High-speed steel rail steel with high fatigue performance and preparation method thereof

Abstract

The invention discloses high-speed steel rail steel with high fatigue performance and a preparation method of the high-speed steel rail steel. Oxide inclusions exist in the steel. The oxide inclusion comprises the following main components in percentage by mass: 50-60% of SiO2, 20-30% of CaO, 5-15% of Al2O3 and less than or equal to 20% of MgO. According to the method, oxide inclusion components are controlled within a certain range, it is guaranteed that the melting point of oxide inclusions is lower than 1400 DEG C, all inclusions are in a low-melting-point and easy-to-deform area, in the hot rolling process, the inclusions and a steel matrix can deform at the same time, and therefore the fatigue performance is effectively improved; the material has the characteristics of excellent fatigue performance and good impact performance. According to the method, the element segregation and inclusion content of the continuous casting billet are remarkably reduced, the harsh high-cycle fatigue performance can be implemented, and the high-speed steel rail with the excellent fatigue performance can be easily manufactured; the steel rail steel has the properties of high strength, corrosion resistance, excellent weldability and the like, and the fatigue property of the high-speed steel rail can be greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, in particular to a high-speed rail steel with high fatigue performance and a preparation method thereof. Background Art

[0002] In order to adapt to the current development trend of high-speed, safe and long-life railways, rails, as the main load-bearing components of railways, have put forward new requirements for cleanliness. my country's high-speed railway steel standards and foreign railway standards require a leap in the requirements for non-metallic inclusions, low-multiple structures, solidification structures, product performance, service life and other indicators in steel. The safety and longevity of high-speed railway rails mainly depend on the excellent fatigue and wear resistance, internal stress reduction, good welding performance and stable performance of rail steel. The presence of large-sized non-metallic inclusions in the rails will directly affect the fatigue and impact performance of the rails, causing nuclear damage or even fracture failure of the railway rails, causing major safety accidents. The high-hardness, high-melting-point, non-deformable oxide inclusions inside the rails will produce internal stress concentration, leading to cracks, brittle fractures and other railway safety threats, significantly reducing the service life.

[0003] A large number of studies have shown that fatigue damage of rails is mainly related to the presence of Al2O3 oxide inclusions in steel. These inclusions are brittle and hard, and can easily scratch the matrix during hot rolling deformation of the rails, and generate stress concentration fields around the inclusions or detach from the matrix to form holes, becoming fatigue sources. Under the action of cyclic stress when the rails are in use, they become the starting point of fatigue cracks. Therefore, the acid-soluble aluminum (Als) and total oxygen (TO) content in the steel of high-speed rails must be strictly controlled. Although the current high-speed rail production process uses aluminum-free deoxidation, a certain amount of aluminum and other high-melting-point intermetallic compound phases often remain in the deoxidizer and alloy.

[0004] Therefore, the purification of impurity elements, the selectivity of non-metallic inclusions, the refinement of their size, the dispersion of their distribution, the homogenization of their alloy elements, and the improvement of their organizational properties are of great significance to the safety and longevity of high-speed and heavy-load railway rails.

[0005] In high-speed rails that require higher fatigue strength, it is necessary to significantly reduce the high-melting-point, high-hardness, non-deformable non-metallic inclusions and harmful elements in the rails. From this point of view, rails used for the above purposes usually need to significantly reduce the above-mentioned non-metallic inclusions. The crack source caused by non-metallic inclusions leads to reduced fatigue performance. Therefore, it is required that the non-metallic inclusion components are selectively distributed in a certain area, the size is reduced, and it has the characteristics of easy deformation and low melting point (the melting point is controlled to be lower than the range of 1400-1500℃), so that it will not become the starting point of fatigue failure and can improve fatigue characteristics.

