Method for improving mechanical property of export steel rail

Abstract

The invention discloses a method for improving mechanical properties of export steel rails, which is characterized by comprising the following steps: dividing a hundred-meter export steel rail after quenching into five sections A, B, C, D and E every 20 meters, continuously sampling 5 samples at the position close to the head end of each section, and ensuring that each sample has the length of 1m and totally comprises 25 samples; and the taken steel rail is sequentially subjected to tempering treatment in a small heating furnace, the tempering temperature ranges from 300 DEG C to 400 DEG C, heat preservation is conducted for 4-20 h, and after heat preservation is conducted, air cooling is conducted to the room temperature. According to the method for improving the mechanical property of the export steel rail, the mechanical property of the export steel rail is further improved, and then the provided export steel rail subjected to heat treatment has excellent wear resistance and very high strength and hardness.

Description

Technical Field

[0001] The invention belongs to the technical field of steel rolling and heat treatment, and in particular relates to a method for improving the mechanical properties of export rails. Background Art

[0002] With the development of overseas railway transportation construction, the quality and performance requirements of rails are becoming more and more stringent, especially the service performance of rail materials requires strict conditions such as ensuring service life. European standard EN13674 is one of the important technical standards for export rails and is the main standard for purchasing rails in countries and regions such as Europe, Africa, and Southeast Asia. The export rails used for heavy-duty lines meet the standard requirements after online heat treatment and cooling. However, with the fierce competition in the export market and the increase in customer service requirements, it is necessary to improve the toughness and service life of rail materials within the scope of standard composition and process requirements. At present, it is increasingly difficult to improve the excavation performance under internal control composition. Therefore, it is necessary to develop high-performance export rails that meet the standards and are higher than the standards through other processes to meet the stringent requirements of customers. According to statistics, the international market has grown steadily every year, and the market demand has continued to grow. Therefore, it is of great production and economic significance to develop European standard high-strength wear-resistant rails that meet the standards and have excellent service performance. Summary of the invention

[0003] The purpose of the present invention is to provide a method for improving the mechanical properties of export rails, further improve the mechanical properties of export rails, and thereby make the provided heat-treated export rails have excellent wear resistance and very high strength and hardness.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The invention discloses a method for improving the mechanical properties of export rails. The method comprises the following steps: dividing the quenched export rails of 100 meters into five sections, namely A, B, C, D and E, at intervals of 20 meters; taking five samples continuously from each section near the head end, each sample having a length of 1 meter, and a total of 25 samples; sequentially performing tempering treatment on the taken rails in a small heating furnace, the tempering temperature being 300-400 DEG C, the heat preservation being 4-20 hours, and air cooling to room temperature after the heat preservation time.

[0006] Furthermore, the rail composition is calculated by mass percentage as follows: C: 0.78%, Si: 0.54%, Mn: 1.12%, P<0.020%, S≤0.025%, Cr: 0.14%, V 0.013%, and the rest is Fe and impurities.

[0007] Furthermore, the tempering temperature is 300°C and the temperature is kept for 8 hours.

[0008] Furthermore, the tempering temperature is 350°C and the temperature is kept for 8 hours.

[0009] Further, the tempering temperature is 450°C and the holding time is 8 hours.

[0010] Further, the tempering temperature is 350°C and the holding time is 4 hours.

[0011] Further, the tempering temperature is 350°C and the holding time is 20 hours.

[0012] Further, the microstructures before and after tempering are both pearlite microstructures.

[0013] Further, for the rail after tempering, the mechanical properties are improved compared with those before tempering, with the tread hardness increased by ≥5 HBW and the tensile strength increased by ≥20 MPa.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are:

[0015] For the exported rail after tempering, performance testing is carried out in accordance with the requirements of the European standard EN13674.1-2017: for the rail after tempering, the mechanical properties are improved compared with those before tempering, with the tread hardness increased by ≥5 HBW and the tensile strength increased by ≥20 MPa. The microstructures before and after tempering are both pearlite microstructures. Description of the Drawings

[0016] The present invention will be further described below in conjunction with the description of the drawings.

[0017] Figure 1 For the microstructures corresponding to different embodiments

[0018] Figure 2 For the comparison of the pearlite lamellar spacing before and after tempering. Detailed Embodiments

[0019] The present invention will be further described below in conjunction with the embodiments.

[0020] A method for improving the mechanical properties of exported rails includes:

[0021] The 100-meter exported rail after quenching is divided into five sections A, B, C, D, and E at intervals of 20 meters. At the position near the head end of each section, 5 samples are continuously taken, and the length of each sample is 1 m. A total of 25 samples are taken.

