Method for improving fatigue performance of heavy rail steel through rare earth alloy and magnesium metallurgical treatment

Abstract

The invention discloses a rare earth alloy and a method for improving the fatigue performance of heavy rail steel through magnesium metallurgical treatment, the rare earth alloy is La or Ce rare earth alloy, and the content of rare earth simple substances in the rare earth alloy is 10%-30%; magnesium alloy or a magnesium wire is added in the magnesium metallurgical treatment, and the magnesium alloy or the magnesium wire is added to ensure that the yield of the magnesium element in the heavy rail steel is larger than or equal to 10%; a component system of the heavy rail steel produced through the rare earth and magnesium metallurgical treatment is not changed, and the properties of inclusions in the heavy rail steel are changed through the rare earth and magnesium metallurgical treatment, so that the inclusions are fined and dispersed; the La or Ce rare earth alloy and the magnesium alloy or the magnesium wire are added after vacuum degassing and before bloom continuous casting. Through modification treatment, the inclusions in the heavy rail steel are denatured and float upwards, the level of the inclusions in the steel is reduced, meanwhile, the inclusions remaining in the steel are refined and dispersed, and therefore the purposes of improving the metallurgical quality of the heavy rail steel and improving the comprehensive mechanical property of the heavy rail steel are achieved.

Description

Technical Field

[0001] The invention belongs to the field of production and application of heavy rail steel treated by rare earth and magnesium metallurgy, and in particular relates to a method for improving fatigue performance of heavy rail steel by rare earth alloy and magnesium metallurgy treatment. Background Art

[0002] With the rapid development of domestic heavy-duty high-speed railways and lines, the railway transportation mode of high-speed, high-density, large-axle-weight passenger-only, mixed passenger-freight and freight-only lines has formed a large-scale. Under increasingly harsh line conditions, the fatigue damage problem of railway rails has become increasingly prominent, seriously affecting the line operation efficiency and driving safety.

[0003] The special production process and service conditions of heavy rail steel make it extremely sensitive to inclusions. There are important and clear requirements for the control and rating indicators of heavy rail steel inclusions at home and abroad. Strict control of the number, size and location of inclusions in heavy rail steel is crucial to the safety of line service. High-speed rails require a rating of B, C, and D inclusions ≤1.0, and conventional rails require a rating of B, C, and D inclusions ≤1.5. However, in the actual production process, B, C, and D inclusions are often greater than 1.5. Since the deformation capacity of B, C, and D inclusions is significantly different from that of the matrix, the presence of inclusions destroys the continuity and integrity of heavy rail steel, significantly reduces the fatigue performance of heavy rail steel, and ultimately leads to rail failure and service performance that does not meet the line service requirements.

[0004] At present, calcium treatment is usually used in the production process of heavy rail steel in China. Most harmful elements and inclusions in steel can be effectively removed, but inclusions still exist in steel and there are excessive inclusions, which still have a great impact on the performance of steel. Under the existing production process, further improving the cleanliness of heavy rail steel will significantly increase the smelting cost and reduce the production rhythm, which will seriously affect the production capacity of heavy rail steel. In recent years, there have been many research results on the clean treatment of heavy rail steel, mainly including the idea of ​​inclusion removal and inclusion modification. Among them, the fine dispersion treatment and modification of inclusions, and the regulation towards harmlessness are more effective technical routes. Summary of the invention

[0005] The purpose of the present invention is to provide a method for improving the fatigue performance of heavy rail steel by metallurgical treatment of rare earth alloy and magnesium. Under the premise of not changing the existing component system and production process of heavy rail steel, the inclusions in the heavy rail steel are denatured and floated through modification treatment, the level of inclusions in the steel is reduced, and the inclusions retained in the steel are miniaturized and dispersed, thereby achieving the purpose of improving the metallurgical quality of heavy rail steel and enhancing the comprehensive mechanical properties of heavy rail steel.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The invention discloses a method for improving fatigue performance of heavy rail steel by rare earth alloy and magnesium metallurgical treatment. The rare earth alloy has the characteristics of La or Ce rare earth alloy, and the rare earth element content in the rare earth alloy is between 10% and 30%. The magnesium metallurgical treatment is to add magnesium alloy or magnesium wire, and the addition of magnesium alloy or magnesium wire ensures that the magnesium element yield in the heavy rail steel is ≥10%. The La or Ce rare earth alloy, magnesium alloy and magnesium wire are added after vacuum degassing and before continuous casting of large square billets.

[0008] Furthermore, the component system of the heavy rail steel produced remains unchanged, and the properties of inclusions in the heavy rail steel are changed through rare earth and magnesium metallurgical treatment, making the inclusions smaller and more dispersed.

[0009] Furthermore, the heavy rail steel production process is: molten iron pretreatment → combined blowing converter smelting → LF refining → vacuum degassing → magnesium treatment → rare earth treatment → large square billet continuous casting → billet slow cooling → billet heating → 100-meter rail rolling → composite straightening → flaw detection.

