Continuous casting and rolling production method for medium plate
By combining surface heating of the billet with differential temperature rolling and multi-pass rolling, the problems of central porosity and shrinkage cavity in the billet were solved, the UT flaw detection level was improved, and the finished product quality of extra-thick plates was ensured.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUNAN VALIN XIANGTAN IRON & STEEL CO LTD
- Filing Date
- 2026-03-28
- Publication Date
- 2026-05-12
AI Technical Summary
Existing technologies are insufficient to effectively control the porosity and shrinkage cavities in the center of the billet during the production of extra-thick plates, resulting in non-compliance of UT testing. Furthermore, surface defects in the billet are easily ground down to cause dimensional defects or scrap.
The billet surface heating device is used to heat unevenly along the width direction. Combined with differential temperature rolling and multi-pass rolling, the temperature difference between the surface and center of the billet is utilized to roll it through a two-roll or four-roll mill. Combined with descaling and grinding finishing processes, the internal quality of the billet is improved.
It effectively improves the problems of central porosity and shrinkage cavities in the billet, enhances the UT inspection level, avoids dimensional defects caused by surface defect grinding, and improves the finished product quality of extra-thick plates.
Smart Images
Figure CN122007163A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of steel plate production technology, and relates to a continuous casting and rolling production method for medium and heavy plates. Background Technology
[0002] Steel plates are classified by thickness, with those thicker than 100mm defined as extra-thick plates. Due to their extremely high strength and toughness, extra-thick plates can withstand extreme loads and harsh environments, and are widely used in heavy industry sectors such as shipbuilding, bridge engineering, pressure vessels, nuclear power equipment, offshore platforms, and large machinery manufacturing. In recent years, with breakthroughs in metallurgical technology, extra-thick plates have gradually developed towards "lightweight, large single-unit weight, and oversized specifications," while improving weldability and promoting integrated design of large structures, becoming an important support for the upgrading of high-end manufacturing.
[0003] With the rapid development of economic construction, the demand for extra-thick steel plates with a single unit weight exceeding 20t and a thickness greater than 100mm, used in pressure vessels, large-span steel structures, hydropower stations, and other applications, is gradually increasing. Considering the safety and stability of large-scale installations, the performance indicators of the steel plates used are becoming increasingly stringent. For example, there are diverse performance requirements such as higher strength, higher low-temperature toughness, resistance to lamellar tearing, easier welding, corrosion resistance, fire resistance, weather resistance, and stricter requirements regarding internal defects. Currently, the main production technologies for extra-thick billets include in-mold casting, welding composite methods, and continuous casting processes for extra-thick slabs. Due to the stringent quality requirements of extra-thick plates, a large thickness of raw billet is needed to ensure a sufficient compression ratio. This necessitates extremely high cleanliness in large ingots or billets, and requires enhanced control of segregation and porosity during solidification. Ultimately, to provide high-quality raw materials for extra-thick plates, a better raw material solidification method needs to be selected and optimized to reduce the impact of segregation and porosity on the resistance to lamellar tearing. This requires high-capacity extra-thick plate rolling equipment that can utilize the penetrating effect of large rolling forces to eliminate defects such as porosity in the raw materials. During rolling, the large rolling force can fully break down and refine the grains to obtain a more uniform and fine microstructure. Furthermore, the "differential temperature rolling" method can be used to ensure that the surface temperature of the billet is low and the deformation resistance is high during rolling, allowing the rolling force to penetrate the core.
[0004] To improve the porosity and segregation during the solidification process of thick plate billets, JP2018114514 A discloses a "continuous casting method for steel" and proposes the PCCS (Porosity Control of Casting Slab) technology. At the end of the billet solidification, a pair of extra-large diameter rolls are used to apply a large reduction to the billet, thereby significantly improving the density of the billet.
[0005] CN201410695742.0 discloses "A heavy-pressure fan-shaped section for improving porosity and shrinkage defects in slabs and its application method," which uses a single-roll heavy-pressure process. At a solid fraction fs=0.95, a single-roll heavy-pressure process with a liquid core is performed. A heavy-pressure fan-shaped section is added at the end of the continuous casting machine. This is a modified version of a standard fan-shaped section with six pairs of φ300mm rollers, by removing two pairs of φ230mm rollers and replacing them with one pair of φ500mm pressure rollers. Its advantages include: the single-roll heavy-pressure process with a liquid core is highly efficient in improving the central porosity of thick slab castings, effectively reducing central porosity. Problems include: First, due to the fixed position under heavy pressure, the position of the solidification end is affected by the steel grade, pouring temperature, cooling, and casting speed, making adjustment difficult; second, when the solid fraction fs is close to 1, the steel has zero strength and zero plasticity, and large deformation at this time is prone to causing central cracks; third, due to insufficient rigidity of the fan-shaped section frame, elastic deformation causes the sensor's compression amount to be greater than the actual deformation amount; fourth, due to excessive single-roll compression, the billet bends, causing the roll gap to open due to insufficient pressure in the fan-shaped section before the heavy-pressure roll and the normal rolls after the heavy-pressure roll, resulting in bulging and worsening of central segregation.
