阅读说明：本技术 一种珠光体钢轨钢及其制备方法 (Pearlite rail steel and preparation method thereof ) 是由 王东梅 陈林 包喜荣 周庆飞 郭瑞华 牛建宇 王慧军 于 2019-10-29 设计创作，主要内容包括：本发明涉及钢轨钢的处理技术领域,尤其涉及一种珠光体钢轨钢及其制备方法。本发明提供的制备方法,包括以下步骤：将具有与珠光体钢轨钢组分相同的钢锭依次进行轧制和控冷,得到珠光体钢轨钢；所述控冷包括第一阶段冷却、第一阶段空冷、第二阶段冷却和第二阶段空冷。本发明提供的方法在添加较少合金元素的前提下,利用较简单的制备方法即可得到平均片层间距在60nm以下的珠光体组织,极大地提高了珠光体钢轨钢的抗疲劳裂纹扩展性能。(The invention relates to the technical field of rail steel treatment, in particular to pearlitic rail steel and a preparation method thereof. The preparation method provided by the invention comprises the following steps: rolling and cooling-controlling steel ingots with the same components as the pearlite rail steel in sequence to obtain the pearlite rail steel; and the controlled cooling comprises first-stage cooling, first-stage air cooling, second-stage cooling and second-stage air cooling. According to the method provided by the invention, on the premise of adding less alloy elements, the pearlite structure with the average lamellar spacing below 60nm can be obtained by a simpler preparation method, and the fatigue crack propagation resistance of the pearlite rail steel is greatly improved.)

1. A preparation method of pearlitic rail steel is characterized by comprising the following steps:

the pearlite rail steel comprises the following element components in percentage by mass:

0.82-0.84% of C, 0.6-0.8% of Si, 0.95-1.05% of Mn, less than or equal to 1.2% of Cr + Nb, less than or equal to 0.1% of RE, less than or equal to 0.025% of P, less than or equal to 0.015% of S, and the balance of iron and inevitable impurities;

rolling and cooling-controlling the steel ingot with the same components as the pearlite rail steel in sequence to obtain the pearlite rail steel;

and the controlled cooling comprises first-stage cooling, first-stage air cooling, second-stage cooling and second-stage air cooling.

2. The preparation method according to claim 1, wherein the final rolling temperature of the rolling is 890-930 ℃.

3. The preparation method according to claim 1 or 2, wherein the first-stage cooling is to cool the rolled ingot to 560 to 580 ℃ at a cooling rate of 7 to 8 ℃/s.

4. The preparation method of claim 1, wherein the air cooling in the first stage is 560-580 ℃ as the initial temperature, and the air cooling is less than or equal to 30 s.

5. The preparation method according to claim 1 or 4, wherein the second-stage cooling is to cool the steel ingot after the first-stage air cooling to 300-350 ℃ at a cooling rate of 7-8 ℃/s.

6. The method according to claim 1, wherein the second stage is air-cooled to room temperature at an initial temperature of 300-350 ℃.

7. The pearlitic rail steel obtained by the production method according to any one of claims 1 to 6, wherein the structure of the pearlitic rail steel is a nano-sized pearlitic microstructure;

the average lamellar spacing of the nanoscale pearlitic microstructure is less than 60 nm.

Technical Field

The invention relates to the technical field of rail steel treatment, in particular to pearlitic rail steel and a preparation method thereof.

Background

With the continuous increase of national economy, people put forward higher requirements on railway transportation, and the railway transportation is continuously developed towards high speed and heavy loading. The performance of the steel rail as an important component of railway transportation is directly related to the efficiency of railway transportation. Therefore, the rails are required to have not only rigidity and strength capable of supporting the running of the vehicle, but also good wear resistance and surface damage resistance of the rail head. With the several times of large speed acceleration of railways in China and the large-scale construction of high-speed railways, the damage form of steel rails in China is mainly changed from abrasion to fatigue crack propagation. This is mainly due to the fact that high speed trains are subjected to increased contact stress caused by the influence of centrifugal force when passing through a line with a large radius of curvature of the steel rail, which leads to the formation and propagation of contact fatigue cracks. And thinning the interlayer spacing of the pearlite plates is an effective means for improving the fatigue crack propagation resistance of the steel rail (engineering FractureMtechnologies, 2015,138: 63-72.).

