Production method of 400HB-grade on-line heat treatment steel rail

Abstract

The invention discloses a production method of a 400HB-grade on-line heat treatment steel rail, which comprises the following steps: on-line heat treatment: the steel rail is air-cooled to 800-30 DEG C and enters a heat treatment line, the cooling mode is aerial fog cooling, the steel rail is rapidly cooled to 510-530 DEG C on the heat treatment line, the roller speed is 1.1 m / s, and the steel rail is naturally air-cooled to room temperature after being taken out of the heat treatment production line; the alloy comprises the following chemical components in percentage by weight: 0.90-1.00% of C; s is 0.50 to 0.80 percent; 0.90 to 1.25 percent of Mn; 0.30% to 0.50% of Cr; less than or equal to 0.020% of P; s is less than or equal to 0.020%, Nb + V is less than or equal to 0.06%, and the balance is Fe and inevitable impurities. The mechanical property Rm of the 400 HB-grade steel rail obtained through the production method is larger than or equal to 1330 MPa, the percentage elongation after fracture A is larger than or equal to 9%, and the tread hardness is 3900-430 HB.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical materials, and in particular relates to a production method for a 400HB-level online heat-treated rail. Background Art

[0002] With the development of heavy load and speed increase of railway, the burden of rails is getting heavier day by day. Especially on small radius curves, the wear of rails is very serious. The laying and use practices at home and abroad show that the use of 1200-1300MPa full-length quenched rails on small radius curves can increase their service life by 2-5 times, which has significant economic benefits. The advantages of rail online heat treatment are as follows:

[0003] 1) Online heat treatment of rails increases production efficiency. The hourly output of online heat treatment of rails is 3 to 4 times higher than that of offline heat treatment.

[0004] 2) Low production cost. Although the investment in online quenching equipment is higher than that in offline quenching, its production cost (manpower, time, energy consumption per ton of product, etc.) is much less.

[0005] 3) The rail quality is good. Since the entire rail structure is cooled from austenite, there will be no coarse-grained softening zone at the junction of the rail head / rail waist, and the rail waist and rail bottom are also properly strengthened. During residual heat quenching, while the rail head is accelerated to cool, compressed air or water is also sprayed on the rail bottom to cool it, so that the contraction, expansion and transformation stresses are balanced during the quenching process, and the conveying guide roller is used to limit the deformation of the rail in a hot state. Therefore, the straightness of the rail is better when it leaves the quenching equipment, and the deformation and residual stress are small during straightening. Summary of the invention

[0006] The purpose of the present invention is to provide a production method for a 400HB grade online heat-treated rail. The 400HB grade rail obtained by the production method has mechanical properties Rm≥1330MPa, elongation after fracture A≥9%, and tread hardness of 3900-430HB.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for producing a 400HB grade online heat-treated rail, comprising:

[0009] 1) Hot metal pretreatment: sulfur content in hot metal ≤ 0.03%, phosphorus content ≤ 0.12%;

[0010] 2) Converter smelting: Control the C content of steel to be ≥0.1% and the tapping temperature to be ≥1630℃. Add lime, silicon calcium barium and fluorite after tapping to modify the slag. Ensure the argon blowing effect during the tapping process and avoid agglomeration of the top slag when the molten steel is refined in place;

[0011] 3) LF furnace refining: During LF refining, the slag basicity is controlled to be ≥2.0, and the off-site temperature is 1585-1595°C; the chemical composition weight percentage of the molten steel is as follows: C 0.90-1.00%; Si 0.50-0.80%; Mn 0.90-1.25%; Cr 0.30-0.50%; P≤0.020%; S≤0.020%, Nb+V≤0.06%, and the rest is Fe and unavoidable impurities;

[0012] 4) VD vacuum degassing: deep vacuum degassing time ≥ 18min, soft blowing time after vacuum degassing ≥ 18min, control the argon flow rate during the soft blowing process to prevent the molten steel from rolling violently and causing slag rolling;

[0013] 5) Continuous casting: The continuous casting process adopts protective casting, low-aluminum protective slag, ultra-weak cooling water distribution in the secondary cooling section, constant casting speed operation throughout the process, superheat ΔT≤30℃, electromagnetic stirring and light pressure of the casting machine are turned on to ensure the quality of the casting.

