Method for eliminating white bright band of LZ50 steel for railway axle

Abstract

The invention discloses a method for eliminating a white bright band of LZ50 steel for a railway axle, which comprises the following steps: in a continuous casting process, adopting three-section gradient electromagnetic stirring: the current intensity of a crystallizer M-EMS is 75-85A, and the stirring frequency is 1-3Hz; the current intensity of the secondary cooling zone S-EMS is 180-220 A, and the stirring frequency is 2-4 Hz; the current intensity of the F-EMS at the tail end is 650-750 A, and the stirring frequency is 5-7 Hz; the degree of superheat of continuous casting molten steel is 20-30 DEG C, and the pulling speed is 0.2-0.5 m / min; by means of the method, the defects of white bright bands of LZ50 steel continuous casting and rolled metal can be thoroughly eliminated, and the problem that macrostructures are unqualified is solved.

Description

Technical Field

[0001] This invention belongs to the field of axle steel preparation technology, specifically relating to a method for eliminating the bright white band in LZ50 steel used in railway axles. Background Technology

[0002] Since axle steel needs to withstand alternating loads, the presence of bright white bands can create weak zones and become the initiation point for fatigue cracks. This poses a significant risk, especially in high-strength applications such as high-speed train axles. If the bright white bands are located close to the axle surface or critical stress areas, subsequent machining processes (such as grinding and drilling) may lead to increased tool wear or dimensional deviations due to differences in material hardness, increasing process adjustment costs.

[0003] The main reason for the formation of the bright white band is that electromagnetic stirring causes the molten steel at the solidification front to flow in a forced manner, which in turn washes away the mother liquor rich in solute elements, forming a negative segregation region with a lower carbon content than the two sides, which appears as a light white band on the low magnification sample.

[0004] Under the existing tooling and process parameter settings, it is difficult to achieve precise control over the distribution of solute elements during the solidification process, resulting in large fluctuations in the width and position of the bright band, unqualified low-magnification microstructure, and a high product scrap rate. At the same time, the insufficient matching between stirring intensity and pulling speed can easily lead to interfacial dendrite remelting, further aggravating segregation inhomogeneity. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a method for eliminating the bright white band in LZ50 steel used for railway axles. This method can completely eliminate the bright white band defect in LZ50 steel continuous casting and rolling, and solve the problem of unqualified low magnification structure.

[0006] The technical solution adopted in this invention is as follows:

[0007] A method for eliminating the bright white band in LZ50 steel used in railway axles, the method comprising: employing a three-stage gradient electromagnetic stirring process during continuous casting: the current intensity of the crystallizer M-EMS is 75~85A, and the stirring frequency is 1~3Hz; the current intensity of the secondary cooling zone S-EMS is 180~220A, and the stirring frequency is 2~4Hz; the current intensity of the final F-EMS is 650~750A, and the stirring frequency is 5~7Hz; the superheat of the continuously cast steel is 20-30℃, and the casting speed is 0.2-0.5m / min.

[0008] Further preferably, the current intensity of the crystallizer M-EMS is 80A and the stirring frequency is 2Hz; the current intensity of the secondary cooling zone S-EMS is 200A and the stirring frequency is 3Hz; and the current intensity of the terminal F-EMS is 700A and the stirring frequency is 6Hz.

[0009] The production method of LZ50 steel for railway axles is as follows: converter smelting - LF refining - RH vacuum treatment - continuous casting - heating - rolling.

[0010] In the converter smelting step, the converter endpoint is controlled to have C ≥ 0.08% and P ≤ 0.012%.

[0011] In the LF refining step, silicon carbide diffusion deoxidation and aluminum particle-assisted deoxidation are used, and the white slag is maintained for ≥20 minutes.

[0012] In the LF refining step, the amount of silicon carbide added is 180 kg / furnace; the amount of aluminum granules added is 20-100 kg / furnace.

[0013] In the RH vacuum treatment step, the RH vacuum degree is ≤50Pa, the vacuum holding time is ≥15min, the hydrogen concentration is ≤1.5ppm, and soft blowing is performed after the calcium wire is fed in.

[0014] The amount of calcium wire added is 50-100m / furnace.

[0015] In the heating process, the temperature of heating stage 1 is 830-880℃, the temperature of heating stage 2 is 1110-1150℃, the temperature of heating stage 3 and the soaking stage is 1210-1250℃, and the heating time in the furnace is 500-600 minutes.

