Normalizing process for thin-gauge electromagnetic stirring steel

Abstract

The invention relates to the technical field of ferrous metallurgy, and provides a normalizing process of thin-gauge electromagnetic stirring steel, which comprises the following steps: molten iron is subjected to converter smelting, LF refining, RH degassing, continuous casting, slab stack cooling, heating, rough rolling, finish rolling, finishing and normalizing treatment to obtain the thin-gauge electromagnetic stirring steel; during normalizing treatment, the temperature is 890-900 DEG C, the total normalizing in-furnace time is 50 min, and the heat preservation time is 18-22 min. According to the technical scheme, the problem that the low-temperature toughness of the thin-gauge electromagnetic stirring steel with the carbon content being 0.1%-0.17% after normalizing treatment is poor in the related technology is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of iron and steel metallurgy, and in particular to a normalizing process for thin-gauge electromagnetic stirring steel. Background Art

[0002] The poor low-temperature performance of thin-gauge electromagnetically stirred steel (6-16mm) with a carbon content of 0.1%-0.17% has long been a problem for manufacturers. While strict controlled rolling processes can achieve low-temperature toughness of 120-160J for this type of steel, normalizing treatment dramatically reduces this toughness to 30-60J. This phenomenon occurs because, while electromagnetic stirring is commonly used to break up columnar grains and improve central segregation, resulting in discontinuous central segregation, thin-gauge electromagnetically stirred steel, due to the impact specimen size, often contains a central segregation band composed of a composite of bainite and martensite, compared to thicker electromagnetically stirred steel (20mm and above). Normalizing treatment has a poor ability to break down this central segregation band in thin-gauge electromagnetically stirred steel. Furthermore, the refined grains achieved through high reduction ratios and rigorous rolling processes in the as-rolled state are weakened after normalizing, leading to the disappearance of subgrains. These factors lead to significant variations in the low-temperature toughness of thin-gauge electromagnetically stirred steel with a carbon content of 0.1%-0.17% before and after normalizing.

[0003] In practice, large steel structure manufacturers require delivery of products in the normalized state, which undoubtedly has a significant negative impact on the steel mill's sales orders. Therefore, it is urgent to develop a normalizing process for thin-gauge electromagnetic stirring steel with a carbon content of 0.1% to 0.17% that can ensure low-temperature toughness. Summary of the Invention

[0004] The present invention proposes a normalizing process for thin-gauge electromagnetic stirring steel, which solves the problem in the related art that thin-gauge electromagnetic stirring steel with a carbon content of 0.1% to 0.17% has poor low-temperature toughness after normalizing treatment.

[0005] The technical solutions of the present invention are as follows: The present invention provides a normalizing process for thin-gauge electromagnetic stirring steel, comprising the following steps: molten iron is subjected to converter smelting, LF refining, RH degassing, continuous casting, slab stack cooling, heating, rough rolling, finish rolling, finishing, and normalizing treatment to obtain thin-gauge electromagnetic stirring steel; during the normalizing treatment, the temperature is 890-900°C, the total normalizing furnace time is 50 minutes, and the holding time is 18-22 minutes.

[0006] As a further technical solution, when the thickness of the thin-gauge electromagnetic stirring steel is 6 mm or less and ≤ 12 mm, the temperature of the normalizing treatment is 890-894° C.; When the thickness of the thin-gauge electromagnetic stirring steel is 12 mm or less and the thickness is ≤ 16 mm, the temperature of the normalizing treatment is 897-890° C.

[0007] In the present invention, the low-temperature toughness of the thin-gauge electromagnetic stirring steel is further improved by further optimizing the relationship between the normalizing process parameters and the thickness of the thin-gauge electromagnetic stirring steel.

[0008] As a further technical solution, the endpoint of the converter smelting is controlled to be: C 0.06%~0.07%, P≤0.008%, S≤0.018%, in weight percentage.

[0009] In the present invention, the end point composition of converter smelting is strictly controlled, thereby reducing the influence of harmful elements such as P on thin-gauge electromagnetic stirring steel.

[0010] As a further technical solution, during the LF refining, the white slag retention time is 16 to 18 minutes.

[0011] In the present invention, by optimizing the holding time of white slag during LF refining, the inclusion removal effect is guaranteed and the purity of molten steel is improved.

