A method for producing X52QS grade corrosion-resistant pipe shell from high-sulfur semi-steel liquid

Abstract

The application provides a method for producing X52QS steel grade corrosion-resistant pipe blanks from high-sulfur semi-liquid steel, which comprises the following steps: firstly, KR desulfurization is used to pretreat the high-sulfur semi-liquid steel, so that the S content is less than or equal to 0.030wt%; then, after the completion of converter steelmaking, the addition amount of aluminum ingot is limited to meet the basic deep deoxidation requirement, no excessive aluminum ingot is added, and refining slag is added according to 1000±30kg / oven, so that a stable foundation of high-aluminum slag system is formed in advance, then LF refining is carried out, and after the first electrode, the target Al content is 0.055-0.070wt%, one-time aluminum wire is used for aluminum supplement, and aluminum particles and lime are added, so that the top slag of the LF refining is high-aluminum slag system, thereby obtaining a corrosion-resistant pipe blank with self-designed components and meeting the performance requirements of X52QS steel grade.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting, and specifically to a method for producing X52QS grade corrosion-resistant tube blanks from high-sulfur semi-steel. Background Technology

[0002] Pipeline steel refers to the steel used in the production of seamless steel pipes for transporting oil, natural gas, etc. In addition to high pressure resistance, pipeline steel requires good toughness, fatigue resistance, low-temperature toughness, and weldability during use. Pipeline steel used in acidic environments has the most stringent quality requirements among pipeline steels. Due to the special nature of its operating environment, it places extremely stringent demands on steel composition design, smelting technology, rolling processes, and the level of metallurgical equipment.

[0003] Corrosion-resistant pipeline steel is used to produce steel pipes for transporting media containing acidic gases and operating in acidic environments for extended periods. Due to the special nature of their operating environment, extremely stringent requirements are placed on the steel's composition design, smelting technology, rolling processes, and the level of metallurgical equipment. Currently, China lacks practical experience in the application of pipeline steel for transporting acidic gases, whether in billet production or seamless pipe manufacturing. With my country's rapid economic development and increasing energy demand, oil and natural gas containing acidic media have been included in the development agenda, leading to higher standards for the strength, toughness, weldability, and corrosion resistance of gas pipeline steel used in acidic environments.

[0004] Generally, high-grade steel, such as X52QS steel, is selected for corrosion-resistant pipelines. However, the requirements for inclusions are extremely strict during the production of X52QS steel grade corrosion-resistant pipe blanks: Class A inclusions ≤ 0.5 grade, and Class B, C, and D inclusions ≤ 1.0 grade, which is a major challenge in production control. Furthermore, Chengde Jianlong Special Steel Co., Ltd. uses a top-and-bottom blowing oxygen converter for steelmaking. Due to its special vanadium extraction process, the converter draws semi-finished steel (i.e., the semi-finished steel after vanadium extraction from molten iron), which has a high average sulfur content. If high-sulfur semi-steel is used directly to produce X52QS grade anti-corrosion tube blanks, the following production control difficulties are often encountered: (1) Because high-grade steel grades have strict requirements for inclusions, high-alumina slag system with strong inclusion adsorption capacity is used, but the desulfurization capacity of high-alumina slag system is poor; (2) The sulfur content in high-sulfur semi-steel is relatively high. In order to meet the sulfur requirements of the design steel grade, a large amount of lime needs to be added for desulfurization, which destroys the stability of high-alumina slag system; (3) The carbon content of peritectic steel converter is low and the oxygen content is high at the end point. Deoxidation and desulfurization are required during the refining process. Deoxidizing materials are usually added, such as aluminum ingots and aluminum granules. At the same time, because of the high requirement of the target component Alt in X52QS grade steel, the Al content in the smelted steel is often high. If Al is not properly handled during the addition of deoxidizing material Al, a large amount of Al2O3 will be formed, which will cause the inclusions to not meet the requirements, affecting the quality of the steel. The continuous casting of this substance will affect the casting; (4) During the smelting process, the amount of desulfurization slag is large, and the inclusion adsorption capacity becomes poor. To address this, one approach is to increase costs by changing the blast furnace feedstock and controlling the initial sulfur content of the molten iron, thus solving the problem of high-sulfur semi-steel at its source. However, this approach is costly and not conducive to widespread adoption. Another approach is to rely on ordinary slag systems for rapid deoxidation and desulfurization, followed by calcium treatment to fully soften and float inclusions after their removal. However, placing inclusion treatment before continuous casting not only carries a high risk of ineffective inclusion removal but also easily leads to blockages in continuous casting.

