阅读说明：本技术 一种降低钢轨脱碳层厚度的方法 (Method for reducing thickness of decarburization layer of steel rail ) 是由 杨大巍 邓勇 袁俊 汪渊 于 2021-09-18 设计创作，主要内容包括：本发明提供了一种降低钢轨脱碳层厚度的方法,按照以下公式确定钢轨脱碳程度系数DI：DI＝(4.61[％C]+2.62[％Si]-2.25[％Mn]-3.78[％Cr])/0.5,式中：[％C]为钢轨中C元素的质量含量；[％Si]为钢轨中Si元素的质量含量；[％Mn]为钢轨中Mn元素的质量含量；[％Cr]为钢轨中Cr元素的质量含量；其中,脱碳程度系数DI与[％C]+[％Si]+[％Mn]+[％Cr]的值之间满足预定的匹配关系。本发明通过对影响脱碳的C、Si、Mn、Cr等主要化学元素的添加量进行优化,并且将[％C]+[％Si]+[％Mn]+[％Cr]的值与脱碳程度系数DI进行匹配,建立各加热段精准化的加热温度、加热时间、加热炉内空气过剩系数,从而使钢轨脱碳层厚度显著降低,同时强韧性匹配和耐磨损性能得到提高,采用本发明生产的产品获得更加优异线路服役性能,更适用于高速铁路。(The invention provides a method for reducing the thickness of a steel rail decarburization layer, which determines a steel rail decarburization degree coefficient DI according to the following formula: DI [% C ] +2.62 [% Si ] -2.25 [% Mn ] -3.78 [% Cr ])/0.5, wherein: [% C ] is the mass content of C element in the steel rail; [% Si ] is the mass content of Si element in the steel rail; [% Mn ] is the mass content of Mn element in the steel rail; [% Cr ] is the mass content of Cr element in the steel rail; wherein the decarburization degree index DI and [% C ] + [% Si ] + [% Mn ] + [% Cr ] satisfy a predetermined matching relationship. The invention optimizes the addition of main chemical elements such as C, Si, Mn, Cr and the like which influence decarburization, matches the value of [% C ] + [% Si ] + [% Mn ] + [% Cr ] with the decarburization degree coefficient DI, and establishes precise heating temperature, heating time and air excess coefficient in a heating furnace of each heating section, thereby obviously reducing the thickness of the decarburization layer of the steel rail, and simultaneously improving the obdurability matching and wear resistance.)

1. A method of reducing the thickness of a decarburized steel rail, wherein the decarburization degree index DI of the steel rail is determined according to the following equation:

DI＝(4.61[％C]+2.62[％Si]-2.25[％Mn]-3.78[％Cr])/0.5

in the formula:

[% C ] is the mass content of C element in the steel rail;

[% Si ] is the mass content of Si element in the steel rail;

[% Mn ] is the mass content of Mn element in the steel rail;

[% Cr ] is the mass content of Cr element in the steel rail;

wherein the decarburization degree index DI and [% C ] + [% Si ] + [% Mn ] + [% Cr ] satisfy a predetermined matching relationship.

2. The method of claim 1, wherein the predetermined matching relationship is: the decarburization degree coefficient DI is 4.5 to 7.0, and the value of [% C ] + [% Si ] + [% Mn ] + [% Cr ] is 1.85 to 3.02 mass%.

3. The method of claim 1, wherein the steel rail has a chemical composition of:

c: 0.70 to 0.82 mass%, Si: 0.50 to 0.80 mass%, Mn: 0.60 to 1.20 mass%, Cr: 0.05-0.20 mass%, and,

also comprises V, Al and one or more of Co, wherein, V: 0.01-0.05 mass%, Al: 0.003 mass% or less, Co: 0.03 mass% or less.

4. The method of claim 1, wherein the steel slab is heated after the continuous casting, sequentially passing through a preheating section, a heating section, and a soaking section, wherein,

the preheating period time is 30-80min, and the preheating period temperature is 540-; the heating period time is 120-180min, and the heating period temperature is 990-1200 ℃; the time of the soaking section is 10-30min, and the temperature of the soaking section is 1150-1250 ℃.

