A method for producing extra-thick structural steel plates with low compression ratio and high Z-axis performance.

Abstract

This invention relates to the field of steel processing technology and discloses a method for producing extra-thick structural steel plates with low compression ratio and high Z-axis performance. The method includes the following steps: LF refining of molten steel; heat treatment; temperature difference control between slab and intermediate billet; controlled rolling and cooling; post-rolling heat treatment; and finished product warehousing. This method for producing extra-thick structural steel plates with low compression ratio and high Z-axis performance employs controlled rolling and cooling processes, eliminating the need for complex quenching / tempering / normalizing heat treatment procedures and the addition of expensive alloys such as Ni, Mo, and Cu. This greatly simplifies the production process, reduces costs, and shortens the delivery cycle. With a compression ratio ≤3, it allows mainstream steel mills to use 300mm cross-section continuous casting billets to replace large cross-section casting billets / ingots for rolling extra-thick plates up to 120mm thick, avoiding additional equipment investment and achieving cost reduction, efficiency improvement, and quality enhancement.

Description

Technical Field

[0001] This invention relates to the field of steel processing technology, specifically to a method for producing extra-thick building structural steel plates with low compression ratio and high Z-axis performance. Background Technology

[0002] Construction steel refers to steel widely used in steel structure buildings such as super high-rise buildings, railway stations, airports, and convention centers. Construction steel is characterized by fast construction speed, good earthquake resistance, and environmental friendliness. Q460GJ grade structural steel has been widely used in various major projects, effectively reducing the self-weight of steel structures while providing higher structural strength.

[0003] Chinese patent CN110616377A proposes a method for producing Q460GJ steel plates with low yield strength ratio and high toughness. However, this method is suitable for steel plates with a thickness ≤80mm, and when producing thicknesses above 100mm, the strength at the 1 / 4 position is too low to meet the Q460GJ steel grade requirements. It also exhibits instability in thick-drawn Z35 steel. Chinese patent CN111748678A proposes a low compression ratio, large-thickness, lamellar tear-resistant steel plate and its manufacturing method. This method does not involve special pressure processing; after roughing and finishing rolling, the semi-finished product needs slow cooling and then heat treatment. This results in high process costs, a long process flow, and a production thickness range of 60-90mm, making it unsuitable for producing thicknesses above 100mm. Chinese patent CN115216701A proposes a low compression ratio, lamellar tear-resistant Q960 high-strength steel and its preparation method. This method does not involve special pressure processing; it requires tempering heat treatment after rolling, resulting in high alloy costs and making it only suitable for producing high-strength steel. Chinese patent CN105925894A proposes an ultra-thick, high-strength, lamellar-tear-resistant Q500D-Z35 hydropower unit steel plate and its manufacturing method. This method uses ingot rolling, requiring quenching and tempering heat treatment after rolling, without special pressure processing, making it unsuitable for low-cost production of high-rise structural steel. Chinese patent CN101987330A proposes a manufacturing method for an ultra-thick, lamellar-tear-resistant steel plate, which uses a die-casting ingot forging production method. The steel plate requires normalizing heat treatment, resulting in high production costs and hindering its widespread application in steel plates with thicknesses in the 100-120mm range. Chinese patent CN108914005B proposes an extra-thick, corrosion-resistant steel plate with a yield strength >460MPa and excellent low-temperature toughness, and its manufacturing method. This method uses a high-alloy composition, with the main alloys being Mn: 2.02–2.35%, Nb: 0.041–0.062%, V: 0.121–0.162%, Ti: 0.022–0.051%, Cu: 0.76–1.02%, and Ni: 0.77–1.08%. The alloy cost is extremely high, and post-rolling normalizing heat treatment is required, making it uneconomical and unsuitable for widespread application in 100-120mm high-strength structural steel. Chinese patent CN114480969A proposes a production method for Q460GJ, a high-toughness, high-Z-axis performance extra-thick steel with a compression ratio ≤4, applicable to thicknesses of 80-100mm. Its chemical composition is as follows: C: 0.1~0.13, Si: 0.1~0.3, Mn: 1.1~1.3, P≤0.012, S≤0.003, Cr: 0.3~0.5, Ti: 0.01~0.02, Nb: 0.01~0.02, Ni: 0.1~0.3, V: 0.06~0.07, Als: 0.025~0.035, etc., and the post-rolling cooling and reddening temperature is 530~550℃. This composition and process are not suitable for extended production of thicknesses greater than 100mm.As thickness increases, the cooling rate must be further increased to improve the plate's strength. However, with a carbon content of 0.1-0.13%, further increasing the cooling rate will further increase the proportion of hard phase on the surface, which will worsen the surface toughness and increase the yield strength ratio, resulting in significant performance differences across the entire thickness and failing to meet steel grade requirements. Chinese patent CN105525209B proposes a low yield strength ratio Q460GJ structural steel and its production method. This method is suitable for producing steel with limited thickness (the upper limit of the example is 50mm), using a carbon content of 0.17-0.19% and a final cooling temperature of 660-680℃. It cannot produce Q460GJ steel with a thickness greater than 100mm.