In recent years, in order to refine the pearlite block interlayer distance, researchers have conducted a great deal of research on the design of alloy components and production processes of steel rails. For example, chinese patent application No. 201410382419.8 discloses a vanadium-chromium microalloyed superfine pearlite steel rail, which comprises the following components in percentage by weight: 0.78 to 0.86%, Si: 0.15 to 0.7%, Mn: 0.40-1.20%, Cr: 0.30-0.80%, V: 0.04-0.12% of S, and less than or equal to 0.01% of S. The preparation method mainly comprises the following steps: and applying water mist mixed gas to the rail head part of the steel rail with the residual heat after the final rolling for accelerated cooling, wherein the cooling speed is 4.0-8.0 ℃/s, stopping applying the water mist mixed gas when the surface temperature of the rail head is reduced to 500-550 ℃, applying compressed air for accelerated cooling, the cooling speed is 1.5-3.5 ℃/s, stopping accelerated cooling when the surface temperature of the rail head is lower than 400 ℃, and air-cooling to room temperature. The steel rail is a complete pearlite structure, and the interlayer spacing is 70-100 nm. The Chinese patent with the application number of 201410285670.2 discloses a preparation method of a nano pearlite steel rail, which comprises the following chemical components in percentage by weight: c: 0.83 to 0.93, Mn: 0.05-0.10, Cr: 1.0 to 1.5, Al: (8-12) Mn, Si: 1.5Al, Co: 0.1 to 0.3, Zr: 0.35-0.55, Mg: 0.02 to 0.06, Cu: 0.01 to 0.05, P: < 0.025, S: less than 0.025, and the balance Fe and other inevitable impurity elements. The preparation method mainly comprises the following steps: the initial rolling temperature is not higher than 1150 ℃, and the rolling deformation rate is 5-8 s^-1The single-pass deformation is 30-50%, the total compression ratio is more than 10, and the final rolling temperature is not lower than 950 ℃; after rolling, air-cooling until the rail head temperature is 850 ℃ and preserving heat for 20-30 min, then cooling at a cooling speed of 30-50 ℃/min until the rail head temperature is not higher than 550 ℃ and preserving heat for 30-40 min, then air-cooling to 350 ℃ and preserving heat for 60-90 min, and finally air-cooling to room temperature; then heating to 250-300 ℃, and preserving heat for 6-90 min for stress relief tempering treatment. The obtained rail had an internal structure of 100% pearlite and an average pearlite lamellar thickness interval of about 60 nm. The Chinese patent with the application number of 201510628532.4 discloses a super pearlite rail steel and a preparation method thereof, wherein the chemical components of the super pearlite rail steel in percentage by weight (wt%) comprise: c: 0.75-0.78, V: 0.05-0.09, wherein the contents of manganese, silicon and chromium satisfy the following three inequalities: 1Mn +2Si +2Cr is less than 4, 1Mn +1Si +2Cr is less than 3, and 1Mn +1Si +3Cr is more than 3. 1Mn +2Si +2Cr < 4 is the requirement of ensuring that the carbon equivalent of the steel is lower and lower than 0.85 wt%; 1Mn +1Si +2Cr < 3 is the requirement for ensuring that the pearlite transformation speed of the steel is high and the transformation is completed within 10min at the temperature of 500-600 ℃; 1Mn +1Si +3Cr > 3 is the requirement of ensuring that the spacing between pearlite plates in steel is small and the average plate spacing is less than 120 nm; the microalloy elements are Al, N and Re elements, 0.1 wt% is larger than Al + N + Re and smaller than 0.3 wt%, and the balance is iron. The preparation method mainly comprises the steps of manufacturing the steel ingot with the components by adopting a controlled rolling and controlled cooling technology, wherein the rolling temperature is 1180-1220 ℃ at the beginning, and the rolling deformation ratio is 8; then cooling to 1100 ℃ at the speed of 250-300 ℃/min, wherein the rolling deformation is 50-65%; cooling to 1000 ℃ at the speed of 150-200 ℃/min, wherein the rolling deformation is 50-70%; the cooling rate is 120-135 ℃/min in the temperature range of 1000-950 ℃, 60-80 ℃/min in the temperature range of 950-600 ℃ and 600-5 DEG CCooling at a speed of 5-10 ℃/min in a temperature range of 00 ℃, and air-cooling to room temperature below 500 ℃.

