A rolling control method for H-shaped steel blooming head defects

Abstract

The application discloses a rolling control method for H-shaped steel flower head defects and belongs to the technical field of steelmaking and continuous casting processes.The H-shaped steel flower head defects rolling control method is suitable for the flange width of the shaped billet being 300-1300 mm, the flange height being 200-510 mm, and the web thickness being 85-140 mm.The control method comprises the following steps: 1) controlling the S content and the Mn / S ratio in the molten steel;2) weakening the secondary cooling strength of the shaped billet continuous casting machine and reducing the inner arc water volume proportion of each cooling section of the secondary cooling zone; and 3) improving the precision of the fan-shaped section supporting roller of the shaped billet continuous casting machine.The H-shaped steel flower head defects rolling control method has the beneficial effects that the generation of internal cracks at the intersection of the flange and the web of the shaped billet can be controlled, the H-shaped steel flower head defects occurring in the rolling process can be fundamentally solved, and the rolling efficiency and the product quality can be improved.

Description

Technical Field

[0001] This invention relates to the field of steelmaking continuous casting technology, and in particular to a rolling control method for H-beams with blooming head defects. Background Technology

[0002] H-beams are profiled steel products with excellent mechanical properties and superior performance characteristics, widely used in steel structures for industrial and civil buildings, with their application areas and usage expanding year by year. Compared with the production of H-beams using rectangular billets or slabs, the production of H-beams using shaped billets requires fewer rolling passes, resulting in higher production efficiency and lower rolling costs. Therefore, most H-beams in China, especially medium and large-sized H-beams, are currently produced using shaped billet rolling.

[0003] During H-beam rolling, a "blooming head" defect frequently occurs at the head of the rolled piece. This necessitates flange-side cutting during tongue trimming, disrupting the rolling rhythm, wasting saw blades, and, in severe cases, preventing subsequent passes from properly engaging, leading to steel jamming, production accidents, and equipment damage. Therefore, it is urgent to address this "blooming head" defect in H-beam rolling. Analysis shows that this defect arises from internal cracks at the junction of the web and flange of the shaped billet. During rolling, these cracks propagate, causing the flange and web to tear at the crack. Because the head area is in a state of tension during rolling, it is prone to forming this defect. The degree of cracking varies depending on the crack size. The "blooming head" defect in H-beam rolling is extremely harmful. On one hand, it severely impacts rolling efficiency; on the other hand, the internal defect at the flange-web junction affects the structural strength of the H-beam cross-section, posing a potential hazard. Therefore, it is necessary to control the generation of internal cracks at the junction of the flange and web of the shaped billet, so as to solve the problem of the opening defect in the H-beam rolling process from the root, and improve the rolling efficiency and product quality of H-beams.

[0004] For example, patent CN112355262B discloses a control device for dynamic light pressure in slab continuous casting. By using a strong buffer spring, the lower slide or buffered pressure seat can provide a certain vertical buffering effect. This allows the rear end of the dynamic roller seat to have a buffering effect. As the continuously cast workpiece moves from the rear pressure roller towards the front pressure roller, a gradual downward pressure is achieved. The elastic downward pressure of the rear pressure roller facilitates the subsequent rigid downward pressure of the front pressure roller, realizing dynamic pressure control, ensuring the performance of the continuously cast billet, preventing internal defects in the billet, and addressing issues such as excessive and concentrated strain during straightening, thus reducing the generation of internal cracks in the continuously cast billet. However, this patent, while aiming to reduce internal cracks in slabs, cannot effectively control the generation of internal cracks at the junction of the web and flange of irregularly shaped billets. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a rolling control method for H-beam bud defects. This method can control the generation of internal cracks at the junction of the flange and web of the shaped billet, fundamentally solving the bud defects that occur during H-beam rolling, thereby improving rolling efficiency and product quality.

[0006] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is: the rolling control method for the opening defect of H-beam, wherein the flange width of the H-beam billet is 300-1300mm, the flange height is 200-510mm, and the web thickness is 85-140mm.

[0007] The control methods include: 1) controlling the S content and Mn / S ratio in the molten steel; 2) reducing the intensity of secondary cooling in the shaped billet continuous casting machine and reducing the proportion of inner arc water volume in each cooling section of the secondary cooling zone; 3) improving the accuracy of the support rollers of the fan-shaped section of the shaped billet continuous casting machine.

[0008] The sulfur content in molten steel is controlled to be 0-0.035%, and the Mn / S ratio in molten steel meets the following requirements: when the sulfur content is 0-0.03%, the Mn / S ratio is ≥15; when the sulfur content is 0.03%-0.035% and not equal to 0.03%, the Mn / S ratio is ≥30.

