Low-cost 24kg-grade low-temperature-resistant hot-rolled l-shaped steel, production method and application thereof

Abstract

The application provides a low-cost 24kg-grade low-temperature-resistant hot-rolled L-shaped steel and a production method and application thereof, and the composition comprises C, Si, Mn, P, S, Ti, Al, N and Fe. Under low-cost micro-alloying and process design, a large number of TiN and AlN second-phase particles are precipitated in the structure, the volume fraction of the AlN second-phase particles is greater than 0.03%, the size of the AlN second-phase particles is less than 30 nanometers, the volume fraction of the TiN second-phase particles is greater than 0.02%, the size of the TiN second-phase particles is less than 25 nanometers, the sum of the volume fraction of the AlN second-phase particles and the TiN second-phase particles with a size less than 16 nm is greater than or equal to 0.04%, the product structure is ferrite and pearlite, the ferrite grain diameter is less than or equal to 13 micrometers, and the 24kg low-temperature-resistant hot-rolled L-shaped steel meeting the requirements of a ship classification society is developed, and the strength and low-temperature toughness of the product are improved. The product can be applied to a reinforcing rib or a supporting component of equipment such as a low-temperature ship in an environment of-40 DEG C and above.

Description

Technical Field

[0001] This invention belongs to the field of steel technology, specifically relating to a low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel, its production method, and its application. Background Technology

[0002] Hot-rolled L-beams, also known as unequal-sided and unequal-thickness angle steel, are complex cross-sectional profiles used in the construction of large ships. They can also be used in marine engineering structures and high-requirement building structures, representing the future development direction of marine steel. Under the same conditions, the strength of hot-rolled L-beams is far greater than that of ordinary marine steel. Therefore, hot-rolled L-beams can enhance the strength of ships, reduce their weight, and increase their load-bearing capacity.

[0003] Advanced ultra-large fully refrigerated liquefied gas carriers are high-tech, highly complex, and high-value-added products, hailed as the "crown jewel" of shipbuilding. Their hull construction requires a large amount of 24kg-grade low-temperature resistant hot-rolled L-shaped steel. Due to the high difficulty in producing high-strength, low-temperature resistant hot-rolled L-shaped steel, steel companies mostly use Ni microalloying, a strategic and precious resource. This results in higher production costs, more complex processes, and significant fluctuations in low-temperature toughness, making stable supply impossible. Consequently, it cannot meet the increasing domestic demand for high-end shipbuilding.

[0004] Chinese Patent CN 114855085 A, published on August 5, 2022, discloses a marine low-temperature L-shaped steel and its welding process. The chemical composition is: C 0.068-0.095%, Si 0.15-0.48%, Mn 1.12-1.70%, Cr 0.015-0.055%, Ni 0.70-0.85%, Mo 0.002-0.005%, Cu 0.012-0.031%, Nb 0.016-0.025%, V 0.004-0.008%, Ti 0.002-0.006%, B ≤ 0.0008%, Alt ≤ 0.03%, As ≤ 0.008%. P≤0.008%, S≤0.005%, balance being Fe and unavoidable impurities; Production process: smelting - converter - electric furnace - smelting - continuous casting - rolling - post-rolling water cooling - heat treatment; Product properties: R eL ≥315MPa, R m ≥480MPa, A≥25%, -60℃KV2≥180J. However, it uses strategic and valuable Ni resources and post-rolling water cooling and heat treatment processes, resulting in complex production processes, high costs, high energy consumption, and resource waste.

[0005] Therefore, it is essential to provide a low-cost 24kg-grade low-temperature resistant hot-rolled L-shaped steel with low microalloying element content and low production energy consumption. Summary of the Invention

[0006] The purpose of this invention is to provide a low-cost 24kg-grade low-temperature resistant hot-rolled L-shaped steel and its production method. Under low-cost microalloying and process design, the large number of nano-sized TiN second-phase particles precipitated during the heating and roughing stages suppress austenite grain growth; strain-induced precipitation during the finishing rolling stage promotes the precipitation of a large number of nano-sized AlN second-phase particles, coupled with TiN second-phase particles precipitated in the high-temperature zone, inhibiting austenite recrystallization, increasing the non-recrystallization temperature, achieving a large amount of strain accumulation, promoting subsequent microstructure transformation, refining the product microstructure, and simultaneously improving the product's strength and low-temperature toughness. Furthermore, by designing the asymmetric roll pass elongation of the hot-rolled L-shaped steel, rolling stability and strip straightness are ensured. Under low-alloy composition design conditions, a 24kg-grade low-temperature resistant hot-rolled L-shaped steel with a yield strength R0 is developed. eH ≥235MPa, tensile strength R m 400-520MPa, elongation A≥22%, longitudinal Charpy V-notch impact energy KV2≥200J at 0℃, Charpy V-notch impact energy KV2≥150J at -20℃, and Charpy V-notch impact energy KV2≥120J at -40℃.

