Online heating method for surface layer and subsurface of large-section casting blank
By installing a laser on a large-section billet continuous casting machine for precise heating, the problem of low surface and subsurface temperatures of the billet was solved, achieving efficient temperature control and plasticity improvement during the straightening process of the billet, and significantly improving the quality of the billet.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- UNIV OF SCI & TECH BEIJING
- Filing Date
- 2026-01-28
- Publication Date
- 2026-05-05
AI Technical Summary
Large-section billets have low surface and subsurface temperatures during continuous casting, resulting in low plasticity and a tendency to crack during straightening. Existing heating methods cannot effectively improve temperature uniformity and control the heating zone, and also suffer from oxidation and low energy efficiency.
Laser heating technology is used, with lasers installed in front of, between, and between the straightening rollers and support rollers of the billet. The laser spot is used to precisely heat the surface of the billet and the area within 20mm below the skin. The shape and power density of the laser spot are controlled to ensure that the heated area is within the thermoplastic temperature range. The laser spot extends along the direction of the billet drawing speed to increase the heating depth.
This method achieves rapid and uniform heating of the surface and subsurface temperature of the billet, improves the thermoplasticity of the billet, inhibits crack generation and defect propagation during the straightening process, and improves the quality and yield of the billet.
Smart Images
Figure CN121972618A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of continuous casting technology, specifically, to a method for online heating of the surface and subsurface of large-section cast billets. Background Technology
[0002] With the development of continuous casting of thick slabs, large square billets, large round billets, large irregular billets, and thick rectangular billets, the cross-sectional dimensions of continuously cast billets are getting larger and larger. However, the casting speed of these large-section billets is relatively low, and the billets dissipate heat more severely during continuous casting production. When entering the straightening section of the continuous casting, the surface temperature of some billets is low. In addition, the straightening stress of the inner and outer arcs of large-section continuously cast billets is relatively large in the straightening section. In particular, the surface and subsurface of the inner arc side are in a state of high tensile stress and tensile strain, which can easily cause surface and subsurface billet defects to expand into serious defects or generate new surface and subsurface defects, resulting in serious billet quality problems.
[0003] Steel exhibits distinct high-temperature brittleness, thermoplasticity, and low-temperature brittleness zones at high temperatures. When the temperature of steel exceeds approximately 1300℃, its plasticity is very low. At this temperature, steel is prone to cracking when subjected to significant deformation stress and strain. This temperature range is called the high-temperature brittleness zone for the corresponding steel. When the temperature of steel is below 800℃-900℃ but above 600-700℃, its plasticity is also very low. At this temperature, steel is also prone to cracking when subjected to significant deformation stress and strain. This temperature range is called the low-temperature brittleness zone for the corresponding steel. Between the temperatures of the low-temperature brittleness zone and the high-temperature brittleness zone, the plasticity of steel is relatively high. In this temperature range, steel is less prone to cracking when subjected to significant deformation stress and strain. This temperature range is called the thermoplasticity zone for the corresponding steel.
[0004] In continuous casting production, to control surface defects in the billet, it is often necessary to maintain the billet temperature in the straightening zone within the thermoplastic zone of the cast steel. This is particularly important for the continuous casting of large-sized billets, as the surface and subsurface areas of the large-section billet experience significant straightening stress and strain during straightening. However, in actual production, due to the slower casting speeds of large-sized billets, the surface and subsurface temperatures of the billet are often lower than the thermoplastic zone temperature when it enters the straightening section of the continuous casting machine. Consequently, the plasticity of the billet surface and subsurface is low, making it unable to withstand the enormous straightening stress and strain.
[0005] Currently, technologies such as optimizing the secondary cooling water volume, semi-dry secondary cooling, and high-speed continuous casting are often used in production to increase the surface temperature of the billet before it enters the straightening section. However, these methods have limited effectiveness in the continuous casting production of large-size billets and often result in problems such as severe billet bulging and increased surface cracks.
[0006] Existing technology discloses a device and method for mitigating corner cracks in cast billets by flame heating. The proposed device includes a flame heater, a gas supply device, and a temperature measuring device. The flame heater consists of 4-8 flame injectors, each arranged at the corner of the cast billet. Each flame injector is individually adjustable. The gas supply device is connected to the flame heater to provide fuel for heating. The temperature measuring device is located behind the flame heater, i.e., behind it along the direction of billet pulling. This method proposes to heat the corner of the cast billet with a flame. During the heating process, the power of the flame heater is adjusted based on the temperature measurement results of the corner of the cast billet by the temperature measuring device. If the corner temperature is lower than T0, the flame heating power is increased, where T0 is the high temperature value of the third brittle zone of the material. However, this technology has many drawbacks: 1) The flame energy is uneven, and it cannot achieve smooth and uniform heating of the heating area, resulting in severely uneven temperature changes and the final temperature distribution; 2) The heating power, heat density, and heating area of the flame are difficult to control precisely online; 3) The flame is an oxidizing gas such as CO2 and H2O, which has an oxidizing effect on the cast billet. Existing technologies also propose devices and methods for controlling the corner straightening temperature of billets based on flame heating. The devices include an oxygen supply system and a temperature measuring device. However, this technology also suffers from many of the problems associated with the aforementioned flame heating technology.