[0009] The goal of reducing the secondary cooling intensity of the shaped billet continuous casting machine is to control the specific water volume at 0.5–0.6 L / kg.

[0010] The secondary cooling zone includes a cooling section zero, a cooling section one, a cooling section two, and a cooling section three arranged sequentially along the continuous casting direction, with the cooling water volume of each cooling section gradually decreasing.

[0011] Each cooling section includes inner arc nozzles, outer arc nozzles, and side nozzles arranged circumferentially along the blank. The water volume of the inner arc nozzles in the first cooling section is 30% to 35% of the total water volume of the first cooling section; the water volume of the inner arc nozzles in the second cooling section is 23% to 28% of the total water volume of the second cooling section and 68% to 73% of the water volume of the outer arc nozzles; the water volume of the inner arc nozzles in the third cooling section is 18% to 23% of the total water volume of the third cooling section and 55% to 60% of the water volume of the outer arc nozzles.

[0012] The fan-shaped section support rollers of the shaped billet continuous casting machine include web rollers and flange rollers arranged vertically opposite each other, and side rollers arranged horizontally opposite each other. Improving the accuracy of the fan-shaped section support rollers of the shaped billet continuous casting machine includes controlling the total offset of web roller eccentricity and bearing clearance, web roller gap deviation value, web roller deviation value relative to the reference arc surface, non-perpendicularity deviation value between support rollers, non-parallelism of adjacent rollers, and non-parallelism of relative rollers.

[0013] The total offset d1 of web roll eccentricity and bearing clearance needs to satisfy: 0≤d1≤0.1mm.

[0014] The deviation value d2 of the web roll gap needs to meet the following condition: -0.2mm≤d2≤0.2mm.

[0015] The deviation d3 of the web roll relative to the reference arc surface must satisfy: -0.2mm≤d3≤0.

[0016] The perpendicularity deviation d4 between the support rollers must meet the following requirements: -0.075mm≤d4≤0.075mm; the non-parallelism d5 between adjacent rollers must meet the following requirements: -0.0125mm≤d5≤0.0125mm; and the non-parallelism d6 between relative rollers must meet the following requirements: -0.075mm≤d6≤0.075mm.

[0017] The beneficial effects of this invention are:

[0018] This invention controls the Mn / S ratio based on the S content in the steel, keeping the S content within a suitable range to balance the internal quality of the shaped billet and reduce smelting costs. Combining the characteristics of the shaped billet continuous casting machine and the billet shape, a weak-intensity secondary cooling process is adopted, improving cooling uniformity, reducing thermal stress on the billet shell, and controlling internal cracking issues. Based on the shape characteristics of the shaped billet, the distribution of water volume in the inner arc nozzles of the secondary cooling zone is controlled, reducing cooling of the inner arc web area and minimizing internal cracking at the intersection of the web and flange. Considering the shape of the shaped billet and the stress on the billet shell during continuous casting, the installation accuracy of the support rollers at different locations in the sector section of the shaped billet continuous casting machine is determined, improving the internal quality of the shaped billet while preventing severe bulging and tearing of the billet shell. Attached Figure Description

[0019] The following is a brief explanation of the contents of each of the accompanying drawings and the markings in the drawings:

[0020] Figure 1 This is a schematic diagram of the irregular-shaped blank of the present invention;

[0021] Figure 2 This is a schematic diagram of the secondary cooling zone of the irregular billet continuous casting machine of the present invention;

[0022] Figure 3 for Figure 2 A schematic diagram of the upper nozzle arrangement in the intermediate cooling section;

[0023] Figure 4 for Figure 2 Schematic diagram of the nozzle arrangement on the upper part of the second-stage intermediate cooling section;

[0024] Figure 5 for Figure 2 A schematic diagram of the nozzle arrangement in the three-stage intermediate cooling system;

[0025] Figure 6This is a cross-sectional view of the sector section of the irregular billet continuous casting machine in this invention;

[0026] The markings in the above figures are: 1. Cooling section 0, 2. Cooling section 1, 3. Cooling section 2, 4. Cooling section 3, 5. Inner arc nozzle, 6. Outer arc nozzle, 7. Side nozzle, 9. Flange roller, 10. Web roller, 11. Side roller. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0028] In the description of this invention, it should be noted that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0029] The technical solution of this invention is: addressing the problem of blooming defects occurring during the rolling process of H-beams, such as... Figures 2-6 As shown, this invention provides a rolling control method for H-beams with blooming head defects. This control method is applicable to irregularly shaped billets with a flange width B of 300–1300 mm, a flange height H of 200–510 mm, and a web thickness t1 of 85–140 mm. Figure 1 As shown.