[0007] Another objective of this invention is to provide an application of low-cost grade 24 low-temperature resistant hot-rolled L-shaped steel for low-temperature shipbuilding, including shipbuilding for use in environments up to -40°C.

[0008] The specific technical solution of this invention is as follows: A low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel contains alloy compound particles of TiN second phase and AlN second phase composite particles. According to the industry standard YB / T 4562 referencing GB / T 2975, the mechanical property test specimens for hot-rolled L-shaped steel should be cut at 1 / 3 of the leg width direction. The volume fraction of AlN second-phase particles is greater than 0.03%, and their size is less than 30 nm; The volume fraction of TiN second-phase particles is above 0.02%, and their size is less than 25 nm.

[0009] The low-cost 24kg low-temperature resistant hot-rolled L-shaped steel must contain a volume fraction of second-phase particles with a size of less than 16 nm that satisfy the following formula: V AlN +V TiN ≥0.04%; In the formula: V AlN V represents the volume fraction of AlN. TiNThe volume fraction of TiN is defined as follows: the sum of the volume fractions of AlN second-phase particles (smaller than 16 nm) and TiN second-phase particles is ≥0.04%, preferably ≥0.06%. This volume fraction of fine second-phase particles effectively pins austenite grain boundaries, inhibits austenite recrystallization, increases the austenite recrystallization temperature, expands the non-recrystallized region, and accumulates a large amount of strain during rolling, thereby increasing the nucleation rate of microstructure transformation and refining the product microstructure. Simultaneously, the large number of fine second-phase particles in the product effectively hinders dislocation movement, improving product strength.

[0010] The metallographic structure of the low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel is ferrite + pearlite, with ferrite grain diameter ≤13μm, of which ferrite with diameter ≤10μm accounts for ≥85% of the total ferrite volume.

[0011] The low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel has the following chemical elements: C, Si, Mn, P, S, Ti, Al, N and Fe.

[0012] The low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel comprises the following chemical composition by weight percentage: C: 0.08%-0.16%, Si: 0.10%-0.60%, Mn: 0.50%-1.30%, P: 0.010%-0.025%, S: ≤0.020%, Ti: 0.008%-0.020%, Al: 0.02%-0.04%, N: 0.0080%-0.0160%, with the balance being iron and unavoidable impurities.

[0013] The steel composition of the aforementioned low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel also meets the following requirements: 250%≤K1=1500×C+100×Mn+2000×P≤350%; 3.0000≤K2=Al / (N-(Ti / 48)×14)≤6.0000; 1.00×10 -7 %%≤K3=(Ti / 48)×(N / 14)≤3.00×10 -7 %%.

[0014] In the above formula, each element represents its percentage content in the steel. For example, if the carbon content is 0.14%, then 0.14% is substituted into the formula for calculation.

[0015] K1 controls the addition of C, Mn, and P elements to meet product strength requirements. K2 controls the Al and N content used to precipitate AlN second-phase particles, ensuring sufficient AlN precipitation. The precipitated AlN particles inhibit austenite recrystallization and growth, thus refining the product microstructure. Simultaneously, the precipitation of a large number of fine and uniform AlN particles strengthens the product and improves its strength. Additionally, K3 controls the Ti and N content in the steel, allowing TiN particles to precipitate in the solid phase. By controlling the size of the precipitated TiN particles, fine and uniform TiN particles are obtained, achieving optimal control of second-phase particle size and strengthening effect.

[0016] The specifications of the low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel are: L200×90×9×14-L450×125×11.5×18.

[0017] The yield strength R of the low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel eH ≥235MPa, tensile strength R m 400-520MPa, elongation A≥22%, longitudinal Charpy V-notch impact energy KV2≥200J at 0℃, Charpy V-notch impact energy KV2≥150J at -20℃, and Charpy V-notch impact energy KV2≥120J at -40℃.