[0005] In conclusion, there is still a need to develop a method for directly producing X52QS grade corrosion-resistant tube blanks using high-sulfur semi-steel, in order to explore how to produce qualified corrosion-resistant tube blanks that meet the X52QS grade requirements without controlling the sulfur content in the high-sulfur semi-steel. Summary of the Invention

[0006] In view of the technical problems existing in the prior art, namely, how to control the S and Al content while ensuring the stability of the slag system after LF refining and its ability to adsorb inclusions in the process of directly producing X52QS grade corrosion-resistant tube blanks using high-sulfur semi-steel, and thus ensuring stable and continuous casting of round billets, this invention provides a method for producing X52QS grade corrosion-resistant tube blanks using high-sulfur semi-steel. The method achieves effective desulfurization before LF refining and focuses on controlling the addition of Al to avoid the large-scale generation of high-melting-point Al2O3, ensuring the stability of the high-alumina slag system and its ability to adsorb inclusions, thereby obtaining a corrosion-resistant tube blank with a self-designed composition that meets the performance requirements of X52QS grade steel.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] The purpose of this invention is to provide a method for producing X52QS grade corrosion-resistant tube blanks from high-sulfur semi-steel, the method comprising the following steps:

[0009] (1) KR desulfurization;

[0010] High-sulfur semi-steel is subjected to KR desulfurization, wherein the sulfur content at the inlet of the KR desulfurization station is 0.170-0.200 wt%, and the sulfur content at the outlet of the KR desulfurization station is ≤0.030 wt%.

[0011] (2) Converter steelmaking;

[0012] After the converter steelmaking process is completed, aluminum ingots are added as a deep deoxidizer, and the amount of aluminum ingots added is determined according to the carbon content at the converter endpoint; specifically: if the carbon content at the converter endpoint is <0.06wt%, the amount of aluminum ingots added is 60kg / heat; if the carbon content at the converter endpoint is 0.06-0.10wt%, the amount of aluminum ingots added is 50kg / heat; if the carbon content at the converter endpoint is >0.10wt%, the amount of aluminum ingots added is 40kg / heat.

[0013] After the converter steelmaking is completed, refining slag is added at a rate of 1000±30 kg / furnace;

[0014] (3) LF refining;

[0015] The LF refining process includes: based on the sample composition of the LF refining process, after the first electrode, using aluminum wire to perform only one aluminum replenishment according to the target Al content of 0.055-0.070wt%;

[0016] The LF refining process includes the addition of aluminum granules and lime to ensure that the top slag from the LF refining process is a high-alumina slag system.

[0017] (4) VD vacuum degassing;

[0018] (5) Continuous casting of round billets;

[0019] After the continuous casting of the round billet is completed, an X52QS grade corrosion-resistant tube blank is obtained, whose composition by mass percentage includes: C 0.12-0.16wt%, Si 0.30-0.45wt%, Mn 1.15-1.30wt%, P≤0.020wt%, S≤0.003wt%, Alt 0.020-0.040wt%, V 0.04-0.06wt%.

[0020] The method described in this invention achieves effective desulfurization before LF refining. During the addition of aluminum ingots after the converter steelmaking endpoint, the addition of excessive Al is controlled to meet the basic deep deoxidation requirements. This avoids the excessive generation of high-melting-point Al2O3, ensuring the stability of the high-alumina slag system and its ability to adsorb inclusions. As a result, a corrosion-resistant tube blank with a self-designed composition that meets the performance requirements of X52QS steel grade is obtained.

[0021] It should be noted that the LF refining process described in step (3) of this invention uses aluminum wire to replenish aluminum only once. This means that the aluminum is replenished only once during the entire LF refining process, based on the sample composition taken at the LF refining station. Regardless of how the Al content changes later, the aluminum composition is not adjusted a second time. The aluminum composition is not required when leaving the station. Instead, it is adjusted to the target Al content in the subsequent VD vacuum degassing process.

[0022] It should be noted that in step (1) of the present invention, the S content at the inlet of the KR desulfurization plant is 0.170-0.200 wt%, such as 0.170 wt%, 0.175 wt%, 0.180 wt%, 0.185 wt%, 0.190 wt%, 0.195 wt%, or 0.200 wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0023] It should be noted that in step (3) of the present invention, the aluminum replenishment is carried out according to the target Al content of 0.055-0.070wt%, such as 0.055wt%, 0.058wt%, 0.060wt%, 0.063wt%, 0.065wt%, 0.068wt%, or 0.070wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0024] As a preferred technical solution of the present invention, the high-sulfur semi-steel in step (1) is obtained by vanadium extraction and blowing of vanadium-containing molten iron.

