阅读说明：本技术 一种高速铁路用在线热处理钢轨及其制造方法 (Online heat treatment steel rail for high-speed railway and manufacturing method thereof ) 是由 金纪勇 陈昕 刘宏 王冬 刘祥 张锐 陈克东 丁宁 徐曦 于 2019-09-02 设计创作，主要内容包括：本发明提供了一种高速铁路用在线热处理钢轨及其制造方法,该钢轨的成分按重量百分比计如下：C：0.68％～0.78％,Si：0.30％～0.58％,Mn：0.50％～0.80％,P：≤0.025％,S：≤0.015％,Cr：0.10％～0.40％,V：0.02％～0.05％,余量为Fe和不可避免的杂质。生产方法,包括冶炼—连铸—再加热—钢轨轧制—在线热处理—矫直；在线热处理：空冷至钢轨轨头表面温度700-750℃,之后分两个阶段进行冷却。采用本发明技术方案生产的钢轨抗拉强度≥1080MPa,延伸率≥11％,硬度≥330HB。(The invention provides an on-line heat treatment steel rail for a high-speed railway and a manufacturing method thereof, wherein the steel rail comprises the following components in percentage by weight: c: 0.68-0.78%, Si: 0.30-0.58%, Mn: 0.50% -0.80%, P: less than or equal to 0.025 percent, S: less than or equal to 0.015 percent, Cr: 0.10% -0.40%, V: 0.02-0.05%, and the balance of Fe and inevitable impurities. The production method comprises smelting, continuous casting, reheating, rolling the steel rail, online heat treatment and straightening; online heat treatment: air cooling to the surface temperature of the rail head of the steel rail of 700-750 ℃, and then cooling in two stages. The tensile strength of the steel rail produced by the technical scheme of the invention is more than or equal to 1080MPa, the elongation is more than or equal to 11 percent, and the hardness is more than or equal to 330 HB.)

1. The on-line heat treatment steel rail for the high-speed railway is characterized by comprising the following components in percentage by weight: c: 0.68-0.78%, Si: 0.30-0.58%, Mn: 0.50% -0.80%, P: less than or equal to 0.025 percent, S: less than or equal to 0.015 percent, Cr: 0.10% -0.40%, V: 0.02-0.05%, and the balance of Fe and inevitable impurities.

2. A method for producing an on-line heat-treated rail for a high-speed railway according to claim 1, comprising the steps of smelting, continuous casting, reheating, rolling of the rail, on-line heat treatment and straightening; the method is characterized in that:

(1) reheating: the soaking temperature of the continuous casting billet is 1250-1300 ℃, and the heat preservation time is 1-1.5 hours;

(2) rolling steel rails: the rough rolling starting temperature of the continuous casting slab is 1150-plus 1200 ℃, the starting temperature of the universal rolling mill is 1000-plus 1050 ℃, and the final rolling temperature is 950-plus 1000 ℃;

(3) online heat treatment: air cooling to the surface temperature of the rail head of the steel rail of 700-750 ℃, and then cooling in two stages, wherein the first stage comprises the following steps: cooling at an average cooling speed of 3.0-5.0 ℃/s to the surface temperature of the rail head of 500-; and a second stage: cooling at an average cooling rate of 2.0-4.0 ℃/s to the surface temperature of 470-510 ℃, and then cooling in air to room temperature for straightening.

Technical Field

The invention belongs to the field of metal materials, and particularly relates to an online heat treatment steel rail for a high-speed railway and a manufacturing method thereof.

Background

The steel rail for the high-speed railway adopts a steel rail made of U71Mn in a steel rail for the high-speed railway (TB/T3276), the axle weight and the transportation capacity of the high-speed railway are far lower than those of a freight transportation or heavy-load line, the operation condition of China for many years shows that the U71Mn hot-rolled steel rail is suitable for straight sections of the high-speed railway with high speed and light load, the stress of the steel rail in the curve section is relatively increased, and the abrasion is intensified, so that the steel rail is subjected to the on-line heat treatment by the U71Mn, and the characteristics of moderate strength and good toughness of the steel rail subjected to the on-line heat treatment by the U71Mn hot-rolled steel and the on. The seamless connection mode of the steel rails has become the mainstream, particularly, the high-speed railways all adopt seamless lines, so the welding quality of the steel rails directly influences the use effect, and the damage in the service cycle of the steel rails mainly takes the defects at the welding seams as the main factor. The U71Mn steel rail mainly uses Mn element as a main strengthening mode, local segregation of Mn in steel cannot be avoided, the Mn segregation position is easy to produce martensite structure under the condition of large supercooling degree in the process of producing heat-treated steel rail or welding normalizing rapid cooling, martensite is not allowed to exist in pearlite steel rail, therefore, a proper heat treatment process must be formulated for avoiding the martensite structure, but the too low cooling speed cannot ensure online heat treatment or the performance of a welding seam meets the standard requirement, therefore, compared with the existing U75V material steel rail, the production and post-welding heat treatment of the U71Mn steel rail by online heat treatment are difficult, the process control window is narrow, and the problems of performance incompatibility or abnormal structure are easy to occur. Pearlite on-line heat-treated steel rails are improved in strength and hardness mainly by elements such as C, Si, Mn, Cr, and V, for example:

1) c, Si component content is increased in steel, V, Cr microalloy steel rail is added, and rail head hardening heat treatment steel rails such as U75VH, U77MnCrH, U78CrVH steel rail and the like are manufactured by accelerating cooling of the rail head part (for example, the heat treatment method of the vanadium-containing alloy steel rail provided by Chinese patent ZL 96117731.4).