[0006] From the perspective of achieving improved fatigue performance, various technologies have been proposed so far. For example, in patent application number CN202310394420.1, a steel rail with excellent corrosion resistance and contact fatigue resistance and its preparation method are mainly described in the chemical composition range, without any requirements for inclusions. Application number CN201710933923.6, a pearlite steel rail with anti-contact fatigue and its manufacturing method, is described only from the chemical composition and hot rolling parameter control and regulation of organizational structure, without any requirements for inclusions. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a high-fatigue performance high-speed rail steel with excellent fatigue performance; the present invention also provides a preparation method of the high-fatigue performance high-speed rail steel to improve fatigue and impact performance.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: the main components of the oxide inclusions and their mass fractions are: SiO2 50-60%, CaO 20-30%, Al2O3 5-15%, MgO≤20%.

[0009] Furthermore, the oxide inclusions also contain Gd2O3≤15%.

[0010] Furthermore, the oxide inclusions also contain BaO 0-15%.

[0011] Furthermore, the oxide inclusion long diameter / oxide inclusion short diameter ≤ 5μm and the oxide inclusion long diameter ≥ 30μm, and the oxide inclusion long diameter / oxide inclusion short diameter > 5μm and the oxide inclusion short diameter is 30μm or more, the total number of oxide inclusions is ≤ 15 / 200mm 2 .

[0012] In order to solve the above technical problems, the technical solution adopted by the method of the present invention includes converter smelting, LF furnace refining and RH vacuum treatment steps.

[0013] The converter smelting: the converter steel tapping deoxidation process only uses silicon-manganese alloy, or ferrosilicon and ferromanganese for deoxidation, without adding any aluminum alloy deoxidizer.

[0014] The LF furnace refining: the binary basicity CaO / SiO2 is controlled at 0.8-1.5 in the slag making process, and CaF2 is used for slag making.

[0015] Furthermore, the converter smelting step requires that the total calcium in the silicon-manganese alloy, or ferrosilicon and ferromanganese is ≤0.001%, and the aluminum is ≤0.0005%.

[0016] Furthermore, in the converter smelting step, the addition amount of silicon-manganese alloy, or ferrosilicon and ferromanganese is 2-4 kg / ton of steel respectively, and the total oxygen mass fraction after deoxidation is controlled to be ≤0.005%.

[0017] Furthermore, in the RH vacuum treatment step, the vacuum degree is ≤100 Pa and the degassing time is ≥15 min.

[0018] The beneficial effect of adopting the above technical solution is that: the present invention controls the oxide inclusion composition within a certain range, ensures that the melting point of oxide inclusions is lower than 1400°C, and all inclusions are in the low melting point and easy deformation area. During the hot rolling process, the inclusions can deform simultaneously with the steel matrix, thereby effectively improving the fatigue performance; it has the characteristics of excellent fatigue performance and good impact performance.

[0019] The inclusions of the continuous casting billet obtained by the method of the present invention are all in the low melting point and easy deformation area. During the hot rolling process, the inclusions can deform simultaneously with the steel matrix, thereby effectively improving the fatigue performance; the element segregation and inclusion content of the continuous casting billet are significantly reduced, severe high-cycle fatigue performance can be implemented, and high-speed rails with excellent fatigue performance can be easily manufactured; in addition to achieving the properties of rail steel such as high strength, corrosion resistance and excellent weldability, the fatigue performance of the high-speed rail can be greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0021] Figure 1 It is a schematic diagram of the effect of non-metallic inclusions on fatigue properties;

[0022] Figure 2 This is a schematic diagram of the range of non-metallic inclusion control. DETAILED DESCRIPTION

[0023] The composition and mass fraction of the high-speed rail steel with high fatigue performance are as follows: C 0.6-0.77%, Si 0.1-0.3%, Mn 0.1-1%, Ca≤0.001%, Al≤0.0005%, rare earth element RE≤0.1%, and the balance Fe and unavoidable impurities; and T.O+N+S+P+H≤0.01%, wherein TO≤0.001%, N≤0.003%, S≤0.005%, P≤0.008%, and H≤0.0001%; ​​the RE is at least one element selected from Gd, La and Ce.