[0012] As a further technical solution, during the RH degassing, the vacuum degree is ≤67 Pa, and the ultimate vacuum treatment time is 13~15 minutes.

[0013] In the present invention, by strictly controlling the vacuum degree and the ultimate vacuum treatment time during RH degassing, a large amount of [H] and [N] in the molten steel is avoided, which helps to reduce the number of defects such as pores, white spots, and high gas content in thin-gauge electromagnetically stirred steel.

[0014] As a further technical solution, during the continuous casting, the superheat is 15-25°C.

[0015] In the present invention, by strictly controlling the superheat degree during continuous casting to 15-25° C., the fluidity of the molten steel is moderate, the mold can be filled evenly, and surface and internal defects of the casting billet caused by poor molten steel flow are reduced.

[0016] As a further technical solution, during the heating, the temperature of the heating section is 1210~1250℃, and the temperature of the soaking section is 1210~1240℃.

[0017] In the present invention, by optimizing the heating process parameters, the temperature inside the steel can be made uniform, the structural transformation can be promoted, and defects such as overburning can be avoided.

[0018] As a further technical solution, during the rough rolling, the starting rolling temperature is 1060~1090℃, and the finishing rolling temperature is 980~1030℃.

[0019] In the present invention, rough rolling is complete recrystallization rolling. In the rough rolling temperature range of the present invention, it can ensure that there is sufficient plasticity to continue deformation in the later stage of rolling, and the recrystallization process can continue to be completed.

[0020] As a further technical solution, during the finish rolling, the starting rolling temperature is 920-1000°C, and the final rolling temperature is 770-830°C; When the thickness of the thin-gauge electromagnetic stirring steel is 6 mm or less and 8 mm or less, the starting temperature of the finishing rolling is ≤ 1000° C. and the final rolling temperature is ≤ 830° C.; When the thickness of the thin-gauge electromagnetic stirring steel is 6 mm or less and the thickness is ≤12 mm, the start rolling temperature of the finishing rolling is ≤950°C and the final rolling temperature is ≤830°C; When the thickness of the thin-gauge electromagnetic stirring steel is 12 mm or less and ≤ 16 mm, the start rolling temperature of the finish rolling is ≤ 930° C., and the final rolling temperature is ≤ 810° C.

[0021] In the present invention, finishing rolling is performed in the non-recrystallized zone, further increasing the deformation and promoting the formation of fine and uniform grains during the subsequent cooling process. In addition, by optimizing the relationship between the finishing rolling temperature range and the thickness of the thin-gauge electromagnetic stirring steel, it helps to further refine the grains.