In the above patents relating to pearlitic rail steels, either a nano-sized pearlitic structure having an average lamellar spacing of less than 60nm is obtained by adding a large amount of alloying elements and a relatively complicated production process, or the average lamellar spacing of the obtained pearlitic structure is more than 70nm although the alloying elements are added less.

Disclosure of Invention

The invention aims to provide pearlitic rail steel and a preparation method thereof, and the method provided by the invention can obtain a pearlitic structure with the average lamellar spacing of below 60nm by using a simpler preparation method on the premise of adding less alloy elements, so that the fatigue crack propagation resistance of the pearlitic rail steel is greatly improved.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a preparation method of pearlite rail steel, which comprises the following steps:

the pearlite rail steel comprises the following element components in percentage by mass:

0.82-0.84% of C, 0.6-0.8% of Si, 0.95-1.05% of Mn, less than or equal to 1.2% of Cr + Nb, less than or equal to 0.1% of RE, less than or equal to 0.025% of P, less than or equal to 0.015% of S, and the balance of iron and inevitable impurities;

rolling and cooling-controlling the steel ingot with the same components as the pearlite rail steel in sequence to obtain the pearlite rail steel;

and the controlled cooling comprises first-stage cooling, first-stage air cooling, second-stage cooling and second-stage air cooling.

Preferably, the final rolling temperature of the rolling is 890-930 ℃.

Preferably, the first stage of cooling is to cool the rolled steel ingot to 560-580 ℃ at a cooling rate of 7-8 ℃/s.

Preferably, the air cooling in the first stage is carried out at 560-580 ℃ as an initial temperature, and the air cooling is less than or equal to 30 s.

Preferably, the second-stage cooling is to cool the steel ingot after the air cooling in the first stage to 300-350 ℃ at a cooling rate of 7-8 ℃/s.

Preferably, the second stage of air cooling is to use 300-350 ℃ as an initial temperature and air cool to room temperature.

The invention also provides the pearlitic rail steel obtained by the preparation method of the technical scheme, and the structure of the pearlitic rail steel is a nano-scale pearlitic microstructure;

the average lamellar spacing of the nanoscale pearlitic microstructure is less than 60 nm.

The invention provides a preparation method of pearlite rail steel, which comprises the following steps: the pearlite rail steel comprises the following element components in percentage by mass: 0.82-0.84% of C, 0.6-0.8% of Si, 0.95-1.05% of Mn, less than or equal to 1.2% of Cr + Nb, less than or equal to 0.1% of RE, less than or equal to 0.025% of P, less than or equal to 0.015% of S, and the balance of iron and inevitable impurities; rolling and cooling-controlling the steel ingot with the same components as the pearlite rail steel in sequence to obtain the pearlite rail steel; and the controlled cooling comprises first-stage cooling, first-stage air cooling, second-stage cooling and second-stage air cooling. According to the preparation method provided by the invention, a small amount of alloy elements are added, and the pearlite structure with the average lamellar spacing below 60nm can be obtained through a simple preparation method, so that the fatigue crack propagation resistance of the pearlite rail steel is greatly improved.