5. The method of claim 4 wherein the billet is heated in a step furnace.

6. The method of claim 5 wherein the preheat section air excess factor is between 1.05 and 1.20, the heat section air excess factor is between 0.90 and 1.05, and the soak section air excess factor is between 0.85 and 1.00.

7. The method of any one of claims 1 to 6 further comprising rolling the steel slab in-line to a rail of 60 to 75 kg/m.

8. The method of claim 7, further comprising performing an in-line heat treatment on the rail, the in-line heat treatment comprising:

and air-cooling the steel rail with the residual heat after the final rolling to 820-890 ℃, then cooling the steel rail head by using the compressed gas agent mixed gas, and air-cooling the steel rail to room temperature when the steel rail head is cooled to 400-560 ℃.

9. The method of claim 8, wherein the cooling rate of the rail head is 1.0-5.2 ℃/s.

10. The method of claim 9, wherein the in-line heat treatment step is further followed by a post-treatment step, the post-treatment step comprising straightening, flaw detection, and machining the rail in that order.

Technical Field

The invention relates to the technical field of steel rail rolling, in particular to a method for reducing the thickness of a decarburized layer of a high-speed railway steel rail.

Background

The steel rail is used as a running part of a railway, the quality of the steel rail is good, the transportation efficiency and the driving safety are severely limited by the performance, and the higher requirements on the production and the quality of the steel rail are provided due to the improvement of the transportation speed of the railway. The decarburization phenomenon generated in the manufacturing process of the steel rail cannot be avoided, but the thickness of the decarburization layer generated on the surface of the steel rail directly influences the matching of the wheel-rail relationship of the high-speed railway, so that the contact stress changes, the driving safety is restricted, and meanwhile, the thickness of the decarburization layer influences the typical performance indexes of the steel rail, such as the mechanical performance, the surface hardness, the wear resistance and the like of the steel rail. Therefore, the reduction of the thickness of the decarburized layer of the high-speed railway steel rail is one of the research hotspots of various manufacturers and experts.

The decarburization of the steel rail means that under the condition of high temperature, carbon atoms on the surface layer of a steel rail casting blank move from the inside to the surface due to the principle of thermal diffusion and react with oxidizing gas in a heating furnace, so that the carbon atoms on the surface layer of the steel are lost within a certain range. The steel rail decarburization is essentially a chemical reaction between carbon element in steel and oxygen, oxide and water in furnace gas in a heating process, and a plurality of factors influencing billet decarburization such as oxidation speed, original decarburization degree of a billet, steel type characteristics, heating temperature, heating time, atmosphere in a heating furnace, rolling speed, cooling process schedule and the like exist.

At present, in order to reduce the thickness of a decarbonized layer of a high-speed railway steel rail in the prior art, the decarbonization degree of the surface of a billet is mainly controlled by controlling the atmosphere, the heating temperature, the heating time and the chemical component ratio in a stepping heating furnace, so that the aim of reducing the decarbonization layer of the steel rail is fulfilled.

In terms of chemical component distribution ratio, the decarburized layer has outstanding problems, and the prior art has no specific embodiment for optimizing the ratio and controlling the fluctuation and the matching relation of each chemical component. CN109023044B, entitled "method for controlling depth of decarburization layer of heavy rail steel", discloses that the purpose of reducing thickness of decarburization layer of steel rail is achieved by adding 0.015-0.025 wt% of titanium element into the composition of heavy rail steel and matching with proper continuous casting control process and heating process, but the patent only adds proper amount of Ti element, and does not relate to main chemical elements such as C, Si, Mn, Cr and the like and the content thereof.

From the perspective of improving heating parameters of steel billets, there are few research reports on reducing the steel rail decarburizing layer by controlling time and temperature accurately in a sectional manner. CN109266830A, entitled "heating production method for controlling depth of decarburization layer of high carbon steel rail" discloses that steel rail casting blank adopts cold charging process, the heating process comprises a preheating section, a heating section and a soaking section, the temperature of the preheating section is not higher than 900 ℃, the temperature of the heating section is 1050-1180 ℃, the temperature of the soaking section is 1130-1180 ℃, and the depth of decarburization layer of high carbon steel rail tread with carbon content of 0.74-0.79 wt% is less than 0.5 mm. The patent application only relates to the content range of C and the temperature control range of each heating furnace section, and does not mention the precise control time of each heating section.