[0006] CN201611196005.1 discloses a "sector-shaped section device under heavy pressure on continuously cast slabs," employing a multi-roller heavy pressure process with 2-3 sector-shaped sections. Each sector has 5-6 pairs of rollers. Besides considering single-roller heavy pressure with a liquid core at a solid fraction fs=0.95, it also considers heavy pressure after complete solidification. Compared to ordinary sector-shaped sections, it appropriately increases the roller diameter and the pressing force of the hydraulic cylinder. A foreign engineering company has proposed a sector-shaped section commercially known as SRD, with a single roller pressing force reaching 5000kN. The only difference between SRD and CN201611196005.1 is that it can be driven by a single roller for heavy or light pressure. Its function is not fundamentally different from CN201611196005.1. Advantages: It avoids the problem of difficulty in adjusting the position of the solidification end under single-point heavy pressure; it can simultaneously achieve multi-roller heavy pressure with a liquid core and complete solidification, and center segregation can be improved. Problems exist: First, when the solid fraction fs is close to 1, the steel has zero strength and zero plasticity, and large deformation at this time is prone to causing central cracks; Second, due to insufficient rigidity of the fan-shaped segment frame, elastic deformation is limited by the pressure of the hydraulic cylinder, the maximum reduction of a single fan-shaped segment is <10mm when it is not fully solidified at the end of solidification, and <5mm after full solidification, which translates to <2mm of reduction per roller. Due to the metal flow on the surface of the billet, it has little effect on the core of the billet and has very limited effect on improving central porosity and shrinkage cavities.
[0007] CN201910448269.9 discloses "A 2+8 roll combined thick slab large reduction casting and rolling mill," with results from its application in plants D and E: Using a single-roll reduction process, the maximum reduction in plant D is 30mm, and in plant E it is 20mm. The casting and rolling mill is placed in the middle of the continuous casting machine; in plant D, it is placed after the solidification end (fs=1) in the last sector section, and in plant E, it is placed before the last sector section of the continuous casting machine. Both are examples of mechanical rolling after full solidification. Advantages: Mechanical rolling after full solidification, due to the large reduction per pass, facilitates center deformation of the slab (differential temperature rolling), and significantly improves the porosity and shrinkage cavities in the center of the slab. Disadvantages: First, due to the uneven transverse temperature of the billet surface, the plasticity of the billet deviates greatly, and surface cracks appear under large reduction. Second, due to the large temperature difference between the transverse edge and core of the billet, the plasticity of the billet deviates greatly, and internal cracks in the triangular area inside the billet are prone to occur. Third, due to the large single-pass reduction, the billet warps during rolling, and the insufficient pressure in the preceding and following sector sections of the casting and rolling mill causes the roll gap to open. Plant D placed the billet in the following sector section at the end of solidification (fs=1), and the preceding sector section of the casting and rolling mill... The following issues were identified: First, the molten steel did not fully solidify, leading to bulging and central segregation in the billet. Second, the large single-pass reduction caused warping and shaking of the billet during rolling, resulting in severe fluctuations in the liquid level in the crystallizer and slag entrainment in the billet. Third, the constant contact between the rolls and the continuously cast billet caused thermal fatigue on the roll surface, resulting in a very short roll life. Fourth, the rolling mill has a power of several thousand kilowatts, while the billet pulling motor for the sector section is usually only a few dozen kilowatts, making power or torque matching difficult. The unit of casting machine pulling speed is usually m / min, while the unit of rolling mill speed is m / s, and the order of magnitude difference in speed also makes matching difficult. Summary of the Invention
[0008] This invention aims to provide a continuous casting and rolling production method for medium and heavy plates, which can avoid the problem of UT inspection failure caused by the loose center of the billet in the production of extra-thick plates in the traditional continuous casting and rolling process, and improve the UT inspection level. At the same time, after the surface defects of the billet are repaired and cleaned, the final thick plate product is prevented from having dimensional defects or scrap due to thickness, width, length, or exceeding tolerance caused by surface defect repair.