According to the description of the examples, the fatigue crack propagation rate and the fatigue performance index of the pearlite rail steel prepared by the preparation method are both superior to the technical indexes specified in TB/T2344-201243 kg/m-75 kg/m steel rail ordering technical conditions, and in a fatigue crack propagation experiment, the total fatigue cycle number before the pearlite rail steel sample is broken is more than 100 ten thousand times. Meanwhile, the preparation method is low in production cost and beneficial to improving the market competitiveness.

Drawings

FIG. 1 is a pearlite microstructure observed under an optical microscope of a pearlitic rail steel prepared in example 1;

FIG. 2 is a fatigue crack propagation curve (a-N curve) of the pearlitic rail steel prepared in example 1;

FIG. 3 is a fatigue crack growth rate curve (da/dN-. DELTA.K curve) of the pearlitic rail steel prepared in example 1.

Detailed Description

The invention provides a preparation method of pearlite rail steel, which comprises the following steps:

the pearlite rail steel comprises the following element components in percentage by mass:

0.82-0.84% of C, 0.6-0.8% of Si, 0.95-1.05% of Mn, less than or equal to 1.2% of Cr + Nb, less than or equal to 0.1% of RE, less than or equal to 0.025% of P, less than or equal to 0.015% of S, and the balance of iron and inevitable impurities;

rolling and cooling-controlling the steel ingot with the same components as the pearlite rail steel in sequence to obtain the pearlite rail steel;

and the controlled cooling comprises first-stage cooling, first-stage air cooling, second-stage cooling and second-stage air cooling.

In the present invention, all the raw material components are commercially available products well known to those skilled in the art unless otherwise specified.

The source of the steel ingot is not limited in any way, and the steel ingot is prepared according to the element proportion by adopting a preparation method well known to a person skilled in the art.

In the invention, the final rolling temperature of the rolling is preferably 890-930 ℃, more preferably 900-920 ℃, and most preferably 900-910 ℃.

In the present invention, the finishing temperature of the rolling is controlled within the above range to further refine the size of the pearlite colony and to avoid precipitation of pro-eutectoid cementite.

In the invention, the first stage of cooling is to cool the rolled steel ingot to 560-580 ℃ at a cooling rate of 7-8 ℃/s, and more preferably 570 ℃. After the first-stage cooling is finished, the air cooling is preferably carried out in the first stage, and the air cooling in the first stage is preferably carried out at the initial temperature of 560-580 ℃ for less than or equal to 30 s; the air cooling time in the first stage is more preferably 10-20 s, and most preferably 14 s.

In the invention, the air cooling time in the first stage is controlled in the range, so that austenite in the steel ingot can be further ensured to be completely transformed into pearlite, and meanwhile, the growth of pearlite caused by overlong time can be further avoided;

controlling the cooling rate of the cooling process and the cooling termination temperature within the above ranges can further refine the pearlite sheet interlayer distance.

After the first-stage air cooling is finished, the second-stage cooling is preferably implemented, wherein the second-stage cooling is to cool the steel ingot subjected to the first-stage air cooling to 300-350 ℃ at a cooling rate of 7-8 ℃/s, and more preferably 320-330 ℃. After the second-stage cooling is finished, the second-stage air cooling is preferably carried out, and the second-stage air cooling is preferably carried out to the room temperature at the temperature of 300-350 ℃.

In the present invention, the cooling rate and the cooling temperature of the second-stage rapid cooling are controlled within the above-mentioned ranges to further avoid the growth of the generated pearlite;

the undercooled austenite before air cooling in the second stage is basically and completely transformed into a pearlite structure in the previous cooling process, and the pearlite structure is not likely to grow at the temperature of 300-350 ℃.

The invention also provides the pearlitic rail steel obtained by the preparation method of the technical scheme, and the structure of the pearlitic rail steel is a nano-scale pearlitic microstructure;

the average lamellar spacing of the nanoscale pearlitic microstructure is less than 60 nm.

The pearlitic rail steel and the method for producing the same according to the present invention will be described in detail with reference to the following examples, but they should not be construed as limiting the scope of the present invention.