[0030] The control method includes:

[0031] 1) Control the S content and Mn / S ratio in the molten steel.

[0032] Sulfur is a harmful element, which exists in steel in the forms of iron sulfide and manganese sulfide. When molten steel solidifies, iron sulfide forms a low-melting-point eutectic with iron. If oxygen is present in the molten steel, the oxide eutectic of sulfur will lower the melting point further. During the cooling process of continuously cast molten steel, this eutectic solidifies last and precipitates at grain boundaries in the form of a network film. At this time, under the effects of the shrinkage force on the outside of the billet shell, the thermal stress during the solidification of molten steel and the hydrostatic pressure of molten steel on the billet shell, crack defects are very prone to occur at the grain boundaries. In the continuous casting process of shaped blanks, the junction of the flange and the web is subjected to the greatest thermal stress and mechanical force, and internal cracks are easily formed in the flange and the junction when the S content is relatively high. Therefore, it is necessary to control the S content of molten steel to a low level. However, due to the low desulfurization rate of converters, adding desulfurization through hot metal pretreatment and LF furnace processes will significantly increase the cost of molten steel. From the perspective of economy, it is not appropriate to control the S content in steel to be too low. Therefore, it is necessary to control an appropriate S content in molten steel, and the S content is controlled within the range of 0≤S≤0.035%.

[0033] The manganese-sulfur ratio refers to the ratio of the weight percentages of manganese and sulfur elements in steel. Since manganese has a relatively strong affinity for sulfur, the formation of high-melting-point manganese sulfide can replace iron sulfide, and this replacement increases as the content of manganese or sulfur in steel increases. Therefore, to reduce the occurrence of cracks and eliminate the influence of iron sulfide eutectic as much as possible, the manganese-sulfur ratio must reach a certain value. The Mn / S ratio shall meet the following requirements: when 0≤S content≤0.03%, Mn / S ratio≥15; when 0.03%<S content≤0.035%, Mn / S ratio≥30.

[0034] 2) Reduce the secondary cooling intensity of the shaped blank continuous caster.

[0035] Relatively high secondary cooling intensity increases the temperature gradient of the shaped blank shell, leads to coarse columnar crystals in the shaped blank, reduces grain boundary strength, and at the same time aggravates uneven cooling, increases the thermal stress on the billet shell, and easily causes internal cracks in the shaped blank. Therefore, a relatively low secondary cooling intensity is adopted, and the specific water flow is controlled at 0.5 to 0.6 L / kg.

[0036] 3) Water flow distribution for each cooling section in the secondary cooling zone of the shaped blank continuous caster

[0037] The cross-section of a shaped blank continuous caster is arranged in an "H" shape. Due to the shape characteristics of the shaped blank, during the continuous casting process, after the secondary cooling water on the inner arc is sprayed onto the casting blank, it will flow downward along both ends of the inner arc web support roller, which enhances the cooling of the inner arc web part, leading to enhanced cooling in this part and making this part prone to internal cracks. Therefore, it is necessary to reduce the proportion of inner arc water flow in each cooling section of the secondary cooling zone.

[0038] The secondary cooling zone comprises a zero cooling section 1, a first cooling section 2, a second cooling section 3 and a third cooling section 4 which are sequentially arranged along the continuous casting direction, and the cooling water flow of each cooling section decreases gradually.

[0039] Each cooling section includes an inner arc nozzle 5, an outer arc nozzle 6, and a side nozzle 7 arranged circumferentially along the billet. The inner arc nozzle 5 is located above the web of the billet, the outer arc nozzle 6 is located below the web of the billet, and the side nozzle 7 is located on the outer sides of the two flanges of the billet. The water volume of the inner arc nozzle 5 in the first cooling section 2 is 30% to 35% of the total water volume of the first cooling section 2; the water volume of the inner arc nozzle 5 in the second cooling section 3 is 23% to 28% of the total water volume of the second cooling section 3, and is 68% to 73% of the water volume of the outer arc nozzle 6; the water volume of the inner arc nozzle 5 in the third cooling section 4 is 18% to 23% of the total water volume of the third cooling section 4, and is 55% to 60% of the water volume of the outer arc nozzle 6.

[0040] 4) Improve the precision of the support rollers in the fan-shaped section of the continuous casting machine for irregular billets.