2) Further increasing the carbon content of the steel, increasing the high wear resistance of the rail by increasing the cementite density, and obtaining hypereutectoid heat treated rails by on-line heat treatment of refined grains (e.g., the new japanese iron works patent "rail excellent in wear resistance and internal damage resistance and method for producing the same" (ZL96190344.9) "and" pearlitic rail excellent in wear resistance and ductility and method for producing the same "(03800576. X) and the chinese patent" heat treatment method of hypereutectoid rail "(201410058292.4)," hypereutectoid rail and method for producing the same "(201510487942.1) and" rail steel having excellent combination of wear resistance and rolling contact fatigue resistance "(200980105903.3), etc.).

3) Chinese patent application No. 201480018025.2 discloses a pearlite steel rail and a manufacturing method of the pearlite steel rail, wherein the method adopts elements with high C, Si, Mn and Cr, and obtains the pearlite steel rail steel with the strength of more than 1300MPa and the hardness of more than 400HB by accelerated cooling, and the steel rail is relatively suitable for heavy haul railway application.

The steel rails are characterized in that high-strength steel rails with the strength of 1180-1300MPa are obtained by online heat treatment by adopting strengthening elements such as Cr or V, the added elements such as Cr and V except C, Si and Mn improve the adaptability of the heat treatment process of the steel rails, the tendency of generating abnormal structures during production and post-weld heat treatment is reduced, but the problem of toughness reduction caused by the improvement of the strength and the hardness is obviously not suitable for high-speed steel rails with light load. By the requirements on the performance of the high-speed railway online heat-treated steel rail, analyzing the problems of the existing U71Mn steel rail online heat treatment and post-weld heat treatment, combining the strengthening effect of each element, determining a scheme of reducing Mn elements and adding Cr and V elements, and matching with a heat treatment process, the high-speed railway online heat-treated steel rail with the same performance as the U71Mn online heat-treated steel rail and better process adaptability is obtained. The invention solves the problem of difficult on-line heat treatment production and welding for the high-speed railway, is applied to high-speed railway construction and maintenance and rail replacement in future, and has wide market prospect.

Disclosure of Invention

The invention aims to overcome the problems and the defects and provide an on-line heat treatment steel rail for a high-speed railway and a manufacturing method thereof, wherein the requirement of the curve section of the high-speed railway on good matching of strength and toughness is met, Cr and V are properly added on the basis of reducing Mn elements which are easy to segregate, so that the reduction of strength and hardness caused by the reduction of the Mn elements is compensated, and the on-line heat treatment production and the post-weld heat treatment are both easy.

The purpose of the invention is realized as follows:

the on-line heat treatment steel rail for the high-speed railway comprises the following components in percentage by weight: c: 0.68-0.78%, Si: 0.30-0.58%, Mn: 0.50% -0.80%, P: less than or equal to 0.025 percent, S: less than or equal to 0.015 percent, Cr: 0.10% -0.40%, V: 0.02-0.05%, and the balance of Fe and inevitable impurities.

The invention has the following design reasons:

c is an element promoting pearlite transformation. When the C content in the pearlite steel rail is lower than 0.68%, a pearlite structure with higher strength and hardness is difficult to obtain, the abrasion of the steel rail is aggravated, the service life of the steel rail is influenced, when the C content is too high, cementite is easy to generate in the phase transformation process, fatigue damage occurs when the steel is used as a fatigue source, and the toughness and plasticity of the steel are reduced along with the increase of the C content, so that the comprehensive consideration of the toughness and plasticity matching is realized, and the addition amount of the C in the steel rail is limited to 0.68-0.78%.

Si plays a role in solid solution strengthening in a ferrite phase, so that the hardness (strength) of a pearlite structure is increased, the wear resistance of the steel rail is improved, elements play a role in deoxidation in a smelting process, the toughness of the steel rail is reduced due to the excessively high content of Si, the welding performance is deteriorated, and the addition amount of Si is limited to 0.30-0.60%.

Mn is a phase-change type strengthening element with the highest cost performance, is also replaced and dissolved in ferrite to play a strengthening role, and is also a good hardenability element, and the segregation of the Mn content can reach 2 times of the average Mn content in general, so that a segregation position is easy to produce a martensite structure when the adding amount of Mn is high in the accelerated cooling process. Therefore, in the present invention, the Mn content is set to 0.50% to 0.80%.