[0024] The high-speed rail steel contains oxide inclusions; the main components and mass fractions of the oxide inclusions are: SiO2 50-60%, CaO 20-30%, Al2O3 5-15%, MgO≤20%; Gd2O3≤15%, BaO 0-15%; SiO2%+CaO%+Al2O3%+MgO%+Gd2O3%+BaO%=100wt%. Among the oxide inclusions, the oxide inclusion long diameter / oxide inclusion short diameter (the inclusion short diameter is also called the inclusion width) ≤5μm and the oxide inclusion long diameter ≥30μm, and the oxide inclusion long diameter / oxide inclusion short diameter>5μm and the oxide inclusion short diameter is 30μm or more can include all oxide inclusions, totaling 15 / 200mm. 2 And below; According to GB / T10561 inclusion evaluation D category, 0.5 level and below is one field of view (0.16mm 2 ) is less than 1 inclusion, and 15 / 200mm 2 This means that there are only 0.012 inclusions in one field of view, and the D-class rating is 0. Among the oxide inclusions, the oxide inclusions with a short diameter of 2 μm or more satisfy SiO2+CaO+Al2O3+MgO≥80% by mass fraction. The melting point of the oxide inclusions is lower than 1400°C.

[0025] The preparation method of high-speed rail steel with high fatigue performance is aimed at the requirements of producing high-speed rails and the reasons for controlling inclusions, reducing the content of impurity elements in molten steel, and controlling the oxide inclusion components within a certain range, including converter smelting, LF furnace refining, RH vacuum treatment and continuous casting steps, specifically starting from adding deoxidizer and alloy components after steel is tapped from the converter, LF furnace refining slag making system and RH vacuum treatment, the process steps are as follows:

[0026] (1) Converter smelting: During the converter steelmaking deoxidation process, only silicon-manganese alloy or ferrosilicon and ferromanganese are used for deoxidation, without adding any aluminum alloy deoxidizer; the total calcium in the silicon-manganese alloy is required to be ≤0.001%, and the aluminum is ≤0.0005%; the total calcium in ferrosilicon is required to be ≤0.001%, and the aluminum is ≤0.0005%, and the total calcium in ferromanganese is ≤0.001%, and the aluminum is ≤0.0005%; when silicon-manganese alloy is used for deoxidation, the amount of silicon-manganese alloy added is 2-4 kg / ton of steel; when ferrosilicon and ferromanganese are used for deoxidation, the amount of ferrosilicon added is 2-4 kg / ton of steel, and the amount of ferromanganese added is 2-4 kg / ton of steel; the total oxygen mass fraction after deoxidation is controlled to be ≤0.005%.

[0027] (2) The LF furnace refining: LF refining slag making adopts CaO for slag making, CaF2 for slagging, and SiO2 is added to adjust the slag basicity; the slag making system is: first add CaO 150-200kg and CaF2 100-150kg; 1-3min later, add CaO 250-300kg and CaF2 100-150kg; then after 1-3min, add CaO250-300kg, CaF2 100-150kg and SiO2xkg, wherein x=the amount of CaO added / binary basicity. As can be seen from the following, R=0.8-1.5, then x=300 / 0.8-300 / 1.5=375-200kg; it is forbidden to add aluminum-containing slag during the slag making process. LF slags quickly to ensure the arc submergence effect. Under the condition of ensuring the adjustment of composition, the binary basicity of the slag is controlled to be R = CaO / SiO2 = 0.8-1.5, which is maintained for at least 10 minutes. No alloy is added during the refining process. The lower slag basicity can effectively inhibit the dissolution of Al2O3 in the slag into the steel, thereby reducing the total aluminum content in the steel. The ideal target range of the final composition of the LF furnace refining slag is shown in Table 1. The LF ladle bottom blowing adopts 8-10Nm 3 / h of argon gas for stirring.

[0028] Table 1: Ideal target range of final composition of LF furnace refined slag (wt%)

[0029] CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> MgO <![CDATA[Gd2O3]]> BaO FeO MnO <![CDATA[CaO / SiO2]]> 15～55 15～30 1～5 1～10 1～15 1～15 ≤1 ≤1 0.8～1.5

[0030] (3) RH vacuum treatment: RH vacuum ≤ 100Pa, degassing time ≥ 15min, argon flow rate 5~8Nm 3 / h.