[0041] The fan-shaped support rolls of the shaped billet continuous casting machine include web rolls 10 and flange rolls 9 arranged vertically opposite each other, and side rolls 11 arranged horizontally opposite each other. The side rolls 11 are located at both ends of the web rolls 10 and contact the sides of the flanges. During the solidification of the shaped billet, the billet shell with a liquid core is subjected to stress in the secondary cooling section of the continuous casting machine, including thermal stress and mechanical stress. Due to the static pressure of the molten steel, the secondary cooling section requires support rolls to support the billet shell to resist the static pressure of the molten steel and prevent severe bulging of the billet shell, which could lead to tearing. Therefore, the accuracy of the fan-shaped support section of the continuous casting machine is very important during the solidification of the shaped billet, and its accuracy plays a decisive role in the internal quality of the shaped billet. The accuracy control of the fan-shaped support section of the shaped billet continuous casting machine includes controlling the total offset of the eccentricity of the web rolls 10 and the bearing clearance, the roll gap deviation of the web rolls 10, the deviation of the web rolls 10 relative to the reference arc surface, the non-perpendicularity deviation between the support rolls, and the non-parallelism of adjacent rolls and relative rolls.

[0042] The total offset d1 of the web roller 10 eccentricity and bearing clearance must satisfy: 0 ≤ d1 ≤ 0.1 mm. The gap deviation d2 (tolerance) between the left and right rows of web rollers 10 must satisfy: -0.2 mm ≤ d2 ≤ 0.2 mm. The deviation d3 of the web roller 10 relative to the reference arc surface must satisfy: -0.2 mm ≤ d3 ≤ 0, where the reference arc surface is the outer edge of the arc of the fan-shaped segment. The perpendicularity deviation d4 between the support rollers (between the web roller 10 and the flange roller 9) must satisfy: -0.075mm≤d4≤0.075mm; the non-parallelism d5 between adjacent rollers (adjacent web roller 10 or adjacent flange roller 9) must satisfy: -0.0125mm≤d5≤0.0125mm; and the non-parallelism d6 between relative rollers (relative web roller 10 or relative flange roller 9) must satisfy: -0.075mm≤d6≤0.075mm.

[0043] After applying the control method of the present invention, no internal cracks occurred at the connection between the web and flange of the shaped billet, no flower head defects occurred during the rolling of H-beams, the rolling was smooth, and the internal quality of the H-beams was good.

[0044] The present invention will now be described in detail with reference to embodiments and comparative examples.

[0045] The rolling control parameters for the irregularly shaped billets with different cross-sectional dimensions in each embodiment and comparative example are shown in Table 1. The cross-sections BB1 to BB7 represent the dimensions of flange width B, flange height H, and web thickness t1. Specifically, the cross-sectional dimensions of BB1 (B×H×t1) are 750×450×120mm; BB2 (B×H×t1) are 500×300×120mm; BB3 (B×H×t1) are 430×300×90mm; BB4 (B×H×t1) are 320×220×85mm; BB5 (B×H×t1) are 900×510×130mm; BB6 (B×H×t1) are 1030×440×130mm; and BB7 (B×H×t1) are 1300×510×140mm.

[0046] Table 1

[0047]

[0048]

[0049] As can be seen from Table 1, in Comparative Example 1, the S content in the molten steel is not within the range set by this invention; in Comparative Example 2, the Mn / S ratio is not within the range set by this invention; in Comparative Example 3, the secondary cooling intensity ratio water volume is not within the range set by this invention; in Comparative Example 4, the proportion of the inner arc water volume of the second cooling section 3 to the total water volume of the second cooling section 3 is not within the range set by this invention; in Comparative Example 5, the proportion of the inner arc water volume of the third cooling section 4 to the total water volume of the third cooling section 4 is not within the range set by this invention; in Comparative Example 6, the total offset of the eccentricity of the fan-shaped web roll 10 and the bearing clearance is not within the range set by this invention; in Comparative Example 7, the roll gap deviation value of the fan-shaped web roll is not within the range set by this invention; in Comparative Example 8, the deviation value of the fan-shaped web roll 10 relative to the reference arc surface is not within the range set by this invention; and in Comparative Example 9, the deviation value of the non-perpendicularity of the fan-shaped web roll 10 relative to the side roll 11 is not within the range set by this invention. Internal cracks were found at the connection between the web and flange of the shaped billets in Comparative Examples 1 to 9, and different degrees of flower head defects appeared during the rolling process of H-beams.

