Low-cost method for producing normalized 355MPa-grade H-shaped steel by adopting special-shaped blank

Abstract

The invention discloses a low-cost method for producing normalized 355MPa-grade H-shaped steel by adopting a special-shaped blank. The method provided by the invention is designed according to the following components: 0.08%-0.11% of C, 0.20%-0.30% of Si, 1.35%-1.45% of Mn, less than or equal to 0.02% of P, less than or equal to 0.010% of S, 0.05%-0.07% of V, 0.015%-0.025% of Nb and the balance of Fe and impurities, the impact energy Akv at the temperature of minus 40 DEG C of the normalized 355MPa-grade H-shaped steel obtained by production is greater than or equal to 150J, and the cost of the provided production method is lower.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a low-cost method for producing normalized 355MPa grade H-beams using irregularly shaped billets. Background Technology

[0002] Q355NE steel, as a typical normalized low-temperature structural steel plate, possesses excellent strength, toughness, and stability in microstructure and mechanical properties, making it a preferred structural material for major engineering projects. However, the production technology for most of these high-performance steel plates serving in harsh low-temperature environments is monopolized by foreign countries. Therefore, developing normallyized high-strength low-temperature structural steel plates with independent intellectual property rights is urgently needed. This requires proposing novel composition design concepts, developing short-process production routes based on microstructure control, and achieving reduced production volume and lower production costs in the manufacture of high-quality steel products. Summary of the Invention

[0003] To address the aforementioned technical problems, the purpose of this invention is to provide a low-cost method for producing normalized 355MPa grade H-beams using shaped billets.

[0004] Specifically, the present invention is mainly achieved through the following technical solutions.

[0005] One aspect of this invention provides a low-cost method for producing normalized 355MPa grade H-beams using shaped billets, wherein the chemical composition of the normalized 355MPa grade H-beams, by mass percentage, is: C 0.08%–0.11%, Si 0.20%–0.30%, Mn 1.35%–1.45%, P ≤0.02%, S ≤0.010%, V 0.05%–0.07%, Nb 0.015%–0.025%, with the remainder being Fe and impurities;

[0006] The method includes the following processes: smelting, continuous casting, billet heating, controlled rolling, and cooling; wherein:

[0007] The smelting and continuous casting process includes: blast furnace hot metal → hot metal pretreatment → converter smelting → LF refining → VD vacuum treatment → continuous casting of shaped billets; wherein, in the continuous casting of shaped billets, protective casting is used throughout, argon blowing is used to control the connection between the ladle and the long nozzle, asbestos bowls are used to control the lower nozzle, the nozzle insertion depth is 65-70mm, weak cooling is used for the secondary cooling method, the secondary cooling water volume is 0.65-0.70L / kg, the superheat is ≤30℃, the melting point of the protective slag is 1235℃, the density is 0.80-0.90g / ml, the viscosity is 7.80Poise, constant casting speed is used, the casting machine speed is controlled at 0.7-0.9m / min; the ingot pressure on the first straightening machine is 140-150bar, and the ingot pressure on the second to sixth straightening machines is 60-70bar; the billets are stacked and slowly cooled for more than 48 hours;

[0008] In the billet heating process, the preheating section temperature is controlled to be ≤1000℃, the first heating section temperature is controlled to be ≤1150℃, the second heating section temperature is controlled to be 1100-1250℃, the soaking section temperature is controlled to be 1100-1250℃, and the total billet heating time is 3-5h.

[0009] In the controlled rolling and cooling process, the initial rolling temperature is controlled at 1150-1160℃, the final rolling temperature is controlled at 850-870℃, and close-packed cooling is performed.

[0010] In some embodiments, during the converter smelting process, the total oxygen supply time at the converter endpoint is controlled to be less than 15 minutes, and the cumulative total oxygen content is less than 4000 mg / L. 3 Ensure one-time drawing, final C > 0.03%, final temperature > 1620℃, control the slag amount in the converter to be less than 50mm, and use aluminum-iron deoxidation in the converter tapping process.

[0011] In some embodiments, during the LF refining process, desulfurization, composition fine-tuning, and temperature increase are carried out according to the composition and temperature of the converter steel. Phosphorus iron is added in the later stage of refining, and 55 kg / furnace of vanadium-nitrogen alloy is also added to ensure that the composition of the steel meets the internal control requirements. The LF refining heating time is less than 40 minutes, and silicon-calcium-barium aluminum-free deoxidation is used to produce white slag. The LF off-site temperature is controlled at 1680-1690℃.