[0022] The taken rails are successively subjected to tempering experiments in a small heating furnace, with the tempering temperature of 300-400°C and the holding time of 4-20 hours. After the holding time, they are air-cooled to room temperature. The specific process scheme is shown in Table 1.

[0023] The heat-treated rails are subjected to performance testing in accordance with the requirements of the European standard EN13674.1-2017.

[0024] Table 1 Tempering Experiment Scheme

[0025]

[0026] Examples 1 - 6 are given in Table 1. Unless otherwise specified, for the rails, other steps in preparing the rails, such as furnace charge smelting, LF refining, vacuum treatment, casting, cooling, heating in a heating furnace, rolling, heat treatment, machining, etc. are all conventional operations in the art. And the corresponding heat-treated rails for export have the same composition. The rail composition is by mass percentage: C: 0.78, Si: 0.54, Mn: 1.12, P < 0.020, S ≤ 0.025, Cr: 0.14, V 0.013, and the rest is Fe and impurities. Under the same composition, different tempering processes and mechanical properties are compared.

[0027] In Examples 1, 2, 3, and 4, the holding time is 8h, and four different heating temperatures are set from 200°C to 400°C to compare the influence law of heating temperature on mechanical properties.

[0028] Compared with Example 5, Example 6 further compares the influence of holding time on the performance law. At a heating temperature of 350°C, the rails are held for a long time or a short time in the tempering temperature range to achieve sufficient holding, so as to achieve uniform structure, reduced pearlite lamellar spacing, and further improve the mechanical properties of the rails for export.

[0029] Table 2 Comparison of mechanical properties of each example and before tempering

[0030]

[0031] As can be seen from Table 2, compared with the comparative example before tempering, except for Example 1, the tensile strength and tread hardness of Examples 2 - 6 have all increased. With the increase of tempering temperature, they all show a trend of first increasing and then decreasing. The elongation also increases compared with before tempering, but there is no obvious change law. And the pearlite lamellar spacing after tempering mostly becomes finer.

[0032] The mechanical properties of the rails for export obtained in the present invention are as follows: the tensile strength is between 1293 - 1306 MPa after tempering from the original strength of 1283 MPa, an increase of 10 - 25 MPa; the tread hardness is increased from 364 HBW before tempering to 368 - 373 HBW, an increase of 4 - 9 HBW; the elongation is also increased from 12% to 12 - 15%, an increase of 0 - 3%. Among them, the tempering process of Example 3, that is, the tempering temperature is 350°C and the holding time is 8h, has the most obvious improvement in mechanical properties and is the optimal tempering process.

[0033] During the process of the examples of the present invention, compared with Examples 1 - 6, the rail structure does not deteriorate and is all pearlite structure.

[0034] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for improving the mechanical properties of export rails, characterized in that: The quenched 100-meter export rails are divided into five sections, A, B, C, D, and E, every 20 meters. Five samples are taken continuously from each section near the head end. The length of each sample is 1 meter, and there are 25 samples in total. The taken rails are tempered in a small heating furnace in turn. The tempering temperature is 300-400℃, and the temperature is kept for 4-20h. After the temperature is kept for a period of time, they are air-cooled to room temperature.

2. The method for improving the mechanical properties of export rails according to claim 1, characterized in that: The rail components are as follows by mass percentage: C: 0.78%, Si: 0.54%, Mn: 1.12%, P<0.020%, S≤0.025%, Cr: 0.14%, V0.013%, and the rest are Fe and impurities.

3. The method for improving the mechanical properties of export rails according to claim 1 or 2, characterized in that: Tempering temperature is 300℃, and the temperature is kept for 8h.

4. The method for improving the mechanical properties of export rails according to claim 1 or 2, characterized in that: Tempering temperature is 350℃, keep warm for 8h.

5. The method for improving the mechanical properties of export rails according to claim 1 or 2, characterized in that: Tempering temperature is 450℃, and the temperature is kept for 8h.

6. The method for improving the mechanical properties of export rails according to claim 1 or 2, characterized in that: Tempering temperature is 350℃, keep warm for 4h.

7. The method for improving the mechanical properties of export rails according to claim 1 or 2, characterized in that: Tempering temperature is 350℃, keep warm for 20h.

8. The method for improving the mechanical properties of export rails according to claim 1 or 2, characterized in that: The microstructures before and after tempering are both pearlite.

9. The method for improving the mechanical properties of export rails according to claim 1 or 2, characterized in that: The mechanical properties of the rails after tempering are compared with those before tempering, with the tread hardness ≥5HBW and the tensile strength ≥20MPa.

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