[0016] In the rolling process, the water descaling pressure is ≥10MPa, the initial rolling temperature is 1115-1128℃, and the final rolling temperature is 895-927℃.

[0017] The method for eliminating bright white bands in LZ50 steel used in railway axles provided by this invention involves progressively increasing stirring intensity from the crystallizer to the end, forming a continuous and controllable solidification disturbance that breaks the chain of bright white bands. Specifically, the low-intensity stirring in the crystallizer (M-EMS) avoids excessive disturbance to the initial billet shell, preventing surface defects; the medium-intensity stirring in the secondary cooling zone (S-EMS) effectively suppresses excessive columnar crystal growth; and the high-intensity stirring in the end (F-EMS) effectively breaks up the dendritic network at the solidification front, preventing solute enrichment and channel formation. Through the synergy of three-stage gradient electromagnetic stirring and precise process parameters, a three-in-one bright white band elimination mechanism of suppression, breaking up, and homogenization is constructed, fundamentally solving the problem of bright white bands in LZ50 steel during the solidification process.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This invention completely eliminates the white bright band defect in LZ50 steel continuous casting and rolled products by using three-stage gradient stirring parameters, combined with superheat control and low casting speed, thus solving the problem of unqualified low magnification microstructure.

[0020] This invention addresses the control of converter smelting, LF refining, RH vacuum treatment, heating, and rolling processes, effectively controlling the quality of axle steel, ensuring product quality meets the processing and usage requirements of downstream customers, effectively reducing scrap rate, lowering processing costs, and simultaneously improving production efficiency. Attached Figure Description

[0021] Figure 1 The low-magnification microstructure of the φ600mm round billet in Example 1;

[0022] Figure 2 The low-magnification microstructure of the 250mm×250mm square rolled material in Example 1;

[0023] Figure 3 The microstructure of the φ600mm round billet in Comparative Example 1 is shown in low magnification.

[0024] Figure 4 The low-magnification microstructure of the 250mm×250mm square rolled material in Comparative Example 1 is shown. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the embodiments.

[0026] Example 1

[0027] A method for producing LZ50 steel for railway axles includes the following steps: converter smelting - LF refining - RH vacuum treatment - continuous casting - heating - rolling, specifically:

[0028] Converter process: final C 0.09%, P 0.010%, tapping temperature 1635℃; aluminum ingots added after furnace, 1.5kg / t, aluminum wire fed 250m;

[0029] Refining process: Add 450kg of lime, 300kg of bearing steel refining slag, and 200kg of slag-reducing agent; add 180kg of silicon carbide and 60kg of aluminum granules in 3 batches, and maintain the white slag for 25 minutes;

[0030] RH treatment: Maintain a vacuum of 50 Pa for 15 minutes, with a constant hydrogen concentration of 1.2 ppm and a constant oxygen concentration of 3.5 ppm; feed with 80 m of calcium wire and gently blow for 20 minutes.

[0031] Continuous casting process: ladle temperature 1580℃ (superheat 26℃), casting speed 0.22m / min; electromagnetic stirring parameters: M-EMS 80A-2Hz, S-EMS 200A-3Hz, F-EMS 700A-6Hz, to obtain φ600mm round billet.

[0032] Rolling process: Cold charge into the furnace, heating section 1 820-850℃, heating section 2 1110-1130℃, heating section 3 1210-1230℃, soaking section 1210-1235℃, furnace time 540min, tapping rhythm 12min / piece; water descaling pressure 12MPa, initial rolling temperature 1115-1128℃, final rolling temperature 895-927℃, rolled into 250mm×250mm square rolled material.

[0033] Results: The rolled material had no bright white bands, the low magnification microstructure pass rate was 100%, and the product quality met the processing and use requirements of downstream customers.

[0034] Comparative Example 1

[0035] A method for producing LZ50 steel for railway axles includes the following steps: converter smelting - LF refining - RH vacuum treatment - continuous casting - heating - rolling, specifically:

[0036] Converter process: final C 0.09%, P 0.011%, tapping temperature 1632℃; aluminum ingots added after furnace, 1.5kg / t, aluminum wire fed 250m;

[0037] Refining process: Add 450kg of lime, 300kg of bearing steel refining slag, and 200kg of slag-reducing agent; add 190kg of silicon carbide and 60kg of aluminum granules in 3 batches, and keep the white slag for 25 minutes;

[0038] RH treatment: Vacuum degree 50Pa, maintain for 15min, constant hydrogen 1.1ppm, constant oxygen 4.7ppm; feed calcium wire 80m, soft blowing for 16min.