[0025] Preferably, the final temperature of the vanadium extraction blowing is ≥1400℃, thereby increasing the temperature of the semi-molten steel entering the KR desulfurization station, which is more conducive to desulfurization.

[0026] Preferably, the vanadium extraction blowing process includes adding vanadium extraction cold feedstock.

[0027] Preferably, the vanadium extraction cold material includes vertical shaft furnace pellets and iron oxide scale.

[0028] Preferably, the amount of pellets added to the vertical shaft furnace is 5-10 kg / t, such as 5 kg / t, 6 kg / t, 7 kg / t, 8 kg / t, 9 kg / t or 10 kg / t, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable. The amount of iron oxide scale added is 5 kg / t.

[0029] Preferably, the oxygen supply intensity during the vanadium extraction blowing process is 2-2.3 m. 3 / (t·min), for example, 2m 3 / (t·min), 2.05m 3 / (t·min), 2.1m 3 / (t·min), 2.15m 3 / (t·min), 2.2m 3 / (t·min), 2.25m 3 / (t·min) or 2.3m 3 / (t·min), etc., but not limited to the listed values; other unlisted values ​​within the above range also apply.

[0030] Preferably, the oxygen blowing time for vanadium extraction is 5-6 minutes, such as 5 minutes, 5.2 minutes, 5.5 minutes, 5.8 minutes or 6 minutes, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0031] As a preferred technical solution of the present invention, the inlet C content of the KR desulfurization in step (1) is ≥3.5wt%, and the inlet V content is ≤0.08wt%.

[0032] As a preferred technical solution of the present invention, the desulfurizing agent of KR desulfurization in step (1) includes fresh lime powder, fluorite and aluminum granules.

[0033] Preferably, the amount of fresh lime powder added is 1500±50 kg / furnace, the amount of fluorite added is 50-90 kg / furnace, such as 50 kg / furnace, 60 kg / furnace, 70 kg / furnace, 80 kg / furnace or 90 kg / furnace, etc., and the amount of aluminum granules added is 60-70 kg / furnace, such as 60 kg / furnace, 62 kg / furnace, 64 kg / furnace, 65 kg / furnace, 68 kg / furnace or 70 kg / furnace, etc., but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0034] As a preferred technical solution of the present invention, the rotation speed of KR desulfurization in step (1) is 80-100 r / min, such as 80 r / min, 85 r / min, 90 r / min, 95 r / min or 100 r / min, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0035] Preferably, the stirring time for KR desulfurization in step (1) is 12-15 min, such as 12 min, 13 min, 14 min or 15 min, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0036] Preferably, the slag removal rate of the KR desulfurization in step (1) is ≥90%.

[0037] As a preferred technical solution of the present invention, oxygen blowing is carried out in the converter steelmaking process in step (2) to realize converter oxygen blowing steelmaking.

[0038] Preferably, the oxygen blowing time is 10-12 minutes, such as 10 minutes, 10.5 minutes, 11 minutes, 11.5 minutes or 12 minutes, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0039] Preferably, the final temperature of the converter steelmaking in step (2) is 1600-1650℃, such as 1600℃, 1610℃, 1620℃, 1630℃, 1640℃ or 1650℃, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0040] As a preferred technical solution of the present invention, the LF refining in step (3) includes four electrodes;

[0041] Based on the sample composition of the LF refining station, after the first electrode, according to the target Al content of 0.055-0.070wt%, aluminum wire is used for only one aluminum replenishment; moreover, lime is added at 300kg / furnace, fluorite at 0-100kg / furnace, aluminum granules at 30-50kg / furnace, and silicon carbide at 0-10kg / furnace.

[0042] During the second electrode process, lime is added at 100-300 kg / furnace, fluorite at 0-50 kg / furnace, aluminum granules at 10 kg / furnace, and silicon carbide at 0-10 kg / furnace.

[0043] It should be noted that the principles for material addition during LF refining include: controlling the amount of aluminum granules added, and widely scattering silicon carbide to prevent carbon increase. Existing technology generally adds lime and refining slag after converter steelmaking and before LF refining to establish a stable foundation for the high-alumina slag system. However, this invention has found that adding only 1000±30 kg / furnace of refining slag after converter steelmaking and before LF refining, without adding lime, can prevent instability caused by lime addition and maintain the stability of the high-alumina slag system. Furthermore... In the first electrode of LF refining, a fixed amount of lime is added at 300 kg / furnace. In the second electrode, lime is added at 100-300 kg / furnace. This is to avoid the total amount of lime added in the two electrodes exceeding the upper limit of 600 kg / furnace. If the composition test of the third or even fourth electrode shows that the sulfur content is still high and lime needs to be added again, the extra amount of lime added exceeding the upper limit of 600 kg / furnace needs to be increased by adding 200 kg / furnace of refining slag for every 100 kg / furnace of lime. Lime and refining slag are added at the same time to ensure the stability of the high-alumina slag system.

