Chromium and vanadium microalloying outlet R350HT heat treatment steel rail and production method thereof

Abstract

The invention discloses a chromium and vanadium microalloying outlet R350HT heat treatment steel rail and a production method thereof. The R350HT heat-treated steel rail at the chromium and vanadium microalloying outlet, provided by the invention, comprises the following chemical components in percentage by mass: 0.76-0.80% of C; 0.50 to 0.58% of Si; 1.0 to 1.20 parts of Mn; p < = 0.020; s is less than or equal to 0.025; 0.10 to 0.15 percent of Cr, 0.01 to 0.03 percent of V and the balance of Fe and impurities. By optimizing the component design and the production process, the R350HT heat treatment steel rail provided by the invention has excellent wear resistance and very high strength and hardness.

Description

Technical Field

[0001] The invention belongs to the field of metallurgical materials, and in particular relates to a chromium and vanadium microalloyed export R350HT heat-treated rail and a production method thereof. Background Art

[0002] With the development of overseas railway transportation construction, the quality and performance requirements of rails are becoming more and more stringent, especially the service performance of rail materials requires strict conditions such as ensuring service life. European standard EN13674 is one of the important technical standards for export rails and the main standard for purchasing rails in Europe, Africa, Southeast Asia and other countries and regions. R350HT is one of the main steel grades in the standard. This steel grade has high strength and hardness and can be used in freight lines. According to the requirements of standard composition, quality and performance, the steel mill uses C-Si-Mn as the main element and meets the standard requirements after online heat treatment and cooling. However, with the fierce competition in the export market and the increase in customer service life requirements, it is necessary to improve the strength and service life of rail materials within the scope of standard composition and process requirements. Therefore, it is necessary to develop high-performance R350HT rails that meet the standards and are higher than the standards to meet the stringent requirements of customers. According to statistics on the annual domestic export of R350HT rails, the annual export is about 50,000 tons. According to statistics, the international market has grown steadily every year, and the market demand has continued to grow. Therefore, developing European standard R350HT high-strength wear-resistant rails that meet the standards and have excellent service performance is of great production and economic significance. Summary of the invention

[0003] The object of the present invention is to provide a chromium and vanadium microalloyed R350HT heat-treated rail with good strength and toughness ratio and excellent wear resistance and a production method thereof. The specific technical scheme of the present invention is as follows:

[0004] One aspect of the present invention provides a chromium and vanadium microalloyed export R350HT heat-treated rail, the chemical composition of which is as follows by mass percentage: C 0.76-0.80; Si 0.50-0.58; Mn 1.0-1.20; P≤0.020; S≤0.025; Cr0.10-0.15, V 0.01-0.03, and the rest is Fe and impurities.

[0005] Compared with the standard and general production, the main trace alloying elements Cr and V are added to this material; the purpose is to improve the strength and toughness of the rail and the hardenability of the cross-section of the heat-treated rail. The C component design in this steel has a large solid solubility with Fe, has a solid solution strengthening effect, and improves the strength and hardness of the steel. The R350HT standard requires high hardness and strength, and the C content needs to be increased according to the material component elements. Mn expands the austenite phase region, increases the stability of the supercooled austenite of the steel, and significantly improves the hardenability of the steel. Si reduces the transformation rate from austenite to ferrite and increases the supercooling. At the same time, considering the weldability of the rail, the Si content should not be too high, because Si has poor heat conductivity and is not conducive to rail welding; V alloy elements can refine the material microstructure, precipitate C and N compounds to improve the strength and toughness of the material, and have a significant effect on the wear resistance of the material. However, due to the limitation of the standard composition, only trace amounts are added. The Cr element is a low-priced element that has a positive effect on the hardenability and hardness of the material. The appropriate amount is added according to the residual element limit of the composition. In addition, Baosteel's unique rare earth ore can purify inclusions in steel through the inheritance of rare earths during the smelting production process. By utilizing the rare earth effect, it can fully aggregate with hard inclusions such as silicates in the steel to form spherical and other deformed forms, thereby improving the service performance of the material.

[0006] In some embodiments, the mechanical properties of the chromium and vanadium microalloyed R350HT heat-treated rail meet the following requirements: tensile strength ≥ 1298 MPa, elongation ≥ 11%, and tread hardness ≥ 364 HBW.

[0007] In some embodiments, the microstructure of the chromium and vanadium microalloyed R350HT heat-treated rail is pearlite.

[0008] In some embodiments, the chemical composition of the chromium and vanadium microalloyed export R350HT heat-treated rail is as follows by mass percentage: C 0.78-0.80; Si 0.53-0.56; Mn 1.08-1.13; P≤0.015; S≤0.005; Cr0.11-0.13, V 0.023-0.028, and the rest is Fe and impurities.