[0022] As a further technical solution, the thin-gauge electromagnetic stirring steel is composed of the following components in weight percentage: C 0.1%~0.17%, Si 0.2%~0.35%, Mn 1.4%~1.5%, P≤0.015%, S≤0.003%, Nb 0.035%~0.045%, V0.04%~0.05%, Alt 0.02%~0.045%, and the rest is Fe and unavoidable impurities. The working principle and beneficial effects of the present invention are: In this invention, a specific normalizing process system has been developed to address the problem of poor low-temperature toughness after normalizing for thin-gauge electromagnetically stirred steel with a carbon content of 0.1% to 0.17%. Given that steel microstructural transformation is extremely sensitive to normalizing temperature and time, thin-gauge electromagnetically stirred steel inevitably has a central segregation band composed of a composite of martensite and bainite, and that normalizing for thin-gauge electromagnetically stirred steel has a poor ability to decompose this central segregation band, which weakens the grain refinement effect of rolling, by strictly controlling the normalizing process temperature to 890-900°C, the total furnace time to 50 minutes, and the holding time to 18-22 minutes, the central segregation band is essentially decomposed, resulting in a uniform microstructure of ferrite and pearlite, avoiding stress concentration caused by abnormal microstructural differences. It also prevents grain coarsening after secondary phase transformation during normalizing, ensuring that the thin-gauge electromagnetically stirred steel has good low-temperature toughness after normalizing. When the normalizing temperature is higher than the range of the present invention and the time is longer than the range of the present invention, the grains of the thin-gauge electromagnetic stirring steel begin to coarsen and the grain refinement effect is weakened; when the normalizing temperature is lower than the range of the present invention and the time is shorter than the range of the present invention, the central segregation band of the thin-gauge electromagnetic stirring steel is not fully decomposed, which will cause structural differentiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Figure 1 This is the metallographic image of the thin-gauge electromagnetic stirring steel at 1 / 4 of the thickness in Example 1. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0026] Example 1 A normalizing process for thin-gauge electromagnetic stirring steel comprises the following steps: molten iron is subjected to converter smelting, LF refining, RH degassing, continuous casting, slab stack cooling, heating, rough rolling, finish rolling, finishing, and normalizing treatment to obtain a 6mm thick thin-gauge electromagnetic stirring steel having a microstructure of ferrite and pearlite. The metallographic diagram at 1 / 4 of the thickness is as follows: Figure 1 As shown in the figure, it can be seen that the central segregation band is basically decomposed; The thin gauge electromagnetic stirring steel is composed of the following components in weight percentage: C 0.1%, Si 0.2%, Mn 1.4%, P 0.015%, S 0.003%, Nb 0.035%, V 0.04%, Alt 0.02%, and the rest is Fe and unavoidable impurities; The temperature of the molten iron is 1321°C. In terms of weight percentage, the molten iron contains 0.024% S, 0.43% Si, and 0.128% P. During converter smelting, the slag basicity is 3.2, and the endpoint is controlled as follows: C 0.07%, P 0.008%, and S 0.018% by weight. The endpoint temperature is 1630°C, the furnace back temperature is 1570°C, the slag drop during tapping is 45mm, and a slag stopper is used to stop the slag before tapping. When the steel is 1 / 3 of the way through, alloys other than ferroniobium and ferrovanadium are added according to the target composition. Silicon manganese alloy, low-carbon ferromanganese, and pure Al blocks are used for deoxidation to an oxygen content of 17ppm. The argon station controls the Alt content to the target composition. When the steel is 2 / 3 of the way through, ferroniobium and ferrovanadium alloy are added according to the target composition. The tapping time is 225 minutes, and the ladle clearance is 400mm. During LF refining, the white slag holding time is 16 minutes, and the molten steel composition is adjusted to the target composition before leaving the station; During RH degassing, the process time is 30 minutes, the vacuum degree in the tank is reduced to 67Pa within 5 minutes, the ultimate vacuum treatment time is 15 minutes, and the H content is 0.9ppm by weight when leaving the station. After breaking the air, 280m of pure calcium wire (the diameter of the pure calcium wire is 9mm and the calcium content of the pure calcium wire is 70g / m3) is fed, and soft blowing is carried out for 12 minutes; During continuous casting, the slab casting speed was 0.95 m / min, the superheat was 21°C, and two pairs of electromagnetic stirrers were used, with one pair installed at each of the four inlets and outlets of the secondary cooling section. The inlet current was 390 A, the outlet current was 360 A, and the static soft pressure was 5 mm, ensuring that the slab met the central segregation C2.0 level specified in YB / T4002-2013 "Grading Chart for Macrostructure Defects of Continuously Cast Steel Square Billets"; When the slab is piled in the windproof place for cooling, the cooling time is 48 hours; During heating, the temperature of the heating section is 1220°C, the temperature of the soaking section is 1223°C, the total time in the furnace is 180 minutes, the heating section time is 40 minutes, and the soaking section time is 50 minutes; Before rough rolling, the slab thickness is 180 mm, and the process parameters for rough rolling are:

[0027] The process parameters of finishing rolling are:

[0028] During normalizing treatment, the temperature is 890℃, the total normalizing time in the furnace is 50min, the heating time is 30min, and the holding time is 20min.

