A method for smelting an L245MH hydrogen transport pipeline steel

Abstract

The application provides a smelting method of L245MH hydrogen conveying pipeline steel, and belongs to the field of steelmaking. The method comprises the following steps: performing KR pretreatment on molten iron, then performing twice deslagging treatment to obtain desulfurized molten iron; performing double-slag converter smelting on the desulfurized molten iron to obtain first molten steel; performing converter tapping on the first molten steel, and adding premelted slag into the molten steel to perform slag washing desulfurization treatment, thereby obtaining second molten steel; adding Al-Fe deoxidizer to the slag surface of the second molten steel, and controlling the ladle slag layer thickness of the second molten steel, thereby obtaining third molten steel; performing LF deep desulfurization refining on the third molten steel to obtain fourth molten steel; performing RH refining on the fourth molten steel, and controlling the circulating time after the last batch of materials is added, thereby obtaining fifth molten steel with a set Mn / Si mass ratio; using high-alkalinity tundish covering agent to cast the fifth molten steel, thereby obtaining a casting billet for L245MH hydrogen conveying pipeline steel. The content of S, P elements and inclusions in the steel is controlled.

Description

Technical Field

[0001] This application relates to the field of steelmaking technology, and more particularly to a method for smelting L245MH hydrogen pipeline steel. Background Technology

[0002] Driven by my country's "dual-carbon" strategic goals, long-distance hydrogen transportation is a future development trend. Pipeline transportation, as an economically viable mode of transport, will play a crucial role in accelerating the allocation and market coverage of hydrogen resources and promoting the optimization of the energy structure. Accelerating the construction of hydrogen pipelines is a key measure for my country to speed up the development of the hydrogen energy industry.

[0003] However, my country's high-pressure hydrogen pipelines have not yet achieved large-scale engineering application, primarily due to hydrogen embrittlement damage in the pipeline materials (i.e., high-pressure hydrogen pipeline steel). Hydrogen embrittlement is a phenomenon where metallic materials absorb hydrogen atoms, leading to a decrease in ductility and toughness, resulting in brittle fracture. Small hydrogen atoms can easily penetrate into metallic materials, accumulating at defects and reducing the stress required for crack initiation and propagation, thus causing material embrittlement. Studies have shown that sulfur (S) is the main element affecting the hydrogen embrittlement resistance of pipeline steel. When the S content in steel is >0.005%, the hydrogen embrittlement sensitivity increases significantly with increasing S content, particularly affecting the performance of high-pressure hydrogen pipeline steel. Furthermore, phosphorus (P) and non-metallic inclusions in the steel also significantly affect the performance of pipeline steel. Specifically, P segregation deteriorates the weldability of the steel and reduces its low-temperature impact toughness, while inclusions easily induce microcracks, increasing the steel's hydrogen embrittlement sensitivity. Summary of the Invention

[0004] This application provides a smelting method for L245MH hydrogen pipeline steel to solve the following technical problem: how to control the content of S, P elements and inclusions in the steel.

[0005] This application provides a method for smelting L245MH hydrogen pipeline steel, the method comprising: Molten iron with a set chemical composition and a set temperature is subjected to KR pretreatment, followed by two slag removal processes to obtain desulfurized molten iron. The desulfurized molten iron is then subjected to converter double-slag smelting to obtain the first molten steel. The first molten steel is tapped from a converter, and pre-melted slag is added to the molten steel for slag washing and desulfurization treatment to obtain the second molten steel; Al-Fe deoxidizer is added to the slag surface of the second molten steel, and the thickness of the slag layer in the ladle of the second molten steel is controlled to obtain the third molten steel; The third molten steel is subjected to LF deep desulfurization refining to obtain the fourth molten steel; Under a set RH refining station idle time, the fourth molten steel is RH refined, and the cycle time after the last batch of material is added is controlled to obtain a fifth molten steel with a set Mn to Si mass ratio; and The fifth molten steel was cast using a high-alkalinity ladle covering agent to obtain a steel billet for L245MH hydrogen pipeline.