[0009] Another aspect of the present invention provides a method for producing chromium and vanadium microalloyed R350HT heat-treated export rails, which includes a steelmaking production process and a rolling process.

[0010] In some embodiments, the steelmaking production process includes: molten iron → converter smelting → LF refining → VD → continuous casting; wherein the converter smelting adopts aluminum-free deoxidation alloying, and the whole process is argon blown according to normal refining; the vacuum degree is ≤0.10KPa, the deep vacuum time is ≥18min, the superheat ΔT is ≤30°C, and V and Cr alloys are mainly added and adjusted in LF refining.

[0011] In some embodiments, the rolling process includes: billet → sawing → heating → BD1 rolling → BD2 rolling → CCS universal rolling mill continuous rolling → online residual heat quenching → sawing → cooling → cutting head and tail → straightening → inspection → packaging → weighing → warehousing; wherein the temperature of the billet heating and preheating section is not greater than 900°C; the total heating time is not less than 3 hours and 15 minutes, the furnace temperature is 1100-1150°C, the start rolling temperature is ≥1080°C, and the final rolling temperature is 910-940°C.

[0012] In some embodiments, the online waste heat quenching cooling medium is wind or mist or a mixture of mist + wind; the heat treatment temperature is determined according to the phase change temperature parameters in the steel and the actual capacity of the industrial equipment; the waste heat treatment temperature after the final rolling of the rail is 745°C to 800°C, and the rail is discharged from the heat treatment production line after 140 to 160s of online heat treatment. In the first stage of the online process, the top surface, both sides, and the lower jaw of the gauge angle and the bottom of the rail head are cooled by wind or mist or a mixture of mist + wind; the cooling rate of the actual cooling section is 3.0 to 4.2°C / s, and the cooling time is 60 to 80s; the final structure of the rail is ensured to be pearlite structure; in the second stage, weak cooling is performed, and the top surface, both sides of the rail head, the lower jaw of the gauge angle and the bottom of the rail are cooled by mist, and the cooling rate is 1.7 to 2.0°C / s. After cooling, the outlet rail head temperature is 460 to 540°C, and then naturally air-cooled to room temperature.

[0013] The beneficial effects of the present invention are as follows: the present invention provides a R350HT heat-treated rail containing trace amounts of chromium and vanadium alloy and a production method thereof. The strength and hardness of the rail are improved by utilizing an online waste heat heat treatment process, while the composition is reasonably designed and the optimal Si, Mn, V, and Cr alloy elements are added to the rail. Under this rolling process, the tensile strength, elongation, tread hardness, hardenability, wear resistance and other properties of the rail can be improved. The R350HT heat-treated rail produced by the present invention has excellent wear resistance. The chromium and vanadium-containing heat-treated rail of the present invention has a unique production process, high production efficiency, energy saving and environmental protection, good economic benefits, is suitable for large-scale production, and has good promotion value. DETAILED DESCRIPTION

[0014] The present invention is described in detail below through specific examples. The examples are intended to help understand the present invention but are not intended to limit the present invention.

[0015] Example

[0016] The production method of the chromium and vanadium microalloyed export R350HT heat-treated rail provided by the present invention comprises: a steelmaking production process and a rolling process; wherein:

[0017] The steelmaking production process includes: molten iron → converter smelting → LF refining → VD → continuous casting. The converter smelting adopts aluminum-free deoxidation alloying, and the whole process is argon blowing as normal refining; vacuum degree ≤ 0.10KPa, deep vacuum time ≥ 18min, superheat ΔT ≤ 30℃. The chemical composition of each example is shown in Table 1.

[0018] Table 1: Composition of each example (mass percentage / %)

[0019]

[0020] The rolling process includes: billet → sawing → heating → BD1 rolling → BD2 rolling → CCS universal rolling mill continuous rolling → online residual heat quenching → sawing → cooling → cutting head and tail → straightening → inspection → packaging → weighing → storage. The temperature of the billet heating and preheating section is not more than 900℃; the total heating time is not less than 3 hours and 15 minutes. The furnace temperature is 1100~1150℃, the rolling start temperature is ≥1080℃, and the final rolling temperature is 910~940℃.

[0021] The cooling medium for online residual heat quenching is wind or mist or a mixture of mist + wind. The heat treatment temperature is determined based on the phase change temperature parameters in the steel and the actual capacity of the industrial equipment. The residual heat treatment temperature of the rail after final rolling is 745℃~800℃. After 140~160s of online heat treatment, it leaves the heat treatment production line. In the first stage of the online process, the top surface, both sides, and the jaw of the gauge angle and the bottom of the rail head of the rail are cooled by wind or mist or a mixture of mist + wind. The actual cooling section has a cooling rate of 3.0~4.2℃ / s and a cooling time of 60~80s. Ensure that the final structure of the rail is pearlite. In the second stage, weak cooling is performed, and the top surface, both sides of the rail head, the jaw of the gauge angle, and the bottom of the rail are cooled by mist. The cooling rate is 1.7~2.0℃ / s. After cooling, the temperature of the rail head at the outlet is 460℃~540℃ (for example, 480℃~520℃), and then naturally cooled to room temperature. The specific rolling process of each example is shown in Table 2 below.

