Preparation method of low-alloy high-strength steel rail

Abstract

The invention discloses a production method of an American-standard low-alloy rare earth high-strength heat treatment steel rail. The production method comprises the processes of smelting, heating, rolling and online heat treatment. The steel rail comprises the following chemical components in percentage by mass: 0.70-0.82% of C; s is 0.40 to 0.80 percent; 0.70% to 1.20% of Mn; 0.40% to 0.60% of Cr; less than or equal to 0.020% of P; less than or equal to 0.020% of S; the rare earth Ce is greater than or equal to 0.002%, and the balance is Fe and inevitable impurities. The mechanical properties of the low-alloy rare earth high-strength heat-treated steel rail obtained by the production method meet the following requirements: the yield strength Rp0.2 of the steel rail is greater than or equal to 830MPa; the tensile strength Rm is greater than or equal to 1300MPa; the percentage elongation A after fracture is greater than or equal to 10%; the hardness of the tread is 380 to 420 HB; the rail head cross section hardness is 22mm and the depth is greater than or equal to 350HB. And other mechanical properties meet AREMA standard requirements.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical materials, and in particular relates to a method for preparing a low-alloy high-strength steel 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 have shown that the use of 370HB grade full-length quenched rails on small radius curves can increase their service life by 2 to 5 times, which has significant economic benefits. At present, the 370HB grade heavy-duty rails commonly used in heavy-duty lines at home and abroad have high strength and low toughness during use. The elongation after tensile fracture of the rails is 9%. The American standard low-alloy rare earth high-strength heat-treated rails invented by this patent have higher strength and toughness. The hardness of the material meets the requirements of 380HB grade, and the toughness is good. The elongation after fracture can reach 10%. The good strength and toughness match can greatly reduce the probability of damage during the service of the rails and increase the service life. Summary of the invention

[0003] The purpose of the present invention is to provide a method for preparing a low alloy high strength steel rail, wherein the mechanical properties of the steel rail obtained by the production method meet the following requirements: the steel rail yield strength Rp0.2≥830MPa; the tensile strength R m ≥1300MPa; elongation after fracture A≥10%; tread hardness 380~420HB; rail head cross section hardness 22mm depth ≥350HB. Other mechanical properties meet the requirements of AREMA standards.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention provides a method for preparing a low alloy high strength steel rail, comprising: smelting, heating, rolling, and online heat treatment processes; wherein:

[0006] During LF furnace refining, the slag basicity is controlled to be ≥2.0, the off-site temperature is 1585~1595℃; the deep vacuum degassing time is ≥18min, and the soft blowing time after vacuum degassing is ≥18min;

[0007] The total heating time of the steel billet is ≥ 3 hours and 20 minutes, of which the preheating temperature of the heating furnace is ≤ 800°C, the first heating temperature is ≤ 1200°C, the second heating temperature is 1100-1280°C, and the soaking temperature is 1150-1260°C;

[0008] 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;

[0009] The rails are air-cooled to 750-800℃ before entering the heat treatment line. The cooling method is air jet cooling. The rails are quickly cooled to 500-540℃ in the heat treatment line, and then the cooling intensity is reduced to maintain the rail temperature at 500-540℃ for a period of time before leaving the heat treatment line. After leaving the heat treatment line, the rails are naturally air-cooled to room temperature. The total online heat treatment time is 100-140s. The temperature of the rails leaving the heat treatment line is 500-540℃, and then slowly cooled to room temperature for straightening and ultrasonic flaw detection.

[0010] The chemical composition of the steel rail includes, by mass percentage: C 0.70-0.82%, Si 0.40-0.80%, Mn 0.70-1.20%, Cr 0.40-0.60%, P≤0.020%, S≤0.020%, rare earth Ce≥0.002%, and the rest is Fe and unavoidable impurities.

[0011] Furthermore, the chemical composition of the steel rail includes, by mass percentage, C: 0.76%, Si: 0.45%, Mn: 0.92%, P: 0.006%, S: 0.016%, Cr: 0.58%, rare earth Ce: 0.026%, and the rest is Fe and unavoidable impurities.

[0012] Furthermore, the molten iron is pretreated: the sulfur content in the molten iron is 0.011%, and the phosphorus content is 0.10%.

[0013] Further, VD vacuum degassing: deep vacuum degassing time is 19 min, and soft blowing after vacuum degassing is 18 min.

[0014] Furthermore, 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 process, pulling speed 0.60m / min, turn on electromagnetic stirring and light pressure of the casting machine to ensure the quality of the casting.

[0015] Furthermore, the rails are finally rolled and air-cooled to 780℃ before entering the heat treatment line. Air jet cooling is used to quickly cool the rails to 520℃ in the heat treatment line. Then the air cooling intensity is reduced to balance the internal temperature return and cooling intensity of the rails. The rail temperature is maintained at 520℃ for a certain period of time before leaving the heat treatment line. The total online heat treatment time is 140s. After leaving the heat treatment line, the rails are naturally air-cooled to room temperature and then straightened and inspected.

