Production method of American standard HH370 on-line heat treatment steel rail

Abstract

The invention discloses a production method of an American standard HH370 on-line heat treatment steel rail. The production method comprises the following steps: 1) heating a steel billet; 2) rolling; the steel rail is cooled to 740-790 DEG C through air cooling and enters a heat treatment line, the cooling mode is aerial fog cooling, the steel rail is rapidly cooled to 580-620 DEG C on the heat treatment line, then the cooling strength is reduced, the temperature of the steel rail is maintained at 580-620 DEG C for a period of time, then the steel rail is taken out of a heat treatment production line, the steel rail is naturally cooled to the room temperature through air after being taken out of the heat treatment production line, the total heat treatment time is 100-120 s, and the steel rail is cooled to the room temperature. And the temperature of the steel rail from a heat treatment line is 580-620 DEG The invention aims to provide an American standard HH370 on-line heat treatment steel rail production method. On the basis of reducing the Cr element, the strength performance is improved by optimizing the heat treatment process.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical materials technology, and in particular relates to a method for producing steel rails with online heat treatment according to American standard HH370. Background Technology

[0002] Compared to low-alloy steel rails, standard carbon steel rails have a lower alloy content, resulting in lower costs. Through heat treatment, the entire rail microstructure cools from austenite, thus avoiding the coarse-grained softening zone at the rail head / web junction. Furthermore, the rail web and base are appropriately strengthened. During residual heat quenching, while the rail head is rapidly cooled, compressed air or water is also sprayed onto the rail base for cooling, balancing the shrinkage, expansion, and transformation stresses during quenching. Conveyor rollers further restrict rail deformation while it is hot, resulting in better straightness when the rail leaves the quenching equipment, and less deformation and residual stress during straightening.

[0003] With the development of heavy-haul and high-speed railways, the burden on rails is increasing. Especially on small-radius curves, rail wear is very severe. Domestic and international laying and usage practices show that using full-length hardened rails of 1200-1300MPa grade on small-radius curves can increase their service life by 2 to 5 times, resulting in significant economic benefits.

[0004] Application No. 202310917885.0 discloses a method for producing American standard low-alloy high-strength online heat-treated rails. The chemical composition by weight percentage includes: C 0.75–0.82%; Si 0.60–0.80%; Mn 0.90–1.10%; Cr 0.40–0.60%; P ≤ 0.020%; S ≤ 0.020%, with the remainder being Fe and unavoidable impurities. The production method includes hot metal desulfurization, converter smelting, LF furnace refining, VD vacuum degassing, large billet continuous casting, billet heating, rolling, online heat treatment, straightening, and ultrasonic flaw detection. The resulting LH rails have a yield strength Rp0.2 ≥ 820 MPa; tensile strength Rm ≥ 1280 MPa; elongation after fracture A ≥ 10%; tread hardness 370–410 HB; and rail head cross-section hardness 22 mm depth ≥ 341 HB. Compared to that patent, this application improves strength performance by optimizing the heat treatment process while reducing the Cr content.

[0005] Reducing the chromium (Cr) content can significantly lower material costs and improve the weldability of rails. Lowering Cr also helps improve these processing properties. This is achieved through Cr reduction and optimized heat treatment. Grain boundaries are an effective barrier to dislocation movement, significantly increasing strength through high dislocation density strengthening. Optimized heat treatment processes refine the pearlite lamellar spacing, preventing microcrack propagation and improving rail performance. Furthermore, reducing Cr content accelerates cooling, and precise control over the microstructure enhances rail performance. Summary of the Invention

[0006] The purpose of this invention is to provide a method for producing HH370 standard steel rails online with heat treatment, which improves strength performance by optimizing the heat treatment process while reducing Cr content.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a method for producing HH370 standard steel rails using online heat treatment, comprising:

[0009] 1) Billet heating: The total heating time of the billet is ≥3 hours and 20 minutes, of which the temperature of the preheating section of the heating furnace is ≤800℃, the temperature of the first heating section is ≤1200℃, the temperature of the second heating section is 1100~1280℃, and the temperature of the soaking section is 1150~1260℃.

[0010] 2) Rolling: The cast billet is rolled into rails by a universal rolling mill. The initial rolling temperature is controlled at 1100-1150℃, and the final rolling temperature is 930-950℃.

[0011] 3) Online heat treatment: The rails are air-cooled to 740-790℃ and then enter the heat treatment line. The cooling method is air mist cooling. The rails are rapidly cooled to 580-620℃ in the heat treatment line. Then the cooling intensity is reduced to maintain the rail temperature at 580-620℃ for a period of time before leaving the heat treatment production line. After leaving the heat treatment production line, the rails are naturally air-cooled to room temperature. The total heat treatment time is 100-120 seconds, and the rail temperature when leaving the heat treatment line is 580-620℃.

[0012] Furthermore, its chemical composition by mass percentage includes: C 0.80–0.86%; Si 0.50–0.70%; Mn 0.90–1.25%; Cr 0.20–0.30%; Ni ≤0.25%; Mo ≤0.06%; P ≤0.020%; S ≤0.020%, with the remainder being Fe and unavoidable impurities.

[0013] Furthermore, the mechanical properties of the HH370 rails obtained by this production method meet the requirements of R0.2P≥820MPa, Rm≥1180MPa, elongation after fracture A≥10%, tread hardness≥370HB, and other mechanical properties meet the requirements of AREMA-2020 standard.

[0014] Furthermore, its chemical composition by mass percentage includes: C: 0.83%; Si: 0.58%; Mn: 1.20%; P: 0.006%; S: 0.016%; Cr: 0.28%; Ni: 0.034%; the remainder being Fe and unavoidable impurities.

