Low-cost high-quality steel variety RH straight-up continuous casting process

Abstract

The application discloses a low-cost high-quality variety steel RH straight-up continuous casting process, which adopts the following RH process according to different steel varieties; for ultra-low carbon steel: the free oxygen [O] in the molten steel entering the RH station is less than or equal to 550ppm, the carbon content [C] is equal to 0.025%-0.055%; when the oxygen content [O] is insufficient for RH decarburization, forced decarburization is carried out by blowing oxygen, the oxygen blowing amount / m 3 is less than or equal to 40% of the weight of the molten steel; when the CO content in the flue gas is less than or equal to 2%, the RH decarburization is ended; the free oxygen [O] of the molten steel at the end of the RH decarburization of the ultra-low carbon steel is controlled to be 250-350ppm; after adding aluminum at the end of the RH decarburization, a low vacuum degree of 50-80mbar is adopted until the RH is broken. The process reasonably selects the optimal process method and process parameter window of the RH straight-up continuous casting of the molten steel according to the different steel characteristics and quality requirements of different varieties of steel, and respectively realizes the purposes of decarburization, deoxidation, dehydrogenation and denitrification with the lowest cost, the highest efficiency and the most stable operation; and the technical effects of low cost, high quality and high efficiency of the RH straight-up continuous casting process of different required varieties of steel are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to a molten steel refining method, in particular, a low-cost high-quality steel RH straight-up continuous casting process. BACKGROUND

[0002] The RH refining process is a metallurgical method that relies on the pressure difference between the vacuum chamber and the atmosphere to lift the molten steel in the ladle to the vacuum chamber, and to cause the molten steel to continuously circulate by argon blowing; its main task is to degas, and through molten steel circulation to make non-metallic inclusions float, uniform molten steel composition and temperature, and at the same time through the material adding system to make it have multiple metallurgical functions such as deoxidation, decarburization, desulfurization, dephosphorization, and composition fine tuning. RH vacuum treatment is not only a reliable guarantee for the full play of the efficiency of the converter, but also an important means to provide high-quality molten steel for continuous casting and stabilize continuous casting production. With the development of the metallurgical industry, the requirements for steel quality are becoming higher and higher, and RH has become the most important refining means for the production of high-value-added steel.

[0003] In particular, in recent years, affected by overcapacity, the domestic steel market has become increasingly severe, and the market has increasingly favored high-value-added steel grades. RH refining is crucial for the smelting of high-value-added steel, and the pursuit of a low-cost, high-quality, and high-efficiency RH straight-up continuous casting process for converter molten steel is an important goal for the development of steel enterprises, but how to ensure the cleanliness of the molten steel while selecting a low-cost, high-quality, and high-efficiency process for RH straight-up continuous casting of the converter molten steel according to the different steel characteristics and quality requirements of different steel grades has always been a major technical focus and difficulty for metallurgical technicians. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a low-cost high-quality steel RH straight-up continuous casting process to meet the different steel characteristics and quality requirements.

[0005] To solve the above technical problems, the technical solution adopted by the present application is as follows: according to the different steel grades, the following RH process is adopted:

[0006] Ultra-low carbon steel: the free oxygen [O] in the RH inlet molten steel is ≤550ppm, and the carbon content [C] is 0.025%-0.055%; when the oxygen content [O] is insufficient for RH decarburization, RH oxygen blowing forced decarburization is performed, and the oxygen blowing amount / m 3 ≤40% of the weight of the molten steel; when the CO content in the flue gas is ≤2%, the RH decarburization is completed; the free oxygen [O] of the ultra-low carbon steel at the end of the RH decarburization is controlled to be 250-350ppm; after adding aluminum at the end of the RH decarburization, a low vacuum degree of 50-80mbar is used until the RH is broken;

[0007] Low carbon steel: the free oxygen [O] in the RH inlet molten steel is less than or equal to 400 ppm; if the free oxygen content [O] in the RH inlet molten steel is greater than or equal to 500 ppm, carbon powder is added for pre-deoxidation, and the carbon powder addition amount is calculated according to the following formula (I):

