses the inflection point of the pearlite transformation curve only when steels containing at least a certain amount of carbon are used. In addition, when the accelerated cooling rate exceeds 10 ^o C / sec, continued cooling to temperatures of only about 300 ^o C leads to the formation of a large amount of martensitic structure in the pearlite structure. This has a negative effect on the wear resistance and toughness of the rail.

However, with accelerated cooling at a rate exceeding 10 ^o C / sec, pearlite transformation can be completed in the entire rail head by stopping the accelerated cooling in the temperature region in which the pearlite structure with high hardness is stably formed and the cooling process is started, which allows subsequent control heat generation during pearlitic transformation with the possibility of natural heat transfer from the inner region of the rail head.

As an example, the steel of FIG. 2 containing 1.0% C, and the concept of the aforementioned manufacturing process is shown in a continuous cooling transformation diagram (thermokinetic diagram). Moreover, in this example, the steel is subjected to accelerated cooling from the temperature of austenization at a rate of from more than 10 to 30 ^o C, and pearlite transformation can be stably completed by further monitoring the subsequent heat generation of pearlite transformation and natural heat transfer from the inner region of the rail itself (1-10 ^o C / sec).

First, we explain the reasons for limiting the termination temperature of accelerated cooling and the accelerated cooling rate in a method involving accelerated cooling of steel from an austenization temperature to a temperature of 750 to 600 ^o C with a cooling rate of more than 10 to no more than 30 ^o C / sec.

When accelerated cooling is stopped at a temperature in excess of 750 ^° C., subsequent controlled cooling at high temperatures results in the formation of hypereutectoid cementite, which leads to a significant decrease in the ductility and viscosity of the rail. In this regard, the termination temperature of accelerated cooling should not be higher than 750 ^o C. When accelerated cooling is carried out to temperatures less than 600 ^o C, during subsequent controlled cooling does not end pearlite transformation. As a result, there is a tendency to the formation of abnormal structures, such as bainite and martensite, which have a negative effect on the viscosity and wear resistance of the rail. In this regard, the termination temperature of accelerated cooling should not be lower than 600 ^o C.

When the steel rail is cooled by a cooling medium other than air and mainly containing water, such as fog and water spray, at a high cooling rate below 10 ^o C / sec, the uniformity of cooling is completely insufficient in the region of such low cooling rates, which is associated with very high cooling capacity, which makes it difficult to control cooling. In addition, with unstable cooling, the hardness varies and it becomes difficult to steadily achieve that the Vickers hardness of the rail head is at least 320. In this regard, the accelerated cooling rate must exceed 10 ^o C / sec. In addition, when the accelerated cooling rate exceeds 30 ^° C./sec, the pearlite transformation during controlled cooling following the accelerated cooling does not end, and there is a tendency to form abnormal structures such as bainite and martensite, which adversely affect viscosity and wear resistance. rail. Therefore, the accelerated cooling rate is limited to a range of from more than 10 to 30 ^o C / sec.

 In addition, the accelerated cooling rate is defined as the average cooling rate from the moment it begins to the end of cooling. Temporary temperature rises are sometimes possible due to heat generation during pearlite transformation or natural heat transfer during accelerated cooling from the inner rail region. However, when the average cooling rate from the beginning to the end of accelerated cooling is within the limits set above, there is no noticeable effect on the characteristics of the pearlitic steel rail of the present invention. The conditions for accelerated cooling of the rails according to the present invention include, therefore, a decrease in the cooling rate caused by a temporary increase in temperature during cooling.

Further, methods for achieving a predetermined cooling rate in the range of more than 10 to 30 ^° C./sec include the following: injection cooling with a mixture of water and air, or a combination thereof; the rail head or the entire rail is immersed in oil, hot water, a mixture of polymer and water, or a salt bath.

Now we explain the reasons for limiting the temperature of termination of controlled cooling and the speed of controlled cooling with a controlled cooling method with a cooling rate of 1 to less than 10 ^o C / s in the temperature range from 750-600 ^o C to 550-450 ^o C.