[0007] Existing technology proposes another method and apparatus for guiding and orienting billets in continuous casting equipment for large-sized round profiles. A porous burner is arranged in the discharge side section of the orienting channel, and its hot exhaust gas circulates circumferentially over the billet surface. This method also belongs to flame-heated billet casting technology, but instead of directly heating the billet with a flame, it uses exhaust gas generated by flame combustion to heat the billet. However, this results in poor heat transfer between the exhaust gas and the billet, low energy efficiency, inability to quickly adjust the heating zone online, and complex and inaccurate online adjustment of the flue gas heat density, heating power, and temperature rise effect. Furthermore, the shortcomings of the original flame heating technology (2 and 3) also exist.
[0008] Existing technology proposes a method to improve the crack defects at the edges and corners of cast billets by using electromagnetic induction heaters to locally heat the edges and corners of the billets. These heaters are installed at locations before the secondary cooling section and / or straightening section of the billet. However, this technology has the following problems: 1) Induction heating, which generates Joule heat by producing an induced current inside the billet, is a volumetric heating method. The heated area is relatively large, making it impossible to concentrate heating on specific areas of the billet's surface and shallow subsurface regions. Most of the heating power is wasted in the unheated internal areas of the billet; 2) It is difficult to heat the surface and subsurface areas of wide-section billets; 3) The induction equipment is large, and the gap between the continuous casting machine's work rolls is sometimes narrow, making installation impossible; 4) During induction heating, a strong electromagnetic field is generated around the heated billet area, which can significantly affect the operation of adjacent work rolls.
[0009] In response to the problems of low surface temperature of billets when they enter the straightening zone during continuous casting of large-section billets, low plasticity of the surface and subsurface of the large-section billets, the easy generation of new surface defects and the aggravation of the expansion of existing defects during the straightening process, and the inability of flame heating and induction heating to meet the needs of continuous casting production, it is urgent to propose a method for online heating of the surface and subsurface of billets, taking into account the characteristics of large-section continuous casting production. Summary of the Invention
[0010] This application research found that existing methods not only have many drawbacks but are also relatively crude. They heat the billet using simple, inefficient heating methods without specifying precise requirements for billet temperature and steel plasticity tailored to the characteristics of continuous casting of large-section billets. In continuous casting of large-section billets, the straightening radius is large, and the straightening tensile stress and strain on the inner arc side of the billet are significant, especially on the surface and subsurface of the inner arc side, where the stress and strain are greatest. If the plasticity of the billet in this area is low, surface and subsurface cracks are easily generated. Because subsurface cracks are close to the surface, they can easily extend to the surface, causing existing small surface and subsurface cracks to expand into larger surface cracks that cannot be eliminated during subsequent billet heating and rolling. Further research revealed that the temperature within 20mm of the surface and subsurface of the large-section billet is low before straightening, reaching the low temperature range for the cast steel grade. The plastic zone is the main cause of surface cracks in large-section continuous casting. Increasing the temperature and plasticity of the billet in this zone is an effective way to solve the problem of surface cracks in large-section continuous casting. Further research shows that lasers can precisely heat the surface of the billet. By homogenizing the laser spot energy density, using rectangular or elongated spots, increasing the spot length in the casting direction, and setting multiple lasers before straightening, the subsurface of the billet can be heated to a depth of up to 20 mm. Further research reveals that the plasticity of the surface and subsurface of the large-section billet must meet the condition of a reduction of area ≥ 0.4 in order to significantly avoid tensile fracture of the billet.
[0011] Laser is a highly efficient, precise, and controllable technology that can destroy or heat objects when interacting with them. Compared to flame heating, laser heating offers advantages such as faster heating speed, more precise laser spot positioning of the heating area, easier power adjustment, no reactive gas generation, no oxidation of the cast billet, and environmental friendliness. However, it often suffers from problems such as significant differences in laser wavelengths produced by different lasers, some lasers being unsuitable for heating steel materials, the lasers often being rod-shaped, resulting in overly concentrated laser spot density and uneven distribution on the irradiated object's surface, and the laser easily destroying the irradiated material. This application addresses these issues and provides improvements.
[0012] To solve the above-mentioned technical problems, this application provides a method for online heating of the surface and subsurface of a large-section billet, comprising the following steps: Heating devices are installed in front of, between, and between the support rollers of the large-section billet continuous casting machine, to heat the surface and subsurface area within 20mm of the large-section billet, such that the temperature of the surface and subsurface area within 20mm of the large-section billet is between the lower limit of the thermoplastic temperature range of the cast steel grade and 1250℃ before the straightening rollers and during the straightening process; the area reduction rate of the surface and subsurface area within 20mm of the large-section billet is ≥0.4; the large-section billet is one of the following: a slab with a thickness ≥220mm, a round billet with a diameter ≥600mm, a rectangular billet with a thickness ≥250mm, or an irregularly shaped billet with a thickness ≥350mm.
[0013] As a preferred embodiment of the online heating method for the surface and subsurface of a large-section billet as described in this application, the heating method is as follows: a laser is installed in front of the straightening rollers, between the straightening rollers, and between the support rollers in front of the straightening rollers of the large-section billet continuous casting machine to irradiate the large-section billet, and the laser spot is controlled to cover the heating area of the surface of the large-section billet, thereby precisely heating the surface of the large-section billet; the surface of the large-section billet conducts heat to the subsurface of the large-section billet, raising the temperature of the area within 20mm of the subsurface of the large-section billet.