CN104878177A, entitled Rolling Process for reducing depth of decarburization layer of Steel Rail, discloses a stepping heating furnace for heating continuous casting billet, wherein temperature of preheating section is less than 900 ℃, temperature of heating section is 1160-1260 ℃, temperature of soaking section is 1220-1250 ℃, temperature difference of thermocouple at two sides of heating furnace is less than or equal to 30 ℃, heating time is 3.5-4.0 h, and depth of decarburization layer of steel rail surface is controlled between 0.18-0.41 mm. The patent only relates to the temperature control interval and the total time of each heating section, and does not relate to a method for controlling decarburization in a synergistic way of component matching and heating temperature and time.

CN102399959A, entitled method for reducing thickness of decarburized layer of steel rail, discloses steps of heating, cogging and universal rolling of steel billet in sequence, wherein the heating step heats the steel billet to be in a range of 1220-1250 ℃, the heating time is not more than 7 hours, in the heating step, when the temperature of the steel billet is not more than 800 ℃, the air excess coefficient is controlled to be 1.10-1.15, when the temperature of the steel billet is 800-1200 ℃, the air excess coefficient is controlled to be 0.95-1.00, when the temperature of the steel billet is not less than 1200 ℃, the air excess coefficient is controlled to be 0.90-0.95, and the compression ratio in the universal rolling step is controlled to be 2.70-2.75, so as to achieve the purpose of decarburizing the layer thickness of the steel rail to be reduced to be less than 0.50 mm. The patent application only relates to the control temperature and air surplus coefficient of each heating section, and does not mention the component proportion and the precise control time of each heating section.

Therefore, in the prior art, the method for reducing the high-speed railway steel rail decarburizing layer mainly focuses on temperature control of the billet heating furnace, and does not relate to the influence and control technology of the main chemical components which are beneficial to decarburization, the accurate time of each heating section, temperature control and the air excess coefficient of each heating section on the high-speed railway steel rail decarburizing layer by comprehensive consideration of the system.

Disclosure of Invention

In view of the shortcomings of the prior art, the invention aims to provide a method for reducing the thickness of a decarburized layer of a steel rail.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a method for reducing the thickness of a steel rail decarburization layer, which determines a steel rail decarburization degree coefficient DI according to the following formula:

DI＝(4.61[％C]+2.62[％Si]-2.25[％Mn]-3.78[％Cr])/0.5

in the formula:

[% C ] is the mass content of C element in the steel rail;

[% Si ] is the mass content of Si element in the steel rail;

[% Mn ] is the mass content of Mn element in the steel rail;

[% Cr ] is the mass content of Cr element in the steel rail;

wherein the decarburization degree index DI and [% C ] + [% Si ] + [% Mn ] + [% Cr ] satisfy a predetermined matching relationship.

Further, the predetermined matching relationship is: the decarburization degree coefficient DI is 4.5 to 7.0, and the value of [% C ] + [% Si ] + [% Mn ] + [% Cr ] is 1.85 to 3.02 mass%.

Further, the chemical components of the steel rail are as follows:

c: 0.70 to 0.82 mass%, Si: 0.50 to 0.80 mass%, Mn: 0.60 to 1.20 mass%, Cr: 0.05-0.20 mass%, and,

also comprises V, Al and one or more of Co, wherein, V: 0.01-0.05 mass%, Al: 0.003 mass% or less, Co: 0.03 mass% or less.

Further, the steel billet is heated after continuous casting and sequentially passes through a preheating section, a heating section and a soaking section, wherein,

the preheating period time is 30-80min, and the preheating period temperature is 540-; the heating period time is 120-180min, and the heating period temperature is 990-1200 ℃; the time of the soaking section is 10-30min, and the temperature of the soaking section is 1150-1250 ℃.

Further, the billet is heated in a step-type heating furnace.