When controlled cooling is stopped at a temperature in excess of 550 ^° C., immediately after controlled cooling, a large amount of a pearlite structure having low hardness is formed. As a result, the Vickers hardness of the rail head is below 320, which does not guarantee the necessary wear resistance of the head. In this regard, the termination temperature of controlled cooling is limited to not more than 550 ^o C. In addition, if controlled cooling is carried out to a temperature of less than 450 ^o C, after the completion of accelerated cooling, it is impossible to expect a sufficient return of energy from the inner regions of the rail, and in the segregation area the formation of a martensitic structure that has a negative effect on the viscosity of the rail occurs. In this regard, the termination temperature of controlled cooling should be at least 450 ^o C.

Let us explain the reasons for limiting the speed of accelerated cooling to a range of 1 to 10 ^o C. When the controlled cooling rate is less than 1 ^o C / sec, during controlled cooling in the high-temperature region, pearlite transformation begins and a large amount of pearlite structure with low hardness is formed. As a result, the hardness of the rail head according to Vickers is less than 320, which does not guarantee the necessary wear resistance. In this regard, the accelerated cooling rate must be at least 1 ^o C / sec. In addition, when controlled cooling is carried out with a cooling rate of at least 10 ^° C / sec, pearlite transformation during cooling does not complete, and during controlled cooling and subsequent cooling, abnormal structures such as bainite and martensite are formed that have a negative effect on viscosity and wear resistance of rails. Therefore, the accelerated cooling rate is limited to a range from 1 to 10 ^o C.

 In addition, the rate of controlled cooling is defined as the average cooling rate from the moment it begins to the end of cooling. Sometimes a temporary increase in temperature is possible, caused by heat generation during pearlite transformation or natural heat transfer during accelerated cooling from the inner region of the rail. However, when the average cooling rate from the beginning to the end of controlled cooling is within the limits set above, there is no noticeable effect on the characteristics of the pearlitic steel rail of the present invention. Therefore, the controlled cooling conditions of the rails of the present invention include a decrease in the cooling rate caused by a temporary increase in temperature during cooling.

A predetermined cooling rate in the range of 1 to 10 ^° C. can be achieved by using a cooling medium containing air, mainly fog or the like, or a combination of these media.

In accordance with the foregoing, in order to obtain a rail with a pearlite structure with a Vickers hardness of at least 320 and excellent wear resistance and weldability, the steel rail head is subjected to accelerated cooling from the austenization temperature at a cooling rate of from more than 10 to 30 ^o C followed by controlled cooling at a cooling rate of 1 to less than 10 ^o C / sec within a temperature range of 750-600 ^o C to 550-450 ^o C using a cooling medium other than air and containing mainly water, such as fog and leading s spray. As a result, a pearlite structure having high hardness can be stably formed.

 Although a pearlite structure is desirable as a rail metal structure, an insignificant amount of hypereutectoid cementite is sometimes formed depending on the component system, accelerated cooling rate, and segregation rate of the steel material. However, even when a small amount of hypereutectoid cementite is formed in the pearlite structure, this hypereutectoid cementite does not have a noticeable effect on ductility, viscosity, wear resistance, and rail strength. The pearlitic steel rail structure of the present invention may therefore comprise a certain amount of hypereutectoid cementite structure.

Examples
The present invention will now be explained with reference to examples.

Example 1
This example relates to the subject matter disclosed in claims 1-3.

 In the table. 1 and 2 (table. 1-16 see the end of the description) shows the chemical composition, data on the hardness and microstructure of the base metal of rail steels, which are the subject of the present invention, as well as comparison for rail steels, as well as the degree of wear after repetition under forced 700,000 test cycles as shown in FIG. 4 Nishihara wear instrument.

 The remainder of the chemical composition is Fe and inevitable impurities.