[0015] Furthermore, the total heating time for the billet is 3 hours and 30 minutes, with the preheating section temperature at 755℃, the first heating section temperature at 1090℃, the second heating section temperature at 1218℃, and the soaking section temperature at 1233℃.

[0016] Furthermore, the initial rolling temperature is 1100℃, and the final rolling temperature is 935℃.

[0017] Furthermore, online heat treatment: The rails are air-cooled to 780°C and then enter the heat treatment line. Air mist cooling is used to rapidly cool the rails to 600°C on the heat treatment line. Subsequently, the cooling intensity is reduced to balance the internal temperature return and cooling intensity of the rails. The rails are maintained at 600°C for a certain period of time before exiting the heat treatment line. The total online heat treatment time is 110 seconds. After exiting the heat treatment line, the rails are naturally air-cooled to room temperature.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0019] This invention achieves improved strength performance by optimizing the heat treatment process while reducing the Cr content through reasonable optimization of the composition and process. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments, so as to better understand the present invention. A heat treatment method for American standard carbon 370HB grade steel rails includes the following steps:

[0021] 1) The chemical composition percentage of the 370HB steel rail, as tested, is as follows: C: 0.83%; Si: 0.58%; Mn: 1.20%; P: 0.006%; S: 0.016%; Cr: 0.28%; Ni: 0.034%; the remainder is Fe and unavoidable impurities.

[0022] 2) Steel billet heating: The total heating time is 3 hours and 30 minutes. The heating time and temperature of each section are shown in Table 1.

[0023] Table 1 Heating process for 370HB steel rails

[0024] Preheating section Heating Section 1 Heating in 2 stages Heat exchanger section Heating time 30min 60min 65min 55min temperature 755℃ 1090℃ 1218℃ 1233℃

[0025] 3) Rolling: The billet is rolled into rails by a universal rolling mill. The initial rolling temperature is 1100℃ and the final rolling temperature is 935℃.

[0026] 4) Online heat treatment: The rails are air-cooled to 780°C and then enter the heat treatment line. The air mist cooling method is used to rapidly cool the rails to 600°C on the heat treatment line. Then the cooling intensity is reduced to balance the internal temperature return and cooling intensity of the rails. The rails are maintained at 600°C for a certain period of time before exiting the heat treatment line. The total online heat treatment time is 110 seconds. After exiting the heat treatment line, the rails are naturally air-cooled to room temperature.

[0027] 5) Rail performance

[0028] After rolling, five heats of finished steel rails were taken and tested in detail according to the requirements of AREMA-2020 standard for strength carbon steel rails, including conventional tensile properties, tread hardness, and other indicators. The test results showed that all conventional and special properties met the standard requirements. The specific test results are shown in Tables 2 and 3.

[0029] Table 2. Tensile property test results of steel rails

[0030]

[0031] Table 3. Results of Hardness and Elongation Tests on Rails

[0032]

[0033] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method of producing AAR standard HH370 online heat treated rail, characterized by: Comprise: 1) billet heating: total heating time of billet ≥ 3 hours 20 minutes, wherein the temperature of preheating section of heating furnace ≤ 800℃, the temperature of first heating section ≤ 1200℃, the temperature of second heating section 1100-1280℃, and the temperature of soaking section 1150-1260℃; 2) rolling: the cast billet is rolled into a rail by a universal rolling mill, and the open rolling temperature is controlled at 1100-1150℃, and the finish rolling temperature is 930-950℃; 3) on-line heat treatment: the rail is cooled to 740-790℃ by air mist cooling, and then cooled to 580-620℃ by reducing the cooling intensity, and then maintained at 580-620℃ for a period of time, and then taken out of the heat treatment production line, and then naturally air cooled to room temperature, and the total heat treatment time is 100-120s, and the temperature of the rail taken out of the heat treatment line is 580-620℃.

2. The AAR standard HH370 on-line heat treated rail production method of claim 1, wherein: The chemical composition thereof comprises, by mass percent: C 0.80-0.86%; Si 0.50-0.70%; Mn 0.90-1.25%; Cr 0.20-0.30%; Ni ≤ 0.25%; Mo ≤ 0.06%; P ≤ 0.020%; S ≤ 0.020%, and the balance of Fe and inevitable impurities.

3. The AAR standard HH370 on-line heat treated rail production method of claim 2, wherein: The mechanical properties of the HH370 rail obtained by the production method meet the requirements of R0.2P ≥ 820MPa, Rm ≥ 1180MPa, elongation A ≥ 10%, and tread hardness ≥ 370HB, and the remaining mechanical properties meet the requirements of the AREMA-2020 standard.

4. The AAR standard HH370 on-line heat treated rail production method of claim 2, wherein: The chemical composition thereof comprises, by mass percent: C: 0.83%; Si: 0.58%; Mn: 1.20%; P: 0.006%; S: 0.016%; Cr: 0.28%, and Ni: 0.034%, and the balance of Fe and inevitable impurities.

5. The AAR standard HH370 on-line heat treated rail production method of claim 1 wherein: The total heating time of the billet is 3 hours 30 minutes, wherein the temperature of the preheating section of the heating furnace is 755℃, the temperature of the first heating section is 1090℃, the temperature of the second heating section is 1218℃, and the temperature of the soaking section is 1233℃.

6. The AAR Standard HH370 on-line heat treated rail production method of claim 1 wherein: The open rolling temperature is 1100℃, and the finish rolling temperature is 935℃.

7. The AAR Standard HH370 on-line heat treated rail production method of claim 1 wherein: On-line heat treatment: the rail is cooled to 780℃ by air mist cooling, and then cooled to 600℃ by reducing the cooling intensity, and then maintained at 600℃ for a period of time, and then taken out of the heat treatment line, and then naturally air cooled to room temperature, and the total heat treatment time is 110s.

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