Low-cost H340-grade high-strength steel rail smelting method based on cooperative control of rare earth treatment and continuous casting soft reduction

Abstract

The invention discloses a low-cost H340-grade high-strength steel rail smelting method based on rare earth treatment and cooperative control under continuous casting soft reduction, which comprises the following steps: 1) optimization of mass percent component design: on the basis of a low-vanadium high-manganese component system, introducing rare earth elements to form a Mn / V / RE multi-element cooperative strengthening mechanism; (2) controlling a continuous casting process; 3) adding and treating rare earth; and (4) other key procedures are accurately regulated and controlled. The invention aims to provide the low-cost H340-grade high-strength steel rail smelting method based on rare earth treatment and cooperative control under continuous casting soft reduction, and unification of high strength, high toughness and low cost of the steel rail is realized by optimizing a component system (introducing rare earth) and cooperatively and accurately regulating and controlling a continuous casting process.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical materials technology, and in particular relates to a low-cost H340 grade high-strength steel rail smelting method based on the synergistic control of rare earth treatment and continuous casting light pressure. Background Technology

[0002] Due to its advantages such as large capacity, high safety, and low carbon emissions, railway transportation has become the core carrier of the national transportation network. With the rapid development of heavy-haul railways, rails need to withstand higher axle loads (≥30t) and more complex working conditions (such as small-radius curves), which places stringent requirements on the strength, toughness, and wear resistance of rails.

[0003] Currently, mainstream H340 grade heat-treated steel rails (such as U75VH) comply with the TB / T2344 standard. Their conventional production process has two major technical contradictions: cost and performance imbalance: relying on high V content (0.06-0.07%) to ensure strength, but ferrovanadium alloy is expensive (about RMB 201,400 / ton). If V is reduced to 0.04-0.05%, the tensile strength is prone to fluctuate to the lower limit of the standard. Bottleneck in continuous casting defect control: conventional continuous casting process is prone to defects such as center segregation and cracks under V reduction conditions, affecting the homogeneity and toughness of the rail.

[0004] Although the "low vanadium, high manganese + light reduction" process can alleviate the above problems to some extent, non-metallic inclusions (such as sulfides and oxides) in steel will still deteriorate toughness and fatigue performance. Rare earth elements, due to their strong deoxidation and desulfurization capabilities, can effectively spheroidize inclusions and inhibit crack initiation. However, in traditional processes, the timing and amount of rare earth addition are not well matched with the continuous casting process, which can easily lead to nozzle blockage or compositional segregation.

[0005] Therefore, developing a rail smelting method that integrates rare earth processing and continuous casting with light pressure control, which combines low cost, high strength and excellent toughness, has significant industrial value. Summary of the Invention

[0006] The purpose of this invention is to provide a low-cost H340 grade high-strength steel rail smelting method based on the synergistic control of rare earth treatment and continuous casting light pressure. By optimizing the composition system (introducing rare earth) and synergistically and precisely controlling the continuous casting process, the method achieves a balance of high strength, high toughness, and low cost for the steel rail.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a low-cost H340 grade high-strength steel rail smelting method based on the synergistic control of rare earth treatment and continuous casting light reduction, comprising:

[0009] 1) Optimization of mass percentage component design

[0010] Based on the "low vanadium, high manganese" composition system, rare earth elements are introduced to form a "Mn / V / RE" multi-element synergistic enhancement mechanism:

[0011] C: 0.75-0.80%, balancing strength and toughness;

[0012] Si: 0.55-0.70%, which stabilizes hardenability when combined with Mn;

[0013] Mn: 0.80-1.00%, to compensate for the loss of strength due to V reduction;

[0014] V: 0.04-0.05%, reducing alloy costs;

[0015] RE: 0.001-0.005%, used to purify molten steel and remove spheroidized inclusions;

[0016] Furthermore, the Mn / V ratio is controlled between 18.0 and 25.0, and the Si / Mn ratio is controlled between 0.55 and 0.88; the remainder consists of Fe and impurities; the sulfide inclusions change from elongated strips to spherical shapes, which significantly improves impact toughness and fatigue life.

[0017] 2) Control of continuous casting process

[0018] Implement a "three-in-one" control system during the continuous casting stage: This system is adapted to rare earth treatment of molten steel.