[0044] As a preferred technical solution of the present invention, the high-alumina slag system in step (3) comprises, by mass percentage: CaO 42-46wt%, SiO2 5.5-6.5wt%, Al2O3 33-34wt%, S content ≤2.0wt%, and alkalinity R guaranteed to be 7-8.

[0045] As a preferred technical solution of the present invention, the vacuum holding time of the VD vacuum degassing in step (4) is ≥12min.

[0046] Preferably, the soft blowing time of VD vacuum degassing in step (4) is ≥25 min.

[0047] Preferably, after the vacuum degassing in step (4) is broken, calcium modification treatment is performed according to the detected Al composition to control the calcium-aluminum ratio ≥1, so as to ensure stable casting of the round billet in step (5). Moreover, by controlling the amount of calcium treatment, the high melting point Al2O3 inclusions are modified and easily floated.

[0048] As a preferred technical solution of the present invention, the method includes the following steps:

[0049] (1) KR desulfurization;

[0050] Vanadium-containing molten iron is subjected to vanadium extraction and blowing to obtain high-sulfur semi-steel; the final temperature of the vanadium extraction and blowing is controlled to be ≥1400℃, and the vanadium extraction and blowing includes the addition of vanadium extraction cold materials; the vanadium extraction cold materials include vertical shaft furnace pellets and iron oxide scale; the amount of vertical shaft furnace pellets added is 5-10 kg / t, and the amount of iron oxide scale added is 5 kg / t; the oxygen supply intensity of the vanadium extraction and blowing is 2-2.3 m. 3 / (t·min); The oxygen blowing time for vanadium extraction is 5-6 min;

[0051] The high-sulfur semi-steel is subjected to KR desulfurization. The sulfur content at the inlet of the KR desulfurization plant is controlled to be 0.170-0.200 wt%, the carbon content at the inlet is ≥3.5 wt%, and the v content at the inlet is ≤0.08 wt%. The desulfurizing agent for the KR desulfurization includes fresh lime powder, fluorite, and aluminum granules. The amount of fresh lime powder added is 1500±50 kg / furnace, the amount of fluorite added is 50-90 kg / furnace, and the amount of aluminum granules added is 60-70 kg / furnace. The rotation speed of the KR desulfurization is 80-100 r / min, the stirring time is 12-15 min, and the slag removal rate is ≥90%. The sulfur content at the outlet of the KR desulfurization plant is ≤0.030 wt%.

[0052] (2) Converter steelmaking;

[0053] Oxygen blowing is carried out in the converter steelmaking process to achieve converter oxygen blowing steelmaking; the oxygen blowing time is 10-12 minutes; the final temperature of the converter steelmaking process is 1600-1650℃.

[0054] After the converter steelmaking process is completed, aluminum ingots are added as a deep deoxidizer, and the amount of aluminum ingots added is determined according to the carbon content at the converter endpoint; specifically: if the carbon content at the converter endpoint is <0.06wt%, the amount of aluminum ingots added is 60kg / heat; if the carbon content at the converter endpoint is 0.06-0.10wt%, the amount of aluminum ingots added is 50kg / heat; if the carbon content at the converter endpoint is >0.10wt%, the amount of aluminum ingots added is 40kg / heat.

[0055] After the converter steelmaking is completed, refining slag is added at a rate of 1000±30 kg / furnace;

[0056] (3) LF refining;

[0057] The LF refining process includes four electrodes;

[0058] Based on the sample composition of the LF refining station, after the first electrode, according to the target Al content of 0.055-0.070wt%, aluminum wire is used for only one aluminum replenishment; moreover, lime is added at 300kg / furnace, fluorite at 0-100kg / furnace, aluminum granules at 30-50kg / furnace, and silicon carbide at 0-10kg / furnace.

[0059] During the second electrode process, lime is added at 100-300 kg / furnace, fluorite at 0-50 kg / furnace, aluminum granules at 10 kg / furnace, and silicon carbide at 0-10 kg / furnace.

[0060] The top slag from the LF refining process is a high-alumina slag system; the composition of the high-alumina slag system by mass percentage includes: CaO 42-46wt%, SiO2 5.5-6.5wt%, Al2O3 33-34wt%, S content ≤2.0wt%, and basicity R guaranteed to be 7-8.