Furthermore, the air excess coefficient of the preheating section is 1.05-1.20, the air excess coefficient of the heating section is 0.90-1.05, and the air excess coefficient of the soaking section is 0.85-1.00.

Further, the method also comprises the step of rolling the steel billet into a steel rail with the thickness of 60-75kg/m on line.

Further, the method also comprises the step of carrying out online heat treatment on the steel rail, wherein the online heat treatment process comprises the following steps:

and air-cooling the steel rail with the residual heat after the final rolling to 820-890 ℃, then cooling the steel rail head by using the compressed gas agent mixed gas, and air-cooling the steel rail to room temperature when the steel rail head is cooled to 400-560 ℃.

Further, the cooling rate of the rail head is 1.0-5.2 ℃/s.

Further, the on-line heat treatment process is followed by a post-treatment process, wherein the post-treatment process comprises the steps of straightening, detecting flaws and processing the steel rail in sequence.

Compared with the prior art, the invention has the beneficial technical effects that: the invention optimizes the addition of main chemical elements such as C, Si, Mn, Cr and the like which influence decarburization, matches the value of [% C ] + [% Si ] + [% Mn ] + [% Cr ] with the decarburization degree coefficient DI, and establishes precise temperature time control of each heating section, thereby obviously reducing the thickness of the decarburization layer of the steel rail, and simultaneously improving the obdurability matching and the wear resistance.

Detailed Description

The embodiments of the present invention are described in further detail in order to make the objects, technical solutions and advantages of the present invention more apparent.

The invention provides a method for reducing the thickness of a steel rail decarburization layer, which determines a steel rail decarburization degree coefficient DI according to the following formula:

DI＝(4.61[％C]+2.62[％Si]-2.25[％Mn]-3.78[％Cr])/0.5

in the formula:

[% C ] is the mass content of C element in the steel rail;

[% Si ] is the mass content of Si element in the steel rail;

[% Mn ] is the mass content of Mn element in the steel rail;

[% Cr ] is the mass content of Cr element in the steel rail;

wherein the decarburization degree index DI and [% C ] + [% Si ] + [% Mn ] + [% Cr ] satisfy a predetermined matching relationship. Specifically, the predetermined matching relationship is: the decarburization degree coefficient DI is 4.5 to 7.0, and the value of [% C ] + [% Si ] + [% Mn ] + [% Cr ] is 1.85 to 3.02 mass%.

The chemical composition of the rail has an influence on the degree of diffusion of carbon atoms, and the composition of the steel is thus a decisive factor in the decarburization thereof. In the decarburization, carbon atoms on the surface of the billet and carbon atoms in the billet form a concentration gradient, so that the carbon atoms are continuously diffused from the interior of the billet to the surface, and the diffusion speed of the carbon atoms depends on the magnitude of the concentration gradient and the chemical energy of the carbon atoms. The C element in the steel rail has the most obvious influence on the decarburization effect of the steel rail, and the decarburization is serious when the C element is high. Although Si elements do not form carbides, they can promote decarburization by increasing the activity of carbon atoms and the diffusion coefficient D and also by making carbon have a tendency to be dissociated or graphitized. Mn and Cr easily reduce the activity of carbon atoms, thereby reducing the diffusion coefficient and inhibiting decarburization. Therefore, the above elements have influence on decarburization and have interaction effects different from each other.

The DI value represents the steel rail decarburization severity and can be used as an index for judging the thickness value of the steel rail decarburized layer. In the invention, if the decarburization degree coefficient DI value is larger than 7.0, it means that the main elements influencing the decarburization of the steel rail are not well matched, or one or more elements are not well controlled, so that the decarburization of the steel rail is serious, and the mechanical property of the steel rail is influenced. If the coefficient DI value of the decarburization degree is less than 4.5, the prior art steel-making technique cannot achieve such precise and strict control of the composition, and is difficult to apply to production practice. Therefore, the DI is 4.5 to 7.0.