[0014] As a preferred embodiment of the online heating method for the surface and subsurface of a large-section cast billet as described in this application, the laser beam is perpendicular to the surface of the large-section cast billet or maintains a certain angle with the surface of the large-section cast billet; the laser outlet of the laser is 20mm-5m away from the surface of the large-section cast billet, and the rated power of the laser is greater than 5kW; the laser spot generated by the laser is a rectangular, elongated, elliptical, or nearly elliptical spot parallel to the central axis of the continuous casting machine support roller and straightening roller, or a circular, elliptical, or rectangular spot covering the corner of the cast billet; the power density of the spot is 10-300W / cm². 2 .
[0015] As a preferred embodiment of the method for online heating of the surface and subsurface of a large-section billet as described in this application, the heating area and heating power of the laser irradiation spot are set according to the temperature distribution of the surface of the large-section billet in front of the straightening rolls during continuous casting. Preferential heating is performed on areas where the large-section billet experiences significant straightening tensile stress and strain, and where the surface temperature of the large-section billet is below the thermoplastic temperature range of the cast steel grade. Heating is carried out between the support rolls in front of the straightening rolls of the continuous casting machine, between the support rolls and the straightening rolls of the first straightening stand, or in part... One or more sets of lasers are arranged between the straightening rollers. By reasonably arranging the number and position of the lasers, and by optimizing the laser spot length and power, the temperature of the surface layer and the area within 20mm below the surface of the heated billet is heated to the thermoplastic temperature range of the cast steel before straightening, and it is ensured that the temperature remains within the thermoplastic temperature range in the straightening zone. When the billet thickness or billet diameter is larger, or the tensile stress and tensile strain of the surface layer of the large-section billet are greater, the heating depth below the surface layer of the large-section billet needs to be greater.
[0016] As a preferred embodiment of the method for online heating of the surface and subsurface of a large-section cast billet as described in this application, the power density of the laser spot is controlled by controlling the operating current or power of the laser. The higher the operating current or power of the laser, the greater the laser spot power density, and the faster the surface of the large-section cast billet heats up. The greater the casting speed of the large-section cast billet and the greater the amount of cast billet whose surface temperature needs to be increased, the higher the required laser power density.
[0017] As a preferred embodiment of the online heating method for the surface and subsurface of a large-section cast billet described in this application, the energy density of the laser spot is homogenized through a reasonable design of the optical path within the laser, achieving uniform heating and gentle temperature rise in the area covered by the laser spot. The heating rate of the cast billet in the heating area is ≤80℃ / s. The specific method of homogenizing the laser spot is as follows: through a reasonable design of the optical path within the laser, a laser collimator is applied to collimate and shape the high-energy Gaussian laser output by the laser, generating a laser spot with a uniform energy density distribution. The energy transition zone of 10%-85% at the edge of the laser spot is ≤1.0mm, and the length of the laser spot area from the edge to the center (where the energy density is less than 85% of the center energy density) is controlled to be ≤1.0mm, so as to achieve uniform heating and gentle temperature rise in the area covered by the laser spot.
[0018] As a preferred embodiment of the online heating method for the surface and subsurface of a large-section slab described in this application, the heating depth under the surface of the large-section slab is the heating depth of the laser penetrating from the surface of the large-section slab to the subsurface. This is achieved by increasing the size of the laser spot along the casting speed direction, or by arranging multiple lasers before straightening, and heating the slab in multiple stages. This ensures even heating of the surface slab while promoting the transmission of laser energy into the interior of the slab. The higher the continuous casting speed and the greater the straightening stress and strain on the slab, the greater the length of the laser spot along the casting speed direction needs to be increased to increase the subsurface heating depth. The subsurface heating depth can be calculated by numerical simulation and / or experimental detection. The relationship between the laser heating power density, the length of the laser spot along the casting speed direction, the continuous casting speed of the steel grade, and the surface temperature can be obtained through numerical regression. This relationship can then be used to achieve online adjustment of the laser spot size and power density.
[0019] As a preferred embodiment of the method for online heating of the surface and subsurface of a large-section cast billet as described in this application, a laser is used to generate a laser with a wavelength in the range of 780nm-11000nm to heat the surface of the cast billet that is being produced and operated; during continuous casting production, the cast billet moves continuously along the casting direction, so as to realize the continuous and stable scanning of the cast billet spot on the heating area of the cast billet, thereby achieving the heating of the cast billet heating area.
[0020] As a preferred embodiment of the method for online heating of the surface and subsurface of large-section cast billets described in this application, the laser position, laser irradiation angle, and size of the irradiation laser spot are reasonably set to avoid direct laser irradiation of the continuous casting machine support rolls and straightening rolls.
[0021] As a preferred embodiment of the method for online heating of the surface and subsurface of a large-section cast billet as described in this application, a shield is provided around the laser to ensure that the laser is in a good temperature environment, wherein the temperature is less than 80°C.
