Rare earth-containing steel rail with excellent low-temperature toughness and online heat treatment method thereof

Abstract

The invention discloses a rare earth-containing steel rail with excellent low-temperature toughness and an online heat treatment method of the rare earth-containing steel rail. The rare earth-containing steel rail comprises the following chemical components in percentage by mass: 0.50-0.70% of C; 0.60%-0.75% of Si; 0.40 to 0.60 percent of Mn; the content of RE is 0.003 to 0.005 percent; 0.50 to 0.70 percent of Cr; 0.03-0.06% of V, and the balance Fe and inevitable impurities. Through component-process-structure coordinated regulation and control, the low-temperature toughness of the provided rare earth-containing steel rail with excellent low-temperature toughness meets the following conditions:-40 DEG C impact energy is greater than or equal to 20J; the fracture toughness at-20 DEG C is greater than or equal to 45 MPa.m < 0.5 >, and the low-temperature toughness performance is excellent.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to a rare earth-containing steel rail with excellent low-temperature toughness and its online heat treatment method. Background Technology

[0002] As a key component of the track structure, the performance of steel rails directly determines the safety, maintenance costs, and service life of the track. Data shows that in environments with altitudes above 4000m and annual temperature differences reaching 80℃, the incidence of low-temperature brittle fracture accidents with traditional steel rails is 3.2 times higher than that of ordinary railways. Existing high-carbon steel rails (C 0.7%-1.0%) achieve tensile strengths of 1100-1300MPa through pearlite strengthening, but this results in a sharp decrease in low-temperature toughness; the impact energy at -40℃ is only 10-15J, and the fracture toughness is <30MPa·m. 0.5 This cannot meet the safety redundancy requirements of high-altitude and cold regions. Low-carbon steel rails (C 0.3%-0.5%): The impact energy at -40℃ is increased to 25-35J by means of ferritic matrix, but the strength is reduced to 800-900MPa, and the insufficient wear resistance leads to a 40% reduction in the wheel-rail contact fatigue crack initiation cycle.

[0003] Rare earth elements, as an industrial additive, can reduce oxygen content in molten steel by 20%-30% as a purifying agent. However, their precipitation behavior is uncontrolled: precipitates such as RE2O3 and RE2S3 tend to agglomerate (size > 5μm) at conventional cooling rates of 3-8℃ / s, becoming crack propagation sources and causing impact energy fluctuations of ±40% (measured 5-21J). Microstructure coarsening effect: Single-stage cooling cannot suppress austenite grain growth, and the precipitation of brittle phases at grain boundaries reduces fracture toughness by 30%. Patent CN112210763A uses "RE+Cr+V" composite microalloying, which increases tensile strength to 1050MPa, but suffers from a strength-toughness imbalance: when tensile strength > 1000MPa, the impact energy at -40℃ is still < 18J, failing to break the safety threshold of 20J.

[0004] Therefore, developing a precise control technology for rare earth precipitates based on online heat treatment to achieve a synergistic improvement in the strength, toughness, and wear resistance of high-carbon steel rails (C0.50-0.70%) has become an urgent need for the construction of railways in cold regions. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention aims to provide a rare-earth-containing steel rail with excellent low-temperature toughness. Its chemical composition, by mass percentage, is: C 0.50-0.70%; Si 0.60-0.75%; Mn 0.40-0.60%; RE 0.003-0.005%; Cr 0.50-0.70%; V 0.03-0.06%, with the remainder being Fe and unavoidable impurities.

[0006] The low-temperature toughness of the rare-earth-containing steel rail with excellent low-temperature toughness satisfies:

[0007] Impact energy at -40℃ ≥20J;

[0008] Fracture toughness at -20℃ ≥45MPa·m 0.5 .

[0009] In some embodiments, the mechanical properties of the rare earth-containing rail with excellent low-temperature toughness also meet the following requirements: tensile strength ≥1100MPa, tread hardness ≥325HB.

[0010] In some embodiments, the chemical composition of the rare earth-containing rail with excellent low-temperature toughness is as follows by mass percentage: C 0.56%, Si 0.60%, Mn 0.58%, P 0.012%, S 0.007%, Cr 0.60%, V 0.03%, RE 0.003%, with the remainder being Fe and unavoidable impurities.

[0011] In some embodiments, the chemical composition of the rare earth-containing rail with excellent low-temperature toughness is as follows by mass percentage: C 0.63%, Si 0.63%, Mn 0.60%, P 0.019%, S 0.003%, Cr 0.58%, V 0.04%, RE 0.004%, with the remainder being Fe and unavoidable impurities.

[0012] In some embodiments, the chemical composition of the rare earth-containing rail with excellent low-temperature toughness is as follows by mass percentage: C 0.68%, Si 0.75%, Mn 0.45%, P 0.011%, S 0.003%, Cr 0.65%, V 0.05%, RE 0.005%, with the remainder being Fe and unavoidable impurities.