[0018] Preferably, the yield strength R of the low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel is... eH ≥300MPa, tensile strength R m ≥450MPa, elongation A≥30%, longitudinal Charpy V-notch impact energy KV2≥250J at 0℃, Charpy V-notch impact energy KV2≥200J at -20℃, and Charpy V-notch impact energy KV2≥180J at -40℃.

[0019] This invention provides a low-cost production method for 24kg grade low-temperature resistant hot-rolled L-shaped steel, comprising the following process flow: Hot metal pretreatment - converter smelting - argon blowing - LF furnace refining - continuous casting - heating furnace heating - high pressure water descaling - rough rolling - high pressure water descaling before finishing rolling - finishing rolling - air cooling - straightening - warehousing.

[0020] The molten iron pretreatment adopts a slag removal bright surface ≥85%, and an exit [S] ≤0.015%; The converter smelting process involves controlling the order of alloy addition: first adding low-carbon ferromanganese (FeMn), then adding the ferrosilicon alloy (FeSi). After tapping, aluminum particles are evenly sprinkled onto the slag surface; the total time is controlled to 25-35 minutes.

[0021] Argon blowing: Aluminum wire is fed in, and the Al content at the outlet is controlled between 0.030% and 0.060%.

[0022] The LF furnace refining process involves controlling the Al content of the ladle samples to be 0.025%-0.045% and the S content to be ≤0.008% after calcium treatment; soft blowing time to be 20-30 min; total time to be 60-90 min; and outlet temperature to be 1565-1625℃.

[0023] The continuous casting process involves: tundish temperature controlled at 1550-1570℃; casting speed controlled at 1.40-2.00 m / min; primary cooling: water flow rate 120-150 m³ / min. 3 / h; Secondary cooling: specific water volume 0.5-0.8 l / kg; The heating furnace has the following heating parameters: heating temperature: 1170-1220℃; heating time: 90-120min; heat spread temperature: 1180-1200℃; heat spread time: 20-25min. The roughing process includes two roughing mills with pass types including box-shaped passes and irregularly shaped passes. The elongation ratio of the long leg to the short leg of the irregularly shaped pass is 0.9-1.1. The roughing process includes two stages: Roughing 1 has a rolling temperature of 1050-1100℃ and a cross-sectional deformation of ≥30%; Roughing 2 has a rolling temperature of 990-1049℃ and a cross-sectional deformation of ≥40%.

[0024] High-pressure water descaling before finishing rolling: pressure ≥15MPa; The finishing mill consists of a continuous rolling mill with 3-6 two-roll stands, a rolling temperature of 780-900℃, a cross-sectional deformation of ≥30%, and an elongation ratio of the long leg to the short leg of the finishing mill pass of 0.9-1.1. Air cooling after finishing rolling.

[0025] After air cooling, the product undergoes straightening, length setting, inspection, and packaging for storage.

[0026] This invention provides an application of a low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel for the manufacture of cryogenic ships, including for the manufacture of ships at -40℃.

[0027] The design concept of this invention is as follows: The carbon (C) content is set at 0.08-0.16%. C is an effective strengthening element for steel; therefore, the lower limit for C content is set at 0.08%. On the other hand, when the C content exceeds 0.16%, it significantly reduces the weldability of hot-rolled L-shaped steel and also decreases its low-temperature toughness. Therefore, the upper limit for C content is set at 0.16%.

[0028] The Si content is set at 0.10-0.60%. Si (silicon) is a deoxidizing element and also contributes to increased strength. Therefore, the lower limit of the Si content is set at 0.10%. On the other hand, if the Si content is greater than 0.60%, it will accelerate high-temperature delamination, worsen toughness, and also have an adverse effect on the surface quality of the steel. Therefore, the upper limit of the Si content is set at 0.60%.

[0029] The Mn content is set at 0.50-1.30%. Mn (manganese) improves both the toughness and strength of steel within a certain range. Therefore, the lower limit of the Mn content is set at 0.50%. On the other hand, if the Mn content is greater than 1.30%, macrosegregation is likely to occur, leading to a significant decrease in the toughness of the steel. Therefore, the upper limit of the Mn content is set at 1.30%.

[0030] The phosphorus (P) content is set at 0.010-0.025%. P can cause welding cracks and reduce toughness in steel, but it can also contribute positively to the strength of the product. Therefore, while ensuring the weldability and toughness of the product, the P content should be maintained appropriately. Considering the role of P, the lower limit of the P content is set at 0.010%, and the upper limit of the P content is set at 0.025%.