[0012] In some embodiments, during the VD vacuum treatment process, the deep vacuum time is ≥15 min, the deep vacuum degree target is <0.1 kPa, the weak stirring time after breaking the vacuum is ≥15 min, the silicon-calcium wire is fed in, the soft blowing time is ≥15 min, and the temperature after VD is controlled at 1595-1605℃.

[0013] In some embodiments, the chemical composition of the normalized 355MPa grade H-beam is as follows by mass percentage: C 0.08%–0.11%, Si 0.25%–0.30%, Mn 1.36%–1.42%, P ≤0.02%, S ≤0.010%, V 0.056%–0.063%, Nb 0.018%–0.025%, with the remainder being Fe and impurities.

[0014] In some embodiments, the cross-sectional dimensions of the cast billet are 555×440×105mm.

[0015] Another aspect of the present invention provides a normalized 355MPa grade H-beam, which is produced by the above-described method.

[0016] In some embodiments, the -40℃ impact energy Akv of the normalized 355MPa grade H-beam is ≥150J.

[0017] In some embodiments, the impact energy Akv of the normalized 355MPa grade H-beam at -40℃ is ≥180J.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0019] The method provided by this invention has a low cost, and the H-beams produced not only have high yield and tensile strength, but also good impact toughness. Detailed Implementation

[0020] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best mode of implementation and do not limit the scope of the invention in any way.

[0021] This invention provides a low-cost method for producing normalized 355MPa grade H-beams using shaped billets, comprising: blast furnace hot metal → hot metal pretreatment → converter smelting → LF refining → VD vacuum treatment → shaped billet continuous casting → billet heating → finish rolling → rough rolling → cooling; specifically:

[0022] Pre-treated desulfurized molten iron was used: [S] < 0.030% entering the converter; molten iron temperature ≥ 1250℃. Re-blown converter smelting was employed, controlling the final slag basicity to 3.0. Final carbon content ≥ 0.03%, final temperature ≥ 1620℃, and final deoxidation using Al deoxidation. Alloy copper and nickel were added with the scrap steel. Quicklime was added during tapping. Refining with white slag was performed. Ar blowing was conducted throughout the refining process. Desulfurization, composition fine-tuning, and temperature increases were performed based on the converter steel composition and temperature. In the later stages of refining, 55 kg / furnace of vanadium-nitrogen alloy was added; if the vanadium content was insufficient, ferrovanadium was used to supplement it, and the composition was fine-tuned.

[0023] During the VD vacuum treatment process, the deep vacuum time is ≥15min, the deep vacuum degree target is <0.1KPa, the weak stirring time after breaking the vacuum is ≥15min, the silicon-calcium wire is fed in, the soft blowing time is ≥15min, and the temperature after VD is controlled at 1595-1605℃.

[0024] During the continuous casting of irregularly shaped billets, protective pouring was employed throughout. Argon blowing was used to control the connection between the ladle and the long nozzle, and an asbestos bowl was used to control the nozzle insertion depth, which was 65-70 mm. Weak cooling was used for the secondary cooling process, with a secondary cooling water volume of 0.65-0.70 L / kg. The superheat was ≤30℃. The protective slag melting point was 1235℃, density was 0.84 g / ml, and viscosity was 7.80 Poise. Constant casting speed was used, with the casting machine speed controlled at 0.7-0.9 m / min. The ingot pressure on the first leveling machine was 140-150 bar, and on leveling machines 2-6, it was 60-70 bar. The billets were stacked and slowly cooled for at least 48 hours. The billet cross-sectional dimensions were 555×440×105 mm. The surface quality of the billets was inspected, and the internal quality was tested using hot acid at low magnification. No obvious surface or internal defects were found during the inspection, indicating good billet quality.

[0025] In the billet heating process, the preheating zone temperature is controlled to be ≤1000℃, the first heating zone temperature to be ≤1150℃, the second heating zone temperature to be 1100-1250℃, the soaking zone temperature to be 1100-1250℃, and the total billet heating time to be 3-5 hours.

[0026] In the controlled rolling and cooling process, the initial rolling temperature is controlled at 1150-1160℃, and the final rolling temperature is controlled at 850-870℃, with close-packed cooling.

[0027] Table 1 lists the chemical composition content (by mass percentage) of each example; Table 2 lists the process parameter control of continuous casting of special-shaped billets for each example; Table 3 lists the process parameter control of billet heating and rolling for each example; and Table 4 lists the mechanical property test results of normalized 355MPa grade H-beams produced in each example.