[0029] Example 2 A normalizing process for thin-gauge electromagnetic stirring steel comprises the following steps: molten iron is subjected to converter smelting, LF refining, RH degassing, continuous casting, slab stack cooling, heating, rough rolling, finish rolling, finishing, and normalizing to obtain 8 mm thick thin-gauge electromagnetic stirring steel having a microstructure of ferrite and pearlite; The thin gauge electromagnetic stirring steel is composed of the following components in weight percentage: C 0.12%, Si 0.24%, Mn 1.42%, P 0.013%, S 0.003%, Nb 0.04%, V 0.045%, Alt 0.038%, and the rest is Fe and unavoidable impurities; The temperature of the molten iron is 1321°C. In terms of weight percentage, the molten iron contains 0.024% S, 0.43% Si, and 0.128% P. During converter smelting, the slag basicity is 3.2, and the endpoint is controlled as follows: C 0.07%, P 0.006%, and S 0.016% by weight. The endpoint temperature is 1630°C, the furnace back temperature is 1570°C, the slag drop during tapping is 40mm, and a slag stopper is used to stop the slag before tapping. When the steel is 1 / 3 of the way through, alloys other than ferroniobium and ferrovanadium are added according to the target composition. Silicon manganese alloy, low-carbon ferromanganese, and pure Al blocks are used for deoxidation to an oxygen content of 17ppm. The argon station controls the Alt content to the target composition. When the steel is 2 / 3 of the way through, ferroniobium and ferrovanadium alloys are added according to the target composition. The tapping time is 230 minutes, and the ladle clearance is 400mm. During LF refining, the white slag holding time is 18 minutes, and the molten steel composition is adjusted to the target composition before leaving the station; During RH degassing, the process time is 30 minutes, the vacuum degree in the tank is reduced to 67Pa within 5 minutes, the ultimate vacuum treatment time is 15 minutes, and the H content is 1.1ppm by weight when leaving the station. After breaking the air, 280m of pure calcium wire (the diameter of the pure calcium wire is 9mm and the calcium content of the pure calcium wire is 70g / m3) is fed, and soft blowing is carried out for 15 minutes; During continuous casting, the slab casting speed was 0.95 m / min, the superheat was 23°C, and two pairs of electromagnetic stirrers were used, with one pair installed at each of the four inlets and outlets of the secondary cooling section. The inlet current was 390 A, the outlet current was 360 A, and the static soft pressure was 5 mm, ensuring that the slab met the central segregation C2.0 level specified in YB / T4002-2013 "Grading Chart for Macrostructure Defects of Continuously Cast Steel Square Billets"; When the slab is piled in the windproof place for cooling, the cooling time is 48 hours; During heating, the temperature of the heating section is 1220°C, the temperature of the soaking section is 1223°C, the total time in the furnace is 180 minutes, the heating section time is 45 minutes, and the soaking section time is 45 minutes; Before rough rolling, the slab thickness is 180 mm, and the process parameters for rough rolling are:

[0030] The process parameters of finishing rolling are:

[0031] During normalizing treatment, the temperature is 892℃, the total normalizing time in the furnace is 50min, the heating time is 30min, and the holding time is 20min.

[0032] Example 3 A normalizing process for thin-gauge electromagnetic stirring steel comprises the following steps: molten iron is subjected to converter smelting, LF refining, RH degassing, continuous casting, slab stack cooling, heating, rough rolling, finish rolling, finishing, and normalizing to obtain a 10 mm thick thin-gauge electromagnetic stirring steel having a microstructure of ferrite and pearlite; The thin gauge electromagnetic stirring steel is composed of the following components in weight percentage: C 0.17%, Si 0.22%, Mn 1.5%, P 0.013%, S 0.003%, Nb 0.045%, V 0.05%, Alt 0.045%, and the rest is Fe and unavoidable impurities; The temperature of the molten iron is 1321°C. In terms of weight percentage, the molten iron contains 0.024% S, 0.43% Si, and 0.128% P. During converter smelting, the slag basicity is 3.2, and the endpoint is controlled as follows: C 0.07%, P 0.006%, and S 0.016% by weight. The endpoint temperature is 1630°C, the furnace back temperature is 1570°C, the slag drop during tapping is 45mm, and a slag stopper is used to block the slag before tapping. When the steel is 1 / 3 of the way through, alloys other than ferroniobium and ferrovanadium are added according to the target composition. Silicon manganese alloy and pure Al blocks are used for deoxidation to an oxygen content of 15ppm. The argon station controls the Alt content to the target composition. When the steel is 2 / 3 of the way through, ferroniobium and ferrovanadium alloys are added according to the target composition. The tapping time is 230 minutes, and the ladle clearance is 400mm. During LF refining, the white slag holding time is 17 minutes, and the molten steel composition is adjusted to the target composition before leaving the station; During RH degassing, the process time is 30 minutes, the vacuum degree in the tank is reduced to 67Pa within 5 minutes, the ultimate vacuum treatment time is 15 minutes, and the H content is 1.1ppm by weight when leaving the station. After breaking the air, 280m of pure calcium wire (the diameter of the pure calcium wire is 9mm and the calcium content of the pure calcium wire is 70g / m3) is fed, and soft blowing is carried out for 15 minutes; During continuous casting, the slab casting speed was 0.95 m / min, the superheat was 15°C, and two pairs of electromagnetic stirrers were used, with one pair installed at each of the four inlets and outlets of the secondary cooling section. The inlet current was 390 A, the outlet current was 360 A, and the static soft pressure was 5 mm, ensuring that the slab met the central segregation C2.0 level specified in YB / T4002-2013 "Grading Chart for Macrostructure Defects of Continuously Cast Steel Square Billets"; When the slab is piled in the windproof place for cooling, the cooling time is 48 hours; During heating, the temperature of the heating section is 1210°C, the temperature of the soaking section is 1211°C, the total time in the furnace is 180 minutes, the heating section time is 45 minutes, and the soaking section time is 45 minutes; Before rough rolling, the slab thickness is 180 mm, and the process parameters for rough rolling are:

[0033] The process parameters of finishing rolling are:

[0034] During normalizing treatment, the temperature is 894℃, the total normalizing time in the furnace is 50min, the heating time is 28min, and the holding time is 22min.

[0035] Example 4 A normalizing process for thin-gauge electromagnetic stirring steel comprises the following steps: molten iron is subjected to converter smelting, LF refining, RH degassing, continuous casting, slab stack cooling, heating, rough rolling, finish rolling, finishing, and normalizing to obtain a 12 mm thick thin-gauge electromagnetic stirring steel having a microstructure of ferrite and pearlite; The thin gauge electromagnetic stirring steel is composed of the following components in weight percentage: C 0.13%, Si 0.24%, Mn 1.48%, P 0.011%, S 0.003%, Nb 0.038%, V 0.046%, Alt 0.03%, and the rest is Fe and unavoidable impurities; The temperature of the molten iron is 1350°C. In terms of weight percentage, the molten iron contains 0.022% S, 0.38% Si, and 0.11% P. During converter smelting, the slag basicity is 3.1, and the endpoint is controlled as follows: C 0.06%, P 0.008%, and S 0.015% by weight. The endpoint temperature is 1635°C, the furnace back temperature is 1580°C, the slag drop during tapping is 45mm, and a slag stopper is used to stop the slag before tapping. When the steel is 1 / 3 of the way through, alloys other than ferroniobium and ferrovanadium are added according to the target composition. Silicon manganese alloy, low-carbon ferromanganese, and pure Al blocks are used for deoxidation to an oxygen content of 15ppm. The argon station controls the Alt content to the target composition. When the steel is 2 / 3 of the way through, ferroniobium and ferrovanadium alloy are added according to the target composition. The tapping time is 230 minutes, and the ladle clearance is 400mm. During LF refining, the white slag holding time is 16 minutes, and the molten steel composition is adjusted to the target composition before leaving the station; During RH degassing, the process time is 30 minutes, the vacuum degree in the tank is reduced to 67Pa within 5 minutes, the ultimate vacuum treatment time is 15 minutes, and the H content is 0.9ppm by weight when leaving the station. After breaking the air, 280m of pure calcium wire (the diameter of the pure calcium wire is 9mm and the calcium content of the pure calcium wire is 70g / m3) is fed, and soft blowing is carried out for 12 minutes; During continuous casting, the slab casting speed was 0.95 m / min, the superheat was 21°C, and two pairs of electromagnetic stirrers were used, with one pair installed at each of the four inlets and outlets of the secondary cooling section. The inlet current was 390 A, the outlet current was 360 A, and the static soft pressure was 5 mm, ensuring that the slab met the central segregation C2.0 level specified in YB / T4002-2013 "Grading Chart for Macrostructure Defects of Continuously Cast Steel Square Billets"; When the slab is piled in the windproof place for cooling, the cooling time is 48 hours; During heating, the temperature of the heating section is 1235°C, the temperature of the soaking section is 1224°C, the total time in the furnace is 180 minutes, the heating section time is 45 minutes, and the soaking section time is 45 minutes; Before rough rolling, the slab thickness is 220 mm, and the process parameters for rough rolling are:

[0036] The process parameters of finishing rolling are:

[0037] During normalizing treatment, the temperature is 900℃, the total normalizing time in the furnace is 50min, the heating time is 32min, and the holding time is 18min.