Cr is an element which obviously improves the hardenability of steel, the strength, hardness and wear resistance of the steel rail are improved by reducing the critical cooling speed of the steel, and when the Cr content is lower than 0.10%, the hardness and proportion of formed carbide are lower, so that the improvement of the wear resistance of the steel rail is limited; when the chromium content is higher than 0.40%, coarse carbide is easily formed, and the toughness and plasticity of the steel rail are reduced. Therefore, the Cr content of the present invention is limited to 0.10% to 0.40%.

V can refine the grain size of ferrite and improve the strength, hardness and wear resistance of a pearlite structure. In the hot rolling process, if existing in austenite grain boundary or other areas, the vanadium carbonitride is precipitated in the form of refined granular, and the growth of austenite grains is inhibited, so that the purposes of refining grains and improving performance are achieved. When the content of V is too high, on one hand, the production cost is increased, and on the other hand, coarse carbonitride is easily formed, so that the toughness and plasticity of the steel rail are reduced. In view of the performance objectives to be achieved by the present invention, V is added in an amount of 0.02-0.05%.

The second technical scheme of the invention provides a manufacturing method of an online heat treatment steel rail for a high-speed railway, which comprises the following steps: smelting, continuous casting, reheating, rolling and straightening a steel rail;

(1) the soaking temperature of the continuous casting billet is 1250-plus-1300 ℃, the heat preservation time is 1-1.5 hours, the temperature is favorable for homogenizing the components of the continuous casting billet, the continuous casting billet is possibly overheated or bent in a hearth due to overhigh temperature, the temperature of a steel rail is reduced when the continuous casting billet is rolled in the later period due to overlow temperature, the deformation resistance is increased, and the rolling specification is difficult to control.

(2) The cogging rolling of the continuous casting billet adopts a hole-shaped rough rolling mill, the cogging temperature is 1150-plus-1200 ℃, the steel rail rolling adopts a universal rolling mill, the rolling temperature is 1000-plus-1050 ℃, the finish rolling temperature is 950-plus-1000 ℃, the steel rail head is cooled by air until the surface temperature of the steel rail head is 700-plus-750 ℃, the cooling is carried out by adopting compressed air in two stages, and the first stage is as follows: cooling at an average cooling rate of 3.0-5.0 ℃/s until the surface temperature of the rail head is 500-: cooling at an average cooling speed of 2.0-4.0 ℃/s to a rail head surface temperature of 470-.

The invention has the beneficial effects that:

(1) the invention considers the segregation problem of Mn element, reduces the Mn content, and simultaneously improves the strength and the hardness of a pearlite structure by Cr and V elements, so that the toughness of the steel rail reaches the level of the prior U71Mn on-line heat treatment steel rail, and the steel rail has good process adaptability of on-line heat treatment and postweld heat treatment.

(2) The invention reasonably optimizes the components of each element, ensures that the components are easy to control stably during smelting, and tests the mechanical properties of the obtained test steel rail show that: within the technical scheme of the invention, the tensile strength (Rm) is more than or equal to 1080MPa, the elongation (A) is more than or equal to 11 percent, and the hardness is more than or equal to 330 HB. The microstructure is pearlite and a small amount of ferrite under the condition of different cooling rates, abnormal structures such as martensite and bainite do not appear, the structure and the performance meet the standard requirements, and the heat treatment process control window. The comparative example is the original U71Mn on-line heat treatment of the steel rail, the performance of the steel rail designed by the heat treatment process parameters needs a slightly higher average cooling speed to meet the standard requirements, and abnormal structures are easy to generate.

Drawings

FIG. 1 is a gold phase diagram of the microstructure of example 3 of the present invention.

Detailed Description

The present invention is further illustrated by the following examples.

According to the embodiment of the invention, smelting, continuous casting, rolling, continuous annealing and leveling are carried out according to the component proportion of the technical scheme. The composition of the steel rail of the embodiment of the invention is shown in table 1. The main process parameters of the steel rail of the embodiment of the invention are shown in the table 2. The properties of the steel rails according to the examples of the present invention are shown in Table 3.

TABLE 1 composition of Steel rails according to examples of the present invention (wt%)

TABLE 2 Main Process parameters of the rails of the examples of the invention

TABLE 3 Properties of the rails of the examples of the invention

In order to express the present invention, the above embodiments are properly and fully described by way of examples, and the above embodiments are only used for illustrating the present invention and not for limiting the present invention, and those skilled in the relevant art can make various changes and modifications without departing from the spirit and scope of the present invention, and any modifications, equivalent substitutions, improvements, etc. made by the persons skilled in the relevant art should be included in the protection scope of the present invention, and the protection scope of the present invention should be defined by the claims.