[0008] M 碳粉 =([O] 进站 -(0.8×[C] 进站 +150ppm))×40 / 100kg (Ⅰ)

[0009] In the formula, M 碳粉 is the carbon powder addition amount during pre-deoxidation, kg; [O] 进站 is the oxygen content in the RH inlet molten steel, ppm; [C] 进站 is the carbon content in the RH inlet molten steel, ppm;

[0010] Steel that must be deeply dehydrogenated or deeply denitrified: the RH deep dehydrogenation requires that the [O] in the molten steel is greater than or equal to 100 ppm; the RH deep denitrification requires that the [O] in the molten steel is less than or equal to 200 ppm, and the sulfur content [S] is less than or equal to 60 ppm.

[0011] Further, the ultra-low carbon steel adopts the present treatment process in the RH, and the holding time of the RH vacuum degree less than or equal to 2 mbar is 20±5 minutes.

[0012] Further, the low carbon steel adopts the light treatment process in the RH, and the holding time of the RH vacuum degree of 50-80 mbar is 10±2 minutes.

[0013] Further, the steel that must be deeply dehydrogenated or deeply denitrified, for the furnace that needs to be heated by oxygen blowing in the RH, the mass fraction of Als in the molten steel after the converter is tapped is controlled to be 0.025%-0.045%; aluminum particles are added before the oxygen blowing in the RH to control the w(Als) in the molten steel after the oxygen blowing in the RH to be greater than or equal to 0.03%.

[0014] Further, the steel that must be deeply dehydrogenated or deeply denitrified, the composition and temperature adjustment are started when the RH vacuum degree reaches 100-150 mbar in the early stage.

[0015] The beneficial effects generated by the above technical solutions are that the present application reasonably selects the optimal process method and process parameter window of the RH straight-up continuous casting of the molten steel according to the different steel characteristics and quality requirements of different steel varieties, and respectively realizes the purposes of decarburization, deoxidation, dehydrogenation and denitrification with the lowest cost, the highest efficiency and the most stable operation. The present application realizes the technical effects of low cost, high quality and high efficiency of the RH straight-up continuous casting process of different required steel varieties. DETAILED DESCRIPTION

[0016] The present application will be further described in detail below in combination with specific embodiments.

[0017] The low-cost high-quality steel RH straight-up continuous casting process reasonably designs the process of RH straight-up continuous casting of molten steel according to different steel characteristics and quality requirements of different steel grades, and the process principle and process are as follows:

[0018] 1. The ultra-low carbon steel must be deeply decarburized and deoxidized:

[0019] The ultra-low carbon steel generally refers to carbon steel with a carbon content of 0-0.02wt%, such as ultra-deep drawing IF steel, automobile panel, electrical steel, etc., such as SPHETi-3, SPHETi-36, SPHETi-32, TGW800-4, etc.

[0020] 1.1. Process principle:

[0021] The traditional theory believes that in order to make RH achieve the best decarburization and deoxidation efficiency, the oxygen content and carbon content of the molten steel discharged from the converter are required to be controlled within a certain range, that is, the initial carbon / oxygen ratio [C] / [O] of the molten steel entering the RH station is 0.75 ([C] / [O]=12 / 16=0.75).

[0022] The present application corrects the technical bias of the traditional RH theory, which believes that:

[0023] (1) In order to minimize the number of Al2O3 inclusions in the converter molten steel (minimize endogenous oxide inclusions), the lower the free oxygen and carbon content in the molten steel entering the RH station, the better, since under certain conditions the carbon-oxygen product [C]*[O] of the converter is a relatively fixed value, under the premise of low-oxygen tapping of the converter, the [C] carbon content can be appropriately increased ([C] is too high will prolong the RH decarburization time and affect the RH decarburization efficiency). Generally, the oxygen content [O] is ≤550ppm, and the carbon content [C] is 0.025%-0.055%.