[0050] In summary, this invention controls the Mn / S ratio based on the S content in the steel, keeping the S content within a suitable range, thus balancing the internal quality of the shaped billet while reducing smelting costs. By combining the characteristics of the shaped billet continuous casting machine and the billet shape, a weak-intensity secondary cooling process is adopted, improving cooling uniformity, reducing thermal stress on the billet shell, and controlling internal cracking issues in the shaped billet. Based on the shape characteristics of the shaped billet, the distribution of water volume in the inner arc nozzles of the secondary cooling zone is controlled, which weakens the cooling of the inner arc web area and reduces internal cracking at the intersection of the web and flange. By combining the shape of the shaped billet and the stress on the billet shell during continuous casting, the installation accuracy of the support rollers at different parts of the fan-shaped section of the shaped billet continuous casting machine is determined, improving the internal quality of the shaped billet while ensuring that severe bulging of the billet shell leading to tearing is avoided.

[0051] The above description is merely an illustration of some principles of the present invention. This specification is not intended to limit the present invention to the specific structures and applicable scope shown. Therefore, all possible modifications and equivalents that may be used fall within the scope of the patent application of this invention.

Claims

1. A rolling control method for H-beams with blooming head defects, characterized in that, The flange width of the H-beam billet is 300~1300mm, the flange height is 200~510mm, and the web thickness is 85~140mm. The control method includes: 1) controlling the S content and Mn / S ratio in the molten steel; controlling the S content in the molten steel to be 0~0.035%, and the Mn / S ratio in the molten steel to meet the following requirements: when the S content is 0~0.03%, the Mn / S ratio ≥15; when the S content is 0.03%~0.035% and not equal to 0.03%, the Mn / S ratio ≥30; 2) reducing the intensity of secondary cooling in the shaped billet continuous casting machine and reducing the proportion of inner arc water volume in each cooling section of the secondary cooling zone; the goal of reducing the intensity of secondary cooling in the shaped billet continuous casting machine is to control the specific water volume at 0.5~0.6L / kg; the secondary cooling zone includes cooling sections arranged sequentially along the continuous casting direction. The cooling process consists of three stages: cooling stage 1, cooling stage 2, and cooling stage 3, with the cooling water volume gradually decreasing in each stage. Each cooling stage includes an inner arc nozzle, an outer arc nozzle, and a side nozzle arranged circumferentially along the billet. The water volume of the inner arc nozzle in cooling stage 1 is 30% to 35% of the total water volume of cooling stage 1. The water volume of the inner arc nozzle in cooling stage 2 is 23% to 28% of the total water volume of cooling stage 2 and 68% to 73% of the water volume of the outer arc nozzle. The water volume of the inner arc nozzle in cooling stage 3 is 18% to 23% of the total water volume of cooling stage 3 and 55% to 60% of the water volume of the outer arc nozzle. 3) Improve the accuracy of the support rollers in the fan-shaped section of the billet continuous casting machine.

2. The rolling control method for H-beam splinter defects according to claim 1, characterized in that: The fan-shaped section support rollers of the shaped billet continuous casting machine include web rollers and flange rollers arranged vertically opposite each other, and side rollers arranged horizontally opposite each other. Improving the accuracy of the fan-shaped section support rollers of the shaped billet continuous casting machine includes controlling the total offset of web roller eccentricity and bearing clearance, web roller gap deviation value, web roller deviation value relative to the reference arc surface, non-perpendicularity deviation value between support rollers, non-parallelism of adjacent rollers, and non-parallelism of relative rollers.

3. The rolling control method for H-beam splinter defects according to claim 2, characterized in that: The total offset d1 of web roll eccentricity and bearing clearance needs to satisfy: 0≤d1≤0.1mm.

4. The rolling control method for H-beam splinter defects according to claim 2, characterized in that: The deviation value d2 of the web roll gap needs to meet the following condition: -0.2mm≤d2≤0.2mm.

5. The rolling control method for H-beam splinter defects according to claim 2, characterized in that: The deviation d3 of the web roll relative to the reference arc surface must satisfy: -0.2mm≤d3≤0.

6. The rolling control method for H-beam splinter defects according to claim 2, characterized in that: The perpendicularity deviation d4 between the support rollers must meet the following requirements: -0.075mm≤d4≤0.075mm; the non-parallelism d5 between adjacent rollers must meet the following requirements: -0.0125mm≤d5≤0.0125mm; and the non-parallelism d6 between relative rollers must meet the following requirements: -0.075mm≤d6≤0.075mm.

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