[0006] Optionally, the specified chemical composition includes: a mass fraction of S ≤ 0.05%, a mass fraction of P ≤ 0.09%; and / or, The set temperature is 1350℃~1380℃.

[0007] Optionally, the area of ​​the bright surface after the two slag removal processes is ≥96%.

[0008] Optionally, the pre-melted slag comprises the following chemical components: fine-grained quicklime: 4.5 kg / t steel to 5.5 kg / t steel, fluorite: 0.7 kg / t steel to 1.0 kg / t steel; and / or, The pre-melted slag is added 1 / 5 of the way before the converter taps the steel.

[0009] Optionally, the Al-Fe deoxidizer is added at a rate of 0.4 kg / t steel to 0.7 kg / t steel; and / or, The thickness of the slag layer in the ladle is ≤80mm.

[0010] Optionally, during the tapping process of the converter, strong bottom blowing argon stirring is performed, the strong bottom blowing argon stirring time is ≥3min, and the flow rate of the strong bottom blowing argon stirring is 250NL / min~350NL / min per channel.

[0011] Optionally, the RH refining station idle time is set to < 1.5h; and / or, The cycle time is ≥6 min.

[0012] Optionally, bottom blowing Ar operation may not be performed during the period from when the ladle enters the RH refining station until vacuuming.

[0013] Optionally, the mass ratio of Mn to Si is set to 6~10.

[0014] Optionally, the chemical composition of the cast billet includes: S mass fraction ≤ 0.001%, P mass fraction ≤ 0.010%; The inclusions in the cast billet are of type A and C ≤ grade 1.0, and type B and D ≤ grade 1.5.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a smelting method for L245MH hydrogen pipeline steel. By controlling the [S] content of molten iron, molten iron temperature, slag removal degree after desulfurization, slag washing after tapping, and LF deep desulfurization, the S content in the billet is achieved to be ≤0.001%. By controlling the [P] content of molten iron, converter double-slag smelting, and slag removal after tapping, the P content in the billet is achieved to be ≤0.010%. By controlling Al-Fe deoxidation after tapping, RH refining station vacancy time, and slag removal after ladle, the inclusions in the billet of types A and C are ≤1.0, and types B and D are ≤1.5, meeting the requirements of high-pressure hydrogen transportation, thereby controlling the content of S, P elements and inclusions in the steel. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart illustrating a smelting method for L245MH hydrogen pipeline steel provided in an embodiment of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described examples are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0021] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. "Parts representation" such as parts by weight or parts by mass indicates the proportional relationship between components. In the proportional relationships discussed in this article, parameters that need to be described by proportion should be understood as the first term of the proportion in the order of description, while the proportion figure should be understood as the second term. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substances A, B, and C should correspond one-to-one with the proportion figure in the proportion in the order of description, i.e., the mass of substance A : the mass of substance B : the mass of substance C = 1:2:3.

[0022] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0023] Figure 1 This is a schematic flowchart illustrating a smelting method for L245MH hydrogen pipeline steel provided in an embodiment of this application.

[0024] like Figure 1 As shown, this application provides a method for smelting L245MH hydrogen pipeline steel, the method comprising: S1. Molten iron with a set chemical composition and a set temperature is subjected to KR pretreatment, followed by two slag removal treatments to obtain desulfurized molten iron. In some embodiments, the specified chemical composition includes: a mass fraction of S ≤ 0.05%, a mass fraction of P ≤ 0.09%; and / or, The set temperature is 1350℃~1380℃.

[0025] In some embodiments, the area of ​​the bright surface after the two slag removal processes is ≥96%.