[0013] Another aspect of this invention aims to provide an online heat treatment method for rare earth-containing steel rails with excellent low-temperature toughness, which includes a rail rolling process and an online heat treatment process. The rail rolling process includes: billet → sawing → heating → BD1 rolling → BD2 rolling → continuous rolling on a CCS universal mill. The online heat treatment process is a three-stage online heat treatment controlled cooling process.

[0014] In some embodiments, in the rail rolling process, the temperature of the preheating section of the billet is controlled to be no greater than 900°C; the heating time is no less than 3 hours and 15 minutes; the furnace exit temperature is no less than 1150°C; the initial rolling temperature is ≥1100°C; and the final rolling temperature is 910-940°C.

[0015] In some embodiments, the three-stage online heat treatment controlled cooling process includes a strong cooling stage I, a weak cooling stage II, and a slow cooling stage III, all completed online, taking 120-160 seconds; wherein:

[0016] In the first stage of intense cooling, the cooling area is the entire rail head area plus the rail bottom. The cooling rate is controlled at 2.5-6.0℃ / s, the cooling duration is controlled at 40-80s, and the target temperature is controlled at 620-660℃ to suppress RE phase coarsening and lock in fine-grained austenite.

[0017] In the weak cooling II stage, the cooling areas are the top surface of the rail head, both sides, the gauge angle, and the bottom of the rail. The cooling rate is controlled at 1.5-2.0℃ / s, the duration is controlled at 60-100s, and the target temperature is controlled at 520-580℃ to promote the refinement of the pearlite lamellar spacing and improve toughness.

[0018] In the slow cooling stage III, the cooling area is the entire region, the cooling rate is controlled at ≤1.0℃ / s, and the target temperature is controlled at 450-520℃, in order to adjust the normal dimensions of the rail and reduce residual stress.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0020] 1. Innovative ingredient design

[0021] Medium carbon matrix: C 0.50-0.70% (solid solution strengthening dominates strength, while also considering weldability);

[0022] Si / Mn synergistic regulation:

[0023] Si 0.60-0.75% (refining pearlite lamellar spacing to ≤150nm);

[0024] Mn 0.40-0.60% (inhibits zonal tissue and improves toughness);

[0025] RE Precise Addition: Add 0.003-0.005% in the form of pure FeCe alloy (control the inclusion spheroidization rate >90%, size ≤2μm);

[0026] Composite microalloying: Cr 0.50-0.70% + V 0.03-0.06% (to improve hardenability, grain size ≥ ASTM 10 grade).

[0027] Innovation: Breaking through the traditional understanding that "high carbon necessarily means low toughness", ultra-fine microstructure is achieved through "increasing Si and reducing Mn + RE morphology control".

[0028] 2. It pioneered a three-stage cooling system of "fast-slow-gradient" to match RE precipitation kinetics.

[0029] 3. Performance advantages

[0030] Based on the composition and manufacturing process, the performance indicators of the rails are obtained:

[0031] Strength: Tensile strength ≥ 1100 MPa;

[0032] Hardness: Tread surface hardness ≥325HB;

[0033] Low temperature toughness:

[0034] Impact energy at -40℃ ≥20J;

[0035] Fracture toughness at -20℃ ≥45MPa·m 0.5 . Detailed Implementation

[0036] The present invention will be described in detail below through specific embodiments. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.

[0037] Example:

[0038] The chemical composition of the rare earth-containing rails in each embodiment is shown in Table 1 below.

[0039] Table 1: Chemical composition content (mass percentage / %) of each example

[0040]

[0041] The rolling process for the rails in each embodiment is as follows: billet → sawing → heating → BD1 rolling → BD2 rolling → continuous rolling on the CCS universal mill. During heating, the preheating temperature is controlled at 890℃; the heating time is 3 hours and 25 minutes; the furnace exit temperature is 1145℃; the initial rolling temperature is 1100℃; and the final rolling temperature is 935℃.

[0042] The online heat treatment process parameters for the rails in each embodiment are shown in Tables 2-4 below.

[0043] Table 2: Online heat treatment process parameters for the rails in Example 1

[0044]

[0045] Table 3: Online heat treatment process parameters for the rails in Example 2

[0046]

[0047] Table 4: Online heat treatment process parameters for the rails in Example 3

[0048]

[0049] Steel specimen performance: Tensile specimen specifications are as follows: diameter d0 = 10 mm, gauge length Lo = 5do. Tread hardness is measured by random sampling on the rail, with a specimen length of 250 mm. 0.5 mm of the rail head top surface is ground off. Five test points are used for Brinell hardness testing, and the average value is calculated. The test temperature is 20℃ ± 5℃. The sampling method, location, and dimensions of the above specimens conform to TB / T2344-2012 standard. Impact sampling conforms to GB / T229-2007. The sampling location is at the center of the tread surface, in the longitudinal direction, with dimensions of 10 mm × 10 mm × 50 mm, classified as A. KU2 Type notch. The experimental results are shown in Table 5.