[0016] Furthermore, the properties of the prepared rails meet the following requirements: tensile strength reaches 1344 MPa, elongation after fracture reaches 12.5%, tread hardness is 386 HB, and cross-sectional hardness of the rail head is 358 HB at a depth of 22 mm.

[0017] Furthermore, the metallographic structure of the rail head is pearlite.

[0018] Furthermore, the rail oxide cleanliness is ≤8.

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

[0020] Compared with existing high-strength heat-treated rails at home and abroad, the hardness of the rails is increased by more than 10HB, the strength is increased by more than 150MPa, and the elongation after fracture is increased by 1%. The rails have better strength and toughness.

[0021] The mechanical properties of the low-alloy rare earth high-strength heat-treated rail obtained by the production method meet the following requirements: rail yield strength Rp0.2≥830MPa; tensile strength R m ≥1300MPa; elongation after fracture A≥10%; tread hardness 380~420HB; rail head cross-section hardness 22mm depth ≥350HB. The other mechanical properties meet the requirements of AREMA standards. After adding rare earth Ce to the rail, the inclusions are fine and dispersed. Using the European standard oxide cleanliness test method, the rail K3≤8, the inclusions are denatured by rare earth, and the rare earth is wrapped on the surface of the inclusions, reducing the sharp corners of the inclusions and reducing the probability of stress concentration cracking of the inclusions during the use of the rail. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings.

[0023] Figure 1 This is the morphology of rare earth inclusions;

[0024] Figure 2 The morphology is without rare earth inclusions. DETAILED DESCRIPTION

[0025] 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).

[0026] Example 1

[0027] A method for preparing a low-alloy high-strength rail comprises the following steps:

[0028] 1) Hot metal pretreatment: The sulfur content in the hot metal is 0.011% and the phosphorus content is 0.10%.

[0029] 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.

[0030] 3) LF furnace refining: During LF refining, the slag basicity is controlled to be ≥2.1 and the off-site temperature is 1588℃;

[0031] 4) VD vacuum degassing: Deep vacuum degassing time is 19 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.

[0032] 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 process, pulling speed 0.60m / min, electromagnetic stirring and light pressure of the casting machine are turned on to ensure the quality of the casting.

[0033] 6) Billet heating: The total heating time is 2 hours and 40 minutes. The heating time and heating temperature of each section are shown in Table 1.

[0034] Table 1 Rail heating process

[0035] Preheating section Heating 1 stage Heating 2 stages Soaking section Heating time 25min 50min 55min 30min temperature 723℃ 935℃ 1212℃ 1244℃

[0036] 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.

[0037] 8) Online heat treatment: The rails are finally rolled and air-cooled to 780℃ before entering the heat treatment line. Air jet cooling is used to quickly cool the rails to 520℃ in the heat treatment line. Then the air cooling intensity is reduced to balance the internal temperature return and cooling intensity of the rails. The rail temperature is maintained at 520℃ for a certain period of time before leaving the heat treatment line. The total online heat treatment time is 140s. After leaving the heat treatment line, the rails are naturally air-cooled to room temperature and then straightened and inspected.

[0038] After inspection, the chemical composition percentages of the rails are as follows: C: 0.76%; Si: 0.45%; Mn: 0.92%; P: 0.006%; S: 0.016%; Cr: 0.58%; rare earth Ce: 0.026%, and the rest are Fe and unavoidable impurities.

[0039] The mechanical properties of the rails are as follows: tensile strength reaches 1344MPa, elongation after fracture reaches 12.5%, tread hardness is 386HB, and the cross-section hardness of the rail head is 22mm deep 358HB. The metallographic structure of the rail head is pearlite. The K3 value of the rail inclusion detection is 5.76. Scanning electron microscope detection and analysis show that rare earth Ce is attached to the surface of the inclusions.

[0040] Example 2

[0041] A method for preparing a low-alloy high-strength rail comprises the following steps:

[0042] 1) Hot metal pretreatment: The sulfur content in the hot metal is 0.011% and the phosphorus content is 0.10%.

[0043] 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.

[0044] 3) LF furnace refining: During LF refining, the slag basicity is controlled to be ≥2.1 and the off-site temperature is 1588℃;

[0045] 4) VD vacuum degassing: Deep vacuum degassing time is 19 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.

[0046] 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 process, pulling speed 0.60m / min, electromagnetic stirring and light pressure of the casting machine are turned on to ensure the quality of the casting.

[0047] 6) Billet heating: The total heating time is 2 hours and 40 minutes. The heating time and heating temperature of each section are shown in Table 1.

[0048] Table 1 Rail heating process

[0049] Preheating section Heating 1 stage Heating 2 stages Soaking section Heating time 25min 50min 55min 30min temperature 723℃ 935℃ 1212℃ 1244℃

[0050] 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.