[0019] (1) Secondary cooling weak cooling water distribution: control the thickness difference between the narrow and wide sides of the billet shell to be ≤15.37mm;

[0020] (2) Constant pulling speed operation: pulling speed 0.61-0.63m / min, solidification endpoint fluctuation ≤0.5m;

[0021] (3) Dynamic control of light reduction: The total reduction of 6.0-7.0 mm is implemented in the range of 0.3-0.8 central solidity, of which the second tension straightening machine undertakes the core reduction of 2.6-2.8 mm to eliminate central cracks and segregation;

[0022] 3) Rare earth addition and processing technology

[0023] Add rare earth alloys in the later stage of LF refining or before VD vacuum treatment, control the addition temperature to 1580-1620℃, and stir with soft blowing argon gas for ≥15min to ensure uniform distribution of rare earths and prevent accumulation and blockage of the water inlet.

[0024] 4) Precise control of other key processes

[0025] VD vacuum degassing: after deep vacuum for ≥15 min, soft blowing for ≥18 min, the molten steel [H] ≤1.5 ppm;

[0026] Continuous casting protective casting: Low-alumina protective slag is used in conjunction with electromagnetic stirring, current 350-360A, equiaxed crystal ratio ≥40%;

[0027] Light pressing: The first press should be 1.8-2.0mm to compensate for solidification shrinkage in advance, with deviation controlled at ≤6%.

[0028] Furthermore, the chemical composition by mass percentage is as follows: C: 0.78%, Si: 0.60%, Mn: 0.92%, V: 0.045%, RE: 0.002%, Mn / V = 20.4, Si / Mn = 0.65, with the remainder being Fe and impurities.

[0029] Furthermore, the chemical composition by mass percentage is as follows: C: 0.77%, Si: 0.62%, Mn: 0.98%, V: 0.048%, RE: 0.003%, Mn / V = 20.4, Si / Mn = 0.63, with the remainder being Fe and impurities.

[0030] Furthermore, the chemical composition by mass percentage is as follows: C: 0.79%, Si: 0.58%, Mn: 0.90%, V: 0.042%, RE: 0.004%, Mn / V = 21.4, Si / Mn = 0.64, with the remainder being Fe and impurities.

[0031] Furthermore, rare earth silicon-iron alloy is added in the later stage of LF refining at a temperature of 1600℃ and argon gas is gently blown in for 18 minutes.

[0032] The water flow rate in the narrow section of the second cooling zone is 58L / min, and the thickness difference of the billet shell is 14.8mm.

[0033] Pulling speed: 0.62 m / min;

[0034] Light pressure: The second tension leveler presses down 2.65mm;

[0035] VD soft blowing for 19 min, [H] = 1.2 ppm; electromagnetic stirring at 350 A, equiaxed crystal ratio 42%.

[0036] Furthermore, rare earth alloys were added before VD treatment at a temperature of 1590℃, followed by argon blowing for 20 minutes.

[0037] The water flow rate in the narrow section of the second cooling zone is 60L / min, and the thickness difference of the billet shell is 15.0mm.

[0038] Pulling speed: 0.61 m / min;

[0039] Light pressure: The second tension leveler presses down 2.70mm;

[0040] VD soft blowing for 18 min, [H] = 1.3 ppm; electromagnetic stirring at 355 A, equiaxed crystal ratio 43%.

[0041] Furthermore, rare earth alloys are added in the later stage of LF refining at a temperature of 1610℃, followed by soft blowing of argon gas for 17 minutes.

[0042] The water flow rate in the narrow section of the second cooling zone is 62 L / min, and the thickness difference of the billet shell is 15.2 mm.

[0043] Pulling speed: 0.63 m / min;

[0044] Light pressure: The second tension leveler presses down 2.68mm;

[0045] VD soft blowing for 20 min, [H] = 1.1 ppm; electromagnetic stirring at 352A, equiaxed crystal ratio 44%.

[0046] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0047] Cost reduction: V content is reduced by 33%, rare earth content is low, and cost is significantly optimized;

[0048] Performance improvements: tensile strength ≥1250MPa, impact toughness increased by 15-20%, center crack grade 0, cross-sectional hardness difference ≤1.0HRC;

[0049] Rare earth elements contribute to: inclusion spheroidization rate ≥80%, fatigue life increased by more than 10%. Detailed Implementation

[0050] Example 1:

[0051] Design of chemical composition by mass percentage:

[0052] C: 0.78%, Si: 0.60%, Mn: 0.92%, V: 0.045%, RE: 0.002%, Mn / V = 20.4, Si / Mn = 0.65, with the remainder being Fe and impurities.

[0053] Rare earth elements added:

[0054] Rare earth silicon-iron alloy is added in the later stage of LF refining at a temperature of 1600℃, followed by argon blowing for 18 minutes.

[0055] Continuous casting process:

[0056] The water flow rate in the narrow section of the second cooling zone is 58L / min, and the thickness difference of the billet shell is 14.8mm.