[0024] The lower the free oxygen in the molten steel entering the RH station, the more likely it is to cause insufficient oxygen content [O] for RH decarburization, which can be solved by forced decarburization by RH oxygen blowing, but the oxygen blowing amount / m 3 ≤40% of the weight of the molten steel, otherwise too much oxygen blowing will cause over-oxidation of the molten steel, and more inclusions will be generated.

[0025] Production practice has proven that, compared with natural decarburization processes, the forced oxygen blowing decarburization process of this invention results in lower average [O] content in the steel entering the RH decarburization station and lower average T.Fe content in the slag. Furthermore, the forced decarburization process effectively reduces the [N] content in IF steel. This is related to the more intense carbon-oxygen reaction in the vacuum chamber of the forced decarburization process, leading to more CO bubbles and a larger gas-liquid reaction area. Moreover, the stirring and exothermic effects of forced oxygen blowing decarburization are beneficial for the melting of cold steel in the RH vacuum tank. This improves RH decarburization efficiency, reduces inclusions, significantly increases the number of continuous casting heats, and significantly reduces the cold rolling inclusion correction rate.

[0026] In addition, while ensuring the RH decarburization effect, efforts should be made to increase the carbon content of the molten steel at the end of the converter and reduce the oxygen content of the molten steel to reduce the corrosion of the refractory materials inside the furnace by high oxidation, effectively protect the furnace body and furnace condition, and improve the converter life.

[0027] The above production practices have completely changed the traditional technical prejudice that RH cannot be blew oxygen and that people are "afraid of oxygen", and have greatly improved production efficiency and product quality.

[0028] (2) The RH process of this invention is adopted. The holding time of RH vacuum degree ≤ 2mbar is 20±5 minutes; the free oxygen [O] in the molten steel is controlled to be 300ppm±50ppm when the RH decarburization ends; the CO content in the flue gas is ≤2% when the RH decarburization ends.

[0029] Traditional theory holds that in order to minimize the number of Al2O3 inclusions in the final molten steel, the lower the free oxygen [O] in the molten steel at the end of RH decarburization, the better. At this time, the lower the free oxygen [O], the less Al is consumed for deoxidation, and the fewer Al2O3 inclusions are generated.

[0030] In practice, this invention has shown that the optimal free oxygen [O] in molten steel at the end of RH decarburization is 300ppm ± 50ppm. This is necessary to reduce Al consumption and the amount of Al2O3 inclusions during deoxidation. Furthermore, deep RH decarburization relies on the carbon-oxygen reaction, and a certain amount of excess free oxygen is essential for effective deep RH decarburization. Excessively low free oxygen levels at the end of RH decarburization will inevitably negatively impact the process. This also corrects the traditional misconception that lower free oxygen [O] levels at the end of RH decarburization are always better, significantly improving the decarburization efficiency of RH.

[0031] (3) Traditional RH theory holds that the higher the vacuum level during RH decarbonization and deoxygenation, the better.

[0032] In practice, this invention has shown that after adding aluminum at the end of RH decarburization, using a low vacuum of 50-80 mbar is more effective in removing inclusions no larger than 20 μm.

[0033] The principle is that the RH internal liquid steel circulation flow and liquid steel flow rate are reduced under the RH low vacuum degree treatment process, the followability of inclusions with liquid steel in the RH treatment process is reduced, the removal efficiency of inclusions of ≤20 μm is improved, the water gap blockage degree is effectively improved, and the plate surface quality is improved. This is also the correction of the technical prejudice that the higher the vacuum degree in the traditional RH decarburization and deoxidation process, the better, and the cleanliness of the molten steel is greatly improved.

[0034] 1.2, Process:

[0035] The decarburization is a limiting link for the ultra-low carbon steel due to the ultra-low carbon content. Due to the carbon-oxygen balance, the carbon content of 0.02% is the limit of decarburization in the conventional primary furnace (such as converter, electric furnace, etc.), and it cannot be further decarburized, and must be decarburized by excess oxygen in the RH.