[0022] The beneficial effects of this application are as follows: This application proposes a method for online heating of the surface and subsurface of large-section cast billets. Lasers are installed at positions directly opposite the surface of the cast billet in front of the straightening rolls, between the straightening rolls, and between the support rolls in front of the straightening rolls of a large-section continuous casting machine. A laser with a specific wavelength range suitable for heating cast billets produced in continuous casting is used to heat the surface of the billet during production and operation. The method utilizes the precise adjustable laser spot size and selects a suitable laser shape to radiate heat onto the surface of the cast billet through the gaps between the work rolls. The relative movement of the laser spot on the surface of the cast billet is achieved through the continuous casting process. This invention discloses a method for controlling the shape of the laser spot, the radiation position of the laser spot, the energy density and distribution of the laser spot, the heat transfer intensity between the laser and the billet during the heating process, the heating rate of the billet surface, the heating temperature of the billet surface, and the heating depth of the billet surface. This method enables online, smooth, and rapid increase in the temperature of the surface and subsurface of the large-section billet, thereby improving the high-temperature thermoplasticity of the surface and subsurface of the large-section billet. This method can effectively improve the control effect of billet surface temperature in continuous casting production, increase the billet temperature when entering the straightening zone, improve the plasticity of the surface and subsurface of the large-section billet during the straightening process, suppress the generation of surface defects and the expansion of existing defects, and improve the surface quality of the continuous casting billet. It provides a flexible and convenient new method for continuous casting billet temperature control in continuous casting production, which can significantly increase the surface and subsurface temperature of the continuous casting billet in the straightening section, improve the plasticity of the surface and subsurface of the large-section billet, significantly suppress defects generated during the billet straightening process, and improve the surface quality and yield of the billet. Attached Figure Description
[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.
[0024] Figure 1 This is a schematic diagram of the technical solution in this application; Figure 2 This is a schematic diagram of the heating of rectangular and round billets in this application; Reference numerals: 1-Ladle; 2-Tundish; 3-Crystallizer; 4-Support roller; 5-Shielding cover; 6-Laser; 7-Large cross-section billet; 8-Roller conveyor; 9-Straightening roller; 10-Laser spot.
[0025] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0026] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.
[0027] This application provides a method for online heating of the surface and subsurface of a large-section cast billet, comprising the following steps: Please see Figure 1 and Figure 2 , Figure 1 This is a schematic diagram of the technical solution in this application; Figure 2 This is a schematic diagram of the heating of rectangular and round billets in this application; Molten steel flows from ladle 1 to tundish 2, solidifies into a large-section billet 7 in crystallizer 3, and is drawn on roller conveyor 8. Lasers 6 with shields 5 are installed at surface-facing positions on the large-section billet 7, in front of straightening rollers 9, between straightening rollers 9, and between support rollers 4 in front of straightening rollers 9. A suitable laser 6 is selected to generate a laser with a wavelength in the range of 780nm-11000nm to heat the surface of the large-section billet 7 during production and operation. A long strip or rectangular laser spot 10 is used to irradiate the surface of the large-section billet 7 moving along the drawing direction between the work rollers. The power density of the laser spot 10 is controlled between 10-300W / cm², ensuring the laser spot 10 covers the area of the large-section billet 7 that needs heating, precisely heating the required surface area. Through the rational design of the optical path within the laser 6, the energy density of the laser spot 10 is homogenized to achieve optimal heat distribution. The heating of the covered area is uniform and gradual, with a heating rate of ≤80℃ / s for the large-section slab 7. The surface temperature of the large-section slab 7 is rapidly increased by the absorption of high-energy photons from the laser spot 10, and further, the temperature of the slab within 20mm of the surface layer is increased through heat conduction from the high-temperature surface layer to the interior of the slab. During continuous casting, the large-section slab 7 moves continuously along the casting direction, allowing the laser spot 10 to continuously and stably sweep across the area requiring heating, thus heating the area. Laser heating raises the surface and subsurface temperatures of the large-section slab 7 within the heating area to the lower limit of the thermoplastic temperature range of the cast steel grade (-1250℃) before and during straightening, improving the high-temperature thermoplasticity of the surface and subsurface slabs. The area reduction rate of the large-section slab 7 in the heating area is ≥0.4.
[0028] Preferably, the laser is installed at a surface-facing position on the billet, and the laser can be perpendicular to the surface of the billet or at a certain angle to the surface of the billet; the laser outlet of the laser is 20mm-5m away from the surface of the billet, and the rated power of the laser is greater than 5kW; the laser spot generated by the laser is a rectangular, elongated, elliptical, or nearly elliptical spot parallel to the central axis of the support roller and straightening roller of the continuous casting machine, or a circular, elliptical, or rectangular spot covering the corner of the billet.
[0029] Preferably, based on the temperature distribution of the slab surface in front of the straightening rolls during continuous casting, the laser irradiation heating area, spot size, and heating power are set. Priority is given to heating areas where the slab surface temperature is lower than the thermoplastic temperature range of the cast steel grade and areas subjected to significant straightening stress and strain. For example, priority is given to heating the inner arc side, edges, and corners of large-section slabs subjected to significant straightening tensile stress and strain, where the surface temperature is lower. Alternatively, heating can be performed based on the distribution of surface defects in the produced slabs and steel. Support rolls and supports are placed in front of the straightening rolls of the continuous casting machine. One or more sets of lasers are arranged between the rollers and the straightening rollers of the first straightening stand, or between some of the straightening rollers. By reasonably arranging the number and position of the lasers, and by reasonably optimizing the laser spot length and power, the temperature of the surface layer and the area within 20mm below the surface of the heated billet is heated to the thermoplastic temperature range of the cast steel before straightening, and it is ensured that the temperature remains in the thermoplastic temperature range in the straightening area. The thermoplastic temperature range of the cast steel can be determined according to the high-temperature tensile thermoplastic curve of the relevant steel in the literature, or it can be determined by using a Gleeble thermodynamic simulation testing machine.