[0014] 6) Billet heating: The total billet heating time is ≥ 3 hours and 45 minutes, of which the preheating section temperature of the heating furnace is ≤ 1000°C, the heating section temperature is 1200~1280°C, and the soaking section temperature is 1150~1260°C.

[0015] 7) Rolling: The ingot is rolled into rails by a universal rolling mill. The starting rolling temperature is controlled at 1100-1150°C and the final rolling temperature is 930-950°C.

[0016] 8) Online heat treatment: The rails are air-cooled to 800-30℃ before entering the heat treatment line. The cooling method is mist cooling. The rails are quickly cooled to 510-530℃ in the heat treatment line with a roller speed of 1.1m / s. After leaving the heat treatment production line, the rails are naturally air-cooled to room temperature.

[0017] Furthermore, the chemical composition of the 400HB grade online heat-treated rail is as follows in percentage by weight: C 0.948%; Si 0.56%; Mn 1.023%; Cr 0.341%; P 0.0111%; S 0.005%, Nb+V 0.052%, and the rest is Fe and unavoidable impurities.

[0018] Furthermore, the chemical composition of the 400HB grade online heat-treated rail is as follows in weight percentage: C 0.936%; Si 0.619%; Mn 1.068%; Cr 0.354%; P 0.0116%; S 0.0033%, Nb+V 0.054%, and the rest is Fe and unavoidable impurities.

[0019] Furthermore, the chemical composition of the 400HB grade online heat-treated rail is as follows in weight percentage: C 0.941%; Si 0.582%; Mn 1.029%; Cr 0.351%; P 0.0092%; S 0.0035%, Nb+V 0.049%, and the rest is Fe and unavoidable impurities.

[0020] Furthermore, the metallographic structure of the rail head is pearlite.

[0021] Compared with the prior art, the beneficial technical effects of the present invention are:

[0022] The 400HB grade rail obtained by the production method has mechanical properties Rm≥1330MPa, elongation after fracture A≥9%, and tread hardness of 3900-430HB. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below in conjunction with specific embodiments to facilitate a clearer understanding of the present invention (all percentages in the following embodiments are by weight).

[0024] A method for producing a 400HB grade online heat-treated rail comprises the following steps:

[0025] 1) Hot metal pretreatment: The sulfur content in the hot metal is 0.011% and the phosphorus content is 0.10%.

[0026] 2) Converter smelting: Control the C content of steel to 0.1% and the tapping temperature to 1644°C. Add lime, silicon calcium barium and fluorite after tapping to modify the slag. Ensure the argon blowing effect during the tapping process. Avoid agglomeration of the top slag when the molten steel is refined in place.

[0027] 3) LF furnace refining: During LF refining, the slag basicity is controlled to be ≥2.1 and the off-site temperature is 1588℃;

[0028] 4) VD vacuum degassing: Deep vacuum degassing time is 15 minutes, and soft blowing is performed for 18 minutes after vacuum degassing. During the soft blowing process, the argon flow rate is stable, and the molten steel creeps without exposure.

[0029] 5) Continuous casting: The continuous casting process adopts protective casting, low-aluminum protective slag, weak cooling water distribution in the secondary cooling section, constant pulling speed operation throughout the whole process, pulling speed of 0.62m / min, electromagnetic stirring and light pressure of the casting machine are turned on to ensure the quality of the casting.

[0030] 6) Billet heating: The total heating time is 3 hours and 50 minutes. The heating time and heating temperature of each section are shown in Table 1.

[0031] Table 1 400HB rail heating process

[0032] Preheating section Heating 1 stage Heating 2 stages Heat soaking section Heating time 50min 60min 65min 60min temperature 723℃ 935℃ 1212℃ 1244℃

[0033] 7) Rolling: The ingot is rolled into rails by a universal rolling mill, with the starting rolling temperature at 1100°C and the final rolling temperature at 935°C.

[0034] 8) Online heat treatment: The rails are air-cooled to 810-820℃ before entering the heat treatment line. Mist cooling is used to quickly cool the rails to 517-520℃ in the heat treatment line. The roller speed is 1.1m / s. After leaving the heat treatment line, the rails are naturally air-cooled to room temperature.

