Rolling method of export high-hardness steel rail

Abstract

The invention discloses a rolling method of a high-hardness steel rail for export. The heating temperature is 1200 + / -15 DEG C; the tapping temperature is not lower than 1100 DEG C; the rolling temperature is 1100-1130 DEG C, and the final rolling temperature is less than 930 DEG C; the high-hardness steel rail for the export comprises the following chemical components in percentage by mass: 0.76-0.85% of C; s : 0.47 to 0.57%; mn: 0.9 to 1.18%; less than or equal to 0.020% of P; less than or equal to 0.020% of S; 0.20 to 0.3% of Cr; and the balance of Fe and inevitable impurities. The invention aims to provide a rolling method of a high-hardness steel rail for export, and provides an HH370HB steel rail which meets the AREMA-2020 standard and is applied to the North America market.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgical materials, and particularly relates to a rolling method for high-hardness steel rails for export. Background Art

[0002] With the acceleration of the urbanization process and the increase in population mobility, the demand for fast and convenient long-distance passenger transportation is also growing day by day. Railway passenger transportation can meet the travel needs of people between different cities and regions, promoting regional exchanges and economic development. The continuous progress of technologies including the planning and design of railway lines, the construction technology of bridges and tunnels, and the laying and fixing technology of tracks enables railways to cross complex terrains and landforms, improving the safety and stability of railways and providing technical support for the development of steel rails. Unified steel rail standards help improve the efficiency and safety of railway transportation, reduce costs, and promote the standardized development of the steel rail industry in the Americas. North America is a region with developed heavy-haul railways and ranks among the top in the world in heavy-haul transportation technology. Railways are mainly for freight transportation, and with the development of heavy-haul transportation, the axle load is constantly increasing. Currently, the axle load of North American railways is mostly 32.4 t, and the maximum axle load is as high as 35.7 t. The American standard is a relatively influential technical standard in the field of steel rails for international heavy-haul freight railways and is regarded by steel rail production enterprises as the threshold for entering the high-end market. The American Railway Engineering and Maintenance-of-Way Association (AREMA) revised the latest "Steel Rail Standard" in 2020 according to the opinions of member units. In the new standard, ordinary carbon steel rails are divided into standard steel rails SS310HB, medium-strength steel rails IS350HB, and high-strength steel rails HH370HB according to the hardness of the rail tread. In short, from the changes in the standards, it can be seen that North American railway steel rails are developing in the direction of high strength, high hardness, cleanliness, and good wheel-rail matching relationship.

[0003] In recent years, with the rapid development of China's railway industry, the heavy-haul railway technology has made rapid progress. However, it is still necessary to draw on and learn from foreign advanced concepts and technologies, combine the characteristics of China's heavy-haul transportation, and continue to promote the development of China's heavy-haul technology. In addition, new technologies and new products of China's heavy-haul railways should be introduced to the North American TrcI test line and test site for testing and use assessment. While learning foreign advanced technologies, the awareness of China's heavy-haul technology abroad should be improved, and technical accumulation should be made for the large-scale export of China's products. In the development of new steel grades, it should be developed towards higher-strength steel rails, and at the same time, attention should be paid to the coordination of the strength and toughness of the steel rails. While increasing the strength, the toughness and plasticity of the steel rails should be improved to enhance the comprehensive service performance of the steel rails. Summary of the Invention

[0004] The object of the present invention is to provide a rolling method for high-hardness steel rails for export, and to provide a steel rail conforming to HH370HB in the AREMA-2020 standard, which is applied to the North American market.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] For the rolling method of the high-hardness steel rail for export of the present invention, the heating temperature is 1200 ± 15 °C; the furnace outlet temperature is not lower than 1100 °C; the rolling temperature is 1100 °C to 1130 °C, and the finishing rolling temperature is less than 930 °C;

[0007] The chemical composition of the high-hardness steel rail for export in terms of mass percentage includes: C: 0.76 - 0.85%; Si: 0.47 - 0.57%; Mn: 0.9 - 1.18%; P ≤ 0.020%; S ≤ 0.020%; Cr: 0.20 - 0.3%; the balance is Fe and unavoidable impurities.

[0008] Further, it also includes heat treatment. The heat treatment process includes: the inlet temperature is 763 - 780 °C, the head and tail temperature is 35 °C - 56 °C, the outlet temperature is 486 - 496 °C, the head and tail temperature is 20 - 40 °C, the reverse temperature is 565 - 576 °C, and the head and tail temperature is 20 - 30 °C.

[0009] Further, after the heat treatment of the steel rail, it satisfies: the tensile strength ≥ 1180 MPa, the yield strength ≥ 820 MPa, the elongation rate ≥ 10%, and the hardness of the steel rail tread ≥ 370 HB.

[0010] Further, the hardness of the tread of the HH steel rail produced by this method is between 370 - 383 HBW.

[0011] Further, the average hardness of the tread of the HH steel rail produced by this method is 373 HBW.

[0012] Further, the strength performance of the HH steel rail produced by this method satisfies: the tensile strength is 1252 - 1321 MPa, and the yield strength is 769 - 910 MPa.

[0013] Further, the performance of the HH steel rail produced by this method all meets the technical requirements of the AREMA-2020 standard.

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

[0015] The present invention will be further described below in conjunction with the description of the drawings.

[0016] Figure 1 It is a view of the Rockwell hardness of the steel rail;

[0017] Figure 2It is a photo of the full-section hardness detection of HH rail;

[0018] Figure 3 They are photos of the metallographic structure, decarburized layer and inclusions of HH rail;

[0019] Figure 4 It is a photo of the pearlite lamellar spacing of the rail head of HH rail. Specific implementation method

[0020] A rolling method for high-hardness rails for export, including:

[0021] (1) Billet heating: The billet is rolled in the rail and beam mill of the steel plant. The heating time and temperature of the rail are shown in Table 1.