[0026] The [S] and [P] content of molten iron before KR pretreatment is controlled at a low level. The purpose is to control the [S] and [P] content of the molten iron entering the furnace after KR pretreatment to reduce the load on the converter for desulfurization and dephosphorization. The purpose of controlling the molten iron temperature at a high level is to ensure the thermodynamic conditions for desulfurization. After desulfurization, slag is skimmed twice, and the bright surface area is required to reduce the amount of desulfurization slag entering the converter and reduce the load on the converter for desulfurization. For example, the mass fraction of S in the molten iron before KR pretreatment can be 0.02%, 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, etc., and the mass fraction of P can be 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, etc. The temperature of the molten iron before KR pretreatment can be 1350℃, 1355℃, 1360℃, 1365℃, 1370℃, 1375℃, 1380℃, etc., and the area of ​​the bright slag surface after two slag removal treatments can be 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, etc.

[0027] S2. The desulfurized molten iron is subjected to converter double-slag smelting to obtain the first molten steel; It should be noted that converter double-slag smelting refers to a method in which, during the converter steelmaking process, a portion of the slag is poured off midway through blowing, and then new slag-forming material is added for a second slag-forming process. In the initial stage of converter smelting, the molten iron contains high levels of elements such as silicon and phosphorus. These elements react with the added slag-forming material during blowing to form slag. By pouring off some of the initial slag, the amount of slag in the furnace can be reduced, avoiding splashing caused by a large slag volume, and a higher dephosphorization efficiency can be achieved. Subsequently, new slag-forming material is added for a second slag-forming process to further purify the molten steel.

[0028] S3. The first molten steel is tapped from the converter, and pre-melted slag is added to the molten steel for slag washing and desulfurization treatment to obtain the second molten steel; S4. Add Al-Fe deoxidizer to the slag surface of the second molten steel and control the thickness of the slag layer in the ladle of the second molten steel to obtain the third molten steel; In some embodiments, the pre-melted slag comprises the following chemical components: fine-grained quicklime: 4.5 kg / t steel to 5.5 kg / t steel, fluorite: 0.7 kg / t steel to 1.0 kg / t steel; and / or, The pre-melted slag is added 1 / 5 of the way before the converter taps the steel.

[0029] In some embodiments, the Al-Fe deoxidizer is added at a rate of 0.4 kg / t steel to 0.7 kg / t steel; and / or, The thickness of the slag layer in the ladle is ≤80mm.

[0030] In some embodiments, during the tapping process of the converter, strong bottom blowing argon stirring is performed, the strong bottom blowing argon stirring time is ≥3 min, and the flow rate of the strong bottom blowing argon stirring is 250 NL / min to 350 NL / min per channel.

[0031] In this embodiment, achieving extremely low sulfur control cannot be fully guaranteed by relying solely on KR pretreatment and LF refining. Fine-grained quicklime is used for slag washing desulfurization during the steel tapping process. Simultaneously, to accelerate the melting of the desulfurizing agent and improve desulfurization efficiency, an appropriate amount of fluorite is added. From a kinetic perspective, increasing the flow of molten steel is beneficial for the rapid desulfurization reaction. The impact of the steel flow during tapping provides better kinetic conditions. Therefore, fine-grained quicklime and fluorite are added with the steel flow in the early stages of tapping, completing the addition before tapping 1 / 5 of the way through, ensuring the subsequent steel flow agitates the slag. Simultaneously, strong bottom-blowing argon stirring is performed during tapping to further improve reaction kinetic conditions. For example, the amount of fine-grained quicklime added can be 4.5 kg / t steel, 4.7 kg / t steel, 4.9 kg / t steel, 5.1 kg / t steel, 5.2 kg / t steel, 5.4 kg / t steel, 5.5 kg / t steel, etc., and the amount of fluorite added can be 0.7 kg / t steel, 0.8 kg / t steel, 0.9 kg / t steel, 1.0 kg / t steel, etc.

[0032] S5. The third molten steel is subjected to LF deep desulfurization refining to obtain the fourth molten steel; S6. Under the set RH refining station idle time, the fourth molten steel is RH refined, and the cycle time after the last batch of material is added is controlled to obtain a fifth molten steel with a set Mn to Si mass ratio; and In some embodiments, the RH refining station idle time is set to < 1.5 h; and / or, The cycle time is ≥6 min.