[0038] Example 5 A normalizing process for thin-gauge electromagnetic stirring steel comprises the following steps: molten iron is subjected to converter smelting, LF refining, RH degassing, continuous casting, slab stack cooling, heating, rough rolling, finish rolling, finishing, and normalizing to obtain a 14 mm thick thin-gauge electromagnetic stirring steel having a microstructure of ferrite and pearlite; The thin gauge electromagnetic stirring steel is composed of the following components in weight percentage: C 0.13%, Si 0.24%, Mn 1.48%, P 0.011%, S 0.003%, Nb 0.038%, V 0.046%, Alt 0.03%, and the rest is Fe and unavoidable impurities; The temperature of the molten iron is 1350°C. In terms of weight percentage, the molten iron contains 0.022% S, 0.38% Si, and 0.11% P. During converter smelting, the slag basicity is 3.1, and the endpoint is controlled as follows: C 0.06%, P 0.008%, and S 0.015% by weight. The endpoint temperature is 1635°C, the furnace back temperature is 1580°C, the slag drop during tapping is 45mm, and a slag stopper is used to stop the slag before tapping. When the steel is 1 / 3 of the way through, alloys other than ferroniobium and ferrovanadium are added according to the target composition. Silicon manganese alloy, low-carbon ferromanganese, and pure Al blocks are used for deoxidation to an oxygen content of 15ppm. The argon station controls the Alt content to the target composition. When the steel is 2 / 3 of the way through, ferroniobium and ferrovanadium alloy are added according to the target composition. The tapping time is 230 minutes, and the ladle clearance is 400mm. During LF refining, the white slag holding time is 16 minutes, and the molten steel composition is adjusted to the target composition before leaving the station; During RH degassing, the process time is 30 minutes, the vacuum degree in the tank is reduced to 67Pa within 5 minutes, the ultimate vacuum treatment time is 15 minutes, and the H content is 0.9ppm by weight when leaving the station. After breaking the air, 280m of pure calcium wire (the diameter of the pure calcium wire is 9mm and the calcium content of the pure calcium wire is 70g / m3) is fed, and soft blowing is carried out for 12 minutes; During continuous casting, the slab casting speed was 0.95 m / min, the superheat was 21°C, and two pairs of electromagnetic stirrers were used, with one pair installed at each of the four inlets and outlets of the secondary cooling section. The inlet current was 390 A, the outlet current was 360 A, and the static soft pressure was 5 mm, ensuring that the slab met the central segregation C1.5 level specified in YB / T4002-2013 "Grading Chart for Macrostructure Defects of Continuously Cast Steel Square Billets"; When the slab is piled in the windproof place for cooling, the cooling time is 48 hours; During heating, the temperature of the heating section is 1248°C, the temperature of the soaking section is 1239°C, the total time in the furnace is 180 minutes, the heating section time is 50 minutes, and the soaking section time is 40 minutes; Before rough rolling, the slab thickness is 220 mm, and the process parameters for rough rolling are:

[0039] The process parameters of finishing rolling are:

[0040] During normalizing treatment, the temperature is 897℃, the total normalizing time in the furnace is 50min, the heating time is 30min, and the holding time is 20min.