[0061] (4) VD vacuum degassing;

[0062] The vacuum holding time of the VD vacuum degassing is ≥12min, and the soft blowing time is ≥25min; after the vacuum is broken, the VD vacuum degassing is subjected to calcium denaturation treatment according to the detected Al composition, and the calcium-aluminum ratio is controlled to be ≥1.

[0063] (5) Continuous casting of round billets;

[0064] After the continuous casting of the round billet is completed, an X52QS grade corrosion-resistant tube blank is obtained, whose composition by mass percentage includes: C 0.12-0.16wt%, Si 0.30-0.45wt%, Mn 1.15-1.30wt%, P≤0.020wt%, S≤0.003wt%, Alt 0.020-0.040wt%, V 0.04-0.06wt%.

[0065] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0066] The method described in this invention achieves effective desulfurization before LF refining. During the addition of aluminum ingots after the converter steelmaking endpoint, the addition of excessive Al is controlled to meet the basic deep deoxidation requirements. This avoids the excessive generation of high-melting-point Al2O3, ensuring the stability of the high-alumina slag system and its ability to adsorb inclusions. As a result, a corrosion-resistant tube blank with a self-designed composition that meets the performance requirements of X52QS steel grade is obtained. Detailed Implementation

[0067] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0068] Example 1

[0069] This embodiment provides a method for producing X52QS grade corrosion-resistant tube blanks from high-sulfur semi-steel, the method comprising the following steps:

[0070] (1) KR desulfurization;

[0071] Vanadium-containing molten iron is subjected to vanadium extraction and blowing to obtain high-sulfur semi-steel; the final temperature of the vanadium extraction and blowing is controlled to be ≥1400℃, and the vanadium extraction and blowing includes the addition of vanadium extraction cold materials; the vanadium extraction cold materials include vertical shaft furnace pellets and iron oxide scale; the amount of vertical shaft furnace pellets added is 8 kg / t, and the amount of iron oxide scale added is 5 kg / t; the oxygen supply intensity of the vanadium extraction and blowing is 2.3 m. 3 / (t·min); The oxygen blowing time for the vanadium extraction is 5 min;

[0072] The high-sulfur semi-steel was subjected to KR desulfurization. Testing revealed that the influent sulfur content (S) was 0.186 wt%, carbon content (C) was 3.72 wt%, and v content (V) was 0.063 wt%. The desulfurizing agent consisted of fresh lime powder, fluorite, and aluminum granules. The actual addition amount of fresh lime powder was 1523 kg / furnace, fluorite was 80 kg / furnace, and aluminum granules was 70 kg / furnace. The KR desulfurization speed was 90 r / min, the stirring time was 15 min, and the slag removal rate was 93%. The outfluent sulfur content (S) was 0.027 wt% after KR desulfurization.

[0073] (2) Converter steelmaking;

[0074] Oxygen blowing is carried out in the converter steelmaking process to achieve converter oxygen blowing steelmaking; the oxygen blowing time is 12 minutes; the final temperature of the converter steelmaking process is 1607℃.

[0075] After the converter steelmaking is completed, aluminum ingots are added as a deep deoxidizer, and the amount of aluminum ingots added is determined according to the C content at the converter endpoint; in this embodiment, the C content at the converter endpoint is found to be in the range of 0.06-0.10wt%, and the amount of aluminum ingots added is 50kg / furnace.

[0076] After the converter steelmaking is completed, refining slag is actually added at a rate of 994 kg / furnace.

[0077] (3) LF refining;

[0078] The LF refining process includes four electrodes;

[0079] Based on the sample composition of the LF refining station, after the first electrode, according to the target Al content of 0.055-0.070wt%, aluminum wire is used for only one aluminum replenishment; moreover, lime is added at 300kg / furnace, fluorite at 30kg / furnace, and aluminum granules at 30kg / furnace.

[0080] During the second electrode process, lime is added at 100 kg / furnace, fluorite at 10 kg / furnace, and aluminum granules at 10 kg / furnace.

[0081] The top slag from the LF refining process is a high-alumina slag system; the composition of the high-alumina slag system, by mass percentage, includes: CaO 45.13wt%, SiO2 6.19wt%, Al2O3 33.03wt%, S content 1.20wt%, and basicity R of 7.291;

[0082] (4) VD vacuum degassing;

[0083] The vacuum holding time for the VD vacuum degassing is 15 min, and the soft blowing time is 27 min. After the vacuum is broken, the VD vacuum degassing is subjected to calcium denaturation treatment based on the detected Al composition, with a calcium-to-aluminum ratio of 2.3.