[0051] 8) Online heat treatment: The rails are finally rolled and air-cooled to 780℃ before entering the heat treatment line. Air jet cooling is used to quickly cool the rails to 520℃ in the heat treatment line. Then the air cooling intensity is reduced to balance the internal temperature return and cooling intensity of the rails. The rail temperature is maintained at 520℃ for a certain period of time before leaving the heat treatment line. The total online heat treatment time is 140s. After leaving the heat treatment line, the rails are naturally air-cooled to room temperature and then straightened and inspected.

[0052] After inspection, the chemical composition percentages of the rails are as follows: C: 0.75%; Si: 0.43%; Mn: 0.92%; P: 0.006%; S: 0.016%; Cr: 0.52%, and the rest are Fe and unavoidable impurities.

[0053] The mechanical properties of the rails are as follows: tensile strength reaches 1289MPa, elongation after fracture reaches 9.5%, tread hardness is 372HB, and cross-section hardness of the rail head is 22mm deep 322HB. The metallographic structure of the rail head is pearlite. The inclusion K3 value is 9.7.

[0054] Comparing Example 1 and Example 2, Example 1 adopts the invention method of this patent, adds rare earth element Ce to the rail, and the yield strength and tensile strength are increased by 40MPa, the elongation is increased by 3%, the tread hardness is increased by 10HB, the number of rail inclusions is reduced, and the K3 value is reduced by 4. The morphology of the inclusions is more rounded. The various performances of the rail are significantly better than those of the rail produced in Example 2. The performance of the rail in Example 1 is better and suitable for heavy-duty railways.

[0055] 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 preparing a low-alloy high-strength rail, characterized in that: include: Smelting, heating, rolling, online heat treatment process; including: During LF furnace refining, the slag basicity is controlled to be ≥2.0, the off-site temperature is 1585~1595℃; the deep vacuum degassing time is ≥18min, and the soft blowing time after vacuum degassing is ≥18min; The total heating time of the steel billet is ≥ 3 hours and 20 minutes, of which the preheating temperature of the heating furnace is ≤ 800°C, the first heating temperature is ≤ 1200°C, the second heating temperature is 1100-1280°C, and the soaking temperature is 1150-1260°C; 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; The rails are air-cooled to 750-800℃ before entering the heat treatment line. The cooling method is air jet cooling. The rails are quickly cooled to 500-540℃ in the heat treatment line, and then the cooling intensity is reduced to maintain the rail temperature at 500-540℃ for a period of time before leaving the heat treatment line. After leaving the heat treatment line, the rails are naturally air-cooled to room temperature. The total online heat treatment time is 100-140s. The temperature of the rails leaving the heat treatment line is 500-540℃, and then slowly cooled to room temperature for straightening and ultrasonic flaw detection. The chemical composition of the steel rail includes, by mass percentage: C 0.70-0.82%, Si 0.40-0.80%, Mn 0.70-1.20%, Cr 0.40-0.60%, P≤0.020%, S≤0.020%, rare earth Ce≥0.002%, and the rest is Fe and unavoidable impurities.

2. The method for preparing a low alloy high strength rail according to claim 1, characterized in that: The chemical composition of the steel rail includes, by mass percentage, C: 0.76%, Si: 0.45%, Mn: 0.92%, P: 0.006%, S: 0.016%, Cr: 0.58%, rare earth Ce: 0.026%, and the rest is Fe and unavoidable impurities.

3. The method for preparing a low alloy high strength rail according to claim 1, characterized in that: Hot metal pretreatment: The sulfur content in the hot metal is 0.011% and the phosphorus content is 0.10%.

4. The method for preparing a low alloy high strength rail according to claim 1, characterized in that: VD vacuum degassing: deep vacuum degassing time is 19 minutes, and soft blowing is 18 minutes after vacuum degassing.

5. The method for preparing a low alloy high strength rail according to claim 1, characterized in that: Continuous casting: The continuous casting process adopts protective casting, low-aluminum protective slag, weak cooling water distribution in the secondary cooling section, constant casting speed operation throughout the process, casting speed 0.60m / min, electromagnetic stirring and light pressure of the casting machine are turned on to ensure the quality of the casting.

6. The method for preparing a low alloy high strength rail according to claim 1, characterized in that: The rails are finally rolled and air-cooled to 780℃ before entering the heat treatment line. Air jet cooling is used to quickly cool the rails to 520℃ in the heat treatment line. Then the air cooling intensity is reduced to balance the internal temperature return and cooling intensity of the rails. The rail temperature is maintained at 520℃ for a certain period of time before leaving the heat treatment line. The total online heat treatment time is 140s. After leaving the heat treatment line, the rails are naturally air-cooled to room temperature and then straightened and inspected.

7. The method for preparing a low alloy high strength rail according to claim 2, characterized in that: The properties of the prepared rails meet the following requirements: tensile strength reaches 1344MPa, elongation after fracture reaches 12.5%, tread hardness is 386HB, and cross-sectional hardness of the rail head is 358HB at a depth of 22mm.

8. The method for preparing a low alloy high strength rail according to claim 1, characterized in that: The metallographic structure of the rail head is pearlite.

9. The method for preparing a low alloy high strength rail according to claim 1, characterized in that: Rail oxide cleanliness ≤8.

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