[0041] Example 6 A normalizing process for thin-gauge electromagnetic stirring steel comprises the following steps: molten iron is subjected to converter smelting, LF refining, RH degassing, continuous casting, slab stack cooling, heating, rough rolling, finish rolling, finishing, and normalizing to obtain a 16 mm thick thin-gauge electromagnetic stirring steel having a microstructure of ferrite and pearlite; The thin gauge electromagnetic stirring steel is composed of the following components in weight percentage: C 0.13%, Si 0.24%, Mn 1.48%, P 0.011%, S 0.003%, Nb 0.038%, V 0.046%, Alt 0.03%, and the rest is Fe and unavoidable impurities; The temperature of the molten iron is 1350°C. In terms of weight percentage, the molten iron contains 0.022% S, 0.38% Si, and 0.11% P. During converter smelting, the slag basicity is 3.1, and the endpoint is controlled as follows: C 0.06%, P 0.008%, and S 0.015% by weight. The endpoint temperature is 1635°C, the furnace back temperature is 1580°C, the slag drop during tapping is 45mm, and a slag stopper is used to stop the slag before tapping. When the steel is 1 / 3 of the way through, alloys other than ferroniobium and ferrovanadium are added according to the target composition. Silicon manganese alloy, low-carbon ferromanganese, and pure Al blocks are used for deoxidation to an oxygen content of 15ppm. The argon station controls the Alt content to the target composition. When the steel is 2 / 3 of the way through, ferroniobium and ferrovanadium alloy are added according to the target composition. The tapping time is 230 minutes, and the ladle clearance is 400mm. During LF refining, the white slag holding time is 16 minutes, and the molten steel composition is adjusted to the target composition before leaving the station; During RH degassing, the process time is 30 minutes, the vacuum degree in the tank is reduced to 67Pa within 5 minutes, the ultimate vacuum treatment time is 15 minutes, and the H content is 0.9ppm by weight when leaving the station. After breaking the air, 280m of pure calcium wire (the diameter of the pure calcium wire is 9mm and the calcium content of the pure calcium wire is 70g / m3) is fed, and soft blowing is carried out for 12 minutes; During continuous casting, the slab casting speed was 0.95 m / min, the superheat was 21°C, and two pairs of electromagnetic stirrers were used, with one pair installed at each of the four inlets and outlets of the secondary cooling section. The inlet current was 390 A, the outlet current was 360 A, and the static soft pressure was 5 mm, ensuring that the slab met the central segregation C2.0 level specified in YB / T4002-2013 "Grading Chart for Macrostructure Defects of Continuously Cast Steel Square Billets"; When the slab is piled in the windproof place for cooling, the cooling time is 48 hours; During heating, the temperature of the heating section is 1225°C, the temperature of the soaking section is 1215°C, the total time in the furnace is 180 minutes, the heating section time is 50 minutes, and the soaking section time is 40 minutes; Before rough rolling, the slab thickness is 220 mm, and the process parameters for rough rolling are:

[0042] The process parameters of finishing rolling are:

[0043] During normalizing treatment, the temperature is 900℃, the total normalizing time in the furnace is 50min, the heating time is 30min, and the holding time is 20min.

[0044] Example 7 The only difference between this embodiment and embodiment 1 is that, in this embodiment, the temperature during normalizing treatment is 895°C.

[0045] Example 8 The only difference between this embodiment and embodiment 6 is that in this embodiment, the temperature during normalizing treatment is 895°C.

[0046] Comparative Example 1 The only difference between this comparative example and Example 1 is that in this comparative example, the temperature during normalizing treatment is 885°C.

[0047] Comparative Example 2 The only difference between this comparative example and Example 1 is that in this comparative example, the temperature during normalizing treatment is 905°C.

[0048] Comparative Example 3 The only difference between this comparative example and Example 1 is that in this comparative example, during the normalizing treatment, the total normalizing time in the furnace is 50 minutes, the heating time is 35 minutes, and the holding time is 15 minutes.

[0049] Comparative Example 4 The only difference between this comparative example and Example 1 is that in this comparative example, during the normalizing treatment, the total normalizing time in the furnace is 50 minutes, the heating time is 25 minutes, and the holding time is 25 minutes.

[0050] Experimental Example 1 Low Temperature Toughness Test The following performance tests were performed on the thin-gauge electromagnetic stirring steels in Examples 1 to 8 and Comparative Examples 1 to 4: ① Low temperature toughness test: A dual-column metal pendulum impact tester was used to measure the longitudinal impact energy KV2 of a V-notch thin-gauge electromagnetic stirring steel specimen at -40°C, -50°C, and -60°C under a 2mm pendulum blade. ② Grain size test: The grain size was measured according to the intercept method in ASTM E112-2013 (R2021).

[0051] The test results are shown in Table 1 below Table 1 Low temperature toughness test results

[0052] By comparing Example 1 with Comparative Examples 1 to 4, it can be seen that by strictly controlling the normalizing process temperature to 890-900°C, the total furnace time to 50 min, and the holding time to 18-22 min, the thin-gauge electromagnetic stirring steel after normalizing has good low-temperature toughness, and the longitudinal impact energy at -40°C can reach more than 120 J, which can meet the performance requirements of the market.