In a preferred embodiment, the steel rail of the present invention has the following chemical components: c: 0.70 to 0.82 mass%, Si: 0.50 to 0.80 mass%, Mn: 0.60 to 1.20 mass%, Cr: 0.05-0.20 mass%, and further comprises one or more of V, Al and Co, wherein V: 0.01-0.05 mass%, Al: 0.003 mass% or less, Co: 0.03 mass% or less. Wherein [% C ] + [% Si ] + [% Mn ] + [% Cr ] has a value of 1.85-3.02 mass%.

When the value of [% C ] + [% Si ] + [% Mn ] + [% Cr ] is less than 1.85 mass%, the purpose of reducing the thickness of the decarburized layer of the steel rail can be realized, but the mechanical property of the steel rail is reduced, and the standard requirement cannot be met. When the value of [% C ] + [% Si ] + [% Mn ] + [% Cr ] is larger than 3.02 mass%, the mechanical property of the rail is ensured, but the purpose of reducing the thickness of the decarburized layer of the rail is not achieved. Therefore, the value of [% C ] + [% Si ] + [% Mn ] + [% Cr ] is preferably 1.85-3.02 mass%.

C is the most important and cheapest element for improving the strength and the wear resistance of the pearlite steel rail and promoting the pearlite transformation, and for the steel rail applied to a passenger-cargo mixed transportation railway or a heavy haul railway, under the condition of the invention, when the content of C is less than 0.70 mass percent, the steel rail has lower strength and hardness after heat treatment, and the abrasion requirement of the steel rail is difficult to meet; when the content of C is more than 0.82 percent by mass, the strength and hardness of the steel rail after heat treatment are too high; meanwhile, the crystal boundary eutectoid cementite is precipitated, and the toughness and the plasticity of the steel rail are deteriorated. Therefore, the C content is limited to 0.70 to 0.82 mass%.

Si exists in ferrite and austenite as a solid solution strengthening element in steel to improve the strength of the structure. Meanwhile, the precipitation of eutectoid cementite can be inhibited, thereby improving the toughness and plasticity of the steel rail. Under the condition of the invention, when the content of Si is less than 0.50 mass percent, the strengthening effect is not obvious because the solid solution amount is low; when the Si content is more than 0.80 mass%, the toughness and plasticity of the steel rail, particularly the crack propagation resistance, are lost. Therefore, the Si content is limited to 0.50 to 0.80 mass%.

Mn can form a solid solution with Fe, and the strength of ferrite and austenite is improved. Meanwhile, Mn is a carbide forming element, and can partially replace Fe atoms after entering a cementite, so that the hardness of the carbide is increased, and the hardness of the steel is finally increased. Under the conditions of the present invention, when the Mn content is less than 0.60 mass%, the strengthening effect is slight; when the Mn content is more than 1.20 mass percent, the hardness of carbide in the steel is too high, and the toughness and plasticity are obviously reduced; meanwhile, high Mn easily causes series segregation problems, and obviously influences the performance of the steel rail. Therefore, the Mn content is limited to 0.60 to 1.20 mass%.

Cr can homogenize carbide distribution in steel, reduce carbide size and improve the wear resistance of steel rail, and the Cr content is limited to 0.05-0.20 mass%.

V can form fine, uniform and highly dispersed carbide and nitride particles in steel, so that the wear resistance of the steel rail is improved, the reduction of the wear resistance caused by the decarburization of the steel rail can be compensated, and the decarburization phenomenon can be inhibited by grain refinement. If the content of the V element is less than 0.01 mass percent, the grain refinement degree of the steel rail material is not high, and the decarburization inhibition is low; if the content of the V element is more than 0.05 mass percent, the hardness value of the secondary surface of the steel rail is not enough. Therefore, the V content is limited to 0.01 to 0.05 mass%.

Al element can increase the decarburization tendency of the steel rail, and simultaneously hard inclusions are easily generated, so that the mechanical property of the steel rail is reduced. Therefore, the Al content is preferably 0.003 mass% or less.

The effect of the Co element on the decarburization of the rail is similar to that of the Al element, and the tendency of the rail to be decarburized can be increased. Therefore, the Co content is preferably 0.03 mass% or less.