[0031] The sulfur content is set to ≤0.020%. Sulfur will form MnS inclusions in the center of the billet due to solidification segregation, causing welding cracks, reduced toughness, etc. Therefore, it should be reduced as much as possible. Taking into account the cost of desulfurization, the sulfur content is limited to below 0.020%.

[0032] The Ti content is set at 0.008-0.020%. Ti (titanium) is used to precipitate sufficient TiN second-phase particles, which, through a pinning effect, hinder austenite grain growth, thus refining the austenite grains. Therefore, the lower limit of the Ti content is set at 0.008%. On the other hand, if the Ti content exceeds 0.020%, the TiN second-phase particles are coarse, making the continuously cast billet prone to cracks, affecting the surface quality of the final product, and also hindering cost control. Therefore, the upper limit of the Ti content is set at 0.020%.

[0033] The Al content is set at 0.02-0.04%. Al (aluminum) is a deoxidizer in steel and an important component in the formation of nitride particles that refine austenite grains through the pinning effect. To achieve the grain refinement effect, the lower limit of the Al content is set at 0.02%. Excessive Al content will generate coarse oxides, clogging the continuous casting nozzle and causing production accidents. Therefore, the upper limit of the Al content is set at 0.04%.

[0034] The nitrogen (N) content is set at 0.0080-0.0160%. Nitrogen (N) is the main element in the formation of TiN and AlN, contributing to microstructure refinement and precipitation strengthening, and is also a key element controlling the size of TiN and AlN precipitates. Therefore, the lower limit of the N content is set at 0.0080%. If the N content exceeds 0.0160%, it will cause TiN particles to become coarse, deteriorating low-temperature toughness, continuous casting surface quality, and strain aging properties of the steel. Therefore, the upper limit of the N content is set at 0.0160%.

[0035] In this invention, by optimizing and controlling the steelmaking and continuous casting processes, high-quality 24kg-grade low-temperature resistant continuous casting billets are produced. The composition meets classification society requirements, and the surface and internal quality are excellent, effectively improving the yield of 24kg low-temperature resistant continuous casting billets. Optimized heating processes ensure fine and uniform austenite grains during billet heating. Optimized rolling processes in the roughing stage result in two dynamic recrystallizations, refining the austenite grain size and providing a foundation for final microstructure refinement. In the finishing stage, strain-induced precipitation promotes the precipitation of a large number of AlN second-phase particles, coupled with TiN second-phase particles present in the billet, inhibiting austenite recrystallization, expanding the non-recrystallized austenite region, increasing strain accumulation in austenite, promoting the nucleation rate of austenite-to-ferrite transformation, and refining the microstructure.

[0036] Compared with existing technologies, this invention employs a low-cost alloy design and, combined with the characteristics of hot-rolled L-shaped steel rolling, achieves stable production of 24kg-grade low-temperature resistant hot-rolled L-shaped steel through pass design and optimized rolling process adjustments, without requiring water quenching or heat treatment. Through low-cost microalloying and process design, the strength of the product is improved by the abundant precipitation of TiN and AlN second-phase particles in the microstructure, resulting in the development of 24kg low-temperature resistant hot-rolled L-shaped steel that meets classification society requirements, with a yield strength R... eH ≥235MPa, tensile strength R m The strength of the product is 400-520 MPa, elongation A≥22%, longitudinal Charpy V-notch impact energy KV2≥200J at 0℃, Charpy V-notch impact energy KV2≥150J at -20℃, and Charpy V-notch impact energy KV2≥120J at -40℃. Product specifications range from L200×90×9×14 to L450×125×11.5×18; the microstructure is ferrite and pearlite, with ferrite grain size ≤13μm; the product can be used as reinforcing ribs or support components in equipment such as cryogenic ships in environments at -40℃ and above. Furthermore, this invention does not require the use of Ni or a large amount of microalloying elements, resulting in low cost. This invention uses air cooling after rolling, eliminating the need for post-rolling water cooling processes and heat treatment, thus reducing production costs and energy consumption. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the shape of a hot-rolled L-shaped steel section. Figure 2 Metallographic image of the rolled piece from Example 1; Figure 3 Metallographic image of the rolled piece from Example 3; Figure 4 Metallographic image of the rolled piece from Example 5; Figure 5 Metallographic image of the rolled piece in Comparative Example 9; Figure 6 Metallographic image of the rolled piece for Comparative Example 10; Figure 7 The image shows the metallographic structure of the rolling mill in Comparative Example 11. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Examples 1-6 A low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel comprises the following composition by mass percentage as shown in Table 1. The balance not shown in Table 1 is Fe and unavoidable impurities.

