High performance rail of a type ahs lh 136 re and method of production thereof

Abstract

The application discloses a kind of AAR LH136RE heat-treated rails and production method thereof, the chemical composition of the rail is as follows in percentage by mass: C 0.70~0.82%; Si 0.40~0.80%; Mn 0.70~1.20%; Cr 0.40~0.60%; P≤0.020%; S≤0.020%, the balance is Fe and inevitable impurities, the obtained LH (136RE) rail: yield strength Rp0.2≥830MPa; tensile strength Rm≥1300MPa; elongation A≥10%; tread hardness 380~420HB; rail head cross section 22mm depth hardness≥350HB.The application significantly improves the comprehensive mechanical properties of 136RE rail, especially realizes the breakthrough of rail head cross section hardness≥350HB, so that it has more excellent wear resistance, deformation resistance and longer service life under heavy load working condition.

Description

Technical Field

[0001] This invention relates to the field of metallurgical materials technology, specifically to a method for producing high-strength American standard LH136RE heat-treated steel rails for use in high axle load, high-capacity heavy-haul railways. Background Technology

[0002] With the development of heavy-haul railway transportation towards higher axle loads and larger transport volumes, the service conditions of rails are becoming increasingly stringent, especially on small-radius curves where rail wear and contact fatigue are more prominent. Using high-strength heat-treated rails (such as those rated 1200-1300 MPa) is an effective way to improve service life. Although online heat treatment processes themselves have advantages such as high efficiency, low cost, and uniform quality (no softening zone), existing technologies have limitations in meeting the requirements for ultimate strength (≥1300 MPa) and deep hardness of the rail head cross section (≥350 HB at a depth of 22 mm) for higher-grade 136RE rails. The standard for rail head cross section hardness of 115RE rails is typically ≥320 HB, which is insufficient to fully cope with the long-term crushing and wear challenges of heavier-load trains. Therefore, there is an urgent need to develop a new heat-treated rail production method specifically for 136RE specifications that can significantly improve strength, toughness, and especially deep hardness.

[0003] In view of the above factors, this paper provides a high-performance rail of American standard LH136RE and its production method, which solves the technical problem of significantly improving the deep hardness of the rail head cross section (22mm depth ≥350HB) and maintaining good toughness (A≥10%) under the premise of ultra-high strength (Rm≥1300MPa), so as to surpass the performance level of 115RE rail and meet the higher standard of heavy-haul railway requirements. Summary of the Invention

[0004] The purpose of this invention is to provide a high-performance rail of American standard LH136RE and its production method, so as to solve the problems mentioned in the background art.

[0005] The objective of this invention is achieved through the following technical solution: a high-performance steel rail conforming to American standard LH136RE, the chemical composition of which, by mass percentage, includes: C 0.70~0.82%; Si 0.40~0.80%; Mn 0.70~1.20%; Cr 0.40~0.60%; P≤0.020%; S≤0.020%, with the balance being Fe and unavoidable impurities.

[0006] The high-performance steel rail of American standard LH136RE has the following chemical composition by mass percentage: C: 0.76%; Si: 0.45%; Mn: 0.92%; Cr: 0.58%; P: 0.006%; S: 0.016%; balance Fe.

[0007] The high-performance steel rail of American standard LH136RE has the following chemical composition by mass percentage: C: 0.78%; Si: 0.48%; Mn: 0.94%; Cr: 0.60%; P: 0.006%; S: 0.016%; balance Fe.

[0008] The production method of high-performance steel rails of American Standard LH136RE includes the following steps:

[0009] S1 Smelting and Purity Control

[0010] Iron pretreatment: Iron [S]≤0.03%, [P]≤0.15%, controlling harmful elements from the source;

[0011] Converter smelting: control the steel tapping [C] ≥ 0.08%, the tapping temperature ≥ 1630℃, and optimize the tapping operation.

[0012] LF furnace refining: Precisely control slag basicity ≥2.0 and off-site temperature 1585~1595℃ to ensure accurate composition (especially C and Cr within the target range) and pure molten steel.

[0013] VD vacuum degassing: Deep vacuum treatment ≥18min, soft blowing ≥18min, strict control of argon flow rate, effectively removes gas inclusions, significantly reduces the content of [H], [O], and [N] in steel, and provides a guarantee for high toughness and high surface quality.