[0036] In the RH treatment process, the decarburization under vacuum is carried out by means of dissolved oxygen in the steel or external oxygen source. The deoxidization and decarburization in the RH vacuum treatment are inseparable and integrated reactions, and the difference lies in that the deoxidization is carried out by means of carbon, and the decarburization is carried out by means of oxygen.

[0037] Therefore, for the RH process of the ultra-low carbon steel, in order to achieve the purpose of deep decarburization with carbon content of 20 ppm or less, deep deoxidization with total oxygen T.O. content of 20 ppm or less, and high cleanliness and high quality of the molten steel, the following control process is adopted:

[0038] In order to minimize the number of Al2O3 inclusions generated in the converter molten steel, the [C] carbon content can be appropriately increased under the premise of low-oxygen tapping in the converter, and the oxygen content [O] is generally required to be ≤550 ppm, and the carbon content [C] is 0.025% to 0.055% (wt);

[0039] When the oxygen content [O] for RH deoxidization is insufficient, the method of forced decarburization by RH oxygen blowing is used, but the oxygen blowing amount / m 3 ≤40% of the weight of the molten steel, for example, the oxygen blowing amount of the 300-ton ladle with 300 tons of molten steel is ≤120 m 3 ;

[0040] The RH adopts the present treatment process, the holding time of the RH vacuum degree ≤2 mbar is 20±5 minutes; the RH decarburization is ended when the CO content in the flue gas is ≤2% (vol); the free oxygen [O] of the molten steel at the end of the RH decarburization is controlled to be 300 ppm±50 ppm;

[0041] After the RH decarburization is ended and the aluminum is added, the low vacuum degree of 50 to 80 mbar is used until the RH is broken, so as to better remove the fine inclusions of ≤20 μm.

[0042] 2, Low-carbon steel that must be deeply deoxidized:

[0043] Low carbon steel generally refers to carbon steel containing carbon in the range of 0.02% to 0.10%wt%. It is also called soft steel because of its low strength and low hardness. The CQ, DQ and part of DDQ grade products produced by it are used to make industrial products such as automobile cab, generator cover, mechanical parts, etc. such as SPHC, SPHC-S, MRT-2.5, MRT-4 steel.

[0044] 2.1, Process principle:

[0045] The principle is the same. In order to minimize the number of Al2O3 inclusions in the converter steel, the lower the free oxygen in the RH inlet steel is required, and the oxygen content [O] is required to be less than or equal to 400ppm.

[0046] 2.2, Process:

[0047] Low carbon steel is limited by deoxidation due to high carbon content. Excess carbon deoxidation should be used as much as possible and less aluminum deoxidation. Through carbon deoxidation, the steel [O] is reduced to a certain level, and then aluminum is used for final deoxidation, which has the advantages of reducing aluminum consumption, reducing the number of inclusions, improving quality, and reducing cost.

[0048] Therefore, for the RH process of low carbon steel, in order to achieve carbon deep deoxidation, i.e. the total oxygen T.O. content is less than 20ppm, the high cleanliness and high quality of the molten steel, the following control process is adopted:

[0049] In order to minimize the number of Al2O3 inclusions in the converter steel, the lower the free oxygen in the RH inlet steel is required, and the oxygen content [O] is required to be less than or equal to 400ppm; the carbon content [C] is the upper limit of the carbon content range of the steel + (0-0.02%) (wt);

[0050] If due to abnormal reasons, the free oxygen content [O] in the RH inlet steel is greater than or equal to 550ppm; then carbon powder pre-deoxidation can be used to pre-deoxidize with carbon; the pre-deoxidation carbon powder addition amount can be calculated according to the following formula (I):

[0051] M 碳粉 =([O] 进站 -(0.8×[C] 进站 +150ppm))×40 / 100kg (Ⅰ)

[0052] In the formula: M 碳粉 is the pre-deoxidation carbon powder addition amount, kg; [O] 进站 is the oxygen content in the RH inlet steel, ppm; [C] 进站 is the carbon content in the RH inlet steel, ppm;

[0053] RH adopts light treatment process, and the holding time of RH vacuum degree 50-80mbar is 10±2 minutes;

[0054] When the free oxygen [O] in the steel is ≤150pm, RH ends the vacuum carbon decarburization; and aluminum is added for final deoxidation.