[0022] Table 2: Rolling process of each example

[0023]

[0024] After rolling, the steel sample performance: The tensile sample specifications are: diameter d0 = 10mm, gauge length Lo = 5do. The tread hardness is randomly sampled on the rail, the sample length is 250mm, the top surface of the rail head is ground off 0.5mm, and there are 5 test points. The Brinell hardness test is carried out and the average value is calculated. The test temperature is 20℃ ± 5℃. The above sample sampling method, location and size are in accordance with EN13674 standard. The experimental results are shown in Table 3.

[0025] Table 3: Mechanical properties of each example

[0026]

[0027] It can be seen from Table 3 that each example has good strength, toughness and mechanical properties. The R350HT rail containing trace amounts of Cr and V alloy produced therefrom has good strength and hardness, satisfying the following requirements: tensile strength ≥ 1298 MPa, elongation ≥ 11%, and tread hardness ≥ 364 HBW.

[0028] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A chromium and vanadium microalloyed R350HT heat-treated rail for export, characterized in that: The chemical composition of the chromium and vanadium microalloyed export R350HT heat-treated rail is as follows by mass percentage: C 0.76-0.80; Si 0.50-0.58; Mn 1.0-1.20; P≤0.020; S≤0.025; Cr 0.10-0.15, V 0.01-0.03, and the rest is Fe and impurities.

2. The chromium and vanadium microalloyed R350HT heat-treated rail for export according to claim 1, characterized in that: The mechanical properties of the chromium and vanadium microalloyed R350HT heat-treated export rail meet the following requirements: tensile strength ≥1298MPa, elongation ≥11%, and tread hardness ≥364HBW.

3. The chromium and vanadium microalloyed R350HT heat-treated rail for export according to claim 1 or 2, characterized in that: The microstructure of the chromium and vanadium microalloyed export R350HT heat-treated rail is pearlite.

4. The chromium and vanadium microalloyed export R350HT heat-treated rail according to any one of claims 1 to 3, characterized in that: The chemical composition of the chromium and vanadium microalloyed R350HT heat-treated export rail is as follows by mass percentage: C 0.78-0.80; Si 0.53-0.56; Mn 1.08-1.13; P≤0.015; S≤0.005; Cr 0.11-0.13, V 0.023-0.028, and the rest is Fe and impurities.

5. The method for producing chromium and vanadium microalloyed R350HT heat-treated export rail according to any one of claims 1 to 4, characterized in that: The production method comprises a steelmaking production process and a rolling process.

6. The production method according to claim 5, characterized in that The steelmaking production process includes: molten iron→converter smelting→LF refining→VD→continuous casting; wherein the converter smelting adopts aluminum-free deoxidation alloying, and the whole process is argon blowing as normal refining; the vacuum degree is ≤0.10KPa, the deep vacuum time is ≥18min, the superheat ΔT is ≤30°C, and V and Cr alloys are mainly added and adjusted in the LF refining.

7. The production method according to claim 5 or 6, characterized in that: The rolling process includes: billet→sawing→heating→BD1 rolling→BD2 rolling→CCS universal rolling mill continuous rolling→online residual heat quenching→sawing→cooling→head and tail cutting→straightening→inspection→packaging→weighing→warehousing; wherein the temperature of the billet heating and preheating section is not greater than 900°C; the total heating time is not less than 3 hours and 15 minutes, the furnace outlet temperature is 1100-1150°C, the start rolling temperature is ≥1080°C, and the final rolling temperature is 910-940°C.

8. The production method according to claim 7, characterized in that: The cooling medium for online waste heat quenching is wind or mist or a mixture of mist + wind; the heat treatment temperature is determined based on the phase change temperature parameters in the steel and the actual capacity of the industrial equipment; the waste heat treatment temperature after the final rolling of the rail is 745℃~800℃, and the rail leaves the heat treatment production line after 140~160s of online heat treatment. In the first stage of the online process, the top surface, both sides, the lower jaw of the gauge angle, and the bottom of the rail are cooled by wind or mist or a mixture of mist + wind; the cooling rate in the actual cooling section is 3.0~4.2℃ / s, and the cooling time is 60~80s; the final structure of the rail is ensured to be pearlite; in the second stage, weak cooling is performed, and the top surface, both sides of the rail head, the lower jaw of the gauge angle, and the bottom of the rail are cooled by mist, with a cooling rate of 1.7~2.0℃ / s. After cooling, the temperature of the rail head at the outlet is 460℃~540℃, and then naturally air-cooled to room temperature.

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