[0009] The technical solution of this invention: A method for continuous casting and rolling of medium-thick plates, comprising the following process steps: continuous casting of slabs, flame cutting of slabs, surface heating of slabs, descaling, rolling of intermediate slabs, surface inspection of slabs or intermediate slabs, removal of slabs from the production line, grinding and finishing, and subsequent conventional rolling of medium-thick plates. Key process steps include: 1) Surface heating of billet: Roller-hearth tunnel kiln heating furnace or induction surface heating device is used for heating. The heating power of the edge of the billet is higher than that of the middle of the billet along the width direction. The surface heating rate of the billet is 20-200℃ / min. The temperature difference of the transverse surface of the billet after heating is 10-60℃. 2) Rolling: The billet is rolled into an intermediate billet using a two-roll or four-roll mill. It can be a reversible mill or a non-reversible mill with unidirectional rolling. The reduction rate per pass is 10% to 20%. The billet mill is a low-speed, high-torque mill with a rolling force of 50,000 to 100,000 kN and a rolling speed of 0.5 to 3 m / s. 3) Descaling: Use a high-pressure water descaling machine or a shot peening device with high-pressure water and sand to remove the iron oxide scale from the surface of the billet. The high-pressure water pressure is 10-30 MPa. 4) Grinding and finishing: Use flame cleaning equipment or mechanical finishing and grinding equipment to finish and grind to remove surface defects of the billet or intermediate billet.
[0010] Further, step 2) rolling: the billet is rolled into an intermediate billet using a two-roll mill. The billet mill is a two-roll irreversible mill with a roll diameter of 1100mm, a roll length of 2500mm, a maximum rolling force of 80000KN, and a maximum reduction rate of 15% per pass.
[0011] Further, step 2) rolling: the billet is rolled into an intermediate billet using a four-high reversible rolling mill with a roll diameter of 1000mm, a roll length of 2400mm, a maximum rolling force of 70000kN, and a single-pass reduction rate of 10%.
[0012] The innovations of this invention are: 1) The billet mill is not placed in the middle of the continuous casting machine, but after the continuous casting machine cuts the billet; 2) An induction heating device for the billet surface is placed before the billet mill; 3) A descaling machine is placed before the billet mill to remove iron oxide scale. In addition to preventing iron oxide scale from being pressed in, its more important function is to facilitate the inspection of the billet surface; 4) An optical intermediate billet surface inspector, a transverse bypass roller conveyor, and a grinding and finishing device are used to clean billets with surface defects or intermediate billets after they are removed from the production line.
[0013] The beneficial effects of this invention are: it can avoid the problem of UT inspection failure caused by the looseness and shrinkage of the billet center in the production of extra-thick plates in the traditional thick plate continuous casting and rolling process, and improve the UT inspection level. At the same time, after the surface defects of the billet are repaired and cleaned, it can prevent the final thick plate product from having dimensional defects or scrap due to thickness, width, length, or exceeding tolerance caused by surface defect repair. Attached Figure Description
[0014] Figure 1 This is a process flow diagram for the continuous casting and rolling production of medium and heavy plates. The production line consists of a slab continuous casting machine, a flame cutting machine, a slab surface heating device, a descaling machine, a billet rolling mill, an optical slab or intermediate billet surface inspector, a transverse bypass roller conveyor, a grinding and finishing device, and a subsequent traditional medium and heavy plate production line.
[0015] Figure 2 This is a process flow diagram for Example 1.
[0016] Figure 3 This is a process flow diagram for Example 2. Detailed Implementation
[0017] The present invention will be further described below with reference to the embodiments. Example 1
[0018] Figure 2 The diagram illustrates a continuous casting and rolling production method for medium-thick plates, using a two-roll irreversible rolling mill. The key process steps include: 1) Surface heating of billet: The R12m 450×2600mm extra-thick plate continuous casting machine with light reduction device and secondary cooling electromagnetic stirring device produces billets with qualified segregation; the flame cutting machine then performs fixed or multiple length cutting; the cut billet enters the billet surface induction heating device, which heats the local surface of the billet edge, with a maximum heating speed of 100 ℃ / min, and the transverse temperature difference of the billet after heating is less than 30 ℃; 2) Descaling: After heating, the billet enters the high-pressure water descaling machine to remove the surface iron oxide scale. The intermediate billet after being rolled by the billet mill enters the high-pressure water descaling machine again to remove the surface iron oxide scale. The high-pressure water pressure is 25MPa. In addition to preventing the iron oxide scale from being pressed into the steel plate, the more important function of this device is to facilitate the inspection of the surface of the intermediate billet. 3) Intermediate Billet Rolling: After descaling, the billet enters a rolling mill to roll it into an intermediate billet. The rolling mill is a two-roll irreversible mill with a roll diameter of 1100mm, a roll length of 2500mm, a maximum rolling force of 80000kN, and a maximum reduction rate of 15% per pass. Differential temperature rolling is achieved by utilizing the temperature difference between the center and surface of the billet, which is used to improve central defects in the billet, especially porosity. 4) Grinding and finishing: Grinding and finishing of billets with surface defects, with flame cleaning by the grinding and finishing device; qualified billets after grinding and finishing or billets with qualified surface inspection are directly fed into the subsequent traditional medium and heavy plate production line (walking beam furnace), and the subsequent double-stand 4-roll mill with a maximum rolling force of 100,000 kN and a roll body length of 5000 mm is used to further roll the billets into qualified finished steel plates with specified length, width and thickness. Example 2