[0030] Preferably, the greater the billet thickness or billet diameter, or the greater the tensile stress and strain on the billet surface during straightening, the deeper the heating depth under the billet surface needs to be. However, in principle, the heating depth under the billet surface should not exceed 20.0 mm.
[0031] Preferably, the laser spot power density is controlled by controlling the laser's operating current or power. Higher laser current or power results in a higher laser spot power density and a faster heating of the billet surface. Higher billet casting speeds and higher required surface temperatures necessitate higher laser power densities. The energy rate supplied by the laser spot to the heated billet surface is: In the formula: Q is the energy rate supplied by the laser spot to the surface of the heated billet, in W; ψ is the radiation coefficient of the billet surface, which is mainly related to the composition and thickness of the oxide layer on the billet surface, and is 0.65-0.90; S is the projected area of the laser spot on the billet surface, in cm². 2 M represents the laser spot power density, W / cm². 2 ; In the formula: η is the photoelectric conversion efficiency coefficient of the laser, which is 0.3-0.5; U is the power supply voltage, V; I is the operating current, A; cosθ is the power factor of the laser, which is 0.8-0.99.
[0032] Preferably, by rationally designing the optical path within the laser and applying a laser collimator and shaper, the high-energy Gaussian laser output from the laser can be collimated and shaped to produce a light spot with uniform energy density distribution. The energy transition zone at the edge of the light spot (10%-85%) is ≤1.0mm, and the length of the area from the edge of the light spot to the region with energy density less than 85% of the energy density at the center of the light spot is controlled to be ≤1.0mm, so as to achieve uniform heating and gentle temperature rise in the area covered by the light spot.
[0033] Preferably, the heating depth beneath the surface of the billet is the heating depth of the laser penetrating the surface of the large-section billet into the interior of the billet. By increasing the size of the laser spot along the billet casting speed direction, or by arranging multiple lasers before straightening and heating the billet in stages multiple times, the surface of the billet is exposed to laser irradiation for a longer period of time. This can promote the transmission of laser energy into the interior of the billet while ensuring the surface of the billet is heated evenly. The higher the continuous casting speed and the greater the straightening stress and strain borne by the billet, the longer the length of the laser spot along the casting speed direction needs to be increased to increase the subsurface heating depth of the billet.
[0034] Preferably, the subsurface heating depth of the billet can be calculated by numerical simulation and / or experimental detection, and the relationship between laser heating power density, laser spot length along the casting speed direction and continuous casting speed and surface temperature of the steel grade can be obtained by numerical regression. This relationship can be applied to achieve online precise adjustment of laser spot size and power density.
[0035] Preferably, the billets cast by the large-section continuous casting machine are slabs with a thickness ≥ 220 mm, round billets with a diameter ≥ 600 mm, square billets with a side length ≥ 250 mm, rectangular billets with a thickness ≥ 250 mm, and irregularly shaped billets with a thickness ≥ 350 mm.
[0036] Preferably, the number and position of lasers, the laser irradiation angle and the size of the irradiation laser spot are reasonably set to avoid the laser directly irradiating the support roll and straightening roll of the continuous casting machine. When the laser passes between the continuous casting work rolls, the closest distance between the laser and the surface of the work roll is preferably greater than 1mm.
[0037] Preferably, a shielding cover should be installed around the laser to ensure the normal operation and long lifespan of the laser by shielding the thermal radiation of the cast billet, water cooling of the shielding cover, and air cooling inside the cover. Generally, the temperature inside the cover should be controlled below 80°C, and preferably below 45°C.
[0038] Preferably, green electricity should be used for heating to reduce carbon emissions.
[0039] The technical solution of this application will be further described below with reference to specific embodiments.
[0040] Example 1 A steel plant continuously casts slabs to produce SS400 steel. The Gleeble thermo-simulation testing machine determined that the thermoplastic temperature range of this steel is 870℃-1300℃. The continuous casting produced slabs have a cross-section of 400mm×2400mm and a casting speed of 0.6m / min. When the slab enters the straightening zone, the temperature of the surface layer of the inner arc edge of the slab, 0-300mm from the corner, is 750-830℃, which is in the brittle zone of this steel. The transverse cracks on the surface layer and corners of the inner arc edge of the continuously cast slab are relatively severe.