[0010] Furthermore, the relative fatigue properties of heavy rail steel treated with rare earth and magnesium metallurgy are improved by 120-140MPa.

[0011] Furthermore, the fatigue properties of heavy rail steel treated with rare earth and magnesium metallurgy can be improved by more than 25%.

[0012] Furthermore, the heavy rail steel B, C, D inclusions are subjected to horizontal and vertical intensified rating inspections, and the ratio of B, C, D inclusions ≤1.5 level is ≥95%.

[0013] Furthermore, according to GB / T 3075 standard, an axial constant amplitude fatigue test was carried out with the number of cycles ≥ 1×10 8 , and thus determine the SN fatigue curve, and conclude that the fatigue strength of heavy rail steel is between 620-640MPa.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are:

[0015] The present invention provides a method for improving the fatigue performance of heavy rail steel by rare earth alloy and magnesium metallurgical treatment. Combining the characteristics and advantages of rare earth treatment and magnesium metallurgical treatment, the inclusions in the heavy rail steel are denatured and floated without changing the existing heavy rail steel component system and production process. The level of inclusions in the steel is reduced, and the inclusions retained in the steel are miniaturized and dispersed, thereby achieving the purpose of improving the metallurgical quality of heavy rail steel and enhancing the comprehensive mechanical properties of heavy rail steel. The fatigue performance of heavy rail steel improved by the present invention is based on the SN fatigue curve measured by high cycle fatigue test. Based on the test data, the relative fatigue performance of heavy rail steel treated with rare earth and magnesium metallurgy is improved by 120-140MPa, and the fatigue performance is improved by more than 25%. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1This is the fatigue performance curve of heavy rail steel. DETAILED DESCRIPTION

[0017] A method for improving fatigue performance of heavy rail steel by rare earth alloy and magnesium metallurgical treatment, wherein the rare earth alloy has La or Ce rare earth alloy characteristics, and the rare earth element content in the rare earth alloy is between 10% and 30%; the magnesium metallurgical treatment is to add magnesium alloy or magnesium wire, and the addition of magnesium alloy or magnesium wire ensures that the magnesium element yield in the heavy rail steel is ≥10%.

[0018] The component system of heavy rail steel produced by the rare earth and magnesium metallurgical treatment remains unchanged, and the properties of inclusions in the heavy rail steel are changed by the rare earth and magnesium metallurgical treatment, so that the inclusions are miniaturized and dispersed.

[0019] The production process of heavy rail steel treated with rare earth and magnesium metallurgy is: molten iron pretreatment → combined blowing converter smelting → LF refining → vacuum degassing → magnesium treatment → rare earth treatment → large square billet continuous casting → billet slow cooling → billet heating → 100-meter rail rolling → composite straightening → flaw detection.

[0020] The La or Ce rare earth alloy and the magnesium alloy or magnesium wire are added after vacuum degassing and before continuous casting of the large square billet.

[0021] Example 1

[0022] Example 1 The weight percentage of the chemical composition of heavy rail steel is C≤0.30%, Si+Mn+Cr: 3.30-4.70%, Ni+Mo+Nb+V: 0.40-1.20%, P≤0.015%, S≤0.010%, Al: ≤0.010%, and the rest is Fe and impurities.

[0023] Step 1: The heavy rail steel production process is: molten iron pretreatment → combined blowing converter smelting → LF refining → vacuum degassing → large square billet continuous casting → billet slow cooling → billet heating → 100-meter rail rolling → composite straightening → flaw detection.

[0024] Step 2: According to GB / T 10561-2005 standard, the heavy rail steel B, C, D inclusions are tested for horizontal and vertical intensive rating. The ratio of B, C, D inclusions ≤1.5 is about 80%.

[0025] Step 3: According to GB / T 3075 standard, carry out axial constant amplitude fatigue test, the number of cycles ≥ 1×10 8 , and thus the SN fatigue curve was determined, and it was concluded that the fatigue strength of heavy rail steel was about 500MPa.

[0026] Example 2

[0027] The weight percentage of the chemical composition of heavy rail steel in Example 2 is C≤0.30%, Si+Mn+Cr: 3.30-4.70%, Ni+Mo+Nb+V: 0.40-1.20%, RE: 5-10ppm, P≤0.015%, S≤0.010%, Al: ≤0.010%, and the rest is Fe and impurities.

[0028] Step 1: The heavy rail steel production process is: molten iron pretreatment → combined blowing converter smelting → LF refining → vacuum degassing → rare earth treatment → large square billet continuous casting → billet slow cooling → billet heating → 100-meter rail rolling → composite straightening → flaw detection.

[0029] Step 2: The rare earth alloy has the characteristics of La or Ce rare earth alloy, and the rare earth element content in the rare earth alloy is between 10% and 30%.