After continuous casting, the casting blank meeting the component requirements is heated in a stepping heating furnace and sequentially passes through a preheating section, a heating section and a soaking section. In a preferred embodiment, the preheating period is 30-80min, and the temperature of the preheating period is 540-; the heating period time is 120-180min, and the heating period temperature is 990-1200 ℃; the time of the soaking section is 10-30min, and the temperature of the soaking section is 1150-1250 ℃.

In the preheating stage, if the preheating period time is less than 30min or the preheating period temperature is more than 800 ℃, the heating rate of the preheating period is too high, the thermal stress of the center of the billet becomes large, the residual stress of the center of the billet is increased, and even the billet is internally cracked; if the preheating section time is more than 80min or the preheating section temperature is less than 540 ℃, the residence time of the billet in the preheating section is too long, the rolling speed is delayed, and the industrial cost is increased. Therefore, the preheating period time is preferably 30-80min, and the preheating period temperature is preferably 540-.

In the heating stage, if the time of the heating section is less than 120min or the temperature of the heating section is more than 1200 ℃, the temperature difference between the surface and the core of the billet is increased, the thermal stress is increased, and the risk of burning cracks exists; if the heating period is longer than 180min or the temperature of the heating period is lower than 990 ℃, the residence time of the billet in the heating stage is too long, so that the risks of decarburization and overburning of the surface of the billet in the heating stage are increased. Therefore, the time of the heating section is preferably 120-180min, and the temperature of the heating section is preferably 990-1200 ℃.

In the soaking stage, if the soaking period time is less than 10min or the soaking period temperature is more than 1250 ℃, the surface and core tissues of the steel billet are uneven, the surface crystal grains of the steel billet are coarse, the core cannot be completely austenite homogenized, the mechanical property of the steel rail is reduced, and the decarburization probability of the steel rail is increased at high temperature; if the soaking period is longer than 30min or the temperature of the soaking period is lower than 1150 ℃, the decarburization probability of the steel rail is increased, the high-temperature mechanical property is easily reduced, and the load of the rolling mill is increased. Therefore, the soaking period time is preferably 10-30min, and the soaking period temperature is preferably 1150-1250 ℃.

In a preferred embodiment, the air excess coefficient of the preheating section is 1.05-1.20, the air excess coefficient of the heating section is 0.90-1.05, and the air excess coefficient of the soaking section is 0.85-1.00.

While satisfying the above-described heating process, when the air excess coefficient of the preheating stage is less than 1.05, the combustion of the heating furnace gas is insufficient, the thermal efficiency is reduced, and when the air excess coefficient of the preheating stage is more than 1.20, the oxidation and decarburization of the billet are easily promoted, so it is preferable to control the air excess coefficient of the preheating stage to 1.05 to 1.20.

When the heating process is satisfied and the air excess coefficient of the preheating stage is satisfied, the heating furnace gas is insufficiently combusted and the thermal efficiency is reduced when the air excess coefficient of the heating stage is less than 0.90, and the oxidation and decarburization of the billet are easily promoted when the air excess coefficient of the heating stage is more than 1.05, so that it is preferable to control the air excess coefficient of the heating stage to 0.90 to 1.05.

When the heating process is satisfied and the air excess coefficients of the preheating section and the heating section are simultaneously satisfied, the heating furnace gas is insufficiently combusted when the air excess coefficient of the soaking section is less than 0.85, the thermal efficiency is reduced, and the oxidation and decarburization of the billet are easily promoted when the air excess coefficient of the soaking section is more than 1.00, so that the air excess coefficient of the soaking section is preferably controlled to be 0.85 to 1.00.

After the billet is heated in the heating furnace, the billet is rolled into a steel rail with 60-75kg/m on line. And carrying out online heat treatment on the hot-rolled steel rail meeting the requirements. The on-line heat treatment process comprises the steps of air cooling the steel rail with the residual heat after the final rolling to 820-. It will be appreciated by those skilled in the art that the post-treatment procedure is a routine operation in the art.