[0055] 3. Micro-alloy and medium-high strength steel that must be deep dehydrogenated or deep denitrified:

[0056] The micro-alloy and medium-high strength steel that must be deep dehydrogenated or deep denitrified generally refers to carbon steel or micro-alloy steel with carbon content in the range of 0.06% to 1.0%wt%, which has the characteristics of hard steel, high tensile strength, light weight, etc., plays an important role in reducing the weight of the automobile body, reducing fuel consumption, and improving the strength of automobile structural parts, and is widely used in automobile structures and industrial steel, with high product added value. Major steel plants at home and abroad have begun to develop and realize industrialized production, such as 380CL, H180BH, H220BH, CR1300, H220Y, etc.

[0057] 3.1. Process principle:

[0058] The harm of hydrogen to steel is twofold: first, it causes "hydrogen embrittlement" leading to fracture; second, "white spots" significantly reduce the elongation of steel. Nitrogen has an aging tendency, which can significantly reduce plasticity, especially toughness, and can worsen weldability and increase cold brittleness. Therefore, many steel varieties, such as micro-alloy steel and special steel, require deep dehydrogenation or deep denitrification treatment of the molten steel.

[0059] Within the refining temperature range, when the RH vacuum degree reaches 2mbar, [H]≤1.5ppm and [N]≤20ppm can be controlled for the steel grade. Research shows that the diffusion of hydrogen atoms or nitrogen atoms to the interface is the slowest in the dehydrogenation or denitrification reaction of RH, which is the limiting link in the vacuum degassing process, and must be deep vacuum for a certain period of time. However, due to the fact that the diffusion speed of hydrogen in the molten steel is much faster than that of nitrogen (about 6 times), RH dehydrogenation is easier than denitrification, and the kinetic conditions affecting dehydrogenation and denitrification are also different.

[0060] 3.2. Process:

[0061] For the RH process of micro-alloy and medium-high strength steel that must be deep dehydrogenated or deep denitrified, the following control process is adopted:

[0062] The converter needs high temperature and low oxygen tapping, and the composition and temperature adjustment should be started when the RH vacuum degree reaches 100-150mbar in the early stage;

[0063] ② High temperature and low oxygen tapping requires that the oxygen content [O] in the converter tapping molten steel is ≤300ppm, and the converter tapping end temperature is controlled at 1670-1690℃;

[0064] ③ RH main treatment, the holding time of RH vacuum degree ≤2mbar is 18±5 minutes;

[0065] IV. Dehydrogenation requires high oxygen content in the steel, [O] > 100 ppm;

[0066] V. Denitrification requires low oxygen content and low sulfur content in the steel: [O] < 200 ppm, and sulfur content in the steel [S] < 60 ppm;

[0067] VI. For heats that require RH oxygen blowing to warm up, the mass fraction of AlS in the molten steel after tapping from the converter should be controlled at 0.025% to 0.045%; a certain amount of aluminum particles should be added before RH oxygen blowing to warm up, so that the w(Als) of the molten steel after RH blowing is greater than or equal to 0.03%, so as to ensure sufficient deoxidation of the molten steel and minimize the number and size of Al203 inclusions.

[0068] Example 1: The RH direct-to-continuous-casting process for the low-cost high-quality steel variety used the following specific process.