[0041] Eight lasers with a rated power of 24kW are installed at the following locations on the inner arc side of the billet between the straightening rollers of the third and second straightening stands of the continuous casting machine: lasers 1# and 2# with a rated power of 24kW are installed at the following locations on the inner arc side of the billet between the straightening rollers of the first straightening stand and the first support roller in front of it; lasers 3# and 4# with a rated power of 48kW are installed at the following locations on the inner arc side of the billet between the straightening rollers of the first straightening stand and the first support roller in front of it; lasers 5# and 6# with a rated power of 48kW are installed at the following locations on the inner arc side of the billet between the first and second support rollers in front of the straightening roller; and lasers 7# and 8# with a rated power of 48kW are installed at the following locations on the inner arc side of the billet between the second and third support rollers in front of the straightening roller. Each laser produces a laser wavelength of 1064nm. The laser spot size is 300mm × 30mm. Through optimization of the laser's internal optical system, collimation and shaping of the output laser are achieved, with the energy transition zone at the 10%-90% edge of the spot ≤ 0.5mm. The length direction of the generated laser spot is parallel to the axial direction of each working roller. The laser only irradiates the low-temperature surface layer of the billet edge between the working rollers, without irradiating the surface layer of the working rollers. The laser head is 1.0m away from the billet surface. The laser is installed in a shielded steel cover, and the laser irradiates the billet surface through a 310mm × 40mm slit at the bottom of the shield. The shield is cooled by cold air, controlling the internal temperature to be below 40℃. By adjusting the operating current, the actual operating power of lasers #7 and #8 is set to 32kW, and the power density of the laser spot is 124W / cm². 2 The actual operating power of lasers #5 and #6 is set to 28kW, and the power density of the laser spot is 109W / cm². 2 The actual operating power of lasers #3 and #4 is set to 25kW, and the power density of the laser spot is 97W / cm². 2 The actual operating power of lasers #1 and #2 is set to 18kW, and the power density of the laser spot is 70W / cm². 2After the billet enters the straightening section, the surface temperature of the inner arc side of the billet rises to 900-970℃, and the maximum heating rate of the surface is 56℃ / s. The temperature 0-10mm below the skin of the inner arc side of the billet in the straightening section is greater than 880℃. The cross-sectional shrinkage rate of the billet in this area is greater than 0.6, and transverse cracks and corner transverse cracks no longer occur on the surface of the inner arc side of the billet.
[0042] Example 2 A steel plant uses a rectangular billet continuous casting machine to produce Q390 steel. The Gleeble thermo-simulation testing machine determined that the thermoplastic temperature range of this steel is 900℃-1300℃. The continuous casting billet has a cross-section of 750mm×1000mm and a casting speed of 0.3m / min. When the billet enters the straightening zone, the temperature of the inner and outer arc surface of the billet is 680-750℃ in the area 0-250mm from the corner, and the temperature of the inner and outer arc center of the billet is 820℃-840℃. The surface of the billet is in the brittle zone of this steel grade, and the surface cracks of the inner arc of the billet produced by continuous casting are relatively serious.
[0043] Eight lasers with a rated power of 24kW were installed on the surface of the billet between the straightening rollers of the third and second straightening stands on both sides of the inner arc side of the continuous casting machine; lasers with a rated power of 48kW were installed between the straightening roller of the first straightening stand and the first support roller in front of it; lasers with a rated power of 48kW were installed between the first and second support rollers in front of the straightening roller; and lasers with a rated power of 48kW were installed between the second and third support rollers in front of the straightening roller. A total of eight lasers were installed. Each laser produces a wavelength of 10600nm. Through optimization of the optical system within the lasers, the output laser wavelength was optimized. The collimation and shaping of the light spot ensures that the energy transition zone between 10% and 90% of the spot is ≤0.5mm. During laser installation, the laser heating head is 1.2m away from the inner arc side of the cast billet. The laser is installed inside a shielding steel cover, with the laser irradiating the billet surface through a 110mm wide slit on the side of the shielding cover closest to the billet surface. The shielding steel cover is cooled by cold air, controlling the temperature inside to be below 40℃. The generated laser spots cover the corresponding low-temperature areas on the outer arc edge of the billet, with the long side of the spot parallel to the long axis of the work roll. The laser only irradiates the surface of the billet between the work rolls, not the surface of the work rolls themselves. The actual working power of lasers #7 and #8 is set to 27kW, with each laser producing a laser spot of 250mm × 100mm and a laser spot power density of 40W / cm². 2 Each laser covers the corresponding low-temperature region on the inner arc edge of the cast billet; the actual working power of lasers #5 and #6 is set to 28kW, and the laser spot produced by each laser is 300mm×100mm, with a laser spot power density of 35W / cm². 2Each laser covers the corresponding low-temperature region on the inner arc edge of the cast billet; the actual working power of lasers #3 and #4 is set to 40kW, and the laser spot produced by each laser is 500mm×100mm, with a laser spot power density of 30W / cm². 2 The lasers, #1 and #2, cover both sides of the inner arc of the cast billet. The actual operating power of lasers #1 and #2 is set to 13kW, with each laser producing a laser spot of 250mm × 100mm and a power density of 20W / cm². 2 The temperature of the inner arc side of the billet is covered on both sides of the inner arc. After the billet enters the straightening section, the surface temperature of the inner arc side of the billet rises to 900-990℃, and the maximum heating rate of the surface is 30℃ / s. The temperature of the 0-15mm subcutaneous layer of the inner arc side of the billet in the straightening section is greater than 900℃. The cross-sectional shrinkage rate of the billet in this area is greater than 0.62, and surface cracks on the inner arc side of the billet no longer occur.
[0044] Example 3 A steel plant uses a round billet continuous casting machine to produce 10Cr9Mo1VNbN steel. The Gleeble thermo-simulation testing machine determined that the thermoplastic temperature range of this steel is 900℃-1300℃. The continuous casting billet has a cross-section of Ф1000mm and a casting speed of 0.3m / min. When the billet enters the straightening zone, the surface temperature of the billet is 750-800℃. The surface of the billet is in the brittle zone of this steel. The surface cracks of the billets produced by continuous casting are relatively serious. The proportion of billets with longitudinal cracks is 90%, and each billet has visible transverse cracks.