[0053] Experimental Example 2 Room Temperature Mechanical Properties Test The lower yield strength, tensile strength, and elongation at break of the thin-gauge electromagnetic stirring steels in Examples 1 to 8 were tested with reference to GB / T 228.1-2021, "Tensile testing of metallic materials - Part 1: Test methods at room temperature." The results showed a lower yield strength of 365 to 426 MPa, a tensile strength of 522 to 566 MPa, and an elongation at break of 31% to 34.5%. This demonstrates that the thin-gauge electromagnetic stirring steels of this invention possess high strength and good ductility, meeting market performance requirements.

[0054] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A normalizing process for thin gauge electromagnetic stirring steel, characterized in that: The following steps are involved: The molten iron is subjected to converter smelting, LF refining, RH degassing, continuous casting, slab stack cooling, heating, rough rolling, finish rolling, finishing, and normalizing treatment to obtain thin-gauge electromagnetic stirring steel. During the normalizing treatment, the temperature is 890-900°C, the total normalizing furnace time is 50 minutes, and the holding time is 18-22 minutes.

2. The normalizing process for thin-gauge electromagnetic stirring steel according to claim 1, characterized in that: When the thickness of the thin-gauge electromagnetic stirring steel is 6 mm or less and 12 mm or less, the normalizing temperature is 890-894°C; When the thickness of the thin-gauge electromagnetic stirring steel is 12 mm or less and the thickness is ≤ 16 mm, the temperature of the normalizing treatment is 897-890° C.

3. The normalizing process for thin-gauge electromagnetic stirring steel according to claim 1, characterized in that: Calculated in weight percentage, the endpoint of the converter smelting is controlled to be: C 0.06%-0.07%, P≤0.008%, and S≤0.018%.

4. The normalizing process for thin-gauge electromagnetic stirring steel according to claim 1, characterized in that: During the LF refining, the white slag retention time is 16 to 18 minutes.

5. The normalizing process for thin-gauge electromagnetic stirring steel according to claim 1, characterized in that: During the RH degassing, the vacuum degree is ≤67 Pa, and the ultimate vacuum treatment time is 13-15 minutes.

6. The normalizing process for thin-gauge electromagnetic stirring steel according to claim 1, characterized in that: During the continuous casting, the superheat degree is 15-25°C.

7. The normalizing process for thin-gauge electromagnetic stirring steel according to claim 1, characterized in that: During the heating, the temperature of the heating section is 1210-1250°C, and the temperature of the soaking section is 1210-1240°C.

8. The normalizing process for thin-gauge electromagnetic stirring steel according to claim 1, characterized in that: During the rough rolling, the starting rolling temperature is 1060-1090°C, and the finishing rolling temperature is 980-1030°C.

9. The normalizing process for thin-gauge electromagnetic stirring steel according to claim 1, characterized in that: During the finish rolling, the starting rolling temperature is 920-1000°C, and the final rolling temperature is 770-830°C; When the thickness of the thin-gauge electromagnetic stirring steel is 6 mm or less and 8 mm or less, the starting temperature of the finishing rolling is ≤ 1000° C. and the final rolling temperature is ≤ 830° C.; When the thickness of the thin-gauge electromagnetic stirring steel is 6 mm or less and the thickness is ≤12 mm, the start rolling temperature of the finishing rolling is ≤950°C and the final rolling temperature is ≤830°C; When the thickness of the thin-gauge electromagnetic stirring steel is 12 mm or less and ≤ 16 mm, the start rolling temperature of the finish rolling is ≤ 930° C., and the final rolling temperature is ≤ 810° C.

10. The normalizing process for thin-gauge electromagnetic stirring steel according to claim 1, characterized in that: The thin-gauge electromagnetic stirring steel is composed of the following components in weight percentage: C 0.1%-0.17%, Si 0.2%-0.35%, Mn 1.4%-1.5%, P≤0.015%, S≤0.003%, Nb 0.035%-0.045%, V 0.04%-0.05%, Alt 0.02%-0.045%, and the remainder is Fe and unavoidable impurities.

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