Smelting method of low-carbon rare-earth-containing microalloyed high-speed steel rail

Abstract

The invention discloses a smelting method of a low-carbon rare-earth-containing microalloyed high-speed steel rail. The smelting method comprises the steps of KR molten iron pretreatment, converter top and bottom combined blowing smelting, LF external refining, VD / RH vacuum treatment and square billet continuous casting. And related process parameters are limited. According to the smelting method of the low-carbon rare-earth-containing and microalloyed high-speed steel rail, on the premise of an existing heavy rail steel production technology, smelting process optimization and smelting component optimization are combined, and the produced low-carbon rare-earth-containing and microalloyed steel rail has more excellent obdurability and weldability on the premise of meeting standard performance requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgical materials, and particularly to a smelting method for low-carbon rare-earth-containing and micro-alloyed high-speed steel rails. Background Art

[0002] High-speed railways are one of the products of the rapid development of modern science and technology, an important driving force for the rapid development of social economy, and have also had a significant impact in the world's transportation field. Rail welding is the foundation of seamless tracks. Welded joints are stress concentration areas and the weakest parts in rail welding. Welding quality is the key to ensuring the normal operation of seamless tracks. In China, flash welding is used for factory welding of railway rails, and post-weld heat treatment is required. Rail welded joints are weak links in the track. Therefore, one of the keys to improving rail performance is to improve the performance of welded joints and ensure the quality of rail welding, which is of great significance for the safe operation of railways.

[0003] At present, the main types of railway rails in China are U71Mn and U75V rails. The rail strengthening elements consist of elements such as C, Si, Mn, Cr, and V. The two types of rails have the characteristics of high strength, can withstand the huge weight of trains and the impact force generated by high-speed driving, and ensure the stability of the track structure; they have the characteristics of high wear resistance, can resist the wear of wheels, reduce the replacement frequency of rails, lower maintenance costs, and extend service life, showing good wear resistance on frequently used railway lines. However, with the increase in usage, many problems have gradually been found. The toughness of the rails is poor, the elongation is basically between 9 - 13%, and the room temperature impact is basically between 10 - 20 J; the welding performance is poor. Since the carbon content of the rails is greater than 0.70%, abnormal structures and welding defects are likely to occur during rail welding, and the process is complex; the corrosion resistance is poor. Especially in the presence of corrosive media such as humidity, acids, and alkalis, rusting is still likely to occur, affecting the service life and performance of the rails; the contact fatigue performance is poor. Under the long-term repeated action of train loads, the rails are prone to damage such as fatigue cracks. By controlling the chemical composition of the rails, appropriately adjusting the content of elements such as C, Si, Mn, Cr, and V in the rails, and adding rare earth and micro-alloying elements at the same time, it helps to improve the welding performance, strength and toughness, contact fatigue performance, and corrosion resistance of the rails. Summary of the Invention

[0004] The purpose of the present invention is to provide a smelting method for low-carbon rare-earth-containing and micro-alloyed high-speed steel rails. On the premise of existing heavy rail steel production technology, combined with the optimization of smelting processes and smelting components, the produced low-carbon rare-earth-containing and micro-alloyed rails have better strength and toughness and weldability on the premise of meeting the standard performance requirements.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A smelting method for a low-carbon rare-earth and micro-alloyed high-speed steel rail of the present invention includes KR hot metal pretreatment - combined blowing top and bottom converter smelting - LF secondary refining - VD / RH vacuum treatment - bloom continuous casting; it is characterized in that: specifically includes the following steps:

[0007] 1) KR hot metal pretreatment: the S content in the hot metal ≤ 0.030%, the hot metal temperature ≥ 1300 °C, the hot metal must undergo desulfurization pretreatment, and the S content after pretreatment ≤ 0.010%;

[0008] 2) Combined blowing top and bottom converter smelting: smelt using an aluminum-free deoxidation process, and use single slag or double slag operation, and control the final slag basicity at 3.0 ± 0.1; after tapping, add quicklime, calcium silicate barium, and fluorite for deoxidation and slag modification, ensure the argon blowing effect during tapping, and there is no caking phenomenon of the top slag when the molten steel is in place for refining; the tapping C content ≥ 0.09%, the P content ≤ 0.015%, and the tapping temperature ≥ 1550 °C;

[0009] 3) LF secondary refining: desulfurize, fine-tune the composition, and raise the temperature according to the composition and temperature of the converter molten steel. It is required that the in-place temperature for refining ≥ 1530 °C and the out-of-place temperature ≥ 1570 °C;

[0010] 4) VD vacuum degassing: the deep vacuum degassing time ≥ 15 min, the soft blowing time after vacuum degassing ≥ 15 min, the vacuum degree ≤ 0.10 KPa, the argon flow rate is stable during soft blowing, the molten steel shall not be exposed during soft blowing, and large argon gas stirring is not allowed after the molten steel in the ladle is soft blown after vacuum degassing;

[0011] 5) Bloom continuous casting: adopt protective casting during continuous casting, use low-aluminum protective slag, adopt weak cooling water distribution in the secondary cooling section, the superheat ΔT ≤ 30 °C, the continuous casting machine adopts constant casting speed pouring, and the casting speed is controlled at 0.60 - 0.65 m / min,

[0012] Start the electromagnetic stirring and soft reduction of the casting machine to ensure the quality of the cast slab.