[0084] (5) Continuous casting of round billets;

[0085] After the round billet is continuously cast, an X52QS grade corrosion-resistant tube blank is obtained. The composition, by mass percentage, includes: C 0.14wt%, Si 0.35wt%, Mn 1.21wt%, P 0.012wt%, S 0.001wt%, Alt 0.025wt%, and V 0.051wt%.

[0086] Example 2

[0087] This embodiment provides a method for producing X52QS grade corrosion-resistant tube blanks from high-sulfur semi-steel. The differences compared to Embodiment 1 are summarized in Table 1, and the relevant test results are also summarized in Table 1.

[0088] Comparative Example 1

[0089] This comparative example provides a method for producing tube blanks from high-sulfur semi-steel. Compared with Example 1, the biggest difference is that the S content at the KR desulfurization station in step (1) is relatively high, and only 987 kg of fresh lime powder, about 1 ton, is added at a rotation speed of 80 r / min, resulting in poor KR desulfurization effect and high S content at the KR station. Other differences are summarized in Table 1, and the relevant test results are also summarized in Table 1.

[0090] The method described in this comparative example, after sequentially completing KR desulfurization and converter steelmaking, encountered difficulties during the LF refining process. Because the first electrode added lime at 300 kg / heat, the desulfurization requirement could not be met, the second electrode added lime at 400 kg / heat, along with 200 kg / heat of refining slag. This combination was used to stabilize the slag system. Furthermore, the third electrode still required adding 100 kg / heat of lime and 100 kg / heat of refining slag. It is evident that if the KR desulfurization effect is poor, resulting in a high sulfur content at the KR station, a large amount of lime needs to be added for desulfurization during the LF refining process. Simultaneously, the lack of clear guidance on adding refining slag to stabilize the slag system led to a serious deviation in the LF refining slag system, even when the sulfur content met internal control requirements. This resulted in a weakened adsorption capacity for inclusions, leading to excessive inclusions in this heat, rendering further operations unnecessary. For Comparative Example 1, it is required to limit the sulfur content at the KR station to reduce the desulfurization pressure of subsequent LF refining, while avoiding excessive material addition. In addition, it is clearly stated that if the lime content exceeds the upper limit of the specification, 200 kg of refining slag per furnace should be added for every 100 kg of lime added per furnace. Both lime and refining slag should be added at the same time to ensure the stability of the high-alumina slag system.

[0091] Comparative Example 2

[0092] This comparative example provides a method for producing tube billets from high-sulfur semi-steel. Compared with Example 1, the biggest difference lies in aluminum control. With perfect control of the sulfur content at the KR desulfurization station, there is no overblowing of carbon at the converter endpoint. The carbon content at the converter endpoint is 0.06 wt%, but 80 kg / furnace of aluminum ingots are added in order to provide a good deep deoxidation environment for the subsequent LF refining and further improve desulfurization. Other differences are summarized in Table 1, and the relevant test results are also summarized in Table 1.

[0093] In the method described in this comparative example, after aluminum replenishment during the first electrode stage in the LF refining process, a second aluminum replenishment is performed during the second electrode stage, considering the high Al content required for this steel grade and the severe aluminum loss. The aluminum replenishment wire is 100 meters long. In actual control, 7 minutes after continuous casting begins, the stopper opening rapidly increases, the second flow stagnates, and the accumulated material at the end of the stopper is aluminum oxide, making it impossible to obtain a finished round billet. For Comparative Example 2, the main consideration is the excessive addition of aluminum. After converter steelmaking is completed, aluminum ingots are added as a deep deoxidizer. To meet the deep deoxidation requirements, with a C content of 0.06-0.10 wt% at the converter endpoint, an aluminum ingot addition of 50 kg / heat is sufficient. LF refining does not consider compositional requirements; only basic desulfurization and deoxidation requirements need to be met. That is, during the first electrode stage, with a target Al content of 0.055-0.070 wt%, only one aluminum replenishment using aluminum wire is required.

[0094] Table 1

[0095]

[0096]

[0097]

[0098]

[0099] Note: " / " in the table indicates that no relevant operation was performed; "√" in the table indicates that the corresponding operation was performed.

[0100] In summary, the method described in this invention achieves effective desulfurization before LF refining. During the addition of aluminum ingots after the converter steelmaking endpoint, the addition of excessive Al is controlled to meet the basic deep deoxidation requirements, thus avoiding the excessive generation of high-melting-point Al2O3. This ensures the stability of the high-alumina slag system and its ability to adsorb inclusions, thereby obtaining a corrosion-resistant tube blank with a self-designed composition that meets the performance requirements of X52QS steel grade.

