Gradient cooling process for ultrahigh-toughness steel rail used in high and cold environment based on rare earth microalloying

Abstract

The invention discloses a gradient cooling process of an ultrahigh-toughness steel rail for a high and cold environment based on rare earth microalloying. The gradient cooling process comprises the following three-stage cooling processes: in the first stage, the strong cooling speed VC1 is equal to [4.0 + 100 * RE%] + / -0.2 DEG C / s to target 650-680 DEG C; in the second stage, the temperature of a constant-temperature platform is 600-630 DEG C, and t = [80-20 * (RE% / 0.01)] seconds is kept; and in the third stage, the cooling speed VC3 is smaller than or equal to 0.8 DEG C / s, and the outlet temperature is 400-450 DEG C. The invention aims to provide a rare earth microalloying-based gradient cooling process for an ultrahigh-toughness steel rail used in a high and cold environment, a rare earth gradient phase change technology is created, critical RE control is coupled through ultralow C design, and an RE-sensitive three-stage cooling model is developed, so that the wear-resistant steel rail with good strength and toughness ratio and excellent performance is realized, and the service life of the wear-resistant steel rail is prolonged. The method can be applied to the environment of alpine regions.

Description

Technical Field

[0001] This invention relates to the field of material cooling technology, and in particular to a gradient cooling process for ultra-high toughness steel rails used in cold environments based on rare earth microalloying. Background Technology

[0002] Currently, three major requirements are placed on steel rails: ultra-low temperature toughness, resistance to cold brittle fracture, and weldability. While current high-carbon steel rails (such as U75V, C > 0.70%) meet strength standards, they suffer from a "high carbon - low toughness" contradiction: when C > 0.65%, cementite coarsens (lamellar spacing > 0.25 μm), and the impact energy at -40℃ drops sharply by 30%; traditional Nb / V microalloying induces secondary embrittlement at low temperatures (NbC precipitates brittle phases). Although rare earth elements (RE) are often referred to as the "MSG" of steel, their application in various industries is limited by a narrow addition window. Existing heat treatment processes do not consider the impact of RE on phase transformation kinetics (RE increases the bainite transformation temperature B by 20-30℃), leading to a shift in the cooling path and the appearance of chain sulfides in the microstructure (impact energy reduction > 40%); rare earth elements also fail to suppress phosphorus grain boundary segregation (increasing the brittle transition temperature at -45℃). Baogang's unique rare earth iron ore contains natural Ce / La (0.001-0.003%), which can reduce the cost of adding RE alloys; ultra-low impurities (P≤0.008%, S≤0.005%) provide a basis for rare earth purification and its role in steel.

[0003] In summary, there is an urgent need for an innovative process that integrates "composition-rare earth-cooling" in three dimensions to overcome the low-temperature toughness bottleneck of cold-resistant steel rails. Summary of the Invention

[0004] The purpose of this invention is to provide a gradient cooling process for ultra-high toughness steel rails for cold environments based on rare earth microalloying. It creates a "rare earth gradient phase transformation" technology, which uses ultra-low C design (0.58-0.62%) coupled with critical RE control (0.001-0.005%), and develops a RE-sensitive three-stage cooling model to achieve a steel rail with a good strength and toughness ratio and excellent wear resistance, making it suitable for use in cold environments.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a gradient cooling process for ultra-high toughness steel rails used in extremely cold environments based on rare-earth microalloying, comprising the following three-stage cooling process:

[0007] Phase 1: Strong cooling rate VC1 = [4.0 + 100 × RE%] ± 0.2℃ / s → Target 650-680℃;

[0008] Second stage: Constant temperature platform 600-630℃, hold for t = [80-20×(RE% / 0.01)] seconds;

[0009] Third stage: Cooling rate VC3≤0.8℃ / s→Outlet temperature 400-450℃.

[0010] Furthermore, the rolling process for ultra-high toughness steel rails for cold environments based on rare earth microalloying is as follows: billet → sawing → heating → BD1 rolling → BD2 rolling → CCS universal mill continuous rolling → online residual heat quenching → sawing → cooling → head and tail trimming → straightening → inspection → packaging → weighing → warehousing.

[0011] Furthermore, the temperature of the preheating section of the billet heating is not greater than 900℃; the heating time is not less than 3 hours and 15 minutes; the furnace exit temperature is not less than 1150℃; the initial rolling temperature is ≥1100℃; and the final rolling temperature is 910~940℃.

[0012] Furthermore, the chemical composition of the ultra-high toughness steel rail for cold environments based on rare earth microalloying is as follows (by weight percentage): C 0.58-0.62%, Mn 0.60-0.75%, Re 0.001-0.005%, S≤0.008%, Si 0.50-0.60%, Cr 0.10-0.40%, V 0.01-0.08%, with the remainder being Fe and unavoidable impurities.

[0013] Furthermore, the chemical composition of the ultra-high toughness steel rail for cold environments based on rare earth microalloying by mass percentage is as follows: C 0.58%, Mn 0.73%, Re 0.0038%, P 0.013%, S 0.007%, Si 0.50%, Cr 0.30%, V 0.08%, with the remainder being Fe and unavoidable impurities.