[0031] (4) Continuous casting: The tundish is sealed and special protective slag for high-speed rail is used to prevent secondary oxidation of the molten steel.

[0032] During production, the following requirements must be met: the refractory material of the ladle does not suffer from significant erosion, flaking or falling off, and the weight loss of the ladle is less than 50kg per furnace; and no new ladle is used, and aluminum-deoxidized steel from the previous furnace is not used.

[0033] After adopting the preparation method, the obtained ingot can meet the above-mentioned requirements of oxide inclusions.

[0034] Example 1: Smelting high-speed rails with a steel grade of U71MnG and a furnace capacity of 140t, including the following steps:

[0035] (1) After desulfurization, ferrosilicon and ferromanganese are added to the molten iron during the steelmaking process after converter smelting for deoxidation and alloying, and the composition is accurately adjusted to the final target composition range of U71Mn steel. The oxygen content at the converter end point is less than 0.035% by mass fraction, and the total oxygen mass fraction in the molten steel after deoxidation is less than 0.005%.

[0036] (2) LF refining adopts 200kgCaO+100kgCaF2, 1min interval, continue to add 300kgCaO+150kgCaF2, 2min interval, continue to add 300kgCaO+150kgCaF2+1000kgSiO2 to form slag. While desulfurization, the binary basicity of the slag is controlled at 0.8 for 10 minutes. No alloy is added during the refining process.

[0037] (3) After LF refining, the molten steel is subjected to RH vacuum treatment, and the high vacuum is maintained for more than 15 minutes without adding any alloy during this period.

[0038] (4) The molten steel is left to stand until it reaches the pouring platform. The tundish needs to be sealed to prevent direct contact between the tundish and the air. The mold protection slag uses special slag for high-speed rails and is not in a red-hot state.

[0039] (5) The molten steel is cooled and solidified into a 280 mm × 380 mm large square billet by the continuous casting machine, and then rolled into a 100-meter long rail at a rolling ratio of 14:1.

[0040] The high-speed rail obtained in this example is 60kg / m. A Japanese Shimadzu high-cycle fatigue testing machine, model USF-2000A, is used to take samples from the head of the finished rail and process them into standard fatigue specimens for testing. The loading stress and the number of cycles after the specimen breaks are recorded. The test results are shown in Figure 1 and Table 2, the control range of non-metallic inclusions is shown in Figure 2 .

[0041] The average composition of inclusions was analyzed by sampling from the continuous casting billet. The mass fraction was SiO2=55%, CaO=24%, Al2O3=8%, MgO=8%, Gd2O3=3%, BaO=2%, and the melting point was 1395°C. The oxide inclusion long diameter / oxide inclusion short diameter was ≤5μm and the oxide inclusion long diameter was ≥30μm, and the oxide inclusion long diameter / oxide inclusion short diameter was >5μm and the inclusion short diameter was 30μm or more. The total number of oxide inclusions was 12 / 200mm. 2 .

[0042] Example 2: Smelting high-speed rails with a steel grade of U71MnG and a furnace capacity of 150t, including the following steps:

[0043] (1) The molten iron is desulfurized to a sulfur content of less than 0.003% by mass. After converter smelting, ferrosilicon and ferromanganese are added during the steelmaking process for deoxidation and alloying, and the composition is accurately adjusted to the final target composition range of U71Mn steel. The oxygen content at the converter endpoint is less than 0.02% by mass, and the total oxygen mass fraction in the molten steel after deoxidation is less than 0.005%.

[0044] (2) LF refining adopts 300kgCaO+150kgCaF2, 1min interval, continue to add 300kgCaO+150kgCaF2, 2min interval, continue to add 200kgCaO+100kgCaF2+800kgSiO2 to form slag. While desulfurization, the binary basicity of the slag is controlled at 1.0 for 10 minutes. No alloy is added during the refining process.

[0045] (3) After LF refining, the molten steel is subjected to RH vacuum treatment, and the high vacuum is maintained for more than 15 minutes without adding any alloy during this period.