[0039] Continuous casting process: ladle temperature 1583℃ (superheat 29℃), casting speed 0.26m / min; electromagnetic stirring parameters: M-EMS150A-2Hz, F-EMS 350A-5Hz, to obtain φ600mm round billet.

[0040] Rolling process: Cold charge into the furnace, heating section 1 820-835℃, heating section 2 1110-1120℃, heating section 3 1210-1222℃, soaking section 1210-1228℃, furnace time 548min, tapping rhythm 12min / piece; water descaling pressure 11MPa, initial rolling temperature 1108-1125℃, final rolling temperature 892-925℃, rolled into 250mm×250mm square rolled material.

[0041] Results: The rolled material had a bright white band at low magnification, the low magnification microstructure pass rate was 0%, and the product quality did not meet the processing and use requirements of downstream customers.

[0042] Comparative Example 2

[0043] The rest is the same as in Example 1, except that the electromagnetic stirring parameters in the continuous casting process are replaced with: M-EMS 400A-4Hz, S-EMS 250A-4Hz, F-EMS 450A-5Hz.

[0044] Results: The rolled material had a bright white band at low magnification, and the pass rate of low magnification structure was 0%.

[0045] The above detailed description of a method for eliminating bright white streaks in LZ50 steel for railway axles, with reference to the embodiments, is illustrative rather than limiting. Several embodiments can be listed within the defined scope. Therefore, variations and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A method for eliminating bright white streaks in LZ50 steel used in railway axles, characterized in that, The method includes: during continuous casting, a three-stage gradient electromagnetic stirring is adopted: the current intensity of the crystallizer M-EMS is 75~85A, and the stirring frequency is 1~3Hz; the current intensity of the secondary cooling zone S-EMS is 180~220A, and the stirring frequency is 2~4Hz; the current intensity of the final F-EMS is 650~750A, and the stirring frequency is 5~7Hz; the superheat of the continuously cast steel is 20-30℃, and the casting speed is 0.2-0.5m / min.

2. The method for eliminating bright white streaks in LZ50 steel used in railway axles according to claim 1, characterized in that, The current intensity of the crystallizer M-EMS is 80A and the stirring frequency is 2Hz; the current intensity of the secondary cooling zone S-EMS is 200A and the stirring frequency is 3Hz; the current intensity of the terminal F-EMS is 700A and the stirring frequency is 6Hz.

3. The method for eliminating bright white streaks in LZ50 steel used in railway axles according to claim 1 or 2, characterized in that, The production method of LZ50 steel for railway axles is as follows: converter smelting - LF refining - RH vacuum treatment - continuous casting - heating - rolling.

4. The method for eliminating the bright white band in LZ50 steel used in railway axles according to claim 3, characterized in that, In the converter smelting step, the converter endpoint is controlled to have C ≥ 0.08% and P ≤ 0.012%.

5. The method for eliminating bright white streaks in LZ50 steel used in railway axles according to claim 1 or 2, characterized in that, In the LF refining step, silicon carbide diffusion deoxidation and aluminum particle-assisted deoxidation are used, and the white slag is maintained for ≥20 minutes.

6. The method for eliminating bright white streaks in LZ50 steel used in railway axles according to claim 5, characterized in that, In the LF refining step, the amount of silicon carbide added is 180 kg / furnace; the amount of aluminum granules added is 20-100 kg / furnace.

7. The method for eliminating bright white streaks in LZ50 steel used in railway axles according to claim 1 or 2, characterized in that, In the RH vacuum treatment step, the RH vacuum degree is ≤50Pa, the vacuum holding time is ≥15min, the hydrogen concentration is ≤1.5ppm, and soft blowing is performed after the calcium wire is fed in.

8. The method for eliminating bright white streaks in LZ50 steel used in railway axles according to claim 7, characterized in that, The amount of calcium wire added is 50-100m / furnace.

9. The method for eliminating bright white streaks in LZ50 steel used in railway axles according to claim 1 or 2, characterized in that, In the heating process, the temperature of heating stage 1 is 830-880℃, the temperature of heating stage 2 is 1110-1150℃, and the temperature of heating stage 3 and the soaking stage is 1210-1250℃; the heating time in the furnace is 500-600 min.

10. The method for eliminating bright white streaks in LZ50 steel used in railway axles according to claim 1 or 2, characterized in that, In the rolling process, the water descaling pressure is ≥10MPa, the initial rolling temperature is 1115-1128℃, and the final rolling temperature is 895-927℃.

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