[0033] In some implementations, bottom blowing Ar operation is not performed during the period from when the ladle enters the RH refining station until vacuuming.

[0034] The purpose of controlling the idle time of the RH refining station is to avoid the impact of oxidizing cold steel in the vacuum chamber on the cleanliness of the molten steel. The purpose of prohibiting bottom blowing Ar operation during the period from when the ladle enters the RH refining station until vacuuming is applied is to prevent secondary oxidation of the molten steel. The purpose of controlling the circulation time after the last batch of material is added is to ensure sufficient flotation of inclusions. For example, the idle time of the RH refining station can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1.1h, 1.2h, 1.4h, 1.45h, etc. The circulation time can be 6min, 6.5min, 7min, 7.5min, 8min, etc.

[0035] In some embodiments, the set mass ratio of Mn to Si is 6 to 10.

[0036] Controlling the mass ratio of Mn to Si in molten steel can control the inclusion crack index, while also improving the fluidity of the molten steel and promoting the flotation of inclusions. For example, the mass ratio of Mn to Si in molten steel can be 6, 6.5, 7, 8, 9, 10, etc.

[0037] S7. Using a high-alkalinity ladle covering agent, the fifth molten steel is cast to obtain a steel billet for L245MH hydrogen pipeline.

[0038] It should be noted that high-alkalinity coating agents are chemical substances used in high-alkalinity media, mainly composed of highly alkaline substances (such as potassium oxide, sodium oxide, and other alkaline compounds) and surfactants. These components can induce a highly alkaline reaction on the surface of the coating, creating a highly alkaline environment.

[0039] In this embodiment, the use of a high-basicity ladle covering agent can reduce the secondary oxidation of the molten steel by the covering agent, while improving the covering agent's ability to adsorb inclusions.

[0040] In some implementations, the amount of steel left in the ladle after casting is controlled at 10t to 15t.

[0041] In some embodiments, the chemical composition of the cast billet includes: a mass fraction of S ≤ 0.001% and a mass fraction of P ≤ 0.010%; The inclusions in the cast billet are of type A and C ≤ grade 1.0, and type B and D ≤ grade 1.5.

[0042] This application provides a method for smelting steel for hydrogen pipelines. By controlling the [S] content of molten iron, molten iron temperature, slag removal degree after desulfurization, slag washing after tapping, and deep desulfurization in LF, the S content in the billet is achieved to be ≤0.001%. By controlling the [P] content of molten iron, converter double-slag smelting, and slag removal after tapping, the P content in the billet is achieved to be ≤0.010%. By controlling Al-Fe deoxidation after tapping, RH refining station vacancy time, and slag removal from the ladle, the inclusions in the billet of types A and C are ≤1.0, and types B and D are ≤1.5, meeting the requirements for high-pressure hydrogen transportation.

[0043] In summary, the smelting method for L245MH hydrogen pipeline steel provided in this application has the following significant advantages: (1) High-efficiency desulfurization and dephosphorization: By combining KR pretreatment and converter double slag smelting, the sulfur (S) and phosphorus (P) content in the molten iron is effectively reduced, ensuring that the molten iron entering the converter has a low S and P content, thereby reducing the desulfurization and dephosphorization burden on the converter. At the same time, pre-melted slag is added during the converter tapping process for slag washing desulfurization treatment, which further reduces the sulfur content in the molten steel and achieves extremely low sulfur control.

[0044] (2) Optimization of the smelting process: The two slag removal processes reduce the amount of desulfurization slag entering the converter, lower the desulfurization load of the converter, and at the same time ensure the fluidity of the slag, which is conducive to the stable operation of the smelting process. Meanwhile, the converter double slag smelting reduces the amount of slag in the furnace by pouring out part of the initial slag, avoids splashing caused by a large amount of slag, and improves the safety and efficiency of smelting.