[0004] In view of this, we propose a method for producing extra-thick building structural steel plates with low compression ratio and high Z-axis performance. Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing extra-thick building structural steel plates with low compression ratio and high Z-axis performance, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for producing extra-thick building structural steel plates with low compression ratio and high Z-axis performance, comprising the following steps:

[0007] S1. Molten steel is refined and smelted using LF refining process;

[0008] S2, Heat treatment;

[0009] S3, temperature difference control between slab and intermediate billet;

[0010] S4, controlled rolling and controlled cooling treatment;

[0011] S5. Post-rolling cold treatment;

[0012] S6. Finished product warehousing process.

[0013] Optionally, S1 includes: molten steel is refined by LF, treated by RH / VD vacuum, the S content is strictly controlled during smelting, and then protected and cast into a 300mm thick continuous casting billet. The billet is judged to be ≤1.5 of national standard C class in low magnification, and 200m of calcium feed line is used per furnace.

[0014] Optionally, S2 further includes: a total slab heating time of ≥280 min, a homogenization temperature of 1170~1260℃, a homogenization time of ≥40 min, and a core temperature of 1170~1260℃ when the slab exits the steel.

[0015] Optionally, S3 further includes: extending the water spraying time using the roughing descaling box, descaling each pass of the descaling water on the roughing mill, and simultaneously using the manifold of the intermediate roller table of the roughing and finishing mills to water cool the upper and lower surfaces of the slab. After water spraying, the thickness of the sandwich layer between the upper and lower surfaces is greater than 20 mm, the temperature difference between the surface and the core of the intermediate slab is greater than 100 °C, and the temperature difference between the surface of the intermediate slab and the core of the finishing mill is greater than 50 °C, so that the steel plate introduces greater plastic deformation and stress into the core during the rolling process.

[0016] Optionally, the total time in the water dispensing time is greater than 15 seconds.

[0017] Optionally, S4 includes: using two-stage controlled rolling, with at least one pass of rough rolling at a rolling temperature ≥1140℃ having a reduction rate ≥18%, the rough rolling end temperature controlled at 1130~1180℃ and the reduction rate of that pass ≥16%; the intermediate billet thickness ≥ finished product thickness +40mm, the finishing rolling temperature being 780~820℃; after rolling, directly immersing in water and cooling to the target temperature at a cooling rate of 3~6℃ / s using a MULPIC device, and then air cooling on a cooling bed after hot straightening.

[0018] Optionally, S5 further includes: air cooling on a cooling bed to a surface temperature of 300-350°C, then stacking in an insulation pit for cooling for more than 60 hours, with a surface temperature of less than 90°C, before unstacking and directly cutting to length without heat treatment.