[0045] Ten lasers with a rated power of 48kW are installed on the inner arc side of the billet, one between the straightening rollers of the 4th and 3rd straightening stands on both sides of the billet. Lasers with a rated power of 60kW are installed on the billet surface between the straightening roller of the 1st straightening stand and its preceding 1st support roller. Lasers with a rated power of 48kW are installed on the billet surface between the straightening roller of the 1st straightening stand and its preceding 1st support roller. Lasers with a rated power of 48kW are installed on the billet surface between the 1st and 2nd support rollers in front of the straightening roller. Laser #10 with a rated power of 48kW is installed on the billet surface between the 2nd and 3rd support rollers in front of the straightening roller. A total of 10 lasers are installed. Each laser... The laser generated by the laser has a wavelength of 1080nm. Through optimization of the laser's internal optical system, collimation and shaping of the output laser were achieved, with the energy transition zone at the edge of the laser spot (10%-90%) ≤0.5mm. The laser head is 1.5m away from the surface of the cast billet. The laser is installed in a shielded steel cover, and the laser beam is emitted through a 110mm wide slit at the bottom of the shield near the surface of the cast billet. The shield is cooled by cold air to keep the internal temperature below 40℃. The actual operating power of the No. 10 laser is set to 34kW, and the laser spot generated is 300mm × 100mm, illuminating the center of the inner arc side of the round billet. The power density of the laser spot is 40W / cm².2 The actual operating power of lasers #7, #8, and #9 is set to 27kW. Each laser produces a laser spot size of 300mm × 100mm, with a laser spot power density of 32W / cm². 2 The radiation spot of laser #8 is directly facing the center of the inner arc of the blank, while the radiation spots of lasers #7 and #9 are located on either side of the laser spot of laser #8. The actual operating power of lasers #4, #5, and #6 is set to 26kW, and each laser produces a laser spot of 300mm × 100mm with a power density of 30W / cm². 2 The radiation spot of laser #5 is directly facing the center of the inner arc of the blank, while the radiation spots of lasers #4 and #6 are located on either side of the laser spot of laser #5. The actual operating power of lasers #1, #2, and #3 is set to 13kW, and the laser spot produced by each laser is 300mm × 100mm, with a power density of 15W / cm². 2 The laser beams cover the corresponding areas on the inner arc side. The length direction of each laser spot is parallel to the axis of each work roll. The laser only irradiates the surface layer of the billet between the work rolls, and does not irradiate the surface layer of the work rolls. After the billet enters the straightening section, the surface temperature of the inner arc rises to 920-990℃, and the maximum heating rate of the surface layer is 28℃ / s. The temperature 0-15mm below the skin of the center of the inner arc side of the billet in the straightening section is greater than 900℃. The cross-sectional shrinkage rate of the billet in this area is greater than 0.64, and surface cracks of the billet no longer occur.
[0046] This application proposes a method for online heating of the surface and subsurface of large-section cast billets. Lasers are installed at positions directly opposite the surface of the cast billet in front of the straightening rolls, between the straightening rolls, and between the support rolls in front of the straightening rolls of a large-section continuous casting machine. A laser with a specific wavelength range suitable for heating cast billets produced in continuous casting is used to heat the surface of the billet during production and operation. The method utilizes the precise adjustable laser spot size and selects a suitable laser shape to radiate heat onto the surface of the cast billet through the gaps between the work rolls. The relative movement of the laser spot on the surface of the cast billet is achieved through the continuous casting process. This invention discloses a method for controlling the shape of the laser spot, the radiation position of the laser spot, the energy density and distribution of the laser spot, the heat transfer intensity between the laser and the billet during the heating process, the heating rate of the billet surface, the heating temperature of the billet surface, and the heating depth of the billet surface. This method enables online, smooth, and rapid increase in the temperature of the surface and subsurface of the large-section billet, thereby improving the high-temperature thermoplasticity of the surface and subsurface of the large-section billet. This method can effectively improve the control effect of billet surface temperature in continuous casting production, increase the billet temperature when entering the straightening zone, improve the plasticity of the surface and subsurface of the large-section billet during the straightening process, suppress the generation of surface defects and the expansion of existing defects, and improve the surface quality of the continuous casting billet. It provides a flexible and convenient new method for continuous casting billet temperature control in continuous casting production, which can significantly increase the surface and subsurface temperature of the continuous casting billet in the straightening section, improve the plasticity of the surface and subsurface of the large-section billet, significantly suppress defects generated during the billet straightening process, and improve the surface quality and yield of the billet.
[0047] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.
Claims
1. A method for online heating of the surface and subsurface of a large-section cast billet, characterized in that, include: Heating devices are installed in front of, between, and between the support rollers of the large-section billet continuous casting machine to heat the surface layer and the area within 20mm below the surface of the large-section billet. This ensures that the temperature of the surface layer and the area within 20mm below the surface of the large-section billet is between the lower limit of the thermoplastic temperature range of the cast steel grade and 1250℃ before the straightening rollers and during the straightening process. The area reduction rate of the surface layer and the area within 20mm below the surface of the large-section billet is ≥0.
4. The large-section billet is one of the following: slab with a thickness ≥220mm, round billet with a diameter ≥600mm, rectangular billet with a thickness ≥250mm, or irregularly shaped billet with a thickness ≥350mm.