 In addition, in table. 1 and 2, the difference in hardness between the butt welded joint and the base metal of any of the rail steels of the present invention and the rail steels for comparison is clearly shown. In addition, the hardness indicators of the base metal and the weld of any of the rail steels indicated in the table. 1 and 2 are mean values for the head and do not represent either maximum or minimum values.

 Along with this in FIG. 5 shows the relationship between hardness and wear of rail steels that are the subject of the present invention and rail steels shown for comparison (eutectoid carbon steels: serial numbers from 10 to 13), listed in table. 1 and 2 to compare wear test results. In FIG. 6 shows examples of the distribution of hardness in welded joints in the heads of rail steels that are the subject of the present invention (serial numbers: 2, 3) and rail steels shown for comparison (serial numbers: 17, 18) shown in the examples in table. 1 and 2. In addition, the rails used in the examples are described below.

 The rails that are the subject of the present invention (9 pieces) with serial numbers from 1 to 9: steel rails, which are heat-treated rails, having each chemical composition described above, and a pearlite structure to a depth of at least 20 mm from the surface of the head as a starting point, moreover, the pearlite structure has a Vickers hardness of at least 320 and the head was subjected to accelerated cooling.

Rails shown for comparison (9 pieces):
rails shown for comparison (4 pieces), with serial numbers from 10 to 13: made of eutectoid carbon steels, the chemical composition of which is beyond the scope of the points of the present invention; and
rails shown for comparison (5 pieces) with serial numbers from 14 to 18: made of hypereutectoid carbon steels, the chemical composition of which is beyond the scope of the points of the present invention.

The conditions for the wear tests were as follows:
testing device: Nishihara wear measuring device, test sample form: disk-like sample
outer diameter: 30 mm; thickness: 8 mm;
test load: 686 N;
slip coefficient: 20%;
opposite material: pearlitic steel (Vickers hardness 390);
atmosphere: in the air;
cooling: forced cooling with compressed air (at a flow rate of 100 nl / min), and
number of cycles: 700,000
The conditions for flash butt welding were as follows:
welding machine: K-355 (made in the USSR);
power: 150 kVA;
secondary current: 20000 A (max);
clamping force: 125 tons (max) and draft value: 10 mm.

Example 2
This example relates to the application of claims 2-3.

 In the table. Figures 3 and 4 show the chemical composition, data on the hardness and microstructure of the base metal of rail steels that are the subject of the present invention, as well as rail steels given for comparison, and the degree of wear after repeating under forced conditions 700,000 test cycles in FIG. 4 in Example 1 of a Nishihara Wear Measurement Instrument under forced cooling.

 In addition, Tables 3 and 4 clearly show the difference in hardness between the butt welded joint and the base metal of any of the rail steels that are the subject of the present invention and the rail steels for comparison. In addition, the hardness indicators of the base metal and the weld of any of the rail steels listed in Tables 3 and 4 are average values for the head and do not represent either maximum or minimum values.

 Along with this in FIG. 7 shows the relationship between hardness and wear of rail steels that are the subject of the present invention and rail steels shown for comparison (eutectoid carbon steels: serial numbers 28 to 31) listed in Tables 3 and 4 to compare the results of wear tests . In FIG. 8 shows examples of the distribution of hardness in welded joints in the heads of the rail steel of the present invention (serial number 21) and the rail steel shown for comparison (serial number 35) shown in the examples in table. 3 and 4.

 In addition, the rails used in the examples are described below.

Rails that are the subject of the present invention (9 pieces) with serial numbers from 19 to 27:
steel rails, which are heat-treated rails, having each chemical composition described above, and a pearlite structure to a depth of at least 20 mm from the surface of the head as the starting point, the pearlite structure having a Vickers hardness of at least 320, and the head was subjected to accelerated cooling.