[0069] Converter molten steel RH direct-to-continuous-casting ultra-low-carbon IF steel SPHETi-3: converter low-oxygen tapping, control the oxygen content [O] < 550 ppm, carbon content [C] = 0.055%. RH ladle 300 tons of molten steel, forced decarburization oxygen blowing amount = 50 m 3 . RH adopts this process, the holding time of RH vacuum degree < 2 mbar is 25 minutes; when the CO content in the flue gas < 2%, the RH decarburization is completed; the free oxygen [O] of the molten steel at the end of RH decarburization is controlled at 350 ppm; after adding aluminum at the end of RH decarburization, low vacuum degree 80 mbar is used until the RH breaks the vacuum.

[0070] The process of this example produced 21115 tons of SPHETi-3 steel in a certain month in 2022, and the inclusion degradation rate in the whole process was reduced from 4.5% to 1.44%.

[0071] Example 2: The RH direct-to-continuous-casting process for the low-cost high-quality steel variety used the following specific process.

[0072] Converter molten steel RH direct-to-continuous-casting ultra-low-carbon IF steel SPHETi-32: converter low-oxygen tapping, control the oxygen content [O] < 400 ppm, carbon content [C] = 0.045%. Ladle 300 tons of molten steel, forced decarburization oxygen blowing to warm up, the total amount of oxygen blowing = 120 m 3 . RH adopts this process, the holding time of RH vacuum degree < 2 mbar is 20 minutes; when the CO content in the flue gas < 2%, the RH decarburization is completed; the free oxygen [O] of the molten steel at the end of RH decarburization is controlled at 300 ppm; after adding aluminum at the end of RH decarburization, low vacuum degree 60 mbar is used until the RH breaks the vacuum.

[0073] The process of this embodiment produced 18778 tons of SPHETi-32 steel in a certain month of 2022, and the inclusion degradation rate in the whole process was reduced from 3.77% to 1.31%.

[0074] Example 3: The RH straight-up continuous casting process for this low-cost high-quality steel variety uses the following specific process.

[0075] Converter steel RH straight-up continuous casting ultra-low carbon IF steel TGW800-4: converter low-oxygen tapping, control tapping [O]≤450ppm, carbon content [C]=0.025%. Ladle 300 tons of molten steel, forced decarburization oxygen blowing amount=20m 3 RH adopts this treatment process, the holding time of RH vacuum degree≤2mbar is 15 minutes; when the CO content in the flue gas≤2%, the RH decarburization ends; the molten steel free oxygen [O]=250ppm at the end of RH decarburization is controlled; after adding aluminum at the end of RH decarburization, low vacuum degree 50mbar is used until RH breaks the vacuum.

[0076] The process of this embodiment produced 1038 tons of TGW800-4 steel in a certain month of 2022, and the inclusion degradation rate in the whole process was reduced from 0.67% to 0.21%.

[0077] Example 4: The RH straight-up continuous casting process for this low-cost high-quality steel variety uses the following specific process.

[0078] Converter steel RH straight-up continuous casting low-carbon steel SPHC: RH inlet molten steel oxygen content [O]≤400ppm, carbon content [C] is the upper limit of the carbon content range of this steel grade 0.06%; for abnormal furnace with [O]≥550ppm, add carbon powder for pre-deoxidization, the pre-deoxidization carbon powder addition amount is calculated according to the above formula (I); RH adopts light treatment process, the holding time of RH vacuum degree 80mbar is 10 minutes. When the free oxygen [O]=150pm in the steel, the RH ends the vacuum decarburization; add aluminum for final deoxidization.

[0079] The process of this embodiment produced 30484 tons of SPHC steel in a certain month of 2022, and the inclusion degradation rate in the whole process was reduced from 1.65% to 0.22%.

[0080] Example 5: The RH straight-up continuous casting process for this low-cost high-quality steel variety uses the following specific process.