[0045] (3) Improving the quality and purity of molten steel: In the LF deep desulfurization refining process, the molten steel was further purified by precisely controlling the smelting parameters and adding an appropriate amount of slag-forming material, thereby improving the purity and quality of the molten steel. At the same time, in the RH refining process, secondary oxidation of the molten steel was avoided by controlling the idle time and circulation time of the refining station and prohibiting bottom blowing Ar operation, thus ensuring the full flotation and removal of inclusions.

[0046] (4) Controlling inclusion formation and morphology: By controlling the amount of Al-Fe deoxidizer added and the thickness of the ladle slag layer, the formation of inclusions in the molten steel was effectively reduced, and the morphology and distribution of inclusions were improved. At the same time, by controlling the mass ratio of Mn to Si in the molten steel, the inclusion crack index was controlled, and the fluidity of the molten steel was improved, which promoted the flotation and removal of inclusions.

[0047] (5) Improved billet quality: The use of a high-basicity tundish covering agent reduced the secondary oxidation of the molten steel by the covering agent and improved the ability of the covering agent to adsorb inclusions, thereby improving the quality of the billet. The final billet chemical composition met the requirements of L245MH hydrogen pipeline steel, with a low level of inclusions, meeting the stringent conditions of high-pressure hydrogen transportation.

[0048] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0049] The following examples and comparative examples all use a 210-ton top and bottom blown converter, LF furnace, and RH furnace for smelting, and a slab continuous casting machine for casting.

[0050] Example 1 This embodiment provides a smelting method for L245MH hydrogen pipeline steel. The smelting process is as follows: KR pretreatment—converter double-slag smelting—slag washing—LF deep desulfurization refining—RH refining—slab continuous casting. Before KR pretreatment, the [S] content of the molten iron was controlled at 0.04%, the [P] content at 0.08%, and the molten iron temperature at 1350℃; after KR pretreatment, two slag removal processes were performed, and the bright surface area of ​​the slag removal area was controlled at 96%. During the tapping of steel from the converter, slag washing and desulfurization are carried out. The amount of fine-grained quicklime added is controlled at 4.5 kg / t steel, and the amount of fluorite added is 0.7 kg / t steel, and the addition is completed before 1 / 5 of the steel is tapped. After the steel is tapped, 0.4 kg / t steel of Al-Fe deoxidizer is added to the slag surface. At the same time, the thickness of the slag layer in the ladle after tapping is controlled at 80 mm. The bottom blowing and strong stirring time is 3 min, and the flow rate is controlled at 250 NL / min for a single channel. The idle time of the RH refining station is controlled to be 1.2h; bottom blowing Ar operation is prohibited during the period from when the ladle enters the RH refining station until vacuuming; the circulation time after the last batch of material is added is controlled to be 6min. A high-basicity ladle covering agent is used during the casting process; the Mn / Si ratio of the molten steel is controlled to be 6; and the amount of steel left in the ladle after casting is controlled to be 10t.

[0051] Example 2 This embodiment provides a smelting method for L245MH hydrogen pipeline steel. The smelting process is as follows: KR pretreatment—converter double-slag smelting—slag washing—LF deep desulfurization refining—RH refining—slab continuous casting. Before KR pretreatment, the molten iron was controlled with [S] content of 0.045%, [P] content of 0.09%, and molten iron temperature of 1360℃; after KR pretreatment, slag was removed twice, and the bright surface area of ​​the slag-removed area was controlled to be 96.5%. During the tapping of steel from the converter, slag washing and desulfurization are carried out. The addition of fine-grained quicklime is controlled at 5 kg / t steel, and the addition of fluorite is controlled at 0.85 kg / t steel, and the addition is completed before 1 / 5 of the steel is tapped. After the steel is tapped, 0.55 kg / t steel of Al-Fe deoxidizer is added to the slag surface. At the same time, the thickness of the slag layer in the ladle after tapping is controlled at 75 mm. The bottom blowing and strong stirring time is 4 min, and the flow rate is controlled at 300 NL / min for a single channel. Control the idle time of the RH refining station to 1 hour; prohibit bottom blowing Ar operation during the period from when the ladle enters the RH refining station until vacuuming; control the circulation time after the last batch of material is added to 7 minutes; A high-basicity ladle covering agent is used during the casting process; the Mn / Si ratio of the molten steel is controlled to be 8; and the amount of steel left in the ladle after casting is controlled to be 12t.