[0014] S2 continuous casting: protective casting, low-alumina protective slag, ultra-weak cooling water distribution in the secondary cooling section, constant casting speed, low superheat (ΔT≤30℃), and application of electromagnetic stirring and light reduction technology to obtain a billet with high uniformity and low defects.

[0015] S3 heating: Total heating time ≥200 min, preheating section ≤800℃;

[0016] S4 rolling: initial rolling temperature 1100~1150℃, final rolling temperature 930~950℃;

[0017] S5 Online Heat Treatment: After final rolling, the rails are air-cooled to 750-800℃ before entering the heat treatment line;

[0018] S6 Post-processing: After slow cooling to room temperature, straightening and ultrasonic flaw detection are performed.

[0019] Furthermore, the heating in step S3 is divided into two stages: the first stage is heated to ≤1200℃, the second stage to 1100~1280℃, and the temperature of the heat spreader is controlled at 1150~1260℃.

[0020] Furthermore, in step S5, the rail is rapidly cooled to 500-540°C using a spray cooling method. Then, the cooling intensity is reduced so that the rail temperature is maintained in the range of 500-540°C for a certain period of time before it leaves the heat treatment line. After leaving the furnace, the rail is naturally air-cooled to room temperature.

[0021] Furthermore, in step S5, the total online heat treatment time is controlled to be 100-140 seconds, and the temperature exiting the heat treatment line is 500-540°C.

[0022] While achieving a high strength of ≥1300MPa, the rail structure also achieves a high hardness of ≥350HB at a depth of 22mm in the rail head cross section and good toughness A≥10%.

[0023] Furthermore, the inlet temperature is 780℃, and the cooling method is air spray cooling, which rapidly cools the rail to 520℃, reducing the intensity of air cooling and maintaining the rail temperature within the 520℃ range.

[0024] Temperature exiting the heat treatment line: 520℃, total heat treatment time: 140s, after exiting the line, it is naturally air-cooled to room temperature.

[0025] Furthermore, the mechanical properties of the finished steel meet the following requirements: yield strength Rp0.2≥830MPa, tensile strength Rm≥1300MPa, elongation after fracture A≥10%, tread hardness 380~420HB, and hardness at a depth of 22mm on the rail head cross section ≥350HB.

[0026] The application of a production method for high-performance rails conforming to American standard LH136RE is described. This method is applied to the production of heat-treated rails with high strength (Rm≥1300MPa), high toughness (A≥10%), and high rail head cross-sectional hardness (22mm depth≥350HB) for high axle load, high capacity, and heavy haul railways.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention significantly improves the comprehensive mechanical properties of 136RE rails through the precise synergy of specific component optimization and key process parameters (such as refining control, homogenization temperature, rolling temperature, and online heat treatment regime). In particular, it achieves a breakthrough in rail head cross-sectional hardness of ≥350HB, giving it superior wear resistance, deformation resistance, and longer service life under heavy load conditions.

[0029] This invention solves the technical challenge of significantly improving the deep hardness (22mm depth ≥350HB) of the rail head cross section while maintaining good toughness (A≥10%) under the premise of ultra-high strength (Rm≥1300MPa), so as to exceed the performance level of 115RE rail and meet the higher standard requirements of heavy-haul railway. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the indicated orientation or positional relationship, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0033] A high-performance steel rail conforming to American standard LH136RE has the following chemical composition by mass percentage: C 0.70-0.82%; Si 0.40-0.80%; Mn 0.70-1.20%; Cr 0.40-0.60%; P≤0.020%; S≤0.020%, with the balance being Fe and unavoidable impurities.

[0034] The high-performance steel rail of American standard LH136RE has the following chemical composition by mass percentage: C: 0.76%; Si: 0.45%; Mn: 0.92%; Cr: 0.58%; P: 0.006%; S: 0.016%; balance Fe.

[0035] The high-performance steel rail of American standard LH136RE has the following chemical composition by mass percentage: C: 0.78%; Si: 0.48%; Mn: 0.94%; Cr: 0.60%; P: 0.006%; S: 0.016%; balance Fe.

[0036] The production method of high-performance steel rails of American Standard LH136RE includes the following steps:

[0037] S1 Smelting and Purity Control

[0038] Hot metal pretreatment: [S]=0.011%, [P]=0.10%, controlling harmful elements from the source;

[0039] Converter smelting: control the steel tapping [C]=0.1%, the tapping temperature is 1644℃, optimize the tapping operation (add quicklime, silicon-calcium-barium, fluorite for modification, and ensure argon blowing), and optimize the tapping operation.