[0046] (4) The molten steel is left to stand until it reaches the pouring platform. The tundish needs to be sealed to prevent direct contact between the tundish and the air. The mold protection slag uses special slag for high-speed rails and is not in a red-hot state.

[0047] (5) The molten steel is cooled and solidified into a 280 mm × 380 mm large square billet by the continuous casting machine, and then rolled into a 100-meter long rail at a rolling ratio of 14:1.

[0048] The high-speed rail obtained in this embodiment has a weight of 60 kg / m. The high-cycle fatigue data of the high-speed rail are shown in Table 2.

[0049] The average composition of inclusions was analyzed by sampling from the continuous casting billet. The mass fraction was SiO2=58%, CaO=22%, Al2O3=10%, MgO=6%, Gd2O3=2%, BaO=2%, and the melting point was 1391°C. The oxide inclusion long diameter / oxide inclusion short diameter was ≤5μm and the oxide inclusion long diameter was ≥30μm, and the oxide inclusion long diameter / oxide inclusion short diameter was >5μm and the inclusion short diameter was 30μm or more. The total number of oxide inclusions was 14 / 200mm. 2 .

[0050] Example 3: Smelting high-speed rails with a steel grade of U71MnG and a furnace capacity of 130t, including the following steps:

[0051] (1) The molten iron is desulfurized to a sulfur content of less than 0.004% by mass. After converter smelting, ferrosilicon and ferromanganese are added during the steelmaking process for deoxidation and alloying, and the composition is accurately adjusted to the final target composition range of U71Mn steel. The oxygen content at the converter endpoint is less than 0.025% by mass, and the total oxygen mass fraction in the molten steel after deoxidation is less than 0.005%.

[0052] (2) LF refining adopts 200kgCaO+100kgCaF2, 1min interval, continue to add 200kgCaO+100kgCaF2, 2min interval, continue to add 200kgCaO+100kgCaF2+500kgSiO2 to form slag. While desulfurization, the binary basicity of the slag is controlled at 1.2 for 10 minutes. No alloy is added during the refining process.

[0053] (3) After LF refining, the molten steel is subjected to RH vacuum treatment, and the high vacuum is maintained for more than 15 minutes without adding any alloy during this period.

[0054] (4) The molten steel is left to stand until it reaches the pouring platform. The tundish needs to be sealed to prevent direct contact between the tundish and the air. The mold protection slag uses special slag for high-speed rails and is not in a red-hot state.

[0055] (5) The molten steel is cooled and solidified into a 280 mm × 380 mm large square billet by the continuous casting machine, and then rolled into a 100-meter long rail at a rolling ratio of 14:1.

[0056] The high-speed rail of this embodiment has a weight of 60kg / m. The high-cycle fatigue data of the high-speed rail is shown in Table 2.

[0057] The average composition of inclusions was analyzed by sampling from the continuous casting billet. The mass fraction was SiO2=60%, CaO=20%, Al2O3=8%, MgO=8%, Gd2O3=2%, BaO=2%, and the melting point was 1389°C. The oxide inclusion long diameter / oxide inclusion short diameter was ≤5μm and the oxide inclusion long diameter was ≥30μm, and the oxide inclusion long diameter / oxide inclusion short diameter was >5μm and the inclusion short diameter was 30μm or more. The total number of oxide inclusions was 11 / 200mm. 2 .

[0058] Example 4: Smelting high-speed rails with a steel grade of U71MnG and a furnace capacity of 135t, comprising the following steps:

[0059] (1) The molten iron is desulfurized to a sulfur content of less than 0.005% by mass. After converter smelting, ferrosilicon and ferromanganese are added during the steelmaking process for deoxidation and alloying, and the composition is accurately adjusted to the final target composition range of U71Mn steel. The oxygen content at the converter endpoint is less than 0.025% by mass, and the total oxygen mass fraction in the molten steel after deoxidation is less than 0.005%.