[0028] Table 1: Chemical composition and content (%) of Examples 1-4

[0029] Example C Si Mn P S V Nb Example 1 0.08 0.30 1.36 0.0125 0.009 0.056 0.018 Example 2 0.10 0.275 1.37 0.0114 0.007 0.059 0.025 Example 3 0.09 0.252 1.39 0.0113 0.005 0.057 0.023 Example 4 0.11 0.274 1.42 0.0090 0.005 0.063 0.025

[0030] Table 2: Process Parameter Control for Continuous Casting of Irregular Billets in Examples 1-4

[0031]

[0032] Table 3: Control of billet heating and rolling process parameters in Examples 1-4

[0033]

[0034] Table 4: Mechanical property test results of normalized 355MPa grade H-beams produced in Examples 1-4

[0035]

[0036] As can be seen from the results in Table 4, the H-beams produced in each example not only have high yield and tensile strength, but also good impact toughness, and the production methods of each example have low costs.

[0037] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-cost method for producing normalized 355MPa grade H-beams using shaped billets, wherein the chemical composition of the normalized 355MPa grade H-beams, by mass percentage, is: C 0.08%–0.11%, Si 0.20%–0.30%, Mn 1.35%–1.45%, P≤0.02%, S≤0.010%, V 0.05%–0.07%, Nb 0.015%–0.025%, with the remainder being Fe and impurities; The method includes the following processes: Smelting, continuous casting, billet heating, controlled rolling and cooling processes; among which: The smelting and continuous casting process includes: blast furnace hot metal → hot metal pretreatment → converter smelting → LF refining → VD vacuum treatment → continuous casting of shaped billets; wherein, in the continuous casting of shaped billets, protective casting is used throughout, argon blowing is used to control the connection between the ladle and the long nozzle, asbestos bowls are used to control the lower nozzle, the nozzle insertion depth is 65-70mm, weak cooling is used for the secondary cooling method, the secondary cooling water volume is 0.65-0.70L / kg, the superheat is ≤30℃, the melting point of the protective slag is 1235℃, the density is 0.80-0.90g / ml, the viscosity is 7.80Poise, constant casting speed is used, the casting machine speed is controlled at 0.7-0.9m / min; the ingot pressure on the first straightening machine is 140-150bar, and the ingot pressure on the second to sixth straightening machines is 60-70bar; the billets are stacked and slowly cooled for more than 48 hours; In the billet heating process, the preheating section temperature is controlled to be ≤1000℃, the first heating section temperature is controlled to be ≤1150℃, the second heating section temperature is controlled to be 1100-1250℃, the soaking section temperature is controlled to be 1100-1250℃, and the total billet heating time is 3-5h. In the controlled rolling and cooling process, the initial rolling temperature is controlled at 1150-1160℃, the final rolling temperature is controlled at 850-870℃, and close-packed cooling is performed.

2. The method according to claim 1, wherein in the converter smelting, the total oxygen supply time at the converter endpoint is controlled to be less than 15 minutes, and the cumulative total oxygen content is less than 4000 mg / L. 3 Ensure one-time drawing, final C > 0.03%, final temperature > 1620℃, control the slag amount in the converter to be less than 50mm, and use aluminum-iron deoxidation in the converter tapping process.

3. The method according to claim 1 or 2, wherein during the LF refining process, desulfurization, composition fine-tuning and heating are carried out according to the composition and temperature of the converter steel. Phosphorus iron is added in the later stage of refining, and 55 kg / furnace of vanadium-nitrogen alloy is also added to ensure that the composition of the steel meets the internal control requirements. The LF refining heating time is less than 40 min, and silicon-calcium-barium aluminum-free deoxidation is used to produce white slag. The LF off-site temperature is controlled at 1680-1690℃.

4. The method according to claim 1 or 2, wherein during the VD vacuum treatment process, the deep vacuum time is ≥15 min, the deep vacuum degree target is <0.1 kPa, the weak stirring time after breaking the vacuum is ≥15 min, the silicon-calcium wire is fed in, the soft blowing time is ≥15 min, and the temperature after VD is controlled at 1595-1605℃.

5. The method according to any one of claims 1-4, wherein the chemical composition of the normalized 355MPa grade H-beam is, by mass percentage: C 0.08%–0.11%, Si 0.25%–0.30%, Mn 1.36%–1.42%, P ≤0.02%, S ≤0.010%, V 0.056%–0.063%, Nb 0.018%–0.025%, with the remainder being Fe and impurities.

6. The method according to any one of claims 1-4, wherein the cross-sectional dimensions of the cast billet are 555×440×105mm.

7. A normalized 355MPa grade H-beam, which is produced by the method according to any one of claims 1-6.

8. The normalized 355MPa grade H-beam according to claim 7 has an impact energy Akv ≥ 150J at -40℃.

9. The normalized 355MPa grade H-beam according to claim 8 has an impact energy Akv ≥ 180J at -40℃.

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