[0040] LF furnace refining: Precise control of slag basicity = 2.1 and off-site temperature 1588℃ to ensure accurate composition (especially C and Cr within the target range) and purity of molten steel.

[0041] VD vacuum degassing: deep vacuum time 19min, soft blowing 18min, stable argon flow rate, no exposed steel molten steel, strict control of argon flow rate, effective removal of gas inclusions, significantly reducing the content of [H], [O], and [N] in steel, providing a guarantee for high toughness and high surface quality.

[0042] S2 continuous casting: protective casting, low-alumina protective slag, secondary cooling with ultra-weak cooling water supply, casting speed 0.60m / min, constant speed, electromagnetic stirring and light reduction, low superheat (ΔT≤30℃), and the application of electromagnetic stirring and light reduction technology to obtain a billet with high uniformity and low defects.

[0043] S3 heating: Heating is divided into two stages. The first stage is ≤1200℃, the second stage is 1100~1280℃, and the temperature of the soaking zone is controlled at 1150~1260℃.

[0044] S4 rolling: initial rolling temperature 1100~1150℃, final rolling temperature 930~950℃;

[0045] 5. S5 Online Heat Treatment: After final rolling, the rail is air-cooled to 780℃ and then enters the heat treatment line. The temperature at which the rail exits the heat treatment line is 520℃. The total heat treatment time is 140s. After exiting the line, the rail is naturally air-cooled to room temperature and then rapidly cooled to 520℃ to reduce the intensity of air cooling and maintain the rail temperature within the 520℃ range.

[0046] S6 Post-processing: After slow cooling to room temperature, straightening and ultrasonic flaw detection are performed.

[0047] The heating is divided into two stages: the first stage is ≤1200℃, the second stage is 1100~1280℃, and the temperature of the soaking zone is controlled at 1150~1260℃.

[0048] While achieving a high strength of ≥1300MPa, the rail structure also achieves a high hardness of ≥350HB at a depth of 22mm in the rail head cross section and good toughness A≥10%.

[0049] The mechanical properties of the finished steel shall meet the following requirements: yield strength Rp0.2≥830MPa, tensile strength Rm≥1300MPa, elongation after fracture A≥10%, tread hardness 380~420HB, and hardness at a depth of 22mm on the rail head cross section ≥350HB.

[0050] Table 1 Heating process for LH steel rails

[0051] Preheating section Heating Section 1 Heating in 2 stages Heat exchanger section Heating time 25min 50min 55min 30min temperature 723℃ 935℃ 1212℃ 1244℃

[0052] Finished rail performance testing: tensile strength (Rm): 1344MPa, elongation after fracture (A): 12.5%, tread hardness: 386HB, hardness at a depth of 22mm on the rail head cross section: 358HB, metallographic structure: pearlite (fine lamellar).

[0053] Performance Comparison and Advantages: A comparison of the performance indicators of the LH(136RE) rail of this invention and the typical LH(115RE) rail:

[0054] Performance indicators LH(115RE) LH(136RE) Performance improvement Yield strength Rp0.2 (MPa) ≥700 ≥830 ≥130MPa Tensile strength Rm (MPa) ≥1200 ≥1300 ≥100MPa Elongation after fracture A (%) ≥10 ≥10 Maintain high toughness Tread hardness (HB) 380～420 380～420 - Hardness (HB) at a depth of 22mm on the rail head cross section ≥320 ≥350 ≥30HB

[0055] The data in the table above fully demonstrates that the LH(136RE) rail production method provided by this invention, while maintaining good toughness and tread hardness, significantly improves the rail's yield strength (≥130MPa) and tensile strength (≥100MPa), and in particular, achieves a breakthrough improvement in the hardness at a depth of 22mm in the rail head cross section (≥30HB), reaching ≥350HB. This improvement in core performance indicators enables 136RE rails to achieve a qualitative leap in wear resistance, contact fatigue resistance, and deformation resistance under heavy loads, especially small radius curve conditions, significantly extending their service life and fully meeting the development needs of higher-grade heavy-haul railways.

[0056] The application of a production method for high-performance rails conforming to American standard LH136RE is described. This method is applied to the production of heat-treated rails with high strength (Rm≥1300MPa), high toughness (A≥10%), and high rail head cross-sectional hardness (22mm depth≥350HB) for high axle load, high capacity, and heavy haul railways.