[0050] Table 5: Mechanical properties of the rails in each embodiment

[0051]

[0052] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A rare earth containing steel rail having excellent low temperature toughness, characterized in that, The chemical composition of the rare earth-containing steel rail with excellent low-temperature toughness is as follows in terms of mass percentage: C 0.50-0.70%; Si 0.60-0.75%; Mn 0.40-0.60%; P 0.010-0.020%; S 0.003-0.010%; Cr 0.50-0.70%; V 0.03-0.06%; RE 0.003-0.005%; and the balance of Fe and inevitable impurities. The chemical composition of the rare earth-containing steel rail with excellent low-temperature toughness is as follows in terms of mass percentage: C 0.50-0.70%; Si 0.60-0.75%; Mn 0.40-0.60%; P 0.010-0.020%; S 0.003-0.010%; Cr 0.50-0.70%; V 0.03-0.06%; RE 0.003-0.005%; and the balance of Fe and inevitable impurities. The low-temperature toughness of the rare earth-containing steel rail with excellent low-temperature toughness satisfies the following conditions: -40℃ impact energy ≥ 20J; - Fracture toughness at 20°C > 45 MPa.m 0.5 .

2. The rare earth containing steel rail having excellent low temperature toughness according to claim 1, characterized in that, The mechanical properties of the rare earth-containing steel rail with excellent low-temperature toughness also satisfy the following conditions: tensile strength ≥ 1100MPa, tread hardness ≥ 325HB.

3. The rare earth containing steel rail having excellent low temperature toughness according to claim 1 or 2, characterized in that, The chemical composition of the rare earth-containing steel rail with excellent low-temperature toughness is as follows in terms of mass percentage: C 0.56%, Si 0.60%, Mn 0.68%, P 0.012%, S 0.007%, Cr 0.60%, V 0.03%, RE 0.003%, and the balance of Fe and inevitable impurities.

4. The rare earth containing steel rail having excellent low temperature toughness according to claim 1 or 2, characterized in that, The chemical composition of the rare earth-containing steel rail with excellent low-temperature toughness is as follows in terms of mass percentage: C 0.63%, Si 0.63%, Mn 0.60%, P 0.019%, S 0.003%, Cr 0.58%, V 0.04%, RE 0.004%, and the balance of Fe and inevitable impurities.

5. The rare earth containing steel rail having excellent low temperature toughness according to claim 1 or 2, characterized in that, The chemical composition of the rare earth-containing steel rail with excellent low-temperature toughness is as follows in terms of mass percentage: C 0.68%, Si 0.75%, Mn 0.85%, P 0.011%, S 0.003%, Cr 0.65%, V 0.05%, RE 0.005%, and the balance of Fe and inevitable impurities.

6. The method of in-line heat treatment of a rare earth containing steel rail having superior low temperature toughness as claimed in any one of claims 1 to 5, comprising a rail rolling process and an in-line heat treatment process, wherein the rail rolling process comprises: The billet is sawed, heated, rolled by BD1, rolled by BD2, and continuously rolled by a CCS universal rolling mill; the on-line heat treatment process is a three-stage on-line heat treatment controlled cooling process.

7. The on-line heat treatment method according to claim 6, wherein in the rail rolling process, the temperature of the billet heating preheating section is controlled to be not more than 900℃; the heating time is not less than 3 hours and 15 minutes; the out-of-furnace temperature is not less than 1150℃, the starting rolling temperature is ≥ 1100℃, and the final rolling temperature is 910-940℃.

8. The on-line heat treatment method according to claim 6, wherein the three-stage on-line heat treatment controlled cooling process comprises a strong cooling I stage, a weak cooling II stage and a slow cooling III stage, which are completed on-line and take 120-160s; wherein: in the strong cooling I stage, the cooling position is the whole area of the rail head + the rail bottom, the cooling speed is controlled to be 2.5-6.0℃ / s, the control time is 40-80s, and the control target temperature is 620-660℃, so as to inhibit RE phase coarsening and lock fine austenite; in the weak cooling II stage, the cooling position is the top surface of the rail head + both sides + the gauge angle + the rail bottom, the cooling speed is controlled to be 1.5-2.0℃ / s, the control time is 60-100s, and the control target temperature is 520-580℃, so as to promote pearlite interlamellar spacing refinement transformation and improve toughness; in the slow cooling III stage, the cooling position is the whole area of the rail head + the rail bottom, the cooling speed is controlled to be 0.5-1.0℃ / s, the control time is 60-100s, and the control target temperature is 550-600℃, so as to promote the transformation of the retained austenite to fine ferrite and improve the strength and toughness of the rail. ​ ​ In the said slow cooling III stage, the cooling position is the whole area, the controlled cooling rate is ≤1.0 ℃ / s, and the controlled target temperature is 450-520 ℃, so as to adjust the general size of the steel rail and reduce the residual stress.

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