[0019] Compared with the prior art, the present invention provides a method for producing extra-thick building structural steel plates with low compression ratio and high Z-axis performance, which has the following beneficial effects:

[0020] 1. This method for producing extra-thick structural steel plates with low compression ratio and high Z-axis performance adopts a controlled rolling and controlled cooling process. It eliminates the need for complex heat treatment processes such as quenching and tempering / normalizing / tempering, and avoids the addition of expensive alloys such as Ni, Mo, and Cu. This greatly simplifies the production process, reduces costs, and shortens the delivery cycle. With a compression ratio ≤3, it enables the production of extra-thick plates with a maximum thickness of 120mm using 300mm cross-section continuous casting billets, which are common in mainstream steel mills, instead of large cross-section casting billets / mold casting ingots. This avoids additional equipment investment and achieves cost reduction, efficiency improvement, and quality enhancement.

[0021] 2. The production method of this extra-thick building structural steel plate with low compression ratio and high Z-direction performance adopts differential temperature rolling and can be realized by using the intermediate water cooling device that is basically equipped in the medium and heavy plate production line. It can stably produce extra-thick Q460GJDZ35 steel plates with a maximum thickness of 120mm, and the performance fully meets the requirements of national standard GBT19879-2023.

[0022] 3. Compared with conventional production methods, the production method of this invention for extra-thick building structural steel plates with low compression ratio and high Z-axis performance can significantly improve the Z35 pass rate and ZL average value. The first-pass pass rate of Z35 for 100-120mm thickness can be stably above 98%, and the average value can be stably above 45%. It can be extended to use 350mm cross-section continuous casting billets and TMCP rolling to produce 120-140mm thickness. It can be extended to use 260mm continuous casting billet cross-section to produce a maximum thickness of 95mm, covering grades from Q345GJ to Q460GJ, and has good scalability. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] This invention provides a technical solution: a method for producing extra-thick structural steel plates with low compression ratio and high Z-axis performance, comprising the following steps:

[0025] S1. Molten steel is refined by LF refining and smelting; molten steel is refined by LF, RH / VD vacuum treatment, and the sulfur content is strictly controlled during smelting. Then it is protected and cast into a 300mm thick continuous casting billet. The billet is judged to meet the national standard C category 1.5 by low magnification. 200m of calcium feed line is used per heat.

[0026] S2. Heat treatment: The total heating time of the slab is ≥280min, the soaking temperature is 1170~1260℃, the soaking time is ≥40min, and the temperature of the core of the cast slab after exiting the steel is 1170~1260℃.

[0027] S3. Temperature difference control between slab and intermediate slab: The water-cooling time is extended using the roughing descaling box. Descaling is performed in each pass on the roughing mill, while the manifolds of the intermediate roller table between the roughing and finishing mills are used to water-cool the upper and lower surfaces of the slab. After water cooling, the thickness of the sandwich layer between the upper and lower surfaces is greater than 20mm, and the temperature difference between the surface and the core of the intermediate slab is greater than 100℃. In the finishing mill, the temperature difference between the surface reddening temperature and the core temperature of the intermediate slab is greater than 50℃, introducing greater plastic deformation and stress into the core of the steel plate during rolling. The total water cooling time is greater than 15s.

[0028] S4. Controlled rolling and cooling treatment; adopt two-stage controlled rolling, with at least one pass of reduction rate ≥18% during rough rolling at a rolling temperature ≥1140℃, and the rough rolling end temperature controlled at 1130~1180℃ with a reduction rate ≥16% for that pass; the intermediate billet thickness ≥ finished product thickness +40mm, and the finishing rolling temperature is 780~820℃; after rolling, directly immerse in water and cool to the target temperature at a cooling rate of 3~6℃ / s using a MULPIC device, and then air-cool on a cooling bed after hot straightening.

[0029] S5. Post-rolling cold stacking treatment: After air cooling on the cooling bed to a surface temperature of 300-350℃, the surface is placed in an insulation pit for cold stacking. The cold stacking time is >60 hours. When the surface temperature is <90℃, the stack is removed and no heat treatment is required. The product is then directly cut to length.

[0030] S6. Finished product warehousing process.