In the invention, the cooling rate of the rail head of the steel rail is controlled to be 1.0-5.2 ℃/s, when the cooling rate is less than 1.0 ℃/s, a refined pearlite structure is difficult to form on the tread surface and the part below the rail (a wheel rail contact area), the temperature of the secondary surface is difficult to transfer under the supercooling degree, the pearlite structure with large lamella is easy to generate, when the cooling rate is more than 5.2 ℃/s, although the heat of the secondary surface of the steel rail can be fully released, the structure is remarkably refined, in the supercooling degree range, martensite or bainite transformation is easy to generate in the area, and the abnormal risk of the structure is caused. Therefore, the cooling speed of the compressed air agent mixture of the rail head of the steel rail is controlled between 1.0 and 5.2 ℃/s.

Hereinafter, the method for reducing the thickness of the decarburized layer of the steel rail according to the present invention will be specifically described with reference to examples. Table 1 shows the matching relationship between the chemical compositions, the decarburization degree coefficients DI, and the values of [% C ] + [% Si ] + [% Mn ] + [% Cr ] of examples 1 to 9 and corresponding comparative examples 1 to 4 of the present invention, wherein the mass content of C in the composition of the rail components is represented by [% C ], the mass content of Si is represented by [% Si ], the mass content of Mn is represented by [% Mn ], the mass content of Cr is represented by [% Cr ], [% C ] + [% Si ] + [% Mn ] + [% Cr ] represents the sum of the mass contents of C, Si, Mn, and Cr. Wherein the heating process parameters shown in Table 2 were selected for examples 1-9 and corresponding comparative examples 1-4.

TABLE 1 match relationship between chemical compositions, decarburization degree index DI, and values of [% C ] + [% Si ] + [% Mn ] + [% Cr ] of examples 1 to 9 and comparative examples 1 to 4

TABLE 2 heating Process parameters used in examples 1-9 and comparative examples 1-4

The steel rails obtained in the examples and the comparative examples are air-cooled to room temperature, rail head decarburized samples are taken at TB/T2344-2012 standard positions, round double-shoulder tensile samples with D0 being 10mm and l0 being 5D0 at the standard positions, and the tensile strength and the yield strength are respectively detected according to GB/T228.1; and wear test sampling is performed on the position to be measured. The wear test requires: the contact stress is 600MPa (Hertz stress), the slip is 10 percent, and the process is carried out in a non-lubrication (dry grinding) environment. It will be appreciated by those skilled in the art that the above described testing procedure is routine in the art. Examples 1-9 and comparative examples 1-4 were run using the same test sites and test methods and the results are detailed in table 3.

TABLE 3 Performance parameters of the rails of examples 1-9 and comparative examples 1-4

The invention selects 9 different composition test steel grades as examples and 4 different composition test steel grades as comparative examples (shown in table 1). Wherein the chemical composition and heating process parameters of the steel rail used in examples 1-9 are within the ranges of the chemical composition and heating process parameters of the steel rail of the present invention, the DI values of examples 1-9 and [% C ] + [% Si ] + [% Mn ] + [% Cr ] values satisfy a predetermined matching relationship, that is, the decarburization degree coefficient DI is 4.5-7.0, and the [% C ] + [% Si ] + [% Mn ] + [% Cr ] value is 1.85-3.02 mass%. The chemical composition of the steel rail used in comparative examples 1 to 4 was outside the range of the chemical composition of the steel rail of the present invention, and the heating process parameters used in comparative examples 1 to 4 were within the range of the heating process parameters of the present invention. The data comparison result shows that the optimized component proportion, the matching relation of DI value and [% C ] + [% Si ] + [% Mn ] + [% Cr ], and the proper heating process parameters obviously affect the thickness of the rail head decarburized layer of the steel rail product and the strengthening and toughening performance of the product.

As shown in Table 1 and 3, examples 1-9, the thickness of the decarburized layer at the standard position of the rail head produced was significantly reduced and was much lower than the comparative examples only when the DI value and [% C ] + [% Si ] + [% Mn ] + [% Cr ] satisfied a predetermined matching relationship; within the range of the same tensile strength, the yield strength and the comprehensive strength and toughness of the standard position of the steel rail are better; has higher wear resistance under the same condition.