[0081] Converter steel RH straight up continuous casting low carbon steel SPHC-S: [O] in RH inlet steel ≤ 350 ppm; the carbon content is the upper limit of the carbon content range of this steel grade 0.04% + 0.02%, so [C] = 0.06%. For abnormal heats with [O] ≥ 550 ppm at the inlet, add carbon powder for pre-deoxidation, and the pre-deoxidation carbon powder addition amount is calculated according to the above formula (I); RH adopts light treatment process, and the holding time of RH vacuum degree 60 mbar is 8 minutes. When the free oxygen [O] in the steel is 120 pm, the RH ends the vacuum carbon decarburization; add aluminum for final deoxidation.

[0082] The process of this embodiment produced 17732 tons of SPHC-S steel in a certain month in 2022, and the inclusion degradation rate in the whole process was reduced from 2.18% to 1.20%.

[0083] Example 6: The RH straight up continuous casting process of this low-cost high-quality steel uses the following specific process.

[0084] Converter steel RH straight up continuous casting low carbon steel MRT-2.5: [O] in RH inlet steel ≤ 300 ppm, and the carbon content is the upper limit of the carbon content range of this steel grade 0.06% + 0.01%, so [C] = 0.07%; for abnormal heats with [O] ≥ 550 ppm at the inlet, add carbon powder for pre-deoxidation, and the pre-deoxidation carbon powder addition amount is calculated according to the above formula (I); RH adopts light treatment process, and the holding time of RH vacuum degree 50 mbar is 12 minutes. When the free oxygen [O] in the steel is 100 pm, the RH ends the vacuum carbon decarburization; add aluminum for final deoxidation.

[0085] The process of this embodiment produced 21939 tons of MRT-2.5 steel in a certain month in 2022, and the inclusion degradation rate in the whole process was reduced from 1.53% to 0.33%.

[0086] Example 7: The RH straight up continuous casting process of this low-cost high-quality steel uses the following specific process.

[0087] Converter steel RH straight up continuous casting micro-alloy steel 380CL: high temperature and low oxygen tapping is required for the converter, and composition and temperature adjustment should be started when the RH vacuum degree reaches 150 mbar; control the oxygen content [O] = 150 ppm, and control the converter tapping endpoint temperature at 1670℃; RH treatment, the holding time of RH vacuum degree ≤ 2 mbar is 13 minutes; low oxygen content and low sulfur content in the steel are required: [O] = 150 ppm, and the sulfur content [S] in the steel ≤ 60 ppm;

[0088] For heats that need to be blown with oxygen in RH to raise the temperature, the mass fraction of Al in the steel after tapping should be controlled at 0.025%; a certain amount of aluminum particles should be added before RH oxygen blowing to ensure that the mass fraction of Al in the steel after RH oxygen blowing is ≥ 0.03%.

[0089] The example process produced 1537 tons of 380CL steel in a certain month of 2022, and the inclusion degradation rate was reduced from 0.33% to 0.10%.

[0090] Example 8: The RH straight-up continuous casting process for this low-cost high-quality steel variety uses the following specific process.

[0091] The micro-alloyed steel H220BH, which must be deep dehydrogenated by RH straight-up continuous casting of converter steel, requires high-temperature and low-oxygen tapping, and composition and temperature adjustment should be started when the RH vacuum degree reaches 120 mbar; the oxygen content [O] is controlled at 250 ppm, and the converter tapping endpoint temperature is controlled at 1680°C; the RH treatment, the RH vacuum degree ≤2 mbar, the holding time is 18 minutes; the dehydrogenation requires high oxygen content in steel [O]=100 ppm;

[0092] For the heats that need to be blown by RH oxygen to warm up, the mass fraction of Als in the steel after converter tapping should be controlled at 0.035%; a certain amount of aluminum particles should be added before RH oxygen heating to ensure that the w(Als) of the steel after RH blowing is ≥0.03%.

[0093] The example process produced 4194 tons of H220BH steel in a certain month of 2022, and the inclusion degradation rate was reduced from 0.89% to 0.37%.