[0035] Comparison of results before and after implementation:

[0036] 1) The chemical composition of the product before and after implementation is shown in Table 2.

[0037] Table 2 Chemical composition of products before and after implementation

[0038]

[0039] 2) The pre- and post-heat treatment processes are shown in Table 3.

[0040] Table 3 Implementation of heat treatment process before and after

[0041]

[0042] 3) Product performance before and after implementation is shown in Table 4.

[0043] Table 4 Product performance before and after implementation

[0044]

[0045] By comparison, after the chemical composition and heat treatment process were improved, the mechanical properties of the rails did not change much, but were slightly improved, but the microstructure was normal, all P, and there was no unacceptable abnormal structure B.

[0046] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for producing 400HB grade online heat-treated rails, characterized in that: include: 1) Hot metal pretreatment: sulfur content in hot metal ≤ 0.03%, phosphorus content ≤ 0.12%; 2) Converter smelting: Control the C content of steel to be ≥0.1% and the tapping temperature to be ≥1630℃. Add lime, silicon calcium barium and fluorite after tapping to modify the slag. Ensure the argon blowing effect during the tapping process and avoid agglomeration of the top slag when the molten steel is refined in place; 3) LF furnace refining: During LF refining, the slag basicity is controlled to be ≥2.0, and the off-site temperature is 1585-1595°C; the chemical composition weight percentage of the molten steel is as follows: C 0.90-1.00%; Si 0.50-0.80%; Mn 0.90-1.25%; Cr 0.30-0.50%; P≤0.020%; S≤0.020%, Nb+V≤0.06%, and the rest is Fe and unavoidable impurities; 4) VD vacuum degassing: deep vacuum degassing time ≥ 18min, soft blowing time after vacuum degassing ≥ 18min, control the argon flow rate during the soft blowing process to prevent the molten steel from rolling violently and causing slag rolling; 5) Continuous casting: The continuous casting process adopts protective casting, low-aluminum protective slag, ultra-weak cooling water distribution in the second cooling section, constant casting speed operation throughout the process, superheat ΔT≤30℃, electromagnetic stirring and light pressure of the casting machine are turned on to ensure the quality of the ingot; 6) Billet heating: The total billet heating time is ≥ 3 hours and 45 minutes, of which the preheating section temperature of the heating furnace is ≤ 1000°C, the heating section temperature is 1200-1280°C, and the soaking section temperature is 1150-1260°C; 7) Rolling: The ingot is rolled into rails by a universal rolling mill, with the starting rolling temperature controlled at 1100-1150°C and the final rolling temperature at 930-950°C; 8) Online heat treatment: The rails are air-cooled to 800-30℃ before entering the heat treatment line. The cooling method is mist cooling. The rails are quickly cooled to 510-530℃ in the heat treatment line with a roller speed of 1.1m / s. After leaving the heat treatment production line, the rails are naturally air-cooled to room temperature.

2. The method for producing a 400HB grade online heat-treated rail according to claim 1, characterized in that: The chemical composition of the 400HB grade online heat-treated rail is as follows in percentage by weight: C 0.948%, Si 0.56%, Mn 1.023%, Cr 0.341%, P 0.0111%, S 0.005%, Nb+V 0.052%, and the rest is Fe and unavoidable impurities.

3. The method for producing a 400HB grade online heat-treated rail according to claim 1, characterized in that: The chemical composition of the 400HB grade online heat-treated rail is as follows in percentage by weight: C 0.936%, Si 0.619%, Mn 1.068%, Cr 0.354%, P 0.0116%, S 0.0033%, Nb+V 0.054%, and the rest is Fe and unavoidable impurities.

4. The method for producing a 400HB grade online heat-treated rail according to claim 1, characterized in that: The chemical composition of the 400HB grade online heat-treated rail is as follows in percentage by weight: C 0.941%; Si 0.582%; Mn 1.029%; Cr 0.351%; P 0.0092%; S 0.0035%, Nb+V 0.049%, and the rest is Fe and unavoidable impurities.

5. The method for producing 400HB grade online heat-treated rail according to claim 1, characterized in that: The metallographic structure of the rail head is pearlite.

Images