[0040] Comparative Examples 7-12 A low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel comprises the following composition by mass percentage as shown in Table 1. The balance not shown in Table 1 is Fe and unavoidable impurities.

[0041] Table 1 Specifications and ingredient content (wt%) of each embodiment and comparative example

[0042] The production method of low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel described in the above embodiments and comparative examples includes the following process flow: Hot metal pretreatment - converter smelting - argon blowing - LF furnace refining - continuous casting - heating furnace heating - high pressure water descaling - rough rolling - high pressure water descaling before finishing rolling - finishing rolling - air cooling - straightening - length setting - inspection - packaging and warehousing; The molten iron pretreatment adopts a low slag removal bright surface ≥85%, and an exit [s] ≤0.015%; The converter smelting process involves controlling the order of alloy addition: first adding low-carbon ferromanganese (FeMn), then adding the ferrosilicon alloy (FeSi). After tapping, aluminum particles are evenly sprinkled onto the slag surface; the total time is controlled to 25-35 minutes.

[0043] The argon blowing station: feeds aluminum wire, and controls the Al content at the outlet to be between 0.030% and 0.060%.

[0044] The LF furnace refining process involves controlling the Al content of the ladle samples to be 0.025%-0.045% and the S content to be ≤0.008% after calcium treatment; soft blowing time to be 20-30 min; total time to be 60-90 min; and outlet temperature to be 1565-1625℃.

[0045] The continuous casting process involves: tundish temperature controlled at 1550-1570℃; casting speed controlled at 1.40-2.00 m / min; primary cooling: water flow rate 120-150 m³ / min. 3 / h; Secondary cooling: specific water volume 0.5-0.8 l / kg; The heating furnace has the following heating parameters: heating temperature: 1170-1220℃; heating time: 90-120min; heat spread temperature: 1180-1200℃; heat spread time: 20-25min.

[0046] The roughing mill includes two roughing mills, with pass types including box-shaped passes and irregularly shaped passes. The ratio of the elongation coefficient of the long leg to the short leg of the irregularly shaped billet is 0.9-1.1. The roughing process includes two stages: Roughing 1 with a rolling temperature of 1050-1100℃ and a cross-sectional deformation of ≥30%; and Roughing 2 with a rolling temperature of 990-1049℃ and a cross-sectional deformation of ≥40%.

[0047] High-pressure water descaling before finishing rolling: pressure ≥15MPa; The finishing mill consists of a continuous rolling mill with 3-6 two-roll stands, a rolling temperature of 780-900℃, a cross-sectional deformation of ≥30%, and an elongation ratio of the long leg to the short leg of the finishing mill pass of 0.9-1.1. Air cooling after finishing rolling.

[0048] The main process parameters for each embodiment and comparative example are shown in Tables 2 and 3.

[0049]

[0050]

[0051] The microstructure and performance tests of the L-shaped steel produced in each embodiment and comparative example are shown in Tables 4 and 5. In Table 4, the second-phase particles were detected using transmission electron microscopy (TEM / STEM) according to the GB / T 43883-2024 standard; the microstructure was detected using image analysis software according to the GB / T 15749-2008 standard. The mechanical properties in Table 5 were tested according to GB / T 228.1 and GB / T 229 standards. In Table 4, F represents ferrite, and P represents pearlite.

[0052]

[0053]

[0054] This invention, produced using the above-mentioned components and processes, results in a large precipitation of TiN and AlN second-phase particles in the microstructure, enhancing the product's strength. It produces 24kg low-temperature resistant hot-rolled L-shaped steel with a yield strength R... eH ≥235MPa, tensile strength R m The steel has a strength of 400-520 MPa, elongation A ≥ 22%, longitudinal Charpy V-notch impact energy KV2 ≥ 200 J at 0℃, KV2 ≥ 150 J at -20℃, and KV2 ≥ 120 J at -40℃. The produced steel can be used to manufacture cryogenic ships.