[0022] Table 1 HH rail heating process

[0023]

[0024]

[0025] (2) Rolling: The billet is rolled into a rail by a universal rolling mill. The starting rolling temperature is 1127°C - 1143°C, and the finishing rolling temperature is 910°C - 922°C. Photos of the rail after heat treatment are shown in Figure 1 .

[0026] Table 2 HH rail heat treatment process

[0027]

[0028] (3) Straightening: The rail is pre-bent and cooled on the cooling bed, and then enters the straightening machine for straightening. The straightened rail is subjected to surface inspection and flatness inspection. No damage is found on the surface, and the flatness inspection meets the standard requirements.

[0029] (4) Ultrasonic flaw detection: The rail is subjected to full-length ultrasonic flaw detection, and the head, web, bottom, bottom corner and other parts are detected. No internal defects exceeding the standard are found in the whole length of the rail.

[0030] (5) Tensile strength and hardness

[0031] HH rail is produced on the No. 2 production line of the rail and beam mill. The rolled section of the rail is 115RE, and the results of the mechanical property inspection are shown in Table 3.

[0032] Table 3 Inspection results of HH rail in the long products inspection room

[0033]

[0034]

[0035] Table 4 Inspection results of HH rail in the long products inspection room

[0036]

[0037] By conducting tensile, microstructure, and hardness tests on the tread of the heat-treated HH115RE rails after production, the tread hardness of the HH rails produced this time is between 370 - 383 (HBW), with an average hardness of 373 (HBW). The tensile strength is between 1252 - 1321 MPa, and the yield strength is between 769 - 910 MPa. The performance meets the technical requirements of the AREMA-2020 standard.

[0038] Conduct a full-section hardness test on the rail to analyze the hardness gradient of the rail. The rail hardness test diagram is shown in Figure 2 , and the test results are shown in Table 5.

[0039] Table 5 Full-section hardness test results of HH rails

[0040]

[0041] According to the analysis of the full-section hardness test results of HH rails, the hardness of the A-line of the rail shows a trend of first decreasing and then increasing from the rail head to the rail bottom. According to the air-blowing position of the waste heat quenching line of Baotou Steel, the main positions of the air nozzles correspond to the top surface of the rail head and the center of the rail bottom. Therefore, the closer to the air nozzle position, the higher the rail hardness, and the hardness of the upper triangle, rail web, and lower triangle areas is uniform, indicating the same cooling rate. The hardness of the F-line of the rail increases first and then decreases from the left end to the right end of the rail bottom corner. The cooling rate of the center of the rail bottom is greater than that of the rail bottom corner, and the hardness is higher, which conforms to the hardness distribution law of waste heat quenching.

[0042] (6) Macrostructure

[0043] For HH370 rails, a full-section metallographic structure inspection was carried out on sections A, B, C, D, and E of No. 1. Samples were taken for metallographic structure inspection at the rail head, rail web, rail bottom, and rail bottom corner respectively. The inspection results show that the metallographic structure is pearlite structure, and no abnormal structure is found. The maximum decarburized layer depth of the rail is 0.35 mm. The metallographic structure photos are shown in Figure 3 .

[0044] The lamellar spacing of pearlite in the rail head of HH rails was measured using a scanning electron microscope. The measurement result shows that the lamellar spacing is 0.15 μm. The photos of the lamellar spacing are shown in Figure 4 .

[0045] In summary, the high-strength and high-hardness rails invented in this patent fully meet the requirements of the AREMA-2020 standard, have excellent performance, meet market demand, and have high economic and social benefits.

[0046] 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 spirit of the present invention, various modifications 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 rolling method for high-hardness steel rails for export, characterized in that: The heating temperature is 1200 ± 15 °C; the tapping temperature is not lower than 1100 °C; the rolling temperature is 1100 °C to 1130 °C, and the finishing rolling temperature is less than 930 °C; The chemical composition of the high-hardness rail for the outlet in mass percentage includes: C: 0.76 - 0.85%; Si: 0.47 - 0.57%; Mn: 0.9 - 1.18%; P ≤ 0.020%; S ≤ 0.020%; Cr: 0.20 - 0.3%; the balance is Fe and inevitable impurities.

2. The rolling method of high-hardness steel rails for export according to claim 1, characterized in that: It also includes heat treatment, and the heat treatment process includes: the inlet temperature is 763 - 780 °C, the head and tail temperature is 35 °C - 56 °C, the outlet temperature is 486 - 496 °C, the head and tail temperature is 20 - 40 °C, the reverse temperature is 565 - 576 °C, and the head and tail temperature is 20 - 30 °C.

3. The rolling method of the high-hardness steel rail for export according to claim 2, wherein: After the rail heat treatment, it meets the requirements: the tensile strength ≥ 1180 MPa, the yield strength ≥ 820 MPa, the elongation ≥ 10%, and the hardness of the rail tread ≥ 370 HB.

4. The rolling method of the high-hardness steel rail for export according to claim 1, characterized in that: The hardness of the tread of the HH rail produced by this method is between 370 - 383 HBW.

5. The rolling method of the high-hardness steel rail for export according to claim 1, characterized in that: The average hardness of the tread of the HH rail produced by this method is 373 HBW.

6. The rolling method of high-hardness steel rails for export according to claim 1, characterized in that: The strength performance of the HH rail produced by this method meets the requirements: the tensile strength is between 1252 - 1321 MPa, and the yield strength is between 769 - 910 MPa.

7. The rolling method of high-hardness steel rails for export according to claim 1, characterized in that: The performance of the HH rail produced by this method all meets the technical requirements of the AREMA-2020 standard.

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