[0057] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

[0058] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A high-performance steel rail conforming to American standard LH136RE, characterized in that: Its chemical composition, by mass percentage, includes: C 0.70–0.82%; Si 0.40–0.80%; Mn 0.70–1.20%; Cr 0.40–0.60%; P ≤ 0.020%; S ≤ 0.020%, with the balance being Fe and unavoidable impurities.

2. The high-performance steel rail of American standard LH136RE according to claim 1, characterized in that: Its chemical composition, by mass percentage, includes: C: 0.76%; Si: 0.45%; Mn: 0.92%; Cr: 0.58%; P: 0.006%; S: 0.016%; balance Fe.

3. The high-performance steel rail of American standard LH136RE according to claim 1, characterized in that: Its chemical composition, by mass percentage, includes: C: 0.78%; Si: 0.48%; Mn: 0.94%; Cr: 0.60%; P: 0.006%; S: 0.016%; balance Fe.

4. The method for producing high-performance steel rails of American standard LH136RE according to any one of claims 2 or 3, characterized in that: The steps include: S1 Smelting and Purity Control Iron pretreatment: Iron [S]≤0.03%, [P]≤0.15%, controlling harmful elements from the source; Converter smelting: control the steel tapping [C] ≥ 0.08%, the tapping temperature ≥ 1630℃, and optimize the tapping operation. LF furnace refining: Precisely control slag basicity ≥2.0 and off-site temperature 1585~1595℃ to ensure accurate composition (especially C and Cr within the target range) and pure molten steel. VD vacuum degassing: Deep vacuum treatment ≥18min, soft blowing ≥18min, strict control of argon flow rate, effectively removes gas inclusions, significantly reduces the content of [H], [O], and [N] in steel, and provides a guarantee for high toughness and high surface quality. S2 continuous casting: protective casting, low-alumina protective slag, ultra-weak cooling water distribution in the secondary cooling section, constant casting speed, low superheat (ΔT≤30℃), and application of electromagnetic stirring and light reduction technology to obtain a billet with high uniformity and low defects. S3 heating: Total heating time ≥200 min, preheating section ≤800℃; S4 rolling: initial rolling temperature 1100~1150℃, final rolling temperature 930~950℃; S5 Online Heat Treatment: After final rolling, the rails are air-cooled to 750-800℃ before entering the heat treatment line; S6 Post-processing: After slow cooling to room temperature, straightening and ultrasonic flaw detection are performed.

5. The method for producing high-performance steel rails of American standard LH136RE according to claim 4, characterized in that: In step S3, the heating is divided into two stages: the first stage is heated to ≤1200℃, the second stage to 1100~1280℃, and the temperature of the heat spreader is controlled at 1150~1260℃.

6. The method for producing high-performance steel rails of American standard LH136RE according to claim 5, characterized in that: In step S5, the rail is rapidly cooled to 500-540°C using a spray mist cooling method. Then, the cooling intensity is reduced so that the rail temperature is maintained in the range of 500-540°C for a certain period of time before it leaves the heat treatment line. After leaving the furnace, the rail is naturally air-cooled to room temperature.

7. The method for producing high-performance steel rails of American standard LH136RE according to claim 5, characterized in that: In step S5, the total online heat treatment time is controlled between 100 and 140 seconds, and the temperature exiting the heat treatment line is between 500 and 540°C. While achieving a high strength of ≥1300MPa, the rail structure also achieves a high hardness of ≥350HB at a depth of 22mm in the rail head cross section and good toughness A≥10%.

8. The method for producing high-performance steel rails of American standard LH136RE according to claim 5, characterized in that: The inlet temperature is 780℃, and the cooling method is air spray cooling, which quickly cools the rail to 520℃, reduces the intensity of air cooling, and maintains the rail temperature in the 520℃ range. Temperature exiting the heat treatment line: 520℃, total heat treatment time: 140s, after exiting the line, it is naturally air-cooled to room temperature.

9. The method for producing high-performance steel rails of American standard LH136RE according to claim 8, characterized in that: The finished steel has the following mechanical properties: yield strength Rp0.2≥830MPa, tensile strength Rm≥1300MPa, elongation after fracture A≥10%, tread hardness 380~420HB, and hardness at a depth of 22mm on the rail head cross section ≥350HB.

10. An application of a production method for high-performance rails according to claim 9, wherein the above production method is applied to the production of high-strength rails with Rm≥1300MPa, high toughness A≥10%, and high rail head cross-sectional hardness 22mm depth≥350HB for high axle load, high-capacity heavy-haul railways.