When the DI value and [% C ] + [% Si ] + [% Mn ] + [% Cr ] are limited to satisfy the predetermined matching relationship, the value ranges of the mass contents of C, Si, Mn and Cr can be determined. As can be seen from Table 1, comparative examples 1 to 4 employ C, Si, Mn, Cr in mass contents outside the ranges of the chemical compositions of the steel rail of the present invention, even if the DI values of comparative examples 1 to 2 satisfy the predetermined ranges (DI is between 4.5 and 7.0), the values of [% C ] + [% Si ] + [% Mn ] + [% Cr ] do not satisfy the predetermined ranges (i.e., are not between 1.85 and 3.02 mass%); even though the values of [% C ] + [% Si ] + [% Mn ] + [% Cr ] of comparative examples 3 to 4 satisfy the predetermined range (i.e., between 1.85 and 3.02 mass%), the DI values thereof do not satisfy the predetermined range (i.e., not between 4.5 and 7.0). In other words, the decarburization degree index DI of comparative examples 1 to 4 does not satisfy a predetermined matching relationship with the value of [% C ] + [% Si ] + [% Mn ] + [% Cr ], so that the resulting steel rail has a high decarburized layer thickness and a poor toughness of the steel rail product.

Combining the data of tables 1 and 3, and comparing example 3 with comparative example 3, for example, to illustrate below, although the tensile strength (1321MPa) of the rail of example 3 is not much different from the tensile strength (1310MPa) of the rail of comparative example 3, the yield strength (912MPa) of the rail of example 3 is significantly greater than the yield strength (854MPa) of the rail of comparative example 3, i.e., the toughness of the rail of example 3 is overall better than the toughness of the rail of comparative example 3. Also for example, comparing example 1 with comparative example 1, the tensile strength (1056MPa) and yield strength (756) of comparative example 1 were significantly lower than those of example 1 (1256MPa) and yield strength (901MPa), although the decarburized layer thickness (0.21mm) of the steel rail of example 1 was not much different from that of the steel rail of comparative example 1 (0.24 mm). Based on the analysis, the thickness of the decarburized layer at the standard position of the rail head of the steel rail produced by the method is obviously reduced and is far lower than that of a comparative example; even with similar decarburized layer thicknesses, the rails of the invention have better tensile and yield strengths than the rails of the comparative examples. In addition, within the range of the same tensile strength, the yield strength is higher, and the obdurability matching is better; has higher wear resistance under the same condition.

The invention provides a method for reducing the thickness of a decarbonization layer of a high-speed railway steel rail, which aims to reduce the thickness of the decarbonization layer of the high-speed railway steel rail, optimizes the addition amount of main chemical elements such as C, Si, Mn, Cr and the like which influence decarbonization, and matches the value of [% C ] + [% Si ] + [% Mn ] + [% Cr ] with a decarbonization degree coefficient DI to establish precise heating temperature, heating time and air excess coefficient in a heating furnace of each heating section, so that the thickness of the decarbonization layer of the steel rail is obviously reduced, and simultaneously, the toughness matching and the wear resistance are improved.

Although the embodiments of the method for reducing the thickness of the decarburized layer of the high-speed railway steel rail according to the invention have been described in detail, the sequence of the embodiments of the invention is merely for description and does not represent the advantages or disadvantages of the embodiments. It should be noted that the discussion of any embodiment above is exemplary only, and is not intended to intimate that the scope of the disclosure, including the claims, of embodiments of the invention is limited to those examples, and that various changes and modifications may be made without departing from the scope, as defined in the claims. The functions, steps and/or actions of the method claims in accordance with the disclosed embodiments described herein need not be performed in any particular order. Furthermore, although elements of the disclosed embodiments of the invention may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated.

Those of ordinary skill in the art will understand that: the discussion of any embodiment above is meant to be exemplary only, and is not intended to intimate that the scope of the disclosure, including the claims, of embodiments of the invention is limited to these examples; within the idea of an embodiment of the invention, also technical features in the above embodiment or in different embodiments may be combined and there are many other variations of the different aspects of an embodiment of the invention as described above, which are not provided in detail for the sake of brevity. Therefore, any omissions, modifications, substitutions, improvements, and the like that may be made without departing from the spirit and principles of the embodiments of the present invention are intended to be included within the scope of the embodiments of the present invention.