Rails shown for comparison (9 pieces):
rails shown for comparison (4 pieces), with serial numbers from 28 to 31: made of eutectoid carbon steels, the chemical composition of which is beyond the scope of the points of the present invention; and
rails shown for comparison (5 pieces) with serial numbers from 32 to 36: made of hypereutectoid carbon steels, the chemical composition of which is beyond the scope of the points of the present invention.

 The conditions for the wear tests and butt contact welding were the same as in example 1.

Example 3
This example relates to the subject matter disclosed in claims 4-6.

 In the table. 5-10 and 11-16 show the chemical composition, heat treatment conditions (temperature ranges of heat treatment, cooling rates and perlite formation indicators), data on the hardness and microstructure of the base metal of rail steels that are the subject of the present invention, as well as rail steels for comparison as well as the degree of wear after repetition under forced conditions of 700,000 test cycles shown in FIG. 4 in Example 1 of a Nishihara Wear Measurement Instrument under forced cooling. In addition, in table. 5-8 and 11-14, the difference in hardness between the flash butt weld obtained by welding and the base metal of the rail steels of the present invention and the rail steels for comparison is clearly shown.

 In addition, the hardness indicators of the base metal and the weld of any of the rail steels indicated in the table. 5-8 and 11-14, are average values for the head and do not represent either the maximum or minimum values.

 Along with this in FIG. 9 shows the relationship between hardness and wear of rail steels that are the subject of the present invention and rail steels shown for comparison (eutectoid carbon steels: serial numbers from 64 to 67), listed in table. 5-10 to compare wear test results. In FIG. 10 shows examples of the distribution of hardness in welded joints in the heads of rail steel that is the subject of the present invention (serial numbers: 41, 44), and rail steels shown for comparison (serial numbers 71, 72) shown in the examples in table. 5-10.

 In addition, in FIG. 11 shows the relationship between hardness and wear of rail steels that are the subject of the present invention and rail steels shown for comparison (eutectoid carbon steels: serial numbers 112 to 115) listed in Table 1. 11-16 for comparing wear test results. In FIG. 12 shows examples of the distribution of hardness in welded joints in the heads of the rail steel of the present invention (serial number 91) and the rail steel shown for comparison (serial number 120) shown in the examples in the table. 11-16.

 In addition, the rails used in the examples are described below.

(Examples from table. 5-10)
The rails that are the subject of the present invention (27 pieces) with serial numbers from 37 to 63:
steel rails, which are heat-treated rails, having each chemical composition described above, and a pearlite structure to a depth of at least 20 mm from the surface of the head as the starting point, the pearlite structure having a Vickers hardness of at least 320 and the head was subjected to accelerated cooling.

Rails shown for comparison (21 pieces):
rails shown for comparison (4 pieces) with serial numbers from 64 to 67: made of eutectoid carbon steels, the chemical composition of which is beyond the scope of the points of the present invention;
rails shown for comparison (5 pieces) with serial numbers from 68 to 72: made of hypereutectoid carbon steels, the chemical composition of which is beyond the scope of the points of the present invention;
and rails shown for comparison (12 pieces) with serial numbers from 73 to 84: manufactured under heat treatment conditions that are beyond the scope of the paragraphs of the present invention.

(Examples from tab. 11-16)
The rails that are the subject of the present invention (8 pieces) with serial numbers from 85 to 111:
steel rails, which are heat-treated rails, having each chemical composition described above, and a pearlite structure to a depth of at least 20 mm from the surface of the head as the starting point, the pearlite structure having a Vickers hardness of at least 320 and the head was subjected to accelerated cooling.

Rails shown for comparison (21 pieces):
rails shown for comparison (4 pieces) with serial numbers from 112 to 115: made of eutectoid carbon steels, the chemical composition of which is beyond the scope of the points of the present invention;
rails shown for comparison (5 pieces) with serial numbers from 116 to 120: made of hypereutectoid carbon steels, the chemical composition of which is beyond the scope of the points of the present invention; and
rails shown for comparison (12 pieces) with serial numbers from 121 to 132: manufactured under heat treatment conditions that are beyond the scope of the paragraphs of the present invention.