[0013] Furthermore, in the step 1), clean scrap steel is used, and the total amount of scrap steel is greater than 20 t.

[0014] Furthermore, the final slag basicity is controlled at 3.0.

[0015] Furthermore, the chemical composition of the steel material for preparing the steel rail by mass percentage: C: 0.65 - 0.70%, Si: 0.32 - 0.40%, Mn: 0.80 - 0.85%, Cr: 0.10 - 0.15%, V: 0.02 - 0.05%, RE: 0.0008 - 0.0013%, P ≤ 0.014%, S ≤ 0.003%, and the rest is Fe and inevitable impurities.

[0016] Furthermore, the chemical composition of the steel material for manufacturing the rail in mass percentage is as follows: C: 0.67%, Si: 0.35%, Mn: 0.80%, Cr: 0.15%, V: 0.03%, RE: 0.0010%, P 0.014%; S 0.002%, and the rest is Fe and inevitable impurities.

[0017] Furthermore, the carbon equivalent is 0.84.

[0018] Furthermore, on the premise that the strength and hardness of the rail meet the standard requirements, the plasticity and toughness are significantly improved.

[0019] Furthermore, the elongation after fracture of the rail meets ≥15%, and the impact at room temperature meets ≥25 J.

[0020] The design principles of each element are as follows:

[0021] C: It directly affects the strength, plasticity, toughness, and welding performance of steel, etc. When the carbon content in the steel is below 0.80%, with the increase of the carbon content, the strength and hardness of the steel increase, while the plasticity and toughness decrease. With the increase of the C content, the welding performance of the steel becomes worse (for steels with a carbon content greater than 0.3%, the weldability decreases significantly), the cold brittleness and aging sensitivity increase, and the atmospheric corrosion resistance decreases.

[0022] Mn: It can strengthen the ferrite matrix and refine pearlite, thereby improving the strength, hardness, and hardenability of the steel. Mn can be infinitely solid-solved with Fe. While increasing the strength of the steel, its influence on plasticity is relatively small. However, the Mn element and the S element are very easy to combine to form MnS inclusions, increasing the possibility of generating fatigue sources inside the rail, and the increase of the Mn content will reduce the plasticity and welding performance of the steel.

[0023] Si: It can dissolve in ferrite and austenite to increase the hardness and strength of the steel. Its effect is second only to phosphorus and is stronger than elements such as manganese, nickel, chromium, tungsten, molybdenum, and vanadium. Si can increase the elastic limit, yield strength, and yield ratio of the steel, as well as the fatigue strength and fatigue ratio, etc. Si can reduce the transformation speed from austenite to ferrite, increasing the strength and elasticity of the steel. Si can reduce the welding performance of the steel. During welding, it is easy to generate low-melting-point silicates, increasing the fluidity of the slag and the molten metal, causing splashing phenomena and affecting the welding quality.

[0024] Cr: It is a solid-solution strengthening element that can refine the pearlite lamellar spacing, thereby increasing the strength of the rail while having little reduction in toughness and plasticity. In the steel, it can also form chromium-containing carbides, thereby improving the wear resistance of the material. Cr also has strong heat resistance and is not easy to combine with oxygen to occur oxidation, so it is not easy to form oxide and silicate inclusions.

[0025] V: It can refine the grain size in alloy steel, improve the strength and toughness of the steel, simultaneously enhance the strength and yield ratio of the steel as well as its low-temperature properties, and improve the welding performance of the steel. V can increase the hardness and wear resistance of carbon steel without making the steel brittle. Vanadium has a very strong affinity with carbon, nitrogen, and oxygen, forming corresponding stable compounds with them.

[0026] RE: The functions of rare earths in steel mainly include purification, modification, and alloying effects. It has strong deoxidation and desulfurization capabilities. Microalloying can also change the deformation ability of rare earth inclusions. Especially to a certain extent, it can modify brittle Al2O3, and can improve the fatigue performance of most steel grades. Like Ca, Ti, Zr, Mg, Be, rare earth elements are the most effective modifiers for sulfides. Adding an appropriate amount of RE to steel can turn oxide and sulfide inclusions into fine and dispersed spherical inclusions, thus eliminating the harmfulness of inclusions such as MnS. Rare earth elements can also improve the oxidation resistance and corrosion resistance of steel, and can also improve the fluidity of steel, reduce non-metallic inclusions, and make the steel structure dense and pure.

[0027] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0028] By adjusting the contents of elements such as C, Si, and Mn in the rail, and simultaneously adding Cr, V microalloying and rare earth elements, the present invention helps to improve the strength and toughness, welding performance, contact fatigue performance, and corrosion resistance of the rail. At the same time, combined with the optimization of the smelting process, the produced low-carbon rare earth-containing and microalloyed rails have more excellent strength and toughness and welding properties under the premise of meeting the standard performance requirements, and have good promotion value. Specific embodiments

[0029] The following further specifically describes the present invention in combination with specific embodiments.

