A method for producing an export h350 grade high-strength heat-treated rail

Abstract

The application discloses a production method of export H350-grade high-strength heat-treated steel rail, which comprises the following steps: steel smelting production process, steel rail rolling process and steel rail on-line heat treatment process; and the mass percentage of the chemical components of the steel rail is as follows: C 0.75-0.80%, Si 0.50-0.65%, Mn 1.00-1.20%, P≤0.020%, S≤0.020%, V≤0.03%, Cr≤0.15%, and the rest is Fe and inevitable impurities, and the total mass percentage is 100%. The application aims to provide a production method of export H350-grade high-strength heat-treated steel rail, and the H350-grade steel rail has good strength and toughness ratio after smelting and heat treatment, so that the steel rail can meet the technical requirements of the European standard.

Description

Technical Field

[0001] This invention relates to the field of metallurgical materials, and in particular to a method for producing export-grade H350 high-strength heat-treated steel rails. Background Technology

[0002] In overseas mining and coal transportation lines, especially on small-radius curves, rail wear is extremely severe. Domestic and international experience shows that using 1200-1300MPa grade full-length hardened rails on small-radius curves can increase their service life by 2-5 times, resulting in significant economic benefits. As my country's railway construction expands internationally, it has the capability to produce rails meeting European and American standards. Among these, the European standard R350HT is a primary source of high-strength heat-treated rails for overseas freight lines, with customers clearly specifying requirements for rail service life.

[0003] In addition to meeting mechanical property requirements such as tensile strength and hardness, R350HT rails also need to meet certain cross-sectional hardness requirements, namely, the hardenability and descent properties of the heat-treated rail cross-sectional hardness. The standard composition of this steel grade is mainly C-Mn. To meet the full standard cross-sectional hardness and service requirements, in addition to designing a reasonable heat treatment process, it is also necessary to rationally control the production composition. Therefore, developing high-strength, wear-resistant R350HT rails that meet European standard cross-sectional performance requirements is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing export-grade H350 high-strength heat-treated steel rails, which, after smelting and heat treatment, produce H350 grade steel rails with a good strength and toughness ratio, thus meeting the technical requirements of European standards.

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

[0006] This invention discloses a method for producing export-grade H350 high-strength heat-treated steel rails, comprising:

[0007] Steel production process: molten iron → converter smelting → LF refining → VD → continuous casting. Converter smelting uses silicon-calcium-barium deoxidation, and the entire process is carried out with normal argon blowing as in refining; vacuum degree ≤0.10KPa, deep vacuum time ≥18min, superheat ΔT ≤30℃, V and Cr alloys are added at the LF station, and the added alloys are medium carbon ferrochrome and ferrovanadium alloys;

[0008] Rail rolling process: 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; the temperature of the billet heating and preheating section 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 900-940℃.

[0009] Online heat treatment process for rails: The cooling medium is mainly natural air. The initial cooling temperature of the rails is 750℃-820℃. In the first stage, the actual cooling rate of the rail head is 3.0℃ / s-4.6℃ / s, cooling to 620℃-670℃ before entering the second stage. In the second stage, the actual cooling rate of the rail head is 2.1℃ / s-3.3℃ / s. In the third stage, the actual cooling rate of the rail head is 0.8℃ / s-1.5℃ / s, cooling to 520℃-560℃ before exiting the heat treatment production line. The total cooling time for heat treatment is 120-150 seconds.

[0010] The chemical composition of the rail by mass percentage is as follows: C 0.75-0.80%; Si 0.50-0.65%; Mn 1.00-1.20%; P≤0.020%; S≤0.020%; V≤0.03%; Cr≤0.15%; the remainder is Fe and unavoidable impurities, totaling 100% by mass.

[0011] Furthermore, the chemical composition of the rail by mass percentage is as follows: C 0.79%; Si 0.54%; Mn 1.05%; P 0.003%; S 0.003%; V 0.017%; Cr 0.11%; the remainder is Fe and unavoidable impurities, with a total mass fraction of 100%.

[0012] Furthermore, the chemical composition of the rail by mass percentage is as follows: C 0.78%; Si 0.58%; Mn 1.09%; P 0.011%; S 0.004%; V 0.018%; Cr 0.09%; the remainder being Fe and unavoidable impurities, totaling 100% by mass.

[0013] Furthermore, the chemical composition of the rail by mass percentage is as follows: C 0.79%; Si 0.57%; Mn 1.11%; P 0.010%; S 0.004%; V 0.016%; Cr 0.09%; the remainder being Fe and unavoidable impurities, totaling 100% by mass.

[0014] Furthermore, the produced rails have a tensile strength greater than 1250 MPa and an elongation greater than 14%.

[0015] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0016] This invention improves the tensile strength, elongation, tread hardness, cross-sectional hardness, and wear resistance of rails through a rationally designed composition and the addition of trace amounts of V and Cr alloying elements during the rolling process. The rails produced by this invention feature a unique manufacturing process, high production efficiency, energy conservation, environmental friendliness, and good economic benefits. They are suitable for large-scale production and have significant potential for widespread application. Detailed Implementation

[0017] A method for producing export-grade H350 high-strength heat-treated steel rails, the steel smelting process being: molten iron → converter smelting → LF refining → VD → continuous casting. The converter smelting employs silicon-calcium-barium-oxygen alloying, with argon blowing throughout the refining process; vacuum degree ≤0.10 kPa, deep vacuum time ≥18 min, superheat ΔT ≤30℃. The chemical compositions of each embodiment are shown in Table 1.