[0057] Pulling speed: 0.62 m / min;

[0058] Light pressure: The second tension leveler presses down 2.65mm.

[0059] Other controls:

[0060] VD soft blowing for 19 min, [H] = 1.2 ppm; electromagnetic stirring at 350 A, equiaxed crystal ratio 42%.

[0061] Table 1 Performance Output Results (Rail / Bill)

[0062] Performance indicators Measured value Standard requirements tensile strength 1268MPa ≥1180MPa Impact energy (-20℃) 18J ≥12J central crack Level 0 ≤ Level 1 Inclusion spheroidization rate 82％ —

[0063] Example 2

[0064] Design of chemical composition by mass percentage:

[0065] C: 0.77%, Si: 0.62%, Mn: 0.98%, V: 0.048%, RE: 0.003%, Mn / V = 20.4, Si / Mn = 0.63, with the remainder being Fe and impurities.

[0066] Rare earth elements added:

[0067] Before VD treatment, rare earth alloys are added at a temperature of 1590℃ and argon gas is gently blown in for 20 minutes.

[0068] Continuous casting process:

[0069] The water flow rate in the narrow section of the second cooling zone is 60L / min, and the thickness difference of the billet shell is 15.0mm.

[0070] Pulling speed: 0.61 m / min;

[0071] Light pressure: The second straightening machine presses down 2.70mm.

[0072] Other controls:

[0073] VD soft blowing for 18 min, [H] = 1.3 ppm; electromagnetic stirring at 355 A, equiaxed crystal ratio 43%.

[0074] Table 2 Performance Output Results (Rail / Bill)

[0075] Performance indicators Measured value Standard requirements Proof of Innovation tensile strength 1255MPa ≥1180MPa tensile strength Impact energy (-20℃) 17J ≥12J Impact energy (-20℃) central crack Level 0 ≤ Level 1 central crack Inclusion spheroidization rate 85％ — Inclusion spheroidization rate

[0076] Example 3:

[0077] Chemical composition by mass percentage:

[0078] C: 0.79%, Si: 0.58%, Mn: 0.90%, V: 0.042%, RE: 0.004%, Mn / V = 21.4, Si / Mn = 0.64, with the remainder being Fe and impurities.

[0079] Rare earth elements added:

[0080] Rare earth alloys were added during the later stages of LF refining at a temperature of 1610℃, followed by 17 minutes of gentle argon blowing.

[0081] Continuous casting process:

[0082] The water flow rate in the narrow section of the second cooling zone is 62 L / min, and the thickness difference of the billet shell is 15.2 mm.

[0083] Pulling speed: 0.63 m / min;

[0084] Light pressure: The second tension leveler presses down 2.68mm.

[0085] Other controls:

[0086] VD soft blowing for 20 min, [H] = 1.1 ppm; electromagnetic stirring at 352A, equiaxed crystal ratio 44%.

[0087] Table 3 Performance Output Results (Rail / Bill)

[0088] Performance indicators Measured value Standard requirements Proof of Innovation tensile strength 1270MPa ≥1180MPa tensile strength Impact energy (-20℃) 19J ≥12J Impact energy (-20℃) central crack Level 0 ≤ Level 1 central crack Inclusion spheroidization rate 88％ — Inclusion spheroidization rate

[0089] This invention introduces rare earth elements and combines an optimized "low vanadium, high manganese" composition design with a continuous casting light reduction process to achieve high strength, high toughness, low cost, and excellent homogeneity of H340 grade steel rails, making them suitable for mass production of heavy-haul railway rails.