[0055] Comparative Example 7 shows that the tensile strength of the product was lower than the design requirement because the content of C, Mn and P elements did not meet the requirements of formula K1. Comparative Example 8 shows that the content of Al and N elements did not meet the required value of formula K2, which resulted in the volume percentage of AlN second phase particles not meeting the design value. Consequently, the total volume of AlN and TiN second phase particles with a diameter of <16nm could not meet the design requirements, affecting the ferrite size and thus causing the product's low-temperature toughness to fail to meet the design requirements. Comparative Example 9 shows that the content of Ti and N elements did not meet the required value of formula K3, which resulted in the TiN second phase particles not reaching the design value. Consequently, the total volume of AlN and TiN second phase particles with a diameter of <16nm could not meet the design requirements, affecting the ferrite size and thus causing the product's low-temperature toughness to fail to meet the design requirements. Comparative Example 10 shows that the product's microstructure and dimensions were affected because the finishing rolling temperature did not reach the design value, resulting in the product's low-temperature toughness not meeting the design requirements. Comparative Example 11 shows that the product's microstructure and dimensions were affected because the deformation of the precision-rolled section did not reach the design value, resulting in the product's low-temperature toughness not meeting the design requirements. Comparative Example 12 was scrapped because the ratio of the elongation coefficients of the long leg to the short leg of the rolled piece did not meet the design requirements during the rolling process, resulting in the rolled piece bending and being scrapped without subsequent microstructure and performance testing.

[0056] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel, characterized in that, The low-cost 24kg-grade low-temperature resistant hot-rolled L-shaped steel contains alloy compound particles that are composite particles of TiN second-phase particles and AlN second-phase particles; wherein, the volume fraction of AlN second-phase particles is above 0.03% and their size is less than 30nm; the volume fraction of TiN second-phase particles is above 0.02% and their size is less than 25nm.

2. The low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel according to claim 1, characterized in that, The sum of the volume fractions of AlN second-phase particles and TiN second-phase particles with a size less than 16 nm is ≥0.04%.

3. The low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel according to claim 1 or 2, characterized in that, The metallographic structure of the low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel is ferrite + pearlite, with ferrite grain diameter ≤13μm, of which ferrite with diameter ≤10μm accounts for ≥85% of the total ferrite volume.

4. The low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel according to any one of claims 1-3, characterized in that, The low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel comprises the following chemical composition by weight percentage: C: 0.08%-0.16%, Si: 0.10%-0.60%, Mn: 0.50%-1.30%, P: 0.010%-0.025%, S: ≤0.020%, Ti: 0.008%-0.020%, Al: 0.02%-0.04%, N: 0.0080%-0.0160%, with the balance being iron and unavoidable impurities.

5. The low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel according to claim 4, characterized in that, The steel composition of the aforementioned low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel also meets the following requirements: 250%≤K1=1500×C+100×Mn+2000×P≤350%; 3.0000≤K2=Al / (N-(Ti / 48)×14)≤6.0000; 1.00×10 -7 %%≤K3=(Ti / 48)×(N / 14)≤3.00×10 -7 %%.

6. The low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel according to any one of claims 1-5, characterized in that, The yield strength R of the low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel eH ≥235MPa, tensile strength R m 400-520MPa, elongation A≥22%, longitudinal Charpy V-notch impact energy KV2≥200J at 0℃, Charpy V-notch impact energy KV2≥150J at -20℃, and Charpy V-notch impact energy KV2≥120J at -40℃.

7. A method for producing low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel according to any one of claims 1-6, characterized in that, The production method includes the following process flow: molten iron pretreatment - converter smelting - argon blowing - LF furnace refining - continuous casting - heating furnace heating - high-pressure water descaling - rough rolling - high-pressure water descaling before finishing rolling - finishing rolling - air cooling - straightening - warehousing.

8. The production method according to claim 7, characterized in that, The heating furnace has the following heating parameters: heating temperature: 1170-1220℃; heating time: 90-120min; heat spread temperature: 1180-1200℃; heat spread time: 20-25min.

9. The production method according to claim 7, characterized in that, The roughing process consists of two stages: Roughing 1 has a rolling temperature of 1050-1100℃ and a cross-sectional deformation of ≥30%; Roughing 2 has a rolling temperature of 990-1049℃ and a cross-sectional deformation of ≥40%.

10. The production method according to claim 7, characterized in that, The finishing rolling process includes: rolling temperature of 780-900℃; cross-sectional deformation ≥30%; and the elongation ratio of the long leg to the short leg of the finishing rolling hole is 0.9-1.

1.

11. An application of the low-cost 24kg grade low-temperature resistant hot-rolled L-shaped steel according to any one of claims 1-6, characterized in that, Used in the manufacture of cryogenic ships.

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