[0018] Table 1. Components of each embodiment (mass percentage / %)

[0019]

[0020] Example 1: The preheating temperature of the steel rail billet was 770℃; the total heating time was 3 hours and 25 minutes; the furnace exit temperature was 1180℃, the initial rolling temperature was 1120℃, and the final rolling temperature was 937℃; the initial cooling temperature of the rail was 770℃, the actual cooling rate of the rail head in the first stage was 4.0℃ / s, and the rail head temperature was cooled to 630℃ before entering the second stage; the actual cooling rate of the rail head in the second stage was 3.0℃ / s; the actual cooling rate of the rail head in the third stage was 0.9℃ / s, and the rail head was cooled to 525℃ before exiting the heat treatment production line; the total heat treatment cooling time was 139s.

[0021] Example 2: The preheating temperature of the steel rail billet was 840℃; the total heating time was 3 hours and 35 minutes; the furnace exit temperature was 1190℃, the initial rolling temperature was 1125℃, and the final rolling temperature was 942℃; the initial cooling temperature of the rail was 783℃, the actual cooling rate of the rail head in the first stage was 4.2℃ / s, and the rail head temperature was cooled to 637℃ before entering the second stage; the actual cooling rate of the rail head in the second stage was 3.2℃ / s; the actual cooling rate of the rail head in the third stage was 0.87℃ / s, and the rail head temperature was cooled to 528℃ before exiting the heat treatment production line; the total heat treatment cooling time was 125s.

[0022] Example 3: The preheating temperature of the steel rail billet was 780℃; the total heating time was 3 hours and 23 minutes; the furnace exit temperature was 1183℃; the initial rolling temperature was 1122℃; the final rolling temperature was 932℃; the initial cooling temperature of the rail was 768℃; the actual cooling rate of the rail head in the first stage was 4.1℃ / s; the rail head temperature was 637℃ before entering the second stage; the actual cooling rate of the rail head in the second stage was 3.0℃ / s; the actual cooling rate of the rail head in the third stage was 0.9℃ / s; the rail head temperature was 523℃ before exiting the heat treatment production line; the total heat treatment cooling time was 127s.

[0023] Performance of steel samples after rolling heat treatment: Tensile test specimens were prepared with a diameter d0 = 10 mm and a gauge length Lo = 5 do. Tread surface hardness was measured by random sampling on the rail, with a specimen length of 250 mm. 0.5 mm of the rail head was ground off at 5 test points, and Brinell hardness tests were performed, with the average value calculated. Cross-sectional hardness was measured at 8 points according to the standard. The sampling methods and locations for all samples conformed to EN13674-2011. Production inspection results are shown in Table 2.

[0024] Table 2 Mechanical properties of each embodiment

[0025]

[0026] 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 for producing export-grade H350 high-strength heat-treated steel rails, characterized in that, include: Steel production process: molten iron → converter smelting → LF refining → VD → continuous casting; converter smelting uses silicon-calcium-barium deoxidation, and the whole process is carried out by normal argon blowing according to the refining process; Vacuum degree ≤ 0.10KPa, deep vacuum time ≥ 18min, superheat ΔT ≤ 30℃, V and Cr alloys are added at the LF station, and the added alloys are medium carbon ferrochrome and ferrovanadium alloys; Rail rolling process: 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; the billet heating and preheating section temperature 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 900-940℃. Online heat treatment process for rails: The cooling medium is mainly natural air. The initial cooling temperature of the rail is 750℃-820℃. In the first stage, the actual cooling rate of the rail head is 3.0℃ / s-4.6℃ / s, cooling to 620℃-670℃ before entering the second stage. In the second stage, the actual cooling rate of the rail head is 2.1℃ / s-3.3℃ / s. In the third stage, the actual cooling rate of the rail head is 0.8℃ / s-1.5℃ / s, cooling to 520℃-560℃ before exiting the heat treatment production line. The total heat treatment cooling time is 120-150 seconds. The chemical composition of the rail by mass percentage is as follows: C 0.75-0.80%; Si 0.50-0.65%; Mn 1.00-1.20%; P≤0.020%; S≤0.020%; V≤0.03%; Cr≤0.15%; the remainder is Fe and unavoidable impurities, totaling 100% by mass.

2. The method for producing export H350 grade high-strength heat-treated steel rails according to claim 1, characterized in that, The chemical composition of the rail by mass percentage is as follows: C 0.79%; Si 0.54%; Mn 1.05%; P 0.003%; S 0.003%; V 0.017%; Cr 0.11%; the remainder is Fe and unavoidable impurities, with a total mass fraction of 100%.

3. The method for producing export H350 grade high-strength heat-treated steel rails according to claim 1, characterized in that, The chemical composition of the rail by mass percentage is as follows: C 0.78%; Si 0.58%; Mn 1.09%; P 0.011%; S 0.004%; V 0.018%; Cr 0.09%; the remainder is Fe and unavoidable impurities, with a total mass fraction of 100%.

4. The method for producing export H350 grade high-strength heat-treated steel rails according to claim 1, characterized in that, The chemical composition of the rail by mass percentage is as follows: C 0.79%; Si 0.57%; Mn 1.11%; P 0.010%; S 0.004%; V 0.016%; Cr 0.09%; the remainder is Fe and unavoidable impurities, with a total mass fraction of 100%.

5. The method for producing export H350 grade high-strength heat-treated steel rails according to claim 1, characterized in that, The produced rails have a tensile strength greater than 1250 MPa and an elongation greater than 14%.

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