[0030] Step 3: La or Ce rare earth alloy is added after vacuum degassing and before continuous casting of large square billet.

[0031] Step 4: According to GB / T 10561-2005 standard, the heavy rail steel B, C, D inclusions are tested for horizontal and vertical intensive rating. The ratio of B, C, D inclusions ≤1.5 is about 88%.

[0032] Step 5: According to GB / T 3075 standard, carry out axial constant amplitude fatigue test, the number of cycles ≥ 1×10 8 , thereby determining the SN fatigue curve, and concluding that the fatigue strength of heavy rail steel is between 530-560MPa.

[0033] Example 3

[0034] The weight percentage of the chemical composition of heavy rail steel in Example 3 is C≤0.30%, Si+Mn+Cr: 3.30-4.70%, Ni+Mo+Nb+V: 0.40-1.20%, RE: 5-10ppm, Mg: 5-10ppm, P≤0.015%, S≤0.010%, Al: ≤0.010%, and the rest is Fe and impurities.

[0035] Step 1: The heavy rail steel production process is: molten iron pretreatment → combined blowing converter smelting → LF refining → vacuum degassing → magnesium treatment → rare earth treatment → large square billet continuous casting → billet slow cooling → billet heating → 100-meter rail rolling → composite straightening → flaw detection.

[0036] Step 2: The rare earth alloy has the characteristics of La or Ce rare earth alloy, and the rare earth element content in the rare earth alloy is between 10% and 30%.

[0037] The third step: magnesium metallurgical treatment is to add magnesium alloy or magnesium wire, and the addition of magnesium alloy or magnesium wire ensures that the magnesium element recovery rate in the heavy rail steel is ≥10%.

[0038] Step 4: La or Ce rare earth alloy and magnesium alloy or magnesium wire are added after vacuum degassing and before continuous casting of large square billet.

[0039] Step 5: According to GB / T 10561-2005 standard, conduct horizontal and vertical intensified rating inspection on B, C and D inclusions of heavy rail steel, and the ratio of B, C and D inclusions ≤1.5 level ≥95%.

[0040] Step 6: According to GB / T 3075 standard, carry out axial constant amplitude fatigue test, the number of cycles ≥ 1×10 8 , and thus determine the SN fatigue curve, and conclude that the fatigue strength of heavy rail steel is between 620-640MPa.

[0041] The heavy rail steel used in the above three embodiments has the same composition and content.

[0042] 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 improving the fatigue performance of heavy rail steel by rare earth alloy and magnesium metallurgical treatment, characterized in that: The rare earth alloy is La or Ce rare earth alloy, and the rare earth element content in the rare earth alloy is between 10% and 30%; the magnesium metallurgical treatment is to add magnesium alloy or magnesium wire, and the addition of magnesium alloy or magnesium wire ensures that the magnesium element yield in the heavy rail steel is ≥10%; the La or Ce rare earth alloy and magnesium alloy or magnesium wire are added after vacuum degassing and before continuous casting of large square billets.

2. The method for improving fatigue performance of heavy rail steel by rare earth alloy and magnesium metallurgy treatment according to claim 1, characterized in that: The component system of the heavy rail steel produced remains unchanged, and the properties of inclusions in the heavy rail steel are changed through rare earth and magnesium metallurgical treatment, making the inclusions smaller and more dispersed.

3. The method for improving fatigue performance of heavy rail steel by rare earth alloy and magnesium metallurgy treatment according to claim 1, characterized in that: The production process of heavy rail steel is: molten iron pretreatment → combined blowing converter smelting → LF refining → vacuum degassing → magnesium treatment → rare earth treatment → large square billet continuous casting → billet slow cooling → billet heating → 100-meter rail rolling → composite straightening → flaw detection.

4. The method for improving fatigue performance of heavy rail steel by rare earth alloy and magnesium metallurgy treatment according to claim 1, characterized in that: The relative fatigue properties of heavy rail steel treated with rare earth and magnesium metallurgy are improved by 120-140MPa.

5. The method for improving fatigue performance of heavy rail steel by rare earth alloy and magnesium metallurgy treatment according to claim 1, characterized in that: The fatigue performance of heavy rail steel treated with rare earth and magnesium metallurgy is improved by more than 25%.

6. The method for improving fatigue performance of heavy rail steel by rare earth alloy and magnesium metallurgy treatment according to claim 1, characterized in that: Conduct horizontal and vertical intensified rating inspections on heavy rail steel Class B, C and D inclusions, and the ratio of Class B, C and D inclusions ≤1.5 is ≥95%.

7. The method for improving fatigue performance of heavy rail steel by rare earth alloy and magnesium metallurgy treatment according to claim 1, characterized in that: According to GB / T 3075 standard, axial constant amplitude fatigue test is carried out, and the number of cycles is ≥1×10 8 , and thus determine the SN fatigue curve, and conclude that the fatigue strength of heavy rail steel is between 620-640MPa.

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