[0014] Furthermore, the chemical composition of the ultra-high toughness steel rail for cold environments based on rare earth microalloying by mass percentage is as follows: C 0.60%, Mn 0.68%, Re 0.0040%, P 0.011%, S 0.003%, Si 0.55%, Cr 0.20%, V 0.06%, with the remainder being Fe and unavoidable impurities.

[0015] Furthermore, the chemical composition of the ultra-high toughness steel rail for cold environments based on rare earth microalloying by mass percentage is as follows: C 0.62%, Mn 0.60%, Re 0.0040%, P 0.019%, S 0.003%, Si 0.53%, Cr 0.15%, V 0.04%, with the remainder being Fe and unavoidable impurities.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0017] This invention utilizes an online waste heat treatment process to improve the strength and hardness of rails. Simultaneously, it rationally designs the composition and adds optimal alloying elements to the rails. Under this rolling process, the tensile strength, elongation, tread hardness, and impact toughness of the rails can be improved. The heat-treated rails produced using this method exhibit excellent tensile strength, tread hardness, and impact resistance.

[0018] Ingredient innovation design (wt%):

[0019] Detailed Implementation

[0020] The chemical composition of the rail materials prepared in each embodiment is shown in Table 1.

[0021] Table 1. Components of each embodiment (mass percentage / %)

[0022]

[0023] The specific implementation of the heat treatment process for steel rails is shown in Table 2.

[0024] Table 2 Examples of Heat Treatment Processes for Rail Materials

[0025]

[0026] The properties of the rolled steel samples were tested according to the TB / T2344-2012 standard. The experimental results are shown in Table 3.

[0027] Table 3 Mechanical properties of each embodiment

[0028]

[0029]

[0030] 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 gradient cooling process for ultra-high toughness steel rails used in cold environments based on rare earth microalloying, characterized in that: This includes the following three-stage cooling process: Phase 1: Strong cooling rate VC1 = [4.0 + 100 × RE%] ± 0.2℃ / s → Target 650-680℃; Second stage: Constant temperature platform 600-630℃, hold for t = [80-20×(RE% / 0.01)] seconds; Third stage: Cooling rate VC3≤0.8℃ / s→Outlet temperature 400-450℃.

2. The gradient cooling process for ultra-high toughness steel rails for cold environments based on rare earth microalloying according to claim 1, characterized in that: The rolling process for ultra-high toughness steel rails for cold environments based on rare earth microalloying is as follows: billet → sawing → heating → BD1 rolling → BD2 rolling → CCS universal mill continuous rolling → online residual heat quenching → sawing → cooling → head and tail trimming → straightening → inspection → packaging → weighing → warehousing.

3. The gradient cooling process for ultra-high toughness steel rails for cold environments based on rare earth microalloying according to claim 2, characterized in that: The temperature of the preheating section of the billet shall not exceed 900℃; the heating time shall not be less than 3 hours and 15 minutes; the furnace exit temperature shall not be lower than 1150℃; the initial rolling temperature shall be ≥1100℃; and the final rolling temperature shall be 910~940℃.

4. The gradient cooling process for ultra-high toughness steel rails for cold environments based on rare earth microalloying according to claim 1, characterized in that: The chemical composition of the ultra-high toughness steel rail for cold environments based on rare earth microalloying is as follows (by weight percentage): C 0.58-0.62%, Mn 0.60-0.75%, Re 0.001-0.005%, S≤0.008%, Si 0.50-0.60%, Cr 0.10-0.40%, V 0.01-0.08%, with the remainder being Fe and unavoidable impurities.

5. The gradient cooling process for ultra-high toughness steel rails for cold environments based on rare earth microalloying according to claim 4, characterized in that: The chemical composition of the ultra-high toughness steel rail for cold environments based on rare earth microalloying is as follows (by weight percentage): C 0.58%, Mn 0.73%, Re 0.0038%, P 0.013%, S 0.007%, Si 0.50%, Cr 0.30%, V 0.08%, with the remainder being Fe and unavoidable impurities.

6. The gradient cooling process for ultra-high toughness steel rails for cold environments based on rare earth microalloying according to claim 4, characterized in that: The chemical composition of the ultra-high toughness steel rail for cold environments based on rare earth microalloying is as follows (by weight percentage): C 0.60%, Mn 0.68%, Re 0.0040%, P 0.011%, S 0.003%, Si 0.55%, Cr 0.20%, V 0.06%, with the remainder being Fe and unavoidable impurities.

7. The gradient cooling process for ultra-high toughness steel rails for cold environments based on rare earth microalloying according to claim 4, characterized in that: The chemical composition of the ultra-high toughness steel rail for cold environments based on rare earth microalloying is as follows (by weight percentage): C 0.62%, Mn 0.60%, Re 0.0040%, P 0.019%, S 0.003%, Si 0.53%, Cr 0.15%, V 0.04%, with the remainder being Fe and unavoidable impurities.

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