[0030] The chemical compositions of each example are shown in Table 1:

[0031] Table 1 Chemical compositions and carbon equivalent calculations of different examples (mass percentage / %)

[0032]

[0033] After the continuous casting billets produced by combining the above-mentioned rails with the above-mentioned smelting process are rolled, performance tests are carried out.

[0034] Table 2 Mechanical properties of rails of different examples

[0035]

[0036]

[0037] Table 3 Inclusion grades of rails of different examples

[0038]

[0039] As can be seen from Tables 1 - 3, compared with Examples 1 to 3, Example 4 reduces the contents of C, Si, and Mn elements in the steel, increases the microalloying elements Cr, V, and rare earth elements, and the carbon equivalent of the steel is significantly reduced, making it more excellent in welding performance. On the premise that the strength and hardness of the rail in Example 4 meet the standard requirements, the plasticity and toughness are significantly improved, the elongation after fracture of the rail is ≥15%, and the room temperature impact is ≥25 J. By comparing Examples 1 to 4, it can be seen that through the optimization of the smelting process and smelting components, the cleanliness level of the rail has also been improved to a certain extent.

[0040] The above-described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A smelting method for low-carbon rare-earth and micro-alloyed high-speed steel rails, including KR hot metal pretreatment - top and bottom combined blowing smelting in a converter - LF secondary refining - VD / RH vacuum treatment - continuous casting of billets; characterized in that: Specifically, it includes the following steps: 1) KR hot metal pretreatment: The S content in the hot metal ≤ 0.030%, the hot metal temperature ≥ 1300 °C. The hot metal must undergo desulfurization pretreatment, and after pretreatment, the S content ≤ 0.010%; 2) Converter top-bottom combined blowing smelting: Smelt using an aluminum-free deoxidation process and adopt single slag or double slag operation. Control the final slag basicity at 3.0 ± 0.1; After tapping, add quicklime, calcium silicobarium, and fluorite for deoxidation and slag modification. Ensure the argon blowing effect during tapping. When the molten steel is in the refining position, there is no caking phenomenon on the top slag; The tapping C content ≥ 0.09%, the P content ≤ 0.015%, and the tapping temperature ≥ 1550 °C; 3) LF secondary refining: Desulfurize, fine-tune the composition, and raise the temperature according to the composition and temperature of the converter molten steel. It is required that the refining in-position temperature ≥ 1530 °C and the off-position temperature ≥ 1570 °C; 4) VD vacuum degassing: The deep vacuum degassing time ≥ 15 min, the soft blowing time after vacuum degassing ≥ 15 min, the vacuum degree ≤ 0.10 KPa. The argon gas flow is stable during soft blowing. The molten steel shall not be exposed during soft blowing. After vacuum degassing and soft blowing of the ladle, large argon gas volume stirring is not allowed; 5) Bloom continuous casting: Adopt protective casting during continuous casting, use low-aluminum protective slag, adopt weak cooling water distribution in the secondary cooling section, the superheat ΔT ≤ 30 °C. The continuous caster adopts constant casting speed pouring, and the casting speed is controlled at 0.60 - 0.65 m / min. Turn on the electromagnetic stirring and soft reduction of the caster to ensure the quality of the cast slab.

2. The smelting method of the low-carbon rare-earth and micro-alloyed high-speed rail steel according to claim 1, characterized in that: In the step 1), clean scrap steel is used, and the total amount of scrap steel is greater than 20 t.

3. The smelting method of the low-carbon rare-earth and micro-alloyed high-speed steel rail according to claim 1, characterized in that: The final slag basicity is controlled at 3.

0.

4. The smelting method of the low-carbon rare-earth and micro-alloyed high-speed rail steel rail according to claim 1, characterized in that: The chemical composition of the steel material for preparing the rail by mass percentage: C: 0.65 - 0.70%, Si: 0.32 - 0.40%, Mn: 0.80 - 0.85%, Cr: 0.10 - 0.15%, V: 0.02 - 0.05%, RE: 0.0008 - 0.0013%, P ≤ 0.014%, S ≤ 0.003%, and the rest is Fe and inevitable impurities.

5. The smelting method of the low-carbon rare-earth and microalloyed high-speed rail steel according to claim 4, characterized in that: The chemical composition of the steel material for preparing the rail by mass percentage: C: 0.67%, Si: 0.35%, Mn: 0.80%, Cr: 0.15%, V: 0.03%, RE: 0.0010%, P 0.014%; S 0.002%, and the rest is Fe and inevitable impurities.

6. The smelting method of the low-carbon rare earth and micro-alloyed high-speed steel rail according to claim 1, characterized in that: The carbon equivalent is 0.

84.

7. The smelting method of the low-carbon rare-earth and micro-alloyed high-speed rail steel rail according to claim 1, characterized in that: On the premise that the strength and hardness of the rail meet the standard requirements, the plasticity and toughness are significantly improved.

8. The smelting method of the low-carbon rare-earth and microalloyed high-speed steel rail according to claim 7, characterized in that: The elongation after fracture of the rail meets ≥ 15%, and the room temperature impact meets ≥ 25 J.

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