2. The method for online heating of the surface and subsurface of a large-section cast billet according to claim 1, characterized in that, The specific heating method is as follows: a laser is installed in front of the straightening roller, between the straightening rollers, and between the support rollers in front of the straightening roller in the large-section billet continuous casting machine to irradiate the large-section billet. The laser spot is controlled to cover the heating area of the surface layer of the large-section billet, and the surface layer of the large-section billet is precisely heated. Heat is conducted from the surface layer of the large-section billet to the subcutaneous layer of the large-section billet, raising the temperature of the area within 20mm of the subcutaneous layer of the large-section billet.
3. The method for online heating of the surface and subsurface of a large-section cast billet according to claim 2, characterized in that, The laser beam is perpendicular to or at a certain angle to the surface of the large-section cast billet; the laser exit is 20mm-5m away from the surface of the large-section cast billet, and the rated power of the laser is greater than 5kW; the laser spot generated by the laser is a rectangular, elongated, elliptical, or nearly elliptical spot parallel to the central axis of the continuous casting machine's support roller and straightening roller, or a circular, elliptical, or rectangular spot covering the corner of the cast billet; the power density of the spot is 10-300W / cm². 2 .
4. The method for online heating of the surface and subsurface of a large-section cast billet according to claim 2, characterized in that, Based on the temperature distribution of the large-section billet surface before the straightening rolls during continuous casting, the heating area and heating power of the laser irradiation spot are set. Priority is given to heating areas where the large-section billet experiences significant straightening tensile stress and strain, and where the surface temperature of the large-section billet is below the thermoplastic temperature range of the cast steel grade. One or more sets of lasers are arranged between the support rolls in front of the straightening rolls of the continuous casting machine, between the support rolls and the straightening rolls of the first straightening stand, or between some straightening rolls. Through reasonable arrangement of the number and position of the lasers, combined with reasonable optimization of the laser spot length and power, the temperature of the surface layer and the area within 20mm below the surface of the billet is heated to the thermoplastic temperature range of the cast steel grade before straightening, and it is ensured that the temperature remains within the thermoplastic temperature range throughout the straightening area. The greater the billet thickness or billet diameter, or the greater the straightening tensile stress and strain on the surface of the large-section billet, the greater the heating depth below the surface of the large-section billet needs to be.
5. A method for online heating of the surface and subsurface of a large-section cast billet according to claim 2, characterized in that, The power density of the laser spot is controlled by controlling the working current or power of the laser. The higher the working current or power of the laser, the greater the power density of the laser spot, and the faster the surface of the large-section billet heats up. The greater the casting speed of the large-section billet and the greater the amount of billet whose surface temperature needs to be increased, the higher the required laser power density.
6. A method for online heating of the surface and subsurface of a large-section cast billet according to claim 2, characterized in that, By rationally designing the optical path within the laser, the energy density of the laser spot is homogenized, achieving uniform heating and gentle temperature rise in the area covered by the laser spot. The heating rate of the cast billet in the heating area is ≤80℃ / s. The specific method of homogenizing the laser spot is as follows: through the rational design of the optical path within the laser, a laser collimator is applied to collimate and shape the high-energy Gaussian laser output by the laser, generating a laser spot with a uniform energy density distribution. The energy transition zone of 10%-85% at the edge of the laser spot is ≤1.0mm, and the length of the laser spot area from the edge to the center with an energy density less than 85% of the center energy density is controlled to be ≤1.0mm, so as to achieve uniform heating and gentle temperature rise in the area covered by the laser spot.
7. A method for online heating of the surface and subsurface of a large-section cast billet according to claim 2, characterized in that, The heating depth under the surface of the large-section slab refers to the heating depth of the laser penetrating the surface of the large-section slab and extending to the subsurface. This is achieved by increasing the size of the laser spot along the casting speed direction, or by arranging multiple lasers before straightening and heating the slab in stages. This ensures even heating of the surface slab while promoting the transmission of laser energy into the interior of the slab. The higher the continuous casting speed and the greater the straightening stress and strain on the slab, the greater the length of the laser spot along the casting speed direction needs to be increased to enhance the heating depth under the slab surface. The heating depth under the slab surface can be calculated through numerical simulation and / or experimental testing. The relationship between the laser heating power density, the length of the laser spot along the casting speed direction, the continuous casting speed of the steel grade, and the surface temperature can be obtained through numerical regression. This relationship can then be used to achieve online adjustment of the laser spot size and power density.
8. A method for online heating of the surface and subsurface of a large-section cast billet according to claim 2, characterized in that, A laser with a wavelength in the range of 780nm-11000nm is used to heat the surface of the billet being produced and operated. During continuous casting production, the billet moves continuously along the casting direction, so that the laser spot of the billet can continuously and stably sweep the heating area of the billet, thereby heating the heating area of the billet.
9. A method for online heating of the surface and subsurface of a large-section cast billet according to claim 2, characterized in that, The laser position, laser irradiation angle, and size of the irradiation laser spot should be set reasonably to avoid direct laser irradiation of the support rolls and straightening rolls of the continuous casting machine.
10. A method for online heating of the surface and subsurface of a large-section cast billet according to claim 2, characterized in that, A shield is placed around the laser to ensure that the laser is in a good temperature environment, which is less than 80°C.