[0094] Example 9: The RH straight-up continuous casting process for this low-cost high-quality steel variety uses the following specific process.

[0095] The micro-alloyed high-strength steel CR1300, which must be deep dehydrogenated and denitrified by RH straight-up continuous casting of converter steel, requires high-temperature and low-oxygen tapping, and composition and temperature adjustment should be started when the RH vacuum degree reaches 100 mbar; the oxygen content [O] is controlled at 300 ppm, and the converter tapping endpoint temperature is controlled at 1690°C; the RH treatment, the RH vacuum degree ≤2 mbar, the holding time is 23 minutes; the dehydrogenation requires high oxygen content in steel [O]=200 ppm; the denitrification requires low oxygen content and low sulfur content in steel: [O]=200 ppm, and the sulfur content in steel [S]≤20 ppm;

[0096] For the heats that need to be blown by RH oxygen to warm up, the mass fraction of Als in the steel after converter tapping should be controlled at 0.045%; a certain amount of aluminum particles should be added before RH oxygen heating to ensure that the w(Als) of the steel after RH blowing is ≥0.03%.

[0097] The example process produced 1349 tons of CR1300 steel in a certain month of 2022, and the inclusion degradation rate was reduced from 0.42% to 0.12%.

Claims

1. A low cost high quality variety steel RH straight up continuous casting process characterized by: According to different steel grades, the following RH process is adopted; Ultra-low carbon steel: free oxygen [O] in RH inlet liquid steel ≤ 550 ppm, carbon content [C] = 0.025% to 0.055%; when the oxygen content [O] is insufficient for RH decarburization, forced decarburization is carried out by RH oxygen blowing, oxygen blowing amount / m 3 ≤ 40% of the weight of the liquid steel; the RH uses the present treatment process, the holding time of the RH vacuum degree ≤ 2 mbar is 20 ± 5 minutes; the RH decarburization ends when the CO content in the flue gas ≤ 2%; the free oxygen [O] of the liquid steel at the end of the RH decarburization of the ultra-low carbon steel is controlled to be 250 to 350 ppm; after the addition of aluminum at the end of the RH decarburization, a low vacuum degree of 50 to 80 mbar is used until the RH is broken. Low carbon steel: the free oxygen content in the molten steel at the RH inlet is ≤400ppm; if the free oxygen content in the molten steel at the RH inlet is ≥500ppm, carbon powder is added for pre-deoxidation, and the amount of the carbon powder is calculated according to the following formula (I): M 碳粉 =([O] 进站 -(0.8×[C] 进站 +150ppm))×40 / 100kg (Ⅰ) wherein: M 碳粉 carbon powder addition amount at pre-deoxidization, kg;[O] 进站 oxygen content in RH inlet molten steel, ppm;[C] 进站 carbon content in RH inlet molten steel, ppm; The RH process is light treatment, the holding time of the RH vacuum degree of 50-80mbar is 10±2 minutes; when the free oxygen content in the steel is ≤150pm, the RH ends vacuum decarburization; aluminum is added for final deoxidation; For the steel grades that must be deeply dehydrogenated or deeply denitrified, the oxygen content in the molten steel at the converter tapping is required to be ≤300ppm, and the end point temperature at the converter tapping is controlled at 1670-1690℃; the composition and temperature adjustment is started when the RH vacuum degree reaches 100-150mbar; the RH treatment, the holding time of the RH vacuum degree of ≤2mbar is 18±5 minutes; the deep dehydrogenation of the RH requires the oxygen content in the molten steel to be ≥100ppm; the deep denitrification of the RH requires the oxygen content in the molten steel to be ≤200ppm, and the sulfur content to be ≤60ppm; for the heats that need to be heated by the RH oxygen blowing, the mass fraction of Als in the molten steel after the converter tapping is required to be controlled at 0.025%-0.045%; aluminum particles are added before the RH oxygen blowing to control the w(Als) in the molten steel after the RH oxygen blowing to be ≥0.03%.