[0060] (2) LF refining adopts 200kgCaO+100kgCaF2, 1min interval, continue to add 300kgCaO+150kgCaF2, 2min interval, continue to add 200kgCaO+100kgCaF2+500kgSiO2 to form slag. While desulfurization, the binary basicity of the slag is controlled at 1.4 for 10 minutes. No alloy is added during the refining process.

[0061] (3) After LF refining, the molten steel is subjected to RH vacuum treatment, and the high vacuum is maintained for more than 15 minutes without adding any alloy during this period.

[0062] (4) The molten steel is left to stand until it reaches the pouring platform. The tundish needs to be sealed to prevent direct contact between the tundish and the air. The mold protection slag uses special slag for high-speed rails and is not in a red-hot state.

[0063] (5) The molten steel is cooled and solidified into a 280 mm × 380 mm large square billet by the continuous casting machine, and then rolled into a 100-meter long rail at a rolling ratio of 14:1.

[0064] The high-speed rail of this embodiment has a weight of 60kg / m. The high-cycle fatigue data of the high-speed rail is shown in Table 2.

[0065] The average composition of inclusions was analyzed by sampling from the continuous casting billet. The mass fraction was SiO2=54%, CaO=25%, Al2O3=9%, MgO=7%, Gd2O3=3%, BaO=2%, and the melting point was 1398°C. The oxide inclusion long diameter / oxide inclusion short diameter was ≤5μm and the oxide inclusion long diameter was ≥30μm, and the oxide inclusion long diameter / oxide inclusion short diameter was >5μm and the inclusion short diameter was 30μm or more. The total number of oxide inclusions was 14 / 200mm. 2 .

[0066] Table 2: Fatigue life of rails in Examples 1 to 4 after high cycle fatigue test

[0067]

[0068] .

Claims

1. A high-speed rail steel with high fatigue performance, characterized in that: Oxide inclusions exist in the steel; the main components and mass fractions of the oxide inclusions are: SiO2 50-60%, CaO 20-30%, Al2O3 5-15%, MgO≤20%.

2. The high-speed rail steel with high fatigue performance according to claim 1, characterized in that: The oxide inclusions also contain Gd2O3≤15%.

3. The high-speed rail steel with high fatigue performance according to claim 1, characterized in that: The oxide inclusions further contain BaO in an amount of 0 to 15%.

4. A high-speed rail steel with high fatigue performance according to claim 1, 2 or 3, characterized in that: The oxide inclusion long diameter / oxide inclusion short diameter ≤ 5μm and the oxide inclusion long diameter ≥ 30μm, and the oxide inclusion long diameter / oxide inclusion short diameter > 5μm and the oxide inclusion short diameter is 30μm or more, the total number of oxide inclusions is ≤ 15 / 200mm 2 .

5. The method for preparing the high-speed rail steel with high fatigue performance according to any one of claims 1 to 4, characterized in that: It includes converter smelting, LF furnace refining and RH vacuum treatment steps; The converter smelting: the converter steel tapping deoxidation process only uses silicon-manganese alloy, or ferrosilicon and ferromanganese for deoxidation, without adding any aluminum alloy deoxidizer; The LF furnace refining: the binary basicity CaO / SiO2 is controlled at 0.8-1.5 in the slag making process, and CaF2 is used for slag making.

6. The method for preparing a high-speed rail steel with high fatigue performance according to claim 5, characterized in that: The converter smelting step requires that the total calcium in the silicon-manganese alloy, or ferrosilicon and ferromanganese is ≤0.001%, and the aluminum is ≤0.0005%.

7. The method for preparing a high-speed rail steel with high fatigue performance according to claim 5, characterized in that: In the converter smelting step, the addition amount of silicon-manganese alloy, or ferrosilicon and ferromanganese is 2-4 kg / ton of steel respectively, and the total oxygen mass fraction after deoxidation is controlled to be ≤0.005%.

8. A method for preparing a high-speed rail steel with high fatigue performance according to claim 5, 6 or 7, characterized in that: In the RH vacuum treatment step, the vacuum degree is ≤100 Pa and the degassing time is ≥15 min.

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