 As shown in FIG. 5, 7, 9, and 11, any of the rail steels that are the subject of the present invention shows a decrease in the degree of wear compared to any corresponding steel having the same hardness, taken for comparison, due to the higher carbon content, which leads to a significant improvement in wear resistance even in the case where the rail steel of the present invention has the same hardness as ordinary steel. In addition, it is possible to stablely form a pearlite structure with excellent wear resistance without the formation of martensite, bainite and hypereutectoid cementite, which have a negative effect on viscosity, wear resistance and ductility, by keeping the chemical composition within an acceptable framework and choosing suitable heat treatment conditions, as shown in Table 1. 1-4.

 As shown in FIG. 6 and 10, a decrease in the hardness of the welded joint, which occurs when the Cr content is less than 0.50% (rails taken with reference numbers 17, 71 taken for comparison) or when abnormal formation occurs with a Cr content of at least 1.00% structures such as martensite (taken for comparison rails with serial numbers 18, 72) can be prevented by setting the Cr content in the range from more than 0.50 to 1.00%, not allowing the difference in hardness between the base metal of the rail and the welded connection exceeded 30. In this way, partial wear, such as local wear, caused by wear of the weld on the upper surface of the head in the state immediately after welding (without heat treatment).

 As shown in FIG. 8 and 12, the decrease in the hardness of the welded joint, which takes place at a time when the Si content is less than 0.40% (taken for comparison rails with serial numbers 35, 120), can be prevented by setting the Si content in the range from 0.40 to 1.00%, not allowing the difference in hardness between the base metal of the rail and the weld to exceed 30. In this way, partial wear, such as a notch of local wear caused by wear of the weld on the top surface of the head, in the state immediately after welding (without thermoset Botko).

Industrial applicability
As shown in FIG. 5, 7, 9, and 11, any of the rail steels that are the subject of the present invention shows a decrease in the degree of wear compared to any corresponding steel having the same hardness, taken for comparison, due to the higher carbon content, which leads to a significant improvement in wear resistance . In addition, it is possible to stablely form a pearlite structure with excellent wear resistance without the formation of martensite, bainite and hypereutectoid cementite, which have a negative effect on viscosity, wear resistance and ductility, by keeping the chemical composition within an acceptable framework and choosing suitable heat treatment conditions, as shown in Table 1. 11-16.

 In addition, the present invention has the following advantages shown in FIG. 6, 8, 10, and 12: the reduction in weld hardness caused by decarburization is reduced; in the welded joint (in the part subjected to reheating to the austenitization temperature) there are no abnormal structures such as martensite, the difference in Vickers hardness between the base metal and the welded joint does not exceed 30 and could prevent partial wear, such as excavation of local wear, caused by wear of the weld on the upper surface of the head in a state immediately after welding (without heat treatment).

 According to the present invention described above, rails having excellent wear resistance and weldability (welding performance, characteristics of welded joints) can be proposed for high-load trunk roads.

Claims (7)