[0019] Figure 3 The diagram illustrates a continuous casting and rolling production method for medium-thick plates, using a four-high reversible rolling mill. The key process steps include: 1) Surface heating of billet: The R12m 450×2300mm extra-thick plate continuous casting machine with light reduction device and secondary cooling electromagnetic stirring device produces billets with qualified segregation; the flame cutting machine then performs fixed or multiple length cutting; the cut billet enters the billet surface induction heating device, which heats the billet surface comprehensively. The heating power of the billet edge along the width direction is higher than that of the billet center to meet the temperature uniformity requirement that the temperature in the middle of the billet surface is higher than that at the edge. The billet surface heating rate is 90℃ / min, and the transverse temperature difference of the billet after heating is less than 15℃. 2) Descaling: The heated billet enters the descaling machine to remove the surface iron oxide scale. The descaling machine is a shot peening descaling device with high pressure water and sand. The high pressure water pressure is 20MPa. In addition to preventing iron oxide scale from being pressed into the steel plate, the more important function of this device is to facilitate the inspection of the surface of the intermediate billet. 3) Intermediate Billet Rolling: After descaling, the billet enters a billet mill to roll it into an intermediate billet. The billet mill is a four-high reversible mill with a work roll diameter of 1000mm, a roll length of 2400mm, a maximum rolling force of 70000kN, and a single-pass reduction rate of up to 10%. Differential temperature rolling is achieved by utilizing the temperature difference between the center and surface of the billet, which is used to improve central defects in the billet, especially porosity. 4) Grinding and finishing: After rolling, the intermediate billet passes through an optical intermediate billet surface inspection instrument to check for various defects on the billet surface (such as transverse cracks, longitudinal cracks, star-shaped cracks, surface inclusions, etc.); the intermediate billets that fail the inspection are removed from the production line by transverse bypass; the grinding and finishing device is used for finishing and grinding the billets with surface defects. The grinding and finishing device is a mechanical finishing and grinding equipment; the qualified billets after grinding and finishing or the billets that pass the surface inspection directly enter the subsequent traditional medium and heavy plate production line (walking beam furnace). The subsequent double-stand 4-roll mill with a roll body length of 5000mm and a maximum rolling force of 100000kN is used to further roll the billets into qualified finished steel plates of specified length, width and thickness.
Claims
1. A method for continuous casting and rolling of medium-thick plates, the process flow including slab continuous casting, slab flame cutting, slab surface heating, descaling, intermediate slab rolling, slab or intermediate slab surface inspection, slab removal from the production line, grinding and finishing, and subsequent conventional medium-thick plate rolling, characterized in that: Key process steps include: 1) Surface heating of billet: Roller-hearth tunnel kiln heating furnace or induction surface heating device is used for heating. The heating power of the edge of the billet is higher than that of the middle of the billet along the width direction. The surface heating rate of the billet is 20-200℃ / min. The temperature difference of the transverse surface of the billet after heating is 10-60℃. 2) Intermediate billet rolling: The cast billet is rolled into an intermediate billet using a two-roll or four-roll mill. It can be a reversible mill or a non-reversible mill with unidirectional rolling. The reduction rate per pass is 10% to 20%. The billet mill is a low-speed, high-torque mill with a rolling force of 50,000 to 100,000 kN and a rolling speed of 0.5 to 3 m / s. 3) Descaling: Use a high-pressure water descaling machine or a shot peening device with high-pressure water and sand to remove the iron oxide scale from the surface of the billet. The high-pressure water pressure is 10-30 MPa. 4) Grinding and finishing: Use flame cleaning equipment or mechanical finishing and grinding equipment to finish and grind to remove surface defects of the billet or intermediate billet.
2. The continuous casting and rolling production method of medium and heavy plates according to claim 1 is characterized in that: step 2) rolling: the billet is rolled into an intermediate billet by a two-roll mill. The billet mill is a two-roll irreversible mill with a roll diameter of 1100mm, a roll length of 2500mm, a maximum rolling force of 80000kN, and a maximum reduction rate of 15% per pass.
3. The continuous casting and rolling production method of medium and heavy plates according to claim 1 is characterized in that: step 2) rolling: the billet is rolled into an intermediate billet using a four-high rolling mill. The rolling mill is a four-high reversible rolling mill with a working roll diameter of 1000mm, a roll body length of 2400mm, a maximum rolling force of 70000kN, and a single pass reduction rate of 10%.