[0052] Example 3 This embodiment provides a smelting method for L245MH hydrogen pipeline steel. The smelting process is as follows: KR pretreatment—converter double-slag smelting—slag washing—LF deep desulfurization refining—RH refining—slab continuous casting. Before KR pretreatment, the [S] content of the molten iron was controlled at 0.05%, the [P] content at 0.085%, and the temperature at 1380℃. After KR pretreatment, two slag removal processes were performed, controlling the bright surface area to be 97%. During the tapping of steel from the converter, slag washing and desulfurization are carried out. The addition of fine-grained quicklime is controlled at 5.5 kg / t steel, and the addition of fluorite is controlled at 1.0 kg / t steel, and the addition is completed before 1 / 5 of the steel is tapped. After the steel is tapped, 0.7 kg / t steel of Al-Fe deoxidizer is added to the slag surface. At the same time, the thickness of the slag layer in the ladle after tapping is controlled at 70 mm. The bottom blowing and strong stirring time is 3.5 min, and the flow rate is controlled at 350 NL / min for a single channel. Control the idle time of the RH refining station to 0.5h; prohibit bottom blowing Ar operation during the period from when the ladle enters the RH refining station until vacuuming; control the circulation time after the last batch of material is added to 7.5min; A high-basicity ladle covering agent is used during the casting process; the Mn / Si ratio of the molten steel is controlled to be 10; and the amount of steel left in the ladle after casting is controlled to be 15t.

[0053] Comparative Example 1 This embodiment provides a smelting method for L245MH hydrogen pipeline steel. The smelting process is as follows: KR pretreatment—converter double slag smelting—LF deep desulfurization refining—RH refining—slab continuous casting. Before KR pretreatment, the [S] content of the molten iron was controlled at 0.07%, the [P] content at 0.10%, and the molten iron temperature at 1330℃; after KR pretreatment, two slag removal processes were performed, and the bright surface area of ​​the slag removal area was controlled at 93%. The thickness of the slag layer in the ladle after tapping is controlled to be 83 mm. Control the idle time of the RH refining station to 2 hours; control the weak bottom blowing Ar operation during the period from when the ladle enters the RH refining station to before vacuuming; control the circulation time after the last batch of material is added to 5 minutes.

[0054] A high-basicity ladle covering agent is used during the casting process; the Mn / Si ratio of the molten steel is controlled to be 5; and the amount of steel left in the ladle after casting is controlled to be 8t.

[0055] Comparative Example 2 This comparative example provides a smelting method for L245MH hydrogen pipeline steel. The smelting process is as follows: KR pretreatment—converter double-slag smelting—slag washing—LF deep desulfurization refining—RH refining—slab continuous casting. Before KR pretreatment, the [S] content of the molten iron was controlled at 0.06%, the [P] content at 0.11%, and the molten iron temperature at 1340℃; after KR pretreatment, two slag removal processes were performed, and the bright surface area of ​​the slag removal area was controlled at 95%. During the tapping of steel from the converter, slag washing and desulfurization are carried out. The addition of fine-grained quicklime is controlled at 4.0 kg / t steel, and the addition of fluorite is controlled at 0.65 kg / t steel, and the addition is completed after 1 / 2 of the steel has been tapped. The addition of Al-Fe deoxidizer to the slag surface after tapping is controlled at 0.38 kg / t steel. At the same time, the thickness of the slag layer in the ladle after tapping is controlled at 85 mm, the bottom blowing and strong stirring time is 2.5 min, and the flow rate is controlled at 220 NL / min for a single channel. Control the RH refining station idle time to 2.0h; prohibit bottom blowing Ar operation during the period from when the ladle enters the RH refining station until vacuuming; control the circulation time after the last batch of material is added to 5.5min.