 1. Rail made of steel with increased wear resistance and weldability, containing carbon, silicon, manganese, iron and inevitable impurities having a perlite structure, characterized in that the rail is made of steel additionally containing chromium, in the following ratio, wt.%: Carbon from more than 0.85 to 1.20; silicon from 0.10 to 1.00; manganese from 0.20 to 1.50; chrome from more than 0.5 to 1.00, and the sum of indicators of the content of silicon / 4 + manganese / 2 + chromium is from 0.80 to 1.80, iron and inevitable impurities are the rest, the structure of perlite at a depth of not less than 20 mm from the angle and the upper surface of the rail head has a hardness of at least 320 HV with a difference in hardness between the base metal and the welded joint of the rail not exceeding 30 HV. 2. The rail according to claim 1, characterized in that the rail is made of steel, optionally containing one or at least two elements selected from among the following elements, wt.%:
Molybdenum - 0.01 - 0.20
Vanadium - 0.02 - 0.30
Niobium - 0.002 - 0.050
Cobalt - 0.10 - 2.00
Boron - 0.0005 - 0.005
Iron and Inevitable Impurities - Else
the pearlite structure at a depth of not less than 20 mm from the angle and upper surface of the rail head has a hardness of at least 320 HV with a difference in hardness between the base metal and the welded joint of the steel rail not exceeding 30 HV.  3. A rail made of steel with increased wear resistance and weldability containing carbon, silicon, manganese, iron and inevitable impurities having a perlite structure, characterized in that the rail is made of steel additionally containing chromium, in the following ratio, wt.%: Carbon from more than 0.85 to 1.20; silicon from 0.40 to 1.00; manganese from 0.20 to less than 0.40; chrome from 0.35 to 0.50, and the sum of the indicators of the content of silicon / 4 + manganese / 2 + chromium is from 0.80 to 0.95 iron and the inevitable impurities are the rest, the structure of perlite at a depth of at least 20 mm from the angle the upper surface of the rail head has a hardness of at least 320 HV with a difference in hardness between the base metal and the welded joint of the steel rail not exceeding 30 HV. 4. The rail according to claim 3, characterized in that the rail is made of steel, optionally containing one or at least two elements selected from among the following elements, wt.%:
Molybdenum - 0.01 - 0.20
Vanadium - 0.02 - 0.30
Niobium - 0.002 - 0.050
Cobalt - 0.10 - 2.00
Boron - 0.0005 - 0.005
Iron and Inevitable Impurities - Else
the perlite structure at a depth of at least 20 mm from the angle and the upper surface of the head has a hardness of at least 320 HV with a difference in hardness between the base metal and the welded joint of the steel rail not exceeding 30 HV. 5. A method of manufacturing a rail from steel with increased wear resistance and weldability, including obtaining a rail from steel, austenitization using the heat energy of a hot-rolled rail or from additional heating, accelerated cooling of the rail head from the austenitization temperature and final cooling, characterized in that the rail is made from steel having the chemical composition according to any of claims 1 - 4, are accelerated cooling rate of 1 - 10 ^o C from austenitizing temperature to 700 - 500 ^o C, the steel rail is pearlite p Keturah at a depth of at least 20 mm from the corner and the upper surface of the rail head having a hardness of at least 320 HV with a difference of hardness between the base metal and the weld of the steel rail, not exceeding 30 HV. 6. A method of manufacturing a rail of steel with increased wear resistance and weldability, including obtaining a rail of steel, austenitization using the thermal energy of a hot-rolled rail or with additional heating, accelerated cooling of the rail head from the austenitization temperature and final cooling, characterized in that the rail is made of steel having a chemical composition according to any one of claims 1 to 4, accelerated cooling is carried out at a rate of 10 - 30 ^o C / s from the temperature of austenitization to obtain 70% perlite from the entire transformation, the steel rail has a pearlite structure at a depth of at least 20 mm from the angle and upper surface of the rail head with a hardness of at least 320 HV, with a difference in hardness between the base metal and the welded joint of the steel rail not exceeding 30 HV. 7. A method of manufacturing a rail from steel with increased wear resistance and weldability, including obtaining a rail from steel, austenitization using the heat energy of a hot-rolled rail or from additional heating, accelerated cooling of the rail head from the austenitization temperature and final cooling, characterized in that the rail is made of steel having a chemical composition according to any one of claims 1 to 4, accelerated cooling is carried out at a rate of 10 - 30 ^o C / s from the temperature of austenitization to 750 - 600 ^o C, then controlled cooling rail head with a cooling rate of 1 to less than 10 ^o C / s in the temperature range from 750 - 600 to 550 - 450 ^o C, the steel rail has a pearlite structure at a depth of at least 20 mm from the angle and upper surface of the rail head with hardness not less than 320 HV, with a hardness difference between the base metal and the welded joint of the steel rail not exceeding 30 HV.

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