[0101] This invention illustrates the detailed process equipment and process flow through the above embodiments. However, this invention is not limited to the detailed process equipment and process flow described above, meaning that this invention does not necessarily depend on the detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the product of this invention, addition of auxiliary components, and selection of specific methods, all fall within the protection scope and disclosure scope of this invention.

Claims

1. A method for producing X52QS grade corrosion-resistant tube blanks from high-sulfur semi-steel, characterized in that, The method includes the following steps: (1) KR desulfurization; High-sulfur semi-steel is subjected to KR desulfurization, wherein the sulfur content at the inlet of the KR desulfurization plant is 0.170-0.200 wt%, and the sulfur content at the outlet of the KR desulfurization plant is ≤0.030 wt%; the carbon content at the inlet of the KR desulfurization plant is ≥3.5 wt%, and the v content at the inlet is ≤0.08 wt%. (2) Converter steelmaking; After the converter steelmaking process is completed, aluminum ingots are added as a deep deoxidizer, and the amount of aluminum ingots added is determined according to the carbon content at the converter endpoint; specifically: if the carbon content at the converter endpoint is <0.06wt%, the amount of aluminum ingots added is 60kg / heat; if the carbon content at the converter endpoint is 0.06-0.10wt%, the amount of aluminum ingots added is 50kg / heat; if the carbon content at the converter endpoint is >0.10wt%, the amount of aluminum ingots added is 40kg / heat. After the converter steelmaking is completed, refining slag is added at a rate of 1000±30 kg / furnace; (3) LF refining; The LF refining process includes: based on the sample composition of the LF refining process, after the first electrode, using aluminum wire to perform only one aluminum replenishment according to the target Al content of 0.055-0.070wt%; The LF refining process includes the addition of aluminum granules and lime to ensure that the top slag from the LF refining process is a high-alumina slag system. The composition of the high-alumina slag system, by mass percentage, includes: CaO 42-46wt%, SiO2 5.5-6.5wt%, Al2O3 33-34wt%, S content ≤2.0wt%, and basicity R guaranteed to be 7-8. (4) VD vacuum degassing; (5) Continuous casting of round billets; After the continuous casting of the round billet is completed, X52QS grade corrosion-resistant tube blank is obtained, whose composition by mass percentage includes: C 0.12-0.16wt%, Si 0.30-0.45wt%, Mn 1.15-1.30wt%, P≤0.020wt%, S≤0.003wt%, Alt 0.020-0.040wt%, V 0.04-0.06wt%.

2. The method according to claim 1, characterized in that, The high-sulfur semi-steel in step (1) is obtained by vanadium extraction and blowing of vanadium-containing molten iron; The final temperature of the vanadium extraction and blowing process is ≥1400℃; The vanadium extraction and blowing process includes adding vanadium extraction cold feedstock; The vanadium extraction cold material includes vertical furnace pellets and iron oxide scale; The amount of pellets added to the vertical shaft furnace is 5-10 kg / t, and the amount of iron oxide scale added is 5 kg / t; The oxygen supply intensity for the vanadium extraction blowing process is 2-2.3 m. 3 / (t‧min); The oxygen blowing time for vanadium extraction is 5-6 minutes.

3. The method according to claim 1, characterized in that, The desulfurizing agent for KR desulfurization in step (1) includes fresh lime powder, fluorite and aluminum granules; The amount of fresh lime powder added is 1500±50 kg / furnace, the amount of fluorite added is 50-90 kg / furnace, and the amount of aluminum granules added is 60-70 kg / furnace.

4. The method according to claim 1, characterized in that, The rotation speed of the KR desulfurization in step (1) is 80-100 r / min; The stirring time for KR desulfurization in step (1) is 12-15 min; The slag removal rate of KR desulfurization in step (1) is ≥90%.

5. The method according to claim 1, characterized in that, Oxygen blowing is carried out in the converter steelmaking process described in step (2) to achieve converter oxygen blowing steelmaking; The oxygen blowing time is 10-12 minutes; The final temperature of the converter steelmaking in step (2) is 1600-1650℃.