[0031] As one application of this embodiment: 1. The production method of this low compression ratio, high Z-axis performance extra-thick building structural steel plate adopts controlled rolling and controlled cooling process, which does not require complex heat treatment processes such as quenching and tempering / normalizing / tempering, nor does it require the addition of expensive alloys such as Ni, Mo, and Cu. This greatly simplifies the production process, reduces costs, and shortens the delivery cycle. When the compression ratio is ≤3, it can replace the large-section cast billet / ingot casting with 300mm cross-section continuous casting billet, which is available in mainstream steel mills, to roll extra-thick plates with a maximum thickness of 120mm, avoiding additional equipment investment and achieving cost reduction, efficiency improvement, and quality improvement. The differential temperature rolling method adopted can be achieved using the intermediate water cooling device that is basically equipped in medium and heavy plate production lines, and can stably produce extra-thick Q460GJDZ35 steel plates with a maximum thickness of 120mm, and the performance fully meets the requirements of national standard GBT19879-2023.

[0032] Compared to conventional production methods, this invention can significantly improve the Z35 pass rate and ZL average value. The first-pass pass rate of Z35 with a thickness of 100-120mm can be stabilized at over 98%, and the average value can be stabilized at over 45%. It can be extended to use 350mm cross-section continuous casting billets and TMCP rolling to produce 120-140mm thickness. It can be extended to use 260mm cross-section continuous casting billets to produce a maximum thickness of 95mm, covering grades from Q345GJ to Q460GJ, and has good scalability.

[0033] The present invention has been described in detail above. However, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, any modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A method for producing extra-thick structural steel plates with low compression ratio and high Z-axis performance, characterized in that: Includes the following steps: S1. Molten steel is refined and smelted using LF refining process; S2, Heat treatment; S3, temperature difference control between slab and intermediate billet; S4, controlled rolling and controlled cooling treatment; S5. Post-rolling cold treatment; S6. Finished product warehousing process; The S1 includes: molten steel is refined by LF, treated by RH / VD vacuum, the S content is strictly controlled during smelting, and then protected and cast into a 300mm thick continuous casting billet, with 200m of calcium feed wire per furnace; The S2 further includes: a total heating time of ≥280 min for the slab, a homogenization temperature of 1170~1260℃, a homogenization time of ≥40 min, and a core temperature of 1170~1260℃ for the cast slab. S3 further includes: extending the water spraying time using the rough descaling box, descaling each pass of the descaling water on the roughing mill, and simultaneously using the manifold of the intermediate roller table of the roughing and finishing mills to water cool the upper and lower surfaces of the slab. After water spraying, the thickness of the sandwich layer between the upper and lower surfaces is greater than 20mm, the temperature difference between the surface and the core of the intermediate slab is greater than 100℃, and the temperature difference between the surface reddening temperature and the core temperature of the intermediate slab in the finishing mill is greater than 50℃, so that the core of the steel plate is introduced with greater plastic deformation and stress during the rolling process. The S4 includes: using two-stage controlled rolling, with at least one pass of rough rolling at a rolling temperature ≥1140℃ having a reduction rate ≥18%, the rough rolling end temperature being controlled at 1130~1180℃ and the reduction rate of that pass being ≥16%; the intermediate billet thickness being ≥finished product thickness + 40mm, and the finishing rolling temperature being 780~820℃; after rolling, the billet is directly immersed in water and cooled to the target temperature at a cooling rate of 3~6℃ / s using a MULPIC device, and then air-cooled on a cooling bed after hot straightening.

2. The method for producing a high-compression-ratio, high-Z-axis performance extra-thick building structural steel plate according to claim 1, characterized in that: The total time for water dispensing is greater than 15 seconds.

3. The method for producing a high-compression-ratio, high-Z-axis performance extra-thick building structural steel plate according to claim 1, characterized in that: The S5 further includes: air cooling on a cooling bed to a surface temperature of 300-350°C, then stacking in an insulation pit for cooling for more than 60 hours, with a surface temperature of less than 90°C, before unstacking and directly cutting to length without heat treatment.