[0056] A high-basicity ladle covering agent is used during the casting process; the Mn / Si ratio of the molten steel is controlled to be 11; and the amount of steel left in the ladle after casting is controlled to be 9t.

[0057] The smelting qualification rate was characterized by the [S] and [P] content and inclusion rating in the billet. The smelting results of the examples and comparative examples are compared in Table 1.

[0058] Table 1. [S] and [P] content and inclusion rating of the cast slabs in the examples and comparative examples.

[0059] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: In this embodiment, by controlling the [S] content of molten iron, the temperature of molten iron, the degree of slag removal after desulfurization, the slag washing after steel tapping, and LF deep desulfurization, the S content in the billet is ≤0.001%.

[0060] In this embodiment of the application, the P content in the molten iron is ≤0.010% by controlling the P content, the converter double slag smelting, and the slag removal during tapping.

[0061] In this embodiment of the application, by controlling the Al-Fe deoxidation during steel tapping, the RH refining station vacancy time, and the slag discharge from the ladle, the inclusions in the billet of types A and C are ≤1.0, and those of types B and D are ≤1.5.

[0062] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for smelting L245MH hydrogen pipeline steel, the method comprising: Molten iron with a set chemical composition and a set temperature is subjected to KR pretreatment, followed by two slag removal processes to obtain desulfurized molten iron. The desulfurized molten iron is then subjected to converter double-slag smelting to obtain the first molten steel. The first molten steel is tapped from a converter, and pre-melted slag is added to the molten steel for slag washing and desulfurization treatment to obtain the second molten steel; Al-Fe deoxidizer is added to the slag surface of the second molten steel, and the thickness of the slag layer in the ladle of the second molten steel is controlled to obtain the third molten steel; The third molten steel is subjected to LF deep desulfurization refining to obtain the fourth molten steel; Under the set RH refining station idle time, the fourth molten steel is RH refined, and the cycle time after the last batch of material is added is controlled to obtain the fifth molten steel with a set Mn to Si mass ratio. as well as The fifth molten steel was cast using a high-alkalinity ladle covering agent to obtain a steel billet for L245MH hydrogen pipeline.

2. The method according to claim 1, characterized in that, The specified chemical composition includes: S mass fraction ≤ 0.05%, P mass fraction ≤ 0.09%; and / or, The set temperature is 1350℃~1380℃.

3. The method according to claim 1, characterized in that, The area of ​​the bright surface after the two slag removal processes is ≥96%.

4. The method according to claim 1, characterized in that, The pre-melted slag comprises the following chemical components: fine-grained quicklime: 4.5 kg / t steel to 5.5 kg / t steel, fluorite: 0.7 kg / t steel to 1.0 kg / t steel; and / or, The pre-melted slag is added 1 / 5 of the way before the converter taps the steel.

5. The method according to claim 1, characterized in that, The Al-Fe deoxidizer is added at a rate of 0.4 kg / t steel to 0.7 kg / t steel; and / or, The thickness of the slag layer in the ladle is ≤80mm.

6. The method according to claim 1, characterized in that, During the steel tapping process in the converter, strong bottom blowing argon stirring is carried out. The strong bottom blowing argon stirring time is ≥3min, and the flow rate of the strong bottom blowing argon stirring is 250NL / min~350NL / min per channel.

7. The method according to claim 1, characterized in that, The specified RH refining station idle time is <1.5h; and / or, The cycle time is ≥6 min.

8. The method according to claim 1, characterized in that, No bottom blowing Ar operation is performed during the period from when the ladle enters the RH refining station until vacuuming.

9. The method according to claim 1, characterized in that, The set mass ratio of Mn to Si is 6~10.

10. The method according to claim 1, characterized in that, The chemical composition of the billet includes: S mass fraction ≤ 0.001%, P mass fraction ≤ 0.010%; The inclusions in the cast billet are of type A and C ≤ grade 1.0, and type B and D ≤ grade 1.5.

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