6. The method according to claim 1, characterized in that, Step (3) of the LF refining process includes four electrodes; Based on the sample composition of the LF refining station, after the first electrode, according to the target Al content of 0.055-0.070wt%, aluminum wire is used for only one aluminum replenishment; moreover, lime is added at 300kg / furnace, fluorite at 0-100kg / furnace, aluminum granules at 30-50kg / furnace, and silicon carbide at 0-10kg / furnace. During the second electrode process, lime is added at 100-300 kg / furnace, fluorite at 0-50 kg / furnace, aluminum granules at 10 kg / furnace, and silicon carbide at 0-10 kg / furnace.

7. The method according to claim 1, characterized in that, The vacuum holding time for VD vacuum degassing in step (4) is ≥12 min; The soft blowing time for VD vacuum degassing in step (4) is ≥25 min; After the vacuum degassing in step (4) is broken, calcium denaturation treatment is carried out according to the detected Al composition to control the calcium-aluminum ratio ≥1.

8. The method according to claim 1, characterized in that, The method includes the following steps: (1) KR desulfurization; Vanadium-containing molten iron is subjected to vanadium extraction and blowing to obtain high-sulfur semi-steel; the final temperature of the vanadium extraction and blowing is controlled to be ≥1400℃, and the vanadium extraction and blowing includes the addition of vanadium extraction cold materials; the vanadium extraction cold materials include vertical shaft furnace pellets and iron oxide scale; the amount of vertical shaft furnace pellets added is 5-10 kg / t, and the amount of iron oxide scale added is 5 kg / t; the oxygen supply intensity of the vanadium extraction and blowing is 2-2.3 m. 3 / (t‧min); The oxygen blowing time for the vanadium extraction is 5-6 min; The high-sulfur semi-steel is subjected to KR desulfurization, with the sulfur content at the inlet controlled at 0.170-0.200 wt%, carbon content ≥3.5 wt%, and v content ≤0.08 wt%. The desulfurizing agent for KR desulfurization includes fresh lime powder, fluorite, and aluminum granules. The amount of fresh lime powder added is 1500±50 kg / furnace, the amount of fluorite added is 50-90 kg / furnace, and the amount of aluminum granules added is 60-70 kg / furnace. The rotation speed of KR desulfurization is 80-100 r / min, the stirring time is 12-15 min, and the slag removal rate is ≥90%. The sulfur content at the outlet of KR desulfurization is ≤0.030 wt%. (2) Converter steelmaking; Oxygen blowing is carried out in the converter steelmaking process to achieve converter oxygen blowing steelmaking; the oxygen blowing time is 10-12 minutes; the final temperature of the converter steelmaking process is 1600-1650℃; After the converter steelmaking process is completed, aluminum ingots are added as a deep deoxidizer, and the amount of aluminum ingots added is determined according to the carbon content at the converter endpoint; specifically: if the carbon content at the converter endpoint is <0.06wt%, the amount of aluminum ingots added is 60kg / heat; if the carbon content at the converter endpoint is 0.06-0.10wt%, the amount of aluminum ingots added is 50kg / heat; if the carbon content at the converter endpoint is >0.10wt%, the amount of aluminum ingots added is 40kg / heat. After the converter steelmaking is completed, refining slag is added at a rate of 1000±30 kg / furnace; (3) LF refining; The LF refining process includes four electrodes; Based on the sample composition of the LF refining station, after the first electrode, according to the target Al content of 0.055-0.070wt%, aluminum wire is used for only one aluminum replenishment; moreover, lime is added at 300kg / furnace, fluorite at 0-100kg / furnace, aluminum granules at 30-50kg / furnace, and silicon carbide at 0-10kg / furnace. During the second electrode process, lime is added at 100-300 kg / furnace, fluorite at 0-50 kg / furnace, aluminum granules at 10 kg / furnace, and silicon carbide at 0-10 kg / furnace. The top slag from the LF refining process is a high-alumina slag system; the composition of the high-alumina slag system by mass percentage includes: CaO 42-46wt%, SiO2 5.5-6.5wt%, Al2O3 33-34wt%, S content ≤2.0wt%, and basicity R guaranteed to be 7-8; (4) VD vacuum degassing; The vacuum holding time of the VD vacuum degassing is ≥12min, and the soft blowing time is ≥25min; after the vacuum is broken, the VD vacuum degassing is subjected to calcium denaturation treatment based on the detected Al composition, and the calcium-aluminum ratio is controlled to be ≥1. (5) Continuous casting of round billets; After the continuous casting of the round billet is completed, X52QS grade corrosion-resistant tube blank is obtained, whose composition by mass percentage includes: C 0.12-0.16wt%, Si 0.30-0.45wt%, Mn 1.15-1.30wt%, P≤0.020wt%, S≤0.003wt%, Alt 0.020-0.040wt%, V 0.04-0.06wt%.

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