[0090] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A low-cost method for smelting H340 grade high-strength steel rails based on the synergistic control of rare earth treatment and continuous casting light reduction, characterized in that, include: 1) Optimization of mass percentage component design Based on the "low vanadium and high manganese" composition system, rare earth elements are introduced to form a "Mn / V / RE" multi-element synergistic enhancement mechanism: C: 0.75-0.80%, balancing strength and toughness; Si: 0.55-0.70%, which stabilizes hardenability when combined with Mn; Mn: 0.80-1.00%, to compensate for the loss of strength due to V reduction; V: 0.04-0.05%, reducing alloy costs; RE: 0.001-0.005%, used to purify molten steel and remove spheroidized inclusions; Furthermore, the Mn / V ratio is controlled between 18.0 and 25.0, and the Si / Mn ratio is controlled between 0.55 and 0.88; the remainder consists of Fe and impurities; the sulfide inclusions change from elongated strips to spherical shapes, which significantly improves impact toughness and fatigue life. 2) Control of continuous casting process Implement a "three-in-one" control system during the continuous casting stage: Implement a "three-in-one" continuous casting control system to adapt to rare earth treatment of molten steel: (1) Secondary cooling weak cooling water distribution: control the thickness difference between the narrow and wide sides of the billet shell to be ≤15.37mm; (2) Constant pulling speed operation: pulling speed 0.61-0.63m / min, solidification endpoint fluctuation ≤0.5m; (3) Dynamic control of light reduction: The total reduction of 6.0-7.0 mm is implemented in the range of 0.3-0.8 central solidity, of which the second tension straightening machine undertakes the core reduction of 2.6-2.8 mm to eliminate central cracks and segregation; 3) Rare earth addition and processing technology Add rare earth alloys in the later stage of LF refining or before VD vacuum treatment, control the addition temperature to 1580-1620℃, and stir with soft blowing argon gas for ≥15min to ensure uniform distribution of rare earths and prevent accumulation and blockage of the water inlet. 4) Precise control of other key processes VD vacuum degassing: after deep vacuum for ≥15 min, soft blowing for ≥18 min, the molten steel [H] ≤1.5 ppm; Continuous casting protective casting: Low-alumina protective slag is used in conjunction with electromagnetic stirring, current 350-360A, equiaxed crystal ratio ≥40%; Light pressing: The first press should be 1.8-2.0mm to compensate for solidification shrinkage in advance, with deviation controlled at ≤6%.

2. The low-cost H340 grade high-strength steel rail smelting method based on the synergistic control of rare earth treatment and continuous casting light reduction as described in claim 1, characterized in that, The chemical composition by mass percentage is as follows: C: 0.78%, Si: 0.60%, Mn: 0.92%, V: 0.045%, RE: 0.002%, Mn / V = 20.4, Si / Mn = 0.65, with the remainder being Fe and impurities.

3. The low-cost H340 grade high-strength steel rail smelting method based on the synergistic control of rare earth treatment and continuous casting light reduction as described in claim 1, characterized in that, The chemical composition by mass percentage is as follows: C: 0.77%, Si: 0.62%, Mn: 0.98%, V: 0.048%, RE: 0.003%, Mn / V = 20.4, Si / Mn = 0.63, with the remainder being Fe and impurities.

4. The low-cost H340 grade high-strength steel rail smelting method based on the synergistic control of rare earth treatment and continuous casting light reduction as described in claim 1, characterized in that, The chemical composition by mass percentage is as follows: C: 0.79%, Si: 0.58%, Mn: 0.90%, V: 0.042%, RE: 0.004%, Mn / V = 21.4, Si / Mn = 0.64, with the remainder being Fe and impurities.

5. The low-cost H340 grade high-strength steel rail smelting method based on the synergistic control of rare earth treatment and continuous casting light reduction as described in claim 2, characterized in that, Rare earth ferrosilicon alloy was added in the later stage of LF refining at a temperature of 1600℃ and argon gas was gently blown in for 18 minutes. The water flow rate in the narrow section of the second cooling zone is 58L / min, and the thickness difference of the billet shell is 14.8mm. Pulling speed: 0.62 m / min; Light pressure: The second tension leveler presses down 2.65mm; VD soft blowing for 19 min, [H] = 1.2 ppm; electromagnetic stirring at 350 A, equiaxed crystal ratio 42%.

6. The low-cost H340 grade high-strength steel rail smelting method based on the synergistic control of rare earth treatment and continuous casting light reduction as described in claim 3, is characterized in that, Before VD treatment, rare earth alloy is added at a temperature of 1590℃ and argon gas is gently blown in for 20 minutes. The water flow rate in the narrow section of the second cooling zone is 60L / min, and the thickness difference of the billet shell is 15.0mm. Pulling speed: 0.61 m / min; Light pressure: The second tension leveler presses down 2.70mm; VD soft blowing for 18 min, [H] = 1.3 ppm; electromagnetic stirring at 355 A, equiaxed crystal ratio 43%.

7. The low-cost H340 grade high-strength steel rail smelting method based on the synergistic control of rare earth treatment and continuous casting light reduction as described in claim 4, is characterized in that, Rare earth alloys were added during the later stage of LF refining at a temperature of 1610℃, followed by 17 minutes of gentle argon blowing. The water flow rate in the narrow section of the second cooling zone is 62 L / min, and the thickness difference of the billet shell is 15.2 mm. Pulling speed: 0.63 m / min; Light pressure: The second tension leveler presses down 2.68mm; VD soft blowing for 20 min, [H] = 1.1 ppm; electromagnetic stirring at 352A, equiaxed crystal ratio 44%.